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Abrading is a process in which graphite is 3-dimensionally machined using an abrasive cutting process.
To abrade an electrode, an electrode model or pattern must be available. The more accurate the model, the more accurate the electrode. To this end, a CNC'd model is normally recommended.
From that model, a silicon carbide stone is cast. The grit of the stone can vary from 120 grit to 340 grit depending on the surface finish required on the electrode. The silicon carbide stone is made of epoxy mixed with silicon carbide. The epoxy acts as a binder for the silicon carbide. Before curing (for about 1 hour), the stone is in a liquid state and, as such, can be cast or poured over the model. Release agents are applied to the model to allow release.
The Hausermann Abrader's upper platen moves up and down with hydraulic force. An orbital table serves as the lower platen. The table orbits or moves in the X-Y axis at 800 RPM. The orbital movement (0.5mm) is so slight that it appears to be a vibration. The table is driven by 2 large and extremely strong spindles located below the table.
The formed silicon carbide stone (called an abrading die) is mounted to the upper platen. The graphite is mounted to the orbital table and located exactly under the abrading die (formed silicon carbide stone).
The CNC control of the Abrader then determines the proper cutting cycles and controls the upper platen's position. The control activates the orbital table and, under hydraulic force, brings the abrading die into contact with the graphite. The rough surface of the abrading die abrades or stones away the graphite into the shape of the electrode model from which the abrading die was cast.
Flushing fluid removes the abraded graphite particles. The fluid is pumped through flushing holes pre-drilled into the graphite. The flushing fluid is filtered and clean fluid returned to the machine. The flushing holes are the same flushing holes used in the EDM.
The Abrader feeds downward in the Z axis, and it abrades with the entire surface of the abrading die. An electrode of almost any shape or size can be abraded very fast and very accurately. While cutting conditions will vary from job to job, the average infeed will be about 10mm per hour, regardless of the size or shape of the electrode. The larger the electrode or the more detailed the electrode, the more efficient the abrader will be.
An abrading die made of silicon carbide can be used many times without wear. This makes it particularly suitable for electrode redressings. The average redress of an electrode (5mm) will require only about 1/2 hour abrading time. Again, remember that abraded electrodes require no hand benching.
With good finishes on the electrode, the proper grade of graphite, and the correct power supply settings, benching of the die can also be eliminated.
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