Numerical studies of melt pool and gas bubble dynamics in laser powder bed fusion process

The formation of pores can severely deteriorate the quality of parts fabricated by laser powder bed fusion (LPBF) technology. However, how the pores formation relates to melt pool and gas bubble dynamics is still not well understood. Here, through the modeling of the metal powder melting and the subsequent solidification under the conduction mode, it was found that the molten liquid near the gas-liquid interface flows centrifugally and vortices including a clockwise and an anticlockwise vortex are produced. The anticlockwise vortex dominates the molten liquid when laser turns off. The motion of gas bubbles originating from the powder bed voids follows the melt pool flow synchronously, where bubbles can coalesce, and some escape from the top and sides of the melt pool, and some remain as pores in the solidified part. For the positive value of surface tension gradient, the centripetal Marangoni convection drives the melt pool to flow in the dual clockwise circulation and obstructs the escaping orbit of bubbles, leading to higher porosity and surface humping. The present study enhances the further understanding of multi-physics in LPBF process.