EDM Drilling of Non-Conducting Materials in Deionised Water

Abstract

Electrical discharge machining (EDM) of non-conducting materials currently is only possible with the help of an auxiliary conductive layer, known as assisting electrode, which must be regenerated after each discharge. Therefore, an assisting conductive layer is applied to the surface of the workpiece to initiate the discharge process. In order to continue erosion, the eroded surface regions must have a new conductive layer in contact with the original assisting conductive layer, which is typically achieved by depositing carbonaceous material through dielectric oil decomposition. In this paper, the renewal of such conductive layer is proposed to be done by material deposition from the tool electrode. This alternative solution enables machining of non-conductive materials in deionized water instead of dielectric oil. The deposition of material from tool electrode is achieved through erosion in very narrow interelectrode gaps and controlled short circuiting. It is shown that machining of zirconium dioxide ceramic (ZrO2) is possible in deionised water using the alternative method. This method shows the feasibility to machine holes up to 1.5mm depth in ceramic applying 1mm diameter electrode in deionised water. Further improvements in the process may lead to industrial applications, where the cooling holes in ceramic coated turbine blades can be drilled by the same machine and process.