Can Stainless Laminated Shim Stock Be Cut By Wire EDM?

Good Afternoon, All --

I'm looking at some shaped shim blanks machined from stainless laminated shim stock (MIL-S-22499) which are a PITA to make because the material tends to delaminate under cutting forces. Wire EDM strikes me as a much better way of making these parts, but the "local expert" says that the laminated stock can't be EDM'd.

An ohmeter check shows that the material is conductive, but the resistance through the 1/8 inch thickness (perpendicular to the plane of the laminations) is between 2 and 3 ohms, which is greater than the fractional-ohm resistance within the foil sheets.

So what's your thought . . . is wire EDMing a workable way of cutting shapes out of this type of laminated stock or not?

Thanks in advance for your replies.

John

It might come with a few problems but I don't see a reason it could not be. You may have to go slower and use very little flushing so the flush pressure does not seperate the laminations, but you shouldn't need much flushing for material that thin anyway. If it conducts electricity an EDM can cut it.

The better question is; how many of these do you need to make, what kind of accuracy do you require, and what are they worth to you? Have you considered other methods like laser? Laser may have the advantage of sealing the laminations, although you run the risk of a small kerf around the edges adding thickness.

John

Yes, that material can easily be cut. Have done it, made a whole bunch of 1.000 x 1.050 square pieces, and then holpopped 20 x .030 through.
As Mitstech said, keep flushing fairly low, don't crunch it when clamping, and don't try to weld it thinking that would be a wise way of stacking them. It isn't.
Also, try not to shear it too close to size. Waterjet is not so great idea, but some lasers can cut it much faster.

Is there some sort of film or something between layers? I'm guessing you were thinking of this when you checked resistance?

Should wire cut no problem, though a consideration might be to find a way to get good contact on an end or edge (to your mounting fixture). This will give good conductivity to every layer... regardless of what might be between layers.

TMD has a ton of experience in this. Maybe he'll pipe in on this thread.

Gentlemen --

Thank you all for the information, I do appreciate it.


precisionmetal --

"Laminated shim stock" is layers of foil -- it can be aluminum, brass, mild steel, stainless, titanium, or Kapton polyamide -- held together with a VERY thin layer of adhesive. The foil can be 0.001 inch, 0.002 inch, 0.003 inch, or 0.005 inch thick, stacked to a total thickness of 1/8 inch or 1/4 inch most commonly. The adhesive layers are no more than a haze between the sheets.

John

As before: I'd think it would be beneficial to have good tooling contact with a flat edge so that each "layer" has good conductivity to machine ground.

John,

The material can easily be cut with wire EDM and to split tenths accuracy. Faced with the possibility of a thin non conductive layer between the shims I would want to establish good conductivity between all the layers. This can be done several ways. The best way would be to rough up one edge or more exposing all the shim layers and paint these exposed areas with silver EDM paint. This should be available from any EDM supplier. I personally prefer EDM Supplies and have no affiliation with them other than purchase materials for my own use. Low flushing pressure here is essential as you may wash away the conductive paint with aggressive flushing

TMD