| Greater demands are being placed on the whole strength and abrasion resistance of cutting tool with the development of high-speed cutting technology, which has been the mainstream of modern machining technology. Superhard cutting tool, represented by PCD, is the main technology to realize high-speed cutting. However, domestic tool manufacturing technology can hardly catch up with foreign technology at present. Thus, to study tool manufacturing technology can provide theory and technology support for the domestic cutting tool Brazing and grinding are the two key procedures that determine the whole strength and abrasion resistance of cutting tool in the manufacturing process. High-frequency induction brazing and diamond wheel grinding are commonly used in the manufacturing process of PCD cutting tool. Above all, the technique and mechanism in high-frequency induction brazing and diamond wheel grinding of PCD cutting tool were systematically investigated in this dissertatioaFirstly, high-frequency induction brazing experiments between PCD compact and YG8 cemented carbide were carried out in order to investigate the influence of different process parameters on the quality of cutting tool. The results show that the shear strength of joint brazed with imported AgZnCuMnNi filler metal is higher than that with domestic AgZnCuCdNi filler metal, and cutting tool brazed with AgZnCuMnNi filler metal and QJ102 soldering flux has the best performance. It also indicates that different process parameters have great influence on the shear strength of brazed joints, and the details are as follows. The shear strength increases and reaches a maximum value when the brazing pressure is 3.91 IMPa, then it decreases with the enhancement of brazing pressure. The relationship between shear strength and brazed joint thickness can be represented accurately by polynomial. The shear strength increases with the enhancement of brazing temperature, and the brazing temperature should be controlled in the range of 670?690?. The microstructural investigation reveales that Ag (s.s), Cu (s.s), Cuo.64Zno.36 and a small amount of MnNi phase exist at the brazed joint, in which the dispersion of gray-black grain that containing Cu (s.s), Cu0.64Zn0.36 and MnNi phase plays an important role in enhancing the shear strength of PCD cutting tool. The analysis reveals that, the smaller the equal-area-circle grain diameter and bigger the roundness of the gray-black grain is, the stronger its dispersion strengthening effects. What's more, strengthening phase with smaller equal-area-circle grain diameter and bigger roundness can be obtained with appropriate holding time during brazing process. The thermal damage of PCD layer deteriorates with the increasing of holding time, and holding time of 15-20s is recommended in the brazing of PCD compact.Secondly, the influence of different treating technique on the quality of cutting tool in pre-welding treatment and post-weld treatment was investigated, and higher shear strength of cutting tool was obtained through proper treatment. The shear strength of cutting tool brazed with domestic AgZnCuCdNi filler metal increases by 2.5 times after the cutter body being pre-brazed with the same filler metal. The shear strength of brazed joint also increases through post-weld treatment. With the increasing of post-weld heat preservation temperature, the segregation of reinforcement elements, such as Cu, Mn, and Ni in AgZnCuMnNi filler metal reduces, and the strengthening phase distribution is more homogeneous in the brazed joint. The shear strength can be further improved within the appropriate time of post-weld heat preservation.On the contrary, the shear strength decreases if the time of post-weld heat preservation is too long because of the oxidation or evaporation of Zn element in the filler metal. The thermal damage of PCD layer deteriorates with the increasing of post-weld heat preservation time. After all, post-weld heat preservation temperature of 500? and post-weld heat preservation time of 1-3hare recommended in the brazing of PCD compact.Afterwards, the micro morphology of the ground PCD surfaces was analyzed through a series of grinding experiments in order to investigate the grinding removal mechanism. The removal forms of PCD in diamond wheel grinding are classified as brittle removal and non-brittle removal The brittle removal includes shock-brittle removal, micro-crack ing, intergranular cracking and transgranular cracking; shock-brittle removal which produces V-shaped gap near tool cutting edge, needs to be reduced during grinding; micro-crack ing, including cleavage micro-crack ing and brittle micro-cracking, happens under any grinding condition; intergranular cracking usually happens in the later stages of wet grinding or the early stages of dry grinding; and transgranular cracking happens when wear particles of diamond wheel are blunt, especially in the later stages of dry grinding. The non-brittle removal includes scoring effect and thermo-chemical removal; scoring effect happens only when the wear particles of diamond wheel are sharp; thermo-chemical removal happens when wear particles of diamond wheel are blunt, and appropriate thermo-chemical removal is helpful to obtain a smooth rear face and cutting edge; indirect evidence of thermo-chemical removal is gained through investigating the ground surface of PCD in dry grinding and wet grinding, respectively; a softened layer on the ground surface of PCD, which formed because of diamond oxidation, graphitization or converting into amorphous carbon, is confirmed directly through a group of grinding experiments.Finally, considering the grinding removal mechanism of PCD, the influence of different grinding parameters on rear face, cutting edge of tool, removal rate Qw, and grinding ratio G-ratio was investigated. The V-shaped gap formed because of shock-brittle removal on PCD cutting edge enlarges and cutting edge quality deteriorates in dry grinding condition, with higher wheel rotation speed, bigger contact force and bigger feed rate. Thermal damage zone formed because of thermo-chemical removal, which worsens mechanical performance of the cutting edge, will appear near the cutting edge of tool in dry grinding condition. In conclusion, in order to enhance removal rate Qw and get a cutting edge with appropriate mechanical performance in coarse grinding, the grinding condition should be selected as:vitrified bond diamond wheel, wet grinding, higher wheel rotation speed, bigger contact force and bigger feed rate. In order to get a cutting edge with the best mechanical performance in refined grinding, the grinding condition should be selected as:metal bond diamond wheel, wet grinding, medium wheel rotation speed, smaller contact force and smaller feed rate. |
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