Improving surface quality using laser scanning and machining strategy combining powder bed fusion and machining processes

This paper focuses on an unconventional laser powder bed fusion (LPBF) technique in which the LPBF and machining processes were executed alternately to fabricate higher quality parts compared to those obtained using subtractive machining processes. The additional machining process modified the stress distribution inside the built part, resulting in the deformation of the surface morphology in the final part. The phenomenon resulting in the combined LPBF and machining-process-based fabrication was investigated, and the influence of the process parameters on the formation of surplus part and the deformation of machined surface was evaluated. In addition, a laser scanning and machining strategy were formulated to improve the surface quality of the built part. The surplus buildup at the edge of the fabricated part occurred owing to the difference in the thermal properties between the solidified part and the deposited metal powder. The principal factors affecting the formation of the surplus part were the laser-irradiated position at the first layer buildup and the energy density. Moreover, the formation of the surplus part was improved using the laser scan strategy, in which the laser-irradiated position was shifted inward. The peripheral face of the built part formed periodical steps, owing to the deformation induced by the change in the thermal distribution inside the built part. These steps could be reduced using a machining strategy combining the rough machining process with a finishing allowance and stepwise finishing process.