Laser welding method and laser welding device used therefor

Abstract

To provide: a laser welding method that can perform welding faster or with deeper penetration using lower energy than conventional methods, on a first planned welding portion and a second planned welding portion; and a laser welding device used therefor.SOLUTION: There is provided a laser welding method for laser welding a first planned welding portion 11K, 21BE1, 31K and a second planned welding portion 12P, 21BE2, 32P by irradiation with a laser beam MB. The method includes: a multibeam generation step S21 of generating, as a laser beam, a radially polarized multibeam MB being a radial laser beam, which is composed of multiple child beams CB, each child beam CB being a radially polarized beam; and an irradiation welding step S22 of laser welding the first planned welding portion and the second planned welding portion by moving an irradiation position HP while irradiating the first planned welding portion and the second planned welding portion with the radially polarized multibeam MB.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a laser welding method for laser-welding a first portion to be welded and a second portion to be welded by irradiating a laser beam, and to a laser welding device used for this method. [Background technology]

[0002] BACKGROUND ART A welding method is known in which welding is performed using a so-called multi-beam laser beam that includes a plurality of beams (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-159931 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 does not consider the polarization direction of each beam. However, it has been found that even in laser welding, the ease of welding varies depending on the polarization direction of the multiple beams irradiated. The present invention has been made in consideration of this current situation, and provides a laser welding method and a laser welding device used therefor that can weld a first portion to be welded and a second portion to be welded more quickly or with deeper penetration using lower energy than conventional methods. [Means for solving the problem]

[0005] (1) One aspect of the present invention for solving the above problem is a laser welding method for laser-welding a first portion to be welded and a second portion to be welded by irradiating a laser beam, the laser welding method comprising: a multibeam generation process for generating a radially polarized multibeam as the laser beam, the radially polarized multibeam being composed of a plurality of child beams, each of the child beams being a radially polarized beam; and an irradiation welding process for laser-welding the first portion to be welded and the second portion to be welded by irradiating the radially polarized multibeam onto the first portion to be welded and the second portion to be welded while moving the irradiation position.

[0006] It is known that when light is shone on a metal plate such as iron or aluminum, the light absorptance changes depending on the angle of incidence, i.e., it is a function of the angle of incidence. Furthermore, the functional relationship between the angle of incidence and absorptance is different for s-polarized light, which is linearly polarized light in which the electric field of the incident light oscillates perpendicular to the plane of incidence, and p-polarized light, which is linearly polarized light in which the electric field of the incident light oscillates perpendicular to the plane of incidence and parallel to the plane of incidence. In general, it is known that the absorptance of p-polarized light is the same as or greater than that of s-polarized light over the entire range of incident angles, and that the absorptance gradually increases as the angle of incidence increases, with the graph showing a peak in absorptance at an angle slightly smaller than 90 degrees (for example, around 88 degrees when light with a wavelength of 1 μm is incident on aluminum).

[0007] When a laser beam is irradiated onto the irradiation position of the area to be welded (first area to be welded, second area to be welded) and the area to be welded is melted to create a recessed hole (keyhole), the angle of incidence of the laser beam incident on the surface of the recessed hole increases over the entire circumference. Here, when a radially polarized beam is used as the irradiated laser beam, p-polarized light is incident on the surface of the hole over the entire circumference, so the increased angle of incidence further increases the absorption rate, allowing the area to be welded at the irradiation position to be efficiently melted. Note that a radially polarized beam is one type of axially symmetric polarized beam, and refers to a laser beam in which an optical electric field is generated radially from the beam center.

[0008] In the present invention, the multibeam generating step generates a radially polarized multibeam, each of whose child beams is a radially polarized beam, and the irradiation welding step moves the irradiation position while irradiating both the first and second portions to be welded with the radially polarized multibeam. Therefore, compared to welding using a multibeam with the same beam pattern but that is not a radially polarized multibeam, the first and second portions to be welded can be welded more quickly with low energy or with deeper penetration with low energy.

[0009] A radially polarized multi-beam is a laser beam that is composed of multiple child beams that are irradiated at different positions on the irradiation surface to form multiple laser spots, and each child beam is a radially polarized beam. Each child beam that makes up a radially polarized multi-beam may be a single radially polarized beam whose beam intensity is distributed in an annular shape, or at least one of the child beams may be a double-annular, double-concentric radially polarized beam.

[0010] Furthermore, in the irradiation welding process, the movement of the irradiation position can be achieved by moving the first and second planned welding portions relative to the laser beam, and the laser beam may be moved by moving the first and second planned welding portions, or by moving both of them.

[0011] The first and second welded portions are portions of the members to be welded that are planned to be welded. Therefore, examples include a first welded portion of a first welded member and a second welded portion of a second welded member that is separate from the first welded member, as well as a first welded portion of a single welded member and a second welded portion at a location separate from the first welded portion. For example, in a case for an electricity storage device, the opening of a case body member can be the first welded portion, and the peripheral edge of a lid that seals the opening can be the second welded portion. Alternatively, a first edge of the case body member can be the first welded portion, and a second edge of the case body member that is separate from the first edge can be the second welded portion.

[0012] (2) In the laser welding method described in (1) above, the multi-beam generating step may include a single beam obtaining step of obtaining one single radially polarized beam, and a branching step of branching the single radially polarized beam to obtain the radially polarized multi-beam.

[0013] A radially polarized multi-beam can also be generated by combining multiple radially polarized beams, which are child beams. However, this requires multiple light sources for the radially polarized beams, and the optical system for combining the individual radially polarized beams tends to be complicated. In contrast, this technology first obtains a single radially polarized beam in the single beam acquisition process, and then obtains a radially polarized multi-beam from the single radially polarized beam in the branching process, making it easy to obtain a radially polarized multi-beam.

[0014] The single radially polarized beam obtained in the single beam obtaining step may be a single radially polarized beam whose beam intensity is distributed in an annular shape, or a double annular double concentric radially polarized beam.

[0015] Methods for obtaining a single radially polarized beam in the single beam acquisition process include, for example, using a metallic grating mirror with radial grooves as the total reflection mirror of the resonator to generate a radially polarized beam (AV Nesterov, VG Niziev and VP Yakunin: “Generation of high-power radially polarized beam,” J. Phys. D: Appl. Phys., 32 (1999) 2871-2875.), and generating a radial beam using a dielectric mirror (GIRO) that reflects only radially polarized light using a diffraction grating with a pitch smaller than the wavelength (T. Moser, J. Balmer, D. Delbeke, P. Muys, S. Verstuyft and R. Baets: “Intracavity generation of radially polarized CO2 laser beams based on a simple binary dielectric diffraction grating,” Appl. Opt., 45 (2006) 8517-8522.). Another method is to generate a radially polarized beam by incorporating a dielectric multilayer mirror with high reflectivity only for radially polarized light, which combines a multilayer optical waveguide and a diffraction grating, into the resonator (MA Ahmed, J. Schulz, A. Voss, O. Parriaux, JC Pommier and T. Graf: “Radially polarized 3 kW beam from a CO2 laser with an intracavity resonant grating mirror,” Opt. Lett., 32 (2007) 1824-1826.) Another method is to generate a radially polarized beam by using a split wave plate that takes advantage of the refractive index anisotropy of liquid crystal molecules (https: / / annex.jsap.or.jp / photonics / kogaku / public / 42-12-kaisetsu1.pdf).

[0016] In addition, in the single beam acquisition process, the laser beam that is the source of the single radially polarized beam can be an unpolarized laser beam obtained from a fiber laser, etc., or a linearly polarized laser beam obtained from a YAG laser oscillator, etc., depending on the method used.

[0017] In addition, the branching process may involve, for example, using a diffractive optical element (DOE) or photonic crystal with a predetermined diffraction pattern to branch a single radially polarized beam into a radially polarized multi-beam consisting of multiple child beams.

[0018] (3) In the laser welding method described in (2) above, the branching step may be a laser welding method in which the single radially polarized beam is irradiated onto a diffractive optical element having a diffraction pattern for obtaining a predetermined number of branched beams from a single beam, thereby obtaining the radially polarized multi-beam.

[0019] In the laser welding method of the present technology, in the branching process, a single radially polarized beam is irradiated onto a diffractive optical element with a predetermined diffraction pattern to obtain the desired radially polarized multi-beam, so that the radially polarized multi-beam can be easily obtained.

[0020] (4) In the laser welding method according to any one of (1) to (3) above, the first portion to be welded has a first opposing surface, the second portion to be welded has a second opposing surface opposing the first opposing surface, and the first opposing surface and the second opposing surface are butt-welded to the first portion to be welded, and in the irradiation welding step, when the irradiation position of the radially polarized multibeam is advanced in a first boundary extension direction among boundary extension directions in which a boundary formed by the first opposing surface and the second opposing surface extends, the plurality of child beams constituting the radially polarized multibeam Preferably, the laser welding method includes one or more first front beams that are irradiated onto the first planned welding portion and melt the first planned welding portion, one or more second front beams that are irradiated onto the second planned welding portion and melt the second planned welding portion, and an inner beam that travels later in the first boundary extension direction than the first front beam and the second front beam and is irradiated onto a molten pool formed by the first planned welding portion melted by the first front beam and the second planned welding portion melted by the second front beam, on the boundary side of the first front beam and the second front beam.

[0021] In this laser welding method, the multiple child beams constituting the radially polarized multi-beam include a first front beam, a second front beam, and an inner beam, all of which are radial beams. The first front beam melts the first portion to be welded, and the second front beam melts the second portion to be welded. The inner beam, which travels later in the first boundary extension direction than the first and second beams, is irradiated onto a molten pool formed across the boundary between the first and second front beams and consisting of the first portion to be welded melted by the first front beam and the second portion to be welded melted by the second front beam. This allows the inner beam to pass through the gap between the boundary between the first and second opposing surfaces, preventing the inner beam from passing to the side opposite (backside) the laser irradiation side, thereby providing energy to a portion closer to the boundary than the first and second front beams, thereby reliably melting and butt-welding the first and second portions to be welded.

[0022] It is advisable to adjust the irradiation position of the radially polarized multi-beam so that the inner beam is irradiated at a position that overlaps the boundary formed by the butted first and second opposing surfaces.

[0023] The first front beam, the second front beam, and the inner beam each may be composed of one or more child beams. For example, the first front beam, the second front beam, and the inner beam may each be composed of one child beam. Alternatively, the first front beam and the second front beam may each be composed of one child beam, and the inner beam may be composed of multiple (e.g., three) child beams. Alternatively, the first front beam and the second front beam may each be composed of multiple (e.g., three) child beams, and the inner beam may also be composed of multiple (e.g., five) child beams. Furthermore, the number and arrangement of the child beams constituting the first front beam and the second front beam may be different, for example, the first front beam may be one and the second front beam may be two.

[0024] (5) Furthermore, in the laser welding method described in (4), it is preferable that the radially polarized multi-beam has a beam pattern in which the beam intensity of the inner beam is higher than the beam intensities of the first front beam and the second front beam.

[0025] In this welding method, the beam strength of the inner beam is greater than the beam strength of the first front beam and the second front beam, so that a weld can be formed that penetrates deeper into the areas near the boundary between the first and second planned weld portions.

[0026] (6) Furthermore, in the laser welding method described in (4) or (5), the first to-be-welded portion may be an opening of a metallic, bottomed, cylindrical or tubular case body, the first opposing surface may be an inner peripheral surface of the opening of the case body, the second to-be-welded portion may be a peripheral portion of a lid body that seals the opening, and the second opposing surface may be an outer peripheral surface of the peripheral portion of the lid body.

[0027] (7) Furthermore, in the laser welding method described in (4) or (5), the first to-be-welded portion may be an opening of a metallic, bottomed, cylindrical or tubular case body, the first opposing surface may be an opening end face of the opening of the case body, the second to-be-welded portion may be a peripheral portion of a lid body that seals the opening, and the second opposing surface may be a peripheral surface on one side of the peripheral portion of the lid body that is located on one side in the thickness direction of the lid body.

[0028] According to these welding methods, the opening of the case body and the peripheral edge of the lid that closes it can be properly welded together.

[0029] The laser welding method according to (8), (4), or (5) may be such that the first portion to be welded is a first edge portion of an unwelded case body made of a metal plate and bent into a cylindrical shape, the second portion to be welded is a second edge portion of the unwelded case body that is brought closer to the first edge portion by the bending, the first opposing surface is a first end face of the first edge portion of the unwelded case body, and the second opposing surface is a second end face that is brought closer to and faces the first end face of the unwelded case body by the bending.

[0030] According to this welding method, the first edge portion and the second edge portion of the unwelded case body can be appropriately welded to form a cylindrical case body.

[0031] (9) Another solution is a laser welding device having a single beam generating optical system that generates one single radially polarized beam, and a branching optical system that branches the single radially polarized beam to obtain a radially polarized multi-beam consisting of multiple child beams, each of which is a radially polarized beam.

[0032] In this laser welding device, a single radially polarized beam is generated by the single beam generating optical system, and then the single radially polarized beam is branched by the branching optical system to obtain radially polarized multi-beams, so that radially polarized multi-beams can be easily obtained.

[0033] (10) Furthermore, in the laser welding apparatus described in (9), the branching optical system may be an optical system that irradiates the single radially polarized beam onto a diffractive optical element having a diffraction pattern that obtains a predetermined number of branched beams from a single beam, thereby obtaining the radially polarized multi-beam.

[0034] In this laser welding apparatus, a single radially polarized beam is split into multiple radially polarized beams using a diffractive optical element in the splitting optical system, so that multiple radially polarized beams can be easily obtained. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a perspective view of a battery in which a case body and a lid are laser-welded according to the first embodiment. FIG. [Figure 2] 4 is an explanatory diagram illustrating how a radially polarized multi-beam is deflected by a laser welding device to laser-weld a case body and a lid body together according to the first embodiment. FIG. [Figure 3] 3 is an enlarged cross-sectional explanatory view of a portion AA in FIG. 2, showing a state before laser welding in which a lid body is placed inside an opening of a case body according to the embodiment. [Figure 4] 3 is an enlarged cross-sectional explanatory view of a portion BB in FIG. 2 according to the first embodiment, showing a state after the opening of the case body and the peripheral edge of the lid body have been laser-welded. [Figure 5] 10 is an explanatory diagram illustrating how the opening of the case body and the peripheral edge of the lid are melted and welded together using radially polarized multi-beams according to the first embodiment. FIG. [Figure 6] 1 is a flowchart showing the steps of the laser welding method according to the first to third embodiments. [Figure 7] FIG. 1 is an explanatory diagram showing a schematic configuration of a laser welding device according to first to third embodiments. [Figure 8] 4 is an explanatory diagram showing the polarization state of a beam generated by a laser oscillator in the laser welding apparatus according to the first to third embodiments. FIG. [Figure 9]1 is an explanatory diagram showing the polarization state of a base beam incident on an axially symmetric polarization conversion element in the laser welding devices according to the first to third embodiments. FIG. [Figure 10] 1 is an explanatory diagram showing the polarization state of a single radially polarized beam that is emitted from an axially symmetric polarization conversion element and incident on a diffractive optical element in the laser welding apparatus according to the first to third embodiments. FIG. [Figure 11] 3 is an explanatory diagram showing the beam pattern and polarization state of radially polarized multi-beams emitted from the laser welding apparatus according to the first to third embodiments and irradiated onto the irradiation position. FIG. [Figure 12] 10 is an explanatory diagram showing the beam pattern and polarization state of radially polarized multi-beams according to Modification 1. FIG. [Figure 13] 10 is an explanatory diagram showing the beam pattern and polarization state of radially polarized multi-beams according to Modification 2. FIG. [Figure 14] 10 is an explanatory diagram showing the beam pattern and polarization state of radially polarized multi-beams according to Modification 3. FIG. [Figure 15] FIG. 10 is an explanatory view showing how a case body is formed by deflecting a radially polarized multi-beam using a laser welding device and laser welding an unwelded case body according to the second embodiment. [Figure 16] 16 is an enlarged explanatory cross-sectional view of a portion CC in FIG. 15 showing the state of the unwelded case body before laser welding, in which the first edge portion and the second edge portion are brought close to each other, according to the second embodiment. FIG. [Figure 17] 16 is an enlarged cross-sectional explanatory view of a portion DD in FIG. 15 according to the second embodiment, showing a state after the first edge portion and the second edge portion have been laser-welded. FIG. [Figure 18] FIG. 11 is an explanatory diagram illustrating a state in which a radially polarized multi-beam is deflected by a laser welding device to laser-weld the case body and the lid body together according to the third embodiment. [Figure 19] 19 is an enlarged cross-sectional explanatory view of a portion EE in FIG. 18 according to the third embodiment, showing the state in which the opening of the case body and the peripheral edge of the lid body are brought into contact with each other before laser welding. [Figure 20]19 is an enlarged cross-sectional explanatory view of the FF portion in FIG. 18, showing the state after the opening of the case body and the peripheral edge of the lid body have been laser-welded according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0036] (Embodiment 1) A first embodiment of the present technology will be described below with reference to the drawings. Fig. 1 is a perspective view of a battery 10 having a flattened rectangular parallelepiped outer shape in which a case body 11 and a lid body 12 are laser-welded according to this embodiment, and Figs. 2 to 4 show how a radially polarized multi-beam MB is deflected to laser-weld the case body 11 and the lid body 12. Fig. 5 shows how the case body 11 and the lid body 12 are melted by the radially polarized multi-beam.

[0037] As shown in FIG. 1, the battery 10 is an electricity storage device including a case body 11 in the shape of a rectangular cylinder with an open top and a closed bottom, and a peripheral edge 12P of a rectangular plate-like lid 12 inserted into the opening 11K of the case body 11 to close the opening 11K, joined together by a weld 14 formed by laser welding along the entire periphery, as shown in FIG. 2. The case body 11 contains an electrode assembly, an electrolyte, and the like (not shown), and a positive terminal 15 and a negative terminal 16 extend through the lid 12 to the outside. A liquid inlet sealing member 17 is fixed to the lid 12 between the positive terminal 15 and the negative terminal 16 to close a liquid inlet (not shown). The battery 10 is a secondary battery, specifically a lithium-ion secondary battery, capable of charging and discharging through the positive terminal 15 and the negative terminal 16. In this embodiment, both the case body 11 and the lid 12 are made of aluminum. In this embodiment 1, the three orthogonal directions in the battery 10 are defined as the longitudinal direction of the lid body 12 as the work X direction XW, the lateral direction as the work Y direction YW, and the depth direction of the case body 11 as the work Z direction ZW, as shown in FIGS. 1 and 2.

[0038] In manufacturing the battery 10 of this embodiment, first, in a setting step S1, the lid body 12 is inserted into the opening 11K of the case body 11. Next, in a welding step S2, a radially polarized multibeam MB is irradiated to butt and laser-weld the opening 11K of the case body 11 and the peripheral edge 12P of the lid body 12 (see FIG. 6).

[0039] First, the setting step S1 (see FIG. 6) will be described. As shown in FIGS. 1 and 2, a positive electrode terminal 15 and a negative electrode terminal 16 are formed on the lid body 12 and extend from the inside. These positive electrode terminal 15 and negative electrode terminal 16 are connected to an electrode assembly (not shown) housed in the case body 11. In the setting step S1, the electrode assembly connected to the positive electrode terminal 15 and the negative electrode terminal 16 is first inserted into the case body 11, and then the lid body 12 is inserted into the opening 11K of the case body 11 (see FIG. 3). As a result, the opening inner circumferential surface 11KS facing inward of the opening 11K of the case body 11 and the outer circumferential surface 12PS of the peripheral portion 12P of the lid body 12 facing this opening inner circumferential surface 11KS are positioned so as to abut or face each other with a small gap G therebetween.

[0040] In addition, in this embodiment, the lid body 12 is inserted into the opening 11K of the case body 11 so that the end face 11KE of the opening 11K of the case body 11 and the outer surface 12PO (top surface in Figure 3) of the peripheral portion 12P of the lid body 12 are aligned with the work Z direction ZW, i.e., so that the end face 11KE and the outer surface 12PO are flush.

[0041] Next, a welding step S2 is performed. Specifically, first, in a multi-beam generating step S21, a laser welding apparatus 100 (see FIG. 7) described later is used to generate a radially polarized multi-beam MB as a laser beam, which is made up of a plurality of (nine in this embodiment) child beams CB that form a beam pattern PA1 described later at an irradiation position HP, and each child beam CB is a radially polarized beam.

[0042] Next, in the irradiation welding step S22, the opening 11K of the case body 11, which is the first portion to be welded, and the peripheral portion 12P of the lid 12, which is the second portion to be welded, of the battery 10 mounted and fixed on the mounting plane 170 of the laser welding apparatus 100 are irradiated with radially polarized multibeams MB while moving the irradiation position HP to laser weld the opening 11K and the peripheral portion 12P (see FIGS. 2 to 4). Specifically, the opening 11K of the case body 11 and the peripheral portion 12P of the lid 12 are set as irradiation positions HP, and the irradiation position HP of the radially polarized multibeams MB is advanced along the boundary BD formed by the opposing inner circumferential surface 11KS and outer circumferential surface 12PS of the opening. Note that the irradiation position HP of the radially polarized multibeams MB advances in one boundary extension direction BDE in which the boundary BD extends, a first boundary extension direction BDE1 (see FIG. 2; in this embodiment, clockwise when viewed from above). In this manner, the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 are laser-welded along the entire periphery of the boundary BD that forms a substantially rectangular ring shape.

[0043] Here, a laser welding apparatus 100 according to this embodiment used for laser welding and a multi-beam generating step S21 performed using this laser welding apparatus 100 will be described with reference to FIGS. 7 to 11. The laser welding apparatus 100 includes a light source unit 110 that obtains a linearly polarized base beam BB (see FIG. 9) with a predetermined collimated beam diameter as a single beam generating optical system for generating a single radially polarized beam SB, and an axially symmetric polarization conversion element 120 that converts the base beam BB into a single single radially polarized beam SB (see FIG. 10). The laser welding apparatus 100 also includes a diffractive optical element 130 that is a branching optical system that branches the single radially polarized beam SB to generate a radially polarized multi-beam MB (see FIGS. 5 and 11). The laser welding apparatus 100 further includes an optical mechanism unit 140 that irradiates the generated radially polarized multi-beam MB onto an irradiation position HP, and a control unit 160 that controls these elements. The optical mechanism unit 140 includes a Z lens 142 that adjusts the focal position SP of the radially polarized multi-beam MB in the optical axis direction LBH along the optical axis LBX, and an XY scanner unit 145 that deflects the radially polarized multi-beam MB.

[0044] Of these, the light source unit 110 comprises a laser oscillator 111 that generates a linearly polarized generated beam GB (see FIG. 8), and a beam expander 112 that expands the diameter of the generated beam GB to form a parallel fundamental beam BB (see FIG. 9). In this embodiment, a YAG laser is used as the laser oscillator 111. The Galilean beam expander 112 has a concave entrance lens 113 and a convex exit lens 114.

[0045] As described above, the linearly polarized fundamental beam BB is incident on the axially symmetric polarization conversion element 120 and converted into a single radially polarized beam SB (see FIG. 10). The single radially polarized beam SB used in this embodiment is a radially polarized laser beam that has a single ring-shaped laser intensity distribution and generates an optical electric field radially in the radial direction. As the axially symmetric polarization conversion element 120, for example, the axially symmetric polarization conversion element SWP series by Photonic Lattice or a radial / azimuth polarization conversion element by Altecna can be used.

[0046] The single radially polarized beam SB is incident on a diffractive optical element 130, which has a diffraction pattern formed thereon for obtaining a predetermined number of branch beams from the single beam, and is converted into a radially polarized multi-beam MB. Therefore, the radially polarized multi-beam MB diffracted by the diffractive optical pattern of the diffractive optical element 130 passes through an optical mechanism 140 and forms a beam pattern PA1 (see FIG. 11) in which a plurality of child beams CB converge at an irradiation position HP (see FIG. 7), which is also a focal position SP where the beam is focused. Note that, like the single radially polarized beam SB, the nine child beams CB constituting the radially polarized multi-beam MB of beam pattern PA1 all become radially polarized laser beams having a single ring-shaped laser intensity distribution.

[0047] Condenser unit 141 of optical mechanism unit 140 is an optical system that adjusts the focal position SP of radially polarized multi-beams MB emitted from diffractive optical element 130, and is made up of Z lens 142, condenser lens 143, and protective glass 144. Z lens 142 of this condenser unit 141 can move the focal position SP of the radially polarized multi-beams MB that pass through in the optical axis direction LBH (up and down in FIG. 7) by moving the lens portion along optical axis LBX.

[0048] Meanwhile, XY scanner unit 145 of optical mechanism unit 140 has X deflection unit 146 consisting of a galvanometer scanner and Y deflection unit 147 also consisting of a galvanometer scanner. X deflection unit 146 deflects the optical axis LBX of radially polarized multibeam MB that has passed through Z lens 142 and is arranged to deflect the optical axis LBX of radially polarized multibeam MB in a deflection X direction Xs along a mounting surface 170 on which an object to be irradiated (battery 10 in this embodiment) is placed by changing the deflection angle θx. Meanwhile, Y deflection unit 147 deflects the optical axis LBX of radially polarized multibeam MB reflected by X deflection unit 146 and is arranged to deflect the optical axis LBX of radially polarized multibeam MB in a deflection Y direction Ys orthogonal to the deflection X direction Xs along a mounting surface 170 on which an object to be irradiated (battery 10 in this embodiment) is placed by changing the deflection angle θy. Then, the radially polarized multi-beams MB reflected and deflected by the Y deflection unit 147 are emitted to the outside via the condenser lens 135 and the protective glass 137, and are focused at a focal position SP.

[0049] Therefore, in laser welding apparatus 100, Z lens 142 adjusts focal position SP at which radially polarized multibeam MB is focused to optical axis direction LBH, and therefore to deflection Z direction Zs perpendicular to deflection X direction Xs and deflection Y direction Ys. At the same time, XY scanner unit 145 deflects radially polarized multibeam MB in deflection X direction Xs and deflection Y direction Ys so that radially polarized multibeam MB is irradiated to each irradiation position HP on the irradiated object (e.g., battery 10). Furthermore, Z lens 142 and XY scanner unit 145 position each irradiation position HP of radially polarized multibeam MB at an appropriate position, for example, on boundary BD between opening inner circumferential surface 11KS of case body 11 and outer circumferential surface 12PS of lid body 12, while causing it to advance in first boundary extension direction BDE1, thereby performing continuous laser welding.

[0050] The operations of laser oscillator 111, Z lens 142, and XY scanner section 145 (X deflection section 146, Y deflection section 147) are controlled in conjunction with each other by control section 160 (see FIG. 7).

[0051] As described above, in the laser welding apparatus 100, in the single beam obtaining step S211 of the multibeam generating step S21, a single radially polarized beam SB is obtained using the light source unit 110 and the axially symmetric polarization conversion element 120 that constitute the single beam generating optical system. Furthermore, in the branching step S212, the single radially polarized beam SB is branched using the diffractive optical element 130 that constitutes the branching optical system to obtain radially polarized multibeams MB.

[0052] In this embodiment, when laser welding the battery 10, the battery 10 is placed and fixed on the flat mounting surface 170 so that the center point 10S of the opening 11K and the planar direction of the lid 12 of the battery 10 coincides with the origin of the deflection X direction Xs and deflection Y direction Ys of the flat mounting surface 170. Therefore, the diffracted multibeam LB is deflected by the XY scanner unit 145 at a deflection angle θ (θx, θy) centered on the center point 10S, and is irradiated onto the irradiation position HP (see FIG. 2).

[0053] Furthermore, in this embodiment, as shown by the arrows in FIGS. 7 and 2 , the battery 10 is placed and fixed on the mounting plane 170 in such a position that the workpiece X-direction XW (the longitudinal direction of the lid 12, from lower left to upper right in FIG. 2 ) coincides with the deflection X-direction Xs, the workpiece Y-direction YW (the lateral direction of the lid 12, from upper left to lower right in FIG. 2 ) coincides with the deflection Y-direction Ys, and the workpiece Z-direction ZW (the depth direction of the case body 11, from up to down in FIG. 2 ) coincides with the deflection Z-direction Zs, with the opening 11K of the case body 11 and the lid 12 facing upward toward the optical mechanism 140 (specifically, the protective glass 144).

[0054] Therefore, when the optical axis LBX of the radially polarized multibeam MB is deflected by the X deflection unit 146, the irradiation position HP of the radially polarized multibeam MB irradiated onto the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 moves in the workpiece X direction XW (longitudinal direction of the lid 12) that coincides with the deflection X direction Xs. Furthermore, when the optical axis LBX of the radially polarized multibeam MB is deflected by the Y deflection unit 147, the irradiation position HP of the diffracted multibeam LB irradiated onto the opening 11K and the peripheral edge 12P of the battery 10 moves in the workpiece Y direction YW (transverse direction of the lid 12) that coincides with the deflection Y direction Ys.

[0055] Using this laser welding device 100, radially polarized multibeams MB are irradiated onto the opening 11K of the case body 11 of the battery 10 and the peripheral edge 12P of the lid 12, while the irradiation position HP is moved in the first boundary extension direction BDE1, thereby laser welding the opening 11K and the peripheral edge 12P all around. Note that, below, as shown in Fig. 2, the state of laser welding during a period in which the irradiation position HP of the radially polarized multibeams MB is moved to one side XW1 in the workpiece X direction XW, which is the longitudinal direction of the lid 12, is described (a period in which the first boundary extension direction BDE1 coincides with the one side XW1).

[0056] First, we will explain the beam pattern PA1 (see FIG. 11) formed by the radially polarized multi-beams MB at the irradiation position HP. The beam pattern PA1 in this embodiment is made up of nine child beams CB. More specifically, the beam pattern PA1 has a single main beam CBM located in the center and having the largest peak energy and spot diameter. In addition, surrounding the main beam CBM, there are eight peripheral beams CBP, each consisting of two beams CBP with smaller peak energy and spot diameter than the main beam CBM, arranged radially in four directions in an X-shape.

[0057] Therefore, when the irradiation position HP of the radially polarized multi-beam MB is advanced to one side XW1, which coincides with the first boundary extension direction BDE1, as shown by the right-facing arrow in Figure 11, the radially polarized multi-beam MB will advance in a state where it is irradiated with not only the main beam CBM, but also eight surrounding beams CBP, namely, two points diagonally forward to the left and two points diagonally forward to the right in the direction of advancement (one side XW1) from the main beam CBM, and two points diagonally backward to the left and two points diagonally backward to the right.

[0058] 5, at the irradiation position HP, the main beam CBM of the radially polarized multi-beam MB is positioned on the boundary BD between the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12. At the same time, of the eight peripheral beams CBP, two left front beams CBFL, which are positioned diagonally forward and left in the traveling direction as seen from the main beam CBM, are irradiated onto the opening 11K of the case body 11. In addition, two right front beams CBFR, which are positioned diagonally forward and right in the traveling direction as seen from the main beam CBM, are irradiated onto the peripheral edge 12P of the lid 12. Then, the two left front beams CBFL and the two right front beams CBFR advance in the traveling direction before the main beam CBM, which is positioned closer to the boundary BDP1 (inner) than them, passes by, and the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 are pre-melted and combined to form a molten pool that fills the gap G. This prevents the main beam CBM, which travels later than these, from passing through the gap G and entering the case body 11, which is known as "laser leakage."

[0059] Furthermore, since the beam intensity of the main beam CBM is greater than the beam intensity of the left front beam CBFL and the right front beam CBFR, a weld 14 can be formed that penetrates deeper into the opening 11K of the case body 11 and the peripheral portion 12P of the lid body 12 near the boundary BD (see Figure 4).

[0060] In this embodiment, the beam pattern PA1 (see Figure 11) of the radially polarized multi-beam MB is a pattern with 90-degree symmetry (four-fold symmetry). Therefore, even if the irradiation position HP of the radially polarized multi-beam MB is advanced to the other side YW2 of the workpiece in the Y-direction YW (downward in Figure 11), the other side XW2 of the workpiece in the X-direction XW (rightward in Figure 11), or one side YW1 of the workpiece in the Y-direction YW (upward in Figure 11), the same effect can be obtained by using the same beam pattern PA1 and the left front beam CBFL and right front beam CBFR that advance ahead of the main beam CBM.

[0061] 11, the nine child beams CB (main beam CBM and eight peripheral beams CBP) constituting the radially polarized multi-beam MB are all radially polarized laser beams. Therefore, even when the radially polarized multi-beam MB is irradiated onto the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 (see FIGS. 2 and 5), the absorption rate of each child beam CB is further increased due to the increased angle of incidence at the recessed hole (keyhole) formed by melting the opening 11K, etc., compared to when non-radially polarized child beams such as linearly polarized beams are used. This allows the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 to be welded more quickly with low energy or to be welded more deeply with low energy.

[0062] (Variations 1 to 4) In the above-described first embodiment, the beam pattern PA1 (see FIG. 11) consisting of nine child beams CB is used as the beam pattern of the radially polarized multi-beams MB. However, other beam patterns can also be used. For example, the beam patterns PA2 to PA4 shown in FIGS. 12 to 14 can also be used as the beam patterns of the radially polarized multi-beams MB.

[0063] Even when these beam patterns PA2 to PA4 are used, when the radially polarized multi-beam MB is advanced in the first boundary extension direction BDE1, the left front beam CBFL and the right front beam CBFR advance ahead of the main beam CBM, melting and combining the opening 11K of the case body 11 and the peripheral portion 12P of the lid body 12 to form a molten pool that fills the gap G, thereby preventing the main beam CBM, which advances later than these, from passing through the gap G and entering the case body 11.

[0064] 12 to 14, each of the child beams CB (main beam CBM and peripheral beams CBP) constituting the radially polarized multi-beam MB is a radially polarized laser beam. Therefore, compared to when non-radially polarized child beams such as linearly polarized beams are used, the opening 11K and the peripheral edge 12P can be melted more efficiently at the irradiation position HP. Therefore, the opening 11K of the case body 11 and the peripheral edge 12P of the lid 12 can be welded more quickly with low energy or can be welded with deeper melting with low energy.

[0065] 12, when using the beam pattern PA2 of Modification 1 consisting of five child beams CB resembling the number 5 on a die, the pattern is 90° symmetric (four-fold symmetric), just like the beam pattern PA1 of the embodiment. Therefore, even when the irradiation position HP of the radially polarized multi-beam MB is advanced to the other side YW2 in the workpiece Y-direction YW (downward in FIG. 11), the other side XW2 in the workpiece X-direction XW (rightward in FIG. 11), or one side YW1 in the workpiece Y-direction YW (upward in FIG. 11), the same effect can be obtained by using the same beam pattern PA1 and the left front beam CBFL and right front beam CBFR that advance ahead of the main beam CBM.

[0066] On the other hand, the beam patterns PA3 and PA4 of the second and third modifications shown in FIGS. 13 and 14 are suitable for moving the irradiation position HP in the first boundary extension direction BDE1 indicated by the arrow in the drawings.

[0067] (Embodiment 2) In the above-described first embodiment, the opening 11K of the case body 11 and the peripheral edge 12P of the lid body 12, which is a separate body, are laser-welded using radially polarized multi-beam MB (see FIGS. 1 and 2).

[0068] In contrast, in this embodiment 2, as in embodiment 1, a radially polarized multi-beam MB is generated and deflected using a laser welding apparatus 100 (see Figure 7), and the first end edge portion 21BE1, which is the first to-be-welded portion, and the second end edge portion 21BE2, which is the second to-be-welded portion, of the single-piece unwelded case body 21B are butt-jointed and laser-welded to form a weld 24, thereby forming a rectangular cylindrical case body 21 (see Figures 15 to 17).

[0069] That is, unwelded case body 21B is formed by bending a rectangular aluminum plate into a square tubular shape. Unwelded case body 21B is bent so that first edge portion 21BE1 and second edge portion 21BE2 are close to each other (see FIGS. 15 and 16). Therefore, second edge surface 21BS2 of second edge portion 21BE2 faces first edge surface 21BS1 of first edge portion 21BE1.

[0070] Therefore, in the setting step S1 (see FIG. 6), an unwelded case body 21B bent as described above is prepared. In the unwelded case body 21B, the first end surface 21BS1 of the first edge portion 21BE1 and the second end surface 21BS2 of the second edge portion 21BE2 are positioned so as to abut or face each other with a small gap G therebetween (see FIG. 16). In the second embodiment, the three orthogonal directions in the unwelded case body 21B and the case body 21 are defined as follows: the longitudinal direction of the unwelded case body 21B is defined as the workpiece X-direction XW; the lateral direction is defined as the workpiece Y-direction YW; and the depth direction of the unwelded case body 21B is defined as the workpiece Z-direction ZW, as shown in FIG.

[0071] Next, as in the first embodiment, in the welding step S2, in the single beam obtaining step S211 of the multibeam generating step S21, a single radially polarized beam SB is obtained using the light source unit 110 and the axially symmetric polarization converting element 120. Furthermore, in the branching step S212, a radially polarized multibeam MB is obtained using the diffractive optical element 130.

[0072] Next, in the irradiation welding step S22, the first edge portion 21BE1, which is the first portion to be welded, and the second edge portion 21BE2, which is the second portion to be welded, of the unwelded case body 21B placed and fixed on the flat mounting surface 170 of the laser welding apparatus 100 are irradiated with radially polarized multibeams MB while moving the irradiation position HP to laser weld the first edge portion 21BE1 and the second edge portion 21BE2 (see FIGS. 15 to 17). Specifically, the irradiation position HP of the radially polarized multibeams MB is advanced along the boundary BD formed between the opposing first end face 21BS1 and second end face 21BS2. Note that, of the boundary extension directions BDE along which the boundary BD extends, the irradiation position HP of the radially polarized multibeams MB is advanced in one first boundary extension direction BDE1 (see FIG. 15; in this embodiment, this direction coincides with one side XW1 in the workpiece X-direction XW). In this manner, the first edge portion 21BE1 and the second edge portion 21BE2 are laser-welded along the entire length of the linear boundary BD.

[0073] In this second embodiment, too, by using a radially polarized multi-beam MB of beam pattern PA1 (see Figure 11), the two left front beams CBFL and the two right front beams CBFR melt and combine the first edge portion 21BE1 and the second edge portion 21BE2 in advance to form a molten pool that fills the gap G, thereby preventing the main beam CBM, which progresses later than these, from passing through the gap G and entering the case body 21, thereby preventing the so-called ``laser miss'' from occurring.

[0074] Furthermore, since the beam intensity of the main beam CBM is greater than the beam intensity of the left front beam CBFL and the right front beam CBFR, a weld 24 can be formed that is more deeply welded in the areas near the boundary BD of the first edge portion 21BE1 and the second edge portion 21BE2 (see Figure 17).

[0075] 11, each of the child beams CB constituting the radially polarized multi-beam MB is a radially polarized laser beam, which allows the first edge portion 21BE1 and the second edge portion 21BE2 to be melted more efficiently than when a non-radially polarized child beam such as a linearly polarized beam is used. This allows the first edge portion 21BE1 and the second edge portion 21BE2 to be welded more quickly with low energy, or to be welded with deeper penetration with low energy.

[0076] In addition, in this embodiment 2, instead of the radially polarized multi-beam MB of beam pattern PA1 (see Figure 11), the first edge portion 21BE1 and the second edge portion 21BE2 may be laser welded using radially polarized multi-beam MB of beam patterns PA2 to PA4 of variants 1 to 3 shown in Figures 12 to 14.

[0077] (Embodiment 3) In the above-described first embodiment, in a setting step S1, a rectangular plate-shaped lid 12 is inserted into an opening 11K of a bottomed square cylindrical case body 11, and an inner peripheral surface 11KS of the opening 11K of the case body 11 faces an outer peripheral surface 12PS of a peripheral edge portion 12P of the lid 12. Then, in a welding step S2, a radially polarized multibeam MB is irradiated from the outer surface 12PO side of the lid 12, thereby laser welding the opening 11K and the peripheral edge portion 12P around the entire circumference (see FIGS. 1 and 2).

[0078] In contrast, in this embodiment 3 (see Figures 18 to 20), in the setting process S1 (see Figure 6), the opening end surface 31KE facing outward of the opening 31K of the square cylindrical case main body 31 and the one-side peripheral surface 32PE1 facing one side (towards the case main body 31) in the lid body thickness direction LT of the peripheral portion 32P of the rectangular plate-shaped lid body 32 placed over the opening are abutted or opposed with a small gap G (see Figure 19).

[0079] Then, in welding step S2, radially polarized multibeams MB are irradiated from the radial outside of the rectangular cylindrical case body 31 to laser weld one side, for example, a portion corresponding to the long side, of the entire rectangular circumference of the opening 31K of the rectangular case body 31 and the peripheral edge 32P of the lid 32. Note that the following describes the laser welding during the period when the portion of the rectangular opening 31K and peripheral edge 32P corresponding to the long side on the near side in FIG. 18 is welded. Furthermore, during this period, the three orthogonal directions in the case body 31 and the lid 32 are defined as follows: the longitudinal direction of the lid 32 is defined as the workpiece X-direction XW, the lateral direction is defined as the workpiece Z-direction ZW, and the depth direction of the case body 31 is defined as the workpiece Y-direction YW, as shown in FIG.

[0080] Next, as in the first and second embodiments, in the welding step S2, in the single beam obtaining step S211 of the multibeam generating step S21, a single radially polarized beam SB is obtained using the light source unit 110 and the axially symmetric polarization converting element 120, using the laser welding apparatus 100. Furthermore, in the branching step S212, a radially polarized multibeam MB is obtained using the diffractive optical element 130.

[0081] Next, in the irradiation welding step S22, radially polarized multibeams MB are irradiated onto the opening 31K, which is the first portion to be welded, and the peripheral edge 32P, which is the second portion to be welded, of the case body 31 and the lid 32, which are placed and fixed on the placement plane 170 of the laser welding apparatus 100, while the irradiation position HP is moved to laser weld the opening 31K and the peripheral edge 32P (see FIGS. 18 to 20). Specifically, the irradiation position HP of the radially polarized multibeams MB is advanced along the boundary BD formed between the opening end face 31KE and the one-side peripheral edge face 32PE1, which face each other. Note that, of the boundary extension directions BDE along which the boundary BD extends, the irradiation position HP of the radially polarized multibeams MB is advanced in a first boundary extension direction BDE1 (see FIG. 18; in the third embodiment, this direction coincides with one side XW1 in the workpiece X-direction XW). In this manner, the opening 31K and the peripheral edge 32P are laser-welded along the boundary BD along one long side.

[0082] For the remaining three sides, the case body 31 and the lid 32 are rotated clockwise in a top view and laser welding is performed, so that the opening 31K and the peripheral edge 32P are laser welded along the entire periphery.

[0083] In this embodiment 3 as well, by using the radially polarized multi-beam MB of beam pattern PA1 (see Figure 11), the two left front beams CBFL and the two right front beams CBFR melt and combine the opening 31K and the peripheral portion 32P in advance to form a molten pool that fills the gap G, thereby preventing the main beam CBM, which progresses later than these, from passing through the gap G and entering the case body 21, thereby preventing the so-called ``laser missing'' from occurring.

[0084] Furthermore, since the beam intensity of the main beam CBM is greater than the beam intensity of the left front beam CBFL and the right front beam CBFR, a weld 34 can be formed that penetrates deeper into the opening 31K and the peripheral portion 32P near the boundary BD (see Figure 20).

[0085] In addition, in this embodiment 3, instead of the radially polarized multi-beam MB of beam pattern PA1 (see Figure 11), the opening 31K and the peripheral portion 32P may be laser welded using radially polarized multi-beam MB of beam patterns PA2 to PA4 of modified examples 1 to 3 shown in Figures 12 to 14.

[0086] While the present invention has been described above in accordance with Embodiments 1 to 3, it goes without saying that the present invention is not limited to the embodiments, etc., and can be appropriately modified and applied without departing from the spirit of the present invention. For example, in Embodiments 1 to 3, to generate a single radially polarized beam SB in laser welding apparatus 100, generated beam GB obtained by linearly polarized laser oscillator 111 is converted into a similarly linearly polarized base beam BB by beam expander 112, and then further converted into a radially polarized single radially polarized beam SB by axially symmetric polarization conversion element 120.

[0087] However, the single beam generating optical system only needs to be able to generate a single radially polarized beam SB, and for example, the single radially polarized beam SB may be obtained using unpolarized laser light generated by a fiber laser, etc. Alternatively, a laser oscillator that oscillates radially polarized laser light may also be used.

[0088] Furthermore, double annular double concentric radially polarized beams may be used as the single radially polarized beam SB and each of the child beams CB of the radially polarized multibeam MB. [Explanation of symbols]

[0089] 100 Laser welding equipment 110 Light source unit (single beam generating optical system) 120 Axisymmetric Polarization Conversion Element (Single Beam Generation Optical System) 130 Diffractive optical element (branching optical system) LBX optical axis GB generated beam BB Foundation Beam SB Single radially polarized beam (single beam) MB Radial Polarized Multi-Beam (Laser Beam) CB radially polarized beam (child beam, branch beam) CBM main beam (inner beam) CBP ambient beam CBFL Left front beam (first front beam) CBFR Right front beam (second front beam) CBBL Left rear beam (first rear beam) CBBR Right Rear Beam (Second Rear Beam) PA1, PA2, PA3, PA4 beam patterns HP irradiation position MP molten pool 10 batteries 11, 21, 31 Case body 11K, 31K Opening (first welding area) 11KS Opening inner surface (first opposing surface) 11KE Open end surface 31KE Opening end surface (first opposing surface) 12,32 Lid 12P, 32P peripheral area (second welding area) 12PS outer peripheral surface (second opposing surface) 12PO outer surface 32PE1 One side peripheral surface (second opposing surface) LT Lid thickness direction LT1 (lid thickness direction) one side 14, 24, 34 Welded parts 21B Unwelded case body 21BE1 First edge portion (first welding portion) 21BE2 Second edge portion (second planned welding portion) 21BS1 1st end surface (1st opposing surface) 21BS2 2nd end surface (2nd opposing surface) 30 Battery Module BD boundary BDE boundary extension direction BDE1 First boundary extension direction BDPI boundary side S1 Setting process S2 Welding process S21 Multi-beam generation process S211 Single beam acquisition process S212 Branching process S22 Irradiation welding process

Claims

1. A laser welding method for laser welding a first portion to be welded and a second portion to be welded by irradiating a laser beam, comprising: a multibeam generating step of generating a radially polarized multibeam as the laser beam, the radially polarized multibeam being composed of a plurality of child beams, each of the child beams being a radially polarized beam; an irradiation welding process of laser-welding the first portion to be welded and the second portion to be welded by moving an irradiation position while irradiating the first portion to be welded and the second portion to be welded with the radially polarized multibeam. Laser welding method.

2. 2. The laser welding method according to claim 1, The multi-beam generating step includes: a single beam obtaining step of obtaining one single radially polarized beam; a branching step of branching the single radially polarized beam to obtain the radially polarized multi-beam. Laser welding method.

3. 3. The laser welding method according to claim 2, The branching step includes: A single radially polarized beam is irradiated onto a diffractive optical element having a diffraction pattern for obtaining a plurality of predetermined branch beams from a single beam, thereby obtaining the radially polarized multi-beams. Laser welding method.

4. 2. The laser welding method according to claim 1, The first portion to be welded has a first opposing surface, the second portion to be welded has a second opposing surface opposing the first opposing surface, and is a portion to be butt-welded to the first portion to be welded by butting the first opposing surface against the second opposing surface, In the irradiation welding step, when the irradiation position of the radially polarized multi-beam is advanced in a first boundary extending direction among boundary extending directions in which a boundary formed by the first opposing surface and the second opposing surface extends, The plurality of child beams constituting the radially polarized multi-beam are one or more first front beams that are irradiated onto the first portion to be welded and melt the first portion to be welded; one or more second front beams that are irradiated onto the second portion to be welded and melt the second portion to be welded; an inner beam that advances later than the first front beam and the second front beam in the first boundary extension direction and is irradiated onto a molten pool formed by the first to-be-welded portion melted by the first front beam and the second to-be-welded portion melted by the second front beam on the boundary side of the first front beam and the second front beam. Laser welding method.

5. 5. The laser welding method according to claim 4, The radially polarized multi-beam The beam pattern has a beam intensity of the inner beam higher than the beam intensity of the first front beam and the second front beam. Laser welding method.

6. The laser welding method according to claim 4 or 5, the first welding portion is a bottomed cylindrical or cylindrical opening of a metal case body, the first opposing surface is an inner circumferential surface of the opening of the case body, the second welding portion is a peripheral portion of a lid that seals the opening, The second opposing surface is an outer peripheral surface of the peripheral edge portion of the lid body. Laser welding method.

7. The laser welding method according to claim 4 or 5, the first welding portion is a bottomed cylindrical or cylindrical opening of a metal case body, the first opposing surface is an opening end surface of the opening of the case body, the second welding portion is a peripheral portion of a lid that seals the opening, The second opposing surface is a one-side peripheral surface located on one side of the peripheral portion of the lid in the thickness direction of the lid. Laser welding method.

8. The laser welding method according to claim 4 or 5, the first portion to be welded is a first edge portion of an unwelded case body made of a metal plate and bent into a cylindrical shape, the second welding target portion is a second edge portion of the unwelded case body that is brought close to the first edge portion by the bending, the first opposing surface is a first end surface of the first edge portion of the unwelded case body, The second opposing surface is a second end surface that is brought close to and opposed to the first end surface of the unwelded case body by the bending. Laser welding method.

9. a single beam generating optical system that generates a single radially polarized beam; a branching optical system that branches the single radially polarized beam to obtain a radially polarized multi-beam that is composed of a plurality of child beams, each of which is a radially polarized beam; Laser welding equipment.

10. 10. The laser welding apparatus according to claim 9, The branching optical system includes: The optical system is one in which a single radially polarized beam is irradiated onto a diffractive optical element having a diffraction pattern for obtaining a predetermined number of branch beams from a single beam, thereby obtaining the radially polarized multi-beam. Laser welding equipment.

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