power electronic design


Posted on Feb 5, 2014

On this page we will discuss the power electronics needed for our EDM machine. The basic mechanism of electrical discharge machining is a controlled spark between the electrode and the workpiece. This part of the electronic design generates the waveforms necessary to induce the spark. We will start by describing the fundamental mechanisms of EDM w


power electronic design
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hich dictate the voltage, current, and frequency needed, then show a very simple circuit satifying these requirements before describing its limitations and addressing these with an improved circuit. I spent some time in the library reading all the material on EDM that I could find. I will attempt to give a bibliographical reference for each essential fact I note below, to allow the curious reader to duplicate my research. Breakdown voltage from 60V [LAN], but 150V is inadequate to cause dielectric breakdown at. 001 -. 010 inch electrode spacings [DOR]. Doret added a 1500V "tickler" (low current, short duration) to trigger breakdown reliably up to. 010 inch. But he reports that the commerical machine made by Elox uses a 85V-90V peak-to-peak square wave to drive its electrode. Doret provided the following table of breakdown voltage versus voltage for Eloxol #13 dielectric (results not exactly reproducible, but are illustrative): Voltage across gap after breakdown is 10V-15V typical, independent of current. Gap resistance is usually around 1 ohm. "Arc voltage remains relatively constant as arc current is varied. " Short circuit between electrode and workpiece is indicated by voltage dropping to almost zero and current increasing sharply [DOR]. Most servo mechanisms use feedback based on average current through or voltage gap across the electrodes. But these mechanisms are just indirectly sensing the number (proportion) of open...




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