Vol. 24 No. 3 2022 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. We sincerely happy to announce that Journal “Obrabotka Metallov” (“Metal Working and Material Science”), ISSN 1994-6309 / E-ISSN 2541-819X is selected for coverage in Clarivate Analytics (formerly Thomson Reuters) products and services started from July 10, 2017. Beginning with No. 1 (74) 2017, this publication will be indexed and abstracted in: Emerging Sources Citation Index. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Affairs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Gerasenko, Director, Scientifi c and Production company “Mashservispribor”, Novosibirsk; Sergey V. Kirsanov, D.Sc. (Engineering), Professor, National Research Tomsk Polytechnic University, Tomsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Evgeniy A. Kudryashov, D.Sc. (Engineering), Professor, Southwest State University, Kursk; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, Institute of Strength Physics and Materials Science, Russian Academy of Sciences (Siberian Branch), Tomsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 24 No. 3 2022 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Permyakov G.L., Davlyatshin R.P., Belenkiy V.Y., Trushnikov D.N., Varushkin S.V., Pang S. Numerical analysis of the process of electron beam additive deposition with vertical feed of wire material...................... 6 Ilinykh A.S., Banul V.V., Vorontsov D.S. Theoretical analysis of passive rail grinding.................................. 22 Chinchanikar S. Modeling of sliding wear characteristics of Polytetrafl uoroethylene (PTFE) composite reinforced with carbon fi ber against SS304........................................................................................................ 40 EQUIPMENT. INSTRUMENTS Abbasov V.A., Bashirov R.J. Features of ultrasound application in plasma-mechanical processing of parts made of hard-to-process materials...................................................................................................................... 53 MATERIAL SCIENCE Stolyarov V.V., Andreev V.A., Karelin R.D., Ugurchiev U.Kh., Cherkasov V.V., Komarov V.S., Yusupov V.S. Deformability of TiNiHf shape memory alloy under rolling with pulsed current....................... 66 Vorontsov A.V., Filippov A.V., Shamarin N.N., Moskvichev E.N., Novitskaya O.S., Knyazhev E.O., Denisova Yu.A., Leonov A.A., Denisov V.V. Microstructure and residual stresses of ZrN/CrN multilayer coatings formed by the plasma-assisted vacuum-arc method........................................................................... 76 Ivanov I.V., Safarova D.E., Bataeva Z.B., Bataev I.A. Comparison of approaches based on the WilliamsonHall method for analyzing the structure of an Al0.3CoCrFeNi high-entropy alloy after cold deformation....... 90 Kryukov D.B. Structural features and technology of light armor composite materials with mechanism of brittle cracks localization.......................................................................................................................... 103 EDITORIALMATERIALS 112 FOUNDERS MATERIALS 123 CONTENTS
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 2 Features of ultrasound application in plasma-mechanical processing of parts made of hard-to-process materials Vagif Abbasov a, Rasim Bashirov b, * Department of Machine Building, Azerbaijan Technical University, 25 H. Cavid avenue, Baku, AZ 1073, Azerbaijan a https://orcid.org/0000-0002-4633-6728, abbasov49@aztu.edu.az, b https://orcid.org/0000-0001-6907-2502, rasim_agma@aztu.edu.az Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2022 vol. 24 no. 3 pp. 53–65 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2022-24.3-53-65 ART I CLE I NFO Article history: Received: 06 April 2022 Revised: 19 April 2022 Accepted: 27 June 2022 Available online: 15 September 2022 Keywords: Hard-to-process materials Plasmatron holder Machinability coeffi cient Ultrasonic Cutter Ultrasonic turning device Plasma-mechanical processing Plasma-ultrasonic treatment Cutter wear Vibrational deformation of the chip. ABSTRACT Introduction. Structural materials, including materials made of heat-resistant and hard-to-work steels, are widely used in various branches of mechanical engineering. To increase the effi ciency of manufacturing parts of thermal equipment from heat-resistant and hard-to-work steels, the technological method of cutting with preliminary plasma heating of the workpiece is used. There is also a technological method of cutting metals, including hard-to-process materials by ultrasonic turning. Proceeding from this, in order to increase the effi ciency of plasma machining of hard-to-process materials, it is necessary to investigate the technological possibilities of using ultrasonic turning of hard-to-process materials during plasma machining. The purpose of the work: to investigate the wear of cutting tools when using ultrasound in the conditions of plasma-mechanical processing of parts made of hard-to-process materials. The paper investigates the features of the plasma-mechanical processing under ultrasonic cutting conditions and determines the wear values of carbide cutters VK8, T5K10 and T15K6 when processing steels of grades 20Cr13Ni18 and 20Cr25Ni20Si2(cast). And also the wear of these cutters was determined under the conditions of conventional turning of the same materials to compare the results of wear of the cutters in different processing conditions. The research method is to determine the linear wear of carbide cutters along the back surface with conventional, plasma-mechanical and plasma-mechanical cutting assisted with ultrasonic cutting using an instrumental microscope and visual estimation with a 10x magnifying glass. Results and discussion. The paper presents the results of experimental studies to determine the wear of cutting tools when processing heat-resistant steels of the 20Cr13Ni18 and 20Cr25Ni20Si2(cast) grades with carbide cutters of the VK8, T5K10 and T15K6 grades. Studies were carried out to determine the wear of carbide cutters as with conventional mechanical cutting, plasma-mechanical cutting, as well as plasma-mechanical cutting using ultrasound. The experiments were carried out when turning these materials on a modernized lathe mod.1A64. A rectifi er with a controlled choke and a plasma torch mod.APR-403 are connected to the lathe; a plasma holder is placed on the lathe carriage. A semiconductor rectifi er serves as a power source with a compressed electric arc of current. The arcing takes place between the cathode (plasma torch) and the anode (blank) at the point of the plasma-forming gas; compressed air passes through the nozzle channel of the plasma torch. During the experiments, the position of the plasma torch was adjusted relative to the part rotation axis. When conducting experiments on studying the wear of cutters under conditions of ultrasonic plasma-mechanical cutting, ultrasound was applied to the cutting edge using a device developed by the authors. When processing heat-resistant steels under the usual turning condition, processing modes were adopted: cutting speed V = 10 m/min, cutting depth t = 3...4 mm, longitudinal feed Sl = 0.31 mm/rev. It is found that when processing steel grade 20Cr13Ni18 by conventional cutting, the back surface of the carbide cutter made of T5K10 wears out to 1 mm in size within 10 minutes, and for the cutter made of VK8 – within 15 minutes. During plasma machining, the cutting speed and the feed rate were increased 2 times; the results of the wear of the cutters show that at the same time T5K10 wears out to 1 mm within 20 minutes, VK8 – within 25 minutes. Plasma-mechanical processing using ultrasound show that the carbide cutter T5K10 wears out by 0.50 mm in less than 50 minutes of cutting, and VK8 wears out by 0.35 mm. The same results are obtained when processing heat-resistant steel 20Cr25Ni20Si2(cast). Thus, the study of wear of carbide cutters in the processing of heat-resistant steels shows that the use of ultrasonic cutting in plasma-mechanical processing of steels can signifi cantly reduce the amount of tool wear. The presented results confi rm the prospects of using ultrasonic plasma-mechanical cutting of heat-resistant steels with blade tools. For citation: Abbasov V.A., Bashirov R.J. Features of ultrasound application in plasma-mechanical processing of parts made of hard-toprocess materials. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2022, vol. 24, no. 3, pp. 53–65. DOI: 10.17212/1994-6309-2022-24.3-53-65. (In Russian). ______ * Corresponding author Bashirov Rasim J., D.Sc. (Engineering), Professor Department of Machine Building, Azerbaijan Technical University, AZ 1073, 25 H. Cavid avenue, Baku, Azerbaijan Tel: +994 (50) 212 22 73,e-mail: rasim_agma@aztu.edu.az
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 4 No. 3 2022 Introduction In mechanical engineering, various hard-to-process materials are widely used for the manufacture of parts and structural elements of equipment for electrochemical, chemical and other industries. The use of hard-to-process and heat-resistant steels for the manufacture of thermal equipment is hampered by the fact that these materials are poorly subjected to machining with edge tools. In this regard, in the production of electrothermal equipment, attempts are being made to increase the effi ciency of processing heat-resistant and hard-to-process materials by using various combined methods of chip removal, one of which is machining with plasma heating of the workpiece before processing. Plasma-heated hightemperature steel machining is a combined process in which mechanical energy, together with lowtemperature plasma energy, is used to increase performance and reduce cutting tool consumption when machining these materials. There are various methods for plasma heating of a workpiece during machining [1–6]. These and other works provide data on the performance of plasma-mechanical turning, milling, etc. It has been established that plasma heating improves the machinability of materials in cutting cases when the increase in tool life due to a decrease in the specifi c cutting work is greater than the negative effect of elevated temperatures on the increase in the intensity of adhesion and tool wear phenomena. As is known, the wear of a cutting tool is an integrated process accompanied with complex and mutually infl uencing phenomena at the points of contact between the tool with the chip and the workpiece, occurring under conditions of high temperatures and pressures. Therefore, it is recommended to use cutting tools with internal cooling during plasmaassisted machining. The analysis of research works [7–20] showed that insuffi cient attention has been paid to the issue of determining the relationship between the wear of the cutting tool and the parameters of plasma-machining of hard-to-process materials. Also, among the available research papers, there are no works devoted to the use of ultrasonic vibrations in combinations of plasma-assisted machining of hard-to-process materials. Therefore, the task was set to investigate the process of plasma-ultrasonic-assisted machining of hard-toprocess materials and the wear of the cutting tool that accompanies it. Hard-to-process materials have a number of such specifi c physical, chemical and mechanical properties as high strength, high temperature strength, heat resistance, toughness, corrosion resistance, refractoriness, etc. Hard-to-process materials have a complex carbide-forming structure. High-temperature steels and alloys belong to hard-to-process materials, which, according to their basic composition, are divided into high-temperature steels based on iron, nickel, cobalt and titanium. These steels and alloys are often used in the manufacture of parts for electrothermal equipment. High-temperature steels based on iron, nickel, cobalt and titanium are diffi cult to machine with an edge tool, that is, turning and milling due to a number of specifi c features, in particular: dependence of the increase in hardening of high-temperature steels in the process of deformation during cutting on the structure of the crystal lattice of these materials, which determines the number of possible sliding directions during plastic strain in the process of machining. For example, crystals of steels of the ferritic-pearlitic group have a lattice of a body-centered cube with eight possible slip directions; crystals of steels of the austenitic class have the shape of a face-centered cube with nineteen possible slip directions [1]; high ductility of high-temperature steels, which leads to an increase in microhardness in the chip formation zone during turning, which, in turn, complicates the process of separating materials along the front surface of the cutting edge; low thermal conductivity of high-temperature steels, which leads to an increase in temperature on the contact surfaces during machining, causing an increase in the intensity adhesion and diffusion phenomena and, as a result, the destruction of the cutting part of the tool; the ability of these materials to maintain its original strength and hardness at elevated temperatures that occur in the zone of deformation and chip fl ow during cutting, which leads to a very high specifi c pressure at the point of contact of the material with the tool during the machining;
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
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 4 No. 3 2022 the tool holder and is closed by a casing. From the power source by an electric wire, the current is brought to the part through the current collector of the machine spindle. The workpiece is placed in a four-jaw chuck and fi xed by the rear center. A tool for ultrasonic turning and cutting of metals is installed on the tool holder. The tool for ultrasonic cutting, fi xed on the tool holder of the machine, forms the fi rst stage of the ultrasonic stepped concentrator of mechanical vibrations with a piezoelectric sensor installed on the end section of its free end [5, 6, 9, 10]. The ultrasonic cutter 1 (Fig. 1) contains a cylindrical and conical concentrator – 2 and a piezoelectric emitter 3, rigidly clamped by a refl ector 4 through a through-hole 5 and a clamping bolt 6 to the free end of the section of the cutting tool, and forms the second stage of the ultrasonic stepped concentrator of mechanical vibrations. The positive electrodes 7 of the piezoelectric sensor are connected to the input of the voltage amplifi er 8 and the indicator, the electrodes 10 of the piezoelectric emitter are connected to the output of the variable frequency generator 12 and the indicator 11, the output of the voltage amplifi er is connected to the control input of the variable frequency generator. One of the electrodes of the piezoelectric emitter is electrically isolated from the contact surface of the refl ectors by a gasket 13 made of a dielectric material. Thus, the device for ultrasonic treatment of materials contains a stepped concentrator of ultrasonic vibrations with a variable profi le, the working end of which acts as a cutter and a piezoelectric emitter in the form of a washer, sandwiched between the concentrator and the refl ector. The operation of the ultrasonic cutting device is carried out as follows. In the process of plasmaassisted machining of high-temperature steels and alloys, at fi rst, an alternating voltage from the generator output 12 with a frequency equal to the natural frequency of the piezoelectric emitter 3 is supplied to its positive electrodes 10. This leads to the appearance of ultrasonic mechanical vibrations on the surface of the piezoelectric emitter. Mechanical vibrations are transmitted to the second stage 2 of the concentrator, then, intensifying, the mechanical vibrations of ultrasonic frequency are transmitted to the fi rst stage, concentrated directly on the cutting tool 1 of the device. The workpiece is fi xed on the spindle and treatment is carried out, while the operating parameters (speed and cutting force) are measured using a piezoelectric sensor 7, which generates an electrical signal on the surface of its electrodes. This signal is fed to the input of the voltage amplifi er 8, from the output of which it is fed to the input of the indicator of the device that converts the analog signal into a digital code. The features of the plasma-mechanical processing process were studied under ultrasonic cutting conditions during the turning of steel grades 20Cr13Ni18 and 20Cr25Ni20Si2(cast) (Table). The outer diameter of the workpieces was 170–196 mm, length – 1500–1800 mm. The workpieces were chunked with an emphasis on the butt end of the chuck and pressed by the rear center. Processing was carried out on the slag and on already machined surface. At the beginning, the pilot arc was turned on and after its automatic transition to the main arc, the longitudinal feed was turned on and a cylindrical section 20-30 mm long was turned to a depth of 7–10 mm. The plasma torch was installed so that the minimum distance from the cutting surface to the plasma torch nozzle at maximum jumping was 5-10 mm. The maximum distance from the plasma torch to the workpiece was taken within L = 30–40 mm. The angular position of the plasma torch was adjusted during the cutting process in order to heat optimally the cutting surface on the workpiece. Fig. 1. Device for ultrasonic turning and cutting of metals
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,
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 4 No. 3 2022 is much greater, therefore, in further studies, tools equipped with inserts made of T15K6 alloy were not used. Fig. 2 shows the results of a study of the wear of carbide inserts T5K10 and VK8, where curve refl ects the dynamics of wear under normal cutting conditions (V = 10 m/min, t = 3 mm; Sl = 0.31 mm/rev); 2-2ʹ – during plasma-assisted machining (V = 20 m/min, t = 6 mm; Sl = 0.31 mm/rev; İ = 250 A; U = 150 V); 3-3ʹ – when cutting with plasma-ultrasonic-assisted machining (V = 20 m/min, t = 6 mm; Sl = 0.31 mm/rev; İ = 250 A; U = 150 V; f = 18 kHz; А = 4 μm): 1, 2, 3 – when machining with T5K10 grade hard alloy inserts: 1ʹ, 2ʹ, 3ʹ –whenmachining with VK8 grade hard alloy inserts. The wear of the inserts in the normal mode of machining was studied at V = 10 m/min, Sl = 0.31 mm/rev. When the cutting modes increase from the specifi ed value, the cutting tool loses its cutting ability within 2-3 minutes. Plasma-machining and plasma-machining with the use of ultrasound were carried out in the same mode of mechanical cutting. When processing high-temperature steel grade 20Cr13Ni18 under various cutting conditions, it was found that Т5K10 carbide inserts compared to VK8 wear faster on the back surface in all types of processing. It was revealed that when turning steel 20Cr13Ni18, both single-carbide carbide inserts and doublecarbide ones wear out signifi cantly more with the usual turning method than with other processing methods [16–23]. Results and discussion Analysis of the results obtained made it possible to fi nd out that during plasma-assisted turning of steel 20Cr13Ni18, despite the fact that the depth of cut is 2 times greater (curves 2, 2ʹ, Fig. 2) than during the conventional turning, (curves 1, 1ʹ, Fig. 2), wear of the end fl ank of the straight turning tool is 1.5–2 times less, subjected to the cutting speed. And during plasma-assisted machining with the use of ultrasound, the wear of inserts (curves 3, 3ʹ, Fig. 2) is 5–10 times less than the wear of inserts during conventional turning (curves 1, 1ʹ). For example, during conventional turning of high-temperature steel 20Cr13Ni18 with a T5K10 carbide insert for 5 minutes of cutting, wear of the insert is achieved within 0.5–0.6 mm (curves 1 in Fig. 2), and when turning the same steel by plasma-assisted machining using ultrasound, wear of the T5K10 cutter up to 0.4 mm is achieved within 52 minutes, which indicates a decrease in insert wear by 10 times. In the current study, fi ve experiments were performed to plot each point. Experiments have shown that, both with the conventional method and with plasma-assisted machining along the slag, turning tools equipped with VK8 single-carbide carbide inserts have a number of advantages compared to turning tools equipped with two-carbide carbide inserts. In particular, studies have shown that the nature of the wear of the end fl ank of the cutting edge of the VK8 hard alloy inserts is more uniform, the intensity and rate of wear are slowed down, no catastrophic damage is observed, which favorably affects the process of turning steels. And when turning high-temperature steels with T5K10 carbide inserts, the wear of the end fl ank of the cutting edge of the insert is uneven, there are traces of microchipping and a wear groove, which leads to a rapid loss of its cutting ability. Studies have established that the most favorable condition arises when turning high-temperature steels by plasma-ultrasonic machining, both when turning with single-carbide and two-carbide inserts (curves 3, 3ʹ, Fig. 2). Fig. 2. Wear on the back surface of the cutter under various processing conditions when turning steel 20Cr13Ni18 slag
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 2 The results of the experiments showed that with the conventional method of turning steel 20Cr13Ni18, the maximum wear of the inserts is observed after machining during 10–15 minutes. And with plasmaassisted machining, the maximum wear of the inserts is observed after machining during 25 minutes. It has been established that in the process of plasma-ultrasonic machining, the maximum wear of inserts (h = 1.0 mm) is achieved after 90 minutes. This is due to the fact that when using ultrasound for plasmaassisted machining of high-temperature steels, the formation of microchips in the contact zone occurs under the infl uence of ultrasonic vibrations by the cutting edge of the inserts. The cutting edge of the cutter receives both in the longitudinal and in the radial ultrasonic vibrations with a frequency of 18 kHz and an amplitude of the order of A = 4 μm, leading to additional deformation of the chip during its descent, which actually eliminates the contact of the chip with the cutting edge. At the same time, the presence of ultrasonic vibrations improves the conditions for sliding and chip fl ow in the zone of its formation, which makes it possible to reduce signifi cantly the friction of chips on the contact surfaces of the insert. Fig. 3 shows the wear curves obtained during the machining of high-temperature steel grade 20Cr25Ni20Si2(cast), where 1, 1ʹ – wear during conventional cutting t = 3 mm, Sl = 0.31 mm/rev: 2, 2ʹ –wear during plasma-assistedmachining t = 6 mm, Sl = 0.31 mm/rev, I = 250 A, U = 150 V: 3, 3ʹ – wear during plasmaultrasonic-assisted machining t = 6 mm, Sl = 0.31 mm/rev, I = 250 A, U = 150 V, f = 18 kHz, A = 4 μm: 1, 2, 3 –whenmachining with T5K10 grade hard alloy inserts: 1ʹ, 2ʹ, 3ʹ – when machining with VK8 grade hard alloy inserts. Depending on the cutting time, the wear of the insert along the end fl ank changes similarly to Fig. 2. In other words, when machining the above material with conventional turning, the wear of the insert is much greater during plasma-assisted and plasma-ultrasonic-assisted machining. An analysis of graphs 1, 1ʹ in Fig. 2 and 3 shows that, as in the turning of high-temperature steels with T5K10 and VK8 carbide inserts, the greatest wear of the inserts is observed when turning steel 20Cr25Ni20Si2(cast). Studies have established that when machining 20Cr25Ni20Si2(cast) hightemperature steel in all processing modes, the linear wear of the tool and its intensity are much higher than when machining steel 20Cr13Ni18. The obtained results are explained by the fact that high-temperature steel 20Cr25Ni20Si2(cast), compared with steel 20Cr13Ni18, contains more alloying elements such as chromium (2 % more), nickel (2 % more), and silicon, which leads to the formation of a large amount of carbides. A large amount of carbides in steels causes an increase in the intensity of wear of the cutting tool during machining, including plasma-assisted and plasma-ultrasonic-assisted machining. From the given curves presented in Fig. 2 and 3, it was possible to fi nd out that during plasma-assisted machining of high-temperature steels, the wear rate of tool material is reduced compared to the conventional cutting method. At the same time, tool life increases by about 1.8–2.5 times compared to the conventional machining method. Studies have shown that with the conventional method of high-temperature steels turning, high specifi c loads and temperatures are observed on the contact surfaces of the cutting insert, which are continuously formed during the cutting process, which creates unfavorable conditions for the operation of the cutting tool. At the same time, high-temperature steels tend to adhere to the tool material and have high strength, Fig. 3. Wear on the end fl ank of the cutter under various processing conditions when turning steel 20Cr25Ni20Si2(cast) slag
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.
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