Electric heating – Metal heating – By arc
Patent
1997-06-23
1999-01-12
Mills, Gregory L.
Electric heating
Metal heating
By arc
21912169, 219137R, B23K 2600, B23K 900
Patent
active
058594027
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for welding work pieces with a laser beam that is focused on the work piece, which is moved relative to the beam causing a vaporization of the material, such that apart from the laser beam, an arc is used in the area of the work pieces that are struck by the laser beam.
Processes having the aforementioned process steps are generally known as laser beam hybrid welding, and they are used, for example, to weld sheet metal. At the welding point, which is determined by the laser beam, not only is energy used with the aid of laser beams, but also with the aid of the arc. In the process, automatic guidance of the arc by its electrode to the area of the weld, which is determined by the laser beam, occurs. This guidance, or even a contraction of the arc, can be explained by several phenomena. If the laser beam merely heats the surface of the work piece, without any vaporization of the metal occurring, thermally-generated electrons give rise to a local increase of electrical conductivity, which gives rise to thermally-produced electrons. A corresponding electrical field results, which contributes to the guidance of the arc. If, as a result of the laser irradiation, metal is vaporized, the composition of the plasma changes, and, as a result of the comparably low ionization energy of the metallic vapor, a pathway of elevated conductivity is formed for the arc. In addition, an interactive effect occurs between the laser beam and the plasma that is formed as a result of ionization. In keeping with the physical parameters and the geometry of the work piece, the guidance of this arc is pronounced, to a greater or lesser degree. For technical applications, stable arcs of high output density are called for.
Accordingly, it is the underlying task of the invention to improve a process having the processing steps enumerated at the outset in such a way that the guidance of the arc, in the sense of stable arcs of high output density is improved.
This task is fulfilled by virtue of the fact that a work piece having a dielectrically free surface which guides the arc is used in a dielectric layer that completely covers the remainder of the area of the weld.
In the process described above, the conductivity on the surface of the work piece is reduced by the application of the dielectric layer. The dielectric layer works as an insulator. The arc will not be based, without further ado, in a superficial area of the work piece with a dielectric layer. It will tend, rather, to have its point of impact on the surface of the work piece in the processing area of the work piece that is determined by the laser beam.
It is particularly advantageous to operate the process in such a way that the work piece consists of an aluminum alloy, and the oxide layer of the work piece is used as the dielectric layer. The aluminum, or aluminum alloy, respectively, forms an oxide layer relatively quickly after the work piece is shaped, which oxide layer exhibits dielectric behavior and may be used as a dielectric layer in the spirit of the invention. By contrast, it is known from WELDING JOURNAL, June 1984, page 18 ff that the surface of the specimens or work pieces are to be brushed and cleaned prior to welding in order to remove oxides and residues. Within the context of the present invention, therefore, it is significant to have recognized that contrary to the practices that have been employed thus far in welding, it is possible to use the oxide layer that is present in the sense of a guide for the arc in the welding pathway.
It is not necessary to allow dielectric layers to develop naturally on work pieces. It is also possible, rather, to perform the process in such a way that the dielectric layer is applied prior to welding as needed to the work piece in the area of the weld, except for the pathway that guides the arc. The application can occur, without any further ado, by artificial means, thus, with the structure that is required of the pathway on the surface. The dielectric layer can, for example, be applied in the s
REFERENCES:
patent: 3278720 (1966-10-01), Dixon
patent: 4167662 (1979-09-01), Steen
patent: 4507540 (1985-03-01), Hamasaki
patent: 5510597 (1996-04-01), Kampmann et al.
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Mills Gregory L.
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