This is one of a pair of miniature punches and dies that could only be produced with the EDM process.
Both parts are extremely hard toolsteel ; over 60 Rockwell C.
The button is A-2 toolsteel hardened to 60-62 RC and still needs to be finish ground.
The openings are 0.0209″ wide.
This is the mating punch.
Die clearance is 0.0013″ total and the punches are 0.156″ long.
They were cut by wire EDM cutting an electrode, then sinker EDM cutting the punch profiles and orbiting the electrode to bring the punches to size.
Shown are 2 shots of a micro sized medical part in 17-4 PH stainless steel. The part is micro drilled, wire EDM cut and the cut-off stub is hand finished. The part is tiny: it is 0.050″ (1.25mm) long and 0.030″ (0.75mm) wide. The wall thickness is 0.004″ (0.1mm) at the thick points and the part is accurate to within 0.0003″. It was a challenge to cut this tiny part, mostly because of the difficulty in not losing or destroying it when it was cut off from its stem.
The part still in the EDM worktank and attached by a tiny stem to the material blank. The 0.015″ start hole for the next part is also visible. The stem is 0.005″ wide
The finished, hand dressed part. Parts this small are hard to hang on to and stabilise for hand finishing. This is microscope and tweezer work, and a minor mis-step with the tweezers means you’ll never find your part again! On the right side of the shot you can see the ruby file and diamond file used to dress off the cutoff vestige from the wire EDM process. The part is the tiny black rectangle just to the left of the penny. (Click the thumbnail to enlarge it)
This is a stainless steel tube that forms part of a needle biopsy instrument. The tubing is very thin…the wall is 0.004″ thick. The slots need square ends and must be precisely oriented around the tube. The slots must be bur-free since other parts slide in the tube. Despite its expense, EDM is the obvious processing choice for a part like this.
The slots are 0.015″ wide. There are six of them around the periphery of the tube which is just over 1.0 mm in diameter. The slots were cut using the sinker EDM by vectoring a six pronged electrode around the tube which was oriented standing up in the worktank. The tube is so flimsy that the first attempts resulted in deformation of the tube when it was clamped into the vee block even though the clamping was performed very gingerly.
Here is the electrode. It is made from copper tungsten which is the material of choice for electrodes that are fragile and must stand up to repeated use. This electrode material is quite difficult to machine on conventional equipment, but wire EDM cuts it very well. The two big flats cut into the body are reference surfaces for aligning the electrode when it’s used. This electrode has burned 6 tubes and still has a good bit of life in it.