Particle-scale computational fluid dynamics study on surface morphology of GH4169 superalloy during multi-laser powder bed fusion with low energy density

Multi-laser powder bed fusion (ML_PBF) can improve the efficiency of traditional single-laser process, but the study on the potential defects causing by the introduction of multiple lasers is still open. In this paper, the particle-scale computational fluid dynamics (CFD) method is used to simulate the molten pool behavior of nickel-based superalloy in triple-laser PBF (TL_PBF) process with low energy density. The processing parameters on the flow and temperature fields and balling phenomenon in the TL_PBF process are mainly studied. The comparison between the simulation and the experimental results shows that the proposed model is reliable and can reproduce the balling phenomenon. The simulation results show that in the competition of three melt flows, the molten track of the main laser is randomly deviated to one of the molten tracks of the auxiliary lasers due to the uneven distribution of the powder bed. In the TL_PBF process, the larger the vertical offset is, the more serious the balling phenomenon is. When the parallel offset is larger than the sum of the radii of the two adjacent lasers, the larger the parallel offset is, the more the pits generated on the surface of the molten tracks are, leading to the extreme degradation of surface quality. It can be concluded that the synchronous TL_PBF with low energy density can obtain better surface quality when the parallel offset is about the sum of the radii of two adjacent lasers. This work can be used to guide multi-laser additive manufacturing to improve products with better surface quality.