A Numerical Study on Laser-Particle Interaction in the Selective Laser Melting Process

Multiple-reflection is considered as one of the important phenomena in laser materials processing. The role of multiple-reflection becomes even more important in SLM process due to the complexity of powder structure in powder bed and the consideration of the interaction between laser and each particle. In this study, there are two main purposes. One is the suggestion of the models, which can be applied in SLM process simulations, and depict the important phenomena in laser material processes, such as laser absorption and multiple-reflection by combining the ray tracing. The other is to analyze the effects of some special structure conditions, such as the gap between particles and the shape of particles by melting efficiency, influence of interface heat conduction and power absorption trends. The partial melting of particles was considered by the set of process parameters adopted in simulations to observe these effects. The CFD numerical simulations where the laser-particle interaction is considered by multiple-reflection are performed to investigate the gap and particle shape effect in Selective Laser Melting process. To calculate the multiple-reflection, ray tracing is applied in simulations. In ray tracing, the real contact point between laser and particle is calculated by solving the surface equation and ray direction vector equation. And Gaussian heat source, recoil pressure, Marangoni flow, and buoyancy force are also applied. To investigate the gap effect, single-layer structures are designed. Multi-layer structures with a sphere and spheroidal shape are also designed to investigate the particle shape effect. And for precise comparisons, the concept of melting efficiency is suggested. The gap has a major effect on the melting efficiency. The gap can cause the higher power absorption by multiple-reflection and decreased heat transfer to other particles. On the other hand, the particle shape has a minor effect on the melting efficiency. In multi-layer structures, the melting efficiency of particle located in the center of the structure is relatively lower than the particles of the third layer because some part of the center particle is covered by the particles of the third layer and relatively large multiple-reflection occurs in the particles of third layer due to the gap.