DYNAMIC BEHAVIOURS OF POWDER PARTICLES IN SELECTIVE LASER MELTING ADDITIVE MANUFACTURING

Laser selective melting (SLM) is one of the most popular technologies in the field of metal additive manufacturing (3D printing), which can directly fabricate complex metal parts with nearly full density and performance similar to forged one. The thermal and kinetic behaviour of powder particles in SLM forming process is complex, which has significant influences on the fusion defects such as pores and cracks and hence on the mechanical properties of the final fabricated parts. This paper introduces the innovative application of the discrete element method (DEM) and computational fluid dynamics (CFD) combined model in the simulation of SLM, and explores the thermal and kinetic behaviour mechanisms of the powder particles the powder spreading and powder melting processes of SLM, combined with in-situ testing and online monitoring on the fabrication process. During the powder spreading process of SLM, it is found that the adhesion effect, wall effect and percolation effect compete with each other to control the dynamic behaviour of powder particles and ultimately determine the packing quality of the deposited thin powder bed. In the process of powder bed melting, the high-temperature metal vapour jetting from the molten pool drives the environmental protection gas to form an internal vortex flow. Then, the vortex flow drives the discrete particles in the powder bed to form complex fluid-solid coupling motion, resulting in spattering and denudation in the powder bed. The thermal buoyancy effect from the laser heating has no dominant effect on powder motions such as spattering and denudation. In this paper, the bi-directional dynamic coupling DEM-CFD model is proposed, which can fully consider the thermodynamic coupling forces between the discrete powder particles and the metal vapour form the molten pool, and provides a new way for the simulation of the thermal-kinetic behaviours of powder particles in SLM such as spattering and denudation.