Experimental Investigation of Residual Stress and its Impact on Machining in Hybrid Additive/Subtractive Manufacturing

Abstract

Hybrid manufacturing leverages the advantages of both additive manufacturing (AM) with machining to create parts that have complex geometries, tight tolerances, and good surface finish. However, the residual stresses induced by both processes present a challenge. These high stresses can induce significant distortion that can damage the part during the additive process or lead to unanticipated distortion during the machining process. The current work investigates the impact of the residual stresses generated during the AM process on the part distortion during the subsequent machining operation. Laser powder bed fusion is used to create stainless steel cylinders and their geometries are measured before and after machining their outer diameter, allowing the resulting distortion to be calculated. The measured distortion is counter to what is anticipated based on the trends exhibited in the residual stress in the cylinders measured before the machining operation using neutron diffraction. This suggests that the machining process imposes significant stresses that, in this case, counter act the remaining stresses from the AM process and/or trigger a material phase change.