Wire electrode for spark erosion cutting

Details Wire electrode for spark erosion cutting Wire electrode for spark erosion cutting

2002-09-13

2004-08-24

Elve, M. Alexandra (Department: 1725)

Electric heating

Metal heating

Cutting or disintegrating

C219S069150

Reexamination Certificate

active

06781081

ABSTRACT:

The invention relates to a wire electrode for spark erosion cutting of metals, electrically-conducting ceramics etc., comprising either a homogenous centre made of a metal or of a metal alloy, or a composite centre and comprising at least two sheath coatings made of Zn alloys, with said coatings wearing during erosion.
In the development of wire electrodes for spark erosion cutting of metals or other electrically-conducting bodies it has been proven advantageous if a sheathed electrode is used in which the centre not only provides the necessary strength but also the electrical conductivity, wherein the actual erosion process is carried out by a sheath coating which comprises pure zinc or a zinc alloy. While a pure coating of zinc provides good removal performance, the pure zinc coating wears however so quickly that it is completely used up before the erosion wire emerges from the cutting gap of a moderately high workpiece, so that eventually, the electrode cuts with the core material. This results in the cutting performance of the electrode being altogether considerably reduced.
For this reason it is known (EP 0 312 674) to provide a &bgr;-sheath coating which, while in theory, due to the reduced zinc content, is said to have a lesser cutting performance than a pure zinc sheath coating, but which due to its far lower rate of wear in the practical cutting process provides a better cutting performance already at low workpiece heights.
Furthermore, from DE 195 10 740 A1 it is known to produce the sheath coating from a &ggr;-brass, which leads to an increased removal performance being achieved because the zinc fraction in the &ggr;-brass is higher than it is in the &bgr;-brass. Practical operation shows however, that this &ggr;-coating wears far more quickly than does a &bgr;-sheath coating, so that the advantages are noticeable only in the case of low workpiece heights.
Furthermore, from DE 199 13 694 A1, the manufacture of a wire electrode comprising two sheath coatings, one on top of the other, is known, wherein the lower sheath coating comprises a &bgr;-brass while the upper sheath coating comprises pure zinc or a zinc alloy comprising in excess of 80% zinc. This electrode is a so-called combination electrode which is equally suitable for high-speed cutting and for fine cutting where rapid wear of the sheath coating is less important. If such an electrode is used for high-speed cutting, then in this method, the outer sheath coating which comprises zinc and which wears rapidly, may improve the ignition behaviour of the electrode, while the actual erosion process takes place by means of the &bgr;-sheath coating. By contrast, if this electrode is used for fine cutting, only the outer sheath coating is consumed while the underlying &bgr;-sheath coating remains. This electrode provides an advantage in that it is possible with one and the same wire electrode, i.e. without any set-up time, to carry out high-speed cutting as well as fine cutting where it is important to achieve an extremely smooth surface.
It is the object of the invention to propose an electrode for high-speed cutting which when compared to an electrode comprising a &bgr;-sheath coating and when compared to an electrode comprising a &ggr;-sheath coating, features a better cutting performance and moreover comparatively less wear.
According to the invention, this object is met in that the inner sheath coating predominantly comprises &bgr;-brass, while the outer sheath coating predominantly comprises &ggr;-brass, wherein the fraction of &bgr;/&bgr;′-phase or &ggr;-phase in the two sheath coatings is at least 60%, and wherein the ratio of the coating thickness of &bgr;-brass to &ggr;-brass is between 0.3 and 7, and the sum of the thicknesses of both sheath coatings in relation to the external diameter of the electrode is between 0.1 and 0.3.
Surprisingly, the combination of an underlying &bgr;-sheath coating with an overlying &ggr;-sheath coating leads to a cutting performance which is better than that which can be achieved with a pure &ggr;-sheath coating or with a pure &bgr;-sheath coating.


REFERENCES:
patent: 4686153 (1987-08-01), Tominaga et al.
patent: 5196665 (1993-03-01), Briffod
patent: 5762726 (1998-06-01), Barthel et al.
patent: 5945010 (1999-08-01), Tomalin
patent: 6448527 (2002-09-01), Barthel et al.
patent: 195 10 740 (1996-10-01), None
patent: 199 13 694 (2000-11-01), None
patent: 0 312 674 (1989-04-01), None
patent: 05 337 741 (1993-12-01), None

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