# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
## 4 Research in EDM of Tool Steel
### Development of New Methods and Methodologies  
Many developments were proposed in EDM processes; for example, one study [197] proposed a new method of determining the energy distribution and plasma diameter. The authors compared the boundary of the melted material in the crater which was obtained via the metallographic method and that which was obtained from the isothermal surface of the thermal-physical model. The boundary of the melted material was calculated from the thermal-physical model using the finite element method. This method was applied to experimentally molded steel 8407, determining the energy distribution and plasma diameter in different dielectrics with different polarities. Figure 11 shows a comparison of the section view of the craters obtained using different dielectrics and polarities.  
[PERSON] et al. [205] proposed a piezoelectric self-adaptive micro-EDM. The proposed machining method realized self-regulation depending on discharge conditions. Compared with conventional micro-EDM, the discharge stability of the working process was improved greatly, and the machining efficiency was higher, while the electrode wear ratio was lower. Furthermore, [PERSON] et al. [198] developed a multi-mode precision pulse power system based on a micro controller unit and double complex programmable logic devices. The effects of capacitance on the achievable processing thickness were analyzed under controllable resistance and capacitance precision pulse power mode. By properly selecting a capacitance that achieved triple the charging time equal to the pulse duration, the best SR and minimum single pulse energy were obtained.  
Figure 11: Comparison of the section view of the craters obtained using different dielectrics and polarities [197].  
[PERSON] et al. [132] studied the capability for the implementation of die-sink EDM in meso-micro-scale machining. The study presented the process parameters that achieved high MRR and TWR with high form accuracy and precision. Additionally, [PERSON] et al. [111] proposed a methodology that guarantees an early detection of instability that can be used to avoid the detrimental effects associated with both unstable machining and wire breakage. The proposed methodology established helpful procedures to understand the causes of wire breakage and instability. [PERSON] [153] proposed a flexible high-speed EDM technology with geometrical transform optimization. Furthermore, [PERSON] et al. [204] studied and analyzed the machining effects developing at high peripheral speeds. The process behavior and surface topography of three different processes, namely, electrical discharge turning, electrical discharge grinding, and wire electrical discharge grinding, were compared for cold-worked steel 90 MnCrV8.  
In the recent past, studies were conducted to assess different methods for several purposes. For example, [PERSON] et al. [180] developed a new wear compensation method based on real-time tool wear sensing. On the other hand, in another investigation [85], a method of optimizing for EDM performance parameters for EDM was developed. [PERSON] and [PERSON] [152] also proposed the development of a new dry wire EDM method, and [PERSON] et al. [128] developed a process of finish machining on free-form surfaces using EDM.