Novel strategy for quality improvement of up-facing inclined surfaces of LPBF parts by combining laser-induced shock waves and in situ laser remelting

Abstract

Insufficient surface quality is one of the common issues encountered in laser powder bed fusion (LPBF). In order to meet the industrial requirements, it is typically necessary to proceed to expensive and time-consuming post-processing. Improving surface quality during the building process would hence be very beneficial. However, in situ remelting (laser polishing) is possible only for horizontal up-facing surfaces. The quality of inclined surfaces remains limited to the as-built state, as after building they are covered with loose powder, excluding the possibility for in situ polishing. This work presents a novel strategy to improve the quality of up-facing inclined surfaces using a dual-laser setup with a continuous wave and a pulsed laser. This approach consists in two steps: after building, the powder is selectively removed from the inclined surfaces using shock waves generated by a nanosecond pulsed laser. These newly exposed surfaces can be subsequently remelted with a continuous wave laser or alternatively treated with a pulsed laser. This paper discusses various scanning strategies for selective powder removal, their efficiency and the surface quality of the treated parts. The initial results are promising and indicate that the surface texture of LPBF parts in maraging steel 300 can be significantly improved for surface inclinations up to 45°, provided a sufficient powder removal efficiency is reached. The latter was found to be dependent on the maximal depth and volume of the powder to be removed, but also on part geometry.