What is EDM
The spark you see in electrical discharge machining is actually the visible portion of an extremely complex mechanism. Here is what it is and how it works.
EDM: Electric Discharge Machining is an extremely complicated effect. The EDM process is useful for precision cutting of many types of tool and die, prototype and production, mold, aerospace, medical and micro medical work. It involves breakdown of the spark gap through a dielectric medium that can be oil, water, and or even air, the quick formation of an electric arc between the workpiece and the electrode, and the removal of material from both. Included in this cycle is the timing of the arc to control the surface finish, and the cutoff of the current and voltage by the power supply. The rate of cutting depends on the current, the duty cycle, the frequency, and the direction of the current. The surface finish also depends upon these factors as well as on the electrode material.
These are the three main types of EDM:
Wire EDM: Wire EDM uses an electrically charged wire electrode to vaporize and melt electrically conductive work pieces, to very smooth and accurate surfaces. The diameter of the wire electrode we use ranges from as small as .0015", and up to .012". EDM wires are usually made of brass alloys, and some have special coatings and must be matched with the EDM generator, work piece material and its thickness. The wire electrode is aligned and presented to the work piece via round diamond guides. The guides are mounted within upper and lower control arms, which controls the position and alignment of the wire. The EDM process requires a dielectric be present, and for Wire EDM, this is in the form of filtered, deionized and temperature-controlled water, maintained within the machine's own closed-loop system. Surrounding the wire guides are plastic or ceramic nozzles called flush cups. They have an opening to allow the wire and water to pass through them. The nozzle opening allows a column of water to envelop the wire and the spark gap, to support cutting, provide cooling, and with varying pressures, to flush contaminants and damaged dielectric from the cut area. Limitations of wire EDM are, that it can cut only electrically conductive and some semi-conductive materials, the part to be cut must be suspended between the upper and lower guides (i.e.: like a band saw).
Sinker/Ram EDM: Sinker EDM uses an electrically charged Copper, Graphite or some combination of them electrode to vaporize and melt electrically conductive work pieces, to very smooth and accurate surfaces. This electrode can be produced by conventional means (i.e. mill, lathe or grinding). This electrode can be a simple square or an extremely intricate 3 Dimensional electrode. You can even use the sinker as a conventional with a stick electrode as your cutter.
Drill EDM: EDM drilling uses a precision brass tube as a drill bit that drills a hole by vaporizing and melting electrically conductive material. The diameter of the electrodes we use are anywhere from .004 to .256 of an inch in diameter. The electrodes come in .004 of an inch increments and this is how we control hole sizes, because of this there are some limitations on hole sizes that can be produced. We can fit up to a 24 inch tall work piece under the head, and have drilled up to 13 inches through 304 stainless steel with a .035 of an inch diameter electrode.
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