Plastic Part Design for Injection Molding - An Introduction

Robert A. Malloy

Plastic Part Design for Injection Molding

An Introduction

2012

564 Seiten

Format: PDF, Online Lesen

E-Book: €  79,99

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ISBN: 9783446433748

 

Preface

8

Contents

10

1 Introduction

16

1.1 Thermoplastic Materials

16

1.2 Thermosetting Plastic Materials

17

1.3 Structure-Property Relationships

18

1.4 Additives for Plastic Materials

22

1.5 General Characteristics of Plastic Materials

23

References

28

2 Manufacturing Considerations for Injection Molded Parts

30

2.1 Introduction

30

2.2 Mold Filling Considerations

31

2.2.1 Gating Considerations

31

2.2.2 Mold Filling Orientation

36

2.2.3 Mold Filling Pressure Losses

42

2.2.4 Flow Leaders, Flow Restrictors and Flow Hesitation

54

2.3 Weld Lines

63

2.3.1 Introduction

63

2.3.2 Types of Weld Lines

67

2.3.3 Material Considerations

70

2.3.4 Improving Weld Performance and Appearance

73

2.4 Shrinkage and Warpage of Injection Molded Parts

78

2.4.1 Introduction

78

2.4.2 Part Wall Thickness Variations

80

2.4.3 Pressure-Volume-Temperature Behavior of Polymers

84

2.4.4 Linear Mold Shrinkage

87

2.4.5 Anisotropic Shrinkage and Part Distortion/Warpage

91

2.5 Cooling and Solidification

101

2.6 Part Ejection

104

2.6.1 Introduction

104

2.6.2 Draft Angles

105

2.6.3 Effect of Cavity and Core Surface Finish

110

2.6.4 Esthetic Considerations

114

2.6.5 Undercuts and Holes

115

2.6.6 Predicting Part Release Forces

121

2.7 Other Injection Molding Processes

124

2.7.1 Gas Assisted Injection Molding

124

2.7.2 Structural Foam Molding

131

2.7.3 Co-Injection Molding

137

2.7.4 Injection-Compression Molding

139

References

141

3 The Design Process and Material Selection

146

3.1 Introduction

146

3.2 The Plastic Part Design Process

149

3.3 Test Standards for Design Related Plastic Material Properties

157

3.4 Mechanical Behavior of Plastic Materials

158

3.4.1 Introduction

158

3.4.2 Short-Term Stress-Strain Behavior

159

3.4.3 Long Term Mechanical Properties: Creep

167

3.4.4 Long-Term Mechanical Properties: Stress Relaxation

178

3.5 Impact Resistance of Plastic Materials

181

3.6 Fatigue Properties

185

3.7 Thermal Properties of Plastic Materials

186

3.7.1 Thermal Mechanical Behavior

186

3.7.2 Deflection Temperature Under Load and the Vicat Temperature

189

3.7.3 Coefficient of Linear Thermal Expansion

189

3.7.4 Aging at Elevated Temperatures

191

3.7.5 Flammability

192

3.8 Melt Flow Properties

192

3.9 Sources of Plastic Material Property Data

194

3.10 Standardized Plastic Material Designations

198

References

200

4 Structural Design Considerations

202

4.1 Introduction

202

4.2 Design Methodology

202

4.2.1 Design by Experience

203

4.2.2 Design by Experimental Approach

203

4.2.3 Design Using an Analytical Approach

204

4.3 Quantifying the Design Problem

207

4.3.1 Simplification of Part Geometry

208

4.3.2 Stress Concentration

209

4.3.3 Type of Support

212

4.3.4 Loading Conditions

214

4.3.5 Plastic Material Properties

217

4.3.6 Safety Factors

225

4.4 Beams

229

4.4.1 Introduction

229

4.4.2 Properties of a Plane Area (Beam Cross Sections)

231

4.4.3 The Use of Reinforcing Ribs to Improve Stiffness

238

4.4.4 Moment of Inertia for Non-Homogeneous Materials and Structures

246

4.4.5 Sample Beam Analysis

248

4.5 Plates

263

4.5.1 Introduction

263

4.5.2 Sample Plate Problems

265

4.5.3 Plate Elements with Non-Uniform Wall Sections

273

4.6 Shells/Pressure Vessels

275

4.6.1 Introduction

275

4.6.2 Thin-Walled Pressure Vessels

276

4.6.3 Thick-Wall Pressure Vessels

279

4.7 Torsion

280

4.7.1 Introduction

280

4.7.2 Torsion for Circular Bars

280

4.7.3 Torsion for Non-Circular Bars

284

4.8 Columns

287

4.9 Dynamic Loads

289

4.9.1 Introduction

289

4.9.2 Fatigue Loading

289

4.9.3 Impact Loading

295

References

298

5 Prototyping and Experimental Stress Analysis

300

5.1 Prototyping Plastic Parts

300

5.1.1 Introduction

300

5.1.2 Machined and Fabricated Plastic Prototypes

302

5.1.3 Some Rapid Prototyping Technologies

305

5.1.4 Simulating a Production Quality Appearance on Prototype Parts

318

5.1.5 Prototype Part Casting Techniques

321

5.1.6 Prototype Injection Mold Tooling

326

5.1.7 Low Pressure Structural Foam Prototypes

337

5.1.8 Coordinate Measuring Machines

339

5.2 Experimental Stress Analysis

340

5.2.1 Introduction

340

5.2.2 Brittle Coatings

341

5.2.3 Strain Gages

342

5.2.4 Solvent/Chemical Testing

348

5.2.5 Photoelastic Testing

350

5.2.6 Optical Strain Measurement Techniques

352

References

352

6 Assembly of Injection Molded Plastic Parts

356

6.1 Introduction

356

6.2 Press Fit Assemblies

359

6.2.1 Introduction

359

6.2.2 Material Considerations

360

6.2.3 Design of Press Fit Assemblies

362

6.3 Snap Joint Assemblies

367

6.3.1 Introduction

367

6.3.2 Types of Snap Joints

368

6.3.3 Molding Cantilever Snaps

377

6.3.4 Design of Snap Joints

382

6.4 Mechanical Fasteners

387

6.4.1 Introduction

387

6.4.2 Screws

389

6.5 Welding of Thermoplastics

431

6.5.1 Introduction

431

6.5.2 Ultrasonic Welding

432

6.5.3 Vibration Welding

451

6.5.4 Spin (Rotational) Welding

453

6.5.5 Electromagnetic Welding

457

6.5.6 Resistance Welding

459

6.5.7 Hot Tool Welding

459

6.5.8 Hot Gas Welding

461

6.5.9 Extrusion Welding

464

6.5.10 Infrared and Laser Welding

464

6.6 Adhesive Bonding

478

6.6.1 Introduction

478

6.6.2 Adhesive Theory

481

6.6.3 Adhesive Selection

489

6.7 Solvent Bonding

492

References

493

7 Design for Enhanced Recyclability and Sustainability

498

7.1 Plastic Part Design: Recycling Related Issues

498

7.2 Designing Thermoplastic Products with Enhanced Recyclability

500

7.2.1 Design for Existing Recycling Infrastructure

501

7.2.2 Standard Material Identification and Marking Systems

504

7.2.3 Minimize Components and Materials of Construction

506

7.2.4 Multi-Component Product Recycling: Design for Disassembly (Pre-Granulation)

508

7.2.5 Multi-Component Product Recycling: Design for Easy Separation (Post-Granulation)

513

7.2.6 Compatible Materials for Commingled Recycling

516

7.2.7 Use Thermoplastic Formulations that Exhibit Good Property Retention

519

7.2.8 Use General Purpose Thermoplastics --- Minimize the Use of Specialty Additives

522

7.2.9 Use Recycling Friendly Labels and Attachments

524

7.2.10 Avoid Contaminating Surface Coatings

528

7.2.11 Scrapless Manufacturing Processes

530

7.3 Design for Enhanced Recyclability Case Studies

532

7.3.1 Case Study 1: More Recyclable Frozen Juice Concentrate Container

532

7.3.2 Case Study 2: One Time Use Camera is Returnable for Reuse and Recycling

533

7.3.3 Case Study 4: Preserve® Consumer Products from Recycled Plastics Returnable for Secondary Recycling

535

7.4 Using Recycled Thermoplastics for Injection Molded Parts

536

7.4.1 Reuse of Manufacturing Scrap: Regrind Specification and Practices

537

7.4.2 General Properties of Recycled Thermoplastics Relative to Virgin Thermoplastics

541

7.4.3 Recycled Thermoplastic Availability, Quality, and Pricing

544

7.4.4 Product Standards and Agency Considerations

547

References

548

Conversion constants

549

Subject Index

552

 

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