Substrate design to minimize residual stresses in Directed Energy Deposition AM processes

Abstract

This paper proposes a strategy to optimize the design of the substrate structures used in Additive Manufacturing (AM) by Directed Energy Deposition (DED) to minimize the residual stresses induced by this fabrication process. To this end, several numerical analyses were performed to analyse different substrate designs in order: (i) to reduce the sensitivity to the initial non-steady stage when the first layers of material are deposited, (ii) to optimize the heat flux through the substrate to reduce the Maximum Temperature Gradients (MTG) and, (iii) to modify the substrate stiffness and its mechanical constraining to the thermal deformations during the building process and the cooling phase. To ensure the reliability of the numerical simulations, an in-house software is calibrated to allow for an accurate analysis of DED. Thus, an experimental setting is undergone to feed the numerical model with suitable values of both material and process parameters through temperature and displacement measurements and numerical fitting. Once calibrated, the software is used to evaluate the performance of several substrate designs to mitigate the residual stresses induced by the DED process. A thin-walled rectangular part selected as industrial demonstrator showed a significant reduction (up to 62%) of the maximum tensile stresses.