Numerical verification of an Octree mesh coarsening strategy for simulating additive manufacturing processes

Thermo-mechanical finite element modeling of additive manufacturing processes, such as Directed Energy Deposition and Laser Powder Bed Fusion, has been widely applied for the prediction and mitigation of part distortion. However, as the size of modeled geometries gets larger, the number of nodes and elements required in the finite element mesh increases significantly. Because runtime will increase as more nodes are added, it is not practical to conduct full simulations of large builds using standard static meshes. Advanced meshing strategy is required to reduce the run time and to retain the accuracy of the prediction. In this work, a mesh coarsening strategy is evaluated for predicting temperature, distortion, and residual stress in additive manufacturing, aiming to achieve feasible run times with reasonable accuracy on large builds. Directed Energy Deposition of thin wall geometries built from Inconel (R) 625 and Ti6Al4V is used as a reference and models with 2 levels of Octree mesh coarsening are investigated. The thermal history, in situ distortion, residual stress, and run times are compared with previously experimentally validated static mesh results. Two levels of mesh coarsening is found to be the most effective case for both materials reducing the computational time by 75% while reporting less than 2.5% error for the peak distortion and negligible error for the thermal history difference as compared to the static mesh. Keeping two fine layers of elements underneath the heat source is found to be the most efficient in terms of prediction accuracy and run time.