Patent ID: 8217296

Claim:
A fluid-quality control method of changing fluid quality of used water-based machining fluid or undiluted fluid into fluid quality of water-based machining fluid for electric-discharge machining, the fluid-quality control method comprising: measuring fluid-quality value of target fluid of which the fluid quality is to be controlled; and controlling the fluid quality, including electrolyte-solutionizing the target fluid, when the measured fluid-quality value is lower than a first condition value, by substituting an impurity anion contained in the target fluid with a predetermined anion and substituting an impurity cation contained in the target fluid with a predetermined cation; and purifying the target fluid, when the measured fluid-quality value is higher than a second condition value that is equal to or higher than the first condition value, wherein the measuring and the controlling are repeated, so that the fluid-quality value of the target fluid falls within a predetermined range, to make the target fluid into electrolyte solution with a correlation between pH and conductivity.