Laser polishing of 3D printed miniaturised titanium components

The aim of the research was to enhance the surface quality of 3D printed miniaturised titanium parts by employing laser polishing (LP). The specimens were produced using a novel 3D printing technology for metallic materials, developed by Digital Metal®, and comprising a two stage production process: a precision ink-jet layer by layer printing of ‘green’ parts in a metal powder bed, followed by a secondary sintering phase. Laser polishing was subsequently utilised to improve the surface integrity of the printed parts. A full factorial experimental design was conducted, consisting of 75 trials under atmospheric condition and involving variation in three LP process parameters, i.e. laser fluence (3 levels), pulse overlap along beam scanning direction (5 levels) and overlap in hatching/step-over direction (5 levels). The optimum processing window was identified at laser fluence of 7 J/cm2 and step-over overlap of 88-91% while the pulse overlap was kept at 95%. Polished surfaces exhibited oxidation and cracks, which were reduced with the reduction of cumulative laser energy, as a result from the overlap decrement in either direction. However, this also triggered lower heat absorption and insufficient melting of material that led to numerous pits/holes on the polished surfaces. Although surface re-melting/shallow melting was the dominant polishing regime observed within the optimised processing window, it is suggested to use an inert gas environment in order to avoid oxidation and surface cracks when LP of titanium.