EDM: EDM (electrical discharge machining) removes metal with controlled electrical sparks between an electrode and the workpiece, cutting hard materials and sharp inside corners.
EDM works only on conductive material. Wire EDM uses a thin brass or coated wire to cut through-profiles like a very precise bandsaw. Sinker EDM pushes a shaped electrode, often graphite or copper, into the part to form a cavity, for example in an injection mould. There is no cutting force, so EDM can cut hardened steel, make sharp inside corners and hold tight tolerances.
What it means for the price
EDM is slow next to milling, and machine time is charged by the hour. Wire EDM time grows with the length of the cut and the thickness of the part. Sinker EDM needs electrodes, which have to be machined first. EDM is usually chosen because milling cannot do the job, not to save money: it is common in tooling and for cutting metal printed parts off their build plate.
Example: a wire cut 400 mm long through 30 mm of steel takes far longer than the same profile through 5 mm, because the cutting speed falls as thickness rises. The figures are an example.
Common confusions
EDM is not laser cutting, although neither touches the part with a tool. Wire and sinker EDM are different machines with different jobs. Read how tolerances drive cost, and see DMLS for where wire EDM appears in metal printing.
Go deeper: How tolerances drive machining cost (and when to loosen them)