Wire and sinker EDM: how it works, costs and design rules

Electrical discharge machining removes conductive material with sparks instead of a cutter. Wire EDM cuts through-profiles with a thin wire; sinker EDM burns a shaped electrode into the part. Both make sharp inside corners and cut hardened steel.

Typical tolerance

±0.01 mm, down to ±0.002 mm

Quantities

1 to a few hundred

Lead time

5–20 working days

Materials

Any conductive material, including hardened tool steel and carbide

How it works

The part sits in a dielectric fluid. Thousands of sparks per second erode material between the electrode (a brass wire or a graphite or copper shape) and the part. Nothing touches, so there is no cutting force and no burr.

Benefits

• Inside corners as small as the wire radius (often under 0.1 mm).
• Cuts hardened material after heat treatment, so there is no distortion afterwards.
• No burrs and no cutting forces on fragile features.

Limitations

• Slow: removal rates are a fraction of milling.
• Only conductive materials.
• Wire EDM makes through-profiles only; blind shapes need sinker EDM and an electrode.

What drives the cost

• Cut length multiplied by material thickness.
• Number of skim passes for accuracy and finish.
• Electrode manufacture for sinker EDM.

Design rules

• Only specify sharp corners where they are functional; everywhere else allow a milled radius.
• Give wire EDM a start hole or an open edge to enter.
• Keep EDM features on a single direction where possible.

Preparing your STEP file

• Export the profile as a clean solid; many shops also want a 2D DXF of the profile.
• Mark which features need EDM on the drawing so they are not quoted as milled.

See also the full STEP export checklist and the comparison of all processes.