Powder bed fusion additive manufacturing of ultra-high molecular weight polyethylene using a novel laser scanning strategy

Current processing routes (ram extrusion, compression molding, and sheet molding) for fabricating ultra-high molecular weight polyethylene (UHMWPE) greatly limit the geometries that can be processed. Due to these limitations, additive manufacturing (AM) of UHMWPE has long been a goal, as the ability to fabricate complex geometries from this polymer could open new applications not possible using these traditional processing routes. UHMWPE’s especially high wear properties also fill a gap in current AM materials. Powder bed fusion (PBF) processing of UHMWPE is challenging due to the high melt viscosity of UHMWPE and melt explosion, which occurs during melting of UHMWPE and causes powder particle expansion during scanning and leads to powder recoating failure. This work demonstrates a novel scan strategy for PBF of UHMWPE, in which layers are scanned using large (1.2 mm) hatch spacings. Scanning with a large hatch spacing reduces conduction between scanlines and distributes energy so as to encourage coalescence without melt explosion. UHMWPE powder is only partially melted during this scanning approach, which causes light coalescence between particles and avoids z-direction expansion that disrupts powder recoating. The lightly coalesced “green” parts are brittle and are densified by thermally post-processing them in the melt. Parts retain their shape during post-processing due to the high melt viscosity of UHMWPE. Using this combination of a novel scan strategy with large hatch spacing and a post-processing thermal treatment, a 3000 kDa UHMWPE was successfully printed, demonstrating the first reported multi-layer PBF of UHMWPE with complex geometries.