Research On Diamond Tool Wear And Its Ultrasonic Vibration Suppression In Ultraprecision Cutting Of Titanium Alloys

Due to the characteristics of small density, high strength, good corrosion resistance, excellent heat resistance and low temperature and non-magnetic, titanium alloys have been widely used in the field of aerospace. With the development of aerospace industry in our country, the demands of machining accuracy and surface quality of some key parts of spacecrafts are becoming higher and higher, so the application demand of ultraprecision cutting methods increses more and more. Due to its excellent properties, natural single crystal diamond is considered to be the most ideal tool material for ultraprecision cutting. However, due to the low thermal conductivity, low elastic modulus and high chemical activity of titanium alloys, the wear of diamond tool is serious in cutting titanium alloys, resulting in that machining precision and surface quality are difficult to grarantee in machining process, and becoming the technological bottlenecks of practical application of ultraprecision cutting technology in cutting titamium alloys.In this paper, according to the problem of serious diamond tool wear in ultraprecision cutting of titanium alloys, the process method and device for the surppress of diamond tool wear were studied. According to the analysis of wear mechanism and wear characteristics of diamond tool in ultraprecision cutting titanium alloys, the technical ways of the inhibition for diamond tool wear were explored in order to provides the basis of improving the machining accuracy and surface quality of titanium alloys.The research on wear mechanism of single crystal diamond tool is an important basis for improving the durability of the cutting tool and realizing the ultra precision cutting of titanium alloys. Firstly, based on the thermodynamics theory of chemical reaction, the essential reasons of the diffusion wear and oxidation wear of diamond tool in ultraprecison cutting titanium alloys were analyzed in this paper. Secondly, according to the thermal interface corrosion experiments between single crystal diamond particles and titanium alloys sheets, the initial temperature of graphite transition, diffusion law and chemical reaction types and conditions of oxidation wear of single crystal diamond were obtained under catalysis of Ti. The above researches provide the theoretical basis for the exploration of the diamond tool wear in ultraprecision cutting titanium alloys.In order to research the wear characteristics and wear laws of single crystal diamond tool in ultraprecision cutting titanium alloys and provide experimental basis for exploring the effective inhibition techniques of tool wear, the wear experiments of diamond tool in ultraprecision cutting titanium alloys using common cutting method were carried out. Combining with thermodynamic analysis results of tool wear mechanism, the forming mechanisms of the wear patterns and wear characteristics of the diamond tool were researched on the basis of the observations of the micro morphologies of diamond tools by using scanning electron microscope(SEM). According to single factor experiments, the effects of the cutting parameter, nose radius of diamond tool and cooling and lubricating condition on the tool wear and machined surface roughness were researched. The results show that the problem of serious tool wear in ultraprecision cutting of titanium alloy could not be solved by using conventional cutting method.On the basis of the above studies, the development of ultrasonic vibration cutting device was carried out in this paper to provide the basis for the subsequent experimental researches on the wear inhibition of diamond tools. Based on the design theory of one dimensional longitudinal ultrasonic vibration transducer and finite element method, an innovative elliptical ultrasonic vibration cutting(EUVC) device was developed. The ultrasonic elliptical vibration cutting device adopts 1st resonant mode of longitudinal vibration and 3rd resonant mode of bending vibration and single-node fixed support, and has the characteristic of essy exciting. Harmonic response analysis and transient analysis of the elliptical ultrasonic vibration cutting device afer mode degeneracy were carried out and preliminarily verified the rationality of the structure of the elliptical ultrasonic vibration cutting device. On the basis of the impedance measurement experiments and amplitude output test experiments for the assembly of elliptical ultrasonic vibration cutting device, comparison experiments of ordinary cutting and elliptical ultrasonic vibration cutting using single crystal diamond cutting tools were carried out and verified the rationality of the design of the elliptical ultrasonic vibration cutting device.According to the contrast experiments of ordinary cutting, one-dimensional ultrasonic vibration cutting and elliptical ultrasonic vibration cutting in ways of tool wear and surface quality, the advantage of the ultrasonic elliptic vibration cutting technology in improving diamond tool life was verified. At last, according to cutting experiments, the effects of cutting parameters and elliptical ultrasonic vibration parameters on the wear of diamond tools, cutting force and surface roughness were researched. Research results would provide the basises for the optimization of ultraprecision cutting process parameters in elliptical ultrasonic vibration cutting of titanium alloys.