Laser welding device and welding method for upper pressure plate

Abstract

The present invention relates to a laser welding device and a welding method for an upper pressing plate, wherein the welding device comprises a pressing unit and two laser welding heads arranged above the pressing unit, wherein the pressing unit comprises a base, a pressing head and a pressing unit, wherein the pressing head and the pressing unit are connected by a plurality of springs. During welding, the moving directions of the two laser welding heads are both from the center to one end, and the moving directions of the two welding heads are opposite; after completing the welding from the center to one end, the laser welding head returns to the center position and welds from the center to the other end. The present invention can make the deformation of the upper pressing plate less than 0.2% during the welding process through the design of the pressing unit and the change of the welding trajectory, thereby meeting the deformation requirements.

Description

Technical Field

[0001] The invention relates to the technical field of battery production, and in particular to a laser welding device and a welding method for an upper pressing plate. Background Art

[0002] The existing battery PACK generally includes an upper cover 3, a battery cell 2 and a bottom box 4. An upper pressure plate 1 is usually installed between the upper cover 3 and the battery cell 2. Figure 1 As shown, its main function is to fix the battery. When the battery cell 2 is slightly deformed by heat, the upper pressure plate 1 can compensate appropriately through its own deformation and reliably restrain the battery cell 2. When the battery cell 2 has thermal runaway, it can slow down the overall burning speed of the PACK, giving the driver and passengers enough time to escape. The upper pressure plate plays a vital role in the safety of the power battery PACK.

[0003] The structure of the upper pressing plate 1 is as follows Figure 2 , Figure 3 As shown, it is welded by two side strips 11 and an aluminum plate 12. The existing upper pressing plate has a length of 1000~2000mm, a width of 300~400mm, and a thickness of 10~15mm. There are 20~50 welds 13 evenly distributed in 2 rows, and the width of the weld 13 is greater than 2mm. It can be seen that the aspect ratio and length-to-thickness ratio of the upper pressing plate 1 are relatively large, and the heat generated during the welding process will cause deformation of the parts. Once the deformation of the parts exceeds 0.2%, after installation, the deformed upper pressing plate and the module are not in close contact to form a cavity, which makes the upper pressing plate's compensation function for the deformation of the battery cell invalid. When the battery PACK has thermal runaway, there is no buffer, which reduces the escape time of the driver and passengers; and large irregular deformation may cause extrusion of the battery cell, which has an adverse effect on the diaphragm and electrolyte inside the battery cell.

[0004] Therefore, there is a need in the art for a device and method that can effectively reduce the deformation of the upper pressing plate during welding. Summary of the invention

[0005] The purpose of the present invention is to provide a laser welding device for an upper pressing plate in order to overcome the defects of the prior art.

[0006] The purpose of this application is also to provide a welding method matching the above-mentioned welding device.

[0007] In order to achieve the purpose of the present invention, this application provides the following technical solutions.

[0008] In the first aspect, the present application provides a laser welding device for an upper pressing plate, wherein the upper pressing plate includes an aluminum plate and side strips welded on both sides of the aluminum plate, the welding device includes a clamping unit and two laser welding heads arranged above the clamping unit, the clamping unit includes a base, a clamping head and a lower pressing unit, and the clamping head and the lower pressing unit are connected by multiple springs.

[0009] In one embodiment of the first aspect, a boss is provided in the center of the base, the height of the boss is the same as the thickness of the side strip, and during welding, one end of the side strip abuts against the edge of the boss, and the aluminum plate is placed on the upper surface of the boss.

[0010] In one embodiment of the first aspect, the crimping head is composed of a plurality of crimping sub-units arranged in parallel along the length direction of the base and abutted in sequence, each crimping sub-unit includes a pressure foot at the bottom and a lower pressure block at the top, and during welding, the pressure foot abuts against the upper surface of the aluminum plate and is parallel to the position of the weld.

[0011] In one embodiment of the first aspect, the lower pressure unit includes a plurality of upper pressure blocks, a conductive column integrally fixed at the center of the upper surface of each upper pressure block, a force guide plate fixed to the top of all the conductive columns, and a lifting unit, and a plurality of springs are arranged between the lower pressure block and the upper pressure block.

[0012] In an implementation manner of the first aspect, the lifting unit is a servo electric cylinder.

[0013] In a second aspect, the present application also provides a welding method using the above-mentioned laser welding device, the welding method comprising the following steps:

[0014] (1) Place the aluminum plate and edge strip to be welded on the base and fix them with the crimping head and the pressing unit;

[0015] (2) Two laser welding heads are respectively aligned with the center of the part to be welded formed by an edge strip and the aluminum plate, and then welding begins;

[0016] (3) The moving directions of the two laser welding heads are both from the center to one end, and the moving directions of the two welding heads are opposite; after completing the welding from the center to one end, the laser welding head returns to the center position and welds from the center to the other end;

[0017] (4) After welding is completed, the lower pressure unit lifts the crimping head upwards, removes the upper pressure plate, and completes the welding.

[0018] In one implementation of the second aspect, the laser welding head is in the form of a swing welding head.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention can make the deformation of the upper pressing plate less than 0.2% during the welding process through the design of the clamping unit and the change of the welding trajectory, thereby meeting the deformation requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the cross-sectional structure of an existing battery PACK;

[0022] Figure 2 Schematic diagram of the cross-sectional structure of the upper pressing plate;

[0023] Figure 3 is a top view of the upper pressing plate;

[0024] Figure 4 is a schematic structural diagram of the welding device in Example 1;

[0025] Figure 5 It is a side structural schematic diagram of the pressing unit in Example 1;

[0026] Figure 6 This is a schematic diagram of the welding trajectory in Example 1;

[0027] Figure 7 Schematic diagram of the test structure of the compression unit in Comparative Example 1;

[0028] Figure 8 This is a schematic diagram of the welding trajectory in Comparative Example 2;

[0029] Fig. 9 This is a schematic diagram of the welding trajectory in Comparative Example 3.

[0030] In the accompanying drawings, 1 is an upper pressure plate, 11 is a side strip, 12 is an aluminum plate, 13 is a weld, 2 is a battery cell, 3 is an upper cover, 4 is a bottom box, 5 is a clamping unit, 51 is a crimping head, 511 is a pressure foot, 512 is a lower pressure block, 513 is a spring, 52 is a lower pressure unit, 521 is an upper pressure block, 522 is a conduction column, 523 is a force guide plate, 524 is a servo electric cylinder, 53 is a base, 531 is a boss, and 6 is a laser welding head. DETAILED DESCRIPTION

[0031] Unless otherwise defined, the technical or scientific terms used in this specification and claims shall have the ordinary meanings understood by persons having ordinary skills in the technical field to which the present invention belongs. All the values ​​from the lowest value to the highest value listed herein refer to all the values ​​obtained by incrementing one unit between the lowest value and the highest value when the difference between the lowest value and the highest value is more than two units.

[0032] The specific embodiments of the present invention will be described below. It should be noted that in the specific description of these embodiments, for the sake of concise description, it is impossible for this specification to describe all the features of the actual embodiments in detail. Without departing from the spirit and scope of the present invention, those skilled in the art may modify and replace the embodiments of the present invention, and the resulting embodiments are also within the scope of protection of the present invention.

[0033] In conventional upper pressure plate welding devices and welding technologies, the deformation of the upper pressure plate is generally between 0.5% and 1%, and the application cannot well protect the safety of the battery core. The purpose of this application is to provide a welding device and a welding method with a smaller deformation.

[0034] In a specific embodiment, the present application provides a laser welding device for an upper pressing plate, wherein the upper pressing plate includes an aluminum plate and side strips welded on both sides of the aluminum plate, and the welding device includes a clamping unit and two laser welding heads arranged above the clamping unit, wherein the clamping unit includes a base, a clamping head and a lower pressing unit, and the clamping head and the lower pressing unit are connected by a plurality of springs. Since a spring is arranged between the clamping head and the lower pressing unit, during the welding process, when the lower pressing unit presses the clamping head downward, thereby clamping the aluminum plate and the side strip, the spring is in a compressed state, which not only plays a role in product clamping, but also reserves additional pressure (i.e., the spring's rebound force), so that it has a "straightening" effect on the product, because when the clamping head rises, the spring will rebound and release the pressure when it rises. After the welding of the welded part is completed, the extrusion force is gradually reduced, so that the internal stress generated by the welded part during welding is gradually released, and the huge deformation caused by the sudden release of the internal stress is prevented. The time for releasing the internal stress is prolonged, the cooling and shaping time of the welding position is long, and the deformation is small.

[0035] In a specific embodiment, a boss is provided in the center of the base, and the height of the boss is the same as the thickness of the side strip. During welding, one end of the side strip abuts against the edge of the boss, and the aluminum plate is placed on the upper surface of the boss. This structure can quickly install and position the aluminum plate and the side strip, and the matching press joint can well restrain the aluminum plate and the side strip.

[0036] In a specific embodiment, the crimping joint is composed of a plurality of crimping sub-units arranged in parallel along the length direction of the base and abutted in sequence, each crimping sub-unit includes a bottom press foot and a top lower pressing block, and during welding, the press foot abuts against the upper surface of the aluminum plate and is parallel to the position of the weld. The crimping joints are arranged separately and in parallel, mainly because: the integral crimping joint (i.e., the long crimping joint), when not deformed, will cause the long crimping head to warp due to the action of the spring rebound force and the condition of unilateral suspension, making the product unevenly stressed, and the welding product may not be pressed tightly while the stress concentration point may be damaged. However, the present application adopts a short crimping joint (i.e., multiple crimping sub-units arranged in parallel). When welding shorter products, because the short crimping heads do not interfere with each other, the pressed product, without the product part pressed on the tray, can better flatten the product and make the stress more uniform; even if some short crimping heads are partially suspended, the product will not be damaged due to the small force, and the stress on other parts of the product is still uniform. Moreover, the crimping joint has high precision requirements, and it is difficult to ensure the flatness of the contact surface if it is too long and the price is high. In addition, when products are changed, when shorter products are pressed with a long pressing head, one end without the product may be deformed, resulting in other models of products not being pressed tightly, resulting in a decrease in the pass rate.

[0037] In a specific embodiment, the lower pressing unit includes a plurality of upper pressing blocks, a conductive column integrally fixed at the center of the upper surface of each upper pressing block, a force guide plate fixed to the top of all the conductive columns, and a lifting unit, and each of the lower pressing blocks is connected to each of the upper pressing blocks by a plurality of springs. Preferably, four springs are provided between the lower pressing block and the upper pressing block, and are distributed in a rectangular shape. The reason why the upper pressing block and the guide column are used in the present application is that when the electric cylinder moves downward, the speed is relatively fast, and the impact generated when the upper pressing plate contacts the product will cause the product to produce a contact "mark", resulting in the product being unqualified. Therefore, the upper pressing plate is set as a movable part, which moves up and down through the guide column; the spring can limit the range of motion of the upper pressing plate and return the upper pressing plate to its original position in time, and play a buffering role when the upper pressing plate contacts the product, so that the impact contact between the two is converted into a "soft contact" with increasing pressure, reducing the indentation of the product. The reason why the force guide plate is split instead of the whole plate is related to the guide column: to ensure the smooth movement of the guide column, the guide column must be concentric with the mounting hole and must not have any deflection, otherwise jamming during operation will cause mechanical damage and product scrapping. The guide column is installed on the upper pressure plate, and the column body passes through the linear bearing on the force guide plate. It is very difficult to ensure that the mounting holes and the bearing holes correspond one by one to ensure high concentricity. There are many holes on the whole plate, which requires too high precision and is difficult to process and expensive. Therefore, the whole plate is reduced to zero and small pieces of force guide plates are used for assembly, which reduces the difficulty of processing, reduces costs, reduces debugging costs, and makes maintenance more convenient.

[0038] In a specific embodiment, the lifting unit is a servo electric cylinder. The pressing force can be conveniently adjusted by accurately controlling the displacement of the pressing part through the servo electric cylinder, which is more convenient to adjust when changing products.

[0039] In a specific embodiment, the present application also provides a welding method using the above-mentioned laser welding device, the welding method comprising the following steps:

[0040] (1) Place the aluminum plate and edge strip to be welded on the base and fix them with the crimping head and the pressing unit;

[0041] (2) Two laser welding heads are respectively aligned with the center of the part to be welded formed by an edge strip and the aluminum plate, and then welding begins;

[0042] (3) The moving directions of the two laser welding heads are both from the center to one end, and the moving directions of the two welding heads are opposite; after completing the welding from the center to one end, the laser welding head returns to the center position and welds from the center to the other end;

[0043] (4) After welding is completed, the lower pressure unit lifts the crimping head upwards, removes the upper pressure plate, and completes the welding.

[0044] When welding is performed using the above welding path, the midpoint is heated twice. At the same time, the welding time interval at both ends is short, resulting in a smaller temperature difference. The time difference in cooling of the molten pool is small, and thermal expansion and contraction occur evenly everywhere. With the external force assistance of the upper pressure plate, the deformation can be effectively reduced.

[0045] In a specific embodiment, the laser welding head is in the form of a swing welding head. There are two small precision motors inside the swing welding head to drive the reflective lens to rotate. Then the deflection angle of the laser beam is changed. It is manifested as the laser beam can be swung along circular, figure 8, S-shaped and other trajectories. The speed and frequency of the welding head swing are adjustable. Therefore, it is very convenient when adjusting the laser parameters. Another advantage of using a swing head is that the laser beam can be controlled to swing in a circular ring in the welding molten pool at a high frequency through the swing of the swing head, so that the laser beam is stirred in the molten pool, which is conducive to the rapid overflow of gasified magnesium and silicon elements during the welding process. To reduce the porosity tendency of the welded joint. The laser welding head in this application selects the MFSC series laser.

[0046] The embodiments of the present invention will be described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. Example 1

[0047] A welding device for an upper pressing plate, the structure of which is shown in Figure 4, comprises two laser welding heads and a pressing unit, wherein the laser welding heads are respectively located on both sides of the pressing unit. The pressing unit comprises a base, a pressing head and a lower pressing unit, as shown in Figure 4. Figure 5 As shown. A boss is provided in the center of the base, and the height of the boss is the same as the thickness of the edge strip. The crimping head is composed of a plurality of crimping sub-units arranged in parallel along the length direction of the base and abutted in sequence, and each crimping sub-unit includes a presser foot at the bottom and a lower pressing block at the top. The lower pressing unit includes a plurality of upper pressing blocks, a conductive column integrally fixed at the center of the upper surface of each upper pressing block, a force guide plate fixed to the top of all the conductive columns, and a servo electric cylinder. Four springs are provided between each lower pressing block and the upper pressing block, respectively located at the four corners of the upper pressing block and the lower pressing block. During welding, one end of the edge strip abuts against the edge of the boss, the aluminum plate is placed on the upper surface of the boss, the presser foot abuts against the upper surface of the aluminum plate, and is parallel to the position to be welded and exposes the position to be welded.

[0048] During welding, the welding tracks of the two laser welding heads are as follows: Figure 6 As shown, both welding heads start welding from the middle of the aluminum plate, and then move to the two ends along track A, and the movement directions of the two laser welding heads are opposite. When the welding reaches the top, the two welding heads return to the middle of the aluminum plate, and then move to the other direction along track B. After multiple welding, the deformation of the upper plate is tested, as shown in Table 1.

[0049] Comparative Example 1

[0050] The same laser welding head, base, crimping head and pressing unit as in Example 1 are used, but the spring between the crimping head and the pressing unit is eliminated, and the crimping head and the pressing unit are directly fixed together, as shown in FIG. Figure 7 The same welding track as in Example 1 was used, and after multiple welding, the deformation of the upper pressing plate was tested, as shown in Table 1.

[0051] Comparative Example 2

[0052] The same welding device as in Example 1 is used, but during welding, only one of the laser welding heads is operated, and the other laser welding head is not operated. Figure 8 As shown, the laser welding head starts welding from one end of the aluminum plate, and after completing the welding of one side strip, it starts welding the other side strip, and the entire welding track C is U-shaped. After multiple welding, the deformation of the upper pressing plate is tested, as shown in Table 1.

[0053] Comparative Example 3

[0054] The same welding device as in Example 1 is used, but during welding, one of the laser welding heads starts welding and moves from the left side to the right side of the aluminum plate, that is, welding is performed along track E, and the other laser welding head is welded along track D. Fig. 9 After multiple welding, the deformation of the upper pressing plate is tested, as shown in Table 1.

[0055] Table 1 Test results of deformation of upper pressure plate after welding (mm)

[0056]

[0057] In all the above welding processes, the length of the aluminum plate used was 1500 mm, from which it can be obtained that the deformation rate in Example 1 is 0.142%, and the deformation rates of the other comparative examples are all greater than 0.2%.

[0058] The above description of the embodiments is to facilitate those of ordinary skill in the art to understand and apply the present application. It is obvious that those familiar with the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to pay creative labor. Therefore, the present application is not limited to the embodiments herein, and improvements and modifications made by those skilled in the art based on the contents disclosed in the present application without departing from the scope and spirit of the present application are within the scope of the present application.

Claims

1. A welding method using a laser welding device for an upper pressing plate, characterized in that: The welding method comprises the following steps: (1) Place the aluminum plate and edge strip to be welded on the base and fix them with the crimping head and the pressing unit; (2) Two laser welding heads are respectively aligned with the center of the part to be welded formed by an edge strip and the aluminum plate, and then welding begins; (3) The moving directions of the two laser welding heads are both from the center to one end, and the moving directions of the two welding heads are opposite; after completing the welding from the center to one end, the laser welding head returns to the center position and welds from the center to the other end; (4) After welding is completed, the lower pressure unit lifts the crimping head upwards, removes the upper pressure plate, and completes the welding; Among them, the upper pressing plate includes an aluminum plate and side strips welded on both sides of the aluminum plate, the welding device includes a clamping unit and two laser welding heads arranged above the clamping unit, the clamping unit includes a base, a crimping head and a lower pressing unit, the crimping head is composed of a plurality of crimping sub-units arranged in parallel along the length direction of the base and abutted in sequence, each crimping sub-unit includes a pressure foot at the bottom and a lower pressing block at the top, a boss is provided in the center of the base, the height of the boss is the same as the thickness of the side strip, during welding, the pressure foot abuts against the upper surface of the aluminum plate and is parallel to the position of the weld, one end of the side strip abuts against the edge of the boss, the aluminum plate is placed on the upper surface of the boss, and the crimping head and the lower pressing unit are connected by multiple springs.

2. The welding method according to claim 1, characterized in that The laser welding head is in the form of a swing welding head.

3. The welding method according to claim 1, characterized in that The lower pressing unit includes a plurality of upper pressing blocks, a conductive column integrally fixed at the center of the upper surface of each upper pressing block, a force guide plate fixed to the top of all the conductive columns, and a lifting unit. A plurality of springs are arranged between the lower pressing block and the upper pressing block.

4. The welding method according to claim 3, characterized in that: The lifting unit is a servo electric cylinder.

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