OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 2 Chemical composition of work materials (according to GOST 5632–72) C Si Mn Cr Ni 20Cr13Ni18 ≤ 0.20 ≤ 1.0 ≤ 2.0 22–25 17–20 20Cr25Ni20Si2 ≤ 0.20 2–3 ≤ 1.5 24–27 18–21 The operating voltage of the power source of the plasma heating device during the experiment varied in the range U = 150–200 V, the operating current varied in the range I = 250–300 A. The above studies have shown that the rational range of heating the cut layer of the workpiece surface made of high-temperature steel 20Cr23Ni8 under conditions of plasma-assisted machining should be within 700–750 oC, and when processing steel 20Cr25Ni20Si2(cast) it should be heated within 800–820 oC. The compressed air pressure supplied by the power source to the plasma torch was regulated within 0.15–0.20 MPa. The plasma torch was cooled by tap industrial water with subsequent drain into the sewer. Ultrasonic vibrations are applied to the cutting edge of the tool, the frequency of which varied within 18–22 kHz, the oscillation amplitude varied within 2–15 μm. During the experiments, it was found that the selecting the diameter of the plasma torch nozzle opening for heating the surface of the workpiece during the chips formation is one of the important parameters of the plasma heating process. Technological parameters such as power supply voltage, current, distance from the nozzle to the cutting zone, compressed air pressure, etc. are calculated in order to determine the modes of the process of stable plasma heating of the workpiece under processing conditions. Therefore, nozzles with hole diameters of 4, 5, 6, 7, 8, and 9 mm were tested. Experiments have shown that when using a nozzle hole with a diameter of 7 mm, the conditions for heating the workpiece are signifi cantly improved, providing a stable fl ame and better removal of combustion products from the working area. The experiments were carried out using turning tools with brazed-tip and disposable inserts. The geometric parameters of the cutting part of the tools were: γ = 5–10o; α = 8–12o; λ = 10–15o; φ = 15–20o; and the radius of the top of the cutting edge r = 1.5 mm. To compare the results of the research, the turning of high-temperature steels was carried out both by plasma-assisted machining and with the use of ultrasonic plasma machining. To compare the results of plasma and plasma ultrasonic cutting, experiments were also carried out without the use of plasma heating and ultrasonic cutting, which showed that when selecting the geometric shape of the inset, it is necessary to provide a chamfer on the front surface of the insert equal to the value of the length feed, as a result of which the tool wedge is hardened [9–11]. At the same time, in order to achieve the appropriate strength of the cutting edge, the value of the clearance angle α was taken a little bit less. Turning without the use of plasma heating was carried out according to the factory technological processing modes, for example: at a cutting speed V = 10 m/min (n = 160 rev/min), depth of cut t = 3–4 mm, length feed Sl = 0.8 mm/rev. When conducting experiments to determine the wear of the cutting tool under normal cutting conditions, moderate modes were used, where the depth of cut was within t = 3 mm, length feed Sl = 0.31 mm/rev. When cutting steels 20Cr23Ni18 and 20Cr25Ni20Si2(cast) at speeds up to 10 m/min, the wear of carbide inserts remains within the permissible. Therefore, in the usual cutting of high-temperature steels, the indicated modes are used. The conducted experiments established that during plasma-assisted machining in order to increase the heating performance, processing should be carried out with an increase in the depth of cut to t = 6 mm [12–16]. The work also studied the wear of inserts made of hard alloy T15K6 when turning high-temperature steels of the 20Cr23Ni18 and 20Cr25Ni20Si2(cast) grades under various processing conditions. It was found that the wear of T15K6 inserts compared to the wear of T5K10 inserts, when turning these materials,
RkJQdWJsaXNoZXIy MTk0ODM1