WELDING ELECTRODE AND USE OF THE WELDING ELECTRODE

Abstract

The invention relates to a welding electrode for resistance welding, formed by a welding tool made of a metal, the welding tool having a contact surface that comes into contact with the workpiece to be welded. In order to avoid adhesion between the contact surface and a workpiece made, in particular of aluminum, it is suggested in the invention that the contact surface is made of diamond doped with boron.

Claims

1. A welding electrode for resistance welding, formed from a welding tool which is made at least in sections from a first metal and has a contact surface (1) which comes into contact with the workpiece (9) to be welded, wherein the contact surface (1) is formed of diamond doped with boron and/or phosphorus.

2. The welding electrode of claim 1, wherein the diamond is doped with 500 to 20,000 ppm boron.

3. The welding electrode according to claim 1, wherein the diamond is produced as a diamond layer (2) by CVD process.

4. The welding electrode according to claim 1, wherein a thickness of the diamond layer (2) is 0.5 to 50 μm, preferably 1 to 10 μm.

5. The welding electrode according to claim 1, wherein the diamond layer (2) has a surface roughness with an average roughness depth of Rz>1 μm.

6. The welding electrode according to claim 1, wherein the contact surface (1) is formed by more than 50% of facets forming the (111) or (001) planes of diamond crystals, preferably of diamond single crystals.

7. The welding electrode according to claim 1, wherein a growth zone of the diamond layer (2) opposite the contact surface (1) is in contact with an intermediate layer (4).

8. The welding electrode according to claim 1, wherein the diamond crystals (7) extend in a [111] or [110] direction from the intermediate layer (4) to the contact surface (1).

9. The welding electrode according to claim 1, wherein the intermediate layer (4) is formed of a carbide and/or nitride and/or boride compound of the first metal or of a second metal different from the first metal.

10. The welding electrode according to claim 1, wherein the first and/or second metal forms a carbide and/or nitride and/or boride compound stable up to a temperature of 800° C.

11. The welding electrode according to claim 1, wherein the first and/or second metal is formed of one or more of the following elements: Cr, Ti, Nb, Mo, W, Ta.

12. The welding electrode according to claim 1, wherein the welding tool is formed in sections from a third metal.

13. The welding electrode according to claim 1, wherein the third metal contains Cu as a main component.

14. Use of the welding electrode according to claim 1 for making a resistance welded joint between workpieces (9) made of a fourth metal with a passivating metal oxide layer (10).

15. Use according to claim 14, wherein the resistance welded joint is made by resistance spot welding, resistance projection welding or resistance seam welding.

16. Use according to claim 14, wherein the fourth metal is selected from the following group: Al, Mg, Ni, Ti, Zn, Cr, Fe, Nb, Ta, Cu.

Description

[0021] In the following, an embodiment of the invention will be explained in more detail with reference to the drawings. It shows:

[0022] FIG. 1 a top view of a welding cap,

[0023] FIG. 2 a sectional view through the welding cap according to the sectional line A-A′ in FIG. 1,

[0024] FIG. 3 a bottom view according to FIG. 1 and

[0025] FIG. 4 a schematic sectional view through the surface of a welding cap and a sheet to be welded.

[0026] FIGS. 1 to 3 show a welding electrode in the form of a cap or welding cap. The welding electrode has a contact surface 1 which forms the free surface of a diamond layer 2. Reference numeral 3 denotes a portion formed, for example, of W or Mo or an alloy containing Mo or W as a main component. Reference sign 4 denotes an intermediate layer, which in the specific example is substantially formed of WC or MoC. The intermediate layer 4 can be formed in-situ during the manufacture of the diamond layer 2 by means of a CVD process.

[0027] Reference numeral 5 indicates a base portion of the welding cap. The base portion 5 may be made of a third metal different from the first metal forming the portion 3. A third metal may be chosen to manufacture the base portion 5, which is less expensive than the first metal used to manufacture the portion 3. For example, the base section 5 may be formed of pure copper or of a copper-alloy, in particular CuAl.sub.2O.sub.3-, CuCr- or CuCrZr-alloys. —It may of course also be the case that the base portion 5 is omitted and the cap is formed from the first metal forming the portion 3.

[0028] According to a further embodiment not shown in the figures, it is also possible that the section 3 is omitted. In this case, the welding cap is made of a conventional copper-alloy, for example. In this case, the intermediate layer 4 must be applied separately. The intermediate layer may be formed of carbide forming metals. For example, the intermediate layer may comprise Ti. The diamond layer 2 can then be deposited on such an intermediate layer 4 by means of a CVD process.

[0029] FIG. 4 schematically shows the section 3 which is made of a W- or Mo-alloy. The alloy may have a grain boundary phase 6 at the grain boundaries, only some of which are shown here by way of example, which is formed from Fe, Ni, Co or Cu, for example. In the case of an in-situ coating, it is convenient to remove the grain boundary phase 6 superficially by etching and/or particle blasting. This increases the strength of the bond between the diamond layer 2 and the intermediate layer 4.

[0030] The diamond crystals 7 extending from the intermediate layer 4 are more than 50% diamond single crystals. The facets of the diamond crystals 7, denoted by the reference sign 8, are formed from either the (111) plane or the (001) plane. The reference sign P denotes arrows representing the direction of current flow through the diamond layer 2. The current flow is parallel to the [111] direction as well as the [110] direction of the diamond crystals 7.

[0031] The contact surface 1 of the diamond layer 2 is formed by the totality of the facets 8. Opposite the contact surface 1 is a workpiece 9 to be welded, which is made of an aluminum-alloy, for example. The workpiece 9 has a metal oxide layer 10 on its surface.

[0032] Although it is not shown in the figures, the welding tool may be formed of a disc instead of the cap. Such a disc is used in roller seam welding devices. In this case, the contact surface 1 is formed on the peripheral edge of the disc. The section 3 and, if applicable, the base section 5 are arranged in a radially inward position in the disc in a sequence analogous to that of the cap shown in FIGS. 1 to 3.

[0033] To produce a welded joint between the workpiece 9 and another workpiece (not shown here), the diamond layer 2 is pressed against the metal oxide layer 10. A current density in the range of 5 to 60 kA/cm.sup.2, preferably in the range of 10 to 20 kA/cm.sup.2, is generated. In this process, the workpiece 9 welds to a further workpiece (not shown here) arranged opposite, which is pressed against the workpiece 9 with a further welding electrode (not shown here) according to the invention.

[0034] With the proposed welding electrode, more than 1,000 spot welds can be performed, especially on aluminum sheets, without adhesion occurring between the welding electrode and the aluminum sheets.

LIST OF REFERENCE SIGNS

[0035] 1 Contact surface [0036] 2 Diamond layer [0037] 3 Section [0038] 4 Intermediate layer [0039] 5 Base section [0040] 6 Grain boundary phase [0041] 7 Diamond crystal [0042] 8 Facet [0043] 9 Workpiece [0044] 10 Metal oxide layer [0045] P Arrow