EDM die sinking (spark erosion) shapes hardened steel and carbide with thousands of small electric sparks between a shaped electrode and the part, in oil. The electrode, usually copper or graphite, sinks into the part and leaves its own shape behind. It makes cavities, ribs, sharp inside corners and blind shapes that cutters cannot reach.
Quick facts
- Works on
- Any conductive material, including hardened steel and carbide
- Electrodes
- Copper, copper-tungsten or graphite
- Typical accuracy
- About ±0.01 mm (±0.0004 inch), finer with care
- Surface finish
- About Ra 0.2–3.2 µm, set by the spark settings
- Speed
- Slow compared with milling; roughing then finishing passes
- Usually priced
- Per hour of machine time plus electrodes
What it is used for
- Mould cavities, ribs and deep narrow slots
- Sharp inside corners that a cutter cannot make
- Shapes in hardened die steel after heat treatment
- Blind holes, text and logos in moulds
- Removing broken taps and drills (tap disintegration)
Die sinking or wire-cut EDM?
| Die sinking EDM | Wire-cut EDM | |
|---|---|---|
| Tool | Shaped electrode | Thin brass wire |
| Shapes | Blind cavities and 3D forms | Through profiles only |
| Typical parts | Mould cavities, ribs | Punches, dies, profiles |
| Extra cost | Electrodes must be made | No electrode |
What to send the toolroom
- 3D model or drawing of the cavity
- Material and hardness of the part
- Surface finish required (Ra or VDI value)
- Which features need EDM and which can be milled
- Whether you supply electrodes or they should make them
- Quantity, and number of identical cavities
Need edm die sinking (spark erosion) done?
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Questions
- Why is copper or graphite used for EDM electrodes?
- Both conduct electricity well and wear slowly in the spark. Copper gives fine finishes; graphite is easy to machine, light and fast for large electrodes.
- Can EDM cut hardened steel?
- Yes. Hardness does not matter to EDM, so moulds and dies are often hardened first and the fine details are spark-eroded afterwards.
- What is a VDI finish?
- A scale used for EDM surface texture on moulds. VDI 12 is quite fine (about Ra 0.4 µm), VDI 30 is a visible matt texture (about Ra 3.2 µm).
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 16 October 2026.