What is EDM and the advantages of using it?
What is EDM? A Brief History
The acronym EDM is derived from Electrical Discharge Machining.
The EDM process as we know it today started in 1770 with the observations of Joseph Preistly. He noticed that electrical discharges had removed material from electrodes used in his experiments. This is also known as electro-discharge erosion.
Later on in the 1940's Soviet researchers developed a machining process that formed the foundation for modern day EDM.
Electric Discharge Machining
The basic EDM process is an electrical spark that is created between an electrode and a work piece. The spark is visible evidence of the electro-discharge. This electric spark produces intense heat with temperatures reaching 8000 to 12000 degrees Celsius, melting almost anything. The spark is very carefully controlled and localized so that it only affects the surface of the material. The EDM process usually does not affect the heat treat below the surface. With wire EDM the spark always takes place in the dielectric of deionized water. The conductivity of the water is carefully controlled making an excellent environment for the EDM process. The water acts as a coolant and flushes away the eroded metal particles.
EDM wire cutting uses a metallic wire to cut a programmed contour in a workpiece. Extrusion dies and blanking punches and various other forms of jigs and fixtures are often machined by wire cutting. Cutting is always through the entire workpiece. To start machining it is first necessary to drill a hole in the workpiece or start from the edge. On the machining area, each discharge creates a crater in the workpiece and an impact on the tool. The wire can be inclined, thus making it possible to make parts with taper or with different profiles at the top and bottom. There is never any mechanical contact between the electrode and workpiece. The wire is usually made of brass or stratified copper, and is between 0.1 and 0.3 mm diameter.
Dependant on the accuracy and surface finish required, a part will either be one cut or it will be roughed and then skimmed. On a one cut the wire ideally passes through a solid part and the scrap piece drops away when it is done. This will give adequate accuracy for some jobs but most of the time skimming is necessary. A skim cut is where the wire is passed back over the roughed surface again with a lower power setting and low pressure flush. During roughing the water is forced into the cut at high pressure in order to provide plenty of cooling and eliminate eroded particles as fast as possible. During skimming (accuracy / finish cuts) the water is gently flowed over the burn so as not to deflect the wire.
Wire EDM Process
* Low work holding forces
* Low cutting forces
* Very accurate process tolerances held +/- 0.0001"
* Complex profile capability
* No tool wear (the wire is continually replenished)
* Hardened materials are easily machined
* Small corners, narrow slots