Formation mechanisms and mitigation strategies of internal void defects during laser powder bed fusion of thin walls

Laser powder bed fusion (LPBF) exhibits distinct internal void defects when fabricating thin-walled structures, differing significantly from bulk component printing. However, the underlying mechanisms governing the spatiotemporal variations of these internal voids remain unclear. This study investigated the formation of internal voids through both experimental analysis and multi-physics modelling. The effects of scanning strategies and laser energy densities on the evolution of keyhole-induced pores and lack of fusion defects were systematically examined. Notably, a pronounced clustering of pores near the sidewalls was identified, attributed to repeated laser repositioning under discrete scanning strategies. Moreover, mitigation strategies were proposed to suppress the internal void defects, and LPBF of thin walls with high relative densities of 99.99% were successfully achieved.