Thermo-mechanical process simulation based parameter study on PBF-LB/M scan patterns

Laser beam powder bed fusion for metals (PBF-LB/M) is an additive manufacturing (AM) process in which a laser selectively melts layers of metal powder to produce complex parts. Residual stresses form during the process due to high thermal gradients and rapid solidification, influencing part distortion, cracking, and mechanical performance. Therefore, understanding and predicting residual stress distribution is essential for improving process reliability and quality. Scan strategies, which determine the laser path during the build process, strongly affect residual stresses. However no reported literature recognized has managed to establish a fundamental understanding of residual stress formation, largely due to a lack of isolation with regard to the parameters. This thesis aims to address this issue by conducting a parameter study to independently investigate the influence of scan vector length and hatch distance with respect to residual stresses in a single layer. To perform the parameter study, a weakly coupled thermo-mechanical process simulation (TMPS) framework is set up. The TMPS consists of a transient thermal simulation coupled with a quasi-static mechanical simulation to predict residual stress formation. The thermal simulation accounts for phase change and considers two material states to distinguish the powder property from the solid and liquid properties. The mechanical simulation makes use of the element birth method (EBM) in order to implement the material addition during the scan process. As reported in literature, the longitudinal stresses are larger than the transversal stresses. Whereas residual stresses are found to be independent of scan vector length for scan vectors longer than 1 mm. Furthermore, it is found that a large hatch distance yields increased residual stresses at the contact line between two adjacent scan vectors.