Method for joining metal members and joined body of metal members

Abstract

To improve joining strength.SOLUTION: Provided is a method that includes overlapping a first metal member 1 and a second metal member 2 and clamping them at a clamping portion P, and then joining the first metal member 1 and the second metal member 2 by heating them from the first metal member 1 side at a joining portion 61 away from the clamping portion P, wherein before joining, an excess portion is provided in the first member 1 at a position between the joining portion 61 and the clamping portion P in order to absorb thermal deformation during joining. The excess portion is a bending portion bent so as to project in an overlapping direction of the first member 1 and the second member 2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for joining metal members and a joined body. [Background technology]

[0002] When two metal components are overlapped and joined by, for example, laser welding, the first component, the component irradiated with the laser, is prone to thermal deformation due to heating. This means that the first component is prone to thermal expansion or contraction during laser irradiation, potentially causing the intended joining location to shift out of position. There are limitations to how firmly the first and second components can be clamped together to prevent the first component from shifting out of position. Even if the first component can be clamped firmly, distortion or residual stress may occur in the first component, potentially preventing the desired joining strength from being achieved.

[0003] Patent Document 1 below proposes a method of laser welding two overlapping zinc-based plated steel sheets. In this method, the portion to be welded of the first member on the laser irradiation side is bent toward the torch in advance, and the curved portion of the first member forms a gap between the members in the portion to be welded. However, because a gap is formed between the members in the portion to be welded, heat is less likely to be transferred to the second member on the opposite side of the torch. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-311453 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to improve the bonding strength. [Means for solving the problem]

[0006] The method for joining metal members according to the present invention involves overlapping a first metal member and a second metal member and clamping them at a clamping point, and joining the first and second members by heating them from the first member side at a joining point away from the clamping point; prior to joining, an excess portion is provided in the first member at a position between the joining point and the clamping point to absorb thermal deformation during joining.

[0007] According to this method, the temperature rises from the first member side during joining. When heating occurs from the first member side during joining, typically when welding is performed by irradiating a laser beam from the first member side, in which case the temperature rise of the first member is greater than that of the second member. Note that, in addition to laser welding, other joining methods include friction stir welding, for example. In the case of friction stir welding, a tool is pressed from the first member side.

[0008] The following describes laser welding as an example. When a laser is irradiated from the first component toward the joining location, the temperature of the first component rises rapidly, causing the first component to thermally expand. The first and second components are clamped at the clamping location, but the first component expands in the region between the joining and clamping locations. In the region between the joining and clamping locations, the first component attempts to expand from the joining location toward the clamping location. However, because an excess portion is provided between the joining and clamping locations, the excess portion absorbs the expansion of the first component. This prevents excessive stress from acting on the clamping location. It also prevents the clamping location from shifting out of position. After the welding process is completed, the first component contracts as its temperature drops. At this time, the excess portion absorbs the force absorbed during joining, allowing the first component to smoothly return to its original state. Therefore, even when the first component contracts, excessive stress is not placed on the clamping location. As a result, the generation of large residual stress or distortion in the first component can be suppressed after joining, enabling accurate joining and ensuring the desired joint strength.

[0009] In particular, it is preferable that the excess portion is a bent portion that is bent so as to protrude in the overlapping direction of the first member and the second member. With this method, the bent portion changes its bent shape when the first member thermally expands and contracts, so that the thermal deformation of the first member can be absorbed smoothly and reliably.

[0010] In particular, it is preferable that the joints have a shape that extends in a predetermined direction, and the bent portions are bent ridges that extend in the extension direction of the joints. According to this method, when joining the joints in the predetermined direction, the bent ridges smoothly deform so as to expand or contract the spacing of their openings. Therefore, the joints can be accurately formed in the predetermined direction.

[0011] Furthermore, it is preferable that a recess be formed on the surface of the second member facing the first member, and that the bending protrusion protrude toward the second member. When the first member and the second member are overlapped, the bending protrusion is inserted into the recess and the side surface of the bending protrusion farther from the joining location is abutted against the wall surface of the recess. According to this method, when the first member and the second member are joined, the bending protrusion is inserted into the recess and the side surface of the bending protrusion farther from the joining location is abutted against the wall surface of the recess. Therefore, the bending protrusion can be used for positioning, and the first member can be accurately overlapped in a predetermined position on the second member. Moreover, when the first member thermally expands during joining, the side surface of the bending protrusion abuts against the wall surface of the recess, so the bending protrusion deforms to reliably shrink its opening. Therefore, the thermal deformation of the first member can be smoothly and reliably absorbed by the bending protrusion.

[0012] It is also preferable to interpose a sealant between the folded ridge and the wall surface of the recess. Interposing a sealant in this manner improves the sealing between the first and second members. This is therefore suitable, for example, for filling the recess with a medium such as a liquid. Furthermore, even if the joint is not continuous along its extension direction but is discontinuous, for example, broken in part, sealing can be easily ensured.

[0013] Furthermore, the joined body of metal members according to the present invention is a joined body of metal members in which a first member and a second member made of metal are overlapped and have a joint that is heat-joined from the first member side, wherein a bent portion is provided in the first member at a location away from the joint that is bent so as to protrude toward the second member side, and a recess is provided on the surface of the second member facing the first member, with the bent portion fitting into the recess and the side of the bent portion farther from the joint abutting against the wall surface of the recess. Note that the heat-joining can be laser welding or friction stir welding, etc.

[0014] With this configuration, the side of the bent portion farther from the joint contacts the wall of the recess, ensuring accurate positioning between the first and second members. Furthermore, the bent portion smoothly absorbs thermal deformation of the first member during thermal joining, such as laser welding. This prevents large residual stresses and distortions from occurring in the joined body, ensuring sufficient joint strength. [Effects of the Invention]

[0015] As described above, the excess portion absorbs the thermal deformation of the first member between the joining portion and the clamping portion during joining, thereby improving the joining strength. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a cross-sectional view showing a main part of a bonded body according to an embodiment of the present invention. [Figure 2] 4A to 4C are cross-sectional views showing a bonding process of the bonded body. [Figure 3] 4A to 4C are cross-sectional views showing a bonding process of the bonded body. [Figure 4] FIG. 4 is a cross-sectional view showing the state of the bonded body after bonding. [Figure 5] 5(a) and 5(b) are enlarged views of the main parts of FIG. 4. [Figure 6] 6(a) and 6(b) are cross-sectional views of a main part of a bonded body according to another embodiment of the present invention. [Figure 7] 10A to 10C are cross-sectional views showing a bonding step of a bonded body according to another embodiment of the present invention. [Figure 8] FIG. 10 is a cross-sectional view showing a main part of a first member in another embodiment of the present invention. [Figure 9] 6(a) to 6(c) are cross-sectional views showing the main part of a first member in another embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional view showing a main part of a first member in another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] A joining method and a joined body according to one embodiment of the present invention will be described below with reference to the drawings. The joined body is made of metal. The joined body is formed by joining two metal members. That is, the joined body includes a first member and a second member made of metal, and the first member and the second member are joined and integrated at a predetermined joining point. The joined body, the first member, and the second member may each have various forms. In this embodiment, a case in which the joined body is a battery case will be described as an example.

[0018] As shown in FIG. 1, the battery case is for accommodating multiple batteries 3. The top of the battery case is open, and the batteries 3 are inserted into the battery case through the top opening. The battery case includes a bottomed case body 2 with a top opening, and a bottom cover 1 attached to the bottom of the case body 2 from below. The case body 2 is made by casting, specifically die-casting, and more particularly aluminum die-casting. The bottom cover 1 is plate-shaped and is preferably made of wrought aluminum. The case body 2 is the second member, and the bottom cover 1 is the first member.

[0019] To explain the details of the case body 2, the case body 2 has an accommodation space for accommodating the battery 3, and the accommodation space can accommodate one or more batteries 3. The number of batteries 3 that can be accommodated is arbitrary. The case body 2 is, for example, rectangular in plan view. The case body 2 has a bottom surface 10 and side surfaces 11 that rise upward from the periphery of the bottom surface 10. The battery 3 is placed on the upper surface of the bottom surface 10. A recess 12 that opens downward is formed on the lower surface of the bottom surface 10. The recess 12 can be used as a cooling space.

[0020] The lower surface of the bottom portion 10 has an attachment surface portion 13 provided around the recess 12 and a mounting surface portion 15 provided outside the attachment surface portion 13 via a step portion 14. The attachment surface portion 13 is provided at the opening edge of the recess 12 and surrounds the recess 12. The bottom cover 1 is attached by being placed on the attachment surface portion 13. The mounting surface portion 15 is located below the attachment surface portion 13. The mounting surface portion 15 forms the peripheral edge of the lower surface of the bottom portion 10. The mounting surface portion 15 serves as a foot when the battery case is placed on the mounting surface P and abuts against the mounting surface P. The vertical dimension between the mounting surface portion 15 and the attachment surface portion 13 is preferably greater than the thickness of the bottom cover 1. It is also preferable that the mounting surface portion 15 is located lower than the bottom cover 1 so that the bottom cover 1 does not abut against the mounting surface P when the battery case is placed on the mounting surface P. The bottom cover 1 and the mounting surface portion 15 may be flush with each other.

[0021] By attaching the bottom cover 1 to the bottom surface portion 10 of the case body 2, the lower opening of the recess 12 is closed. The recess 12 of the case body 2 and the bottom cover 1 can form a cooling passage. A refrigerant for cooling the battery 3 flows through the cooling passage. The recess 12 can be configured arbitrarily, but as an example, the recess 12 extends along the direction normal to the paper surface in FIG. 1 (directions toward the depth and front). The direction normal to the paper surface in FIG. 1 will be simply referred to as the paper surface normal direction. In addition, a partition wall 20 protrudes downward from the lower surface of the bottom surface portion 10 to form the recess 12 and to divide the recess 12 into left and right sections. Both side surfaces of the partition wall 20 form the wall surfaces of the recess 12. The lower surface of the partition wall 20 forms the mounting surface portion 13.

[0022] The partition wall 20 extends in the direction normal to the paper surface. Preferably, one of the cooling passages on the left and right sides of the partition wall 20 serves as an outgoing path and the other as a returning path, so that the cooling passages reciprocate in the direction normal to the paper surface. Furthermore, a rib 21 is preferably provided on the lower surface of the bottom portion 10 so as to protrude downward. The rib 21 is preferably formed parallel to the partition wall 20 and is preferably formed in the center of each cooling passage. The protrusion amount of the rib 21 is smaller than the protrusion amount of the partition wall 20. A pair of communication holes 22 is formed in the lower part of the side portion 11. One communication hole 22 is for a refrigerant inlet, and the other communication hole 22 is for a refrigerant outlet. The refrigerant is sent into the cooling passages through the inlet communication hole 22 and is discharged through the outlet communication hole 22.

[0023] The bottom cover 1 is joined to the case body 2 by laser welding. The battery case is formed by welding the case body 2 and the bottom cover 1 together while they are overlapped. A joint is formed at the welded location, and a weld bead is formed at the joint. The location where the joint is formed, i.e., the joining location, may be various, but in this embodiment, it is the partition wall 20 and both end portions of the bottom cover 1. The partition wall 20 is located at the first joint 51, and a first joint 61 is formed at the partition wall 20. Both end portions of the bottom cover 1 are located at the second joint 52, and second joints 62 are formed at both end portions of the bottom cover 1, respectively. The first joint 61 is formed by lap welding, and the second joint 62 is formed by lap fillet welding. The first joint 61 and the second joint 62 have a shape that extends along a predetermined direction, and the extension direction is normal to the plane of the drawing.

[0024] Bottom cover 1 has a first surface 1a, which is a first plate surface, and a second surface 1b, which is a second plate surface opposite to first surface 1a. Of first surface 1a and second surface 1b of bottom cover 1, first surface 1a is the surface facing the case main body 2. In other words, first surface 1a is the surface facing upward when in the battery case state. First surface 1a is superimposed on the underside of bottom surface portion 10 of case main body 2. When in the battery case state, first surface 1a of bottom cover 1 is the upper surface of bottom cover 1, and second surface 1b is the lower surface. More specifically, bottom cover 1 is attached to mounting surface portion 13 on the lower surface of bottom surface portion 10 of case main body 2, and first surface 1a of bottom cover 1 is superimposed on mounting surface portion 13 of the case main body 2.

[0025] Near both ends of the bottom cover 1, fold ridges 30 are formed, each folded so as to protrude upward. In this embodiment, the fold ridges 30 are bent portions and excess portions. The fold ridges 30 are folded in half upward, i.e., toward the case body 2. The fold ridges 30 are formed so that the first surface 1a of the bottom cover 1 is convex. The cross-sectional shape of the fold ridges 30 may vary, but in this embodiment, they are U-shaped, and the folded portion 30a of the fold ridges 30 is curved. The fold ridges 30 have a ridge opening 30b that opens toward the second surface 1b.

[0026] The bending ridges 30 are spaced apart from the first joints 61 in the horizontal direction (a direction perpendicular to the normal to the paper surface and the overlapping direction). The bending ridges 30 extend along the recesses 12, i.e., are formed along the normal to the paper surface. The extension direction of the bending ridges 30 is the extension direction of the first joints 61. The bending ridges 30 are recessed into the recesses 12. The amount by which the bending ridges 30 protrude is smaller than the amount by which the recesses 12 are recessed.

[0027] Of the two side surfaces of the folded protrusion 30, the side surface farther from the first joint 61 is referred to as the first side surface 30c, and the side surface closer to the first joint 61 is referred to as the second side surface 30d. Furthermore, of the wall surfaces of the recess 12, the wall surface facing the partition wall 20 is referred to as the first wall surface 12a, and the wall surface opposite the partition wall 20 and away from the partition wall 20 is referred to as the second wall surface 12b. The first wall surface 12a of the recess 12 forms the side surface of the partition wall 20.

[0028] The first side surface 30c of the bending ridge 30 abuts against the second wall surface 12b of the recess 12. The contact between the first side surface 30c of the bending ridge 30 and the second wall surface 12b of the recess 12 is preferably line contact along the direction normal to the paper, and particularly preferably surface contact. In this embodiment, the second wall surface 12b of the recess 12 and the bending ridge 30 are both formed continuously along the direction normal to the paper. Therefore, it is preferable that the first side surface 30c of the bending ridge 30 and the second wall surface 12b of the recess 12 are in continuous contact along the direction normal to the paper. However, for example, there may be discontinuous portions in the bending ridge 30 or in the second wall surface 12b of the recess 12.

[0029] FIG. 2 shows the state before joining. In FIG. 2, the case body 2 is shown upside down, with the underside of the bottom portion 10 of the case body 2 facing upward. The bottom cover 1 has a bent ridge 30 formed in advance before joining. Then, as shown in FIG. 3, the bottom cover 1 is placed on the mounting surface 13 of the underside of the bottom portion 10 of the case body 2. At this time, the bent ridge 30 is inserted into the recess 12 so that the first side surface 30c of the bent ridge 30 abuts against the second wall surface 12b of the recess 12. In this way, the bottom cover 1 is positioned relative to the case body 2 by the first side surface 30c of the bent ridge 30 abutting against the second wall surface 12b of the recess 12. In particular, FIG. 2 shows that the bottom cover 1 can be positioned relative to the case body 2 in the left-right direction. This allows the bottom cover 1 to be easily and accurately placed on the case body 2. Furthermore, because the bent ridges 30 of the bottom cover 1 are fitted into the recesses 12 of the case body 2, the bottom cover 1 is less likely to shift position or come off the case body 2. In other words, the bottom cover 1 is temporarily fixed to the case body 2. Therefore, when the bottom cover 1 is clamped to the case body 2 in the next step, it can be easily clamped.

[0030] With the bottom cover 1 placed on the case body 2, the bottom cover 1 and the case body 2 are clamped together. Clamping points 70 are indicated by arrows in FIG. 3. The clamping points 70 are near the second wall surface 12b of the recess 12, at both ends of the bottom cover 1. With the bottom cover 1 clamped to the case body 2 in this manner, a laser 100 is irradiated onto the joining points. The laser 100 is irradiated from the second surface 1b side of the bottom cover 1. First, the first joining point 51 is joined, and then the second joining point 52 is joined.

[0031] By irradiating the bottom cover 1 at the first joint 51 with the laser 100, the bottom cover 1 is heated, centered around the first joint 51. Because the laser 100 is irradiating the bottom cover 1, the temperature of the bottom cover 1 rises rapidly, becoming higher than the temperature of the case body 2. As the temperature of the bottom cover 1 rises, the bottom cover 1 stretches left and right between the first joint 51 and the clamping point 70. That is, the bottom cover 1 stretches from the first joint 51 toward both the left and right. The stretching of the bottom cover 1 is absorbed by the bent ridges 30. The bent ridges 30 deform to contract their ridge openings 30b, thereby absorbing the stretching of the bottom cover 1. In particular, because the first side surface 30c of the bent ridges 30 abuts against the second wall surface 12b of the recess 12, the bent ridges 30 smoothly contract and deform. In this way, the bent ridges 30 contract to narrow the width of the ridge openings 30b, absorbing the expansion of the bottom cover 1, preventing excessive stress from acting on the clamping points 70. After the first joining points 51 are joined, the temperature of the bottom cover 1 at the first joining points 51 decreases. As the temperature of the bottom cover 1 decreases, the bottom cover 1 contracts, but at this time, the bent ridges 30 deform to expand the ridge openings 30b. Therefore, the bottom cover 1 can smoothly return to its original state. After joining the first joining points 51 in this way, the second joining points 52 are joined, and the bottom cover 1 is joined to the case body 2 as shown in Figure 4.

[0032] FIG. 5(a) shows an enlarged view of the first joint portion 61. As indicated by the two-dot chain line, if the first joint portion 61 is formed so as to protrude downward (upward in the drawing) from the second surface 1b of the bottom cover 1, a bulge 61a protruding from the second surface 1b of the bottom cover 1 may be removed after the joining process. However, if the bulge 61a of the first joint portion 61 does not protrude beyond the mounting surface 15, the bulge 61a does not need to be removed. FIG. 5(b) shows an enlarged view of the second joint portion 62. Similarly, a bulge 62a protruding from the second surface 1b of the bottom cover 1 at the second joint portion 62 may be removed by cutting; however, if the bulge 62a does not protrude beyond the mounting surface 15, the bulge 62a does not need to be removed by cutting.

[0033] Alternatively, as shown in FIG. 6, a sealant 65 may be interposed between the bent ridge 30 and the second wall surface 12b of the recess 12. In the case of FIG. 6(a), after the case body 2 is cast, a groove 66 is formed in the second wall surface 12b of the recess 12 by post-processing, and a sealant 65 is interposed in the groove 66. By interposing the sealant 65, the sealing performance between the first side surface 30c of the bent ridge 30 and the second wall surface 12b of the recess 12 is improved. Alternatively, as shown in FIG. 6(b), a chamfered portion 67 may be formed at the corner of the second wall surface 12b of the recess 12, and the sealant 65 may be interposed in the chamfered portion 67. In this case, the chamfered portion 67 can be formed when the case body 2 is cast. However, the chamfered portion 67 may also be formed by post-processing.

[0034] In the above embodiment, the bending protrusion 30 protrudes toward the second member, but conversely, as shown in Fig. 7, when the first member 81 and the second member 82 are overlapped to form one or more third joints 83, the bending protrusion 30 may protrude toward the side opposite the second member 82. As shown by the two-dot chain line in Fig. 7, an auxiliary clamping point 70 may be provided in the center of the first member 81 in the left-right direction.

[0035] Furthermore, the bending ridges 30 may be arranged in a mixture of those projecting toward the second member 82 and those projecting away from the second member 82. For example, as shown in Fig. 8, the first member 81 may be provided with alternating first bending ridges 85 projecting in a first direction in the overlapping direction and second bending ridges 86 projecting in a second direction in the overlapping direction that is opposite to the first direction. In this case, the second bending ridges 86 may be formed continuously adjacent to the first bending ridges 85, thereby forming the first member 81 in a corrugated cross section.

[0036] Furthermore, the folded portion 30a of the bending protrusion 30 does not have to be curved. For example, as shown in FIG. 9(a), the folded portion 30a of the bending protrusion 30 may be pointed, or the bending protrusion 30 may be V-shaped in cross section. Furthermore, as shown in FIG. 9(b), the bending protrusion 30 may be U-shaped in cross section. As shown in FIG. 9(c), the U-shaped folded protrusion 30 may be continuously formed, or adjacent U-shaped folded protrusions 30 may protrude in opposite directions. Furthermore, as shown in FIG. 10, the first member 81 may have a folded step 90 as a bending portion, or the first member 81 may have a stepped upper portion 91 and a stepped lower portion 92 via the folded step 90. As shown, the shape of the bending portion may be various. Furthermore, for example, a concave-convex portion may be formed by embossing a predetermined portion of the first member 81, and the concave-convex portion may be used as a surplus portion.

[0037] As described above, the first member 81 and the second member 82 may have various shapes, and for example, both the first member 81 and the second member 82 may be plate-shaped. [Explanation of symbols]

[0038] 1 Bottom cover (first part) 1a 1st page 1b 2nd side 2 Case body (second component) 3 Battery 10 Bottom part 11 Side part 12 recess 12a First wall 12b Second wall 13 Mounting surface 14 Step 15 Placement surface 20 Bulkhead 21 Ribs 22 Communication hole 30 Bending ridge (bending part, excess part) 30a Folded part 30b Projection opening 30c 1st side 30d Second side 51 First Joint 52 Second Joint 61 1st joint 61a Bulge 62 Second joint 62a Bulge 65 Sealing material 66 Groove 67 Chamfered part 70 clamp points 81 First member 82 Second member 83 Third joint 85 First bending ridge 86 Second bending ridge 90 Bending step (bending part, excess part) 91 Upper step 92 step bottom 100 Laser P Placement surface

Claims

1. A method for joining a first member and a second member made of metal by overlapping them and clamping them at a clamping point, and then heating the first member and the second member from the first member side at a joining point away from the clamping point, A method for joining metal members, comprising providing an excess portion in the first member between the joining point and the clamping point before joining, in order to absorb thermal deformation during joining.

2. 2. The method for joining metal members according to claim 1, wherein the excess portion is a bent portion that is bent so as to protrude in the direction in which the first member and the second member are overlapped.

3. The joint has a shape that extends along a predetermined direction, 3. The method for joining metal members according to claim 2, wherein the bent portion is a bent ridge extending in the extension direction of the joining portion.

4. a recess is provided on a surface of the second member facing the first member, The bent protrusion protrudes toward the second member, 4. A method for joining metal members according to claim 3, wherein when the first member and the second member are overlapped, the bent protrusion is inserted into the recess and the side of the bent protrusion farther from the joining point is abutted against the wall surface of the recess.

5. 5. The method for joining metal members according to claim 4, wherein a sealing material is interposed between the bent ridge and the wall surface of the recess.

6. A joined body of metal members, comprising a first member and a second member made of metal superimposed on each other and having a joint portion heat-joined from the first member side, a bent portion bent so as to protrude toward the second member at a location away from the joint portion in the first member; a recess is provided on a surface of the second member facing the first member, A joint of metal members, in which a bent portion is inserted into a recess, and the side of the bent portion farther from the joint abuts against the wall of the recess.

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