## 3 Results and Discussion
### Effect of Electrode Design on Machining Time (MT)  
The effect of different electrodes on the machining time is graphically presented in Figure 5. The electrode with conventional design, i.e., cylindrical tool with no relief angle, completed the through a hole of 4 mm length in 338 min. As the design type was changed from the conventional (D\({}_{\text{CR0}}\)) to the relief angle (D\({}_{\text{R}}\)) and the relief with land (D\({}_{\text{RL}}\)), a substantial reduction in machining time was observed. The time to complete the hole by using the design type D\({}_{\text{R}}\) ranges from 185 to 205 min. Since, in the design type D\({}_{\text{R}}\) the relief angles were further varied, therefore as the degree of relief was increased to a certain extent (30\({}^{\circ}\)) the machining time was also increased. For example, the time taken by the 10 degree relief (D\({}_{\text{R10}}\)) was 185.42 min and the time consumed by 30 degree relief was found to be 212.2 min. However, by a further increase in relief angle (45\({}^{\circ}\)) the time was slightly reduced (205.65 min). It can be noticed that the pattern of machining time was somehow irregular as the relief angle was changed, but the machining time was substantially smaller than the time taken by conventional design. The fluctuation in machining time was around 12 min when the relief angles were 20, 30, and 45\({}^{\circ}\). This fluctuation became more compact (less than 1 min) in the case of D\({}_{\text{RL}}\) type  
Figure 4: EDM produced holes in WC using different designed tool electrodes: (**a**) hole produced though conventional tool design; D\({}_{\text{C}}\), (**b**) holes produced through relief angle design tools; D\({}_{\text{R}}\), and (**c**) holes produced through relief angle with land design tools; D\({}_{\text{RL}}\). designs when relief angles were 20, 30, and 45\({}^{\circ}\). The reason behind this fluctuation could be the change in current characteristics due to the presence of relief angles that need further research. Since EDM is a complex phenomenon and the prediction of discharge current and other parametric behaviors is difficult [23], therefore due to the complex nature of the process slight variations in the machining results can be expected. Thus the involvement of multiple aspects (current characteristics, discharge phenomenon, relief angle, debris flushing, etc.) could be another possibility behind a certain amount of variations among the machining results under relief angled electrodes. Within the subdesigns of \(\rm D_{R}\) the design with 10 degree relief offered the shortest machining time of 185 min. The third design type, i.e., relief with land (\(\rm D_{RL}\)) followed a similar increasing trend. Since in this design type the thickness of the land was kept constant and the relief angles were varied, therefore with the increase in relief angle the machining time also increased. Among the subdesigns of \(\rm D_{RL}\), the minimum time was also observed in the case of 10 degree relief (\(\rm D_{RL10}\)) amounting to be 172 min. However, the time taken by 20, 30, and 45 degree reliefs were somewhat closer to each other. As the relief degree was further increased to a level of 90\({}^{\circ}\) the machining time tended to rise. Comparing all the nine designs of relief angled tools with the conventional cylindrical design the shortest time (172 min) was resulted by the tool having a 10 degree relief angle with a land thickness of 1 mm (\(\rm D_{RL10}\)). Considering the machining time corresponding to the conventional design as a reference, a 49% reduction in machining time could be achieved using the modified tool design (\(\rm D_{RL10}\)). Such a huge amount of time reduction might be recognized as a massive contribution in the field of EDM. Reduction in machining time eventually improved the material removal rate. Since, EDM is a very slow machining process and many decisions in machining industry declined due to the slow nature of this process, the use of relief angled tool design could boost up the machining rate of EDM.