Selective Laser Sintering, a powder-bed fusion additive manufacturing (AM) technique produces end-use parts with excellent mechanical properties with almost no design limitations. Unfortunately, the high material costs (~$100 per kilogram) and the low conversion rate – only about 15 % of the powder is consumed – has limited its adoption. The degradation of the unused powder further exacerbated this problem as powder cannot simply be recycled. Typically, 30 to 60 % virgin material is arbitrarily blended with recovered powder to refresh material properties to ensure successful future prints.
Ideally, there would be a quick and simple test(s) that could be conducted on the unused powder to quantify the degradation, which in turn could determine at what rate virgin powder should be blended at. The goal of this research is to use various thermal, spectrochemical, bulk powder and other tests to measure the properties of the powders used in the process. To date, the most successful technique for measuring the changes due to thermal and thermoxidative degradation has been differential scanning calorimetry (DSC), which indirectly captures molecular changes, e.g., a molecular weight decrease due to chain scission, from the change in the melting endotherm and crystallization exotherm.
The Tm,peak of PA12 that was controllably degraded under conditions that emulate the SLS machine environment that was then mixed with 0 to 60 % virgin powder. The increase in melting temperature due to thermal degradation (white bars) was mitigated by adding virgin powder, which almost returned the melting temperature to that of virgin powder (green range).