Electric heating – Metal heating – By arc
Patent
1998-01-26
2000-03-07
Evans, Geoffrey S.
Electric heating
Metal heating
By arc
21912163, B23K 2600
Patent
active
060343478
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a process for continuous butt-welding of metal sheets, in particular for car body building in the car industry. Furthermore, this invention concerns a device for performing the continuous butt-welding process described.
BACKGROUND OF THE INVENTION
With the customary welding processes, in particular beam welding (electron beam welding, laser beam welding), there are two methods known: welding tool, clamped, and welded. This process is not a continuous welding process. templates, are introduced into and welded by a stationary beam welding tool. With this process the metal sheets are welded continuously.
Both methods entail considerable work in creating the requisite mechanical precision (approx. 0.03 mm) and pose problems with respect to mechanical wear incurred during the production. This wear leads to losses in quality when metal sheets are welded.
Previously known from DE 38 30 892 is a process for determining the relative position of a weld seam to a specifiable target position in order to be able to rectify the relative position of the welding laser beam to the weld seam. In the rectification process a collimated laser measuring beam around the seam path is alternately deflected and focused and, after reflection from the workpiece arrangement forming the weld seam, received by an optoelectronic sensor and transmitted to a repositioning device. This process serves to determine the position of a weld seam relative to a specifiable target position in order to be able to rectify the relative position of the welding laser beam to a weld seam. Here the deflecting frequency of the deflected laser measuring beam should be at least 100 Hz, whereby the intensity of the laser measuring beam is modulated with at least 200 kHz in such a manner that the laser measuring beam impinges on the workpiece arrangement at a distance of no greater than 10 mm from the axis of the welding laser beam, whereby a single light-sensitive element only is used as an optoelectronic sensor. This has as a result that feed and weld speeds of 100 mm/s can be reached, whereby, at this feed speed, the seam path can be determined in a specified grid. Modulation of the laser diode radiation and further, subsequent demodulation of the sensor signal, amplitude modulated in addition by the workpieces, facilitate the elimination of disruptive influences exerted by the laser welding plasma and the Planck's radiation from the weld pool.
In DE 38 30 892 a level of the technology is also described with which, in the cases of a line weld, the starting and end points of the weld seam are determined with the assistance of a measuring beam superimposed precisely along the axis of the main laser or welding beam. The points thus determined are entered into the control program for the main laser beam, and the seam is welded between the determined points in accordance with the program specified--in the assumed case, a line weld.
Described in addition in DE 28 30 892 is a weld tracking system for automated arc welding with which the prepared weld seam is scanned with an alternately focused laser measuring beam at a measuring frequency of no greater than 10 Hz across the weld seam, and the position of the laser welding beam or the electrode holder relative to the weld seam is rectified accordingly in the event of a deviation of the weld seam from the target position. Used as the sensor with this known weld tracking system is a photodiode cell. Owing to the large number of measuring points and the time required for the evaluation, this weld tracking system has a measuring accuracy of only 0.2 to 0.5 mm.
Further described is that the diameter of the focused spot of a focused operating laser or welding beam may at times only be 0.1 to 0.2 mm. However, owing to this very low expansion of the focused spot, the weld seams intended for laser welding likewise exhibit very small cross sections. Assumed, therefore, for the welding of such weld seams can be a measuring accuracy of half the diameter of the focused spot, i.e
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Alber Gerhard
Neurohr, deceased Gerhard
Evans Geoffrey S.
Thyssen Industrie AG
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