Welding method and welding equipment

Abstract

To provide a new welding method and a new welding device which are improved.SOLUTION: A welding method and a welding device, which weld a metal member to a plurality of metal foils by emitting laser beams to the plurality of metal foils laminated in a first direction on a first surface of the metal member from the opposite side of the metal member, emit laser beams to second surfaces at the opposite side of the metal member of the metal foils furthest away from the metal member in the first direction of the plurality of metal foils and sweep the laser beams on the second surfaces, where the laser beams include a first laser beam with wavelengths of 800 [nm] or more and 1200 [nm] or less and a second laser beam with wavelengths of 500 [nm] or less. On the second surface, a whole region of a first intensity region where peak intensity of the first laser beam is 1 / e2 or more overlaps with a second intensity region where peak intensity of the second laser beam is 1 / e2 or more, and the second intensity region may have a region positioned at a front side and a region positioned at a rear side in a sweeping direction with respect to the first intensity region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, batteries in which a plurality of tabs and terminals are joined by laser welding are known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-4643 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of welding, it is important not only to ensure the required joint strength, but also to prevent welding defects such as spatters and blowholes from occurring in the workpiece.

[0005] Therefore, one object of the present invention is to provide an improved new welding method and welding apparatus that can weld, for example, a laminate in which a plurality of metal foils and metal members are superimposed. [Means for solving the problem]

[0006] The welding method of the present invention is, for example, a welding method in which a metal member and a plurality of metal foils stacked in a first direction on a first surface of the metal member are welded together by irradiating laser light from the opposite side of the metal member to the metal foils, wherein the laser light includes a first laser light having a wavelength of 800 nm or more and 1200 nm or less and a second laser light having a wavelength of 550 nm or less, and the laser light is irradiated onto a second surface of the metal foil that is farthest from the metal member in the first direction among the plurality of metal foils, on the opposite side of the metal member.

[0007] In the welding method, the second laser light may have a wavelength of 400 nm or more and 500 nm or less.

[0008] In the welding method, the laser light is swept on the second surface in a sweep direction along a second direction intersecting the first direction, and at least a portion of a second spot formed on the second surface by the second laser light may be located forward in the sweep direction of a first spot formed on the second surface by the first laser light.

[0009] In the welding method, the first spot and the second spot may at least partially overlap on the second surface.

[0010] In the welding method, a second outer edge of the second spot may surround a first outer edge of the first spot on the second surface.

[0011] In the welding method, a ratio of the first energy density of the first laser beam on the second surface to the second energy density of the second laser beam on the second surface may be 1 or more and 10 or less.

[0012] In the welding method, a ratio of the first energy density of the first laser beam on the second surface to the second energy density of the second laser beam on the second surface may be 2 or more and 8 or less.

[0013] In the welding method, a ratio of the first energy density of the first laser beam on the second surface to the second energy density of the second laser beam on the second surface may be 1 or more and 10 or less.

[0014] In the welding method, the metal member and each of the plurality of metal foils may be made of any one of a copper-based metal material, an aluminum-based metal material, a nickel-based metal material, an iron-based metal material, and a titanium-based metal material.

[0015] In the welding method, the thickness of the metal component in the first direction may be 0.05 mm or more and 2.0 mm or less, and the thickness of the multiple metal foil layers may be 0.05 mm or more and 2.0 mm or less.

[0016] The welding apparatus of the present invention is a welding apparatus for welding a metal member and a plurality of metal foils, comprising a laser oscillator and an optical head that irradiates laser light from the laser oscillator onto a plurality of metal foils stacked in a first direction on a first surface of the metal member from the opposite side of the metal member, wherein the laser light includes a first laser light having a wavelength of 800 nm or more and 1200 nm or less, and a second laser light having a wavelength of 500 nm or less, and the optical head irradiates the laser light onto a second surface of the metal foil that is farthest from the metal member in the first direction, on the opposite side of the metal member.

[0017] The welding device may include a beam shaper that splits the laser light into a plurality of beams.

[0018] The welding apparatus may be provided with a galvanometer scanner that changes the emission direction of the laser light so that the laser light moves in a sweeping direction along a second direction intersecting the first direction on a second surface of the metal foil that is farthest from the metal member among the plurality of metal foils, on the side opposite the metal member.

[0019] The metal laminate of the present invention includes, for example, a metal member having a first surface, a plurality of metal foils stacked on the first surface in a first direction, and a welded portion formed by welding the metal member and the plurality of metal foils, wherein the welded portion has a weld metal extending from a second surface of the metal foil farthest from the metal member in the first direction, on the side opposite the metal member, toward the metal member, and a heat-affected zone positioned around the weld metal, and the weld metal has a first portion and a second portion in which the average cross-sectional area of ​​the crystal grains in a cross section along the first direction is larger than that of the first portion.

[0020] In the metal laminate, for example, the average cross-sectional area of ​​the crystal grains included in the second portion may be 1.8 times or more the average cross-sectional area of ​​the crystal grains included in the first portion.

[0021] In the metal laminate, for example, the welded portion may extend in a second direction intersecting the first direction.

[0022] The metal laminate of the present invention may be, for example, a metal laminate having a metal member and a plurality of metal foils superposed on the metal member, the metal laminate including a first surface on the side opposite to the metal member, a second surface on the back side of the first surface, and a welded portion extending along the first surface, the welded portion having a weld metal extending from the first surface toward the second surface and a heat-affected zone positioned around the welded metal, and a first grain boundary number ratio expressed by the following formula (3-1): Rb1=N12 / N11 (3-1) (where Rb1 is the first grain boundary number ratio, N11 is the number of grain boundaries that intersect with a straight test line of a predetermined length along the first surface in a test cross section that is orthogonal to the first surface and along the extension direction of the weld, and N12 is the number of grain boundaries that intersect with the straight test line of the predetermined length that extends in a direction orthogonal to the first surface in the test cross section), the weld metal has a third portion that is positioned away from the first surface in the thickness direction from the first surface toward the second surface, and a fourth portion that is positioned between the third portion and the first surface and in which the first grain boundary number ratio is lower than the first grain boundary number ratio of the third portion.

[0023] The metal laminate of the present invention may include, for example, a metal laminate having a metal member and a plurality of metal foils superposed on the metal member, the metal laminate including a first surface on the opposite side to the metal member, a second surface on the back side of the first surface, and a welded portion extending along the first surface, the welded portion having a weld metal extending from the first surface to the second surface and a heat-affected zone positioned around the welded metal, and the second grain boundary number ratio is expressed by the following formula (3-2): Rb2=max(N22 / N21,N21 / N22) ···(3-2) (where Rb2 is the second grain boundary number ratio, N21 is the number of grain boundaries that intersect with a straight test line having a predetermined length extending in a first direction between a direction along the first surface and a direction perpendicular to the first surface, in a test cross section that is perpendicular to the first surface and along the extension direction of the weld, N22 is the number of grain boundaries that intersect with the straight test line having the predetermined length extending in a second direction perpendicular to the first direction, in the test cross section, and max(N22 / N21, N21 / N22) is When (N22 / N21) is equal to or greater than (N21 / N22), it is expressed as (N22 / N21), and when (N22 / N21) is less than (N21 / N22), it is expressed as (N21 / N22). When this is expressed as above, the weld metal has a third portion located away from the first surface in the thickness direction from the first surface toward the second surface, and a fourth portion located between the third portion and the first surface, in which the second grain boundary number ratio is higher than the second grain boundary number ratio of the third portion.

[0024] The metal laminate of the present invention may be, for example, a metal laminate having a metal member and a plurality of metal foils superposed on the metal member, the metal laminate including a first surface on the side opposite to the metal member, a second surface on the back side of the first surface, and a welded portion extending along the first surface, the welded portion having a weld metal extending from the first surface toward the second surface and a heat-affected zone positioned around the welded metal, and a first grain boundary number ratio expressed by the following formula (3-1): Rb1=N12 / N11 (3-1) (where Rb1 is the first grain boundary number ratio, N11 is the number of grain boundaries that intersect with a straight test line of a predetermined length along the first surface in a test cross section that is perpendicular to the first surface and along the extension direction of the weld, and N12 is the number of grain boundaries that intersect with the straight test line of the predetermined length that extends in a direction perpendicular to the first surface in the test cross section), and the second grain boundary number ratio Rb2 is expressed by the following formula (3-2): Rb2=max(N22 / N21,N21 / N22) ···(3-2) (where Rb2 is the second grain boundary number ratio; N21 is the number of grain boundaries that intersect with a straight test line having a predetermined length extending in a first direction between a direction along the first surface and a direction perpendicular to the first surface, in a test cross section that is perpendicular to the first surface and along the extension direction of the weld; N22 is the number of grain boundaries that intersect with a straight test line having the predetermined length extending in a second direction perpendicular to the first direction, in the test cross section; and max(N22 / N21, N21 / N22) is the ratio of (N22 / N21) to (N21 / N When (N22 / N21) is equal to or greater than (N22 / N22), it is expressed as (N22 / N21), and when (N22 / N21) is less than (N21 / N22), it is expressed as (N21 / N22). When this is expressed as (N22 / N21), the weld metal has a third portion located away from the first surface in the thickness direction from the first surface toward the second surface, and a fourth portion located between the third portion and the first surface, in which the first grain boundary number ratio is lower than the first grain boundary number ratio of the third portion and the second grain boundary number ratio is higher than the second grain boundary number ratio of the third portion.

[0025] The electrical component of the present invention includes, for example, the metal laminate as a conductor.

[0026] The electrical appliance of the present invention includes, for example, the metal laminate as a conductor. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide a novel and improved welding method and welding apparatus that are capable of welding, for example, a laminate in which a plurality of metal foils and metal members are superimposed. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is an exemplary schematic configuration diagram of a laser welding device according to the first embodiment. [Figure 2] FIG. 2 is an exemplary schematic cross-sectional view of a metal laminate as an object to be processed by the laser welding apparatus of the first embodiment. [Figure 3]FIG. 3 is an exemplary schematic cross-sectional view of a battery including a metal laminate as an object to be processed by the laser welding apparatus of the first embodiment. [Figure 4] FIG. 4 is an exemplary schematic diagram showing a beam (spot) of laser light formed on the surface of the object to be processed by the laser welding apparatus of the first embodiment. [Figure 5] FIG. 5 is a graph showing the light absorptance of each metal material versus the wavelength of the irradiated laser light. [Figure 6] FIG. 6 is an exemplary schematic cross-sectional view of a welded portion according to an embodiment. [Figure 7] FIG. 7 is an exemplary schematic cross-sectional view showing a part of a welded portion of the embodiment. [Figure 8] FIG. 8 is a graph showing the correlation between the output ratio, which is the ratio of the power of the second laser beam to the power of the first laser beam, and the spatter suppression rate, obtained by the laser welding device of the embodiment. [Figure 9] FIG. 9 is an enlarged view of a portion of FIG. [Figure 10] FIG. 10 is an explanatory diagram showing a case where a first reference line is applied to one position in the cross section of the welded portion of the embodiment. [Figure 11] FIG. 11 is an explanatory diagram showing a case where a second reference line is applied to one position in the cross section of the welded portion of the embodiment. [Figure 12] FIG. 12 is an exemplary schematic configuration diagram of a laser welding device according to the second embodiment. [Figure 13] FIG. 13 is an explanatory diagram showing the concept of the principle of the diffractive optical element included in the laser welding device of the second embodiment. [Figure 14] FIG. 14 is an exemplary schematic configuration diagram of a laser welding device according to the third embodiment. [Figure 15] FIG. 15 is an exemplary schematic configuration diagram of a laser welding device according to the fourth embodiment. [Figure 16] FIG. 16 is an exemplary schematic configuration diagram of a laser welding device according to the fifth embodiment. [Figure 17]FIG. 17 is a schematic diagram showing an example of a laser beam (spot) formed on the surface of the object to be processed by the laser welding device of the fifth embodiment. [Figure 18] FIG. 18 is a schematic diagram showing an example of a laser beam (spot) formed on the surface of the object to be processed by the laser welding device of the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] Exemplary embodiments of the present invention are disclosed below. The configurations of the embodiments described below, as well as the actions and results (effects) brought about by the configurations, are merely examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

[0030] The following embodiments have similar configurations. Therefore, according to the configurations of each embodiment, similar actions and effects based on the similar configurations can be obtained. Furthermore, in the following, similar configurations are given similar reference numerals, and duplicated explanations may be omitted.

[0031] In each figure, the X direction is represented by an arrow X, the Y direction is represented by an arrow Y, and the Z direction is represented by an arrow Z. The X direction, Y direction, and Z direction intersect and are perpendicular to each other. The X direction is the sweep direction SD, and the Y direction is the sweep width direction. The Z direction is the normal direction to the surface Wa (processing surface, welding surface) of the workpiece W, the thickness direction of the metal foil 12, and the stacking direction of the metal foil 12 and the metal laminate 10.

[0032] In this specification, ordinal numbers are given for convenience to distinguish between parts, members, portions, laser beams, directions, etc., and do not indicate priority or order.

[0033] [First embodiment] Fig. 1 is a schematic configuration diagram of a laser welding apparatus 100 according to the first embodiment. As shown in Fig. 1, the laser welding apparatus 100 includes a laser device 111, a laser device 112, an optical head 120, and an optical fiber 130. The laser welding apparatus 100 is an example of a welding apparatus.

[0034] The laser devices 111 and 112 each have a laser oscillator and are configured to be able to output laser light with a power of, for example, several kW. The laser devices 111 and 112 emit laser light with a wavelength of 380 nm or more and 1200 nm or less. The laser devices 111 and 112 each have a laser light source therein, such as a fiber laser, a semiconductor laser (element), a YAG laser, or a disk laser. The laser devices 111 and 112 may be configured to output multi-mode laser light with a power of several kW as the total output of multiple light sources.

[0035] The laser device 111 outputs a first laser light having a wavelength of 800 [nm] or more and 1200 [nm] or less. The laser device 111 is an example of a first laser device. As an example, the laser device 111 has a fiber laser or a semiconductor laser (element) as a laser light source. The laser oscillator of the laser device 111 is an example of a first laser oscillator.

[0036] On the other hand, the laser device 112 outputs a second laser light having a wavelength of 500 [nm] or less. The laser device 112 is an example of a second laser device. As an example, the laser device 112 has a semiconductor laser (element) as a laser light source. The laser device 112 preferably outputs a second laser light having a wavelength of 400 [nm] or more and 500 [nm] or less. The laser oscillator included in the laser device 112 is an example of a second laser oscillator.

[0037] The optical fiber 130 guides the laser beams output from the laser devices 111 and 112 to the optical head 120 .

[0038] The optical head 120 is an optical device for irradiating the laser light input from the laser devices 111 and 112 toward the workpiece W. The optical head 120 includes a collimating lens 121, a condensing lens 122, a mirror 123, and a filter 124. The collimating lens 121, the condensing lens 122, the mirror 123, and the filter 124 may also be referred to as optical components.

[0039] The optical head 120 is configured to be able to change its position relative to the workpiece W in order to sweep the laser light L while irradiating the laser light L over the surface Wa of the workpiece W. The relative movement between the optical head 120 and the workpiece W can be achieved by moving the optical head 120, moving the workpiece W, or moving both the optical head 120 and the workpiece W.

[0040] The optical head 120 may be configured to have a galvanometer scanner (not shown) or the like so as to be able to sweep the laser light L over the surface Wa.

[0041] The collimating lenses 121 (121-1, 121-2) each collimate the laser light input via the optical fiber 130. The collimated laser light becomes parallel light.

[0042] The mirror 123 reflects the first laser light that has been collimated by the collimator lens 121-1. The first laser light reflected by the mirror 123 travels in the opposite direction of the Z direction toward the filter 124. Note that in a configuration in which the first laser light is input to the optical head 120 so as to travel in the opposite direction of the Z direction, the mirror 123 is not necessary.

[0043] Filter 124 is a high-pass filter that transmits the first laser light and reflects but does not transmit the second laser light. The first laser light passes through filter 124 and travels in the opposite Z direction toward condenser lens 122. On the other hand, filter 124 reflects the second laser light that has been collimated by collimator lens 121-2. The second laser light reflected by filter 124 travels in the opposite Z direction toward condenser lens 122.

[0044] The condenser lens 122 condenses the first laser light and the second laser light as parallel light, and irradiates the object W to be processed with the condensed light as laser light L (output light).

[0045] The workpiece W is a metal laminate 10 in which a metal member 11 and a plurality of metal foils 12 are laminated in the Z direction. The metal laminate 10 is an example of a laminate. The metal laminate 10 has the metal member 11, a plurality of metal foils 12, and a weld 14. The weld 14 mechanically and electrically connects the metal member 11 and the plurality of metal foils 12.

[0046] 2 is a cross-sectional view of the metal laminate 10. As an example, the metal member 11 has a plate-like shape that extends across the Z direction. However, the metal member 11 is not limited to a plate-like member. A plurality of metal foils 12 are laminated in the Z direction on an end face 11a of the metal member 11 in the Z direction.

[0047] When the metal laminate 10 is welded by the laser welding apparatus 100, the metal laminate 10 is temporarily fixed together in the above-described stacked state by a fixing jig (not shown), and is set in an orientation in which the normal direction of the surface Wa of the metal foil 12 is approximately parallel to the Z direction. The fixing jig is, for example, two metal plates spaced apart from each other in the Z direction. The two metal plates are oriented intersecting the Z direction and sandwich the stacked metal member 11 and the multiple metal foils 12 in the Z direction. Of the two metal plates, the metal plate facing the optical head 120 is provided with a through-hole through which the laser light L can pass. The through-hole has a slit-like shape that is elongated in the sweep direction SD (X direction).

[0048] The surface Wa is an end face of the metal laminate 10 in the Z direction, and is the surface of the metal foil 12 farthest from the metal member 11 among the multiple metal foils 12, on the side opposite the metal member 11. The laser light L is directed in the opposite direction of the Z direction to the surface Wa, in other words, from the side opposite the metal member 11 to the surface Wa along the Z direction. The surface opposite the end face 11a of the metal member 11 is the back face Wb of the metal laminate 10. The surface Wa is the irradiated surface with the laser light L, and may also be referred to as the opposing surface facing the optical head 120. The Z direction is an example of a first direction. The end face 11a is an example of a first surface, and the surface Wa is an example of a second surface. The surface Wa is also an example of a first surface, and the back face Wb is an example of a second surface.

[0049] By irradiating the laser beam L in this manner, the welded portion 14 extends from the surface Wa in the direction opposite to the Z direction. The direction opposite to the Z direction may also be referred to as the depth direction of the welded portion 14. Furthermore, by sweeping the laser beam L in the X direction (sweeping direction SD) on the surface Wa, the welded portion 14 also extends in the X direction with a cross-sectional shape substantially similar to that shown in FIG. 2. The X direction is an example of a second direction. It may also be referred to as the longitudinal direction or extension direction of the welded portion 14. The Y direction may also be referred to as the width direction of the welded portion 14.

[0050] The welded portion 14 includes a weld metal 14a. The weld metal 14a extends from the surface Wa toward the metal member 11. The weld metal 14a has a first portion 14a1 and a second portion 14a2. The first portion 14a1 is formed primarily by irradiation with the first laser beam, and the second portion 14a2 is formed primarily by irradiation with the second laser beam. In the example of FIG. 2, the second portion 14a2 extends from the surface Wa in the opposite direction to the Z direction. The second portion 14a2 is adjacent to the first portion 14a1 in the Z direction. That is, the first portion 14a1 is adjacent to the second portion 14a2 in the opposite direction to the Z direction. The second portion 14a2 is formed within at least the plurality of metal foils 12. The first portion 14a1 extends across the plurality of metal foils 12 and the metal member 11. Furthermore, the weld metal 14a does not penetrate the metal laminate 10 as a whole in the Z direction. However, the shape of the weld metal 14a is not limited to this. The structure of the weld metal 14a including the first portion 14a1 and the second portion 14a2 will be described in detail later.

[0051] FIG. 3 is a cross-sectional view of a battery 1 as an electrical product having a metal laminate 10. The battery 1 is one application example of the metal laminate 10. In this case, the metal laminate 10 is an example of an electrical component as a conductor, and is an example of an electrical component included in an electrical product. An electrical component can also be referred to as a component of an electrical product.

[0052] The battery 1 shown in FIG. 3 is, for example, a laminated lithium-ion battery cell. The battery 1 has two film-like exterior materials 20. A storage chamber 20a is formed between the two exterior materials 20. A plurality of flat positive electrode materials 13p, a plurality of flat negative electrode materials 13m, and a plurality of flat separators 15 are stored in the storage chamber 20a. The positive electrode materials 13p and the negative electrode materials 13m are alternately stacked in the storage chamber 20a with the separators 15 interposed therebetween. Metal foils 12 extend from the plurality of positive electrode materials 13p and the plurality of negative electrode materials 13m, respectively. In the example of FIG. 3, the plurality of metal foils 12 extending from each of the positive electrode materials 13p are overlapped on a metal member 11 at the end of the battery 1 opposite in the Y direction, and a metal laminate 10 is formed by welding the metal member 11 and the plurality of metal foils 12 at this end. On the positive electrode side, only a portion of the metal member 11 is exposed to the outside of the exterior packaging material 20, while another portion of the metal member 11, the plurality of metal foils 12, and the welded portion 14 are not exposed to the outside of the exterior packaging material 20. The metal member 11 constitutes the positive electrode terminal of the battery 1. On the other hand, the plurality of metal foils 12 extending from each of the negative electrode materials 13m are overlapped on the metal member 11 at the Y-direction end of the battery 1, and a metal laminate 10 is formed in which the metal member 11 and the plurality of metal foils 12 are welded to each other at the end. On the negative electrode side, only a portion of the metal member 11 is exposed to the outside of the exterior packaging material 20, while another portion of the metal member 11, the plurality of metal foils 12, and the welded portion 14 are not exposed to the outside of the exterior packaging material 20. The metal member 11 constitutes the negative electrode terminal of the battery 1.

[0053] As shown in FIG. 3 , each metal laminate 10 is sandwiched between two exterior materials 20. Airtightness or liquid-tightness is ensured between the metal laminate 10 and the exterior materials 20 using a sealing material or the like. Therefore, it is preferable that the front surface Wa and back surface Wb of the metal laminate 10 have as little or no unevenness as possible. In this regard, the welding method of this embodiment can suppress the occurrence of welding defects, as described in detail below, thereby reducing unevenness on the front surface Wa due to welding defects. Therefore, the metal laminate 10 welded by the welding method of this embodiment is suitable for the positive and negative terminals of the battery 1. When the battery 1 is a lithium-ion battery cell, the metal foil 12 constituting the metal laminate 10 as the positive terminal is made of, for example, an aluminum-based metal material, and the metal foil 12 constituting the metal laminate 10 as the negative terminal is made of, for example, a copper-based metal material. The positive and negative terminals are examples of electrical components. The metal laminate 10 or the metal member 11 may also be called an electrode tab or a tab. The metal member 11 may also be called a conductive member.

[0054] FIG. 4 is a schematic diagram showing a beam (spot) of laser light L irradiated onto a surface Wa. Each of beams B1 and B2 has a power distribution, e.g., a Gaussian shape, in the radial direction of a cross section perpendicular to the optical axis of the beam. However, the power distribution of beams B1 and B2 is not limited to a Gaussian shape. In addition, in the diagrams in which beams B1 and B2 are represented by circles, as in FIG. 4, the diameter of the circle representing beams B1 and B2 is the beam diameter of each beam B1 and B2. The beam diameter of each beam B1 and B2 is defined as the diameter of the region including the peak of the beam and having an intensity equal to or greater than 1 / e2 of the peak intensity. Although not shown, in the case of a non-circular beam, the beam diameter can be defined as the length of the region having an intensity equal to or greater than 1 / e2 of the peak intensity in the direction perpendicular to the sweep direction SD. The beam diameter on the surface Wa is also referred to as the spot diameter.

[0055] 4, in this embodiment, as an example, the beam of laser light L is formed such that a beam B1 of the first laser light and a beam B2 of the second laser light overlap on the surface Wa, the beam B2 is larger (wider) than the beam B1, and the outer edge B2a of the beam B2 surrounds the outer edge B1a of the beam B1. In this case, the spot diameter D2 of the beam B2 is larger than the spot diameter D1 of the beam B1. On the surface Wa, the beam B1 is an example of a first spot, and the beam B2 is an example of a second spot.

[0056] 4, the beam (spot) of the laser light L on the surface Wa has a point-symmetric shape with respect to the center point C, so the shape of the spot is the same for any sweep direction SD. Therefore, when a movement mechanism is provided that moves the optical head 120 and the workpiece W relatively to sweep the laser light L on the surface Wa, the movement mechanism only needs to have a mechanism that can translate relatively, and a mechanism that can rotate relatively can sometimes be omitted.

[0057] The metal member 11 and the metal foil 12 serving as the processing object W can each be made of a conductive metal material. Examples of the metal material include copper-based metal materials, aluminum-based metal materials, nickel-based metal materials, iron-based metal materials, and titanium-based metal materials, and more specifically, copper, copper alloys, aluminum, aluminum alloys, tin, nickel, nickel alloys, iron, stainless steel, titanium, and titanium alloys. The metal member 11 and the metal foil 12 can be made of the same material or different materials.

[0058] [Wavelength and light absorption rate] Here, the light absorptance of metal materials will be explained. Figure 5 is a graph showing the light absorptance of each metal material versus the wavelength of the irradiated laser light L. The horizontal axis of the graph in Figure 5 represents wavelength, and the vertical axis represents absorptance. Figure 5 shows the relationship between wavelength and absorptance for aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), tantalum (Ta), and titanium (Ti).

[0059] Although the characteristics differ depending on the material, it can be seen that for each metal shown in Figure 5, the energy absorption rate is higher when using blue or green laser light (second laser light) than when using general infrared (IR) laser light (first laser light). This characteristic is particularly noticeable in copper (Cu), gold (Au), etc.

[0060] When laser light is irradiated onto a workpiece W with a relatively low absorption rate for the wavelength used, most of the light energy is reflected and does not affect the workpiece W as heat. Therefore, a relatively high power must be applied to obtain a melted region of sufficient depth. In this case, the sudden input of energy into the center of the beam causes sublimation and the formation of a keyhole.

[0061] On the other hand, when laser light is irradiated onto a workpiece W that has a relatively high absorption rate for the wavelength used, most of the input energy is absorbed by the workpiece W and converted into thermal energy. In other words, since there is no need to apply excessive power, no keyhole is formed and melting occurs by thermal conduction.

[0062] In this embodiment, the wavelength of the first laser beam, the wavelength of the second laser beam, and the material of the object-to-be-processed W are selected so that the absorptance of the second laser beam in the object-to-be-processed W is higher than the absorptance of the first laser beam. In this case, when the sweep direction is the sweep direction SD shown in Fig. 5, by sweeping the spot of the laser beam L, the part of the object-to-be-processed W to be welded (hereinafter referred to as the welded part) is first irradiated with the second laser beam by the region B2f of the beam B2 of the second laser beam located in front of SD in Fig. 5. Thereafter, the welded part is irradiated with the beam B1 of the first laser beam, and then the second laser beam is again irradiated by the region B2b of the beam B2 of the second laser beam located behind it in the sweep direction SD.

[0063] Therefore, a thermally conductive molten region is first formed in the welded portion by irradiating the second laser beam, which has a high absorption rate, in the region B2f. Then, a deeper keyhole-shaped molten region is formed in the welded portion by irradiating the first laser beam. In this case, since a thermally conductive molten region is already formed in the welded portion, a molten region of the required depth can be formed with a lower power first laser beam than in the case where the thermally conductive molten region is not formed. Then, the molten state of the welded portion is changed by irradiating the second laser beam, which has a high absorption rate, in the welded portion. From this perspective, the wavelength of the second laser beam is preferably 550 nm or less, and more preferably 500 nm or less.

[0064] Furthermore, experimental research by the inventors has confirmed that welding defects such as spatter and blowholes can be reduced in welding by irradiating laser light L of a beam such as that shown in Figure 4. This is presumably because the molten pool of the workpiece W formed by beam B2 and beam B1 becomes more stable when the workpiece W is preheated by region B2f of beam B2 before beam B1 arrives.

[0065] Furthermore, the inventors' experimental research has revealed that when the temperature of the metal foil 12 becomes higher than the temperature of the metal member 11 due to irradiation with the laser light L, the metal foils 12 are stretched by thermal expansion, and are bent and buckled so as to swell away from the metal member 11, creating gaps between the metal foils 12 and the metal member 11, which may result in welding of only the metal foils 12 or welding with gaps between the metal foils 12 and the metal member 11. Furthermore, the inventors have found that welding with such gaps can be prevented by setting appropriate conditions. The suitable conditions will be described later.

[0066] [Welding method] In welding using the laser welding apparatus 100, first, a metal laminate 10, in which a metal member 11 and a plurality of metal foils 12 are temporarily joined together by a holder, is set so that a laser beam L is irradiated onto the surface Wa. Then, while the laser beam L including beams B1 and B2 is irradiating the surface Wa, the laser beam L and the metal laminate 10 are moved relative to each other. As a result, the laser beam L moves (sweeps) over the surface Wa in a sweep direction SD while being irradiated onto the surface Wa. The portions irradiated with the laser beam L melt and then solidify as the temperature drops, thereby welding the metal member 11 and the plurality of metal foils 12 together and integrating the metal laminate 10.

[0067] [Weld cross section] FIG. 6 is a cross-sectional view of a weld 14 formed on a workpiece W. FIG. 6 is a cross-sectional view perpendicular to the sweep direction SD (X direction) and along the thickness direction (Z direction). The weld 14 extends in the sweep direction SD, i.e., in a direction perpendicular to the plane of the paper in FIG. 6. Note that FIG. 6 shows a cross-section of the weld 14 formed on the workpiece W, which is a single copper plate with a thickness of 2 mm. It can be assumed that the shape of the weld 14 formed on the metal laminate 10, which is made of a metal member 11 and multiple metal foils 12 stacked in the Z direction, is substantially the same as the shape of the weld 14 formed on the workpiece W, which is a single sheet of metal material, shown in FIG. 6.

[0068] As shown in Fig. 6, the weld 14 has a weld metal 14a extending from the surface Wa in the opposite direction to the Z direction, and a heat-affected zone 14b located around the weld metal 14a. The weld metal 14a is a portion that melts upon irradiation with laser light L and then solidifies. The weld metal 14a may also be referred to as a molten solidification zone. The heat-affected zone 14b is a portion of the base material of the workpiece W that is thermally affected but does not melt.

[0069] The width of the weld metal 14a in the Y direction becomes narrower as it gets farther away from the surface Wa. That is, the cross section of the weld metal 14a has a tapered shape that becomes narrower in the opposite direction to the Z direction.

[0070] Furthermore, detailed analysis of the cross section by the inventors revealed that the weld metal 14a includes a first portion 14a1 away from the surface Wa and a second portion 14a2 between the first portion 14a1 and the surface Wa.

[0071] The first portion 14a1 is a portion obtained by keyhole-shaped melting due to irradiation with the first laser beam, and the second portion 14a2 is a portion obtained by melting due to irradiation with the second laser beam B2 in a region B2b located behind the beam B2 in the sweep direction SD. Analysis using an electron backscattered diffraction (EBSD) method revealed that the crystal grain sizes in the first portion 14a1 and the second portion 14a2 are different, and specifically, in a cross section perpendicular to the X direction (sweep direction SD), the average cross-sectional area of ​​the crystal grains in the second portion 14a2 is larger than the average cross-sectional area of ​​the crystal grains in the first portion 14a1.

[0072] The inventors confirmed that when the object W is irradiated with only the beam B1 of the first laser light, i.e., when the region B2b located behind the beam B2 in the sweep direction SD is not irradiated, the second portion 14a2 is not formed and the first portion 14a1 extends deeply from the surface Wa in the opposite direction to the Z direction. That is, in this embodiment, the second portion 14a2 is formed near the surface Wa by irradiating the region B2b located behind the beam B2 in the sweep direction SD, and therefore it can be estimated that the first portion 14a1 is formed on the opposite side of the second portion 14a2 from the surface Wa, in other words, at a position away from the surface Wa in the opposite direction to the Z direction.

[0073] FIG. 7 is a cross-sectional view of a portion of the weld 14. FIG. 7 shows grain boundaries obtained by EBSD analysis. In FIG. 7, as an example, crystal grains A with a grain size of 13 μm or less are colored black. Note that 13 μm is not a threshold value for physical properties but a threshold value established for analyzing the experimental results. FIG. 7 also reveals that crystal grains A are present in relatively large numbers in the first portion 14a1 and in relatively small numbers in the second portion 14a2. That is, the average cross-sectional area of ​​the crystal grains in the second portion 14a2 is larger than the average cross-sectional area of ​​the crystal grains in the first portion 14a1. The inventors confirmed through experimental analysis that the average cross-sectional area of ​​the crystal grains in the second portion 14a2 is 1.8 times or more the average cross-sectional area of ​​the crystal grains in the first portion 14a1.

[0074] As shown in region I in Figure 7, these relatively small crystal grains A are densely packed in a position away from the surface Wa in the Z direction, elongated and elongated in the Z direction. Furthermore, analysis of multiple locations at different positions in the X direction (swiping direction SD) confirmed that the region where crystal grains A are densely packed also extends in the sweeping direction SD. Because welding is performed while sweeping, it can be assumed that crystals are formed in a similar form in the sweeping direction SD.

[0075] When it is difficult to distinguish the first portion 14a1 from the second portion 14a2 based on the appearance or hardness distribution in the cross section, a first region Z1 and a second region Z2 geometrically defined by the position and width wb on the surface Wa of the weld metal 14a, as shown in Figures 6 and 7, may be designated as the first portion 14a1 and the second region 14a2, respectively. As an example, the first region Z1 and the second region Z2 may be rectangular regions extending in the Z direction and having a width wm (equal width in the Y direction) in a cross section perpendicular to the sweep direction SD. The second region Z2 may be a region extending from the surface Wa to a depth d in the Z direction, and the first region Z1 may be a region deeper than the depth d, in other words, a region on the opposite side of the surface Wa from the position of the depth d. The width wm may be, for example, 1 / 3 of the width wb (average bead width) on the surface Wa of the weld metal 14a, and the depth d (height, thickness) of the second region Z2 may be, for example, 1 / 2 of the width wb. Furthermore, the depth of the first region Z1 can be, for example, three times the depth d of the second region Z2. The inventors have confirmed through experimental analysis of multiple samples that, with such settings for the first region Z1 and the second region Z2, the average cross-sectional area of ​​the crystal grains in the second region Z2 is greater than the average cross-sectional area of ​​the crystal grains in the first region Z1, and is at least 1.8 times that of the crystal grains in the first region Z1. This determination can also be evidence that the first portion 14a1 and the second portion 14a2 have been formed in the weld metal 14a by welding.

[0076] The inventors also experimentally analyzed the ratio of the energy density of the first laser beam on the surface Wa to the energy density of the second laser beam on the surface Wa. Here, the effective energy density E on the surface Wa for each laser beam is defined by the following formula (1): En = Am × Pn / (Dn × V) (1) where En is the effective energy density [J / mm2], Am is the absorptivity of the material of the workpiece W, Pn is the laser light output [W] from the laser device, Dn is the spot diameter [mm] on the surface Wa, and V is the sweep speed [mm / s]. Here, the subscript n distinguishes between the parameters, with n=1 indicating the parameter of the first laser light and n=2 indicating the parameter of the second laser light.

[0077] As a result, the ratio R of the effective energy density E1 of the first laser beam to the effective energy density E2 of the second laser beam on the surface Wa can be expressed by the following formula (2). R=E1 / E2 (2) The ratio R is a dimensionless number. The effective energy density E1 is an example of a first energy density, and the effective energy density E2 is an example of a second energy density.

[0078] The inventors conducted experiments under the following conditions: the ratio R was 2 or more and 47 or less, and the ratio R was irradiated only with the first laser beam and the ratio R was irradiated only with the second laser beam. The inventors' experimental analysis revealed that, from the viewpoints of suppressing spatter, suppressing blowholes in the metal foil 12, and achieving a penetration depth of the weld 14 above a threshold, the ratio R is preferably 1 or more and 10 or less, and more preferably 2 or more and 8 or less. Furthermore, with regard to gaps between the metal foils 12 and the metal member 11, it was found that when the ratio R is low, such as less than 1, the heat imparted to the metal foils 12 by the irradiation of the second laser beam does not reach the metal member 11, and the metal foils 12 are primarily heated, causing the metal foils 12 to stretch, bend, and buckle, resulting in the formation of the gaps. In other words, the inventors discovered that setting the ratio R to 1 or more can prevent gaps from forming between the metal foils 12 and the metal member 11.

[0079] Regarding the ratio R, specifically, when welding 50 stacked metal foils 12 made of oxygen-free copper and each having a thickness of 8 μm to the metal member 11, the best welding state with the least amount of spatter and blowholes was obtained when the output of the first laser beam B1 was 500 W or more, the output of the second laser beam B2 was 100 W or more, and the ratio R was approximately 6. Furthermore, when welding 100 stacked metal foils 12 made of oxygen-free copper and each having a thickness of 8 μm to the metal member 11, the best welding state with the least amount of spatter and blowholes was obtained when the output of the first laser beam B1 was 1000 W or more, the output of the second laser beam B2 was 400 W or more, and the ratio R was approximately 3.7.

[0080] The inventors also conducted experimental analysis of the case where the Z-direction thickness of the metal member 11 is within a practically expected range of 0.05 mm to 2.0 mm, and the Z-direction thickness of the layers of the metal foils 12 is within a practically expected range of 0.05 mm to 2.0 mm. Because the thicknesses of the metal member 11 and the layers of the metal foils 12 are thin, heat diffusion is suppressed. Therefore, when irradiated with laser light, a rapid temperature rise occurs, causing sublimation of the material, which may ultimately result in cutting. In this regard, the inventors confirmed through the experimental analysis that such cutting does not occur when the Z-direction thickness of the metal member 11 and the layers of the metal foils 12 is 0.05 mm or greater.

[0081] [Spatter suppression by the power ratio of the first laser beam and the second laser beam] 8 is a graph showing the correlation between the output ratio (Rp=Pw2 / Pw1), which is the ratio of the power (Pw2) of the second laser beam to the power (Pw1) of the first laser beam, and the sputter suppression rate, where Rs is defined as in the following formula (3): Rs=1-Nh / Nir (3) Here, Nh is the number of spatters generated within a predetermined area when both the first laser beam and the second laser beam are irradiated, and Nir is the number of spatters generated within a predetermined area when only the first laser beam is irradiated at the same power as when Nh was measured. Fig. 8 also shows the results of multiple experiments conducted at each output ratio. The line corresponding to the output ratio indicates the range of variation in the spatter suppression rate in the experimental results of multiple samples (at least three samples) at that output ratio, and the square indicates the median value of the spatter suppression rate for each output ratio.

[0082] As shown in FIG. 8, experimental research by the inventors has revealed that the output ratio Rp is preferably equal to or greater than 0.1 and less than 0.18 (◯), more preferably equal to or greater than 0.18 and less than 0.3 (◎), and even more preferably equal to or greater than 0.3 and less than 2 (◎◎).

[0083] [Distinguishing between different crystal grain orientations] FIG. 9 is an enlarged view of a portion of FIG. 2. Experimental studies by the inventors have revealed that, as shown in FIG. 9, in a weld 14 formed by irradiation with both the first laser beam and the second laser beam, the orientation (longitudinal direction, growth direction) of crystal grains varies depending on the depth from the surface Wa. This is thought to be due to the difference in the growth conditions of crystal grains during solidification between the third portion 14a3 obtained by keyhole-shaped melting due to irradiation with the first laser beam and the fourth portion 14a4 obtained by melting due to irradiation with the second laser beam B2 in the region B2b located behind the beam B2 in the sweep direction. Here, the third portion 14a3 is a portion located away from the surface Wa and corresponds to the first portion 14a1 described above. The fourth portion 14a4 is a portion located between the third portion 14a3 and the surface Wa and corresponds to the second portion 14a2 described above.

[0084] In order to numerically express such a configuration, the inventors defined an index representing the orientation (longitudinal direction) of crystal grains at each part in the weld 14 in accordance with A.2: cutting method of JIS G 0551:2020.

[0085] Specifically, as shown in FIG. 9, two types of reference lines, a first reference line R1 and a second reference line R2, are used in the cross-sectional image, each including two mutually orthogonal straight test lines. In FIG. 9, the first reference line R1 is shown as a solid line, and the second reference line R2 is shown as a dashed line. The first reference line R1 has two mutually orthogonal diameters of a reference circle R0 as straight test lines L11 and L12. One straight test line L11 extends in the X direction (sweep direction) along the surface Wa, and the other straight test line L12 extends in the Z direction perpendicular to the surface Wa. The second reference line R2 has two mutually orthogonal diameters of the same reference circle R0 as the first reference line R1 as straight test lines L21 and L22. One straight test line L21 extends in a direction between the X direction and the Z direction, and the other straight test line L12 extends in a direction between the opposite direction of the X direction and the Z direction or between the opposite direction of the Z direction and the X direction. The angle difference between the straight test line L11 and the straight test line L21 is 45° or 135°, and the angle difference between the straight test line L12 and the straight test line L22 is 45° or 135°. The length of the diameter of the reference circle R0, i.e., the lengths of the straight test lines L11, L12, L21, and L22, is, for example, a length corresponding to 200 μm (an example of a predetermined length), but can be set appropriately depending on the size of the crystal grains.

[0086] Then, at each point P in the weld 14, the first reference line R1 and the second reference line R2 are applied, and the first grain boundary number ratio Rb1 and the second grain boundary number ratio Rb2 are calculated by the following equations (3-1) and (3-2). Rb1=N12 / N11 (3-1) Rb2=max(N22 / N21,N21 / N22) ···(3-2) Here, N11 is the number of crystal grains intersecting the straight test line L11, and N12 is the number of crystal grains intersecting the straight test line L12. N21 is the number of crystal grains intersecting the straight test line L21, and N22 is the number of crystal grains intersecting the straight test line L22. The number of crystal grains may also be referred to as the number of grain boundaries. In addition, in formula (3-2), when (N22 / N21) is equal to or greater than (N21 / N22), max(N22 / N21, N21 / N22) is (N22 / N21), and when (N22 / N21) is less than (N21 / N22), max(N22 / N21, N21 / N22) is (N21 / N22). In actual measurements, the above measurements are made at any predetermined number of locations, for example, 10 or more locations, in a micrograph of the XZ cross section taken at 50x magnification, and the average values ​​can be taken as Rb1 and Rb2. Note that if any of N11, N12, N21, and N22 is 0 at point P in the weld 14, the number of grain boundaries at that point P does not need to be used in calculating Rb1 and Rb2.

[0087] 10 and 11 are schematic explanatory diagrams showing the application of the first reference line R1 ( FIG. 10 ) and the application of the second reference line R2 ( FIG. 11 ) to a point P in the cross section of the weld 14. As shown in FIGS. 10 and 11 , the number of intersections of the crystal grain A (grain boundary) with the linear test lines L11, L12, L21, and L22 is different. In the example of FIGS. 10 and 11 , the angular difference between the linear test line L21 and the crystal grain A is relatively small, so the number of grain boundaries N21 is smaller than the numbers of other grain boundaries N11, N12, and N22. Therefore, point P shown in the example of FIGS. 10 and 11 is a point P where the second grain boundary number ratio Rb2 is higher than the first grain boundary number ratio Rb1. Similarly, in the above definition, at point P where the angular difference between the longitudinal direction of the crystal grain A and the X direction is relatively small within the reference circle R0, the first grain boundary number ratio Rb1 is relatively high and is larger than the second grain boundary number ratio Rb2. Furthermore, at point P where the angle difference between the longitudinal direction of crystal grain A and the direction between the X direction and the Z direction (45° direction) is relatively small, the second grain boundary number ratio Rb2 is relatively high and is greater than the first grain boundary number ratio Rb1.

[0088] Experimental studies by the inventors have revealed that the first grain boundary number ratio Rb1 at each point P in the fourth region 14a4 is lower than the first grain boundary number ratio Rb1 at each point P in the third region 14a3. It has also been revealed that the second grain boundary number ratio Rb2 at each point P in the fourth region 14a4 is higher than the second grain boundary number ratio Rb2 at each point P in the third region 14a3. It has also been revealed that the first grain boundary number ratio Rb1 is higher than the second grain boundary number ratio Rb2 at each point P in the third region 14a3, and that the second grain boundary number ratio Rb2 is higher than the first grain boundary number ratio Rb1 at each point P in the fourth region 14a4. The presence of regions in the weld 14 with different first grain boundary number ratios Rb1 and second grain boundary number ratios Rb2 is considered to be a factor in achieving strong weld strength in the workpiece W, and can also be evidence that welding was performed by irradiating both the first laser beam and the second laser beam.

[0089] As described above, in the welding method of this embodiment, for example, a metal laminate 10 (laminate) in which a plurality of metal foils 12 are stacked in the Z direction (first direction) on an end face 11a (first surface) of a metal member 11 is irradiated with laser light L along the Z direction from the opposite side of the metal member 11 to the plurality of metal foils 12, in other words, in the opposite direction of the Z direction. This results in a metal laminate 10 in which the metal member 11 and the plurality of metal foils 12 are welded together via welds 14.

[0090] If the metal member 11 and all of the metal foils 12 are to be welded together using laser light L irradiated onto the metal member 11, the molten region (molten pool) forming the weld 14 needs to penetrate from the metal member 11 through all of the metal foils 12. In this case, if the output of the laser light L is too low, the weld 14 may not reach the metal foils 12 far from the metal member 11, resulting in failure to weld the metal foils 12. Conversely, if the output of the laser light L is too high, the metal foils 12 far from the metal member 11 may tear, resulting in poor welding. In this regard, according to the configuration and method of the present embodiment, as described above, the weld 14 is formed by irradiating the metal foils 12 from the opposite side of the metal member 11 with laser light L. This makes it easier to form the weld 14 that penetrates the multiple metal foils 12 and reaches the metal member 11, and also avoids the above-described disadvantages that occur when laser light L is irradiated onto the metal member 11. Furthermore, if a keyhole-type molten state occurs in the layers of the plurality of metal foils 12 from the beginning of the irradiation of the laser beam, there is a risk of welding defects such as blowholes in the metal foils 12. In this regard, in the present embodiment, a heat conduction-type molten state is obtained in the layers of the plurality of metal foils 12 from the beginning of the irradiation of the laser beam to the plurality of metal foils 12, so that welding defects such as blowholes in the metal foils 12 can be avoided.

[0091] In this embodiment, for example, the wavelength of the second laser light is not less than 400 [nm] and not more than 500 [nm].

[0092] According to such a configuration and method, for example, it is possible to obtain a metal laminate 10 of higher quality with less or no spatter and no blowholes in the metal foil 12.

[0093] In this embodiment, for example, on the surface Wa, at least a part of the beam B2 of the second laser light (second spot) is located further forward in the sweep direction SD than the beam B1 of the first laser light (first spot).

[0094] In this embodiment, for example, the beam B1 and the beam B2 at least partially overlap on the surface Wa.

[0095] In this embodiment, for example, the beam B2 is wider than the beam B1 on the surface Wa.

[0096] In this embodiment, for example, on the surface Wa, the outer edge B2a (second outer edge) of the beam B2 surrounds the outer edge B1a (first outer edge) of the beam B1.

[0097] As described above, the inventors have confirmed that welding by irradiating the laser beam L that forms such beams B1 and B2 on the surface Wa can further reduce spatter and blowholes. This is presumably because, as described above, preheating the workpiece W by region B2f of beam B2 before the arrival of beam B1 stabilizes the molten pool of the workpiece W formed by beam B2 and beam B1. Therefore, laser beam L having such beams B1 and B2 can perform welding with higher welding quality, for example, with fewer spatters and blowholes. Furthermore, setting beams B1 and B2 in this way also has the advantage of allowing the power of the first laser beam to be lowered. Furthermore, when beams B1 and B2 are irradiated coaxially, it also has the advantage of eliminating the need for relative rotation between the optical head 120 and the workpiece W.

[0098] In this embodiment, for example, the ratio of the effective energy density E1 (first energy density) of the first laser light on the surface Wa (second surface) to the effective energy density E2 (first energy density) of the second laser light on the surface Wa (second surface) is 1 or more and 10 or less.

[0099] According to such a configuration and method, for example, a metal laminate 10 of even higher quality can be obtained.

[0100] In this embodiment, the workpiece W is made of, for example, any one of a copper-based metal material, an aluminum-based metal material, a nickel-based metal material, an iron-based metal material, and a titanium-based metal material.

[0101] The effect of the welding method of this embodiment can be obtained when the workpiece W is made of any of the above materials.

[0102] [Second embodiment] 12 is a schematic configuration diagram of a laser welding apparatus 100A according to the second embodiment. In this embodiment, an optical head 120 has a DOE 125 between a collimator lens 121-1 and a mirror 123. Except for this, the laser welding apparatus 100A has the same configuration as the laser welding apparatus 100 according to the first embodiment.

[0103] The DOE 125 shapes the shape of the beam B1 of the first laser light (hereinafter referred to as the beam shape). As conceptually illustrated in Fig. 13, the DOE 125 has a configuration in which, for example, a plurality of diffraction gratings 125a with different periods are superimposed. The DOE 125 can shape the beam shape by bending the parallel light in a direction influenced by each diffraction grating 125a or by superimposing the diffraction gratings 125a. The DOE 125 may also be referred to as a beam shaper.

[0104] The optical head 120 may have a beam shaper that is provided after the collimator lens 121-2 and adjusts the beam shape of the second laser light, or a beam shaper that is provided after the filter 124 and adjusts the beam shapes of the first laser light and the second laser light. By appropriately adjusting the beam shape of the laser light L with the beam shaper, the occurrence of spatters and blowholes during welding can be further suppressed.

[0105] [Third embodiment] 14 is a schematic diagram of a laser welding apparatus 100B according to the third embodiment. In this embodiment, the optical head 120 has a galvanometer scanner 126 between the filter 124 and the condenser lens 122. Except for this, the laser welding apparatus 100B has the same configuration as the laser welding apparatus 100 according to the first embodiment.

[0106] The galvanometer scanner 126 has two mirrors 126a and 126b, and is a device that can move the irradiation position of the laser light L and sweep the laser light L without moving the optical head 120 by controlling the angles of the two mirrors 126a and 126b. The angles of the mirrors 126a and 126b are each changed by, for example, a motor (not shown). With this configuration, a mechanism for relatively moving the optical head 120 and the workpiece W is not required, which has the advantage of allowing the device configuration to be made more compact, for example.

[0107] [Fourth embodiment] 15 is a schematic diagram of a laser welding apparatus 100C according to the fourth embodiment. In this embodiment, the optical head 120 has a DOE 125 (beam shaper) between the collimator lens 121-2 and the filter 124. Except for this, the laser welding apparatus 100C has a configuration similar to that of the laser welding apparatus 100B according to the third embodiment. With this configuration, it is possible to obtain the same effect as in the third embodiment by having the galvano scanner 126, and the same effect as in the second embodiment by having the DOE 125 (beam shaper).

[0108] In this embodiment, the optical head 120 may also have a beam shaper provided after the collimator lens 121-1 to adjust the beam shape of the first laser light, or a beam shaper provided after the filter 124 to adjust the beam shapes of the first laser light and the second laser light.

[0109] [Fifth embodiment] 16 is a schematic diagram of a laser welding apparatus 100D according to a fifth embodiment. In this embodiment, the optical head 120 includes a first portion 120-1 that irradiates the first laser beam L1 and a second portion 120-2 that irradiates the second laser beam L2, each of which is formed by a separate body (housing). With this configuration, the same actions and effects as those of the above-described embodiments can be obtained.

[0110] 17 and 18 show examples of laser beams B1 and B2 formed on a surface Wa by a laser welding apparatus 100D. As shown in FIGS. 17 and 18, the laser welding apparatus 100D allows the relative positions of beams B1 and B2 to be arbitrarily set by setting the relative positions and orientations of the first and second portions 120-1 and 120-2. Research by the inventors has revealed that when at least a portion of beam B2 (second spot) is located forward of beam B1 (first spot) in the sweep direction SD on the surface Wa, as shown in FIGS. 17 and 18, and when beams B1 and B2 are in contact with or at least partially overlap each other, a similar effect to that of the first embodiment due to the preheating effect of beam B2 can be obtained. It has also been found that when at least a portion of beam B2 is located forward of beam B1 in the sweep direction SD, beams B1 and B2 may be spaced apart by a small distance. 17 and 18 are merely examples, and the arrangement of the beams B1 and B2 obtained by the laser welding apparatus 100D and the size of each beam B1 and B2 are not limited to the examples of FIGS.

[0111] While the embodiments of the present invention have been described above, they are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate.

[0112] For example, the present invention can be applied to lithium-ion battery cells having configurations different from those of the above-described embodiments, and can also be applied to batteries other than lithium-ion battery cells. Furthermore, a battery is an example of an electrical product, and the electrical product of the present invention is not limited to a battery. Furthermore, a battery terminal is an example of an electrical component, and the electrical component of the present invention is not limited to a battery terminal.

[0113] Furthermore, when sweeping the laser beam over the workpiece, the sweep may be performed by known wobbling, weaving, output modulation, or the like, to adjust the surface area of ​​the molten pool.

[0114] The laser beam may be swept multiple times over the workpiece. In this case, [1] the power of the laser beam in the subsequent sweep may be lower or higher than the power of the laser beam in the previous sweep, [2] the sweep speed of the subsequent sweep may be higher or faster than the sweep speed of the previous sweep, or [3] the power of the laser beam in the subsequent sweep may be higher than the power of the laser beam in the previous sweep and the sweep speed of the subsequent sweep may be higher than the sweep speed of the previous sweep.

[0115] The object to be processed may also be a metal plated metal plate or the like, in which a thin layer of another metal is present on the surface of the metal. [Industrial Applicability]

[0116] The present invention can be used in welding methods, welding devices, metal laminates, electrical components, and electrical products. [Explanation of symbols]

[0117] 1...Batteries (electrical appliances) 10...Metal laminate (laminate, electrical component) 11...Metal parts 11a...End surface (first surface) 12...Metal foil 13p...cathode material 13m…Negative electrode material 14...Welded section 14a...weld metal 14a1…first part 14a2…Second part 14a3…Third part 14a4…Fourth part 14b…Heat affected zone 15...Separator 20...Exterior material 20a…Containment room 100, 100A to 100D...Laser welding equipment (welding equipment) 111...Laser device (first laser oscillator) 112...Laser device (second laser oscillator) 120...Optical head 120-1…First part 120-2…Second part 121, 121-1, 121-2...Collimating lenses 122...Condenser lens 123...Mirror 124...Filter 125...DOE (diffractive optical element) 125a...diffraction grating 126...Galvanometer scanner 126a, 126b...Mirror 130...Optical fiber A...Crystal grain Am...Absorption rate B1...Beam (first spot) B1a…Outer edge B2...Beam (second spot) B2a…Outer edge B2b…area B2f…area C...center point D1...Spot diameter (outer diameter) D2: Spot diameter (outer diameter) Dn: Spot diameter d...depth E: Effective energy density E1...effective energy density (first energy density) E2: Effective energy density (second energy density) I…area L...laser light L1: First laser beam L2: Second laser beam L11, L12, L21, L22...Straight test lines N11,N12,N21,N22…Number of grain boundaries P…point Pn...Output R…ratio R0: Reference circle R1…First reference line R2…Second reference line Rb1…first grain boundary number ratio Rb2…Second grain boundary number ratio SD: Sweep direction V…Sweep speed W...Processing target Wa…Surface (second side) Wb…Back side wb: width (at the surface of the weld metal) wm: width (of the first and second regions) X…direction (second direction) Y...direction Z…direction (first direction) Z1...first area (first part) Z2…Second area (second part)

Claims

1. A welding method for welding a metal member and a plurality of metal foils stacked in a first direction on a first surface of the metal member by irradiating a laser beam from an opposite side of the metal member to form a weld metal spanning the plurality of metal foils and the metal member, the method comprising: the laser light includes a first laser light having a wavelength of 800 nm or more and 1200 nm or less, and a second laser light having a wavelength of 550 nm or less, the laser light is irradiated onto a second surface of the metal foil farthest from the metal member in the first direction among the plurality of metal foils, the second surface being opposite to the metal member, and the laser light is swept over the second surface; On the second surface, 1 / e of the peak intensity of the first laser beam ２ The entire first intensity region is 1 / e of the peak intensity of the second laser beam. ２ the second intensity region overlaps with the first intensity region, the second intensity region having a region located forward and a region located rearward of the first intensity region in the sweep direction, the region not overlapping with the first intensity region; A welding method in which the second laser beam is used to thermally melt at least a portion of the second surface side of the plurality of metal foils, thereby forming a second portion of the weld metal that remains within the plurality of metal foils, and the first laser beam is used to cause keyhole-type melting, thereby forming a first portion of the weld metal that extends from a position adjacent to the second portion on the opposite side of the second surface to within the metal member.

2. 2. The welding method according to claim 1, wherein the thickness of the metal component in the first direction is 0.05 mm or more and 2.0 mm or less, and the thickness of the plurality of metal foil layers is 0.05 mm or more and 2.0 mm or less.

3. The welding method according to claim 1 or 2, wherein the laser beam is irradiated onto the second surface while being wobble, weaved, or output-modulated.

4. 4. The welding method according to claim 1, wherein the laser beam is swept a plurality of times on the second surface.

5. 5. The welding method according to claim 1, wherein the laser beam is swept on the second surface, and a sweep speed on the second surface is changed midway through the sweep on the second surface.

6. 6. The welding method according to claim 1, wherein the laser beam is swept over the second surface, and the power of the laser beam is changed midway through the sweep over the second surface.

7. The welding method according to any one of claims 1 to 6, wherein the metal member includes a plated metal plate.

8. 8. The welding method according to claim 1, wherein a second spot formed on the second surface by the second laser beam is wider than a first spot formed on the second surface by the first laser beam.

9. 9. The welding method according to claim 1, wherein the laser light is irradiated onto the second surface in a state where a normal direction of the second surface is approximately parallel to the first direction.

10. 10. The welding method according to claim 1, wherein a shape of a spot formed on the second surface by the laser light has a point-symmetric shape with respect to a center of the spot.

11. The welding method according to any one of claims 1 to 10, wherein the first laser beam and the second laser beam are emitted coaxially.

12. 12. The welding method according to claim 1, wherein a center of a first spot formed on the second surface by the first laser beam and a center of a second spot formed on the second surface by the second laser beam substantially coincide with each other.

13. 10. The welding method according to claim 1, wherein a first spot formed on the second surface by the first laser beam and a second spot formed on the second surface by the second laser beam are offset from each other on the second surface.

14. a laser oscillator; an optical head that irradiates a laser beam from the laser oscillator onto a plurality of metal foils stacked in a first direction on a first surface of a metal member from an opposite side of the metal member; a welding apparatus for welding the metal member and the plurality of metal foils by forming a weld metal spanning the plurality of metal foils and the metal member, the laser light includes a first laser light having a wavelength of 800 nm or more and 1200 nm or less, and a second laser light having a wavelength of 500 nm or less, the optical head irradiates the laser light onto a second surface of the metal foil farthest from the metal member in the first direction among the plurality of metal foils, the second surface being on an opposite side to the metal member, and sweeps the laser light over the second surface; On the second surface, 1 / e of the peak intensity of the first laser beam ２ The entire first intensity region is 1 / e of the peak intensity of the second laser beam. ２ the second intensity region overlaps with the first intensity region, the second intensity region having a region located forward and a region located rearward of the first intensity region in the sweep direction, the region not overlapping with the first intensity region; A welding device that forms a second portion of the weld metal that remains within the plurality of metal foils by thermal conduction melting at least a portion of the second surface side of the plurality of metal foils with the second laser light, and forms a first portion of the weld metal that extends into the metal member from a position adjacent to the second portion on the opposite side of the second surface with the first laser light.

15. 15. The welding apparatus of claim 14, further comprising a beam shaper that splits the laser light into a plurality of beams.

16. 16. The welding device according to claim 14 or 15, further comprising a galvanometer scanner that changes the emission direction of the laser light so that the laser light moves on the second surface in a sweep direction along a second direction that intersects with the first direction.

17. 17. The welding device according to claim 14, wherein the optical head irradiates the second surface with the laser light while performing wobbling, weaving, or output modulation.

18. 18. The welding device according to claim 14, wherein the optical head irradiates the first laser beam and the second laser beam coaxially.

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