Understanding Injection Mold Design

Understanding Injection Mold Design
اسم المؤلف
Herbert Rees
التاريخ
6 سبتمبر 2019
المشاهدات
270
التقييم
(لا توجد تقييمات)
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Understanding Injection Mold Design
Herbert Rees
Contents
1 Introduction . 1
1.1 Economics of Mold Design 3
2 Starting New in the Mold Design Field 5
3 The Basics of an Injection Molding Machine . 7
4 Understanding the Basics of the Injection Mold . 9
4.1 Design Rules 9
4.2 The Basic Mold . 9
4.2.1 Mold Cavity Space . 9
4.2.2 Number of Cavities 10
4.2.3 Cavity Shape and Shrinkage 11
4.3 Cavity and Core . 11
4.4 The Parting Line 12
4.4.1 Split Molds and Side Cores . 13
4.5 Runners and Gates . 14
4.6 Projected Area and Injection Pressure 15
4.6.1 Clamping Force . 16
4.6.2 Strength of the Mold 16
4.6.3 Why are High Injection Pressures Needed? 17
4.7 Venting . 18
4.8 Cooling 18
4.8.1 Basics of Cooling . 19
4.8.2 Plate Cooling . 22
4.9 Ejection 22
4.9.1 Automatic Molding . 25
4.10 Shrinkage . 26
4.10.1 Variable Shrinkage . 26
4.11 Alignment 27
ix4.11.1 No Provision for Alignment 27
4.11.2 Leader Pins and Bushings . 28
4.11.3 Taper Lock Between Each Cavity and
Core 29
4.11.4 Taper Locks and Wedges 30
4.11.5 Taper Pins . 31
4.11.6 Too Many Alignment Features . 31
5 Before Starting to Design a Mold 33
5.1 Information and Documentation . 33
5.1.1 Is the Product Design Ready? 33
5.1.2 Are the Tolerances Shown? 33
5.1.3 Are the Tolerances Reasonable? 34
5.1.4 What are the Cycle Times? 34
5.1.5 What is the Expected Production? 34
5.1.6 What are the Machine Specifications? . 35
5.1.6.1 Mechanical Features 35
5.1.6.2 Productivity Features 37
5.1.6.3 Additional Requirements for Some Molds . 39
5.2 Start of Mold Design 42
5.2.1 Mold Shoes 42
5.2.1.1 No Mold Shoe Used 42
5.2.1.2 Standard Mold Shoes . 43
5.2.1.3 Home-Made Mold Shoes 44
5.2.1.4 Special Mold Shoes . 44
5.2.1.5 Universal Mold Shoes . 44
5.2.1.6 Mold Hardware 45
5.2.2 Mold Drawings 45
5.2.2.1 Assembly and Detail Drawings . 45
5.2.2.2 How Many Drawings and Views? 46
5.2.2.3 Arrangement of Views 46
5.2.2.4 Notes on Drawings . 47
5.2.2.5 Additional Information on the Drawings . 47
5.2.3 The Stack Layout . 48
5.2.3.1 Significant Cross Section 48
5.2.3.2 Will the Product Slide (Pull) out of the
Cavity? 48
5.2.3.3 Will the Product Eject Easily from the
Core? . 49
x Contents5.2.3.4 Establishing the Parting Line 51
5.2.3.5 Is the Cavity Balanced? 54
5.2.3.6 Determining the Method of Cavity
Construction 54
5.2.3.7 Determining the Total Area of the Stack 55
5.2.3.8 Determining the Core Construction 56
5.2.4 Selection of a Suitable Runner System . 56
5.2.4.1 Cold Runner, Single-Cavity Molds . 56
5.2.4.2 Cold Runner, 2-Plate Molds . 57
5.2.4.3 Cold Runner, 3-Plate Molds . 58
5.2.4.4 Hot Runner (HR) Molds 59
5.2.4.5 Cold and Hot Runner Molds, in
Combination 60
5.2.4.6 Insulated Runner Molds 62
5.2.4.7 Common Rules for Runner Systems . 63
5.2.4.8 L=t Ratio . 65
5.2.5 Venting . 65
5.2.5.1 What is a Vent? . 65
5.2.5.2 Design Rules that Apply to All Molds . 66
5.2.6 Ejection . 68
5.2.7 Cooling . 69
5.2.7.1 Purpose of Cooling a Mold . 69
5.2.7.2 Show Cooling Lines in Stack . 71
5.2.7.3 Screws . 72
5.2.8 Alignment of Stack 73
5.2.9 Design Review 73
5.3 Preload 73
5.4 Mold Materials Selection 74
5.4.1 Effect of Expected Production . 75
5.4.2 Forces in Molds . 75
5.4.3 Characteristics of Steels and Other Mold Materials . 75
5.4.3.1 Availability 76
5.4.3.2 Strength of Material 76
5.4.3.3 Fatigue . 76
5.4.3.4 Wear . 77
5.5 Stack Molds . 78
5.6 Mold Layout and Assembly Drawings . 79
5.6.1 Machine Platen Layout . 79
5.6.2 Symmetry of Layout, Balancing of Clamp 79
5.6.3 The Views 80
Contents xi5.6.4 Completing the Assembly Drawing . 80
5.6.5 Bill of Materials (BoM) and ‘‘Ballooning’’ . 81
5.6.6 Finishing Touches . 81
6 Review and Follow-up 82
7 Typical Examples . 83
7.1 Containers or Other Cup-Shaped Products 83
7.2 Technical Products . 87
7.3 Mold with Fixed Cores . 88
7.4 Mold with Floating Cores 89
7.5 Molds with Side Cores or Splits . 90
8 Estimating Mold Costs 92
8.1 Need for Estimate . 92
8.2 Precedents 93
8.3 No Precedents . 93
8.4 Methods of Estimating . 94
8.5 Mold Cost and Mold Price . 95
9 Machining, Mold Materials, and Heat Treatment . 97
9.1 Machining of Mold Components 97
9.2 Materials Selection 101
9.2.1 Steel Properties . 102
9.3 Heat Treatment 106
Appendix 1 CAD = CAM (Computer-Assisted Design–ComputerAssisted Manufacturing) 108
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