Finite Element Modeling of Orthogonal Machining Process

Abstract

Machining processes are difficult to model for various reasons. Unlike metal forming processes, where almost the whole work-piece gets plastically deformed, in machining processes, the plastic deformation is localized near the cutting edge. Therefore, we need to analyze only a small region of the work-piece around the cutting edge (called the cutting zone). As a result, the selection of the domain dimensions and the appropriate boundary conditions becomes a difficult task. Further, even at a moderate cutting speed, the strain rates are quite high, almost of the order of 10⁴ per second. Further, the temperature rise is also quite large. As a result, the viscoplasticity and temperature-sofening effects become more important compared to strain-hardening. Therefore, the material properties associated with these two effects should be known for a range of strain rates and temperatures occurring in typical machining processes. These properties are not readily available. Additionally, to incorporate the temperature rise in the analysis, one needs to solve the heat transfer equation governing the temperature field in conjunction with the usual three equations governing the deformation field. For plastic deformation, these equations are coupled, and hence difficult to solve. We can decouple this problem as follows. We first estimate the average temperature in the cutting zone either experimentally or by simple analytical methods. Then we solve the governing equations of the deformation field by evaluating the material properties at the estimated average temperature of the cutting zone.