Welding method

Abstract

For example, a novel and improved welding method capable of welding a laminate in which multiple metal foils and metal members are overlapped, and a metal laminate, electrical components, and electrical products welded by this welding method. [Solution] The welding method involves, for example, irradiating a metal foil on the opposite side of a plurality of metal foils overlapping a metal member with a laser beam containing a first laser beam and a second laser beam with a lower energy density than the first laser beam, thereby welding a metal member and a plurality of metal foils, comprising the steps of irradiating with laser beam to form a molten pool spanning the plurality of metal foils and the metal member, and solidifying the molten pool to form a weld, wherein in the step of forming the molten pool, the spot of the laser beam is swept over the surface of the metal foil, and the absorbed energy absorbed by the plurality of metal foils and the metal member from the laser beam, with the absorbed energy per unit length in the sweeping direction being 0.14 [J / mm] or less.

Description

Technical Field

[0001] The present invention relates to a welding method.

Background Art

[0002] Conventionally, a battery in which a plurality of tabs and terminals are joined by laser welding is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In this type of welding, it is important not only to ensure the required joining strength but also to prevent defects such as cutting of a plurality of metal foils at a site irradiated with laser light and partial fracture of the metal foil.

[0005] Therefore, one of the problems of the present invention is to provide a novel and improved welding method capable of welding, for example, a laminate in which a plurality of metal foils and metal members overlap, and to obtain a metal laminate, an electrical component, and an electrical product welded by the welding method.

Means for Solving the Problems

[0006] The present invention relates to a welding method for welding a metal member to a plurality of metal foils, for example, by irradiating a metal foil on the opposite side of a plurality of metal foils overlapping in a first direction on a metal member with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, the welding method comprising the steps of irradiating with the laser light to form a molten pool extending between the plurality of metal foils and the metal member, and solidifying the molten pool to form a weld, wherein in the step of forming the molten pool, the spot of the laser beam is swept over the surface of the metal foil, and the absorbed energy absorbed by the plurality of metal foils and the metal member from the laser light, with the absorbed energy per unit length in the sweeping direction being 0.14 [J / mm] or less.

[0007] In the welding method described above, the absorbed energy may be greater than or equal to the amount that can melt the metal foil in contact with the metal member among the plurality of metal foils.

[0008] In the welding method described above, the absorbed energy may be 0.05 [J / mm] or more when the thickness of the multiple metal foils stacked in the first direction is 400 [μm] or more.

[0009] In the welding method described above, the sweep speed of the spot may be 300 mm / s or more and 10,000 mm / s or less.

[0010] In the welding method described above, the wavelength of the first laser beam may be 800 nm or more and 1200 nm or less, and the wavelength of the second laser beam may be 550 nm or less.

[0011] In the welding method described above, the wavelength of the second laser light may be 400 nm or more and 500 nm or less.

[0012] In the welding method described above, the laser beam may be formed by a beam shaper.

[0013] In the welding method described above, the beam shaper may be a DOE.

[0014] In the welding method described above, in the step of forming the molten pool, the sweeping trajectory of the spot on the metal foil may be set such that, in at least a portion of the sweeping trajectory, at least a portion of the spot has already been melted by the irradiation of the laser light.

[0015] In the welding method described above, the sweeping trajectory may include an endless portion.

[0016] In the welding method described above, the sweeping trajectory may have an overall endless shape.

[0017] In the welding method described above, in the step of forming the molten pool, after the endless portion is formed in the sweeping trajectory, the spot of the laser beam may be swept in the region inside the endless portion on the surface.

[0018] In the welding method described above, the sweeping trajectory may include a plurality of adjacent sections.

[0019] In the welding method described above, the sweeping trajectory may include a linear segment connecting two points on the sweeping trajectory.

[0020] In the welding method described above, the sweeping trajectory may include a spiral section.

[0021] In the welding method described above, the sweeping trajectory may include a wobbling section in which the spot rotates around the reference point while the reference point moves in a second direction.

[0022] In the welding method described above, the sweeping trajectory may include a section extending linearly in the second direction and a wobbling section that is swept after the linearly extended section and partially overlaps with the linearly extended section.

[0023] In the welding method, the scanning locus may include a portion where the scanning loci intersect each other.

[0024] In the welding method, the width of the formed welded portion may be 30 [μm] or more and 300 [μm] or less.

[0025] The welding method of the present invention is, for example, a welding method in which a laser beam including a first laser beam and a second laser beam having an energy density lower than that of the first laser beam is irradiated onto a metal foil on the opposite side of the plurality of metal foils overlapping in a first direction on a metal member, and the metal member and the plurality of metal foils are welded. The method includes a step of irradiating the laser beam to form a molten pool extending over the plurality of metal foils and the metal member, and a step of solidifying the molten pool to form a welded portion. In the step of forming the molten pool, the outer diameter of the welded portion formed when a spot of the laser beam is irradiated onto the metal foil on the opposite side of the plurality of metal foils from the metal member, or the width of the welded portion formed when the spot of the laser beam is scanned on the metal foil on the opposite side of the plurality of metal foils from the metal member is 30 [μm] or more and 300 [μm] or less.

[0026] The welding method of the present invention is, for example, a welding method in which a laser beam including a first laser beam and a second laser beam having an energy density lower than that of the first laser beam is irradiated onto a metal foil on the opposite side of the plurality of metal foils overlapping in a first direction on a metal member, and the metal member and the plurality of metal foils are welded. The method includes a step of irradiating the laser beam to form a molten pool extending over the plurality of metal foils and the metal member, and a step of solidifying the molten pool to form a welded portion. In the step of forming the molten pool, a spot of the laser beam is irradiated onto the metal foil on the opposite side of the plurality of metal foils from the metal member, and the input energy of the laser beam to the plurality of metal foils and the metal member is 1.0 [J] or less.

[0027] In the welding method, the input energy may be greater than or equal to a size at which the metal foil in contact with the metal member among the plurality of metal foils can be melted.

[0028] The present invention relates to a welding method for welding a metal member to a plurality of metal foils, for example, by irradiating a metal foil on the opposite side of a plurality of metal foils overlapping in a first direction on a metal member with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, the welding method comprising: irradiating with the laser light to form a molten pool extending between the plurality of metal foils and the metal member; and solidifying the molten pool to form a weld, wherein in the step of forming the molten pool, the spot of the laser beam is swept over the surface of the metal foil, and the sweeping trajectory of the spot on the metal foil includes a wobbling section in which the spot orbits around a reference point while the reference point moves in a second direction, and a section that extends linearly in the second direction and partially overlaps with the wobbling section.

[0029] The metal laminate of the present invention comprises, for example, a metal member, a plurality of metal foils overlapping the metal member in a first direction, and a welded portion formed by welding the metal member and the plurality of metal foils, wherein, in the metal foils of the plurality of metal foils opposite to the metal member, the outer diameter when the welded portion is formed as a point, or the width when the welded portion is formed as a line, is 30 [μm] or more and 300 [μm] or less.

[0030] The electrical component of the present invention comprises, for example, the metal laminate as a conductor.

[0031] The electrical product of the present invention includes, for example, the metal laminate as a conductor. [Effects of the Invention]

[0032] According to the present invention, for example, an improved and novel welding method is available that can weld a laminate in which multiple metal foils and metal members are overlapped, as well as a metal laminate, an electrical component, and an electrical product welded by this welding method. [Brief explanation of the drawing]

[0033] [Figure 1] Figure 1 is an illustrative schematic diagram of a laser welding apparatus according to the first embodiment. [Figure 2] Figure 2 is an exemplary and schematic cross-sectional view of a metal laminate used as a processing target for the laser welding apparatus of the embodiment. [Figure 3] Figure 3 is an exemplary and schematic cross-sectional view of a battery including a metal laminate as the workpiece of the laser welding apparatus of the embodiment. [Figure 4] Figure 4 is a schematic diagram illustrating the laser beam (spot) formed on the surface of a workpiece by the laser welding apparatus of the first embodiment. [Figure 5] Figure 5 is a graph showing the light absorption rate of a metal as a function of the wavelength of the irradiated laser light. [Figure 6] Figure 6 is an exemplary flowchart illustrating the procedure of the welding method according to the embodiment. [Figure 7] Figure 7 is an illustrative and schematic cross-sectional view illustrating the mechanism by which a fracture occurs at the boundary between the weld and the metal foil in a metal laminate. [Figure 8] Figure 8 is an illustrative cross-sectional view showing a case where cutting occurs in the welded area due to the welding method described in the reference example. [Figure 9] Figure 9 is an illustrative cross-sectional view showing a good joint condition obtained by the welding method of the embodiment. [Figure 10] Figure 10 is an illustrative cross-sectional view showing a case where a portion of the metal foil breaks due to the welding method described in the reference example. [Figure 11] Figure 11 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 12] Figure 12 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 13] Figure 13 is a cross-sectional view taken along line XIII-XIII in Figure 12. [Figure 14] Figure 14 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 15]Figure 15 is a cross-sectional view taken along line XV-XV in Figure 14. [Figure 16] Figure 16 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 17] Figure 17 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 18] Figure 18 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 19] Figure 19 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 20] Figure 20 is a schematic diagram showing an example of the trajectory of a laser beam spot on the surface of a metal foil by the welding method of the embodiment. [Figure 21] Figure 21 is an illustrative schematic diagram of a laser welding apparatus according to a second embodiment. [Figure 22] Figure 22 is an explanatory diagram illustrating the concept of the principle of the diffractive optical element included in the laser welding apparatus of the second embodiment. [Figure 23] Figure 23 is a schematic diagram showing an example of a laser beam (spot) formed on the surface of a workpiece by the laser welding apparatus of the second embodiment. [Figure 24] Figure 24 is an illustrative schematic diagram of a laser welding apparatus according to the third embodiment. [Modes for carrying out the invention]

[0034] Illustrative embodiments of the present invention are disclosed below. The configurations of the embodiments shown below, as well as the actions and results (effects) brought about by such configurations, are examples only. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derived effects) that can be obtained by the configuration.

[0035] The embodiments shown below have similar configurations. Therefore, the configurations of each embodiment provide similar functions and effects based on those similar configurations. In the following, similar components are given the same reference numerals, and redundant explanations may be omitted.

[0036] In each figure, the X direction is represented by the arrow X, the Y direction by the arrow Y, and the Z direction by the arrow Z. The X, Y, and Z directions intersect and are orthogonal to each other. The Z direction is the normal direction to the surface Wa (machined surface, welded surface) of the workpiece W, the thickness direction of the metal foil 12, and the lamination direction of the metal foil 12 and the metal laminate 10.

[0037] Furthermore, in this specification, ordinal numbers are assigned for convenience to distinguish parts, components, sections, laser beams, directions, etc., and do not indicate priority or order.

[0038] [First Embodiment] Figure 1 is a schematic diagram of the laser welding apparatus 100 according to the first embodiment. As shown in Figure 1, the laser welding apparatus 100 comprises a laser device 111, a laser device 112, an optical head 120, and an optical fiber 130. The laser welding apparatus 100 is an example of a welding apparatus.

[0039] Each laser device 111 and 112 has a laser oscillator and is configured to output laser light with a power of several kW, for example. Laser devices 111 and 112 emit laser light with a wavelength of 400 nm or more and 1200 nm or less. Laser devices 111 and 112 have laser light sources inside, such as fiber lasers, semiconductor lasers (elements), YAG lasers, and disk lasers. Laser devices 111 and 112 may be configured to output multimode laser light with a power of several kW as the sum of the outputs of multiple light sources.

[0040] The laser device 111 outputs a first laser beam with a wavelength of, for example, 800 nm or more and 1200 nm or less. The laser device 111 is an example of a first laser device. For example, the laser device 111 has a fiber laser or a semiconductor laser (element) as a laser light source. The laser oscillator of the laser device 111 may also be called the first laser oscillator.

[0041] On the other hand, the laser device 112 outputs a second laser beam with a wavelength of, for example, 550 nm or less. The laser device 112 is an example of a second laser device. For example, the laser device 112 has a semiconductor laser (element) as a laser light source. The laser device 112 preferably outputs a second laser beam with a wavelength of 400 nm or more and 500 nm or less. The laser oscillator of the laser device 112 may also be called a second laser oscillator.

[0042] The optical fiber 130 optically connects the laser devices 111 and 112 to the optical head 120. In other words, the optical fiber 130 guides the laser light output from the laser devices 111 and 112 to the optical head 120.

[0043] The optical head 120 is an optical device that irradiates the laser light input from the laser devices 111 and 112 toward the workpiece W. The optical head 120 includes a collimating lens 121, a focusing lens 122, a mirror 123, a filter 124, and a galvanoscanner 126. The collimating lens 121, focusing lens 122, mirror 123, filter 124, and galvanoscanner 126 may also be referred to as optical components.

[0044] The collimating lenses 121 (121-1, 121-2) each collimate the laser light input via the optical fiber 130. The collimated laser light becomes parallel light.

[0045] Mirror 123 reflects the first laser beam, which has become parallel light by the collimating lens 121-1, and directs it towards the galvanoscanner 126.

[0046] Filter 124 is a high-pass filter that transmits the first laser beam but reflects the second laser beam without transmitting it. The first laser beam from mirror 123 passes through filter 124 and heads towards the galvanoscanner 126. On the other hand, the second laser beam from collimating lens 121-2 is reflected by filter 124 and heads towards the galvanoscanner 126.

[0047] The galvanoscanner 126 has multiple mirrors 126a and 126b. By changing the angles of the multiple mirrors 126a and 126b, the direction of emission of the laser beam L from the optical head 120 can be switched, thereby changing the irradiation position of the laser beam L on the surface of the workpiece W. The angles of the mirrors 126a and 126b are changed by motors (not shown) controlled by, for example, a control device. The optical head 120 can sweep the laser beam L on the surface Wa of the workpiece W by changing the direction of emission of the laser beam L while irradiating it.

[0048] The focusing lens 122 focuses the laser light, which arrives from the galvanoscanner 126 as parallel light, and irradiates the workpiece W with the laser light L (output light).

[0049] The object to be processed W is a metal laminate 10 in which a metal member 11 and a plurality of metal foils 12 are stacked in the Z direction. The metal laminate 10 may also be referred to as a laminate. The metal laminate 10 has a metal member 11, a plurality of metal foils 12, and a welded joint 14. The welded joint 14 welds the metal member 11 and the plurality of metal foils 12 together, connecting them mechanically and electrically.

[0050] Figure 2 is a cross-sectional view of the metal laminate 10. The metal member 11, as an example, has a plate-like shape that extends in a direction intersecting the Z direction. However, the metal member 11 is not limited to a plate-like member. Multiple metal foils 12 are laminated in the Z direction on the Z-direction end face 11a of the metal member 11.

[0051] When the metal laminate 10 is welded by the laser welding apparatus 100, it is temporarily fixed in the laminated state described above by a fixing jig (not shown), and set in a position where the normal direction of the surface Wa of the metal foil 12 is approximately parallel to the Z direction. The fixing jig is, for example, two metal plates spaced apart from each other in the Z direction. The two metal plates are positioned perpendicular to the Z direction, sandwiching the laminated metal member 11 and the multiple metal foils 12 in the Z direction. One of the two metal plates, the one facing the optical head 120, is provided with a through hole through which the laser beam L can pass.

[0052] Surface Wa is the end face in the Z direction of the metal laminate 10, and is the metal foil 12 on the opposite side of the metal member 11 from the multiple metal foils 12, in other words, the side of the metal foil 12 furthest from the metal member 11 that is opposite to the metal member 11. The laser beam L is irradiated to surface Wa in the opposite direction of the Z direction, in other words, from the side of surface Wa opposite to the metal member 11 along the Z direction. The side of the metal member 11 opposite to the end face 11a is the back surface Wb of the metal laminate 10. Surface Wa can also be referred to as the irradiation surface of the laser beam L, or as the opposing surface facing the optical head 120. The Z direction is an example of a first direction.

[0053] When the laser beam L is irradiated in this manner, the welded portion 14 extends from the surface Wa in the opposite direction to the Z direction. The direction opposite to the Z direction can also be referred to as the depth direction of the welded portion 14. Furthermore, when the laser beam L is swept over the surface Wa in the sweep direction SD, the welded portion 14 extends in the sweep direction SD with a cross-sectional shape substantially the same as that shown in Figure 2. Note that the sweep direction SD is a temporary direction at the position where the laser beam L is irradiated. Also, as shown in Figures 1 and 2, when the sweep direction SD is the X direction, the Y direction perpendicular to the X direction can also be referred to as the width direction of the welded portion 14.

[0054] Figure 3 is a cross-sectional view of a battery 1 as an electrical product having a metal laminate 10. Battery 1 is one application example of the metal laminate 10. In this case, the metal laminate 10 is an example of an electrical component as a conductor, and an example of an electrical component included in an electrical product. Electrical components can also be called components of an electrical product.

[0055] The battery 1 shown in Figure 3 is, for example, a laminate-type lithium-ion battery cell. The battery 1 has two film-like outer coverings 20. A housing chamber 20a is formed between the two outer coverings 20. Multiple flat positive electrode materials 13p, multiple flat negative electrode materials 13m, and multiple flat separators 15 are housed in the housing chamber 20a. In the housing chamber 20a, the positive electrode materials 13p and negative electrode materials 13m are alternately stacked with separators 15 interposed between them. Metal foils 12 extend from each of the multiple positive electrode materials 13p and multiple negative electrode materials 13m. In the example of Figure 3, the multiple metal foils 12 extending from each of the positive electrode materials 13p are stacked on a metal member 11 at opposite ends in the Y direction of the battery 1, and a metal laminate 10 is provided at that end where the metal member 11 and the multiple metal foils 12 are welded together. On the positive electrode side, only a portion of the metal member 11 is exposed to the outside of the outer casing material 20, while the other portion of the metal member 11, the multiple metal foils 12, and the welded portion 14 are not exposed to the outside of the outer casing material 20. The metal member 11 constitutes the positive electrode terminal of the battery 1. On the other hand, the multiple metal foils 12 extending from each of the negative electrode material 13m are superimposed on the metal member 11 at the Y-direction end of the battery 1, and a metal laminate 10 is provided at that end where the metal member 11 and the multiple metal foils 12 are welded together. On the negative electrode side as well, only a portion of the metal member 11 is exposed to the outside of the outer casing material 20, while the other portion of the metal member 11, the multiple metal foils 12, and the welded portion 14 are not exposed to the outside of the outer casing material 20. The metal member 11 constitutes the negative electrode terminal of the battery 1.

[0056] As shown in Figure 3, each metal laminate 10 is sandwiched between two outer materials 20. The space between the metal laminate 10 and the outer materials 20 is sealed or liquid-tight with a sealing material or the like. For this reason, it is preferable that the surface Wa and back surface Wb of the metal laminate 10 have as few, if not many, or no irregularities as possible. When the battery 1 is a lithium-ion battery cell, the metal foil 12 constituting the metal laminate 10 as the positive electrode terminal is made of, for example, an aluminum-based metal material, and the metal foil 12 constituting the metal laminate 10 as the negative electrode terminal is made of, for example, a copper-based metal material. The positive electrode terminal and the negative electrode terminal are examples of electrical components. The metal laminate 10 or metal member 11 may also be called an electrode tab or a tab. The metal member 11 may also be called a conductive member.

[0057] Figure 4 is a schematic diagram showing the beam (spot) of laser light L irradiated onto surface Wa. Beams B1 and B2 each have a power distribution in the radial direction of a cross-section perpendicular to the optical axis of the beam, for example, a Gaussian shape. However, the power distributions of beams B1 and B2 are not limited to a Gaussian shape. Also, in each diagram where beams B1 and B2 are represented by circles as in Figure 4, the diameter of the circle representing beam B1 and B2 is the beam diameter of each beam B1 and B2. The beam diameter of each beam B1 and B2 includes the peak of the beam and is 1 / e of the peak intensity. 2 This is defined as the diameter of the region with the above intensity. Note that, although not shown in the illustration, for non-circular beams, it is defined as 1 / e of the peak intensity in the direction perpendicular to the sweep direction SD. 2 The length of the region where the intensity is as described above can be defined as the beam diameter. Furthermore, the beam diameter at surface Wa is referred to as the spot diameter.

[0058] As shown in Figure 4, in this embodiment, as an example, the laser beam L is formed such that the first laser beam B1 and the second laser beam B2 overlap on the surface Wa, with beam B2 being larger (wider) than beam B1, and the outer edge B2a of beam B2 surrounding the outer edge B1a of beam B1. In this case, the spot diameter D2 of beam B2 is larger than the spot diameter D1 of beam B1. Also, the energy density of beam B2 is set lower than the energy density of beam B1. On the surface Wa, beam B1 is an example of a first spot, and beam B2 is an example of a second spot.

[0059] Furthermore, in this embodiment, as shown in Figure 4, the laser beam (spot) on the surface Wa has a point-symmetric shape with respect to the center point C, so the shape of the spot is the same for any sweeping direction SD. Therefore, if a moving mechanism is provided to move the optical head 120 and the workpiece W relative to each other for sweeping the laser beam L on the surface Wa, the moving mechanism only needs to have a mechanism that can translate relatively, and a mechanism that can rotate relatively may be omitted.

[0060] The metal member 11 and metal foil 12, which are the objects to be processed W, can each be made of a conductive metal material. Examples of metal materials include copper-based metal materials, aluminum-based metal materials, nickel-based metal materials, iron-based metal materials, and titanium-based metal materials. Specifically, these include copper, copper alloys, aluminum, aluminum alloys, tin, nickel, nickel alloys, iron, stainless steel, titanium, and titanium alloys. The metal member 11 and metal foil 12 may be made of the same material or of different materials.

[0061] [Wavelength and light absorption rate] Here, we will explain the light absorption rate of metallic materials. Figure 5 is a graph showing the light absorption rate of each metallic material as a function of the wavelength of the irradiated laser light L. In the graph in Figure 5, the horizontal axis is wavelength and the vertical axis is absorption rate. Figure 5 shows the relationship between wavelength and absorption rate for aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), tantalum (Ta), and titanium (Ti).

[0062] Although the properties differ depending on the material, it can be seen that for each metal shown in Figure 5, the energy absorption rate is higher when using blue or green laser light (second laser light) than when using general infrared (IR) laser light (first laser light). This characteristic is particularly pronounced for copper (Cu) and gold (Au), among others.

[0063] When laser light is shone onto a workpiece W with a relatively low absorption rate relative to the wavelength used, most of the light energy is reflected and does not affect the workpiece W as heat. Therefore, relatively high power is required to obtain a melted region of sufficient depth. In that case, the rapid energy input to the center of the beam causes sublimation and the formation of a keyhole.

[0064] On the other hand, when laser light is irradiated onto a workpiece W with a relatively high absorption rate relative to the wavelength used, much of the input energy is absorbed by the workpiece W and converted into thermal energy. In other words, since there is no need to apply excessive power, the melting process is thermal conduction type and does not involve the formation of a keyhole.

[0065] In this embodiment, the wavelength of the first laser beam, the wavelength of the second laser beam, and the material of the workpiece W are selected such that the absorption rate of the workpiece W to the second laser beam is higher than the absorption rate to the first laser beam. In this case, when the sweep direction is the sweep direction SD shown in Figure 4, the welding area of ​​the workpiece W (hereinafter referred to as the workpiece) is first irradiated with the second laser beam by the region B2f of the second laser beam B2 located in front of SD in Figure 4, as the spot of the laser beam L is swept. Subsequently, the workpiece is irradiated with the first laser beam B1, and then the workpiece is irradiated again with the second laser beam B2 by the region B2b of the second laser beam B2 located behind the sweep direction SD.

[0066] Therefore, first, a heat conduction type melting region is created in the area to be welded by irradiation with a second laser beam that has a high absorption rate in region B2f. Subsequently, a deeper keyhole type melting region is created in the area to be welded by irradiation with a first laser beam. In this case, since a heat conduction type melting region has already been formed in the area to be welded, a melting region of the required depth can be formed with a first laser beam of lower power compared to when such a heat conduction type melting region is not formed. Furthermore, the melting state of the area to be welded changes due to irradiation with a second laser beam that has a high absorption rate in region B2b. From this viewpoint, it is preferable that the wavelength of the second laser beam be 550 [nm] or less, and more preferably 500 [nm] or less.

[0067] Furthermore, experimental studies by the inventors have confirmed that welding defects such as spatter and blowholes can be reduced in welding using laser beam L as shown in Figure 4. This is presumed to be because preheating the workpiece W by region B2f of beam B2 before the arrival of beam B1 stabilizes the molten pool of the workpiece W formed by beams B2 and B1.

[0068] [Welding Method] Figure 6 is a flowchart illustrating an example of the procedure for laser welding a workpiece W using a laser welding apparatus 100. As shown in Figure 6, first, a metal laminate 10, i.e., the workpiece W, in which a metal member 11 and a plurality of metal foils 12 are tacked together by a holder, is set up in a state where laser light L is irradiated onto its surface Wa (S11). Then, by irradiating the surface Wa of the workpiece W with laser light L, a molten pool is formed spanning the plurality of metal foils 12 and the metal member 11 (S12). In S12, the laser light L is irradiated substantially along the opposite direction of the Z direction. Also, in S12, while the laser light L, including beams B1 and B2, is irradiating the surface Wa, the laser light L and the metal laminate 10 may be moved relative to each other. In this case, the spot of laser light L on the surface Wa moves across the surface Wa in the sweep direction SD, in other words, it is swept. The molten pool formed by irradiation with laser light L solidifies as the temperature decreases, forming a welded joint 14 (S13). In this way, multiple metal foils 12 and metal members 11 are welded together, and the metal laminate 10 is integrated.

[0069] [rupture] The inventors discovered that when welding multiple metal foils 12 to a metal member 11, fractures may occur at the boundary B between the welded portion 14 and the metal foil 12, and that these fractures can be avoided by setting appropriate conditions.

[0070] Figure 7 is a cross-sectional view showing the mechanism by which a fracture occurs, where (a) shows the state in which the molten pool M is formed (S12), and (b) shows the state in which the molten pool M has solidified and the welded joint 14 has been formed. In the example of Figure 7, as shown in (b), a fracture 14a occurs at the boundary B between the welded joint 14 and the multiple metal foils 12. It is presumed that this occurs because the molten pool M shrinks when it cools and solidifies to become the welded joint 14, and the metal foils 12 are unable to follow this shrinkage, resulting in a fracture 14a at the boundary B.

[0071] [Conditions under which rupture is unlikely] The inventors obtained the following findings (1) to (4) through experimental research. In the experiment, the workpiece W (metal laminate 10) included metal members 11 and metal foils 12 made of aluminum-based material, with a thickness of 20 [μm] for the metal foils 12 and 20 sheets of metal foil 12. The wavelength of the first laser beam was 1070 [nm], and the wavelength of the second laser beam was 465 [nm].

[0072] (1) The smaller the volume of the weld 14, the less likely cracking 14a is to occur. Specifically, it was found that cracking 14a is less likely to occur when the outer diameter when the weld 14 is formed as a point, or the width when the weld 14 is formed as a line, is 30 [μm] or more and 300 [μm] or less. When the outer diameter when the weld 14 is formed as a point, or the width when the weld 14 is formed as a line, is greater than 300 [μm], the volume of the molten pool M (weld 14) increases, and cracking 14a occurs at the boundary B between the weld 14 and the metal foil 12. In addition, in order to obtain a sufficient weld state between the multiple metal foils 12 and the metal member 11, it is necessary for the metal foil 12 in contact with the metal member 11 to melt by irradiation with laser light L. In this regard, when the processing speed is fast (or the amount of energy input is small), the molten pool M (weld portion 14) cannot reach the metal member 11 from the surface Wa. In other words, the metal foil 12 in contact with the metal member 11 cannot be melted, and a sufficient weld state between the multiple metal foils 12 and the metal member 11 by the weld portion 14 cannot be obtained (see "non-joining" below). As a countermeasure, if the power of the first laser beam is increased relative to the second laser beam, the molten pool M cannot be formed in the multiple metal foils 12, and the multiple metal foils 12 are cut (see "cutting" below). Note that the spot diameter D2 is also the beam width when the spot of the laser beam L is swept over the surface Wa.

[0073] (2) When the laser beam L spot is not swept over the surface Wa, i.e., in the case of spot welding, it was found that fracture 14a is less likely to occur when the energy input to the multiple metal foils 12 and the metal member 11 is 1.0 [J] or less. When the input energy is greater than 1.0 [J], the volume of the molten pool M (welded area 14) increases, and fracture 14a occurs at the boundary B between the welded area 14 and the metal foil 12. Furthermore, as described above, in order to obtain a sufficient welded state between the multiple metal foils 12 and the metal member 11, it is necessary for the metal foil 12 in contact with the metal member 11 to melt when irradiated with the laser beam L. From this viewpoint, the input energy must be greater than or equal to the amount that can melt the metal foil 12 in contact with the metal member 11.

[0074] (3) When the spot of the laser beam L is swept over the surface Wa, it was found that if the absorbed energy E (Equation (1)) by the multiple metal foils 12 and metal members 11 is 0.14 [J / mm] or less, fracture 14a is unlikely to occur. The absorbed energy E is defined as shown in Equation (1) below. E = A·Pw / V ···(1) Here, E is the absorbed energy [J / mm], A is the absorptivity by the metal, Pw is the power of the laser beam L [W], and V is the sweep rate [mm / s]. Table 1 shows the experimental results, including the sweep rate [mm / s], absorbed energy [J / mm], and results for each sample (experiment No.). [Table 1]

[0075] In the "Results" section of Table 1, "Cutting" refers to a state where multiple metal foils 12 separate in a direction intersecting the sweep direction SD (width direction, Y direction), and no welded portion 14 is formed. Figure 8 is a cross-sectional view showing an example of the "Cutting" state. As shown in Figure 8, in this case, no welded portion 14 is formed, a gap 14c is formed, and the multiple metal foils 12 are cut in the Y direction (width direction) intersecting the sweep direction SD. In addition, the metal material melted by the irradiation of the multiple metal foils 12 by the laser beam L moves between the multiple metal foils 12 and the metal member 11 due to the energy of the laser beam L and gravity, and remains as residue 14b.

[0076] "Joining" refers to a state in which a welded joint 14 is formed across multiple metal foils 12 and metal members 11, and the multiple metal foils 12 and metal members 11 are well mechanically and electrically joined through the welded joint 14. Figure 9 is a cross-sectional view showing an example of the "joining" state. In the "Results" section of Table 1, only "joining" is an acceptable state.

[0077] "Fracture" refers to a state in which a break occurs between the welded joint 14 and one of the metal foils 12 at boundary B, i.e., a fracture 14a occurs. Figure 10 is a cross-sectional view showing an example of a fracture. As shown in Figure 10, fractures 14a tend to occur in areas T close to the laser beam L emission source, in other words, in areas T far from the metal member 11. From Figure 10, it can be seen that fractures 14a occur when the metal foil 12 is stretched in the Y direction (width direction).

[0078] Furthermore, "non-joined" indicates a state in which the welded joint 14 has not penetrated all of the metal foils 12 and has not reached the metal member 11.

[0079] From the experiments and studies described above, it was found that when the absorbed energy is 0.14 [J / mm] or less, "fracture" does not occur, but "joining" occurs, meaning a good bonding state is obtained. Furthermore, the absorbed energy must be large enough to prevent "non-joining," that is, large enough to melt the metal foil 12 that is in contact with the metal member 11 among the multiple metal foils 12. For example, in a case where the metal member 11 and metal foil 12 are made of an aluminum-based material, the thickness of the metal foil 12 is 20 [μm], and there are 20 sheets of metal foil 12, the amount of absorbed energy large enough to melt the metal foil 12 that is in contact with the metal member 11 among the multiple metal foils 12 is 0.05 [J / mm]. It was found that when the total thickness of the metal foils 12 is 400 [μm] or more, it is preferable to set the absorbed energy to 0.05 [J / mm] or more. Note that in Experiment No. 1 in Table 1, "cutting" occurred because only the first laser beam was irradiated and the second laser beam was not irradiated. Furthermore, the inventors found that in order to obtain such a range of absorbed energy, the sweep speed is preferably 300 mm / s or more and 10,000 mm / s or less.

[0080] (4) When the spot of the laser beam L is swept over the surface Wa, fractures 14a are likely to occur at the start and end points of the sweeping trajectory, and when the sweeping trajectory has an endless section, fractures 14a are less likely to occur in the endless section. At the ends of the sweeping trajectory in the sweeping direction, the area of ​​the boundary B between the welded part 14 and the multiple metal foils 12 becomes larger, making fractures 14a more likely to occur. In this respect, in the endless section of the sweeping trajectory, the area of ​​the boundary B between the welded part 14 and the multiple metal foils 12 can be made smaller, making fractures 14a less likely to occur. Figures 11 to 20 show examples of various trajectories P that yield a suitable joining state.

[0081] Figure 11 illustrates the trajectory P1(P) of a laser beam L spot on a surface Wa. The thick solid lines in Figures 11, 12, 14, 16-20 indicate the trajectory of the laser beam L spot's center position. As shown in Figure 11, the trajectory P1 has an endless section Pe and multiple linear sections Pl. The endless section Pe can also be called a closed loop. The endless section Pe has an oval shape. In Figure 11, the starting point Pes and ending point Pee are at the same position in the endless section Pe, but the starting point Pes and ending point Pee do not necessarily have to be at the same position. For example, the starting point Pes and ending point Pee may be positioned to overlap with other positions on the laser beam L spot trajectory Pe, or they may be spaced apart from the laser beam L spot trajectory Pe by a distance less than or equal to the beam width (spot diameter D2) of the laser beam L. The endless section Pe is an example of an endless portion. The linear section Pl spans between parallel, spaced-apart linear portions of the endless section Pe. That is, the linear section Pl begins at point Pls and ends at point Ple, with point Pls located on or touching the endless section Pe, and point Ple located on or touching another endless section Pe. In other words, the linear section Pl begins at a previously melted portion and ends at a previously melted portion. The trajectory P1 in Figure 11 can be said to have multiple endless sections or cycles. Note that the linear section Pl may also be curved.

[0082] Figure 12 illustrates the trajectory P2(P) of a laser beam L spot on the surface Wa. As shown in Figure 12, the trajectory P2, like the example in Figure 11, has an endless section Pe and a linear section Pl. Furthermore, the starting point Pls of the linear section Pl is located on or touches the endless section Pe, and the ending point Ple is located on or touches another endless section Pe. That is, in the example in Figure 12, the linear section Pl starts from a previously melted area and ends at a previously melted area. The trajectory P2 in Figure 12 can also be said to have multiple endless sections or cycles. However, in the example in Figure 12, the linear sections Pl are each spanned between curved sections of the endless section Pe that are spaced apart from each other, and are parallel to the linear sections of the endless section Pe. The linear portion of the endless interval Pe and the multiple linear segments Pl extend adjacent to each other.

[0083] In the example shown in Figures 11 and 12, all the starting points Pls and ending points Ple of the linear segment Pl are located on or touch the endless segment Pe, however, some of the starting points Pls and ending points Ple of the linear segment Pl may be located on the endless segment Pe. However, it is preferable that all the starting points Pls and ending points Ple of the linear segment Pl are located on or touch the endless segment Pe.

[0084] Figure 13 is a cross-sectional view taken along line XIII-XIII in Figure 12. In Figure 13, the previous molten pool M (or weld 14) is shown by a dashed line, and the latest molten pool M is shown by a solid line. As shown in Figure 13, the latest molten pool M, formed by sweeping the latest linear section Pl, is set to partially overlap with the previous molten pool M (or weld 14) formed by sweeping the previous endless section Pe (linear portion) or the linear section Pl. In this example, adjacent molten pools M (or adjacent latest molten pools M and previous welds 14) partially overlap in the width direction (Y direction). In this way, when the latest molten pool M partially overlaps with the previous molten pool M (or weld 14), no boundary B is created between the weld 14 and the multiple metal foils 12, and therefore no fracture 14a occurs. To achieve this overlap, the linear section Pl is set such that a portion of its spot partially overlaps with the area melted by the irradiation of the laser beam L during the sweep of the previous endless section Pe or the linear section Pl. In this example, the inside of the endless section Pe is filled with a molten pool M (weld area 14).

[0085] Figure 14 illustrates the trajectory P3(P) of the laser beam L spot on the surface Wa. As shown in Figure 14, the trajectory P3 has a spiral shape and an overall endless shape. That is, the trajectory P3 has only an endless section Pe. The endless section Pe starts from the starting point Pes and ends at the ending point Pee, with the starting point Pes being located on or touching the endless section Pe, and the ending point Pee also being located on or touching the endless section Pe. In other words, the endless section Pe starts from a previously melted area and ends at a previously melted area.

[0086] Figure 15 is a cross-sectional view taken along line XV-XV in Figure 14. In Figure 15, the previous molten pool M (or weld 14) is shown by a dashed line, and the latest molten pool M is shown by a solid line. As shown in Figure 15, the latest molten pool M formed by sweeping the latest endless section Pe is set to partially overlap with the previous molten pool M (or weld 14) formed by sweeping the previous endless section Pe. In this example as well, adjacent molten pools M (or the latest molten pool M and the previous weld 14) partially overlap in the width direction (Y direction). To obtain such overlap, the endless section Pe is set so that a part of its spot partially overlaps with the area melted by irradiation with laser light L during the sweeping of the previous endless section Pe. In this example as well, the inside of the endless section Pe is filled in with the molten pool M (weld 14).

[0087] Figure 16 illustrates the trajectory P4(P) of a laser beam L spot on surface Wa. As shown in Figure 16, the trajectory P4 also has an overall endless shape. That is, the trajectory P4 has only an endless section Pe. However, in this example, as shown in Figure 16, the section before the endless section Pe is an oval section, and the section after the endless section Pe is a wobbling section inside the oval section in which the laser beam L spot orbits a reference point while the reference point moves in the X direction. The dashed arrow Lc in Figure 16 is the trajectory of the reference point moving in the X direction. The X direction is an example of a second direction. The inventors have confirmed that wobbling is effective in terms of not causing fracture 14a, and that even under conditions where the absorbed energy is higher and fracture 14a would occur without wobbling, a suitable bonding state can be obtained with wobbling.

[0088] In Figures 14 and 16, an example is shown where the trajectory P has one starting point Pes and one ending point Pee, but it is not limited to this. The trajectory P can have an endless shape overall, and for example, it may have multiple starting points Pes and ending points Pee. Furthermore, the trajectory P may have other sweep paths locally, as long as they do not hinder the effects obtained in this embodiment.

[0089] Figure 17 illustrates the trajectory P5(P) of a laser beam L spot on surface Wa. As shown in Figure 17, the trajectory P5 has a wobbling section Pw and a linear section Pl extending in the X direction that partially overlaps the wobbling section Pw. In this example, the laser beam L spot is swept through the linear section Pl and then through the wobbling section Pw. The wobbling section Pw has multiple endless sections (closed loops). Therefore, in this example as well, the same effect as in other examples where the trajectory P has an endless section Pe can be obtained.

[0090] Figure 18 illustrates the trajectory P6(P) of the laser beam L spot on the surface Wa. In this example, the trajectory P6 has multiple linear segments Pl, but does not have an endless segment Pe, which is different from the example in Figure 12. However, in this example as well as in the examples in Figures 12 and 13, the linear segments Pl are set so that a part of the spot partially overlaps with the area melted by the irradiation of the laser beam L during the sweep of the previous linear segments Pl. In this example as well, a predetermined area is filled with a molten pool M (weld part 14), and the same effect as in the examples in Figures 12 and 13 is obtained.

[0091] Figure 19 illustrates the trajectory P7(P) of a laser beam L spot on the surface Wa. In this example, the trajectory P7 has an oval-shaped endless section Pe, and multiple spots Pp are arranged inside this endless section Pe. In this case, the outer diameter when the weld 14 is formed as a point, or the width when the weld 14 is formed as a line, is set to be 30 [μm] or more and 300 [μm] or less, and the input energy is set to be 1.0 [J] or less. Also in this example, the latest molten pool M formed in the latest spot Pp is set to partially overlap with the previous molten pool M (or weld 14) formed in the previous spot Pp. To obtain such overlap, a part of the spot Pp is set to partially overlap with the area melted by the irradiation of the laser beam L in the spot Pp that has already been irradiated. In this example as well, the inside of the endless section Pe is filled with the molten pool M (welded part 14).

[0092] Figure 20 illustrates the trajectory P8(P) of the laser beam L spot on the surface Wa. In this example, the trajectory P8 has the same shape as the trajectory P7 example in Figure 19, except that it does not have an oval-shaped endless section Pe. Thus, even in the absence of an endless section Pe, a good bonding state without fractures 14a or breaks can be obtained by appropriately setting conditions for multiple spots Pp.

[0093] As explained above, through the inventors' diligent research, it has been found that, according to the welding method of this embodiment, by appropriately setting various parameters when irradiating with the spot of laser light L, a suitable joining state can be obtained without fracture 14a, cutting, or non-joining.

[0094] [Second Embodiment] Figure 21 is a schematic diagram of the laser welding apparatus 100A of the second embodiment. In this embodiment, the optical head 120 has a DOE 125 between the collimating lens 121-2 and the filter 124. Except for this point, the laser welding apparatus 100A has the same configuration as the laser welding apparatus 100 of the first embodiment.

[0095] DOE125 shapes the shape of the first laser beam B1 (hereinafter referred to as the beam shape). As conceptually illustrated in Figure 22, DOE125 has a configuration in which multiple diffraction gratings 125a with different periods are superimposed. DOE125 can shape the beam by bending or superimposing parallel light in the direction influenced by each diffraction grating 125a. DOE125 may also be called a beam shaper.

[0096] The optical head 120 may also include a beam shaper provided after the collimating lens 121-1 to adjust the beam shape of the first laser beam, or a beam shaper provided after the filter 124 to adjust the beam shapes of the first and second laser beams. By appropriately shaping the beam shape of the laser beam L with a beam shaper, a better bonding state can be obtained.

[0097] Figure 23 shows an example of a beam spot obtained by the laser welding apparatus 100A. In the example in Figure 23, due to beam shaping by DOE125, multiple beam spots B2 are arranged on the surface Wa in a roughly arc-shaped (roughly ring-shaped) manner around the spot of one beam B1. In such a case, the width w (spot diameter) of the beam spot is defined as the distance between the centers of the two furthest beams in the direction perpendicular to the sweep direction SD, as shown in Figure 23. Furthermore, by using a roughly axially symmetric beam pattern as in the example in Figure 23, it is not necessary to rotate the optical head 120 to match the trajectory P when sweeping along a curved path, allowing for more efficient sweeping, as well as advantages such as simplifying the device configuration of the optical head 120 and making it easier to control the optical head 120.

[0098] [Third Embodiment] Figure 24 is a schematic diagram of the laser welding apparatus 100B of the third embodiment. In this embodiment, the optical head 120 does not have a galvanoscanner 126 and is configured to change its relative position to the workpiece W in order to sweep the laser beam L while irradiating the workpiece W surface Wa with the laser beam L. The relative movement between the optical head 120 and the workpiece W can be achieved by moving the optical head 120, moving the workpiece W, or moving both the optical head 120 and the workpiece W. The same effects as in the above embodiment can be obtained with this laser welding apparatus 100B as well.

[0099] Although embodiments of the present invention have been illustrated above, these embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, each configuration, shape, and other specifications (structure, type, orientation, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate.

[0100] For example, the present invention is applicable to lithium-ion battery cells with configurations different from those of the embodiments described above, and is also applicable to batteries other than lithium-ion battery cells. Furthermore, a battery is just one example of an electrical product, and the electrical product of the present invention is not limited to batteries. Also, battery terminals are just one example of an electrical component, and the electrical component of the present invention is not limited to battery terminals.

[0101] Furthermore, the object to be processed may be a metal plated metal sheet, where a thin layer of another metal exists on the surface of the metal. [Explanation of symbols]

[0102] 1…Batteries (for electrical appliances) 10…Metal laminates (laminated structures, electrical components) 11… Metal components 11a...End surface (first surface) 12… Metal foil 13p... Positive electrode material 13m…Negative electrode material 14... Welded section 14a…rupture 14b...residue 14c...gap 15... Separator 20… Exterior materials 20a... Confinement chamber 100, 100A, 100B… Laser welding equipment (welding equipment) 111…Laser device (first laser oscillator) 112…Laser device (second laser oscillator) 120…Optical head 121, 121-1, 121-2… Collimating lenses 122... Focusing lens 123...Mirror 124... Filter 125...DOE (Diffractive Optical Element) 125a...Diffraction grating 126... Galvanometer Scanner 126a, 126b…Mirror 130… Fiber optic B…boundary B1... Beam (First Spot) B1a...outer edge B2... Beam (Second Spot) B2a...outer edge B2b…area B2f…area C...center point D1…Spot diameter (outer diameter) D2…Spot diameter (outer diameter) L... Laser light Lc…(Trajectory of the reference point) M...Melting pool P,P1~P8…Trajectory (sweep trajectory) Pe...endless section Pes... Starting point Pee... Final stop Pl...Linear segment Pls... Starting point Please... End of the line Pp... Spot Pw... Wobbling section SD…Sweep direction T…part w…width W...Item to be processed Wa... Surface Wb…Back side X…direction (second direction) Y... Direction Z…direction (first direction)

Claims

1. A welding method for welding a metal member and a plurality of metal foils, wherein the metal foil on the opposite side of a plurality of metal foils that are overlapped in a first direction on a metal member is irradiated with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, A step of irradiating the plurality of metal foils and the metal member with the laser light to form a molten pool, The process of solidifying the molten pool to form a welded joint, It has, In the process of forming the molten pool, The spot of the laser beam is swept over the surface of the metal foil, The absorption energy absorbed by the plurality of metal foils and the metal members from the laser light is such that the absorption energy per unit length in the sweeping direction is 0.14 [J / mm] or less. A welding method wherein a keyhole-shaped molten region is formed by irradiation with the first laser beam.

2. The welding method according to claim 1, wherein the absorbed energy is greater than or equal to the amount that can melt the metal foil in contact with the metal member among the plurality of metal foils.

3. The welding method according to claim 2, wherein the absorbed energy is 0.05 [J / mm] or more when the thickness of the plurality of metal foils stacked in the first direction is 400 [μm] or more.

4. The welding method according to any one of claims 1 to 3, wherein the sweeping speed of the spot is 300 mm / s or more and 10,000 mm / s or less.

5. The welding method according to any one of claims 1 to 4, wherein the wavelength of the first laser beam is 800 nm or more and 1200 nm or less, and the wavelength of the second laser beam is 550 nm or less.

6. The welding method according to claim 5, wherein the wavelength of the second laser beam is 400 nm or more and 500 nm or less.

7. The welding method according to any one of claims 1 to 6, wherein the laser beam is formed by a beam shaper.

8. The welding method according to claim 7, wherein the beam shaper is a DOE.

9. The welding method according to any one of claims 1 to 8, wherein in the step of forming the molten pool, the sweeping trajectory of the spot on the metal foil is set such that, in at least a portion of the sweeping trajectory, at least a portion of the spot has already been melted by irradiation with the laser light.

10. The welding method according to claim 9, wherein the sweeping trajectory includes an endless portion.

11. The welding method according to claim 10, wherein the sweeping trajectory has an overall endless shape.

12. The welding method according to claim 10 or 11, wherein in the step of forming the molten pool, after the endless portion is formed in the sweeping trajectory, the spot of the laser beam is swept in the region inside the endless portion on the surface.

13. The welding method according to any one of claims 9 to 12, wherein the sweeping trajectory includes a plurality of adjacent sections.

14. The welding method according to any one of claims 9 to 13, wherein the sweeping trajectory includes a linear segment connecting two points on the sweeping trajectory.

15. The welding method according to any one of claims 9 to 14, wherein the sweeping trajectory includes a spiral section.

16. The welding method according to any one of claims 9 to 15, wherein the sweeping trajectory includes a wobbling section in which the spot orbits around a reference point while the reference point moves in a second direction.

17. The welding method according to claim 16, wherein the sweeping trajectory includes a section extending linearly in the second direction and a wobbling section that is swept after the linearly extended section and partially overlaps with the linearly extended section.

18. The welding method according to any one of claims 9 to 17, wherein the sweeping trajectory includes a portion where the sweeping trajectories intersect.

19. The welding method according to any one of claims 1 to 18, wherein the width of the formed welded portion is 30 [μm] or more and 300 [μm] or less.

20. A welding method for welding a metal member and a plurality of metal foils, wherein the metal foil on the opposite side of a plurality of metal foils that are overlapped in a first direction on a metal member is irradiated with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, A step of irradiating the plurality of metal foils and the metal member with the laser light to form a molten pool, The process of solidifying the molten pool to form a welded joint, It has, In the process of forming the molten pool, The outer diameter of the weld formed when a point-shaped spot of the laser beam is irradiated onto the metal foil on the side of the plurality of metal foils opposite to the metal member, or the width of the weld formed when the spot of the laser beam is swept over the metal foil on the side of the plurality of metal foils opposite to the metal member, is 30 [μm] or more and 300 [μm] or less. A welding method wherein a keyhole-shaped molten region is formed by irradiation with the first laser beam.

21. A welding method for welding a metal member and a plurality of metal foils, wherein the metal foil on the opposite side of a plurality of metal foils that are overlapped in a first direction on a metal member is irradiated with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, A step of irradiating the plurality of metal foils and the metal member with the laser light to form a molten pool, The process of solidifying the molten pool to form a welded joint, It has, In the process of forming the molten pool, A point-shaped spot of the laser light is irradiated onto the metal foil of the plurality of metal foils that is on the side opposite to the metal member. The energy of the laser beam applied to the plurality of metal foils and the metal members is 1.0 [J] or less. A welding method wherein a keyhole-shaped molten region is formed by irradiation with the first laser beam.

22. The welding method according to claim 21, wherein the input energy is greater than or equal to the amount that can melt the metal foil in contact with the metal member among the plurality of metal foils.

23. A welding method for welding a metal member and a plurality of metal foils, wherein the metal foil on the opposite side of a plurality of metal foils that are overlapped in a first direction on a metal member is irradiated with laser light including a first laser beam and a second laser beam with a lower energy density than the first laser beam, A step of irradiating the plurality of metal foils and the metal member with the laser light to form a molten pool, The process of solidifying the molten pool to form a welded joint, It has, In the process of forming the molten pool, The spot of the laser beam is swept over the surface of the metal foil, The sweeping trajectory of the spot on the metal foil includes a wobbling section in which the spot orbits a reference point while the reference point moves in a second direction, and a section that extends linearly in the second direction and partially overlaps with the wobbling section. A welding method wherein a keyhole-shaped molten region is formed by irradiation with the first laser beam.

24. The welding method according to any one of claims 1 to 23, wherein the metal member and the plurality of metal foils are made of an aluminum-based metal material.

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