Patent ID: 7737380

Claim:
An electrical-discharge-machining apparatus including an apparatus for controlling pH of a dielectric fluid, wherein the apparatus includes a dielectric-fluid tank that stores the dielectric fluid; a water purifying unit that generates pure water by eliminating impurity ions from the dielectric fluid so that the dielectric fluid contains a predetermined amount of impurity ions consisting of impurity cations and impurity anions; a corrosion-protection-ion generating unit that generates corrosion protection ions, substitutes predetermined cations for the impurity cations contained in the dielectric fluid, and substitutes the corrosion protection ions for the impurity anions contained in the dielectric fluid; a switching unit that switches a supply of the dielectric fluid stored in the dielectric-fluid tank between the water purifying unit and the corrosion-protection-ion generating unit; a conductivity measuring unit that measures a conductivity of the dielectric fluid stored in the dielectric-fluid tank; and a switching control unit that controls the switching unit based on the conductivity measured.