Laser welding method

Abstract

Provided is a laser welding method for joining a laminated metal foil in which a plurality of copper-based foils are laminated and a tab plate of a copper-based material, said method comprising: a step for placing one end of the laminated metal foil on the tab plate; and a step for irradiating the one end of the laminated metal foil and the tab plate with a blue laser beam such that the blue laser beam reciprocates a plurality of times along a weld line on the tab plate along the one end of laminated metal foil, wherein the laminated metal foil and the tab plate that have been irradiated with the blue laser beam have a joining part that joins, obliquely to the surface of the tab plate, the one end of the laminated metal foil and the surface of the tab plate irradiated with the blue laser beam.

Description

Laser welding method

[0001] The present disclosure relates to laser welding methods.

[0002] Patent Document 1 discloses a method for overlapping and joining metal foils, which includes a first step of temporarily joining multiple overlapping metal foils so that adjacent metal foils are in close contact with each other, and a second step of non-contact welding the temporarily joined close contact areas.

[0003] Japanese Patent Application Publication No. 2014-140890

[0004] An object of the present disclosure is to provide a laser welding method for joining a plurality of metal foils and a metal plate.

[0005] The present disclosure provides a laser welding method for joining a laminated metal foil having a plurality of copper-based foils laminated together and a tab plate made of a copper-based material, the laser welding method comprising the steps of placing one end of the laminated metal foil on the tab plate and irradiating one end of the laminated metal foil and the tab plate with a blue laser beam so as to move back and forth multiple times along a welding line on the tab plate along one end of the laminated metal foil, wherein the laminated metal foil and the tab plate irradiated with the blue laser beam have a joint between the surface of the tab plate irradiated with the blue laser beam and the one end of the laminated metal foil, joined at an angle to the surface of the tab plate.

[0006] According to the present disclosure, regardless of deviations in the laser light irradiation position and variations in the metal foils, the spacing between adjacent metal foils in the stacking direction can be made approximately constant from the upper end side in the stacking direction near the surface of the laminated metal foil to the lower end side in the stacking direction.

[0007] 7 is a schematic diagram showing an example of the configuration of a blue laser welding system according to embodiments 1 to 3; Schematic diagram showing the A-A cross section of the laser oscillator shown in FIG. 1; Figure showing an example of a method for laser welding a laminated metal foil and a tab plate by a conventional laser welding method; Figure explaining an example of the relationship between the focal length of a blue laser beam and the occurrence of spatter; Figure showing an example of laser welding between a laminated metal foil and a tab plate at a focal position (=-2.5 mm); Figure showing an example of a result of laser welding between a laminated metal foil and a tab plate shown in FIG. 5; Figure showing an example of a method for laser welding between a laminated metal foil and a tab plate in embodiment 2; Figure showing an example of a result of laser welding between a laminated metal foil and a tab plate shown in FIG. 7; Figure showing an example of a method for laser welding between a laminated metal foil and a tab plate in a modified embodiment of embodiment 2; Figure explaining an example of a change in the amplitude of laser welding;

[0008] (Background to the present disclosure) Generally, copper-based materials, which are primarily composed of copper, have high reflectivity, high thermal conductivity, and high heat capacity, making laser welding of copper-based materials extremely difficult. Welding methods have been developed for laser welding copper-based materials, such as IR laser welding using light with wavelengths in the IR (infrared) band and ultrasonic welding. However, even with these welding methods, it is said that it remains difficult to perform high-quality laser welding on copper-based materials while shortening the takt time. Products resulting from laser welding of laminated copper-based materials are used, for example, as electrodes for secondary batteries (batteries) installed in electronic devices or autonomous vehicles. Therefore, technologies for high-quality welding of copper-based materials are inevitably attracting attention in the context of battery production. In other words, there is a demand for laser welding technologies that shorten the takt time and achieve excellent weld quality.

[0009] In the configuration of Patent Document 1, in order to join multiple sheets of metal foil together, a pair of electrodes sandwich the welding target portion of the workpiece, apply a predetermined pressure to bring the multiple sheets of metal foil into contact, and then energize the pair of electrodes to apply Joule heat to the contacting metal foils to perform a tack joining (tack joining process). However, when performing the tack joining process using electrodes and the welding process using laser welding in this way, these processes are performed in different processes using different equipment, which poses a problem of increasing the number of manufacturing processes.

[0010] Furthermore, in recent years, in the manufacture of electrodes for secondary batteries (batteries) mounted on electronic devices or self-driving cars, there has been a demand for a technique for joining the above-mentioned multiple sheets of metal foil and a metal plate made of a copper-based material by laser welding. However, when the metal foil overlap joining method described in Patent Document 1 is applied to joining the multiple sheets of metal foil and the metal plate made of a copper-based material, there is a problem that the number of manufacturing steps increases due to the addition of the above-mentioned tack joining step.

[0011] Therefore, in the following embodiments, examples of laser welding methods for joining a plurality of metal foils and a metal plate will be described.

[0012] Hereinafter, with reference to the drawings as appropriate, embodiments specifically disclosing the laser welding method according to the present disclosure will be described in detail. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0013] <Definition of Terms> In the following description, unless expressly stated otherwise, the term "laser welding" is intended to have the broadest possible meaning and includes welding, soldering, melting, joining, annealing, softening, tackifying, resurfacing, peening, heat treating, fusing, sealing, and stacking.

[0014] In the following description, unless expressly stated otherwise, the term "copper-based material" is intended to have the broadest possible meaning, and includes copper, copper materials, copper metals, materials electroplated with copper, metallic materials containing at least about 10% to 100% by weight of copper, metals and alloys containing at least about 10% to 100% by weight of copper, metals and alloys containing at least about 20% to 100% by weight of copper, metals and alloys containing at least about 50% to 100% by weight of copper, metals and alloys containing at least about 70% to 100% by weight of copper, and metals and alloys containing at least about 90% to 100% by weight of copper.

[0015] In the following description, unless expressly stated otherwise, the terms "blue laser beam" and "blue laser" have the broadest possible meaning and generally refer to a system that provides a laser beam, a laser beam, or a laser source (e.g., a diode laser) that provides or propagates a laser beam or light having a wavelength of about 400 nm to about 500 nm.

[0016] <System Configuration> First, a configuration example of blue laser welding system 100 according to the present embodiments 1 to 3 will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing a configuration example of blue laser welding system 100 according to the present embodiments 1 to 3. Figure 2 is a schematic diagram showing a cross section taken along line AA of the laser oscillator shown in Figure 1.

[0017] In the following description, the X, Y, and Z axes are defined as the directions shown in Figures 1 and 2. That is, in Figure 2, the direction in which the blue laser beam 70 travels toward the partial transmission mirror 13 is defined as the Y direction, the direction from the partial transmission mirror 13 toward the transmission fiber 40 is defined as the Z direction, and the direction perpendicular to the Y and Z directions is defined as the X direction. The Z direction coincides with the optical axis direction of the blue laser beam 70 emitted from the focusing lens unit 20 within the assembly tolerance of the optical system of the blue laser welding system 100.

[0018] As shown in Fig. 1, the blue laser welding system 100 includes a laser oscillator 10, a condenser lens unit 20, a laser head 30, a transmission fiber 40, a control unit 50, and a stage STG. The laser oscillator 10, the condenser lens unit 20, and a laser beam incident portion 44 (see Fig. 2) of the transmission fiber 40 are housed in a housing 60. In this embodiment, a laser beam (blue laser beam 70) having a blue wavelength (i.e., 400 nm to 500 nm) is used when laser welding the laminated metal foil. This is because light having a blue wavelength has the property of being highly absorbed by copper (up to approximately 65%).

[0019] The laser oscillator 10 includes multiple laser modules 11 and a beam combiner 12. While FIG. 1 illustrates four laser modules 11, the number is not limited to four and may be one. When the laser oscillator 10 is configured with one laser module 11, the configuration of the beam combiner 12 can be simplified. The laser oscillator 10 combines laser beams of different wavelengths (e.g., wavelengths of 400 nm to 500 nm, such as 400 nm, 420 nm, 440 nm, and 480 nm) emitted from the multiple laser modules 11 into a single blue laser beam 70 using the beam combiner 12. The laser oscillator 10 may also be referred to as a Direct Diode Laser (DDL) oscillator. The laser module 11 itself includes multiple laser diodes, and may be configured, for example, as a semiconductor laser array.

[0020] 2, blue laser beam 70 combined by beam combiner 12 is focused by focusing lens 21 disposed in focusing lens unit 20 and enters transmission fiber 40. By configuring laser oscillator 10 in this manner, a high-power blue laser welding system 100 with a laser beam output exceeding several kW can be obtained. Beam combiner 12 also includes a partially transmitting mirror 13 and an output light monitor 14 therein.

[0021] The partially transmitting mirror 13 is configured to deflect the blue laser beam 70 wavelength-combined in the beam combiner 12 toward the focusing lens unit 20, while transmitting a portion (e.g., 0.1%) of the blue laser beam 70.

[0022] The output light monitor 14 is disposed in the beam combiner 12 so as to receive the blue laser beam 70 that has passed through the partially transmitting mirror 13 and generate a detection signal corresponding to the light amount of the received blue laser beam 70. The laser oscillator 10 receives power from a power supply device (not shown) to perform laser oscillation.

[0023] The focusing lens unit 20 includes a focusing lens 21, a slider 22, and a reflected light monitor 23. The focusing lens 21 focuses the blue laser beam 70 at the incident end face 46 of the transmission fiber 40 to form a spot diameter smaller than the diameter of the core 41 of the transmission fiber 40. The slider 22 holds the focusing lens 21 so that it can automatically move in the Z direction in response to a control signal from the control unit 50. The slider 22 is connected to, for example, a ball screw (not shown) driven by a motor (not shown) and moves in the Z direction as the ball screw rotates. The slider 22 mainly moves in the X and Y directions when adjusting the initial position of the optical system and moves along the Z direction when compensating for a shift in the focal position. The slider 22 may move in the X and Y directions manually or automatically. When moving automatically, the above-mentioned ball screw (not shown) or the like is connected to the slider 22. The reflected light monitor 23 receives the blue laser beam 70 reflected or scattered by the laser beam incident portion 44 of the transmission fiber 40, and generates a detection signal corresponding to the light amount of the received blue laser beam 70. The condenser lens unit 20 also has a connector 24. The laser beam incident portion 44 of the transmission fiber 40 is connected to the connector 24. The connector 24 also holds a quartz block 25 provided in contact with the incident end face 46 of the transmission fiber 40. The quartz block 25 has a function of protecting the incident end face 46.

[0024] The transmission fiber 40 is optically coupled to the laser oscillator 10 and the condenser lens 21, and transmits the blue laser beam 70 received from the laser oscillator 10 via the condenser lens 21 to the laser head 30. The transmission fiber 40 also has a core 41 that transmits the blue laser beam 70, a cladding 42 that is provided around the core 41 and has the function of confining the blue laser beam 70 within the core 41, and a coating 43 that covers the surface of the cladding 42. The connector 24 also has a mode stripper (not shown) at a laser beam incident portion 44 of the transmission fiber 40. The mode stripper is a mechanism that prevents the blue laser beam 70 that has leaked into the cladding 42 from propagating within the cladding 42 when the blue laser beam 70 is guided to the core 41, and converts the blue laser beam 70 that has leaked into the cladding 42 into heat to remove it. Although not shown, a mode stripper is also implemented in the connector on the laser beam exit side of the transmission fiber 40 in order to remove the blue laser beam 70 that was not completely removed on the incident side (i.e., the laser beam incident portion 44 side) and has propagated through the clad 42 just before it is emitted.

[0025] The laser head 30 irradiates the blue laser beam 70 transmitted through the transmission fiber 40 toward the outside (e.g., a laminated metal foil, described below). The laser head 30 includes optical components such as a collimation lens, a reflecting mirror, a condenser lens, and a laser beam scanner. These optical components are housed within the housing of the laser head 30 while maintaining a predetermined positional relationship (see, for example, Figures 1 and 2 of Japanese Patent Application Laid-Open No. 2022-60808). The laser head 30 is connected to a drive unit (not shown) and configured to be displaceable in the Z direction in response to a control signal from a control unit 50. The blue laser welding system 100 displaces the laser head 30 in the Z direction to change the focal position of the blue laser beam 70 and appropriately irradiate the blue laser beam 70 according to the shape of the workpiece WK (specifically, the laminated metal foil AF and the tab plate TB).

[0026] The focal position of the blue laser beam 70 may be adjusted using a collimation lens. In this case, the collimation lens receives the blue laser beam 70 emitted from the transmission fiber 40, converts it into parallel light, and directs it to the reflecting mirror. The collimation lens is connected to a drive unit (not shown) and is configured to be displaceable in the Y direction in response to a control signal from the control unit 50. By displacing the collimation lens in the Y direction, the focal position of the blue laser beam 70 can be changed, allowing the blue laser beam 70 to be appropriately irradiated according to the shape of the workpiece WK (specifically, the laminated metal foil AF and the tab plate TB). In other words, the collimation lens, in combination with the drive unit (not shown), also functions as a focal position adjustment mechanism for the blue laser beam 70. The focal position of the blue laser beam 70 may be changed by displacing the condenser lens using the drive unit (not shown).

[0027] The reflecting mirror reflects the blue laser beam 70 that has passed through the collimation lens and makes it incident on the laser light scanner. The surface of the reflecting mirror is arranged so as to form an angle of approximately 45 degrees with the optical axis of the blue laser beam 70 that has passed through the collimation lens.

[0028] The condenser lens 21 condenses the blue laser beam 70, which has been reflected by the reflecting mirror and scanned by the laser light scanner, onto the surface of the workpiece WK placed on the stage STG.

[0029] The laser light scanner is a known galvanometer scanner having a first galvanometer mirror and a second galvanometer mirror. The first galvanometer mirror has a first mirror, a first rotation axis, and a first drive unit. The second galvanometer mirror has a second mirror, a second rotation axis, and a second drive unit. The blue laser beam 70 transmitted through the condenser lens is reflected by the first mirror and then by the second mirror, and is irradiated onto the surface of the workpiece WK.

[0030] For example, the first drive unit and the second drive unit are galvanometer motors, and the first rotation shaft and the second rotation shaft are output shafts of the motors. Although not shown, the first drive unit is rotationally driven by a driver that operates in response to a control signal from the control unit 50, causing the first mirror attached to the first rotation shaft to rotate about the axis of the first rotation shaft. Similarly, the second drive unit is rotationally driven by a driver that operates in response to a control signal from the control unit 50, causing the second mirror attached to the second rotation shaft to rotate about the axis of the second rotation shaft.

[0031] The first mirror rotates around the axis of the first rotation shaft to a predetermined angle, causing the blue laser beam 70 to scan in the X direction. The second mirror rotates around the axis of the second rotation shaft to a predetermined angle, causing the blue laser beam 70 to scan in the Z direction. In other words, the laser light scanner is configured to two-dimensionally scan the blue laser beam 70 within the XZ plane and irradiate the workpiece WK with the blue laser beam 70.

[0032] The laser head 30 has optical components such as a collimation lens, a reflecting mirror, a condenser lens, and a laser beam scanner. These optical components are housed in a housing of the laser head 30 while maintaining a predetermined positional relationship (see, for example, FIGS. 1 and 2 of Japanese Patent Application Laid-Open No. 2022-60808).

[0033] For example, when this blue laser welding system 100 is used to weld (e.g., join) a workpiece WK composed of a laminated metal foil AF, which is a plurality of metal foils, and a tab plate TB, the blue laser beam 70 is emitted toward the workpiece WK placed at a predetermined position on the stage STG. The stage STG may be movable along one or more of the X, Y, and Z axes, and may be able to adjust the irradiation position or irradiation posture of the blue laser beam 70 on the workpiece WK.

[0034] The control unit 50 controls the laser oscillation of the laser oscillator 10. Specifically, the control unit 50 controls the laser oscillation by controlling the output, on-time, etc. of a power supply device (not shown) connected to the laser oscillator 10. The control unit 50 may also have a lens movement control unit (not shown). This lens movement control unit (not shown) receives detection signals from the reflected light monitor 23 and the output light monitor 14 and moves the slider 22 to adjust the condenser lens 21 to a desired position. When the blue laser welding system 100 is used for welding (e.g., joining) multiple sheets of copper foil as described above, the control unit 50 may also control the operation of a manipulator (not shown) to which the laser head 30 is attached.

[0035] The following description will explain the laser welding method performed by the blue laser welding system 100 described above, which welds and joins multiple sheets of metal foil (hereinafter referred to as "laminated metal foil") made of a copper-based material to a metal plate (hereinafter referred to as "plate tab") made of a copper-based material.

[0036] (Background to the First Embodiment) Generally, laser welding is a welding method with a high power density, which makes it prone to spatter. Spatter can become trapped between copper foils and cause short circuits, or can cause defects in products such as batteries incorporating a manufactured workpiece (a bonded assembly of a laminated metal foil AF and a tab plate TB). Therefore, it is desirable to set welding conditions that result in no spatter when welding the laminated metal foil AF and the tab plate TB. Therefore, the first embodiment described below describes the focal position of a blue laser beam for more stable welding between the laminated metal foil AF and the tab plate TB.

[0037] (Embodiment 1) A laser welding method according to embodiment 1 will be described with reference to Figures 3 and 4. Figure 3 is a diagram showing an example of a conventional laser welding method for laser welding a laminated metal foil AF and a tab plate TB. Figure 4 is a diagram explaining an example of the relationship between the focal length of a blue laser beam LB1 and the occurrence of spatter.

[0038] The conventional laser welding method shown in Figure 3 illustrates conventional laser welding in which a blue laser beam LB1 is irradiated onto a laminated metal foil AF (workpiece WK) and a tab plate TB. The blue laser welding system 100 performs welding by irradiating a weld line WL1 set on a laminated metal foil AF (a plurality of copper foils) on the tab plate TB while wobbling (rotating) the blue laser beam LB1. After irradiation with the blue laser beam LB1, a weld bead is formed on the laminated metal foil AF and the tab plate TB within an irradiation range AR11 of the blue laser beam LB1. In this laser welding method, the presence or absence of spatter is shown in Figure 4 when the focal position of the blue laser beam LB1 is varied between 0 (zero), -1 mm, -2 mm, and -2.5 mm.

[0039] The focal position here refers to a position (height) along the Z-axis direction, and indicates the position (height) at which the beam spot diameter of the blue laser beam LB1 irradiated onto the workpiece is smallest. When the blue laser beam LB1 is irradiated with its focal position adjusted to 0 (zero) mm, the beam spot diameter is smallest at the welding position (height) on the workpiece. In other words, the closer the focal position of the blue laser beam LB1 is to 0 (zero) mm, the smaller the beam spot diameter at the irradiation position and the higher the power density. On the other hand, the smaller the focal position of the blue laser beam LB1 is, which is a negative number, the greater the distance between the workpiece and the laser head 30, and the larger the beam spot diameter irradiated onto the workpiece and the lower the power density.

[0040] When the blue laser beam LB1 is irradiated at a focal position of 0 (zero) mm on the laminated metal foil AF and the tab plate TB, a weld bead BD11 is formed, and damage to the laminated metal foil AF and the generation of spatter SP11 occur due to the power density of the blue laser beam LB1 being too high.

[0041] When the blue laser beam LB1 is irradiated at a focal position of -1 mm on the laminated metal foil AF and the tab plate TB, a weld bead BD12 is formed, and damage to the laminated metal foil AF and the generation of spatter SP12 occur due to the power density of the blue laser beam LB1 being too high.

[0042] When the blue laser beam LB1 is irradiated at a focal position of −2 mm on the laminated metal foil AF and the tab plate TB, a weld bead BD13 is formed and spatter SP13 is generated. The spatter SP13 generated here is sufficiently small and in a sufficiently small amount compared to the spatter SP11 and SP12 generated when the focal position is 0 (zero) mm and −1 mm, and is not determined to be a welding defect.

[0043] When the blue laser beam LB1 is irradiated at a focal position of -2.5 mm on the laminated metal foil AF and the tab plate TB, a weld bead BD14 is formed and no spatter occurs.

[0044] As described above, the blue laser welding system 100 in the first embodiment can reduce the power density of the blue laser beam LB1 and suppress the occurrence of spatter by setting the focal position of the blue laser beam LB1, which is one of the welding conditions, to −2 mm or more. This allows the blue laser welding system 100 to more effectively suppress the occurrence of welding defects due to spatter when welding the laminated metal foil AF and the tab plate TB, thereby further stabilizing the production of the product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined. While the focal position of the blue laser beam LB1 is preferably −2.5 mm, it is sufficient if it is −2 mm or more.

[0045] Furthermore, by setting the focal position of the blue laser beam LB1 to -2 mm or more, the blue laser welding system 100 can increase the distance between the laser head 30 and the laminated metal foil AF onto which the blue laser beam LB1 is irradiated. Therefore, even if spatter or fumes are generated during laser welding, the blue laser welding system 100 can protect the protective glass of the laser head 30 from the spatter or fumes. As a result, the blue laser welding system 100 can further reduce the frequency of replacing the protective glass and further improve the manufacturing efficiency of the product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0046] (Background to embodiment 2) In embodiment 1, when laser welding was performed by adjusting the focal position of the blue laser beam LB1 to 0 (zero) mm to -2.5 mm and irradiating the blue laser beam LB1 onto the welding line WL1 while wobbling it, the welding result was that the laminated metal foil AF or the tab plate TB was damaged.

[0047] Therefore, in order to consider a method of irradiating a blue laser beam suitable for welding the laminated metal foil AF and the tab plate TB, laser welding was performed on the laminated metal foil AF and the tab plate TB using a laser welding method that was modified from the welding method in embodiment 1, as shown in Figure 5, by adjusting the focal position of the blue laser beam LB1 to -2.5 mm, irradiating the blue laser beam LB2 in a straight line rather than a wobbling manner, and continuing to irradiate the blue laser beam LB2 while the blue laser beam LB2 makes three round trips on the welding line WL1.

[0048] Fig. 5 is a diagram showing an example of laser welding between the laminated metal foil AF and the tab plate TB using the focal position (=-2.5 mm) shown in embodiment 1. Fig. 6 is a diagram showing an example of the result of laser welding between the laminated metal foil AF and the tab plate TB shown in Fig. 5.

[0049] The blue laser welding system 100 performs laser welding using the laser welding method shown in Fig. 5. Although the occurrence of spatter on the laminated metal foil AF after laser welding is suppressed by adjusting the focal position of the blue laser beam LB2, the laminated metal foil AF may be melted (broken) along the irradiation locus (weld line WL1) of the blue laser beam LB2 due to three round trips of irradiation with the blue laser beam LB2.

[0050] Therefore, in the following embodiment 2, a method of applying a blue laser beam LB2 that is more suitable for joining the laminated metal foil AF and the tab plate TB will be described. In the following description, the same components as those in embodiment 1 will be denoted by the same reference numerals, and their description will be omitted. In the laser welding method described in embodiment 2, the focal position of the blue laser beam LB2 is adjusted to −2.5 mm.

[0051] (Embodiment 2) A laser welding method in embodiment 2 will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a diagram showing an example of a laser welding method for the laminated metal foil AF and the tab plate TB in embodiment 2. Fig. 8 is a diagram showing an example of a result of laser welding the laminated metal foil AF and the tab plate TB shown in Fig. 7.

[0052] The blue laser welding system 100 according to the second embodiment welds the laminated metal foil AF and the tab plate TB using a welding method in which the blue laser beam LB2 is moved back and forth multiple times along the weld line WL2 so that the irradiation locus traces a desired irradiation locus. Here, the irradiation locus of the blue laser beam LB2 is set arbitrarily in advance by the user. The blue laser beam LB2 is irradiated so as to trace a desired shape (e.g., a sine wave, a circular shape, an elliptical shape, or a figure "8") previously set by the user. Furthermore, in the laser welding method according to the second embodiment, the weld line WL2 is set on the tab plate TB along one end (a break portion) of the laminated metal foil AF, which is placed on the tab plate TB and has multiple copper foils laminated thereon. The other end of the laminated metal foil AF is clamped by a clamp CLP2 to prevent misalignment of the laminated copper foils. The irradiation range AR12 indicates the irradiation range of the blue laser beam LB2, which is irradiated along a desired irradiation locus during welding.

[0053] 7 has joints BD21A and BD21B where the laminated metal foil AF and the tab plate TB are joined. The weld bead BD21 is formed in a state where, among the multiple copper foils stacked in the Z-axis direction, the copper foil (laminated metal foil AF) that is placed closer to the tab plate TB is more firmly joined to the tab plate TB at locations other than the joints BD21A and BD21B.

[0054] As described above, the blue laser welding system 100 in the second embodiment can gradually melt the laminated metal foil AF and the tab plate TB by irradiating the blue laser beam LB2 back and forth multiple times while tracing an arbitrary shape on the weld line WL2 set along one end of the laminated metal foil AF. This allows the blue laser welding system 100 to bond the laminated metal foil AF and the tab plate TB more firmly, thereby more stably manufacturing the product (workpiece) in which the laminated metal foil AF and the tab plate TB are bonded.

[0055] (Variation of Second Embodiment) Blue laser welding system 100 according to the second embodiment is an example of a laser welding method in which welding is performed by reciprocating multiple times along weld line WL2, and in which the irradiation width (amplitude) of blue laser beam LB2 in a direction substantially perpendicular to weld line WL2 is adjusted to a predetermined size (constant). Blue laser welding system 100 according to a variation of the second embodiment is an example of a laser welding method in which welding is performed by reciprocating multiple times along weld line WL2, and in which the irradiation width (amplitude) of blue laser beam LB2 increases with each reciprocating movement.

[0056] A laser welding method according to a modified example of the second embodiment will be described with reference to Figures 9 to 11. Figure 9 is a diagram showing an example of a laser welding method for a laminated metal foil AF and a tab plate TB according to a modified example of the second embodiment. Figure 10 is a diagram explaining an example of changes in the amplitude of laser welding. Note that the weld line is omitted from Figure 9 for clarity. Figure 10 shows, as an example, an example in which a blue laser beam LB2 is irradiated while weaving to trace a predetermined sine wave. Figure 11 is a process diagram schematically showing the time-series operational procedure for laser welding a laminated metal foil AF and a tab plate TB.

[0057] The blue laser welding system 100 according to a modified example of embodiment 2 welds the laminated metal foil AF and the tab plate TB using a laser welding method in which the irradiation width (amplitude) of the blue laser beam LB2 increases with each return movement along the welding line WL2.

[0058] 10 , the blue laser welding system 100 controls the irradiation of the blue laser beam LB2 so that the amplitude of the irradiation locus of the blue laser beam LB2 increases as the number of times the blue laser beam LB2 travels back and forth across the weld line WL2 increases. An irradiation range AR21 is the irradiation range of the blue laser beam LB2 on the first round trip. An irradiation range AR22 is the irradiation range of the blue laser beam LB2 on the second round trip. An irradiation range AR23 is the irradiation range of the blue laser beam LB2 on the third round trip.

[0059] Irradiation locus LB21A indicates the irradiation locus of the blue laser beam LB2 on the outward or return path of the blue laser beam LB2 irradiated during the first round trip. Irradiation locus LB22A indicates the irradiation locus of the blue laser beam LB2 on the outward or return path of the blue laser beam LB2 irradiated during the second round trip. Irradiation locus LB23A indicates the irradiation locus of the blue laser beam LB2 on the outward or return path of the blue laser beam LB2 irradiated during the third round trip.

[0060] The blue laser welding system 100 welds the weld line WL2 with an amplitude W1 in the first reciprocation, welds the weld line WL2 with an amplitude W2 in the second reciprocation, and welds the weld line WL2 with an amplitude W3 in the third reciprocation. Here, the magnitude relationship among the amplitudes W1 to W3 is W1<W2<W3. For example, the blue laser welding system 100 changes the irradiation pattern of the blue laser beam LB2 so that the amplitude W1 is 300 μm, the amplitude W2 is 600 μm, and the amplitude W3 is 900 μm.

[0061] The centers of the amplitudes W1 to W3, i.e., the centers of the irradiation ranges AR21 to AR23 of the blue laser beam LB2, do not have to coincide with the weld line WL2. For example, the blue laser beam LB2 may be irradiated so that the center of the amplitudes W1 to W3 is shifted from the weld line WL2 toward the tab plate TB or the laminated metal foil AF only in the third reciprocation, or the blue laser beam LB2 may be irradiated so that the center of the amplitudes W1 to W3 shifts from the weld line WL2 toward the tab plate TB or the laminated metal foil AF with each reciprocation.

[0062] In addition, the blue laser welding system 100 increases the moving speed of the irradiation position of the blue laser beam LB2 so that the irradiation time of the blue laser beam LB2 is the same in each of the first, second, and third round trips, that is, the more round trips there are, the more the movement speed of the irradiation position of the blue laser beam LB2 increases.

[0063] When the above-described laser welding method is carried out, the laminated metal foil AF and the tab plate TB are welded and joined through the process shown in FIG.

[0064] During the first round of irradiation with the blue laser beam LB21, the copper foil located near the tab plate TB of the laminated metal foil MM21 irradiated with the blue laser beam LB21 is broken and melted by the blue laser beam LB21, which has a high power density. The tab plate TB is melted by the heat input by the irradiation with the blue laser beam LB2, and mixes with the broken and melted copper foil and solidifies, thereby forming a joint MM21A between the laminated metal foil AF and the tab plate TB.

[0065] During the second round of irradiation with the blue laser beam LB22, the joint MM21A between the laminated metal foil AF and the tab plate TB is melted by the heat input by the irradiation of the blue laser beam LB22. Furthermore, the surfaces of the laminated metal foil MM22 and the tab plate TB are further melted and solidified by the heat input by the blue laser beam LB22 and the heat transferred from the melted joint MM21A, thereby forming a joint MM22A. The melting amounts of the laminated metal foil AF and the tab plate TB are greater at the joint MM22A than at the joint MM21A, realizing a more stable joint between the laminated metal foil AF and the tab plate TB.

[0066] During the third round of irradiation with the blue laser beam LB23, the joint MM22A between the laminated metal foil AF and the tab plate TB melts due to the heat input by the irradiation of the blue laser beam LB23. Furthermore, the surfaces of the laminated metal foil MM23 and the tab plate TB are remelted and solidified by the heat input by the blue laser beam LB23 and the heat transferred from the molten joint MM22A, thereby forming the joint MM23A. The remelting and solidification of the joint MM22A realizes a more stable joint between the laminated metal foil AF and the tab plate TB. Furthermore, the joint MM23A is more uniformly joined between the laminated metal foil AF and the tab plate TB due to the expanded irradiation range of the blue laser beam LB23 during the third round of irradiation.

[0067] Next, a description will be given of a result of laser welding performed by the laser welding method shown in Fig. 9 with reference to Fig. 12. Fig. 12 is a diagram showing an example of a result of laser welding between the laminated metal foil AF and the tab plate TB shown in Fig. 9.

[0068] 9, a weld bead BD22 is formed by the laser welding method shown in Fig. 9, and a joint BD22A is formed where the laminated metal foil AF and the tab plate TB are joined together. The weld bead BD22 is formed in a state where the copper foils stacked in the Z-axis direction are more tightly joined together at locations other than the joint BD22A.

[0069] As described above, the blue laser welding system 100 according to the second embodiment can increase the amplitude of the blue laser beam LB2 each time the blue laser beam LB2 travels back and forth over the weld line WL2, thereby increasing the irradiation range of the blue laser beam LB2 and reducing the power density. This allows the amount of melting of the laminated metal foil AF and the tab plate TB to be gradually increased, resulting in a more stable joint. Furthermore, by increasing the irradiation range of the blue laser beam LB2 and reducing the power density, the blue laser welding system 100 can more effectively suppress localized heat during welding and reduce damage to the laminated metal foil AF and the tab plate TB. This allows the blue laser welding system 100 to more stabilize the joint between the laminated metal foil AF and the tab plate TB, thereby more stably manufacturing a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0070] Although the second embodiment and the modified example of the second embodiment have been described with reference to an example in which the welding wire is moved back and forth three times along the welding line WL2, the number of times of movement is not limited to this. For example, the number of times of movement may be set arbitrarily depending on the number of copper foils, the thickness of the copper foil, the material of the copper foil or the tab plate TB, etc.

[0071] (Background to Embodiment 3) In the modified example of Embodiment 2, when a laser welding method was performed in which a blue laser beam LB2 tracing an arbitrary shape was made to reciprocate multiple times on the weld line WL2 and the irradiation width of the blue laser beam LB2 was increased with each reciprocation, a welding result was obtained in which the laminated metal foil AF and the tab plate TB could be more stably joined. However, with the laser welding method in the modified example of Embodiment 2, when the blue laser beam LB2 was irradiated in the first reciprocation, which had the highest power density, one end of the laminated metal foil AF sometimes rose from the tab plate TB due to heat.

[0072] Therefore, in the following embodiment 3, a method of applying a blue laser beam LB2 that further reduces lifting of the laminated metal foil AF when welding the laminated metal foil AF and the tab plate TB will be described. Note that in the following description, the same components as those in the first embodiment, the second embodiment, and the modified example of the second embodiment will be designated by the same reference numerals, and description thereof will be omitted.

[0073] (Embodiment 3) The blue laser welding system 100 according to embodiment 3 describes an example of a laser welding method in which a process of joining multiple copper foils that make up the laminated metal foil AF is performed before a welding process of welding along the welding line WL2.

[0074] A laser welding method according to embodiment 3 will be described with reference to Fig. 13 and Fig. 14. Fig. 13 is a diagram showing an example of a laser welding method for the laminated metal foil AF and the tab plate TB according to embodiment 3. Fig. 14 is a diagram showing an example of a result of laser welding the laminated metal foil AF and the tab plate TB shown in Fig. 13.

[0075] 14, the defective laser welding locations of each of the weld beads BD31 to BD34 shown in Fig. 14 are indicated with a circle, and the temporary attachment locations are indicated with a ▽, omitting the assignment of symbols. Each temporary attachment location (▽) is also labeled with a number indicating the order in which each temporary attachment was formed.

[0076] The blue laser welding system 100 according to the third embodiment performs a step of joining together the multiple copper foils that make up the laminated metal foil AF (hereinafter referred to as a "tack-joining step") before performing the laser welding method (welding step) shown in the second embodiment or the modified example of the second embodiment. Note that the blue laser welding system 100 according to the third embodiment performs the tack-joining step and the welding step by adjusting the focal position of the blue laser beam LB2 to -2.5 mm, similar to the laser welding method shown in the second embodiment or the modified example of the second embodiment.

[0077] As shown in Fig. 13, the blue laser welding system 100 performs tack welding to join multiple copper foils constituting the laminated metal foil AF at each of multiple tack locations along the weld line WL2. In the example shown in Fig. 13, the blue laser welding system 100 performs tack welding by irradiating a blue laser beam LB2 in a spiral shape (whirlpool shape) having a diameter DM1 starting from each of the multiple tack locations, thereby forming multiple tack locations SPW1, ..., SPWN at one end of the laminated metal foil AF to be joined to the tab plate TB, where the multiple copper foils are joined together. Note that the multiple tack locations SPW1, ..., SPWN do not need to be arranged at equal intervals.

[0078] The diameter DM1 of the temporary affixing portions SPW1, ..., SPWN is, for example, 300 μm, which is equal to or smaller than the amplitude W1 of the blue laser beam LB2 irradiated in the first round trip. The temporary affixing portions may be formed at least at both ends (start point and end point) of the welding line WL2.

[0079] In order to disperse heat generated by irradiation with the blue laser beam LB2, the blue laser welding system 100 tacks the multiple tack locations in an order in which the tack welding order of the multiple tack locations does not completely match the welding direction of the weld line WL2. Note that the blue laser welding system 100 may also be configured such that the tack welding order of some of the multiple tack locations partially matches the welding direction of the weld line WL2, such as the two tack welding locations indicated by the numbers "5" and "6" on the weld bead BD32 in FIG. 14 .

[0080] First, blue laser welding system 100 performs tack welding on both ends (start point and end point) of weld line WL2 to form two tack portions SPW1 and SPWN. Specifically, blue laser welding system 100 performs tack welding on both ends of weld line WL2 at tack points corresponding to numbers "1" and "2" shown in FIG.

[0081] After tack welding both ends of the weld line WL2, the blue laser welding system 100 alternately tack welds the incomplete tack welding points located on one end of the weld line WL2 and the tack welding points located on the other end of the weld line WL2. For example, as in weld bead BD32 (see FIG. 14 ), the blue laser welding system 100 tack welds the tack welding points (both ends of the weld line WL2) corresponding to the numbers "1" and "2." Then, it tack welds the tack welding points indicated by the number "3" located on one end of the weld line WL2, the tack welding point indicated by the number "4" located on the other end of the weld line WL2, the tack welding point indicated by the number "5" located on one end of the weld line WL2, and the tack welding point indicated by the number "6" located on the other end of the weld line WL2, in this order. This allows the blue laser welding system 100 to more effectively suppress localized heat caused by irradiation with the blue laser beam LB2 during tack welding.

[0082] After performing the temporary joining process, the blue laser welding system 100 performs a welding process using the laser welding method shown in embodiment 2 or a modified example of embodiment 2 to join the laminated metal foil AF and the tab plate TB.

[0083] Each of the weld beads BD31, BD32, and BD33 shown in Figure 14 is a weld bead formed by performing the same welding process after a tack process in which different numbers of tack portions are formed. Weld bead BD34 is a weld bead formed when the tack process is omitted, that is, when the number of tack portions is zero. Note that while Figures 13 and 14 show an example in which the length of the weld line WL2 is 30 mm, it goes without saying that the length of the weld line WL2 is not limited to this.

[0084] Weld bead BD31, which has ten tack parts formed, and weld bead BD32, which has six tack parts formed, have fewer defects than weld bead BD33, which has two tack parts formed, and weld bead BD34, in which the formation of tack parts is omitted.

[0085] As described above, in the example shown in FIG. 14 , the blue laser welding system 100 forms six or more tacks along the 30 mm-long weld line WL2 when welding the laminated metal foil AF and the tab plate TB. This reduces variations between the multiple copper foils constituting the laminated metal foil AF and prevents the laminated metal foil AF from lifting off the tab plate TB, thereby achieving more suitable laser welding between the laminated metal foil AF and the tab plate TB. The number of tacks may be adjusted as desired depending on the length of the weld line WL2. For example, when the length of the weld line WL2 is 30 mm or greater, the spacing between the tacks becomes large, so the number of tacks may be set to six or more to adjust the spacing between the tacks. On the other hand, when the length of the weld line WL2 is less than 30 mm, the spacing between the tacks becomes small, so the number of tacks may be set to fewer than six. The number of temporary attachment portions may be changed as desired depending on the number of copper foils, the thickness of the copper foils, the material of the copper foils or the tab board TB, and the like.

[0086] Furthermore, by performing tack welding from two locations (starting point and ending point) of the welding line WL2, the blue laser welding system 100 can more effectively suppress lifting of both ends of the laminated metal foil AF, which are prone to lifting due to the heat of the blue laser beam LB2, thereby achieving laser welding that is more suitable for joining the laminated metal foil AF and the tab plate TB.

[0087] Furthermore, the blue laser welding system 100 can disperse heat generated by the irradiation of the blue laser beam LB2 by alternately tack welding the tack welding points located on one end side of the weld line WL2 and the tack welding points located on the other end side of the weld line WL2 for tack welding points that are incomplete after tack welding has been performed at two locations on both ends (start point and end point) of the weld line WL2. Therefore, the blue laser welding system 100 can suppress variations among the multiple copper foils that make up the laminated metal foil AF or lifting of the laminated metal foil AF from the tab plate TB during tack welding, thereby achieving laser welding that is more suitable for joining the laminated metal foil AF and the tab plate TB.

[0088] Although the third embodiment has been described with reference to an example in which a temporary attachment portion having a spiral shape (whorl shape) is formed, the shape or method of forming the temporary attachment portion is not limited thereto. For example, the temporary attachment portion may be formed by irradiating a blue laser beam LB2 at a fixed point for a predetermined time, or by irradiating the blue laser beam LB2 a predetermined number of times by pulse-controlling the output of the blue laser beam LB2. The shape of the temporary attachment portion may also be circular. The shapes or formation methods may be arbitrarily combined depending on the number of copper foils, the thickness of the copper foil, the material of the copper foil or the tab plate TB, etc.

[0089] In addition, the beam shape of the blue laser beam LB2 irradiated in this embodiment 3 may be, for example, a ring shape, a ring type, or a shape that is a combination of peak types, and may be set arbitrarily depending on the number of copper foils, the thickness of the copper foils, the material of the copper foils or tab plate TB, etc.

[0090] Next, a description will be given of the results of laser welding performed using the tack joining process and the welding process shown in each of the first embodiment, the modified example of the second embodiment, and the third embodiment with reference to Fig. 15. Fig. 15 is a cross-sectional view taken along the line B-B of the weld bead BD31 shown in Fig. 14.

[0091] The weld bead BD31 formed by the tack joining process and the welding process shown in each of the first embodiment, the modified example of the second embodiment, and the third embodiment is generated by melting and solidifying the laminated metal foil AF and the tab plate TB with the blue laser beam LB2 that is irradiated in a round trip manner three times along the weld line WL2. The welding position WL21 indicates the position of the weld line WL2.

[0092] The blue laser welding system 100 diagonally joins the laminated metal foil AF, in which the weld bead BD31 is unmelted, and the unmelted tab plate TB with a substantially uniform thickness by irradiating the blue laser beam LB2 over a wide irradiation range. This allows the blue laser welding system 100 to expand the area of ​​the weld bead BD31 (i.e., the joint area) at the joint between the laminated metal foil AF and the tab plate TB, thereby achieving a more stable joint between the laminated metal foil AF and the tab plate TB. Therefore, the blue laser welding system 100 reduces the risk of metal foil breakage by more uniformly applying tension to the weld bead BD31 at the joint between the laminated metal foil AF and the tab plate TB. Furthermore, the blue laser welding system 100 reduces the resistance value in the electrical connection by expanding the joint area between the laminated metal foil AF and the tab plate TB, thereby improving the performance of a battery using the joined laminated metal foil AF and the tab plate TB and enabling the battery to have a longer life.

[0093] After laser welding, the laminated metal foil AF and the tab plate TB maintain a predetermined gap between the copper foils, and the laminated metal foil AF and the tab plate TB are joined in a substantially parallel state. This allows the blue laser welding system 100 to more uniformly apply tension to the weld bead BD31, which is the joint between the laminated metal foil AF and the tab plate TB, thereby more effectively suppressing breakage at the joint between the laminated metal foil AF and the tab plate TB and achieving a more stable joint.

[0094] Furthermore, a gap GP is formed between the laminated metal foil AF and the tab plate TB after laser welding.

[0095] As described above, the blue laser welding system 100 in embodiment 3 performs a temporary welding process to join multiple copper foils that make up the laminated metal foil AF by temporary welding multiple temporary attachment points along the welding line WL2, and then performs a welding process to weld the laminated metal foil AF and the tab plate TB, thereby making it possible to more stabilize the production of a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0096] Furthermore, the tack process and the welding process can be performed using the same equipment. Therefore, blue laser welding system 100 can minimize the amount of process equipment required and suppress a decrease in productivity, while further stabilizing the production of workpieces, thereby improving the productivity of non-defective workpieces.

[0097] Although different laser welding methods have been described in the first to third embodiments, the laser welding methods shown in the first to third embodiments may be combined in any desired manner.

[0098] (Additional Notes) The above description of each embodiment discloses the following techniques.

[0099] (Technology 1-1) A laser welding method for joining a laminated metal foil AF, which is composed of multiple copper-based foils, to a tab plate TB made of a copper-based material, includes the steps of placing one end of the laminated metal foil AF on the tab plate TB and irradiating one end of the laminated metal foil AF and the tab plate TB with a blue laser beam 70, LB2 so as to travel back and forth multiple times along a weld line WL2 on the tab plate TB along one end of the laminated metal foil AF. With this configuration, the blue laser welding system 100 can gradually increase the amount of melting of the laminated metal foil AF and the tab plate TB by traveling back and forth multiple times along the weld line WL2, thereby forming a more stable joint. Therefore, the blue laser welding system 100 can more steadily manufacture products (workpieces) in which the laminated metal foil AF and the tab plate TB are joined.

[0100] (Technology 1-2) The laser welding method described in (Technology 1-1), in which the blue laser beam 70, LB2 is irradiated over a different irradiation area each time it travels back and forth along the weld line WL2. With this configuration, the blue laser welding system 100 more effectively prevents heat from being localized in the irradiation area of ​​the blue laser beam LB2, gradually increasing the amount of melting of the laminated metal foil AF and the tab plate TB, thereby forming a more stable joint. This allows the blue laser welding system 100 to more stably manufacture a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0101] (Technology 1-3) The laser welding method described in (Technology 1-1) or (Technology 1-2), in which the blue laser beam 70, LB2, increases its irradiation range each time it travels back and forth over the weld line WL2. With this configuration, the blue laser welding system 100 increases the amplitude of the blue laser beam LB2 each time it travels back and forth over the weld line WL2, thereby widening the irradiation range of the blue laser beam LB2 and gradually increasing the melting amount of the laminated metal foil AF and the tab plate TB, thereby forming a more stable joint. Furthermore, the blue laser welding system 100 reduces the power density while widening the irradiation range of the blue laser beam LB2, thereby more effectively suppressing heat localization and reducing damage to the laminated metal foil AF and the tab plate TB. This allows the blue laser welding system 100 to more stabilize the joint between the laminated metal foil AF and the tab plate TB, thereby more stably manufacturing a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0102] (Technology 1-4) The laser welding method according to any one of (Technology 1-1) to (Technology 1-3), wherein the time it takes for the blue laser beam to travel back and forth along the weld line is constant. With this configuration, the blue laser welding system 100 keeps the time it takes for the blue laser beam LB2 to travel back and forth constant, and by increasing the irradiation range, the scanning speed of the blue laser beam LB2 increases, reducing the power density per unit time during welding. This more effectively suppresses localized heat and reduces damage to the laminated metal foil AF and the tab plate TB. This allows the blue laser welding system 100 to more stabilize the bond between the laminated metal foil AF and the tab plate TB, thereby more stabilizing the production of a product (workpiece) in which the laminated metal foil AF and the tab plate TB are bonded.

[0103] (Technology 1-5) The laser welding method according to any one of (Technology 1-1) to (Technology 1-4), wherein the blue laser beam 70, LB2, is irradiated with a wobbling or weaving motion. With this configuration, the blue laser welding system 100 can more effectively suppress localized heat in the irradiation area of ​​the blue laser beam LB2, suppressing damage to the laminated metal foil AF and the tab plate TB, and can form a more stable joint by increasing the amount of melting of the laminated metal foil AF and the tab plate TB. This allows the blue laser welding system 100 to more stabilize the joint between the laminated metal foil AF and the tab plate TB, thereby more stabilizing the production of a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0104] (Technology 1-6) The laser welding method according to any one of (Technology 1-1) to (Technology 1-5), wherein the focal position of the blue laser beam 70, LB2 is set at a predetermined height from the surface of the tab plate TB. With this configuration, the blue laser welding system 100 can reduce the power density of the blue laser beam LB1 to suppress the occurrence of spatter. This allows the blue laser welding system 100 to more effectively suppress the occurrence of welding defects due to spatter when welding the laminated metal foil AF and the tab plate TB, thereby more stabilizing the production of a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0105] (Technology 2-1) A laser welding method for joining a laminated metal foil AF, which is formed by stacking multiple copper-based foils, to a tab plate TB made of a copper-based material, the laser welding method comprising the steps of: placing one end of the laminated metal foil AF on the tab plate TB; irradiating multiple temporary attachment positions on one end of the laminated metal foil AF with a blue laser beam (70, LB2); and irradiating a weld line WL2 on the tab plate TB along one end of the laminated metal foil AF with the blue laser beam (70, LB2). With this configuration, the blue laser welding system 100 forms multiple temporary attachment positions, thereby suppressing variations between the multiple copper foils that make up the laminated metal foil AF and suppressing lifting of the laminated metal foil AF from the tab plate TB, thereby achieving laser welding that is more suitable for joining the laminated metal foil AF and the tab plate TB.

[0106] (Technology 2-2) The laser welding method according to (Technology 2-1), wherein the plurality of tack welding positions include at least one end and the other end of the weld line WL2. With this configuration, the blue laser welding system 100 tack-welds the plurality of tack welding positions, including two locations at both ends (start point and end point) of the weld line WL2, thereby more effectively suppressing lifting of both ends of the laminated metal foil AF, which is prone to lifting due to the heat of the blue laser beam LB2.

[0107] (Technology 2-3) The laser welding method according to (Technology 2-2), wherein the step of irradiating the plurality of tack positions with the blue laser beam 70, LB2 includes, when the number of tack positions is three or more, irradiating the one end and the other end of the weld line WL2 among the plurality of tack positions with the blue laser beam 70, LB2, and then irradiating the tack positions other than the one end and the other end of the weld line WL2 with the blue laser beam 70, LB2. With this configuration, the blue laser welding system 100 performs tack welding from two locations, the two ends (start point and end point) of the weld line WL2, thereby more effectively suppressing lift-up of the both ends of the laminated metal foil AF, which is prone to lift-up due to the heat of the blue laser beam LB2, and thereby achieving laser welding that is more suitable for joining the laminated metal foil AF and the tab plate TB.

[0108] (Technology 2-4) The laser welding method according to (Technology 2-2), wherein the step of irradiating the plurality of tack positions with the blue laser beam 70, LB2 includes irradiating the plurality of tack positions with the blue laser beam 70, LB2 alternately to a first tack position located on the one end side of the weld line WL2 and a second tack position located on the other end side of the weld line WL2, when there are a plurality of tack positions other than the one end and the other end of the weld line WL2. With this configuration, the blue laser welding system 100 can more effectively suppress localized heat caused by irradiation with the blue laser beam LB2 during tack welding.

[0109] (Technology 2-5) The laser welding method according to any one of (Technology 2-1) to (Technology 2-4), wherein the step of irradiating the plurality of tack welding positions with the blue laser beam 70, LB2 irradiates the plurality of tack welding positions with the blue laser beam 70, LB2 in a spiral pattern. With this configuration, the blue laser welding system 100 can more effectively suppress localized heat caused by irradiation of the blue laser beam LB2 during tack welding.

[0110] (Technology 2-6) The laser welding method according to any one of (Technology 2-1) to (Technology 2-5), wherein the focal position of the blue laser beam 70, LB2 is set at a predetermined height from the surface of the tab plate TB. With this configuration, the blue laser welding system 100 can reduce the power density of the blue laser beam LB1 to suppress the occurrence of spatter. This allows the blue laser welding system 100 to more effectively suppress the occurrence of welding defects due to spatter when welding the laminated metal foil AF and the tab plate TB, thereby more stabilizing the production of a product (workpiece) in which the laminated metal foil AF and the tab plate TB are joined.

[0111] (Technology 3-1) A laser welding method for joining a laminated metal foil AF, which is made of a plurality of copper-based foils laminated together, and a tab plate TB made of a copper-based material, the laser welding method comprising the steps of: placing one end of the laminated metal foil AF on the tab plate TB; and irradiating one end of the laminated metal foil AF and the tab plate TB with a blue laser beam (70, LB2) so as to travel back and forth a plurality of times along a weld line WL2 on the tab plate TB that is along one end of the laminated metal foil AF, wherein the laminated metal foil AF and the tab plate TB irradiated with the blue laser beam (70, LB2) have a joint portion where the surface of the tab plate TB irradiated with the blue laser beam (70, LB2) and the one end of the laminated metal foil AF are joined at an angle to the surface of the tab plate TB. With this configuration, blue laser welding system 100 can more uniformly apply tension to weld bead BD31, which is the joint between laminated metal foil AF and tab plate TB, thereby more effectively suppressing breakage at the joint between laminated metal foil AF and tab plate TB and achieving a more stable joint. Therefore, blue laser welding system 100 can more stabilize the production of products (workpieces) in which laminated metal foil AF and tab plate TB are joined.

[0112] (Technology 3-2) The laser welding method according to (Technology 3-1), wherein the joint connects the plurality of copper-based foils and the surface of the tab plate TB in a substantially parallel manner. With this configuration, the blue laser welding system 100 can more uniformly apply tension to the weld bead BD31, which is the joint between the laminated metal foil AF and the tab plate TB. Furthermore, the blue laser welding system 100 can reduce the resistance value in the electrical connection by increasing the joint area between the laminated metal foil AF and the tab plate TB, thereby improving the performance of a battery using the joined laminated metal foil AF and tab plate TB and enabling the battery to have a longer life.

[0113] (Technology 3-3) The laser welding method according to (Technology 3-1) or (Technology 3-2), wherein the irradiation range of the blue laser beam 70, LB2 increases with each reciprocal movement on the weld line WL2. With this configuration, the blue laser welding system 100 can increase the area of ​​the weld bead BD31 (i.e., the joining area) that is the joining portion between the laminated metal foil AF and the tab plate TB, thereby realizing a more stable joining between the laminated metal foil AF and the tab plate TB.

[0114] (Technology 3-4) The laser welding method according to any one of (Technology 3-1) to (Technology 3-3), wherein the blue laser beam 70, LB2 is irradiated while wobbling or weaving. With this configuration, the blue laser welding system 100 can increase the area of ​​the weld bead BD31, which is the joint between the laminated metal foil AF and the tab plate TB (i.e., the joint area), thereby achieving a more stable joint between the laminated metal foil AF and the tab plate TB.

[0115] (Technology 3-5) The laser welding method according to any one of (Technology 3-1) to (Technology 3-4), wherein the focal position of the blue laser beam 70, LB2 is set at a predetermined height from the surface of the tab plate TB. With this configuration, the blue laser welding system 100 can reduce the power density of the blue laser beam LB1 to suppress spattering. This allows the blue laser welding system 100 to more effectively suppress the occurrence of welding defects due to spattering when welding the laminated metal foil AF and the tab plate TB, thereby stabilizing the production of products (workpieces) in which the laminated metal foil AF and the tab plate TB are joined. With this configuration, the blue laser welding system 100 can more effectively suppress the occurrence of welding defects due to spattering when welding the laminated metal foil AF and the tab plate TB, thereby stabilizing the production of products (workpieces) in which the laminated metal foil AF and the tab plate TB are joined.

[0116] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention.

[0117] This application is based on a Japanese patent application (Patent Application No. 2023-159151) filed on September 22, 2023, the contents of which are incorporated herein by reference.

[0118] The present disclosure is useful as a laser welding method for joining a plurality of metal foils and a metal plate.

[0119] REFERENCE SIGNS LIST 10 Laser oscillator 11 Laser module 12 Beam combiner 50 Control unit 60 Housing 70, LB1, LB2 Blue laser beam 100 Blue laser welding system AF Laminated metal foil BD21A, BD21B, BD22A Joint SPW1, SPW2, SPWN Temporary joint STG Stage TB Tab plate W1, W2, W3 Amplitude WK Work WL1, WL2 Weld line

Claims

1. A laser welding method for joining a laminated metal foil having multiple copper-based foils laminated thereon to a tab plate made of a copper-based material, comprising the steps of: placing one end of the laminated metal foil on the tab plate; and irradiating one end of the laminated metal foil and the tab plate with a blue laser beam so as to go back and forth multiple times along a weld line on the tab plate that runs along one end of the laminated metal foil, wherein the laminated metal foil and the tab plate irradiated with the blue laser beam have a joint where the surface of the tab plate irradiated with the blue laser beam and the one end of the laminated metal foil are joined at an angle to the surface of the tab plate.

2. The laser welding method according to claim 1, wherein the joints connect the plurality of copper-based foils and the surface of the tab plate in approximately parallel relation.

3. The laser welding method according to claim 1, wherein the irradiation range of the blue laser beam increases each time the blue laser beam travels back and forth on the weld line.

4. The laser welding method according to claim 1, wherein the blue laser beam is irradiated with a wobbling or weaving motion.

5. The laser welding method according to claim 1, wherein the focal position of the blue laser beam is set at a predetermined height from the surface of the tab plate.