Residual stress prediction in machining of parts fabricated by directed energy deposition

Abstract

The residual stress exhibited in post-machined metallic components fabricated by directed energy deposition (DED) determines their final mechanical performance and reliability in mission-critical applications. This study develops a numerical model to predict the final surface residual stress after the orthogonal cutting of DED-produced IN718, which integrates two critical factors: DED-induced initial residual stress states and microstructure properties. Using the developed modeling procedure, the penetration depth of post-machining into the initial residual stress distribution can be effectively quantified, which aligns with residual stress measurements through X-ray diffraction. The developed model is further employed to quantify the cumulative effects of initial residual stress states and grain size on cutting forces and final surface residual stress profiles. The results suggest that, under the given orthogonal cutting conditions of DED parts, variations in the initial residual stress states of the chip formation region have negligible effects on cutting forces. However, magnitudes of surface compressive residual stress in the longitudinal direction reduce by 21.8 %-52.3 % as the initial residual stress states shift from compressive-dominant to tensile-dominant, and decrease by 23.8 %-54.0 % as the built-in grain size (d_{g_x}) increases from 10 μm to 100 μm. With a comprehensive understanding of post-machining DED processes using this numerical modeling procedure, post-treatment techniques can now be tailored to achieve surface residual stress profiles on DED-generated or other additively manufactured metallic components to meet various industrial requirements.