The flushing process during spark erosion

Every experienced spark erosion expert knows that the flushing process is of utmost importance, when metals are subjected to this procedure. The dielectric must flush away the eroded particles from the gap between electrode and work piece, otherwise they may form bridges, which cause short circuits. Such arcs can burn big holes in the work piece and in the electrode. Modern spark erosion plants therefore have a built in power adaptive control system, which increases pulse spacing as soon as this happens and reduces or shuts off the power supply completely. The more thin-bodied a dielectric and the lower its surface tension, the better it is able to meet flushing requirements.

Open flushing
Open flushing is the most common form of flushing and is used when it is impossible to flush through the electrode or workpiece.

Offene Spülung

Pressure flushing
Next to open flushing, pressure flushing is the most important form. The dielectric is either pushed through a flushing hole in the electrode from above, or through a flushing hole in the work piece from below. The amount of dielectric flowing through is more important for effectivity than the pressure of flushing.

Druckspülung durch die Elektrode

When calculating the smaller than specified dimension of the electrode, it must be remembered that in this type of flushing particles rising up through the lateral gap are continuously causing additional erosion. This leads to minor defects in precision, sometimes called secondary erosion.

Suction flushing
In suction flushing the eroded particles are sucked out of the gap between electrode and work piece. This type of flushing is best in those cases, where a fine finish and paralell walls are required in the work piece. When using this method with narrow gaps and small amounts of dielectric flowing through, care must be taken that enough dielectric gets into the spark gap, so that the spark erosion process will remain stable.

Combined flushing
In very complex jobs it may be advisable to combine suction and pressure flushing.

Kombinierte Spülung

Interval flushing
In interval flushing the erosion process is interrupted after a while and the electrode is retracted. This improves the flushing out of the eroded particles. The retraction and return of the electrode has the additional effect of suction and pumping respectively, which improves the effectivity of the flushing process. This method is particularly suitable, when deep depressions or thin electrodes are involved, and also during finishing work.

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