Laser welding method for repair, and laser welding repair device

A laser welding repair device that melts and erases a crack generated in a structural member of an existing structure, comprising:

• a laser oscillator;
• a shielding gas supply;
• a laser head that moves while irradiating the structural member with laser light supplied from the laser oscillator;
• a temperature sensor that detects a temperature distribution of the structural member irradiated with the laser light;
• and
• a control unit that is communicatively coupled to the temperature sensor and controls the laser oscillator, the laser head and the shielding gas supply, wherein the control unit is configured to:
• set a spot diameter of the laser light applied from the laser head to be less than 3 mm,
• move the laser head to a heat input area that surrounds the crack,
• control the laser head to irradiate a first region within the heat input area,
• control the shielding gas supply to adjust a cross-sectional shape of the first region via cooling of the first region, wherein the cross-sectional shape of the first region is adjusted to maintain a shape coefficient that is 1.0 or greater and equal or less than 1.15,
• control the laser head to irradiate a second region within the heat input area after a temperature detected by the temperature sensor of a portion of the first region cools to or less than or equal to a mechanical melting temperature of the structural member, wherein the portion cools from a molten state that resulted from being irradiated with the laser light.