EDM electrodes consist of highly conductive and/or arc erosion-resistant materials such as graphite or copper. EDM is an acronym for electric discharge machining, a process that uses a controlled electrical spark to erode metal. EDM electrodes include components made from brass, copper and copper alloys, graphite, molybdenum, silver, and tungsten.
Electric Discharge Machining
Electrical discharge machining (EDM) makes it possible to work with metal for which traditional machining techniques are ineffective. It only works (except by specific design) with materials that are electrically conductive. Using recurring electric discharge, it is possible to cut small, odd-shaped angles and detailed contours or cavities in hardened steel as well as exotic metals such as titanium and carbide.
Types of EDM Electrode Materials
EDM electrode materials need to have properties that easily allow charge and yet resist the erosion that the EDM process encourages and stimulates in the metals it machines. Alloys have properties which provide different advantages based on the needs of the application.
- Brass is an alloy of copper and zinc. Brass materials are used to form EDM wire and small tubular electrodes. Brass does not resist wear as well as copper or tungsten, but is much easier to machine and can be die-cast or extruded for specialized applications. EDM wire does not need to provide wear or arc erosion resistance since new wire is fed continuously during the EDM wiring cutting process.
- Copper and copper alloys have better EDM wear resistance than brass, but are more difficult to machine than either brass or graphite. It is also more expensive than graphite. Copper is, however, a common base material because it is highly conductive and strong. It is useful in the EDM machining of tungsten carbide, or in applications requiring a fine finish.
- Copper tungsten materials are composites of tungsten and copper. They are produced using powder metallurgy processes. Copper tungsten is very expensive compared to other electrode materials, but is useful for making deep slots under poor flushing conditions and in the EDM machining of tungsten carbide. Copper tungsten materials are also used in resistance welding electrodes and some circuit breaker applications.
- Graphite provides a cleaning action at low speeds. Carbon graphite was one of the first brush material grades developed and is found in many older motors and generators. It has an amorphous structure.
- Molybdenum is used for making EDM wire. It is the wire of choice for small slot work and for applications requiring exceptionally small corner radii. Molybdenum exhibits high tensile strength and good conductivity, making it ideal where small diameter wire is needed for demanding applications.
- Silver tungsten material is tungsten carbide particles dispersed in a matrix of silver. Silver offers high electrical conductivity and tungsten provides excellent erosion resistance and good anti-welding characteristics in high-power applications. This composite is thus the perfect choice for EDM electrode applications where maximizing conductivity is crucial.
- Tellurium copper is useful in EDM machining applications requiring a fine finish. Tellurium copper has a machinability that is similar to brass and better than pure copper.
When selecting EDM electrodes, the most important considerations alongside its form and function are the material’s conductivity (or resistivity) and it’s erosion resistance. Conductivity promotes cutting efficiency, since electric current is the “cutting tool”. Erosion resistance (a factor of melting point, hardness, and structural integrity) gives the electrode a longer service life and lowers the frequency of replacement. These properties, which vary almost exclusively by the type of alloy or material used, must be the deciding factors when selecting an electrode.
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