After 60 years of EDM the discharge process remains still disputed

doi:10.1016/j.jmatprotec.2003.11.060

Journal of Materials Processing Technology

Volume 149, Issues 1–3, 10 June 2004, Pages 376-381

https://doi.org/10.1016/j.jmatprotec.2003.11.060 Get rights and content

Abstract

The ignition of electrical discharges in a dirty, liquid filled gap, when applying EDM, is mostly interpreted as ion action identical as found by physical research of discharges in air (Lichtenberg figures) or in vacuum (radio tubes) as well as with investigations on the breakthrough strength of insulating hydrocarbon liquids. The state of the servo-controlled gap in real ED-machining, however, differs very much from such condition. The author stipulates ignition of electrical discharges by the evaporation of particle bridges in the gap through excessive current. The follow-up spot of a discharge is conditioned by the remaining particles, removed from the electrodes, as well as gas bubbles from earlier discharges. The material removal reaction is grouped in an evaporation phase at start of ignition and later in the ejection of fused material by instantaneous boiling at the discharge spots. The gap width derives from the gap contamination average, depending from process settings.

Section snippets

Ignition of electrical discharges

Sixty years passed since Lazarenko [1] proposed 1943 to invert the effect of metal removal from electric circuit breakers and maximise it for metal machining purposes. In the early years of development and while searching for applications relaxation-type generators (charging condensers to store and define discharge energy) were used. The pause between discharges was very long and ignition from ionisation effects in the gap through high field strength between the electrodes was assumed by

Theory on practical EDM

After 50 years of meanwhile important application of EDM as production technology, the description of the enrolment of the process in the small gap by different authors has not yet found a uniform interpretation. This paper therefor tries to create a new consensus base.

The importance of gap measurements

The common record in literature and in user instructions of equipment is that servo systems are used to set the gap width during EDMing. “Set parameter” in former times was the “voltage-average” over the gap and in more advanced systems also the gain of the signal amplifier. Digitised systems of today basically operate identical while only referring to intricate measurements of more elementary discharge parameters. Barz with his research [13] has shown that the process efficiency and stability

Conclusions

Ionisation of the space between the electrodes or ion emission under high field strength in the gap cannot successfully be used to explain ignition of discharges in EDM applications for practical machining purposes.

The different influences of the selected machining parameters (on-time, duty-cycle, peak current, ignition-voltage, servo and flushing) compared with the resulting gap width and measurable stock removal and wear rates suggest the begin of discharge by evaporation of miniature

References (14)

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B.N. Solotych, Fundamental physics of electroerosion on metals, Physics-Mathematical Library (Gostekhisdat), Moscou,...
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