Research Of Electrical Discharge Machining In Mist Based On MQL

The electrical, mechanical and thermal properties of the dielectric influence Material Removal Rate (MRR), surface quality in EDM. Traditional EDM takes oil fluid as dielectric medium to achieve stable discharging. But it has the risk of fire hazards and environmental problems. With economic concern, the disposal of the used oil also costs additional expense. Besides, the dielectric working fluid must be circulated with the assistance of a filtration system; it also increases the cost of the machine tool. To thoroughly overcome the shortages mentioned above, Kunieda et al proposed the EDM in gas, which used high-pressure gas (air or oxygen etc.) to replace the dielectric liquid, therefore it is also regarded as'Dry EDM'. This method is a green process .But since the discharging gap of dry EDM is very narrow; it is difficult to control the machining process with ordinary ED machine, and the efficiency is low.Comparing with fluid and gas, EDM in mist is proposed, it takes mist as dielectric medium. The properties of the mist are not available but are expected to be in-between those of liquid and gas. This enables the adjustment or tuning of the gas-liquid composition in EDM in mist. Using different compositions and properties of the dielectric medium, EDM in mist can have a diverse process performance as compared to that of conventional wet EDM. It's expected that EDM in mist can take advantage of both fluid and gas and conquer disadvantage of both.The machine tool was changed and special platform and electrode was designed first. Mist working as dielectric media was generated by MQL (Minimum Quantity Lubrication). Exploratory experiments were conducted to ascertain appropriate polarity and pulse duration for EDM in mist. Then effect of pulse duration, pulse interval, peak current, servo voltage, and electrode size on MRR and TWR (Tool Wear Rate) was discussed. A series of comparing experiments were conducted, including EDM in oil and EDM in mist, different gas of mist, semi-finish and finish machining in mist and oil.Because the mist is a kind of two-phase fluid, the electric field in the gap distorts as for the effect of tiny water drips, it results in a longer breakdown distance hence widening the discharge gap as compared with dry EDM. The experimental results show that, the right polarity for EDM in mist is workpiece positive, and the right pulse duration in this experiment is 10~240μs. Compared with EDM in oil and gas, EDM in mist has the highest MRR and lowest TWR, the surface quality is also better, especially with low energy input. As the high-speed mist can blow molten metal away, there almost aren't any white layer and cracks. Through the investigation of EDM in mist, more materials about EDM were provided and it's also good for the improvement and application of EDM in mist.