Structural design and optimization of a turning tool embedded with thin-film strain sensors for in-process cutting force measurement

A tool system integrated with machining and measurement is constructed by using thin film strain sensors and tool integration technology, which provides a new research method for studying the machining mechanism and automatic monitoring of the machining process. In this paper, three kinds—elastic sleeve type, fast insert type, and insert type—of tool cutting force measurement systems of the turning tool embedded with thin-film micro-sensors are designed. High strain sensitivity can be obtained through setting the elastic region of the tool bar on the premise of meeting the tool strength and stiffness. The system can realize integration between the thin-film strain sensor and tool bar quickly and efficiently. It is simplified as a cantilever beam structure for analysis after setting the shape of the sensor elastic substrate as a rectangle. The expression between strain and deflection of the elastic substrate is established when the free end is subjected to tangential force and bending moment, and the influence of the substrate’s structural parameters on the deflection is analyzed. In order to further improve the strain effect, six kinds of other shapes of the substrate structure are optimized, deducing the expression between the structure parameters and deflection; the corresponding substrate structure atlas is established, comparing and analyzing the deflection of the rectangular structure substrate. Five kinds of metal substrate materials are selected. In the functional film system of the thin-film strain sensor, the scheme of aluminum oxide and titanium nitride as the transition layer, silicon nitride as the insulating layer, and Ni–Cr alloy as the resistance grid layer is adopted. The research results show that this scheme can improve the adhesion between the insulating layer and the substrate, improve the resistance sensitivity coefficient of the sensor, and meet the application requirements of the cutting force measurement system.