Investigation on residual stress evolution in nickel-based alloy affected by multiple cutting operations

Machining-induced residual stresses in a part can significantly influence its performance and service time. It is common that the final surface of the part is produced after multiple cuts in the machining process. In multiple cuts, the previous cuts could often generate accumulated strain/stress and temperature on the part surface. These accumulated strain/stress and temperature will be brought to the subsequent cut or final cut and continuously affect the cutting forces, process temperatures, deformation zones, etc. in subsequent cut, and eventually affect the final residual stresses on the part. This paper reports on a joint experimental and numerical investigation to explore the influence of previous cuts on surface residual stresses with consideration of cutting parameters, cutting procedure, and tool geometries in multiple cut of Inconel 718 alloy. Coupled Eulerian and Lagrangian (CEL) formulation is used in a two/three-cuts numerical model. The loading cycles of the selected material nodes are characterised based on isotropic constitutive model (Johnson-Cook model) to analyse the underlying mechanism of residual stress evolution during cutting sequences. The results show that accumulated stress/strain induced by previous cuts lead to a more curled chip morphology, a slight decrease in cutting force and a slight increase in feed force in the subsequent cut. An increased magnitude and depth of compressive residual stresses in the finished workpiece are generated owing to the influence of previous cuts, and this is more obvious when the previous cut is implemented at a larger uncut chip thickness, using a more negative rake angle or a larger edge radius tool. The residual stress level might be controlled by optimizing the previous cuts to get the desired surface integrity.