OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 Today, there is a diverse range of PCM; new promising materials based on carbon fi ber, developed at FSUE “VIAM”, are of particular interest. One of these materials is carbon fi ber prepreg grade Vku-39/ Vtku-2.200. This material is made on the basis of equally strong carbon fabric grade VTkU-2.200 and binder grade VSE-1212. To process products made of PCM, including carbon fi ber reinforced plastics of the VKU-39, it is advisable to use electrophysical processing methods. Copy-piercing electrical discharge machining (EDM) is one of these methods. The use of such processing methods for PCM is due to its high physical and mechanical characteristics and the complexity of processing by blade methods. Considering the fact that the PCM element is a binder – epoxy resin, which is destroyed at the edges of the resulting holes and grooves during EDM, PCM can be considered diffi cult to process. During the EDM of holes in PCM products, the temperature rises, and ineffi cient cooling often occurs in the processing zone [2–3]. In papers [4-6] the methods and features of the EDM of PCM are presented. On the basis of these works, it is shown that a product made of PCM is subjected to the action of electrical impulses during EDM. The plasma channel appears and has an internal temperature of about 9,000-9,500 °C. This leads to a change in the state of the PCM material. A phase transition occurs from a solid material to a vaporous substance. This subsequently leads to the fact that PCM vapors and molten pieces of electrode-tool (ET) sludge solidify upon cooling and form products of electroerosive sludge, which negatively affects the quality and performance of the EDM [7, 8]. Accumulation of erosive sludge and other erosion products in the zone of EDM of PCM products is caused by poor fl ushing of the space between the ET and the workpiece being processed when deep holes are obtained, as well as slotted and key grooves. This phenomenon leads to the appearance of secondary dendritic structures on the surface of the ET and the workpiece, as well as to a decrease in the EDM quality and productivity when processing products made of PCM [7]. It has been established that the movement of sludge during the EDM of PCM products is formed by the process of formation and movement of gas bubbles in the processing zone [8–11]. Due to the fact that the dielectric (usually mineral or transformer oil) is viscous, electroerosion sludge can move in the shell of the gas bubble. As a result of the studies carried out in [8–11], it becomes possible to show visually the process of erosive sludge movement in the interelectrode space. It is proposed to vary the parameters of the height of the rise of the ET from the zone of the EDM, as well as the speed of the rise of this ET. However, in these works there are no practical recommendations for increasing the productivity and effi ciency of the EDM of PCM products. The structure of erosive sludge is shown in [12, 13]. This sludge is obtained as a result of the destruction of ET and the workpiece material. This forms spherical and hemispherical particles shown in Figure 1, a. The direct formation of the shape of particles in the form of a sphere occurs in the process of cooling the evaporated material of the workpiece. Most of the obtained spherical and hemispherical particles of erosive sludge have a dendritic structure. This indicates the low cooling rates of the EDM process. The formation of erosive sludge from the destroyed ET occurs by thermal crumbling (Figure 1, b). а b Fig. 1. EDM sludge: a – from the workpiece surface; b – from the surface of the electrode-tool
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