Electric heating – Metal heating – By arc
Patent
1999-11-03
2000-11-21
Shaw, Clifford C.
Electric heating
Metal heating
By arc
21912512, B23K 9095
Patent
active
061506311
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a root gap detecting method in an arc welding, and a welding condition control method.
BACKGROUND TECHNOLOGY
Conventionally, a root gap of a groove in the arc welding has been detected using a laser beam sensor or an image pick-up sensor to detect the groove shape considerably forward of the arc during the welding or before the welding is executed, but no technology to detect the gap just below the arc during the welding has been established.
On the other hand, when the welding is executed by an automatic apparatus using a welding robot, etc., an operation program is prepared by an offline programming method before the welding is executed. However, the offline programming is based on the CAD data, and differences are generated between the CAD data and the actual work position and dimensions due to the machining accuracy, the fitting accuracy, the dynamic thermal deformation etc. of the work during the welding. There exist problems of degrading the welding quality such that desired leg length can not be obtained due to the presence of the gap attributable to said difference.
To solve the problems, it has been strongly requested to develop a technology to select an appropriate welding condition and execute the proper welding operation by in-process sensing the fluctuation of the gap.
Generally, in the adaptive control technology on the welding condition, the welding condition database has been priorly constructed by skilled workers, and an appropriate welding condition has been determined before the welding is executed based on the information on the geometrical shape of a member to be welded, and the information such as the leg length. The welding condition during the welding is thus of open loop control. This is attributable to the fact that no technology for in-process sensing the root gap of the groove or the leg length has been established. Though there is a technology to control the welding condition by combining an image processing unit with a laser beam sensor to measure the gap and detect the bead width as a conventional technology, there has been no technology for controlling the welding condition by sensing the gap immediately below the arc during the welding and achieving the feedback to a controller.
Further, in a case of the welding by the automatic apparatus using the welding robot, etc., an operation program is prepared by the offline programming method before the welding is achieved. In the operation program, the starting point and the finishing point of the welding joint which are the operating path points of the robot, and the operating path point of a position changing point, etc., for the interference avoidance processing are calculated based on the CAD data, thus the parameters such as the welding current, the welding voltage, the welding speed and the torch angle which are the welding conditions are allotted to said points.
In executing the welding operation, the welding starting point is detected by a wire-touch sensor, and the welding is executed by achieving the sequential interpolation of the operating path point while achieving the groove tracking control by the arc sensor during the welding because there exists a difference between the dimensions of actual members and the CAD data. However, there is a problem that the change of the parameters for the welding condition accompanied by the interpolation of the operating path point has not been adapted. That is, the feedback routine by the arc sensor, etc. has been available for the operating path point while the welding condition is subjected to the open-loop control without feedback. Thus, there are some cases that the leg length becomes insufficient, and appropriate welding quality becomes difficult to keep if the welding is executed under the unchanged welding condition though there is a gap in the actual member selected from the CAD database which was made before the welding is achieved. Still worse, such a gap is inevitably generated due to the machining accuracy and the fitt
REFERENCES:
patent: 5532452 (1996-07-01), Lechner et al.
patent: 5938955 (1999-08-01), Ikeda et al.
Gotoh Naoyuki
Kanjo Yoshihiro
Murayama Masatoshi
Ozamoto Daisuke
Serizawa Hitoshi
NKK Corporation
Shaw Clifford C.
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