Wire EDM (Electrical Discharge Machining) uses electric current and fine wire to cut conductive materials. The cutting typically occurs while the object is submerged in deionized water, which helps to cool the process and flush away the cut material. It leaves a smooth surface that often requires no further finishing or polishing. Note that the cutting wire should not touch the material and that the cutting itself is due to the erosion that occurs when a spark forms between the cutting wire and the raw material. The EDM process is generally computer-controlled (CNC) and as a result is highly accurate and repeatable. A typical wire EDM process will consist of several passes, moving at various speeds. The first pass is typically a fast-moving, lower accuracy cut which is used to remove large quantities of material. Later skim passes will retrace the cuts at lower speed, removing less material and improving the surface quality and accuracy of the cut. Also note that machining occurs after heat treatment so the finished dimensions of the machined items are not adversely affected by heat treatment.
Most sophisticated EDM setups allow the rotation of the cutting wire through several axes and through large angles, allowing products to be tapered and finished in 3 dimensions. The ability to taper the finished product is very useful when creating stamping dies and extrusion molds.
Complex cutouts can be formed by drilling a hole through the raw material, threading the EDM wire through the hole and cutting. Materials that can be cut include most metals and metal alloys, graphite, carbide and diamond.
Applications of Wire EDM include the manufacture of extrusion dies, blanking punches and metal and tool fabrication. The process is most suitable for low production volumes of items which require tight manufacturing tolerances.