Cutting a carbon sinker electrode with a wire EDM machine

Hi,
I am posting this for a friend who would like to know if anyone has machined a carbon electrode for sinking, using a wire EDM machine? He will be using a JAPAX model LU3B with the 3F control cutting POCO and would like to know proper settings etc to do a decent job.

Thanks in advance for any replies.

Ernie

I've heard of it being done...once. But it caused a small disruption in the space time continuum and the operator and machine were reduced to a single dimension and teleported to a parallel universe where machines get better the more they are used.

Thanks James,

The humor is appreciated.

Ernie

Ernie,

It is completely possible to Wire EDM a graphite electrode, but you will need to use a high grade / high quality electrode material. The preference would be to use POCO 3 type, with is a fine grain graphite material. I cannot help you with settings for your particular model, but the conditions are usually relaxed significantly from a standard STEEL material. If too much power is used on graphite, it might be common to see "chipping" occur on the material, and the machining speed will also be slower than STEEL. Good luck!

-Brian

Hi ErnieD:
I've cut POCO electrode graphite and it is a royal pain in the ass.
It IS possible, but there are some specific things to pay attention to.
All of what Brian Pfluger has said is the same as my experience has been; here are the details I remember:

First; if your machine doesn't have dedicated graphite settings (and a machine as old as a Japax may not) you need to do the following if you start with settings for steel:
1) Open up the Servo Gap
2) Bump the Off Time way way up
3) Drop the feed rate (if your machine has a setting for that) way way down

Other things to remember:
a) Do not try to cut without almost perfect flushing (so no cutting from the edge on a non-submerged machine)
b) Stick with only the best grades of graphite or copper graphite: POCO 3 or Angstrofine are good. POCO C3 is a good grade for copper graphite.
c) Do not attempt to do milling or any other operations on the electrode that could open up a space between the flushing nozzles and the trode surface before burning it...you MUST have sealed flushing especially on a non-submerged machine.
d) Expect lots and lots and lots of wire breaks
e) Expect it to go SLOWLY...very very slowly, so schedule it in when there's no other pressure on the wire.
f) Charge a lot...it's a pain in the ass and dirty as hell, so you'll have to clean the machine afterward.
g) Talk the sinker EDM operator that's going to use the electrodes into using telco copper or copper tungsten instead of graphite if there's any way you can; both wire beautifully compared to graphite.
h) Dry the electrodes really really well before you put them in the sinker. A lit 100 watt bulb for 24 hours in a box with venting to let the moisture out is a good start.

Good luck with it; let us know how well it worked out.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

I'd advise using graphite that has not previously been exposed to dielectric oil. If you use graphite that has been in dielectric oil it will pollute your wire EDM water dielectric, as well as cause many other problems like rapidly wasting your deionization resins. The point Marcus makes above (h) is the counterpoint to this advice, and is just as important. Do not allow cross contamination between different dielectric types.

I've cut it before plenty of times with no problems at all and good results, though the machine had settings for graphite. As mentioned it did cut slowly though.

implmex said:

I've cut POCO electrode graphite and it is a royal pain in the ass.

<snip>

g) Talk the sinker EDM operator that's going to use the electrodes into using telco copper or copper tungsten instead of graphite if there's any way you can; both wire beautifully compared to graphite.

Click to expand...

This ^ ( up there ). I have little experience with sinking compared to others, but have wired POCO for others that have their own sinkers as well. Listen to Marcus. It really, really, really, really sucks... Did I say "really"? I've also wired TelCo a lot. Muuuuuuuuuuuuuuuch easier... And gives perfectly acceptable results.

Seriously. Quadruple your price or get it changed to Cu.

In the shop where I served my apprenticeship, we cut "new" Poco 1, 2 and 3, as well as copper impregnated Poco daily without any problems. Our shop built a lot of Powered Metal Tooling, and reverse burning heeled punches was a daily occurrence. I was not the Wire machine operator, so I can't comment on what settings were required, but I'm sure a call to Poco and they will have the data to help you get it wire cut. I did all of the conventional EDM work, and many of our fabricated electrodes went across the wire machine. As I recall, graphite that had already been in EDM oil was slightly more difficult to cut, but it was possible. Never heard any complaints about contaminating the DI water in the Wire Machine. We also wire cut quite a bit of copper electrodes as well. On one occasion, I do remember putting a "used" slab of Poco 3 in the oven, and cooking out the trapped oil, but usually we just went straight to the wire machine.

Copper electrode material.................................WAY better to wire. It's like night and day.

moldman7n said:

Copper electrode material.................................WAY better to wire. It's like night and day.

Click to expand...

Agreed, Copper is a dream to cut where as graphite can be quite slow.

We recently cut some graphite on our 1 year old Agie progress, it only gave the option of 1 cut, with a finish of something like 2Ra from memory. Were as I remember on my old HSS 250 I think you could get down to 0.9 Ra with 3 cuts. Seems strange that the newer machine with a better generator doesn't give the same options as our old machine.

Consider this...

ErnieD,

A better choice for wire cutting graphite is Cobra Cut B from Bedra GmbH. It has a copper core for higher conductivity against graphite and an "open" or "rough", zinc-oxide coating for improved cutting speed via better flushing and a lot fewer wire-breaks. However, due to it's lower tensile strength (only 87,000 psi for CCB vs. 130,000 psi for brass), you will have reduced auto-threading reliability. Skimming will be also difficult, so select single-pass parameters and don't try to push it.

This wire is no longer stocked by suppliers, but it is still available as a special order. I'm certain there is a minimum purchase involved. As for this; wire is sold by weight, but for spooling purposes, this is converted into length depending upon what spool size you specify. Therefore, you will have to purchase more small spools than you would larger ones.

Good thread, guys! All sound advice!

Bud Guitrau

Hello to everyone who commented or otherwise provided information and or tips.

My friend ended up machining the electrode in a CNC milling machine. He then went to the shop of a friend where they have a sinker with a C axis spindle.
He then dropped the electrode down to depth, rotated it to position 1, raised it up, rotated it, dropped down to depth, etc, until all 3 webs were done. He
then turned the electrode over and proceded to do the opposite side of the each web. When I talked to him, he said that there was very little to bench and
the customer was happy.

Thanks,

Ernie

Using a wire machine to cut graphite electrodes should be used only if necessary to create the geometry needed, such as small internal radii or other miniature features. If the electrode can be produced by other "conventional" machining methods, by all means, do so. Wire EDM only as a last resort.