P. Michaleris, E. Denlinger, G. Adams, E. Pierson
Keywords: FEA, distortion, stress, LPBF, DED
Summary:During additive manufacturing (AM) processing, plastic-deformation, metallurgical transformations, and thermal expansion/contraction cycles cause a buildup of residual stress which can lead to a loss of dimensional accuracy, cracking, support failure, recoater jams, and/or fixturing failures. To avoid these costly failures, thermomechanical FEA is typically integrated into the design and build-prep workflow to predict and provide insight into these issues before printing. However, as the AM industry continues to move toward printing increasingly complex geometries (e.g. heat exchangers) the level of geometric detail in these parts places them beyond what can be meshed, let alone solved, using existing AM thermomechanical modeling approaches. Here a novel approach to modeling AM temperatures, stresses, and distortions is presented. A periodic adaptive meshing architecture capable of generating multi-million node FEA meshes in seconds, is combined with a highly parallelized and vectorized code to allow for fast simulation of problems containing over 100 million equations. The modeling approach is demonstrated on two real-world use cases. The first investigates distortion prediction on a large heat exchanger manufactured using Laser Powder-Bed Fusion. It is shown that even at this level of complexity, simulation times are around 1 day long on a desktop computer and the predicted distortions match with the experimental results. The second use case investigates residual stress in an impeller manufactured using Directed Energy Deposition. A previous attempt to manufacture the impeller, which experienced cracking at the interface of the vanes and the build plate, is considered as the baseline in this study. Three additional cases are simulated to compare the change in residual stress resulting from adding fillets at the interface of the deposition and the build plate, adding an intermediate heat-treatment during the manufacturing process, and relaxing the fixturing constraints, respectively. The results of each case are compared and thoughts on possible fracture criteria are discussed.