An experimental and theoretical study of variable tool-chip interfacial friction and cyclic chip formation in machining with flat-faced and grooved tools

Cyclic chip formation characterized by curled chip formation and breaking is an intrinsic facet of turning operations. Attainment of a high degree of chip control improves machining performance as well as satisfies modern industrial requirements. Traditional machining theories have been mired under the assumptions of constant (or average) tool-chip interfacial friction and straight, continuous chip formation. Hence, an experimental-based study of cyclic chip formation in 2-D and 3-D machining with both flat-faced and grooved tools, including the effects of variable tool-chip interfacial friction was undertaken in this dissertation.; The effect of variation of work material properties due to heat-treatment was studied and the resultant cyclic forces and tool-chip contact variations were evaluated. The work materials were heat-treated to obtain varying hardnesses and microstructure. The effect of cutting tool material properties (as characterized by varying cutting tool thermal conductivity) on the cyclic chip formation process in 2-D machining with grooved tools was studied and established. The tool-chip contact length in grooved tools was characterized, defined and measured. The effect of the tool material properties on chip-form, cyclic forces and deformation within the chip was assessed. In both cases (variability of work material and tool material properties), the variable tool-chip interfacial friction was prevalent due to the cyclic nature of chip formation and tool geometry effects (including chip-groove features).; The dissertation then focused on practical turning operations with flat-faced tools, wherein the regime of side-curled chip formation was focused upon. The nonlinear effects of the tool noise radius led to wide variations of tool geometry all along the cutting edge, leading to variable friction. The variable tool-chip interfacial friction was characterized by measuring the variations in tool-chip contact length, chip thickness and chip deformation across the chip width. A new technique for measuring the tool-chip contact in turning with flat-faced tools was developed and used.; Finally, the complex 3-D cyclic chip formation process and tribological interactions when turning with grooved tools was studied. The tool-chip contact length and chip morphology were mapped for varying cutting conditions. The 3-D chip morphology is found to be strongly influenced by the combination of cutting conditions (resulting in varying transverse chip cross-sections), tool geometry (especially the boundary limits of the chip-groove shape) and the tool-chip interfacial friction. The material deformation at the tool-chip interface and the consequent elongation of grains in the bulk of the chip was observed to affect the chip morphology and the chip curling and breaking patterns.; The results from this dissertation throw new light on the strong influence of variable tool-chip interfacial friction and cyclic chip formation on the machining process. The importance of modeling tool-chip contact and 3-D chip curl in 3-D machining with grooved tools has been highlighted.