Laser cladding

Capitalizing on the rapid growth and reduced costs of laser systems, laser cladding is gaining momentum, and in some instances replacing conventional techniques of depositing thin films because it can accommodate a great variety of materials, achieve uniform thickness and precise widths of layers, and provide improved resistance to wear and corrosion in the final product. Laser cladding technology also offers a revolutionary layered manufacturing and prototyping technique that can fabricate complex components without intermediate steps.

Laser Cladding reviews the parameters, techniques and equipment, process modeling and control, and the physical metallurgy of alloying and solidification during laser cladding. The authors clarify the interconnections laser cladding has with CAD/CAM design; automation and robotics; sensors, feedback, and control; physics, material science, heat transfer, fluid dynamics, and powder metallurgy to promote further development and improved process quality of this growing technology. As the first book entirely dedicated to the topic, it also offers a history of its development and a guide to applications and market opportunities.

While a considerable part of Laser Cladding is dedicated to industrial applications, this volume brings together valuable information illustrated with real case studies based on the authors' vast experience, and research and analysis in the field to provide a timely source for both academia and industry.

1 Introduction	p. 1
1.1 What is Laser Cladding?	p. 1
1.2 Different Names, Same Technology	p. 2
1.3 Why Laser Cladding?	p. 3
1.4 History of Laser Cladding	p. 5
1.5 Applications and Market Opportunities	p. 8
1.5.1 Coating	p. 8
1.5.2 Parts Repair and Refurbishment	p. 10
1.5.3 Rapid Prototyping and Tooling	p. 12
1.6 Future Direction of Laser Cladding Technology	p. 19
1.7 Looking Ahead	p. 22
2 Background and Basic Overview	p. 23
2.1 Laser Material Techniques	p. 23
2.2 Differences Between Laser Cladding, Alloying and Glazing	p. 23
2.3 Different Methods of Laser Cladding	p. 25
2.3.1 Two-Step Laser Cladding (Pre-placed Laser Cladding)	p. 27
2.3.2 One-Step Laser Cladding	p. 28
2.4 Clad Dimensional Characteristics	p. 30
2.5 Important Parameters in Laser Cladding by Powder Injection	p. 30
2.5.1 Dilution	p. 31
2.5.2 Wetting Angle and Interfacial Free Energies	p. 32
2.5.3 Laser Pulse Shaping	p. 33
2.6 Combined Parameters	p. 34
2.6.1 Aspect Ratio	p. 34
2.6.2 Combined Energy and Powder Densities' Parameters	p. 34
2.7 Comparison Between Laser Cladding and Other Metallic Coating Techniques	p. 38
2.8 Comparison Between Laser Cladding and Other Prototyping Techniques	p. 39
3 Laser Cladding Fquipment	p. 41
3.1 Lasers	p. 41
3.1.1 Laser Types	p. 44
3.1.2 Laser Beam Characteristics	p. 53
3.1.3 Types of Lasers and Laser Beam Characteristics in Laser Cladding Process	p. 58
3.2 Powder Feeders and Powder Delivery Nozzles	p. 66
3.2.1 Powder Feeder Types	p. 67
3.2.2 Applications of Powder Feeders to Laser Cladding	p. 73
3.2.3 Nozzles	p. 74
3.3 Positioning Devices	p. 77
3.3.1 CAD/CAM System for Trajectory Generation	p. 80
4 Laser Cladding Process Modeling	p. 87
4.1 Physics of the Process	p. 87
4.2 Governing Equations	p. 88
4.2.1 Essential Boundary Conditions	p. 89
4.3 Laser Cladding Models in Literature	p. 90
4.3.1 Steady-State Models	p. 92
4.3.2 Dynamic Models	p. 93
4.4 Lumped Models	p. 94
4.5 Analytical Modeling	p. 98
4.6 Numerical Modeling--A Case Study	p. 99
4.6.1 Thermal Mathematical Model	p. 101
4.6.2 Solution Algorithm	p. 104
4.6.3 Numerical Parameters	p. 107
4.6.4 Numerical Results	p. 107
4.6.5 Experimental and Numerical Analysis	p. 112
4.6.6 Comparison Between Numerical and Experimental Results	p. 118
4.7 Flow Field Modeling at the Exit of Coaxial Nozzle	p. 122
4.7.1 Laminar Model	p. 123
4.8 Experimental-Based Modeling Techniques	p. 126
4.8.1 Stochastic Analysis	p. 129
4.8.2 Artificial Neural Network Modeling	p. 140
5 Control of Laser Cladding Process	p. 149
5.1 Sensors	p. 152
5.2 Closed-Loop Control of Laser Cladding	p. 154
5.3 Closed-Loop Control of Laser Cladding, An Example	p. 156
5.3.1 Equipment and Configuration	p. 156
5.3.2 Optical CCD-based Detector	p. 158
5.3.3 Control Strategy	p. 164
5.3.4 Closed-Loop vs. Open-Loop	p. 166
5.3.5 Application of the Developed Controller to Fabrication of Two Simple Components	p. 171
5.4 Application of Knowledge-Based Control to Laser Cladding	p. 173
5.4.1 Fuzzy Logic Controller	p. 174
6 Physical Metallurgy and Material Systems of Laser Cladding	p. 179
6.1 Cladability	p. 179
6.1.1 Processing Parameter Considerations	p. 180
6.1.2 Metallurgical Considerations	p. 195
6.2 Solidification Conditions Encounter in Laser Cladding	p. 208
6.2.1 Process Conditions	p. 210
6.2.2 Constitutional Supercooling	p. 211
6.2.3 Rapid Solidification	p. 215
6.2.4 Microstructure Maps	p. 216
6.2.5 Microstructural Scale	p. 219
6.3 Material Systems Used in Laser Cladding	p. 222
6.3.1 High Temperature Alloys	p. 223
6.3.2 Composites	p. 224
7 Safety	p. 227
7.1 Laser Classification	p. 227
7.2 Laser Hazards	p. 228
7.2.1 Eye Hazards	p. 228
7.2.2 Collateral Radiation	p. 231
7.2.3 Electrical Hazards	p. 232
7.2.4 Chemical Hazards	p. 232
7.2.5 Fire Hazards	p. 233
7.2.6 Explosion Hazards	p. 233
7.2.7 Eye Protection	p. 233
7.3 Powder Hazards	p. 234
References	p. 235
Index	p. 257

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