Novel Simulation-Inspired Roller Spreading Strategies for Fine and Highly Cohesive Metal Powders
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When fine powders are to be used in powder bed metal additive manufacturing (AM), a roller is typically utilized for spreading. However, the cohesive nature of fine metal powder still presents challenges, resulting in low density and/or inconsistent layers under sub-standard spreading conditions. Here, through computational parameter studies with an integrated discrete element-finite element (DEM-FEM) framework, we explore roller-based strategies that are predicted to achieve highly cohesive powder layers. The exemplary feedstock is a Ti-6Al-4V 0-20 um powder, that is emulated using a self-similarity approach based on experimental calibration. The computational studies explore novel roller kinematics including counter-rotation as well as angular and transverse oscillation applied to standard rigid rollers as well as coated rollers with compliant or non-adhesive surfaces. The results indicate that most of these approaches allow to successfully spread highly cohesive powders with high packing fraction (between 50 layer uniformity provided that the angular/oscillatory, relative to the transverse velocity, as well as the surface friction of the roller are sufficiently high. Critically, these spreading approaches are shown to be very robust with respect to varying substrate conditions (simulated by means of a decrease in surface energy), which are likely to occur in LBPF or BJ, where substrate characteristics are the result of a complex multi-physics (i.e., powder melting or binder infiltration) process. In particular, the combination of the identified roller kinematics with compliant surface coatings, which are known to reduce the risk of tool damage and particle streaking in the layers, is recommended for future experimental investigation.
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