A mechanism-based optimization strategy with adaptive laser power for laser powder bed fusion

The presence of keyhole-induced porosity significantly limits the application of laser powder bed fusion (L-PBF) in the additive manufacturing industry. Typically, a trial-and-error approach is used to select the best printing strategies for material type, powder bed, and laser beam to optimize the manufacturing process. This paper proposes an optimization strategy that uses adaptive laser power based on key understanding of the physical mechanisms of keyhole fluctuations. We identify and analyze five stages of the keyhole pore formation process, including the "J"-like keyhole formation, keyhole closure, keyhole pore collapse, keyhole pore splitting, and keyhole pore motion. Our simulation results suggest that reducing the laser power at the onset of "J"-like keyhole formation is an appropriate optimization approach. We propose adaptive indices to quantify keyhole fluctuations and predict the onset of "J"-like keyhole formation, which facilitates the use of adaptive laser power for optimization. Two parametric studies are conducted to investigate the impact of the optimization criterion and laser power adjustment on keyhole instability. The results demonstrates that our optimization strategy can effectively stabilize the keyhole and reduce the occurrence of keyhole porosity.