Sinker EDM is a type of EDM machining that uses an electrode in the shape of the cavity to be machined, submerged in a dielectric fluid and connected to a power supply. The electrode and workpiece are separated by this dielectric fluid, which acts as an insulator between these parts during normal operation. Electric discharge machining (EDM) is a time- and cost-effective method of producing complex contours, intricate cavities and fine details in hardened steel and other hard metals. The process was developed independently in the U.S. and Russia during the 1950s. In EDM, electrical current discharges between two electrodes that are separated by a dielectric fluid, usually deionized water. As the electrode approaches the workpiece, an electric spark jumps through the fluid to produce a small crater or "microjet" that melts away a tiny portion of the workpiece material. The resulting spark continues to erode the workpiece until it breaks off in a molten state. The EDM process is repeated thousands of times per second with each microjet forming specific shapes or profiles on the workpiece surface according to preprogrammed X-Y coordinates from a computer numerical control (CNC) unit like those used on milling machines, lathes and grinders. This process creates holes, slots and cavities in hardened steel without cutting tools. https://cncble.com/milling-machine-frame/