Laser welding method, laser welding conditions determining method, and laser welding system

1. A laser welding method comprising:

irradiating a welding target with a laser beam so as to form a beam spot that moves relatively with respect to the welding target along a locus having a spiral shape rotating around a rotation center moving in a welding direction; and

welding the welding target using the laser beam, wherein

the irradiating of the welding target with the laser beam comprises irradiating the welding target with the laser beam based on an interval coefficient which is a value indicating an overlapping degree of the locus having the spiral shape in the welding direction,

and wherein the interval coefficient is a ratio of a first width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in the welding direction to a second width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in a direction opposite to the welding direction.

2. The laser welding method of claim 1 , wherein the interval coefficient is set such that the beam spot of the laser beam passes so as to only contact an outer edge of a region through which the beam spot of the laser beam has passed once, the region being in a vicinity of center line of a bead formed in the welding target with the laser beam in the welding direction.

3. The laser welding method of claim 1 , wherein the interval coefficient is the ratio of the first width to the second width, and ranges from 1.5 to 3.

4. The laser welding method of claim 3 , wherein the interval coefficient ranges from 2 to 2.5.

5. A method of determining a laser welding condition, the method being used in a laser welding system of welding a welding target by irradiating the welding target with a laser beam so as to form a beam spot that moves relatively with respect to the welding target along a locus having a spiral shape rotating around the rotation center moving in a welding direction, the method comprising:

determining, based on welding target information which is information of the welding target, one or more of a welding speed at which the rotation center moves in the welding direction, a bead width of a bead formed in the welding target with the laser beam, and a penetration depth of a welded portion of the welding target with the laser beam, wherein the welding target information includes information of at least one of a material of the welding target, a shape of a joint, and a thickness of the welding target;

setting laser beam information which is information of the laser beam, wherein the laser beam information includes information of a beam diameter of the laser beam and an interval coefficient which is a value indicating an overlapping degree of the locus having the spiral shape; and

determining a rotational frequency at which the beam spot rotates around the rotation center based on the welding speed, the interval coefficient, the bead width, and the information of the beam diameter,

wherein the interval coefficient is a ratio of a first width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in the welding direction to a second width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in a direction opposite to the welding direction.

6. The method of claim 5 , wherein the interval coefficient ranges from 1.5 to 3.

7. The method of claim 6 , wherein the interval coefficient ranges from 2 to 2.5.

8. The method of claim 6 , further comprising:

displaying the determined one or more of the welding speed, the bead width, and the penetration depth, and the determined one or more of the rotational frequency and the laser output on a display;

changing and redetermining at least one of the determined one or more of the welding speed, the bead width, and the penetration depth; and

redetermining one or more of the rotational frequency and the laser output based on the redetermined at least one of the determined one or more of the welding speed, the bead width, and the penetration depth.

9. A laser welding system comprising:

a laser head that irradiates a welding target with a laser beam; and

a controller that controls the laser head and the laser beam such that the welding target is irradiated with the laser beam so as to form a beam spot that moves relatively with respect to the welding target along a locus having a spiral shape rotating around a rotation center moving in the welding direction, wherein

the controller includes:

a welding-target-information input unit to which welding target information which is information of the welding target is input, the welding target information including information of at least one of a material of the welding target, a shape of a joint, and a thickness of the welding target;

a laser-beam-information input unit to which laser beam information which is information of the laser beam is input, the laser beam information including an interval coefficient which is a value indicating an overlapping degree of the locus having the spiral shape and information of a beam diameter of the laser beam; and

a welding-condition determining unit configured to,

based on the welding target information, determine one or more first recommended values of a welding speed at which the rotation center moves in the welding direction, a bead width of a bead formed in the welding target with the laser beam, and a penetration depth of a welded portion of the welding target with the laser beam, and

based on the interval coefficient and the information of the beam diameter of the laser beam information, and first recommended values among the one or more first recommended values of the welding speed and the bead width, determine one or more second recommended values of a rotational frequency at which the beam spot rotates around the rotation center and a laser output of the laser beam,

wherein the interval coefficient is a ratio of a first width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in the welding direction to a second width in the welding direction within which the beam spot rotates around the rotation center at a moving velocity having a component in a direction opposite to the welding direction.

10. The laser welding system of claim 9 , wherein

the laser-beam-information input unit includes an interval coefficient input unit to which the interval coefficient is input, and

the welding-condition determining unit calculates a rotational frequency F with the welding speed V, the interval coefficient L, the bead width W, and a beam diameter φ of the beam spot by the following formula:

F=V ×{( L+ 1)/( L− 1)}/{2×( W −φ)}.

11. The laser welding method of claim 1 , wherein

the welding of the welding target using the laser beam comprises forming a molten pool by melting the welding target with the laser beam, and

the irradiating of the welding target with the laser beam comprises irradiating with the laser beam an unmolten portion of the welding target located at an outer edge of the molten pool in front of the molten pool in a direction in which the beam spot moves along the locus.

12. The laser welding method of claim 1 , wherein

the welding of the welding target using the laser beam comprises forming a bead on the welding target using the laser beam, and

the interval coefficient L is represented with the beam diameter φ of the beam spot, the welding speed V at which the beam spot moves in the welding direction, and the rotational frequency F of a rotation component of the locus by a following formula:

L=A/B;

A=W−φ+V /(2× F ); and

B=W−φ−V /(2× F ).

13. The laser welding method of claim 12 , wherein the rotational frequency F is determined with the welding speed V, the interval coefficient L, the bead width W, and the beam diameter y of the beam spot by a following formula:

F=V ×{( L+ 1)/( L− 1)}/{2×( W −φ)}.

14. The method of claim 5 , wherein the rotational frequency F is determined with the welding speed V, the interval coefficient L, the bead width W, and the beam diameter φ of the beam spot by a following formula:

F=V ×{( L+ 1)/( L− 1)}/{2×( W −φ)}.