Friction stir welding method and battery pack

Abstract

The present invention provides a friction stir welding method capable of improving the welding strength at the terminal part of friction stir welding, and a battery pack welded by the friction stir welding method. A friction stir welding method for welding metal members (M1, M2) together by overlapping the metal members (M1, M2) and moving a welding tool (10), the method comprising: a terminal part forming step for forming a closed space at the terminal part of a welding line (20), which is the movement trajectory of the welding tool (10); and a pull-out step for moving the bonding tool (10) to the inside of the closed space and pulling out the bonding tool (10) from the metal members (M1, M2).

Description

Technical Field

[0001] The present invention relates to a friction stir welding method and a battery pack formed by the friction stir welding method. Background Art

[0002] As a method for joining metal parts to each other, friction stir welding (FSW) is known. In this friction stir welding, two metal parts to be joined are overlapped with each other, and a joining tool is pressed against one of the metal parts while rotating, so that the metal part on one side is softened and penetrated by friction heat, and the rotational force of the joining tool is used to stir the metal part on one side and cause plastic flow. After that, the plastically flowing material rapidly loses friction heat and cools and solidifies, thereby joining one metal part to the other metal part.

[0003] However, in this friction stir welding method, when the welding tool is pulled out at the terminal end, a hole portion (hereinafter referred to as a probe hole portion) is formed.

[0004] Figure 1 is a cross-sectional view showing a state where the bonding tool 10 is pulled out at the terminal end. Figure 2 Schematic diagram of the bonding end portion when the bonding tool 10 is moved linearly and the bonding tool is pulled out at the terminal end. Figure 2 ( Figure 3 , Figure 4 In the same manner, reference numeral 11A is a joining trace formed by the shoulder 11, and reference numeral 12A is a probe hole formed when the probe 12 is pulled out. In addition, the thick solid line in the figure is a joining line 20 which is a moving track of the axis of the probe 12. In addition, the joining line 20 is an imaginary line for explanation, and generally does not remain after joining.

[0005] like Figure 1 As shown in FIG. 1 , the bonding tool 10 has a probe (protrusion) 12 protruding from the front end of a cylindrical shoulder 11 along the axis. Figure 2 As shown, when the bonding tool 10 is moved linearly as indicated by arrow Y1 and the bonding tool 10 is pulled out at the terminal end of the bonding wire 20, a probe hole 12A having the shape of the probe 12 is formed at the bonding end. When the probe hole 12A is formed, the interface between the metal component M1 on one side and the metal component M2 on the other side is exposed (see Figure 1 ). In addition, the bonding range around the probe hole portion 12A is narrow and the bonding strength is weak.

[0006] In order to solve such a problem, the following contents are recorded in Patent Document 1: Figure 3As shown, after the welding tool 10 is moved linearly as indicated by arrow Y2, the welding tool is moved in an arc, more specifically, in a J-shape, at the terminal end of the welding line 20 to form a welding end portion.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2012-152759 Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, even the joining method described in Patent Document 1 has room for improvement in terms of joining strength. In particular, when a flow path is formed between two joined components, water pressure acts on the periphery of the probe hole, so when the joining strength is weak, water leakage may occur.

[0012] The present invention provides a friction stir welding method capable of improving the joining strength of a terminal end portion of friction stir welding, and a battery pack joined by the friction stir welding method.

[0013] Means for solving problems

[0014] The present invention is a friction stir welding method, in which at least two parts to be joined are overlapped, and the parts to be joined are joined to each other by moving a joining tool.

[0015] in,

[0016] The friction stir welding method comprises:

[0017] a terminal portion forming step of forming a closed space at a terminal portion of a bonding line which is a moving trajectory of the bonding tool; and

[0018] In the pulling-out step, the bonding tool is moved to the inside of the closed space, and the bonding tool is pulled out from the bonded member.

[0019] Furthermore, the present invention is a battery pack comprising:

[0020] A battery module having a plurality of cells stacked on top of each other;

[0021] a battery housing that receives the battery module; and

[0022] a plate member which is joined to the battery case to form a flow path for a fluid for battery temperature control to flow between the plate member and the battery case,

[0023] in,

[0024] At least one of the battery case and the plate member has a convex portion protruding toward the other.

[0025] The protrusions are joined by friction stir welding to form a joined portion,

[0026] The joining portion includes a linear portion extending along the extending direction of the convex portion and a circular portion formed at one of the ends of the linear portion.

[0027] The circular portion has a width greater than that of the linear portion.

[0028] Effects of the Invention

[0029] According to the present invention, it is possible to improve the bonding strength formed by the bonding tool at the terminal end portion of the bonding wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a cross-sectional view showing a state where the welding tool 10 is pulled out at the terminal end.

[0031] Figure 2 This is a schematic diagram of the bonding end portion when the bonding tool 10 is moved linearly and the bonding tool 10 is pulled out at the terminal end.

[0032] Figure 3 This is a schematic diagram of a joining end portion when the joining tool 10 is moved linearly, then moved in an arc (J-shape) at the terminal end and then pulled out.

[0033] Figure 4 This is a schematic diagram of a bonding end portion when the bonding tool 10 is moved linearly, then moved in a circular shape at the terminal end, and then the bonding tool 10 is pulled out.

[0034] Figure 5 Yes means Figure 4 Schematic diagram of the joint end.

[0035] Figure 6 It is a perspective view showing the interior of the battery pack 50 .

[0036] Figure 7 The diagram shows the cover plate 70 that is friction stir-welded to the bottom plate 61 of the battery case 60 .

[0037] Figure 8 It is a diagram showing the bottom surface of the battery case 60 to which the cover plate 70 is joined.

[0038] Fig. 9 is along Figure 8 Cross-sectional view along line AA.

[0039] Fig.10 yes Figure 8 Magnified view of part B.

[0040] Description of Reference Numerals

[0041] 10. Joining tools

[0042] 12 Probe (protrusion)

[0043] 12A Probe hole (hole)

[0044] 20 Bonding wire

[0045] 21 Linear part

[0046] 22 round part

[0047] 50 Battery Pack

[0048] 51 Battery module

[0049] 60 Battery housing

[0050] 70 Cover plate (plate component)

[0051] 80 Refrigerant flow path (flow path)

[0052] D1 diameter (diameter of the enclosed space)

[0053] D2 diameter (diameter of the protrusion)

[0054] R1: Area where the linear portion is formed

[0055] R2: Area where the rounded portion is formed

[0056] T1 Width

[0057] T2 Width DETAILED DESCRIPTION

[0058] Hereinafter, one embodiment of the friction stir welding method and the battery pack formed by the friction stir welding method according to the present invention will be described with reference to the drawings.

[0059] Figure 4 This is one embodiment of the friction stir welding method of the present invention, and is a schematic diagram of a case where the welding tool 10 is moved linearly and then moved in a circular manner at the terminal end to pull out the welding tool 10.

[0060] The friction stir welding method of this embodiment includes: a terminal portion forming step, forming a closed space at the terminal portion of the welding line 20 which is the moving trajectory of the probe 12 of the welding tool 10; and a pulling out step, moving the welding tool 10 to the inside of the closed space and pulling out the welding tool 10.

[0061] In the terminal forming process, Figure 4 As shown, after the probe 12 of the bonding tool 10 is moved linearly as indicated by arrow Y11, it is moved from a position (position P1 in the figure) in front of the target pull-out position G in a circle centered at the target pull-out position G. In addition, the dotted line Q1 in the figure represents the shoulder 11 when the probe 12 is at the position P1. As an example, the position P1 is the location where the shoulder 11 reaches the target pull-out position G. The target pull-out position G is a target position corresponding to the axis of the probe 12 when the bonding tool 10 is pulled out.

[0062] The processing in the terminal portion forming process is described in more detail. For example, as shown by arrows Y12 and Y13, the bonding tool 10 is moved counterclockwise around the target pull-out position G at the terminal portion so that the probe 12 moves in the manner of position P1 → position P2 → position P3 → position P4 → position P5 (position P1).

[0063] By moving the bonding tool 10 to draw a circle around the target pull-out position G, a circular closed space is formed at the bonding line 20. When the diameter of the circular closed space is D1 and the diameter of the probe 12 is D2, D1>D2 is preferably satisfied.

[0064] In addition, it is preferable to form a closed space in a manner that a portion of the bonding line 20 overlaps. That is, in the present embodiment, the trajectory of the probe 12 from the position P5 to the position P6 overlaps a portion of the trajectory of the probe 12 from the position P1 to the position P2. In this way, by moving the bonding tool 10 in a manner that a portion of the bonding line 20 overlaps, a closed space can be reliably formed.

[0065] However, when the amount of overlap is too large, the time required for the joining process increases. Therefore, the amount of overlap is preferably 180° or less centered at the target pull-out position G, more preferably 90° or less, and further preferably 60° or less.

[0066] Next, the probe 12 is moved to the inner side of the circular closed space and moved to the target pull-out position G.

[0067] In the pulling-out process, the bonding tool 10 is pulled out after the probe 12 reaches the target pulling-out position G. At this time, by presetting the diameter D1 of the closed space to be larger than the diameter D2 of the probe 12, the probe 12 of the bonding tool 10 that forms the probe hole 12A after the bonding tool 10 is pulled out can be located inside the closed space.

[0068] In this way, by pulling out the joining tool 10 inside the closed space formed at the terminal end of the joining line 20, a joining region of the two joined parts is formed outside the pulling-out position (target pulling-out position G). Figure 5 In the figure, only the area in the joining area that does not overlap with the shoulder 11 of the joining tool 10 during the pull-out is hatched. That is, the joining area where the metal parts M1 and M2 are stirred and plastically flowed is formed at a position outside the probe hole 12A. Therefore, even if the joining strength of the joining area at the pull-out position (target pull-out position G) is low, it is possible to firmly join at a position outside the probe hole 12A, thereby improving the joining strength.

[0069] In this embodiment, the bonding tool 10 is moved counterclockwise around the target pull-out position G, but the bonding tool 10 may be moved clockwise. In addition, the closed space may be any closed space when viewed from above, and is not limited to a circle, but may be a polygon such as a triangle or a quadrilateral, or an ellipse.

[0070] Next, refer to Figures 6 to 8 A battery pack to which the above-mentioned friction stir welding method is applied is described. In the following description, for convenience, a coordinate system consisting of mutually orthogonal front-back directions, left-right directions, and up-down directions is used for description. In the accompanying drawings, the front is represented as Fr, the rear is represented as Rr, the left side is represented as L, the right side is represented as R, the top is represented as U, and the bottom is represented as D. However, these directions have nothing to do with the direction in which the battery pack is mounted on the equipment. For example, when the battery pack is mounted on a vehicle, the up-down direction of the battery pack can be oriented in the direction of travel of the vehicle when mounted on the vehicle, or it can be oriented in the direction of the vehicle width.

[0071] Figure 6 is a perspective view showing the interior of the battery pack 50, Figure 7 2 is a diagram showing a cover plate 70 that is friction stir bonded to a bottom plate 61 of a battery case 60. Figure 8 2 is a diagram showing the bottom surface of the battery case 60 to which the cover plate 70 is joined. Fig. 9 is along Figure 8 The cross-sectional view of line AA, Fig.10 yes Figure 8 Magnified view of part B.

[0072] like Figure 6 As shown in FIG. 1 , the battery pack 50 includes a battery module 51 in which a plurality of cells are stacked, and a battery case 60 in which the battery module 51 is housed. Figure 6 , only two battery modules 51 are described, and description of the other battery modules 51 is omitted. The number and arrangement of the battery modules 51 accommodated in the battery case 60 can be set as appropriate.

[0073] like Figure 6As shown, the battery case 60 includes a rectangular bottom plate 61 on which the plurality of battery modules 51 are mounted, a side wall 62 erected from the outer edge of the bottom plate 61 , and a plurality of cross beams 63 .

[0074] The battery case 60 is formed of, for example, an aluminum alloy containing aluminum. More specifically, the bottom plate 61, the side wall 62, and the plurality of cross beams 63 of the battery case 60 are formed by aluminum die casting. Aluminum die casting is formed by melting an aluminum alloy, filling it into a mold at high speed using a die casting machine, and then applying high pressure. By forming the battery case 60 from an aluminum alloy, the battery pack 50 can be made lighter.

[0075] like Figure 7 As shown, the bottom plate 61 of the battery case 60 is covered by the cover plate 70 by friction stir welding with the plate-shaped cover plate 70 disposed below. The cover plate 70 is, for example, a press-formed product made of iron. Figure 8 A coolant flow path 80 is formed between the bottom plate 61 of the battery case 60 and the cover plate 70. The battery module 51 housed in the battery case 60 is cooled and / or heated by the coolant flowing through the coolant flow path 80, so that the temperature of the battery can be adjusted.

[0076] More specifically, the bottom plate 61 and the cover plate 70 are provided with projections and depressions. The bottom plate 61 is provided with a projection 611 protruding toward the outside of the battery case 60, that is, toward the cover plate 70, and a depression 612 recessed toward the side opposite to the cover plate 70 relative to the projection 611.

[0077] The cover plate 70 is provided with a convex portion 701 protruding toward the bottom plate 61 side and a concave portion 702 recessed toward the side opposite to the bottom plate 61 with respect to the convex portion 701 .

[0078] like Figure 8 As shown, in the friction stir welding, the bonding tool 10 is moved along the extending direction of the convex parts 611 and 701 while the convex parts 611 of the bottom plate 61 and the convex parts 701 of the cover plate 70 are in contact with each other. At this time, the above-mentioned terminal portion forming step of forming a closed space at the terminal portion of the bonding wire 20 as the moving trajectory of the probe 12 of the bonding tool 10 and the pulling-out step of moving the bonding tool 10 to the inside of the closed space and pulling the bonding tool 10 out are performed.

[0079] In the terminal portion forming step, the bonding tool 10 is moved in a circle with the target pull-out position G as the center, so that Fig.10 As shown, the joint portion on the convex portion 611, 701 is provided with a linear portion 21 extending along the extension direction of the convex portion 611, 701 and a circular portion 22 formed at one end of the linear portion 21, i.e., the terminal portion. The width, i.e., the diameter, of the circular portion 22 is greater than the width of the linear portion 21 extending in a straight line.

[0080] In the pulling-out process, after the bonding tool 10 is moved to the inside of the circular portion 22 as the closed space, the probe 12 is pulled out of the bonding tool 10 at the target pulling-out position G, thereby forming a probe hole 12A at the center of the circular portion 22 (see FIG. Figure 5 ).

[0081] like Figure 7 , Figure 8 and Fig.10 As shown, the width T1 of the convex portions 611 and 701 in the region R1 where the linear portion 21 is formed is smaller than the width T2 of the convex portions 611 and 701 in the region R2 where the circular portion 22 is formed. Originally, when considering the heat capacity of the refrigerant flow path 80, it is preferred to minimize the width of the convex portions 611 and 701. On the other hand, in order to implement the above-mentioned terminal portion forming process and the pulling process, the convex portions 611 and 701 having a width greater than the circular portion 22 are required. Therefore, by only increasing the width of the terminal portion of the convex portions 611 and 701 where the circular portion 22 is formed, the heat capacity of the refrigerant flow path 80 can be ensured, and the circular portion 22 can be formed in the terminal portion forming process and the pulling process.

[0082] In this way, by applying the friction stir welding method to the manufacture of the battery pack 50, the refrigerant flow path 80 is formed between the bottom plate 61 of the battery case 60 and the cover plate 70, and the bonding strength between the bottom plate 61 and the cover plate 70 can be improved. In addition, by improving the bonding strength between the bottom plate 61 and the cover plate 70, even if the water pressure of the refrigerant flowing between the bottom plate 61 and the cover plate 70 acts on the bonding area, the refrigerant leakage can be prevented.

[0083] In addition, in this embodiment, the convex portion 611 of the bottom plate 61 and the convex portion 701 of the cover plate 70 are brought into contact with each other to perform friction stir welding, and the coolant flow path 80 is formed by the concave portions 612 and 702, but the present invention is not limited thereto. For example, only one side may be a convex portion and the other side may be a flat portion, and the coolant flow path 80 may be formed between the flat portion and the concave portion.

[0084] Above, various embodiments have been described with reference to the accompanying drawings, but the present invention is certainly not limited to this example. Obviously, those skilled in the art can obviously think of various variations or modifications within the scope of the technical solution, and it should be understood that these variations and modifications also belong to the technical scope of the present invention. In addition, the various constituent elements in the above-mentioned embodiments can also be arbitrarily combined within the scope of the main purpose of the invention.

[0085] For example, the battery pack 50 is described as an example of application of the friction stir welding method, but the method is not limited thereto, and can be applied to a battery pack in which at least two metal members as members to be joined are joined to each other.

[0086] In this specification, at least the following matters are described. In addition, although the corresponding components and the like in the above-mentioned embodiment are shown in brackets, the present invention is not limited thereto.

[0087] (1) A friction stir welding method, comprising: overlapping at least two members to be joined (metal members M1, M2), and joining the members to be joined by moving a welding tool (welding tool 10);

[0088] in,

[0089] The friction stir welding method comprises:

[0090] a terminal portion forming step of forming a closed space at a terminal portion of a bonding line (bonding line 20 ) which is a moving trajectory of the bonding tool; and

[0091] In the pulling-out step, the bonding tool is moved to the inside of the closed space, and the bonding tool is pulled out from the bonded member.

[0092] According to (1), the joining tool is pulled out inside the closed space at the terminal end of the joining line as the moving track of the joining tool, so that the joining area can be formed at a position outside the pulled-out position, thereby improving the joining strength. In addition, when a closed space is formed between two joined parts, the sealing performance can be improved.

[0093] (2) The friction stir welding method according to (1), wherein:

[0094] The closed space is circular in shape,

[0095] The bonding tool has a cylindrical shape with a protrusion (probe 12) provided at the front end.

[0096] The joining line is the moving track of the axis of the protrusion.

[0097] The diameter of the closed space (diameter D1 ) is larger than the diameter of the protrusion of the bonding tool (diameter D2 ).

[0098] According to (2), the protrusion of the joining tool that forms the hole portion after being pulled out can be located inside the closed space, so the joining strength and the sealing performance can be appropriately improved.

[0099] (3) The friction stir welding method according to (1) or (2), wherein:

[0100] In the terminal portion forming step, the closed space is formed so that parts of the bonding wires overlap.

[0101] According to (3), by moving the bonding tool so that parts of the bonding lines overlap, a closed space can be reliably formed.

[0102] (4) The friction stir welding method according to (3), wherein:

[0103] The amount of overlap of the bonding wires is 180° or less.

[0104] According to (4), by setting the amount of overlap of the bonding wires to 180° or less, the time required for the bonding process can be shortened.

[0105] (5) A battery pack (battery pack 50) comprising:

[0106] A battery module (battery module 51) having a plurality of cells stacked on top of each other;

[0107] A battery case (battery case 60 ) that accommodates the battery module; and

[0108] a plate member (cover plate 70 ) which is joined to the battery case to form a flow path (coolant flow path 80 ) for flowing a fluid for battery temperature control between the plate member and the battery case,

[0109] in,

[0110] At least one of the battery case and the plate member has a convex portion (convex portion 611, 701) protruding toward the other.

[0111] The protrusions are joined by friction stir welding to form a joined portion,

[0112] The bonding portion includes a linear portion (linear portion 21) extending along the extending direction of the convex portion, and a circular portion (circular portion 22) formed at one end of the linear portion.

[0113] The circular portion has a width greater than that of the linear portion.

[0114] According to (5), the joint between the battery case and the plate member is formed with a circular portion having a width greater than the width of the linear portion at one end of the linear portion, thereby improving the joint strength. In addition, the sealing performance of the flow path formed between the battery case and the plate member for the flow of the fluid for battery temperature control can be improved.

[0115] (6) The battery pack according to (5), wherein:

[0116] The circular portion has a hole portion (probe hole portion 12A) that is recessed from the plate member side toward the battery case side.

[0117] According to (6), since the circular portion exists around the hole portion through which the welding tool is pulled out, the welding strength around the hole portion can be improved.

[0118] (7) The battery pack according to (5) or (6), wherein:

[0119] The width (width T1) of the convex portion in the region (region R1) where the linear portion is formed is smaller than the width (width T2) of the convex portion in the region (region R2) where the circular portion is formed.

[0120] According to (7), the heat capacity of the flow path through which the fluid for battery temperature control flows can be ensured, and a circular portion having a high joining strength can be formed at one end of the linear portion by friction stir welding.

Claims

1. A friction stir welding method, comprising: overlapping at least two parts to be joined, and joining the parts to be joined to each other by moving a welding tool, wherein: The friction stir welding method comprises: a terminal portion forming step of forming a closed space at a terminal portion of a bonding line which is a moving trajectory of the bonding tool; and In the pulling-out step, the bonding tool is moved to the inside of the closed space, and the bonding tool is pulled out from the bonded member.

2. The friction stir welding method according to claim 1, wherein: The closed space is circular in shape, The joining tool has a cylindrical shape with a protrusion provided at the front end portion, The joining line is the moving track of the axis of the protrusion. The closed space has a diameter greater than a diameter of the protrusion of the bonding tool.

3. The friction stir welding method according to claim 1 or 2, wherein: In the terminal portion forming step, the closed space is formed so that parts of the bonding wires overlap.

4. The friction stir welding method according to claim 3, wherein: The amount of overlap of the bonding wires is 180° or less.

5. A battery pack comprising: A battery module having a plurality of cells stacked on top of each other; a battery housing that receives the battery module; and a plate member which is joined to the battery case to form a flow path for a fluid for battery temperature control to flow between the plate member and the battery case, in, At least one of the battery case and the plate member has a convex portion protruding toward the other. The protrusions are joined by friction stir welding to form a joined portion, The joining portion includes a linear portion extending along the extending direction of the convex portion and a circular portion formed at one of the ends of the linear portion. The circular portion has a width greater than that of the linear portion.

6. The battery pack according to claim 5, wherein: The circular portion has a hole portion that is recessed from the plate member side toward the battery case side.

7. The battery pack according to claim 5 or 6, wherein: The width of the convex portion in the region where the linear portion is formed is smaller than the width of the convex portion in the region where the circular portion is formed.

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