# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
## 4 Research in EDM of Tool Steel
### Electrode Material and Shape in the EDM of Tool Steel  
Many issues related to electrodes and the effect of electrode materials on the EDM performance were studied by many researchers. For example, [PERSON] et al. [170] studied the influence of a graphite grade electrode on the MRR and TWR in the sinking EDM roughing process for Bohler steel W300 (1.2343) material. The physical characteristics of graphite, including specific electric resistance, thermal conductivity, and grain size, were considered. The authors reported that there was no direct link between the performance and the grain size in term of MRR and TWR. It was found that the most important factor of the electrode regarding MRR was the electrode material electrical conductivity, while, for TWR, the most important factor was a combination of the grain size and electric resistance. Furthermore, [PERSON] and [PERSON] [185] studied the origin of concavity at the end-tip in the micro-EDM of blind micro-holes. The shape of tip deformation was investigated experimentally. The study considered open gap voltage, pulse energy, and tool rotation speed as the influence parameters on such tip shapes. The study implemented cross-sectional and topographical analysis on the micro-hole and micro-tool electrode to study the influence of the mentioned parameters on the final tip shape. Figure 14 shows the micro-tool electrodes and optical section views of machined micro-holes using very short pulses and open gap voltages of 60, 75, and 90 V. Finally, the study proposed an accumulation of debris phenomenon to describe the wear mechanism at the tip shapes encountered.  
[PERSON] and [PERSON] [196] studied the effect of electrode rotation and external magnetic field on EDM performance. The authors reported that the machining performance was improved with a rotary electrode. The externally applied magnetic field reduced the inactive pulses, including arcing, short circuit, and open circuit, while it also helped in the ionization. It was found that the application of the magnetic field led to an improvement in surface quality, wherein SR decreased upon increasing the rotational speed.  
[PERSON] and [PERSON] [78] investigated the influence of the electrode lead, tilt angles, and dielectric fluid flow rate on MRR, TWR, and SR in the near-dry EDM milling process. The study developed a computational fluid dynamics model to predict the flow rate of dielectric fluid. [PERSON] et al. [192] compared the influence of copper and graphite electrodes on the performance of the EDM process for XW42. The authors reported that the copper electrode achieved higher MRR than the graphite electrode; thus, the authors recommended using the copper electrode for rough cutting and the graphite electrode for finish cutting. It was found that the EWR of the copper electrode was lower than the EWR of the graphite electrode.  
Earlier studies related to electrodes were also presented. For example, a study by [PERSON] et al. [211] improved the wear resistance of machined surfaces using EDM with tungsten carbide power compact electrodes, whereas [PERSON] and [PERSON] [210] studied the machining characteristics of cylindrical tools in the cutting of 3D shapes using EDM.