Effect of cutting fluids on surface residual stress in machining of waspaloy

Cutting fluid is essential in machining aerospace alloys for extending tool life and enhancing surface quality. This study explains the formation mechanism of surface residual stress in wet machining of Waspaloy through a fully coupled thermal-mechanical finite element model. The model consists of a two-stage procedure, which uses the coupled Eulerian-Lagrangian technique to feature tool/workpiece/fluid interactions in the material removal process, followed by a Lagrangian-based technique to cool the machined workpiece down. The cutting fluid flow is determined by considering the velocity losses caused by the change in the fluid states. The model is experimentally validated by comparing the simulation results with the measured cutting forces and residual stress profiles. Residual stress measurements show that cutting fluid application reduces surface tensile residual stresses by 350 MPa and 128 MPa compared to dry cutting at the cutting speed of 86 m/min and the uncut chip thickness of 0.06 mm and 0.12 mm, respectively. The analyses of local contact stress and temperature distribution at the tool/fluid-workpiece interfaces quantitatively determine the thermal effect on the evolution of machined surface residual stress. In wet cutting, the cutting fluid contributes to the reduction of the surface tensile residual stress by creating a more uniform shrinkage of the workpiece material at the finished surface. This is due to lower thermal gradients caused by the forced heat convection on the machined surface with cutting fluid compared to dry cutting. These findings provide guidance for the application of cutting fluid to control the surface residual stress generation.