Influence of the Inert Gas Flow on the Laser Powder Bed Fusion (LPBF) Process

Abstract

The inert gas flow is known to have a significant impact on the laser powder bed fusion (LPBF) process in terms of process stability and consistent process results across the whole build platform. Thus, the optimization of the inert gas flow leads to both direct and indirect improvements of the part quality as follows. If the gas flow can steadily and efficiently remove soot particles emerging from the melting process, scattering and attenuation of the laser beam or debris on the laser windows can be avoided, which would indirectly impair the quality of the built parts. Spatter particles should be removed as well because they can directly lead to bonding defects inside the produced parts. Therefore, the gas flow in a self-constructed LPBF machine has been optimized systematically based on computational fluid dynamics (CFD), particle tracking and experimental studies. Herein the effect of the process gas flow and gas type on spatter and soot particles is presented in detail. According to the simulation results, the soot removal is improved by a smaller shielding gas inlet height at the cost of a potential deterioration of the soot removal at extreme process parameters. The simulation results have been validated by measurements of the gas flow velocity and of the density of the built parts. The advantages and disadvantages of different process gas types are shown and recommendations for the gas flow design are derived.