Improving energy utilization efficiency of electrical discharge milling in titanium alloys machining

Electrical discharge milling(ED-milling) can be a good choice for titanium alloys machining and it was proven that its machining efficiency can be improved to compete with mechanical cutting. In order to improve energy utilization efficiency of ED-milling process, unstable arc discharge and stable arc discharge combined with normal discharge were implemented for material removal by adjusting servo control strategy. The influence of electrode rotating speed and dielectric flushing pressure on machining performance was investigated by experiments. It was found that the rotating of electrode could move the position of discharge plasma channel, and high pressure flushing could wash melted debris out the discharge gap effectively. Both electrode rotating motion and high pressure flushing are contributed to the improvement of machining efficiency.

Ultrasonic Vibration Electrical Discharge Machining in Gas

A new method of ultrasonic vibration electrical discharge machining(UEDM) in gas is proposed in this paper. In UEDM in gas, the gap between tool electrode and workpiece is small(about 0.01mm), and the voltage between them is higher than EDM in liquid, so short circuit is easy to take place. It is very important for improving the MRR to avoid short circuit. Therefore, some measures have been taken, a rotation and a planetary motion are superimposed upon the tool electrode. During UEDM in gas, workpiece is vibrating with ultrasonic frequency, which can have the molten workpiece material ejected out from base body of workpiece without being reattached to it again, it is very useful to increase MRR. The electrode is formed to be thin-walled pipe, the high pressure gas is supplied through the internal hole and flow over the machining gap with a high velocity. It can enhance the removal of molten and evaporated workpiece material. The gas with a high velocity also cools and solidifies the removed material and prevents them from adhering onto the surface of the tool electrode. Furthermore, during the pulse interval, the gas with a high velocity blows off the plasma formed by the previous discharge and decreases the temperatures of the discharge spots on the tool electrode and the workpiece due to heat transfer, thus guaranteeing the recovery of the dielectric strength of the gap. The experiments were performed on an electrical discharge small hole machine DK730(made in China, modified by author). The worktable of the machine was especially designed to accept an ultrasonic vibration unit, and the clamp of the machine was designed to accept high pressure gas when it turning. 45# steel and copper were selected as workpiece and tool electrode respectively. Air and oxygen gas were selected as gas mediums. Five sets of experiments were carried out to show the effects of open voltage, pulse duration, wall thickness of pipe electrode, amplitude of ultrasonic vibration and gas medium on the MRR. Some observations of the roughness of the machined surface were also made. Experimental results show that electrical discharge machining with ultrasonic aid can be achieved well in gas medium. UEDM is a method with a high material removal rate(MRR). The greatest advantages of this technique are lower pollution and low electrode wear ratio.