Electric heating – Metal heating – Cutting or disintegrating
Patent
1988-11-23
1990-12-25
Valentine, Donald R.
Electric heating
Metal heating
Cutting or disintegrating
219 6917, 204238, 2041295, 2041297, 204224M, B23H 106, B23H 724, B23H 732
Patent
active
049805339
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Phase application of PCT/CH88/00095 filed May 19, 1988 and based upon Swiss application No. 2004/87 May 22, 1987.
FIELD OF THE INVENTION
My present invention relates to an electrode for electroerosive cutting of workpieces by means of at least one electrode, the electrode and the workpiece being separated from each other by a working gap and an erosion generator supplying the working current.
BACKGROUND OF THE INVENTION
As is known, an electrode for electroerosive cutting can be a thin wire having a diameter which lies in the range of 0.02 to 0.35 mm. During the cutting process the wire is unwound from a supply bobbin. Within a complicated mechanism which is located above and beneath the workpiece, the wire electrode is deviated and tensioned. The tension may be for example, 16 Newton. Furthermore diamond and sapphire guides for strictly maintaining the position of the wire electrode are provided in the mechanism and, in particularly during conical cutting, apply high friction to the wire electrode so that the latter is tensioned up to its tensile strength.
The working current which is up to several hundred amperes per pulse at repetition frequencies of up to 250 kHz, is applied to the thin wire electrode by means of thin wiper contacts. The transition areas for the working current are very small. Due to the rise in temperature as a result of the high working current the areas in the dielectric insulator in which the specific erosion process between the workpiece and the wire electrode takes place must be cooled. The disadvantage of this cooling is that the areas for the current transition are subjected to electroerosion, too, which leads to their early destruction.
In addition, the areas for the current transition increase the friction on the wire electrode. During the erosion process the known wire electrode is adversely affected by the following forces in the working gap: electrostatic forces, spark discharge forces as well as mechanical forces arising from the flow of the dielectric fluid and from gas bubbles. These forces in the working gap create undesirable vibrations of the wire electrode which lie in the range of the natural frequency of the tensioned wire electrode of approximately 1 kHz. This lowers the efficiency of the erosion process by a factor of 2 to 3. A further disadvantage resides in the fact that on the known wire electrode material is removed in an undesirable manner (electrode wear) due to the spark discharge in the working gap. This leads to an additional reduction of the diameter of the thin wire electrode. This disadvantage cannot even be compensated by a higher feed velocity of the wire electrode because that velocity is greatly restricted by the characteristics of the material such as, for instance, the elasticity modulus of the wire electrode.
In addition the wire electrode, already stressed to its limit by the above mentioned effects, will be torn apart by unpredictable troubles in the erosion process, e.g. short circuits and arc discharges.
OBJECT OF THE INVENTION
It is an object of the invention to overcome these deficiencies of the known wire electrodes and in addition to adapt itself in a flexible manner to the actual working process.
SUMMARY OF THE INVENTION
The object is achieved by constituting the electrode as a jet of a medium of high electric conductivity, the jet emerging from a nozzle under pressure and being shaped by the cross-section of said nozzle. The medium can be in a liquid, gel-like, paste-like or powderous state or in a combination of said states.
Advantageously the nozzle generating the jet is arranged in the vicinity of the one surface of the workpiece and a basin collecting the medium is arranged in the vicinity of the other surface of the workpiece. The mouthpiece of the nozzle can be arranged at a small adjustable distance to one surface of the workpiece. The nozzle imparts a predetermined cross-section to the jet emerging from the mouthpiece, the cross-section remain
REFERENCES:
patent: 3371022 (1968-02-01), Inoue
patent: 3403085 (1968-09-01), Berger et al.
patent: 3810829 (1974-05-01), Fletcher
patent: 3928154 (1974-12-01), Andrews
patent: 4289947 (1981-09-01), Inoue
patent: 4414456 (1983-11-01), Inoue
patent: 4599154 (1986-07-01), Bender et al.
Dubno Herbert
Valentine Donald R.
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