Sinker EDM, also known as ram EDM, cavity category EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid such as, more commonly, oil or, less frequently, other dielectric fluids. The electrode and workpiece are linked to a suitable power supply. The power supply generates an electrical potential between the two portions. As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma channel, and a small spark jumps
These sparks generally strike one at a time, because it is very unlikely that different locations in the inter-electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations. These sparks happen in huge quantities at seemingly random locations between the electrode and the workpiece. As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine so that the process can continue uninterrupted. Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters. These monitoring cycles are sometimes known as "on time" and "off time", which are more officially defined in the literature
In wire electrical discharge machining (WEDM), as well known as wire-cut EDM and wire cutting,a thin single-strand metal wire, usually brass, is fed through the workpiece, submerged in a tank of dielectric fluid, usually deionized water.Wire-cut EDM is typically used to cut plates as thick as 300mm and to make punches, tools, and dies from hard metals that are problematic to machine with new techniques. The wire, which is frequently fed from a spool, is held between upper and lower diamond guides which is centered in a water nozzle head.
Fast hole drilling EDM
Fast hole drilling EDM was designed for producing fast, perfect, small, and deep holes. It is theoretically akin to sinker EDM but the electrode is a rotating tube conveying a pressurized jet of dielectric fluid. It can make a hole an inch deep in about a minute and is a good way to machine holes in materials too tough for twist-drill machining. This EDM drilling type is used largely in the aerospace industry, producing cooling holes into aero blades and other mechanisms. It is also used to drill holes in industrial gas turbine blades, in molds and dies, and in bearings.