Laser welding device and laser welding method with improved fillet formation

1 . A laser welding method for joining a first member in the shape of a plate and made of a metal material to a second member made of a metal material by laser welding, the laser welding method comprising:

an arranging step of bringing the second member into contact with or close to one main surface of the first member; and

a laser beam irradiation step of irradiating a laser beam to the other main surface of the first member, the other main surface being a main surface opposite to the one main surface of the first member which the second member is brought into contact with or brought close to, wherein

in the laser beam irradiation step, the first member and the second member are melted to form:

a weld portion having a substantially circular or oval shape in a plan view;

a linear weld portion connected to the weld portion and having a linear shape in the plan view; and

a fillet on a joined portion between the first member and the second member,

in the arranging step, the second member is arranged relative to the first member so that the second member is brought into contact with or brought close to the one main surface of the first member in only a linear region in the plan view,

the second member is curved in the linear region, and

in the laser beam irradiation step, the linear weld portion is formed so that a whole of or a part of the linear weld portion extends beyond the linear region in the plan view.

2 . The laser welding method according to claim 1 , wherein

an area in which a gap between a surface of the second member and the one main surface of the first member which the second member is brought into contact with or brought close to is equal to or smaller than ½ of a thickness of the first member is projected over the other main surface of the first member and the projected area is a given area that is irradiated with the laser beam.

3 . The laser welding method according to claim 2 , wherein

in the laser beam irradiation step, the laser beam is orbitally scanned around a given part having a center within the given area of the first member until reaching a circle having a diameter larger than a diameter of a spot of the laser beam.

4 . The laser welding method according to claim 1 , wherein

in a case where a gap between an end face of the second member and the one main surface of the first member which the end face of the second member is brought close to is equal to or larger than ½ of a thickness of the first member, the end face of the second member is projected over the other main surface of the first member and the projected area is a given area that is irradiated with the laser beam, and

in the laser beam irradiation step, the laser beam is orbitally scanned around a given part having a center within the given area of the first member until reaching a circle having a diameter larger than a diameter of a spot of the laser beam, and a filler metal is supplied to an area irradiated with the laser beam.

5 . The laser welding method according to claim 1 , wherein a plurality of weld portions are formed.

6 . The laser welding method according to claim 5 , wherein in the laser beam irradiation step, after a plurality of weld portions are formed at a distance from each other, the linear weld portion is formed to connect the weld portions adjacent to each other.

7 . The laser welding method according to claim 5 , wherein in the laser beam irradiation step, forming of weld portions at a distance from each other and forming of the linear weld portion to connect the weld portions adjacent to each other are performed one after another.

8 . A laser welding device that joins a first member in the shape of a plate and made of a metal material to a second member made of a metal material by laser welding, the laser welding device comprising:

a laser oscillator that generates a laser beam;

a scanning unit that scans the laser beam to form a spot while condensing the laser beam on a welding position; and

a control unit that controls the laser oscillator and the scanning unit,

wherein the control unit allows the other main surface of the first member to be irradiated with the laser beam, the other main surface being a main surface opposite to the one main surface of the first member which the second member is brought into contact with or brought close to, in a state in which the second member is brought into contact with or brought close to one main surface of the first member,

whereby the irradiation of the laser beam melts the first member and the second member to form a weld portion having a substantially circular or oval shape in a plan view, form a linear weld portion connected to the weld portion and having a linear shape in the plan view, and form a fillet on a joined portion between the first member and the second member,

the second member is arranged relative to the first member so that the second member is brought into contact with or brought close to the one main surface of the first member in only a linear region in the plan view,

the second member is curved in the linear region, and

at a time of irradiation with the laser beam, the linear weld portion is formed so that a whole of or a part of the linear weld portion extends beyond the linear region in the plan view.

9 . The laser welding device according to claim 8 , wherein an area in which a gap between a surface of the second member and the one main surface of the first member which the second member is brought into contact with or brought close to is equal to or smaller than ½ of a thickness of the first member is projected over the other main surface of the first member, the projected area is a given area that is irradiated with the laser beam.

10 . The laser welding device according to claim 9 , wherein at a time of irradiation with the laser beam, the laser beam is orbitally scanned around a given part having a center within the given area of the first member until reaching a circle having a diameter larger than a diameter of a spot of the laser beam.

11 . The laser welding device according to claim 8 , further comprising a filler metal feeder that supplies a filler metal,

wherein

in a case where a gap between an end face of the second member and the one main surface of the first member which the end face of the second member is brought close to is equal to or larger than ½ of a thickness of the first member, the end face of the second member is projected over the other main surface of the first member and the projected area is a given area that is irradiated with the laser beam, and

at a time of irradiation with the laser beam, the laser beam is orbitally scanned around a given part having a center within the given area of the first member until reaching a circle having a diameter larger than a diameter of a spot of the laser beam, and the filler metal is supplied to an area irradiated with the laser beam.

12 . The laser welding device according to claim 8 , wherein a plurality of weld portions are formed by irradiation of the laser beam.

13 . The laser welding device according to claim 12 , wherein at the time of irradiation with the laser beam, after a plurality of weld portions are formed at a distance from each other, the linear weld portion is formed to connect the weld portions adjacent to each other.

14 . The laser welding device according to claim 12 , wherein at the time of irradiation with the laser beam, forming of weld portions at a distance from each other and forming of the linear weld portion to connect the weld portions adjacent to each other are performed one after another.