Welding method and welding structure

Abstract

To provide a welding method and a welding structure capable of suppressing an influence on welding strength of upper two layers even in welding when a metal different from the upper two layers exists in a lower layer.SOLUTION: The first metal layer, the second metal layer, and the third metal layer are disposed in this order from an upper side, and the first metal layer and the second metal layer are joined by laser welding. A welding method, wherein a first metal layer and a second metal layer are made of a first metal material of a same kind, a third metal layer is made of a second metal material different from the first metal material, and when the first metal layer and the second metal layer are joined by laser welding by irradiating and scanning a laser beam from a side of the first metal layer, the first metal layer is irradiated with the laser beam while rotating the laser beam from an inner side toward an outer side.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to welding methods and welded structures. [Background technology]

[0002] Patent Document 1 (WO 2015 / 129231) discloses a technique relating to a laser welding method in which a laser beam is irradiated in a spiral pattern onto a workpiece for a lap joint. According to the laser welding disclosed in Patent Document 1, the laser beam is irradiated while moving in a spiral trajectory so that the laser beam is not re-irradiated onto the liquid phase portion melted by the laser beam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 129231 Summary of the Invention [Problem to be solved by the invention]

[0004] In some battery packs, aluminum is used for the bus bars, and the electrode terminals attached to the battery cells have a two-layer structure with an aluminum layer on the outside and a copper layer on the inside. In this case, the bus bars are fixed to the outer aluminum layer of the electrode terminals by laser welding.

[0005] At the welding point, from the outside, the first layer is an aluminum layer, the second layer is an aluminum layer, and the third layer is a metal layer. In this case, the first and second layers are made of the same metal material, and the third layer is made of a different metal material from the first and second layers.

[0006] When laser welding is performed on such a metal laminate structure, it is possible that the welded joint between the two upper layers of the same metal may reach the third layer of dissimilar metal and melt the third layer of dissimilar metal, resulting in the formation of an intermetallic compound, which may reduce the weld strength of the two upper layers.

[0007] In conventional laser welding to fix busbars to electrode terminals, welding is performed while rotating from the outside to the inside, but the weld tends to become deeper in the latter half of the welding process. This is because the weld points come close to each other in the latter half of the welding process, and the weld (molten pool) becomes deeper due to the thermal influence of each other, causing the weld to reach deep into the third layer of dissimilar metal and melt.

[0008] The object of the present disclosure has been made to solve the above-mentioned problems, and is to provide a welding method and welding structure that can suppress the impact on the weld strength of the upper two layers, even when welding is performed when the lower layer contains a metal different from the upper two layers. [Means for solving the problem]

[0009] [1] The welding method disclosed herein is a welding method in which a first metal layer, a second metal layer, and a third metal layer are arranged in this order from above, and the first metal layer and the second metal layer are joined by laser welding, wherein the first metal layer and the second metal layer are made of the same first metal material, and the third metal layer is made of a second metal material different from the first metal material, and when irradiating and scanning a laser beam from the side of the first metal layer to join the first metal layer and the second metal layer by laser welding, the laser beam is irradiated onto the first metal layer while rotating from the inside to the outside.

[0010] [2] The welding method according to [1], wherein the scanning of the laser light is performed by rotating the laser light from the inside to the outside along a rectangular shape.

[0011] [3] The welding method according to [1] or [2], wherein the first metal material is aluminum and the second metal material is copper.

[0012] [4] The welding method according to any one of [1] to [3], wherein the first metal layer is a bus bar used in a battery pack, the second metal layer and the third metal layer are electrode terminals that constitute the battery pack, and the bus bar is welded to the electrode terminals using the laser light.

[0013] [5] The welding structure disclosed herein is a welding structure in which a first metal layer, a second metal layer, and a third metal layer are arranged in this order from above, and the first metal layer and the second metal layer are joined by laser welding, wherein the first metal layer and the second metal layer are made of the same first metal material, and the third metal layer is made of a second metal material different from the first metal material, and when a laser beam is irradiated from the first metal layer side to join the first metal layer and the second metal layer by laser welding, the laser beam is irradiated and scanned onto the first metal layer while rotating from the inside to the outside, and when viewed in a cross section along the irradiation direction of the laser beam after the laser welding, the welding depth of the weld between the first metal layer and the second metal layer is shallower on the inside than on the outside.

[0014] [6] The welding structure according to [5], wherein the scanning of the laser light is performed by rotating the laser light from the inside to the outside along a rectangular shape.

[0015] [7] The welded structure according to [5] and [6], wherein the first metal material is aluminum and the second metal material is copper.

[0016] [8] The welding structure according to any one of [5] to [7], wherein the first metal layer is a bus bar used in a battery pack, and the second metal layer and the third metal layer are electrode terminals that constitute the battery pack. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a welding method and a welding structure that can suppress the impact on the weld strength of the upper two layers, even when welding is performed when the lower layer contains a metal different from that of the upper two layers. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a basic configuration of a battery pack. [Figure 2] 2 is a diagram showing battery cells and end plates in the battery pack shown in FIG. 1. FIG. [Figure 3] 2 is a diagram showing a battery cell in the battery pack shown in FIG. 1. FIG. [Figure 4] FIG. 2 is a diagram showing the arrangement of bus bars in a battery pack. [Figure 5] FIG. 5 is a partial cross-sectional view taken along the arrow V in FIG. 4. [Figure 6] 5A to 5C are schematic diagrams illustrating a method for welding an electrode terminal and a bus bar together. [Figure 7] FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6. [Figure 8] 7 is a cross-sectional view of the related art taken along line VII-VII in FIG. 6. [Figure 9] 10A and 10B are schematic diagrams showing another method of welding an electrode terminal and a bus bar. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the following, embodiments of the present technology will be described. The same or corresponding parts are denoted by the same reference characters, and description thereof may not be repeated.

[0020] In the embodiments described below, when numbers, amounts, etc. are mentioned, the scope of the present technology is not necessarily limited to those numbers, amounts, etc., unless otherwise specified. In the embodiments described below, each component is not necessarily essential to the present technology, unless otherwise specified. The present technology is not necessarily limited to those that achieve all of the effects mentioned in the present embodiments.

[0021] In this specification, the words "comprise," "include," and "have" are open-ended, meaning that when a certain feature is included, other features may or may not be included.

[0022] When geometric terms and terms expressing positional and directional relationships, such as "parallel," "orthogonal," "45° diagonal," "coaxial," and "along" are used in this specification, these terms allow for manufacturing errors and slight variations. When terms expressing relative positional relationships, such as "upper side" and "lower side," are used in this specification, these terms are used to indicate relative positional relationships in a single state, and the relative positional relationships can be reversed or rotated to any angle by changing the installation direction of each mechanism (for example, by turning the entire mechanism upside down).

[0023] The battery pack 1 described below can be mounted in an electric vehicle (BEV: Battery Electric Vehicle), a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle), a hybrid electric vehicle (HEV: Hybrid Electric Vehicle), etc. However, the use of the battery pack 1 is not limited to being mounted in a vehicle.

[0024] (Battery 1) Fig. 1 is a diagram showing the basic configuration of a battery pack 1. Fig. 2 is a diagram showing battery cells 100 and end plates 200 included in the battery pack 1. Fig. 3 is a diagram showing the battery cells 100 in the battery pack 1.

[0025] As shown in FIGS. 1 and 2, a battery pack 1, which is an example of a “power storage module,” includes battery cells 100, end plates 200, and restraining members 300.

[0026] As an example, the battery cell 100 is a lithium ion battery, but the battery cell 100 may be another battery such as a nickel metal hydride battery.

[0027] The multiple battery cells 100 are arranged in a line in the Y-axis direction (arrangement direction). Each battery cell 100 includes an electrode terminal 110. Separators (not shown) may be interposed between the multiple battery cells 100. The multiple battery cells 100 sandwiched between the two end plates 200 are pressed by the end plates 200 and are constrained between the two end plates 200.

[0028] The end plates 200 are arranged on both ends of the battery pack 1 in the Y-axis direction (arrangement direction). The end plates 200 are fixed to a base such as a case that houses the battery pack 1.

[0029] The restraining member 300 connects the two end plates 200 to each other. The restraining member 300 is attached to the two end plates 200.

[0030] When a compressive force in the Y-axis direction is applied to the stack of multiple battery cells 100 and end plates 200, the restraining members 300 are engaged with the end plates 200, and the compressive force is then released, causing a tensile force to act on the restraining members 300 connecting the two end plates 200. In reaction to this force, the restraining members 300 press the two end plates 200 in a direction that brings them closer together.

[0031] As shown in Fig. 3, the battery cell 100 is formed in the shape of a flat rectangular parallelepiped. The electrode terminals 110 include a positive terminal 111 and a negative terminal 112. The electrode terminals 110 are formed on the upper surface of a rectangular housing 120. The housing 120 contains an electrode body and an electrolyte (not shown). For convenience in explaining the shape of the battery cell 100, the X direction may be referred to as the width direction, the Y direction as the thickness direction, and the Z direction as the height direction in the following description.

[0032] Fig. 4 is a diagram showing the arrangement of bus bars 400 in the battery pack 1. In the example of Fig. 4, the positive electrode terminals 111 and negative electrode terminals 112 of adjacent battery cells 100 are electrically connected by the bus bars 400, and the plurality of battery cells 100 are electrically connected in series.

[0033] That is, the battery pack 1 includes a plurality of battery cells 100, each having an electrode terminal 110, arranged in a predetermined direction, and a bus bar 400 that connects the electrode terminals 110 of the plurality of battery cells 100 together.

[0034] (Welding method and welded structure) 5 and 6, a description will be given of a welding method and welding structure for electrode terminal 110 and bus bar 400. As electrode terminal 110, a case where negative electrode terminal 112 and bus bar 400 are welded together will be described as an example.

[0035] The bus bar 400 (first metal layer) is made of aluminum. The negative electrode terminal 112 has a first electrode member 112a connected to a battery element (not shown) provided inside the battery cell 100, and a second electrode member 112b provided to cover the first electrode member 112a and be integrated with the first electrode member 112a. The second electrode member 112b is made of aluminum (second metal layer) because the bus bar 400 is fixed to the second electrode member 112b by welding. The first electrode member 112a is made of copper (third metal layer) to ensure good electrical connection with the battery element (not shown) provided inside the battery cell 100.

[0036] Between the bus bar 400 and the negative electrode terminal 112, a first metal layer, a second metal layer, and a third metal layer are arranged in this order from above, and the first metal layer and the second metal layer are joined by laser welding. The first metal layer and the second metal layer are made of the same first metal material (aluminum), and the third metal layer is made of a second metal material (copper) different from the first metal material.

[0037] 6, the bus bar 400 and the second electrode member 112b are fixed by welding using a laser beam (L11). In this embodiment, when the laser beam (L11) is irradiated from the bus bar 400 side to join the bus bar 400 and the second electrode member 112b by laser welding, the laser beam (L11) is scanned over the bus bar 400 while rotating from the inside to the outside.

[0038] In this embodiment, the laser light (L11) is scanned by rotating the laser light (L11) from the inside to the outside along a rectangular shape. The rectangular shape is preferably a rectangular shape with the long side extending in the width direction (X direction) of the battery cell 100 and the short side extending in the thickness direction (Y direction).

[0039] For example, when the thickness of the busbar 400 is approximately 0.8 mm, the thickness of the first electrode member 112a is approximately 0.7 mm, and the thickness of the welded portion of the second electrode member 112b is approximately 0.7 mm, the output of the laser light (L11) is 1500 W, the scanning speed is 400 mm / s, and the long side (L1) of the rectangular shape after irradiation with the laser light (L11) is approximately 5 mm and the short side (L2) is approximately 1 mm.

[0040] 7, when the above-described welding method is used, the laser beam (L11) is rotated from the inside to the outside while scanning the bus bar 400 with the laser beam (L11), and therefore the welding depth of the molten pool (W1) is deeper on the outside than on the inside. However, the welding points welded by the laser beam (L11) are welded at longer intervals toward the outside, making them less susceptible to the effects of heat. Furthermore, because heat can escape to the outside, the thermal effects on each other can be minimized.

[0041] As a result, even if the welding depth of the molten pool (W1) on the outside reaches the second electrode member 112b of the third metal layer, the depth (D1) is kept to a minimum, and the generation of intermetallic compounds can also be suppressed.

[0042] On the other hand, the cross-sectional structure of the welded portion in Fig. 8 shows a case where the laser beam (L11) is scanned over the bus bar 400 while rotating from the outside to the inside under the same conditions as above. In this case, the welded portion by the laser beam (L11) is welded at shorter intervals as it moves inward, and is therefore more susceptible to the effects of heat. Furthermore, heat is less likely to escape to the outside and accumulates inside, resulting in a higher temperature inside.

[0043] As a result, the depth (D2) of the molten pool (W1) becomes deeper at the inner side (center), and the third metal layer reaches deeply into the second electrode member 112b, promoting the generation of intermetallic compounds.

[0044] In the irradiation of the above-mentioned laser light (L11) shown in Figure 6, the laser light (L11) is irradiated in a counterclockwise direction, but as shown in Figure 9, the laser light (L11) may also be irradiated in a clockwise direction.

[0045] Although the above description describes the case where the bus bar 400 is welded to the electrode terminal 110 provided on the battery cell 100, the application is not limited to this example and can be applied to connection points having a similar configuration.

[0046] Although the embodiments of the present disclosure have been described above, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0047] 1 battery pack, 100 battery cell, 110 electrode terminal, 111 positive electrode terminal, 112 negative electrode terminal, 112a first electrode member (third metal layer), 112b second electrode member (second metal layer), 120 housing, 200 end plate, 300 restraint member, 400 bus bar (first metal layer).

Claims

1. A welding method comprising: arranging a first metal layer, a second metal layer, and a third metal layer in this order from above; and joining the first metal layer and the second metal layer by laser welding; the first metal layer and the second metal layer are made of the same first metal material; the third metal layer is a second metal material different from the first metal material; When the first metal layer and the second metal layer are joined by laser welding by irradiating and scanning a laser beam from the side of the first metal layer, irradiating the first metal layer with the laser light while rotating the laser light from the inside to the outside; Welding method.

2. The scanning of the laser light is performed by rotating the laser light from the inside to the outside along a rectangular shape. The welding method according to claim 1 .

3. the first metallic material is aluminum; the second metallic material is copper; The welding method according to claim 1 .

4. the first metal layer is a bus bar used in a battery pack, the second metal layer and the third metal layer are electrode terminals that constitute the battery pack, welding the bus bar to the electrode terminal using the laser beam; The welding method according to claim 1 .

5. A welded structure in which a first metal layer, a second metal layer, and a third metal layer are arranged in this order from above, and the first metal layer and the second metal layer are joined by laser welding, the first metal layer and the second metal layer are made of the same first metal material; the third metal layer is a second metal material different from the first metal material; When irradiating a laser beam from the side of the first metal layer to join the first metal layer and the second metal layer by laser welding, the laser beam is irradiated and scanned onto the first metal layer while rotating from the inside to the outside; When viewed in a cross section along the irradiation direction of the laser light after the laser welding, a welding depth of the weld between the first metal layer and the second metal layer is shallower on the inside than on the outside; Welded construction.

6. The scanning of the laser light is performed by rotating the laser light from the inside to the outside along a rectangular shape. The welded structure of claim 5.

7. the first metallic material is aluminum; the second metallic material is copper; The welded structure of claim 5.

8. the first metal layer is a bus bar used in a battery pack, the second metal layer and the third metal layer are electrode terminals that constitute the battery pack. The welded structure according to any one of claims 5 to 7.

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