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small.planes
05-25-2013, 04:46 PM
Evening all,
Following some less than successful attempts to drill 0.8 mm holes in Ti Ive been contemplating...

I need to build a small hole drilling edm machine.

Now I do have various power electronics bits and bobs lying around, and a stepper drive I can steal from a 4th axis.
It seems to me that an inverter tig set might be a ready made generator?
I have a set which does pulsed dc, which I think is ideal for edm?
its a jasic wse200 iirc.

I know there are some edm gurus out ther on this board, any thoughts/ideas?

Cheers
Dave

John Stevenson
05-25-2013, 05:20 PM
Evening all,
Following some less than successful attempts to drill 0.8 mm holes in Ti Ive been contemplating...


Cheers
Dave


Told you you were a clumsy bastard.

Mind you i have the exact same set so will be following this post closely.

small.planes
05-25-2013, 05:24 PM
Maybe ;)
However I havent snapped the tiny tap (yet), only drills.

Dave

small.planes
05-27-2013, 04:59 PM
OK, heres the TIG front:

http://i306.photobucket.com/albums/nn274/small_planes/machining/DSC_1116_zpscc4a125c.jpg (http://s306.photobucket.com/user/small_planes/media/machining/DSC_1116_zpscc4a125c.jpg.html)

I can setup a pulsed DC current from 10 - 200 A peak, 0.5 to 300hz, with a low of 20%, and a pluse duty of 10 - 90 % according to the panel.
WOuld shuch a pulse train work for EDM? The capaciter discharge method doesnt take it all the way to zero as far as I can determine.

Ill try a little handheld EDM machining later this week hopefully (Copper electrode in the tig torch), but if anyone knows if this is likely (or not) to work it would be nice to find out.

Im the meantime Ive been a little distracted building this:

http://i306.photobucket.com/albums/nn274/small_planes/DSC_1113_zps523a09b6.jpg (http://s306.photobucket.com/user/small_planes/media/DSC_1113_zps523a09b6.jpg.html)

:cool:

Dave

John Stevenson
05-27-2013, 05:03 PM
You need some better fly spray.............

wierdscience
05-27-2013, 09:33 PM
Watching this one myself,given the TIG's various settings it should work for a tap burner at least.

I am assuming there is a pile of printer carcasses nearby from the plastic printer build?;)

Jaakko Fagerlund
05-27-2013, 11:50 PM
Sure it burns, but those amps are quite high for small electrodes. The other would be quite slow operation due to low frequency, but I don't see anything that would otherwise hinder the operation.

The easy option is to purchase or build a power supply (unregulated works fine) with around 60-100 VDC output, put in a resistor to the positive side to limit the maximum current and put a capacitor in parallel with the spark gap. This is a basic RC type power supply for EDM, is fast to build and you can control the maximum spark energy or spark size with the size of the capacitor.

For example, my own power supply was 60 V, limited with 50 ohm power resistor to give out a maximum 1.2 A (as the power supply could only do 1.5 A) and a 2.2 uF cap across the gap compeleted it. This is at the moment in my wire EDM, that is why the cap is so small.

small.planes
05-28-2013, 04:37 PM
What is the typical frequency that an EDM runs at?
I assume the TIG rule of thumb of 1A per thou (IIRC) doesnt apply to EDM. What would a rule of thumb be? is there an amps / diameter sort of relationship?

The simplicity of the RC psu is appealing, but is there a better way? I dont know if commercial sparkers have an RC psu, but I doubt it.

I have 4 CM75DY-12H half bridge IGBT modules, and 4 PK25GB80 thyristor modules I could use, but my background is in software, so how to hook them up is a minor mystery...

Dave

Jaakko Fagerlund
05-28-2013, 11:52 PM
Just go with the RC power supply, it is by far the easiest route and has been used and still is in commercial machines, though most of them nowadays have pulsed power supplies. But for tap burning etc. there is no need to get fancy, otherwise you spend your time doing the power supply and not working.

I can check the amps at work, but they are usually listed as amps per area of the electrode. There is no right and wrong, anything works, but there is always some sweetspot where the electrode doesn't consume itself much.