Electric heating – Metal heating – By arc
Patent
1997-06-05
1998-10-13
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912159, 21912164, 21912145, 219137R, B23K 1000, B23K 2600
Patent
active
058214933
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national stage of PCT/DE95/100965 which is based on German national applications P44 34 125.3 filed 23 Sep. 1994 and 195 00 512.0 filed 10 Jan. 1995 under the International Convention.
FIELD OF THE INVENTION
The invention relates to a process for welding workpieces with a laser radiation causing the vaporization of the material, wherein workpieces with angled surfaces and at least one edge, particularly tailored blanks or galvanized sheets, are placed in the weld seam area.
BACKGROUND OF THE INVENTION
Laser welding methods are used in the welding of sheet metal and of components made of sheet metal. Such components are known as tailored blanks and are for instance parts of a group of components for motor vehicle bodies. Strongly curved, tunnel-shaped pieces of sheet metal used for encasing the cardanic shaft of a motor vehicle with rear-wheel drive can be mentioned as a concrete example for tailored blanks. In order to achieve the desired high-grade welding of such tailored blanks, the respective sheet metal pieces have to undergo very precise weld seam preparations, as well as an accurate positioning for welding. Special steps are required for the positioning of the work head of the laser welding device, so that the laser beam can be effective where it is needed for producing a high-quality weld, without being disturbed by the projecting edge of the thicker component.
OBJECTS OF THE INVENTION
It is therefore the object of the invention to improve a process with the aforementioned process steps so that the efforts for the precise preparation of the weld seam during the production of the workpiece and during its positioning for welding can be eliminated, without any adverse effects on the quality of the weld.
SUMMARY OF THE INVENTION
This object is achieved due to the fact that during the welding of the workpiece, in addition to the laser beam, an arc is guided close to the workpiece in the process range of the laser beam, whereby the guidance of the arc takes place on the edge of a workpiece.
Since in the case of tailored blanks or workpieces with different thickness in the weld seam area, it is always difficult to achieve satisfactory results with only one means for supplying the welding energy, the main concept of the invention resides foremost in the fact that, in addition to the laser beam, welding energy is also supplied with an arc. The energy supplied by the arc serves for at least partially melting the projecting edge of the thicker workpiece, whereby the arc is essentially guided by the electrode with this projecting edge. The metal vapor or plasma generated by the laser radiation process, as well as the high field strength at the edge influence the arc in such a way that a stable melting of the free cutting edge and an incoming flow of melt in the weld zone of the sheet metal pieces take place also at high process speeds. Thereby this edge is melted off and rounded. The melted off material flows into the welding zone and in a gap possibly located there, which as a result is at least partially filled, respectively filled up. Particularly a collapse of the weld seam causing a notch effect in the workpiece is avoided. Generally a rounding of the weld zone or of the weld seam area, takes place. The melt flowing into the weld seam area makes it possible to allow for less precise preparation of the weld seam and for higher tolerances in the positioning precision of the workpieces to be welded together. The occurrence of errors is less frequent due to the larger volume of melt, so that the welding process is more reliable. In addition higher welding speeds become possible, because comparatively more energy is brought in due to the arc. Therefore the welding process becomes more cost-effective.
However the process of the invention is suitable not only for welding tailored blanks. It is rather suitable for all workpieces which have angular surfaces and at least one edge in area of the weld seam. In this case the guidance of the arc
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patent: 4507540 (1985-03-01), Hamasaki
patent: 4782205 (1988-11-01), Shira
patent: 5006688 (1991-04-01), Cross
patent: 5532454 (1996-07-01), Kuhnen
patent: 5591360 (1997-01-01), Mombo-Caristan
Beyer Eckhard
Imhoff Ralf
Maier Christof
Neuenhahn Jan
Dubno Herbert
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Paschall Mark H.
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