A review of tool-chip contact length models in machining and future direction for improvement

Tool-chip contact length can be a critical parameter in machining as it provides the path for heat flow from the secondary deformation zone into the tool. This is particularly critical in dry or high-speed machining, where elevated temperatures can activate wear mechanisms and hence reduce tool life. A number of analytical, dimensional analyses, empirical and statistical models have been used to predict contact length. However, more research is required to significantly raise the model accuracy in quantitative prediction and to elucidate the mechanisms that control contact length. In this study, cutting tests were performed at cutting speeds ranging from conventional to high cutting speed, and tool-chip contact length, chip thickness, sticking and sliding contact phenomena and cutting forces were characterised. Twenty-two contact length models reported in the literature were evaluated and benchmarked to experimental data. While dimensional analysis-based models have an improved quantitative predictive capability, they do not provide comprehensive insight into contact phenomenon. To this end, this work builds upon Tay et al.'s contact length model that has been benchmarked as promising in the literature. Parameters that influence the contact area, in particular, tool-chip sticking phenomenon, were characterised. Suggestions for improving contact length modelling are proposed.