Warpage Reduction in Additively Manufactured Parts Based on Thermomechanical Modeling and a Novel Simulation Strategy for Laser Scanning

The reduction of part distortion and the associated minimization of residual stresses is still a major challenge in Selective Laser Melting (SLM). Modeling of the coupled thermomechanical system in the moving laser frame is analyzed with resect time and length scales in view of the laser process design and the need to consider thermal and mechanical couplings for constitutive laws and industrial manufacturing oriented Finite Element Method (FEM) simulations by means of the eigenstrain method. Based on reviewed research, the influence of the laser scanning strategy on part distortion is investigated. The eigenstrain method is used to explain the anisotropic distortion behavior with respect to the direction of the laser scan path, the absolute path lengths and geometrical boundaries. The findings from the technical-physical analyses are utilized to develop a novel alternative approach for minimizing warpage. An averaged surface displacement is obtained from purely mechanical static field simulations of the process based on the FEM. To simplify this still computationally expensive approach, a new calculation method of the mean minimum path length on a cross section is introduced herein. Accordingly, an approach for a proportional adjustment of the laser paths hatch angle is developed and evaluated. Finally, the results are compared in terms of efficiency and precision by application to a standardized comb-shaped cantilever beam specimen and to a console. In addition, stress strain curves of specimens manufactured by variants of the developed scanning method prove significant influences on constitutive properties of the used stainless steel.