Simulation of Powder Packing and Thermo-Fluid Dynamic of 316L Stainless Steel by Selective Laser Melting

Abstract

A mesoscopic model was established to investigate thermo-fluid dynamic behavior in selective laser melting of 316L stainless steel. A powder packing model, including particle size distribution based on the discrete element method, was developed to describe the relative density variation of the powder bed with different layer thicknesses. A finite element method model with Gaussian laser beam was established to predict the dynamic thermal behavior and flow mechanism of the particles for a single-line scanning. The level-set method was used to trace the free surface of the molten metal with temperature-dependent surface tension. A function to describe the relative density of the powder bed with its thickness was obtained. An evaporation model considering the influence of mass, energy loss, and evaporation on the surface morphology of the molten pool was established. According to the temperature and velocity field in the molten pool, a vortex formed by the Marangoni effect might decrease the depth and increase the width of the molten pool. The molten pool was not disconnected by Plateau–Rayleigh instability due to the small length/diameter ratio at low scanning speeds. The model assuming regularly arranged powder bed underestimates the maximum temperature as compared to the model considering a randomly packed powder bed because a higher relative density of the former facilitates heat conduction. The simulated results are consistent with experimental results, including porosity, material loss, and surface defects.