Laser Welding of Plastics: Materials, Processes and Industrial Applications

This is the first detailed description in English of radiation and polymeric material interaction and the influences of thermal and optical material properties. As such, it provides comprehensive information on material and process characteristics as well as applications regarding plastic laser welding.
The first part of this practical book introduces the structure and physical properties of plastics, before discussing the interaction of material and radiation in the NIR and IR spectral range. This is followed by an overview of the physical foundations of laser radiation and laser sources used for plastic welding. The third part describes the main processes of laser welding thermoplastics, as well as possibilities of process control, design of joint geometry, material compatibilities and adaptation of absorption of plastics to NIR radiation. Finally, the author explains applications of laser welding plastics using several industrial case studies from the automotive industry, household goods, and medical devices.
Tailored to the needs of everyone dealing with laser welding of plastics, especially engineers in packaging, component manufacturing, and the medical industry.


Spis treści:
Introduction 1
1 Material Properties of Plastics 3
1.1 Formation and Structure 3
1.2 Types of Plastics 7
1.2.1 Thermoplastic Resins 9
1.2.1.1 Amorphous Thermoplastics 10
1.2.1.2 Semicrystalline Thermoplastics 10
1.2.2 Elastomers 13
1.2.3 Thermosets 13
1.2.4 Polymer Compounds 14
1.2.4.1 Polymer Blends 14
1.2.4.2 Copolymers 15
1.2.4.3 Thermoplastic Elastomers 15
1.2.5 Polymer Composites 18
1.3 Thermal Properties 19
1.3.1 Phase Transitions 20
1.3.1.1 Glass Transition (Tg) 20
1.3.1.2 Flow Temperature (Tf) 20
1.3.1.3 Crystallite Melting Temperature (Tm) 20
1.3.1.4 Thermal Decomposition (Td) 21
1.3.2 Specific Volume 22
1.3.3 Heat Capacity 24
1.3.4 Heat Conduction 27
1.3.5 Temperature Conduction 30
1.3.5.1 Amorphous Thermoplastics 32
1.3.5.2 Semicrystalline Thermoplastics 33
1.4 Optical Properties 35
1.4.1 Optical Constants 36
1.4.2 Reflection, Transmission and Absorption Behavior 42
1.4.3 Scattering of NIR– and IR–Radiation in Plastics 46
1.4.4 Absorption of NIR–Laser Radiation (l ¼ 800 nm to 1200 nm) 49
1.4.4.1 Electronic Excitation 50
1.4.4.2 Vibronic Excitation 51
1.4.4.3 Summarizing Comment 52
1.4.5 Absorption of NIR–Laser Radiation (l ¼ 1200 nm to 2500 nm) 54
1.4.6 Absorption of MIR–Laser Radiation (l ¼ 2.5 mm to 25 mm) 55
1.4.7 Adaptation of NIR–Radiation Absorption by Additives 59
1.4.7.1 Carbon Black 59
1.4.7.2 Inorganic Pigments 61
1.4.7.3 Organic Dyes 66
1.4.7.4 Summarizing Comment 66
References 66
2 Laser Sources for Plastic Welding 71
2.1 Properties of Laser Radiation 71
2.1.1 Laser Wavelength 73
2.1.2 Intensity Distribution 74
2.1.3 Beam Propagation 74
2.1.4 Focusing Properties 76
2.2 Types of Lasers 78
2.2.1 Diode Lasers (800 to 2000 nm) 78
2.2.2 Nd:YAG–Lasers (1064 nm) 80
2.2.3 Fiber Lasers 83
2.2.4 CO2–Lasers (10.6 mm) 85
2.2.5 Summary 87
2.3 Beam Guiding and Focusing 88
2.3.1 Beam–Guiding Systems 88
2.3.1.1 Glass–Fiber Systems 88
2.3.1.2 Mirror Systems 93
2.3.2 Focusing Systems 95
2.3.2.1 Static Focusing Systems 95
2.3.2.2 Dynamic Focusing Systems 99
2.3.3 Beam–Shaping Optics 100
2.4 Principle Setup of Laser Welding Systems 101
References 107
3 Basics of Laser Plastic Welding 109
3.1 Heat Generation and Dissipation 109
3.1.1 Absorption of Laser Radiation 109
3.1.1.1 Direct Absorption 109
3.1.1.2 Indirect Absorption 110
3.1.1.3 Hindered Absorption by Internal Scattering 111
3.1.2 Transfer of Laser Energy into Process Heat 114
3.1.3 Dissipation of Process Heat 118
3.1.4 Process Simulation by Complex Computation 121
3.2 Theory of Fusion Process 126
3.2.1 Interdiffusion Process (Reptation Model) 127
3.2.2 Interchange of Macromolecules by Squeeze Flow Process 132
3.2.3 Mixing of Crystalline Phases 133
3.3 Material Compatibility 135
References 138
4 Process of Laser Plastic Welding 141
4.1 Basic Process Principles 141
4.1.1 Butt–Joint Welding 141
4.1.2 Through–Transmission Welding 143
4.2 Process Types 145
4.2.1 Contour Welding 145
4.2.2 Quasisimultaneous Welding 148
4.2.3 Simultaneous Welding 150
4.2.4 Special Processes 154
4.2.4.1 Mask Laser Welding 154
4.2.4.2 TWIST Laser Welding 155
4.2.4.3 Globo Laser Welding 156
4.2.4.4 IR–Hybrid Laser Welding 158
4.2.4.5 Ultrasonic Hybrid Laser Welding 159
4.2.4.6 Laser–Assisted Tape Laying and Winding 160
4.3 Adaption of Absorption 163
4.3.1 Use of Surface Coatings 163
4.3.2 Use of Absorbing Additives 172
4.3.3 Use of Special Lasers 178
4.4 Design of Joint Geometry 181
4.4.1 Joint Geometries 182
4.4.2 Tolerances and Clamping 186
4.4.3 Obstacles to Avoid 191
4.4.4 Gap Bridging 193
4.5 Methods of Quality Monitoring and Control 195
4.5.1 Quality Control before Processing 196
4.5.2 Quality Control During Processing 199
4.5.2.1 Pyrometric Monitoring 199
4.5.2.2 Thermography Monitoring 203
4.5.2.3 Digital Imaging Monitoring 205
4.5.2.4 Optical Reflection Monitoring 207
4.5.2.5 Mechanical Set–Path Monitoring 208
4.5.2.6 Summary of Monitoring Techniques 209
References 212
5 Case Studies 217
5.1 Automotive Components 218
5.2 Consumer Goods 223
5.3 Electronic Devices 227
5.4 Medical Devices 232
5.5 Others 238
Index 243

Nota biograficzna:
Dr. Rolf Klein was educated as physicist at the University of Darmstadt and received his PhD in mechanical engineering from RWTH, Aachen. He worked at the Fraunhofer ILT, involved in R&D f or laser processing polymers. Prior to starting his own business in July 2009, he held senior positions within a number of German laser companies, working for R&D of metal processing, system development as well as polymer welding with laser. For several years he worked for Gentex Corp., an US based company, as technical senior engineer in the field of absorbing additives for laser plastic welding and development of related processes.
Rolf Klein has authored several scientific and technical publications with topics of laser material processing and laser system design. He is also a member of VDI and SPE and active in the DVS working group for plastic laser welding.