Laser polishing of additive manufactured tool steel components using pulsed or continuous-wave lasers

Tool steel has been widely used for injection molding and die-casting applications, as well as functional components. Laser polishing could be very suitable for tool steel workpieces made by additive manufacturing (AM) techniques since these manufactured objects usually have poor surface quality that cannot meet the smooth surface requirements and tight geometric tolerances. However, related references on the applications of laser polishing on tool steel work pieces made by AM are sparse. Previous experimental and theoretical studies are also lacking in regard to changes in the microstructures, surface morphology, and surface energy after surface polishing. This study focuses on finding out the effects of laser polishing on tool steel parts prepared by one of the AM techniques—SLM (selective laser melting). Tool steel components were polished using pulsed or continuous-wave lasers under different process conditions in order to achieve superior surface quality. Distinct characterization approaches, i.e., SEM, EDX, water contact angle, and optical profiling, are developed, based on the experimental outcomes. The results show that the surface roughness of tool steel components by low-power (below 100 W) pulsed lasers and by high-power (above or equal to 100 W) continuous-wave lasers can be reduced from 12.0 to 4.7 μm, and from 12.0 to 0.7 μm respectively. The hardness of the laser polished samples was also characterized by the Vickers hardness test. The results indicated the surface hardness of the samples was enhanced by about 14.6%. This work has demonstrated the effectiveness of the proposed laser polishing approach to optimize the process parameters using different lasers from a high energy density to a low energy density, and to improve the surface roughness and hardness of additive manufactured tool steel components.