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Jerry Fischer
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5 أكتوبر 2023
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Handbook of Molded Part Shrinkage and Warpage
2nd Edition
Jerry Fischer
Table of contents
PDL Handbook Series
Preface
Acknowledgments
- Introduction to Injection Molding
1.1 Introduction to Plastics
1.2 Interactivity Basics
1.3 Thermal Principles Governing Injection Molding
References - Shrinkage and Warpage
2.1 In-Mold Shrinkage
2.2 Warpage
2.3 Postmold Shrinkage
References - Causes of Molded-Part Variation: Part Design
3.1 Wall Thickness
3.2 Ribs
3.3 Bosses
3.4 Example of Proper Part Design
3.5 Other Design Considerations
References - Causes of Molded-Part Variation: Material
4.1 Amorphous and Semicrystalline Resins
4.2 Effects of Fillers, Reinforcements, Pigments, Time, and Stress
4.3 Shrinkage Predictions: Using PVT Relationships
References - Causes of Molded-Part Variation: Mold Design
5.1 Cavity Dimensions and Design Factors
5.2 Gate Types
5.3 Gate Location
5.4 Gate Size
5.5 Gate Design Systems
5.6 Runner Design
5.7 Mold Cooling Design
5.8 Mold Construction Materials
5.9 Prototype Molding with Stereolithography or Similar Type Molds
5.10 Pitfalls to Avoid
References - Causes of Molded Part Variation: Processing
6.1 Molding Conditions
6.2 Injection Melt Temperature
6.3 Injection Rate and Pressure
6.4 Holding Pressure and Time
6.5 Mold Temperature
6.6 Demolding Temperature
6.7 Molded-In Stresses
6.8 Other Molding Processes
References - Factors Affecting Postmold Shrinkage and Warpage
7.1 Effects of Temperature on Dimensions
7.2 Effects of Moisture on Dimensions
7.3 Creep
References - Controlling Mold and Postmold Shrinkage and Warpage
8.1 Finding the Cause
8.2 Processing Considerations
8.3 Material Considerations
8.4 Tooling Considerations
8.5 Part Geometry
8.6 Controlling Warpage
References - Computer-Aided Analysis
9.1 Capabilities of CAA
9.2 Limitations of CAA
9.3 Selecting a CAA Program
9.4 Customer Requirements
9.5 Management Tools
9.6 Filling Analysis
9.7 Packing and Holding Simulation
9.8 Shrinkage/Warpage Simulation
9.9 Cooling Analysis
9.10 Costs
9.11 Conclusions
References - Case Studies
10.1 Unexpected Housing Shrink
10.2 Changing Materials Triggers Warpage
10.3 Creep in a Water Heater Stand
10.4 Oversize Part Injection-Molding Alkyd Thermoset
10.5 Inadequate Baby Dish Mold
10.6 Gas Entrapment in Baby Dish Mold
10.7 Warpage in a Molded Spool
10.8 Daisy-Wheel Breakage
10.9 PVC Part-Flashing Problems
10.10 Polycarbonate Switch Failure
10.11 Square Poker-Chip Tray: Inadequate Shot Size
10.12 Problem Ejecting Square Poker Chips
10.13 Military Cup Material “Shrinkage”
10.14 Core-Deflection Problems
10.15 Elevator Gib Warpage
10.16 Sucker-Rod Guide Brittleness
10.17 Bottle-Cap Thread Distortion
10.18 Plastic Post Creep
10.19 Excessive Shrinkage of Glass-Filled Nylon
10.20 Preventing Warpage in Thin Molded Lids
10.21 A Printed Circuit Board That Did Not Work
10.22 A Cup with a Handle that Won’t Fill
10.23 Leaking Hot Runner Mold
References - Data
11.1 Unfilled Materials
11.2 Effects of Fillers
11.3 Shrinkage vs. Various Parameters
11.4 Moisture Absorption Curves
11.5 Pressure–Volume–Temperature Curves
11.6 Shrinkage and Warpage of Molded Disks
11.7 Angular Warpage
11.8 General Shrinkage Characteristics for Various Plastics
11.9 Material-Specific Shrinkage Characteristics
References
Appendix A. Conversion Factors and Equivalents
Appendix B. Abbreviations, Acronyms, and Material Names
B.1 Abbreviations and Acronyms
B.2 Material Names
Glossary
Index
Color Plates
Index
Page references followed by “f” indicate figure, and “t” indicate table.
A
Acetal, 28, 99
Acetal polyoxymethylene (Delrin) (DuPont)
Acrylonitrileebutadieneestyrene (ABS), 1e2, 27
Amorphous plastics, 2, 5, 25e30
amorphous polymers, 27e28, 37e38
fillers and fibers, effect of, 30e33
flow-direction shrinkage values, 27t
gradual stress relaxation, impact, 7
processing conditions, effect of, 27e28
volume vs temperature, 5, 6f
Angular warpage, 204e208, see also Warpage
Anisotropic shrinkage
of fiber-reinforced polymers, 31
Annealing, 27
ASME Y14.5, 25e26
B
Bosses, 22e23
recommended design, 23f
C
CAE software, 50
CAMPUS
“The Global Plastics Database”, 173
Carbazole violet, 35
Case studies
baby dish mold, 156e158
bottle-cap thread distortion, 167e168
core deflection problems, 164e165
creep in a water heater stand, 154e155
cup handle, problem in molding, 170
daisy-wheel printer breakage, 160
elevator gib warpage, 165e167
excessive shrinkage of glass-filled nylon, 168e169
inject-molding alkyd thermoset, 155e156
“leaking” hot runner system, 170e171
military cup material shrinkage, 163e164
molded spool, warpage issue in, 158e160
PCB, issues with, 169e170
phenomena of differential shrinkage, 154
plastic post creep, 168
polycarbonate switch failure, 161e162
problem with ejection of square poker-chip, 162e163
PVC part-flashing problems, 160e161
square poker-chip tray, 162
sucker-rod guide brittleness, 167
unexpected shrinkage, 153
warpage prevention in thin molded lids, 169
Cellulosics, 17
Computer-aided analysis (CAA)
capabilities, 132e133
cooling analysis, 148e149
cooling time estimate, 143
cost, 149e151
customer requirements, 138e140
dual domain FEA method, 142
filling analysis, 140e147
of frozen skin, 143
holding and packing analysis programs, 147e148
of isochrone, 143
limitations, 133e135
management tools, 140
mid-plane FEA method, 141e142
moldflow family of programs, 131
no-flow time, estimating, 144
of opening force, 144
orientation, calculation of, 144e145
of pressure distribution, 145
selecting a program, 135e138
of shear rate, 146
of shear stress, 146
shrinkage/warpage simulation, 148
solid FEA method, 142e147
of temperature, 146e147
two-dimensional (2D) method analysis, 141
Cooling design, 72e78
cavity side, 75
channels, 73e76
corners, effects of, 76e77
laminar flow channel, 73
reducing heat transfer problem, 75e76, 76f
runnerless molds, 77e78
size and location, 74
slides, 78
thickness, effects of, 77
turbulent flow channel, 73
uniform flow channel, 73
venting, 78
Cooling efficiency of mold, 99
Cooling phase in injection-molding process, 6e7
Cooling-rate/percentecrystallinity relationship, 15
Cooling time, approximating, 74e75
Creep rate, 36e37, 105
Cross-linking reactions, 1
Crystalline plastics, 2
crystalline regions, 5
shrinking of, 5
volume vs temperature, 5, 6f
257D
Delrin 500, 35, 37f, 88e90, 99, 101
mold shrinkage for, 89e90, 89t
postmolding shrinkage, 100f
Demolding temperature, 94e95, 94f, 95f
recommended, 95t
Density vs. shrinkage, 182
Diallyl phthalate, 1
E
Ejector pins, 72
Engineering grades of plastic, 16
Epoxy, 1
F
Fiber-reinforced polymers, 35
Fillers and fibers, effect of
relaxation of orientation, 32
semicrystalline plastics, 30e33
shear and elongational flow, 31
spherical fillers, 48
standard warp measurement, 48, 48f
stiffness and creep-resistance, 30e31
Fillers and fibers, effect of, 48
amorphous plastics, 30e33
center gated, 60
differential shrinkage, 33
on flow/cross-flow shrinkage, 175e178
methods for minimizing, 33e35
platelet fillers, 48
reduction in shrink, 31
as reinforcing agents in polymers, 31
relaxation of orientation, 31
Filling in injection-molding process, 3e5
amorphous plastics, shrinking of, 5
crystalline plastics, shrinking of, 5
effect of ribs, 20e21
parameters affecting stress, 3e4
pressure loss estimates, 4
semicrystalline plastics, shrinking of, 5
temperature profile of a flowing melt, 4f
Fixturing, 100
Flake-type reinforcements, effect of, 33e34
Foaming agent, 97
Free shrinkage, 27
Freeze line, 44
G
Gas-assist or gas-injection molding, 96e98
Gate freeze, 27e28
Gate location, 57e61
determining, 60e61
shrinkage and, 25
side, end, and center gates, 58e60
Gate locations, 117e118
Gate size, 61e63, 117e118
minimum, 61e63
Gate types, 53e57, 54f
diaphragm, and ring gates, 56
disk gates or cone gates, 56
edge and a straightedge gate, 55
fan gate, 55
film gate, 55e56, 56f
multiple gates, 56e57
pin or pinpoint gates, 53e55, 54f
tab gates, 56
tunnel or submarine gates, 54, 55f
Gating schemes, 34e35
Gears, 122e123
German Standard DIN 16901, 25e26
Glass-fiber reinforced semicrystalline polymer, shrinkage
behavior of, 32e33
Glass-fiber reinforcements, effect of, 33
Glass-filled polypropylene, 16
H
High-density polyethylene (HDPE), 29
Holding pressure, 88e90
vs. shrinkage, 183e184
Hybrid composite materials, effect of, 33, 34f
Hygroscopic materials, 17
I
Indanthrone blue, 35
Injection rate and injection pressure, 85e88
Injection temperature vs. shrinkage, 180
Injection-molding machine, 3f, 4f, 83f
Injection-molding process, thermal principles
cooling phase, 6e7
filling process, 3e5
holding phase, 5
In-mold shrinkage, 9e13
ASTM D3641-10a standardisation, 11
ASTM D955-08 standardisation, 10e11
biaxial orientation (BO), 12
cavity size measurement, 11
change in molding conditions, 9t
determination of shrinkage, 10e11
environmental factors, effect on mold, 9, 9t
mechanical properties of reinforced plastic, 12
molded-in stress, 11e13
and reversible properties, 11e12
of RPs, 12
shrink factor, 11
tensile strength, 12
Interactivity, 1
basics, 1e3
ISO2768-1 & 2, 25e26
L
Liquid crystal polymer (Zenite) (DuPont)
shrinkage characteristics of, 234
Lost-core process of molding, 96
M
Manganese violet, 35
Materials, behavior of different materials
amorphous, 25e30
considerations, 114e117
effects of fillers, reinforcements, pigments, time, and stress, 30e38
effects of time and stress on dimensional stability, 36e38
semicrystalline resins, 25e30
shrinkage predictions, 38e50
Melt temperature, 84e85
vs. shrinkage, 181
Modern Plastics Encyclopedia, 16e17
Moisture absorption curves, 187
258 INDEXMold design
cavity dimensions and design factors, 51e53
construction materials, 78e79
cooling design, 72e78
dimensional tolerances, 51, 52f
gate design systems, 63e64
gate location, 57e61
gate size, 61e63
gate types, 53e57
molding with stereolithography (SLA), 79e80
pitfalls to avoid, 80
runner design, 64e72
use of copper or aluminum alloys, 53
Mold temperature vs. shrinkage, 182
Mold-cooling layout, 118
Molded disks
warpage of, shrinkage and, 202e203
Molded-in stresses, 95e96
Molding conditions, 81e84
Molding window, 13, 84
Mold temperature, 91e94
predicting, 91e92
shrinkage and, 92e93
Molecular orientation, 2, 2f, 14, 19, 58, 82
and shrinkage relationship, 19
N
Nonuniform in-mold shrinkage
causes, 13e14
consequences, 13
due to differential cooling, 14
due to differential crystallinity, 14
due to differential orientation, 14
due to differential thermal strain, 14
material characteristics, 13e14
molding conditions, 14
molding constraints, 14
from poor part or tool design, 13
Nylon, 17, 28, 101
water absorption, 102, 102t
Nylon (Zytel) (DuPont)
shrinkage characteristics of, 235e237
P
Part design elements
boss-designs, 126f, 127f
bosses, 22e23
design considerations, 23e24
dimensional stability, 23e24
example, 23
geometry, 123e127
molecular orientation and shrinkage relationship, 19
overall tolerances and dimensions, 125
in reinforced thermoplastics, benefits, 24
ribs, 20e22
shrinkage-restricting features, 126e127
troubleshooting shrinkage and warpage, 129te130t
“U”-shaped flange, use of, 19
wall and boss configurations for uniform thickness, 20f
wall thickness, 19e20
wall thickness of a plastic part, 125e126
warpage controlling, 127e130
Phthalocyanine blue, 35
Pigments, effect of, 35, 36t
Plastic data, from the web, 238
Polybutylene terephthalate (PBT), 35
shrinkage characteristics of, 216
Polycarbonate, 27, 115e116, 119
shrinkage characteristics of, 221
Polycarbonate resin, 25e26
recommended tolerances for, 26f
Polyethylene, 28
shrinkage values, 30t
Polyethylene terephthalate (Rynite) (DuPont), shrinkage
characteristics of, 233
Polymer crystallization, 28
Polyphenylene sulfide (PPS) (Fortron), shrinkage characteristics of,
222e223
Polypropylene, 28
glass-filled, 31e32, 32f
shrinkage characteristics of, 225e232
Polypropylene homopolymers, 88
Polystyrene, 27
Postmolding shrinkage
annealing procedures and, 100e101
Post-mold shrinkage, 9, 16e17, 28
creep phenomenon, influence of, 105
moisture, influence of, 101e104
temperature, influence of, 99e101
Pressureevolumeetemperature (PVT), 188
Primary creep, 37
Processing considerations
clamping force, 111
degree of liquid absorption, 116
demolding temperature, 94e95
draft angles, 119
ejection-system design, 119e121
elastic deformation issues, 121
excessive shrinkage, issue of, 113
fillers, 116
filling and packing pressure, 109e110
foaming agent, 97
gas-assist or gas-injection molding, 96e98
gate locations, 117e118
gate size, 117e118
gears, 122e123
general molding condition, 81
holding pressure, 88e90, 109e110
holding time, 110e111
injection rate and injection pressure, 85e88
IZOD impact strength, 82
lost-core process of molding, 96
material considerations, 114e117
melt temperature, 84e85
mold contamination issues, 121e122
mold-cooling layout, 118
molded-in stress, 95e96
molding conditions, 81e84
mold temperature, 91e94
mold wear issues, 121
nozzles, selection and use of, 112e113
part temperature at ejection, 111
positioning variations, 122
post-mold fixturing and annealing, 111
quality control, 114
regrind aspects, 116e117
runner systems, 118
secondary machining, 113
shrinkage of gas-assisted, 97e98
thick wall sections, issues with, 111e112
time for holding pressure, 90
INDEX 259Processing considerations (Continued)
tooling considerations, 117e123
tool tolerance factors, 119
uniformity of melt temperatures, 108e109
uniformity of mold temperatures, 109
PVT relationships, 38e50
amorphous polymer, 38e40, 39f
behavior of Valox, 41e42, 41f
compressibility of a polymer, 40
data modeling of, 41e43
degree of crystallinity, 42e43
demolding temperature, 95
density, 40
difference between CTE and, 39e40
premature freeze-off, 47
semicrystalline polymers, 38, 41, 42f
specific volume, 40
Tait Equation, 42
temperature and pressure, 40e41, 41f
and thermal properties, 39e43
Q
Quinacridone violet, 35
R
Ribs
filling, effect on, 20e21
relationship of pressure and rib width, 21
ribbing, problems with, 20
warpage, effect on, 20
Runnerless molds, 77e78
Runner systems, 64e72, 118
ejector pins, 72
melt properties, 71f
multiple-cavity molds, 65e72
shear-rate distribution through a circular flow channel, 71f
shrinkage values, 67, 68t, 69t, 70t
S
Secondary crystallization, 28
Semicrystalline plastics, 5
accuracy of shrinkage prediction, 49e50
anisotropic shrinkage, 28
cooling rate, influence on, 81
creep rate, 37e38
crystalline regions, 5
fillers and fibers, effect of, 30e33
gradual stress relaxation, impact, 7
nucleation point, 28
pigments, effect of, 35
polymer, 28
presence of side chains, 29
resin, 28
shrinkage behavior, 15
shrinkage values, 29e30, 29t
spherulite, 28
as toothpicks, 5
Semicrystalline thermoplastics, 2f
Short-shot, 84
Shrinkage, 9, 180e186
accuracy of prediction, 49e50
calculation, 79
cavity pressure and, 87
controlling, 35
vs. density, 182
differential shrinkage, 30
filler effects on, 175e178
of gas-assisted processing, 97e98
gate location and, 25
hold pressure and, 27e28
vs. holding pressure, 183e184
HPT and, 90, 90f
identifying cause, 107e108
injection rate and, 86e87, 87f
vs. injection temperature, 180, 180f
of liquid crystal polymer, 234
melt temperature and, 85f, 181
method for estimating, 38e50
mold temperature and, 92e93, 182
of nylon, 235e237
optimum hold time and, 27
of plastics, 209
of polybutylene terephthalate, 216
of polycarbonate, 221
of polyethylene terephthalate, 233
of polyphenylene sulfide, 222e223
of polypropylene, 225e232
relationship between part-wall thickness and, 19
of thermoplastic elastomer ether ester block copolymer, 224
thickness and, 93e94, 185e186
of unfilled materials, 174
of a variety of polycarbonate grades in steel and SLA-mold
cavities, 79t
volume shrinkage, 45
and warpage of molded disks, 202e203
Slides, 78
Society of Plastics Industries (SPI), 25e26
Solidification, 99
Spherulite, 28
Standards and Practices of Plastics Custom Molders, 25e26
Stereolithography (SLA), 79e80
T
Thermal contraction, 7
Thermal expansion behavior, 38, 38f
Thermodynamics, 1
Thermoplastic elastomer ether ester block copolymer (TEEE)
(Hytrel) (DuPont)
shrinkage characteristics of, 224
Thermoplastics, 1
electrical wall outlets, 1e2
in everyday life, 1e2
in medical application, 2
processing temperatures, 1
resins, 2
semicrystalline, 2f
types of, 2
Thermoset plastic, 1
Thermoset polyurethane, 1e2
Thickness vs. shrinkage, 185e186
Time for holding pressure, 90
U
Ultramarines, 35
Undercooling, 43
Unfilled materials, shrinkage of, 174
V
Volumetric shrinkage, 100, 110, 147
260 INDEXW
Wall thickness, 13, 19e20
boss-wall thickness, 22e23
of cavity walls, 16
cooling and, 77
cooling time and, 27, 33
for Delrin 500
demolding temperature and, 94
effect on shrinkage, 19
gate dimension and, 61e63, 89
injection pressure and, 87f
in micromolding, 24
in molding conditions, 14e15
nonuniform, 19
shrinkage and, 33, 93e94
uniform, 19e20, 20f
Warpage, 9, 13e16
angular, 204e208
causes of nonuniform shrinkage, 13e14, 19
cooling-related shrinkage, 15
cooling-related shrinkage differences and, 15
direction of fiber orientation and, 48
in fiber-reinforced materials, 15
gate location and, 59e60
identifying cause, 107e108
method for estimating, 47e49
method for minimizing, 33
moisture, effect of, 102f, 103
of molded disks, shrinkage and, 202e203
principles of minimizing, 14e16
as a result of anisotropic shrinkage, 32f
ribbing and, 20
of semicrystalline polymer, 15
shape of the part and, 24
thickness and crystallization time, 15
Z
Zytel 500, 103, 103f, 104f
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