Simulation of powder-based additive manufacturing and post-processing operations

Discussed first is a new Dynamic Kinetic Monte Carlo (KMC) method for predicting grain structures in additively manufactured metals fabricated by laser-based powder bed fusion techniques. The distinguishing technical feature in the Dynamic KMC method is that, unlike existing KMC methods, it updates both the melt pool (MP) and heat affected zone (HAZ) boundaries at every frame of time within the underlying Potts model during grain nucleation and growth. The model thus captures evolution of microstructure due to both intralayer and interlayer heat accumulation during the additive build process. Results are demonstrated for a 6-layer, thin-walled, Inconel 625 structure. Following introduction of the Dynamic KMC microstructure prediction tool, the importance of capturing microstructure and residual stress in additively manufactured metal parts is demonstrated for three post-processing operations, including laser shock peening, laser impact welding, and machining. In the laser shock peening simulations, the inhomogeneous and anisotropic material response due to the Inconel 625 microstructure reveals asymmetric distributions of the resulting residual stress field. In the laser impact welding of aluminum 1100 and stainless steel 316L, it is shown that the microstructure influences the degree of material jetting as well as the peak temperatures observed. In the high-speed end milling of an Inconel 625 directed energy deposition (DED) part, significant influence of the inherent DED residual stress is observed on the machining-induced distortion, and this influence is seen to vary greatly with the machining strategy.