Balling phenomena in selective laser melting (SLM) of pure gold (Au)

Selective Laser Melting (SLM) is the process of melting metal powder using laser to produce intricate and difficult to manufacture metallic components for wide variety of applications. SLM is a highly nonlinear process and the understanding of melt pool flow physics and associated heat transfer is important. This research work focuses on the numerical simulation of heat flux driven flow in the melt pool of 24 carat gold (Au) powder using 50W fibre laser. Balling phenomenon was observed at low as well as high scan speeds in the experimental work. The size of the droplets formed during balling was observed to increase at high laser power with lower scan speeds, however no clear trend was observed for the changes in the spatial gap between the droplets. It was observed that these patterns indicate zones of melt pool splitting and can be linked to the negative surface tension gradient of pure metals. An initial simulation was performed using equations suitable for incompressible flow coupled with heat transport in porous media showing thermal gradients within the meltpool.