Injection mold/ and molding

П Practical manual Second Edition

Jo/eph B. Dqm

Ei CHAPMAN & HALL

New York • London

Contents

Preface vii

1 Introduction 1

2 Plastics Mold Design 5 Nature of Plastics 5 Mold Design 6 Computer-aided Design and Manufacturing 10

Benefits and Costs of the System 14

3 Injection Molds for Thermoplastics 16 Mold Base 16 Cavity and Core 19

4 Consideration of Product 23 Dimensions for Product Performance 23 Material Considerations 23 Shrinkage 24 Postmolding Shrinkage 27 Flow Length 28 Mold Temperature 28 Molding Stresses 28 Parting Line 29 Gate Location 30 Weld Line 30 Taper Addition, Also Called Draft Angles 31 Projections, Bosses, and Internal Venting 33 Identification of Supplier and Cavity 33 Ejector Pins 34 Visibility or Clarity Requirement 34 Requirements for Alignment 35 Product Design Points 35

xii CONTENTS

5 Mold Size and Strength 40 Number of Cavities 40

Cavity Material 40 Strength of Cavity 48 Steel and Size of Mold Base 68 Pillar Supports 69 Alignment of Halves 71

6 Mold and Press 72 Machine Size 72 Clamp and Platen Data 77 Eyebolt Holes 81 Mold Connections for Fluid 81 Clamp Tonnage and Mold Size 82

7 Moldability Features 83 Removal of Parts from Mold 83 Material Paths and Pressure Drop 83 The Sprue 84 Runner System 85 Cold-Slug Well 89 Gate Location 91

Weld-line Strength 91 Gas Entrapment 91 Jetting 93 Other Considerations 94

Transition Shape 94 Gate Size 96

Gate Blemishes—Splay and Similar Defects 98 Gates and Cores 99 Concluding Note on Gates 101

Types of Gate 102 Land of Gate 106 Vents 107 Undercuts 108 Melt Rheology 108

Theoretical Considerations 109 Graphic Presentation and Description of Viscosity

CONTENTS xiii

8 Details of Molds 116 Ejection Pins 116 Cavities and Cores 120 Molding Inserts 121 Movable Mold Plates 121 Protruding Cores 122 Stress Level in Steel 122 Drilling Holes for Coolant 124 Dimensioning Mold Components 126 Mold Protection 128

9 Types of Bases and Molds 129 Most Common Type of Mold Base 129 Mold Base Without Backup Plates 138 Three-Plate Mold Base 138 Stripper Plate Base 140 Bases for Interchangeable Cavities 141

10 Cavity Materials 144 Strength of Materials 144 Hardness Determination and Allied Properties 155 Wear Resistance 158 Tool Steels 159 Steels for Plastics 162 Heat-Treating 168

11 Cavity Fabrication 172 Machining 173 Casting 174 Hobbing 175 Electric Discharge Machining 179 Electroforming 181 Vapor-forming Nickel Shells 183 Cavities for Sample and/or Low-Activity Moldings 184 Finishing Mold Surfaces 186 Polishing 188

Machined Cavities 188 Hobbed Cavities 189 EDM'd Cavities 190 Final Note 190

Welding 190 Textured Surface 192 Hard Chrome Plating 192 Concluding Note 192

xiv CONTENTS

12 Mold Temperature Design 193 Basic Principles 193 Figuring a Cooling System 193

Heat Content 195 Cooling Design 198 Difficult Cooling 203 Coolant Passages 205

Examples of Cooling 207 Temperature Variation in Mold 209

13 Runnerless Molding 218 Considerations for Runnerless Application 219 Hot Manifold 222

Combination Hot and Short Runner 224 Insulated Manifold 229 Heaters 237

14 Molding Thermoplastics 241 Injection Machines for Thermoplastics 241 Plunger Machine 241 Screw Machine and Its Processing—All-Hydraulic 242 Machine Components and Their Part in the Process 243

Hopper and/or Dryer 243 Throat 247 Screw 247 Machine Capacity 252 Injection Rate 255 Recharging for Shot 258 Shutoff Valve 259 Nozzle 259 Chamber 261 Clamp Closing 262 Clamp Opening 263 Mold Protection 263

Molding Properties 263 Time, Temperature, and Pressure 263 Stresses and Mold Proving 264 Weld Line 266 Parameter Control for Properties 266

Machine Maintenance 267 Toggle Press 271

CONTENTS xv

Processing of Reinforced Thermoplastics 272 Mold 273 The Machine 274 General 275

15 Setup Data 276 Press Manufacturer and Size 276 Material Specifications 276 Drying Specifications 278 Shot Weight 278 Cushion 278 Rate of Injection 279 Injection High Timer 281 Injection Hold Timer 282 Mold Closed Timer 283 Injection psi on Material 283 Screw Back Pressure on Material 284 Melt Decompress 285 Melt Temperature 285 Nozzle Type 285 Screw Torque 285 Mold Temperature 286 Mold Daylight 286 Size and Number of Stripper Rods 286 Limit Switches 286 Safety Check 288

16 Mold Placement 289 Handling a Mold 289 Clamping a Mold 290 Mold Placement 291 Mold Removal from Press 293 Purging 296

17 Molding Problems and Solutions 298

18 Material Processing Data: Thermoplastics 313 Design Factors 314 Mold Factors 315 Machine Factors 316 Processing Factors or "Material Processing Data" 316 Material Processing Data Sheets 318 Notes for Material Processing Data 322

xvi CONTENTS

19 Foamed Engineering Plastics Molding and Molds 331 Description of Process 332 High-Pressure System 332 Low-Pressure System 335 Processing 336 Processing Parameters 339 Troubleshooting Guide 340

20 Reaction Injection Molding and Molds 342 The Process 343

Monomer or Component Tanks 344 Heat Exchanger 344 Metering System 346 Mixing Head 346

The Mold 348 Mold Materials 349 Mold Features 350

Press Features 356 Product Properties 358 Molding Problems of RIM Process 359

21 Injection Molding and Molds of Thermosets 360 Injection Molding of Thermosets 361 Elements of the Process 362 Miscellaneous 366 Troubleshooting of Thermosets 367 Starting and Adjusting Molding Conditions 369 Thermoset Injection Molds 371

Mold Materials 371 Cavity Design 372 Sprue Bushing 375 Runners and Gates 375 Mold Vents 378 Shrinkage 379 Warm Manifold Molding 379

Heating the Mold 382 Heater Installation 385

Index 387