Info on EDM needed

[cjs83]

I'm thinking of getting an EDM, it would be used to cut out parts from a steel sheet. I have a couple of questions because I know nothing about how they work.

I want to cut holes with it, so do I need a diesinker?

How do you clamp the work piece to the machine?

If a part is cut out completly, does the part just fall randomly?

What kind of learning curve am I looking at just to cut out 2d parts?

I have experience with CNC, so I don't think that it is going to be too hard to figure out, but I don't even know where to start looking at the moment for information.

[ynneb]

Yes I would like to know more about EDM too. How does it work? Is it similar to plasma cutting?
What are the advantages and dissadvantages of EDM over plasma?

[Al_The_Man]

There is a design for home made edm put out by HSM Home shop Machinist Magazine with a stepper driven servo ram. There are two types of EDM one is wire and the other is by electrode die, Both work on the same principal of a DC (90 volts or so) pulsating voltage with the Work at positive potential the Neg Electrode in the shape of the item you want to cut out is advanced to the work and an arc is drawn causing an erosion of the work piece, the electrode will keep on advancing maintaining about 5 thou clearance between the electrode to maintain the arc. The electronics sense whenever the gap is too large or if the electrode touches (shorts) to the work.
The work is usually kept under a special liquid, home made operators some times use ethylene glycol.
This differs from a 'Tap Disintegrator' used for removing broken taps from expensive castings etc. these work in similar fashion, but use low voltage 6 to 12 v AC high current and the resulting arc burns away both the sacraficial electrode and the offending tap. EDM is a finer, more precise than Plasma and is used to make press dies etc or to 'machine' very delicate objects like surgery tools etc. BTW the die electrode is usually made from a graphite material.
Al

[ty1295]

Like mentioned, two types.

Sinker: Like a drill in a way, but you can make custom size "bits"

Wire: Like plasma cutter.


I have a Fanuc EDM wire at work. Makes excellent cuts, is nice to use and very accurate.

It is SLOW. For sheetmetal I don't think it is what you want, unless you are looking for VERY accurate small parts.

EDMs are generaly used for molds, dies, etc. as the arc LIKES hard material. The harder material is, faster it cuts. Soft stuff like aluminum and brass cut slow.

What kind of parts you wanting to make?

EDM work envelopes are generall small also 12x12" is common, i have seen bigger but only at tool shows, and with high price tags.

[ynneb]

What would a home EDM setup cost, excluding the CNC machine?

[Klox]

Cjs83,
Edm is a SLOW process as Ty1295 said. You can cut virtually any matl that's conducive. Sometimes it's quite an ordeal to edm castings due to impurities in it.

Some edm machines (older type) makes use of DC generators that causes dicolouration when cutting matl such as titanium and tungsten, the surface finish on non ferrous matl such copper, brass and ally is not so good as machines that makes use of an AC generator. The AC machines (newer technology) also cuts faster with less rust accumulation.

Edm machines are usually very expensive and running cost are also relatively high (wire, electrodes, filters, dielecrtric fluid etc).

On wire edm you get machines manufactured by Charmilles (Swiss), Fanuc (Japanese), Ona (Spanish), Makino (Japanese), Hitachi (Japanese), Chmer (Taiwanese?), Joemars (Taiwanese), Agie (Swiss?), Mitsubishi (Japanese) etc

On Die sinker edm machines you get Charmilles, Ona, Makino etc

The other day i stumble across an interesting article on edm. I'll see if i could find it & ask the author if i could post a link to cnc zone......

Klox

[Klox]

Ty1295,
I forgot to explain, it's not how hard the matl is that determines the cutting speed. Normally matl that's hardened normally has less impurities in it's composition.....
I presume your Fanuc has DC generator that's why you might battle to get a decent feed rate on the non ferrous materials.
For interest sake, on a medium setting i get a feed rate of a 4.8mm/min on tool steel (k110/ 476) 10mm thick, but on ally (6082 T6) i get a feed rate of 12.5mm/min on the same thickness.

Thanx for your inputs, i always enjoy hearing from guys that's into EDM!

Klox

[jstuedle]

Another advantage of EDM is the ability to cut irregular shapes. Any shape that can be cut, carved, milled, polished etc. on a graphite rod can be cut. You will also find the harder the material being cut, the easier EDM will cut it as a general rule. Example, its easier to cut a star shape into a carbide insert, than a round hole in aluminum. Flushing the electrode is a key to efficient EDM’ing. A center hole is most often used in the electrode and the EDM fluid is pumped through it to the cutting surface, forcing the debris from the bottom of the hole in the work piece. Some material\electrode combinations will result in electrode “wear” of less than 1/10 ratio of the hole depth, while in others it might be worse than 1 to 1.