How does a EDM work?

[cncman2]

How does a EDM work, anyone got any pics of work cut out using this process?

[Stevie]

I don't have any pics; but

The EDM works by a high frequency charge is passed through the medium (water/oil) this ionizes the medium to pass the main charge; the power supply is producing a square wave; once the high fequency has ionized the medium to pass the main spark the power supply dumps the stored charge in the main Caps; this melts the surface of the material to be cut; the end of the square wave comes and the current is shut off; the medium is then free to flow into the ionized channel and rapidly cools the melted metal; this in turn causes the molten particals to condense into small round beads; these float away or are flushed away and the cycle repeats; as the cycles are only 1000's of a sec apart it looks like there are sparks all over the cut; but in fact there is only 1 spark going at any one time
On a Fanuc machine (new type) the cuttings are so small it needs a sub micron filter to catch them

Hope that helps

[Al_The_Man]

A couple of other points is that the high power square wave is usually connected with the + potential on the workpiece and the - electrode is controlled by fast acting servo circuit which monitors the electrode voltage in order to maintain the most efficient spacing between electrode and work.
To avoid damage if the electrode comes in too close, a cut off circuit is applied and the servo backs off until a correct arc gap is sensed.
Al

[snaggletto]

Hey,
I operate an older ram type EDM (sinker) at work. The cutting tool, or electrode, can be made into about any shape you want. Popular materials are carbon graphite, copper, tungsten carbide etc... The material being cut also has to conduct electricity (obviously), which can be virtually any metal, including aluminum or even solid carbide, which is way to hard for conventional machining. They work great for burning out broken taps, drills, or cutting internal blind keyways, or square holes, or hex paterns etc... Flushing is vital to efficient operation. When the small pieces of material is realeased to the dielectric oil, it can fill the 'gap' and cause arcing which can ruin your electrode and workpiece.

[Dan C]

about 6 years ago I worked for a small company in the Uk which made a wire and sinker EDM as an electronic engineer.

I think was a rippoff of an agie and I had been brought in to try and improve the electronics and speed up the cutting speed.

It was a real nightmare as there were no electronic engineers there ( they had all left should have been a clue)
The system copied was called isosparK or similar.

Basically it worked something like this

You have 2 voltages you can turn on, 100V and 270V. You turn on the 100V and move the wire/bit towards the work, when the annode and cathode are very close a sparK form and you have to detect that, then make sure its a true sparK rather than a collision, then turn on the 270V charge for about 6uS, then turn every thing off and repeat until you drop. Adjusting the servo feed as it went so you got the best cutting speed.

On the machine I was working on if it sparked at 27kHz the machine had a problem and if working as god had intended it would have been sparking at 110 Khz

The above system used to stain titanium etc so I was give a budget of a bar of choclate and a large orange to develope an "AC" spark box but was never given the funds or time to do it.

Interesting machines EDM cutters for a electronic engineer.