Numerical simulation of meltpool instability in the selective laser melting (SLM) process

Selective laser melting (SLM) is a nonlinear process which involves melting of powder metal using laser to manufacture intricate metallic parts. During laser melting, the meltpool dynamics are influenced by initial laser processing parameters such as laser power and scan speed. Understanding of the meltpool flow physics and associated heat transfer is important for producing stable meltpool and hence high quality layers and parts. This research work focuses on the steady state numerical simulation of heat flux driven flows in the meltpool of pure metal (24 carat gold powder). Experimental observations indicated a relationship between the sizes of balling and the laser energy density, while no such relationship could be deduced for the change in the spatial gap between the droplets or balling. The splitting of meltpool away from the path of scan and first line balling was also observed. Simulation results predict the formation of different types of balling at different scan speeds and heat flux to be linked with heat transfer from the meltpool. Results indicate that the size of meltpool is largely dependent on the applied heat flux and its rate of transport to the surroundings i.e. boundary conditions. The steady state velocity patterns in the meltpool, driven by heat flux from the neighbouring surfaces, match well with experimental results.