Re: [CAD_CAM_EDM_DRO] Re: EDM Fluid

Hi all:
The issues around what dielectric to use and how to condition it for
sinker vs wire edm has been around in the EDM industry for a long time.
The main theoretical determinants of what to use, center around the
dielectric properties of the flushing media in question.
The system acts a bit like a giant capacitor, and each discharge implosively
removes a little bite of metal from the workpiece.
Keeping the dielectric properties of the fluid in the gap between anode and
cathode the same over time is what makes the process so tricky to implement.
Ionization of the media, and gross contamination will disturb the dielectric
properties sufficiently to halt the whole works very quickly.
The flushing media is therefore tailored to maintain this all important
dielectric constant, and the delivery system is as important in practical
terms as the medium.
Deionized water is used for wire EDM for a number of reasons, but one of the
principal ones, is that it can be delivered to the spark gap zone very
efficiently with high pressure.
Its low viscosity facilitates flushing into a small gap; a process which is
far more difficult to do with an oil.
On the other hand, water has some significant disadvantages too, one of
which, is that maintenance of a deionized state is more difficult than with
oils.
Wire EDM machines use a Cationic/Anionic resin bed to strip ions out of the
solution and render it "nonconductive".
They also use extensive filtration both to preserve the expensive high
pressure pumps from wear, and to preserve the expensive resin bed from
contamination.
A common misconception is that deionized and distilled water are the same
animal...they are not.
Deionized water means exactly what it says...no ions in it.
Distilled water, on the other hand , refers only to water that has been
evaporated and then recondensed.
It implies nothing about the ion burden in the water... and can actually be
made worse by the distillation process if the still contains metals in its
condensation or collection system.
So much for basic EDM fluid info.
Homemade wire EDM systems will always be limited by their ability to provide
adequate flushing of a fluid of appropriate dielectric constant that can be
delivered consistently to the spark gap.
This translates to limitations of the metal thickness that can be cut.
Commercial machines exist that can cut thicknesses of 36" and more.
I would expect a homemade machine to bog down with material much over 1/16"
in thickness because of this flushing problem.
The more forgiving nature of the oil dielectric media (in terms of its
resistance to ionization) would make me favour EDM oil as a flushing medium
for a home brew system, unless a total loss system is contemplated.
Disposal of the used contaminated water needs to be addressed...it is toxic
enough that you can't ethically just dump it into the sewer!!!
I'd avoid kerosene (fire hazard) and I'd avoid vegetable oil (rancidity and
smell).
I've heard of people having success with ethylene glycol and water.
Probably worth a look, but I'd still bite the bitter pill and spring for
some decent EDM oil.
Cheers

Marcus

----- Original Message -----
From: <bjammin@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, June 08, 2002 8:53 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: EDM Fluid


> At 12:54 PM 6/8/02 -0000, you wrote:
> >(wire) is close enough to the part the dielectric is "ionised"
>
> This is an instantaneous process that is reversed instantly by nature,
with
> no action on your part.
>
> > I would
> >be interested to hear from anybody who knows why the two processed
> >use different dielectric media.
>
> You can use just about any insulating fluid in any EDM. I've used junk
> motor oil and new ATF, with similar results. De-ionized water is distilled
> water, nothing more; it works because its conductivity depends on the ions
> it has dissolved, which are removed by distilling.
>
> Regards, Hoyt
>
>
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