PROBLEM TO BE SOLVED: To allow welding to be performed without lifting a work-piece by reasonably detecting welding variation due to an unstable rotation speed such as sliding of the work-piece with respect to a chuck caused by friction between a jig and the work-piece or the like when the work-piece which cannot be clamped only with weak force and has polygonal portions concentrically on an outer circumferential surface is chucked, is irradiated with a laser beam and is circumferentially subjected to laser welding while performing constant-velocity rotation without lifting the work-piece from the jig.;SOLUTION: A laser welding method includes a welding normal/defective determination process of setting upper limit standard time TU and lower limit standard time TL with upper and lower allowance as time required for rotation of center angle α content which pinches a side of one of a polygonal portion 14 and performing normal/defective determination according to computer control when actual measurement required time Ta required for each rotation of the center angle α content of the work-piece 10x holds on relation of TU≥Ta≥TL in all of them in comparison to time TU, TL on a circumferential laser welding process while subjecting the work-piece 10X to constant-velocity rotation.;SELECTED DRAWING: Figure 1;COPYRIGHT: (C)2019,JPO&INPIT
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