Wire EDM
Also: wire EDM, EDM wire cutting, wire erosion, WEDM, wire electrical discharge machining, spark erosion, wire cut EDM, wire burning
Wire EDM erodes a profile through conductive metal with a thin charged wire: hardened tool steel, carbide and superalloys cut to ±0.005 mm with no cutting force.
353 shops tagged EDM among 5,104 CNC machining companies in the Noramark directory
A brass wire, 0.10-0.30 mm (0.004-0.012") in diameter, runs continuously from a spool between an upper and a lower guide while the workpiece sits submerged in deionized water. Tens of thousands of sparks a second jump the gap between wire and work and vaporize specks of metal; the wire never touches the part. The table moves the part along the programmed path, so the wire cuts like a bandsaw blade that never dulls, and the guides can offset to cut tapers up to about 30° or two different profiles top and bottom.
Hardness does not matter: hardened D2, carbide and Inconel cut about as readily as annealed steel, so parts are hardened first and cut finished, with no distortion to correct afterwards. There is no cutting force, so thin, delicate parts and stacks of sheet cut true. Internal corners can be as sharp as the wire radius plus the spark gap, about 0.15 mm (0.006") with standard wire. With skim passes the process holds ±0.005 mm (±0.0002") and 0.2-0.4 µm Ra (8-16 µin), which is why it makes punches, dies, extrusion dies, gauges, gears, splines and keyways.
It is slow. A 25 mm (1") thick steel part cuts at a few millimeters a minute on the rough pass, so a 300 mm perimeter takes an hour or two before the skims. Every profile is a through-cut, every internal profile needs a start hole, and non-conductive materials cannot be cut at all. The cut face carries a thin recast layer that fatigue-critical and corrosion-critical parts may need removed.
At a glance
| Typical tolerances | Standard ±0.013 mm (±0.0005") with a rough cut and one skim; ±0.005 mm (±0.0002") with care and two or three skims; ±0.0025 mm (±0.0001") on the best machines in a temperature-controlled room. Position between features is the machine's, typically 0.003-0.005 mm (0.0001-0.0002"). Straightness through the thickness is within 0.005 mm per 25 mm (0.0002" per inch) with skims; parts over 100 mm (4") thick need attention to wire deflection. |
|---|---|
| Size limits | Common machines cut parts up to 400 x 300 mm (16 x 12") in X-Y and 250-300 mm (10-12") thick; larger machines reach 800 x 600 x 500 mm (32 x 24 x 20"). Thickness beyond 300 mm is possible on a few machines but slow. The smallest wires, 0.05-0.10 mm (0.002-0.004"), cut slots as narrow as 0.1 mm (0.004") and inside radii of 0.05 mm (0.002"). |
| Surface finish | Rough cut 1.6-3.2 µm Ra (63-125 µin), a matte, evenly pitted surface; one skim 0.8 µm Ra (32 µin); two or three skims 0.2-0.4 µm Ra (8-16 µin); fine-finish machines reach 0.1 µm Ra (4 µin). A recast (white) layer of a few micrometres remains after skims and up to 0.03 mm (0.001") after a rough cut only; grinding, polishing or a light etch removes it where fatigue or corrosion matters. |
| Lead time | Single parts in 3-7 business days; production in 2-4 weeks. Cutting time governs: thick, high-perimeter parts with skims take hours each, so quantity stretches lead time almost linearly unless the shop stacks parts or runs lights-out. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Any electrically conductive material: hardened tool steels (D2, A2, O1, M2, H13, S7), 52100, 440C, 17-4 PH, 316, 4140, tungsten carbide, Inconel, titanium, copper, brass, aluminum and graphite. Aluminum and brass cut fastest; carbide, titanium and copper cut slower and want specific wire and settings. Plastics, glass, ceramics, G10 and carbon-fiber laminates cannot be cut; a resistive or oxide-coated surface has to be broken through before the first spark.
What drives the cost
- Cut length times thickness: machine time scales with the area of the cut face, and skims multiply it
- Number of skim passes for tolerance and finish: a three-skim finish costs two to three times a rough cut
- Start holes: every internal profile needs a drilled or EDM-drilled start hole
- Material: carbide, titanium and copper cut slower than tool steel; aluminum faster
- Wire consumption: 0.25 mm brass wire is used continuously, more on thick parts
- Fixturing and squaring of odd shapes; stacking sheet parts for one cut spreads the cost
- Quantity: programming is quick, so unit price falls slowly; each part still takes the same cutting time
When to use it
- Profiles in hardened tool steel, carbide or superalloys cut after heat treatment, so there is no distortion to correct
- Sharp internal corners and narrow slots a rotating cutter cannot make
- Punches, dies, extrusion dies, gauges, gears, splines and keyways
- Thin, delicate or stacked parts that would deflect under cutting force
- Prototype quantities of parts that will later be stamped or fine-blanked
When not to
- Non-conductive materials: plastics, ceramics, glass, composites
- Blind cavities and pockets: the wire has to pass through, so use sinker EDM or milling
- Large volumes of simple profiles, where laser cutting, stamping or milling is orders of magnitude faster
- Parts where a ±0.13 mm (±0.005") profile is fine: milling or laser cutting costs less
Design tips
- Give internal corners a radius of at least 0.15 mm (0.006") for standard 0.25 mm wire; sharper corners need thinner wire and cost more.
- Every internal profile needs a start hole: leave room for one, or pre-drill it before hardening.
- Design the part as a through-profile; a stepped profile needs a second setup or a taper cut.
- Specify skims by tolerance and finish, not by count, and let the shop choose the pass strategy.
- Say whether recast removal is required (fatigue, corrosion or a coating to follow) and how much stock is left for it.
- For tapers, give the angle and the reference face; standard machines cut up to about 30°.
- Ask for a small tab if the slug must not drop, or say when the slug is the part.
Wire EDM by material
Frequently asked questions
- What tolerances can wire EDM hold?
- ±0.013 mm (±0.0005") with a rough cut and one skim is standard. Two or three skims bring it to ±0.005 mm (±0.0002"), and the best machines in a temperature-controlled room hold ±0.0025 mm (±0.0001"). Position between features is essentially the machine's accuracy, a few micrometres.
- How thick can wire EDM cut?
- Most machines cut 250-300 mm (10-12") of thickness and a few go to 400-500 mm. Speed falls and wire deflection grows with thickness, so tolerances loosen above about 100 mm (4") unless the shop slows the cut and adds skims.
- What materials can be wire EDM cut?
- Anything that conducts electricity: hardened tool steel, carbide, stainless, Inconel, titanium, copper, brass, aluminum and graphite. Plastics, glass, ceramics and fiberglass laminates cannot be cut. Hardness is irrelevant, which is the main reason to choose it.
- Wire EDM or laser cutting?
- Laser cutting is fast, cheap and holds ±0.1 mm (±0.004") in sheet up to about 25 mm, with a small heat-affected zone. Wire EDM is slow, cuts any thickness up to 300 mm, holds ±0.005 mm (±0.0002") and leaves the hardness alone. Use laser for sheet parts and EDM for tooling, gauges and precision profiles in hardened material.
- Does wire EDM change the material?
- There is no mechanical stress, but the spark leaves a thin recast layer with micro-cracks: a few micrometres after skim passes, up to 0.03 mm (0.001") after a rough cut. For fatigue-critical or corrosion-critical parts specify recast removal by grinding, polishing or etching.
