OBRABOTKAMETALLOV Vol. 27 No. 1 2025 technology The cooling time was determined taking into account the pulse duty cycle, which was adopted as 26 %. The simulation was carried out for two EDM modes, presented in Table 1. Within the scope of this study, models were developed for low-alloy 0.4C-Cr steel and medium-alloy 0.35C-Cr-Mn-Si steel. The material properties used as input parameters for the modeling are presented in Table 2. Ta b l e 2 Input parameters for simulation Parameter Designation Units of measurement Meaning 40C-Cr 0.35C-Cr-Mn-Si Thermal diffusivity coefficient K W/(m∙°C) 46 36 Specific heat C J/(kg∙°C) 466 496 Density ρ kg/m3 7,800 7,800 Share of pulse energy µ 0.6 0.6 Heat transfer coefficient k W/(m∙°C) 300 300 Melting point Tmelt °C 1,250 1,280 Ta b l e 1 Parameters of the copy-piercing EDM modes Parameter Processing mode min max Current I, A 2 8 Voltage U, V 50 100 Pulse duration Ton, µs 40 150 The solution was implemented using the finite element method. To simulate pit formation, an element was removed when its temperature exceeded the melting point. Element removal was achieved by zeroing the “rigidity” of the elements in the heat problem. Experiments on the EDM of samples were conducted using the same modes as in the simulation (Table 1). An Electronica Smart CNC copy-piercing EDM machine was selected for the EDM of samples made of chromium-containing steels 0.4C-Cr and 0.35C-Cr-Mn-Si. Processingwas performed in transformer oil environment (GOST 982-80). For experimental studies of the thickness, continuity, and cracking of the white layer formed during CPEDM, depending on the processing parameters and the workpiece material, cylindrical samples with a diameter of 35 mm and a length of 20 mm were made from low-alloy 0.4C-Cr steel and medium-alloy 0.35C-Cr-Mn-Si steel. For experiments using the milling method, copper tool-electrodes (M1 copper grade, GOST 1173-2006) with dimensions of 20×20×5 mm were fabricated. After CPEDM, metallographic specimens were prepared. A Top Tech Presidon hot mounting press was used to embed the samples in bakelite. Final specimen preparation was performed on a Top Tech Plato grinding and polishing unit. Grinding was performed using abrasives with grit sizes ranging from P240 to P1500. The processed surface was examined for cracks, and metallographic specimens were examined to determine the thickness and continuity of the white layer, using metallographic techniques. Metallographic
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