Injection Mold Design Engineering 2E / Edition 2

by David O. Kazmer

Overview

This book provides a structured methodology and scientific basis for engineering injection molds. The topics are presented in a top-down manner, beginning with introductory definitions and the big picture before proceeding to layout and detailed design of molds. The book provides very pragmatic analysis with worked examples that can be readily adapted to real-world product design applications. It will help students and practitioners to understand the inner workings of injection molds and encourage them to think outside the box in developing innovative and highly functional mold designs. This new edition has been extensively revised with new content that includes more than 80 new and revised figures and tables, coverage of development strategy, 3D printing, in-mold sensors, and practical worksheets, as well as a completely new chapter on the mold commissioning process, part approval, and mold maintenance.

Product Details

ISBN-13:	9781569905708
Publisher:	Hanser Publications
Publication date:	04/11/2016
Edition description:	2nd Revised ed.
Pages:	529
Product dimensions:	6.90(w) x 9.60(h) x 1.10(d)
Age Range:	18 Years

About the Author

David O. Kazmer (Ph.D. Mechanical Engineering, Stanford University) is Professor fat the Department of Plastics Engineering at the Universityof Massachusetts Lowell. He performs research and teaches courses related to plastics product and process development. He was also Chair of the Department of Engineering at the Universityof Massachusetts Lowell from 2016 to 2019.



Prior to his current appointment, he was an Applications Engineer at General Electric and Director of Research and Development at Synventive HotRunners. He is a licensed professional manufacturing engineer, and is a fellow of the American Society of Mechanical Engineers and the Society of Plastics Engineers. He is also the recipient of the ASME Kos Ishii-Toshiba Award for sustained, meritorious contributions to the field of design for manufacturing.

Table of Contents

Preface V

Nomenclature XV

1 Introduction 1

1.1 Overview of the Injection Molding Process 1

1.2 Mold Functions 3

1.3 Mold Structures 4

1.3.1 External View of Mold 4

1.3.2 View of Mold during Part Ejection 6

1.3.3 Mold Section and Function 7

1.4 Other Common Mold Types 9

1.4.1 Three Plate, Multi-Cavity Family Mold 9

1.4.2 Hot Runner, Multi-Gated, Single Cavity Mold 11

1.4.3 Comparison 12

1.5 The Mold Development Process 13

1.6 Chapter Review 15

2 Plastic Part Design 17

2.1 The Product Development Process 17

2.1.1 Product Definition 18

2.1.2 Product Design 18

2.1.3 Business and Production Development 19

2.1.4 Scale-Up and Launch 19

2.1.5 Role of Mold Design 19

2.2 Design Requirements 20

2.2.1 Application Engineering Information 20

2.2.2 Production Data 21

2.2.3 End Use Requirements 22

2.2.4 Product Design Methodology 24

2.2.5 Plastic Material Properties 26

2.3 Design for Injection Molding 28

2.3.1 Uniform Wall Thickness 28

2.3.2 Rib Design 29

2.3.3 Boss Design 29

2.3.4 Corner Design 30

2.3.5 Surface Finish and Textures 31

2.3.6 Draft 33

2.3.7 Undercuts 34

2.4 Chapter Review 35

3 Mold Cost Estimation 37

3.1 The Mold Quoting Process 37

3.2 Cost Drivers for Molded Parts 39

3.2.1 Effect of Production Quantity 40

3.2.2 Break-Even Analysis 41

3.3 Mold Cost Estimation 43

3.3.1 Cavity Cost Estimation 44

3.3.1.1 Cavity Set Cost 45

3.3.1.2 Cavity Materials Cost 45

3.3.1.3 Cavity Machining Cost 46

3.3.1.4 Cavity Discount Factor 51

3.3.1.5 Cavity Finishing Cost 51

3.3.2 Mold Base Cost Estimation 53

3.3.3 Mold Customization 55

3.4 Part Cost Estimation 60

3.4.1 Mold Cost per Part 60

3.4.2 MaterialCost per Part 61

3.4.3 Processing Cost per Part 62

3.4.4 Defect Cost per Part 65

3.5 Chapter Review 66

4 Mold Layout Design 67

4.1 Parting Plane Design 67

4.1.1 Determine Mold Opening Direction 67

4.1.2 Determine Parting Line 70

4.1.3 Parting Plane 71

4.1.4 Shut-Offs 73

4.2 Cavity and Core Insert Creation 74

4.2.1 Height Dimension 74

4.2.2 Length and Width Dimensions 75

4.2.3 Adjustments 76

4.3 Mold Base Selection 77

4.3.1 Cavity Layouts 77

4.3.2 Mold Base Sizing 79

4.3.3 Molding Machine Compatibility 81

4.3.4 Mold Base Suppliers 83

4.4 Mold Material Selection 84

4.4.1 Strength vs. Heat Transfer 84

4.4.2 Hardness vs. Machinability 85

4.4.3 Mold-Maker's Cost vs. Molder's Cost 86

4.4.4 Material Summary 88

4.5 Chapter Review 89

5 Cavity Filling Analysis and Design 91

5.1 Overview 91

5.2 Objectives in Cavity Filling 92

5.2.1 Complete Filling of Mold Cavities 92

5.2.2 Avoid Uneven Filling or Over-Packing 92

5.2.3 Control the Melt Flow 93

5.3 Viscous Flow 94

5.3.1 Shear Stress, Shear Rate, and Viscosity 94

5.3.2 Pressure Drop 95

5.3.3 Rheological Behavior 96

5.3.4 Newtonian Model 98

5.3.5 Power Law Model 99

5.4 Validation 102

5.5 Cavity Filling Analyses and Designs 104

5.5.1 Estimating the Processing Conditions 104

5.5.2 Estimating the Filling Pressure and Minimum Wall Thickness 107

5.5.3 Estimating Clamp Tonnage 109

5.5.4 Predicting Filling Patterns 112

5.5.5 Designing Flow Leaders 114

5.6 Chapter Review 117

6 Feed System Design 119

6.1 Overview 119

6.2 Objectives in Feed System Design 119

6.2.1 Conveying the Polymer Melt from Machine to Cavities 119

6.2.2 Impose Minimal Pressure Drop 120

6.2.3 Consume Minimal Material 121

6.2.4 Control Flow Rates 122

6.3 Feed System Types 123

6.3.1 Two-Plate Mold 123

6.3.2 Three-Plate Mold 125

6.3.3 Hot Runner Molds 130

6.4 Feed System Analysis 132

6.4.1 Determine Type of Feed System 133

6.4.2 Determine Feed System Layout 134

6.4.3 Estimate Pressure Drops 138

6.4.4 Calculate Runner Volume 140

6.4.5 Optimize Runner Diameters 141

6.4.6 Balance Flow Rates 145

6.4.7 Estimate Runner Cooling Times 148

6.4.8 Estimate Residence Time 149

6.5 Practical Issues 150

6.5.1 Runner Cross-Sections 150

6.5.2 Sucker Pins 154

6.5.3 Runner Shut-Offs 155

6.5.4 Standard Runner Sizes 157

6.5.5 Steel Safe Designs 157

6.6 Chapter Review 158

7 Gating Design 161

7.1 Objectives of Gating Design 161

7.1.1 Connecting the Runner to the Mold Cavity 161

7.1.2 Provide Automatic De-Gating 161

7.1.3 Provide Aesthetic De-Gating 162

7.1.4 Avoid Excessive Shear or Pressure Drop 162

7.1.5 Control Pack Times 163

7.2 Common Gate Designs 163

7.2.1 Sprue Gate 163

7.2.2 Pin-Point Gate 164

7.2.3 Edge Gate 165

7.2.4 Tab Gate 166

7.2.5 Fan Gate 167

7.2.6 Flash/Diaphragm Gate 168

7.2.7 Tunnel/Submarine Gate 169

7.2.8 Thermal Gate 172

7.2.9 Valve Gate 174

7.3 The Gating Design Process 175

7.3.1 Determine Type of Gate 175

7.3.2 Calculate Shear Rates 176

7.3.3 Calculate Pressure Drop 178

7.3.4 Calculate Gate Freeze Time 179

7.3.5 Adjust Dimensions 182

7.4 Chapter Review 182

8 Venting 185

8.1 Venting Design Objectives 185

8.1.1 Release Compressed Air 185

8.1.2 Contain Plastic Melt 185

8.1.3 Minimize Maintenance 186

8.2 Venting Analysis 186

8.2.1 Estimate Air Displacement and Rate 186

8.2.2 Identify Number and Location of Vents 186

8.2.3 Specify Vent Dimensions 189

8.3 Venting Designs 192

8.3.1 Vents on Parting Plane 192

8.3.2 Vents around Ejector Pins 194

8.3.3 Vents in Dead Pockets 196

8.4 Chapter Review 197

9 Cooling System Design 199

9.1 Objectives in Cooling System Design 199

9.1.1 Maximize Heat Transfer Rates 199

9.1.2 Maintain Uniform Wall Temperature 199

9.1.3 Minimize Mold Cost 200

9.1.4 Minimize Volume and Complexity 200

9.1.5 Minimize Stress and Corrosion 200

9.1.6 Facilitate Mold Usage 201

9.2 The Cooling System Design Process 201

9.2.1 Calculate the Required Cooling Time 201

9.2.2 Evaluate Required Heat Transfer Rate 206

9.2.3 Assess Coolant Flow Rate 208

9.2.4 Assess Cooling Line Diameter 209

9.2.5 Select Cooling Line Depth 211

9.2.6 Select Cooling Line Pitch 213

9.2.7 Cooling Line Routing 216

9.3 Cooling System Designs 219

9.3.1 Cooling Line Networks 219

9.3.2 Cooling Inserts 222

9.3.3 Conformal Cooling 222

9.3.4 Highly Conductive Inserts 223

9.3.5 Cooling of Slender Cores 224

9.3.5.1 Cooling Insert 225

9.3.5.2 Baffles 226

9.3.5.3 Bubblers 227

9.3.5.4 Heat Pipes 227

9.3.5.5 Conductive Pin 229

9.3.5.6 Interlocking Core with Air Channel 229

9.3.6 One-Sided Heat Flow 230

9.4 Chapter Review 232

10 Shrinkage and Warpage 233

10.1 The Shrinkage Analysis Process 235

10.1.1 Estimate Process Conditions 235

10.1.2 Model Compressibility Behavior 235

10.1.3 Assess Volumetric Shrinkage 237

10.1.4 Evaluate Isotropic Linear Shrinkage 241

10.1.5 Evaluate Anisotropic Shrinkage 242

10.1.6 Assess Shrinkage Range 244

10.1.7 Establishing Final Shrinkage Recommendations 245

10.2 Shrinkage Analysis and Validation 247

10.2.1 Numerical Simulation 247

10.2.2 "Steel Safe" Mold Design 249

10.2.3 Processing Dependence 249

10.2.4 Semi-Crystalline Plastics 251

10.2.5 Effect of Fillers 251

10.3 Warpage 252

10.3.1 Sources of Warpage 252

10.3.2 Warpage Avoidance Strategies 256

10.4 Chapter Review 257

11 Ejection System Design 259

11.1 Objectives in Ejection System Design 261

11.1.1 Allow Mold to Open 261

11.1.2 Transmit Ejection Forces to Moldings 262

11.1.3 Minimize Distortion of Moldings 262

11.1.4 Actuate Quickly and Reliably 262

11.1.5 Minimize Cooling Interference 263

11.1.6 Minimize Impact on Part Surfaces 264

11.1.7 Minimize Complexity and Cost 264

11.2 The Ejector System Design Process 265

11.2.1 Identify Mold Parting Surfaces 265

11.2.2 Estimate Ejection Forces 265

11.2.3 Determine Ejector Push Area and Perimeter 269

11.2.4 Specify Type, Number, and Size of Ejectors 271

11.2.5 Layout Ejectors 273

11.2.6 Detail Ejectors and Related Components 276

11.3 Ejector System Analyses and Designs 278

11.3.1 Ejector Pins 278

11.3.2 Ejector Blades 280

11.3.3 Ejector Sleeves 282

11.3.4 Stripper Plates 283

11.3.5 Elastic Deformation around Undercuts 285

11.3.6 Core Pulls 287

11.3.7 Slides 291

11.3.8 Early Ejector Return Systems 294

11.3.9 Advanced Ejection Systems 296

11.4 Chapter Review 296

12 Structural System Design 299

12.1 Objectives in Structural System Design 300

12.1.1 Minimize Stress 300

12.1.2 Minimize Mold Deflection 304

12.1.3 Minimize Mold Size 305

12.2 Analysis and Design of Plates 306

12.2.1 Plate Compression 306

12.2.2 Plate Bending 309

12.2.3 Support Pillars 312

12.2.4 Shear Stress in Side Walls 317

12.2.5 Interlocks 319

12.2.6 Stress Concentrations 321

12.3 Analysis and Design of Cores 325

12.3.1 Axial Compression 326

12.3.2 Compressive Hoop Stresses 327

12.3.3 Core Deflection 329

12.4 Fasteners 332

12.4.1 Fits 332

12.4.2 Socket Head Cap Screws 336

12.4.3 Dowels 338

12.5 Review 340

13 Mold Technologies 343

13.1 Introduction 343

13.2 Coinjection Molds 343

13.2.1 Coinjection Process 345

13.2.2 Coinjection Mold Design 346

13.2.3 Gas Assist/Water Assist Molding 347

13.3 Insert Molds 350

13.3.1 Low Pressure Compression Molding 350

13.3.2 Insert Mold with Wall Temperature Control 351

13.3.3 Lost Core Molding 353

13.4 Injection Blow Molds 355

13.4.1 Injection Blow Molding 355

13.4.2 Multilayer Injection Blow Molding 357

13.5 Multi-Shot Molds 358

13.5.1 Overmolding 359

13.5.2 Core-Back Molding 360

13.5.3 Multi-Station Mold 362

13.6 Feed Systems 364

13.6.1 Insulated Runner 364

13.6.2 Stack Molds 365

13.6.3 Branched Runners 368

13.6.4 Dynamic Melt Control 369

13.7 Mold Wall Temperature Control 372

13.7.1 Pulsed Cooling 372

13.7.2 Conduction Heating 373

13.7.3 Induction Heating 375

13.7.4 Managed Heat Transfer 377

13.8 In-Mold Labeling 378

13.8.1 Statically Charged Film 379

13.8.2 Indexed Film 380

13.9 Ejection 381

13.9.1 Split Cavity Molds 381

13.9.2 Collapsible Cores 383

13.9.3 Rotating Cores 384

13.9.4 Reverse Ejection 387

13.10 Review 388

Appendix 389

Appendix A Plastic Material Properties 390

Appendix B Mold Material Properties 394

B.1 Non-Ferrous Metals 394

B.2 Common Mold Steels 395

B.3 Other Mold Steels 396

B.4 Notes 397

Appendix C Properties of Coolants 398

Appendix D Statistical Labor Data 399

D.1 United States Labor Rates 399

D.2 International Labor Rates 399

D.3 Trends in International Manufacturing Costs 401

Appendix E Unit Conversions 402

E.1 Length Conversions 403

E.2 Mass/Force Conversions 403

E.3 Pressure Conversions 403

E.4 Flow Rate Conversions 404

E.5 Viscosity Conversions 404

E.6 Energy Conversions 404

Appendix F Advanced Derivations 405

Bibliography 409

Subject Index 413