The Role of Powder Dynamics in Metal Additive Manufacturing
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Many additive manufacturing processes rely on metal powder as feedstock material. The powder dynamics can critically influence the resulting part quality. For example, fine metal powders exhibit high cohesive forces that can lead to particle agglomeration which deteriorates the spreadability and thus the powder bed quality. But even a perfect powder bed is disturbed e.g., by the melt pool and gas dynamics in powder bed fusion (PBF) or by the binder droplet impact in binder jetting (BJ). This contribution focuses on the the authors' ongoing work on the modeling of powder dynamics in powder bed-based additive manufacturing processes. First, a smoothed particle hydrodynamics (SPH) framework is presented to model coupled microfluid-powder dynamics problems with thermo-capillary flow and reversible phase transitions. By considering the interaction of a liquid and a gas phase with mobile powder particles the model allows to study important powder redistribution effects in AM processes. Melt pool simulations show a significant rearrangement of the powder bed in front of the laser beam as well as an ejection of partially molten powder particles from the melt pool due to evaporation-induced recoil pressure. In binder jetting powder particles are displaced or even ejected from the powder bed by the impact momentum of binder droplets.