Influences of Powder Packing Density in Laser Powder Bed Fusion Metal Additive Manufacturing

Laser powder bed fusion (LPBF) technology is one of the most widely used forming technologies in the field of metal additive manufacturing because of its high forming accuracy, low surface roughness, and excellent performance of the formed parts. In this paper, we review the factors influencing powder packing density in LPBF technology, which is a key part of LPBF technology. First, the methods of powder bed quality characterization and evaluation, such as image analysis, X-ray in-situ monitoring, and sampling method, are summarized. On this basis, the influence of powder particle size, powder morphology, powder preparation method, powder recycling, and powder recoating process parameters on the powder bed packing density is described from powder characteristics and powder recoating process, respectively. Among them, the particle size distribution and morphology of the powder are the key factors affecting the powder packing density, and the wider single-peak distribution and the bimodal distribution of coarse and fine particles are favorable to improve the powder packing density; the closer the powder morphology is to spherical shape, the better the powder flowability is, which is favorable to improve the powder spreading homogeneity. The powder packing density and spreading homogeneity together will improve the powder bed packing density and the density of formed samples. The change of powder recoating process conditions can influence the powder spreading quality and packing density, among which controlling reasonable recoating speed, choosing roller type scraper, and increasing the roughness of substrate will further improve the powder bed packing density. Finally, this paper presents the prospect of methods and techniques to further improve the powder bed density.