Numerical Simulation of Residual Stresses and Deformations in Laser Beam Melting

Laser Beam Melting (LBM) is an additive manufacturing technology. In this process, metal powders are selectively molten by laser beam as individual weld beads in a layer-wise manner. Depending on the material-specific thermal conductivity, cooling rates in LBM reach speeds up to 3.5 x 106 K/s, leading to extremely high temperature gradients resulting in microscopic elastic and plastic deformations. Again, these deformations lead to residual stresses and hardly controllable macroscopic part distortions or even component and process failures. Therefore, structure simulations of LBM are a useful tool to attain a better process understanding and to minimize trial and error approaches in setting up and optimizing process parameters like laser scanning strategies. Based on a description of the basic principles of the LBM process, this article comprises the main differences of LBM compared to conventional welding processes. On this basis, special requirements for LBM structure simulations are addressed. Following, first approaches in using the welding simulations software Simufact.welding are presented. The main challenge here is to represent a micro weld bead of only about the size of 0.25 x 0.10 mm², on the one hand, and macroscopic layer / part sizes of up to several hundred millimeters in x and y direction, on the other hand. The associated finite element mesh size and number of elements quickly face limitations of modern computing technology. In this context, a model with a base area of 1 x 2 mm² and three layers height was set up, which can be simulated within a few hours computing time. In addition, an evaluation of resulting stresses and deformations of additively manufactured parts in comparison to experimental results are presented within this article.