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  • BMW Adopts Scanning Method for Spot Welding

Photonics Spectra
Jan 2004
Brent D. Johnson

Changing the tooling and equipment of a factory requires an investment that few manufacturers are willing to consider -- unless the benefits of the retrofit are so significant that the eventual reward far outweighs the immediate expense. Consequently, when a major automobile manufacturer adopts a new generation of industrial automation equipment, people take notice. Recently, BMW AG of Munich, Germany, qualified and approved a laser scanner welding system from Trumpf Group of Ditzingen, Germany, for use in the production of its new 3 series vehicles.

BMW Adopts Scanning Method for Spot Welding

BMW selected the Trumpf TLW 60 S laser scanner welding system for the production of the 3 series automobile. The system achieves positioning speeds of up to 700 m/min.

The TLW 60 S laser scanner works with the laser company's series of TLF lasers, including its 6000-W CO2. In operation, the system focuses the laser beam with an adaptable mirror optic and guides it to the weld spot with a pair of tilting galvo mirrors located 1 m above the workpiece. The beam path can be displaced with only a minor adjustment to the mirror over a work area of up to 1200 × 1200 × 250 mm.

Focusing optics

Because the scanner is built with reflecting focusing mirrors instead of a transmissive lens, thermal instability from high laser powers is reduced. The mounting of the focusing optics on a fast linear axis also means that the focal spot can be directed at any point in three dimensions.

Hans Hornig, head of welding and joining technology at BMW, said that an advantage of this process is the considerably shorter time required for positioning the focal spot from one weld to another. Compared with conventional beam-positioning systems, the highly dynamic beam deflection achieved by the TLW 60 S permits positioning speeds of up to 700 m/min. In a weld test performed on a reinforcing element, the scanner reduced the required machining time from 30 to 5 s. Besides the high rate of welding, Hornig also said that the system showed no wear on parts and that a single scanner can replace several robots.

The device has been tested on more than 10,000 welded assemblies of the BMW 3 series, and dynamic and static stress testing have shown good results. The next step will be serial deployment of the system.

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