About Electrical Discharge Machining
As with all EDM machining, measured voltages between two electrodes are required to produce a current of electricity. These electrodes create a spark, generating temperatures of over 14,000°F to vaporize and erode the material being machined.
With wire EDM, voltage is sent through the wire and a current path is established between the work piece and the wire, which serve as the two electrodes. A precise servo motor ensures constant gap between the wire and the piece. If the wire were to touch the work piece, a short circuit would occur, stopping the process.
In some ways, it is helpful to compare the wire EDM cutting action to that of a band saw, except the teeth of the band saw are replaced with the spark, which jumps from the wire to the work piece nearly a million times per second to erode the material. Eroded materials shed from the work piece are no larger than specks of dust.
Like a band saw, the thin wire is spooled and constantly fed between two computer assisted guides. This constant spooling action provides a fresh cutting surface throughout the wire cutting process. Because the cutting action produces constant erosion of both electrodes, long lengths of wire must be used – around 11 miles long (19 km) – and spools can weigh about 18 pounds, depending on the wire’s gauge. Once the cutting dimensions are entered into the CNC machine, the process is ready to begin.
Pressurized and de-ionized water, or any dielectric fluid, provides resistance to the spark. This resistance helps to precisely control the level of voltage jumping from the wire to the work piece, providing a consistent cut.
Unfiltered water does not work for this purpose. The minerals present in normal water act as a conductor of electricity which would mean uncontrollable cutting at lower levels of voltage. Resin tanks filter out the minerals, producing pure de-ionized water, which does not conduct electricity under normal circumstances. Only after enough voltage is applied will dielectric fluid ionize to conduct a current.
Dielectric water also serves to flush any shed material from the environment, ensuring a clean cut.