To enable continuous welding at an applied section and to improve water-tightness, rigidity and strength by combining a device measuring the laser reflected light intensity from a processing point, a device for vibrating a condenser optical system and a device for controlling the relative distance between the condenser optical system and the processing point and making online correction of the misalignment of a focal position.
The reflection from the laser beam 2 from the processing point 10 is less when laser welding is keyhole welding and good welding quality is obtd. The formation of the keyhole at the processing point 10 is no longer possible when the focal density changes and the power density at the processing point 10 changes and falls below a certain threshold. Consequently, the laser beam reflectivity from the processing point 10 increases and the reflectivity when the keyhole is not formed attains about 60%. An oscillation device control section 15 receives the time signal attaining the differential peak value of the reflected light intensity from a photodetecting intensity computing section 14 and corrects the central value of amplitude to a correct direction from the position of the condenser optical system 8 of this time.
SAKAMOTO HIRONORI
IWASE TAKAKUNI
