Fundamental Study on Influence of Dielectric Oil Cooling Effect on Wire EDM Characteristics

Deionized water has been conventionally used as dielectric fluid in wire electrical discharge machining (EDM), while oil in dielectric die-sinking EDM. The discharge gap distance using dielectric oil is generally smaller than that using deionized water, since the electric resistivity of dielectric oil is higher. In addition, EDM in oil can prevent oxidization and anodization of the machined surface. For these reasons, dielectric oil has been recently used also in wire EDM for achieving high-precision machining. However, the influence of dielectric oil properties on wire EDM characteristics has not yet been clarified sufficiently. This study fundamentally investigated the influence of the dielectric oil cooling effect on wire EDM characteristics. Three prototypes of dielectric oil differing only in cooling effect were made, and linear cutting experiments were carried out using these oils. The experiment results showed that the removal rate and machined kerf width increased with dielectric oil cooling effect, while the surface roughness decreased. Analysis of spark locations by high-speed observation indicated that the increase in removal rate would be caused by the enhancement of discharge stability with the cooling effect. It was also found that the increase in bubble generation with high cooling effect enhanced smooth debris exclusion from the gap, leading to a reduction in surface roughness.