Modelling of keyhole dynamics and melt pool flow in laser powder bed fusion process

The keyhole dynamics in the laser powder bed fusion (LPBF) process and its relationship with driving forces of surface tension, Marangoni force and recoil pressure have not been well addressed and quantified. In this work, through the modelling of melt pool dynamics, the keyhole life cycle including formation and drilling, fluc-tuation, and disappearance is captured. The results show that pores are sourced from the powder bed voids, the ejected keyhole protrusion, and the liquid eroded gas bubbles at the end of the track. An anticlockwise vortex is generated at the rear of melt pool, and the molten liquid travels in a clockwise path ahead of the melt pool. The variation of the powder layer thickness breaks the force equilibrium on the keyhole rim and leads to the depth fluctuation. The compressed rear keyhole is dominated by the surface tension, and the expanded front rim is con -trolled by the recoil pressure. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study addresses and quantifies the dynamics of keyholes in the laser powder bed fusion (LPBF) process, specifically focusing on the driving forces of surface tension, Marangoni force, and recoil pressure. Through modeling the melt pool dynamics, the complete life cycle of keyholes, including formation, drilling, fluctuation, and disappearance, is captured. The study reveals that pores in the keyholes originate from powder bed voids, ejected keyhole protrusions, and gas bubbles eroded by the liquid at the end of the track. The presence of an anticlockwise vortex at the rear of the melt pool and the clockwise path of molten liquid ahead of the melt pool are observed. The fluctuation in the depth of keyholes is attributed to the variation in the powder layer thickness, which breaks the force equilibrium on the keyhole rim. The compressed rear keyhole is predominantly controlled by surface tension, while the expanded front rim is influenced by recoil pressure.