Wire EDM
EDM is essentially a thermal process whereby an electrode (wire) is brought into contact with the workpiece, and by discharge of electricity (spark) the metal is eroded away.  Wire EDM uses a power supply, a thin wire electrode, and a workpiece holding table controlled by CNC to feed the workpiece into the wire. It utilizes either flush cooling or total immersion in deionized water to wash away the eroded metal. Wire size can vary from .012" to .002" dia.  Wire is usually either pure brass or brass tungsten alloys.  The wire is constantly fed from a spool, through diamond or ruby guides and flush heads so that fresh wire is always doing the cutting. The work is clamped to a holder that is mounted on a XY stage whose motion is controlled by ball screws driven by stepper motors which are driven by a computer program which defines its path. Wire EDM is a highly controlled process so that with carefully set parameters of spark cycle, voltage, current, feed rates, etc. a very accurate path can be cut through a variety of conducting materials, including hardened steels, carbon, and carbide.  It is capable of cutting through materials over 4" thick.  A good machine, under optimal conditions, can cut contours within less than .0001" accuracy with surface finishes of better than 4 microns.  A WEDM machine with all its attendent peripherals such as filters, power supply, chiller, can fill up a 200 sq.ft. room in a hurry. They're usually operated in an air conditioned environment ...