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Thread: Has anyone made an EDM/Spark Eroder?

  1. #11
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    The commercial Tap Disintegrators such as ElectroArc use a much simpler principle than EDM, for one there is no large DC supply, but low voltage, high current AC, much the same as a welder supply but around 9~12vac IIRC,
    The electrode is advanced, often manually and with a simple 60hz vibrator moving the electrode on and off the part for erosion.
    The electrode is hollow tube for coolant flush, made from hard copper or the like.
    Max.

  2. #12
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    I think it would take an awful long time to punch down through a tap with something like that.
    Beauty about a simple system like this PeteF is that it's cheap to make for HSM use and you can leave it to its own devices rather than standing watching it.

    If you're in a rush, a commercial operator is usually available, - - - at a cost.

    Regards Ian.
    You might not like what I say,but that doesn't mean I'm wrong.

  3. #13
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    An EDM would be fun to play with--but if all you wanted to do was remove busted taps, I'd suggest that making single-edge drills from tungsten carbide blanks would be a lot easier and faster.

    A diamond wheel on a Dremel tool will grind them; when shaped properly it only takes light pressure at 200 RPM and they'll just sink right through a HSS tap.

  4. #14
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    I have the Ben Fleming book and Robert Langlois book, just out of interest. Both use RC type circuitry, meaning resistors and capacitors. They do work and are easy to build, but I like to have more control of the process than that.

    That is the reason I'm at the moment designing a pulsed type EDM electronics, I have the circuits already sketched on a paper but have to get time to prototype them and to build the actual machine to test them out. The thing has all the bells and whistles - ON/OFF times, current selector, pulsed flushing, manual and automatic modes, edge finder and what else there is in a "basic" commercial machine

    Though, I'm not publishing the work as such in a long time as I'm intending to have it published in HSM magazine and to get it as a book, but as said, it is a long way up to that.

  5. #15
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    Quote Originally Posted by MaxHeadRoom
    The electrode is hollow tube for coolant flush, made from hard copper or the like.
    Max.
    Thanks Max, that's a good idea and should speed up erosion too.

    Ian, it's not so much about being in a rush, I don't think the word can even go in a sentence with EDM I've seen some very simple RC type devices operating with a solenoid to pulse and I thought it could be something that would be easy enough to build. However I'd also read they were getting erosion rates of only around 3 mm per hour.

    I've never had any luck in trying to remove a tap with commercial extractors, but then again I've never had a tap that I simply HAD to get out either, so maybe my efforts were a bit too token? What I tend to find however is broken end of the tap is typically as an angle, and on the small taps I use, the drill won't start properly. I'll certainly look more in to this however, because sooner or later there will be one that I absolutely need to get out.

    Pete

  6. #16
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    Electrode materials can be copper, tungsten copper, steel, brass or graphite, these work the best. Brass has the problem of "exploding", as it has zinc in it which has too low melting point for spark erosion use. If using copper, it doesn't matter if it is hardened or not. Tungsten copper works best on carbide materials with reverse polarity (electrode is the negative terminal).

    That solenoid actuated EDM head doesn't seem to be a good idea, as it doesn't hold a gap but merely makes repeated shorts, so no wonder it is slow as a granny in snow.

  7. #17
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    Quote Originally Posted by Jaakko Fagerlund
    Electrode materials can be copper, tungsten copper, steel, brass or graphite,
    what ratio is the erosion/wear between work and electrode....the electrode must suffer some wear as they don't reuse the wire in a wire EDM...but it erodes magnitudes more slowly than the work?
    .

  8. #18
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    [QUOTE=what ratio is the erosion/wear between work and electrode

    With a copper electrode eroding steel on my solenoid operated spark eroder I find that the copper erodes at about 1/6 of the rate that the steel does. Brass erodes much faster when eroding steel. It is a combination of the thermal conductivity of the electrode and the vapourisation energy of the electrode (roughly correlates with the melting point) that determines the erosion rate of the electrode.
    Mike

  9. #19
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    Quote Originally Posted by Mcgyver
    what ratio is the erosion/wear between work and electrode....the electrode must suffer some wear as they don't reuse the wire in a wire EDM...but it erodes magnitudes more slowly than the work?
    There are a few things that can influence electrode wear, among them: flushing, power settings, polarity, the material being burned, and the grade and composition of the electrode used. Almost all of my burning was done with graphite electrodes, so I canít speak for other materials.

    For our typical mold cavities, we would use three electrodes and the wear on the last trode usually was under a half thou. The older machines without all the bells and whistles would take five to six trodes to accomplish the same thing. Of course, wear is a product of time in the burn, so deep burns might need more electrodes.

    At my last shop, we had a recurring job to burn nozzle holes through a few inches of steel and about 1/4" of carbide to within .0002Ē. We used copper impregnated graphite and dressed the electrode down between burns. Itís been a while, but I think it took over a dozen finishing passes to get the size. The electrode was definitely eroding quicker than the carbide.

    George

  10. #20
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    Quote Originally Posted by Mcgyver
    what ratio is the erosion/wear between work and electrode....the electrode must suffer some wear as they don't reuse the wire in a wire EDM...but it erodes magnitudes more slowly than the work?
    Graphite and copper can have as low as 0.2 % volumetric wear compared to the workpiece (steel), if everything goes as in movies. Mainly it is a factor of flushing, flushing and flushing and power settings.

    Carbides tend to erode poorly as the cobalt is the only thing in it that conducts and wears away and most carbides have only a few to 16 % of cobalt as a binder in them, so electrode wear is significant.

    In wire EDM they don't reuse the wire as it is usually brass and as I said, brass tends to "explode" so the wire is not anymore round but resembles more of a small hacksaw blade. The wire would break easily if reused and it would not do anything close tolerance work anymore.

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