Characterization of a Yb:YAG Disk Laser Line Welder for Ultra-thin Steel Strip in Industrial Cold-Rolling Mill
A laser line welder that uses a Yb:YAG disk laser was manufactured and applied to produce ultra-thin coils by continuous operation in a cold-rolling mill. The coils welded range from 0.15 to 0.30 mm in thickness and from 800 to 1100 mm in width. Because the strip is very thin compared to its width, the laser line welding is likely to cause defects such as pinholes on the weld bead. Depending on the diameter of pinholes, the hole-shaped defects on the seam can significantly reduce weld quality including tensile strength and bending strength. To prevent generation of such defects, a hydraulic control device is integrated into the laser line welder so that the positions for cutting and welding by laser are placed with ±30 μm of the target; furthermore, to avoid weld failure, a vision system has been optimized for real-time inspection of the weld zone and detection of weld defects both before and after welding.
Keywords: Yb:YAG disk laser, laser line welder, ultra-thin coil, weld quality inspection, steelworks, cold-rolling mill