EDM Fundamentals
Electrical Discharge Machining (EDM) removes metal with controlled sparks, not with a cutting tool. There's no contact, no force, and it works on any conductive material regardless of hardness. This makes EDM essential for hardened steel, carbide, and complex internal shapes.
How EDM Works
A tool electrode and the workpiece sit in a dielectric fluid. A rapid series of electrical sparks jumps the gap, eroding tiny bits of metal. The gap (0.01–0.05 mm) is maintained by a servo. No cutting forces — the electrode barely touches the part.
Two Main Types
| Sinker EDM (Ram EDM) | Wire EDM | |
|---|---|---|
| Electrode | Graphite or copper, machined to the inverse shape | Thin brass wire (0.1–0.3 mm) |
| How it cuts | Electrode sinks into the workpiece | Wire travels through the part like a bandsaw |
| Best for | Mold cavities, internal geometries, ribs | Extrusion dies, punch/die components, precise profiles |
| Accuracy | ±0.005 mm | ±0.002 mm |
EDM doesn't work on non-conductive materials. It also leaves a recast layer (a thin, heat-affected surface) — for highly stressed parts, finish grinding or polishing after EDM. Deep narrow ribs and internal corners are where EDM shines; conventional milling can't reach them.