OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 R2, and R3 values (Trial 11: 4.264, 4.276, 4.271), suggesting high repeatability due to consistent process parameters. Trials with higher deviations between R1, R2, and R3 indicate process variability, which could be caused by inconsistent spark energy, wire tension, or thermal effects. Impact of process variables for utility function with S/N data The provided main effects plot for S/N ratios visualizes the influence of process parameters on the S/N ratio derived from the utility function in an EDM experiment (Fig. 3). For WEC (workpiece electrical conductivity), the obtained levels are 3268, 4219, 5515, 5625, 5645, and 5902. The plot shows fluctuations in S/N ratios across different wire electrode compositions. The peak S/N ratio is observed around level 4219, indicating better performance. Performance decreases at levels 5645 and 5902, suggesting suboptimal wire materials for efficient machining. Fig. 3. Impact of process variables for utility function (UMRR, SR, TWR) with S/N data In the case of gap current (Ig), levels are 8, 12, and 16. The S/N ratio increases steadily with higher discharge current. Higher currents (e.g., level 16) improve performance, likely due to faster material removal. However, excessively high current could increase surface roughness and tool wear. Considering gap voltage (Vg), the levels are 40, 55, and 70. The S/N ratio decreases significantly with increasing gap voltage. Lower voltages (e.g., 40) result in better S/N ratios, likely due to enhanced spark stability and controlled discharge energy. Ton (pulse on time) was varied in the range from 13 µs to 38 µs (with an intermediate value of 26 µs). Analysis of the graph demonstrates a slight increase in the S/N ratio with increasing Ton. Longer pulse-on time (Ton = 38 µs) potentially improves the material removal rate while maintaining the required surface quality. Toff (pulse off time) levels are 5, 7, and 9. The S/N ratio decreases with increasing Toff. Lower pulse-off times (e.g., 5) improve S/N ratios, likely due to reduced idle time and higher efficiency in spark discharge. Gap voltage (Vg) has the most significant impact on the S/N ratio, as indicated by the steep slope of its main effects line. Gap current (Ig) and pulse on time (Ton) also show notable effects, although their trends are less steep compared to Vg. Pulse-off time (Toff) and WEC have comparatively less impact but still contribute to performance. Optimal settings (based on larger S/N ratios) are given in Table 8. Optimized WEC, gap current (Ig), and gap voltage (Vg) settings are critical for achieving a higher S/N ratio, reflecting better overall performance. Improper adjustments in Vg or Toff can significantly degrade performance, highlighting the importance of precise control in EDM.
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