Mon Jul 04 15:32:20 CST 2022
Carbide cutting tool has high hardness, brittleness, poor thermal conductivity and high thermal shrinkage, so diamond grinding wheel should be used for grinding. However, because of the high price of diamond grinding wheel, it is not easy to repair after wear, so many factories still use ordinary grinding wheel for grinding. In the process of grinding, due to the high hardness of Cemented carbide , the abrasive particles of ordinary grinding wheel are easy to be passivated. The intense friction causes local high temperature on the surface of the cutting tools, and forms additional heating stress, which is easy to cause hot deformation and hot crack, which directly affects the tooling life and processing quality . Therefore, necessary measures should be taken to prevent the occurrence of grinding crack. Through processing practice, the following effective measures to prevent or reduce grinding crack are summarized.
The negative edge grinding method is to grind a negative edge belt on the front or back edge before sharpening the cutting tool. Cemented carbide is a hard and brittle material. The vibration of grinding wheel makes the tool subjected to impact load, which is easy to occur vibration crack. At the same time, the instantaneous heating and cooling of the grinding zone may cause the thermal stress to exceed the strength limit of the cemented carbide and produce the hot crack. The negative edge grinding method can improve the strength of the carbide insert, enhance the vibration resistance and the ability to withstand the impact load, and increase the heating area, prevent the grinding heat to guide a large number of carbide insert, so as to reduce or prevent the crack.
At normal temperature, the powder molybdenum disulphide and anhydride ethanol are made into a mixed solution, and then the new ordinary grinding wheel is soaked in the mixed solution in a closed container (to prevent ethanol volatilization). After 14 hours, it is taken out and naturally dried for 18 ~ 20 hours, so that the grinding wheel is completely dried. After the above treatment, the internal gap of the grinding wheel is full of molybdenum disulfide, which can lubricate the abrasive particles, so that the grinding wheel has a good chip removal and is not easy to be blocked. The test results show that when grinding the carbide blade with molybdenum disulfide impregnated grinding wheel, the grinding is sharp, the abrasive particles are not easy to be passivated, the workpiece is small deformation, the chip is smooth, and the chip is basically in the shape of banded, most of the grinding heat can be taken away, so as to improve the grinding effect and the yield of the carbie insert.
If the friction force in the grinding process is too large, it can lead to a sharp rise in grinding temperature, and the carbide cutting tool is prone to burst. Therefore, it is very important to choose a reasonable grinding amount. The commonly used reasonable grinding dosage is: circumferential speed V =10 ~ 15m/min, feed f longitudinal =0.5 ~ 1.0m/min, F horizontal =0.01 ~ 0.02mm/ stroke. Manual grinding, longitudinal and transverse feed should not be too large.
The insufficient rigidity of the tool holder, the unstable clamping of the tool and the runout of the machine tool spindle may cause the grinding cracks. Therefore, the processing system composed of the machine tool, the grinding wheel, the fixture and the tool should be sufficiently rigid, and the axial and radial runout of the grinding wheel should be controlled.
There are many factors that cause the grinding crack of cemented carbide insert. Only by selecting proper grinding wheel and reasonable grinding process can the crack be avoided effectively and the grinding quality be improved.