Interdependent evolution of deformation, fracture and recovering deposition during laser powder bed fusion

Abstract

Common defects such as fracture and deformation seriously affect the quality of laser powder bed fusion (PBF) components. This work focuses on the understanding and the in situ monitoring of structural fracture and deformation during laser PBF. The transient interactive processes of normal deposition, fracture, severer warping deformation and recovering deposition during laser PBF are explored via a series representative cantilever structures. The interdependent evolutions of the critical factors are revealed via a novel model with validations of critical experimental results. The inherent strain and the cohesive force methods are integrated and the coupled stress-deformation-fracture processes can be computed by the model. It was found that the parts experienced different stages of the four interdependent processes of deposition, stresses, deformation, and fracture, depending on the structural features, input energy densities, and intermediate layer-wise processes. A typical phenomenon was discovered that components can exhibit a near-flat top surface but a curved bottom delaminated from the substrate, which implied the misleading monitoring information from the printing plane. The revealed mechanisms and visualized processes provide a useful guidance for the determination of the optimum time window for in situ monitoring which can judge the underneath fracture and deformations from the surface features.