## 5 Conclusions  
This work aimed to optimize cutting parameters in wire electric discharge machining (WEDM) to minimize energy consumption when machining AISI D2 steel. To ensure that the quality of the machining process was not sacrificed, surface roughness was also considered as a performance response. The analysis was performed based on [PERSON]'s method, using a smaller-the-better type of response. Six process variables were considered factors for the analysis: pulse online, pulse off-time, servo voltage, wire tension, wire speed, and voltage. The design of the experiments was carried out using an \(L_{27}\) orthogonal array. Two plate thicknesses, 19 and 25 mm, were considered to simulate that the optimization process should be insensitive to the thickness of the plate being machined. Six control factors were considered in the experiment: pulse on-time (Ton), pulse off-time (Toff), servo voltage (SV), wire tension (WT), wire-speed (WS), and the voltage in the wire (V). From the experiments, two control factors contributed 90% of the variations in the responses: pulse on-time and voltage in the wire. Pulse off-time, servo voltage, and wire speed had no effect on any of the responses. Considering pulse on-time and the voltage were the more important factors in the experiment, it was found that for surface roughness, both the S/N ratio and the mean improved as the pulse on-time and the voltage decreased. On the other hand, for the energy consumption, both the S/N ratio and the mean improved as the pulse on-time and the voltage increased. The result that increasing pulse on-time and voltage may reduce the overall energy consumption of the WEDM process requires an explanation, as it may be counterintuitive. This is due to an increased material removal rate as a longer pulse on-time allows each discharge to remove more material, thus achieving the desired cut faster. The effect of an increasing voltage is similar. A higher voltage increases the energy density of each spark, resulting in more effective material removal per discharge. To reduce energy consumption without sacrificing the surface roughness, a pulse on-time of 10 us, a pulse off-time of 11 us, a servo voltage of 44 V, a wire tension of 50 g, a wire speed of 7 m/min, and a voltage available on the wire of 9 V should be used. This combination of values reduced the energy consumption by 8%, whereas surface roughness was improved by 1% when compared with the baseline values. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c c c} \hline \hline \multicolumn{13}{c}{**Surface Roughness**} & \multicolumn{4}{c}{**Energy Consumption**} \\  & & \multicolumn{3}{c}{**S/N (dB)**} & \multicolumn{3}{c}{**Mean (\(\mu\)m)**} & \multicolumn{3}{c}{**S/N (dB)**} & \multicolumn{3}{c}{**Mean (KWh)**} \\ \hline Baseline & \(-9.494\) & \(2.983\) & \(-3.298\) & \(1.435\) & \(-9.385\) & \(2.946\) & \(-2.577\) & \(1.315\) & \(-9.385\) & \(1.435\) & \\ Optimal & \(-9.385\) & \(2.946\) & \(-2.577\) & \(1.315\) & \(-9.315\) & \(-9.315\) & \(-9.315\) & \(-9.315\) & \(-9.315\) & \(-9.315\) & \(-9.315\) & \\ Gain & \(0.109\) & \(-0.037\) & \(0.721\) & \(-0.12\) & \(-0.12\) & \(-0.12\) & \(-0.12\) & \(-0.12\) & \(-0.12\) & \(-0.12\) & \\ Improvement & \(1.3\%\) & \(1.2\%\) & \(8.0\%\) & \(8.4\%\) & \(8.4\%\) & \(8.4\%\) & \(8.4\%\) & \(8.4\%\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Improvement on surface roughness and energy consumption compared to baseline values.