Rheology Of Ss-316l Metal Powders Exposed To Laser Powder Bed Machine Cycles: An Interlaboratory Study

Powder flowability has an important impact on additive manufacturing (AM) processes. Rheology is a technique that has been used to assess the flowability of powders in different applications. In order to use the technique fir AM quality control and certification, it is essential to validate how sensitive the measurements are to particle characteristics and assess the relevance, repeatability and robustness of the method. The objectives of this interlaboratory study were to determine how the theology of SS-316L powder was affected by repeated use in a laser-beam powder-bed-fusion machine, evaluate if theology could be used to differentiate the behavior of virgin and recycled powders, and determine if the flow behavior correlates with other powder characteristics. The study was concluded blind using four samples of a SS-316L powder that were labeled Samples A, B, C, and D. All that the participants knew about the samples was their composition, that they had a particle-size distribution suitable for PBP-LB processing, and that they represented virgin and recycled feedstock. After the tests were completed, it was revealed that Samples B and D were virgin feedstock from the same powder lot, Sample A was a feedstock that had been reused eight times in a laser-beam powder-bed-fission machine (recycled), and Sample C was a 50:50 blend of the virgin and recycled powders. The results show that it was possible to identify the two identical powders and to differentiate the recycled powder from the virgin ones. This differentiation was possible despite the fact that the modifications of the powder were very small, as suggested by the fad that they were difficult to differentiate using other standard methods and still had adequate build performance after reuse. Globally, the BFE showed a relatively good capability to study the impact of recycling on powder behavior. However, absolute values differed significantly from lab to lab. The origin of these variations should be further investigated, and strategies should be identified to reduce them. Development of standard procedures should contribute to improving the reliability of the approach.