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WELDING BY FEEDBACK CONTROLLED LASER SYSTEM

Objective


Improvements have been made in the quality of carbon dioxide laser-welding technology, particularly in terms of better seam-tracking. An efficient to cope with the external deformations of the output coupler was designed and patented. This resulted in an outstanding beam quality. This resulted in an outstanding beam quality: up to 4 kW, 80% of the diffraction limit was reached. At 5kW, a monomode beam was achieved with a static beam axis shift of 0.4 mrad and zero random drift around this point. If using switched mode power supplies, a further reduction to 0.1 mrad is possible.

A solid laboratory prototype of the Intelligent Welding Head (IWH) was developed and successfully tested for seam-tracking and focal point adjustments. It can also focus a 5 kW laser beam for welding operations. This IWH uses a parabolic mirror for beam focussing and the CCD camera and laser diode with a Z-axis separate control for seam tracking and focus adjustment.

A comparative study of direct current (DC) versus radio frequency (RF) excitation concluded that RF is counter-indicated for high power and highquality laser beams because of the non-uniform gain profile. Gas catalysts were tested to reduce gas consumption and improve power efficiency, but were found to have only marginal influence.

A thermal sensor was designed to monitor weld quality. At this stage in the project, only warnings from the operator can be given, but with some refinement it is expected that such a device could be used for feedback control of laser parameters.

Finally, laser parameters for welding complex joint shapes such as wheel rims, suspension arms etc, were thoroughly investigated and optimized. Some joint design recommendations were established to increase laser welding efficiency on such components.

The objectives of this project were the development of a thermal sensor for seam tracking, the development of an intelligent welding head and the development of a laser suitable for welding applications. It was intended that these 3 components should be integrated into a robot system capable of handling a laser for welding applications but this has not been realised.
The thermal sensor has been used for trials on conventional welding machines and it could be used as part of seam tracking systems for industrial welding.
Offaxis parabola technology, which is an important component of the intelligent welding head for weld team tracking, has achieved commercial success with hundreds of units using this technology being sold. This development is continuing to extend its ability to detect seam width in order to control a filler wire feeder.
The improved laser system has applications in industrial cutting and welding. A patent has been filed on this system.
THE QUALITY OF A LASER WELD IS DEPENDENT ON SEVERAL PARAMETERS: LASER BEAM OPTICS, FOCUSSING, GAS FLUX, NOZZLE GEOMETRY AND SYSTEM PARAMETERS SUCH AS THE WELDING SPEED. THESE ALL HAVE TO BE VERY PRECISELY CONTROLLED TO AVOID UNACCEPTABLE IRREGULARITIES IN WELD QUALITY. THE AIM OF THIS PROJECT IS TO ARRIVE AT AN ACCURATE AND INTEGRATED SYSTEM INCORPORATING A DEDICATED LASER ASSEMBLY, AN INTELLIGENT WELDING HEAD EQUIPPED WITH SENSORS AND A 6-AXIS UP-GRADED ROBOT.
THE SYSTEM IS INTENDED TO FIND STRATEGIC WELDING APPLICATIONS FOR THE AUTOMOBILE INDUSTRY. IT WILL BE ASSOCIATED WITH THREE MICROCOMPUTERS USED FOR DECENTRALIZED CONTROL OF THE PROCESS AND TO ADJUST THOSE CONTROL PARAMETERS IN ORDER TO ACHIEVE PERFORMANCES REQUIRED BY INDUSTRY.

SPECIFIC OBJECTIVES ARE THE FOLLOWING:
- LASER POWER : 5KW
- DEVIATION FROM THE IDEAL TRAJECTORY : < 0.1 MM
- STABILITY OF LASER POWER : 1 % UP TO 20 HZ, 5 % UP TO 1000 HZ
THE ROBOT SYSTEM WILL BE REQUIRED SOLELY TO FOLLOW REMOTELY THE PRE-PROGRAMMED WELD-SEAM CURVE. BY SEPARATING THIS ELEMENT FROM THE REMAINDER OF THE LASER CONTROL PARAMETERS A MUCH HIGHER DEGREE OF CONTROLLABILITY SHOULD BE ACHIEVED.
AN ULTRALIGHT OPTICAL HEAD WILL CONTROL THE WELDING CONDITIONS (AUTOFOCUS, SEAM TRACKING, PLASMA DIAGNOSTICS) IN REAL TIME FOR WELD SPEEDS OF UP TO 6M/MIN. A THERMAL SENSOR KEEPS TRACK ON LINE OF THE HEAT AFFECTED ZONE.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Euro Laser Technology
Address

9700 Oudenaarde
Belgium

Participants (3)

Bias - Forschungs- und Entwicklungslabor Angewandte Strahltechnik GmbH
Germany
Address
2,Klagenfurter Strasse
28359 Bremen
Commissariat à l'Energie Atomique (CEA)
France
Address
Centre D'études De Saclay
91191 Gif-sur-yvette
Sciaky Industries SA
France
Address
119 Quai Jules Guesde
94401 Vitry-sur-seine