Electric heating – Metal heating – By arc
Patent
1999-02-08
2000-07-04
Evans, Geoffrey S.
Electric heating
Metal heating
By arc
21912164, 21912183, B23K 2628, B23K 2604
Patent
active
060842032
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and a device for welding two pieces, abutted in an assembling position, by means of a welding beam. While mainly developed for laser beam welding, this technology also may be appropriate for other spot welding processes, such as the plasma torch, TIG, MIG, MAG, or electron beam processes.
1. Field of the Invention
The invention particularly relates to the welding of tube lengths for realizing hydrocarbon transportation pipes, in particular on sea bottoms. This welding can take place in difficult conditions, such as is the case on a barge being subjected to movements induced by the sea, and to many vibrations generated by the equipment and motors located on board.
2. Description of the Related Art
For this purpose, a welding machine has already been conceived, comprising a fixed laser source which is spaced away from the tube lengths to be welded and the beam of which is guided, with the help of articulated optical path means, out to a laser head which bears a focussing device and is fixed on a support table rotating around the axis of the tube lengths, which are kept abutted by their ends. For the welding, the support table is rotated by means of the first electric motor around the tube lengths, while the laser head position is adjusted by an axial translation by means of a second electric motor. Such a device is described in the French Patent 93 04642 published under the reference number 2 704 166.
Laser welding requires an extremely precise positioning of the laser beam focussed onto the joint to be welded, namely +/-0.2 mm. The joint tracking control usually needs using a sensor fixed on the laser head, for detecting the eddy currents. This joint tracking system guides the laser head but not the laser beam itself. As a result, any misalignment of the optical path induces a deviation between the laser beam position and the joint to be welded, which may cause a defective welding since the laser beam kinematics cannot be simply deduced from the laser head kinematics. The eddy current sensor furthermore does not allow detecting the joint in an abutting assembly without clearance.
The object of the present invention is to realize a direct and precise piloting of the welding beam and of its impact by servo-controlling its position, where the welding plasma is formed, at the position of the joint to be welded.
For this purpose, the invention concerns a method for laser beam welding two pieces abutted in an assembling position along an assembly joint, to be welded by means of a welding head with a spot shaped beam, characterized in that at least during the welding phase a joint is continuously observed by means of a camera mounted integral with the welding head, by moving the welding head and camera assembly along the joint and by sensing the orthogonal position of the joint for each position of the welding head and camera assembly along the joint, in that the impact position of the welding beam is continuously observed, and in that a piloting of the configuration of an optical path for guiding said beam is insured by servo-controlling the impact position at the position of a joint detected by controlling a translation of the welding head and cameral assembly orthogonally to the joint.
The camera particularly may consist of either a standard camera, or more particularly a CCD camera or an infrared camera for the laser beam position finding operation.
A tracking of the welding plasma is thus performed by servo-controlling its position on the joint as a function of the detected joint position; in other words, the laser beam itself, and not just the laser head, is positioned in real time onto the joint to be welded. This allows reaching for the laser beam, and consequently for the created welding plasma, a positioning precision which is sufficient to insure a good weld, as opposed to the state of the art.
In an embodiment of the invention, during a learning phase, the welding head and camera assembly is moved along the entire assembly joint and
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patent: 5229571 (1993-07-01), Neiheisel
patent: 5685999 (1997-11-01), Wiedemann et al.
Axal
Evans Geoffrey S.
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