Effects of Powder Recycling in Selective Laser Melting

The following report analyzes 316L stainless steel powder characteristics of new powder and powder that has been used in the selective laser melting process for 40-50 builds. A literature review was done of powder characteristics, different ways flowability can be tested, and effects of recycling other types of metal powders in Additive Manufacturing. Flowability improved over 21 reuses of the titanium alloy Ti-6Al-4V and resulted in stronger printed parts. Flow of S17-4 PH steel powder was measured with a Hall flowmeter and increased significantly over the course of 10 reuses. Heavily recycled (estimated 50 reuses) 316L SS powder and brand new powder were examined with a particle size analyzer and a Freemantech FT4 Powder Rheometer. The recycled powder was freer flowing, denser, and has slightly larger particles. The increase in particle size is hypothesized to be a result of partial sintering. The recycled powder is likely to have a higher flow and lower cohesion because of the repeated handling over time. The denser, freer flowing powder should result in stronger SLM parts; a plan to print and test SLM parts is described to confirm the hypotheses