# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
## 4 Research in EDM of Tool Steel
### Effect of EDM Process on the Surface Integrity  
Many studies with a focus on the surface integrity of tool steel materials during machining with different EDM variants were performed. For example, in an investigation [182], the effect of electrode material on resulting residual stresses, SR, and cracks in the surface of tool steel workpieces was studied. The research compared the machining performance while using Dura graphite 11 and Poco graphite. The authors reported that the SR of DIN 1.2080 was lower with Poco graphite. Regarding the surface cracks, the results showed that the machining surface with Dura graphite 11 had more cracks and fewer micro-cracks than the machining with DIN 1.2080. Figure 6a-d show the surface crack during rough machining of the two workpiece materials machined by the two electrode materials. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Authors** & **Process** & **Machining** & **Remarks** \\  & & & **parameters** & **Performance** & **Remarks** \\ \hline
35 & \
\begin{tabular}{c} ([PERSON] et al. \\ 2003) \\ [105] \\ \end{tabular} & EDM & Is, Ton, and & T\_RL, SR, &
\begin{tabular}{c} The recast layer becomes thicker as \\ the pulse current and pulse-on \\ duration increase. As the peak \\ current is achieved, the melting of \\ the material and damage of \\ the surface and subsurface area \\ increase. \\ \end{tabular} \\ \hline
36 & \
\begin{tabular}{c} ([PERSON] et al. \\ 2003) \\ [105] \\ \end{tabular} & EDM & Is, Ton, and & T\_RL, SR, &
\begin{tabular}{c} The combination of low-frequency \\ vibration and electrode rotation did \\ not give a satisfactory effect on MRR. \\ The combination of ultrasonic \\ vibration and electrode rotation led \\ to an increase in MRR. \\ The combination of high-frequency \\ vibration and electrode rotation was \\ the best for the finishing cut. In \\ the semi-finishing cut, \\ the vibro-rotary EDM increased \\ MRR by 35\% and 100\% compared to \\ vibratory and rotary EDM, \\ respectively. \\ \end{tabular} \\ \hline
37 &
\begin{tabular}{c} ([PERSON] \\ and \\ [PERSON] \\ 2001) \\ [152] \\ \end{tabular} & Dry EDM & The MRR and waviness could be improved by increasing the wire \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._It was also found that the Dura graphite 11 electrode resulted in lower residual stresses compared to another electrode. Furthermore, soft EDM machining exhibited higher residual stresses as a result of a higher pulse-on duration time. Figure 6: **(a)** Surface cracks of DIN 1.2379 rough machining using Dura graphite 11 electrode; (**b**) surface cracks of DIN 1.2080 rough machining using Dura graphite 11 electrode; (**c**) surface cracks of DIN 1.2379 rough machining using Poco graphite EDMC-3 electrode; (**d**) surface cracks of DIN 1.2080 rough machining using Poco graphite EDMC-3 electrode [182]. Moreover, [PERSON] et al. [148] have comprehensively compared the surface integrity of S390 and SKD11 with multi-cutting. The authors reported that the surface roughness, white layer thickness, and surface residual stress decreased as the number of cutting passes increased. They also reported that more pinholes and slightly larger craters were produced in the finish trim cut surface of the S390 workpiece, while micro-cracks were found in the finish trim cut surface of the SKD11 workpiece. Additionally, [PERSON] and [PERSON] [116] studied the surface modification of three die steel materials achieved by EDM machining with powder-mixed tungsten. Process parameters including peak current, pulse-on time, and pulse-off time were considered to study the micro-hardness of the machined surface. The study utilized the Taguchi experimental design technique to independently conduct the experiments on each work material. The authors reported that a significant amount of material was transferred from the powder suspended in the dielectric medium to the work material. For example, a range of \(\sim\)0% to 3.25% tungsten in the base material was recorded in the machined surface of H13 die steel.