## 1 Introduction  
Tungsten carbide is a material of choice in numerous applications requiring higher values of melting point, hardness, strength, toughness, wear resistance, and abrasion resistance. The automotive, tooling, die and mold, and aerospace are the common industries wherein the use of tungsten carbide and its allied family materials are widely practiced. The drawing and extrusion dies, squeeze casting and high pressure die casting, punches, cutting tools (tool inserts), cutting blades, water jet nozzles, conical pick for drilling, and high wear resistant parts are the specific and exemplary applications of tungsten carbide [1; 2; 3]. The machining of tungsten carbide is frequently required to fulfill the above-said industry needs and associated applications. Shaping of WC through conventional means of machining is considered as challenging because of high tool wear rates and the catastrophic failure of the cutting tools [4]. The use of diamond tool is therefore practiced to cut the WC materials. The use of diamond tool makes the machining process costly. Among the nonconventional machining practices, electric discharge machining (EDM) is a competent process wherein tool failure can be avoided. Since,the tool and work do not make a physical contact during EDM, therefore the hardness of the material does not impart any significant challenge. In comparison of other commonly used metallic materials, the die-sinking EDM of carbides (WC) has not been widely attempted because of its low machining rate [5]. However, the EDM is reported as a potential process for machining WC [6; 7]. Upgrading the EDM performance has always been remained the researchers' interest. Besides having a long list of advantages, low machining rate of EDM is a very well-known limitation of EDM. That is why, in addition to other performance measures of EDM, the improvement in the rate of material removal (MRR) is one of the preferred objectives of the researchers. Many attempts are being carried out to achieve high MRR and geometrical accuracy by employing different concepts. For example, to get the better machining performance, the search for appropriate tool material is one of the basic requirements of EDM. It becomes more critical if the substrate material is hard, e.g., tungsten carbide, titanium, and nickel-based super alloys. The search for the suitability of the tool electrode material is not only limited in old studies [8] but also in the recent researches [9]. In some researches the copper is reported and some researchers recommend copper-tungsten as the appropriate tool electrode materials for the EDM of hard materials. Another route for the improvement of process performance is to seek the optimized parametric combinations [10; 11]. Mixing of powder in the dielectric is another commonly reported route by means of which the MRR of the electric discharge erosion process and surface morphology of the machined region can be improved [12]. The process is well-known by its name of powder mixed-EDM (PMEDM). The main interelectrode discharge distributes by the addition of powder particles and secondary discharges are developed. The machined surface topography becomes unique under the action of modified discharges [13]. The additive powders have a significant effect on many performance characteristics such as discharge energy, surface integrity [14], microhardness, and MRR [15; 16]. Providing vibrations to the tool electrode is another method opted for the sinking EDM of WC to improve the machinability measures [17]. It has been stated that the use of ultrasonic vibrated tool electrode uplifts the MRR four times as compared with the MRR under conventional EDM conditions. However, the vibrations in the tool severely affect the tool wear and surface finish [18]. Creating holes in hard materials with high geometrical accuracy is considered as challenging for the manufacturing industry. The presence of overcut and taper angle are the critical challenges [19; 20].