Residual stress formation mechanisms in laser powder bed fusion : a numerical evaluation

Abstract

Additive manufacturing methods, such as the laser powder bed fusion, do not need any special tool or casting mold. This enables the fast realization of complex and individual geometries with integrated functions. However, the local heat input during the manufacturing process often leads to residual stresses and distortion. This in turn causes poor quality, scrap parts or can even terminate a job prematurely if the powder recoating mechanism collides with a distorted part during the process. This study investigates the generation mechanisms of residual stresses and distortion during laser powder bed fusion (LPBF) of stainless steel 316L in order to reduce these effects and thus contribute to improved process safety and efficiency. Therefore, numerical investigations with a finite element model on the scale of a few melt tracks and layers serve to develop a detailed understanding of the mechanisms during production. The work includes an investigation of the build plate temperature, the laser power and speed and the layer thickness. The results show a strong dependency on the build plate preheating and energy per unit length. A higher build plate temperature and a reduction of the energy per unit length both lead to lower residual stresses.