A system for improving weld flash on a roof perimeter weld

Abstract

The utility model discloses a system that improves the welding tumor of top cover periphery, including aluminium shell, apron and laser welder, and aluminium shell is welded with apron by laser welder, and the assembly tolerance is arranged between aluminium shell and apron, and the interference fit is arranged at the corner position of aluminium shell and the corner position of apron, and the side of apron towards the shell body installation is provided with chamfering. Through the assembly tolerance of aluminium shell and apron of control, the interference fit is used to the corner position of aluminium shell and the corner position of apron, and the design purpose is to reduce the clearance between aluminium shell and apron, and the excessive clearance can lead to the collapse of molten pool and form the fusion tumor, and the chamfering of apron bottom is convenient for apron to enter the shell body, improves the shell press -fit yield, and through the energy proportion of laser welder inner ring and outer ring, the molten pool flow direction can be optimized, and the molten metal accumulation is avoided, and the spot diameter can be increased to disperse energy and reduce the unit area heat input, and through the above adjustment, the fusion tumor can be improved, but the melting depth must be ensured to reach the standard, and the molten pool stability is ensured simultaneously.

Description

Technical Field

[0001] This utility model relates to the field of lithium battery manufacturing technology, specifically to a system for improving weld beads around the top cover. Background Technology

[0002] In the manufacturing process of lithium-ion batteries, perimeter welding is crucial. It seals the metal casing, enhances structural strength, ensures stable current transmission, and affects thermal management, thereby ensuring the physical integrity and safety of the battery. High-precision welding technology is key to the preparation of high-performance batteries.

[0003] There are two common welding methods for the perimeter of lithium batteries: side welding and vertical welding. Side welding usually results in a smoother weld, but it requires strict control of welding parameters and speed to avoid defects. Side welding also demands higher standards for welding equipment and techniques. Vertical welding, where the weld is perpendicular to the ground, causes the molten metal and droplets to tend to fall due to gravity, making it prone to weld beads. Vertical welding is typically used for lithium-ion battery welding.

[0004] In lithium-ion battery manufacturing, electrode damage and weld beads are a key challenge. They disrupt electrode integrity, reduce reaction area, and affect capacity, especially in thin-film, high-energy-density batteries where the risk is even higher. If weld beads touch the separator, they increase the risk of internal short circuits, leading to a 10%–30% capacity loss, increased internal resistance, and intensified heat generation, thus threatening performance and safety, and potentially triggering thermal runaway. Furthermore, weld beads damage the casing seal, causing electrolyte leakage and environmental corrosion. Aesthetically, weld beads create defects, affecting appearance, and in large-scale production, they increase battery performance variability, reduce battery pack consistency, and increase the difficulty of BMS (Battery Management System) control. Therefore, controlling peripheral weld beads is crucial for improving battery performance, safety, and consistency. Utility Model Content

[0005] The technical problem to be solved by this utility model is: how to improve the welding bead on the periphery of the top cover, eliminate the generation of welding bead, and thus improve the welding yield and production efficiency of the periphery.

[0006] To solve the above-mentioned technical problems, this utility model provides the following technical solution: A system for improving weld beads around the perimeter of a top cover includes an aluminum shell, a cover plate, and a laser welding machine. The laser welding machine welds the aluminum shell to the cover plate. Assembly tolerances are provided between the aluminum shell and the cover plate. An interference fit is provided at the corner positions of the aluminum shell and the cover plate. Chamfers are provided at the bottom of the four sides of the cover plate.

[0007] This application controls the assembly tolerances of the aluminum shell and the cover plate. The corner positions of the aluminum shell and the cover plate are made with an interference fit. The purpose of this design is to reduce the gap between the aluminum shell and the cover plate. An excessive gap will cause the molten pool to collapse and form a molten nodule. The bottom of the cover plate is designed with a chamfer to facilitate the cover plate entering the shell and improve the yield of the press-fitting process.

[0008] As a further aspect of this utility model: the inner ring power range of the laser welding machine is 800±100W, and the outer ring power range of the laser welding machine is 1300±200W.

[0009] This application can optimize the flow direction of the molten pool and avoid molten metal accumulation by adjusting the energy ratio between the inner and outer rings of the laser welding machine (e.g., low energy preheating in the inner ring and high energy deep penetration in the outer ring); increasing the spot diameter can disperse energy and reduce heat input per unit area; increasing the welding speed can shorten the residence time of the molten pool and reduce heat accumulation. These adjustments can improve the weld bead effect, but it is necessary to ensure that the penetration depth meets the requirements while ensuring the stability of the molten pool. Reasonable control of penetration depth / width can prevent molten pool collapse and the formation of weld beads.

[0010] As a further aspect of this utility model, the defocusing range of the laser welding machine is -1±1mm.

[0011] This application can be verified by controlling welding parameters such as power, speed, and defocusing amount of the laser welding machine to reasonably control the penetration depth and penetration width ratio.

[0012] As a further aspect of this utility model: the laser welding machine uses a multimode 2kW optical fiber.

[0013] As a further aspect of this utility model: the inner length of the aluminum shell in the length direction is 0.1 mm longer than the inner length of the cover plate in the length direction.

[0014] As a further aspect of this utility model: the inner width of the aluminum shell in the width direction is 0.1mm larger than the inner width of the cover plate in the width direction.

[0015] As a further embodiment of this utility model: the laser welding machine uses alternating welding of the long side and the short side for welding the aluminum shell and the cover plate.

[0016] As a further embodiment of this utility model: when welding the aluminum shell and the cover plate, the long side is welded first, then the short side, and finally the four corners are welded.

[0017] In this application, the long and short sides of the peripheral welding trajectory are welded in a segmented, alternating reverse manner, and the corner positions are welded separately; while meeting the standards for penetration depth and width and appearance conditions, the welding trajectory is shifted towards the cover plate side.

[0018] This application employs a segmented welding strategy involving long and short sides to effectively control heat input distribution, reduce molten pool fluctuations and molten metal accumulation, thereby suppressing weld bead formation. The long and short sides are welded alternately. After the long side is welded, the short side starts from the other side and continues to the end position of the long side welding. After both long and short sides are welded, corner welding is performed. The laser direction needs to be offset towards the cover plate side to avoid overheating of the shell. Gravity is used to guide the molten metal to the weld seam, reducing weld bead formation.

[0019] As a further embodiment of this utility model: the tolerance of the inner length and inner width of the aluminum shell is ±0.1mm, and the tolerance of the thickness of the aluminum shell is ±0.5mm.

[0020] As a further embodiment of this utility model: the tolerance of the inner length and inner width of the cover plate is -0.1mm, and the tolerance of the outer length and outer width of the cover plate is ±0.05mm. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the aluminum shell and cover plate in an embodiment of the present invention; Figure 2 This is a schematic diagram of the segmented welding method in an embodiment of the present utility model; Figure 3 This is a schematic diagram showing the presence of weld beads in the metallographic structure of an embodiment of this utility model. Figure 4 This is a bottom view of the upper and lower substrates of this utility model; Explanation of reference numerals in the attached figures: 1. Aluminum shell; 2. Cover plate; 21. Upper substrate; 22. Lower substrate; 23. Brake frame. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0023] Reference Figure 1A system for improving weld beads around the top cover includes an aluminum shell 1 and a cover plate 2. The cover plate 2 can be interference-fitted onto the aluminum shell 1. The cover plate 2 includes an upper substrate 21, a lower substrate 22, and a brake frame 23. The lower substrate 22 is located below the upper substrate 21 and forms a "T" shape with the upper substrate 22. The bottom of the four sides of the lower substrate 22 is not a right angle, but is chamfered with a C-angle. The brake frame 23 is installed below the lower substrate 22. During subsequent installation, both the lower substrate 22 and the brake frame 23 can be installed into the aluminum shell 1. The upper substrate 21 is located above the aluminum shell 1. Assembly tolerances are set between the aluminum shell 1 and the cover plate 2, namely, the inner length of the aluminum shell 1 in the longitudinal direction is 0.1mm larger than the inner length of the cover plate 2 in the longitudinal direction (i.e., the length of the lower substrate 22), and the inner width of the aluminum shell 1 in the width direction is 0.1mm larger than the inner width of the cover plate 2 in the width direction (i.e., the width of the lower substrate 22); wherein the four corners of the aluminum shell 1 and the four corners of the bottom of the cover plate 2 (i.e., the corners of the lower substrate 22) are interference fit, that is, the inner radius (R) of the four corners of the aluminum shell 1 and the inner radius (R) of the four corners of the lower substrate 22 in the bottom view are interference fit (refer to...). Figure 4 The purpose of this design is to reduce the gap between the aluminum shell 1 and the cover plate 2. An excessively large gap will cause the molten pool to collapse and form a molten nodule.

[0024] The bottom of the cover plate 2 is designed with a chamfer to facilitate the cover plate entering the shell 1 and improve the shell pressing yield. However, the chamfered slope will guide the molten pool to flow in a specific direction, causing the molten metal to accumulate. Therefore, the size of the C-angle of the cover plate needs to be designed reasonably.

[0025] By adjusting the energy ratio between the inner and outer rings of the laser welding machine (e.g., low energy preheating in the inner ring and high energy deep penetration in the outer ring), the flow direction of the molten pool can be optimized, avoiding molten metal accumulation. Increasing the spot diameter can disperse energy and reduce heat input per unit area. Increasing the welding speed can shorten the residence time of the molten pool and reduce heat accumulation. These adjustments can improve the weld bead, but it is necessary to ensure that the penetration depth meets the requirements while ensuring the stability of the molten pool. Reasonable control of penetration depth and width can prevent the molten pool from collapsing and forming a weld bead. It is necessary to explore a set of relatively perfect parameters while meeting the penetration depth and width requirements, and then perform DOE verification based on these parameters to output the optimal welding parameters.

[0026] Reference Figure 2 By employing a segmented welding strategy between the long and short sides of the aluminum shell 1 and the cover plate 2, heat input distribution can be effectively controlled, molten pool fluctuations and molten metal accumulation can be reduced, thereby inhibiting weld bead formation. The long and short sides are welded alternately; after the long side welding is completed, the short side welding begins from the other side and continues to the end position of the long side welding. After both long and short sides are welded, the four corner R-angle positions are welded, with the welding direction referring to... Figure 2 The arrow and serial number indicate that the laser direction should be offset towards the two sides of the cover plate to avoid overheating of the aluminum shell. Gravity should be used to guide the molten metal to the weld seam to reduce weld beads.

[0027] Specifically, the battery is welded around the top cover, and the positive and negative electrode cover plates 2 are welded on both sides of the aluminum shell 1. The initial design dimensions of the aluminum shell 1 and cover plate 2 are as follows: the outer length of the aluminum shell opening is 119.7±0.1mm, the outer width is 21.8±0.1mm, the thickness of the aluminum shell is 0.45±0.5mm, the outer radius of the aluminum shell is R1.4±0.15mm, and the inner radius of the aluminum shell is R1±0.15mm; the outer length of the negative electrode cover plate is 119.7±0.05mm, the outer width of the cover plate (i.e., the width of the upper substrate 21) is 21.8±0.05mm, the inner length of the cover plate (i.e., the length of the lower substrate 22) is 118.8mm (tolerance is -0.1), the inner width of the cover plate (i.e., the width of the lower substrate 22) is 21mm (tolerance is -0.1), the C-angle of the substrate is R0.3mm, and the inner radius of the substrate is R1.2±0.05mm.

[0028] The peripheral welding laser uses a multimode 2kW fiber. Welding parameters include an inner ring power of 800W, an outer ring power of 1300W, a defocusing distance of -1mm, and good welding results at a speed of 500mm / s. During welding, both long and short sides are welded continuously, with the laser emitting light continuously. The welding trajectory is directly aligned with the gap between the aluminum shell and the cover plate. Under these welding conditions, weld beads appear at the triangular area where the aluminum shell and cover plate connect. Metallographic analysis shows a schematic diagram of the weld beads (e.g.,...). Figure 3 As shown in the figure, the appearance of the welding trajectory and the metallographic test results showed no abnormalities.

[0029] Therefore, in order to avoid the impact of weld beads on the battery, this application makes optimizations; the assembly tolerance of the aluminum shell and the cover plate is adjusted. The main reason for the accumulation of weld beads when they drip down to the chamfer position is that there is a gap at the connection position between the aluminum shell 1 and the cover plate 2 to guide the directional movement of the molten pool. If there is no gap at all the connection positions between the aluminum shell 1 and the cover plate 2, the yield of the casing press assembly will be reduced, and the risk of short circuit caused by the introduction of foreign objects will also increase.

[0030] The welding parameters were verified based on the current optimal welding conditions (inner ring power of laser welding machine 800±100W, outer ring power of laser welding 1300±200W, defocusing amount -1±1mm). The verification scheme and verification results are shown in Table 1.

[0031] Table 1 shows the welding parameter verification scheme and verification results. The above experiments verified that the order of importance of the significant factors affecting weld penetration is: inner ring power > outer ring power > decoking amount, with the inner ring power showing a significant correlation. The order of importance of the significant factors affecting weld width is: outer ring power > inner ring power > decoking amount, with the outer ring power showing a significant correlation. An inner ring power of 800W, an outer ring power of 1300W, a decoking amount of -1mm, and a welding speed of 200mm / s are considered the optimal welding parameters. However, using these parameters did not completely eliminate weld beads in the metallographic structure, therefore adjustments to the structural components are necessary.

[0032] The combined verification of the cover plate's C-angle, R-angle, and inner length was conducted. The verification scheme and results are shown in Table 2. After changing the cover plate's C-angle from 0.3 to 0.2, no weld bead phenomenon appeared. Reducing the C-angle improved the weld bead phenomenon. There was no significant difference in the penetration depth and width of the surrounding welds. Therefore, the structural components were modified. The R-angle was adjusted from 1.2 to 1.1, the C-angle from 0.3 to 0.2, and the inner diameter of the cover plate from 21.0 mm to 21.3 mm. At this time, there were small weld beads in the triangular area of ​​the cover plate, but it was significantly improved compared to before.

[0033]

[0034] Table 2 shows the verification scheme and results of the cover plate structure. Simultaneously adjust the welding trajectory, moving it 0.05mm from the weld seam towards the cover plate side. To disperse heat, alternate welding along the long and short sides. Figure 2 As shown, after adjusting the welding trajectory, no weld beads were found in the metallographic analysis, thus eliminating the generation of weld beads in this way.

[0035] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A system for improving weld beads around the perimeter of a top cover, characterized in that, It includes an aluminum shell (1), a cover plate (2) and a laser welding machine. The laser welding machine welds the aluminum shell (1) and the cover plate (2). An assembly tolerance is set between the aluminum shell (1) and the cover plate (2). An interference fit is made at the corner of the aluminum shell (1) and the corner of the cover plate (2). The bottom of the four sides of the cover plate (2) is chamfered.

2. The system for improving weld beads around the top cover according to claim 1, characterized in that: The inner ring power range of the laser welding machine is 800±100W, and the outer ring power range is 1300±200W.

3. The system for improving weld beads around the top cover according to claim 1, characterized in that: The defocusing range of the laser welding machine is -1±1mm.

4. The system for improving weld beads around the top cover according to claim 1, characterized in that: The laser welding machine uses a multimode 2kW optical fiber.

5. The system for improving weld beads around the top cover according to claim 1, characterized in that: The inner length of the aluminum shell (1) in the longitudinal direction is 0.1 mm longer than the inner length of the cover plate (2).

6. The system for improving weld beads around the top cover according to claim 1, characterized in that: The inner width of the aluminum shell (1) in the width direction is 0.1 mm larger than the inner width of the cover plate (2) in the width direction.

7. The system for improving weld beads around the top cover according to claim 1, characterized in that: The laser welding machine uses alternating long and short side welding for welding the aluminum shell (1) and cover plate (2).

8. The system for improving weld beads around the top cover according to claim 7, characterized in that: When welding the aluminum shell (1) and the cover plate (2), the long side is welded first, then the short side, and finally the four corners are welded.

9. The system for improving weld beads around the top cover according to claim 1, characterized in that: The tolerance for the inner length and inner width of the aluminum shell (1) is ±0.1mm, and the tolerance for the thickness of the aluminum shell is ±0.5mm.

10. The system for improving weld beads around the top cover according to claim 1, characterized in that: The tolerance of the inner length and inner width of the cover plate (2) is -0.1mm, and the tolerance of the outer length and outer width of the cover plate (2) is ±0.05mm.

Images