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Production B (Machining)
Dr. Mh-El 3asy
1
Ch 1
Q1: What are the reasons for using the machining process?
– Casting improves severe problems from the point of view of material
properties and accuracy, whereas forming becomes impractical when
the job is either very large; which requires very large forming force and
consequently very large machines; or the material is not suitable for the
forming operation. A part from these, the geometric complexity of the
final job may be such that these methods are of no use.
Q2: What is the meaning of machining?
– The method used is such that the desired shape, size, and finish are
obtained through the removal of excess material from the original work
piece of a suitable size and shape in the form of small chips.
Q3: Define the cutting tool?
– The body which removes the excess material through a direct
mechanical contact.
Q4: Define the machine tool?
– The machine which provides the necessary relative motions between
the work piece and the tool.
Q5: Define the cutting (or primary) motion?
– The relative motion between the tool and the work piece responsible
for the cutting actionProduction B (Machining)
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Q6: Define the feed (secondary) motion?
– The responsible for gradually feeding the uncut portion.
Q7: What is the turning?
– This is a very basic operation and produced a cylindrical
surface. The machine tool used for this type of an operation is
known as a lathe. The figure 1 shows:
FIGURE 1: TURNING OPERATION
Q8: What is shipping?
– The cutting tool is given a reciprocating motion, and after every
cutting stroke, the work is fed. The figure 2 shows:
FIGURE 2: SHAPING OPERATION FIGURE 2Production B (Machining)
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Q9: What is planning?
– For a long job, it becomes inconvenient to provide long cutting strokes
with the mechanism used in a shaping machine. In such a case, the
work is provided with the cutting motion, whereas the feed is given to
the tool; this is known as planning .The basic geometry of the
machining operation is the same as that of shaping.
Q10: What is milling?
– The tool, normally known as a milling cutter, possesses a number of
cutting edges. It is provided with a rotary motion and the work piece is
gradually fed. Small chips are removed by each cutting edge during
revolution, and finally a flat surface is produces. The figure 3 shows:
FIGURE 3 SCHEME OF MILLING OPERATIONProduction B (Machining)
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Q11: What is grinding?
– In grinding, the cutting tools are the sharp edges of the abrasive grains
of the grinding wheel .The figure 4 shows:
Figure 4 scheme of grinding operationProduction B (Machining)
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Q12: What is drilling?
– This is used for making a hole in a solid body. The cutting
motion is provided to the cutting edged (lips) by rotating the drill, and
the feeding is done by giving a rectilinear motion to the drill in the axial
direction the final surface obtained is an internal cylindrical surface.
The figure 5 shows:
Figure 5 DRILLING OPERATION
Q13: Draw a sketch showing the cutting tools angels and state
the functions of each angle?
– Figure 6 shows the basic mechanic operation and important
parameters which can be summarized as follows:Production B (Machining)
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1-the thickness of uncut layer (t1)
2- The thickness of chips produced (t2)
3-the inclination of the chip-tool interface with respect to the cutting
velocity i.e., the rake angle (a)
4-the relative velocity of the work piece and tool (v)
**To make the cutting possible by reducing the friction between the
machined surface and the flank surface of the tool, a clearance angle (
): is also provided.
**Tool angle: is angle between rake surface and flank surface.
FIGURE 6 IMPORTANT PARAMETERS IN MACHINING OPERATION
Q14: Define the orthogonal cutting?
The relevant velocity of the work and the tool is perpendicular to the
cutting edge. Figure 7
FIGURE 7 ORTHOGONALProduction B (Machining)
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Q15: Define the oblique cutting?
The relative velocity of the work piece and the tool in not perpendicular
to the cutting edge as shown in figure 8
FIGURE 8 OBLIQUE
Q16: Explain with the aid of neat sketch the mechanism of chip
formation?
– The uncut layer deforms into a chip after it goes through a sever
plastic deformation in the primary shear zone as shown in figure 9 just
after its formation, the chip flows over the rake surface of the tool andProduction B (Machining)
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the newly-formed chip surface results in some sticking .thus,
the chip material at this surface undergoes a further plastic
deformation since, despite the sticking, it flows. This zone is
referred to as the secondary shear zone.
FIGURE 9 SHEAR ZONES
Q17: Explain with the aid of neat sketch formation of built –up
edge (BUE)?
– *continuous chips with BUE:
1- Strong adhesion between the chips and tool face.
2- Low rake angle.Production B (Machining)
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3- Large uncut thickness.
4- The cutting fluid is not efficient.
Figure 10 shows:
FIGURE 10 BUILT UP EDGE FORMATIONProduction B (Machining)
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Q18: What are the conditions for the various types of
chips?
-1-discontinuous chips:
(a) Brittle work piece material
(b) Low cutting speed
(c) Small rake angle
(d) Large uncut thickness
2- Continues chips:
(a) Ductile work piece material
(b) High cutting speed
(c) Large rake angel
(d) Small uncut thickness
(e) Using suitable cutting fluid
3- Continuous chips with BUE:
(a) Strong adhesion between the chips and tool face
(b) Low rake angle
(c) Large uncut thickness
(d) The cutting fluid is not efficientProduction B (Machining)
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FIGURE 11 FORMATIONS OF DISCONTINUOUS
CHIPS
Q19: What are the disadvantages of BUE formation?
1-Changes the geometry of cutting
2-Produced bad surface finish
3-Decreaser tool life (crater wear as explained later)
4-Leads of the distraction of the hard cutting tool
Q20: Explain the single point tool geometry?
-*Single point tools have shanks of rectangular cross-section which is
the part from which the tool is clamped as shown in FIGURE 12,the
cutting edges are formed on *the front end (called the point ) of the
tool . There are *three main surfaces (unusually planes) in the tool
head
*They are *the face (the area adjacent to the Machined surface) and
*end flank (the area adjacent to the machining surface).Production B (Machining)
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*The cutting edges are classified as the side- and end-cutting
edges. The side-cutting edge is formed by the intersection of
the face and side flank. The chips are removed by this cutting
edge. The end-cutting edge is formed by the intersection of the face
and end flank. The nose of a single-point tool is the conjunction of the
side-and end-cutting edges.
FIGURE12 ELEMENTS OF A SINGLE POINT TOOLProduction B (Machining)
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Q20: How to measure the tool life?
– Tool time is the time elapsed between two successive grinding of the
cutting tool.
The tool life may be measured in the following ways:
1- Actual cutting time to failure
2- Volume of metal removed to failure
3- Number of components to failure
4- Cutting speed for a given time to failure.
Q21: list the factors affecting the tool life?
1- Material of the tool.
2- Material of the work piece.
3- The tool geometry.Production B (Machining)
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4- The cooling facilities.
5- The cutting conditions.
Q22: What is the failure of cutting modes?
– 1- plastic deformation of tool due to high temperature and large
stress. Figure 13 a
2- Mechanical breakage of the tool due to high force and insufficient
strength and toughness of the tool material. Figure 13 b
3- Blunting of the cutting edge of the tool through a process of gradual
wear .figure 13c
FIGURE 13
Q23: How to prevent plastic deformation and the mechanical
failure?
– By 1- a proper selection of the cutting tool material.
2- Tool geometry.Production B (Machining)
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3- Cutting conditions.
4- The cooling facilities.
Q24: What are the two types of tool wear?
– The crater wear: which takes place on the rake surface where the
chip flows over the tool.
The flank wear: which takes place on the flank surface where the
rubbing between the work piece and the tool occurs.
FIGURE 14: CRATER AND FLANK WEARProduction B (Machining)
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Q25What are the reasons for the tool removal?
– 1
– Fracture or shipping of the cutting edge.
2-finish of the work piece is too rough.
3- Tolerances in dimensions are exceeded.
4- Cutting forces are excessive.
5- The tool has reached a practical limit of wear.
Q26: What are the properties of an ideal tool material?
-1-Hot hardness: the cutting tool should maintain its hardness at
elevated temperature.
2-Hardness and toughness: the tool must be harder than the work
piece material. It should be tough enough to withstand shocks.
3- Wear resistance: the tool should provide a large resistance to the
wearing action so that excessive wear does not occur.
4- Thermal resistance: the thermal conductivity and specific heat of the
cutting tool should be high.Production B (Machining)
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Q27: List the materials commonly used for making the
cutting tool?
– 1- high carbon steel.
2- Medium alloy steel.
3- High speed steel (HSS).
4-cast alloys.
5-Cemented carbides.
6- Ceramics.
7- Diamonds.
Q28: What is High Carbon Steels?
– contain from 0.7 to 1.4 carbons. A disadvantage of carbon steel tool is
their comparatively low heat- and wear-resistance. Therefore they may
only used in the manufacture of tools operating at low cutting speeds.
Q29: What is High Speed Steels (HSS)?
– (HSS) are widely used in metal cutting. They have a relatively high
percent of alloying elements which provide for the high heat- and wearresistance of these steels. Therefore, tools made of HSS can be
operating at cutting speeds 5 or 6 times higher than for carbon steelProduction B (Machining)
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tools. HSS is used for manufacturing ordinary and tools, milling
cutters, etc.
Q30: What is the cutting fluids purpose?
-1- To remove heat generated during cutting.
2-To lubricate and reduce friction.
3-To wash away the chips and cleaning the machining zone.
Q31: What is the direct effect of using an efficient cutting fluid?
-1- Reducing the energy consumption.
2- Increase the tool life. The cutting fluid is preventing the formation
of BUE, so that crater wear disappears.
Decreasing the flank wear.
3- Improve the surface finish.
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