The wire EDM is precisely cut and explained

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  Key takeaways
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  How wire EDM explained: the spark gap does the cutting
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  What tolerance and finish you can actually hold
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  Feature size, corner radius and taper
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  Which parts belong on a wire EDM
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  How the job runs in the shop
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  Step by step: prepare a wire EDM part
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  Wire EDM compared with milling and other EDM

A wire EDM machine feeds a thin brass or coated wire from a spool, through the workpiece, and into a take-up bin. The wire travels continuously, so the same section never lingers in the cut. Between the wire and the workpiece sits a gap, typically 0.02–0.05 mm, flooded with deionized water. The generator pulses voltage across that gap, the water breaks down, and a spark jumps. Each spark melts and vaporizes a microscopic crater of metal.

Thousands of these discharges fire per second. The dielectric water flushes the debris out of the gap, cools the wire, and re-ionizes for the next pulse. The wire itself is not a cutter. It is an electrode that gets consumed slowly, which is why the machine keeps feeding new wire into the cut. Nothing pushes against the part. There is no tool pressure and no chatter.

That single fact changes what you can machine. Thin walls do not deflect. Slots a few tenths of a millimeter wide can be cut cleanly. Hardened steel, Inconel and carbide cut as readily as mild steel, because the removal mechanism does not care about hardness. It cares about electrical conductivity. Non-conductive materials such as plastics, ceramics and glass cannot be wire cut at all.

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  Wire electrodeBrass or coated wire, consumed and replaced continuously during the cut.
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  DielectricDeionized water at controlled conductivity, flushed through the gap.
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  Spark gapRoughly 0.02–0.05 mm; this is why the wire path is offset from the finished profile.

A single rough pass leaves a recast layer on the cut face and a wider spark gap. To hit tight numbers, the machine runs a sequence: one rough pass, then two to four skim passes with progressively lower energy. Each skim pass shaves a few micrometers and stabilizes the surface. On a well-maintained machine, this sequence holds ±0.005 mm (±0.0002 in) on position and profile.

Surface finish tracks the number of skim passes. A rough-only cut lands near Ra 1.6–3.2 μm, a two-skim cut around Ra 0.8–1.6 μm, and a full finishing sequence at Ra 0.2–0.8 μm. Pushing to the fine end costs cycle time, often two to three times the rough-pass time. Decide early whether the drawing needs the fine number or whether a callout of Ra 1.6 μm will pass inspection.

The recast layer matters on fatigue parts and on anything that gets coated or welded afterward. Skim passes remove most of it. If a part will be heat treated after cutting, cut it oversize and finish after treatment, because heat treatment moves dimensions more than the EDM gap does.

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  Rough onlyFast, Ra 1.6–3.2 μm, visible recast layer on the cut face.
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  With skim passesSlower, down to Ra 0.2–0.8 μm, recast layer largely removed.
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  After heat treatmentRe-cut or finish-grind, since distortion from treatment exceeds the gap.

The wire diameter sets the floor on feature size. A 0.25 mm wire leaves an inside corner radius near 0.13 mm plus the gap, so plan on roughly 0.15–0.20 mm minimum inside radius. Thinner wire down to 0.02 mm exists and cuts narrower slots, but it breaks more often and cuts slower. Tell us the smallest slot and the smallest inside corner on the drawing and we can pick the wire for it.

Taper cutting is the second geometry lever. The upper and lower wire guides move independently, so the wire enters the part at an angle. That lets a single setup cut a die with relief, a punch with clearance, or an extrusion die with draft. Taper angles depend on part height: on a short section the machine can swing several degrees, on a tall part the usable angle drops.

Four-axis and five-axis wire machines add the ability to tilt the wire in two planes while the part rotates or the table moves. That opens up ruled surfaces and shaped punches that a straight two-axis cut cannot reach. It does not turn wire EDM into a 3D milling machine. You still cut a contour, just a more complex one.

Wire EDM wins on hardened material, thin walls, sharp internal corners and one-piece prototypes of stamping dies. If you have a 58 HRC punch with a 0.2 mm inside corner, milling will need a tool smaller than the corner and will likely break it. Wire EDM cuts it in one pass with no tool wear and no heat input beyond the spark zone.

It also wins on parts where you need the outline and the holes in one setup, so the relationship between them stays tight. Cutting the profile and the dowel holes in a single program removes a re-fixturing error from the stack. For a die plate with a dozen dowel holes on a 0.01 mm center distance, that matters more than the surface finish callout.

It loses on deep 3D cavities, blind pockets and large volumes of removed material. Milling removes cubic centimeters per minute; wire removes cubic millimeters. A part that is mostly a pocket should be milled and then, if needed, wire cut only for the critical profile.

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  Good fitHardened dies and punches, thin-walled seals, sharp-cornered profiles, one-off prototypes.
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  Poor fitDeep pockets, blind cavities, high-volume stock removal, non-conductive material.

The work starts with a start hole. The wire has to be threaded through the part, so a small drilled hole is placed inside the profile to be cut, or outside if the cut is open. Hole position sets the thread point, not the final geometry, but a poorly placed hole can force a long approach cut. On a hardened part the start hole is usually made by small-hole EDM drilling.

The part is then clamped on the table and the wire is aligned to the machine axes. On a 4,000 mm travel machine, a long part can be cut in one setup, which keeps the profile straight over its full length. We run 127 high-precision CNC machines across three plants in Dongguan and Singapore, and wire work is quoted alongside the milling and turning so the routing is decided before the first cut.

After cutting, the part is inspected. We check 100% of parts before shipment, with raw material verification, in-process monitoring and a final inspection, and reports are available on request. For hardened tooling, we usually check the critical profile on a CMM and record the corner radii and hole positions against the drawing.

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  Start holeDrilled or EDM-drilled inside the profile to thread the wire.
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  SetupPart clamped once; profile and holes cut in the same program.
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  Inspection100% check before shipment; CMM reports on request.