Loading...Plastic Injection Molding – Volume III – Mold Design and Construction Fundamentals
Fundamentals of Injection Molding series
By Douglas M. Bryce
Table of Contents
Preface xv
Chapter 1 – A Primer on Molds
The Injection Molding Concept 1
Importance of the Mold . 1
Mold Base Components 4
The Injection Half of the Mold . 5
The Sprue Bushing/The A and B Plates/Runners and Gates/
The Cavity Image
The Ejector Half of the Mold 9
The Ejector Housing/Support Plate/Support Pillars/Ejector
Pins, Return Pins, and Sprue Pullers/Ejector System Guide
Pins and Bushings
Summary 13
Questions . 13
Chapter 2 – Mold Design Basics
Gathering Information 15
Which Plastic? 15
Determining Shrinkage . 15
Pressure and Viscosity . 17
How Many Cavities? . 18
Which Mold Material? . 21
Steels/Aluminum/Beryllium-Copper Alloys/Other Materials
Mold Material Surface Enhancements 23
Tool Surface Treatments 23
Thin Metallic Coatings/PTFE Metallic Fused Coatings/PTFE
Metallic Codepositions/Metallic Platings/Surface Hardening
Treatments/Thin Film, Hi-Hard Coatings/Impregnated Polymer
Product Surface Finish and Special Requirements . 27
Gate Method and Location 28
Ejector Method and Location . 29
Location of Cavities and Cooling Channels 31
Runner Cross Section 33
Venting Concepts 35
Dimensioning the Mold Design . 35Mold Life Expectancies 36
Rapid Systems 37
Fabrication . 38
Thermoforming 38
Casting 38
Injection Molding 38
Ownership of the Mold (and Other Tools) 39
Summary 39
Questions . 41
Chapter 3 – Basics of Mold Construction
Deformation Tendencies 43
Cavities, Cores, and Shut-off Lands . 43
Cut-in-the-solid Sets/Free-standing Sets/Pocketed Cavity
Sets/Laminated Construction
Cavity Retainer Plates 47
Waterline Locations . 51
Support Plates and Support Pillars . 54
Ejector Housings . 57
Cavity and Core Construction 57
Determining the Parting Line . 58
Shutoff Areas 61
Machining Methods 62
Other Fabrication Methods . 64
Casting (Ceramic)/Hobbing/Electrical Discharge Machining
(EDM)/Electrochemical Machining (ECM)/Chemical Etching/
Electroforming (Electrolytic Deposition)/Vapor Forming Nickel
Shells/Stereolithography Apparatus (SLA)/Miscellaneous
Polishing and Finishing . 68
Textures 69
Plating 71
Summary 71
Questions . 72
Chapter 4 – Action Areas of the Mold
Overview 75
Slides 75
Cams . 77
viLifters . 78
Unscrewing Devices 78
Hand Loaded Inserts . 81
Ejection Systems 82
Standard Ejection Design 82
Stripper Ejector Systems 85
Split Cavity Concept 87
Three-plate System with Delayed Ejection 87
Compressed Air Ejection . 89
Summary 90
Questions . 91
Chapter 5 – Runners, Gates, and Venting
Overview 93
Role of the Sprue Bushing 93
Runner Systems . 95
Surface Runners 95
Insulated Runners . 100
Hot Runners . 101
Gating Methods and Designs 103
Determining Gate Location and Number . 103
Sprue Gates . 105
Various Surface Gates . 106
Basic Surface Gate/Edge Gate/Disc Gate/Ring Gate
Drop Gates (Three-plate Molds) 110
Tunnel Gates 112
Venting . 115
Why Vent? 115
Types, Sizes, and Location of Vents 115
Summary 119
Questions . 120
Chapter 6 – Controlling Mold Temperatures
Overview 121
Waterlines . 121
Control Units versus Manifolds 121
Control Units/Manifolds
Laminar Flow versus Turbulent Flow . 123
viiDetermining Location of Waterlines . 126
Bubblers and Cascades 131
Cooling Pins . 131
Heat Transfer Metals . 132
Aluminum 133
Copper Alloys . 134
Zinc Alloys 134
Air Cooling . 134
Summary 134
Questions . 135
Chapter 7 – Mold Alignment Concepts
Purpose of Alignment 137
Alignment of Mold Halves . 137
Leader Pins and Bushings 137
Tapered Locks . 139
Alignment of Mold Components 141
Typical Action Lock Mechanisms 141
Slides/Cams/Lifter System/Telescoping Components
Alignment of Mold to Machine . 146
Platens, Tie Bars, and Platen Bushings . 148
Summary 150
Questions . 150
Chapter 8 – Repairing, Protecting, and Storing Molds
Methods of Repair . 151
What Causes Damage? 151
Designing for Repair and Maintenance 152
Repairs by Welding . 153
Metal Deposition Process 154
Protecting the Mold . 154
New Molds . 154
Molds in Production 155
Installing and Setting Up the Mold . 156
Sizing and Inspection/Installation Procedure
Storing Molds 161
Short-term Storage . 162
Long-term Storage 162
viiiSummary 162
Questions . 163
Chapter 9 – Troubleshooting Product Defects Caused by Molds
Overview 166
What Causes Defects? . 166
Common Defects and Remedies 167
Black Specks or Streaks . 167
Blisters . 167
Blush 168
Bowing . 168
Brittleness . 169
Bubbles (Voids) . 169
Burn Marks . 169
Clear Spots 170
Cloudy Appearance 170
Contamination . 170
Cracking 171
Crazing 171
Delamination . 171
Discoloration 171
Flash 172
Flow Lines 172
Gloss (Low) 172
Jetting 173
Knit Lines (Weld Lines) . 173
Nonfill (Short Shots) 173
Shrinkage (Excessive) 174
Sink Marks . 174
Splay (Silver Streaking) 174
Warpage 175
Bibliography 177
Appendix A – An Injection Mold Design Check List . 179
Appendix B – History of Plastics . 181
Answers to Chapter Questions . 183
Index .
INDEX
Index Terms Links
A
A and B plates of a mold, (figure 1-8) 7
A-series finish 70
actions 75 141
air cooling 134
alignment 137
alignment of mold components 141
action lock mechanisms 141
cams 143
lifter system 144
slides 142
telescoping components 145
alignment of mold to machine 146
platens, tie bars, and platen bushings 148
aluminum for cooling, (figure 6-11) 133
angled pin slide activator, (figure 4-2) 77
anisotropic shrinkage 16
B
B-series finish 70
balanced runner system 174
banana gate 112
black specks or streaks 167Index Terms Links
blisters 167
blush 168
bowing 168
brittleness 169
bubbler 131
bubbles (voids) 169
burn marks 169
C
C-series finish 70
cam
activators, (figure 4-4) 79
mechanism, (figure 4-3) 78
mechanism alignment, (figure 7-7) 143
cams 77
cascade 131
casting (ceramic) 64
cavity 69
cavity and core construction 57
determining the parting line 58
machining methods 62
other fabrication methods 64
casting (ceramic) 64
chemical etching 66
hobbing 64
electrical discharge machining
(EDM) 65
electrochemical machining (ECM) 66Index Terms Links
cavity and core construction (Cont.)
electroforming (electrolytic
deposition) 67
miscellaneous 68
stereolithography apparatus (SLA) 68
vapor-forming nickel shells 67
plating 71
polishing and finishing 68
shut-off areas 61
textures 69
cavity image 1 43
cavity set 43
chemical etching 66
clear spots 170
cloudy appearance 170
compressed-air ejection,
(figure 4-17) 90
contamination 170
cooling channel spacing,
(figure 2-8) 32
cooling pin 131
(figure 6-10) 132
cracking 171
crazing 171
curved or banana gate design,
(figure 5-19) 114
cut-in-the-solid 43
(figure 3-2) 45Index Terms Links
D
D-series finish 70
dead half 4
defect causes, (figure 9-1) 166
defect remedies 167
deformation tendencies
cavities, cores, and shut-off lands 43
cut-in-the-solid sets 43
free-standing sets 44
laminated construction 47
pocketed cavity sets 47
cavity retainer plates 47
ejector housings 57
support plates and support pillars 54
waterline locations 51
delamination 171
designing for repair
and maintenance 152
metal deposition process 154
repairs by welding 153
what causes damage? 151
dimensioning
sprue bushing, (figure 1-7) 7
starting point, (figure 2-14) 37
the mold design 35
disc gate design, (figure 5-14) 110
discoloration 171Index Terms Links
drop gate (pin gate) concept,
(figure 5-16) 111
E
edge gate design, (figure 5-13) 109
EDM process, (figure 3-24) 66
ejecting molded part
from mold, (figure 2-6) 30
ejection systems 82
compressed-air ejection 89
split cavity concept 87
standard ejection design 82
stripper ejector systems 85
three-plate system with delayed
ejection 87
ejector
bar 83
box 9
housing 9
housing assembly, (figure 4-11) 84
housing shape, (figure 3-17) 57
method and location 29
pin interference with waterline,
(figure 3-10) 53
pin length, (figure 4-12) 85
pin witness marks, (figure 2-7) 31
pins, (figure 1-13) 11
(figure 4-9) 83Index Terms Links
ejector (Cont.)
plate and ejector bar, (figure 4-10) 83
plates surrounding support pillars,
(figure 3-16) 56
system guide pins and bushings 4
(figure 1-14) 12
electrical discharge
machining (EDM) 65
electrochemical machining (ECM) 66
electroforming
(electrolytic deposition) 67
engagement of shoulder
pin and bushing, (figure 7-2) 139
estimating cycle times, (figure 2-3) 20
F
fabricated metal components
of product, (figure 1-2) 3
female component 43
flash 172
flow index 17
flow lines 172
flowability 104
fountain 131
free-standing cavity block 45
(figure 3-3) 46
freeze off 168
freezing off 112Index Terms Links
G
gate 103
dimensions, (figure 5-12) 107
method and location 28
gathering information 15
determining shrinkage 15
how many cavities? 18
pressure and viscosity 17
which mold material? 21
aluminum 22
beryllium-copper alloys 22
other materials 23
steels 21
4130 alloy steel 21
6145 alloy steel 21
A-2 alloy tool steel 22
1020 carbon steel 21
1030 carbon steel 21
1040 carbon steel 21
420 stainless steel 22
A-6 tool steel 22
D-2 tool steel 22
H-13 tool steel 22
O1 tool steel 21
P-20 tool steel 22
S-7 tool steel 21
which plastic? 15Index Terms Links
gating methods and designs 103
determining gate
location and number 103
drop gates (three-plate molds) 110
into the thickest section
of the part (figure 2-5) 29
sprue gates 105
surface gates 106
basic surface gate 106
disc gate 108
edge gate 108
ring gate 109
to fill from thick to thin,
(figure 5-10) 104
tunnel gates 112
gloss (low) 172
H
hand-loaded inserts 81
heat pin 131
heat transfer metals 132
aluminum 133
copper alloys 134
zinc alloys 134
heel lock 143
high shrink 16
hobbing 64Index Terms Links
horizontal shut-off land,
(figure 3-21) 62
horn pins 75
hot runner concept, (figure 5-9) 102
I
injection molding concept 1
injection molding machine, (figure 1-1) 2
injection pressure directed at B plate,
(figure 3-11) 54
inserts 81
installing and setting up the mold 156
procedure 157
sizing and inspection 157
molds in production 155
new molds 154
insulated runner 100
(figure 5-8) 101
interlocks 137
isotropic shrinkage 16
J
jackscrews to remove wedge blocks,
(figure 3-6) 50
jetting 173
K
knit lines (weld lines) 173Index Terms Links
L
laminar construction 47
(figure 3-7) 51
laminar flow versus turbulent flow
(figure 6-3) 124
land 173
leader pin and bushing components
(figure 7-1) 138
lifter mechanism, (figure 4-5) 80
lifter system alignment, (figure 7-8) 144
lifters 78
live half 4
locating ring used for alignment,
(figure 7-11) 147
location of cavities and cooling channels 31
long-term storage 162
low shrink 16
M
male component 43
medium shrink 16
melt
flow 17
index 17 104
index test apparatus or viscosity
indicator, (figure 2-2) 18
rate 17
methods of repair 151Index Terms Links
microsurface of a
molding cavity, (figure 2-4) 28
mold base components, (figure 1-4) 4
ejector half of the mold 9
housing 9
pins, return pins, and sprue-pullers 11
support pillars 10
support plate 10
system guide pins and bushings 11
injection half of the mold 5
A and B plates 6
cavity image 9
runners and gates 6
sprue bushing 5
mold halves alignment 137
leader pins and bushings 137
tapered locks 139
mold importance 1
mold life expectancies 36
casting 38
fabrication 38
injection molding 38
rapid systems 37
thermoforming 38
mold material surface enhancements 23
product surface finish and special
requirements 27
tool treatments 23
impregnated polymer 26Index Terms Links
mold material surface
enhancements (Cont.)
Micro-tuff 26
metallic platings 25
Armoloy 25
electroless nickel 25
electrolizing 25
industrial hard chrome 25
nutmeg tungsten nickel 26
PTFE—metallic codepositions 25
Nicklon 25
Nicotef 25
Nutmeg chromium-plus 25
Nye-tef 25
PTFE—metallic fused coatings 24
Nedox-SF2 24
Nituff 24
Poly-ond 24
TFE-Lok 24
surface hardening treatments 26
ion nitriding 26
melonite 26
thin film, hi-hard coatings 26
Diamond Black 26
titanium nitriding 26
thin metallic coatings 24
Dicronite Dl-5 24
WS2 24
venting concepts 35Index Terms Links
mold open at the parting line, (figure 1-5) 5
mold temperature control unit, (figure 6-2) 123
molding area without support pillars,
(figure 3-13) 55
multiple parting line, (figure 3-19) 60
N
neat 16
nonfill (short shots) 173
O
offsetting one leader pin
unit, (figure 7-3) 140
original surface finish
standards, (tables 3-1, 3-2) 69
ownership of the mold (and other tools) 39
P
part shrinkage, (figure 2-1) 16
parting line 4 58
(figure 3-18) 59
locks 137
pin gates 110
plastic molding with integrated
components, (figure 1-3) 3
plastic part and cavity image, (figure 3-1) 44
plastometer 17
platens 148Index Terms Links
platens and tie bars, (figure 7-13) 149
pocketing 47
pockets for retaining
cavity set, (figure 3-4) 48
prehard 22
protecting the mold 154
pry bar slots,
(figure 8-1) 155
Q
questions
Chapter 1: A Primer on Molds 11
Chapter 2: Mold Design Basics 41
Chapter 3: Basics of
Mold Construction 72
Chapter 4: Action Areas of the Mold 91
Chapter 5: Runners,
Gates, and Venting 120
Chapter 6: Controlling Mold
Temperatures 135
Chapter 7: Mold Alignment Concepts 150
Chapter 8: Repairing, Protecting and
Storing Molds 163
R
regrind 101
retainer plate 83
return pins 11Index Terms Links
Reynolds number 124
Eq. 1 125
ring gate designs, internal and external,
(figure 5-15) 111
round runner cross section compared with
trapezoid, (figure 5-3) 96
runner
block 95
(figure 5-2) 96
cross section 33
cross sections and stresses,
(figure 2-12) 34
diameter increased by 20%,
(figure 5-5) 99
diameters for common materials,
(table 5-1) 97
length measurement,
(figure 5-4) 98
system and gates,
(figure 1-9) 8
systems 95
hot 101
insulated 100
surface 95
S
short-term storage 162
shrinkage 15 174Index Terms Links
shut-off 61
shut-off land area 43
side hole created by special shut-off
(figure 3-23) 63
sink marks 174
slide mechanism, 75 (figure 4-1) 76
(figure 7-6) 142
splay (silver streaking) 174
split cavity ejection system,
(figure 4-15) 88
spoke concept for cavity layout,
(figure 2-9) 33
sprue 5 93
bushing 93
dimensions, (figure 5-1) 94
used to position nozzle,
(figure 7-12) 148
function, (figure 1-6) 6
gate concept, (figure 5-11) 106
puller pins 12
squared versus spoke layouts,
(figure 2-10) 33
steel allowance surrounding cavity set,
(figure 3-8) 52
stereolithography apparatus (SLA) 68
storing molds 161
straight side interlocks,
(figure 7-5) 141Index Terms Links
stripper
plate 86
plate ejection, (figure 4-13) 86
sleeve ejection, (figure 4-14) 87
summary
Chapter 1: A Primer on Molds 11
Chapter 2: Mold Design Basics 39
Chapter 3: Basics of Mold
Construction 71
Chapter 4: Action
Areas of the Mold 90
Chapter 5: Runners, Gates, and
Venting 119
Chapter 6: Controlling Mold
Temperatures 134
Chapter 7: Mold
Alignment Concepts 150
Chapter 8: Repairing,
Protecting and
Storing Molds 162
support
pillars (figure 1-12), 10, (figure 3-12)
54, (figures 3-14, 3-15) 55
plate, (figure 1-11) 10
sweeping radius runner path,
(figure 5-6) 99
sweeping turn runner system,
(figure 2-11) 33Index Terms Links
T
taper lock system, (figure 7-4) 140
telescoping 145
core pins, (figure 7-9) 145
to eliminate preload, (figure 7-10) 146
thermal pin 131
thread undercuts, (figure 4-6) 80
three-plate parting lines, (figure 3-20) 61
three-plate system with delayed ejection,
(figure 4-16) 89
tie bars 149
toe in of clamps, (figure 8-2) 156
troubleshooting defects
caused by molds 165
tunnel gate
with pointed tunnel, (figure 5-17) 113
with truncated tunnel, (figure 5-18) 113
tunnel gating into an ejector pin,
(figure 5-20) 114
turbulent flow 124
U
unscrewing device 78
for the mold component,
(figure 4-7) 81
for the plastic part, (figure 4-8) 82
U-shaped ejector housing,
(figure 1-10) 9Index Terms Links
V
vapor-forming nickel shells 67
vent depths, (table 5-2) 117
venting 35 115
cavity perimeter, (figure 5-22) 118
concept, (figure 2-13) 36
(figure 5-21) 116
nonparting line areas, (figure 5-23) 119
types, sizes, and location of vents 115
why vent? 115
vertical shut-off condition, (figure 3-22) 62
vestige 29
viscosity 17
viscosity effect on physical properties,
(table 2-1) 19
W
wagon-wheel runner layout, (figure 5-7) 100
warpage 175
water cascade (bubbler), (figure 6-9) 131
water viscosity versus temperature,
(table 6-1) 125
waterline 121
and interference items, (figure 6-8) 130
bubblers and cascades 131
control units versus manifolds 121
control units 122
manifolds 122Index Terms Links
waterline (Cont.)
cooling pins 131
determining location
of waterlines 126
distance
from cavity set, (figure 3-9) 53
to cavity, (figure 6-7) 130
laminar flow versus
turbulent flow 123
layout, (figure 6-1) 122
pattern,
(figures 6-4, 6-5, and 6-6) 127 128 129
wedge lock 143
wedges used for
locking cavity block,
(figure 3-5) 49
witness mark 30
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