To perform irradiation position alignment in a short time and to eliminate the need for enlarging flange width by intentionally bringing both plate materials surface treated into contact, gradually enlarging the clearance of both plate from the contact place, setting the region of an appropriate clearance in the range where the clearance is gradually changed and being irradiated with a laser beam in the range.
Plate materials 10, 11 are laser beam welded at both flanges 12, 13. Over a nearly over the whole width of the flange 12, a shallow depth groove 15 of a circular arc shape cross section is formed, a curved face 15 gradually changing is formed on this projecting face side. The flanges 13 are a flat plate, both flanges are brought into line contact at the deepest place 16 of the groove, a clearance 17 is formed from the contact place 16 along both sides. The clearance 17 is gradually enlarged starting at the contact place 16 toward the left and right, the places of the plate material corresponding to the lower limit and the upper limit of the appropriate clearance are shown in a range L, the range L is irradiated with a laser beam 19.
KUROSHIMA KAZUHIKO
MIZUKOSHI AKIRA
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