Dielectric fluid for electrical discharge machining

#The present invention relates to a dielectric fluid particularly intended for use in electrical discharge machining.

#As is well known, electrical discharge machining (EDM) can be performed either by a diesinking method using a die electrode or a wire cutting method using a wire electrode. In either method, a workpiece spaced by a predetermined distance, called a machining gap, from a machining electrode and immersed in a dielectric fluid bath is machined by the action of a spark discharge generated between the electrode and workpiece. The dielectric fluid is rapidly vaporized and evaporated in the spark column to provide a high pressure that blows off molten portions of the workpiece while at the same time the unvaporized fluid cools the metal particles removed from the workpiece and removes work chips and decomposed carbon from the machining gap.

#Electrical discharge machining with a wire electrode involves little fire hazard since water is generally used as the dielectric fluid. However, the dielectric used in the diesinking method is generally an inflammable oil such as a mineral oil since only a low machining speed can be achieved with water. With the use of inflammable oils, if the level of the dielectric in the bath drops below a certain safe level, a fire may be caused by the discharge sparks. Therefore, many precautions must be undertaken to provide a safe and reliable machining system. However, observance of the strictest controls upon the use of inflammable oils does not assure complete safety if unattended EDM operations are carried out over many hours. Moreover, mineral oils typically used for EDM operations have a disagreeable odor. Another problem with mineral oils is that they tend to cause skin rashes if the hands of the operator should accidentally come into contact with the oil. It has been proposed to eliminate the fire hazard by using a nonflammable oil such as silicone oil, fluorinated oil or chlorinated oil as the dielectric for EDM but silicone and fluorinated oils are too expensive to be economically feasible and chlorinated oil is toxic.

#The invention is characterized by the use of an ester solution in the dielectric fluid for EDM. The preferred ester solution is water-soluble, has a high flash point, for example, higher than 100.degree. C., is difficult to ignite and is not easily ionizable for causing a discharge. When such a dielectric fluid is employed, the machining speed may be slightly lower than obtained with an ordinary dielectric fluid such as kerosene. On the other hand, with the use of ester solution, wear of the machining electrode is reduced and the fire hazard involved with the use of kerosene is eliminated.

#A preferred embodiment of an ester solution used in the dielectric fluid for EDM is an aqueous solution of acetate ester having high flash point. Acetate ester is water-soluble and a mixture of acetate ester with water becomes uniform solution by simply by stirring the mixture for about one minute.

#To test the combustability of the aqueous solution of acetate ester, a burning test was conducted with aqueous solutions of varying concentrations of diethylene glycol monoethyl ether acetate in a crucible by igniting a glass wick in the solution with a Bunsen burner. The test results are shown in Table 1.