Influence of particle size distribution on the powder bed quality in the powder bed fusion additive manufacturing process

Optimizing powder bed quality is crucial for enhancing the quality of objects manufactured through the powder bed fusion additive manufacturing (PBF-AM) process. In this study, we propose an optimal particle size distribution (PSD) to improve powder bed density and homogeneity during the recoating process. Four PSD types, including unimodal, bimodal, trimodal, and original, were prepared using sieved stainless steel 304 powder for evaluation. The influence of PSDs on flowability and cohesive forces was assessed using Hall flowmeter and rotating drum tests. The results revealed that adding fine particles <53 μm increased cohesive interactions owing to their higher specific surface area and lower weight, while increasing the fraction of intermediate particles >53 μm alleviated cohesive interactions. Bimodal PSD led to deteriorated powder bed homogeneity due to the inhomogeneous segregation of fine particles <53 μm. However, the homogeneity of the powder bed improved in the trimodal PSD by increasing the fraction of particles >53 μm. In-situ observations, combined with particle image velocimetry analysis, showed that the kinetic energy of particles was primarily dissipated within the shear stress zone, caused by velocity discrepancies between upper and lower particle layers. In bimodal PSD, the formation of fine particle clusters suppressed the segregation of particles <53 μm in the initial recoating area. In contrast, trimodal PSD enabled homogeneous fine particle segregation through granular convection by increasing the fraction of intermediate particles >53 μm. Thus, it was demonstrated that trimodal PSD is more suitable for PBF-AM, as it enhances powder bed density and homogeneity by facilitating the granular convection of particles smaller than 53 μm.