| Metal cutting is a kind of machining technology widely used in modern mechanical manufacturing industry. With the development of modern machining, high quality and high efficiency of metal cutting is put forward. Cutting force is one of the most important physical parameters, which directly influence cutting heat, machining quality, tool wear and tool life. However, in existing measuring instrument of cutting force, its application is greatly constrained by large volume and small space, as a result, it has important realistic significance to develop some new theories, methods and techniques of cutting force to monitor cutting process effectively.In this paper, a new measuring system based on the integration of cutting tool and thin film sensors was put forward, and the research object was the theory, simulation, design, preparation and test of thin film sensor embedded in cutting tool. It was focused on the relevant principle, film and substrate materials, design of resistance grid, preparation technology, detection and test methods. The main research contents of this paper were as follows:(1) Taking cylindrical turning for example, a cutting tool embedded thin film sensors were developed. The strain of thin film sensors and the relationship between applied load and the output voltage was studied. The results showed that there was the output voltage from thin film sensors had a good linear relationship with different loads.(2) While straight and bend external tool with thin film sensor were loaded with onedimension, the theoretical relationship between output voltage and the applied load was discussed. The results showed that the output voltage generated from thin film sensors was not only dependent on the applied load, but also on cutter holder size, thin-film material and the distance between sensors and the holder.(3) The solid model of external tool embedded thin film sensor was established. When the one-dimension(two-dimension or three-dimension) load was applied to external tool, the relationship between the output voltage and the load was studied. On the one hand, The results showed that the output voltage in Z direction was higher than in X or Y direction, which verified the idea that the cutting force in Z direction was main force in turning surface. On the other hand, the results showed that under various loading conditions the output voltage was consistent with the linear superposition principle.(4) This paper mainly explained the main influence of thin-film micro-sensor, selected the base and thin-film material of micro-sensor, determined thin-film sputtering technology, designed resistance grid structure and parameters according to manufacturing technology, discussed the horizontal effect of resistance grid on resistance variation and indicated the horizontal effect had a little effect on output voltage and could be ignored.(5) The thin film sensor was made, and thickness, directional resistance, micro hardness were tested, and structure and component of resistance grid were observed and analyzed using Scanning Electron Microscopy(SEM) and Energy Dispersive Spectrometer(EDS). The results showed that surface of film had dense structure, greater micro-hardness, stable alloy percentage and no defects such as porosity and crack, and the composition of thin film remained stable, which met the testing requirements of thin film sensors.(6) Thin film sensors were tested through applied load experiment, which were adhered on the holder of external tool and the cantilever beam. The results showed that there was a step-gradient increase for the strain with the increase of load, and a good linearity relationship between the output voltage and the load, which verified the effectiveness of the proposed theory and method.(7) The simulation value, the theoretical value and experimental value of output voltage were analyzed compared with test strain value under applied load. It could be found the simulation output voltage value was minimum, and it again proved that the main principle of measuring cutting force of thin film sensors was based on strain effects. Meanwhile, the difference value increased while applying load increased, and this showed that under higher load condition the output voltage from piezoresistive effect could not be ignored.(8) A complete force measurement system was composed of the embedded thin film sensors and signal processing system. The program module about signal amplification and A/D conversion was designed, and the strain and the output voltage of thin film sensor could be collected and analyzed. |
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