Tailored Light 2 (eBook)

Prof. Dr. Reinhart Poprawe holds an M. A. in Physics from California State University (Fresno, 1977). After completion of his diploma and PhD in Physics (Darmstadt 1984) he joined the Fraunhofer Institute for Laser Technology in Aachen, where he began working as head of the department "Laser Oriented Process Development." From 1988 to 1996 he served as managing director of Thyssen Laser Technik GmbH in Aachen. Since then he has been managing director of the Fraunhofer ILT and holds the University Chair for Laser Technology at the RWTH Aachen.

Preface 5
Contents 8
Contributors 11
1 Introduction 15
References 17
2 The Behavior of Electromagnetic Radiation at Interfaces 18
2.1 The FRESNEL Formula 18
2.1.1 FRESNEL Formulae with Absorption 21
2.1.2 Analysis of the FRESNEL Formula and BREWSTER Effect 22
2.1.3 Total Reflection 24
2.2 Applications of the FRESNEL Formulae in the Field of Laser Technology 24
2.2.1 BREWSTER Effect 24
2.2.2 Total Internal Reflection 25
References 26
3 Absorption of Laser Radiation 27
3.1 Description of the Phenomena 28
3.1.1 Field Relationships 30
3.1.2 Wave Equation 31
3.1.3 Geometry of the Workpiece 32
3.2 Isolators 32
3.2.1 Electronic Polarization 33
3.2.2 Ionic Polarizability 34
3.2.3 Supplementary Substances in Polymers 37
3.3 Dielectric Properties of Plasmas 37
3.3.1 Collision-Free Plasma 39
3.3.2 Collision-Dominated Plasma 41
3.4 Absorption of Metallic Materials 42
3.5 The DRUDE Model of Absorption 44
3.6 Temperature Dependence of the Absorption of Metals 47
3.7 Influence of the Surface Conditions 50
References 52
4 Energy Transport and Heat Conduction 54
4.1 Energy Transport Equation 54
4.2 Heat Conduction Mechanisms 56
4.3 Heat Conduction Equation with Constant Coefficients and the Method of GREEN’s Functions 58
4.3.1 Point Source 60
4.3.2 Line Source 62
4.3.3 Transversal Infinitely Extended Surface Source 65
4.3.4 Transversal Infinitely Extended Volume Source 69
4.3.5 GAUSSian Intensity Distribution 70
4.3.6 Finite Workpiece Thickness 70
4.4 Temperature-Dependent Thermo-physical Coefficients 71
4.5 Heat Conduction in Case of Short Laser Pulse Durations 72
References 73
5 Thermomechanics 74
5.1 Elastic Deformations 74
5.1.1 Uniaxial Loading 75
5.1.2 Uniaxial Strain 75
5.2 Thermal Induced Stress 76
5.3 Plastic Deformation 77
5.3.1 Examples of Plastic Deformations 78
References 78
6 Phase Transformations 79
6.1 Fe-C Diagram 79
6.1.1 Pure Fe 79
6.1.2 Fe-C Mixtures 81
6.2 Hardening of Perlitic Structures 83
6.2.1 C Diffusion 84
References 86
7 Melt Flow 87
7.1 Mass, Momentum, and Energy Conservation 87
7.2 Boundary Conditions 88
7.3 Plane Potential Flow 91
7.3.1 Source and Dipole Flow 92
7.3.2 Flow Around a Cylinder 94
7.4 Laminar Boundary Layers 96
7.4.1 Friction-Dominated Boundary Layer Flow 99
7.4.2 Inertia-Dominated Boundary Layer Flow 101
References 101
8 Laser-Induced Vaporization 102
8.1 Vapor Pressure in Thermodynamic Equilibrium 102
8.2 Vaporization Rate 104
8.3 Particle and Energy Conservation During Laser-Induced Vaporization 108
8.4 Description of the Evaporation Process as a Combustion Wave 112
8.5 Kinetic Model of the Evaporation and The KNUDSEN Layer 117
References 120
9 Plasma Physics 121
9.1 Debye Radius and Definitions 123
9.2 Some Results from Thermodynamics and Statistics of a Plasma 126
9.2.1 Partition Function of an Ideal Plasma 128
9.2.2 State Variables of an Ideal Plasma 131
9.2.3 Coulomb Corrections 132
9.2.4 Law of Mass Action and SAHA Equation 135
9.3 Transport Characteristics of Plasmas 137
9.4 Interaction Between Electromagnetic Waves and Plasmas 144
9.5 Non-equilibrium Processes 150
9.6 Plasma Radiation in the LTE Model 154
9.6.1 Line Radiation 155
9.6.2 Radiation Transport 157
9.6.3 Radiation Power of Line Radiation 158
9.6.4 Line Shapes 158
9.6.5 Bremsstrahlung 160
9.6.6 Recombination Radiation 160
9.6.7 Influence of the Apparatus on Measured Spectra 161
References 162
10 Laser Beam Sources 163
10.1 CO2 Laser 163
10.1.1 Principles 163
10.1.2 Types of Construction 163
10.2 Solid-State Lasers 166
10.2.1 Principles 166
10.2.2 Types of Construction 166
10.3 Diode Lasers 171
10.3.1 Fundamentals 171
10.3.2 Configurations and Characteristics 173
10.4 Excimer Laser 177
10.4.1 Principles 177
10.4.2 Setup 178
References 179
11 Surface Treatment 181
11.1 Transformation Hardening 181
11.1.1 Motivation 181
11.1.2 Process Description 182
11.1.3 Physical Background 185
11.1.4 Experimental Results 186
11.1.5 Applications 190
11.2 Remelting 194
11.2.1 Physical Fundamentals 195
11.2.2 Process 199
11.2.3 Examples for Laser Remelting 200
11.2.4 Application 202
11.3 Polishing with Laser Radiation 204
11.3.1 Polishing by Large-Area Ablation 204
11.3.2 Polishing by Localized Ablation 205
11.3.3 Polishing by Remelting – Metals 205
11.3.4 Polishing by Remelting – Glass 208
11.3.5 Polishing by Remelting – Thermoplastics 210
11.3.6 Summary of the Three Process Variants 210
11.4 Structuring by Remelting 211
11.4.1 Active Principle 211
11.4.2 Process and Relevant Procedural Parameters 212
11.4.3 Achieved Structures and Perspective 214
11.5 Alloying and Dispersing 215
11.5.1 Motivation 215
11.5.2 Physical Fundamentals 216
11.5.3 Process 216
11.5.4 Powder Injection Nozzles [40] 217
11.5.5 Material Combinations for Alloying and Dispersing 220
11.6 Laser Metal Deposition 224
11.6.1 Motivation 224
11.6.2 Process Description 224
11.6.3 Materials 227
11.6.4 Applications 228
11.7 Pulsed Laser Deposition 233
11.7.1 Fundamentals 234
11.7.2 Kinetic Energy of the Film-Forming Particles 236
11.7.3 Plasma and Thin Film Properties 241
References 245
12 Forming 248
12.1 Bending 248
12.1.1 Introduction 248
12.1.2 Process Models 250
12.1.3 Forming Results 254
12.1.4 Applications of Laser Beam Forming for Actuators 254
12.1.5 Conclusion 258
References 258
13 Rapid Prototyping and Rapid Tooling 260
13.1 Selective Laser Sintering (SLS) 260
13.1.1 Introduction 260
13.1.2 Selective Laser Sintering of Polymer Powders 261
13.1.3 Indirect Selective Laser Sintering of Metals 262
13.1.4 Direct Selective Laser Sintering of Metals 263
13.1.5 Selective Laser Melting (SLM) 264
13.2 Stereolithography 266
13.2.1 Description of the Process 266
13.3 Laminated Object Manufacturing (LOM) 268
References 270
14 Joining 271
14.1 Heat Conduction Welding 271
14.1.1 Introduction 271
14.1.2 Principle and Analysis of the Heat Conduction Welding Processes 272
14.1.3 Characteristic Curves for Welds with High–Power Diode Laser and Different Materials 273
14.1.4 Example of Use 275
14.2 Deep Penetration Welding 277
14.2.1 Introduction 277
14.2.2 Principle of Deep Penetration Welding and Physical Foundations 279
14.2.3 Function of Vapor Capillary (Keyhole) 280
14.2.4 Significant Parameters for Laser Beam Deep Penetration Welding 280
14.2.5 Example of Use 281
14.3 Hybrid Welding 284
14.3.1 Fundamentals 285
14.3.2 Integrated Hybrid Welding Nozzle 287
14.3.3 Welding of Steel and Aluminum 287
14.4 Laser Beam Welding of Thermoplastics 290
14.4.1 Motivation 290
14.4.2 Process Basics 292
14.4.3 New Approaches for Plastic Welding 303
14.4.4 Applications and Further Prospects 311
14.5 Laser Transmission Bonding 313
14.5.1 Introduction 313
14.5.2 Thermochemistry of Bonding 315
14.5.3 Principle of Laser Transmission Bonding 316
14.5.4 Laser Transmission Bonding of Silicon-to-Glass 317
14.5.5 Laser Transmission Bonding of Silicon-to-Silicon 322
14.6 Soldering 324
14.6.1 Introduction 324
14.6.2 Physical-Technical Fundamentals 327
14.6.3 Process Description 328
14.6.4 Applications 331
14.7 Laser Beam Microwelding 334
14.7.1 Introduction 334
14.7.2 Laser Beam Microwelding 334
14.7.3 Processes and Results 337
14.7.4 Beam Delivery 338
14.7.5 Spot Welding 339
14.7.6 Spaced Spot Welding 339
14.7.7 Continuous Welding 339
14.7.8 Applications of SHADOW® in Fine Mechanics and Electronics 341
14.7.9 Comparison of Conventional Pulsed Mode Welding to SHADOW® 342
14.7.10 Preconditions and Limits of Laser Beam Microwelding 343
14.7.11 Conclusion 343
References 344
15 Ablation 348
15.1 Micro- and Nanostructuring 348
15.1.1 Introduction 348
15.1.2 General Aspects for Laser Ablation 349
15.1.3 Process Principles for Laser Ablation 355
15.1.4 Examples 359
15.2 Cleaning 361
15.2.1 Basics of Cleaning with Laser Radiation 362
15.2.2 Example Applications for Laser Cleaning 363
References 367
16 Drilling 369
16.1 Introduction 369
16.2 Single-Pulse Drilling 371
16.2.1 Process Description 371
16.2.2 Influence of Process Parameters 373
16.2.3 Application Examples 374
16.3 Percussion Drilling 376
16.3.1 Process Description 376
16.3.2 Influence of Process Gases 376
16.3.3 Influence of Beam Parameters 378
16.3.4 Applications 379
16.4 Trepanning 382
16.4.1 Process Description 382
16.4.2 Process Gas and Gas Pressure 383
16.4.3 Type of Process Gas 384
16.4.4 5-Axis Trepanning 385
16.4.5 Applications 386
16.5 Helical Drilling 386
16.5.1 Process Description 386
16.5.2 Characterization of the Process 388
16.5.3 Helical Drilling Optic 391
16.5.4 Applications 392
References 393
17 Cutting 398
17.1 Laser Oxygen Cutting 398
17.1.1 Introduction 398
17.1.2 Power Balance for Laser Oxygen Cutting 399
17.1.3 Autogenous Cutting 400
17.1.4 Procedural Principle 401
17.1.5 Burning-Stabilized Laser Oxygen Cutting 404
17.2 Fusion Cutting 406
17.2.1 Introduction 406
17.2.2 Process Parameters 407
17.2.3 Fusion Cutting with Mirror Optics and Autonomous Nozzles 410
17.2.4 Sample Applications 411
17.3 High-Speed Cutting 412
17.3.1 Introduction 412
17.3.2 Process Description 414
17.3.3 Application Examples 416
17.4 Sublimation Cutting 417
17.4.1 Introduction 417
17.4.2 Power Balance for Laser Sublimation Cutting 418
17.4.3 Sample Applications for Sublimation Cutting of Non-metals 420
17.5 Laser Fine Cutting 421
17.5.1 Introduction and Application Areas 421
17.5.2 Process Principle 422
17.5.3 Laser Sources for Fine Cutting 424
17.5.4 Applications 425
References 428
18 System Technology 430
18.1 Process Monitoring 430
18.1.1 Introduction 430
18.1.2 Sensors 431
18.1.3 Electromagnetic Radiation Sensors 433
18.1.4 Measurement Techniques Based on Optoelectronic Sensor Systems 434
18.1.5 Examples – Laserwelding of Metal 443
18.1.6 Conclusion 453
18.2 Numerically Controlled Tooling Machines for Laser Materials Processing 454
18.2.1 Models of Tooling Machines 454
18.2.2 Components of the Basic Model 457
18.2.3 NC Control 461
18.2.4 Functional Extensions of Numerically Controlled Machine Tools for the Material Treatment with Laser Radiation 464
References 473
19 Laser Measurement Technology 476
19.1 Laser Triangulation 476
19.1.1 Introduction 476
19.1.2 Measurement of Geometric Quantities 477
19.1.3 Scheimpflug Condition and Characteristic Curve of Triangulation Sensors 479
19.1.4 Application Examples 481
19.1.5 Economic Benefit 489
19.2 Interferometry 490
19.2.1 Michelson Interferometer 492
19.2.2 Mach–Zehnder Interferometer 494
19.2.3 Fizeau Interferometer 496
19.2.4 Speckle Interferometer 496
19.2.5 White Light Interferometer 499
19.3 Laser-Induced Fluorescence 503
19.3.1 Basics of Fluorescence 503
19.3.2 Fluorescence Spectroscopy 505
19.3.3 Laser-Induced Fluorescence Spectroscopy 505
19.3.4 Fluorescence Markers in the Life Sciences 507
19.3.5 Economic Relevance of Laser-Induced Fluorescence 512
19.4 Confocal Microscopy 512
19.4.1 Motivation 512
19.4.2 Basic Principles 513
19.4.3 Resolution 514
19.4.4 Typical Applications 515
19.5 Reading of Optical Storage Media 518
19.5.1 Motivation 518
19.5.2 Fundamentals 519
19.5.3 Technical Realization of the Pick-Up System 520
19.5.4 Further Development of DVD 521
19.6 Laser-Induced Breakdown Spectroscopy 523
19.6.1 Motivation 523
19.6.2 Differentiation to Conventional Methods 524
19.6.3 Basics 524
19.6.4 Method Description 527
19.6.5 Time-Resolved Spectroscopy 530
19.6.6 Data Evaluation 531
19.6.7 Measurement Range 532
19.6.8 Examples of Applications 533
References 536
A Optics 540
A.1 Derivation of the FRESNEL Formulae 540
A.2 Dielectric Characteristics of Plasmas 543
A.3 Description of Electromagnetic Fields by Complex Quantities 546
Reference 548
B Continuum Mechanics 549
B.1 Coordinate Systems and Deformation Gradient 549
B.2 Deformation 551
B.2.1 Physical Meaning of the Components of GREEN’s Strain Tensor 553
B.3 Derivation with Respect to Time 554
B.4 REYNOLDS's Transport Theorem 556
B.5 Mass Conservation 557
B.6 Momentum Conservation 558
B.7 Material Equations 560
B.7.1 Elastic Solids 560
B.7.2 NEWTONian Fluids 562
B.8 Energy Conservation 564
B.9 Compilation of Mathematical Formulas Used in Energy Transport Computations 568
B.9.1 Integration Over Space 568
B.9.2 Integration Over Time 570
B.9.3 Error Functions 572
B.9.4 Exponential Integral 573
B.10 Diffusion in Metals 573
Reference 575
C Laser-Induced Vaporization 576
C.1 Equation of Clausius–Clapeyron 576
C.2 Temperature Dependence of the Evaporation Enthalpy 577
C.3 Velocity Moments 578
References 579
D Plasma Physics 580
D.1 Some Results of Thermodynamics 580
D.2 Generalization in Case of Multiply Ionized Ions 583
Reference 584
E Glossary of Symbols and Constants 585
E.1 Used Symbols 586
E.2 Physical Constants 591
E.3 Characteristic Numbers 591
E.4 Reference State 591
E.5 Material Constants 592
References 594
F Übersetzung der Bildbeschriftungen 595
Index 602