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Micro-EDM: Dielectric oil matters December 29, 2012

Posted by viboon in : Manufacturing technologies , trackback

The four basic functions of dielectric oil are:

1. Insulation. The dielectric must insulate the workpiece from the electrode. The disruptive electrical discharge must take place across a gap that is as narrow as possible. As gap width decreases, achievable process accuracy increases.

2. Ionization. Optimal conditions for the production of an electrical field must be created as quickly as possible, then a spark path must be provided. After the impulse, the spark path must be rapidly deionized or extinguished so the next discharge can be made. The dielectric must constrict the spark path to achieve high energy density, which also increases discharge efficiency.

3. Cooling. The EDM process involves elevated temperatures. Because the discharge spark has a temperature range of 8,000°C to 12,000°C when it punctures the workpiece, dielectric oil must cool both the workpiece and the electrode. In high-precision microEDMing, centralized dielectric chillers must be able to effectively remove absorbed heat from the dielectric oil to maintain overall operating temperatures within ±2°C — a critical factor in achieving part and feature accuracies below 2μm.

4. Removal of waste particles. Eroded material particles must be removed from the discharge area to avoid EDM process disruptions. Excess debris will “short circuit” the gap, decreasing process efficiency. A high-efficiency fluid filtration system must be part of any high-precision microEDM. Average particulate filtration media, used in-line with a standard dielectric reservoir, should be rated at 5μm to 8μm. If the EDM has a fine-hole machining option, a 1μm prefilter should be installed in the high-pressure pump reservoir.

Ref: Bradford, J.W. (2008). Low-viscosity dielectric oils improve microEDM operations. Micromanufacturing, Vol. 1(2), pp.8-11.

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