Sinker EDM (Die-Sink)
Also known as: Die-Sink EDM, Ram EDM, Sinker Electrical Discharge Machining, Cavity EDM
Sinker EDM erodes a cavity into a conductive workpiece using a shaped electrode (graphite or copper) that is the mirror image of the desired feature. Spark discharges across a dielectric gap remove material without cutting force, producing sharp internal corners, deep slots, blind cavities, and fine features that milling cannot reach. Unlike wire EDM (which cuts through-profiles with a wire), sinker EDM sinks a 3D electrode form into the part.
Why AM parts need this
Sinker EDM machines features into hardened AM tool steel and superalloy parts that milling cannot reach: sharp internal corners (zero radius), deep narrow ribs, blind cavities, and fine keyways in aged hardened steels (MS1, H13 at 50–54 HRC) or nickel superalloys (IN718, IN625). These are the geometries AM builds toward but cannot finish to tolerance with milling — EDM closes that gap. For aerospace and medical parts, sinker EDM cuts precise injector ports, nozzle features, and blind internal profiles after heat treatment and HIP. As a secondary application, sinker EDM is used for AM injection-mould and die inserts to cut the sharp-cornered geometry that the conformal-cooled AM insert was built around — combining AM's internal channel freedom with EDM's sharp-feature capability.
Achievable surface finish
Achievable Ra
0.2–0.8 µm
Sinker EDM is a feature-creation process, not a whole-surface finisher. Finish quoted is for the EDM'd cavity walls.
Key parameters
Graphite: faster removal, larger features. Copper: finer finish, small precise features. Electrode wear must be compensated in the electrode design.
Roughing: Ra 2–3.2 µm. Finishing (low-energy spark): Ra 0.2–0.8 µm. VDI 3400 scale used to specify EDM texture.
Internal corner radius limited by electrode tip radius — far sharper than milling (which is limited by cutter radius).
Heat-affected re-solidified layer; finishing passes minimise it. Remove for fatigue-critical features.
Roughing with graphite: high. Finishing: low. Trade-off against surface finish and electrode wear.
Compatible materials
Limitations
- Only works on electrically conductive materials — not for polymer AM
- Requires a custom electrode per feature — adds lead time and cost; only economic for features milling cannot produce
- Recast layer and heat-affected zone form on EDM surfaces — remove for fatigue-critical parts
- Slow material removal at fine-finish settings — not a bulk stock-removal process
- Electrode wear must be compensated — deep cavities may need roughing + finishing electrodes
Related tools
Providers
Sodick — Wire EDM for AM Support Removal
Japanese precision machining OEM Sodick — wire EDM and die-sink EDM systems widely used in AM post-processing to cut support structures, separate LPBF parts from build plates, and achieve tight-tolerance features.
Yokohama, JP
GF Machining Solutions (AgieCharmilles)
Georg Fischer AG machining division — AgieCharmilles wire EDM and die-sink EDM alongside high-speed milling centres for AM post-processing, hybrid additive-subtractive workflows, and precision finishing of LPBF parts.
Geneva, CH
Relevant standards
Surface-finish and MRR ranges from Sodick and GF AgieCharmilles die-sink EDM published specifications (manufacturer tier). EDM texture per VDI 3400.
All post-processing