Research On Tool Wear And Its Inhibition In Diamond Cutting Of Ferrous Metals

Ferrous metals have been widely used in the fields of industry national economy in virtue of its excellent mechanical properties. However, a great many high precision and complex parts made of ferrous metals have been machined by conventional processes, i.e. grinding, lapping and polishing, it’s hard to guarantee the demands for machining cycle, machining cost and machining accuracy. In this case, there is an urgent need for high efficiency and ultraprecision micro-cutting way of turning instead of grinding, in order to improve the machining efficiency and machining accuracy. Although natural single crystal diamond is recognized as ultraprecision cutting tool material used in the world, it can not be used in the fabrication of ferrous metals in conventional conditions due to the high wear rate of diamond tool. Consequently, investigating on the tool wear and its inhibition in diamond cutting of ferrous metals has great significance for expanding the application areas of diamond ultraprecision machining.Research on tool wear mechanisms of diamond is the foundation to realize the ultraprecision machining of ferrous metals. Currently, the generally accepted thermochemical wear mechanism ignored the influence of friction behavior on tool wear under the effect of mechanical force in the actual machining process. Therefore, this work analysed the main influence factors of diamond tool wear under the action of thermal-mechanical coupling based on the tribochemistry theory. Subsequently, the interfacial tribochemistry reaction types and conditions were obtained by thermal erosion tests between the ferrous metals and diamond. Moreover, the influence laws of mechanical force, frictional speed, workpiece material component and interfacial temperature were systematically investigated by the frictional wear tests. It provided a theoretical basis for exploring new inhibition technologies of tool wear.For the sake of further investigating on the frictional wear behavior between ferrous metals and diamond, the interfacial friction process was analyzed by the finite element simulation technology, and the influence of the frictional load and frictional speed on the distributions of temperature and stress was obtained. Based on the results of frictional wear tests, the mathematic prediction model of tribochemistry wear of diamond tool was established. In addition, single point diamond cutting tests of typical ferrous metals were performed for verifying the experimental results of the erosion and friction tests and the correction of the proposed tool wear model.On the basis of the aforementioned research, the diamond wear processes of graphitization, diffusion and oxidation were individually researched. The catalytic effect of transition metals on the transformation of diamond crystal structure to graphite was analyzed by the molecular dynamics simulation technique. Subsequently, the mathematic prediction model of the carbon atoms of diamond tool diffusing into the iron lattice was established, and the diffusion process of diamond cutting of ferrous metal are studied by numerical simulation and related experimental verification. Moreover, the process of diamond oxidation wear was analyzed by thermodynamic theory and experimental verification for a better understanding of the oxidation wear mechanism of diamond.Combining the analysis of the influence of mechanical force and temperature on tool wear, this work performed the simulation and experimental investigation of tool wear inhibition based on ultrasonic vibration effect, and the mechanism of reducing tool wear in ultrasonic vibration cutting was analyzed. In addition, experimental study on cutting of typical die steels with single crystal diamond tool was finished, and the influence of processing parameters on tool wear and surface quality was obtained. Moreover, the simulation and experimental investigation of tool wear inhibition was performed based on cryogenic minimal quantity lubrication technique, and the influence of different cooling and lubricating types and different cutting fluids on tool wear in cutting of die steels was achieved. The experimental results showed the cryogenic minimal quantity lubrication and nanofluids had obvious advantages in reducing tool wear. Consequently, this work proposed the combined machining technology of ultrasonic vibration cutting and cryogenic nanofluid minimal quantity lubrication cutting for ensuring the diamond tool wear. The results revealed this combined machining technology could remarkably improve the diamond tool life.