Application of a new thick zone model to the cutting mechanics during end-milling

In this paper, a modified Oxley׳s predictive machining theory was utilized to analyze the mechanics of cutting in end milling using helical end mill tools. The milling tool is modeled along its axis as discrete segments. Each segment of the tool is treated as a single point cutter performing oblique cutting with an instantaneous uncut chip thickness determined by angular position and tool run-out. Subsequently, the cutting force and thrust force are calculated based on the instantaneous chip load. The total forces at a given angular position are obtained by summing up forces contributed by every cutting edge segment engaged into cutting. A modified Oxley׳s predictive machining theory was utilized as the foundation to obtain the desired milling force components through the work hardening and temperature dependent flow stress. First of all, Oxley׳s approach was extended by substituting Johnson-Cook constitutive equation by the velocity-modified-temperature dependent power law in order to generalize the applicability of the model for a wider range of work materials. Then, the equidistance thick primary shear zone model has been revised by considering the non-equidistant primary shear zone configuration as a framework to propose a more realistic nonlinear shear strain rate distribution. Finally, several cutting tests have been performed on AISI1045, Al7075 and Ti6Al4V and the predicted cutting forces using the proposed model have been compared with the experimental ones to validate the extended Oxley׳s model.