Tack welding method and tack welding apparatus

1. A tack welding method of tack-welding a part of a joint portion of a first joint and a second joint at a predetermined interval before main welding, the tack welding method comprising:

disposing the second joint which has a smaller plate thickness than that of the first joint below the first joint which has a larger thickness than the second joint and is disposed above the first joint,

positioning the first joint and the second joint in a state where an end portion of the first joint and an end portion of the second joint are abutted to form a step of the joint portion located at a front side to be tack welded,

supplying a filler metal to the step of the joint portion while the joint portion is being pressed along with the filler metal and in a state where the filler metal is inclined by a predetermined angle, setting a deflection width of laser light to be larger than a gap Δg in the joint portion, irradiating laser light sideways to the joint portion while deflecting the laser light, and cutting the filler metal with the laser light to be welded to the joint portion.

2. The tack welding method according to claim 1 , wherein the first joint is constituted by both end portions of a cross section of a steel material having a substantially U-shaped or substantially semicircular cross section, and the second joint is constituted by a steel material having a cross section including both end portions facing the both end portions of the first joint.

3. The tack welding method according to claim 2 , wherein two joint portions on left and right sides of the steel material are simultaneously welded.

4. A tack welding apparatus that tack-welds a part of a joint portion of a first joint and a second joint at a predetermined interval before main welding, the tack welding apparatus comprising:

a filler metal supply device that supplies a filler metal to the joint portion; and

a laser welding device that irradiates laser light to the joint portion while deflecting the laser light,

a mounting table that supports a first workpiece that has the first joint and a second workpiece that has the second joint,

a pair of guide rails that extend along left and right side of the mounting table,

a movement unit that has a gate shape and moves along the guide rails, wherein

the filler metal supply device and the laser welding device are disposed on the movement unit,

the movement unit includes a pair of first pressing devices that press the first workpiece and the second workpiece inward from the left and right sides and a second pressing device that presses the upper workpiece and the lower workpiece downward from an upper side, wherein

the mounting table, the first pressing device, and the second pressing devise are used to dispose the second workpiece including the second joint which has a smaller plate thickness than that of the first joint below the first joint and dispose the first workpiece including the first joint which has a larger plate thickness than that of the second joint above the second joint, the first joint and the second joint are positioned in a state where an end portion of the first joint and an end portion of the second joint are abutted to form a step of the joint portion located at a front side to be tack welded,

wherein the laser welding device is configured so that the deflection width of the laser beam can be set larger than a gap Δg of the joint portion, and

wherein the filler metal supply device is configured to supply a filler metal to the step of the joint portion while the joint portion is being pressed along with the filler metal and in a state where the filler metal is inclined by a predetermined angle.