A precision blade mechanism for powder recoating in Selective Laser Melting

Abstract

Selective Laser Melting (SLM) is an industrially viable means of additively manufacturing metal components with complex geometries from a wide variety of alloys. In this process, a metal powder is spread onto a build surface in a thin layer, and then the powder is selectively melted to form a cross-sectional slice of the part. This process is repeated until the part is complete. The packing density and uniformity of the powder layer are key to creating robust SLM parts. In commercial SLM equipment, the layer is spread using a moving blade or roller mechanism (the "recoater"). There is still opportunity to optimize the process and understand how powder mechanics influence the layer quality. This thesis focuses on experimental and computational methods to study powder recoating in SLM. An instrumented recoater was built with the capability to measure forces and vary important recoating parameters, such as recoating velocity, blade height and blade geometry. The instrumented recoater was then manufactured, assembled, tested and incorporated into a custom built SLM testbed at MIT. The recoater demonstrated the ability to vary the blade height with a 70 pm stroke and measure force in the milinewton range. Furthermore, angle of repose measurements were performed on powders of various size distributions and used to calibrate a model (developed by collaborators), which demonstrates the influence of cohesion on these powders. In addition, preliminary single-particle adhesion tests were performed. Together, these capabilities allow the rational development of powder spreading parameters to achieve uniform layers in SLM.