Reducing porosity at the starting layers above supporting bars of the parts made by Selective Laser Melting

Abstract

This study has investigated the causes of pores' formation during fabrication of the first few layers on the support structure and the process of product improvement in Selective Laser Melting. The notable pores are, fundamentally, formation of the void with uneven shape and the voids containing partially melted or stuck particles. The voids spread over a few consecutive layers from the starting one. The porosity occurred due to unsupported areas among supporting points, improper melt pool formation, melt pool's instability, inconsistency of heat transfer, crescent shape formation, uprooting of the lifted edge by the powder re-coater, and materials' spattering. These phenomena can be regulated by controlling the amount of energy input, melting time, amount of re-melting, delaying between melting and re-melting, and reheating and cooling timing using the combinations of laser powers, scanning speeds, and hatch spacings. Eventually, a sample having almost flawless starting layers was fabricated from Ti-6Al-4V powder.