Wire EDM

What it does

Wire EDM cuts hardened, conductive metal to accuracies conventional machining cannot reach, using electrical sparks instead of a cutting edge. Nothing mechanical ever touches the workpiece, which means there is no cutting force, no tool pressure and therefore no distortion in a thin or delicate part.

How it works

A fine brass or coated wire is fed continuously from a spool, through the workpiece, and away to a waste bin, so the "tool" is always new. The wire and the part are both submerged in or flooded with deionised water. A pulsed DC supply creates a spark across the tiny gap between wire and workpiece. Each spark reaches thousands of degrees and vaporises a microscopic crater of metal; the dielectric flushes the debris away and quenches the site before the next pulse. The wire never touches the part, and the gap is held constant by the control as the spark erodes material. CNC drives move the part or the wire guides along the programmed path, and on machines with a tilting upper guide the top and bottom profiles can differ, producing tapers and true ruled surfaces.

The numbers

Working tolerances are quoted from about plus or minus 0.005 mm to plus or minus 0.02 mm depending on material, thickness and how many passes are run. Plus or minus 0.005 mm is a fair routine expectation in tool steel. Getting to plus or minus 0.002 mm takes several skim passes, a stable temperature and a machine in good order, and 2 microns is about where the tightest published figures sit. Finish passes called skim cuts remove a few microns each to bring the size and the surface home.

Who uses one

Tool and die shops, punch and die makers, aerospace and medical part suppliers, prototype shops and anyone cutting a shape into material already hardened.