Laser welding device

1. A laser welding device configured to weld two overlapping workpieces by emitting a laser beam to the workpieces to form a weld bead, the laser welding device comprising:

an irradiation unit configured to emit, to the workpieces, the laser beam and a measurement beam having a wavelength different from a wavelength of the laser beam;

a measurement unit configured to measure a depth from a predetermined reference surface based on the measurement beam emitted by the irradiation unit and reflected from the workpieces;

an irradiation position switching part configured to switch an irradiation position of the measurement beam between a keyhole position coaxial with an optical axis of the laser beam and a weld bead position behind a center of the optical axis of the laser beam in a welding direction, wherein the weld bead has a surface where a recess is formed; and

a controller configured to determine an amount of a gap between the two workpieces based on a measured value of a recess depth measured at the weld bead position, by making a comparison with recess depth previously measured in a state where there is no gap between the two workpieces.

2. The laser welding device of claim 1 , wherein the controller is further configured to correct, based on the amount of the gap, a measured value measured at the keyhole position.

3. The laser welding device of claim 1 , wherein the controller is configured to change a welding condition to increase a molten amount of the workpieces when the amount of the gap is larger than a predetermined reference value by increasing the output of the laser beam, reducing the welding speed, or emitting the laser beam along a spin trajectory.

4. The laser welding device of claim 1 , wherein, if the amount of the gap is larger than a predetermined upper limit, the controller determines that the amount of the gap is abnormal.

5. A laser welding device configured to weld two overlapping workpieces by emitting a laser beam to the workpieces,

the two workpieces being offset in an in-plane direction to expose part of one of the workpieces behind the other workpiece as viewed from an irradiation direction of the laser beam, the laser welding device comprising:

an irradiation unit configured to emit, to the workpieces, the laser beam and a measurement beam having a wavelength different from a wavelength of the laser beam;

a measurement unit configured to measure a depth from a predetermined reference surface based on the measurement beam emitted by the irradiation unit and reflected from the workpieces;

an irradiation position switching part configured to switch an irradiation position of the measurement beam between a keyhole position coaxial with an optical axis of the laser beam and a boundary position between the two workpieces in front of a center of an optical axis of the laser beam in a welding direction; and

a controller configured to determine an amount of a gap between the two workpieces based on a plurality of measured values measured before and after the measurement beam crosses the boundary position,

wherein the irradiation position switching part switches the irradiation position of the measurement beam such that the irradiation position gyrates around a center of rotation moving along a predetermined welding path.

6. The laser welding device of claim 5 , wherein the controller is further configured to correct, based on the amount of the gap, a measured value measured at the keyhole position.

7. The laser welding device of claim 5 , wherein

if the amount of the gap is larger than a predetermined upper limit, the controller determines that the amount of the gap is abnormal.