# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 2 Materials and Methods
### Electrode Designs and Fabrication  
The tool electrodes used in this work are made of copper, as the cooper electrode has been widely used as a suitable tool electrode for the EDM of tool steels. Three different tool designs are used to \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Elements** & **C** & **Si** & **Mn** & **Mo** & **Cr** & **Ni** & **V** & **Co** & **Fe** \\ \hline
**Contents \%** & 1.5 & 0.3 & 0.3 & 1 & 12 & 0.3 & 0.8 & 1 & Balance \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Elemental composition of D2 steel [33]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Physical Properties** & \multicolumn{3}{c}{**Mechanical Properties**} & \multicolumn{3}{c}{**Thermal Properties**} \\ \hline
**Properties** & **Value (Units)** & **Properties** & **Value (Units)** & **Properties** & **Value (Units)** \\ \hline Density & \(7.7\times 1000\) kg/m\({}^{3}\) & Hardness, Rockwell C & 62 & Thermal expansion & \(10.5\times 10^{-6}\)\(\times\)C\({}^{-1}\) \\ \hline Melting point & 1421 \({}^{\circ}\)C & Hardness, Vickers & 748 & Thermal conductivity & 20 W/mK \\ \hline  & Poisson’s ratio & 0.27–0.30 & & & \\ \hline  & Elastic modulus & 190–210 GPa & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical, mechanical, and thermal properties of tool steel D2-grade [34]. machine through-holes in the substrate. Additionally, drilling a circular hole through the EDM die sinker is carried out using a traditional cylindrical electrode, as it has a uniform cross-sectional area. One of the tool designs used in this research is a conventional design represented as \(\mathrm{D_{C}}\). It consists of an 8 mm face and shank diameter and height of 50 mm. The second design is named the relief angled tool design and is denoted as \(\mathrm{D_{R}}\). In this type of design, taper turning is performed from the tool face up to a certain length to develop a relief angle at one end of the tool. The remaining tool length is simply turned to develop a shank as can be seen in Figure 1b. The diameter of the face remains at 8 mm while the diameter of the shank is kept at 5 mm. In this way, two lengths are generated and named \"face height\" and \"shank height\". These heights are such that the overall length of the tool remained at 50 mm as in the case of the conventional design. The face diameter is also kept at 8 mm. The third type of design is the modification of the second design and is named as relief angle with land and denoted as \(\mathrm{D_{RL}}\). In this design, the tool is the same as that of the relief angle design except the tool face. In the case of the relief angle design, the taper starts immediately at the end of the face, whereas, in the case of \(\mathrm{D_{RL}}\), the taper starts after 1 mm distance from the tool end, leaving the end with 1 mm thickness as is schematically illustrated in Figure 1c. This 1 mm thick end is named as land. The face diameter is again 8 mm and shank diameter is 5 mm. The only difference is in the length of its different sections. However, the total length of the tool is kept at 50 mm. It must be noted that with each of the two designs, \(\mathrm{D_{R}}\) and \(\mathrm{D_{RL}}\), five sub-designs are developed by varying the angle of taper (relief angle). Schematics of each of the sub-designs are shown in Figure 2. Relief angles of \(5^{\circ}\), \(10^{\circ}\), \(20^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\) are provided in each tool. Full details of each design are provided in Table 3. Hence, in this way, EDM was performed with one conventional tool and 10 newly designed tools. All the tools were prepared from the same rod of copper having an initial diameter of 10 mm. The tool preparation is carried out under the constant and same machining conditions. Figure 1: Schematic of electrode designs; (**a**) conventional, (**b**) relief angled, and (**c**) relief with land. Figure 2: Schematic of electrode designs; (**a**) sub-designs of \(\mathrm{D_{R}}\), and (**b**) sub-design of \(\mathrm{D_{RL}}\).