ADDITIVE MANUFACTURING AND RESIDUAL STRESSES

The paper discusses an important issue in metal Additive Manufacturing (AM); the residual stresses that are generated during AM. We investigate this phenomenon using the Finite Element Analysis software, ABAQUS. We worked on a solid-state AM process, which is very similar to the stir friction welding. We developed several models of varying complexity, and getting closer and closer to the real model. The first model involved adding a hot layer on top of a layer that is at room temperature and allowing the top layer to cool to room temperature, and computing the curvature of the layers and the substrate resulting from the cooling. The results were compared very well to those available in the literature. An issue with these preliminary models is that the temperature gradient between the two layer is quite high as compared to the reality, wherein the top layer is deposited when the bottom layer is at a high temperature. Next, we developed a model where we simulated the hot material that was being deposited. We have also implemented the heat transfer due to radiative and convective cooling along with two different boundary conditions on the substrate: (1) totally free and (2) fixed. We found out that the substrate boundary conditions play an important role in the residual stresses and the overall deformation of the part. When we fix the substrate, the printed part reaches very high stresses and can reach the breaking point. When we let the substrate free, the substrate gets distorted, but the residual stresses inside the part are lower.