# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 1 Introduction  
Tool steels are high carbon and chromium content alloys used in a variety of industrial applications. D2 steel is one of the materials widely used in mold and die making industry. Forging dies, die blocks of die-casting, drawing dies, and different cutting tools are typical examples where D2 steel is used [1]. Such applications need to have various features to be produced through machining [2]. Blind and through-holes are one of the common features [3] and holes can be produced through electric discharge machining (EDM) [4]. The material removal mechanism of EDM is very complex and debatable due to the involvement of multiple factors. However, it is stated by the fundamental theories that the material removal is governed by the electrical conduction between both the electrodes. Heat is produced from the arc channels and immediately dissipated into the tool and work substrate. The result is melting, vaporization, and flushing of debris under dielectric action [5]. In this way, by the utilization of thermalenergy, 2D and 3D features can be obtained. The formation of various kinds of holes is possible as per the shape of the tool, such as triangular, hexagonal, deep, inclined, blind holes, and through-holes. Such variety of holes is highly difficult by other single process, especially when the work material is hard metal or alloy [6]. Selection of the most appropriate tool material and electrode polarity play vital roles in the erosion mechanism of EDM [7]. Improvement in the performance of the EDM process can be realized by several methods such as employing different dielectric fluids, mixing of additives like boron carbide in the dielectric, polarity changing between tool and work sample, and rotation of electrodes [8]. Although EDM die-sinking is the widely used machining process in industry, it is a well-known fact that the machining rate of EDM is very low [9]. Machining inaccuracies in the form of overcut and tapered sidewalls, circularity, and undercut, etc. are other limitations of EDM [10; 11]. To address these two issues, several researchers have worked in different directions to improve the machining rate and machining accuracy of EDM. Seeking for the most appropriate tool electrode material for a particular or group of substrate materials is the foremost direction approached by researchers to get better machining results. For example, the brass electrode has been recognized as the most suitable material for EDM of a group of substrate materials including stainless steel, aluminum, and tungsten carbide if low tool wear [12] and low surface hardness [13] are the objectives. [PERSON] et al. [14] evaluated the EDM performance against different electrode materials such as copper, cryogenically treated copper, and tungsten and identified the suitable electrode resulting efficient material removal rate. Similarly, among four electrode materials (graphite, copper, brass, and aluminum), the copper electrode with negative polarity has been identified as the most suitable material to machine Ti6 Al4V with minimum geometrical errors (radial and axial overcut) [15]. Optimization of machining parameters is one of the commonly used approaches to improve the machining rate and the feature accuracy [16; 17]. For example, [PERSON] et al. [18] optimized the EDM parameters for the machining of aluminum boride composite and [PERSON] et al. [19] performed multi-response optimization to deal with tungsten carbide samples. On similar lines, multi-objective optimization of EDM process parameters has also been attempted in another study to machine titanium alloy [20]. The use of different dielectrics and powder mixing in the dielectric is another route widely followed by numerous researchers to improve the machining rate of EDM and feature accuracies. In a study presented in [21], several dielectric mediums are tested to evaluate their performance on MRR. The authors used different combinations of dielectrics such as air, air-oxygen, distilled water-air, and distilled water-air-oxygen.