Advanced Powder Spreadability Assements

Conference Abstract: Metallic powders are widely used in Additive Manufacturing (AM) processes, with for example Selective Laser Melting (SLM) and Selective Laser Sintering (SLS). In such processes, the spreadability, i.e. the ability of the powder to spread under shear, must be good enough to obtain homogenous successive layers. In a previous study, the spreadability of metal powders has been shown to be strongly linked to their rheological properties measured in a rotating drum. The findings of this study have been recently published as an ISO/ASTM Technical report (ISO/ASTM TR 52952:2023), demonstrating the importance of providing a suitable method for predicting spreadability to the industry. In the present work, a more extensive experimental study has been carried on to complement the previous results, with an in situ evaluation of the spreadability in the printer (SLM280, SLM Solutions). The study covers a broad range of materials commonly used in SLM (Ti alloys, Al alloys, SS316, FeCo alloys), including different size distributions. To evaluate the spreadability, several powder layers are deposited with the recoater, and pictures of the powder bed are taken after each recoater pass. An image analysis processing is applied to extract the interface fluctuation, a measure of the homogeneity of the layer associated with the spreadability of the powder. The spreadability is then correlated with the cohesiveness and the rheology of the powders evaluated with a rotating drum method (GranuDrum, Granutools, Belgium). Especially, we demonstrate that the Cohesive Index metric, based on the powder/air interface fluctuations, is a good indicator for predicting the spreadability of the powder in the printer. Therefore, the powder ability to spread can be estimated beforehand without requiring to produce large batch to fill the machine. This provides a cost-effective way to select the optimal powder and recoating configurations that lead to better layer quality.