Influences of powder morphology and spreading parameters on the powder bed topography uniformity in powder bed fusion metal additive manufacturing

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Powder spreading is a crucial step in the powder bed fusion process, which controls the quality of powder bed and consequently affects the quality of printed parts. To date, however, powder spreadability has received very little attention and substantial fundamental work is still needed, largely because of the lack of experimental studies. Therefore, the focus of the present study addresses the influences of powder morphology, spreading velocity and layer thickness on the powder bed topography uniformity. The experiments were conducted with a laser powder bed fusion printer and the powder layers were spread systematically and comprehensively assessed. In summary, it was found that particle sphericity and surface texture dictates the degree of impact that the spreader velocity and the layer thickness exert on the quality of powder bed topography in spread layers. The spreader velocity has substantial influence on powder bed uniformity, such that better uniformity is achieved with low spreading velocities, ≤ 80 mm/s. Powders with a wide particle distribution and containing large number of fine particles (< 25 µm) enabled formation of uniform and dense powder beds, however such powders were found to be more affected by segregation. In addition to these observed effects, for the first time, the major process related challenges to powder spreadability and powder bed quality are reported in this study. • Powder flowability alone does not ensure the formation of powder layers of uniform quality. • Powder bed topography is influenced by the powder morphology, spreading conditions and the particles net interaction. • Powder bed topography uniformity is maximised as particle sphericity and smoothness increases. • Particle segregation is highly influenced by particle size distribution, spreading velocity and depth of irradiated material.