Formation mechanisms of lack of fusion and keyhole-induced pore defects in laser powder bed fusion process: A numerical study

The presence of manufacturing defects is one of the major causes of limited applications of laser powder bed fusion (LPBF) technology in fabricating engineering metallic parts. This paper presents a three-dimensional numerical modelling approach to study the pore defects formation mechanisms during the full LPBF process. The discrete element method and finite volume method were utilized to simulate the powder bed generation and thermo-fluid flowing process within the molten pool, respectively. A ray-tracing heat source model was intro-duced to account for the multiple reflection behavior of laser beam inside the keyhole. The formations of lack-of -fusion pore defects and keyhole-induced pore defects under different operating conditions were numerically reproduced. The dynamic processes and the underlying formation mechanisms of the pore defects were eluci-dated. The simulation results may provide guidelines on defects prevention in the LPBF fabrication.