What is wire EDM?

Wire EDM is a form of electrical discharge machining. A thin wire electrode, usually brass or coated brass and typically 0.1 to 0.3 mm thick, runs through the workpiece and removes material by electrical discharges in a dielectric, usually deionised water. Wire and workpiece never touch, so the process puts almost no force on the part. The workpiece has to conduct electricity. Wire EDM can only cut profiles that run right through the part, straight or tapered; an internal profile starts from a start hole. A blind pocket cannot be wire cut.

What does wire EDM cutting time depend on?

Cutting rate is usually given as area cut per minute: profile length times workpiece height, in mm²/min. It depends on the material (conductivity and melting behaviour), the height, flushing, the wire and the machine's technology settings. Hardness has little effect, which is why wire EDM is common in hardened tool steel. The main cut is often followed by skim cuts at a smaller offset. These improve size, form and roughness and reduce the heat-affected layer at the surface. How many skim cuts are needed follows from the tolerance and the roughness requirement together with machine and material. The smallest internal radius is roughly the wire radius plus the spark gap.

How does wire EDM work in practice?

Wire EDM often follows hardening or milling: a die plate, a punch, a profile, or a keyway in a hardened hub. The job usually needs a start hole, alignment to a datum face and a plan for the slug. Cutting through material with residual stress can distort the part; a first cut that leaves stock on lets the stress release and can take up most of that distortion. If the customer supplies the part, there is no material line. Because the machine can cut unattended for long periods once set up, setup time carries a different weight than in milling. Machining shops often subcontract wire EDM. What it costs depends on the area cut, the number of cuts and start holes, the quantity and the way the EDM shop charges.

What is wire EDM often confused with?

Wire EDM is not sinker EDM, where a shaped electrode forms a cavity in the workpiece, including blind ones. Nor is it hole EDM, which drills small, deep holes with a tube electrode, often as start holes for wire EDM. All three are spark erosion processes: no defined cutting edge and no chips.

How do you see wire EDM in Blake?

In Blake the roughness, tolerance and material of a wire EDM part sit with the part as proposals from the drawing; you confirm or correct them, and who did so and when stays visible. You record your wire EDM machines in the machine park with their work envelope and their own hourly rate. More on wire EDM.