Wire EDM (Electrical Discharge Machining), also called wire cutting or wire erosion, uses a thin brass or copper wire (typically 0.10–0.35 mm diameter) as an electrode. The wire is continuously fed from a spool through the workpiece, creating a tiny spark gap between the wire and the conductive material. Each spark erodes a microscopic particle from the workpiece, and deionized water flushes away the debris. The CNC-controlled wire path cuts through the material like a precision bandsaw — but without physical contact, so there is no cutting force. Achieving tolerances of ±0.005 mm (5 μm) with a surface finish as fine as Ra 0.2 μm is routine on modern machines.
China has the largest concentration of wire EDM machines in the world — from cheap two-axis domestic machines (Sodick clones made by Dongguan Chienwei, Sanguang, Huazhi etc.) that can do basic through-cutting, to high-end five-axis AgieCharmilles and Fanuk machines capable of precision die-making. The technology is available at nearly every Chinese tool and die shop, mold shop, and precision machining job shop.
| Parameter | Standard (Brass Wire) | Precision (Coated Wire) | High-Speed / Roughing |
|---|---|---|---|
| Wire Diameter | 0.20–0.30 mm | 0.10–0.25 mm | 0.25–0.35 mm |
| Max Material Thickness | 200–400 mm (standard machine) | 100–200 mm | 200–600 mm |
| Cutting Speed | 80–150 mm²/min | 30–80 mm²/min | 150–300 mm²/min |
| Dimensional Accuracy | ±0.010 mm | ±0.003–0.005 mm | ±0.020–0.050 mm |
| Surface Finish (Ra) | 0.4–0.8 μm (1 finish pass) | 0.2–0.4 μm (3–5 skim passes) | 1.2–2.5 μm (rough cut only) |
| Max Taper Angle | ±15° (standard head) | ±30° (5-axis tilt head) | ±5° |
| Corner Radius (minimum) | ≈ 1.2× wire Ø (0.12–0.36 mm) | 0.05–0.15 mm | 0.15–0.30 mm |
| Conductivity Required | > 0.01 S/cm (most metals) | > 0.01 S/cm | > 0.01 S/cm |
The dominant wire EDM hub in China — thousands of shops. Most have 5–20 wire EDM machines each (Sodick, AgieCharmilles, Makino, Fanuk or Chinese domestic brands). Wire EDM is primarily used for mold insert cutting, precision sheet parts, and prototype work. Pricing: ¥8–25/hour ($1.20–3.70/hr) for standard accuracy (±0.01 mm), ¥25–50/hour ($3.70–7.50/hr) for precision (±0.005 mm). Lead time: 24–72 hours for standard work. Smaller shops often run 24/7 to reduce turnaround time. Watchpoint: some small shops pack 3 machines into a room without adequate water filtration, causing poor surface finish on thick parts.
Premium wire EDM hub — higher-end machines (AgieCharmilles CUT series, Fanuk α-C series) and tighter process control. Typical precision: ±0.003–0.005 mm achievable. These shops serve the semiconductor, medical device, and automotive mold industries, often with ISO 13485 or IATF 16949 certification. Good for complex parts with multiple tapers, micro-precision (wire Ø 0.10 mm), and long-run production. Pricing: ¥35–80/hour ($5.20–12.00/hr). Lead time: 2–5 days.
Large workpiece wire EDM hub — machines with 800–2,000 mm X/Y travel for cutting thick plate (up to 600 mm) for heavy molds, gear segments, and steel structural components. Less common for precision work under ±0.02 mm. Pricing: ¥10–30/hour ($1.50–4.50/hr). Good for large-scale cutting where speed matters more than tolerance.
Cost trick: Wire EDM pricing is based on machine time — the slowest part of the job is the heat-dissipating finish passes (skim cuts). A standard rough cut (Ra 1.2–2.5 μm) takes about 30% of total time. Each skim pass to improve surface finish adds 40–60% more time. If you only need Ra 0.8 μm, one rough + one trim pass is often enough — but many Chinese shops quote 3–5 trim passes by default (it's the "safe" setting). Tell them explicitly: "one rough + one trim cut only" and you can cut costs by 40%.
When cutting with a taper angle (e.g., 10–30°), the wire wears faster on the upper guide — causing premature wire breaks if the shop uses standard brass wire. For any job with > 5° taper: specify zinc-coated brass wire (which dissipates heat better) or the shop should reduce the trim power setting. If they don't adjust their EDM parameters for taper, expect 2–3× more wire breaks and a 15–25% reject rate on the cut parts.
Wire EDM creates a thin recast layer (resolidified material) on the cut surface, typically 0.002–0.015 mm thick. This layer contains micro-cracks and can be harder (and thus more brittle) than the base material. For tools, dies, and critical components: specify the recast layer be removed by light polishing or a final low-energy skim pass at Ra ≤ 0.4 μm. The last skim should use the lowest energy setting (typically < 1 A) to minimize recast. For a mold cavity, an unremoved recast layer can cause premature wear or fail under thermal cycling.
Wire EDM naturally rounds sharp interior corners because the spark erosion field extends slightly beyond the wire path. A 90° internal corner will have a radius approximately equal to the wire radius + 2× spark gap (roughly 0.12–0.30 mm for standard wire). If you need sharp internal corners (< 0.10 mm radius), the options: (1) use a finer wire (Ø 0.10 mm) with slower speed, (2) add a relief hole at the corner (broached or drilled) for the wire to pass through, (3) EDM rough + hand-filing final shape. Discuss with the supplier during the quoting phase — not after the parts are scrapped.
| Cost Component | % of Total | Notes |
|---|---|---|
| Machine time (cutting) | 55–70% | Dominant cost factor. Billed per hour: ¥15–80/hr. Thin parts are cheap; thick parts are expensive |
| Wire consumption | 8–12% | Brass wire ~¥80–150/kg ($12–22/kg). A spool of 5 kg lasts ~20–40 hours of cutting |
| EDM filter + DI resin | 5–10% | Consumables that must be periodically replaced. For precision work, filter replacement is more frequent |
| Setup + programming | 10–15% | CAM path generation, wire threading through start holes. If the part has multiple start holes, this rises |
| Post-processing (deburring) | 3–8% | Entry hole burrs and surface recast layer clean-up. Manual work can add hours per piece |
Typical per-piece pricing: Starting hole drilling: ¥10–50 ($1.50–7.50) per hole, plus ¥0.30–2.00 per linear cm of cutting path depending on material and thickness. A 100 × 100 × 20 mm steel part with a simple square cutout: approximately ¥80–200 ($12–30) at standard precision.
Any material that conducts electricity (conductivity > 0.01 S/cm). This includes: all steels (from mild steel to hardened tool steel), stainless steel (304, 316, 17-4PH), aluminum (all alloys including 7075), copper and brass, titanium, nickel alloys (Inconel, Hastelloy), tungsten carbide, and some conductive ceramics. Materials that CANNOT be wire EDM cut: glass, plastic (unless impregnated with conductive filler), ceramic without conductive phase, rubber, most composites. The workpiece must have through-thickness conductivity — laminated or coated materials may not work.
Key rules: (1) Close all contours — every line must connect end-to-end. (2) Specify the wire compensation direction — left of path (G41/G42) cuts the actual contour, centerline cuts oversize by one wire radius. Most shops prefer DXF where zero is the final part contour, and they auto-compensate in CAM. (3) Include a start hole position (either marked on drawing or as a separate operation note). (4) For pierced start holes: ∅ 2–5 mm holes within the scrap area, placed 5–10 mm from the cutting path. (5) Indicate the desired surface finish on the drawing (e.g., "Ra 0.4 μm on cut surfaces" or "rough cut only").
Yes — this is called "multi-cavity" or "gang cutting." The machine cuts the outline of each part, leaving micro-joints or using adhesive tabs to prevent parts from falling out when the cut finishes. After cutting, you separate the parts. For gang cutting: ensure 3–5 mm minimum spacing between parts for wire passage. Some shops charge a "slug handling" fee for collecting the separate pieces. For very small parts (< 10 × 10 mm), the parts may stick to the table through dielectric tension, requiring careful handling.
Standard wire EDM cuts with the wire perpendicular to the workpiece (90°), producing straight vertical walls. Conical (or tapered) EDM uses upper and lower wire guide movements independent of each other to tilt the wire up to ±30° from vertical. This allows cutting parts with draft angles (for mold ejection) or taper profiles. The 5-axis wire EDM machine can also cut complex freeform 3D surfaces. However, accurate taper cutting requires careful calibration of the taper head — mis-calibration produces inaccurate angle on thick parts (error compounds with thickness).
Rule of thumb: If the material is conductive and you need accuracy ±0.01 mm or better → choose wire EDM. If you need speed and cost efficiency on thin sheet metal (< 6 mm) → choose laser cutting. Key comparison: wire EDM cuts any conductive material regardless of thickness with ±0.005 mm accuracy and no HAZ, but is 10–50× slower than laser. Laser is 10–50× faster, works on thin sheet metal only (< 25 mm max), creates a 0.1–1.0 mm HAZ, and cannot cut highly reflective materials (copper, brass) on older machines. For precision mold inserts and dies: wire EDM is the only option.