Laser welding method, laser welding system, and metal bonded body

Abstract

In this laser welding method, during a first step, for example, a first member and a second member having a curved protruding surface protruding toward the first member are caused to approach each other so as to compress a plurality of metal foil sheets in a state of being sandwiched between the first member and the curved projecting surface in the stacking direction, whereby a compressed section bent in a state of protruding in a first direction along the curved projecting surface is formed in the plurality of metal foil sheets such that at least the metal foil positioned at an end portion of the compressed section in the first direction is partially plastically deformed. In a second step following the first step, a metal member and a site including the compressed section of the plurality of metal foil sheets are bonded in a state where the metal member and the end portion of the compressed section in the first direction contact each other.

Description

Laser welding method, laser welding system, and metal joint

[0001] The present invention relates to a laser welding method, a laser welding system, and a metal joined body.

[0002] BACKGROUND ART Conventionally, there has been known an electricity storage device that includes a portion where a metal member and a plurality of metal foils are joined by laser welding (for example, see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2020-4643

[0004] In laser welding, which joins a metal member and a plurality of metal foils, it can be difficult to set the conditions for laser welding because the metal foils are thin and easily stretched or cut by irradiation with laser light.

[0005] Furthermore, a metal joined body formed by laser welding a metal member and a plurality of metal foils in a stacked state may be subjected to tensile forces that pull the metal member and the plurality of metal foils in opposite directions, which are intersecting the stacking direction, and the metal joined body may be required to have a required breaking strength (hereinafter, this breaking strength will be referred to as tensile shear strength) that can withstand such tensile forces.

[0006] Therefore, one object of the present invention is to provide a new and improved laser welding method, laser welding system, and metal joined body that can prevent metal foils from stretching or breaking and can produce a metal joined body with higher tensile shear strength, for example, when joining a metal member and multiple metal foils by laser welding.

[0007] The laser welding method of the present invention is, for example, a laser welding method for welding a metal member and a plurality of metal foils by irradiating them with laser light, and includes: a first step of compressing the stacked plurality of metal foils in a stacking direction; and a second step of irradiating the plurality of metal foils or the metal member with laser light to form a weld that penetrates the plurality of metal foils in the stacking direction and exists within the metal member, thereby joining the metal member and the plurality of metal foils. In the first step, a first member and a second member having a convex curved surface that is convex toward the first member are brought relatively close to each other, and the plurality of metal foils are compressed while being sandwiched in the stacking direction between the first member and the convex curved surface, thereby forming compressed portions in the plurality of metal foils that are curved and protrude in a first direction approximately along the convex curved surface, so that at least the metal foils located at the ends of the compressed portions in the first direction are partially plastically deformed. In the second step, the portions of the plurality of metal foils including the compressed portions are joined to the metal member, with the ends of the compressed portions in the first direction in contact with the metal member.

[0008] In the laser welding method, in the first step, metal foils adjacent to each other in the stacking direction may be partially joined at least at the end of the compressed portion in the first direction or at the end of the compressed portion in the opposite direction to the first direction.

[0009] In the laser welding method, in the first step, for all metal foils included in the plurality of metal foils, the metal foil and the metal foil adjacent to the metal foil in the stacking direction may be partially joined in the compressed portion.

[0010] In the laser welding method, the first step may include integrating the plurality of metal foils.

[0011] In the laser welding method, in the first step, adjacent metal foils in the stacking direction may be partially joined at the compressed portion by room temperature joining at any position in the stacking direction.

[0012] In the laser welding method, the first step and the second step may be performed at different locations.

[0013] In the laser welding method, the second member may have a higher Young's modulus than the metal member.

[0014] In the laser welding method, in the first step, the thickness of the compressed portion in the stacking direction may be 40% or more and 60% or less of the thickness of the plurality of metal foils in the stacking direction when stacked without being compressed.

[0015] In the laser welding method, the convex curved surface may be formed into a cylindrical shape extending in a third direction substantially perpendicular to a protruding direction of the convex curved surface.

[0016] In the laser welding method, the convex curved surface may be formed into a cylindrical shape having a predetermined width in a fourth direction that is approximately perpendicular to the protruding direction and the third direction, and extending longer in the third direction than the predetermined width.

[0017] In the laser welding method, the convex curved surface may be a cylindrical surface.

[0018] In the laser welding method, the convex curved surface may be the outer peripheral surface of a roller that rolls around a rotation axis extending in the third direction, and in the first step, the plurality of metal foils may be compressed while the roller is rolling.

[0019] In the laser welding method, in the first step, a restricting portion located on the opposite side of the plurality of metal foils from the first member may restrict a portion of the plurality of metal foils other than the compressed portion from moving in a direction away from the first member.

[0020] In the laser welding method, in the second step, the metal member and the plurality of metal foils may be sandwiched in the stacking direction by a support mechanism at a position away from the compressed portion.

[0021] In the laser welding method, in the second step, the support mechanism may sandwich the metal member and the plurality of metal foils in the stacking direction while applying a surface pressure to the plurality of metal foils that is lower than the surface pressure acting on the compressed portion in the first step.

[0022] In the laser welding method, in the second step, the laser light may be irradiated onto a surface of a metal foil of the plurality of metal foils located at an end opposite to the metal member.

[0023] In the laser welding method, the second step may include irradiating the metal members with the laser light.

[0024] In the laser welding method, the welded portion may include a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

[0025] In the laser welding method, the bead extending in the second direction may be approximately along a direction intersecting the stacking direction in which the tensile force acting on the metal joint formed by joining the metal member and the plurality of metal foils by the weld is greatest, as a result of the metal member being pulled in one direction intersecting the stacking direction and the plurality of metal foils being pulled in the other direction intersecting the stacking direction.

[0026] In the laser welding method, the plurality of beads may be provided so as to be spaced apart from each other in the fifth direction at positions that are boundaries between the plurality of metal foils and the metal member in the stacking direction.

[0027] In the laser welding method, the interval at the boundary position may be 1.5 times or more the width of the bead in the fifth direction.

[0028] In the laser welding method, the plurality of beads may be formed such that ends in the second direction are spaced apart from each other in the fifth direction.

[0029] In the laser welding method, the plurality of beads may be provided so as to straddle the boundaries between the compressed portions and the non-compressed portions of the plurality of metal foils.

[0030] In the laser welding method, the boundary may have a first boundary and a second boundary spaced apart from the first boundary in a direction intersecting the stacking direction, and the plurality of beads may be arranged so as to straddle the first boundary and the second boundary.

[0031] In the laser welding method, the metal member and the plurality of metal foils may be made of an aluminum-based material.

[0032] In the laser welding method, the metal member and the plurality of metal foils may be made of a copper-based material.

[0033] In the laser welding method, the second step may include a third step of forming a first welded portion by welding the compressed portion and the metal member by irradiating the laser light, and a fourth step of melting and solidifying, after the third step, an adjacent portion to the gap between the first welded portion and the metal foil, or a connection portion between the first welded portion and the metal foil by irradiating the laser light.

[0034] In the laser welding method, in the fourth step, the laser light may include a first laser light and a second laser light having a wavelength shorter than that of the first laser light.

[0035] In the laser welding method, in the fourth step, the irradiation of the laser light may include a plurality of irradiations each of which melts and solidifies a different portion.

[0036] In the laser welding method, in the fourth step, the irradiation of the laser light may include multiple irradiations that melt and solidify portions of the metal foil that are located at different positions in the stacking direction.

[0037] In the laser welding method, in the fourth step, the irradiation of the laser light may include irradiating the metal foil with the laser light a plurality of times at different irradiation positions.

[0038] In the laser welding method, in the fourth step, the irradiation of the laser light may include a plurality of irradiations with different powers of the laser light.

[0039] In the laser welding method, an energy amount per irradiation of the laser light in the fourth step may be smaller than an energy amount of the laser light irradiated in the third step.

[0040] In the laser welding method, in the fourth step, the laser light may be scanned on the metal foil.

[0041] In the laser welding method, in the third step, the laser light may be scanned on the metal foil, and the fourth step may include scanning the laser light at a scanning speed faster than the scanning speed of the laser light in the third step.

[0042] In the laser welding method, in the fourth step, the laser beam may be irradiated in a direction inclined with respect to the irradiation direction of the laser beam in the third step.

[0043] The laser welding method of the present invention is a laser welding method for joining the first metal member and the second metal member, for example, by irradiating laser light to one of a first metal member and a second metal member that are overlapping each other in a sixth direction, and forming a weld that penetrates the one metal member in the sixth direction and is present within the other metal member of the first metal member and the second metal member, wherein the weld includes a plurality of beads extending in a second direction that intersects with the sixth direction, the plurality of beads being spaced apart in a fifth direction that intersects with the sixth direction and the second direction, and the beads extending in the second direction are generally along a direction in which the tensile force acting on a metal joined body in which the first metal member and the second metal member are joined by the weld is greatest, as a result of the first metal member being pulled in one direction that intersects with the sixth direction and the second metal member being pulled in the other direction that intersects with the sixth direction, among directions that intersect with the sixth direction.

[0044] The laser welding system of the present invention is, for example, a laser welding system that welds a metal member and a plurality of metal foils by irradiating them with laser light, and includes: a compression device that compresses the stacked metal foils in a stacking direction; and a joining device that irradiates the plurality of metal foils or the metal member with laser light to form a weld that penetrates the plurality of metal foils in the stacking direction and exists within the metal member, thereby joining the metal member and the plurality of metal foils. The compression device brings a first member and a second member having a convex curved surface that convex toward the first member relatively close to each other, and compresses the plurality of metal foils while sandwiching them in the stacking direction between the first member and the convex curved surface, thereby forming a compressed portion in the plurality of metal foils that is curved and protrudes in a first direction along the convex curved surface, so that at least the metal foil located at the end of the compressed portion in the first direction is partially plastically deformed. The joining device joins the plurality of metal foils to the metal member with the end of the compressed portion in the first direction in contact with the metal member.

[0045] In the laser welding system, the weld may include a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

[0046] Furthermore, the metal joined body of the present invention comprises, for example, a plurality of stacked metal foils, a metal member in contact with a metal foil located at one end of the plurality of metal foils in the stacking direction, and a welded portion that penetrates the plurality of metal foils in the stacking direction and is present within the metal member, joining the plurality of metal foils to the metal member, wherein the plurality of metal foils have a compressed portion that is compressed in a curved state that is convex toward the metal member, and in the compressed portion, at least the metal foil that is in contact with the metal member is partially plastically deformed.

[0047] In the metal joined body, the welded portion may include a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

[0048] SUMMARY OF THE INVENTION In accordance with the present invention, new and improved laser welding methods, laser welding systems, and metal joints are provided.

[0049] FIG. 1 is an exemplary schematic configuration diagram of a joining apparatus according to a first embodiment. FIG. 2 is an exemplary and schematic cross-sectional view of a battery including a metal bonded body as a processing target of the joining apparatus according to the first embodiment. FIG. 3 is a graph showing the light absorption rate of metal versus the wavelength of irradiated laser light. FIG. 4 is an exemplary and schematic plan view showing a laser light spot formed on a surface of a processing target by the joining apparatus according to the first embodiment. FIG. 5 is an exemplary configuration diagram of a laser welding system according to the first embodiment. FIG. 6 is an exemplary flowchart showing a procedure of a laser welding method according to the first embodiment. FIG. 7 is an exemplary and schematic side view illustrating a first step of the laser welding method according to the first embodiment. FIG. 8 is an exemplary and schematic side view illustrating a second step of the laser welding method according to the first embodiment. FIG. 9 is a schematic plan view illustrating an example of a metal bonded body formed by the laser welding method according to the first embodiment. FIG. 10 is a schematic plan view illustrating an example (variation 1) of a metal bonded body formed by the laser welding method according to the first embodiment. FIG. 11 is a schematic plan view showing an example (Variation 2) of a metal joined body formed by the laser welding method of the first embodiment. FIG. 12 is an exemplary and schematic side view illustrating another technique (Variation 3) of the first step of the laser welding method of the first embodiment. FIG. 13 is an exemplary and schematic side view illustrating another technique (Variation 4) of the second step of the laser welding method of the first embodiment. FIG. 14 is an exemplary flowchart showing another example of the procedure of the laser welding method of the second embodiment. FIG. 15 is an exemplary and schematic cross-sectional view of the workpiece at a stage during the fourth step of the laser welding method of the second embodiment. FIG. 16 is an exemplary and schematic cross-sectional view of the workpiece at a stage after the fourth step of the laser welding method of the second embodiment has been completed. FIG. 17 is an exemplary and schematic cross-sectional view of the workpiece at a stage during the fourth step of the laser welding method of a variation (Variation 5) in which the irradiation direction of the laser light of the second embodiment is changed. FIG. 18 is an exemplary and schematic plan view of a metal joined body formed by the laser welding method of the reference example. 19 and 20 are schematic plan views showing an example of a metal joined body formed by the laser welding method of the third embodiment.Fig. 21 is a schematic plan view showing an example (Modification 6) of a metal bonded body formed by the laser welding method of the third embodiment. Fig. 22 is an exemplary schematic cross-sectional view of a portion of the metal bonded body shown in Fig. 21. Fig. 23 is a schematic plan view showing a portion of an example (Modification 7) of a metal bonded body formed by the laser welding method of the third embodiment. Fig. 24 is a schematic plan view showing an example (Modification 8) of a metal bonded body formed by the laser welding method of the third embodiment. Fig. 25 is a schematic plan view showing an example (Modification 9) of a metal bonded body formed by the laser welding method of the third embodiment. Fig. 26 is a schematic plan view showing an example (Modification 10) of a metal bonded body formed by the laser welding method of the third embodiment.

[0050] Exemplary embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the actions and effects brought about by these configurations, are merely examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments and modifications. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by these configurations.

[0051] Furthermore, the following embodiments and modifications have similar configurations. According to the embodiments and modifications, similar actions and effects based on the similar configurations can be obtained. In the following, similar components included in the embodiments and modifications are given common reference numerals, and duplicated explanations may be omitted.

[0052] In each figure, the X direction is represented by an arrow X, the Y direction is represented by an arrow Y, and the Z direction is represented by an arrow Z. The X direction, Y direction, and Z direction intersect with each other and are substantially perpendicular to each other. The Z direction is substantially vertically upward, and the X direction and Y direction are substantially horizontal. For simplicity, each metal foil 12 is not shown in each figure.

[0053] In this specification, ordinal numbers are given for convenience to distinguish between processes, components, parts, laser beams, times, etc., and do not limit the priority or order.

[0054] [First embodiment] [Configuration of joining device] Fig. 1 is a schematic configuration diagram of a joining device 100 according to an embodiment. As shown in Fig. 1, the joining device 100 includes a laser device 111, a laser device 112, an optical head 120, and optical fibers 131 and 132. The joining device 100 can laser weld a workpiece W by irradiating it with laser light L. The joining device 100 is also referred to as a laser welding device.

[0055] The laser devices 111 and 112 each have a laser oscillator and are configured to output laser light with a power of, for example, several kW. The laser devices 111 and 112 each output laser light with a wavelength of 400 nm or more and 1200 nm or less. The laser devices 111 and 112 each have a laser light source therein, such as a fiber laser, a semiconductor laser (element), a YAG laser, or a disk laser. The laser devices 111 and 112 may also be configured to output multimode laser light with a power of several kW as the total output of multiple light sources. The laser device 111 outputs a first laser light, and the laser device 112 outputs a second laser light.

[0056] The optical fibers 131 and 132 optically connect the laser devices 111 and 112 to the optical head 120. In other words, the optical fibers 131 and 132 guide the laser light output from the laser devices 111 and 112 to the optical head 120, respectively.

[0057] The optical head 120 is an optical device that irradiates the workpiece W with laser light input from the laser devices 111 and 112. The optical head 120 includes a collimator lens 121, a condenser lens 122, a mirror 123, a filter 124, and a galvanometer scanner 126. The collimator lens 121, the condenser lens 122, the mirror 123, the filter 124, and the galvanometer scanner 126 are also referred to as optical components. The galvanometer scanner 126 may also be referred to as a laser scanner.

[0058] The collimating lenses 121 (121-1, 121-2) collimate the laser beams input via the optical fibers 131, 132. The collimated laser beams become parallel beams.

[0059] The mirror 123 reflects the first laser light, which has been collimated by the collimator lens 121 - 1 , and directs it toward the galvano scanner 126 .

[0060] The filter 124 is a high-pass filter that transmits the first laser beam and reflects but does not transmit the second laser beam. The first laser beam from the mirror 123 passes through the filter 124 and heads toward the galvanometer scanner 126. On the other hand, the second laser beam from the collimator lens 121-2 is reflected by the filter 124 and heads toward the galvanometer scanner 126.

[0061] The galvanometer scanner 126 has multiple mirrors 126a and 126b. By changing the angles of the multiple mirrors 126a and 126b, the output direction of the laser light L from the optical head 120 can be switched, thereby changing the irradiation position of the laser light L on the surface Wa of the workpiece W. The angles of the mirrors 126a and 126b are each changed by a motor controlled by, for example, a control device. The optical head 120 can scan the laser light L on the surface Wa of the workpiece W by changing the output direction of the laser light L while irradiating the laser light L. The galvanometer scanner 126 is an example of a laser scanner. Note that the optical head 120 may have a laser scanner different from the galvanometer scanner 126.

[0062] The condenser lens 122 condenses the laser light emitted by the galvanometer scanner 126 as parallel light, and irradiates the laser light as laser light L (output light) onto the workpiece W. The laser light L output from the optical head 120 includes a first laser light and a second laser light.

[0063] The workpiece W includes a metal member 11 and a laminate 16 of metal foils 12 placed on the metal member 11. The metal member 11 is, for example, a plate-like member that extends across the Z direction at the site to be welded and its surrounding area. The laminate 16 includes a plurality of metal foils 12 laminated in the Z direction in an arrangement that intersects the Z direction at the site to be welded and its surrounding area.

[0064] The metal member 11 and the laminate 16 are stacked in the Z direction. The laminate 16 is stacked on a surface 11a located at an end of the metal member 11 in the Z direction. The surface located at the end of the laminate 16 in the Z direction is a surface Wa of the workpiece W, and the surface located at the end of the metal member 11 on the opposite side in the Z direction is a surface Wb of the workpiece W. The laser light L is output from the optical head 120 in a direction substantially opposite to the Z direction and is irradiated onto the surface Wa. By operation of the galvano scanner 126, the spot of the laser light L scans the surface Wa.

[0065] Irradiation with the laser light L forms a weld 14 that penetrates from the surface Wa through the laminate 16 to the metal member 11, and forms a metal joined body 10 in which the metal member 11 and the laminate 16 are joined via the weld 14. In other words, the metal joined body 10 has the metal member 11, the laminate 16, and the weld 14. The weld 14 may also be referred to as weld metal.

[0066] The metal member 11, the plurality of metal foils 12, and the welds 14 are all conductors. The welds 14 electrically connect the metal member 11 and the plurality of metal foils 12. The metal member 11 and the metal foils 12 are made of, for example, an aluminum-based metal such as pure aluminum or an aluminum alloy. However, the metal member 11 and the metal foils 12 may also be made of a material other than an aluminum-based metal, such as a copper-based metal such as oxygen-free copper or a copper alloy.

[0067] 2 is a cross-sectional view of a battery 1 as an electrical product having a metal bonded body 10. The battery 1 is one application example of the metal bonded body 10. In this case, the metal bonded body 10 is an example of an electrical component as a conductor, and is an example of an electrical component included in an electrical product. An electrical component may also be referred to as a component of an electrical product.

[0068] The battery 1 shown in FIG. 2 is, for example, a laminated lithium-ion battery cell. The battery 1 has two film-like exterior materials 20. A storage chamber 20a is formed between the two exterior materials 20. The storage chamber 20a contains a plurality of flat positive electrode materials 13p, a plurality of flat negative electrode materials 13m, and a plurality of flat separators 15. The positive electrode materials 13p and the negative electrode materials 13m are alternately stacked in the storage chamber 20a with the separators 15 interposed therebetween. Metal foils 12 extend from the plurality of positive electrode materials 13p and the plurality of negative electrode materials 13m. In the example shown in FIG. 2, the plurality of metal foils 12 extending from each of the positive electrode materials 13p are superimposed on the metal member 11p (11) at the Y-direction end of the battery 1, and a metal joint 10 is formed by welding the metal member 11p (11) and the plurality of metal foils 12 at the end. On the positive electrode side, only a portion of the metal member 11p is exposed to the outside of the exterior packaging material 20, while the other portion of the metal member 11p, the plurality of metal foils 12, and the welded portion 14 are not exposed to the outside of the exterior packaging material 20. The metal member 11p constitutes the positive electrode terminal of the battery 1. On the other hand, the plurality of metal foils 12 extending from each of the negative electrode materials 13m are overlapped on the metal member 11m(11) at the end opposite the Y direction of the battery 1, and a metal joined body 10 is provided in which the metal member 11m(11) and the plurality of metal foils 12 are welded to the end. On the negative electrode side, only a portion of the metal member 11m is exposed to the outside of the exterior packaging material 20, while the other portion of the metal member 11m, the plurality of metal foils 12, and the welded portion 14 are not exposed to the outside of the exterior packaging material 20. The metal member 11m constitutes the negative electrode terminal of the battery 1.

[0069] [Wavelength and Light Absorption Rate] Here, the light absorption rate of metal materials will be described. Fig. 3 is a graph showing the light absorption rate of each metal material versus the wavelength of the irradiated laser light L. The horizontal axis of the graph in Fig. 3 represents wavelength, and the vertical axis represents absorption rate. Fig. 3 shows the relationship between wavelength and absorption rate for aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), tantalum (Ta), and titanium (Ti).

[0070] Although the characteristics differ depending on the material, it can be seen that for each metal shown in Figure 3, the absorption rate of light energy is higher when using blue or green laser light with shorter wavelengths than when using infrared (IR) laser light.

[0071] When a workpiece W is irradiated with a laser beam having a relatively long wavelength and a relatively low absorption rate, the light energy is reflected by the workpiece W, making it less likely to have a thermal effect on the workpiece W. Therefore, a relatively high power is required to obtain a melted region of sufficient depth. In this case, the sudden input of energy to the center of the beam causes sublimation and the formation of a keyhole. However, irradiating a high-power laser beam can destabilize the molten pool, potentially causing spattering or voids. Furthermore, if the workpiece W includes a metal foil 12, the metal foil 12 is thin and therefore more likely to stretch or tear.

[0072] On the other hand, when a laser beam with a relatively short wavelength and a relatively high absorption rate is irradiated onto the workpiece W, most of the input light energy is absorbed by the workpiece W, making it easier to obtain thermal energy. In other words, no keyhole is formed, and melting occurs by thermal conduction, making it easier to stabilize the molten pool.

[0073] Therefore, in this embodiment, laser light L including two laser lights (first laser light and second laser light) with different wavelengths is output from the optical head 120, and the laser light L is irradiated onto the surface Wa of the workpiece W, thereby welding the metal member 11 and the laminate 16.

[0074] The laser device 111 (see FIG. 1 ) outputs a first laser beam having a wavelength longer than that of the second laser beam, for example, a laser beam having a wavelength of 800 nm or more and 1200 nm or less. The laser device 111 has, as a laser light source, for example, a fiber laser or a semiconductor laser (element).

[0075] The laser device 112 outputs a second laser beam having a wavelength shorter than that of the first laser beam, for example, a laser beam having a wavelength of 550 nm or less. The laser device 112 has a semiconductor laser (element) as a laser light source. The laser device 112 more preferably outputs a second laser beam having a wavelength of 400 nm or more and 500 nm or less, which has a higher absorption rate.

[0076] FIG. 4 shows an example of a spot S of the laser beam L formed on the surface Wa. As shown in FIG. 4 , the spot S of the laser beam L includes a spot S1 formed by the first laser beam L1 and a spot S2 formed by the second laser beam L2. The spots S, S1, and S2 are instantaneous irradiation areas of the laser beams. d, d1, and d2 represent the diameters of the spots S, S1, and S2. In this embodiment, as shown in FIG. 4 , the size (diameter d2) of the spot S2 is larger than the size (diameter d1) of the spot S1, and the spot S1 is located within the spot S2. In other words, the outer edge S1a of the spot S1 is located inside the outer edge S2a of the spot S2. By setting the spots S1 and S2 in this way, thermal energy generated by irradiation with the second laser beam L2 can be applied to the irradiation area of ​​the first laser beam L1 from its periphery. This facilitates the formation of a deeper molten pool with less energy than when the first laser beam L1 is irradiated alone. In addition, since the temperature change of the molten pool over time can be alleviated, the molten pool can be made more stable, the occurrence of spatter and voids can be suppressed, and the metal foil 12 is less likely to stretch or break.

[0077] Furthermore, when the spot S of the laser beam L is scanned on the surface Wa in a scanning direction intersecting the Z direction, i.e., along the plane of the drawing in FIG. 4 , it is preferable that at least a portion A2f of the spot S2 is located forward of the spot S1 in the scanning direction. This allows the area (spot S1) irradiated with the first laser beam L1 to be preheated by the second laser beam L2 when the spot S (laser beam L) is scanned. This also facilitates the formation of a deeper molten pool with less energy than when the first laser beam L1 is irradiated alone. Furthermore, since the temperature change of the molten pool over time can be mitigated, the molten pool can be more stabilized, suppressing the occurrence of spatter and voids and making the metal foil 12 less likely to stretch or tear.

[0078] In the example of Fig. 4, the center C of the spot S1 and the center C of the spot S2 overlap, but the two centers may be offset from each other. For example, the spot S1 may partially extend rearward in the scanning direction from the spot S2. The diameters of the spots S1 and S2 on the surface Wa are 1 / e of the peak intensity. ２ For non-circular spots, the diameter of the area of ​​peak intensity is 1 / e ２ The length of the region having the above intensity in a direction (width direction) perpendicular to the scanning direction and perpendicular to the Z direction can be defined as the diameter or width of the spot.

[0079] When the laser beam L is scanned on the surface Wa in the scanning direction, the welded portion 14 extends in the scanning direction with the cross-sectional shape shown in FIG.

[0080] [Laser Welding System] Fig. 5 is an exemplary schematic diagram of a laser welding system 1000. As shown in Fig. 5, the laser welding system 1000 includes a compression device 200 and a joining device 100. The compression device 200 partially presses and compresses a stack 16 of a plurality of metal foils 12 in the Z direction to form a compressed portion 16a. The compression device 200 will be described later.

[0081] The laminate 16 with the compressed portion 16a formed therein is transported from the compression device 200 to a joining device 100 provided separately from the compression device 200, where it is joined to the metal member 11 by laser welding to obtain a metal joined body 10 (see FIG. 1 ). That is, the process by the compression device 200 (pre-compression step, described below) and the process by the joining device 100 (joining step, described below) are performed at different locations. In this way, by performing each process at different locations, i.e., by different devices, it becomes easier to improve the processing accuracy of each process.

[0082] When the laminate 16, on which the compressed portion 16a has been formed in the compression device 200, is transported from the compression device 200 to the joining device 100, the plurality of metal foils 12 are integrated in the laminate 16. In this case, the laminate 16 may be one in which the stacked state of the plurality of metal foils 12 is maintained by other members or mechanisms such as a jig, or the plurality of metal foils 12 may be integrated so as to maintain the stacked state by themselves without using other members or mechanisms.

[0083] 6 is a flowchart showing an example of a procedure for laser welding the workpiece W using the laser welding system 1000. First, in the compression device 200, a stack of multiple metal foils 12 is partially pressed and compressed in the Z direction to form a compressed portion 16a (S11). S11 is an example of a first step and can also be referred to as a pre-compression step.

[0084] Next, in the joining device 100, a jig or the like is used to hold the laminate 16 on which the compressed portion 16a is formed and the metal member 11 in an overlapping state (S12).

[0085] Next, a laser beam L is irradiated onto the surface Wa of the workpiece W, and the molten pool formed by the irradiation of the laser beam L is cooled and solidified to form a weld 14 joining the laminate 16 and the metal member 11, thereby welding the plurality of metal foils 12 and the metal member 11 (S13). In S13, the weld 14 is formed so as to penetrate the plurality of metal foils 12 in the Z direction and to be present within the metal member 11, as shown in FIG. 1. S13 is an example of a second step, and may also be referred to as a welding step.

[0086] [First Step (Pre-Compression Step)] FIG. 7 is a side view showing an example of step S11 performed in the compression device 200. In step S11, first, as shown in FIG. 7, a plurality of metal foils 12 are stacked on a surface 210a of a first member 210 to form a laminate 16 (S111). In the compression device 200, the first member 210 has a substantially constant thickness in the Z direction and extends perpendicularly to and intersects the Z direction. The first member 210 has a surface 210a facing the Z direction. The surface 210a extends perpendicularly to and intersects the Z direction. The plurality of metal foils 12 are stacked in the Z direction while extending across the Z direction. The Z direction is an example of a stacking direction of the plurality of metal foils 12 in the laminate 16 and is also an example of a stacking direction in which the first member 210 and the laminate 16 are stacked.

[0087] Next, with the laminate 16 sandwiched between the first member 210 and the second member 220 in the Z direction, the first member 210 and the second member 220 are brought relatively close to each other, thereby compressing the laminate 16. Here, the second member 220 is provided with a protruding portion 222 that is convex toward the first member 210. Therefore, the laminate 16 is compressed while being sandwiched between the first member 210 and the outer surface 222a of the protruding portion 222. As a result, a compressed portion 16a that is curved substantially along the outer surface 222a and convex toward the first member 210 is formed in the laminate 16 (S112).

[0088] Through extensive research, the inventors have found that when forming welds 14 (see FIGS. 1 and 8 ) penetrating multiple metal foils 12 in S13 (see FIGS. 6 and 8 ), the wider the gap between adjacent metal foils 12 in the Z direction, the more likely the metal foils 12 are to stretch or tear. This is presumably because gaps between adjacent metal foils 12 at or near the laser beam irradiated area hinder the conduction of heat generated by the laser beam irradiation between the adjacent metal foils 12, which makes it more likely that heat will concentrate at the laser beam irradiated area. In this regard, in the present embodiment, by forming compressed portions 16 a, the gaps between adjacent metal foils 12 at the compressed portions 16 a can be made smaller (preferably, eliminated or made extremely small) than before compression. Therefore, welding multiple metal foils 12, i.e., the laminate 16, at the compressed portions 16 a can prevent the metal foils 12 from stretching or tearing.

[0089] In the compression device 200, the second member 220 has a plate-like portion 221 and a protruding portion 222. The plate-like portion 221 has a substantially constant thickness in the Z direction, intersecting the Z direction and extending perpendicularly. The plate-like portion 221 has a surface 221a facing the opposite direction of the Z direction. The surface 221a intersects the Z direction and extends perpendicularly. The protruding portion 222 protrudes from the surface 221a toward the first member 210 in the opposite direction of the Z direction. The protruding portion 222 is configured as a convex strip extending in the Y direction with a predetermined width Wp in the X direction and a predetermined height Hp in the Z direction. The outer surface 222a of the protruding portion 222 has a curved shape that protrudes in the opposite direction of the Z direction at least in a portion that contacts the stack 16, and further has a cylindrical shape that protrudes in the opposite direction of the Z direction and extends in the Y direction at least at the end portion opposite the Z direction. Specifically, for example, a portion of the outer surface 222a closer to the first member 210 than a position halfway through the protruding height of the protruding portion 222 is formed into a cylindrical surface. This configuration can prevent the metal foil 12 from stretching or breaking in S112 (S11). The direction opposite the Z direction is an example of a protruding direction of the protruding portion 222 and an example of a first direction as a protruding direction of the compressed portion 16a. The Y direction is an example of a third direction. The X direction is an example of a fourth direction. Furthermore, the outer surface 222a is an example of a convex curved surface that convex toward the first member 210 in S112.

[0090] In S112, it is preferable that the metal foil 12 is plastically deformed in the compressed portion 16a. This is because the metal foil 12 that is elastically deformed rather than plastically deformed will return to its original shape before pressing when the pressure from the protruding portion 222 is released, which may widen the gap between adjacent pieces of metal foil 12 or cause the metal foil 12 to stretch or break when returning to its original shape.

[0091] Through extensive research, the inventors have found that when the hardness (rigidity) of the first member 210 is insufficient, the metal foil 12 is more likely to elastically deform at the tip end of the compressed portion 16a in the direction opposite to the protruding direction, i.e., the Z direction (first direction). This is because the first member 210 itself elastically deforms due to the pressing force acting in S112, thereby reducing the pressing force acting on the metal foil 12. For this reason, in S112, the compressed portion 16a is preferably formed so that at least the metal foil 12 located at the end opposite to the Z direction undergoes plastic deformation partially, i.e., at least a portion of the portion overlapping the protruding portion 222 in the Z direction. Furthermore, the first member 210 is preferably made of a material with as high a rigidity (Young's modulus) as possible, at least in the portion overlapping the protruding portion 222 in the Z direction. From this perspective, the first member 210 is preferably made of a material with a Young's modulus higher than that of the metal member 11. Similarly, the second member 220 is preferably made of a material with as high a rigidity (Young's modulus) as possible, at least in the protruding portion 222, and is preferably made of a material with a higher Young's modulus than that of the metal member 11. The metal foil 12 located at the end opposite to the Z direction is the metal foil 12 that will be in contact with the metal member 11 later in S12, S13, and the metal joined body 10 (see FIG. 8 ).

[0092] Furthermore, in S112, it is preferable that adjacent metal foils 12 are partially joined together in the compressed portion 16a. By joining adjacent metal foils 12 together, it is possible to prevent the gap between adjacent metal foils 12 from widening when the pressure from the protruding portion 222 is released, and to prevent the metal foils 12 from stretching or breaking when returning to their original shape.

[0093] Through diligent research by the inventors, it has been found that when the metal foil 12 is made of an aluminum-based material or a copper-based material, adjacent metal foils 12 are partially bonded together by room-temperature bonding (low-temperature bonding) by pressing under appropriate conditions in S112. In other words, in S112, it is preferable that adjacent metal foils 12 are partially bonded together at room temperature in the compressed portions 16 a at any position in the Z direction.

[0094] Furthermore, as shown in FIG. 5, when transporting the laminate 16 from the compression device 200 to the joining device 100, if the multiple metal foils 12 are integrated by S112, the metal foils 12 will not fall apart, which has the advantage of making transportation easier.

[0095] From this viewpoint, it is preferable that in the compressed portion 16a, all of the metal foils 12 are in a state in which they are partially bonded to adjacent metal foils 12. However, even if all of the metal foils 12 in the laminate 16 are not partially bonded to adjacent metal foils 12, in other words, even if the laminate 16 includes metal foils 12 that are not partially bonded to adjacent metal foils 12, when the laminate 16 is integrated without using other members or mechanisms such as jigs, the same effects as when all of the metal foils 12 are partially bonded to adjacent metal foils 12 in the compressed portion 16a, i.e., effects such as suppression of stretching or tearing of the metal foils 12 and reduction of transportation effort, may be obtained.

[0096] Furthermore, since the metal foil 12 located at the end in the Z direction or the end in the opposite direction to the Z direction is prone to stretching or breaking due to contact with the metal member 11 in S13 or irradiation with laser light, it is preferable that it be partially joined to adjacent metal foils 12 in the compressed section 16a.

[0097] Through extensive research by the inventors, it has been found that the thickness tc of the compressed portion 16a in the stacking direction is preferably 40% or more and 60% or less of the thickness of the plurality of metal foils 12 in the stacking direction when stacked without gaps and without compression. If the thickness is less than 40%, the metal foil 12 breaks in S112, while if the thickness is more than 60%, plastic deformation of the metal foil 12 is unlikely to occur. Note that the thickness of the plurality of metal foils 12 in the stacking direction when stacked without gaps and without compression may be calculated using the formula: average thickness of the metal foils 12 x number of layers.

[0098] 7 , in step S112, it is preferable to restrict movement of the laminate 16 in the Z direction by a surface 221a of the plate-like portion 221 located on the opposite side of the first member 210 with respect to the laminate 16. Without the surface 221a, the laminate 16 would be deformed into a substantially V-shape with the tip of the compressed portion 16a at the base due to pressure from the protruding portion 222. When the laminate 16 is overlaid on the metal member 11 in steps S12 and S13, a gap between the laminate 16 and the metal member 11 would be large at a location away from the compressed portion 16a, making it difficult to obtain the desired shape of the metal bonded body 10. Furthermore, transporting the laminate 16 from the compression device 200 to the bonding device 100 and setting the laminate 16 in step S12 would also be difficult. In this regard, in the present embodiment, the surface 221a is provided at a required distance from the surface 210a of the first member 210, thereby preventing the laminate 16 from deforming into a V-shape. The surface 221a is an example of a limiting portion.

[0099] 8 is a side view showing an example of steps S12 and S13 performed in the bonding apparatus 100. As shown in Fig. 8, first, the metal member 11 is placed on the stage 101, and then the laminate 16 is placed on it. At this time, the laminate 16 is overlapped with the metal member 11 in the Z direction so that the end 16b of the compressed portion 16a on the opposite side in the Z direction contacts the surface 11a of the metal member 11 (S12).

[0100] In S12, the workpiece W, which is the overlapping of the metal member 11 and the laminate 16, is supported by the stage 101 and the pressing member 102 in a state where it is sandwiched between the stage 101 and the pressing member 102 in the Z direction. The stage 101 and the pressing member 102 are an example of a support mechanism.

[0101] At this time, the pressing member 102 presses the laminate 16 at a position away from the compressed portion 16a in the X direction or in the direction opposite to the X direction so that the pressing force does not directly act on the compressed portion 16a. This makes it possible to prevent the pressing force from the pressing member 102 from causing peeling of the metal foil 12 at the compressed portion 16a, misalignment of adjacent metal foils 12 with each other, or release of the bonded state between adjacent metal foils 12.

[0102] Furthermore, at this time, it is preferable that the stage 101 and the pressing member 102 sandwich the metal member 11 and the laminate 16 in the Z direction in a state in which a surface pressure acting on the laminate 16 is lower than the surface pressure acting on the portion of the laminate 16 that overlaps the protruding portion 222 in the opposite direction of the Z direction in S11. If the pressing force of the pressing member 102 is too large, there is a risk that the metal foil 12 will peel off at the compressed portion 16a, adjacent metal foils 12 will shift, or the bonded state between adjacent metal foils 12 will be broken, as well as bending of the laminate 16 and deformation of the compressed portion 16a.

[0103] Next, as described above, the workpiece W is supported by the stage 101 and the pressing member 102 so as not to move, and the workpiece W is irradiated with laser light (S13). In the example of FIG. 8 , the laser light L is irradiated onto the surface of the laminate 16 opposite the metal member 11, i.e., the surface Wa located at the end of the laminate 16 in the Z direction. A molten pool is formed in the workpiece W, penetrating the laminate 16 and reaching the metal member 11, and a weld 14 is formed as the molten pool cools. That is, the weld 14 penetrates the laminate 16 and exists within the metal member 11. The weld 14 welds the laminate 16, i.e., the multiple metal foils 12, to the metal member 11, forming a metal joined body 10. The weld 14 may also be referred to as weld metal.

[0104] FIG. 9 is a plan view of the metal joined body 10A (10). As shown in FIG. 9, in this embodiment, the welded portion 14 penetrates only the compressed portion 16a in the laminate 16. In addition, in the example of FIG. 9, the length Lc of the compressed portion 16a in the Y direction is greater than its width Wc in the X direction. With this configuration, by forming the welded portion 14 longer, the joining area formed by the welded portion 14 is enlarged, making it easier to ensure the required joining strength. This configuration is achieved by the shape of the protruding portion 222. That is, in this case, the outer surface 222a of the protruding portion 222 is formed into a cylindrical shape extending longer in the Y direction than its width in the X direction.

[0105] As described above, according to this embodiment, by forming a compressed portion 16a in the laminate 16, it is possible to eliminate or make extremely small the gaps between adjacent metal foils 12 in the compressed portion 16a, and therefore by welding multiple metal foils 12, i.e., the laminate 16, in the compressed portion 16a, it is possible to prevent the metal foils 12 from stretching or breaking.

[0106] [Modification 1] Fig. 10 is a plan view of a metal joined body 10B (10) of Modification 1. As shown in Fig. 10, in Modification 1, the welded portion 14 is not limited to the compressed portion 16a but extends to the outside of the compressed portion 16a. In other words, the welded portion 14 straddles the boundary 16d between the compressed portion 16a and the non-compressed portion 16c in the laminate 16. With this configuration, the joining area by the welded portion 14 can be made larger.

[0107] [Modification 2] Fig. 11 is a plan view of a metal joined body 10C (10) of Modification 2. As shown in Fig. 11, in Modification 2, the metal member 11 and the laminate 16 are joined by a plurality of welds 14 extending in the X direction and spaced apart in the Y direction. Also in Modification 2, the welds 14 are not limited to the compressed portion 16a but extend to the outside of the compressed portion 16a. This configuration also allows the joining area by the welds 14 to be larger.

[0108] [Modification 3] Fig. 12 is a side view showing S112 (S11) of Modification 3. As shown in Fig. 12, in Modification 3, the protrusion 222 is a roller that can roll around a rotation axis Ax extending in the Y direction. In this case, the protrusion 222 rolls in the X direction or the direction opposite to the X direction, pressing the laminate 16 in the direction opposite to the Z direction, compressing the laminate 16 and forming the compressed portion 16a. With this configuration, it is possible to form the compressed portion 16a that is wider in the X direction. In this case, the outer surface 222a of the protrusion 222 is the outer peripheral surface of the roller and is formed in a cylindrical shape.

[0109] [Modification 4] Fig. 13 is a side view showing S13 of Modification 4. As shown in Fig. 13, in Modification 4, the orientation (stacking order) of the metal member 11 and the laminate 16 in the processing object W is reversed in the Z direction from S13 in Fig. 8, and laser light L is irradiated onto the metal member 11, i.e., onto a surface Wa of the metal member 11 located at the end opposite the laminate 16 (plurality of metal foils 12). In this case, the welded portion 14 penetrates not only the metal member 11 but also the compressed portion 16a. In this modification, as in the first embodiment, the effect of providing the compressed portion 16a can be obtained.

[0110] Second Embodiment Fig. 14 is a flowchart showing another example of the procedure for laser welding the workpiece W by the joining device 100. As shown in Fig. 14, in this embodiment, S13 (see Fig. 6) in the first embodiment includes S131 and S132.

[0111] In S131, the surface Wa of the workpiece W is irradiated with laser light L, and the molten pool formed by the irradiation of the laser light L is cooled and solidified, thereby forming a first welded portion 14F that welds the compressed portion 16a of the laminate 16 to the metal member 11. S131 is an example of a third step.

[0112] Furthermore, when welding the metal foil 12, there is a risk that the metal foil 12 may tear near the boundary between the welded portion and the metal foil 12, forming a gap, or that the metal foil 12 may stretch at the portion in contact with the welded portion, forming an excessively thin portion. S131 is performed under conditions in which such gaps or thin portions are basically not formed or are unlikely to be formed, but, for example, when there are a relatively large number of metal foils 12, there is a risk that local gaps or excessively thin portions may be formed depending on the individual pieces.

[0113] Therefore, in this embodiment, after S131, a laser beam L is irradiated toward the vicinity of the boundary B between the first welded portion 14F and the metal foil 12, thereby forming a second welded portion 14R as shown in FIG. 15 (S132). In S132, if a gap exists between the first welded portion 14F and the metal foil 12, the portion adjacent to the gap melts and solidifies to form the second welded portion 14R. Furthermore, if an excessively thin portion exists at the connection between the first welded portion 14F and the metal foil 12, the thin portion and its vicinity melt and solidify to form the second welded portion 14R. According to this embodiment, S132 can more reliably prevent the formation of gaps or excessively thin portions. S132 can be considered a process for repairing or improving the joint condition in S131. In the example of FIG. 15, the laser beam L is irradiated while scanning the surface Wa in the scanning direction SD, but this is not limited thereto and fixed-point irradiation may also be used. In this case, the fixed-point irradiation is performed on a plurality of locations on the surface Wa. S132 is an example of a fourth step.

[0114] In addition, in S132, as in the example of FIG. 15, the laser light L may be irradiated multiple times to form the second welded portion 14R at multiple locations.

[0115] Furthermore, in S132, the irradiation conditions of the laser light L may be appropriately set to form the second welded zones 14R at a plurality of locations that are different in position in the stacking direction of the metal foil 12.

[0116] 16 is a cross-sectional view of the workpiece W on which a plurality of second welds 14R1 (14R) and a plurality of second welds 14R2 (14R) have been formed by multiple irradiations of the laser beam L in S132. In the example of FIG. 16, after the second weld 14R1 shown in FIG. 15 has been formed, the laser beam L is again irradiated toward the vicinity of the boundary B between the first weld 14F and the metal foil 12 on the surface Wa, whereby the first weld 14F, the second weld 14R1, and a portion of the metal foil 12 are melted, cooled, and solidified, thereby forming the second weld 14R2.

[0117] As shown in Figure 16, the second welded portion 14R1 and the second welded portion 14R2 differ in their positions in the Y1 direction, in other words, in the direction intersecting the Z direction, the direction along the surface Wa, or the direction intersecting the stacking direction of the metal foil 12, and also differ in their positions in the Z direction, in other words, in the stacking direction of the metal foil 12.

[0118] The position of the second welded portion 14R along the surface Wa can be changed by changing the irradiation position of the spot of the laser light L on the surface Wa. In S132, the laser light L travels in the negative Z direction while its energy is absorbed by the metal foil 12. Therefore, as shown in FIGS. 15 and 16 , the first welded portion 14F has a tapered shape whose width decreases with increasing distance from the surface Wa. Accordingly, the boundary B between the first welded portion 14F and the multiple metal foils 12 often inclines toward the center (center line CL in this case) of the width direction (Y1 direction) of the first welded portion 14F with increasing distance from the surface Wa. Therefore, it is preferable that the multiple second welded portions 14R that melt and solidify near the boundary B be located closer to the center of the width direction of the first welded portion 14F the further away from the surface Wa they are. In the example of Figure 16, the widthwise center of the second welded portion 14R1, which is formed near the portion of the boundary B farther from the surface Wa, is located closer to the widthwise center (center line CL) of the first welded portion 14F than the widthwise center of the second welded portion 14R2, which is formed near the portion of the boundary B closer to the surface Wa.

[0119] Furthermore, the position of the second welded portion 14R in the stacking direction of the metal foil 12, in other words, the position in the irradiation direction of the laser light L, can be changed by changing the power of the laser light L. Specifically, the higher the power, the farther the second welded portion 14R can be formed from the surface Wa, in other words, at a deeper position, or further forward in the irradiation direction. In other words, the lower the power, the closer the second welded portion 14R can be formed from the surface Wa, in other words, at a shallower position, or further backward in the irradiation direction.

[0120] 16 , the end portion of the second welded portion 14R1 in the negative Z direction as the bottom is positioned farther from the surface Wa than the end portion of the second welded portion 14R2 in the negative Z direction as the bottom, in accordance with the shape of the boundary B. That is, the second welded portion 14R2 is positioned further rearward in the irradiation direction of the laser light L than the second welded portion 14R1.

[0121] In addition, the second weld 14R2 may be formed by irradiating laser light L toward the vicinity of the boundary between the second weld 14R1 and the metal foil 12 on the surface Wa, causing a portion of the second weld 14R1 and the metal foil 12 to melt, cool, and solidify.

[0122] In the example of FIG. 16 , second welds 14R1 and 14R2 are formed at four locations by irradiating laser light L four times. However, this is not limited to this, and various specifications, such as the number of second welds 14R (i.e., the number of times laser light L is irradiated in S132), as well as specifications such as their positions, widths, depths, and lengths, can be set. In the example of FIG. 16 , two stages of second welds 14R1 and 14R2 are formed at different positions in the stacking direction (irradiation direction) of the metal foil 12. However, three or more stages of second welds 14R at different positions in the stacking direction may be formed. Furthermore, in the example of FIG. 16 , second weld 14R2, which is located further rearward than second weld 14R1 in the irradiation direction, is formed after second weld 14R1. However, the order in which multiple second welds 14R are formed is not limited to this, and various settings can be made, such as forming second weld 14R1 after second weld 14R2.

[0123] As shown in FIG. 16 , according to this embodiment, a metal joined body 10E (10) is formed by joining a stack 16 and a metal member 11 together using a weld 14 including a first weld 14F and a second weld 14R. When the metal joined body 10 is cut to form a cross section similar to that shown in FIG. 16 , the first weld 14F and the second weld 14R (14R1, 14R2) may be distinguishable as separate regions based on, for example, differences in surface roughness, crystal orientation, grain size, and other properties in the cross section, differences in brightness in images of the cross section, and the like. The presence of multiple regions with such differences in the cross section can be evidence that the method of this embodiment has been carried out. If the weld 14 including the first weld 14F and the second weld 14R is in a good state of connection at the stage shown in FIG. 15 , a metal joined body 10D (10) is formed by joining the stack 16 and a metal member 11 together using the weld 14.

[0124] [Variation 5] In S132, the laser beam L may be irradiated in a direction inclined with respect to the irradiation direction of the laser beam in S131, i.e., the negative Z direction. FIG. 17 is a cross-sectional view of the workpiece W on which the second welded portion 14R1 (14R) is formed in this case. As described above, the boundary B often inclines toward the center (center line CL) of the width direction of the first welded portion 14F as it moves away from the surface Wa. Therefore, by irradiating the laser beam L at an angle inclined with respect to the negative Z direction so as to follow the inclination of the boundary B, the second welded portion 14R may be formed more efficiently along the boundary B. Although not shown, second welded portions 14R other than the second welded portion 14R1, such as the second welded portion 14R2, may also be formed by irradiating the laser beam L in a direction inclined with respect to the negative Z direction so as to follow the boundary B. The irradiation direction of the laser light L can be changed or set, for example, by controlling or setting the angle of the mirrors 126a and 126b of the galvano scanner 126, or by controlling or setting the tilt angle of the optical head 120 relative to the support base. If the joining state of the welded portion 14 including the first welded portion 14F and the second welded portion 14R is good at the stage of Fig. 17, the welded portion 14 joins the laminate 16 and the metal member 11 to form a metal joined body 10F(10).

[0125] [Conditions for performing S132] Based on experimental research, the inventors have found that suitable second welded zone 14R can be formed by irradiating laser light L under predetermined conditions in S132 as described above. In the experiments, first welded zone 14F and second welded zone 14R were formed by scanning spot S of laser light L on surface Wa in both S131 and S132. By scanning, first welded zone 14F and second welded zone 14R can be formed over a wider area in a shorter time.

[0126] The experiment was conducted on a case where the metal member 11 and the 20 sheets of metal foil 12 were both made of aluminum-based metal. In addition, in steps S131 and S132, the diameter d1 of the spot S1 of the first laser beam L1 was set to 20 to 40 μm, and the diameter d2 of the spot S2 of the second laser beam L2 was set to 300 to 350 μm. In S131, the power of the first laser light L1 is set to 80 to 200 [W], the power of the second laser light L2 is set to 100 to 200 [W], and the scanning speed is set to 0.1 to 0.2 [m / sec]; in S132, the power of the first laser light L1 is set to 80 to 350 [W], the power of the second laser light L2 is set to 100 to 200 [W], and the scanning speed is set to 0.5 to 1.5 [m / sec]; and in S132, the power of the first laser light L1 is set to 300 to 500 [W], the power of the second laser light L2 is set to 100 to 200 [W], and the scanning speed is set to 0.5 to 1.2 [m / sec].

[0127] Experimental studies have revealed that it is preferable to irradiate the laser light L under the following conditions (1) to (3).

[0128] (1) The scanning speed in S132 is set to be faster than the scanning speed in S131. (2) The total amount of energy imparted to the workpiece W by the irradiation of the laser light L in each irradiation to form each second welded portion 14R in S132 is set to be smaller than the total amount of energy imparted to the workpiece W by the irradiation of the laser light L in S131. By using the above (1) and (2), the width of the second welded portion 14R in the direction perpendicular to the scanning direction (Y1 direction) can be made narrower than the width of the first welded portion 14F in the direction perpendicular to the scanning direction SD. This allows the second welded portion 14R to be formed near the boundary B with an appropriate width that is not too wide. This reduces unnecessary energy consumption. Note that if the laser light L is irradiated multiple times in S132, the scanning speed may be changed for each irradiation to form the second welded portion 14R. (11) The power of the laser light L in S132 is set lower than the power of the laser light L in S132. This allows the second welded portion 14R to be formed to an appropriate depth in S132.

[0129] In this embodiment, similar to the first embodiment, the effect of providing the compression portion 16a can be obtained.

[0130] In this embodiment, the weld 14 includes at least one bead 141 (see FIGS. 19 to 26). Each part including the bead 141 (weld 14) can be made by the same method as in the first embodiment, the second embodiment, and their modifications.

[0131] [Tensile shear strength of a metal joined body according to the relative angle between the direction in which a tensile force acts and the extension direction of a bead] Fig. 18 is a plan view of a metal joined body 10 of a reference example. Fig. 19 is a plan view of a metal joined body 10 of the present embodiment. In the examples of Figs. 18 and 19, the laminate 16 and the metal member 11 are each joined by a weld 14 including only one bead 141. In either case, as shown in Fig. 8, the bead 141 penetrates the laminate 16, i.e., the multiple metal foils 12, in the Z direction and is present within the metal member 11.

[0132] The extension direction of the beads 141 is different between the reference example of Fig. 18 and the present embodiment of Fig. 19. In the reference example of Fig. 18, the beads 141 extend along the Y direction, whereas in the present embodiment of Fig. 19, the beads 141 extend along the X direction. Note that although the extension direction of the beads 141 is different between the reference example of Fig. 18 and the present embodiment of Fig. 19, the specifications of the beads 141, such as width, length, and depth, and the conditions in the compression process and the joining process are the same.

[0133] The inventors conducted extensive research through experiments and simulations into the fracture strength (tensile shear strength) of the metal joined body 10 shown in Figures 18 and 19 when a tensile force Fs1 acts on the metal member 11 in the X direction and a tensile force Fs2 acts on the laminate 16 (plurality of metal foils 12) in the opposite direction to the X direction. The tensile forces Fs1 and Fs2 are equal in magnitude but act in opposite directions. The action of the tensile forces Fs1 and Fs2 generates shear stress in the welded joint 14. The tensile forces Fs1 and Fs2 can also be referred to as shear forces.

[0134] The research yielded the following findings: That is, it was found that: under conditions in which tensile forces Fs1 and Fs2 act, cracks are more likely to occur at boundary portions 14a1 and 14a2 between bead 141 (weld portion 14) and base metal than at other portions of metal joined body 10; that cracks are more likely to occur at portions of boundary portions 14a1 and 14a2 that extend in a direction intersecting the acting direction of tensile forces Fs1 and Fs2 (X direction and the direction opposite to the X direction), and that cracks are most likely to occur at boundary portion 14a1 that extends in a direction substantially perpendicular to the acting direction of tensile forces Fs1 and Fs2 (Y direction) as included in the reference example of FIG. 18; and that cracks are less likely to occur at boundary portion 14a2 of boundary portions 14a1 and 14a2 that extends substantially along the acting direction of tensile forces Fs1 and Fs2 as included in the present embodiment of FIG. 19 than at other portions including boundary portion 14a1. That is, it was found that the metal bonded body 10 having the boundary portion 14a2, i.e., the bead 141, extending long in the acting direction of the tensile forces Fs1 and Fs2, as in the present embodiment of Fig. 19, has a higher tensile shear strength than the metal bonded body 10 having the boundary portion 14a1, i.e., the bead 141, extending long in the direction intersecting the acting direction of the tensile forces Fs1 and Fs2, as in the reference example of Fig. 18. Furthermore, it was found that: a crack generated in the boundary portion 14a1 extending long in the direction intersecting the acting direction of the tensile forces Fs1 and Fs2, as in the reference example of Fig. 18, propagates along the boundary portion 14a1 due to the action of the tensile forces Fs1 and Fs2, so that the tensile shear strength decreases as the boundary portion 14a1 becomes longer; and even if a crack occurs in the boundary portion 14a2 extending long in the acting direction of the tensile forces Fs1 and Fs2, as in the present embodiment of Fig. 19, it is difficult for the crack to propagate. The X direction and the direction opposite to the X direction are examples of directions intersecting the Z direction in which the tensile forces Fs1 and Fs2 acting on the metal bonded body 10 are greatest.

[0135] FIG. 20 is a plan view showing an example of the configuration of a weld 14 in a metal joined body 10A (10) having a relatively high tensile shear strength based on the above-described findings. In the example of FIG. 20 , in the metal joined body 10A in which tensile forces Fs1 and Fs2 act on the laminate 16 and the metal member 11 in the X direction and the direction opposite to the X direction, the weld 14 includes multiple beads 141 extending in the X direction, and the multiple beads 141 are provided at predetermined intervals (the distance between the center lines of the beads 141) in the Y direction. With this configuration, even when the tensile forces Fs1 and Fs2 act, cracks are less likely to occur at the interface between the beads 141 and the base metal because the beads 141 extend in the X direction and the direction opposite to the X direction. Even if cracks do occur at the interface, they are less likely to propagate. That is, according to this embodiment, a metal joined body 10A having a higher tensile shear strength can be obtained. The X direction or the direction opposite to the X direction is an example of a second direction, and the Y direction or the direction opposite to the Y direction is an example of a fifth direction.

[0136] Furthermore, when the weld 14 has only one bead 141 extending long in the X direction, as in Figure 19, a long area in the X direction is required to form the weld 14, which may limit the areas where it can be applied. In this regard, in the example of Figure 20, multiple linear beads 141 extending in the X direction are provided at intervals in the Y direction, so the area required to form the weld 14 can be made shorter in the X direction and longer in the Y direction than in the example of Figure 19. Note that the required conductance of the weld 14 can be ensured by the total length of the multiple beads 141 included in the weld 14 (the area of ​​the weld 14 in a planar view in the direction opposite the Z direction). In other words, the longer the length of the bead 141, the higher the conductance, i.e., the lower the electrical resistance.

[0137] 20, the bead 141 does not remain within the compressed portion 16a but extends outside the compressed portion 16a. In other words, the bead 141 straddles the boundaries 16d1, 16d2 (16d) between the compressed portion 16a and the non-compressed portion 16c in the laminate 16. This configuration further increases the joining area of ​​the welded portion 14, thereby increasing conductance. Furthermore, even in a situation where stress concentration occurs at the boundary 16d due to tensile forces Fs1, Fs2 or other external forces, the bead 141 can reinforce the boundary 16d, thereby preventing deformation or fracture originating from the boundary 16d.

[0138] 20, the bead 141 is provided so as to straddle two boundaries 16d1 and 16d2 that are spaced apart in the Y direction. This configuration allows the two boundaries 16d1 and 16d2 to be reinforced through the joining process of forming one bead 141. In other words, the boundaries 16d1 and 16d2 can be reinforced efficiently with a relatively simple configuration and a relatively easy process. One of the two boundaries 16d1 and 16d2 is an example of a first boundary, and the other is an example of a second boundary.

[0139] [Modification 6] Fig. 21 is a plan view of a metal joined body 10H (10) according to Modification 5. As is clear from comparing Fig. 21 with Fig. 20, the example of Fig. 21 has a larger number of beads 141, the length of each bead 141 in the X direction is shorter, and the spacing between the beads 141 in the Y direction is narrower than in the example of Fig. 20. With this configuration, even if the region where the weld 14 is formed is even shorter in the X direction, it is possible to ensure the required conductance and tensile shear strength.

[0140] Fig. 22 is a cross-sectional view of the metal joined body 10H(10) of Fig. 21. In Fig. 22, Ib is the spacing between the multiple beads 141 in the Y direction (the spacing between the centers in the Y direction), and wb is the width of each bead 141 at a position Bp that is the boundary between the compressed portion 16a of the laminate 16 and the metal member 11. Through extensive research by the inventors, it has been found that if the spacing Ib is too narrow, a crack that occurs at the boundary 16d of one bead 141 may propagate to the boundary 16d of the adjacent bead 141 in the Y direction. From this perspective, it has been found that the spacing Ib is preferably 1.5 times or more the width wb, and more preferably 2 times or more the width wb.

[0141] [Variation 7] FIG. 23 is a plan view of a metal joined body 10I (10) according to Variation 7. As shown in FIG. 23 , in Variation 7, beads 141 adjacent to each other in the Y direction are in contact with each other in the Y direction. However, for beads 141 adjacent to each other in the Y direction, the ends (boundary portions 14a1) of the beads 141 in the X direction and in the opposite direction of the X direction are spaced apart from each other in the Y direction. With this configuration, even if a crack occurs at the end (boundary portion 14a1), the crack may not propagate to an adjacent bead 141, thereby ensuring a required tensile shear strength against tensile forces Fs1 and Fs2 acting in the X direction and in the opposite direction of the X direction. Furthermore, in Variation 6, since adjacent beads 141 are in contact with each other, the weld 14 including multiple beads 141 can be formed with higher density. This results in the advantage of being able to make the metal joined body 10, and therefore the battery 1, smaller while still ensuring the required conductance.

[0142] [Variations 8 to 10] Fig. 24 is a plan view of a metal joined body 10J (10) of Variation 8, Fig. 25 is a plan view of a metal joined body 10K (10) of Variation 9, and Fig. 26 is a plan view of a metal joined body 10L (10) of Variation 10. As shown in Figs. 24 to 26, the metal joined body 10 can include a plurality of beads 141 of various shapes. For example, in Variation 8 of Fig. 24 and Variation 10 of Fig. 26, the weld 14 includes beads 141J1, 141L extending in the X direction and in a direction intersecting the opposite direction of the X direction (in the Y direction or in a direction obliquely intersecting the X direction and the Y direction) in which the tensile forces Fs1, Fs2 act. Thus, even if the beads 141J1 and 141L extend in a direction intersecting the direction in which the tensile forces Fs1 and Fs2 act, if the length of the beads 141J1 and 141L is short, even if a crack occurs, it will not propagate far and will not propagate to other beads 141. Furthermore, in the ninth modification of Fig. 25, the boundary between each bead 141K and the base material is formed in a curved shape, such as a circle or an ellipse, rather than a straight line, making it difficult for cracks to occur. Furthermore, because each bead 141K is short and separated from the other beads 141K, even if a crack occurs, it will not propagate.

[0143] As described above, in the third embodiment and its modifications, even when tensile forces Fs1 and Fs2 are applied, cracks are unlikely to occur between the bead 141 (weld 14) and the base material, or even if a crack does occur, the crack is unlikely to propagate. In other words, according to the third embodiment and its modifications, it is possible to manufacture a metal joined body 10 having higher tensile shear strength.

[0144] The bead 141 of the third embodiment and its modified example can also be applied to the first embodiment, the second embodiment, and their modified examples.

[0145] While the above describes exemplary embodiments of the present invention, the above 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, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be appropriately modified and implemented.

[0146] For example, the shape, number, arrangement, size, and other specifications of the protrusions and the surfaces of the ends of the protrusions in the protruding direction can be changed in various ways. For example, the shape of the surface may be a convex curved surface other than a cylindrical surface, and the protrusions may include multiple convex curved protrusions spaced apart from each other.

[0147] Additionally, the beads and welds can be implemented with various specifications, such as number, shape, width, spacing, length, etc.

[0148] Furthermore, if the metal member has sufficient rigidity, the metal member may be used as the second member. In this case, the subassembly in which the metal member and the multiple metal foils are stacked may be transported from the compression device (i.e., the location where the compressed portion is formed) to the joining device (i.e., the location where the laser welding is performed).

[0149] Furthermore, the joining device does not necessarily have to emit laser light of two wavelengths, but may emit laser light of one wavelength. The shape of the spot can also be changed in various ways. Furthermore, the scanning of the laser light may be achieved by relative movement between the optical head and the workpiece, or by a combination of this relative movement and a laser scanner. Furthermore, the laser scanner is not limited to a galvano scanner.

[0150] Furthermore, the laser welding method and laser welding system of the present invention may form a weld in an object to be processed that includes a single metal member instead of multiple metal foils (laminates), i.e., an object to be processed in which a first metal member and a second metal member are overlapped in a sixth direction, and in which tensile forces act on the first metal member and the second metal member in opposite directions along a direction intersecting the sixth direction, the weld including multiple beads extending in a second direction intersecting the sixth direction and spaced apart in a fifth direction intersecting the sixth direction and the second direction. In this case, too, a metal joined body with higher tensile shear strength can be obtained.

[0151] The present invention can be used in a laser welding method, a laser welding system, and a metal joint.

[0152] DESCRIPTION OF SYMBOLS 1... Battery (electrical appliance) 10, 10A to 10L... Metal bonded body 11, 11m, 11p... Metal member 11a... Surface 12... Metal foil 13m... Negative electrode material 13p... Positive electrode material 14... Welded portion 14F... First welded portion (welded portion) 14R, 14R1, 14R2... Second welded portion (welded portion) 14a1, 14a2... Boundary portion 15... Separator 16... Laminated body 16a... Compressed portion 16b... End portion 16c... Non-compressed portion 16d... Boundary 16d1, 16d2... Boundary (first boundary, second boundary) 20... Sheathing material 20a... Storage chamber 100... Bonding device 101... Stage (support mechanism) 102... Pressing member (support mechanism) 111, 112... Laser device 120... Optical head 121, 121-1, 121-2...Collimating lens 122...Condenser lens 123...Mirror 124...Filter 126...Galvano scanner 126a, 126b...Mirror 131, 132...Optical fiber 141, 141J1, 141J2, 141K, 141L...Bead 200...Compression device 210...First member 210a...Surface 220...Second member 221...Plate-shaped portion 221a...Surface (restriction portion) 222...Protrusion 222a...Outer surface (convex curved surface) 1000...Laser welding system A2f...Area Ax...Rotation axis B...Boundary Bp...Position C...Center CL...Center line d, d1, d2...Diameter Fs1, Fs2...Tensile force Hp...Predetermined height Ib...Spacing L...Laser light Lc...length L1...first laser beam L2...second laser beam S, S1, S2...spot S11...step (first step) S12...step S13...step (second step) S131...step (third step) S132...step (fourth step) S1a, S2a...outer edge SD...scanning direction tc...thickness W...processing object Wa...surface Wb...surface Wc...width Wp...predetermined width wb...width X...direction (fourth direction, second direction) Y...direction (third direction, fifth direction) Y1...direction (width direction) Z...direction (opposite direction to first direction, opposite direction to protrusion direction, sixth direction)

Claims

1. A laser welding method for welding a metal member and a plurality of metal foils by irradiating a laser beam, comprising: a first step of compressing the plurality of stacked metal foils in a stacking direction; and a second step of irradiating the plurality of metal foils or the metal member with a laser beam to form a weld that penetrates the plurality of metal foils in the stacking direction and exists within the metal member, thereby joining the metal member and the plurality of metal foils, wherein in the first step, a first member and a second member having a convex curved surface that convexly protrudes toward the first member are brought relatively close to each other, and the plurality of metal foils are compressed in a state in which they are sandwiched between the first member and the convex curved surface, thereby forming compressed portions in the plurality of metal foils that are curved in a state in which they protrude in a first direction approximately along the convex curved surface, such that at least the metal foils located at an end portion in the first direction of the compressed portions are partially plastically deformed, and in the second step, a portion of the plurality of metal foils including the compressed portions is joined to the metal member with an end portion in the first direction of the compressed portions being in contact with the metal member.

2. A laser welding method as described in claim 1, wherein in the first step, adjacent metal foils in the stacking direction are partially joined at least at the end of the compressed portion in the first direction or at the end of the compressed portion in the opposite direction to the first direction.

3. A laser welding method as described in claim 1, wherein in the first step, for all metal foils included in the plurality of metal foils, the metal foil and the metal foil adjacent to the metal foil in the stacking direction are partially joined in the compressed portion.

4. The laser welding method according to claim 1, wherein in the first step, the plurality of metal foils are integrated together.

5. A laser welding method according to any one of claims 1 to 4, wherein in the first step, adjacent metal foils in the stacking direction are partially joined at the compressed portion at any position in the stacking direction by room temperature joining.

6. A laser welding method according to any one of claims 1 to 4, wherein the first step and the second step are carried out at different locations.

7. A laser welding method according to any one of claims 1 to 4, wherein the second member has a higher Young's modulus than the metal member.

8. A laser welding method according to any one of claims 1 to 4, wherein in the first step, the thickness of the compressed portion in the stacking direction is set to be 40% or more and 60% or less of the thickness of the plurality of metal foils in the stacking direction when stacked without being compressed.

9. A laser welding method according to any one of claims 1 to 4, wherein the convex curved surface is formed into a cylindrical shape extending in a third direction substantially perpendicular to the protruding direction of the convex curved surface.

10. A laser welding method as described in claim 9, wherein the convex curved surface has a predetermined width in a fourth direction substantially perpendicular to the protruding direction and the third direction, and is formed into a cylindrical shape extending in the third direction longer than the predetermined width.

11. The laser welding method according to claim 10, wherein the convex curved surface is a cylindrical surface.

12. A laser welding method as described in claim 11, wherein the convex curved surface is the outer peripheral surface of a roller that rolls around a rotation axis extending in the third direction, and in the first step, the plurality of metal foils are compressed while the roller is rolling.

13. A laser welding method as described in any one of claims 1 to 4, wherein in the first step, a limiting portion located on the opposite side of the plurality of metal foils from the first member limits movement of portions of the plurality of metal foils other than the compressed portion in a direction away from the first member.

14. A laser welding method according to any one of claims 1 to 4, wherein in the second step, the metal member and the plurality of metal foils are sandwiched in the stacking direction by a support mechanism at a position away from the compressed portion.

15. A laser welding method as described in claim 14, wherein in the second step, the support mechanism sandwiches the metal member and the multiple metal foils in the stacking direction while a surface pressure acting on the multiple metal foils is lower than the surface pressure acting on the compressed portion in the first step.

16. A laser welding method according to any one of claims 1 to 4, wherein in the second step, the laser light is irradiated onto a surface of a metal foil among the plurality of metal foils that is located at an end opposite to the metal member.

17. A laser welding method according to any one of claims 1 to 4, wherein in the second step, the metal members are irradiated with the laser light.

18. The laser welding method of claim 1, wherein the welded portion includes a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

19. The laser welding method according to claim 18, wherein the bead extending in the second direction is approximately along a direction intersecting the stacking direction in which the tensile force acting on a metal joint formed by joining the metal member and the multiple metal foils with the weld is greatest as a result of the metal member being pulled in one direction intersecting the stacking direction and the multiple metal foils being pulled in the other direction intersecting the stacking direction.

20. A laser welding method as described in claim 18 or 19, wherein the plurality of beads are arranged so as to be spaced apart from each other in the fifth direction at positions that are boundaries between the plurality of metal foils and the metal member in the stacking direction.

21. The laser welding method according to claim 20, wherein, at the boundary position, the interval is 1.5 times or more the width of the bead in the fifth direction.

22. A laser welding method according to claim 18 or 19, wherein the plurality of beads are formed such that their ends in the second direction are spaced apart from each other in the fifth direction.

23. A laser welding method according to claim 18 or 19, wherein the plurality of beads are provided so as to straddle the boundaries between the compressed and non-compressed portions of the plurality of metal foils.

24. The laser welding method according to claim 23, wherein the boundary has a first boundary and a second boundary spaced apart from the first boundary in a direction intersecting the stacking direction, and the plurality of beads are provided so as to straddle the first boundary and the second boundary.

25. A laser welding method according to any one of claims 1 to 4, wherein the metal member and the plurality of metal foils are made of an aluminum-based material.

26. The laser welding method according to any one of claims 1 to 4, wherein the metal member and the plurality of metal foils are made of a copper-based material.

27. A laser welding method as claimed in claim 1, wherein the second step comprises: a third step of forming a first welded portion by welding the compressed portion and the metal member by irradiating the laser light; and a fourth step, after the third step, of melting and solidifying an adjacent portion to the gap between the first welded portion and the metal foil, or a connection portion between the first welded portion and the metal foil, by irradiating the laser light.

28. The laser welding method according to claim 27, wherein in the fourth step, the laser light includes a first laser light and a second laser light having a shorter wavelength than the first laser light.

29. The laser welding method according to claim 27, wherein in the fourth step, the irradiation of the laser light includes multiple irradiations each of which melts and solidifies a different portion.

30. A laser welding method as described in claim 27, wherein in the fourth step, the irradiation of the laser light includes multiple irradiations that melt and solidify different portions of the metal foil at different positions in the stacking direction.

31. A laser welding method as set forth in claim 27, wherein in the fourth step, the irradiation of the laser light includes a plurality of irradiations of the laser light at different irradiation positions on the metal foil.

32. The laser welding method according to claim 27, wherein in the fourth step, the irradiation of the laser light includes multiple irradiations with different powers of the laser light.

33. A laser welding method as set forth in claim 27, wherein the amount of energy per irradiation of the laser beam in the fourth step is smaller than the amount of energy of the laser beam irradiated in the third step.

34. The laser welding method according to claim 27, wherein in the fourth step, the laser light is scanned on the metal foil.

35. The laser welding method according to claim 34, wherein in the third step, the laser light is scanned on the metal foil, and the fourth step includes scanning the laser light at a scanning speed faster than the scanning speed of the laser light in the third step.

36. The laser welding method according to claim 27, wherein in the fourth step, the laser beam is irradiated in a direction inclined with respect to the direction of irradiation of the laser beam in the third step.

37. A laser welding method for joining a first metal member and a second metal member, the first metal member and the second metal member being overlapped with each other in a sixth direction, by irradiating one of the first metal member and the second metal member with laser light to form a weld that penetrates the one metal member in the sixth direction and is present within the other of the first metal member and the second metal member, the weld including a plurality of beads extending in a second direction intersecting with the sixth direction, the plurality of beads being spaced apart in a fifth direction intersecting with the sixth direction and the second direction, the beads extending in the second direction being approximately along a direction in which a tensile force acting on a metal joined body in which the first metal member and the second metal member are joined by the weld is greatest as a result of the first metal member being pulled in one direction intersecting with the sixth direction and the second metal member being pulled in the other direction intersecting with the sixth direction, among directions intersecting with the sixth direction.

38. A laser welding system for welding a metal member and multiple metal foils by irradiating a laser beam, comprising: a compression device that compresses the multiple stacked metal foils in a stacking direction; and a joining device that irradiates the multiple metal foils or the metal member with laser beam to form a weld that penetrates the multiple metal foils in the stacking direction and exists within the metal member, thereby joining the metal member and the multiple metal foils, wherein the compression device brings a first member and a second member having a convex curved surface that convex toward the first member relatively close to each other and compresses the multiple metal foils in a state in which they are sandwiched in the stacking direction between the first member and the convex curved surface, thereby forming a compressed portion in the multiple metal foils that is curved and protrudes in a first direction along the convex curved surface, such that at least the metal foil located at an end portion in the first direction of the compressed portion is partially plastically deformed, and the joining device joins the multiple metal foils to the metal member with the end portion in the first direction of the compressed portion in contact with the metal member.

39. The laser welding system of claim 38, wherein the weld includes a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

40. A metal joint comprising: a plurality of stacked metal foils; a metal member in contact with a metal foil located at one end of the plurality of metal foils in the stacking direction; and a welded portion penetrating the plurality of metal foils in the stacking direction and present within the metal member, joining the plurality of metal foils to the metal member, wherein the plurality of metal foils have compressed portions that are curved convexly toward the metal member, and in the compressed portions, at least the metal foil in contact with the metal member is partially plastically deformed.

41. A metal joint as claimed in claim 40, wherein the welded portion includes a plurality of beads extending in a second direction intersecting the stacking direction and spaced apart in a fifth direction intersecting the stacking direction and the second direction.

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