Advancement of Selective Laser Melting by Laser Beam Shaping (Light Engineering für die Praxis)

Selective Laser Melting (SLM), also referred to as Laser Powder Bed Fusion (L-PBF), offers significant advantages for the manufacturing of complex, high-quality parts. However, its market share is still small compared to conventional manufacturing technologies. Major drawbacks hindering an industrial ramp-up are low productivity, high part costs and issues with quality and reproducibility. Comprehensive research has been done to overcome these challenges, but little attention has been paid to addressing them by optimizing the laser beam profile. Therefore, the author examines the effect of the laser beam profile on the productivity and process stability through both numerical and experimental investigations. The results show clear advantages an optimized laser beam profile offers. The content First comprehensive research on the effect of the laser beam profile on SLM process Understand the effect of the laser beam profile on the process stability and feasible productivity of the SLM process Discover the benefits in terms of manufacturing costs and time that are offered by an optimized laser beam profile The author Tim Marten Wischeropp studied mechanical engineering at the Technical University of Hamburg (TUHH), Germany. After graduating with a focus on product development, he worked as a research fellow at the Institute of Laser and System Technologies (TUHH) as well as group leader for 3D printing at the LZN Laser Zentrum Nord GmbH. Since 2018 he leads the design department at the Fraunhofer Institution for Additive Manufacturing Technologies IAPT Abstract 8 Table of Contents 9 Nomenclature 12 Abbreviations 18 1 Introduction 20 1.1 Background 20 1.2 Motivation 22 1.3 Approach 23 2 Fundamentals 25 2.1 Additive Manufacturing 25 2.2 Selective Laser Melting 27 2.2.1 General Principle 27 2.2.2 Overview of Process Chain 29 2.2.3 Advantages and Challenges 30 2.2.4 Essential Process Parameters and their Influence 32 2.2.5 Details of Laser-Material Interaction and Melt Pool Dynamics 38 2.2.6 Defects in SLM 44 2.3 Simulation of SLM and Related Processes 46 2.3.1 Overview of Simulation in SLM 46 2.3.2 Relevant Numerical Models 48 2.3.3 Summary 53 2.4 Laser Beam Shaping 55 2.4.1 Laser Beam Shaping Techniques 55 2.4.2 Laser Beam Shaping in SLM and Related Processes 56 2.4.3 Summary 58 3 Numerical Model 60 3.1 General Considerations 60 3.2 Setup of Numerical Model 61 3.2.1 Domain and Boundary Conditions 61 3.2.2 Implementation of Powder Bed 62 3.2.3 Material Properties 64 3.3 Evaluation of Numerical Results 65 3.4 Validation of Numerical Model 67 4 Experimental Set-Up 70 4.1 Design of Experiments 70 4.2 Equipment 72 4.3 Material 74 4.4 Analysis of Spatters 76 5 Effect of Laser Beam Profile on SLM Process 78 5.1 Numerical Assessment of Effect on Melt Pool 78 5.1.1 Melt Pool Size and Shape 78 5.1.2 Thermo-Capillary Flow 81 5.1.3 Vaporization 87 5.1.4 Summary of Results 91 5.2 Effect on Single Tracks of AlSi10Mg 92 5.2.1 Appearance 92 5.2.2 Width and Depth 95 5.2.3 Summary of Results 98 5.3 Effect on Multi-Layer SLM Process of AlSi10Mg 99 5.3.1 Effect on Process Stability 99 5.3.2 Effect on Build Rate 112 5.3.3 Comparison to Single Track Results 117 5.3.4 Summary of Results 117 5.4 Effect on Multi-Layer SLM process of AlSi16Sc 118 5.4.1 Effect on Process Stability 118 5.4.2 Effect on Build Rate 126 5.4.3 Summary of Results 129 6 Industrial Relevance of Results 130 6.1 Effect on Manufacturing Quality, Time and Costs 130 6.2 Effect of (Potential) Future Enhancements 136 7 Summary and Outlook 138 References 141 List of Figures 164 List of Tables 169 A. Appendix 171 A.1 Description of Numerical Model 171 A.1.1 Governing Equations for Heat and Mass Transfer 172 A.1.2 Free Surface Heat and Mass Transfer 173 A.1.3 Laser Beam and Multiple-Reflection 175 A.1.4 Vaporization 177 A.1.5 Solidification 178 A.2 Mesh Convergence Study 181 A.3 Image-Processing for Spatter Analysis 183 A.4 Results of Spatter Analysis 185 A.5 Single Track experiments 187 A.6 Wilcoxon-Signed-Rank-Test 189 A.7 Micro-sections of AlSi10Mg density cubes 191 A.8 Micro-sections of AlSi16Sc density cubes 197 A.9 Hourly Machine Rate of SLM 500 HL Machine 200