Spattering trajectory, residing pattern and trap ratio under various gas flow conditions in large-scale laser powder bed fusion: Experiment and simulation

The larger build platform in large-scale laser powder bed fusion (LPBF) equipment results in a higher incidence of residual spatters, which can adversely affect the consistency of part quality. Inert gas flow is an efficient way to transport spatters to outlet, but a comprehensive understanding of spatter trajectory and residing pattern under gas flow effect remains unclear. In this study, Computational Fluid Dynamics (CFD) coupled with a Discrete Phase Model (DPM) is employed to simulate spatter trajectories, and the distribution of residual spatters are validated against experimental data obtained by processing images captured by camera. A significant quantity of sizable spatters land in close proximity to the melt region. According to our statistics, 96.5 % of droplet spatter are trapped on the powder bed when the gas flow velocity is 0.5 m/s, with the trap ratio diminishing as gas flow becomes stronger. Excessively high gas flow velocities result in droplet spatter engaging in secondary circulation by gas flow vortex within the building chamber, finally leading to a decline in the melted surface quality. The simulation approach can offer practical guidance in optimizing the design of the building chamber and inlet/outlet in large-scale LPBF equipment to minimize the impact of spattering on built quality.