# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 4 Conclusions  
Electric discharge machining (EDM) of D2 steel has been performed to produce circular holes with different electrode designs under constant machining conditions. Two-stage experimentation was performed using several tool designs. EDM results with reference to machining time (MT), hole taper  
Figure 8: Main effects plots of machining performance measures; (**a**) machining time (MT), (**b**) taper angle (**a**), (**c**) radial overcut (ROC), and (**d**) surface roughness (SR). angle (o), radial overcut (ROC), and surface roughness (SR) are compared with conventional cylindrical tool design. Based on the results and discussion, following important conclusions can be established:  
1. During the EDM of D2 steel, relief angled tool electrode performs better than the traditional cylindrical electrode. 2. In comparison with the cylindrical electrode (D\({}_{\rm C}\)) the modified tool designs (D\({}_{\rm R}\) and D\({}_{\rm RL}\)) complete the through-hole in substantially shorter time. Approximately 50% time can be saved by the use of electrode design D\({}_{\rm RL}\). Minimum time taken by D\({}_{\rm C}\) and D\({}_{\rm RL}\) tools is 22.25 min and 11.72 min, respectively. 3. Taper angle (o) of the eroded hole increases with the increase in relief angle. The conventional cylindrical tool produces hole with minimum taper angle of 2.34\({}^{\circ}\). However, the tool having relief with land (D\({}_{\rm RL}\)) creates 2.54\({}^{\circ}\) taper indicating that D\({}_{\rm RL}\) design can also be considered in place of conventional design. 4. Tool design having relief with land (D\({}_{\rm RL}\)) offers lowest value of radial overcut (ROC) amounting to be 322 um. Comparing with the overcut caused by conventional cylindrical tool (ROC = 464.50 um), a 30.6% reduction in overcut can be realized. 5. Most of the relief angles produce holes with smaller surface roughness as compared to traditional tool (D\({}_{\rm C}\)). The smallest surface roughness against D\({}_{\rm C}\) and D\({}_{\rm RL}\) designs are 13.7 um and 8.4 um respectively. Compared to conventional electrode, a reduction of 38.7% in surface roughness can be realized by the use of D\({}_{\rm RL}\). 6. Among the three main electrode designs (D\({}_{\rm C}\), D\({}_{\rm R}\), & D\({}_{\rm RL}\)), the design having relief angle with land (D\({}_{\rm RL}\)) offers less machining time, radial overcut, and surface roughness of the machined holes. 7. There is a close competition between the performance of 5\({}^{\circ}\) and 10\({}^{\circ}\) relief angles. The influence of the relief angle (between 5\({}^{\circ}\) & 10\({}^{\circ}\)) on all the four machining responses is found to be statistically insignificant. However, 10\({}^{\circ}\) relief angle could be the most preferred choice to get better machining results. 8. The effect of land thickness (within 1-4 mm) over the machining responses is statistically insignificant, however land thickness gets consumed during machining therefore it should be just enough to withstand the machining process till completion. 9. Relief angled electrode based EDM is at its very initial stage and extensive future research on this topic is expected to be carried out in several domains such as modeling of spark area and material removal rate, tool wear rate phenomenon, performance of relief angled electrode based EDM over difficult-to-machine materials, and further modifications in electrode designs etc. Conceptualization, M.R. and N.A.M. ; Data curation, M.R. ; Formal analysis, M.R., N.A.M. and N.A. ; Funding acquisition, N.A. and A.M.A. ; Investigation, M.R. and A.H.; Methodology, N.A. and A.M.A. ; Project administration, A.M.A. ; Resources, N.A.M., N.A., and A.H.; Software, M.R. and A.H.; Supervision, N.A.M. ; Validation, A.M.A. and A.H.; Writing--original draft, M.R., N.A.M. and N.A. ; Writing--review & editing, A.M.A. and A.H. All authors have read and agreed to the published version of the manuscript. Raytheon Chair for Systems Engineering, King Saud University, Saudi Arabia.