# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
## 4 Research in EDM of Tool Steel
### Performance Measures in EDM of Tool Steels
The EDM parameters used in the study were power, voltage, pulse-off time, and spindle rotational speed; the effect of these parameters on MRR was analyzed using ANOVA. The paper also used RSM to study surface integrity. The authors reported that the only influential design factors and interaction effects for a confidence level of 95% were power, voltage, pulse-off time, and spindle rotational speed. The MRR was modeled in terms of process parameters as follows:  
\[\mathrm{MRR}\Big{(}\frac{\mathrm{mm}^{3}}{\mathrm{min}}\Big{)} = 8.96796+3.23882\times\mathrm{power}-0.68118\times\mathrm{voltage}\] \[+2.08759\times\mathrm{pulse\;off\;time}+0.13699\times\mathrm{ spindle\;rotational\;speed}\] \[+0.00375\times\mathrm{voltage\;}\times\mathrm{voltage}\] \[-0.21999\times\mathrm{power}\times\mathrm{pulse\;off\;time}\] \[-0.00137\times\mathrm{voltage\;}\times\mathrm{spindle\;rotational\;speed}.\]  
[PERSON] and [PERSON] [177; 178] investigated the effect of machining parameters including pulse-on time, pulse-off time, pulse-peak current, and wire tension on the SR of wire EDMed DC53 die steel by utilizing the ANOVA technique. The authors reported that the pulse-on time and pulse-peak current were the significant variables to SR of wire EDMed DC53 die steel. Similarly, [PERSON] and [PERSON] [164] studied the effect of EDM parameters including pulse current, pulse-on time, and pulse-off time on SR for machining 40 CrMnNiMo864 tool steel (AISI P20). The authors reported that the SR was increased with higher values of pulsed current and pulse-on time parameters, and better surface finish was achieved with lower current, lower pulse-on time, and relatively higher pulse-off time. Additionally, [PERSON] et al. [158] investigated the influence of surfactant and Al powders added to the dielectric on the SR of an SKD61 steel workpiece during the EDM process. The machining parameters for EDM optimization were also proposed. Al powders in the dielectric were agglomerated by the electrostatic force among fine Al particles, and a surfactant homogeneously separated the Al powder in the dielectric. The authors reported that the best distribution effect was found when the concentrations of the Al powder and surfactant in the dielectric were 0.1 and 0.25 g/L, respectively. An optimal SR value of 0.172 \(\upmu\)m was achieved under the following parameters: positive polarity, discharge current of 0.3 A, pulse duration time of 1.5 \(\upmu\)s, open circuit potential of 140 V, gap voltage of 90 V, and surfactant concentration of 0.25 g/L. Furthermore, [PERSON] and [PERSON] [161] studied the influence of EDM process parameters on the performance parameters for AISI P20 tool steel under finish machining. Other research studies also discussed the machining characteristics for other grades of tool steel. For example, [PERSON] and [PERSON] [122] studied the machining characteristics of AISI D5 tool steel in the wire EDM process, and, in another investigation [23], the effects of machining parameters on the performance parameters in EDM of En-31 tool steel were studied. The effect of process parameters on the performance parameters was also analyzed using the Taguchi method. For example, in one study [190], the effect of wire EDM process parameters was investigated for normal SR during the machining of powder metallurgical cold-worked tool steel, VANADIS 4e. The study utilized the Taguchi method to determine the optimum SR. The process parameters considered in this study included pulse-on time, pulse-off time, servo voltage, peak current, wire tension, and water pressure. The authors reported that the most important interactions impacting the SR of machined surface were between the pulse-on time and pulse-off time, pulse-on time and peak current, and pulse-off time and peak current. Furthermore, the influence of process parameters on the breathing zone concentration of respirable aerosol generated from the EDM process was analyzed using Taguchi methodology [195].