By controlled electrical discharge. The electrode and workpiece are held a small distance apart in a dielectric fluid, and a voltage is applied until the gap breaks down and a spark jumps, vaporising a tiny amount of material from both. The discharge is then extinguished, the debris flushed away, and the cycle repeats thousands of times per second. Material is eroded rather than cut.

Because the process depends on electrical conductivity and melting behaviour, not on mechanical strength. A hardened tool steel or a tungsten carbide erodes at a rate similar to annealed steel, where a cutting tool would fail immediately. This allows parts to be heat treated first and machined afterwards, avoiding the distortion that occurs when a finished component is hardened.

Speed and material. EDM removes metal far more slowly than cutting, so it is used where the geometry or the material makes cutting impractical rather than as a general alternative. The workpiece must conduct electricity, which rules out ceramics, plastics and most composites. The process also leaves a recast layer and heat-affected zone that must be considered where fatigue life matters.

A thin surface layer of material that was melted by the discharge and resolidified in place, together with a heat-affected zone beneath it. It can be harder, more brittle and contain micro-cracks and residual tensile stress, which reduces fatigue strength. Fine finishing settings minimise it, and critical components are often polished, etched or stress relieved afterwards to remove or mitigate it.

Deionised water for wire EDM and specialist hydrocarbon or synthetic oil for sinker EDM. The fluid insulates the gap so the discharge occurs at a controlled point, cools the workpiece and electrode, and flushes eroded debris away. Flushing quality has a large influence on cutting speed and stability, so fluid condition, filtration and delivery are operational matters rather than background maintenance.

Tool, die and mould making above all: cavities, cores, ejector pin holes, ribs and sharp internal corners in hardened steel. Also punches and dies, extrusion tooling, carbide components, aerospace parts in heat-resistant alloys, and small precise features that would be impossible to cut. It is a routine part of any toolroom rather than a specialist outlier.

Very. Wire EDM in particular holds tight tolerances and produces excellent surface finishes with fine settings, and because there is no cutting force there is no deflection to compensate for. Accuracy depends on machine build, thermal stability, wire or electrode wear and the number of finishing passes. Multiple passes at decreasing energy are standard practice where both size and finish must be held.