Graphite selection is critical to the success of the job. It is important to understand the characteristics and physical properties of the different manufactured brands and grades produced. The various grades should fall within one of the four EDM classifications:
Angstrofine – Less than one-micron particle size material is used when extremely fine surface finishes are required.

Ultrafine – Less than five-micron particle size materials are most often used for finishing electrodes.
Superfine – Six- to 10-micron particle size materials are generally used for speed in larger detailed cavities.

Fine – 11- to 20-micron particle size materials are used for speed in large cavities.

Materials within these classifications can be expected to have specific performance characteristics consistent with that particular grade. As a precaution, care should be taken when selecting a “house brand” of graphite. It is important to know the original maker and the performance characteristics, as graphite that is sold under a house brand may change from time to time and unexpected results could cause problems.

Using high quality graphite actually can reduce overall production costs. The graphite for the electrode is generally a small portion of the overall cost of the job. The best graphite for the application should allow the cavity to be produced with fewer electrodes due to the graphite’s resistance to wear. The reduced wear also means that there will be less debris in the gap for consistent cutting. High quality graphite electrodes can handle more aggressive machine parameters than graphite with poor microstructure. Improved accuracy of the cavity is another benefit. The finishing process is predictable due to the consistency of the graphite from block to block.

Because the grade of graphite is the critical element in the EDM process, it is important to familiarize yourself with the various grades of graphite. Selecting graphite on price alone can result in a pitted or out of tolerance cavity that can cost thousands of dollars in rework costs as well as delay the delivery of the mold. The best grade of graphite for the job will certainly give a shop the competitive advantage over a shop that selects graphite based strictly on price.