Simulation study of the spatter removal process and optimization design of gas flow system in laser powder bed fusion

An urgent need in the laser powder bed fusion (LPBF) process is to efficiently remove emissions from or around the moving melt pool since the powder bed contamination by spatter can potentially damage fabricated part quality. The objective of this study is to propose new designs of the gas flow system in the build chamber to enhance the removability of spatter. Specifically, a Computational Fluid Dynamics (CFD) model for the LPBF gas flow system has been developed to simulate the complicated flow behavior inside the build chamber. The movement of spatter has been calculated by the Discrete Phase Model (DPM). The fully coupled CFD-DPM fluid-particle interaction method has been applied to capture the influence of gas flow on solid particles accurately. Additionally, an analytical expression is utilized to obtain the threshold velocity of inert gas flow upon the powder bed. The spatter distribution in a generic gas chamber design was studied. It was found that the Coanda effect, a gas flow downward tendency toward the substrate, can have a significant impact on the spatter removal process. With the proposed new designs, the Coanda effect is minimized, and most of the spatters can be removed from the build region without blowing up powder bed particles.