Abstract
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, fluctuation, 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 controlled by the recoil pressure.
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