## 3 Materials and Methods
### Experimentation  
Considering previous research reported in Section 2, six control factors were considered for the experiments: pulse on-time (Ton), pulse off-time (Toff), servo voltage (SV), wire tension (WT), wire speed (WS), and voltage (V). The six factors were expected to be able to model the machining process and explain most of the variation in the responses chosen: total energy consumption and surface roughness.  
The experiments were performed on a WEDM Zodick VZ 300L machine like the one shown in Figure 3.  
The electrical power was measured by employing a Fluke 43B power analyzer. To know the power measurements during machining, the power analyzer was connected to the main power lines, as shown in Figure 4. This ensured that the measurement contemplated the necessary electrical energy to power the actuators, display, fans, cooling system, and other machine components. Figure 5 shows the electrical connection diagram recommended by Fluke. Surface roughness was calculated with the Mitutoyo SJ-210 roughness meter, with a sampling length of 2.5 mm. The value considered for each sample was based on average measurements taken from the central area of each of the three flat surfaces of the machined pieces.  
Figure 3: Zodick VZ 300L Wire EDM machine used for the experiments.  
To define an initial or baseline combination of values for the machining process, the values for pulse on-time, pulse off-time, servo voltage, wire tension, wire speed, and voltage shown in Table 2 were taken as a starting point. These values were selected based on pilot experiments and considering the values recommended by the manufacturer of the WEDM machine. This set of values represents a typical selection for machining AISI D2 steel.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Factor** & **Units** & **Value** \\ \hline Pulse on-time (Ton) & \(\mu\)s & 13 \\ Pulse off-time (Toff) & \(\mu\)s & 14 \\ Servo voltage (SV) & volts & 44 \\ Wire tension (WT) & gram-force & 30 \\ Wire speed (WS) & m/min & 7 \\ Voltage (V) & volts & 7 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Baseline values for the experiment.  
Figure 4: Connection of the power analyzer (Fluke 43B) on the main lines of the Zodick VZ300L machine.  
Figure 5: Connection diagram recommended by Fluke to measure the total energy consumption of the machine.  
The manufacturer's recommendations and the same experiments used to select the baseline values were used to define the levels 1, 2, and 3 for each factor. The levels are intended to explore the variation in the response around the baseline values without moving too far from the manufacturer's recommended values to cause excessive wear in the wire or break it. This is especially true for the wire tension and wire speed, whose values were kept well below the maximum allowed by the machine. Table 3 shows the selected levels for each one of the factors.  
Following [PERSON]'s methodology, an \(L_{27}\) orthogonal array was employed to analyze the WEDM process. Each of the 27 experiments was conducted with five repetitions for a total of 270 experimental runs: 135 for the 19 mm thick plate and 135 for the 25 mm thick plate.  
Other factors were also considered, which were kept constant during the experiments. These factors were a 0.25 mm diameter brass electrode, vertical cutting angle, a peak current of 2215 units, a servo feed of 60 units, 55 units of water pressure, and the use of deionized water as a dielectric fluid. The MAO, the machine setting that controls the sensitivity level and the amount of adjustment to the \"On\" and \"Off\" times, was set to 250.