Sharp corners.
Hardened steel.
No cutting forces.

EDM (Electrical Discharge Machining) removes material through controlled electrical sparks between an electrode and the workpiece — no mechanical cutting forces, no tool wear on the part. Use EDM when: material is hardened (above 50 HRC) where conventional cutting is difficult; features have sharp internal corners impossible with rotating tools; parts are delicate and would deform under cutting forces; deep small-diameter holes need straightness better than drilling achieves.

Sinker EDM: uses a custom-shaped copper or graphite electrode plunged into the workpiece. Used for blind-bottom cavities (mold cavities, buttons, logos, internal features). Wire EDM: uses a continuous brass wire cutting through the workpiece like a band saw. Used for through-cuts with sharp internal corners, profiles, gear teeth, extrusion dies. If the feature exits both sides of the workpiece, wire EDM. If it's a blind cavity, sinker EDM.

Wire EDM: ±0.005 mm on profile, straightness below 0.002 mm/inch, surface finish Ra 0.4 µm standard, Ra 0.1 µm with fine-finishing passes. Sinker EDM: ±0.005 mm on cavity depth and width, surface finish Ra 0.8 µm standard, polishable to Ra 0.1 µm. For gauge-quality tolerances below ±0.002 mm, grinding or honing follow EDM.

Yes — EDM works on any electrically conductive material regardless of hardness. This is its unique advantage: hardened tool steels (D2 at 62 HRC, H13 at 52 HRC), carbide, titanium, Inconel, even aerospace superalloys. Non-conductive materials (plastics, ceramics) cannot be EDM'd. For non-conductive hard materials, laser cutting or abrasive water-jet is used instead.

Fast-hole EDM drills small-diameter (0.3–6 mm) deep holes at rates 10–50× faster than conventional drilling. Uses a tubular rotating electrode with high-pressure dielectric flush. Standard for starter holes before wire EDM, cooling passages in mold inserts, fuel injection orifices, and turbine blade cooling holes. Aspect ratios 100:1 (length:diameter) achievable — impossible with twist drills.

EDM is slow by modern cutting standards. Metal removal rate on wire EDM is typically 5–40 mm²/min of profile, on sinker EDM 2–30 mm³/min of cavity. A complex injection mold cavity can take 8–40 hours of sinker EDM time. This is why EDM is reserved for features where no other process works — the cost per cubic millimeter is high, but for hardened materials and sharp corners, it's often the only option.