Precision Lens Molding of Glass: A Process Perspective (eBook)

Acknowledgements 6
Contents 7
About the Author 11
Abbreviations 12
List of Figures 14
List of Tables 17
1 Overview of Glass Molding Processes 19
1.1 History of Lens Molding 19
1.2 Principle of Operation 20
1.3 Equipment 21
1.4 Process Development 21
1.5 Molding of Oxide Glasses 22
1.6 Molding of Infrared Materials 23
1.6.1 Infrared Optics—Crystals 23
1.6.2 Molding of Infrared Materials—Glasses (Chalcogenides) 24
1.7 Finished Lens Molding 26
1.8 Types of Optical Surfaces 28
1.9 Preform Types and Manufacture 28
1.10 Process Capabilities and Tolerances 29
1.11 Applications 30
1.12 Conclusion 32
References 32
2 Tool Materials and Tooling Package Design 33
2.1 Material Requirements and Considerations for Molding Precision Surfaces 33
2.1.1 Traditional Tool Materials 33
2.1.2 Thermal Properties of Tool Materials 35
2.1.3 Compatibility with Heat Source 37
2.2 Tool Package Design 45
2.2.1 Tool Design 48
2.2.2 To Shim or Not to Shim? 49
2.2.3 Free Diameter Molding 50
2.2.4 Mold to Diameter 50
2.3 Fixed Die and Die Transfer Systems 51
2.4 Tools for Low Temperature Applications 51
2.5 Temperature Sensing 52
2.6 Conclusion 54
References 55
3 Molding Surface Design and Useful Equations 56
3.1 Thermal Compensation and the Molding Surface 56
3.2 Thermal Energy Transfer 57
3.2.1 Radiation and Absorption 57
3.2.2 Convection 59
3.2.3 Conduction 59
3.3 Thermal Expansion of Tooling 63
3.3.1 Thermally Induced Stress 63
3.3.2 Stress Induced Wavefront Distortion 64
3.4 Tool Design for Isotropic Materials 65
3.5 Tool Design for Non-isotropic Materials [1] 65
3.6 Design of the Molding Surface 66
3.6.1 Spherical and Aspheric Surfaces 66
3.6.2 Diffractive Terms 68
3.6.3 Putting It All Together 68
3.7 Conclusion 68
Reference 69
4 Tool Coatings 70
4.1 Chemical Interactions 70
4.2 Protective Coatings 73
4.2.1 Protective Coatings—General Information 73
4.2.2 Protective Coatings for Oxide Glass Applications 74
4.2.3 Protective Coatings for Chalcogenide Glass Applications 79
4.3 Release Coatings 80
4.3.1 Release Coatings—General Information 80
4.3.2 Release Coatings for Oxide Glass Applications 81
4.3.3 Release Coatings for Chalcogenide Glass Applications 82
4.4 Coated Preforms 85
4.4.1 Coated Preforms—General Information 85
4.5 Conclusion 86
References 86
5 Moldable Glasses 87
5.1 Background 87
5.2 Chemical Compositions 88
5.2.1 Oxide Glasses 88
5.2.2 Government Regulations Affecting Glass Manufacture [2, 3] 93
5.2.3 Compatibility with Coatings 95
5.2.4 Infrared Glasses 95
5.3 Desirable Properties for Precision Glass Molding Processes 97
5.3.1 Thermal Properties 97
5.3.2 Physical Properties 98
5.3.3 Chemical Properties 99
5.4 Index Drop 100
5.4.1 Causes of Index Drop 100
5.4.2 Oxide Glasses 102
5.4.3 Infrared Glasses 103
5.4.4 Index Homogeneity 103
5.5 Special Handling 104
5.6 Conclusion 105
References 106
6 Crystallization Kinetics 107
6.1 Nucleation and Growth 107
6.2 Crystallization 109
6.3 Glass Formation 110
6.4 Inherent Stresses in Preforms 111
6.5 Stresses Formed During Molding 112
References 112
7 Molding Processes 114
7.1 Background 114
7.2 Preform Selection 116
7.3 Temperature Sensing 117
7.4 Vacuum Assisted Molding 120
7.5 Finished Lens Molding 121
7.6 Precision Lens Molding 122
7.7 Sleeve Molding 123
7.8 Position Control Molding 124
7.9 Force Control Molding 124
7.10 Constant Flow Molding 127
7.11 Stress Relaxation 129
7.12 Insert Molding 132
7.13 Molding Special Features 133
References 136
8 Applications 137
8.1 Background 137
8.1.1 Technology Impacts 137
8.1.2 Glass Types 138
8.1.3 Optical Surfaces 139
8.2 Design for Moldability 140
8.2.1 Design Tips for Molded Glass Elements 140
8.2.2 Oxide Glass 141
8.2.3 Chalcogenide Glass 142
8.3 Planning the Process 142
8.4 Conclusion 146
Reference 149