Moldflow Design Guide

The origins of this book not only include Moldflow Design Principles, but also includes Warpage Design Principles published by Moldflow, and C-Mold Design Guide. Collectively, these documents are based on years of experience in the research, theory and practice of injection molding. These documents are now combined into one book, the Moldflow Design Principles. This book is intended to help practicing engineers solve problems they encounter frequently in the design of parts and molds, as will as during production. This book can also be used as a reference for training purpose at industrial, as well as educational institutions.

Contents:

- Polymer Flow Behaviour in Injection Molds
- Molding Conditions and Injection Pressure
- Filling Pattern
- Moldflow Design Principles
- Meshes used in Moldflow
- Product Design
- Gate Design
- Runner System Design
- Cooling System Design
- Shrinkage and Warpage
- Moldflow Design Procedure
- Part Defects
- Injection Molding
- Injection Molding Machine, System, and Operations
- Injection Molding Process Control
- Plastics Materials

1;Foreword;6 2;Preface;8 3;Acknowledgements;10 4;Contents;12 5;1 Polymer Flow Behavior in Injection Molds;22 5.1;1.1 Phases of Injection Molding;22 5.1.1;1.1.1 How Plastic Fills a Mold;22 5.1.2;1.1.2 The Filling Phase;24 5.1.3;1.1.3 The Pressurization Phase;27 5.1.4;1.1.4 The Compensation Phase;27 5.2;1.2 How Do Plastics Flow?;28 5.2.1;1.2.1 Material Behavior;28 5.2.2;1.2.2 Deformation;29 5.2.3;1.2.3 Viscoelastic Behavior;29 5.2.4;1.2.4 Melt Shear Viscosity;30 5.2.5;1.2.5 Newtonian Fluid vs. Non-Newtonian Fluid;31 5.2.6;1.2.6 Shear-thinning Behavior;31 5.2.7;1.2.7 Shear Rate Distribution;32 5.2.8;1.2.8 Pressure-driven Flow;32 5.2.9;1.2.9 Pressure Gradient and Injection Times;34 5.2.10;1.2.10 Melt Flow Length;34 5.2.11;1.2.11 Injection Pressure vs. Fill Time;34 5.2.12;1.2.12 Flow Instability;36 6;2 Molding Conditions and Injection Pressure;38 6.1;2.1 Injection-pressure Overview;38 6.1.1;2.1.1 Pressure Drives the Flow Front;39 6.2;2.2 Factors Influencing Injection-pressure Requirements;39 6.3;2.3 Equations;41 6.3.1;2.3.1 Circular Channel Flow;41 6.3.2;2.3.2 Strip Channel Flow;41 6.4;2.4 Effect of Molding Conditions;42 6.4.1;2.4.1 Part Quality;42 6.4.2;2.4.2 Melt Temperature;43 6.4.3;2.4.3 Mold Temperature;43 6.4.4;2.4.4 Fill Time;44 6.4.5;2.4.5 Shear Stress Variation;44 6.4.6;2.4.6 Packing Pressure and Time;45 6.4.7;2.4.7 Summary;46 6.4.8;2.4.8 Back Flow;47 6.5;2.5 Using Moldflow to Determine Optimum Molding Conditions;47 6.5.1;2.5.1 Part;48 6.5.2;2.5.2 Molding Window Size;48 6.5.3;2.5.3 Injection Pressure;49 6.5.4;2.5.4 Flow Front Temperature;50 6.5.5;2.5.5 Cooling Time;51 6.5.6;2.5.6 Summary;52 7;3 Filling Pattern;54 7.1;3.1 Filling Pattern Overview;54 7.1.1;3.1.1 What Is the Filling Pattern?;54 7.2;3.2 Flow in Complex Molds;55 7.2.1;3.2.1 Overpack;55 7.2.2;3.2.2 Racetrack Effect;56 7.2.3;3.2.3 Varying Injection Rate;56 7.2.4;3.2.4 Underflow Effect;57 7.2.5;3.2.5 Hesitation Effect;58 7.2.6;3.2.6 Weld Lines;59 7.2.7;3.2.7 Meld Lines;59 7.2.8;3.2.8 Sink Marks;59 7.2.9
;3.2.9 Multidirectional Flow;60 7.2.10;3.2.10 Unstable Flow;61 7.2.11;3.2.11 Simple Flow Pattern;62 7.3;3.3 Flow-front Velocity and Flow-front Area;62 7.3.1;3.3.1 What are FFV and FFA?;62 7.3.2;3.3.2 Flow-front Velocity Influences Filling Pattern;62 7.3.3;3.3.3 Equation;63 7.4;3.4 Using Moldflow to Determine the Filling Pattern;64 7.4.1;3.4.1 Computer Simulation Can Eliminate Molding Trials;64 7.4.2;3.4.2 Using a Flow Analysis;64 7.5;3.5 Using Moldflow to Achieve Constant FFV;65 7.5.1;3.5.1 Controlling the FFV Through Ram Speed;65 8;4 Moldflow Design Principles;68 8.1;4.1 Product Design and Moldflow;68 8.2;4.2 Sequence of Analysis;68 8.2.1;4.2.1 Part Filling Optimization;69 8.2.2;4.2.2 Molding Conditions;69 8.2.3;4.2.3 Runner Design;69 8.2.4;4.2.4 Cooling Optimization;70 8.2.5;4.2.5 Packing Optimization;70 8.2.6;4.2.6 Warpage Optimization;70 8.3;4.3 Moldflow Flow Concepts;70 8.3.1;4.3.1 Unidirectional and Controlled Flow Pattern;71 8.3.2;4.3.2 Flow Balancing;72 8.3.3;4.3.3 Constant Pressure Gradient;73 8.3.4;4.3.4 Maximum Shear Stress;74 8.3.5;4.3.5 Uniform Cooling;75 8.3.6;4.3.6 Positioning Weld and Meld Lines;76 8.3.7;4.3.7 Avoid Hesitation Effects;76 8.3.8;4.3.8 Avoid Underflow;76 8.3.9;4.3.9 Balancing with Flow Leaders and Flow Deflectors;78 8.3.10;4.3.10 Controlled Frictional Heat;79 8.3.11;4.3.11 Thermal Shutoff of Runners;79 8.3.12;4.3.12 Acceptable Runner/Cavity Ratio;80 9;5 Meshes Used In Moldflow Analyses;82 9.1;5.1 Mesh Types Used by Moldflow;82 9.1.1;5.1.1 Finite Elements Used in Moldflow;82 9.1.2;5.1.2 Mesh Types;83 9.1.3;5.1.3 Solver Assumptions;84 9.2;5.2 Mesh Requirements;85 9.2.1;5.2.1 Mesh Density Considerations;85 9.2.2;5.2.2 Part Details;88 9.3;5.3 Geometry Creation;89 9.4;5.4 Importing Geometry;90 9.5;5.5 Using Different Mesh Types;90 9.5.1;5.5.1 Door Panel;90 9.5.2;5.5.2 Manifold;91 10;6 Product Design;92 10.1;6.1 Material Properties for Product Design;92 10.1.1;6.1.1 Plastics Are Sensitive to Operating Conditions;92 10.1.2;6.1.2 Stress-Strain
Behavior;93 10.1.3;6.1.3 Creep and Stress Relaxation;98 10.1.4;6.1.4 Fatigue;100 10.1.5;6.1.5 Impact strength;101 10.1.6;6.1.6 Thermal Mechanical Behavior;101 10.2;6.2 Design for Strength;103 10.2.1;6.2.1 Predicting Part Strength;103 10.2.2;6.2.2 Loading/Operating Conditions;103 10.3;6.3 Part Thickness;107 10.3.1;6.3.1 Part Thickness Drives Quality and Cost;107 10.3.2;6.3.2 Cycle Time Increases with Thickness;107 10.3.3;6.3.3 Thick Parts Tend to Warp;107 10.3.4;6.3.4 Thin, Uniform Parts Improve Surface Quality;108 10.3.5;6.3.5 Reducing Part Thickness;108 10.4;6.4 Boosting Structural Integrity with Ribs;109 10.4.1;6.4.1 Structural Integrity: the Goal of Every Design;109 10.4.2;6.4.2 Designing Ribs;109 10.5;6.5 Design for Assembly;111 10.5.1;6.5.1 Molding One Part vs. Separate Components;111 10.5.2;6.5.2 Tolerances: Fit between Parts;111 10.5.3;6.5.3 Press-fit Joints;112 10.5.4;6.5.4 Snap-fit Joints;114 10.5.5;6.5.5 Cantilever Snap Joints;116 10.5.6;6.5.6 Torsion Snap-fit Joints;117 10.5.7;6.5.7 Fasteners;119 10.5.8;6.5.8 Inserts;122 10.5.9;6.5.9 Welding Processes;122 11;7 Gate Design;124 11.1;7.1 Gate Design Overview;124 11.1.1;7.1.1 What Is a Gate?;124 11.1.2;7.1.2 Single vs. Multiple Gates;124 11.1.3;7.1.3 Gate Dimensions;124 11.1.4;7.1.4 Gate Location;125 11.2;7.2 Gate Types;125 11.2.1;7.2.1 Manually Trimmed Gates;125 11.2.2;7.2.2 Automatically Trimmed Gates;131 11.3;7.3 Design Rules;134 11.3.1;7.3.1 Determining the Number of Gates;134 11.3.2;7.3.2 Flow Patterns;136 11.3.3;7.3.3 Gate Position;137 11.3.4;7.3.4 Avoiding Common Problems;143 11.3.5;7.3.5 Gate Length;143 11.3.6;7.3.6 Gate Thickness;143 11.3.7;7.3.7 Freeze-off Time;144 11.4;7.4 Using Moldflow for Gate Design;144 11.4.1;7.4.1 Gate Location;144 11.4.2;7.4.2 Molding Window Size for the Three Gate Locations;145 11.4.3;7.4.3 Filling Pattern;146 11.4.4;7.4.4 Gate Size Based on Shear Rate;146 12;8 Runner System Design;148 12.1;8.1 Definitions;148 12.1.1;8.1.1 Feed System;148 12.1.2;8.1.2 Runner System;148 12.1
.3;8.1.3 Cold Runner;148 12.1.4;8.1.4 Hot Runner;149 12.1.5;8.1.5 Hot Manifold;149 12.1.6;8.1.6 Hot Drop;149 12.1.7;8.1.7 Sprue;149 12.2;8.2 Runner System Design Principles;150 12.2.1;8.2.1 Benefits of Good Runner Design;150 12.2.2;8.2.2 Runner Design Philosophy;150 12.2.3;8.2.3 Flow Balancing;151 12.2.4;8.2.4 Flow Control;151 12.2.5;8.2.5 Frictional Heating in Runners;153 12.2.6;8.2.6 Thermal Shutoff;153 12.2.7;8.2.7 System and Runner Pressures;153 12.2.8;8.2.8 Constant Pressure Gradient;154 12.2.9;8.2.9 Cold Slug Wells;154 12.2.10;8.2.10 Easy Ejection;155 12.3;8.3 Runner Types;155 12.3.1;8.3.1 Cold Runners;155 12.3.2;8.3.2 Hot Runner Systems;156 12.4;8.4 Runner Layout;157 12.4.1;8.4.1 Determining the Number of Cavities;157 12.4.2;8.4.2 Planning the Runner System Layout;159 12.4.3;8.4.3 Partially Balanced Runners;160 12.4.4;8.4.4 Geometrically Balanced Runners;162 12.5;8.5 Initial Runner Sizing;162 12.5.1;8.5.1 Determining Sprue Dimensions;162 12.5.2;8.5.2 Designing Runner Cross Sections;163 12.5.3;8.5.3 Determining Runner Diameters;166 12.6;8.6 Runner Balancing;168 12.6.1;8.6.1 How Runner Balancing Works;168 12.6.2;8.6.2 When Are the Runner Sizes Optimized?;168 12.6.3;8.6.3 Validating the Balance;168 12.6.4;8.6.4 Processing Window;169 12.7;8.7 Using Moldflow for Runner Balancing;170 12.7.1;8.7.1 Runner Balancing a 48-cavity Tool;170 12.7.2;8.7.2 Runner Balancing for a Family Mold;172 12.7.3;8.7.3 Runner Balancing for a Multigated Part;173 13;9 Cooling System Design;174 13.1;9.1 Mold Cooling System Overview;174 13.1.1;9.1.1 Importance of Cooling System Design;174 13.1.2;9.1.2 Mold Cooling System Components;175 13.2;9.2 Cooling-channel Configuration;177 13.2.1;9.2.1 Types of Cooling Channels;177 13.3;9.3 Alternative Cooling Devices;178 13.3.1;9.3.1 What Do They Do?;178 13.3.2;9.3.2 Baffles;179 13.3.3;9.3.3 Bubblers;180 13.3.4;9.3.4 Thermal Pins;180 13.3.5;9.3.5 Cooling Slender Cores;181 13.3.6;9.3.6 Cooling Large Cores;182 13.3.7;9.3.7 Cooling Cylinder Cores;183 13.
4;9.4 Cooling System Equations;183 13.4.1;9.4.1 Cooling Time;183 13.4.2;9.4.2 Reynolds Number and Coolant Flow;184 13.5;9.5 Design Rules;184 13.5.1;9.5.1 Mold Cooling Design Considerations;184 13.5.2;9.5.2 Location and Size of Channels;185 13.5.3;9.5.3 Flow Rate and Heat Transfer;187 13.6;9.6 Using Moldflow for Cooling System Design;188 13.6.1;9.6.1 Example Setup;189 13.6.2;9.6.2 Cycle Time Determined by Design and Processing Parameters;190 14;10 Shrinkage and Warpage;194 14.1;10.1 Injection Molding and Shrinkage;194 14.1.1;10.1.1 What Are Shrinkage and Warpage?;194 14.1.2;10.1.2 Shrinkage and Machine Settings;194 14.1.3;10.1.3 Mold Filling and Packing;195 14.1.4;10.1.4 How Pressure and Time Affect Shrinkage;196 14.1.5;10.1.5 Thermally Unstable Flow;197 14.2;10.2 Basic Causes of Shrinkage and Warpage;198 14.2.1;10.2.1 Causes of Shrinkage;198 14.2.2;10.2.2 Causes of Warpage;202 14.2.3;10.2.3 Relating Orientation and Area Shrinkage to Warpage;203 14.3;10.3 Designing Accurate Parts Considering Warpage;204 14.3.1;10.3.1 Material Selection;205 14.3.2;10.3.2 Wall Thickness Variation;205 14.3.3;10.3.3 Gate Position and Runner Dimensions;206 14.3.4;10.3.4 Molding Conditions;208 14.3.5;10.3.5 Cooling Line Layout;211 15;11 Moldflow Design Procedure;212 15.1;11.1 Determine Analysis Objectives;212 15.2;11.2 Moldflow Analysis Steps Framework;213 15.2.1;11.2.1 The Whole Process;213 15.2.2;11.2.2 Optimize Fill;213 15.2.3;11.2.3 Balance and Size the Runners;218 15.2.4;11.2.4 Optimize Cooling;220 15.2.5;11.2.5 Optimize the Packing Profile;221 15.2.6;11.2.6 Optimize Warpage;222 15.3;11.3 Using Moldflow to Evaluate an Initial Design;226 15.3.1;11.3.1 Description of this Example;226 15.3.2;11.3.2 Molding Window;226 15.3.3;11.3.3 Filling Analysis;227 15.3.4;11.3.4 Gate and Runner Design;227 15.3.5;11.3.5 Cooling System Design;228 15.3.6;11.3.6 Packing Analysis;230 15.3.7;11.3.7 Warpage Analysis;230 15.4;11.4 Using Moldflow to Optimize the Design;231 15.4.1;11.4.1 Determine the Cause of
Warpage;231 15.4.2;11.4.2 Investigating Different Gate Locations;231 15.4.3;11.4.3 Validating the Best Gate Location;232 16;12 Part Defects;236 16.1;12.1 Air Traps;236 16.1.1;12.1.1 What Is an Air Trap?;236 16.1.2;12.1.2 Problems Caused by Air Traps;237 16.1.3;12.1.3 Remedies;237 16.2;12.2 Black Specks and Black Streaks;238 16.2.1;12.2.1 What Are Black Specks and Black Streaks?;238 16.2.2;12.2.2 Causes of Black Specks and Black Streaks;238 16.2.3;12.2.3 Remedies;239 16.3;12.3 Brittleness;240 16.3.1;12.3.1 What Is Brittleness?;240 16.3.2;12.3.2 Causes of Brittleness;240 16.3.3;12.3.3 Remedies;240 16.4;12.4 Burn Marks;241 16.4.1;12.4.1 What Is a Burn Mark?;241 16.4.2;12.4.2 Causes of Burn Marks;242 16.4.3;12.4.3 Remedies;243 16.5;12.5 Delamination;243 16.5.1;12.5.1 What Is Delamination?;243 16.5.2;12.5.2 Causes of Delamination;244 16.5.3;12.5.3 Remedies;244 16.6;12.6 Dimensional Variation;245 16.6.1;12.6.1 What Is Dimensional Variation?;245 16.6.2;12.6.2 Causes of Dimensional Variation;245 16.6.3;12.6.3 Remedies;245 16.7;12.7 Discoloration;246 16.7.1;12.7.1 What Is Discoloration?;246 16.7.2;12.7.2 Causes of Discoloration;246 16.7.3;12.7.3 Remedies;247 16.8;12.8 Fish Eyes;248 16.8.1;12.8.1 What Are Fish Eyes?;248 16.8.2;12.8.2 Causes of Fish Eyes;248 16.8.3;12.8.3 Remedies;248 16.9;12.9 Flash;249 16.9.1;12.9.1 What Is Flash?;249 16.9.2;12.9.2 Causes of Flash;249 16.9.3;12.9.3 Remedies;250 16.10;12.10 Flow Marks;251 16.10.1;12.10.1 What Is A Flow Mark?;251 16.10.2;12.10.2 Causes of Flow Marks;251 16.10.3;12.10.3 Remedies;251 16.11;12.11 Hesitation;252 16.11.1;12.11.1 What Is Hesitation?;252 16.11.2;12.11.2 Problems Caused by Hesitation;252 16.11.3;12.11.3 Remedies;253 16.12;12.12 Jetting;253 16.12.1;12.12.1 What Is Jetting?;253 16.12.2;12.12.2 Problems Caused by Jetting;254 16.12.3;12.12.3 Remedies;254 16.13;12.13 Ripples;256 16.13.1;12.13.1 What Are Ripples?;256 16.13.2;12.13.2 Cause of Ripples;256 16.13.3;12.13.3 Remedies;257 16.14;12.14 Short Shots;257 16.14.1;12.14.
1 What Is a Short Shot?;257 16.14.2;12.14.2 Causes of Short Shots;258 16.14.3;12.14.3 Remedies;258 16.15;12.15 Silver Streaks;259 16.15.1;12.15.1 What Are Silver Streaks?;259 16.15.2;12.15.2 Causes of Silver Streaks;260 16.15.3;12.15.3 Remedies;260 16.16;12.16 Sink Marks and Voids;261 16.16.1;12.16.1 What Are Sink Marks and Voids?;261 16.16.2;12.16.2 Causes of Sink Marks and Voids;261 16.16.3;12.16.3 Remedies;262 16.17;12.17 Weld Lines and Meld Lines;264 16.17.1;12.17.1 What Are Weld Lines and Meld Lines?;264 16.17.2;12.17.2 Problems Caused by Weld Lines;264 16.17.3;12.17.3 Strength of Weld Lines;265 16.17.4;12.17.4 Remedies;266 17;Appendix A: Injection Molding;268 17.1;A.1 Injection-molding Overview;268 17.1.1;A.1.1 Process;268 17.1.2;A.1.2 Applications;269 17.2;A.2 Development of the Injection-molding Machine;269 17.2.1;A.2.1 Benefits of the Reciprocating Screw;269 17.3;A.3 Development of the Injection-molding Process;270 17.4;A.4 Alternative Injection-molding Processes;270 17.4.1;A.4.1 Co-injection (Sandwich) Molding;270 17.4.2;A.4.2 Fusible Core Injection Molding;271 17.4.3;A.4.3 Gas-assisted Injection Molding;272 17.4.4;A.4.4 Injection-compression Molding;273 17.4.5;A.4.5 Lamellar (Microlayer) Injection Molding;274 17.4.6;A.4.6 Live-feed Injection Molding;274 17.4.7;A.4.7 Low-pressure Injection Molding;275 17.4.8;A.4.8 Push-pull Injection Molding;275 17.4.9;A.4.9 Reactive Molding;276 17.4.10;A.4.10 Structural Foam Injection Molding;277 17.4.11;A.4.11 Thin-wall Molding;277 18;Appendix B: Injection-molding Machine: System and Operations;280 18.1;B.1 Injection-molding Machine;280 18.1.1;B.1.1 Components;280 18.1.2;B.1.2 Machine Specification;281 18.1.3;B.1.3 Machine Function;281 18.1.4;B.1.4 Auxiliary Equipment;281 18.2;B.2 Machine Components;282 18.2.1;B.2.1 Injection System;282 18.2.2;B.2.2 Mold System;284 18.2.3;B.2.3 Hydraulic System;285 18.2.4;B.2.4 Control System;285 18.2.5;B.2.5 Clamping System;285 18.3;B.3 Molded System;286 18.3.1;B.3.1 The Delivery System
;286 18.4;B.4 Machine Operating Sequence;287 18.4.1;B.4.1 Process Cycle;287 18.5;B.5 Screw Operation;289 18.5.1;B.5.1 Back Pressure;289 18.5.2;B.5.2 Injection Speed;289 18.5.3;B.5.3 Screw Rotation Speed;289 18.5.4;B.5.4 Cushion;290 18.6;B.6 Secondary Operations;290 18.6.1;B.6.1 Assembly;290 18.6.2;B.6.2 Decoration;290 18.6.3;B.6.3 Other Secondary Operations;291 19;Appendix C: Injection-molding Process Control;292 19.1;C.1 Importance of Process Conditions;292 19.1.1;C.1.1 Setting Machine Process Conditions;292 20;Appendix D: Plastic Materials;302 20.1;D.1 What Are Plastics?;302 20.1.1;D.1.1 Polymerization Process;302 20.1.2;D.1.2 Structure of Polymers;302 20.1.3;D.1.3 Polymer Alloys and Blends;304 20.1.4;D.1.4 Polymer Composites;304 20.2;D.2 Classification of Plastics;304 20.2.1;D.2.1 Classes of Plastics;305 20.2.2;D.2.2 Structures and Properties of Plastics;305 20.3;D.3 Thermoplastics;306 20.3.1;D.3.1 Market Share Distribution of Thermoplastics;306 20.3.2;D.3.2 Structures and Properties of Thermoplastics;307 20.3.3;D.3.3 Amorphous Polymers;307 20.3.4;D.3.4 Semicrystalline Polymers;308 20.4;D.4 Thermosets;309 20.5;D.5 Properties and Applications of Thermoplastics;310 20.5.1;D.5.1 ABS;311 20.5.2;D.5.2 PA 12;312 20.5.3;D.5.3 PA 6;314 20.5.4;D.5.4 PA 66;315 20.5.5;D.5.5 PBT;317 20.5.6;D.5.6 PC;318 20.5.7;D.5.7 PC/ABS;320 20.5.8;D.5.8 PC/PBT;321 20.5.9;D.5.9 HDPE;322 20.5.10;D.5.10 LDPE;324 20.5.11;D.5.11 PEI;325 20.5.12;D.5.12 PET;326 20.5.13;D.5.13 PETG;327 20.5.14;D.5.14 PMMA;328 20.5.15;D.5.15 POM;330 20.5.16;D.5.16 PP;331 20.5.17;D.5.17 PPE/PPO;333 20.5.18;D.5.18 PS;334 20.5.19;D.5.19 PVC;335 20.5.20;D.5.20 SAN;337 20.5.21;D.5.21 Additives, Fillers, and Reinforcements;338 20.5.22;D.5.22 Modifying Polymer Properties;339 20.5.23;D.5.23 Low-aspect Fillers;340 20.5.24;D.5.24 High-aspect Fillers: Fibers;340 21;Index;342