# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
## 4 Research in EDM of Tool Steel
### Research on Dielectric Fluid  
Many studies focused on dielectric fluids in terms of performance improvement and a reduction of the side effects on the process environment. [PERSON] and [PERSON] [74] explored the feasibility of using waste vegetable oil (WVO) as an alternative dielectric fluid. The study presented a comparison between WVO and other conventional dielectric fluids such as hydrocarbon oil and kerosene in terms of their effect on the EDM performance. The authors reported that the WVO-based bio-dielectric fluid could be used as an alternate to hydrocarbon-, water-, and synthetic-based dielectric fluids for EDM. [PERSON] et al. [159] studied the effect of surfactant on the performance of the EDM process of SKD61 mold steel. Peak current, pulse duration, open voltage, and gap voltage were considered as process parameters. The study reported that the dispersed debris in dielectric fluid improved the effects of carbon accumulation and dreg discharge, while it reduced the unstable concentrated discharge. It was found that the particle agglomeration was reduced after surfactant molecules covered the surface of debris and carbon dregs in the kerosene solution. The authors reported that the addition of Span 20 (30 g/L) to the dielectric increased the conductivity of the dielectric and, therefore, the machining efficiency, as a result of the shorter relay time of electrical discharge. Furthermore, it was found that the MRR was improved by as much as 40%-80% with proper working parameters.  
[PERSON] and [PERSON] [130] studied EDM with a powder-mixed dielectric in terms of high-quality surface generation, and they compared the process performance with the conventional EDM process. It was found that the use of powder-mixed dielectric EDM reduced the SR, crater diameter, crater depth, and the white layer thickness. It was also found that the powder-mixed dielectric significantly reduced surface heterogeneity.  
[PERSON] et al. [115] studied the influence of adding silicon powder mixing into the dielectric fluid of EDM for AISI D2 die steel. The authors reported that peak current, concentration of the silicon powder, pulse-on time, pulse-off time, and gain significantly affected the MRR in powder-mixed EDM. Among all parameters, peak current and the concentration of silicon powder were the most significant parameters enhancing the MRR. [PERSON] and [PERSON] [155] studied the effect of additive properties on the surface of SKD-11 machined by EDM. The research experimentally studied the different thermo-physical properties of additives including aluminum, chromium, copper, and silicon carbide powders. It was found that the additive practical size in the dielectric fluid affected the surface quality of the machined surface. Furthermore, the SR improved as the particle size became smaller. However, the particle size had the opposite effect on the recast layer, whereby a smaller particle size resulted in a thicker recast layer of the EDM machined surface. The authors reported that the aluminum powder produced the best surface finish and the thinnest recast layer in the machined work, whereas the process without foreign particles and with copper powder generated the worst surface characteristics.  
Many other earlier studies also verified the influence of the powder-mixing on the EDM process performance for many grades of tool steels. For example, [PERSON] et al. [61] optimized the process parameters of powder-mixed EDM, [PERSON] and [PERSON] [129] studied the effect of silicon powder-mixed dielectric on the EDM of AISI H13 tool steel, [PERSON] et al. [136] introduced a near-mirror-finish phenomenon in EDM using powder-mixed dielectric, and [PERSON] et al. [76] studied the effect of flushing on the machined surface of AISI01 tool steel using EDM.