Tool-electrode, thermal conductivity

The heat power PE will only partially be transferred to the machined substrate (i.e., P0 = ePE)- The fraction of the heat flux transmitted to the substrate will depend on, besides the geometry of the problem, the ratio of the coefficients of thermal conductivity of the electrolyte (typically around 0.6 W m 1 K1 for NaOH) and the substrate. Another important parameter is the heat conductivity of the tool-electrode. As the tool-electrode has the highest heat conductivity, most part of the heat is evacuated through it. 

M. Mousa, A. Allagui, H.D. Ng, R. Wiithrich The effect of thermal conductivity of the tool electrode in spark assisted chemical engraving gravity-feed micro-drilling. Journal of Micromechanics and Microengineering 19 (2009), accepted (November 2008). 

EDM is thermal erosion for electrically conductive materials, which is based on electrical discharging (sparking) between the tool (electrode) and a conductive work-piece. Therefore, every electrically conductive material can be processed, especially steel and aluminum, in mold making. This applies particularly for very hard materials where the limit can be reached with traditional machining processes. Both the workpieces as well as the mold are immersed in a non-conductive liquid medium, the so-called dielectric fluid (usually oil or deionized water). This dielectric fluid is necessary for the functionality of EDM. 

---