Electric Discharge Machining (EDM) is an alternative machining process to traditional machining process for the precise machining of complex shaped electrically conductive machine parts. In EDM, machining is not affected by the mechanical properties of workpiece. The material is removed by spark erosion process. It is commonly used in advanced industry in which precise part of high quality required such as the aerospace, automobile, die manufacturing and moulds industries to machine hard metals and its alloy. The economics of machining depends on the proper selection of EDM machining parameters, tool material and dielectric. Dielectric fluid have significant impact on EDM processes. The AISI 4140 steel is a chromium-manganese-molybdenum grade used for making the dies for plastic injection moulds, extrusion dies for thermoplastics and for compression moulds.