محاضرة بعنوان Introduction of Machining, Geometry of Tool and Nomenclature

محاضرة بعنوان Introduction of Machining, Geometry of Tool and Nomenclature
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غير معروف
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3 سبتمبر 2022
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محاضرة بعنوان
Introduction of Machining, Geometry of Tool and Nomenclature
Subject: Manufacturing Science & Technology-II
Department of Mechanical Engineering
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-1 /Lecture No: 1
Manufacturing
Manufacturing is the application of physical and chemical processes to change the geometry, properties and appearance of a given raw material to make parts or products based on customer’s specifications and expectations. Manufacturing commonly employs a man-machine setup with division of labor in a large scale production.
Classification of Manufacturing Processes
Classification of “material removal” processesMachining
• Machining is the process of removing excess material from a work surface in the
form of chips. The removal of the material occurs by the shearing action of the
cutting tool. The shear stress is developed due to relative motion between tool
and work piece. This shear stress causes the plastic deformation of the material in
the form of chips.
• Objective of Machining: Parts are manufactured either by casting, forming or
powder metallurgy process. These parts require further operations before the
product is ready for use. So machining of materials is basically adopted to get –
1: Excellent dimensional accuracy
2: Excellent geometrical accuracy
3: Excellent surface finish
4: Complex geometrical features like Sharp corners, grooves, fillets etc.
Machining System
• A machining system consists of following components:
1: Machine tool 2: Cutting tool
3: Workpiece 4. Work holding devices• Machine Tool: A machine tool is one which is used for machining purpose and
operated by external energy. Machine tool holds the cutting tool as well as
workpiece and provides necessary relative motion between the cutting tool and
work piece. Ex: Lathe machine, drilling machine, milling machine etc.
• Cutting Tool: The body which removes the excess material through a direct
mechanical contact is called cutting tool. Ex: Single point cutting tool, drill bit,
milling cutter etc.
• Workpiece: It is the metallic or non-metallic parts needs to be machine.
• Work holding devices: Work holding devices are used to hold the workpiece
and guide it against the cutting tool.
Manufacturing Process Selection
Two stage decision process

  1. Feasibility Criteria:
     Can the shape be produced by the process?
     Can the material be shaped by the process?
  2. Process performance criteria:
     Cycle time
     Material utilization,
     Process flexibility,
     Operating costs
     Surface finishMachining Conditions
  3. Cutting parameters
     Cutting velocity
     Depth of cut
     Feed rate
  4. Cutting environment
     Cutting Fluid
     Cutting temperature
     Presence of air (oxygen )
  5. Work and tool holding devices
     Jigs
     Fixtures
    Cutting tool
    • Both material and geometry of the cutting tools play very important roles on
    their performances in achieving effectiveness, efficiency and overall economy of
    machining.
    • The word tool geometry is basically referred to some specific angles or slope of
    the salient faces and edges of the tools at their cutting point.
    • Rake angle and clearance angle are the most significant for all the cutting tools.Rake Angle:
    It is the angle between rake face of the tool and a plane perpendicular to the
    machining direction. Rake angle is provided for ease of chip flow and overall
    machining.
     Higher the rake angle, less are the cutting forces
     Increasing the rake angle reduces the strength of the tool tip.
     There is maximum limit to the rake angle and this is generally 20º for HSS
    tools cutting mild steel.
    • It is possible to have rake angles “positive, zero or negative”. Relative
    advantages of such rake angles are:
    Positive rake – helps to reduce cutting force and thus cutting power
    requirement.
    Negative rake – helps to increase edge-strength and life of the tool.
    Zero rake – to simplify design and manufacture of the form tools.
    • Zero or negative rake angles are generally used in the case of highly brittle tool
    materials such as carbides or diamonds for giving extra strength to the tool tip.
    Example:
    HSS: +5° < rake angle< +20°
    Carbides: -5° < rake angle < +10°
    Ceramics: -5° < rake angle < -15°Clearance Angle:
    • It is the angle between the machined surface and the flank face of the tool. The
    clearance angle is provided such that tool will not rub the machined surface thus
    spoiling the surface and increasing the cutting force.
    • A very large clearance angle reduces the strength of the tool tip, and hence
    normally an angle of the order of 5 – 6º is used. It is always positive.
    Geometry of single point turning tool• The single point cutting tool have 6 different angles. These are:
  6. Back rake angle: The back rake angle is the angle between the face of the
    tool and a line parallel with base of the tool measured in a perpendicular
    plane through the side cutting edge. Back rake angle helps in removing the
    chips away from the workpiece.
  7. Side rake angle: Side rake angle is the angle by which the face of tool is
    inclined side ways. It is the angle between the surface of the flank
    immediately below the point and the line down from the point to the base. It
    is provided on tool to provide clearance between workpiece and tool so as to
    prevent the rubbing of workpiece with end flank of the tool.
  8. End relief angle: It is defined as the angle between the portion of the end
    flank immediately below the cutting edge and a line perpendicular to the base
    of the tool measured at right angles to the flank. End relief angle allows the
    tool to cut without rubbing on the workpiece.
  9. Side relief angle: It is the angle between the portion of the side flank
    immediately below the side edge and a line perpendicular to the base of the tool
    measured at right angles to the side. It provides relief between flank face and the
    work surface.
  10. End cutting edge angle: It is the angle between the end cutting edge and a
    line perpendicular to the shank of the tool. It provides clearance between tool
    cutting edge and workpiece.
  11. Side cutting edge angle: It is the angle between straight cutting edge on the
    side of tool and the side of the shank. It is responsible for turning the chip away
    from the machined surface.Thank
    You
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-1 /Lecture No: 2
    (Orthogonal vs. Oblique cutting)Mode of Machining
    • Based on the orientation of cutting edge with respect to the direction of cutting
    velocity, there are two methods of metal cutting.
  12. Orthogonal Cutting 2. Oblique Cutting
    Orthogonal Cutting: When the cutting edge of the tool is perpendicular to
    the direction of cutting velocity, the process is called orthogonal cutting.
     The chip generated flows on the rake face of the tool and the chip velocity
    is perpendicular to the cutting edge.
     The cutting forces act along X and Z directions only.Oblique Cutting: When the cutting edge of the tool is inclined at an Angle “i”
    with the normal to the direction of cutting velocity, the process is called oblique
    cutting.
    • The chip generated flows on the rake face at an angle approximately equal to “i”
    with normal to the cutting edge. The cutting forces acts along all the three X, Y
    and Z directions.
    • In actual machining, Turning, Milling, Drilling etc/ cutting operations are
    oblique cutting
    Difference between orthogonal and oblique cutting
    Orthogonal cutting
    • The cutting angle of tool make right
    angle to the direction of motion.
    • The chip flow in the direction
    normal to the cutting edge.
    • In orthogonal cutting only two
    components of force considered
    cutting force and thrust force which
    can be represent by 2D coordinate
    system, so it is known as 2D cutting.
    Oblique cutting
    • The cutting angle of tool not make
    right angle to the direction of
    motion.
    • The chips make an angle with the
    normal to the cutting edge.
    • In oblique cutting three component
    of force are considered, cutting
    force, thrust force and radial force
    which is represented by 3D
    coordinate system, so it is known as
    3D cutting.Difference between orthogonal and oblique cutting
    Orthogonal cutting
    • The chips flow over the tool.
    • The shear force act per unit area is
    high which increase the heat
    developed per unit area.
    • This tool has lesser cutting life
    compare to oblique cutting.
    Oblique cutting
    • The chips flow along the sideways.
    • The shear force per unit area is low,
    which decreases heat develop per
    unit area hence increases tool life.
    • This tool has higher cutting life.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I /Lecture No: 3
    (Mechanics of chip formation, types of chips)
    Mechanics of chip formation
    • Machining is a process of gradual removal of excess material from the work
    surface in the form of chips. Knowledge of basic mechanism of chip
    formation helps to understand the characteristics of chips and to attain
    favorable chip forms.
    • Two mechanics of chip formation are:
  13. Mechanics of chip formation in ductile materials
  14. Mechanics of chip formation in brittle materials1. Mechanics of chip formation in ductile materials
    • During continuous machining the uncut layer of the work material just ahead of
    the cutting edge is subjected to compression. Due to such compression, shear
    stress develops, within that compressed region, and rapidly increases in
    magnitude. Whenever the value of the shear stress exceeds the shear strength of
    that work material in the deformation region, yielding takes place resulting
    shear deformation in that region along the plane of maximum shear stress. Then
    the deformed metal (called chip) flows along the tool rake face.
    • The region of maximum shear stress is called primary shear zone. If the friction
    between the tool rake face and the underside of the chip is considerable, the
    chip gets further deformed, which is termed as secondary shear zone.
    In ductile material, the chips are initially compressed ahead of the tool tip, the final
    deformation is accomplished mostly by shear in machining ductile materials.Primary and secondary deformation zone: The pattern and extent of total
    deformation of the chips due to the primary and the secondary shear deformations of
    the chips ahead and along the tool face is shown in fig.
    Machining of ductile materials generally produces flat, curved or coiled continuous
    chips.
  15. Mechanics of chip formation in brittle materials
    • During machining, first a small crack develops at the tool tip as shown
    in fig. due to wedging action of the cutting edge. At the sharp crack-tip
    stress concentration takes place. In case of ductile materials
    immediately yielding takes place at the crack-tip and reduces the effect
    of stress concentration and prevents its propagation as crack. But in
    case of brittle materials the initiated crack quickly propagates, under
    stressing action, and total separation takes place from the parent
    workpiece through the minimum resistance path as indicated in fig.
    • Machining of brittle material produces discontinuous chips and mostly
    of irregular size and shape.Mechanics of chip formation in brittle materials……..
    • During machining of brittle materials, chip formation occurs due to brittle
    fracture of the work material.
    Types of Chip
    • Depending on the properties of work material and cutting conditions, three
    basics types of chips are produced by the machining process. These are:
  16. Continuous chips
  17. Continuous chips with Built-Up Edge
  18. Discontinuous chipsContinuous Chip:
    • Continuous chips are normally produced when machining ductile metals at high
    cutting speeds. Continuous chip which is like a ribbon flows along the rake face
    of the tool. Production of continuous chips is possible because of the ductility of
    the metal. Thus on a continuous chip you do not see any notches.
    • Some ideal conditions which promote the formation of continuous chips are:
  19. Ductile work material
  20. Small uncut thickness
  21. High cutting speed
  22. Large rake angle
  23. Sharpe cutting edge
  24. Less friction
    Continuous Chip with BUE:
    • In the cutting zone, when friction is high while machining ductile materials,
    some particles of the chip get welded to the tool rake face near the tool tip.
    • Such sizeable particles piles upon the rake face and forms the built-up edge.
    • The BUE grows up to a certain size but finally breaks due to the increased
    forced exerted on it by the adjacent flowing material. After it breaks, the broken
    fragments adhere to the finished surface and the chip surface, results in a rough
    finish.• Some ideal conditions which promote the formation of continuous chip with
    BUE chips are:
  25. Ductile work material
  26. Large uncut thickness
  27. Low cutting speed
  28. Small rake angle
  29. High friction between chip-tool interface
    Discontinuous chips
    • When brittle materials like cast iron are cut, the deformed material gets fractured
    very easily and thus the chip produced in the form of discontinuous segments. In
    this type the deformed material instead of flowing continuously gets ruptured
    periodically.
    • Conditions which promote the formation of discontinuous chips are:
  30. Brittle work material
  31. Low cutting speed
  32. Small rake angle
  33. Large uncut thicknessTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 4
    (Shear angle relationship)Shear Angle (φ)
    • It is the angle made by the shear plane with the direction of cutting
    speed. Higher the shear angle better is the cutting performance.
    Importance of shear angle:
    • If all other factors remain the same, a higher shear angle results in
    a smaller shear plane area. Since the shear strength is applied across this area,
    the shear force required to form the chip will decrease when the shear plane
    area is decreased. This tends to make machining easier to perform, and
    also lower cutting energy and cutting temperature.
    Determination of Shear angle• Chip thickness ratio (r ) also known as cutting ratio.
    • Chip thickness ratio is always less than 1. this is because, chip
    thickens and due to volume constancy shortens.
    • 1/r is known as chip compression ratio.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 5
    (Merchant’s force circle diagram)Orthogonal machining
    Forces in orthogonal metal cutting
    • Forces in the secondary deformation zone:
    1- Friction force along the rake face, Fr
    2- Force perpendicular to rake face, Nr
    • Forces in the Primary deformation zone:
    1- Force along the shear plane, Fs (shear force)
    2- Force normal to the shear plane, Ns
    • Forces on the cutting tool:
    1- Cutting force, Fc
    2- Thrust force, Ft1. Forces on the cutting tool
    2-Forces in the secondary deformation zone:3-Forces in the Primary deformation zone:
    The resulting diagram Merchant,s force circle diagramForce analysis
    1- Friction force along the rake face
    F = F
    c sin α + Ft cosα
    2- Force perpendicular to rake face
    F
    c cosα – Ft sinα
    3-Force along the shear plane (shear force)
    F
    c cosφ – Ft sin φ
    4- Force perpendicular to the shear plane
    F
    c sin φ + Ft cosφ
    Shear strain in chip formationShear strain rate
    Shear strain rate (γ ) is given by:
    • where Δt is the time required for the metal to travel the distance Δs along the
    shear plane.
    • Δy is the distance between two successive shear planes.
    • A reasonable value of spacing between successive planes (Δy) would be
    around 25×10-4 mm.Velocity analysis in orthogonal machining
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 7
    (Cutting forces, power required in metal cutting)
    Force analysis
    From Merchant,s force circle diagramCoefficient of friction between chip-tool interface
    • The coefficient of friction between two sliding surfaces is defined as
    • Here, it is implied that the forces F and N are uniformly distributed over the
    entire chip-tool contact area.
    Shear angle relationship based on Merchant’s theoryWhat the Merchant’s relation tells us?
    To increase shear plane angle
     Increase the rake angle
     Reduce the friction angle (or coefficient of friction)Cutting energy or power requirement
    • The cutting energy required for machining depends on the cutting force and
    cutting velocity. It can be express as:
    Cutting energy = Cutting force × Cutting velocity
    Parameters which affects the cutting force & power requirement
    The variables that have significant effect on tool life are:
    1- Cutting conditions

Speed
Feed
Depth of cut
2- Tool geometry
Rake angle
Clearance angle
Nose radius
3- Work material
4- Cutting fluid
5- Built-Up-EdgeTHANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 7
(Thermal aspects of machining)Thermal Aspect of Machining Process
The machining operation is basically a deformation process of the work material
through the application of force by the cutting tool. In all the machining
processes where plastic deformation is involved, the mechanical energy
dissipated in cutting is converted into heat which in turn, raises the temperature
in the cutting zone. During machining almost 99% of the energy is converted in
to heat.
Sources of Heat Generation in Machining: The heat generation
occurs in three distinct regions:
1- Primary shear zone
2- Secondary shear zone (at chip-tool interface)
3- Tool-work interface
• Primary shear zone: In primary shear zone heat is generated due to plastic
deformation of the work material. About 80 – 85% heat is generated in this
zone.
• Secondary shear zone: In this zone, heat is generated due to frictional rubbing
between the rake face of the tool and chip. Some plastic deformation also
occurs in this zone. About 15 – 20% heat is generated in this zone.
• Tool – Work Interface: At the tool-work interface, heat is generated due to
frictional rubbing between flank face of the tool and machined work piece
surface.
• In this region only 1 – 3% heat is generated.Heat Flow in Metal Cutting
The heat generated is shared by the chip, cutting tool and the workpiece. The
percentage of sharing that heat depends upon the configuration, size and
thermal conductivity of the tool – work material and the cutting condition.
 About 80 – 85 % of the total heat generated during machining is carried
away by the chip.
 About 15 – 20% of the total heat is flows in to the tool.
 Less than 5% heat is conducted in to the work piece.Temperature distribution in metal cutting process
• Figure shows temperature distribution during orthogonal cutting. The workpiece
material is free cutting mild steel where the cutting speed is 0.38 m/s, the depth
of cut is 6.35 mm.Temperature distribution in metal cutting process
• From figure it is clear that the maximum temperature in the cutting process
occurs not at the tool tip but at some distance away from the cutting edge.
• Point X. The material at point x gets heated as it passes through the shear zone
and finally leaves as chip.
• Point Y. Material at point y first heated in shear zone but heating is continued
until they cross the frictional heat zone. This point losses some shear zone heat
while moving up but gains more frictional heat.
• Point Z. Point such as z remains in the workpiece and are heated due to
conduction of heat into the workpiece as they pass below the cutting edge.
• The above factors cause maximum tool temperature to occur at some
distance away from the cutting edge.
Effect of the High Cutting Temperature on Tool and Job
The high temperature in machining zone is harmful for both the tool and the
job. The major portion of the heat is taken away by the chips. But it does not
matter because chips are thrown out. So attempts should be made such that the
chips take away more and more amount of heat leaving small amount of heat to
harm the tool and the job.
Effect of cutting temperature on the tool:
1- Rapid tool wear, which reduces tool life.
2- Plastic deformation of the cutting edges if the tool material is not enough
hot-hard .
3- Chipping of the cutting edges due to thermal stresses.
4- Built-up edge formation.Effect of cutting temperature on the machined job:

  1. Dimensional inaccuracy of the job due to thermal distortion and
    expansion-contraction during and after machining.
  2. Surface damage by oxidation, rapid corrosion, burning etc.
  3. Excessive temperature rise can induce metallurgical changes in the
    machined surface, adversely affecting its properties
  4. Induction of tensile residual stresses and micro-cracks at the surface /
    subsurface.
    Factors Affecting the heat generation in Cutting Zone
    The following factors influence the cutting temperature:
    1- Machining parameters
    Speed
    Feed rate
    Depth of cut
    2- Properties of workpiece material
    Hardness
    Strength
    3- Tool geometry
    Rake angle
    Clearance angle
    Nose radius
    4- Cutting fluids
    5- Built-up-edgeTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 8
    (Cutting fluid)Cutting Fluids
    • Need: During machining process, friction between work-tool and chip-tool
    interfaces causes high heat generation which results high temperature in
    machining zone. The effect of this generated heat decreases tool life,
    increases surface roughness and decreases the dimensional accuracy of work
    material. This case is more important when machining of difficult-to-cut
    materials, when more heat would be observed. Due to this reason, most
    machining operation is carried out in the presence of a cutting fluid.
    Functions of a cutting fluid
    1- Lubrication: Lubrication at the chip–tool and tool-work interface to reduce
    friction force and thus the amount of heat generation.
     Lubrication of cutting zone is very important at low cutting speeds.
    2- Cooling: Cooling of the job and the tool to reduce the detrimental effects of
    cutting temperature on the job and the tool.
     The cooling of the workpiece is very important at high cutting speeds.
    3- Cleaning: Cleaning the machining zone by washing away the chip – particles and
    debris which, if present, spoils the finished surface and accelerates damage of the
    cutting edges.
    4- Corrosion Protection. A thin layer of the cutting fluid sticks to the machined
    surface and thus prevents it from harmful atmospheric gases like SO2, O2, NxOy
    present in the atmosphere.Principles of cutting fluid action
    The chip-tool contact zone is usually comprised of two parts; plastic or bulk
    contact zone and elastic contact zone as indicated in Fig.
    Principles of cutting fluid action…………………
    • The cutting fluid cannot penetrate or reach the plastic contact zone but
    enters in the elastic contact zone by capillary effect. With the increase in
    cutting velocity, the fraction of plastic contact zone gradually increases and
    covers almost the entire chip-tool contact zone. Therefore, at high speed
    machining, the cutting fluid becomes unable to lubricate and cools the tool
    and the job only by bulk external cooling.
    • The chemicals like chloride, phosphate or sulphide present in the cutting
    fluid chemically reacts with the work material at the chip under surface
    under high pressure and temperature and forms a thin layer of the reaction
    product. The low shear strength of that reaction layer helps in reducing
    friction.Essential properties of cutting fluids:
    • It should have high thermal conductivity and specific heat.
    • Have low viscosity and molecular size (to help rapid penetration into the chiptool interface).
    • Should have good spreading and wetting ability.
    • Friction reduction at extreme pressure and temperature.
    • Chemical stability, non-corrosive to the tool and work materials.
    • Odourless and also colourless.
    • Non toxic in both liquid and gaseous stage.
    • Easily available and low cost.
    Types of Cutting Fluid:
    Generally, cutting fluids are employed in liquid form but occasionally also
    employed in gaseous form. Only for lubricating purpose, often solid lubricants
    are also employed in machining and grinding. The cutting fluids, which are
    commonly used, are:
  5. Compressed air
  6. Water
  7. Straight oils (or neat oils)
  8. Water Soluble oils ( or soluble oils)
  9. Synthetic oils (chemical fluid)
  10. Solid or semi-solid lubricant• Compressed Air: Machining of some materials like grey cast iron become
    inconvenient or difficult if any cutting fluid is employed in liquid form. In such
    case only compressed air is recommended for cooling and cleaning purpose.
    • Water: For its good wetting and spreading properties and very high specific
    heat, water is considered as the best coolant and hence employed where cooling
    is most urgent.
    • Straight Oils: These fluid composed of a base petroleum oil or vegetable oils
    with extreme pressure additives of chlorine, sulphur and phosphorus. Straight
    oils provide the best lubrication and the poorest cooling characteristics among
    all the cutting fluids.
     These fluids are used where cutting speed is very low, feed and depth of cut
    is high.
    • Water Soluble Oils: (water + mineral oil + emulsifier agent + rust inhibitor
    agent and EPA). These oils are used in diluted form and provide good
    lubrication as well as cooling performance. Soluble oils are widely used in
    industry.
    Water………………..Provides cooling
    Mineral oils………..Provides lubricity
    Emulsifier…………..Breaks oil into small globules
    Rust inhibitor……. Since water can cause rusting
    • Synthetic Oils: Synthetic Fluids contain no petroleum or mineral oils. These
    oils are formulated from alkaline inorganic and organic compounds along with
    EPA additives for corrosion inhibition. Synthetic fluids provide the best cooling
    performance among all cutting fluids but limited lubricity.
    • Solid or semi-solid lubricant: Paste, waxes, soaps, graphite, Moly-disulphide
    (MoS2) may also often be used as cutting fluids.Cutting Fluid Application Methods
    The effectiveness and expense of cutting fluid application significantly depend
    also on how it is applied in respect of flow rate and direction of application. In
    machining, depending upon the requirement and facilities available, cutting
    fluids are generally employed in the following ways.
    • Flood Application: In this method tool and workpiece are supplied with high
    volume of the cutting fluids which are generally in liquid condition.
    • Jet Application: In this method the cutting fluids which may be either gas or
    liquid are applied with high pressure on the tool and workpiece.
    • Mist (atomised) Application: In this method cutting fluid is atomised by a jet of
    air and the mist is directed at the cutting zone. This method gives maximum
    cooling effect.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 9
    (Cutting tool materials)Cutting Tool Materials
    • Since machining is accomplished by the deformation of work material and so
    cutting tool is subjected to :
     High temperatures
     High contact stresses
     Rubbing along the chip-tool and tool-work interface.
    • Under these condition, the stability of geometric form (or shape) of the tool is
    key factor. Thus, the cutting tool must provide the maximum resistance to any
    tendency of alteration of its geometric form. To achieve this, the cutting tool
    material must be properly selected.
    Desirable properties of cutting tool material
    The cutting tool materials must possess a number of important properties to
    avoid excessive wear, fracture failure and high temperatures in cutting. The
    following characteristics are essential for cutting materials to withstand the
    heavy conditions of the cutting process and to produce high quality and
    economical parts:
    1- High Hardness
    2- Hot hardness (or Red hardness )
    3- Toughness
    4- Wear resistance
    5- Low friction
    6- High thermal conductivity and specific heat
    7- Chemical stabilityHigh Hardness: A cutting tool material must have higher hardness than that of
    the workpiece material being machined, so that it can penetrate into the work
    material.
    Hot hardness: It is defined as ability to retain hardness at elevated (high)
    temperatures in view of the high temperatures existing in the cutting zone. Thus,
    the tool retains its shape and sharpness. This requirement becomes more and more
    important when machining under high cutting speeds to increase the production
    rate.
    Diamond is having the highest hot hardness. Ceramics also maintain their
    hardness at high temperatures. While carbon tool steels rapidly begin to lose their
    hardness at moderate temperatures (cannot be used at high speeds Æ high
    temperatures).
    Toughness: Toughness is a resistance to shock or impact forces. Higher the
    toughness, more shock load material can withstand. It is desired so that impact
    forces on the tool encountered repeatedly in interrupted cutting operations (such
    milling) do not chip or fracture the tool.
    Wear resistance: It is the ability of material to resist wear. Wear resistance
    depends on hardness as well as undissolved carbides. It is desired so that an
    acceptable tool life is obtained before the tool has to be replaced.
    Low friction: The coefficient of friction between the tool and work should be
    low. This will lead to improve the surface finish, reduction in frictional heat
    generation and absorbs less cutting energy.
    High thermal conductivity and specific heat: These properties ensure
    rapid dissipation of heat generated during cutting process, thus avoid softening
    of the cutting tool material and improves its life.Chemical stability: A cutting tool material should be chemically stable with
    respect to the work material and cutting fluid, so that any adverse reaction
    contributing tool wear are avoided.
    Types of Cutting Tool Material
    • The demand for higher productivity has led to the development of a variety of
    cutting tool materials with vastly improved properties. Each stage of
    development has facilitated the use of higher cutting speeds. No one cutting
    material is best for all purposes. No tool material has been able to fully replace
    the older one since each one of them has a unique combination of properties.
    The following cutting tools materials are still in use are:
    1- High carbon steel
    2- High speed steel
    3- Cemented Carbides
    4- Ceramics
    5- Cubic boron nitride (CBN)
    6- DiamondHigh Carbon Steel
    • This is the oldest material used for making cutting tools is much less used
    today. It contains 0.8 – 1.2% carbon and some very small alloy additions such
    as manganese, tungsten, molybdenum, chromium and vanadium.
    • These steel have very good hardenability and wear resistance at low
    temperature. The major disadvantage of these cutting tool materials is their
    inability to withstand high temperature.
    • Beyond 200ºC they lose their hardness and become soft. Therefore, they are
    useful only for very low cutting speeds (about 0.15 m/s). Due to this, high
    carbon steel mainly used with low temperature generating operations or
    machining of the soft materials such as wood, magnesium, brass and
    aluminium etc.
    High Speed Steel
    • These steel are called high speed steel because they can cut metal at three to
    five times higher speeds than that can be done by the high carbon steel. They
    can retain their hardness up to about 650ºC.
    • These are carbon steel with major alloying elements such as tungsten,
    molybdenum, chromium, vanadium and cobalt.
    • Toughness of HSS is highest among all the cutting tool materials. Thus they are
    extensively used in interrupted cutting such as milling. HSS also used for
    making drill, reamer, milling cutter, single point cutting tool etc.Cemented Carbides
    • Three group of cutting tool materials just described (high carbon steel, HSS and
    cast-cobalt alloys) possess the necessary toughness, impact strength and thermal
    shock resistance. But, still these materials are limited in their hot hardness, wear
    resistance and strength. Consequently, they cannot be used very effectively
    where high cutting speeds (and therefore high temperature) are required. To meet
    the challenge of higher speeds for higher production rates, cemented carbides
    were developed around 1930 in Germany.
    • Cemented carbide tool consists of carbide particles (carbides of tungsten and
    titanium) bound together in a cobalt matrix by powder metallurgy process.
    • The two groups used for machining are :
    1- Tungsten carbide
    2- Titanium carbide
    Ceramics
    • Ceramics are inorganic compounds, and usually made either of oxides, carbides, or
    nitrides. The following ceramic materials used as cutting tool material:
    1- Aluminium Oxides (Al2O3) or alumina
    2- Silicon Carbides (SiC)
    3- Silicon Nitrides (Si3N4)
    4- Titanium Carbide
    5-Titanium Oxides
    Properties:
    • Ceramic cutting tools are harder and more heat-resistant than carbides tools, but more
    brittle.
    • They can withstand very high temperatures, due to which the cutting edge retains its
    hardness almost up to 1200ºC.
    • They have higher wear resistance than other cutting tool materials.
    • They are chemically more stable than carbides.• Cubic boron nitride (CBN): Cubic boron nitride is the second hardest material
    available for machining purpose. It is not a natural material, it is produced in
    laboratory.
    • CBN mainly used as coating material. But cubic boron nitride tools are also
    made in small sizes without a carbide insert.
    • Diamond: Diamond is the hardest known material that can be used as cutting
    tool material. Diamond tools are available as insert. Diamonds are suitable for
    cutting very hard materials like glass, ceramics and other abrasive materials.
    Use is limited because it gets converted into graphite at high temperature (700
    °C). Graphite diffuses into iron and makes it unsuitable for machining steels.
    • The curve shows that:
    High speed steel is much better than carbon tool steel (high carbon
    steel).
    Cemented carbides and ceramics are significantly harder at elevated
    temperatures.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 10
    (Tool life)Tool Life
    • During machining, the cutting edge of the tool gradually wears out and it does not perform
    satisfactorily. When the wear reaches a certain stage, it is said that the tool has lost its
    utility and its life is over. It must be reground or replace by a new tool if machining is to
    be continued.
    The time interval during which a cutting tool performs given function
    satisfactorily is called tool life.
    Flank wear generally considered as the decisive factor to measure the tool life.
    However, at higher cutting speed, crater wear also used as tool failure criterion.
    • Measuring tool life: There are various ways in which tool life can be specified.
    Actual cutting time to failure.
    Length of work cut to failure.
    Volume of metal removed to failure.
    Number of components produced to failure.
    Taylor’s equation of tool life
    • Wear and hence tool life of any tool for any work material is governed mainly
    by the level of the machining parameters i.e., cutting velocity, feed, and depth
    of cut . Cutting velocity affects maximum and depth of cut minimum.
    • Taylor gave the relation between cutting speed and tool life. That is:
    Where
    V= cutting speed(m/min)
    T=tool life(in minutes)
    C=machining constant
    n= Tool life exponent(it depends on tool material)Parameters Affecting Tool Life
    1-Cutting conditions
    Speed
    Feed
    Depth of cut
    2- Tool geometry
    Rake angle
    Clearance angle
    Nose radius
    3- Tool material
    Hardness
    Wear resistance
    Thermal conductivity
    4- Work material
    5- Cutting fluid
    6- Built-Up-Edge
    Effect of cutting conditions on tool life
    1- Speed: The tool life decreases with the increase in cutting speed. This is
    because; temperature in the cutting zone increases with increase in cutting
    speed, which makes the tool soft. Higher cutting temperature also increases the
    rate of abrasive, adhesive, and diffusion wear.
    2- Feed: Tool life decreases with increase in feed rate. This is because cutting
    force increases with the increase in feed rate. Due to increase in cutting force,
    temperature in cutting zone increases and finally tool life decreases.
    3- Depth of Cut: Tool life decreases with increases in depth of cut. This is
    because, as the depth of cut increases, the chip-tool contact area and cutting
    force increases which rises the temperature due to increasing frictional heat.Tool Life Criteria
    The following are some of the possible tool life criteria that could be used for
    limiting tool life.
    Direct Criteria (based on tool wear).
    • Wear land size
    • Crater depth and width.
    • Total destruction of the tool
    Indirect Criteria (based on effects of a worn tool).
    • Limiting value of surface finish.
    • Limiting value of change in component dimensions.
    • Limiting value of increase in cutting force.
    Wear land size: Wear land size on the flank face of the tool is widely used
    criteria to assess tool life. When the wear land reaches a critical value, cutting
    becomes difficult and tool leaves rough marks on the machined surface. Under
    this condition it is said that life of the tool is over.
    The length of wear land is not of uniform. It is larger near the two ends of the
    active portion of the side cutting edge. The maximum width of the wear land is
    at the rear end of the flank face. The tool life values as suggested by ISO are:
    VB = 0.3 mm, if the flank is regularly worn in zone B
    VB
    max = 0.6mm, if the flank is irregularly worn in zone BCrater depth and width: At high speeds and feeds crater wear is
    more, therefore, it is also used as tool life criteria. Since, larger the depth of
    crater, weaker is the tool. According to ISO recommendation, the maximum
    allowable crater depth can be given as:
    KT = 0.06 + 0.3f (f = feed in mm/rev)
    Total destruction of the tool: Tool destruction occurs when the tool is unable
    to support the cutting force over the tool-chip contact area and results in fracture
    of small part of cutting edge. It is Common in interrupted cuts and in non rigid
    setups.
    Limiting value of surface finish: According to this criterion, the surface is
    continuously monitored and RMS values of surface roughness are compared with
    the limiting value. Whenever, the measured value of the surface roughness
    exceeds the limiting value, the tool is said to have failed and must be reground.
    Limiting value of change in component dimensions: In this method, the
    dimensions of the each component are measured. When the dimensional accuracy
    falls below a limiting value, the tool is said to have failed.
    Limiting value of increase in cutting force: The change in cutting force is
    measured with the help of a tool dynamometer or power meter. If the cutting force
    increases beyond a limiting value, the tool is said to have failed.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 11
    (Tool wear)Failure of Cutting Tools
    • The success of machining process depends on the sharpness of the tool. The use of a
    blunt tool results in a large power consumption and poor surface finish.
    • When a cutting tool unable to cut, consuming large power, and cannot produce an
    acceptable surface finish, it is considered to have failed. The failure of a cutting tool
    may be due to one or a combination of the following modes:
    1- Plastic deformation of the tool.
    Plastic deformation of the tool occurs due to high temperature and
    stresses.
    2- Mechanical breakage of the tool.
    Mechanical breakage of the tool occurs due to large forces and shocks.
    The other factors are insufficient strength and toughness of the tool material.
    3- Progressive or gradual wear failure.
    The progressive wear makes the tool blunt. It occurs due to relative sliding
    between two surfaces.
    • The plastic deformation and mechanical failure can be prevented by
    proper selection of cutting tool material, tool geometry and cutting
    conditions.
    • But failure by gradual wear cannot be prevented but can be slowed
    down only to enhance the service life of the tool.Progressive Tool Wear
    • The wear is generally defined as loss of material from surfaces. The wearing
    action takes place on those surfaces along which there is a relative sliding with
    other surfaces. Thus, the wear takes place on the rake face where the chip flows
    over the tool. The wear also takes place on the flank face where rubbing between
    the work and tool occurs.
    Types of progressive tool wear: The progressive wear of a cutting tool takes
    place into distinct ways:
    1- Crater wear (measured in terms of the “depth of crater”)
    2- Flank wear (measured in terms of the “length of the wear land”)
    Crater Wear: Crater wear occurs on the rake face of the tool due to relative
    sliding between rake face and chip. In orthogonal cutting this typically occurs
    where the tool temperature is highest
    Diffusion process is mainly responsible in the development of crater
    wear.
    • Flank Wear: Flank wear occurs on the flank face of the tool, due to rubbing
    between flank face and machined surface. It modified the tool geometry and
    changes the cutting parameters (depth of cut).
    The abrasion and adhesion are primarily responsible for the flank wear.
    Flank wear directly affects the surface finish produced. Thus there is
    always a close limit kept on the value of the wear land.Progressive tool wear
    workpiece
    tool
    crater wear
    flank wear
    chip
    Tool Wear Mechanisms:
    • Under high temperature, high pressure, high sliding velocity and mechanical or
    thermal shock in cutting area, cutting tool has normally complex wear
    mechanism. A number of wear mechanisms have been proposed to explain the
    tool wear phenomenon. These mechanisms are:
    1- Abrasion wear
    2- Adhesion wear
    3- Diffusion wear
    4- Oxidation wear
    5- Chemical decomposition
    6- Chipping (or Thermal fatigue wear)• Abrasion wear: Abrasion wear occurs when hard particle of the chip material
    abrading (rubbing) the tool surface. The rate of wear depends on the relative
    hardness of the contacting surfaces, as well as mating geometries.
    • This is a mechanical wear, and it is the main cause of the tool wear at low
    cutting speeds.
    • Adhesion wear: Under high pressure and temperature when two surfaces come
    in close contact, strong metallic bonds are formed due to welding of the surface
    asperities. The spot weld results in an irregular flow of chips over the tool face.
    Sliding of chip causes the fracture of these small weld joints and some tool
    material carried along with them. Adhesive wear can be reduced by using a
    suitable cutting fluid which can provide a protective film on the contacting
    surfaces.• Diffusion wear: Diffusion wear means the material loss due to diffusion of
    atoms of the tool material into the workpiece moving over it. Requirements
    for diffusion wear are metallurgical bonding of the two surfaces so that
    atoms can move freely across the interface and high temperature.
    • Oxidation wear: Oxidation is the result of a chemical reaction between the
    tool surface and oxygen at high temperature. It forms a layer of oxides on the
    surface. When this layer is destroyed during the cutting process by abrasion,
    another layer begins to form. Tool wear takes as this removal and formation of
    the corrosive layer is repeated.
    • Chemical decomposition: This type of wear occurs due to interaction
    between the tool and work material in the presence of chemicals (cutting fluid).
    • Chipping: Chipping means breaking away of a small metal piece from the
    cutting edge of the tool. The chipped piece may be very small or may be
    relatively large. Unlike gradual wear, chipping results in a sudden loss of tool
    material and a corresponding change in shape, and has a major detrimental
    effect on surface finish and dimensional accuracy of the workpiece.• The two main cause of chipping are
     Mechanical Shock (impact due to interrupted cutting, as in milling)
     Thermal Fatigue (cyclic variations in temperature of the tool in interrupted
    cutting).
    Variables Affecting Tool Wear
    The important parameters which affect the tool wear are:
    1-Cutting conditions
    Speed
    Feed
    Depth of cut
    2- Tool geometry
    Rake angle
    Clearance angle
    Nose radius
    3- Tool material
    Hardness
    Wear resistance
    Thermal conductivity
    4- Work material
    5- Cutting fluid
    6- Built-Up-EdgeTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 12
    (Machinineability)Machineability
    • It is already known that pre-formed components are essentially machined to
    impart dimensional accuracy and surface finish for desired performance and
    longer service life of the product.
    • It is attempted to accomplish machining effectively, efficiently and
    economically as far as possible by removing the excess material smoothly and
    speedily with lower power consumption, tool wear and surface deterioration.
    But this may not be always and equally possible for all the work materials and
    under all the conditions.
    • The machining characteristics of the work materials widely vary and also
    largely depend on the conditions of machining. A term; ‘Machinability’ has
    been introduced for gradation of work materials w.r.t. machining
    characteristics.
    Machineability…..
    • A term; ‘Machineability’ has been introduced for gradation of work materials
    w.r.t. machining characteristics or machining properties .
    • It is defined as “ easy to machine”.
    • A material is said to have good machineability if;
    The tool wear is low
    The metal removal rate is high (or high cutting speed)
    The surface finish produced is good
    Power consumption is low
    Good dimensional accuracy
    Formation of small chipsCriteria’s for judging Machineability
    • For judging the machineability, the criteria to be chosen depends on the type
    of operation and production requirements. The following criteria may be
    considered for judging the machineability of a metal.
    1- Tool life criteria (or tool wear criteria)
    2- Surface finish criteria
    3- Power consumption criteria
    4- Production rate criteria
    5- Chip forms
    • But practically it is not possible to use all those criteria together for
    expressing machineability.
    Tool Life Criterion:
    • When tool life criterion is used, machinability is expressed in terms of ‘cutting
    speed’for given tool life.
    • A material with higher cutting speed for a given tool life will have better
    machinability.
    • In this method, the effect of surface finish is not accounted. This is most widely
    used criterion for assessing machinability of a material.
    Assessing machinability: For assessing machinability, a common material (free
    steel) is chosen as a standard and the machineability of the other materials is
    compared and expressed as a machinability index or machinability rating.
    Let , Vs = Cutting speed of standard material for a given tool life (T).
    V
    m = Cutting speed of the test material for same given tool life (T).• Than the machinability Index (MI) can be calculated as:
    • Thus, a material with higher cutting speed for a given tool life will have greater
    machinability.
    • Surface Finish Criterion: This criterion is used in a situation where poor surface
    finish is the cause of rejection on machined parts.
    A material that produces better surface finish under a given set of conditions
    may be considered to have better machinability.
    Some materials may permit use of higher cutting speed or lower cutting forces but
    give poor surface finish. In such situations, the surface finish criterion is important.
    • Power Consumption Criterion: The power consumption during machining is
    related to the cutting force. Higher the cutting force, the greater is the power
    consumption. The material requiring higher cutting forces will have lower
    machinability.
    • Production Rate Criterion: The metal removal rate is directly related to the
    cutting speed, and hence, production rate. For given surface finish and tool life, if a
    material permits high cutting speeds or higher metal removal rate will have higher
    machinability.Parameters Affecting Machineability
    The important parameters which affect the machineability are:
    1-Cutting conditions
    Speed
    Feed
    Depth of cut
    2- Tool geometry
    Rake angle
    Clearance angle
    Nose radius
    3- Tool material
    Hardness
    4- Work material (Hardness, Toughness)
    5- Cutting fluid
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-I / Lecture No: 13
    (Machine tool vibration and surface finish)
    Machining tool vibration
    • Introduction: Machine tool structures are multi-degree-of-freedom systems
    and always subjected to vibration during machining. Vibrations during a
    cutting operation affect the accuracy of the machining, which in turn affects
    the surface finish and dimensional accuracy. Severe noise is also an
    important factor which is induced by tool holder vibrations.
    • The cutting process with variable feed is one of the principles cause of
    arising of vibrations. That results in the variable dynamic cutting force.
    • These vibrations affects the machine tool, quality of work-piece, cutting tool
    and the cutting conditions (feed rate, depth of cut, and cutting velocity.Effect of Vibration
    The vibration of machine tools during cutting, affects
    • Life of machine tool , particularly transmission elements
    • Life of the cutting tool
    • Quality of the workpiece
    • Cutting conditions
    Effect of vibrations on life of machine tool: The machine tool is made of
    various parts and when vibrations are produced, they also start vibrating at
    same frequency. If this frequency approaches the natural frequency of
    vibration of that part then amplitude of vibrations will be very excessive
    and the part may break even.
    • Effect of vibrations on life of the cutting tool: As the tool-life is a function of
    the cutting variables only, the tool-life is greatly affected by presence of
    vibrations in machine tools. It is found out that the tool life is decreased by
    about 70—80% of the normal value if vibrations are present.
    • Effects of vibrations on work-piece: Due to presence of vibrations the surface
    finish obtained will be very poor and thus this aspect is very important for fine
    finishing operations of grinding and boring etc.
    • Due to vibrations, the dimensional accuracy and geometrical accuracy of the
    job is also affected.• Effect of vibrations on cutting conditions:
    Due to presence of vibrations in machine tools, the chip thickness as
    removed by the cutting tool does not remain constant and so the cutting forces
    also vary.
    Also due to vibrations, vibratory displacement of tool takes place in the
    direction of motion of the job which results in the chatter of tool.
    The penetration rate also varies and therefore penetration force does not
    remain constant. Further due to vibration of the tool, cutting velocity does not
    remain constant and it varies about the correct value.
    Sources of Vibrations
    Machine tools operate in different configurations (positions of heavy parts,
    weights, dimensions, and positions of work pieces) and at different regimes
    (spindle rpm, number of cutting edges, cutting angles, etc.). Due to this machine
    tool and cutting tool are always subjected to vibration. These vibrations are due to
    one or more of the following causes:
  11. In-homogeneities in the workpiece material.
  12. Variation of chip cross section area
  13. Disturbances in the workpiece or tool drives.
  14. Dynamic loads generated by acceleration/deceleration of moving
    components.
  15. Intermittent cutting.
  16. Self-excited vibration .• Vibration Due to in homogeneities in the Work piece: Hard spots or a crust
    in the material being machined impart small shocks to the tool and work piece,
    as a result of which free vibrations are set up. When machining is done under
    conditions resulting in discontinuous chip removals, the segmentation of chip
    elements results in a fluctuation of the cutting thrust. If the frequency of these
    fluctuations coincides with one of the natural frequencies of the structure,
    forced vibration of appreciable amplitude may be excited.
    • Vibration Variation of chip cross section area: Variation in the crosssectional area of the removed material may be due to the shape of the machined
    surface or to the configuration of the tool. In both cases, pulses of appreciable
    magnitude may be imparted to the tool and to the work piece, which may lead
    to undesirable vibration.
    Disturbances in the workpiece or tool drives: Unbalance and disturbances in
    the drives caused due to rotating unbalanced masses, faulty arrangement of
    drive and fault in the supporting bearings.
    Dynamic loads generated by acceleration/deceleration of moving
    components: In dynamically stable system, the amplitude of vibration keeps
    on decaying with time whereas in dynamically unstable system, it
    exponentially increases with time
    Intermittent cutting: Intermittent cutting as in milling. Due to it, forced
    vibrations may be generated due to elastic nature of system.
    Self-excited vibration: Self-excited vibration or chatter due to the interaction
    of cutting process and machine tool dynamicsVibration Control in Machine Tools
    • The tolerable level of vibration between tool and workpiece, i.e., the maximum
    amplitude and to some extent the frequency, is determined by the required
    surface finish and machining accuracy as well as by detrimental effects of the
    vibration on tool life and by the noise which is frequently generated.
    The vibration behavior of a machine tool can be improved by:
    Rigidify the workpiece, the tool and the machine as much as possible
    Choose the tool that will excite vibrations as little as possible (modifying
    angles, dimensions, surface treatment, etc.)
    Choose exciting frequencies that best limit the vibrations of the machining
    system (spindle speed, number of teeth and relative positions, etc.)
    Choose tools that incorporate vibration-damping technology.
    Surface finish & its importance
    • Functioning of machine parts, load carrying capacity, tool life, fatigue life,
    bearing corrosion, and wear qualities of any component of a machine have
    direct relation with its surface texture. Therefore, these effects made the
    control of surface texture very important.
    • The root of any surface irregularity acts as sharp corner and such part fails
    easily.
    • Thus in order to increase the life of any part which is subjected to fatigue
    loading, the working and non-working surfaces of that part must be given
    very good finish.Importance of surface finish
    • It improves the service life of the components
    • Better surface finish improves the fatigue strength of the component.
    • It reduces initial wear of parts due to increased surface to surface contact.
    • It gives close dimensional tolerance on the parts
    • It reduce corrosion by minimizing depth of irregularities
    • It give good surface texture.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No: 14
    (Lathe Operations)
    Introduction to the Lathe
    • The lathe is a very useful and versatile machine tool and is capable of
    performing a wide range of machining operations.
    • The workpiece is held by a chuck in one end and when possible also by a
    tailstock at the opposite end. The chuck is mounted on a headstock, which
    incorporates the engine and gear mechanism. The chuck is holding the
    workpiece with three or four jaws and a spindle engine causes the chuck and
    workpiece to rotate.
    • A tool-post is found between the headstock and tailstock, which holds the
    cutting tool. The tool-post stands on a cross-slide that enables it to move along
    the workpiece. An ordinary lathe can accommodate only one cutting tool at the
    time, but a turret lathe is capable of holding several cutting tools on a revolving
    turret.Types of Lathe
    1-Engine Lathe
    2- Bench Lathe
    3- Automatic Lathe
    4- Turret Lathe
    5- Computer Controlled Lathe
    • Engine Lathe : The most common form of lathe, motor driven and comes in
    large variety of sizes and shapes.
    • Bench Lathe: A bench top model usually of low power used to make
    precision machine small work pieces.• Automatic Lathe: A lathe in which the work piece is automatically fed and
    removed without use of an operator.
    • Turret Lathe: Lathe which have multiple tools mounted on turret either
    attached to the tailstock or the cross-slide, which allows for quick changes in
    tooling and cutting operations.
    • Computer Controlled Lathe: A highly automated lathe, where both cutting,
    loading, tool changing, and part unloading are automatically controlled by
    computer coding.Lathe Operations
    • Turning: To produce straight, conical, curved, or grooved work pieces .
    • Facing: To produce a flat surface at the end of the part or for making face grooves.
    • Drilling: To produce a hole by fixing a drill in the tailstock
    • Boring: To enlarge a hole or cylindrical cavity made by a previous process or to
    produce circular internal holes.
    • Reaming : It is used for finishing internal diameter of holes.
    • Threading: To produce external or internal threads
    • Knurling: To produce a regularly shaped roughness on cylindrical surfaces
    • Parting: To cut a piece in to two or more pieces.
    • Forming : To generate specific geometry on work surface.
    • Chamfering: Chamfering is the operation of beveling the extreme end of a
    workpiece. Chamfering is an essential operation before thread cutting so that the
    nut may pass freely on the threaded workpiece.
    Turning OperationFacing Operation
    Drilling OperationBoring Operation
    Reaming OperationThreading Operation
    Knurling OperationParting operation
    Forming OperationChamfering Operation
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No: 15
    (Shaper, planner, slotter)
    Shaper Machine
    • Introduction: Shaper is a machine tool that uses reciprocating straight line
    motion of the tool and a perpendicular feed of the job or the tool to produce flat
    work surfaces. The shaper is used primarily for:
  17. Producing a flat or plane surface which may be in a horizontal, a vertical
    or an angular plane.
  18. Making slots, grooves and keyways
  19. Producing contour of concave/convex or a combination of these.
    • Features:
    1- Single point cutting tool is used for machining. The tool is clamped on
    the tool post mounted on the ram of the machine.
    2- The ram reciprocates to and fro, tool cuts the material in forward stroke
    only, no cutting during return stroke.
    3- It uses linear relative motion between the tool and workpiece.
    4- The cross-feed is provided by the machine table on which workpiece is
    fixed.Working Principle:
    The job is rigidly fixed on the machine table. The single point cutting tool held
    properly in the tool post is mounted on a reciprocating ram. The reciprocating
    motion of the ram is obtained by a quick return motion mechanism. As the ram
    reciprocates, the tool cuts the material during its forward stroke. During return,
    there is no cutting action and this stroke is called the idle stroke. The forward and
    return strokes constituteone operating cycle of the shaper.
    Construction of shaper
    The main parts of the shaper are:
    1- Base 2- Column 3- Ram
    4- Table 5- Cross rail 6- Tool head• Base: The base is a heavy cast iron casting which is fixed to the shop floor. It
    supports the body frame and the entire load of the machine. The base absorbs
    and withstands vibrations and other forces which are likely to be induced
    during the shaping operations.
    • Column: It is mounted on the base and houses the drive mechanism
    compressing the main drives, the gear box and the quick return mechanism for
    the ram movement.
    • Ram: It is the reciprocating member with tool head mounted on its front face.
    The ram is connected to with the quick-return mechanism housed inside the
    hollow of the column. The back and forth movement of ram is called stroke
    and it can be adjusted according to the length of the workpiece to bemachined.
    • Table: The worktable of a shaper is fastened to the front of the column. The
    table moves across the column on crossrails to give the feed motion to the job.
    • Cross rail: The cross rail is mounted on the front of the body frame and can
    be moved up and down. The vertical movement of the cross rail permits jobs
    of different heights to be accommodated below the tool.
    • Tool Head- It holds the cutting tool and is fastened to the front of the ram.
    Crank and slotted link mechanism
    • Slotted link mechanism is very common in mechanical shapers.
    • It converts the rotary motion of the electric motor into the reciprocating
    motion of the ram. The return stroke allow the ram to move at a faster rate
    to reduce the idle time which is known as “quick return mechanism”,
    reduces the time waste during return stroke.
    • Bull gear is driven by a pinion which connects to the motor shaft through
    gear box.
    • The bull wheel has a slot. The crank pin A secured in to this slot, at the
    same time it can slide in the slotted crank B.Crank and slotted link mechanism
    • As the bull gear rotates causes the crank pin A also to turn and side by side
    slides through the slot in the slotted crank B.
    • This makes the slotted crank to oscillate about its one end C.
    • This oscillating motion of slotted crank (through the link D) makes the ram
    to reciprocate.
    • The intermediate link D is necessary to accommodate the rise and fall of
    the crank.Principle of Quick Return Mechanism
    • When the link is in position AP1, the ram will at extreme backward
    position of stroke.
    • When the link position is at AP2, the extreme forward position ram will
    have been reached.
    • AP1 and AP2…….Tangent to the crank pin circle.
    • Forward cutting stroke takes place when the crank rotates through an angle
    C1KC2.
    • Return stroke ……the crank rotates through angle C1LC2
    • It is seen that C1KC2 > C1LC2
    • The angular velocity of crank pin remains constant.Planer Machine
    • Like shaping machines, planning machines are also basically used for
    producing flat surfaces in different planes. A planer is generally used for
    machining large workpieces which cannot be held in a shaper.
    • In planer the worktable reciprocates during the cutting motion and cutting tools
    remains stationary.
    • The regular feed is provided by moving the cutting tool at right angles to the
    direction of the worktable motion.
    Planer MachineSlotter Machine
    • Slotting machines can simply be considered as vertical shaping machine
    where the single point cutting tool reciprocates vertically (but without quick
    return effect) and the workpiece, being mounted on the table, is given slow
    longitudinal or rotary feed. The workpieces which cannot be conveniently held
    in shaper can be machined in a slotter.
    • The main difference between a shaper and a slotter is the direction of the
    cutting action. In slotter, the tool moves vertically rather than in horizontal
    direction.
    • Unlike shaping and planing machines, slotting machines are generally used to
    machine internal surfaces (flat, formed grooves and cylindrical).
    Slotter MachineApplications of slotter
    The usual and possible machining applications of slotting machines are :
    • Internal flat surfaces
    • Enlargement or finishing non-circular holes bounded by a number of flat
    surfaces as shown in Fig.
    • Blind geometrical holes like hexagonal socket as shown in Fig.
    • Internal grooves and slots of rectangular and curved sections.
    • Internal keyways and splines, straight tooth of internal spur gears, internal
    curved surface of circular section, internal oil grooves etc. which are not
    possible in shaping machines.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No: 16
    (Milling Construction, Milling cutters, up & down millin)
    Milling Process
    • Milling is a process in which metal is removed by means of a rotating
    circular multiple points cutting tool known as milling cutter. The milling
    machine consists basically a motor driven spindle, which mounts and
    revolves the milling cutter, and a reciprocating adjustable worktable, which
    mounts and feeds the workpiece.
    • In a milling machine the work is supported by various methods on the
    worktable, and may be fed to the cutter longitudinally, transversely or
    vertically.
    • Milling process is mainly used to produce flat, curved or intricate shapes.Characteristics of Milling:
    The milling process is characterized by:
    • Intermittent Cutting: In the milling process, the equally spaced peripheral
    teeth on the cutter come in contact with the workpiece intermittently and
    machine the workpiece. This is called intermittent or interrupted cutting.
    • High metal removal rate: In milling process metal removal rate is high as
    compared to turning operation. This is because of high cutting speed and large
    number of cutting edges.
    Each of the cutting edges removes material for only a part of the
    rotation of the milling cutter.As a result, the cutting edge has time to
    cool before it again removes material. Thus the milling operation is much
    cooler compared to turning operation. This allow for high cutting speed.
    • Variation in chip thickness: In milling process the chip thickness is varies
    either from zero to maximum or from maximum to zero, depends on the type
    of milling.
    • Small size of chips: Compared to turning process, milling produces chip of
    small size.Types of Milling Process:
    1- Up Milling 2- Down Milling
    Up Milling: In up milling the cutting tool rotates in the opposite
    direction to the feed motion (or table movement).
    • In up milling, the chip starts as zero thickness and gradually increases to
    the maximum size. This tends to lift the workpiece from the table. So, up
    milling needs stronger holding of the workpiece.
    • There is a possibility that the cutting tool will rub the workpiece before
    starting of the metal removal. The initial rubbing of the cutting edge
    during the start of the cut tends to dull the cutting edge and consequently
    have a lower tool life.
    • Also since the cutter tends to cut and slide alternatively, the surface
    generated is left with the machining marks (poor surface finish).• Down Milling: In down milling the cutting tool rotates in the same direction
    as that of the feed motion.
    • In down milling, the chip starts as maximum thickness and goes to zero
    thickness gradually. This gives very fine finish on the workpiece.
    • The cutting force acts downwards and as such keeps the workpiece firmly in
    the work holding device. This is good for thin workpieces.
    Difference between up milling and down millingTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No: 17
    (max. chip thickness and power required)Maximum Chip thickness
    Length of chip in Up and Down millingTooth contact angle
    Maximum chip thicknessTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No: 18
    (Drilling, boring, reaming tool)Hole Making Operations
    The various types of hole making operations are:
  20. Drilling
  21. Boring
  22. Reaming
  23. Counter sinking
  24. Counter boring
  25. Tapping
    Drilling
    • Drilling is the operation of producing a cylindrical hole in a work piece using a
    rotating tool called drill or twist drill. The work piece is held in the chuck and the
    drill is held in the tailstock. The feed is provided by means of moving the sleeve
    of the tailstock. Drilled holes can be either through holes or blind holes.Drilling Operations:
    • The various drilling operations are:
    • Drilling: This process is used to drill a round blind or through hole in solid
    material.
    • Core Drilling: Core drilling is used to increase the diameter of an existing hole
    by using a drill bit of larger diameter than the diameter of the existing hole.
    • Step Drilling: This operation is carried out to drill a stepped (multi-diameter)
    hole in a solid material.
    • Boring: Boring is an operation of enlarging an existing hole to the required
    accurate size and finish. A single point cutting tool is used for boring operation.
    • Counter Boring: Enlarging an existing hole for a limited depth is called
    counter boring. The enlarged hole, which is concentric with the existing hole, is
    flat at the bottom. Counter boring is used mainly to set bolt heads and nuts
    below the workpiece surface.• Counter Sinking: Counter sinking is the operation of angular enlargement
    of the end, of an existing hole. This is done to accommodate the conical
    seat of a flat headed screw.
    • Centre Drilling: Centre drilling is used to drill a starting hole to precisely
    define the location for subsequent drilling. The tool is called centre drill. A
    centre drill has a thick shaft and very short flutes. It is therefore very stiff
    and will not walk as the hole is getting started;
    • Gun Drilling: Gun drilling is a specific operation to drill holes with very
    large length-to-diameter ratio up to L/D ~300. There are several
    modifications of this operation but in all cases cutting fluid is delivered
    directly to the cutting zone internally through the drill to cool and lubricate
    the cutting edges, and to remove the chips.
    Boring Process
    • During drilling operation, drill tend to wander, making hole location inaccurate.
    Also, if the lips of the drill are not equal, the hole will be oversized. When
    accurately located holes are needed, they are first drilled and then bored.
    • Boring is a process of enlarging an existing hole, may be drilled or cored
    during casting.
    • Boring corrects the location of a hole, makes concentric, and bring them to the
    exact required size. This is because; boring bar does not follow the hole, but
    bores on its own centre of axis.Boring process
    Reaming Process
    • Reaming is an operation of finishing an existing hole to get smooth surface and
    closer tolerances (±0.005mm) on the diameter of a hole. This is carried out by
    using a multi-point cutting tool known as reamer. Reamer rotates and feed
    linearly into an existing hole. In this operation very little material is removed.
    • Generally the reamer follows the already existing hole and therefore will not be
    able to correct the hole misalignment.
    • The reamer is expected to cut from the sides and not from the end. These types
    reamer are most suitable for reaming through holes. However for reaming blind
    holes with a flat bottom, special end cutting reamers are used. They too have
    cutting edges formed at the end.Reaming Process
    Reamer geometryTapping Process
    • Tapping is an operation in which internal threads are cut in the existing hole.
    This operation is carried out with a multi-fluted cutting tool known as tap.
    • A tap is a cutting tool with threads cut accurately on its periphery. These threads
    are hardened and ground and act as cutting edges. The tap removes metal when
    screwed into the hole and generates internal threads.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-II / Lecture No:19
    (geometry of twist drill)
    Geometry of twist drill:
    A drill is generally called twist drill, since it has a sharp twisted edges formed
    around a cylindrical tool provided with a helical groove along its length to allow
    the cut material to escape through it.Drill Flutes: These are helical grooves cut on the cylindrical surface of the drill.
    A twist drill generally has two flutes. They serve the following purposes;
    To provide clearance to permit the removal of the chips.
    To allow cutting fluid to reach the cutting edges.
    Cause the chips to curl so that it occupies minimum space.
    Flute Length: It is the length of the measured from the drill point to the end of
    the flute. Flute length determines the maximum depth of drilling.
    Land : It is the part of the drill body between the flutes. The lands provide the
    drill with much of its torsional strength.
    Web: It is the thickness of the drill between the flutes. The web also provides
    torsional strength to the drill.
    Point Angle: The angle included between the cutting lips projected upon a plane
    parallel to the drill axis and parallel to the two cutting edges.
    • Larger value of point angle is used for hard and brittle materials, while smaller
    values are used for soft and ductile materials.
    • In general 118º is found to be suitable for mild steel and other general materials.
    Chisel Edge: The edge at the end of the web that connects the cutting lips is
    called chisel edge.
    Lip Relief Angle: The axial relief angle at the outer corner of the lip; it is
    measured by projection into a plane tangent to the periphery at the outer corner of
    the lip.
    Helix Angle: It is the angle between the leading edge of the land and the axis of
    the drill.
    The helix angle of the flutes performs the function of lifting the chips
    from the hole being drilled.
    The typical helix angle of a general purpose twist drill is 18 – 30º.THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 23
    (Grinding wheels, abrasive & bonds, cutting action.)
    Grinding Process
    • Grinding is a finishing process carried out with a revolving abrasive wheel for
    removing very fine quantities of material from the work surface.
    • The wheel used for performing the grinding action is called grinding wheel.
    • An abrasive is a small, non-metallic hard particle having sharp cutting edges
    and an irregular shape. Each individual abrasive grain acts as a cutting edge.Purpose of grinding process:
    Grinding is a process used for the following purposes:
    • Machining those materials which are too hard for other machining
    processes such as tool and die steels and hardened steel materials.
    • To achieve close dimensional accuracy of the order of 0.3 to o.5µm.
    • To achieve high degree of surface finish such as Ra = 0.15 to 1.25µm.
    • It is used for sharpening the cutting tools.
    Cutting Action
    • The grinding wheel-workpiece interaction can be divided in to the following:
    1- Grit-workpiece (forming chip)
    2- Chip-bond
    3- Chip-workpiece
    4- Bond-work piece
    • Except the grit workpiece interaction which is expected to produce chip, the
    remaining three undesirable increases the total grinding force and power
    requirement.Interaction of the grit with the workpiece: The importance of the grit shape
    can be easily realized because it determines the grit geometry e.g. rake and
    clearance angle as illustrated in Fig. It appears that the grits do not have definite
    geometry unlike a cutting tool and the grit rake angle may vary from +45° to –
    60° or more.
    Grit with favorable geometry can produce chip in shear mode. However, grits
    having large negative rake angle or rounded cutting edge do not form chips but
    may rub or make a groove by ploughing leading to lateral flow of the workpiece
    material as illustrated in fig.Grinding Wheel
    Grinding wheels are made by mixing the appropriate grain size of the abrasive
    with the required bonding material and pressed in to required shape (by powder
    metallurgy process).
    Types of abrasive material.
    Aluminum oxide (Al2O3)
    Silicon carbide (SiC)
    Cubic Boron nitride (cBN)
    Diamond
    • Properties of abrasive grains: The desirable properties of abrasive grains
    are:
    Friability
    Hardness
    Toughness
    High hot hardness
    Chemically Inert
    Difference between grinding and milling
    • The abrasive grains in the wheel are much smaller and more numerous than
    the teeth on a milling cutter.
    • Cutting speeds in grinding are much higher than in milling.
    • The abrasive grits in a grinding wheel are randomly oriented.
    • A grinding wheel is self-sharpening.
    Particles on becoming dull either fracture to create new cutting
    edges or are pulled out of the surface of the wheel to expose new
    grains.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 21
    (Grinding wheels specification.)Grinding Wheel Specification
    The performance of a grinding wheel depends upon a number of parameters. These are:
  26. Types of abrasive material.
    Aluminum oxide (Al2O3)
    Silicon carbide (SiC)
    Cubic Boron nitride (cBN)
    Diamond
    2-Bonding Material
    Vitrified
    Silicate
    Synthetic resin / plastic
    Rubber
    Shellac
    Metal
  27. Grain size
    Course grain size
    Fine Grain Size
    Very fine grain size
  28. Grade
    (bond strength or wheel hardness)
    Soft wheel
    Hard wheel
    5- Structure of the wheel
    Open Structure
    Dense Structure1-Types of abrasive material:
    • Aluminum oxide: It is most widely used abrasive in industry. As it is very tough
    and is not easily fractured, it is better adopted to grinding materials of high
    tensile strength, such as carbon steels, high speed steels, bronze etc.
    • Silicon carbide: Silicon carbide is harder than aluminum oxide but less tough.
    Silicon carbide is also inferior to Al2O3 because of its chemical reactivity with
    iron and steel. Silicon carbide is used for grinding non-ferrous metals such as
    brass, aluminum, titanium etc.
    • Cubic boron nitride: Cubic boron nitride is a super abrasive material with
    hardness second to the diamond. It is chemically inert with relatively high
    toughness than diamond. It is used for grinding carbon and alloy steels. .
    • Diamond: Diamond is a super abrasive material with the highest known
    hardness. It is used for grinding non-ferrous metals, ceramics, glass, stone, and
    building materials.
    2- Bonding Material (Bond)
    It is the material that is used to hold the abrasive grain together. The function of
    the bond is to keep the abrasive grain together under the action of the high
    grinding force and temperature. The various bonding materials are:
    Vitrified (Strong and Rigid, commonly used).
    Silicate (Provides softness, grains dislodge quickly)
    Synthetic resin / plastic (Provides shock absorption and elasticity,
    strong enough).
    Rubber (For making flexible wheels)
    Shellac (Used for making thin but strong wheels)
    Metal (For diamond wheels only)3- Grain Size:
    • Choice of grain size depends upon the properties of the work material (hard
    or soft), surface finish, and desired rate of metal removal etc.
    • Coarse grains give faster rate of metal removal, but yield a poor surface
    finish. Fine grains take a very small depth of cut and hence provide a better
    surface finish but the rate of metal removal is slow.
    • Coarse grains have higher friability; therefore, coarse grain wheels are
    suitable for grinding soft and ductile materials. For hard and brittle
    materials finer grains are preferred.
    4- Grade:
    • The grade of a grinding wheel is a measure of the strength of a bond. The grade
    of a wheel depends on the kind of bonding material, volume of bonding
    material used, structure of wheel, and amount of abrasive grains.
    • Hard grade: A hard wheel means strong bonding and the abrasive grains can
    withstand large forces without broken away from the wheel.
    • Soft grade: Wheels from which the abrasive is more easily broken away is
    known as soft wheel.5- Structure of wheel:
    • The structure of a grinding wheel represents the grain spacing or density of
    the wheel. A grinding wheel must have some space between grains to allow
    space for the chips to collect. This helps avoiding the loading of the
    grinding wheel.
    • A wheel may have an open structure or dense structure.
    Structure of wheel…..Grinding Wheel Specification
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 22
    (Grinding wheel wear)
    Grinding wheel wear
    • Grinding wheel wear is an important consideration, because it adversely affects
    the efficiency of the grinding process and quality of the ground surface.
    Grinding wheels wear by three different conditions:
    1- Attrition wear
    2- Fracture wear
    Grain fracture
    Bond fractureAttrition Wear: In attrition wear, the cutting edges : of a sharp grain become dull,
    developing a wear flat. Such type wheel wear is caused by:
    • Wear due to frictional interaction between workpiece and abrasive grain.
    • Chemical reaction between abrasive and workpiece material at elevated
    temperatures and in the presence of grinding fluids.
    Fracture Wear:
    • Grain Fracture: Because abrasive grains are brittle in nature, they get fractured
    under high mechanical and thermal loads. The applied thermal and mechanical
    loads, cause initiation and further development of cracks that leads to fracture and
    the formation of new irregular surfaces.
    • Bond Fracture: If the wear flat caused by the attrition wear is excessive, the
    grain becomes dull and produces high pressure and temperature at the cutting
    zone. Under these conditions, grains are fractured continuously at moderate rate.
    Grinding wheel wearDressing of grinding wheel
    • With continuous use, a grinding wheel becomes dull (sharp cutting edges
    becomes rounded). Further some grinding chips get lodged into the space
    between grains. Such type glazed and lodged wheel makes the grinding
    process inefficient.
    • Dressing is a process that applied to worn out wheel for re-sharpening
    and cleaning purpose. Dressing is done:
    • To restore the cutting ability of the wheel by fracturing away the dull grains
    to expose new sharp cutting edges.
    • To remove the lodged metal chips and particles.
    • Since dressing is done manually it does not produce a concentric surface of
    the wheel.
    Truing of grinding wheel
    • After dressing process, the form and concentricity of the grinding wheel is
    destroyed. Truing process is carried out to restore the form and
    concentricity of the wheel.
    • Truing is process of regenerating the required geometry on the grinding wheel,
    whether the geometry is a special form or flat profile.
    • It is also used to make the wheel concentric with its axis of rotation.
    • In practice the truing of a grinding wheel is of vital importance because the
    dimensional accuracy of the grounded workpiece is directly related to the
    effective wheel geometry. Truing is also required on a new conventional wheel
    to ensure concentricity with specific mounting system.Truing tools:
    1- Steel cutter
    2- Abrasive sticks and wheels
    3- Diamond dressers
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 27
    (Surface and Cylindrical grinding. Centerless grinding.)
    Surface grinding:
    • Surface grinding is used for generating flat surfaces by using either the
    peripheral or diametrical face of the grinding wheel.Cylindrical grinding:
    • Cylindrical grinding process used for of grinding cylindrical or tapered
    surfaces while they are rotated between centres or supported on a spindle.
    The grinding wheel cuts the material from its peripheral face.
    Centreless Grinding:
    • In conventional cylindrical grinding the workpiece is supported between
    centres or a chuck and rotated against the grinding wheel. Centreless
    grinding makes it possible to grind cylindrical workpiece without actually
    fixing the workpiece between centres or a chuck. As a result no work
    rotation is separately provided.Types of Centreless Grinding:
    1- Through-feed centreless grinding
    2- In-feed centreless grinding (or plunge cut grinding)
    3- End-feed centreless grinding
    1- Through-Feed Centreless Grinding: It is used for grinding straight
    cylindrical parts having uniform cross section. In through-feed grinding, a
    workpiece is inserted between the regulating and grinding wheels, causing
    the workpiece to rotate and move forward. The work is driven axially
    between the wheels by inclination of the regulating wheel relative to the
    grinding wheel.2- In-Feed Centreless Grinding:
    • This method is used when the workpiece has an obstruction which will not allow
    it to ground by the through-feed method. The obstruction could be multiple
    diameters, a shoulder, head etc. Such type workpieces are centreless grounded
    by in-feed method.
    3-End-Feed Centreless Grinding:
    • This method is used for grinding short tapered workpieces. The grinding and
    regulating wheels are dressed to the correct taper. The grinding wheel, regulating
    wheel and the work rest are set in fixed relation to each other. The workpiece is
    fed automatically from the front to a fixed end stop.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 24
    (Super finishing process.)Surface Finishing Processes
    • To ensure reliable performance and prolonged service life of modern machinery,
    its components require to be manufactured not only with high dimensional and
    geometrical accuracy but also with high surface finish.
    • The surface finish has very great influence on most important functional
    properties such as wear resistance, fatigue strength, corrosion resistance and
    power loss due to friction.
    Purpose of surface finishing processes:
    • To improve the geometrical and dimensional accuracy.
    • To improve the surface finish and appearance.
    • To improve the functional properties of the machine parts (wear resistance,
    corrosion resistance, fatigue strength etc).
    Super finishing Processes
    • Honing
    • Super finishing
    • Lapping
    • Polishing
    • BuffingHoning:
    • Honing process is mainly used to improve the surface finish of bored or
    grounded holes. This process removes common errors left by boring or grinding
    process such as taper, waviness, and tool marks.
    • The honing tool consists of a set of grinding stones arranged in a circular
    pattern. These stones are mounted on a mandrel which is then given a
    reciprocating motion (along the hole axis) with uniform rotary motion.
    Because of the nature of the path of the abrasive grit on the surface of the
    work, a random cross-marked surface finish is obtained (desirable for
    lubrication).Super finishing
    • Super finishing is also an abrasive process mainly used to finish the external
    surfaces of the machine parts. This also uses bonded abrasive stick (like honing)
    moved with a reciprocating motion and pressed against the surface to be
    finished. The relative motion between the abrasive stick and the workpiece is
    varied so that individual grains do not retrace the same path, results in very high
    surface finish.
    Lapping
    • Lapping is an abrasive surface-finishing process and used to produce very high
    degree of surface finish.
    • In lapping process a layer of fine abrasive particles, usually suspended in a
    liquid, is held between the workpiece and the lap. Softer lap material causes the
    abrasive grains to get embedded on to the lap surface when pressure is applied
    between the lap and the workpiece. These grains cut the workpiece in the same
    way as in grinding when relative motion is provided between the workpiece
    and the lap.Polishing
    • Polishing process is used to remove scratches and burrs from a machined surface. It
    develops a very smooth surface with glossy finish. A very small amount of material
    is removed in polishing.
    • Polishing is carried out by a wheel or belt rotating at high speed. The polishing
    wheels are made of softer materials like leather or cloths and coated with very fine
    abrasive particles. Thus, the wheels are enough flexible to finish the cavities and
    intricate shapes.
    Buffing
    • Buffing is similar to polishing in appearance, but its function is different. Buffing is
    used to provide attractive surfaces with high luster. Negligible amount of material is
    removed in this process.
    • Buffing is carried out with the help of a buffing wheel which is made by a cloth or
    lather. The abrasive is applied intermittently to the wheel in a lubricating medium.
    The abrasives used are extremely fine powder.Gradual improvement of surface roughness produced by various processes ranging
    from precision turning to super finishing including lapping and honing.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 25
    (Limits, Fits, Tolerances)
    Introduction of metrology
    • In manufacturing it is impossible to produce all the components to an exact
    size.
    • In any production process, regardless of how well it is designed or how
    carefully it is maintained, a certain amount of natural variability will always
    exist. Usually, variability arises from uncontrollable causes like
     Improper adjusted machines
     Operator error
     Tool wear
     Defective raw materials.
    • Thus some variability in dimension within certain limits must be tolerated
    during manufacture. When the tolerance allowed is sufficiently greater than the
    process variation, no difficulty arises during manufacturing.Limit
    • The range of permissible variation in dimension form actual dimension is
    called limit. The permissible variation may exist on either sides of the actual
    size.
    • Upper Limit: It is the largest permissible variation in dimension of the
    component.
    • Lower Limit: It is the minimum permissible variation in dimension of the
    component.
    Tolerance
    • The difference between upper limit and lower limit is called tolerance.
    • It is also the total amount that a specific dimension is permitted to vary
    from actual size.Fit
    • Manufactured parts are required to mate with one another during assembly.
    • The degree of tightness or looseness between two mating parts at the time
    of assembly is called a fit.
    Types of fit:
  29. Clearance fit
  30. Interference fit
  31. Transition fit• Clearance fit: In clearance fit, an air space or clearance exists
    between the shaft and hole as shown in Figure. Such fits give loose joint. A
    clearance fit has positive allowance, i.e. there is minimum positive
    clearance between high limit of the shaft and low limit of the hole.
    • Interference fit: A negative difference between diameter of the hole
    and the shaft is called interference. In such cases, the diameter of the shaft
    is always larger than the hole diameter. In Figure. Interference fit has a
    negative allowance, i.e. interference exists between the high limit of hole
    and low limit of the shaft.• Transition Fit: It may result in either clearance fit or interference fit
    depending on the actual value of the individual tolerances of the mating
    components. Transition fits are a compromise between clearance and
    interference fits. They are used for applications where accurate location is
    important but either a small amount of clearance or interference is
    permissible. As shown in Figure, there is overlapping of tolerance zones of
    the hole and shaft.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-III / Lecture No: 26
    (Surface roughness)
    Surface Roughness
    With the more precise demands of modern engineering products, the control of surface
    texture together with dimensional accuracy has become more important. It has been
    investigated that the surface texture greatly influences the functioning of the
    machined parts. The properties such as appearance, corrosion resistance, wear
    resistance, fatigue resistance, lubrication, initial tolerance, ,load carrying capacity, noise
    reduction in case of gears are influenced by the surface texture.
    Whatever may be the manufacturing process used, it is not possible to produce perfectly
    smooth surface. The irregularities are bound to occur. The irregularities on the surface are
    in the form of succession of hills and valleys varying in height and spacing. These
    irregularities are usually termed as surface roughness or surface finish.Factors Affecting Surface Roughness
    The following factors affect the surface roughness:
  32. Vibrations
  33. Material of the workpiece
  34. Type of machining (conventional or unconventional)
  35. Rigidity of the system consisting of machine tool, cutting tool and work .
  36. Rigidity of the fixture.
  37. Type and sharpness of cutting tool
  38. Cutting conditions i.e., feed, speed and depth of cut
  39. Type of cutting fluid used
    Reasons for Controlling Surface Roughness
    • To improve the service life of the components
    • To improve the fatigue resistance
    • To reduce initial frictional wear of parts
    • To have a close dimensional toleranceon the parts
    • To reduce corrosion by minimizing depth of irregularities
    • For good appearance .Orders of Geometrical Irregularities
    • As we Know that the material machined by chip removal process can’t be
    finished perfectly due to some departures from ideal conditions as specified by
    the designer. Due to conditions not being ideal, the surface Produced will have
    some irregularities, these geometrical irregularities can be classified into four
    categories.
    • First Order: The irregularities caused by inaccuracies in the machine tool
    itself are called as first order irregularities. These include:
    1- Irregularities caused due to lack of straightness of guide ways on which
    the tool most moves.
    2- Surface regularities arising due to deformation of work under the action
    of cutting forces.
    3- Due to the weight of the material itself.
    • Second Order: The irregularities caused due to vibrations of any kind are
    called second order irregularities.
    • Third order: Even if the machine were perfect and completely free from
    vibrations some irregularities are caused by machining itself due to the
    characteristics of the process.
    • Fourth Order: The fourth order irregularities include those arising from the
    rupture of the material during the separation of the chip.Type of irregularities on the surface of the part
    • The irregularities on the surface of the part produced can also be grouped into
    two categories:
    1- Roughness or primary texture
    2- Waviness or secondary texture.
    Roughness: The surface irregularities of small wavelength are called
    primary texture or roughness. These are caused by direct action of the cutting
    element son the material i.e., cutting tool shape, tool feed rate or by some other
    disturbances such as friction, wear or corrosion.
    Waviness: The surface irregularities of considerable wavelength of a
    periodic character are called secondary texture or waviness. These irregularities
    result due to inaccuracies of slides, wear of guides, misalignment of centers,
    non-linear feed motion, deformation of work under the action of cutting forces,
    vibrations of any kind etc.Measurement of surface roughness
    • The following three methods of evaluating primary texture
    (roughness) of a surface are used:
    1- Peak to valley height method
    2- The average roughness
    C.L.A Method
    R.M.S Method
    Measurement of surface roughness
    Peak to valley height method: It measures the maximum depth of
    the surface irregularities over a given sample length, and largest value of
    the depth is accepted as a measure of roughness. The drawback of this
    method is that it may read the same ℎ for two largely different texture. The
    value obtained would not give a representative assessment of the surface.Measurement of surface roughness
    • C.L.A Method: In this method, the surface roughness is measured as the
    average deviation from the nominal surface. Arithmetic Average is defined as
    the average values of the ordinates from the mean line, regardless of the
    arithmetic signs of the ordinates
    Measurement of surface roughness
    • R.M.S. Method: In this method also, the roughness is measured as the
    average deviation from the nominal surface. Root mean square value measured
    is based on the least squares.
    • Let us assume that the sample length ‘L’ is divided into ‘n’ equal parts and 1, 2,
    3 ….are the heights of the ordinates erected at those pointsTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 33
    (Survey of welding and allied process)Welding and allied process
    • The joining of materials by a solid joint or the cutting of materials without the
    use of mechanical cutting tools, usually by means of heat, comprise the
    following processes: welding, brazing, thermal spraying and thermal cutting.
    • Soldering and brazing involve melting a lower-melting-point material between
    the workpieces to form a bond between them, without melting the workpieces.
    In this process, the melting point of solder should be at a temperature of at least
    50o C lower than the melting point of base material to be joined.
    • Thermal spraying is a process in which a molten metal is sprayed onto a surface.
    Thermal cutting is a process used for the cutting of materials by means of heat.
    No cutting tools are used in the process.
    • An allied process to welding may be adhesive bonding because it also involves
    the joining of materials by a solid joint. However adhesive bonding is different
    from welding in terms of operating conditions and equipments.
    Various welding and allied processes involving addition or deposition of
    metal on work surface are classified as:
  40. Welding processes
     Cast weld processes
     Fusion weld processes
     Resistance weld processes
     Solid state weld processes
  41. Allied welding processes
     Metal depositing processes
     Soldering & Brazing
     Adhesive bonding
     Metal sprayingWelding process
    • Welding is a metal joining process in which two or more parts are joined
    together at their contacting surfaces by a suitable application of heat or
    pressure. Some time parts are joined together by application of pressure only
    without external heat. In some welding processes a filler material is added to
    facilitate joining.
    • The term assembly usually refers to mechanical methods of fastening the
    parts together. Some of these methods allow easy disassembly, while other
    do not.
    Classification of Welding Processes
    1- Fusion Welding Processes
    Arc welding
    Resistance welding
    Gas welding
    Thermit welding (cast weld process)
    2- Solid State Welding Processes
    Friction welding
    Explosive welding
    Ultrasonic welding
    Diffusion bonding
    3- Solid-Liquid State Welding Processes
    Brazing
    Soldering
    Adhesive bondingArc Welding Processes
    • Shielded metal arc welding
    • TIG welding
    • MIG welding
    • SAW
    • Atomic hydrogen welding
    • Electro-slag welding
    • Electro-gas welding
    Resistance Welding Processes
    • Spot welding
    • Seam welding
    • Projection weldingSolid State Welding Processes
     Friction welding
     Explosive welding
     Ultrasonic welding
     Diffusion bonding
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 28
    (Gas welding)
    Oxy-Acetylene Welding
    • Gas Welding: Gas welding refers to a group of fusion welding processes in
    which heat required for welding is obtained from the combustion of a fuel
    gas (acetylene, propylene, propane, methyl-acetylene propadiene or
    hydrogen) in combination with oxygen. Generally acetylene gas is used as
    fuel gas because it generates highest flame temperature.
    • Oxy-Acetylene Welding: Oxy-acetylene welding is a fusion welding
    process in which heat required for welding is obtained from the combustion
    of acetylene gas in combination with oxygen. The heat produced by the
    combustion of gas is sufficient to melt any metal.Oxy-Acetylene Welding
    The flame is directed by a welding torch and a filler metal in the form of rod is
    added, if required. A flux may be used to deoxidize and cleanse the weld metal.
    The flux melts, solidifies, and forms a slag skin on the resultant weld metal.
    Principle of Oxy-Acetylene Welding
    • In oxy-acetylene welding heat is obtained from the combustion of acetylene gas
    in combination with oxygen. The combustion takes place in two stages:
    • Primary Combustion: In first stage, oxygen reacts with acetylene and
    produces carbon monoxide and hydrogen. This reaction occurs near the tip of
    the torch and generates intense heat.
    C2H2 + O2 = 2CO + H2 + Heat (67%)
    • The inner cone is the area where the primary combustion takes place through
    the chemical reaction between O2 (from cylinder) and C2H2. The heat of this
    reaction accounts for about two-thirds of the total heat generated.
    • Secondary Combustion: The products of the primary combustion, CO and H2,
    react with O2 (from the surrounding air) and form CO2 and H2O (vapour). Thus,
    two separate reactions occur in outer envelope.
    2CO + O2 = 2CO2 + Heat
    H2 + O2 = H2O + Heat
    • The heat of this reaction accounts for about one-thirds of the total heat
    generated. The area where this secondary combustion takes place is called the
    outer envelope.• The two stage combustion process produces a flame having two distinct
    regions, inner cone and outer envelope. The maximum temperature occurs near
    the end of the inner cone, where the first stage of combustion is completed.
    Most welding should be performed with the torch positioned so that this point
    of maximum temperature is just above the metal being welded.
    Types of Flames
    Three different types of flames can be obtained by changing the
    oxygen/acetylene ratio.
    1- Neutral Flame (O2 = C2H2)
    2- Oxidizing Flame (O2 > C2H2)
    3- Carburizing Flame (O2 < C2H2)• Neutral Flame: When the ratio of oxygen/acetylene is equal (O2:C2H2 = 1:1), a
    neutral flame is obtained. All the acetylene present in the mixture is completely
    burned.
    • This cone consists of two regions, short inner cone and longer outer envelope.
    The inner cone has the highest temperature, around 3300ºC.
    • Neutral flame is mainly used for welding ferrous metals such as carbon steels.
    This is because, neutral flame have least chemical effect on the molten metal
    and produces high temperature.
    • Carburizing Flame: Carburizing flame is obtained when excess of acetylene
    (O2:C2H2 = 0.9:1) is supplied than which is theoretically required. The
    combustion of acetylene is incomplete because of insufficient amount of
    oxygen.
    • A carburizing flame consist three regions, inner cone, acetylene feather, and
    outer envelope. The acetylene feather is developed due to incomplete
    combustion of acetylene. The length of feather is increases as the acetylene
    proportion increases.
    • The excess acetylene decomposes into carbon and hydrogen, thus flame
    temperature is lowered (about 3100ºC).
    • Oxidizing Flame: When excess oxygen is used (O2:C2H2 = 1.5:1), the flame
    becomes oxidizing because of the presence of unconsumed oxygen. A short
    white inner cone characterizes an oxidizing flame. The oxidizing flame is
    similar to neutral flame in appearance with the exception that the inner cone is
    little small.
    • The oxidizing flame produces highest tip temperature (3500ºC) than the other
    two flames.
    • In oxidizing flame, the inner cone is hotter than the other two flames because
    the combustible gases will not have to search so far to find the necessary
    amount of oxygen.
    • Applications: There is unconsumed oxygen in the flame, which badly oxidizes
    the weld metal. Because of the burning of the molten metal (due to low
    temperature oxide formation during process), foams and sparks are formed in
    the weld pool. This also produces loud noise during welding.
    • Oxidizing flame is used for welding those metals and alloys which are not
    oxidized easily. So, it is used for welding Copper based alloys and zinc based
    alloys such as brass and bronze.
    • Oxidizing flame will introduce oxygen into the weld metal and so not preferred
    for steel.Gas Cutting Process
    • For cutting metallic plates, general purpose machine tools are used. These
    tools are useful for only straight-line cuts and also for cuts up to a thickness of
    40 mm. For thicker plates and when the cut is to be made along a specified
    contour, machine tools cannot be used.
    • Thus, for cutting thicker plates or cutting along a specified contours oxyacetylene cutting process is used. The oxy-acetylene cutting is the most widely
    used industrial thermal cutting process because it can cut thicknesses from 0.5
    mm to 2 meters; the equipment cost is low and can be used manually or
    mechanized
    Gas Cutting Process
    • Principle of gas cutting: The main theory behind the oxy-acetylene cutting is
    that the melting point of metal oxides is nearly half of that is of pure metals.
    Oxy-acetylene cutting uses acetylene and oxygen to preheat metal to red hot
    temperature (800 – 1000ºC) and then uses pure oxygen jet to burn away the
    preheated metal. Because this is achieved by oxidation, it is only effective on
    metals that are easily oxidized at this temperature. Such metals are mild steel
    and low allow steels. Aluminum, stainless steel, and other metals and alloys
    cannot be cut with a cutting torch.
    • The term for this oxygen flame is the “Preheating Flame”. Next, you direct a jet
    of pure oxygen at the heated metal by pressing a lever on the cutting torch. The
    oxygen causes a chemical reaction known as “oxidation” to take place rapidly.
    When oxidation occurs rapidly, it is called “ combustion or Burning” . When it
    occurs slowly, it is known as “Rusting”.Gas Cutting Process
    • When you uses the oxy-gas torch method to cut metal, the oxidation of the
    metal is extremely rapid and part of the metal actually burns. The heat, liberated
    by the burning of the iron or steel, melts the iron oxide formed by the chemical
    reaction and accelerates the preheating of the object you are cutting. The molten
    material runs off as slag, exposing more iron or steel to the oxygen jet.
    • Difference between Cutting Torch and Welding Torch: The main
    difference between the cutting torch and the welding torch is that the
    cutting torch has an additional tube for high-pressure cutting oxygen. Thus,
    the tip has a central hole for the oxygen jet with surrounding holes for
    preheating flames.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 29
    (SMAW welding )Shield Metal Arc Welding
    • In shield metal arc welding an arc is established between a consumable metal
    electrode (coated) and workpiece to be welded. The intense heat of the arc forms
    a molten pool in the metal being welded, and at the same time melts the tip of
    the electrode. As the arc is maintained, molten filler metal from the electrode tip
    is transferred across the arc, where it fuses with the molten base metal.
    Shield Metal Arc Welding……
    • In this process coated stick electrodes is used. During welding electrode coating
    disintegrates, giving of vapour that serves as shielding gas and providing a layer
    of slag. Vapour and layer of slag both protect the weld area from atmospheric
    contaminations. Due to this the process is called shielded metal arc welding.Equipments for SMAW
    • Welding power source: Shielded metal arc welding can be done with either an
    AC or DC power source, but in either case, the power source selected must be
    of the constant current type.
    • Welding current: Shielded metal arc welding can be done with either an AC
    or DC power source. Both AC and DC power source produces good quality
    welds, but depending upon welding situations one may be preferred over other.
    • Welding electrode: SMAW uses a consumable electrode coated with the flux.
    The heat of the welding process melts the coating to provide a protective
    gaseous shield and slag for the welding operation.
    Functions of the electrode coating
    1- Protection: The coating materials burns off faster than core wire and creates
    gaseous atmosphere and protect the weld pool and arc from atmospheric
    contaminations.
    The coating also provided the flux to the molten metal pool. This flux mixed with
    the oxides and other impurities present in the pool, forms slag. The slag being
    lighter, floats on the top of the molten metal and protect it against atmospheric
    contaminations.2- Improves mechanical properties: The thickness of slag layer formed on the
    metal surface also controls the cooling rate of the weld metal. Thus, improves
    the mechanical properties of the weld joint.
    3- Oxide remover: Flux removes the impurities (oxides and trapped gases) from
    the molten metal.
    4- Metal addition: Coating also provides alloy addition to the weld metal which
    necessary to produce desired arc and metal transfer characteristics.
    5- Helps in concentrating the arc: Since electrode coating is disintegrated at
    slower rate compare to the filler metal, the coating would be extended beyond
    the electrode. This extended coating helps in concentrating the arc and directing
    the filler metal towards the weld joint. Thus gives deeper penetration.
    Advantages of SMAW
    • It is best suited for welding steels (carbon steels, alloy steels, stainless steels
    etc) and cast iron.
    • Welding can be carried out in any position (Flat, vertical or horizontal
    position) with highest weld quality.
    • Joints which because of their positions are difficult to weld by any other
    process, can be easily weld by SMAW.
    • All metals for which electrodes are available can be welded by this process.Disadvantage of SMAW
    • Those metals which having low melting point (aluminum, copper, lead tin etc)
    cannot be welded by this process.
    • It cannot be used for welding thin metal pieces.
    • Metal deposition rate is very low, gives slow welding speed. The deposition rate is
    limited by the fact that the electrode covering tends to overheat and fall off when
    excessively high welding currents are used.
    • Because of slow welding speed it gives large HAZ and distortion.
    • During multi-pass welding, there are more chances of slag inclusions in weld bead.
    • A lot of electrode material is wasted in the form of unused end, slag and gas.
    • Due to use of stick electrode, automation is not possible.
    Application of SMAW
    • Depending upon the coated electrodes available, it finds extensive use in all
    major fabrication industries. Common applications include construction,
    pipelines, machinery structures, shipbuilding, fabrication job shops, and repair
    work.
    • It is preferred over oxy-fuel welding for thicker sections above 5 mm because of
    its higher heat density.
    • The equipment is portable and low cost, making SMAW highly versatile and
    probably the most widely used of the AW welding processes.
    • Base metals include steels, stainless steels, cast irons can be welded by this
    process.THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 29
    (TIG process and their parameters.)
    TIG Welding
    Tungsten inert gas (TIG) welding process developed in 1940s for joining
    magnesium and aluminium. Using an inert gas shield instead of a slag to protect
    the weld pool, the process was a highly attractive replacement for gas and
    manual metal arc welding. TIG has played a major role in the acceptance of
    aluminium for high quality welding and structural applications.
    In the TIG welding process the arc is formed between a non consumable
    tungsten electrode and the workpiece in an inert atmosphere of argon or helium.
    The small intense arc provided by the pointed electrode is ideal for high quality
    and precision welding. Because the electrode is not consumed during welding,
    the welder does not have to balance the heat input from the arc as the metal is
    deposited from the melting electrode. When filler metal is required, it must be
    added separately to the weld pool.Working Principle of TIG
    In the tungsten inert gas welding process, the arc is produced between a nonconsumable tungsten electrode and the workpiece in a protective inert gas
    atmosphere. The shielding gas protects both the tungsten electrode and the weld
    pool from the atmospheric contaminations. The shielding gases commonly used
    are argon, helium or their mixture. Any filler material needed is supplied
    externally.Equipments f or TIG
    There are four basic components of TIG welding system namely
    • The power source
    • Polarity
    • Tungsten electrode
    • Shielding gas
    Power sources: The power sources used are always constant current type. Both
    DC and AC power supplies can be used for TIG welding.
    Polarity: Depending upon the material to be welded, three types of polarity can
    be used in TIG welding.
    1- Direct Current Electrode Negative (DCEN or Straight polarity)
    2- Direct Current Electrode Positive (DCEP or Reverse polarity)
    3- Alternating Current (AC)
    Tungsten electrode
    • The electrode used in TIG is made of either pure tungsten or tungsten alloys.
    Tungsten provides the desired properties such as high melting temperature
    (3410ºC), low electrical resistance, good heat conductivity and has the ability to
    emit electrons easily.
    • Pure tungsten electrode: Pure tungsten electrodes are usually preferred for AC
    welding of aluminum and magnesium.
    • Alloyed tungsten electrode: The current carrying capacity of pure tungsten
    electrode is lower and easily gets contaminated. Pure tungsten electrode is alloyed
    with some impurities like zirconium oxide, thorium oxide and cerium oxide.
    • Pure tungsten electrode is alloyed with some impurities:
    1- To increase the current carrying capacity.
    2- To avoid the melting of the electrode (to increase melting temperature)
    3- To improve arc stability and arc initiation.
    4- To increase the resistance to contamination of the tip.Shielding gases for TIG
    • Argon and helium are the major shielding gases used in TIG welding. In some
    applications, a mixture of these two gases is also used.
    • Shielding gases are used to keep harmful atmospheric gases (O2, N2, H2 and
    moisture) away from the weld pool as the metal solidifies. These gases, when
    not effectively kept away, produces weld defect such as porosity and brittleness.
    Oxygen: It reacts with metals and forms undesirable metal oxides.
    Nitrogen: At elevated temperature, it reacts with metals and forms very
    hard and brittle metal nitrides. It reduces ductility and impact strength of
    the weld joint and can causes weld cracking.
    Hydrogen: It is highly soluble at elevated temperature and causes porosity
    in weld zone.
    Advantages of TIG welding:
    • TIG welding is suitable for joining thin sections because of its controlled heat inputs.
    Metal thickness ranging 1 to 6 mm is generally joined by TIG process.
    • It can weld all metals in any configuration, but is not economically competitive on
    heavy and thick sections, because of low metal deposition rate as compared to MIG
    welding.
    • TIG welding can be used for joining similar or dissimilar metals.
    • The concentrated heat input of the TIG process helps to increase the welding speed,
    minimize distortion and improve the metallurgical quality of the weld.
    • TIG welding is more precise because the arc heat and filler metal additions are
    controlled independently. Thus TIG welding produces the highest quality welds most
    consistently.
    • Since flux is not required, therefore, no slag formation occurs. This gives better
    control on welding process, because of clear visibility of the arc and the job.Disadvantages of TIG welding:
    • Welding speed and metal deposition rate is low as compared to other
    processes. Due to this, it is not used for welding thick and heavy sections.
    • Excessive welding currents can cause melting of the tungsten electrode and
    results brittle tungsten inclusions in the weld metal.
    • Filler metal rod, if it comes out of the gaseous shield, can cause weld metal
    contamination.
    • High equipment cost.
    Applications of TIG welding:
    • This process is most extensively used for welding aluminum and stainless steel
    alloys where weld integrity is of the utmost importance.
    • TIG is often used for root pass in pressure components and other critical
    applications, as it gives a clean and accurate weld joint.
    • TIG process can be easily mechanized (movement of torch and feeding of filler
    wire), so it can be used for precision welding in nuclear, aircraft, chemical,
    petroleum, automobile and space craft industries. Aircraft frames and its skin,
    rocket body and engine casing are few examples where TIG welding is very
    popular.
    • TIG welding may be used for welding almost all metals — mild steel, low alloys,
    stainless steel, copper and copper alloys, aluminum and aluminum alloys, nickel
    and nickel alloys, magnesium and magnesium alloys, titanium, and others.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 30
    (MIG Process)Gas Metal Arc Welding (GMAW or MIG)
    • MIG welding is a process that melts and joins metals by heating them with an
    arc established between a continuously fed consumable wire electrode and
    the metals to be joined.
    • Shielding of the arc and the molten weld pool is obtained by using inert gases
    such as argon, helium, and some active gases such as carbon dioxide, etc.
    • Continuous welding with coiled wire helps high metal deposition rate and high
    welding speed.
    • Metal inert gas process is similar to TIG welding except that it uses the
    automatically fed consumable electrode therefore it offers high deposition rate
    and so it suits for good quality weld joints required for industrial fabrication.
    Consumable electrode is fed automatically while torch is controlled either
    manual or automatically. Therefore, this process is found more suitable for
    welding of comparatively thicker plates.
    MIG weldingMIG Equipments:
    • The power source
    • Polarity
    • Consumable wire electrode
    • Shielding gas
    Power sources: The power sources used are always constant voltage type.
    Both DC and AC power supplies can be used for MIG welding.
    Polarity: Depending upon the material to be welded, three types of polarity
    can be used in MIG welding.
    1- Direct Current Electrode Negative (DCEN or Straight polarity)
    2- Direct Current Electrode Positive (DCEP or Reverse polarity)
    3- Alternating Current (AC)The power source….
    • MIG welding always carried out using DCEP mode. The filler wire is connected
    to the positive polarity of DC source forming one of the electrodes. The work
    piece is connected to the negative polarity.
    • DCEP mode gives stable arc and smooth metal transfer with least spatter for the
    entire current range which results a good quality weld. It also gives arc cleaning
    action.
    • DCEN mode, though gives higher metal deposition rate, is also not preferred
    because it causes unstable and erratic arc which results in large spatter. It
    eliminates the advantage of arc cleaning action on the work surface.
    • AC power is found unsuitable for MIG welding because it results in arc
    extinguishing every half cycle.
    Consumable wire electrode:
    • For MIG welding, the electrode wire comes generally in the form of coils. The
    normal size of the electrode may be of the order of 1 – 3 mm. The electrode wires
    of mild steel and low alloyed steel, are coated with copper to avoid atmospheric
    corrosion, increase current carrying capacity and for smooth movement through
    contact tube.
    • Electrode selection is based primarily on the composition of the metal being
    welded, the process variation being used, joint design and the material surface
    conditions.Shielding gases
    • Shielding gases are necessary for MIG welding to protect the welding area
    from atmospheric gases such as nitrogen, oxygen and moisture.
    • The various shielding gases used are:
    1- Argon
    2- Helium
    3- Argon-helium mixture
    4- Carbon dioxide
    Advantages of MIG:
    • Continuous welding with coiled wire gives high metal deposition rate and high
    welding speed, which allow thicker workpieces to be welded at higher
    welding speeds.
    • High welding speed and metal deposition rate gives less HAZ and distortions.
    • Because of the good control on the rate of heat input, MIG can be used for
    welding nearly all metals (ferrous or non-ferrous) including carbon steel,
    stainless steel, alloy steel and aluminum.
    • It provides a stable arc and smooth metal transfer with least spatter for the
    entire current range.
    • Since MIG is carried out with DCEP mode so it gives excellent oxide film
    removal during welding.Disadvantages of MIG:
    • Absence of slag on the work surface gives higher cooling rate of the weld zone
    and hence joints made on hardenable steels are susceptible to weld metal
    cracking.
    • It cannot be used for welding critical sections (difficult to reach positions).
    • Equipments used are costlier and less portable.
    Applications of MIG:
    • All commercially important metals such as carbon steel, high-strength low
    alloy steel, stainless steel, aluminum, copper, titanium, and nickel alloys can be
    welded in all position with MIG process by choosing appropriate shielding gas,
    electrode, and welding variables.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 31
    (Mode of metal transfer in MIG welding)Modes of metal transfer in MIG welding
    Metal transfer in MIG refers to the process of transferring material of the
    consumable wire electrode in the form of molten liquid droplets to the workpiece. Depending on the welding conditions, the molten metal at the electrode
    tip can be transferred to the weld pool by five basic transfer modes:
    1- Short circuit transfer
    2- Globular transfer
    3- Spray transfer
    4- Pulsed spray transferForces affecting the metal transfer
    The various forces which affect the metal transfer from the electrode tip to the
    weld pool are:
    1-Gravity force: The force of gravity may be a retaining or detaching force;
    depending on the electrode is position (upward or downward).
    2- Surface tension: Surface tension always tends to retain the liquid drop at the
    tip of the electrode. This force depends on the radius of the electrode, density of
    the liquid metal and the capillary constant.
    3- Electromagnetic force: This force is set up due to the interaction of the
    current with its own magnetic field. This is always a detaching force and
    accelerates the process of separation of a droplet as the current is increases.
    4- Hydrodynamic pressure (hydrodynamic action of plasma).
    Short Circuit Transfer
    • In the short circuit transfer, the liquid drop at the tip of
    the electrode gets in contact with the weld pool before
    being detached from the electrode.
    • Short circuit metal transfer occurs with the lowest
    welding currents and voltages, which consequently
    produces very low heat input, results poor depth of
    penetration and amount of fusion.
    Applications:
    • It requires low heat input, gives shallow penetration,
    and hence is commonly used in welding thin sheets.
    • It produces a small and fast-freezing weld pool that is
    desirable for welding thin sections and out-of position
    welding (such as overhead-position welding).Globular transfer
    • Globular metal transfer occurs at relatively low
    operating currents and voltages but these are still
    higher than those used in short circuiting transfer.
    • Globular transfer is characterized by the transfer of
    molten metal in large size drops across the arc. The
    diameter of the drops may be two or three times larger
    than the electrode diameter. Each drop grows so large
    that it falls from the electrode due to its own weight.
    Application:
    • Large molten metal droplets are transferred across the
    welding arc mainly by the action of gravity. Therefore
    this mode of working is applied to the welding in flat
    position. This method cannot be used out-of-position
    welding.
    • Because of large spatters, globular transfer is typically
    used in welding parts which has relatively poor quality
    requirements.
    Spray Transfer
    • In the spray transfer mode, a stream of molten metal
    travels axially across the arc in the form of fine
    droplets which is induced by the magnetic force
    acting on the molten electrode tip.
    • Spray transfer occurs when current and voltage
    increases beyond the range of globular transfer. As
    the current density increases, an arc is formed at the
    end of the filler wire, producing a stream of small
    metal droplets.
    Applications:
    • High heat input gives high metal deposition rate
    which produces a large weld-pool with high fluidity
    (because of high temperature). This molten weld
    pool cannot be supported only by the surface tension
    of the molten metal in vertical and overhead welding
    position. So spray transfer welding is limited to use
    in the flat and horizontal positions.Pulsed-Spray Transfer
    • In order to overcome the limitation of spray
    transfer, pulsed spray transfer is used. Pulsedspray transfer is similar to the spray transfer
    except that the current required for melting the
    electrode tip is given in regular pulses rather than
    continuously.
    Application
    • Pulse spray transfer mode can be used for
    welding all types of metal, ferrous or nonferrous.
    • It is well suited for vertical and overhead
    welding positions.
    Pulsed-Spray Transfer
    • This mode of metal transfer can only be possible if the power source is
    able to supply a pulsed type current. The level of a welding current
    supplied by a pulsing type of power source varies between two levels,
    high peak current and steady background current.
    • Steady background current: Background level of the current is set
    below the transition level. So, during background current period arc is
    maintained but melting of electrode does not occurs.
    • Peak current: Peak current level is high enough to causes melting of
    the droplets from the electrode tip that are then transferred across the
    arc. Ideally, one droplet is transferred during each pulsePulsed-Spray Transfer
    Pulsed-Spray Transfer
    Advantages:
    • The pulses allow the average current to be lower, decreasing the overall
    heat input and thereby decreasing the size of the weld pool and heataffected zone.
    • Because of controlled heat input and metal transfer it is possible to weld
    thin workpieces.
    • The smaller weld pool with lower fluidity makes it possible to weld in all
    positions (flat, horizontal, vertical and overhead).
    • Pulse current provides stable arc and smooth metal transfer without
    spatter.
    • The lower overall heat input reduces distortion and size of the heat
    affected zone.
    • Increased travel speed and higher deposition rate, compared with the
    dip/short circuit metal transfer mode.Pulsed-Spray Transfer
    Limitations:
    • High cost of pulsed current power sources
    • Setting of optimum welding data is more complicated.
    • Only argon based shielding gas mixtures can be used with conventional
    pulsing current power sources.THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 32
    (Resistance welding )
    Resistance Welding
    Introduction: Resistance welding is a fusion welding process in which both
    heat and pressure are applied to achieve a sound weld joint. The heat necessary
    for the melting of the workpiece interface is obtained by the electrical
    resistance offered by the material against flow of the current.• Process: In resistance welding, two parts being welded are put in direct
    contact under the welding electrodes. A current is then passed with the
    help of electrodes. The flow of current through a resistance generates
    intense heat at the interface. Heat produced by the current is sufficient for
    local melting of the work piece at the contact point and formation of small
    weld pool (nugget). The molten metal is then solidified under a pressure
    and joins the pieces. The pressure of the electrode tips on the workpiece
    holds the part in close and intimate contact during the making of the weld.
    Principle of Resistance Welding:
    • In resistance welding, heat required for melting is obtained by passing a very
    high current (around 15000A) through the workpiece for a short period of
    time (around 0.25 seconds). The flow of high current through the material
    heats the joint, due to contact resistance at the joint and melts it. The pressure
    on the joint is continuously maintained and the metal fused together under
    this pressure. The amount of heat generated can be given as:
    H = kI2Rt
    Where, H = total heat generated in Joule, k = constant, I = electric current,
    R = electrical resistance of the joint.
    • Thus, the heat generated depends upon the current, the time the current is
    passed and the resistance at the interface.Total Resistance between the Electrodes
    Resistance Welding Parameters
    The parameters which affect the quality of weld in resistance welding are:
    1- Power source ( AC or DC)
    2- Welding current
    3- Welding voltage
    4- Welding time
    5- Holding time
    6- Electrode pressure
    7- Contact resistance
    8- Material properties
    Electrical and thermal conductivity
    9- Electrode
    Electrode material
    Electrode sizeResistance Welding Processes
    The different resistance welding processes are
    1- Spot welding
    2-Seam welding
    3- Projection welding
    Spot welding
    • Spot welding is most common resistance welding process which is used to join
    two sheet-metal pieces in a lap joint. Spot welding is accomplished when
    electric current is flow through the metal piece, interface melts due to resistance
    heating, and a small nugget if formed.Seam Welding:
    Seam welding is a resistance welding process of continuous joining of
    overlapping sheets by passing them between two rotating electrode wheels. Heat
    generated by the electric current flowing through the contact area and pressure
    provided by the wheels are sufficient to produce a leak-proof weld.
    Projection Welding
    • Projection welding is a variation of spot welding. In this method, one of the
    sheets to be welded is provided with a number of projections at the location
    where weld is desired. These projections comes into contact with the another
    sheet to be welded, thus, current flows through these small projections. As the
    current passes through these projections, they melted and a fusion joint is made
    under the pressure applied from the electrode.Advantages of Projection Welding:
    • It is possible to produce more than one spot weld at a time. The number of spot
    welds depends on the number of projections that can come under the tip of the
    electrode.
    • Because large-sized electrodes used, their life is much longer than that of the
    convention spot welding electrodes. The larger contact area gives very less
    deformation of the electrode tip.
    • The welds may be placed closer than possible in spot welding.
    • Proper heat balance can be easily obtained in projection welding by making the
    projections in thicker plates while welding sheets of different thickness. For
    welding dissimilar metals, the projections are to be made on the material having
    higher electrical conductivity to provide proper heat balance.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 34
    (Submerged arc welding )
    Submerged Arc Welding (SAW)
    • The demand for high metal deposition rates and the failure to
    mechanize SMAW, results in the development of submerged arc
    welding process.
    • Submerged arc welding is a welding process in which arc is
    established between a continuously fed consumable wire electrode
    and the workpiece. The weld zone is protected by the granular flux
    applied around the weld. No shielding gas is used.Submerged Arc Welding……
    • The electrode wire is fed automatically from a coil into the arc. The arc
    heat melts both the work pieces edges and the electrode wire. The
    molten electrode material is transferred towards the surface of the
    workpieces, fills the weld pool and joins the work pieces. Since the
    electrode is submerged into the flux, the arc is invisible.
    • The flux is supplied slightly ahead of the electrode by means of a
    feeding mechanism (hopper). A part of the flux is melts and forms slag
    which protects the weld pool from oxidation and other atmospheric
    contaminations. The melted flux also reacts with the metal pool and
    removes impurities.
    • The rest un-melted flux acts as insulator and controls the cooling rate of the
    molten metal. The un-melted flux also provides additional shielding to the
    welding zone. It can be recycled.
    • Because the arc is totally submerged, high welding current can be
    employed. Thus, high metal deposition rate, deep penetration, high welding
    speed, slower solidification and cooling all are the characteristics of SAW
    process.Submerged Arc WeldingProcess Parameters
    • Quality of the weld deposit depends on the type of flux, the electrode, the
    welding current, arc voltage, speed of arc and heat input rate. Thus the process
    variables are:
    1- Welding current and voltage.
    2- Welding speed
    3- Electrode stick out
    4- Joint design
    5- Wire electrode
    6- Width and depth of flux
    Advantages of SAW:
    • The blanket of granular flux completely submerges the arc welding operation,
    preventing sparks, spatter, and radiation that are so harmful in other arc welding
    processes.
    • The melted flux along with the flux that is not melted provides good thermal
    insulation. The slow cooling of the weld metal helps to produce soft and ductile
    welds.
    • SAW is carried out with very high current (300 – 2000A) which increases the
    melting rate of the electrode. This gives very high metal deposition rate (around
    35 kg/hr) with deep penetration.
    • Because of high metal deposition rate, higher welding speed can be employed.
    • It gives less distortion and HAZ, because of high welding speed.Disadvantages of SAW:
    • Since this process uses loose granular flux to protect the joint, it can be carried
    out only in flat welding position. The out-of-position welds are difficult to
    make. High current used in SAW gives a large metal pool which takes more
    time for solidification, also makes it difficult to carry in out-of-position
    welding.
    • Flux may get contaminated and lead to porosity in weld.
    • It is not suitable for welding of metal thickness less than 6 mm.
    • Need of slag removal and flux handing system.
    • High heat input and slow cooling rate give a weld with large grain size.
    Applications of SAW
    • SAW is used for doing faster welding jobs. It is possible to use larger welding
    electrodes (12 mm diameter) as well as very high current (300 – 2000 A) so that
    very high metal deposition rates of the order of 25 kg/h or more can be achieved
    with this process. Also, very high welding speeds (5 m/min) are possible in
    SAW. Metal piece thickness up to 100 mm can be welded by this process.
    Carbon, alloy and stainless steels up to 12 mm thick can be safely welded in
    single pass, while thicker cross section requires multi-pass welding.
    • The ability to produce high quality, defect free welds at high deposition rates
    and with deep weld penetration makes the SAW process highly suitable for all
    mechanized and automatic welding and surfacing applications.
    • SAW is widely used for welding carbon, carbon manganese, alloy and stainless
    steels. It is also used for joining some nickel based alloys.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 35
    (Electroslag and friction welding.)Electro-slag welding
    • The electro-slag welding is a single pass welding process mainly used to
    produce joints of thick metal plates in vertical position. Workpieces which
    having thickness more than 15 mm (no upper thickness limit), can be welded in
    a single pass.
    • Electro-slag welding is a process in which heat required for melting is obtained
    from a pool of molten slag held between the metal plates. The filler metal to be
    deposited is obtained by melting of continuously fed electrode wire under the
    pool of molten slag.
    • The pool of molten slag is formed by the resistance heating of the current
    passing through the conductive slag from the electrode to the workpiece. The
    weld pool is covered with molten slag and moves upward as welding
    progresses.
    Electro-slag welding• The flux should have high melting and boiling point to enable melting of
    base metal and the filler wires.
    • It must have good conductivity and viscosity so as to maintain the
    temperature of the slag pool and to prevent the flow of the slag through
    gaps between work piece and the cooling shoes.
    Advantages of electro slag welding:
    • The ESW process is completely continuous and so productivity will be high. No
    edge preparation of the parts to be joined is necessary.
    • It gives extremely high metal deposition rates and only one single pass is required,
    no matter how thick the workpiece is.
    • No arc flash and spatter during welding.
    • In ESW, the weld metal stays molten for a long time and permits slag-refining action,
    escape of dissolved gases and transfer of non-metallic inclusions to the slag-bath.
    Thus gives a high quality weld.
    Disadvantages of electro slag welding :
    • ESW gives a wide coarse grained HAZ, results in poor strength and toughness of the
    weld joint.
    • Electro-slag welding is carried out only in vertical position because of the very large
    pools of the molten metal and slag.• Applications of electro-slag welding: Typical examples of the application
    of ESW include the welding of ship hulls, storage tanks, and bridges. Plates
    and other heavy sections up to 450 mm are commonly welded by electroslag process. Heavy pressure vessels for chemical, petrochemical and
    power generating industries are usually welded by ES process only.
    Friction Welding
    • Friction welding is a solid state joining process that uses rotational motion and
    high axial pressures to convert rotational energy into frictional heat at a circular
    interface. The heat produced by this rubbing action raises the interface
    temperature of the two parts to the plastic state. When sufficient plasticity has
    occurred, the rotation is stopped and axial pressure increased, to forge the parts
    together and form a solid state bond. The flash may be removed as part of the
    machine cycle.Friction Welding
    • The sequence of operations in the friction-welding process is as follows:
    1- One part is held stationary in a fixed clamp. The other part is held in a
    rotating chuck.
    2- The chuck is accelerated at a high speed (around 3000rpm) and the
    stationary parts brought into contact under a light force. As soon as parts
    come into contact to each other, friction heat is generated.
    3- The force is increased, plastic material starts to extrude from the weld
    interface. Contact is maintained until sufficient material has been extruded.
    4- Rotation is stopped, the force increased and the parts forged together.
    1- One part is held stationary in a fixed clamp. The other part is held in a rotating chuck.
    2- The chuck is accelerated at a high speed and the stationary parts
    brought into contact under a light force.3- The force is increased, plastic material starts to extrude from the weld interface.
    4- Rotation is stopped, the force increased and the parts forged together.
    Final assemblyParameters in friction welding:
    The major variables in the friction welding are:
    1- Axial pressure
    The axial pressure applied depends on the strength and hardness of the
    metal being welded. The pressure may range from 40 – 450 MPa for steel
    components.
    2- Rotational speed
    The amount of heat developed depends on the rotational speed as well as
    applied pressure.
    3- Time of contact
    The amount of heat developed is also depends on the time of contact
    between rotating component and stationary components.
    Friction Welding
    Advantages:
    • Friction welding achieves 100 per cent metal-to-metal joints, giving high quality welds.
    • Edge cleaning is not a problem, since the oxides and other impurities present would easily be
    removed during the initial rubbing.
    • Dissimilar metals can be joined easily.
    • The heat generated being small and well below the melting temperature, there will be no
    distortion and warping.
    • Very little heat affected zone.
    • It has no need of flux, filler. So it is free of smoke, spatter and slag.
    Disadvantages:
    • This method is limited to smaller components.
    • The part to be welded must be essentially similar in cross-section and must be able to
    withstand the high torque developed during welding.Friction Welding
    • Application: Because of high quality of weld obtained, friction welding has been
    widely accepted in the aerospace industry as well as automobile industry for the
    welding critical parts.
    • This is particularly useful in aerospace, where it is used to join lightweight
    aluminum stock to high-strength steels.
    • Other common uses of friction welding are joining dissimilar metal in the nuclear
    industry, where copper-steel joints are common in the reactor cooling systems; and
    in the transport of cryogenic fluids, where friction welding has been used to join
    aluminum alloys to stainless steels and high-nickel-alloy materials for cryogenicfluid piping and containment vessels.
    • Friction welding is also used with thermoplastics. The heat and pressure used on
    these materials is much lower than metals. It can also be used to join metals to
    plastics.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 36
    (Atomic Hydrogen Welding )
    Atomic Hydrogen Welding
    • Atomic hydrogen welding is an arc welding process in which the work pieces
    are joined by the heat obtained from a stream of hydrogen gas passing through
    an electric arc struck between tow tungsten electrodes.Atomic Hydrogen Welding………
    • As the hydrogen gas passes through the arc, the hydrogen molecules are
    dissociated into atoms. A large quantity of heat is absorbed by the hydrogen
    during dissociation.
    • When the atoms leave the arc they recombine on contact with the cooler base
    metal, forming molecules of hydrogen and liberating intense heat. When
    hydrogen atom recombines near the workpiece surface, they generate a
    temperature of the order of 4000ºC.
    • Thus, heat librated during recombination is sufficient to melt the workpieces to
    be welded. The hydrogen gas also shields the welding zone and protects it from
    atmospheric gases. Filler metal may or may not be used.
    Advantages
    • Separate flux or shielding gas is not required. Hydrogen itself acts as a shielding
    gas and avoids weld metal oxidation.
    • Concentrated arc is obtained which gives faster welding speed with less
    distortion of the workpiece.
    • The workpiece does not form a part of the electrical circuit; the arc is obtained
    between two tungsten electrodes only. Hence, problems like striking the arc and
    maintaining the arc length are eliminated and can be moved to other places
    easily without getting extinguished.
    • It gives extremely clean weld with excellent quality.Disadvantages
    • Higher operating cost compared to the other welding processes.
    • Welding is limited to flat positions only. The high welding temperature
    (4000ºC) produces weld pool with high fluidity. Due to this, atomic hydrogen
    welding is suitable only for flat position.
    Applications:
    • Atomic hydrogen welding being expensive is used mainly for high grade
    work on stainless steel and super alloys.
    • It is used for welding of tool steels containing tungsten, nickel and
    molybdenum and also for hard surfacing of moulds, dies and tools.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 37
    (Welding Metallurgy)
    Weld and Heat Affected Zone
    • A welded joint consists of:
  42. Weld metal – melted and re-solidified base metal mixed with filler
    metal (if added)
  43. Heat affected zone (HAZ) – the region around the weld whose
    properties or microstructure are affected by the thermal cycle –
    reheating also alters the structure of under1ying weld metal in multipass welds
    3- Base metal: The unaffected part of the parent metal.Metallurgical Phenomena
    • Welding is a complex process that involves: –
    1- Gas-metal reaction
    2- Slag-metal reactions –
    3- Solidification
  44. Heat Affected Zone
    These metallurgical phenomena control weld strength and ductility
    Gas-Metal Reactions
    • Reactive gases (especially N2, 02, H2) may be present in the arc atmosphere .
    These gases dissociate in the arc and react rapidly with the high temperature,
    turbulent liquid metal in the weld pool.
    • Once dissolved in the metal, oxygen and nitrogen combine with deoxidizers
    such as Si or AI. The resulting oxides or nitrides remain as small inclusions in
    the weld metal.
    • Excess dissolved gas is rejected during solidification and may cause porosity.
    • Dissolved hydrogen can cause cracking in steelsSlag-Metal Reactions
    • Fluxes and slag interact with the molten weld metal.
    • The slag used in flux shielded processes are designed to absorb deoxidation
    products and other contaminants.
    • The cleanliness and properties of the weld metal depend on the oxidation
    potential of the arc and on the type of flux used.
    • Highly basic fluxes reduce weld metal oxygen content and give superior weld
    toughness. Acid fluxes tend to give higher oxygen contents and poor weld
    toughness.
    • Fluxes may also be used to modify weld metal composition by transfer of
    alloying elements from the slag to the liquid metal.
    Dilution
    • Dilution ratio is the mass of base metal melted divided by the total mass of
    melted metal. Dilution results from mixing of filler and base metals.
    • Weld pool mixing results in a uniform fused zone, except when large
    differences exist between filler and parent composition.
    • A sharp boundary lies between the fused zone and base metal.
    • Dilution is influenced by joint preparation, welding process and procedureSolidification
    • Factors controlling the solidification of metals are:
    1- Temperature gradient
    2- Composition
    3- Rate of solidification
    Heat affected zone (HAZ)
    • A heat-affected zone (HAZ) is the portion of the base metal that is not melted
    during welding but its microstructure and mechanical properties are altered by
    the heat. This alteration can be detrimental, causing stresses that reduce the
    strength of the base material, leading to catastrophic failures.
    • The amount of change in microstructure in HAZ depends on the amount of
    heat input, peak temp reached, time at the elevated temp, and the rate of
    cooling. As a result of the marked change in the microstructure this zone
    remains as the weakest section in a weldment.THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 38
    (Residual stress in weld.)
    Residual Stresses in weld
    • Residual stress can be defined as the stress which remains within a welded
    structure when all external loads and reactions are removed.
    • Residual stresses are the result of restraint to thermal expansion and contraction
    offered by the metals during heating and cooling cycles.
    • As metals are heated they expand and when cooled they contract. During
    welding, continuous heating and cooling of metals occurs which causes uneven
    expansion and contraction of the material, resulting in high residual stresses in
    the weld structure.Development of residual stresses:
    • In a welding process, the expansion and contraction forces act on the weld
    metal and adjacent base metal. When two pieces of metal are welded together,
    expansion and contraction may not be uniform throughout all parts of the metal.
    This is due to the difference in the temperature between the actual welding point
    and surrounding base metal.
    • Before application of heat: Before application of heat, component is stress
    free.
    • Heating phase: During the rapid heating cycle of a fusion welding process,
    material near to the weld heats and expands in all directions. This expansion is
    restrained (compressed) by the much larger and cooler surrounding base metal.
    Thus, the heated metal near the joint is under compression. Rest cooler base
    metal is under tension.
    • Melting phase: When metal melts, stress relaxation occurs. This is because
    molten metal cannot transmit forces at the weld pool.
    • Cooling phase: On cooling, the deposited weld metal and the heated
    volume of the adjacent base metal contracts in all directions. This
    contraction is restrained by the neighboring cooler base metal. Thus, tensile
    stresses are developed in weld metal. This is called residual stress.
    • Higher heat input welds are more prone to residual stresses.Development of residual stresses…….Effect of Residual Stresses:
    • Residual stresses in weld are very harmful if the weld structure having
    notches, porosity or cracks etc. Residual stresses can:
    1- Causes distortion, warping or buckling of the welded structure.
    2- Causes weld cracking or stress corrosion cracking.
    3- Causes brittle fracture
    4- Reduces fatigue life
    5- Reduces creep strength.
    • These residual stresses are relieved by suitable heat treatment process.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-IV / Lecture No: 39
    (Defects and distortions in weld)
    Welding Defects
    • Any discontinuity in weld metal or in heat affected zone is called defect. The
    various types of welding defects are:
    1- Cracks
    Cold cracking (or hydrogen induced cracking)
    Hot cracking (solidification cracking)
    2- Undercut
    3- Lack of fusion
    (or incomplete fusion)
    Lack of side fusion
    Lack of inter-run fusion
    4- Incomplete penetrations
    5- Solid inclusion
    (slag inclusion and metallic inclusion)
    6- Porosity
    7- SpatterWelding Defects
    Welding DefectsParameters which causes the weld defects:
    The following are the main sources of defects for most of the conventional
    welding processes.
    1- Too long arc length
    2- Incorrect welding speed
    3- High alloy composition
    4- Rapid cooling
    5- Insufficient heat input rate
    6- Poor joint preparation
    7- Incorrect welding technique
    8- Improper selection of welding process
    9- Inadequate shielding of the welding zone
    Weld Distortion
    A component is said to be distorted when there is any change in its original
    shape.
     Weld distortion occurs due to solidification shrinkage and thermal
    contraction of the weld metal.
    Welding involves highly localized heating of the metal being joined
    together. The temperature distribution in the weldment is therefore nonuniform. Normally, the weld metal and the heat affected zone (HAZ) are at
    much higher temperatures that of the unaffected base metal.
    Upon cooling, the weld pool solidifies and shrinks, exerting shrinkage stresses
    on the surrounding weld metal and HAZ. If the shrinkage stresses produced
    from thermal expansion and contraction exceed the yield strength of the parent
    metal, localized plastic deformation of the metal occurs. Plastic deformation
    causes change in the component dimensions and distorts the structure.Types of distortions:
    Several types of distortion are listed below:
    1- Longitudinal shrinkage
    2- Transverse shrinkage
    3- Angular distortion
    4- Longitudinal distortion (Bowing or Bending)
    5- Buckling
    6- Rotational distortion
    Types of distortionsTypes of distortions
    Weld Decay
    Weld decay is a form of inter-granular corrosion, usually of stainless steels or
    certain nickel-base alloys, that occurs as the result of sensitization (regions
    susceptible to corrosion) in the heat-affected zone during the welding operation.During welding of stainless steels, local sensitized zones often develop.
    Sensitization is due to the formation of chromium carbide along grain
    boundaries, resulting in depletion of chromium in the region adjacent to the
    grain boundary . This chromium depletion produces very localized galvanic
    cells.
    If this depletion drops the chromium content below the necessary 12 wt% that is
    required to maintain a protective passive film, the region will become sensitized
    to corrosion, resulting in inter-granular attack.
    This type of corrosion most often occurs in the HAZ. Inter-granular corrosion
    causes a loss of metal in a region that parallels the weld deposit. This corrosion
    behavior is called weld decay
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 40
    (Need and application of UCMP)
    Unconventional Machining Process
    • Unconventional manufacturing processes is defined as a group of processes that
    remove excess material by various techniques involving mechanical, thermal,
    electrical or chemical energy or combinations of these energies but do not use
    a sharp cutting tools as it needs to be used for traditional manufacturing
    processes.
    • The unconventional manufacturing processes are not affected by hardness,
    toughness or brittleness of material
    • The unconventional manufacturing processes can produce any intricate shape
    on any workpiece material by proper control over the various parameters of the
    processes.Need for Unconventional Machining Processes
    • The main reasons for using unconventional manufacturing processes are:
    1- Development of new and harder materials with low machinability
    2- Higher Dimensional accuracy and surface finish requirements
    3- Production of complicated geometries
    4- Higher production rate and economy requirements
    5- Machining of fragile workpiece
    6- Temperature rise or residual stresses are undesirable .1-Development of new and harder materials with low machinability:
    Need to machine newly developed metals and non-metals having high
    strength, high hardness and high toughness. A material having the above
    mentioned properties is difficult to be machined by the conventional
    machining methods.
    Examples: Titanium alloys, Inconel, super alloys, fiber-reinforced
    composites, ceramics, carbides, stainless steels etc.
    2-Higher Dimensional accuracy and surface finish requirements: The
    dimensional accuracy and surface finish desired in hard and tough workpiece
    materials cannot be obtained by conventional machining as it is done at very
    slow speed, making it uneconomical.
    3-Production of complicated geometries: Producing complicated
    geometries in very hard materials becomes extremely difficult with
    conventional processes.
    Ex. Non-circular holes, square holes, micro holes, very long holes,
    steam turbine blade etc.
    4-Higher production rate and economy requirements. Conventional
    machining is carried out with slow speed, thus become uneconomic. The
    higher production rate can be achieved by using unconventional machining
    processes.
    5- Machining of fragile workpiece: UCMP is used when workpiece is too
    fragile to resist cutting forces or too difficult to clamp.
    6- Temperature rise or residual stresses are undesirableor unacceptable.Classification of UCMP
    Thus, these non-conventional processes can be classified as:
    1-Mechanical Processes
    Abrasive Jet Machining (AJM)
    Water Jet Machining (WJM)
    Ultrasonic Machining (USM)
    2- Electrochemical Processes
    Electrochemical Machining (ECM)
    3- Electro-thermal Processes
    Electro-discharge machining (EDM)
    Electron Beam Machining (EBM)
    Lesser Beam Machining (LBM)
    Plasma Arc Machining
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 41
    (Abrasive Jet Machining)
    Abrasive Jet Machining
    • Abrasive jet machining is a process where material is removed by high velocity
    jet of air/gas and abrasive mixture.
    • In AJM, a stream of very fine abrasive particles suspended in air or carrier gas is
    made to strike the workpiece surface at very high velocity (200 – 400 m/s). The
    impact of high velocity abrasive particles causes a tiny brittle fracture and the
    flowing air (or gas) carries away the fractured small workpiece particle, resulting
    into material removal by erosion.
    • Thus, in AJM the material is removed due to brittle fracture, so it is more
    suitable when the work piece material is brittle and fragile.Abrasive Jet Machining…..
    Abrasive Jet Machining…..
    • The AJM process is characterized by relatively low power consumption and
    small capital cost.
    • This process has been employed for cutting, cleaning, polishing and deburring.
    • This method of material removal is quite effective on hard and brittle materials
    (viz., glass, silicon, tungsten, ceramics, composites etc.) but not so effective on
    soft materials like aluminum, rubber, etc.
    • It is especially useful for the parts having thin sections but not suitable for the
    parts having sharp corners.AJM System
    AJM System…….
    • In AJM, air is compressed in an air compressor and compressed air at a
    pressure of around 5 bars is used as the carrier gas. Figure shows the other
    major parts of the AJM system. Gases like CO2 and N2 can also be used as
    carrier gas which may directly be issued from a gas cylinder.
    • The carrier gas is first passed through a pressure regulator to obtain the desired
    working pressure. The gas is then passed through an air dryer to remove any
    residual water vapour. To remove any oil vapour or particulate contaminant the
    same is passed through a series of filters. Then the carrier gas enters a closed
    chamber known as the mixing chamber.AJM System…….
    • The abrasive particles are then carried by the carrier gas to the machining
    chamber via an electro-magnetic on-off valve.
    • The high velocity stream of abrasive is generated by converting the
    pressure energy of the carrier gas to its kinetic energy and hence high
    velocity jet. The nozzle directs the abrasive jet in a controlled manner onto
    the work material, so that the distance between the nozzle and the work
    piece and the impingement angle can be set desirably. The high velocity
    abrasive particles remove the material by micro-cutting action as well as
    brittle fracture of the work material.
    Advantages of AJM:
    • The main advantage of AJM process is that it can be used to cut intricate
    shapes in very hard and brittle materials. Specially suitable for thin sections
    • No heat is generated; therefore there is no thermal stress, thermal
    distortion, or thermal damage.
    • The operation does not leave any burrs, so no secondary smoothing
    operation is required.
    • Environmentally friendly process (almost no pollution).
    • Initial cost is low and lower power consumption.Disadvantages of AJM:
    • Only hard and brittle materials can be machined. Soft materials cannot be
    machined by this process.
    • Poor accuracy due to stray cutting. Tapering occurs due to flaring of the jet
    • Slow MRR (around 15 mm3/ min) and hence its applications are limited.
    • Nozzle wear rate is high.
    Applications of AJM:
    • It is used to clean metallic mould cavities.
    • For drilling holes of intricate shapes in hard and brittle materials
    • For machining fragile, brittle and heat sensitive materials
    • AJM can be used for drilling, cutting, deburring, cleaning and etching.
    • Micro-machining of brittle materials
    Abrasive Jet Machining
    Effect of process parameters on MRRSummary of AJMTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 42
    (Electric Discharge Machining)Electric Discharge Machining (EDM)
    • Introduction: EDM is a thermoelectric non-traditional machining process in
    which heat energy of an electric spark is used to remove material from the
    workpiece. Electric spark, in the presence of dielectric fluid, produces enough
    heat to melt and vaporize a tiny volume of the workpiece material, leaving a
    small crater on its surface. This process requires the workpiece material to be
    electrically conductive and the hardness of the material is not critical.
    Working of EDM:
    • In EDM, the tool (electrode) and the workpiece are immersed in a dielectric
    fluid. Generally kerosene or de-ionized water is used as the dielectric fluid. A
    suitable spark gap is maintained between the tool and the workpiece.Working of EDM:
    • Initially the gap between the tool and workpiece, which consists of dielectric
    fluid, is not conductive. When high frequency electrical pulses of DC current
    (generated by the pulse generator unit) are applied between the tool and
    workpiece, the dielectric fluid in the spark gap is ionized and becomes
    conductive. This ionized dielectric fluid enables the spark to take place
    between tool and workpiece.
    • When a spark (or discharge) occurs between the gap, the intense heat generated
    near the zone. This intense heat melts and evaporates the material in the
    sparking zone. Most of the molten and vaporized material is carried away from
    the inter-electrode gap by the flowing dielectric fluid in the form of debris
    particles.
    EDM – Process Parameters
    The important process variables which affect the metal removal rate, surface
    finish and tool wear in EDM process are:
    • Electrical Parameters
    1- Open circuit voltage (supply voltage)
    2- Breakdown voltage (working voltage)
    3- Pulse current (spark current)
    4- Pulse on time (discharge time)
    5- Pulse off time (spark off time)
    6- Pulse frequency (spark frequency)
    7- Spark gapEDM – Process Parameters…..
    • Non Electrical Parameters
    1- Flushing condition
    2- Type of dielectric fluid used
    3- Tool material
    4- Workpiece material
    Advantages of EDM:
    • Any material that is electrically conductive can be cut using the EDM process.
    Physical and metallurgical properties of work material are not barrier in its
    application.
    • By this process, materials of any hardness or brittleness can be machined easily.
    • During EDM operation there is no direct contact between tool and workpiece and so
    no cutting forces. This makes the process more suitable for machining thin and
    fragile (weak) workpieces, without the risk of distortion.
    • It can be used to produce complex shapes internal or external that would otherwise
    be difficult to produce with conventional cutting tools.
    • A good surface finish with higher accuracy can be obtained.
    • It produces burr free machined components.
    • It can be used to perform different kinds of operations like drilling, slotting, contour
    cutting, multiple hole drilling etc.Disadvantages of EDM:
    • EDM process can only be employed for machining electrically conductive
    materials. It cannot be employed for non-conducting materials.
    • Material removal rate is low and the process overall is slow compared to
    conventional machining processes.
    • When forced circulation of dielectric fluid is not possible, MRR is very low.
    • High specific energy consumption compared to conventional machining processes.
    • Undesired erosion and over cutting of material can occur.
    • Heat generated during the machining can affect the mechanical properties of the
    component.
    • Tool wear rate is also very high.
    • This process cannot be applied on very large sized workpieces as size of workpiece
    is constrained by the size of set up.
    • EDM process is not capable to produce sharp corners.
    Applications of EDM:
    Material application:
    • EDM can be applied to all electrically conducting metals and alloys irrespective of
    their melting points, hardness, toughness, or brittleness.
    • It is used to machine extremely hard materials which are difficult to machine by
    conventional process such as super alloys, tool steel, tungsten carbide, ceramics etc.
    Shape application:
    • EDM can be employed for machining complex geometry and irregular shapes. It is
    used for making forging dies, extrusion dies, wire drawing dies, mould making and
    non-circular profile holes etc.
    • It is used for internal thread cutting and gear cutting.
    • It is used for drilling micro holes in super alloy turbine blades, injection nozzles etc.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 43
    (Mechanism of material removal in EDM)Spark Generation in EDM
    • When a suitable voltage is applied between tool and workpiece, an electrostatic
    field of sufficient strength is established. As the electric field is established
    between the tool and the job, the free electrons on the tool are subjected to
    electrostatic forces. If the work function or the bonding energy of the electrons
    is less, electrons would be emitted from the tool. Such emission of electrons is
    called “cold emission”.
    • The “cold emitted” electrons are then accelerated towards the job through the
    dielectric medium. After gaining a sufficient velocity, the electrons collide with
    the neutral molecules of the dielectric fluid, breaking them into electrons and
    positive ions (ionization of dielectric molecule). The electrons produced due to
    ionization of dielectric fluid molecules also accelerated towards the job and
    collide with the other dielectric molecules.• Thus, as the electrons get accelerated, more positive ions and electrons would
    get generated due to collisions. This continuous process would increase the
    concentration of electrons and positive ions in the dielectric fluid between the
    tool and the job. The concentration would be so high that a narrow column of
    ionized dielectric fluid molecules is established, called plasma.
    • The electrical conductivity of such plasma column is very high. Thus all of a
    sudden, a large number of electrons will flow from the tool to the job and
    positive ions from the job to the tool. Such movement of electrons and
    positive ions can be visually seen as a spark.
    Metal Removal in EDM
    • Though the surfaces of both electrodes may appear smooth but some asperities
    and irregularities are always present. As a result, the local gap between tool and
    workpiece varies.
    • In EDM, electrical spark occurs at higher frequencies but only one spark
    occurs at any instant. First sparks occurs at the spot where the tool and
    workpiece surface are at minimum distance (because of least electrical
    resistance). The spark removes material from both the electrode and workpiece,
    which increases the distance between the electrode and the workpiece at that
    point. This causes the next spark to occur at the next-closest spot between the
    electrode and workpiece. Thus, due to changing spot location continuously, the
    several sparks occur all over the surface. This results in a uniform metal
    removal all over the surface and finally the tool produces required impression
    in the workpiece.Metal Removal in EDM• If the tool is held stationary, machining would stop at this stage. However if
    the tool is fed continuously towards the work piece then the process is
    repeated and more material is removed. The tool is fed until the required
    depth of cut is achieved. Finally, a cavity corresponding to replica of the
    tool shape is formed on the work piece. For maintaining the predetermined
    spark gap, a servo-control unit is generally used.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 44
    ( EDM System)
    Electric Discharge Machining System
    The main elements of electric discharge machining unit are:
    1- DC pulsed power supply.
    2- Tool or electrode
    3- Workpiece material
    4- Dielectric fluid
    5- Servo control unit
    6- Flushing• DC Pulsed Power Supply: In EDM, a separate generator is used to apply
    voltage pulses between the tool and the job. A constant voltage is not applied.
    Only sparking is desired in EDM rather than arcing. Arcing leads to localized
    material removal at a particular point whereas sparks get distributed all over
    the tool surface leading to uniformly distributed material removal under the
    tool.
    • Tool (Electrode): In the EDM process the shape of the tool is impressed on
    the workpiece in its complementary form. Thus, the shape and accuracy of
    machined part depends mainly on the shape and accuracy of the tool. Further,
    the shape and accuracy of the tool depends on tool wear
    • Workpiece Material: The important point for workpiece is that any material
    which is electrically conductive can be machined by this process, hardness of
    the material is not critical. The geometry which is to be machined into the
    workpiece decides the shape and size of the tool.Dielectric Fluid:
    Functions of Dielectric Fluid:
    1- As Insulator:
    Serves as insulator between tool and workpiece until required voltage
    reached, thus preventing a spark to occur until the gap voltage is
    correct (more than breakdown voltage).
    2- Spark Conductor:
    Initially the dielectric fluid serves as insulator between tool and
    workpiece. When high frequency electrical pulses of DC current are
    applied between the tool and workpiece, the dielectric fluid in the spark
    gap is ionized and becomes conductive. This ionized dielectric fluid
    enables the spark to take place between tool and workpiece.
    3- As Coolant:
    It acts as coolant and carries away the heat generated in sparking zone,
    cooling the workpiece and electrode.
    4- Flushing Medium:
    It acts as a flushing medium for carry away the wear particles or
    workpiece material and electrode (debris) from the sparking gap.
    Flushing:
    • For efficient machining, the wear out particles (debris) must be removed from
    the sparking area. Removal of wear particles is accomplished by flowing
    dielectric fluid through the sparking gap.
    • Flushing is a method of introducing clean filtered dielectric fluid into the
    sparking gap.
    • Methods of Flushing
    1- Injection flushing (or pressure flushing)
    2- Suction flushing (vacuum flushing)
    3- Jet flushing
    4- Ultrasonic vibration of electrode
    5- Rotating electrode flushingInjection flushing
    Suction Flushing:Jet Flushing:
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 45
    ( Introduction of Electrochemical Machining)
    Electrochemical Machining (ECM)
    • Introduction: Electrochemical machining is a non-traditional machining
    process in which electrical energy is used to produce chemical reactions in an
    electrolytic medium. These chemical reactions remove the material (atom by
    atom) from the workpiece. The removed material appears as precipitated solid
    of metal hydroxides.
    • Working Principle of ECM: ECM is based on the Faraday law of
    electrolysis. Faraday discovered that if two electrodes are placed in a bath
    containing a conducting liquid (electrolyte) and a DC potential is applied
    across them, then metal is depleted from the anode and plated on the cathode.
    Thus, the flow of current through an electrolyte is always achieved by the
    movement of matter.Working Principle of ECM
    Working Principle of ECM
    • In ECM the objective is to remove the metal, so the workpiece is connected to
    the positive terminal (anode) and tool to the negative terminal (cathode). Tool
    and workpiece are separated by an electrolyte.
    • When DC potential is applied between workpiece and tool, the dissolution of
    the anode occurs. The dissolution rate is more where the gap between tool and
    workpiece is less or current density is higher (current density is inversely
    proportional to gap).
    • If the tool is given a feed motion, the work surface tends to take the same
    shape as that of the tool. At a steady state, the gap is uniform and tool shape is
    reproduced into the workpiece. The removed material appears as precipitated
    solid of metal hydroxides, called sludge. The flowing electrolyte removes
    sludge from the gap.Advantages of ECM:
    • ECM can machine highly complicated and curved surfaces in a single pass.
    That is why gas and steam turbine blades are machined by ECM.
    • Fragile parts, which are difficult to machine by conventional machining, can be
    machined easily by ECM.
    • Theoretically tool wear is zero. A single tool can be used to machine a large
    number of pieces without any loss in its shape and size.
    • The process is capable of machining any electrically conductive metals and
    alloys irrespective of their strength and hardness.
    • Machined surfaces are stress and burr free having good surface finish.
    • ECM produces high dimensional accuracy.
    • No elevated temperatures are involved, so no metallurgical changes take place
    in the workpiece.
    Disadvantages of ECM
    • Electrically non-conductive metals cannot be machined by ECM.
    • This process cannot be used to machine edges and corners because of very high
    current density at those points.
    • Fatigue properties of the machined surface may reduce as compared to
    conventional machining (around 20%).
    • Controlling the electrolyte flow may be difficult, so irregular cavities may not
    be produced to the desired shape with acceptable dimensional accuracy.
    • High capital cost of equipment.
    • Design and tooling system is complex.
    • ECM requires relatively high skilled staff.Applications of ECM
    • ECM can be used to make disc for turbine rotor blades made up of HSTR
    alloys
    • ECM can be used for slotting very thin walled collets.
    • ECM can be used for copying of internal and external surfaces, cutting of
    curvilinear slots, machining of intricate patterns, production of long curved
    profiles, machining of gears and chain sprockets, production of integrally
    bladed nozzle for use in diesel locomotives, production of satellite rings
    and connecting rods, machining of thin large diameter diaphragms.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 46
    (Mechanism of metal removal in ECM)
    Mechanics of Metal Removal in ECM:
    • In ECM, material removal takes place due to atomic dissolution of work
    material. Electrochemical dissolution is governed by Faraday’s laws:
    • The amount of electrochemical dissolution or deposition is proportional to
    the quantity of electricity passed through the electrochemical cell.
    • The amount of different substances dissolved or deposited by the same
    quantity of electricity are proportional to their chemical equivalent weights
    (atomic weight / valency). Mathematically:
    m = ItE/F
    Where m = weight (in grams) of a material dissolved, I = current (in Amp),
    t = time (in seconds) and E = gram equivalent weight of the material.Mechanics of Metal Removal in ECM……..
    • Let us take an example of machining of low carbon steel which is primarily a
    ferrous alloy mainly containing iron. For electrochemical machining of steel,
    generally a neutral salt solution of sodium chloride (NaCl) is taken as the
    electrolyte.
    Mechanics of Metal Removal in ECM……..Mechanics of Metal Removal in ECM……..
    Mechanics of Metal Removal in ECM………
    • Thus in ECM of iron, using NaCl as the electrolyte, iron is removed as iron
    hydroxide Fe(OH)2. These hydroxides are insoluble in water hence they
    appear as solid precipitates and no further affect the electrochemical reaction.
    The iron hydroxide produced during the process must be removed
    continuously from the electrolyte by filtration before it is re-circulated.
    • The sodium chloride is recovered back and not consumed in the
    electrochemical process; therefore, for keeping constant concentration of
    electrolyte, it may be necessary to add more water.Mechanics of Metal Removal in ECM…………..
    • The net result of all this is iron getting dissolved from the anode and
    forming solid precipitates, consuming electricity and water, nothing else.
    The reaction products are iron hydroxide and hydrogen gas. Based on this,
    following observations are made:
    • The metal from the anode is dissolved (atom by atom) electrochemically
    and hence the metal removal rate depends upon the atomic weight, valency,
    the current passed, and the time for which current is passed.
    • At the cathode only hydrogen gas is generated and no other reaction takes
    place, hence there is practically no tool wear. The shape of the cathode
    remains unaffected.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 47
    (Ultrasonic Machining)
    Ultrasonic machining
    • Ultrasonic machining is a mechanical material removal process used to
    machine holes and cavities in very hard and brittle workpieces by using
    shaped tools, high-frequency mechanical vibration, and an abrasive slurry.
    • In this process, a tool of desired shape vibrates at very high frequency and
    low amplitude over the workpiece. The small gap between the tool and
    workpiece is flooded with continuous flow of abrasive slurry. As the tool
    vibrates over the workpiece, the impact of the hard abrasive grains fractures
    the hard and brittle work surface, resulting in the removal of work material in
    the form of small wear particles. These wear particles are carried away by
    the abrasive slurry. As the material is removed, the tool is gradually fed into
    the workpiece by a servomechanism to maintain a constant gap between the
    tool and the workpiece.The shape and dimensions of the workpiece depends on those of the tool. Since
    material removal is based on brittle fracture, this process is suitable for
    machining hard and brittle materials such as glass, ceramics, silicon, hardened
    steels, titanium carbide etc.
    Process Parameters:
    Performance (MRR, accuracy and surface finish) of the USM process
    depends upon the following parameters:
    1- Amplitude of vibration (25 – 100 microns).
    2- Frequency of vibration (15 – 30 kHz).
    3- Feed force
    4- Abrasive size (15 – 150 microns)
    5- Concentration of abrasive in the slurry
    6- Slurry pressure
    7- Hardness ratio of the work and tool material
    8- BrittlenessUltrasonic Machining System:
    The main elements of ultrasonic machining unit are:
    1- High power sine wave generator
    2- Transducer
    3- Tool holder
    4- Tool
    5- Abrasive slurry
    6- Too Feeding mechanism
    Ultrasonic Machining SystemAdvantage of USM
  45. It is used for machining very hard and brittle materials like diamond, carbides, glass,
    ceramics, precious stones, titanium etc. These materials are difficult to machine by
    any conventional process.
  46. Since the cutting force involved is very small, the process produces stress free
    machined surface.
  47. This machining process is non- thermal, non-chemical, and non-electrical. It does not
    change the metallurgical, chemical or physical properties of the workpiece.
  48. It gives better surface finish and higher structural integrity.
  49. Any materials either electrically conductive or non-conductive can be machined by
    this process. But it is especially suitable for machining of brittle materials.
  50. Non-metal (because of the poor electrical conductivity) that cannot be machined by
    EDM or ECM can be machined effectively by USM.
    Disadvantages of USM
  51. Very low metal removal rate. It cannot be used for machining large cavities.
  52. Fast tool wear rate, which in turn, makes it very difficult to maintain close
    tolerances.
  53. Machining area and depth is restraint in USM, because of slurry circulation is
    restricted. It is difficult to drill deep holes.
  54. It is not recommended for machining soft and ductile materials, due to their
    ductility.
  55. The flowing slurry wears the side wall of the machined hole as it passes back
    towards the surface, which limits the accuracy, particularly for small holes.
  56. USM can be efficiently used only when the hardness of work is more than 40
    RC (Rockwell hardness on C-scale).Applications of USM
  57. Most successful USM application is machining of round, square, irregular
    shaped holes, slots and surface impressions in brittle materials.
  58. Used to machine fragile components in which otherwise the scrap rate is
    high.
  59. Used in machining of dies for wire drawing, punching and blanking
    operations.
  60. For machining large number of holes of small diameter (0.10mm).
  61. Complex geometric shapes and 3-D contours can be machined with
    relative ease in brittle materials.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 48
    (Electron Beam Machining)
    Electron Beam Machining (EBM)
    • Introduction: Electron beam machining is an electro-thermal process that
    uses high velocity beam of electrons to machine the materials. When high
    velocity beam of electrons is strikes on the work surface, the kinetic energy
    of electrons converted into heat which is responsible for local melting and
    vaporization of the work material.
    • It is used for machining electrically conducting as well as non-conducting
    materials like metals, ceramics, plastics etc.Working of EBM
    • Electron Beam Machining is required to be carried out in vacuum. Otherwise
    the electrons would collide with the air molecules, thus they would lose their
    energy and cutting ability. Thus the workpiece to be machined is located under
    the electron beam and is kept under vacuum. The diameter of the electron beam
    focused on to the work surface should be slightly smaller than the desired hole
    diameter. As the electron beam strikes the work surface, the material gets
    heated, melted and partially vaporized.
    • On the exit side of the hole, an organic backing material (support) is used. The
    electron beam after complete penetration into the workpiece, also partially
    penetrates in the auxiliary backing material. The backing material vaporizes and
    comes out of hole at a high pressure. The molten material is also expelled along
    with the vaporized backing material.Electron Beam Machining Parameters
    The process parameters, which directly affect the machining characteristics in
    Electron Beam Machining, are:
    1- Accelerating voltage
    2- Beam current
    3- Pulse duration (or pulse on-time)
    4- Power per pulse
    5- Lens current
    6- Spot size
    7- Power density
    Electron Beam Machining – Equipment
    There are three important elements of EBM system
  62. Electron beam gun:
    Cathode
    Bias grid
    Electron accelerating system (anode)
  63. Beam focusing system
    Magnetic lens
    Aperture
  64. Beam controlling system
    Electromagnetic lens
    Deflection coil
  65. Power supply
  66. Machining chamberElectron beam machining setup
    Electron Beam Gun: Electron beam gun is the heart of any EBM system. The
    basic functions of any electron beam gun are:
    • It produces free electrons at the cathode.
    • It accelerates free electrons to a sufficiently high velocity
    • It focused electron beam over a small spot size.
    Cathode: The cathode is generally made of tungsten or tantalum. Such cathode
    filaments are heated (inductively) to a temperature of around 2500°C. Such
    heating leads to thermo-ionic emission of electrons. Moreover, this cathode
    filament is highly negatively biased so that the electrons are strongly repelled
    away from the cathode.Bias grid: After the cathode there is a negatively biased grid. But this negative
    bias is operated in pulse mode. Bias grid generates a barrier field which allow
    only certain quantity of electrons to pass. So whenever there is appropriate
    bias, it will allow the flow of electrons and when it is not appropriately bias it
    would not allow the flow of electrons. Thus, biased grid is used as a switch to
    operate the electron beam gun in pulsed mode.
    Electron accelerating system (anode): To increase the velocity of electrons,
    there is a positively biased anode just after negatively biased grid. The
    positively biased anode now attracts the electron beam and gradually gets
    accelerated. As electron beam leaves the anode section, the electrons may
    achieve a velocity as high as half the velocity of light.
    • Beam focusing system: After the anode, the electron beam passes through a series
    of magnetic lenses and apertures.
    Magnetic lens: Magnetic lens are the magnets used to concentrate the
    electron beam in order to increase its energy density.
    Aperture: From the moving beam some of the electrons diverge, may
    be due to repulsive force. So, just after the magnetic lenses there is an
    aperture. The aperture allows only the convergent electrons to pass
    and captures stray and low energy electrons.
    • Beam controlling system: The final section of the electron beam gun is
    electromagnetic lens and deflection coil.
    Electromagnetic lens: The electromagnetic lens focuses the electron beam to
    a desired spot on the workpiece.
    Deflection coil: The deflection coil can defect the electron beam by small
    amount, if you are not getting a proper hole shape. Thus deflection coil is
    used to improve the quality of hole.Power Supply: The current used for heating the filament is DC current. This is
    because AC current can influence the direction of beam.
    Machining Chamber: The EBM process is carried out in a vacuum chamber
    to prevent electrons from colliding with molecules of the atmospheric air and to
    prevent tungsten filament from getting oxidizing with air.
    Advantages of EBM:
  67. EBM provides very high drilling rates when small holes with large aspect
    ratio (depth/diameter)are to be drilled.
  68. It can machine almost any material irrespective of their mechanical
    properties.
  69. As it applies no mechanical cutting force, work holding and fixturing cost
    is very less.
  70. Because of absence of mechanical force, fragile and brittle materials can
    also be processed easily.
  71. The heat affected zone in EBM is rather less due to shorter pulses.
  72. There is no mechanical contact between tool and work piece, hence no
    tool wear.Limitations of EBM:
  73. The primary limitation is the high capital cost of the equipment and
    necessary regular maintenance cost.
  74. Very high specific energy consumption.
  75. Though heat affected zone is rather less in EBM but recast layer
    formation cannot be avoided.
  76. It can be used for small cuts only
  77. A vacuum requirement limits the size of workpiece.
    Applications of EBM:
    • A wide range of materials such as steel, stainless steel, Ti and Ni super-alloys,
    aluminium as well as plastics, ceramics, leathers can be machined successfully
    using electron beam. As the mechanism of material removal is thermal in
    nature, there would be thermal damages associated with EBM. However, the
    heat-affected zone is rather narrow due to shorter pulse duration in EBM.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 49
    (Laser Beam Machining)Laser
    • A laser is an optical amplifier that generates light
    by a process called stimulated emission.Laser Beam Machining (LBM)
    • Introduction: Laser beam machining is a thermoelectric machining process
    which utilizes high energy coherent laser beam to remove the material from the
    workpiece by melting and vaporization.
    • Like a beam of high velocity electrons, a laser beam is also capable of
    producing very high power densities. Laser is a highly coherent and
    monochromatic beam of electromagnetic radiation with wavelength varying
    from 0.1 – 70µm. Because of the fact that the rays of the laser beam are
    perfectly parallel and monochromatic, it can be focused to a very small diameter
    and can produce a power density as high as 1MW/mm2. As laser interacts with
    the material, the energy of the photon is absorbed by the work material leading
    to rapid substantial rise in local temperature. This in turn results in melting and
    vaporisation of the work material and finally material removal.
    Working Principle of LBM:
    • A coiled xenon flash tube is placed around the ruby rod and the internal surface
    of the container walls is made highly reflecting so that maximum light falls on
    the ruby rod for the pumping operation.
    • The capacitor is charged and a very high voltage is applied to the switching
    electrode (or triggering electrode) for initiation of flash.
    • The emitted laser beam is focused by the lens. As laser interacts with the
    material, the energy of the photon is absorbed by the work material leading to
    rapid substantial rise in local temperature. This in turn results in melting and
    vaporisation of the work material and finally material removal.
    • A very small fraction of the molten metal is vaporized so quickly that a
    mechanical impulse is generated which helps in removing most of the molten
    metal from the hole.Working Principle of LBM:
    Process Parameters:
    Important parameters in LBM are:
    1- Power intensity of laser beam.
    2- Pulse duration
    3- Focused diameter of laser beam
    4- Thermal properties of the work material
    Melting temperature of workpiece material.
    Thermal conductivity
    Specific heat
    Latent heat
    5- Optical properties of work material
    Reflectivity
    Absorptivity
    TransmitivityTypes of Laser
    Basically lasers are of two types:
    1- Solid State Laser
    Ruby Laser
    Nd: YAG Laser (Neodymium doped Yttrium Aluminium
    Garnet).
    2- Gas Laser
    CO2 Laser
    Argon
    Helium – Neon
    Advantages of LBM:
  78. The laser beam can be focused to a very small spot, giving a very high
    density as high as 1MW/mm2. Thus, a laser beam can machine any known
    material.
  79. In laser machining there is no physical tool. This eliminates the chances of
    workpiece deterioration due to cutting tool force.
  80. There is no tool wear problem.
  81. The laser beam can operates through any transparent environment like air,
    gas, vacuum and even certain liquids.
  82. Application of heat is very much focused so rest of the workpiece is least
    affected by the heat.Disadvantages of LBM
  83. High initial capital cost.
  84. High maintenance cost.
  85. High operating cost.
  86. Low operating efficiency.
  87. Cannot be effectively used to machine highly conductive and reflective
    materials like Aluminium, copper etc.
  88. Its application is limited to only thin sections or where a very small
    amount of metal removal is required.
  89. Highly skilled operators are needed.
    Applications of LBM
    Process applications:
    1- Laser can be used in wide range of manufacturing applications
    2- Material removal – drilling, cutting and tre-panning
    3- Welding, soldering, brazing
    4- Cladding
    5- Surface hardening
    Material applications
    LBM is used for cutting difficult-to-machine materials like hardened
    steels, composites, ceramics, refractory alloys, Hastealloy, tantalum,
    titanium etc.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 50
    (Plasma Arc Machining)Plasma arc machining
    • Plasma arc machining is a thermal machining process in which a jet of plasma is
    used to remove the material by melting and vaporization. The source of heat
    generation in plasma is the recombination of electrons and ions into atom, and
    then atoms into molecules. PAM can be used on all electrically conductive
    metals.
    Plasma:
    Gas which is heated to an extremely high temperature and ionized so that it
    becomes electrically conductive.
    PAM process uses this plasma to transfer an electric arc to the work surface.
    The metal to be machine is melted by the intense heat of the arc and
    vaporizes.
    Principle of PAM
    • A plasma state is obtained by the dissociation of gaseous molecules in to
    electrons and positive ions. During the dissociation process large amount of
    heat is absorbed by the gas molecules.
    • The source of heat generation in plasma is the recombination of electrons and
    ions into atom, and then atoms into molecules. During the recombination
    process large amount of heat is released, causes the rapid increases in
    temperature.
    • The heat librated by the recombination process is used for machining and
    welding of the metals. This is because, the recombination process occurs at the
    surface of the workpiece.
    • The temperature of plasma can be of the order of 33000°C, sufficient to melt
    any metal.Working of PAM
    • Plasma is generated by passing a gas through strong electric arc. For this, first
    the arc is setup between the tungsten electrode (cathode) and the anode (nozzle)
    and then gas is forced to flow through this arc.
    • When gas passes through the arc, there is a collision between molecules of gas
    and electrons of the established arc. As a result of this collision gas molecules
    get ionized and converted into plasma. This high temperature plasma is directed
    to the workpiece with high velocity. When plasma jet strikes the work surface,
    recombination occurs. During the recombination large amount of heat is
    released, causes the rapid increases in temperature. When such high temperature
    source reacts with the work material, the work material melts out and vaporizes,
    and finally is cut into pieces.Types of PAM
    1- Non-Transferred PAM: In this system tungsten electrode is
    cathode and nozzle tip is anode. The arc is formed between the tungsten
    electrode and the nozzle tip. Plasma comes out of the nozzle as a flame. Just
    like oxy-acetylene cutting torch, it can be moved from one place to another and
    can be better controlled, because workpiece is not a part of the electrical circuit.
    • The non-transferred arc plasma possesses comparatively less energy density as
    compared to transferred arc plasma and it is employed for welding and in metal
    spraying.• 2-Transferred PAM: In this system tungsten electrode is cathode and
    the workpiece is anode. The arc is formed between the tungsten electrode and the
    workpiece. In other words, arc is transferred from the electrode to the work piece.
    • A transferred arc possesses high energy density and plasma jet velocity. For this
    reason it is employed to cut and melt metals.
    • Transferred arc can also be used for welding at high arc travel speeds.
    Difference between transferred and non-transferred PAMProcess Parameters
    The important process parameters which affect the performance of PAM are:
    Gas type
    Gas flow rate
    Nozzle size
    Stand-off distance
    Arc current
    Arc voltage
    Advantages of PAM:
    • It gives faster production rate.
    • It can be cut metals as thick as 150 mm.
    • Very hard and brittle metals can be machined.
    • Small cavities can be machined with good dimensional accuracy.
    • Plasma cutting is used to cut particularly those metals, such as stainless steel,
    aluminium etc, which cannot be cut by the rapid oxidation induced by the
    ordinary oxy-acetylene torch.
    • Cutting speed is much faster (5 – 10 times) than oxy-acetylene flame cutting.Disadvantages of PAM:
    • Initial cost of equipments is very high.
    • The work surface may undergo some metallurgical changes.
    • The process requires over safety precautions which further enhance the initial
    cost of the setup.
    • The plasma arc emits strong ultraviolet and infra-red radiations that may cause
    skin and eye damage.
    Applications of PAM:
    • This process has been used in cutting applications of stainless steel, hardened
    and high melting-point metal and hardened alloys.
    • It is also used for cutting non-ferrous metals such as aluminium alloys.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 51
    (Laser Beam Welding)Laser Beam Welding
    • Laser is an acronym for light amplification by stimulated emission of radiation.
    Laser Beam Welding (LBW) is a fusion joining process that produces
    coalescence of materials with the heat obtained from a concentrated beam of
    coherent, monochromatic light impinging on the joint to be welded.
    • In the LBM process, the laser beam is directed by flat optical elements, such as
    mirrors and then focused to a small spot (for high power density) at the
    workpiece using either reflective focusing elements or lenses.
    • It is a non-contact process, requiring no pressure to be applied. Inert gas
    shielding is generally employed to prevent oxidation of the molten puddle and
    filler metals may be occasionally used.
    Laser beam welding is done through following phases:
    • Interaction of laser beam work material.
    • Heat conduction and temperature rise.
    • Melting and joining.How does laser welding work
    • During welding laser beam interact with the work material in three different
    modes:
    1- Conduction (limited welding)
    2- Conduction / Penetration (limited welding)
    2- Keyhole welding.
    • Conduction mode welding is performed at low energy density forming a weld
    nugget that is shallow and wide.
    • Conduction/penetration mode occurs at medium energy density, and shows
    more penetration than conduction mode.
    • The penetration or keyhole mode welding is characterized by deep narrow
    welds. Laser welding is more usually accomplished using higher power
    densities, by a keyhole mechanism. When the laser beam is focused to a small
    enough spot to produce a power density typically > 106-107 W/cm2, the
    workpiece surface vaporizes before significant quantities of heat can be
    removed by conduction. The focused laser beam penetrates the workpiece and
    forms a cavity called a ‘keyhole’, which is filled with metal vapour or ionized
    metal vapour (plasma). This expanding vapour or plasma contributes to the
    prevention of the collapse of the molten walls of the keyhole in to this cavity.LBW Advantages
    • Heat input is close to the minimum required to fuse the weld metal, thus
    heat affected zones are reduced and workpiece distortions are minimized.
    • Time for welding thick sections is reduced and the need for filler wires and
    elaborate joint preparations is eliminated by employing the single pass laser
    welding procedures.
    • No electrodes are required; welding is performed with freedom from
    electrode contamination, indentation or damage from high resistance
    welding currents.
    • LBM being a non-contact process, distortions are minimized and tool wears
    are eliminated.
    LBW Advantages
    • Laser beam can be focused on a small area, permitting the joining of small,
    closely spaced components with tiny welds.
    • Welding in areas that are not easily accessible with other means of welding can
    be done by LBM, since the beams can be focused, aligned and directed by
    optical elements.
    • Laser welds are not influenced by magnetic fields, as in arc and electron beam
    welds. They also tend to follow weld joint through to the root of the workpiece, even when the beam and joint are not perfectly aligned.
    • Wide variety of materials similar or dissimilar can be welded.Disadvantages of LBM
    • Joints must be accurately positioned laterally under the beam and at a controlled
    position with respect to the beam focal point.
    • In case of mechanical clamping of the weld joints, it must be ensured that the final
    position of the joint is accurately aligned with the beam impingement point.
    • The maximum joint thickness that can be welded by laser beam is somewhat
    limited. Thus weld penetrations of larger than 19 mms are difficult to weld.
    • High reflectivity and high thermal conductivity of materials like Al and Cu alloys
    can affect the weldability with lasers.
    • Lasers tend to have fairly low energy conversion efficiency, generally less than 10
    percent.
    • Some weld-porosity and brittleness can be expected, as a consequence of the rapid
    solidification characteristics of the LBM.
    Applications of LBW
    • Laser beam welding is being used in the following sectors
    1- Defense
    2- Aerospace
    3-Automotive
    4- Medical
    5- MarineTHANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 52
    (Electron Beam Welding)Electron Beam Welding
    • Electron beam welding is a liquid state welding process. In this welding
    process, a high jet of electrons strikes at welding plates where its kinetic
    energy converts into heat energy. This heat energy is sufficient to melt the
    work pieces and fuse them into one piece. This whole process carried out in
    vacuum otherwise the electrons collides with air particles and loses its
    energy.
    • Principle of EBW: This welding works on same principle of electron beam
    machining. This process uses kinetic energy of electrons to produce heat. This
    heat is further used to weld two welding plates. When a high jet of electrons
    strike at welding plates, its kinetic energy converts into heat energy. This heat
    energy is sufficient to fuse two metal plates together to form a weld joint.Working of EBW
    Its working can be summarized as follow.
  90. First the electron gun, which is a cathode, produces electrons. These electrons
    move towards anode which is positive charged and placed right after electron
    gun.
  91. The anode accelerates the electrons and form a electron jet which is further
    move towards magnetic lenses.
  92. The magnetic lenses are a series of lenses which are used to absorb low energy
    electrons and does not allow to divergent electron to passes through it. It
    provides a high intense electron jet.
  93. Now this electron beam passes through electromagnetic lens and defecting coil
    which are used to focus and deflect the electron beam at the required spot. This
    unit direct high velocity electron beam to the weld cavity where its kinetic
    energy converts into heat energy due to collision. This heat energy is used to
    create weld by fusion. This whole welding process carried out in a vacuum
    chamber otherwise the electrons collides with air particle in the way and loses
    its energy.Process Parameters:
    The important parameters are:
  94. Accelerating voltage
  95. Beam current
  96. Welding speed
  97. Beam focusing
    Advantages of EBW
    • High penetration to width can be obtained.
    • High welding speed is obtained.
    • Material of high melting temperature can be welded.
    • Superior weld quality due to welding in vacuum, welds are corrosion free.
    • Distortion is less due to less heat affected zone.
    • Very wide range of sheet thickness can be joined.Disadvantages of EBW
    • Very high equipment cost.
    • Vacuum is required.
    • X-rays generated during welding.
    • Skilled person is needed.
    • Transportation of equipment is difficult.
    Applications of EBW
    • It is used in aerospace industries and marine industries for structure work
    • It is used to join titanium and its alloy.
    • This welding process is widely used to join gears, transmission system,
    turbocharger etc in automobile industries.
    • It is used to weld electronic connectors in electronic industries.
    • This process is also used in nuclear reactors and in medical industriesComparison of EBW with conventional welding
    • Compared with arc welding process, EBW improves joint strength 15
    percent to 25 percent.
    • It has narrow heat affected zone, results less distortion.
    • Geometric shape and dimensions are highly stable, particularly when it is
    used as finish operation.
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 53
    (Plasma Arc Welding)
    Plasma arc welding
    • Plasma arc welding is a welding technique that is closely related to gas
    tungsten arc welding. In plasma arc welding the electric arc is created
    between an electrode and the metal you are working with.
    • The main difference between plasma arc welding and gas tungsten arc
    welding is that in plasma welding the welder is able to position the electrode
    within the body of the torch, this allows for the plasma arc to be separated
    from the shielding gas. The plasma is then fed through a nozzle which
    constricts the arc and forces the plasma out at a much higher speed and
    temperature.Working Principle of PAW
    Plasma:
    Gas which is heated to an extremely high temperature and ionized
    so that it becomes electrically conductive.
    PAW process uses this plasma to transfer an electric arc to the work
    surface.
    The metal to be welded is melted by the intense heat of the arc and
    fuses together
    Objective of PAW:
    To increase the energy level of the arc plasma in a controlled manner.
    This is achieved by providing a gas nozzle around a tungsten electrode
    operating in DCEN mode
    Working Principle of PAWEquipment’s for PAW:
    • Power Source: PAW process needed a high power DC supply to generate
    electric spark in between tungsten electrode and welding plates (For transferred
    PAW Process) or in between tungsten electrode and discharge nozzle (For Nontransferred PAW process).
    • Plasma arc torch: This is most important part of PAW process. This torch
    is quite similar as used in TIG welding but too complex. It consist four main
    parts which are tungsten electrode, collets, inner nozzle, and outer nozzle. The
    tungsten electrode is hold by the collet. The inner gas nozzle supply inert gases
    inside the torch to form plasma. The outside nozzle supply shielding gases
    which protect the weld area from oxidation. These nozzles wear out rapidly.
    PAW torches are water cooled because arc is contained inside the torch which
    produces high heat, so a water jacket is provided outside the torch.
    Equipment’s for PAW:
    • Shielding and Plasma Gas Supply: Generally, plasma gas is same as
    shielding gas which is supplied by a same source. Mainly inert gases like argon,
    Helium etc. are used as both inert and shielding gases. This inert gas is supplied
    at both inner and outer nozzle.
    • Filler Material: Mostly no filler material is used in this welding process. If
    filler material is used, it is directly feed into weld zone.Types of PAW
    • Non-transferred plasma arc welding: In this welding process, straight
    polarity DC current is used. In this process, the tungsten electrode is connected
    to the negative and the nozzle is connected to the positive pole. The arc produces
    between tungsten electrode and nozzle inside the torch. This will increase the
    ionization of gas inside the torch. The torch transfers this ionized gas for further
    process. It is used to weld thin sheets.
    • Transferred plasma arc welding: This process also uses straight polarity
    DC current. In this process, the tungsten electrode is connected to the negative
    terminal and the work piece is connected to the positive terminal. The arc is
    produces between tungsten electrode and work piece. In this process both
    plasma and arc transferred to the work piece which increases the heating
    capacity of process. It is used to weld thick sheets.
    Types of PAW TorchProcess Parameters
    The important process parameters which affect the performance of PAM are:
    Gas type and
    Gas flow rate
    Nozzle size
    Stand-off distance
    Arc current
    Arc voltage
    Advantages of PAW:
  98. High welding speed.
  99. High energy available for welding. It can be easily used to weld hard and
    thick work pieces.
  100. The distance between tool and work piece does not effects the arc
    formation.
  101. Low power consumption for same size weld.
  102. More stable arc produced by PAW method.
  103. High intense arc or high penetration rate.
  104. It can work at low amperage.Disadvantages of PAW:
  105. Higher equipment cost.
  106. Noisy operation.
  107. More radiation.
  108. High skill labor required.
  109. High maintenance cost.
    Application of PAW:
    • This welding is used in marine and aerospace industries.
    • It is used to weld pipes and tubes of stainless steel or titanium.
    • It is mostly used in electronic industries.
    • It is used to repair tools, die and mold.
    • It is used to welding or coating on turbine blade.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No: 54
    (Ultrasonic Welding)Ultrasonic welding
    Introduction: Ultrasonic welding is a solid state welding process in
    which ultrasonic vibrations are used to generate heat for welding.
    • Ultrasonic vibration creates a dynamic shear stress between the contacts of
    two work piece. Due to local plastic deformation and heat generate due to
    friction between contact surfaces, joint formation will take place at the
    interface.
    • The two components being welded are subjected to static normal force and a
    oscillating shear stress. The shear stress is applied at the tip of the
    transducer.
    Ultrasonic welding mechanism
    • A static force is applied perpendicular to the interface between the work pieces.
    • The contacting sonotrode oscillates parallel to the interface.
    • Due to local plastic deformation and heat generate due to friction between
    contact surfaces, joint formation will take place at the interface.Working of USWThis welding works as follow.
    • At the start, high frequency current passes through a piezoelectric transducer. This
    transducer converts high frequency electrical signal into mechanical vibration.
    • This vibration further supplied to the booster which amplify its frequency. The
    amplified high frequency vibration passes through horn which is in contact with
    welding plate.
    • This welding creates lap joint. One plant of the weld is fixed into fixture and other
    one is in direct contact with horn. These plates are fixed under moderate pressure
    force.
    • The horn supply high frequency mechanical vibration to the welding plate.
    • Due to this vibration, oscillation shear force act at the interface between welding
    plates which result plastic deformation at interface.
    • It also create a localize temperature rise due to mechanical force and friction. This
    heat helps in plastic deformation at interface and makes a strong joint without
    melting of work piece or using filler metal.
    Equipments for USW:
    • Power Supply: The ultrasonic welding needs high frequency and high voltage
    power supply. This power is needed by the transducer to generate vibrations.
    • Transducer: Transducer is a device which can convert high frequency electric
    signal into high frequency mechanical vibration. This is connected with the
    welding head. The converter or piezoelectric transducer used in this welding
    process.
    • Booster and Horn: The mechanical vibration created by the transducer is
    supplied to the booster which amplifies this vibration and supply to the horn.
    Horn is a device which supply this amplified vibration to the welding plates.
    • Fixture or clamping devices: This device is essential in the ultrasonic welding.
    This uses either electrical, hydraulic, pneumatic or mechanical energy to hold
    the plates into desire location.Advantages and Disadvantages of USW:
    Advantages:
    • This welding can be easily automated and fast.
    • This produces high strength joint without applying external heat.
    • This is clean and provides good surface finish after welding.
    • Ultrasonic process used to weld wide variety of dissimilar metal.
    • It does not develop high heat so there is no chance of expel molten metal form
    joint.
    Disadvantages:
    • It does not weld thick harder metal. The thickness of welds about 2.5 mm for
    aluminum.
    • Tooling cost for fixture is high and they also need special design.
    • The vibration generates through transducer, can damage electronic component.
    Applications of USW
  110. This welding is used in fabrication of nuclear reactor components.
  111. It is used in automotive industry for key, head lamp parts, button and
    switches etc.
  112. Ultrasonic is used in electronic industries like armature winding, switches
    etc.
  113. This is clean welding process so it is used in medical industries to make
    parts like filters, masks etc.THANK
    YOU
    Department of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No:55
    (Explosive Welding and cladding)Explosive Welding
    • It is a solid state welding process wherein welds are produced by the high
    velocity impact of the workpiece as a result of the controlled detonation. The
    explosion accelerates the metal to a speed at which the metallic bond gets
    formed between them, when they collide against each other. The weld is
    produced within a fraction of a second, without the addition of a filler metal.
    Explosive Welding
    • Working Principle: This welding process works on basic principle of
    metallurgical bonding. In this process, a controlled detonation of explosive is
    used on the welding surface. This explosion generates a high pressure force,
    which deform the work plates plastically at the interface. This deformation
    forms a metallurgical bond between these plates.
    • This metallurgical bond is stronger than the parent materials. The detonation
    process occurs for a very short period of time which cannot damage the parent
    material.
    • This welding is highly depend on welding parameters like standoff distance,
    velocity of detonation, surface preparation, explosive etc. This welding is
    capable to join large area due to high energy available in explosive.Elements of Explosive Welding
    • Base Plate: This is one of the welding plate which is kept stationary on a avail.
    It involves a backer which supports the base plate and minimizes the distortion
    during the explosion.
    • Flyer Plate: This is another welding plate which is going to be weld on base
    plate. It has lowest density and tensile yield strength compare to base plate. It is
    situated parallel or at an angle on the base plate.
    • Buffer Plate: Buffer plate is situated on the flyer plate. This plate is used to
    minimize the effect or explosion on upper surface of flyer plate. This protects
    the flyer plate from any damage due to explosion.
    • Standoff distance: Stand-off distance plays a vital role in explosion welding. It
    is distance between flyer plate and base plate. Generally it is taken double of
    thickness of flyer plate for thin plates and equal to thickness of flyer plate for
    thick plates.
    • Explosive: Explosive is placed over the flyer plate. This explosive is situated
    in a box structure. This box placed on the flyer plate. Mostly RDX, TNT,
    PTEN etc used as explosive.
    • Velocity of detonation: It is the rate at which the explosive detonate. This
    velocity should be kept less than 120% of sonic velocity. It is directly
    proportional to explosive type and its density.Types of Explosive Welding:
    According to the setup configuration explosive welding is classified into two
    types:
    1- Direct stand-off welding
    2- Angular stand-off welding
    1- Direct stand-off welding
    • As the name implies, in this welding configuration filler plate is parallel to
    the base plate. There is some standoff distance between base plate and flyer
    plate. This configuration is used to weld thick and large plates.Angular stand-off welding
    • In this type of welding process base plate is fixed on an anvil and filler plate
    makes an angle with the base plate. This welding configuration is used to join
    thin and small plates.
    Advantages of explosive welding:
  114. It can join both similar and dissimilar material.
  115. Simple in operation and handling.
  116. Large surface can be weld in single pass.
  117. High metal joining rate. Mostly time is used in preparation of the welding.
  118. It does not effect on properties of welding material.
  119. It is solid state process so does not involve any filler material, flux etc.
    Disadvantages of explosive welding:
  120. It can weld only ductile metal with high toughness.
  121. It creates a large noise which produces noise Pollution.
  122. Welding is highly depends on process parameters.
  123. Higher safety precautions involved due to explosive.
  124. Designs of joints are limited.Explosive weld jointApplication of explosive welding:
  125. Used to weld large structure sheets of aluminum to stainless steel.
  126. It is used to weld cylindrical component like pipe, concentric cylinder, tube
    etc.
  127. Weld clad sheet with steel in a heat exchanger.
  128. Join dissimilar metals which cannot be weld by other welding process.
  129. For joining cooling fan etc.
    Cladding
    • Many industries including automotive, aerospace, electronics, shipbuilding,
    offshore, railway and heavy equipment needs modification in surface
    properties of a manufactured product. This modification is achieved by the
    cladding process.
    • Cladding is a widely used process for improving the surface and near surface
    properties (e.g. wear, corrosion or heat resistance) of a part or to re-surface a
    component that has become worn through use.
    • Cladding is a deposition technique used for adding one material to the
    surface of another in a controlled manner.Cladding
    THANK
    YOUDepartment of Mechanical Engineering
    Subject: Manufacturing Science & Technology-II
    (RME-503)
    Faculty: Mr. Brijesh Kumar
    Unit-V / Lecture No:56
    (Diffusion bonding)
    Diffusion Bonding
    • Diffusion bonding is a solid state welding process in which, no liquid or
    fusion phase involves and the weld joint is form in pure solid state. It does
    not melt the welding material and mostly a little plastic deformation takes
    place at interface and weld is form due to inter-molecular diffusion. This
    bonding process conducted in vacuum or in inert environment to reduce
    oxidation. This is widely used to join refectory materials in aerospace and
    nuclear industries.
    • This type of welding can be used to weld both similar and dissimilar
    materials with the help of high pressure and temperature.Principle of Diffusion Bonding
    This process works on basic principle of diffusion. Diffusion means movement
    of molecules or atoms from high concentration region to low concentration
    region.
    • In this welding process both the welding plates are placed one over other in
    high pressure and temperature for a long period of time. This high pressure
    force starts diffusion between interface surfaces. This diffusion can be
    accelerated by the application of high temperature. This temperature does not
    melt the welding plates.
    • The temperature range is about 50-60% of melting temperature. This whole
    process takes place in vacuum or in inert environment which protects the
    welding plates form oxidation.Advantages of diffusion bonding
    • The joint have same mechanical and physical properties as parent material.
    • This process produces clean joint which is free from interface discontinuity
    and porosity.
    • Both similar and dissimilar material can be joint by diffusion bonding
    process.
    • It provides good dimension tolerance. So it is used to make precision
    components.
    • Low running cost.
    • It is simple in working.
    • It does not use filler material, flux etc. which are used in arc welding process.
    • It can weld complex shapes.
    Disadvantages of diffusion bonding
    • High initial or setup cost.
    • It is time consuming process. It takes more time compare to other welding
    process.
    • Surface preparations of welding plates are more critical and difficult.
    • Size of the weld is limited according to equipment available.
    • This process is not suitable for mass production.
    • Highly depend on welding parameters like surface finish, welding material,
    temperature, pressure etc.Application of diffusion bonding:
    • It is mostly used to weld refectory materials used in aerospace and nuclear
    industries.
    • Diffusion bonding is used to weld titanium, zirconium and beryllium
    metals and its alloy.
    • It can weld nickel alloy like Inconel, Wrought Udimet etc.
    • It is used to weld dissimilar metals like Cu to Ti, Cu to Al etc.

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