Effect of DED process parameters on distortion and residual stress state of additively manufactured Ti-6Al-4V components during machining

One of the major challenges in high-deposition rate Directed Energy Deposition processes is the resultant residual stresses generated during material deposition, often leading to distortion and poor material characteristics. Important part families suitable for DED process in aerospace sector are thin-wall components, characterized by a large base surface area with rib-like strengthening structures. Here, the substrate plate can be designed to be a part of the final component. The integration of substrate plate into final component results in possible deformation due to residual stress release during machining. This paper therefore investigates the effect of various powder-based Laser Metal Deposition process parameters and strategies on the residual stress state of the additively manufactured Ti-6Al-4V components and the resulting stress release during machining process. The analysis has been carried out during the machining process by including in-process strain measurements of the substrate. The embraced layer removal method allows the determination of machining zone specific stress release mapping, based on an analytical and FEM-model. Hence, the initial residual stress state of the builds was calculated, which revealed that although the heat treatment resolved most of the residual stresses, also in heat treated parts residues were identified depending on the part clamping during the treatment. Furthermore, the study revealed that the significant residual stresses are present in the layers close to the substrate.