# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 3 Results and Discussion
### Analysis of Machining Time (MT)
However, against the higher relief angles like 45\({}^{\circ}\), the time tends to increase (17.2 min). Within the sub-designs of D\({}_{\text{R}}\), the tools having 20\({}^{\circ}\) and 30\({}^{\circ}\) angles offer the lowest machining time (~11.3 min). The next design type, i.e., D\({}_{\text{RL}}\), follows the similar pattern. Within this design, D\({}_{\text{RL5}}\) and D\({}_{\text{RL10}}\) consumed almost equal time (~11.6 min). After 20\({}^{\circ}\), the time taken by relief with land tools increases. Among the sub-designs of D\({}_{\text{RL}}\), the minimum time has been observed in the case of 10\({}^{\circ}\) and 20\({}^{\circ}\) relief amounting to be ~11.6 min. However, the time taken by 30\({}^{\circ}\) and 45\({}^{\circ}\) reliefs are somewhat closer to each other. Comparing the results with conventional tool design, approximately 50% reduction in machining time can be achieved during EDM of D2 steel using the novel designs of electrodes. It can be considered as an appreciable contribution in the field of electric discharge machining. Whenever the use of EDM is avoided in the industry, its low machining rate is one of the major factors. The use of newly presented electrode designs has the potential to substantially reduce the machining time, and ultimately, the productivity of EDM can be improved. The phenomenon behind this reduction in erosion time is believed to be a different sparking behavior in the case of altered tool designs as compared to sparking offered by conventional design since the erosion is carried out by electrode surfaces close to the substrate surfaces. At the initial cuts, the erosion phenomenon is the same for all the designs. Electric discharges are only produced between the electrode's bottom face and the top surface of the work sample. However, as the hole formation progresses, the sparking occurs at two regions, i.e., at the tool's bottom face and around the periphery of the tool's segment penetrated inside the partially formed hole. The conventional cylindrical tool design has straight vertical walls throughout its length (face and shank diameters are equal, i.e., 8 mm). Thus, the sparking area continuously increased in case of conventional design (D\({}_{\text{C}}\)). However, the design with relief angle (D\({}_{\text{R}}\)) allows the electric discharges to be produced just at the machining end of the tool. The presence of relief angle prevents the peripheral sparking since the face diameter is of 8 mm and the shank diameter is of 5 mm (refer to Figure 1). In the presence of relief angle, the inter-electrode gap between the shank and inner walls of the hole gets so high that sparking does not occur. Thus, the same input energy is focused at the bottom face of the tool, leading to high energy density. As a result, the machining time is soundly reduced. In the case of the third design (D\({}_{\text{RL}}\)), the sparking area also remains constant but less than the sparking area observed  
Figure 4: Effect of electrode designs on machining time. with the cylindrical electrode. Sparking occurs at the footing end and at the 1 mm land area. It remains constant until the complete hole is produced. On the other end, since the sparking area continuously increased by the cylindrical tool; therefore, the same amount of input energy is consumed to erode larger areas, and as a result, more time is taken to complete the hole.