# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 3 Results and Discussion
### Experimentation of Stage 2
#### 3.6.3 Main Effects Plot Analysis  
The main effect plot corresponding to the machining time is shown in Figure 8a. It can be observed that the effect of relief angle over the machining time is inversely proportional. As the relief angle is increased from 5\({}^{\circ}\) to 10\({}^{\circ}\) the machining time is reduced. However, this reduction in machining time is found to be statistically insignificant as per ANOVA results. On the other end, less amount of land thickness seems to be better in order to produce holes. The increase in land thickness takes longer time to complete the erosion of through-holes. However, again, the extra time taken by the larger land thickness is statistically insignificant. It can be stated that any of the relief angle between 5\({}^{\circ}\) to 10\({}^{\circ}\) and any of the land thickness among 2, 3, and 4 mm can be taken to reduce the machining time. However, the tool with 10\({}^{\circ}\) relief and 2 mm land thickness takes relatively less machining time to complete the hole through EDM. Main effects plot for hole taper angle against relief angle and land thickness is shown in Figure 8b. As the relief angle is increased from 5\({}^{\circ}\) to 10\({}^{\circ}\) the hole taper angle also increases but this increase is not significant as determined by ANOVA tests. For example, the mean values of hole taper angles are approximately 2.2\({}^{\circ}\) and 2.5\({}^{\circ}\) when the relief angle is changed from 5\({}^{\circ}\) to 10\({}^{\circ}\). Likewise, the effect of land thickness over the hole taper angle is directly proportional. As the land thickness is increased the taper angle of the machined hole also gets increased. But this increase is statistically insignificant. However, the relief angle of 5\({}^{\circ}\) and land thickness of 2 mm produce smaller taper angle. Hence, the tool with 5\({}^{\circ}\) relief and 2 mm land thickness can be selected as the most appropriate tool design in order to achieve minimum hole taper angle during EDM of D2 steel. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**Source**} & \multicolumn{4}{c}{**Measures**} & \multicolumn{2}{c}{**Significance**} \\ \hline \multicolumn{6}{c}{**Machining Time**} \\ \hline \multirow{4}{*}{**Relief angle**} & DF & Adj SS & Adj MS & F-Value & \(p\)-Value & \multirow{4}{*}{Non-significant} \\  & 1 & 6.222 & 6.222 & 0.44 & 0.575 & \\
**Land thickness** & 2 & 4.223 & 2.112 & 0.15 & 0.870 & Non-significant \\
**Error** & 2 & 28.152 & 14.076 & & & \\
**Total** & 5 & 38.597 & & & & \\ \hline \hline \multicolumn{6}{c}{**Taper Angle**} \\ \hline \multirow{4}{*}{**Relief angle**} & DF & Adj SS & Adj MS & F-Value & \(p\)-Value & \multirow{4}{*}{Non-significant} \\  & 1 & 0.1930 & 0.1930 & 1.80 & 0.311 & Non-significant \\
**Land thickness** & 2 & 0.4894 & 0.2447 & 2.29 & 0.304 & Non-significant \\
**Error** & 2 & 0.2138 & 0.1069 & & & \\
**Total** & 5 & 0.8961 & & & & \\ \hline \hline \multicolumn{6}{c}{**Radial Overcut**} \\ \hline \multirow{4}{*}{**Relief angle**} & DF & Adj SS & Adj MS & F-Value & \(p\)-Value & \multirow{4}{*}{Non-significant} \\  & 1 & 513.4 & 513.4 & 0.62 & 0.515 & Non-significant \\
**Land thickness** & 2 & 4585.6 & 2292.8 & 2.75 & 0.266 & Non-significant \\
**Error** & 2 & 1665.4 & 832.7 & & & \\
**Total** & 5 & 6764.4 & & & & \\ \hline \hline \multicolumn{6}{c}{**Surface Roughness**} \\ \hline \multirow{4}{*}{**Relief angle**} & DF & Adj SS & Adj MS & F-Value & \(p\)-Value & \multirow{4}{*}{Non-significant} \\  & 1 & 0.4538 & 0.4538 & 1.85 & 0.307 & Non-significant \\
**Land thickness** & 2 & 1.3633 & 0.6817 & 2.78 & 0.264 & Non-significant \\
**Error** & 2 & 0.4900 & 0.2450 & & & \\
**Total** & 5 & 2.3071 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Analysis of variance for machining responses. The main effect plot associated with radial overcut (ROC) is shown in Figure 8c. The mean value of ROC follows directly proportional trend against each variable.