Mits EA12E electrode dressing on machine

Does anybody here run a Mits sinker and dress small (less than .01") electrodes on the machine? I know there was a thread about this in 2011 with some good information but I am looking for a little more hand holding than was in that thread. I would love a start to finish process description but any good direction is appreciated. So far all of my programming has been simple move to X, Y point and sink to Z -.XXXXX. So I am not familiar at all with more complex programming on this machine or any CNC sinker for that matter. I have a lot of .012" gates to burn and I know or think I know that the minimum overburn is .0015 so that makes .009 dia. electrodes. These are in very small MIM molds. Mold material is CPM10V and trode material could be either copper-tungsten or tungsten-carbide

Thanks in advance

Hi William:
Some things about discharge dressing:
First, you need to set the cutting conditions for maximum wear on the electrode so when you drive your dressing block past the trode it will preferentially burn the trode rather than the dressing block.
Second, you want your electrode to be burnable ie, not too wear resistant.

Both of these things are exactly opposite to what you normally want in your electrode, so it seems a bit counter intuitive until you think about it as the electrode becoming the workpiece temporarily while the discharge dressing takes place.

So normally, the trodes are copper or Telco and the dressing block is copper tungsten or tungsten or tungsten carbide or even graphite.
You give up wear resistance in the trode to get the ability to discharge dress it, and you accept that you will have to re-dress the trodes a lot.

Also, you need a means to rotate the trodes if the gates are round, so either a C axis on the ram, or a Rotobore.

The method is to drive the dressing block past the trode so the trode is eroded to the proper shape by the profile you've put onto the dressing block.

The details of how to do it on your machine are what you have to figure out.
I've had best success taking a NO-WEAR setting for copper vs carbide and just reversing the polarity; whatever those settings are they should give you a good start point.

Having said all that, I've had better luck overall with pre-made trodes than discharge dressed trodes for round features in super small diameters.
I've been successful with pure tungsten wire, with tungsten carbide with copper tungsten and with POCO Angstrofine graphite, depending on what I was trying to do.

My current favourite is pure tungsten if I can buy wire in the proper diameter.
I have a range of tiny home built collets for clamping and centering the wire and I find I get best, most trouble free performance that way.

Often the secret to success is the have the wire a bit eccentric to the axis of the rotary; that way there's room for dielectric to get down the developing bore a bit better
A thou or so of runout is all it takes.

That's it in a nutshell; it's not very complicated to do with no real super sophisticated programming to do either.
Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Hi William,

What's the exact problem?

You could start making the electrode for dressing. I usually wire edm that. In a Erowa fixture, so that I can go back and forth to the wire edm without re-aligning.

When you have your dressing elektrode in place and your actual electrode in a holder, you can begin writing the program. It's the same as the programs you are used to write - positioning in X, Y and Z only burning sideways: in X (or Y) towards the dressing block. With a RPM that works for you. Usually as high as it goes. And keep in mind that you reverse polarity since your elektrode is on the table and your workpiece is in the electrode holder.

If that works, you might want to dress the electrode at several locations along rhe profile of the dressing block, since the block will wear. You'll get a roughing, semi-finishing and finishing location.

This set-up will be your dressing set-up. Use another program, and datum point for burning the actual product.

I hope that helps.

Kind regards from Holland - Nobby

Ah... Marcus replied while I was typing. :-)

I forgot to mention that I find an optical comparator quite useful for measuring the electrodes.

As Marcus is saying: dressing is more like a last resort. You might be able to get the small electrodes by (swiss) turning.

Thanks Marcus and Nobby. I took a long drive in the mountains on Saturday and resolved most of my mental blocks around this. I'm trying the rotary dressing this morning and so far it is working well. I'm going to have to fiddle with settings a bit to get it to work reliably but it looks good so far.

The reason that I went down this road in the first place is that I was having troubles with concentricity of the gate feature to what we call the runner drop. Our runner drop is a tapered hole anywhere from .550" to .750" deep from the injection side of the tool to the .015" dia. gate. There is supposed to be a .002" land between the runner drop and the gate itself. if the concentricity is out then the gate vestige is too tall and QC won't buy them like that.

If I can control the gate position consistently with this process then I can look at other ways of doing this.

Marcus i would be interested in seeing your collet arrangement. I think I would rather go that way with solid wire than have to burn electrodes every time.

Thanks again