| CPC B23K 26/032 (2013.01) [B23K 26/0643 (2013.01); B23K 26/0648 (2013.01); B23K 26/082 (2015.10); B23K 26/21 (2015.10); B23K 31/125 (2013.01); G01B 11/22 (2013.01)] | 8 Claims |

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1. A laser welding method for welding a welding part with a laser light, the laser welding method comprising:
overlapping the laser light and a measurement light coaxially with each other and applying the laser light and the measurement light to the weld part, a wavelength of the measurement light being different from a wavelength of the laser light;
repeatedly measuring a weld penetration depth of the weld part based on the measurement light that is emitted from an irradiator and reflected on the weld part so as to generate a plurality of measured values while the measurement light is being moved;
determining the weld penetration depth of the weld part based on: (i) one or more of the plurality of measured values; or (ii) an average value of the one or more of the plurality of measured values, the one or more of the plurality of measured values being included within a predetermined range with reference to a greatest side measured value of the plurality of measured values; and
changing: (i) an irradiation position of the measurement light such that the irradiation position of the measurement light moves on a predetermined welding path; and (ii) an optical axis position as the irradiation position of the measurement light such that the optical axis position moves within a region of the weld part having a radius of rotation that is smaller than half of a spot diameter of the laser light.
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