Laser welding method and laser welding device

Abstract

This laser welding method comprises: a first step for setting, for example, a processing target containing a metal member and a plurality of metal foils having been laminated, in a state in which a surface of the processing target is irradiated with laser light from a laser welding device, on a support device; and a second step for joining the metal member and the plurality of metal foils by irradiating the surface with laser light so as to form a welded part existing in the metal member and penetrate the plurality of metal foils in the laminating direction. In the second step, the welded part is formed at least on the surface so as to be connected in a direction in which the plurality of irradiation reference positions are arranged, by sequentially performing, at each of a plurality of irradiation reference positions arranged at intervals on the surface, point-shape irradiation in a stopped state or in a state of revolving about a corresponding irradiation reference position.

Description

Laser welding method and laser welding device

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

[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 to join multiple metal foils, the presence of air gaps between the metal foils can easily cause voids to remain in the molten pool and, ultimately, in the welded joint after the molten pool has solidified. If voids remain in the welded joint, there is a risk that the required strength and conductivity will not be obtained.

[0005] Therefore, one object of the present invention is to provide a new and improved laser welding method and laser welding apparatus that can reduce the amount of voids remaining in the weld, for example.

[0006] The laser welding method of the present invention includes, for example, a first step of setting an object to be processed, which includes a metal member and a plurality of stacked metal foils, on a support device in a state in which laser light from a laser welding device is irradiated onto the surface of the object to be processed, and a second step of irradiating the surface with the laser light to form a weld that is present within the metal member and penetrates the plurality of metal foils in the stacking direction, thereby joining the metal member and the plurality of metal foils.In the second step, point irradiation is performed sequentially at a plurality of irradiation reference positions arranged at intervals on the surface, while stationary or while rotating around the irradiation reference positions, thereby forming the weld so that the weld is connected at least on the surface in the direction in which the plurality of irradiation reference positions are arranged.

[0007] The laser welding method of the present invention includes, for example, a fifth step of setting a plurality of stacked metal foils on a supporting device in a state in which laser light from a laser welding device is irradiated onto the surface of a metal foil located at an end of the plurality of metal foils in the stacking direction, and a sixth step of irradiating the surface with the laser light to form a weld that integrates the plurality of metal foils.In the sixth step, point irradiation is performed sequentially at a plurality of irradiation reference positions arranged at intervals on the surface, while stationary or while rotating around the irradiation reference positions, thereby forming the weld so that the weld is connected at least on the surface in the direction in which the plurality of irradiation reference positions are arranged.

[0008] Furthermore, the laser welding device of the present invention includes, for example, a laser light source and an optical head that irradiates the laser light output from the laser light source onto the surface of an object to be processed, which includes a metal member and a plurality of metal foils, to form a weld that is present within the metal member and penetrates the plurality of metal foils in the stacking direction, thereby joining the metal member and the plurality of metal foils, and by sequentially performing point irradiation at a plurality of irradiation reference positions arranged at intervals on the surface, while stationary or rotating around the irradiation reference positions, the weld is formed so that it is connected at least on the surface in the direction in which the plurality of irradiation reference positions are arranged.

[0009] According to the present invention, it is possible to provide a new and improved laser welding method and laser welding apparatus that can reduce the amount of voids remaining in the weld, for example.

[0010] FIG. 1 is an exemplary schematic diagram of the joining apparatus of the 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 of the first embodiment. FIG. 3 is a graph showing the light absorption rate of metal versus the wavelength of the irradiated laser light. FIG. 4 is an exemplary and schematic plan view showing a laser light spot formed on the surface of a processing target by the joining apparatus of the first embodiment. FIG. 5 is an exemplary flowchart showing the procedure of the laser welding method of the first embodiment. FIG. 6 is a schematic plan view of an example of a metal bonded body obtained by the laser welding method of the first embodiment. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 6. FIG. 8 is an X-ray transmission image of an example of a metal bonded body obtained by the laser welding method of the first embodiment. FIG. 9 is an X-ray transmission image of an example of a metal bonded body obtained by the laser welding method of the reference example. FIG. 10 is a timing chart showing an example of changes over time in the laser light power and the laser light irradiation target position in the laser welding method of the first embodiment. FIG. 11 is an exemplary schematic plan view showing irradiation areas of laser light at adjacent irradiation reference positions in the laser welding method of the first embodiment. FIG. 12 is an exemplary schematic plan view showing irradiation areas of laser light when wobbling is performed at the irradiation reference position in the laser welding method of the first embodiment. FIG. 13 is a schematic plan view of another example of a metal joined body obtained by the laser welding method of the first embodiment. FIG. 14 is a cross-sectional view taken along XIII-XIII in FIG. 13. FIG. 15 is an X-ray transmission image of another example of a metal joined body obtained by the laser welding method of the first embodiment. FIG. 16 is an X-ray transmission image of yet another example of a metal joined body obtained by the laser welding method of the first embodiment. FIG. 17 is an exemplary flowchart showing some steps of a laser welding method of the second embodiment. FIG. 18 is an exemplary schematic cross-sectional view of an object to be processed at an intermediate stage of S122 in the flowchart of FIG. 17 in the laser welding method of the second embodiment. FIG. 19 is an exemplary schematic cross-sectional view of the object to be processed at the stage where step S122 in the flowchart of FIG. 17 in the laser welding method according to the second embodiment is completed.FIG. 20 is an exemplary schematic cross-sectional view of an object to be processed at a stage midway through S122 of the flowchart of FIG. 17 in a laser welding method according to a modified example in which the irradiation direction of laser light is changed from that of the second embodiment. FIG. 21 is an exemplary configuration diagram of a laser welding system according to a third embodiment. FIG. 22 is an exemplary flowchart showing the procedure of the laser welding method according to the third embodiment. FIG. 23 is an exemplary schematic side view illustrating S13 of the flowchart of FIG. 22 in the laser welding method according to the third embodiment. FIG. 24 is an exemplary schematic side view illustrating S11 and S12 of the flowchart of FIG. 22 in the laser welding method according to the third embodiment. FIG. 25 is an exemplary flowchart showing the procedure of a laser welding method according to a fourth embodiment. FIG. 26 is an exemplary schematic cross-sectional view of an object to be processed at a stage at which S15 of the flowchart of FIG. 25 in the laser welding method according to the fourth embodiment is completed. FIG. 27 is an exemplary schematic cross-sectional view of an object to be processed at a stage at which S16 of the flowchart of FIG. 25 in the laser welding method according to the fourth embodiment is completed. FIG. 28 is an exemplary schematic cross-sectional view of the object to be processed at the stage where step S17 in the flowchart of FIG. 25 in the laser welding method according to the fourth embodiment is completed.

[0011] 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.

[0012] 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.

[0013] 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 approximately perpendicular to each other. The Z direction is approximately vertically upward, and the X direction and Y direction are approximately horizontal. For simplicity, the thickness of the metal foil 12 is depicted in each figure as being thicker than it actually is. The opposite direction of each direction may also be referred to as the negative direction.

[0014] In this specification, ordinal numbers are given for convenience to distinguish between steps, positions, laser beams, times, etc., and do not limit the priority or order.

[0015] [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 laser devices 111 and 112, an optical head 120, optical fibers 131 and 132, and a movement mechanism 140. The joining device 100 can laser weld a workpiece W by irradiating it with laser light L. The joining device 100 is an example of a laser welding device.

[0016] 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.

[0017] The optical fibers 131 and 132 optically connect the laser devices 111 and 112 to the optical head 120. The optical fibers 131 and 132 guide the laser light output from the laser devices 111 and 112 to the optical head 120, respectively.

[0018] The optical head 120 is an optical device that irradiates the laser light input from the laser devices 111 and 112 onto the workpiece W. 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.

[0019] 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.

[0020] 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 .

[0021] 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.

[0022] 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 change the irradiation position of the laser light L on the surface Wa of the workpiece W or scan the laser light L by changing the output direction of the laser light L while irradiating the laser light L. The surface Wa is an example of a front surface. 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.

[0023] 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.

[0024] The workpiece W has a metal member 11 and a plurality of stacked metal foils 12, i.e., a laminate 16. The metal member 11 is, for example, a plate-like member that extends across the Z direction at the portion to be welded and its surrounding area. The laminate 16 has a plurality of metal foils 12 stacked in the Z direction in an arrangement that intersects the Z direction at the portion to be welded and its surrounding area. The Z direction is an example of a stacking direction of the plurality of metal foils 12. The Z direction is also an example of a thickness direction of the metal member 11 and the metal foils 12.

[0025] In this embodiment, 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 Z direction is an example of a stacking direction between the metal member 11 and the multiple metal foils 12 (laminate 16). The surface located at the end of the laminate 16 in the Z direction is the surface Wa of the workpiece W, and the surface located at the end of the metal member 11 in the opposite direction in the Z direction is the surface Wb of the workpiece W. The laser light L is output from the optical head 120 substantially in the opposite direction of the Z direction and irradiated onto the surface Wa. By operation of the galvanometer scanner 126, the spot of the laser light L scans the surface Wa.

[0026] The moving mechanism 140 can move the workpiece W and the optical head 120 relatively. By operating the moving mechanism 140, it is possible to change the irradiation position of the laser light L on the surface Wa of the workpiece W or to scan the laser light L. That is, changing the irradiation position of the laser light L on the surface Wa or scanning the laser light L may be achieved by operating the galvano scanner 126 alone, by operating the moving mechanism 140 alone, or by a combination of operations of both the moving mechanism 140 and the galvano scanner 126.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] [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).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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 reduced, and the metal foil 12 can be made less likely to stretch or break.

[0039] When the spot S of the laser beam L scans 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 of the spot S2 be 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, resulting in reduced spatter and void generation and less stretching or tearing of the metal foil 12.

[0040] 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 from the spot S2 in the scanning direction.

[0041] The diameter of the spots S1 and S2 on the surface Wa is 1 / e 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.

[0042] [Laser Welding Method] FIG. 5 is a flowchart showing an example of the procedure of a laser welding method for a workpiece W using the joining device 100. First, in the joining device 100, a metal member 11 and a laminate 16 as the workpiece W are set on the stage 101 and the pressing member 102 (see FIG. 1 ) (S11). As shown in FIG. 1 , the metal member 11 and the laminate 16 are stacked in the Z direction, with the metal foil 12 located at the end of the laminate 16 in the Z direction facing the optical head 120, and the metal member 11 is located on the opposite side of the laminate 16 from the optical head 120. The stage 101 and the pressing member 102 sandwich and support the metal member 11 and the laminate 16 in the Z direction in the state shown in FIG. 1 . In this case, the surface of the metal foil 12 located at the end of the laminate 16 in the Z direction facing the Z direction becomes the surface Wa of the workpiece W. S11 is an example of a first step. The stage 101 and the pressing member 102 are an example of a support device. The supporting device and the manner in which the supporting device supports the workpiece W are not limited to the example shown in FIG.

[0043] Next, a laser beam L is irradiated from the optical head 120 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, thereby forming a first weld 14F that joins the laminate 16 and the metal member 11. As shown in FIG. 1 , the first weld 14F is formed so as to penetrate the multiple metal foils 12 in the Z direction and to be present within the metal member 11. The multiple metal foils 12 and the metal member 11 are joined by this first weld 14F (S12). S12 is an example of a second step. The first weld 14F is an example of a weld 14.

[0044] [Point Irradiation (Fixed-Point Irradiation)] Figure 6 is a plan view of a metal joined body 10A (10) obtained by the laser welding method of this embodiment. In this embodiment, in S12, as shown in Figure 6, point irradiation with laser light L is performed sequentially at multiple irradiation reference positions Pi (i = 1, 2, ..., n, where i and n are positive integers, i < n) arranged at predetermined intervals on the surface Wa. Point irradiation refers to irradiation of an area with laser light L having each irradiation reference position Pi as its approximate center (e.g., geometric center). The molten pool formed by irradiation at the irradiation reference position Pi, i.e., the weld 14, is larger than the irradiation area in plan view. Note that Figure 6 illustrates an example in which the shape of the irradiation area in point irradiation is circular, but the shape of the irradiation area is not limited to circular.

[0045] As shown in FIG. 6 , the irradiation reference position Pi at which point irradiation is performed moves sequentially along the direction MD, for example, from P1 to Pn. In this case, the irradiation reference position Pi-1 for the previous point irradiation is adjacent to the irradiation reference position Pi for the current point irradiation in the opposite direction of the direction MD, and the irradiation reference position Pi+1 for the next point irradiation is adjacent to the direction MD. The direction MD may also be referred to as the movement direction. Note that the spacing between two adjacent irradiation reference positions Pi is constant in the example of FIG. 6 , but is not limited to this and may vary depending on the location. Furthermore, although the multiple irradiation reference positions Pi are arranged in a straight line in the example of FIG. 6 , this is not limited to this and may be arranged in a curved or bent line, for example.

[0046] In this embodiment, in each point irradiation, the center C (see FIG. 4) of the spot S of the laser light L is fixed at the irradiation reference position Pi for a predetermined time. Such irradiation at the irradiation reference position Pi can also be referred to as fixed-point irradiation.

[0047] FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6 . As shown in FIG. 7 , the first welded portion 14F has a continuous portion 14a connected in the direction MD and multiple independent portions 14b spaced apart in the direction MD. The continuous portion 14a is located near the surface Wa, i.e., at a relatively shallow position, while the independent portions 14b extend from the continuous portion 14a to a position farther from the surface Wa, i.e., a relatively deep position. The portions of the continuous portion 14a located between the multiple reference irradiation positions Pi are the portions where a molten pool is formed by thermal energy imparted by the irradiated laser beam L and conducted within the workpiece W, and where keyholes do not form in the molten pool. On the other hand, the portions of the continuous portion 14a located at the reference irradiation positions Pi and the independent portions 14b are the portions where keyholes form in the molten pool formed primarily by the energy of the first laser beam. The continuous portion 14a is formed within the laminate 16, and the independent portion 14b penetrates the laminate 16 and extends into the metal member 11. The first welded portion 14F, which includes the continuous portion 14a and the plurality of independent portions 14b, penetrates the laminate 16 in this form and is present within the metal member 11.

[0048] FIG. 8 is an X-ray transmission image of an example of the metal bonded body 10A (10) of this embodiment (an example corresponding to FIGS. 6 and 7 ). This image is an image of X-rays transmitted in the Z direction or in the direction opposite to the Z direction. In this image, higher brightness, i.e., whiter color, indicates a higher air content in the Z direction. The image in FIG. 8 shows three regions A1 to A3 with different air contents. In FIG. 8 , region A1 approximately corresponds to the independent portion 14b of the first welded portion 14F, region A2 approximately corresponds to the boundary between the independent portion 14b and the surrounding base material, and region A3 approximately corresponds to the base material. Furthermore, FIG. 9 is an X-ray transmission image of a metal bonded body of a reference example in which point irradiation was not performed and the spot S of the laser light L was scanned along the direction SD. The image in FIG. 9 is an image of X-rays transmitted in the Z direction or in the direction opposite to the Z direction, as in FIG. 8 . Region A3 in FIG. 9 approximately corresponds to the base material, and region A4 approximately corresponds to the portion where the weld was formed. White areas A41 are randomly included within area A4. The inventors' investigation revealed that these areas A41 correspond to voids remaining in the weld.

[0049] 8 and 9 , it was found that sequential point-by-point irradiation of the laser beam L at multiple irradiation reference positions Pi arranged at a predetermined interval on the surface Wa, as in this embodiment, can reduce the occurrence of voids compared to scanning the surface Wa with the laser beam spot S. When scanning the laser beam spot S, the molten pool begins to solidify sequentially from the rear in the scanning direction, and it is presumed that voids generated due to the formation of keyholes may not completely escape from the molten pool and may remain. In contrast, with the point-by-point irradiation of this embodiment, the molten pool is kept at the irradiation reference position Pi for a predetermined time, maintaining the molten state of the molten pool, i.e., a state in which voids can escape, which is presumed to facilitate the void escape.

[0050] As described above, the first welded portion 14F of this embodiment has a surface Wa and a continuous portion 14a connected in the direction MD near the surface Wa. If the first welded portion 14F only had a plurality of independent portions 14b, a boundary between the independent portions 14b and the base material would be formed between adjacent irradiation reference positions Pi, resulting in a larger boundary area compared to when the first welded portion 14F had a continuous portion 14a. Strength and conductivity are more likely to decrease at the boundary between the welded portion and the base material than in other portions. Therefore, the first welded portion 14F can have higher strength and conductivity due to the continuous portion 14a compared to when the first welded portion 14F only had the independent portions 14b.

[0051] FIG. 10 is a timing chart showing an example of changes over time in the power of the laser beam and the irradiation target position. The irradiation target position Pt is the position that corresponds to the center C (see FIG. 4) of the spot S of the laser beam L when the laser beam L is output from the optical head 120. The irradiation target position Pt moves on the surface Wa by the operation of at least one of the galvanometer scanner 126 and the moving mechanism 140. When the irradiation target position Pt is at an irradiation reference position (Pi-1, Pi, Pi+1), the laser beam L is irradiated at a predetermined timing. In the example of FIG. 10, the irradiation start times ts at the multiple irradiation reference positions (Pi-1, Pi, Pi+1) are set at a fixed time interval T1 (e.g., 5 ms). The irradiation time T2 from the irradiation start time ts to the irradiation end time te at each of the irradiation reference positions (Pi-1, Pi, Pi+1) is set to a fixed time (e.g., 2 ms). The time T3 from the irradiation end time te to the next irradiation start time ts is set to a fixed time (e.g., 3 ms). Furthermore, the operation of at least one of the galvano scanner 126 and the movement mechanism 140 is controlled so that the irradiation target position Pt is positioned at the irradiation reference position (Pi-1, Pi, Pi+1) at a time tp before the irradiation start time ts. The timing and speed of movement of the irradiation target position Pt between the irradiation reference positions (Pi-1, Pi, Pi+1) can be changed as appropriate.

[0052] As shown in FIG. 10 , in this embodiment, during each irradiation time T2, the first laser beam L1 is irradiated in pulses, and the second laser beam L2 is irradiated continuously. Adjusting parameters of the first laser beam L1, such as the maximum value PIh and minimum value PIl of each pulse during output, the pulse frequency, the duty ratio, and the diameter d1 (see FIG. 4 ), can change the depth and width of the first welded zone 14F and further stabilize the molten pool, thereby reducing the occurrence of voids. Furthermore, to ensure that the molten pool extends in the depth direction (opposite the Z direction) at the irradiation reference position Pi, these parameters of the first laser beam L1 are set to form a keyhole. For example, the maximum value PIh is set to 250 W or more and 300 W or less, the minimum value PIl is set to 150 W or more and 200 W or less, the pulse frequency is set to 5 kHz, the duty ratio is set to 50%, and the diameter d1 is set to 22 μm, but this is not limiting. On the other hand, by adjusting parameters such as the maximum power PBh and diameter d2 (see FIG. 4 ) of the second laser beam L2, the molten pool can be further stabilized and voids can be reduced. As an example, the maximum power PBh is set to 400 W or more and 500 W or less, and the diameter d2 is set to 600 μm, but these are not limited thereto. In this embodiment, as shown in FIG. 10 , the laser beam L is not irradiated between adjacent irradiation reference positions. However, this is not limited thereto, and the laser beam L may be irradiated between adjacent irradiation reference positions under conditions that do not result in keyhole formation. For example, only the second laser beam L2 may be irradiated between adjacent irradiation reference positions, or the first laser beam L1 may be irradiated at a low power that does not result in keyhole formation. If the irradiation target position Pt were to move under conditions that would result in keyhole formation between adjacent irradiation reference positions, the laser beam L would scan the surface Wa, resulting in the formation of a molten pool containing a keyhole. In this case, there is a risk that voids occurring in the molten pool would not be removed. If the conditions are such that no keyholes are formed, such a problem is unlikely to occur.

[0053] 11 is a plan view showing the irradiation areas (spots S) of the laser light L at adjacent irradiation reference positions Pi-1 and Pi. The spot Sp(S) at the previous irradiation reference position Pi-1 includes a spot S1p of the first laser light L1 and a spot S2p of the second laser light L2. Furthermore, the spot Sc(S) at the current irradiation reference position Pi includes a spot S1c of the first laser light L1 and a spot S2c of the second laser light L2. As shown in FIG. 11 , in this embodiment, the spot S1c of the first laser light L1 at the current irradiation reference position Pi (first irradiation reference position) and the spot S2p of the second laser light L2 at the previous irradiation reference position Pi-1 (second irradiation reference position) overlap. The overlap of the spot S1c and the spot S2p in this manner means that, in irradiation at the current irradiation reference position Pi, the first laser beam L1 is irradiated onto the region (spot S2p) that was heated by the second laser beam L2 at the previous irradiation reference position Pi-1. If a sudden temperature rise occurs in the region irradiated with the first laser beam L1, the movement of the molten pool becomes more intense, making it more likely that voids will occur. This phenomenon can occur if the spot S1c is irradiated onto a region that has not been heated in advance. In this regard, according to the present embodiment, the first laser beam L1 is irradiated onto a region that has been heated in advance, thereby reducing the sudden temperature rise of the molten pool corresponding to the spot S1c, and thus the movement of the molten pool, and thus reducing the occurrence of voids.

[0054] [Point-like Irradiation (Wobbling Irradiation)] FIG. 12 is a plan view showing the irradiation area (spot S) of the laser light L when wobbling is performed at the irradiation reference position Pi. As shown in FIG. 12 , at each irradiation reference position Pi, the point-like irradiation may be irradiation of the laser light L that revolves around the irradiation reference position Pi. In this case, the center C of the spot S moves, for example, along a circumferential movement path MP centered on the irradiation reference position Pi from a start point Ps to an end point Pe at a substantially constant speed (a speed in the tangential direction of the movement path MP) or angular velocity. The start point Ps is the position of the center C of the spot S at the irradiation start time ts in FIG. 10 , and the end point Pe is the position of the center C of the spot S at the irradiation end time te in FIG. 10 . In this case, a first welded portion 14F similar to that in the case of fixed-point irradiation shown in FIGS. 6 and 7 can be formed, and the same effect as that in the case of fixed-point irradiation can be obtained. By performing irradiation with such wobbling at each irradiation reference position Pi, the depth and width of the first weld 14F can be changed by adjusting parameters such as the wobbling radius (radius of the movement path MP) and frequency (number of revolutions per second), and the molten pool can be further stabilized to reduce the occurrence of voids. This type of irradiation may also be referred to as wobbling irradiation. As an example, the wobbling radius is set to 11 μm and the frequency is set to 500 Hz, but this is not limiting. In the example of FIG. 12 , the start point Ps and the end point Pe are located at approximately the same position, but they may also be located at different positions. Also, in the example of FIG. 12 , the center C of the spot S moves along a circumferential movement path. However, the movement path may be semicircular, figure-eight shaped, elliptical, linear, or other.

[0055] [Spacing of Irradiation Reference Positions] FIG. 13 is a plan view of a metal joined body 10B (10) in an example in which the irradiation reference positions Pi are narrower than those in FIG. 6 . FIG. 14 is a cross-sectional view taken along the line XIII-XIII of FIG. 13 . When the spacing between the multiple irradiation reference positions Pi is narrowed as shown in FIG. 13 , a first welded zone 14F can be formed, as shown in FIG. 14 , which has only a continuous portion 14a and no independent portion 14b (see FIG. 7 ). FIG. 15 is an X-ray transmission image of a metal joined body 10B (10) corresponding to the example of FIGS. 13 and 14 . The image in FIG. 15 was captured under substantially the same conditions as in FIG. 8 . In this example, compared to the example in FIG. 8 , the region A2 approximately corresponding to the boundary between the first welded zone 14F and the base metal is connected and narrower overall, resulting in higher strength and conductivity of the first welded zone 14F. 16 is an X-ray transmission image of the metal bonded body 10 in an example in which the irradiation reference position Pi is narrower than in the cases of FIGS. 6 and 13. The image of FIG. 16 was captured under substantially the same conditions as in FIG. 8. In this example, compared to the cases of FIGS. 8 and 15, the region A2 is less curved and therefore narrower overall, resulting in higher strength and conductivity of the first welded zone 14F. By narrowing the spacing between the multiple irradiation reference positions Pi in this way, in the first welded zone 14F, the continuous portion 14a that is continuous in the direction MD penetrates the laminate 16 rather than only in the vicinity of the surface Wa. In other words, the portion that penetrates the laminate 16 is continuous in the direction MD, so that the first welded zone 14F can be formed with higher joint strength.

[0056] As described above, in this embodiment, point irradiation is sequentially performed at multiple irradiation reference positions Pi arranged at intervals on the surface Wa, either while stationary or while rotating around the irradiation reference positions Pi. This method facilitates the removal of voids in the molten pool during point irradiation at each irradiation reference position Pi, thereby reducing the number of voids remaining in the first welded portion 14F. Furthermore, in this embodiment, the first welded portion 14F is formed so as to have a continuous portion 14a that is connected in the direction MD of the multiple irradiation reference positions Pi at least on the surface Wa and in the vicinity of the surface Wa. This reduces the boundary between the first welded portion 14F and the base metal compared to when the first welded portion 14F has only independent portions 14b, thereby resulting in a welded portion 14 and a metal joined body 10 with higher strength and electrical conductivity.

[0057] Furthermore, in this embodiment, the first welded portion 14F can be formed so that the portion that penetrates the laminate 16 (the plurality of metal foils 12) is continuous in the direction MD in which the plurality of irradiation reference positions Pi are arranged, in other words, so that the continuous portion 14a penetrates the laminate 16. According to such a method, the boundary between the first welded portion 14F and the base material can be reduced, and therefore, a welded portion 14 and a metal joined body 10 having even higher strength and conductivity can be obtained.

[0058] 17 is a flowchart showing some steps of a method for laser welding an object W to be processed by joining device 100. As shown in Fig. 17 , in this embodiment, S12 in the first embodiment is replaced with S121 and S122. Note that the laser welding method of this embodiment includes S11, similar to that of the first embodiment, before S12.

[0059] In S121, 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 laminate 16 and the metal member 11. In S121, point irradiation is performed in the same manner as in the first embodiment. S121 is an example of the second step.

[0060] 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 and form an excessively thin portion at the portion in contact with the welded portion. S121 is performed under conditions that basically prevent or make it difficult for such gaps or thin portions to form, 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 occur depending on the individual pieces.

[0061] Therefore, in this embodiment, in S122 after S121, laser light L is irradiated toward the vicinity of the boundary B between the first welded portion 14F and the metal foil 12 to form the second welded portion 14R (S122). FIG. 18 is a cross-sectional view of the workpiece W at an intermediate stage of S122, and FIG. 19 is a cross-sectional view of the workpiece W at the end of S122. If a gap exists between the first welded portion 14F and the metal foil 12 in S121, the portion adjacent to the gap melts and solidifies in S122 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 in S121, the thin portion and its vicinity melt and solidify in S122 to form the second welded portion 14R. According to this embodiment, S122 can more reliably prevent gaps and excessively thin portions from occurring. S122 can be said to be a process for repairing or improving the bonding state in S121. In the example of Fig. 18, the laser light L is irradiated while being scanned on the surface Wa in the direction SD, but this is not limited to this and fixed-point irradiation may also be used. In this case, the fixed-point irradiation is performed on multiple points on the surface Wa. S122 is an example of a third process.

[0062] In addition, in S122, as in the example of FIG. 18, the laser light L may be irradiated multiple times to form the second welded portion 14R at multiple locations.

[0063] Furthermore, in S122, 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.

[0064] 19 is a cross-sectional view of the object 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 laser light L in S122. In the example of Fig. 19, second weld 14R2 is formed by again irradiating laser light L toward the vicinity of boundary B between first weld 14F and metal foil 12 on surface Wa after second weld 14R1 shown in Fig. 18 has been formed, causing first weld 14F, second weld 14R1, and a portion of metal foil 12 to melt, cool, and solidify.

[0065] As shown in Figure 19, the second welded portion 14R1 and the second welded portion 14R2 have different positions in the Z direction and the direction intersecting with the direction SD, in other words, the direction along the surface Wa or the direction intersecting with the stacking direction of the metal foil 12, and also have different positions in the Z direction, in other words, the positions in the stacking direction of the metal foil 12.

[0066] The position of the second welded portion 14R in the direction 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 S122, the laser light L travels in the opposite direction to the Z direction while its energy is absorbed by the metal foil 12. Therefore, as shown in Figures 18 and 19, 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 of the width direction of the first welded portion 14F (in this case, the center line CL) 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 18, 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.

[0067] 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.

[0068] 19 , the end portion of the second welded portion 14R1 that is located in the opposite direction in the Z direction as the bottom is positioned farther from the surface Wa than the end portion of the second welded portion 14R2 that is located in the opposite direction in the Z direction as the bottom, in accordance with the shape of the boundary B. In other words, the second welded portion 14R2 is positioned further rearward in the irradiation direction of the laser light L than the second welded portion 14R1.

[0069] 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.

[0070] In the example of FIG. 19 , second welds 14R1 and 14R2 are formed at four locations by four irradiations of laser light L. However, this is not limited to this, and various specifications, such as the number of second welds 14R (i.e., the number of irradiations of laser light L in S132), as well as specifications such as their positions, widths, depths, and lengths, can be set. In the example of FIG. 17 , two stages of second welds 14R1 and 14R2 are formed at different positions in the stacking 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. 19 , second weld 14R2, which is located further rearward in the irradiation direction than second weld 14R1, 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.

[0071] As shown in FIG. 19 , according to this embodiment, a metal joined body 10D (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. 19 , 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 an image 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. 18 , a metal joined body 10C (10) is formed by joining the stack 16 and the metal member 11 together using the weld 14.

[0072] Furthermore, in S122, the laser beam L may be irradiated in a direction inclined relative to the irradiation direction of the laser beam in S121, i.e., the opposite direction to the Z direction. FIG. 20 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 is often inclined so as to approach 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 relative to the opposite direction to the 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. Furthermore, 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 relative to the opposite direction to the 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. 20, the welded portion 14 joins the laminate 16 and the metal member 11 to form a metal joined body 10E (10).

[0073] [Conditions for performing S122] 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 S122 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 S121 and S122. By scanning, first welded zone 14F and second welded zone 14R can be formed over a wider area in a shorter time.

[0074] 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 S121 and S122, 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 S121, 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 S122, 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 S122, 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].

[0075] Experimental studies have revealed that it is preferable to irradiate the laser light L under the following conditions (1) to (3).

[0076] (1) The scanning speed in S122 is set to be faster than the scanning speed in S121. (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 S122 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 S121. By using the above (1) and (2), the width of the second welded portion 14R in the direction perpendicular to the scanning direction and the Z direction can be made narrower than the width of the first welded portion 14F in the direction perpendicular to the 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 when the laser light L is irradiated multiple times in S122, the scanning speed may be changed for each irradiation to form the second welded portion 14R. (3) The power of the laser light L in S122 is set to be lower than the power of the laser light L in S121. This allows the second welded portion 14R to be formed to an appropriate depth in S122.

[0077] According to this embodiment, in step S121, point irradiation is performed in the same manner as in the first embodiment, and therefore, the same effects as in the first embodiment can be obtained. Furthermore, by forming the second welded portion 14R, it is possible to configure the welded portion 14 and the metal joined body 10 having higher strength and conductivity.

[0078] 21 is an exemplary schematic configuration diagram of a laser welding system 1000 according to a third embodiment. As shown in FIG. 21 , 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 16 a. The compression device 200 will be described later.

[0079] 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 form 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. By performing each process at different locations, i.e., by different devices, it becomes easier to improve the processing accuracy of each process.

[0080] 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.

[0081] 22 is a flowchart showing an example of the steps of a method 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 (S13). S13 is an example of a fourth step, and may also be referred to as a pre-compression step.

[0082] Next, in the joining device 100, the laminate 16 on which the compressed portion 16a is formed and the metal member 11 are set in a predetermined state on a supporting device (S11).

[0083] Next, 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 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 (S12). S12 is the same as in the first or second embodiment. S12 includes a second step.

[0084] [Pre-compression Process] FIG. 23 is a side view illustrating step S13 performed in the compression device 200. As shown in FIG. 23, in step S13, a plurality of metal foils 12 are first stacked on a surface 210a of a first member 210 to form a laminate 16 (S131). 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 for the plurality of metal foils 12 in the laminate 16, and is also an example of a stacking direction for overlapping the first member 210 and the laminate 16.

[0085] 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 (S132). Here, the first member 210 is provided with a protruding portion 222 that protrudes 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 and protrudes toward the first member 210 substantially along the outer surface 222a is formed in the laminate 16.

[0086] Through extensive research, the inventors have found that when forming a weld 14 (see FIG. 24 ) penetrating multiple metal foils 12 in S12 (see FIG. 22 ), 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 the presence of a gap between adjacent metal foils 12 at or near the site irradiated with laser light inhibits the conduction of heat generated by the laser light irradiation between the adjacent metal foils 12, thereby making it easier for heat to concentrate at the site irradiated with laser light. In this regard, in the present embodiment, by forming the compressed portion 16 a, the gap between adjacent metal foils 12 in the compressed portion 16 a can be made smaller (preferably, the gap is eliminated or made extremely small) than before compression. Therefore, by welding multiple metal foils 12, i.e., the laminate 16, at the compressed portion 16 a, stretching or tearing of the metal foils 12 can be suppressed.

[0087] 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 protrusion height of the protrusion 222 is formed into a cylindrical shape. This configuration can prevent the metal foil 12 from stretching or breaking in S132 (S13). The direction opposite to the Z direction is an example of a protrusion direction of the protrusion 222, and the outer surface 222a is an example of a convex curved surface that convex toward the first member 210 in S132.

[0088] In addition, in S132, 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.

[0089] 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 applied in S132, thereby reducing the pressing force acting on the metal foil 12. For this reason, in S132, 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 S11, S12, and the metal joined body 10F(10) (see FIG. 24).

[0090] Furthermore, in S132, it is preferable that adjacent metal foils 12 are partially joined together in the compressed portion 16a because joining adjacent metal foils 12 together prevents the gap between adjacent metal foils 12 from widening when the pressure from the protruding portion 222 is released, and prevents the metal foils 12 from stretching or breaking when returning to their original shape.

[0091] 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 S132. In other words, in S132, 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.

[0092] Furthermore, as shown in FIG. 21, when transporting the laminate 16 from the compression device 200 to the joining device 100, if multiple metal foils 12 are integrated by S132, the metal foils 12 will not fall apart, which has the advantage of making transportation easier.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 23 , in step S132, it is preferable to restrict movement of the laminate 16 in the Z direction by the surface 221a of the plate-like portion 221 located on the opposite side of the first member 210 relative 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.

[0097] 24 is a side view illustrating steps S11 and S12 performed in the bonding apparatus 100. As shown in Fig. 24, 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).

[0098] In S11, the workpiece W, which is made by stacking the metal member 11 and the laminate 16, is supported by the stage 101 and the pressing member 102 in the Z direction while being sandwiched between the stage 101 and the pressing member 102. The stage 101 and the pressing member 102 are an example of a supporting device.

[0099] 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.

[0100] 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.

[0101] 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 (S12). As described above, S12 is the same as in the first or second embodiment. In this example, 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.

[0102] According to this embodiment, by performing step S12 similar to that of the first or second embodiment, the same effects as those of the first or second embodiment can be achieved. Furthermore, by performing the pre-compression step, gaps between adjacent metal foils 12 in the compressed portion 16a can be eliminated or minimized. Therefore, welding multiple metal foils 12, i.e., the laminate 16, in the compressed portion 16a can prevent the metal foils 12 from stretching or breaking. Furthermore, the inventors' extensive research has revealed that the presence or absence of point irradiation makes a significant difference when pre-compression is performed. This is presumably because, when gaps between adjacent metal foils 12 are eliminated or minimized by pre-compression, voids are less likely to escape from the molten pool and are more likely to remain.

[0103] [Fourth embodiment] Fig. 25 is a flowchart showing an example of the procedure of a laser welding method according to a fourth embodiment. As shown in Fig. 25, in this embodiment, first, in steps S14 and S15, a laminate 16, i.e., a plurality of metal foils 12, are welded together. Fig. 26 is a cross-sectional view of the workpiece W at the stage when S15 is completed.

[0104] First, in the joining apparatus 100, the laminate 16 as the workpiece W is set on the stage 101 and pressing member 102 similar to those shown in FIG. 1 so that the laser beam L is irradiated onto the surface Wa (see FIG. 26 ) of the metal foil 12 located at the end in the Z direction (S14). Next, in the joining apparatus 100, point-like irradiation is sequentially performed at multiple irradiation reference positions Pi to form a first weld 14F that penetrates the laminate 16 and integrates the multiple metal foils 12 (S15), as in the first embodiment. S14 is an example of a fifth step, and S15 is an example of a sixth step. Note that in this embodiment, the first weld 14F has only the continuous portion 14a, as in FIG. 14 , but this is not limited thereto. The first weld 14F may have both the continuous portion 14a and the independent portion 14b, as in FIG. 7 . Furthermore, in S15, a step similar to S122 of the second embodiment may be performed to form a second weld 14R (see FIGS. 18 to 20 ).

[0105] Next, as shown in FIG. 25, in steps S16 and S17, the metal member 11 and the integrated laminate 16 (plurality of metal foils 12) are welded together.

[0106] 27 is a cross-sectional view of the workpiece W at the stage when S16 is completed. As shown in Fig. 27, the workpiece W has metal members 11 stacked in the Z direction and a laminate 16 formed by integrating a plurality of metal foils 12 in S15. Here, the workpiece W is set, for example, on a stage 101 and a pressing member 102 similar to those in Fig. 1 so that the laser light L is irradiated onto a surface Wa of the metal foil 12 located at an end of the laminate 16 in the Z direction (S16).

[0107] Next, a laser beam L is irradiated onto an area of ​​the surface Wa of the workpiece W that at least partially includes the first weld 14F. The molten pool formed by the irradiation of the laser beam L is cooled and solidified, thereby forming a third weld 14T (S17). In S17, the laser beam L is scanned in the same direction SD as the direction MD in which the first weld 14F extends. As shown in FIG. 28 , the third weld 14T formed in S17 penetrates the first weld 14F and reaches the metal member 11. That is, the third weld 14T welds the first weld 14F and the metal member 11. As a result, a metal joined body 10G (10) is formed in which the laminate 16 and the metal member 11 are joined by the weld 14 including the first weld 14F and the third weld 14T. S17 is an example of a seventh step.

[0108] In S17, the third welded zone 14T is adjacent to the portion where the first welded zone 14F melted and solidified. Because the first welded zone 14F is a portion where multiple metal foils 12 were integrated into a mass in S16, multiple metal foils 12 are not present within the first welded zone 14F. Therefore, when the third welded zone 14T is formed in S17, the metal foil 12 does not break or stretch at the portion where the first welded zone 14F melts to become the third welded zone 14T. Therefore, as in the present embodiment, in S17, laser light L is irradiated onto an area of ​​the surface Wa of the workpiece W that at least partially includes the first welded zone 14F, and at least a portion of the first welded zone 14F is melted and solidified to form the third welded zone 14T, thereby preventing breakage and excessive stretching of the metal foil 12.

[0109] Furthermore, during welding of the metal foil 12, the metal foil 12 may tear at the boundary between the weld and the metal foil 12, forming a gap, or the metal foil 12 may stretch at the contact point with the weld, forming an excessively thin portion. This is thought to be due to the volume reduction of the weld as it cools from a molten state and solidifies, causing the metal foil 12 to be pulled away from the weld. Therefore, as shown in FIG. 28 , the third weld 14T is preferably formed in a state separated from the plurality of metal foils 12 so as to prevent the formation of a boundary between the third weld 14T (the molten pool) and the metal foil 12. In this embodiment, the third weld 14T preferably penetrates the first weld 14F while being separated from the boundary B (connection portion) between the first weld 14F and the plurality of metal foils 12. From this perspective, the first weld 14F is preferably formed to have a size (volume) and a width (area) on the surface Wa that can more reliably surround the third weld 14T.

[0110] According to this embodiment, the same effect as in the first embodiment can be obtained by performing point irradiation similar to that in the first embodiment on the laminate 16 as the processing object W. Furthermore, according to this embodiment, a first welded portion 14F is formed to weld together the plurality of metal foils 12, and then a third welded portion 14T is formed to weld together the first welded portion 14F and the metal member 11, thereby making it possible to obtain a suitable metal joined body 10 more easily and reliably.

[0111] 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.

[0112] DESCRIPTION OF SYMBOLS 1... Battery (electrical appliance) 10, 10A to 10G... Metal joint 11, 11m, 11p... Metal member 11a... Surface 12... Metal foil 13m... Negative electrode material 13p... Positive electrode material 14... Welded portion 14a... Continuous portion 14b... Independent portion 14F... First welded portion (welded portion) 14R, 14R1, 14R2... Second welded portion (welded portion) 14T... Third welded portion (welded portion) 15... Separator 16... Laminated body 16a... Compressed portion 16b... End 20... Sheathing material 20a... Storage chamber 100... Bonding device 101... Stage (support device) 102... Pressing member (support device) 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...Mirrors 131, 132...Optical fiber 140...Moving mechanism 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 A1 to A4, A41...Area B...Boundary C...Center CL...Center line d, d1, d2...Diameter Hp...Predetermined height L...Laser light L1...First laser light L2...Second laser light MD...Direction PBh...Maximum value Pe...End point Pi...Irradiation reference position PIh...Maximum value PIl...Minimum value Ps...Start point Pt...Irradiation target position S, S1, S1c, S1p, S2, S2c, S2p, Sc, Sp...Spot S11...Step (first step) S12...Step (second step) S121...Step (second step) S122...Step (third step) S13...Step (fourth step) S131...Step S132...Step S14...Step (fifth step) S15...Process (sixth process) S16...Process S17...Process (seventh process) S1a, S2a...Outer edge SD...Direction tc...Thickness te...Irradiation end time tp...Time ts...Irradiation start time T1...Time interval T2...Irradiation time T3...Time W...Processing target Wa...Surface (surface) Wb...Surface Wp...Predetermined width X...Direction Y…direction Z…direction

Claims

1. A laser welding method comprising: a first step of setting an object to be processed, including a metal member and a plurality of laminated metal foils, on a supporting device in a state in which a laser beam from a laser welding device is irradiated onto a surface of the object to be processed; and a second step of irradiating the surface with the laser beam to form a weld that is present within the metal member and penetrates the plurality of metal foils in the lamination direction, thereby joining the metal member and the plurality of metal foils, wherein in the second step, point-like irradiation is performed sequentially at a plurality of irradiation reference positions lined up at intervals on the surface, while being stopped or while rotating around the irradiation reference positions, thereby forming the weld so that the weld is connected at least on the surface in the direction in which the plurality of irradiation reference positions are lined up.

2. The laser welding method according to claim 1, wherein in the second step, the weld is formed so that the portion of the weld that penetrates the multiple metal foils is continuous in the direction in which the multiple irradiation reference positions are arranged.

3. The laser welding method according to claim 1, wherein in the second step, a keyhole is formed when the laser light is irradiated at each of the irradiation reference positions where the point irradiation is performed, and no keyhole is formed at a position where the point irradiation is not performed.

4. A laser welding method as described in claim 1, wherein in the second step, the laser light includes a first laser light and a second laser light having a shorter wavelength than the first laser light.

5. A laser welding method as described in claim 4, wherein in the second step, the laser light is irradiated so that an irradiation area on the surface of the first laser light at a first irradiation reference position as the irradiation reference position overlaps with an irradiation area on the surface of the second laser light at a second irradiation reference position as the irradiation reference position immediately before the first irradiation reference position.

6. A laser welding method as described in claim 1, comprising a third step, which is performed after the second step, of melting and solidifying an adjacent portion to the gap between the welded portion and the metal foil, or a connection portion between the welded portion and the metal foil, by irradiating the laser light.

7. The laser welding method according to claim 1, further comprising a fourth step of compressing the laminated metal foils in a lamination direction before the first step.

8. The laser welding method according to claim 4, wherein at least the first laser beam is irradiated in a pulsed manner.

9. The laser welding method according to claim 4, wherein the first laser beam is irradiated in a pulsed manner and the second laser beam is irradiated continuously.

10. A laser welding method comprising: a fifth step of setting a plurality of stacked metal foils on a supporting device in a state in which a laser beam from a laser welding device is irradiated onto the surfaces of the metal foils located at the ends of the plurality of metal foils in the stacking direction; and a sixth step of irradiating the surface with the laser beam to form a welded portion that integrates the plurality of metal foils, wherein in the sixth step, point-like irradiation is performed sequentially at a plurality of irradiation reference positions arranged at intervals on the surface, while being stopped or while rotating around the irradiation reference positions, thereby forming the welded portion so that it is connected at least on the surface in the direction in which the plurality of irradiation reference positions are arranged.

11. A laser welding method as described in claim 10, further comprising a seventh step of irradiating a laser beam onto a surface of an object to be processed, the surface including the plurality of metal foils and the metal member integrated in the sixth step, to weld the integrated plurality of metal foils and the metal member together.

12. A laser welding device comprising: a laser light source; and an optical head which irradiates a surface of a workpiece including a metal member and a plurality of metal foils with laser light output from the laser light source to form a weld that is present within the metal member and penetrates the plurality of metal foils in a stacking direction, thereby joining the metal member and the plurality of metal foils; wherein the laser welding device sequentially performs point irradiation at a plurality of irradiation reference positions arranged at intervals on the surface, while stopped or while rotating around the irradiation reference positions, thereby forming the weld so that the weld is connected at least on the surface in the direction in which the plurality of irradiation reference positions are arranged.

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