Surface roughness of Selective Laser Melted Ti-6Al-4V alloy components

A rational design of experiments was employed to evaluate the correlation between scan parameters and the resulting surface roughness of Selective Laser Melted Ti-6Al-4V components. There is a statistically significant difference in surface roughness values from specimens built with identical laser exposure parameters but located at different positions on the build platform. We hypothesise that this is a consequence of changing powder particle size distributions across the powder bed resulting from the combined actions of the recoater arm and gas flow. We further hypothesise that orientation of a part and the projected shape of the incident laser beam play a part in surface roughness variation at any given location. We found that during the powder re-coating process, fine particles tend to settle within a short distance from the re-coater starting position, accompanied by higher variability of local powder size distribution. Spatter material was found to be distributed across the powder bed by the gas flow. However, once at any given location the surface roughness of inclined surfaces is affected by the orientation of the surface to the centre of the build platform at which the laser beam originates. Each of these factors affects the surface roughness and has implications for the order in which parts are built in Selective Laser Melting.