Tool-chip thermal conductance coefficient and heat flux in machining: Theory, model and experiment

This study proposes a technique for determining a tool-chip thermal conductance coefficient and heat flux in machining. The technique is based on solving an inverse heat transfer problem (IHTP). Because the IHTP is ill-posed, a priori information is required for its effective solution. To derive this information, substantial qualitative and quantitative analysis of a mixed boundary value problem for the heat equation and an illustrative test case for IHTP are provided. It has been established that the averaged interfacial chip temperature is needed for an effective IHTP solution. Thermal imaging combined with a special experimental setup was used to determine chip temperature. It was also found that a function describing the heat flux time dependency belongs to a set of decreasing functions. Tool-chip thermal conductance coefficients were obtained for high-speed steel and cemented carbide tooling. On the microscale, this data was interpreted in terms of a conforming rough surface contact conductance model, where tool wear was found to govern variations in the thermal conductance coefficient.