OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 Introduction Currently, one of the pressing challenges in domestic industry is the need for high-effi ciency production of non-ferrous metal and alloy blanks for the fabrication of large-scale components and structures. Flame cutting and waterjet cutting methods are capable of cutting thick sheet metal but suff er from low performance [1-3]. Laser cutting off ers high performance but is not suitable for producing thick-section blanks [4, 5]. Conventional mechanical cutting methods do not have the necessary fl exibility for manufacturing complexshaped parts. Plasma cutting combines high performancewith the ability to process thick sheet metal [6-8]. Thismethod is well-suited for both steels and ferrous metals [9, 10], as well as copper, aluminum, and titanium alloys [11-16]. Plasma cutting can produce blanks from thick sheet metal, including materials with thicknesses of 100 mm or more. However, cutting such thick blanks using plasma torches operating on direct polarity current presents signifi cant challenges and leads to considerable wear of the working elements [17, 18]. Moreover, most of the available plasma torches of this type are produced by foreign manufacturers and are not domestically manufactured. Therefore, there is a need to develop alternative plasma cutting equipment of domestic origin. For this purpose, a joint project between the Institute of Strength Physics and Materials Sciences (ISPMS SB RAS) and LLC ITS-Siberia is currently focused on developing equipment for reverse polarity plasma cutting of thick sheet non-ferrous metals and alloys [13-16, 18, 19]. Reverse polarity plasma cutting off ers several advantages over direct polarity. First of all, the consumption of nozzles and electrodes included in the plasma torches is reduced [17, 18]. The second, but no less important factor, is the increase in the thickness of sheet metal that can be cut [15]. Reverse polarity plasma cutting also delivers higher performance at the same power level compared to direct polarity [18, 20-23]. Additionally, it improves the quality of the cut surface and reduces the extent of structural changes caused by thermal eff ects [18]. However, reverse polarity plasma cutting is more complex in terms of optimizing cutting parameters [13-16] and involves specifi c challenges related to the degradation and wear of plasma torch components [18]. Despite the fairly long history of using plasma cutting, there is almost no information in the modern literature regarding the eff ects of the cutting process on the structure and surface quality of sheet metal with a thickness of 100 mm or more when using reverse polarity plasma torches. The aim of this study is to investigate the structural organization, edge distortion, and changes in chemical and phase composition during reverse polarity plasma cutting of aluminum, copper, and titanium alloys. Materials and methods Experimental studies were carried out at the production site of LLC ITS-Siberia and on experimental equipment at the Institute of Strength Physics and Materials Sciences (ISPMS SB RAS). The cutting process was performed using a reverse polarity plasma torch developed as part of a joint scientifi c and technical project. The materials used were 100 mm thick plates of Al-6Mg aluminum alloy, Cu-9Al-2Mn bronze, and Ti-5Al-5Mo-5V titanium alloy in its as-received condition. The schematic of the plasma torch operation and the plasma cutting process is shown in Fig. 1, a. The cutting of 100 mm thick plates (1) was performed using a plasma jet (2) formed in a protective gas environment (3), initiated by the pilot arc (4) at the start of the process and maintained by the main arc (5) during the cutting operation. The supply of the protective and plasma-forming gas (6) to the cutting zone was maintained at a fi xed pressure in the system. The nozzle (7) was secured with a nut (8). Inside the nozzle, a dense vortex stream of gas and plasma (9) was formed, driven by the swirl generator (10) and arc combustion. Additionally, in the developed plasma torch design, water injection (11) into the discharge chamber was implemented through an opening in the working electrode (14). This setup was necessary to improve cut quality and reduce nozzle and electrode wear [16, 18, 19]. To prevent overheating of the nozzle and electrode, a constant fl ow of water (12) was maintained through channels in the torch body (13). Due
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