DISCRETE-ELEMENT SIMULATION OF POWDER SPREADING PROCESS IN BINDER JETTING, AND THE EFFECTS OF POWDER SIZE

摘要

Binder Jetting has gained particular interest amongst Additive Manufacturing (AM) techniques because of its wide range of applications, broader feasible material systems, and absence of rapid melting-solidification issues present in other AM processes. Understanding and optimizing printing parameters during the powder spreading process is essential to improve the quality of the final part. In this study, a Discrete Element Method (DEM) simulation is employed to evaluate the powder packing density, flowability, and porosity during powder spreading process utilizing three different powder groups. Two groups are formed with monoidal size distributions (75-84 μm and 100-109 μm, and the third one consisting of a bimodal distribution (50 μm +100 μm). A thorough investigation into the effects of powder size distribution during the powder spreading step in a binder jetting process is conducted using ceramic foundry sand. It was observed that coarser particles result in higher flowability ( 62% decrease in repose angle) than finer ones due to the cohesion effect present in the latter. A bimodal size distribution yields the highest packing density (8% increase) and lowest porosity (～12% reduction) in the powder bed. as the finer particles fill in the voids created between the coarser ones. Findings from this study are directly applicable to binder-jetting AM process, and also offer new insights for AM powder manufacturers.