Electrical discharge machining (EDM) is generally carried out in a dielectric liquid. It is a thermal process where material is removed by a succession of electrical discharges occurring between an electrode and a workpiece plunged in a dielectric fluid. Every discharge ionizes a localized plasma canal, where temperature can become very high (up to 1000 ◦C), leading to fusion and ebullition of metal of both facing materials [1]. The use of liquid has been regarded as indispensable for the stability and efficiency of the process, because it is known that the liquid serves as a cooling medium in the discharge gap and removed and flushed machining
debris out of the working gap. So it plays one of the most important roles in the materials removal mechanism.
EDM is a useful machining method. It has a great advantage in machining workpiece with special shape or hard-machining materials, such as plastic moulds, blanking die, carbide materials and engineering materials [2,3]. Now it has been applied widely in manufacture engineering. Despite their wide using in industry today, EDM has some disadvantages. One of the most serious disadvantages is that it can result in environment pollution [4]. It is known that EDM can produce waste dielectric liquid, it is very harmful, we should try our best to avoid letting into the surrounding environment. On the other hand, dielectric liquid is generally kerosene-based oil, it will decompose and release harmful vapor (CO and CH4) during EDM, which will do harm to the health of operator. For environment protection reason, the green method of EDM without pollution has become a hot studying subject in the word recently.
EDM in gas is a new machining method which was proposed by Kunieda in 1997 [5]. In this method, EDM is achieved in gas instead of kerosene-based oil, so the pollution decreases. When this new method appears, all world is astounded. It is regarded as one of most important method with good outlook. But this method has a fatal disadvantage, short of stability and low material removal rate (MRR).
To overcome the shortage of EDM in gas, a new method, ultrasonic vibration electrical discharge machining (UEDM) in gas, is developed in this paper.