OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 4 No. 3 2022 which leads to signifi cant inclinations during plastic deformation of the contact zone when cutting, and to an increase in the wear rate of the cutting blade during conventional cutting. When processing high-temperature steels with plasma heating, the loads acting on the cutting face of the tool are reduced due to preheating. Also, the contact pressures on the back surface of the cutting blade are signifi cantly reduced compared to the pressure when cutting with the conventional method, i.e. without preheating. Therefore, when processing materials by cutting with plasma heating, the working conditions of the tool are improved, and the probability of plastic deformation of the cutting edge of the insert is reduced. The experiments performed (Fig. 2 and 3)showed that when processing heat-resistant steels by plasmaultrasonic-assisted machining, the durability of the cutting tool, both hard alloy grade VK8 and hard alloy grade T5K10, is 4-5 times higher compared to the plasma method of processing, and is 10–12 times higher compared to compared to conventional machining (without plasma heating). This is due to the kinematic feature of the ultrasonic cutting process and the source of ultrasonic vibrations. Cutting tools, in the designs of which a concentrator of mechanical vibrations made of a titanium alloy of grade VT-1 is used, are used in the processing of high-temperature steels. The use of a titanium alloy as a concentrator of ultrasonic vibrations can signifi cantly reduce the frequency loss in the process of transmitting vibrations to the cutting edge and reduces the heating temperature of the insert body. This is due to the fact that titanium alloys have a suffi ciently high mechanical strength and low wave resistance, as well as a low sound absorption coeffi cient. Experiments have shown that when using ultrasonic vibrations in the process of turning high-temperature steels under plasma heating, the durability of the cutting tool increases due to the vibration of the cutting edge of the tool. This phenomenon makes it possible to improve chip formation in the contact zone of machining. When turning, ultrasonic waves vibrate the cutting edge of the insert 18,000 times for one minute about (18 kHz), which creates additional chip deformation, and the presence of ultrasonic vibrations moves the tip of the cutting edge of the tool both in the radial and longitudinal directions. Therefore, under these conditions, the formation of chips is fundamentally different from the conventional method of metal cutting. Namely, during ultrasonic turning, the transmission of ultrasonic vibrations to the tool signifi cantly reduces shear deformations in the cutting zone; also, in the chip shear zone, many microcracks form in its metal separation plane. In addition, the presence of high-frequency vibrations in the cutting edge of the tool does not allow the accumulation of build-up on its surface, the sharpness of the wedge in the contact zone is maintained, which reduces the friction conditions of the chips on the cutting face, thus reducing the cutting force and heating of the cutting tool. It should be noted that with the varying the parameters of ultrasonic vibrations, it is possible to control the process of chip formation in such a way that the cutting edge of the tool can retain its geometric shape due to which the point of contact of the chip changes when it leaves the cutting zone. For example, with an increase in the amplitude of ultrasonic vibrations in the contact zone, the cyclic effect of ultrasonic vibrations on the working surface increases, leading to an increase in the fatigue strength of the surface. In addition, during ultrasonic cutting of metals, due to ultrasonic vibrations, the kinematic rake angle of the tool increases, which leads to an improvement in the conditions for the insert wedge feeding-in into the material being machined and, therefore, the dynamics of material machinability decreases. Thus, on the basis of a comprehensive study, the following conclusions are made: 1. The use of ultrasound in the plasma-assisted machining of high-temperature steels makes it possible to reduce (up to 10 times) the wear of hard-alloy inserts. 2. It has been established that with conventional machining of steel 20Cr13Ni18, the wear of T5K10 carbide inserts is 1.5...2 times greater than that of VK8 inserts. 3. When turning high-temperature steels 20Cr13Ni18 and 20Cr25Ni20Si2(cast) both with the conventional method and with the plasma-assisted method using ultrasound, the wear of single-carbide hard alloy VK8 is much less than when machining with two-carbide hard alloy T5K10.
RkJQdWJsaXNoZXIy MTk0ODM1