Discussion of electrical discharge machining in gas

Summary form only given. For the microcosmical understanding of electrical discharge machining (EDM) in gas (dry EDM), the influences of such parameters as polarity and gas pressure on EDM in gas were discussed based on theory of gas discharge and experiments; meanwhile, the influencing factors of material remove rate (MRR) in dry EDM and reasons for the low relative wear ratio (RWR) are analyzed mainly according to the gas medium characteristics. Positive polarity was recommended in dry EDM because electrodes play main roles in collision and ionization; the notable feature of dry EDM is very low RWR and the reasons for low RWR are analyzed as follows: (1) the passage developing to anode is stronger than the passage toward cathode, which can be used to explain that the energy absorbed by anode is larger than the energy absorbed by cathode, and that is main reason for lower RWR. (2) Tool electrode was protected by the debris adheres on the tool. Additionally, discharge passage extends rapidly in gas medium although it is limited by liquid in conventional EDM, which leads to weaker workpiece cool effect and low MRR in dry EDM; Finally, to ensure machining process stable at the sparkle discharge state, a certain gas pressure is necessary to strengthen deionization in dry EDM and to keep discharge points disperse in gap.