Analysis and a new model for the orthogonal machining process in the presence of edge-radiused (non-sharp) tools

Changes in cutting conditions used in practice over the past half a century have made the assumption of a perfectly sharp tool in Merchant's model questionable in many applications. In this thesis, the action of the extreme edge radius (or sharpness) of the tool on the orthogonal machining process is studied. The study starts with a comprehensive review of literature concerned with the approaches used to model cutting processes, followed by some specific attempts at understanding the effects of edge radius. It is realized that the task of modeling the action of the edge radius is complicated by the fact that it is difficult to accurately measure the edge radius. A new non-contact instrument based on white light interferometry is identified and used to accurately measure edge radius. Experiments are conducted to study the effect of changes in edge radius on cutting forces and energy. The geometry of the deformation process is studied by in situ observation of the cutting process. The edge radius imparted an apparent negative rake effect on the process, particularly at low ratios of uncut chip thickness to edge radius. A geometric model for an average rake angle that considers that negative rake effect is proposed and validated.;With the insights and understanding developed following these studies, a new geometric model for orthogonal cutting process is proposed. Based on this model, cutting conditions and material shear flow stress are related to the machining forces through a force balance on the work material. Experimental machining force data obtained during this research, and others previously published are analyzed. The analysis indicates that the material, as characterized by relating the shear flow stress to cutting experiments through this model, behaves consistently with a constant strain and strain rate sensitivity that does not depend on cutting conditions or the edge radius of the tool. The ploughing mechanism as well the phenomenon of size effect in metal cutting are reviewed in light of the results obtained from the new model. The experiments conducted, and the analysis tools developed, further our understanding of the cutting processes.