Abstract: One issue of manufacturing fully dense metal parts via selective laser melting (SLM) can be addressed by maximizing the packing density of the powder feedstock in the powder bed before melting. Voids between particles can result in poor mechanical behavior due to low relative densities and warping due to non-uniform shrinkage. In this study, our objective was to improve the density of 316L stainless steel samples produced by SLM by using a bimodal powder size distribution. To do this, a primary powder of a larger size range was combined with a smaller particle size that fills the interstitial regions between the larger particles. The packing density and flowability of the mixed bimodal feedstock powder was determined by measuring tap density and Hausner ratio. These mixed powders were then processed by SLM and the resulting samples were measured for density relative to the parent material. Bimodal feedstock powder mixtures with the powders used in this study did not yield higher density SLM powders than a normally distributed, single mode feedstock. However, maximum (tapped) density of the bimodal size distributions were up to 2% greater than the normally distributed powder. This indicates the potential for future studies to explore the use of bimodal powders to increase powder bed density.
Authors: Hannah G. Coe and Somayeh Pasebani
Keywords: 316L, Selective laser melting, Additive manufacturing, Bimodal powder size distribution