CNC Wire Cutting Machine Tool Program

• 1
  What the program actually controls
• 2
  How the CAM side builds the path
• 3
  Where the accuracy comes from
• 4
  What the wire can and cannot cut
• 5
  When the wire cut loses to milling
• 6
  Five checks before the wire starts
• 7
  Wire EDM vs CNC milling: pick by feature

A wire EDM program does not turn a cutter. It tells a servo table where to move a charged wire while a generator pulses current through the gap. The wire never touches the part. Instead, thousands of tiny sparks per second erode a kerf roughly 0.02–0.05 mm wider than the wire itself. That kerf is why the program carries a wire offset, not a cutter compensation value like you would use on a mill.

The program has four jobs. It defines the XY path of the profile. It sets the wire offset for rough and skim passes. It sets the Z heights and taper angles when the machine has an upper and lower guide. It calls the generator settings: on-time, off-time, peak current, and servo voltage. Get the path right and the power wrong, and the part comes out with a recast layer and a tapered wall.

On a typical program block you will see G01, G02, G03 for linear and arc moves, G41 or G42 for offset direction, and M-codes for wire feed, flushing and power. The coordinate values come from the CAM post, but the offset numbers come from the machine operator's tech table. Those two halves have to agree.

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  PathG01, G02, G03 moves in XY, plus UV for taper on four-axis wire machines.
• 2
  OffsetWire radius plus spark gap, split into rough and skim passes.
• 3
  GeneratorOn-time, off-time, current and servo voltage set the surface and the cut rate.
• 4
  HeightZ values and taper angle define the wall geometry for tapered parts.

The CAM side starts from a 2D profile or, on a four-axis wire, from matched upper and lower contours. For a simple die plate, the programmer imports the DXF, closes the contour, and picks a start point. The start point matters more than most people expect. Put it in a corner and the lead-in scar lands on a functional edge. Put it in a scrap slug and the mark disappears with the waste.

Lead-in type depends on what the edge does. For a punch or a die insert, a perpendicular lead-in is short and predictable. For a fine blanking die or a medical blade, a tangential arc lead-in blends the entry so no witness line shows on the cutting edge. The program may also add a small lead-out and a wire-cut tab so the slug does not fall and pinch the wire.

Corner control is the other CAM decision. On a wire machine the wire lags the programmed path, so a sharp inside corner comes out rounded unless the control slows down or the program inserts a corner stop. Most controllers handle this in the tech table. If your CAM post does not emit it, ask for it, because corner rounding of 0.01–0.03 mm is enough to fail a gauge check.

• 1
  Start pointPlace it on a non-critical face or in the scrap slug.
• 2
  Lead-inPerpendicular for punches, tangential arc for cutting edges.
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  TabLeave a small tab so the slug does not drop onto the wire.
• 4
  Corner controlLet the tech table slow the wire at tight internal corners.

Wire EDM holds tight dimensions because the cutting force is near zero. There is no tool deflection, no chatter from a long end mill, and no work hardening from a cutter rubbing a thin wall. On a well-maintained machine, a rough pass plus two or three skim passes can reach ±0.005 mm on a 50 mm tall part. That is the same number we quote for our tightest CNC milling work, but wire EDM gets there on features a mill cannot reach.

Height changes the picture. As the part gets taller, the wire has more chance to drift and the flush becomes harder to maintain. At 150 mm tall, expect the achievable tolerance to open up and the surface to get rougher unless you slow the cut. For a 300 mm tall punch, the top and bottom of the wall may differ by more than the drawing allows, and the fix is a slower skim schedule, not a tighter program.

Surface finish is set by the number of passes. One rough pass gives Ra 3.2–6.3 μm. Add one skim and you are near Ra 1.6 μm. Two or three skims bring it to Ra 0.8 μm or better. Each skim is a full trip around the profile, so a four-pass program takes roughly three times longer than a single pass. That is the trade you make for a ground-like finish.

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  No cutting forceThin walls and slender features survive the cut.
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  Height limitTolerance opens up as part height grows past about 100 mm.
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  Pass countMore skims mean better finish and longer cycle time.

Wire EDM cuts anything conductive, and that is a wider list than most people assume. Hardened tool steel at 60 HRC cuts as easily as annealed stock, because the process does not care about hardness. That is why die inserts, punches and extrusion tooling often skip the soft-machining step and go straight to wire after heat treat. No distortion from a cutter pushing on a hardened, brittle part.

The list includes 4140 and 4340 steel, 17-4PH stainless, Inconel, titanium, copper alloys and most carbides. Aluminium cuts, but it is not always the best use of the machine. Aluminium conducts heat away fast and the oxide layer can make the spark unstable, so the cut rate drops. For a simple aluminium bracket, a 3-axis mill is faster and cheaper. Use the wire when the aluminium part has a sharp internal corner or a thin wall.

Non-conductive material is a hard stop. Plastics, ceramics, glass and most composites cannot be wire cut unless you add a conductive coating or a sacrificial backing. If your part is PEEK or carbon fibre, this is the wrong process, and no amount of program tuning will fix it.

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  Hardened steelNo anneal needed; cut after heat treat at full hardness.
• 2
  Exotic alloysInconel, titanium and 17-4PH cut with slower schedules.
• 3
  AluminiumCuttable but often slower than milling; use for corners.
• 4
  Non-conductivePlastics, ceramics and glass cannot be cut without a coating.

Wire EDM is slow in volume removal. The material comes off at a rate measured in cubic millimetres per minute, and a deep pocket that a 12 mm end mill would clear in ten minutes can take hours on the wire. If the feature is a pocket, a slot wider than the wire, or a 3D contour, the wire is the wrong tool. Milling removes bulk; wire finishes edges.

Blind cavities are another boundary. The wire is a straight line between two guides, so it cannot cut a pocket with a closed bottom unless you start from a drilled hole and thread the wire through. Each start hole is an extra operation, usually drilled or small-hole EDM'd before the wire cut. That is fine for a die plate with a few openings. It is painful for a part with forty small cavities.

Cost follows the same logic. The wire is consumed, the machine runs slowly, and the operator has to thread the wire at every start hole. For a flat plate with a simple outline and a ±0.05 mm tolerance, a mill and a deburr pass win on price. For a hardened die insert with a ±0.005 mm profile and a sharp corner, the wire is the only process that holds the drawing.

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  PocketsBulk removal belongs to milling, not to the wire.
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  Blind cavitiesEach one needs a start hole and a wire thread.
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  Simple platesLoose tolerance and a flat outline favor milling.

A wire program that looks clean on screen can still scrap the part in the first minute. The failure modes are predictable, and most of them are caught by a short checklist before the run. We run this list on every wire job, whether it is a one-off prototype or a 200-piece die insert order.

Check the offset direction first. G41 and G42 are easy to swap, and a swapped offset cuts the part undersize on one side and oversize on the other. Then confirm the lead-in sits on a non-critical face. A lead-in mark on a sealing surface is a leak. Third, verify the tab holds the slug. A dropped slug wraps around the wire and stops the cut mid-profile.

The last two checks are about the machine, not the file. Confirm the wire diameter and the tech table match the program's offset. A 0.25 mm wire running on a 0.30 mm offset will cut oversize every time. Finally, check the flush pressure and the nozzle gap. Poor flushing leaves debris in the gap, and the wire breaks or the wall tapers.

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  Offset directionG41 vs G42; verify against the contour side.
• 2
  Lead-in locationKeep the entry mark off sealing and mating faces.
• 3
  TabHold the slug so it cannot pinch the wire.
• 4
  Wire vs offsetMatch the tech table to the actual wire diameter.
• 5
  FlushingCheck nozzle gap and pressure before the rough pass.