Whole-process cross-scale modelling of laser direct deposition with semi-resolved VOF-DEM coupling

Compared to casting and other traditional manufacturing techniques, metallic powder-based additive manufacturing is manifesting its superiority in many fields like aerospace engineering, bio-medical engineering due to its short product cycle and feasibility. Among them, laser direct deposition, which has higher degree of freedom, has been widely employed in manufacturing and repairing complicated components. However, during its process, cross-scale multi-physics phenomena and phase change simultaneously happen under the laser spot, with extremely high temperature and pressure gradient, which makes experiments per se incompetent in investigations. In previous simulation frameworks, powders are inserted as Lagrangian points without consideration of ambient fluid, particle-particle interactions and phase change. The proposed framework here introduces volume of fluid technique into the recently-developed kernel approximation-based semi-resolved CFD-DEM, leading to a new semi-resolved VOF-DEM (or semi-resolved CFD-DEM-VOF) method which takes both thermodynamics, solid particles, phase change and free surfaces into consideration. Therefore, for the first time, the developed semi-resolved VOF-DEM model realizes the simulation of real physics involved in direct laser deposition. In this framework, shielding gas and metal, either melted or solidified, are two phases in VOF, and the interface between them is reconstructed by iso-Advector. DEM represents the unmelted solid particle, and CFD cells herein can resolve the metal particles thanks to the kernel approximation. Hence, the collision, adhesion, melting and coalescence of metallic particles, formation and evolution of molten pool and tracks are all reproduced. It is believed that this semi-resolved VOF-DEM modeling framework can provide a paradigm for simulation of direct laser deposition, along with other fields where particle system evolves with phase change. Copyright © 2021 Chinese Journal of Theoretical and Applied Mechanics. All rights reserved.