Resilience of laser powder bed fusion additive manufacturing to programmatically induced laser power anomalies

Abstract

Spatter interactions, varying power or scanner parameters, and uneven powder spreading in laser powder bed fusion (LPBF) can trigger the formation of lack-of-fusion or keyhole pores. In this paper, a strategy to mimic natural process anomalies is developed by varying the programmed laser power in a predefined region over sequential layers in order to understand the physics of pore formation and enable the systematic study of the sensitivity of LPBF processed Ti-6Al-4V to process anomalies. Results indicate that lack-of-fusion pores, caused by a decreased laser power input, and located at a depth equal to or less than the subsequent melt pool depth, are partially or fully healed by subsequent, nominally processed layers. Under conditions tested here, lack-of-fusion pores as deep as two layers (∼120 μm) below the surface are healed on subsequent layers. Conversely, local increases in laser power cause persistent keyhole pores, owing to the depth at which keyhole pores become entrapped into the melt—in this work, up to eight layers or 420 μm deep. These results show that while keyhole-induced porosity remains unaffected by the processing of subsequent layers, LPBF is resilient to a set of process anomalies, which would result in lack-of-fusion if not for subsequent remelting on layers above.