Significant Improvements of Machined Surface Qualities by Electrical Multi-channel Discharging in Precision Manufacturing

Abstract

Electrical discharge machining (EDM) has been widely utilized in manufacturing for decades because of its remarkable advantages of noncontact machining and machining conductive materials of any hardness over traditional manufacturing technologies. However, the original EDM mechanism prevents the further improvements of surface qualities in precision manufacturing. In fact, although current and pulse duration were commonly set to be small to obtain small discharging energy in precision EDM, conventional EDM tools still employ single-channel discharging mechanism to form precise surfaces. This kind of machining concentrates the whole pulse discharging energy on one area, leaving the created crater wide and deep, and surface qualities are difficult to be improved. If the energy of the pulse is separated into several plasma channels, the craters generated by these small energies on the machined surface will be smaller. This kind of machining is called electrical multi-channel discharge machining. It was observed that multi-channel discharging can be formed only when transient arc pulses were generated in the gap. Nevertheless, in precision EDM, it is high probabilities to form stable arc pulses from transient arc pulses damaging machined surface. Therefore, an intelligent strategy should be exploited to realize electrical multi-channel discharging and avoid stable arc pulses occurred as well. To this end, a new adaptive control system of electrical multi-channel discharge machining was studied. Arcing ratio was chosen to be a controlled index and gap-servo voltage was a control variable. Because discharging pulses were transient arc pulses and crates were generated almost in the whole pulse duration, the integrity of the machined surface can be obtained. Experiments demonstrated that surface roughness (SR) on machined 1mm depth can reach up to Ra 0.2μs with a copper electrode of diameter 30mm around 2 hours. The significance of the study is that multi-channel discharging is a new perspective of discharging phenomenon and breaks through the inherent awareness of EDM precision machining in the past years.