OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 model explains most of the data variability. Adjusted R-Sq (88.5 %) accounts for the number of predictors in the model; it is slightly lower but still high, indicating a well-fitting model. Gap voltage (Vg) is the most influential parameter, with an 84.102 % contribution to the utility function. Its P-value (0.000) indicates a statistically significant impact at the 95 % confidence level. Optimization of gap voltage is critical for improving EDM performance. Discharge current (Ig) has a moderate influence, contributing 5.344 %. Its P-value (0.051) suggests it is marginally significant. Increasing gap current likely improves material removal but may also lead to tradeoffs with surface quality. Toff has minimal impact on the utility function, with only a 3.089 % contribution. Its P-value (0.149) indicates it is not statistically significant. Although the Toff adjustment is less critical, it can still affect processing efficiency and time. The residual error accounts for 7.465 % of variability, which could be due to noise or unaccounted factors in the model. The model explains 92.5 % of the variability (R-Sq), with a strong Adjusted R-Sq of 88.5 %. This indicates that the utility function and process parameters are well represented by the model. Since gap voltage has the highest contribution and significance, its optimization is critical for improving EDM performance. Gap current also impacts performance, though its effect is less dominant. Pulse-off time is less critical and may not require extensive optimization. The utility function for S/N data yielded a response table with measurements from the utility of MRR, SR, and TWR. Table 10 demonstrates how the three process parameters – gap current (Ig), gap voltage (Vg), and pulse-off time (Toff) – influence the utility function that unites multiple responses (UMRR, TWR, SR) through a single performance index. Ta b l e 1 0 Response table with utility function (UMRR, SR, TWR) pertaining to SN data Level Ig Vg Toff 1 10.10 12.47 10.96 2 10.57 10.90 10.65 3 11.13 8.44 10.19 Delta 1.02 4.02 0.77 Rank 2 1 3 Each row shows the computed average utility function based on the specified factor levels. The utility performance at different gap current (Ig) levels demonstrates 10.108 at level 1, 10.570 at level 2, and reaches 11.130 at level 3. The difference between the maximum and minimum values (Delta) measures 1.022, reflecting the response variation due to Ig changes. The second rank position indicates that Ig affects the utility function with medium strength. At Vg levels 1 through 3, the average utility values were measured as 12.470, 10.903, and 8.444, respectively. The maximum parameter difference (Delta) is 4.026, indicating that Vg is the strongest determining parameter, as confirmed by its first rank position — the highest in the analysis. The utility function reveals Toff as the least influential factor during pulse-off time operations, with values at levels 1, 2, and 3 equal to 10.969, 10.653, and 10.195, respectively, and a Delta value of 0.774 – the lowest among all parameters. Its position at the bottom of the ranking confirms Toff as the least significant factor for the utility function. Overall, the utility function shows that gap voltage (Vg) is the most important factor affecting the combined responses (MRR, TWR, SR). The evaluation with a Delta value of 4.026 validates Vg as the leading factor. The second most predominant factor is gap current (Ig), with a Delta value of 1.022. The response
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