Simulation of different laser interaction modes on melt flow and heat transfer behavior during laser powder bed fusion process of IN718 alloy

Among the numerous parameters of the laser powder bed fusion (LPBF) process, laser power, scanning speed, and laser spot diameter directly affect the melt pool size. In this work, a single-pass simulation of the LPBF process for IN718 alloy with different process parameters was carried out using computational fluid dynamics. Results show that laser spot diameter is the most important parameter affecting the depth-to-width ratio of the molten pool and the laser melting mode, followed by laser power, and finally scanning speed. An increase in laser spot diameter induces a transition in the laser melting mode from keyhole mode to conduction mode, passing through a transition mode. Heat transfer in the conduction mode is dominated by thermal conduction, whereas convection is the dominant heat transfer mechanism in the keyhole mode, with the transition mode in between. The flow field analysis shows that two vortices appear in the upper part of the melt pool cross-section in the conduction mode. This is significantly different from the keyhole mode, where vortices appear at the bottom of the melt pool. This difference in flow leads to differences in temperature distribution in the melt pool and therefore leads to different solidification microstructures, mainly in terms of equiaxed grain content. The findings of this study provide valuable insights for simpler and more practical process optimization in controlling solidification microstructures during the LPBF process.