1 INTRODUCTION .................................................. 1
1.1 Manufacturing Technologies ................................ 1
1.2 Laser Materials Processing ................................ 2
1.3 Laser Cutting ............................................. 5
2 SYSTEMS AND PROCESS PARAMETERS ................................ 7
2.1 Set-Up of a Laser Cutting System .......................... 7
2.2 Laser Sources and Unfocused Laser Beam .................... 8
2.2.1 Types of Laser Sources .............................. 8
2.2.2 Unfocused Laser Beam ............................... 10
2.2.3 State-of-the-Art of Laser Sources and Process
Parameters ......................................... 12
2.3 Beam Guidance and Focusing ............................... 13
2.3.1 Beam Guidance ...................................... 13
2.3.2 Beam Focusing ...................................... 14
2.3.3 State-of-the-Art of Beam Guidance and Focusing
and Process Parameters ............................. 16
2.4 Motion Systems ........................................... 18
2.4.1 Types of Motion Systems ............................ 18
2.4.2 State-of-the-Art of Motion Systems and Process
Parameters ......................................... 21
2.5 Nozzles and Gas Jet ...................................... 22
2.5.1 Standard Nozzles ................................... 22
2.5.2 State-of-the-Art of Nozzles and Process
Parameters ......................................... 24
2.6 Innovative Methods ....................................... 26
2.7 Process Sensors .......................................... 27
2.8 Survey on the Process Parameters ......................... 29
3 PHYSICAL MECHANISMS AND MODELING ............................. 31
3.1 Mechanism of Laser Beam Cutting .......................... 31
3.2 Geometry of the Cutting Front ............................ 32
3.3 Optical Mechanisms ....................................... 34
3.3.1 Absorption ......................................... 34
3.3.2 Interaction Cross-Section .......................... 37
3.4 Thermodynamic Mechanisms ................................. 40
3.4.1 Heat Conduction .................................... 40
3.4.2 Phase Transitions .................................. 49
3.5 Fluidmechanic Mechanisms ................................. 52
3.5.1 Survey ............................................. 52
3.5.2 Transonic Gas Jet .................................. 52
3.5.3 Geometry Nozzle-Workpiece .......................... 55
3.5.4 Melt Film .......................................... 56
3.5.5 Drop Ejection ...................................... 60
3.5.6 Vapor Flow and Plasma Formation .................... 61
3.6 Chemical Mechanisms ...................................... 63
3.7 Transient and Periodic Behavior .......................... 69
3.8 Quality Criteria ......................................... 70
3.9 Mathematical Process Models .............................. 71
3.9.1 Steady-State Balances of Energy and Mass ........... 71
3.9.2 Method of Existence Diagrams ....................... 71
3.9.3 Process Model ...................................... 74
3.9.4 Dynamic Balances of Energy and Mass ................ 76
3.9.5 Further Analytical Models .......................... 77
3.9.6 FE-Simulations ..................................... 78
4 INFLUENCE OF THE PROCESS PARAMETERS .......................... 79
4.1 Cutting Speed ............................................ 79
4.2 Beam Parameters .......................................... 85
4.2.1 Beam Power ......................................... 85
4.2.2 Intensity Distribution ............................. 86
4.2.3 Pulsing Conditions ................................. 88
4.2.4 Focus Diameter ..................................... 89
4.2.5 Rayleigh Length .................................... 91
4.2.6 Focal Plane Position ............................... 92
4.2.7 Polarization ....................................... 93
4.3 Gas Jet Parameters ....................................... 94
4.3.1 Gas Type ........................................... 94
4.3.2 Gas Pressure ....................................... 96
4.3.3 Nozzle Stand-Off Distance .......................... 98
4.3.4 Nozzle Exit Diameter ............................... 98
5 INFLUENCE OF THE MATERIAL ................................... 101
5.1 Comparison .............................................. 101
5.2 Steel ................................................... 105
5.2.1 Mild Steel ........................................ 105
5.2.2 Stainless Steel ................................... 113
5.3 Non-Ferrous Metals ...................................... 115
5.3.1 Aluminum Alloys ................................... 115
5.3.2 Copper-Based Alloys ............................... 116
5.3.3 Other Metals ...................................... 117
5.4 Non-Metals .............................................. 118
5.4.1 Polymers .......................................... 118
5.4.2 Ceramics .......................................... 119
5.4.3 Composite Materials ............................... 120
5.4.4 Other Materials ................................... 123
6 ECONOMIC ASPECTS ............................................ 127
6.1 Costs ................................................... 127
6.2 Competing Techniques .................................... 128
6.3 Industrial Applications ................................. 135
7 CONCLUSIONS ................................................. 137
8 APPENDIX .................................................... 139
8.1 Appendix A: Fresnel-Absorption .......................... 139
8.2 Appendix B: Heat Conduction ............................. 140
8.3 Appendix C: Fluid Flow .................................. 145
8.4 Appendix D: List of Symbols ............................. 147
9 LITERATURE .................................................. 149
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