# EDM of D2 Steel: Performance Comparison of EDM Die Sinking Electrode Designs
## 1 Introduction
An improvement of 6.6% in material removal rate and a reduction of 5.2% in tool wear rate can be realized through the addition of graphite powder during the powder mixed electric discharge machining (PMEDM) of tungsten carbide [22]. [PERSON] et al. [23] narrated that the machining of tungsten carbide with aluminum powder mixed in the dielectric result in higher MRR. Similarly, an increase of 12% in MRR have been reported by mixing graphene oxide flames in the dielectric [24]. The use of multi-hole electrodes in EDM sinking is also reported as promising choice to achieve close form tolerances and high material removal rate as compared to a conventional cylindrical electrode. However, it has been stated that the use of optimized parameters is required to get more benefit from a multi-hole electrode [25]. The use of composite tool electrodes (consisting of two different materials) is another emerging trend to improve the performance of the EDM die sinker. However, the investigations of the behavior of multi-material tool electrodes are at the initial stages and limited to the study of electric discharge breakdowns occurred between the anodes (tool and work) [26]. Multi-channel tool electrodes are found to have better drilling time, dimensional accuracy, and surface roughness during electric discharge drilling of Inconel 718 [27]. Changing the bottom profile of the tool electrode also affects the machining characteristics. [PERSON] et al. [28] compared the EDM performance using flat bottom and convex/concave bottom electrodes. A convex/concave shape at the bottom of electrode exhibits a thin recast layer, better surface finish, and machined geometriesduring EDM of nickel alloy. Other efforts to improve the EDM process performance are in the direction of assistive technologies and concepts. Some additional sources of energy assistance are combined with the primary EDM thermal energy. These include EDM with surfactant mixed dielectric [29], ultrasonic assisted machining [30], and magnetic stirring, etc. [31]. EDM is a very slow machining process and produces geometrical inaccuracies. It can be inferred from the literature that different efforts are being made to improve the machining rate and machining accuracy of EDM. Traditionally, a cylindrical electrode is used to machine holes through EDM die-sinking. In our previous study [32], relief angled electrodes were used for the first time to improve the machining performance of EDM to produce through-holes in tungsten carbide. With the use of relief angled electrodes, the machining time was significantly reduced (49% reduction) along with other machining characteristics. The process can be termed as relief angled electrode-based EDM. The goal of the present research is to study the relief angled electrode-based EDM process performance for D2 grade of steel and to validate previous results. Three different designs, i.e., conventional cylindrical design, relief angled design, and modified relief angled design, are introduced to produce through-holes in D2 steel. Each of the modified tool designs is further varied by providing different relief angles and land thickness. Machining time, hole taper angle, overcut, and surface roughness of machined holes are taken as the response measures. Performances of designed tool electrodes have been compared with the machining results corresponding to conventional cylindrical tool design. Two-stage experimentation is conducted to seek for an appropriate design having a potential of gifting better machining results.