OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 2 the increased abrasive capacity of these steels is due to the presence in it, in addition to the solid solution phase, the so-called “second phase”, which forms intermetallic or carbide inclusions leading to increased tool wear during processing; low vibration resistance during cutting motion, due to the high hardenability of these materials with uneven fl ow of the process of its plastic deformation. The above and other problems associated with the specifi c characteristics of high-temperature steels require the creation of new technological solutions to improve the machinability of these materials. Research methodology One of the methods to improve the machinability of high-temperature steels and alloys is plasmaassisted machining. During plasma-assisted machining of high-temperature steels with an edge tool, the workpiece is heated by a plasma arc. Heating a workpiece made of high-temperature steels improves the machinability of these materials with an edge tool. The use of preheating in the cutting process makes it possible to increase the difference between the contact hardness of the tool and the hardness of the material being processed, which leads to an increase in the durability of the edge tool. That is, during preheating of workpieces made of high-temperature materials during machining with edge tools, a greater softening of the material being processed occurs than the softening of the working surfaces of the cutting tool. The experiments have shown that during plasma-assisted machining, a high concentration of heat in a small volume makes it possible to control the heating process well, achieving suffi cient stability; it is most advisable to use plasma heating when machining hard-to-process materials with a low machinability coeffi cient. It has been established that the performance of the plasma heating process is higher, the lower the machinability coeffi cient of high-temperature materials; it should be noted that during plasma-assisted machining, for effective metal cutting, it is necessary to heat the workpiece layer to the cutting depth and the feed rate to the optimum cutting temperature, which is the sum of the temperature preheating and temperature resulting from chip formation. That is, the plasma heating mode should be determined depending on the composition, physical and mechanical parameters of the high-temperature material being processed [3, 4, 6–8]. During plasma-assisted machining, an increase in the heating temperature of the workpiece changes the physical, chemical and mechanical properties of not only the material being processed, but also the material of the tool. It has been established [1-5] that with an increase in the heating temperature of the wear surface, on the one hand, the plasticity of the material being processed increases, and on the other hand, the degree of the chip plastic strain increases. The local heating of the surface layers of the material being processed, which occurs upon contact with the plasma arc, causes a temperature fi eld of a high degree of nonuniformity in the workpiece, which leads to the appearance of extremely nonuniform stress fi elds in the metal being processed. The nonuniformity of the stress fi elds is enhanced by structural transformations that occur in part of the volume of the heated metal and the melting of its individual sections. Such a mechanism of action of the plasma arc can lead to microfracture and other discontinuances in the surface layer of the workpiece and help to facilitate the deformation of chip formation during turning and milling. The decisive infl uence on the nature and intensity of tool wear is exerted by the ratio between the hardness of the workpiece and tool materials under plasma heating conditions. This ratio is called coeffi cient of the shape stability. The experiments carried out showed that during the plasma-assisted machining of high-temperature materials the shape stability of hard alloy tools is much higher than that of other tool materials. Therefore, the experiments were carried out with turning tools equipped with inserts made of hard alloys T15K6, T5K10, VK8. To carry out turning experiments, an installation was created on the basis of a 1A64 type screw-cutting lathe, on which the dimensions of the workpiece being machined make it possible to study the machinability of all types of cylindrical parts used in the production of electrothermal equipment. The installation consists of a screw-cutting lathe, a power source APR-403 UKhLCh-2, a plasma torch holder, a plasma torch, an air duct for supplying to the plasma torch. The plasma torch holder is mounted on
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