Category: Sinker EDM

Miniature Punch and Die Set

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.

Aircraft Assembly Fixture

These clamping devices need to have a textured gripping surface of a specific roughness. Sinker EDM is a good means to achieve that goal. Shown are a before and after picture. The parts are hardened tool steel and the heads are about 1 inch in diameter.

Wire and Sinker EDM on the same job

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.

Torque clutch

Shown are a pair of parts used in a torque clutch for a surgical instrument. These are made of 17-4 PH stainless steel and required turning, milling and sinker EDM to complete. The biggest part is just under 1 inch in diameter.

sinker EDM: mold cavity

This is an injection mold for a rubber part. On the right, the cavity has been EDM machined to a coarse finish to give the part a matte texture. The left side of the mold and most of the right side was milled with CNC.

sinker EDM: electrodes

Shown are a couple of electrodes used to EDM a mold cavity. These are machined from copper or graphite and are consumed in the EDM process. The wear on the corners of the blackened electrode on the right is normal for the process; a second or even third electrode must be made and used up to finish the part to correct geometry.Each electrode is time consuming to make and set up in the machine. The process is also intrinsically slow, these electrodes are about 2 inches long and are burned into a hardened steel block about 3/8 inch deep. Each burn took several days to complete and required 3 electrodes to get the detail and finish required in the part.

sinker EDM: fine finishing

This is a 32 microinch finish; about as fine as can be produced in a reasonable amount of time.This tiny gear required about an hour on the machine; making the finish significantly better would require another electrode and many hours of additional burning. Extremely fine finishes are very time consuming and expensive to obtain.


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