Influence of Gas Flow on Vapour Plume Removal and Particle Pickup in Selective Laser Melting of Metal Powders

In Selective Laser Melting (SLM) of metal powders, the fast scanning and full-melting process is usually coupled with strong material evaporation. The metal vapour quickly condensates into fine particles and forms a plume around the scanning area. This vapour plume can attenuate the laser beam and result in defects in the printed parts. An inert gas flow across the powder bed is usually introduced in SLM systems to remove the vapour plume around the laser beam and to prevent the condensate particles from contaminating the laser optics. While a high gas flow speed is desired to minimise the influence of plume-laser attenuation, it is limited by the particle pickup speed of the metal powder. This research first measured the pickup speeds of several metal powders and proposed an empirical model to predict the particle pickup speed for different powders. Secondly, test parts were built with different gas flow settings to study the influence of the plume-laser attenuation at low gas flow speed and particle pickup at high gas flow speed on the quality of printed parts. The related defects are characterised and the gas flow settings suitable for different metal powders were proposed.