## 2 Materials and Methods  
Tungsten carbide was machined through EDM using a copper electrode. EDM involves the electrical and thermal energies in order to produce the spark between both the electrodes (tool and substrate). Under the action of successive electric sparks, electrodes' surfaces get melted and vaporized. In this respect, the type of the conductor (electrode), elemental composition, and properties of the electrodes (physical, thermal, and electrical) play a vital role during machining. Therefore, the elemental composition (as per datasheet provided by the manufacturer) is presented in Table 1 and the important properties of the substrate (WC) are presented in Table 2. A strip of WC consisting of 145 mm length, 40 mm width, and 4 mm thickness was taken as a substrate. Perpendicularity between both the tool and substrate's exposed surfaces was considered as important to get a symmetrical machined feature. It was very carefully ensured that the tool and workpiece were mutually perpendicular to each other. Firstly, the workpiece was placed on a flat plate and the tool (held in the tool holder) was brought very close (1 mm) to the upper surface of the work sample. Secondly, the tool was slightly loosened from the holder and let it dropped over the work surface under the action of gravity. At that time the tool and work acquired a physical contact and became perpendicular to each other. Then the reference for the machining was established. Through hole of a circular cross-section (8 mm diameter) was taken as the machining feature. A minimum distance of 2 mm between the circumferences of successive holes was maintained so that the machining effects associated with a particular hole could be completely avoided for the following hole. The machining was carried out using a copper electrode and all the EDM parameters were set fixed. Parametric values were taken from the ranges, available in literature as cited in the introduction section, pertaining to EDM through a copper electrode. Parametric values were taken from the ranges, available in the literature as cited in the introduction section, pertaining to EDM through copper electrode. Since the EDM parameters were kept constant throughout the experimentation so the effect of EDM parameters remained uniform. Each experiment reflected only the effect of tool designs. The fixed set of parameters is presented in Table 3. In addition to EDM parameters the other machining conditions were also kept constant, e.g., the dielectric type, flushing rate, the position of the workpiece with respect to the worktable, etc. \begin{table}
\begin{tabular}{c c} \hline
**Element** & **Percentage** \\ \hline
**W** & 88.3 \\
**Fe** & 0.16 \\
**C** & 4.9 \\
**Co** & 5.9 \\
**Ni** & 0.31 \\ \hline \end{tabular}
\end{table} 
Table 1: Elemental composition of tungsten carbide. Different relief angles were taken as the variables of the current research. In order to produce a circular hole (blind or through) using EDM, conventionally a cylindrical electrode with a uniform cross-section (throughout the length of the tool) is commonly used. In this research, the conventional cylindrical design was modified by different design types through providing relief angle on the sides of the tool. Three different electrode types namely conventional (D\({}_{\text{C}}\)), relief angle (D\({}_{\text{R}}\)), and relief angle with land (D\({}_{\text{RL}}\)) were designed and fabricated for this investigation. The concept of the relief angle was borrowed from the tools (single-point tool especially) used in conventional machining [31]. On the other end, the concept of land was derived from the design features of punches and dies [32]. The relief angle design type (D\({}_{\text{R}}\)) was further categorized into four subdesigns in which relief angles were varied. Relief angles of 10, 20, 30, and 45\({}^{\circ}\) were provided and the corresponding tools were named as D\({}_{\text{R10}}\), D\({}_{\text{R20}}\), D\({}_{\text{R30}}\), and D\({}_{\text{R45}}\).