Re: [CAD_CAM_EDM_DRO] EDM - Should it have a burned appearance?

garyswindell@... wrote:

> I have small EDM that I am doing some experiments with. It uses an
> RC type oscillator. 42 Volts 1Amp. Petroleum based dielectric fluid.
>
> The general question to those who have actually seen these work
> is...Does the area being cut end up looking slightly burnt? Two
> possible answers:
>
> 1) You are using electrical sparks to cut something and these are
> quite hot so naturally there is some burning
>
> OR
>
> 2) It should not look burnt and the only reason it does is because
> you are getting some arcing.

There is no difference between arcing and EDM. In either case, some
amount of workpiece metal is vaporized, and condenses out as extremely
microscopic particles. There may also be breakdown of the EDM
dielectric, laving some free carbon if it is a hydrocarbon-type fluid.
I think this is unavoidable. I have only used EDM to burn out
broken taps, but the result looks like this. It is not actually burning
of the workpiece, rather it is STAINING by the black fluid that results.
I know this, because if the fluid spatters, anything it touches gets
turned deeply black.

The RC EDM may be partly the culprit, as it takes a while for the
cap to discharge, leaving the arc going for a moment. During this
time, probably more EDM fluid is broken down than if an electronic
switch shut down the discharge after a short interval.

Probably, a fluid flushing system with filters, or going to distilled
water might fix the problem. Clearly it would eliminate breakdown
of the fluid into carbon.

Jon