To minimize the weld defect in manufacturing of the CO{sub}2 laser welded tube for one-body formed automobile bumper beam, the monitoring of the welding quality and the seam tracking along the butt-joint lengthwise to the tube axis are studied. The longitudinal butt-joint is formed from 60kgf/mm{sup}2 grade steel sheet by 2 roll bending method, and welded by the CO{sub}2 laser welding system equipped with the seam tracker and plasma sensor. The laser welded tube has the thickness of 1.5mm, diameter of 105.4mm and length of 2,000mm. The precise positioning of the laser beam on the butt-joint to be assembled is obtained within 200μm by the laser vision sensor. The artificial defects in the butt-joint are well observed by the signal of plasma intensity measured from the plasma sensor of UV wavelength range within 400nm. The developed CO{sub}2 laser tube welding system has the function of the precision seam tracking and the real-time monitoring of the welding quality. Finally, the laser welded tube can be used for manufacturing of automobile chassis and components after tubular hydro-forming.
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