Electrical discharge machining is a long-established metalworking process just like the mechanical, metal-cutting processes used in machine production as well as mold and toolmaking.
In electrical discharge machining, the material is melted by a rapid series of electric sparks and removed by an electrode. Each individual spark creates a small, crater-shaped depression in the workpiece. The desired shape then emerges as the totality of these craters.
To produce the sparks, a generator is used to convert the mains AC voltage into a pulsating DC voltage from 20 to 150 volts. The erosion rate, surface finish, and electrode wear are determined by the selected pulse duration, current, direction, and pulse frequency.
Scope of application for EDM filters
Electrical discharge machining can be used to process any electrically conductive material, regardless of its machinability or hardness. This process is particularly suitable for one-off production of counterbores or breakthroughs in materials such as hardened steels or hard metals, which are difficult to machine.
EDM filter variants
EDM processes fall into two categories: die-sinking EDM and wire-cut EDM.
• In die-sinking EDM (ablation), the electrode has the opposite shape of the desired recess and is positioned a short distance from the workpiece, creating a spark gap. This process is mainly used to machine forging dies and injection molds, such as casting dies.
• In wire-cut EDM (cutting), a wire is used as the electrode. This process is used to produce all kinds of internal and external molds. Cutting tools and the associated components are ideal areas of application.
The die-sinking electrodes are made of electro copper, a copper-tungsten alloy or graphite. The wire electrodes consist of brass or copper wire.
A dielectric is used to focus the discharge at the point with the smallest gap width. Extreme temperatures are generated in the discharge channel, which cause the material to melt and vaporize. Thin-bodied mineral oils, such as petroleum or transformer oil are used as the dielectric in wire-cut EDM, as well as non-conductive water. In order for the dielectric to remain non-conductive, flushing and filtering are necessary to remove any debris – which brings us to the significant benefits of filtration.
EDM filter requirements
Despite all the various factors that influence the EDM process, it is the filtration of the dielectric that ultimately determines the quality of the finished workpiece. Highly efficient filter elements are needed for this. Increasing demands with regard to the surface finish and roughness values, as well as the ever-shorter process times, have made continuous development of conventional EDM filters necessary.
Modified manufacturing techniques in combination with the latest multilayered media and double-bellows technology have enabled the filter manufacturers to meet the exacting demands of this market.
Structure of EDM filters
All EDM filter elements are characterized by a round, cylindrical design and are installed in a housing in one or more rows. Modern EDM machine tools rely on filter elements with a hose connection / threaded nipple and are typically installed in the supply tank.
A wide range of accessories, such as reusable threaded nipples and reducers, allows the filter elements to be installed in all common machine types, regardless of the manufacturer.
The filter fineness of these EDM filters ranges from 3–5 µm for conventional paper filters. There are also long-life filter elements as well as multilayered filter elements with a fineness of 1–2 µm. By carefully matching the filter elements to the specific application, the longest possible service life and first-class surface quality can be achieve
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