Real-time evaluation of tool flank wear by in-process contact resistance measurement in face milling

This paper reports in-process detection of tool wear by using tool-work thermo-electromotive force (E.M.F.) as a sensor signal in face milling. In the case of using a single cutting edge, E.M.F. at the beginning of cut increased slowly corresponding to the width of tool flank wear. We assume this phenomenon is due to variations in electric resistance by increase of the contact area between the workpiece and the tool, so electric current between tool and workpiece was also detected. The variations of contact electric resistance calculated from both the E.M.F. and the electric current reveal that the electric resistance decreases as the tool flank wear progresses because contact areas between tool and workpiece increase. We developed a measurement system of variations of the contact resistance during face milling process. By monitoring the contact resistance using this system, the real-time detection of the width of tool flank wear can be achieved stably during intermittent cutting operations.