Manufacturing Process
Wire EDM
线切割
Using a travelling wire electrode to cut precise profiles in conductive materials with no cutting force.
Process Steps
- Program created
- Wire threaded
- Contour cut
- Surface check
What is wire EDM?
Direct answer: wire EDM (wire electrical discharge machining) cuts conductive metal with a thin travelling wire electrode. Material is removed by controlled spark erosion in a bath of deionised water, not by a cutting edge — so there is no cutting force on the part and no work hardening.
The wire is normally brass, 0.20–0.30 mm in diameter, and the kerf it leaves is the wire plus the spark gap. Because nothing pushes on the workpiece, wire EDM will cut hardened tool steel, thin walls and sharp internal corners that no milling cutter can reach.
What wire EDM holds
| Property | Typical value | Note |
|---|---|---|
| Dimensional tolerance | ±0.003–0.010 mm | Depends on machine, number of passes and workpiece thickness |
| Surface finish | Ra 1.6–0.4 µm single pass; Ra 0.2–0.4 µm multi-pass | Each extra pass improves finish and tolerance |
| Hardness of the workpiece | Not a limit | Cuts past 60 HRC; material is eroded, not cut |
| Internal corner radius | Wire radius plus spark gap | About 0.15 mm with 0.25 mm wire — far sharper than milling |
| Maximum thickness | Up to 200–300 mm on our machines | Cutting speed falls as thickness rises |
| Cutting speed | Roughly 20–200 mm²/min | Faster on thin, clean, conductive stock; slower on thick or hard material |
Wire EDM compared with laser cutting and milling
| Wire EDM | Laser cutting | Milling | |
|---|---|---|---|
| Tolerance | Best: ±0.003 mm | ±0.05–0.1 mm | ±0.01–0.05 mm |
| Cutting force | None | None | High — needs clamping, can deflect thin walls |
| Hardened material | Yes | Yes, with edge effects | Difficult and slow |
| Speed | Slow | Fast | Medium |
| Best for | Die details, punches, hardened inserts, fine corners | Sheet profiles, prototypes, thicker plate | 3D shapes, threads, bores |
Where Balford uses wire EDM
Most wire EDM work is tooling. Die plates, punches, stripper apertures and hardened inserts are cut after heat treatment, so the final geometry is not distorted by the quench. That is why the wire department sits inside the tool room rather than next to the presses: a die that is being built or repaired goes straight from the grinding room to the wire machines.
Our tool room runs five medium-wire EDM sets plus one fast-wire set. Medium wire handles the tolerance-critical apertures; fast wire removes the bulk when there is no reason to pay for precision. Slower wire work that needs ultra-fine finish or deep taper — slow-wire EDM — goes to a long-term audited partner, which is the only tooling step we do not do in-house. See in-house tooling design & build.
Common problems and how they are avoided
- Wire breakage. Usually flushing or power settings: too much energy for the thickness, poor water conductivity, or debris that cannot escape. Fixed by adjusting the cutting regime, not by slowing everything down.
- Corner rounding. The wire is a circle following a path; sharp corners round by roughly the wire radius. Compensated in the program, and visible on the part if it is not.
- Taper and straightness errors. Caused by poor flushing through a tall cut. Verified on a test cut before a production aperture is finished.
- Recast layer on the cut face. A thin re-melted skin left by roughing. Removed by the finishing passes where the surface matters.
Frequently asked
What is wire EDM used for?
Cutting hardened tool steel and precision metal profiles where there must be no cutting force and where tolerances are in the micron range: die plates, punches, inserts, fine internal corners, and small production parts.
Can wire EDM cut hardened steel?
Yes — that is its main advantage in tool making. Because the metal is eroded rather than cut, hardness is irrelevant; the die is heat treated first and wire-cut afterwards, so the finished geometry is the geometry you measured.
Why is wire EDM so slow?
It removes material one spark at a time, and only along the wire. For a large profile that does not need micron accuracy, laser cutting or milling is the cheaper route. Wire EDM earns its cost on the last 0.05 mm.
Does wire EDM leave a burr?
Very little. There is no mechanical shear, so the edge is essentially clean; a light deburr or stone is usually enough before assembly or surface treatment.
Related: laser cutting · heat treatment · in-house tooling · deep drawing · precision stamping