Exploratory Research On The Machining Characteristics Of Micro EDM Based In Plasma

For now,oil-based,water-based and gas dielectric are commonly used in EDM.In the process of EDM,particularly in oil-based dielectric,the releasing of harmful substance is harmful to the environment.What's more,the tool electrode wear will affect the machining accuracy when oil-based,water-based working fluid are used.Although the tool electrode wear ratio is almost zero when gas is used as dielectric in EDM,a short circuit is likely to occur when the discharge gap is so narrow.The plasma dielectric has more desirable conductivity than the gas providing a larger discharge gap during the EDM process,which obtains more stable machining process than that in gas,and improves the surface quality to a certain extent.But the short-circuit frequency is still higher than the deionized water.In this paper,to reduce the shortcircuit frequency of micro EDM in nitrogen plasma jet,the transistor pulsed generator is used as the pulsed power source to carry out the experiment on the self-made micro-EDM machine.This paper investigates the characteristics of micro electrical discharge machining(EDM)in oxygen-assisted nitrogen plasma jet,nitrogen-oxygen mixed plasma jet and external compressed air assisted nitrogen plasma jet.It was found that better surface quality is achieved in oxygen,compressed air assisted NPJ dielectric when compared with deionized water,kerosene,NJ +CA and other dielectrics in micro EDM.In the experiment of NPJ+O2,it was found that the flow rate of oxygen is sensitive to the successful machining.NPJ+CA dielectric has some advantages in surface quality,edge quality,negative tool electrode wear ratio and economy when compared with other dielectrics,so this paper further study the effect of electrical parameters on machining characteristics of micro EDM in NPJ+CA dielectric.The results show that the discharge gap of NPJ + CA is larger than that of deionized water and compressed air,which proves that the plasma medium can increase the discharge gap.It was also found that the tool electrode wear ratio is negative as a whole when machined in NPJ+CA.What's more,the increasing of discharge frequency is benefit to improve the surface quality in NPJ+CA dielectric.Finally,in order to verify the ability of machining three-dimensional cavity in NPJ+CA dielectric,the experiment of machining heart-shaped cavity is proposed.On one hand,better surface quality is achieved in NPJ+CA dielectric when compared with deionized water,kerosene and compressed air;on the other hand,since the tool electrode wear ratio in NPJ+CA dielectric is almost close to zero which makes the amount of electrode extension to be much lower,so higher machining precision is got in NPJ+CA than that of pure compressed air.A larger discharge gap is helpful for the removal of debris,so the better edge quality is achieved in NPJ+CA when compared with pure compressed air.