(292d) Spreadability of Metal Powders: Combining Powder Characterization and DEM Simulations

Good powder spreadability is essential in powder bed-based AM to prevent the deposition of irregular layers that will induce defects in the built part. Investigating the powder spreadability by directly spreading it in the printer, despite being the obvious way to do it, is usually not feasible practically as it requires a large amount of material to fill in the machine and is a waste of machine time. Previous studies have demonstrated the link between the Cohesive Index metric [1] of the GranuDrum (Granutools, Belgium) and the irregularity of the layer measured inside an SLM printer. The methodology has been recently published as an ISO/ASTM technical report [2].

However, the in-situ evaluation of the spreadability suffers from some limitations. The interface fluctuations are measured based on the analysis of optical images of the powder bed acquired with the camera device available in the printer. Therefore, the observed defects can change depending on the angle of the lighting used. Also, this method does not give access to detailed topography of the layer as well as defects size in the direction orthogonal to the powder bed. The in-situ evaluation is thus interesting to get a measure of the global spreadability of the powder but does not allow to go deep in the analysis of the defects shape and size.

Discrete Element Method (DEM) has gained a lot of interest in simulating particle-based materials. The main advantage is that the properties of the particles (size/shape, position, velocity) are known at any time of the simulation. Investigating spreadability with DEM allows performing deep analysis of the powder layer defects. However, obtaining accurate results requires a precise calibration of the model parameters that is usually time consuming. We propose an approach using characterization results obtained with the GranuDrum to precisely calibrate the simulations with a digital twin of the GranuDrum system [3]. The calibrated virtual material is then used to investigate the influence of material parameters such as cohesive strength, particle size or shape, and recoater speed, on spreadability. The results of the simulation are validated with experimental data obtained with a spreading test bench in which powder layers are sequentially deposited, and the layer quality is evaluated between each layer. The device is instrumented with a confocal microscope used to precisely measure profiles of the height variation across the layer. The layer local topology is thus directly accessible. We show that combining experimental characterization with DEM simulations of spreadability helps to give a clearer picture of the effect of cohesiveness on powder spreability.

[1] Neveu et al., “Measuring powder flow properties in a rotating drum”, Measurements 200 (2022).

[2] ISO/ASTM TR 52952:2023, Additive manufacturing of metals — Feedstock materials — “Correlation of rotating drum measurement with powder spreadability in PBF-LB machines”.

[3] Windows-Yule C.R.K and Neveu A., “Calibration of DEM simulations for dynamic particulate systems”, Papers in Physics, vol. 14, art. 140010 (2022).