Tiny slots to wire edm

I have 36 slots to put in to .010 thick 304. The finished slot width is .0050 + - .0001. I need to burn probably .003 start holes. What is the procedure for "turning" small dia. electrodes on my sinker using the C axis? The slots are on a .012 pitch leaving .007 land in between. Slots are 3mm long.

Best material for the electrode to use here? Tungsten carbide rod?

TMD

When the shop I worked in had a job like this we used a short length of uncoated brass wire in a shop made fixture. It was a little plate on a 20 mm 3R shank.
We used the Wire EDM to etch the little groove into a plate and had another plate and thumb screw as the clamp
The wire worked well as a hole punch electrode in the AGIE Mondo sinker and we just fed out a tiny bit at a time as was needed by the thin stock.

We used the sinker to positioning between holes.

Tim

tiny start holes and trodes for them

Hi TMD:
The most successful way I've found is to discharge dress the trodes to get them round and running concentrically.
Copper tungsten is the trode material most commonly recommended for these tiny holes...the way to get them to dress well is to pick parameters for the burn so the trode wears aggressively... so reverse polarity, high capacitance, high frequency etc etc: all the things you'd normally try to avoid with sinker work.
Your dressing block can be tungsten or copper tungsten...make it reasonably long and program the trode to traverse past the face as it's dressing.
Another way, if you have a rotary axis on your wire EDM is to turn and burn them...this is how Makino does it on their super high end small hole EDM.
The biggest problem you'll have is flushing...the aspect ratio of these holes is equivalent to a 5/16" hole through an inch of material...doable but not easy to get the flushing into the bottom of the hole.
You may actually find you have better success with a blade trode: you can direct a jet along the length of it and jump flush to keep it clean.
Tungsten copper wires beautifully so making the trodes becomes pretty straightforward for you with your setup.
They'll be a lot stronger and easier to handle than 0.002" wire trodes and they'll tolerate a lot more power too so they might even go a good bit faster than round trodes...the biggest drawback is you obviously can't rotate them to keep the dielectric circulating.
Another possible strategy to help get flushing into the hole is to use a round trode almost like you'd ramp a slot into a part with a milling cutter...program a zigzag ramp into the part with a spinning trode, making some room for you to get flushing down into the hole.
All these options are worth trying if you find you're having problems just sinking straight down with a 0.002" round trode.
Let us know how it goes
Cheers

Marcus
Implant Mechanix – Design & Innovation - home

Another thought

Hi TMD:
I have just had another thought on this job...you might want to consider making an electrode that burns all the start openings in one shot.
One of your problems with these tiny electrodes is the very limited amount of power you can put into them.
Increasing the surface area in contact with the workpiece allows you to bump up the power without evaporating your trode.
Making a comb shaped electrode should be simple for you to do on the wire...you can then get the pitch and overall dimensions correct without special measures and sinker burn the whole array to the point where you just need to skim it with the wire to clean it up and bring it to size and finish.
An additional benefit is your wire work now creates no micro sized slugs to deal with.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home

Small slots

Marcus,

I had considered making a comb type trode, but was concerned about all the heat this would generate since my land between the slots is only .005 (I thought it was .007, but .005 is the right number). Guess this will require some r&d. I did sand a thin pc of graphite down to .004 and tried to cut a single slot, the slot burned nice and ended up .005 x 5mm long. This went through the .010 thick in about 30 sec. and gave me a nice slot, although this was longer than needed. I guess to reduce the heat I could shape the entry so that is enters on an angle and would burn the slot progressively longer as it goes down on the z.

Will report back on what I find out.

TMD

Why does the heat matter?

Hi TMD:
I'm curious why you're concerned about the heat generated by the burn.
Are you more worried about uncontrolled thermal expansion or about losing the physical properties of the material?
I've never given it much thought in my work...maybe I should start paying more attention to it.
I always assumed that with the large volume of temperature controlled dielectric, the thermal effects would be small and localized to the immediate vicinity of the burn.
I suppose though, with your ribs being only 0.005" thick, "localized" takes on a whole new meaning.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home

TMD,

Depending on what your pattern looks like, you might be able to get away with a ganged-up electrode. I agree with your concerns about generating too much heat with a 0.005" webbing, but you might be able to make your electrode configuration with every-other row, and then just position around.

-Brian

Small slots

I wire edm-d a comb type electrode with .003 wide fingers (12 fingers). The job went pretty well, but not in the + - .0001 range like my customer wants, but I probably am in the + - .0003 range. I got slots .005 wide with .005 land inbetween, but there was some deflection in these small members as it is 304 sst. Trode took 2 hours to wire edm using .002 wire.

TMD

TMD,
You have a P.M.