Laser welding method for laminated metal foil

Abstract

To provide a laser welding method for laminated metal foils suppressing a melting part on a lower end side of the laminated metal foils in a lamination direction from being curved to the center side of the melting part.SOLUTION: A laser welding method for laminated metal foils where a plurality of copper foils are laminated, includes: a step of vertically laminating the plurality of copper foils; a step of arranging the laminated metal foils on a fixture in a blue laser welding system; and a step of irradiating the laminated metal foils with blue laser beams while determining the direction thereof. The lower end surface of a welding area generated on the laminated metal foils does not curve toward the center side of the welding area in a cross section along the lamination direction of the copper foils of the laminated metal foils after irradiation of the blue laser beams.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a method for laser welding laminated metal foils. [Background technology]

[0002] Patent Document 1 discloses a method for welding a laminated metal foil, in which a laminated metal foil sandwiched between a pair of metal plates is welded to the pair of metal plates. Specifically, this welding method includes a process of locally pressing the laminated metal foil sandwiched between the pair of metal plates in the lamination direction at a planned welding location to crimp, and a process of welding the crimped pair of metal plates and the laminated metal foil at the planned welding location. In particular, in the welding process, a laser beam is irradiated to the planned welding location to perform welding, and the irradiation conditions of the laser beam are feedback-controlled based on the intensity of thermal radiation light emitted from a molten pool formed by irradiating the laser beam, and based on the intensity of the thermal radiation light, it is detected that the molten pool has come into contact with a base on which the pair of metal plates and the laminated metal foil are placed, and when it is detected that the molten pool has come into contact with the base, the irradiation of the laser beam to the molten pool is terminated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-5768 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide a method for laser welding of laminated metal foils that suppresses curvature of the molten portion at the lower end of the laminated metal foil in the lamination direction toward the center of the molten portion, regardless of deviation in the irradiation position of the laser light and variation in the metal foil. [Means for solving the problem]

[0005] The present disclosure provides a laser welding method for a laminated metal foil having a plurality of copper-based foils stacked on top of one another, the method comprising the steps of stacking the plurality of copper-based foils on top of one another, placing the laminated metal foil on a jig in a blue laser welding system, and directing and irradiating a blue laser beam onto the laminated metal foil, wherein after irradiation of the blue laser beam, a lower end face of a molten region generated in the laminated metal foil is not curved toward the center of the molten region in a cross section of the laminated metal foil along the stacking direction of the copper-based foils. Effect of the Invention

[0006] According to the present disclosure, regardless of deviation in the irradiation position of the laser light and variations in the metal foil, it is possible to suppress curvature of the molten portion at the lower end side in the stacking direction of the laminated metal foil toward the center of the molten portion. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of a laser welding system according to an embodiment of the present invention. [Diagram 2] Schematic diagram showing a cross section taken along line AA in Figure 1. [Diagram 3] A diagram showing how the laminated metal foil is clamped to the jig. [Figure 4] A schematic diagram showing an example of vector decomposition of the force applied in the lamination direction when laser welding a laminated metal foil with a blue laser beam. [Diagram 5] A schematic diagram of the chronological sequence of steps in laser welding of laminated metal foils. [Figure 6] A diagram showing a central cross section near the melted area caused by the first laser welding [Figure 7] A diagram showing the central cross section near the melted area caused by the second laser welding [Figure 8] Contrasting examples of laser welding results depending on the jig shape DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] (Background to this disclosure) In general, it is known that laser welding of copper-based materials, which are mainly composed of copper, is very difficult because of their high reflectivity, high thermal conductivity, and high heat capacity. As laser welding of copper-based materials, welding methods such as IR laser welding using light with a wavelength in the IR (Infrared) band and ultrasonic welding have been developed. However, even if these welding methods are used, it is said that it is still difficult to perform high-quality laser welding on copper-based materials while shortening the tact time. The result of laminating and laser welding copper-based materials is used, for example, as an electrode for a secondary battery (battery) mounted on an electronic device or an autonomous vehicle. Therefore, a technology for high-quality welding of copper-based materials is inevitably attracting attention when considering the production of batteries. In other words, there is a demand for laser welding technology that shortens the tact time and obtains excellent welding quality.

[0009] In the configuration of Patent Document 1, it is unavoidable to perform a crimping process in order to minimize the gap between each of the multiple metal foils constituting the laminated metal foil. In addition, since the laminated metal foil, in which multiple metal foils are stacked vertically, is sandwiched from the upper side to the lower side by a pair of metal plates, there is a problem that laser welding cannot be performed on only the metal foil. On the other hand, for example, when the metal foil is crimped and laser welding is performed in a hollow state (i.e., not sandwiched by a pair of metal plates), the cross-sectional structure of the fusion part, which is the welding point, tends to be curved inward (i.e., in the direction toward the center of the fusion part of the entire fusion part) at the end face of the lower part of the fusion part (non-irradiated side) where the laser is difficult to irradiate. This is thought to be due to thermal contraction caused by irradiation with laser light.

[0010] In laser welding of laminated metal foils, it is desirable to make the cross-sectional area of ​​the molten part as large as possible from the viewpoint of improving electrical conductivity, and not to curve the end faces of the molten part near the surface of both the upper and lower parts of the molten part. However, in an actual production site (process), although there may be deviations in the laser irradiation position or variations in the workpiece (laminated metal foil) itself, regardless of these, the end face of the lower part of the molten part (non-irradiated side) where the laser is difficult to irradiate tends to curve inward (i.e., toward the center of the molten part of the entire molten part). For this reason, if it is possible to perform laser welding so that the end face of the lower part of the molten part of the workpiece (laminated metal foil) is prevented from curving inward, it will be possible to realize high-likelihood (in other words, high-quality) laser welding of copper-based materials, and an ideal cross-sectional structure of the molten part can be obtained from the viewpoint of the above-mentioned electrical conductivity.

[0011] Therefore, in the following embodiment, an example of a laser welding method for laminated metal foil is described that suppresses curvature of the molten portion at the lower end of the laminated metal foil in the stacking direction toward the center of the molten portion, regardless of deviation in the irradiation position of the laser light and variation in the metal foil.

[0012] Hereinafter, with reference to the drawings as appropriate, an embodiment specifically disclosing a laser welding method for laminated metal foils according to the present disclosure will be described in detail. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following explanation are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0013] [Terminology definition] In the following description, the term "laser welding" is intended to have the broadest possible meaning, unless expressly stated otherwise, 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% copper by weight, metals and alloys containing at least about 10% to 100% copper by weight, metals and alloys containing at least about 20% to 100% copper by weight, metals and alloys containing at least about 50% to 100% copper by weight, metals and alloys containing at least about 70% to 100% copper by weight, and metals and alloys containing at least about 90% to 100% copper by weight.

[0015] In the following description, the terms "blue laser beam" and "blue laser" have the broadest possible meaning unless expressly stated otherwise and generally refer to a system providing 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, with reference to FIG. 1 and FIG. 2, a configuration example of the blue laser welding system 100 according to the present embodiment will be described. FIG. 1 is a schematic diagram showing a configuration example of the blue laser welding system 100 according to the present embodiment. FIG. 2 is a schematic diagram showing a cross section along the line AA in FIG. 1. In the following description, the XYZ axes are defined as the directions shown in FIG. 1 and FIG. 2. That is, the direction in FIG. 2 in which the blue laser beam 70 faces 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 direction and the Z direction is defined as the X direction. The Z direction coincides with the optical axis direction of the blue laser beam 70 emitted from the condenser lens unit 20 within the range of the assembly tolerance of the optical system of the blue laser welding system 100.

[0017] As shown in Fig. 1, the blue laser welding system 100 includes a laser oscillator 10, a condenser lens unit 20, a laser beam emission head 30, a transmission fiber 40, and a control unit 50. The laser oscillator 10, the condenser lens unit 20, and a laser beam incidence unit 44 (see Fig. 2) of the transmission fiber 40 are housed in a housing 60. Here, 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 a characteristic of having a high absorption rate (maximum of about 65%) for copper.

[0018] The laser oscillator 10 has a plurality of laser modules 11 and a beam combiner 12. Although 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 wavelength-combines laser beams of different wavelengths (for example, different wavelengths such as 400 nm, 420 nm, 440 nm, 480 nm, etc. within a range of 400 nm to 500 nm) emitted from each of the plurality of laser modules 11 into one blue laser beam 70 by the beam combiner 12. The laser oscillator 10 may be called a DDL (Direct Diode Laser) oscillator. The laser module 11 itself is composed of a plurality of laser diodes, and is configured with, for example, a semiconductor laser array.

[0019] 2, blue laser beam 70 wavelength-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 way, it is possible to obtain high-output blue laser welding system 100 with a laser beam output exceeding several kW. Beam combiner 12 also has a partially transmitting mirror 13 and an output light monitor 14 therein.

[0020] The partially transmitting mirror 13 is configured to deflect the blue laser beam 70, the wavelength of which has been combined in the beam combiner 12, toward the focusing lens unit 20, while transmitting a portion of the blue laser beam 70 (for example, 0.1%).

[0021] The output light monitor 14 is disposed in the beam combiner 12 so as to receive the blue laser beam 70 transmitted through the partial transmission 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.

[0022] The focusing lens unit 20 has therein 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 surface 46 of the transmission fiber 40 so that the spot diameter is 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 be moved automatically in the Z direction in response to a control signal from the control unit 50. The slider 22 is connected to a ball screw (not shown) driven by a motor (not shown), for example, and moves in the Z direction with the rotation of the ball screw. The slider 22 mainly moves in the XY direction 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 XY direction 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 further 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.

[0023] 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 beam emitting 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. A mode stripper (not shown) is provided at the laser beam incident portion 44 of the transmission fiber 40. Although not shown, a mode stripper is also provided at the laser beam emitting portion of the transmission fiber 40.

[0024] The laser beam emitting head 30 irradiates the blue laser beam 70 transmitted through the transmission fiber 40 toward the outside (for example, a laminated metal foil described later). The laser beam emitting head 30 has optical components such as a collimation lens, a reflecting mirror, a condenser lens, and a laser light scanner. These optical components are housed in the housing of the laser beam emitting head 30 while maintaining a predetermined positional relationship (for example, see Figures 1 and 2 of Japanese Patent Application Laid-Open No. 2022-60808).

[0025] The collimation lens receives the blue laser beam 70 emitted from the transmission fiber 40, converts it into parallel light, and makes it incident on the reflection 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, and the blue laser beam 70 can be appropriately irradiated according to the shape of the workpiece (e.g., laminated metal foil). In other words, the collimation lens also functions as a focal position adjustment mechanism for the blue laser beam 70 in combination with the drive unit (not shown). The focus lens may be displaced by the drive unit (not shown) to change the focal position of the blue laser beam 70.

[0026] The reflecting mirror reflects the blue laser beam 70 that has passed through the collimation lens and makes it enter the laser light scanner. The surface of the reflecting mirror is provided 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.

[0027] The condenser lens condenses the blue laser beam 70, which is reflected by the reflecting mirror and scanned by the laser light scanner, onto the surface of a workpiece (eg, a laminated metal foil).

[0028] 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 is further reflected by the second mirror, and is irradiated onto the surface of the workpiece (e.g., laminated metal foil).

[0029] For example, the first driving unit and the second driving unit are galvano motors, and the first rotating shaft and the second rotating shaft are output shafts of the motors. Although not shown, the first driving unit is rotated by a driver that operates in response to a control signal from the control unit 50, so that the first mirror attached to the first rotating shaft rotates around the axis of the first rotating shaft. Similarly, the second driving unit is rotated by a driver that operates in response to a control signal from the control unit 50, so that the second mirror attached to the second rotating shaft rotates around the axis of the second rotating shaft.

[0030] The first mirror rotates around the axis of the first rotation shaft to a predetermined angle, whereby the blue laser beam 70 scans in the X direction. The second mirror rotates around the axis of the second rotation shaft to a predetermined angle, whereby the blue laser beam 70 scans 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 it toward a workpiece (e.g., a laminated metal foil).

[0031] For example, when this blue laser welding system 100 is used to weld (e.g., join) multiple sheets of copper-based material foil (hereinafter simply abbreviated as "copper foil"), a blue laser beam 70 is emitted toward multiple sheets of copper foil (an example of laminated metal foil) that are stacked so as to sandwich the flat top surface TOP1 at a predetermined position (e.g., jig JG1 described below).

[0032] 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, and the like 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). Upon receiving detection signals from the reflected light monitor 23 and the output light monitor 14, the lens movement control unit (not shown) moves the slider 22 and adjusts the condenser lens 21 to a desired position. When the blue laser welding system 100 is used for welding (e.g., joining) a plurality of copper foils as described above, the control unit 50 may control the operation of a manipulator (not shown) to which the laser beam emission head 30 is attached.

[0033] [Laminated metal foil arrangement] Next, with reference to Fig. 3 and Fig. 4, the arrangement of the laminated metal foil LF50 on the jig JG1 in the blue laser welding system 100 according to the present embodiment will be described. Fig. 3 is a diagram showing a state in which the laminated metal foil LF50 is clamped to the jig JG1. Fig. 4 is a diagram showing a schematic illustration of a vector decomposition example of the force applied in the lamination direction to the laminated metal foil LF50 during laser welding by the blue laser beam 70. In the present embodiment, as an example, the laminated metal foil LF50 is formed by vertically laminating 50 sheets of copper foil (thickness 10 µm). However, it goes without saying that the number of copper foils constituting the laminated metal foil LF50 is not limited to 50, and the thickness of the copper foil is not limited to 10 µm.

[0034] The laminated metal foil LF50 is placed on the jig JG1 in a state where 50 sheets of copper foil are stacked in the stacking direction (vertical direction or Y direction). The jig JG1, together with a pair of clamp parts CLL and CLR, plays a role of stably supporting and fixing the laminated metal foil LF50 during irradiation with the blue laser beam 70. The jig JG1 is integrally formed with a pair of flat parts PLT1 and a protruding part PJ1 protruding in the Y direction from each of the pair of flat parts PLT1. The protruding part PJ1 is formed in a trapezoidal column shape, and has a flat zenith surface TOP1 corresponding to the upper surface of the trapezoidal column, and a pair of tapered surfaces LTP1 and RTP1 inclined approximately in the direction of gravity (i.e., the -Y direction) on the left and right sides from both ends of the flat zenith surface TOP1. The lower surface of the trapezoidal column of the protruding part PJ1 is formed to be flush with the pair of flat parts PLT1. The shape of the jig JG1 does not have to be limited to the shape shown in Figure 3, but even if it is a shape other than that shown in Figure 3, it is necessary to form both a flat zenith surface TOP1 and a pair of tapered surfaces LTP1, RTP1 inclined from both ends of the flat zenith surface TOP1.

[0035] In the example of FIG. 3, the laminated metal foil LF50 is shown fixed (clamped) to the jig JG1 across the tapered surface LTP1, the flat apex surface TOP1, and the tapered surface RTP1. Specifically, one side (e.g., the left side) of the laminated metal foil LF50 is held (fixed) by the clamp part CLL in advance, and the other side (e.g., the right side) of the laminated metal foil LF50 is held (fixed) by the clamp part CLR in a later time. For this reason, as shown in FIG. 3, it can be seen that the laminated metal foil LF50 is in contact with the tapered surface LTP1 more than the laminated metal foil LF50 is in contact with the tapered surface RTP1. It is not necessary that the laminated metal foil LF50 is in contact with the tapered surface RTP1 more than the laminated metal foil LF50 is in contact with the tapered surface LTP1. In any case, a slight gap is formed between the bottom layer of the laminated metal foil LF50 and the flat apex surface TOP1.

[0036] In Fig. 4, only a portion of the laminated metal foil LF50 shown in Fig. 3 having a length in the Z direction equivalent to the width length l1 of the flat zenith surface TOP1 is illustrated. The ratio of the width length l1 of the flat zenith surface TOP1 of the protrusion PJ1 of the jig JG1 to the width length l2 of the bottom surface of the protrusion PJ1 of the jig JG1 is preferably 3:5 or more and less than 1:1 (see Fig. 8). With the laminated metal foil LF50 held (fixed) by the protrusion PJ1 having such tapered surfaces LTP1 and RTP1, a blue laser beam 70 is irradiated from the upper side (see Fig. 4) to the lower side (see Fig. 4) of the laminated metal foil LF50.

[0037] Here, a comparative example is considered in which the laminated metal foil LF50 is disposed on a rectangular parallelepiped protruding portion where the tapered surfaces LTP1 and RTP1 are not provided on the protruding portion PJ1 (see FIG. 8). In this case, it is considered that the tensile force of each copper foil pressing the laminated metal foil LF50 on the rectangular parallelepiped protruding portion occurs only in the vertical direction (i.e., the -Y direction or downward in the lamination direction).

[0038] However, in this embodiment, the tapered surfaces LTP1 and RTP1 are provided on the protruding portion PJ1. Therefore, for example, the tensile force P1 of each copper foil pressing the laminated metal foil LF50 against the trapezoidal columnar protruding portion PJ1 at the position of the tapered surface RTP1 shown in FIG. 4 is distributed in the vertical direction (for example, the vector P1v in the -Y direction) and the horizontal direction (for example, the vector P1h in the Z direction). The action of this horizontal tensile force further reduces or eliminates the gaps between each copper foil. In this way, with the laminated metal foil LF50 placed on the jig JG1 with the tapered surfaces LTP1 and RTP1 provided on the protruding portion PJ1, the blue laser beam 70 is irradiated from the upper side (see FIG. 4) to the lower side (see FIG. 4) of the laminated metal foil LF50.

[0039] By irradiating the blue laser beam 70, each copper foil of the laminated metal foil LF50 gradually starts to melt, and a force acts stronger so as to expand the molten area (molten volume) in the left-right direction from the upper side (i.e., the side farther from the tapered surfaces LTP1, RTP1) of the molten area formed as a result of melting to the lower side (i.e., the side closer to the tapered surfaces LTP1, RTP1). In other words, by applying forces F1 and F2 in the direction opposite to the direction of thermal contraction occurring in the molten area formed based on the irradiation of the blue laser beam 70 (specifically, the direction from the sides of the molten area toward the center, see the eight dotted arrows in FIG. 6), the curvature of the lower end face (lower end face) of the molten area of ​​the laminated metal foil LF50 toward the center of the molten area is reduced, resulting in a structure that does not bend.

[0040] [Laser welding of laminated metal foils] Next, a chronological operation procedure of laser welding the laminated metal foil LF50 by the blue laser beam 70 will be described with reference to Fig. 5 to Fig. 7. Fig. 5 is a process diagram that shows a schematic chronological operation procedure of laser welding the laminated metal foil. Fig. 6 is a diagram showing a central cross section near the melted region by the first laser welding. Fig. 7 is a diagram showing a central cross section near the melted region by the second laser welding. The chronological operation procedure shown in Fig. 5 shows a laser welding method of the laminated metal foil LF50 using the blue laser welding system 100.

[0041] In FIG. 5, a plurality of copper foils (for example, 50 sheets) are arranged so as to be laminated on the flat zenith surface TOP1 of the protruding portion PJ1 of the jig JG1 (step St1). Although not shown in FIG. 5, after a plurality of copper foils (for example, 50 sheets) are arranged on the flat zenith surface TOP1, they are gripped (fixed) by the clamping parts CLL and CLR (see FIG. 3) so as to be aligned along the tapered surfaces LTP1 and RTP1. After this step St1, the direction of irradiation of the blue laser beam 70 (blue laser light) from the laser beam emission head 30 of the blue laser welding system 100 is determined so as to be perpendicular to the upper side of the laminated metal foil LF50, and then the blue laser beam 70 (blue laser light) is irradiated from the upper side to the lower side of the laminated metal foil LF50 (step St2). As a result, the portions of each copper foil constituting the laminated metal foil LF50 that are irradiated with the blue laser beam 70 gradually melt.

[0042] After the irradiation of the blue laser beam 70 is completed, the melting of the copper foil of the laminated metal foil LF50 converges and solidification begins (step St3). By the irradiation of the blue laser beam 70, the gaps between the copper foils of the laminated metal foil LF50 (particularly the sides close to the tapered surfaces LTP1, RTP1 of the laminated metal foil LF50) are narrower than the gaps between the copper foils of the laminated metal foil LF50 before the irradiation (particularly the sides close to the tapered surfaces LTP1, RTP1 of the laminated metal foil LF50). In other words, as described with reference to FIG. 4, when each copper foil arranged from the flat zenith surface TOP1 to the pair of tapered surfaces LTP1, RTP1 melts, the gaps between the copper foils become narrower (shorter) due to the pulling force in the horizontal direction (see FIG. 4). Furthermore, forces F1 and F2 begin to occur throughout the entire molten region MLT1 (see FIG. 6) of the laminated metal foil LF50 that resist the thermal contraction caused by the irradiation of the blue laser beam 70 (in other words, forces F1 and F2 that occur in the opposite direction to the direction in which thermal contraction occurs (see above, the eight dotted arrows in FIG. 6)).

[0043] When the solidification of the copper foil of the laminated metal foil LF50 is completed, the laser welding to the laminated metal foil LF50 is completed (step St4). At the time of this step St4 (i.e., when solidification is completed), the gaps between the copper foils of the laminated metal foil LF50 (particularly the sides close to the tapered surfaces LTP1, RTP1 of the laminated metal foil LF50) are narrower than the gaps between the copper foils of the laminated metal foil LF50 before irradiation (particularly the sides close to the tapered surfaces LTP1, RTP1 of the laminated metal foil LF50) at the time of step St3 (during melting to the start of solidification). Furthermore, since the time of step St3, the forces F1 and F2 that resist the thermal contraction caused by the irradiation of the blue laser beam 70 in the entire melted region MLT1 (see FIG. 6) of the laminated metal foil LF50 (in other words, that occur in the opposite direction to the direction of thermal contraction (see above, see the eight dotted arrows in FIG. 6)) reduce the curvature of the lower end face (lower end face) of the melted region of the laminated metal foil LF50 toward the center of the melted region MLT1 (see FIG. 6), resulting in a structure that does not curve. In other words, in a cross section of the laminated metal foil LF50 along the lamination direction of the copper foil, a cross-sectional shape is obtained in which the shape of the melted region MLT1 (see FIG. 6) is three-dimensionally cylindrical. If the width of the molten region is narrow overall in the lamination direction, the copper foil may break due to the external force applied during mounting. However, the central portion of the molten region MLT1 (see FIG. 6) of the laminated metal foil LF50 is less likely to be subjected to external force during mounting in the production (manufacturing) of batteries to be mounted on electronic devices or electric vehicles, etc., so the central portion may be narrower than the upper and lower portions of the laminated metal foil LF50.

[0044] For example, as shown in Fig. 6, as a result of the first laser welding by the blue laser beam 70, in a cross section along the lamination direction of the copper foil of the laminated metal foil LF50, the lower end face (lower end face BTM1) of the melted region MLT1 (see Fig. 6) of the laminated metal foil LF50 is not curved toward the center of the melted region MLT1 (see Fig. 6) of the laminated metal foil LF50. Note that, since the amount of melting is originally large and the conductive region is also wide on the irradiated side of the blue laser beam 70, the upper end face (upper end face UPP1) of the melted region MLT1 (see Fig. 6) of the laminated metal foil LF50 is curved toward the center of the melted region MLT1 (see Fig. 6) of the laminated metal foil LF50, but this curved portion is not a deep recess and is not considered to deteriorate the electrical conductivity.

[0045] For example, as shown in Fig. 7, as a result of the second laser welding with the blue laser beam 70 for confirming reproducibility, in a cross section along the lamination direction of the copper foil of the laminated metal foil LF50, the lower end face (lower end face BTM1) of the melted region MLT1 (see Fig. 7) of the laminated metal foil LF50 is not curved toward the center of the melted region MLT1 (see Fig. 7) of the laminated metal foil LF50 or is reversely curved so as to bulge downward from the center. Note that, since the amount of melting is originally large and the conductive region is also wide on the irradiated side of the blue laser beam 70, the upper end face (upper end face UPP1) of the melted region MLT1 (see Fig. 7) of the laminated metal foil LF50 is curved toward the center of the melted region MLT1 (see Fig. 7) of the laminated metal foil LF50 as in Fig. 6, but this curved portion is not a deep recess and is not considered to deteriorate the electrical conductivity.

[0046] Next, examples of results of laser welding according to the shape of the jig JG1 (especially the tapered surface) will be described in a contrastive manner with reference to Fig. 8. Fig. 8 is a diagram showing examples of results of laser welding according to the shape of the jig in a contrastive manner. In Fig. 8, the results of laser welding experiments in which, for example, three types of shapes were selected are summarized in a table.

[0047] For example, in sample #1, when the base shape (i.e., the shape of the jig) is a rectangular parallelepiped and no tapered surface exists, laser welding by wobbling (for example, width 600 μm and frequency 300 Hz) was performed, and it was found that holes were generated on the surface of the melted area (i.e., the upper side of the laminated metal foil LF50). Here, wobbling is a welding method in which a wobbling pattern such as a circle or an ellipse is drawn at high speed on the part to be welded. This wobbling can stabilize the melted state and improve the welding quality. On the other hand, even if the wobbling method is used, holes may be generated if the workpiece has a rectangular parallelepiped shape. For this reason, if the shape of the jig is a rectangular parallelepiped, it is difficult to perform high-quality laser welding on a laminated metal foil in which multiple copper foils are laminated.

[0048] For example, in sample #2, when the base shape (i.e., the shape of the protruding part of the jig) is not rectangular but trapezoidal columnar and has a tapered surface, it was found that laser welding could be performed properly (i.e., satisfying w1>w3 and w2>w3 shown in Figures 6 and 7) without holes being generated on the surface of the molten area (i.e., the upper side of the laminated metal foil LF50). For example, the ratio of the width length of the upper side to the lower side of the protruding part of sample #2 is 4:5. Therefore, if the protruding part of the jig has a tapered surface that satisfies the ratio of the width length of the upper side to the lower side of "3:5 to 1:1", high-quality laser welding can be performed on a laminated metal foil made of multiple copper foils.

[0049] For example, in sample #3, when the base shape (i.e., the shape of the protruding part of the jig) is not rectangular but trapezoidal columnar and has a tapered surface, it was found that laser welding could be performed properly (i.e., satisfying w1>w3 and w2>w3 shown in Figures 6 and 7) without generating holes on the surface of the molten area (i.e., the upper side of the laminated metal foil LF50). For example, the ratio of the width length of the upper side to the lower side of the protruding part of sample #2 is 3:5. Therefore, if the protruding part of the jig has a tapered surface that satisfies the ratio of the width length of the upper side to the lower side of "3:5 to 1:1", it is possible to perform high-quality laser welding on a laminated metal foil made of multiple copper foils.

[0050] As described above, the laser welding method for laminated metal foil according to the present embodiment includes a step of stacking a plurality of copper-based foils vertically, a step of placing the laminated metal foil LF50 on the jig JG1 in the blue laser welding system 100, and a step of directing and irradiating the laminated metal foil LF50 with a blue laser beam. After irradiation with the blue laser beam, in a cross section along the lamination direction of the copper-based foil of the laminated metal foil LF50, the lower end surface BTM1 of the molten region MLT1 generated in the laminated metal foil LF50 is not curved toward the center of the molten region MLT1. As a result, according to the laser welding method for laminated metal foil, regardless of the deviation of the irradiation position of the blue laser light (blue laser beam 70) and the presence or absence of variation in the metal foil, it is possible to suppress the curvature of the molten portion at the lower end side of the lamination direction of the laminated metal foil LF50 toward the center of the molten portion. Therefore, it is possible to realize high-quality laser welding of copper-based materials, which have been said to be difficult to laser weld in the past, while shortening the tact time.

[0051] Moreover, the protruding portion PJ1 of the jig (jig JG1) has a flat zenith surface TOP1 on which multiple copper-based foils are arranged, and a pair of tapered surfaces LTP1, RTP1 that are inclined approximately in the direction of gravity to the left and right of the flat zenith surface TOP1. As a result, according to the laser welding method for laminated metal foils, the gaps between the copper foils constituting the laminated metal foil LF50 (particularly the sides close to the tapered surfaces LTP1, RTP1) can be further reduced or eliminated.

[0052] Furthermore, the multiple copper-based foils are arranged across the flat vertex surface TOP1 and the pair of tapered surfaces LTP1, RTP1, and are fixed by clamp parts CLL, CLR arranged opposite the pair of tapered surfaces LTP1, RTP1, respectively. As a result, according to the laser welding method for laminated metal foils, the laminated metal foil LF50 is stably held while the blue laser beam 70 is irradiated onto the laminated metal foil LF50, and a molten region is appropriately formed without deterioration of the welding quality (for example, occurrence of appearance disturbance such as holes or loss of the weld bead).

[0053] Furthermore, after irradiation with the blue laser beam 70, in a cross section (a cross section along the lamination direction of the copper-based foil of the laminated metal foil LF50), the lower end surface BTM1 of the melted region MLT1 is flat (plain) or curved in the opposite direction to the center side of the melted region MLT1 (in other words, reverse curved). As a result, according to the laser welding method for laminated metal foils, in a cross section along the lamination direction of the copper foil of the laminated metal foil LF50, the shape of the melted region MLT1 is obtained as a three-dimensional cylindrical cross section, and a structure that is less susceptible to deterioration in electrical conductivity is obtained, making it possible to perform high-quality laser welding.

[0054] In addition, in a cross section (cross section along the lamination direction of the copper-based foil of the laminated metal foil LF50), the ratio of the width (width l1) of the flat vertex surface TOP1 to the width (width l2) of the bottom surface of the protruding portion PJ1 of the jig JG1 is 3:5 or more. As a result, according to the laser welding method for laminated metal foils, no welding defects such as holes occur in the melted region formed by irradiation with the blue laser beam 70, and high-quality laser welding can be performed.

[0055] In addition, wobbling or weaving is used in the irradiation of the blue laser beam. Here, weaving is a welding technique in which the laser welding is performed while the blue laser beam 70 is swung back and forth relative to the weld line. As a result, when wobbling is used, the molten state of the molten region MLT1 formed by the irradiation of the blue laser beam 70 can be stabilized, and the welding quality can be improved. In addition, when weaving is used, laser welding can be performed with a small number of passes (in other words, the number of welding times), and the tact time of the entire laser welding can be reduced.

[0056] 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, corrections, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure. In addition, the components in the various embodiments described above may be arbitrarily combined within the scope of the invention.

[0057] This application is based on a Japanese patent application (Patent Application No. 2023-001232) filed on January 6, 2023, the contents of which are incorporated by reference into this application. [Industrial Applicability]

[0058] The present disclosure is useful as a laser welding method for laminated metal foils that suppresses curvature of the molten portion at the lower end in the lamination direction of the laminated metal foil toward the center of the molten portion, regardless of deviation in the irradiation position of the laser light and variations in the metal foil. [Explanation of symbols]

[0059] 10 Laser Oscillator 11 Laser module 12 Beam combiner 13 Partially transparent mirror 20 Condenser lens unit 40 Transmission Fiber 41 cores 42 Clad 43 Coating 44 Laser beam entrance part 50 Control section 70 Blue Laser Beam 100 Blue laser welding system CLL, CLR Clamp section LF50 Laminated Metal Foil LTP1, RTP1 Tapered surface MLT1 melting region TOP1 Flat zenith surface

Claims

1. A method for laser welding a laminated metal foil in which a plurality of copper-based foils are laminated, comprising the steps of: stacking the plurality of copper foils one above the other; placing the laminated metal foil on a fixture in a blue laser welding system; directing a blue laser beam at the laminated metal foil; having After the irradiation of the blue laser beam, in a cross section of the laminated metal foil along the lamination direction of the copper-based foil, a lower end surface of the molten region generated in the laminated metal foil is not curved toward the center of the molten region. A method for laser welding laminated metal foils.

2. The jig has a flat zenith surface on which the plurality of copper-based foils are arranged, and a pair of tapered surfaces inclined approximately in the direction of gravity to the left and right of the flat zenith surface, A method for laser welding a laminated metal foil according to claim 1.

3. The plurality of copper-based foils are arranged across the flat apex surface and the pair of tapered surfaces, and are fixed by clamp portions arranged opposite each of the pair of tapered surfaces. A method for laser welding a laminated metal foil according to claim 2.

4. After the irradiation of the blue laser beam, in the cross section, the lower end surface of the melted region is flat or curved opposite to the center side of the melted region. A method for laser welding a laminated metal foil according to claim 1.

5. In the cross section, the ratio of the width of the flat zenith surface to the width of the bottom surface of the jig is 3:5 or more; A method for laser welding a laminated metal foil according to claim 2.

6. In irradiating the blue laser beam, wobbling or weaving is used. A method for laser welding a laminated metal foil according to claim 1.

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