Negative electrode lug cover plate laser welding method

Abstract

The invention discloses a negative electrode tab cover plate laser welding method which comprises the following steps: attaching a tab to a to-be-welded piece, and welding two layers by adopting a spiral welding track; the whole track of the tab is spirally welded on the first layer, and variable power welding is adopted as the first layer spiral welding power; the first one-fifth track of the tab is rewelded on the second layer in a spiral mode, and constant-power welding is adopted as the second layer in spiral welding power. The spiral track can provide a continuous and smooth movement path, the stable welding speed can be kept, the welding efficiency is improved through the stability, and due to the fact that the laser welding head does not need to be started and stopped frequently, the non-production time is shortened; the same welding mark is welded twice in total, the first layer is welded with the whole track, the second layer is welded with the first one-fifth part, the two layers of welding tracks are different in spiral line density, and the second layer mainly aims at modifying the welding appearance and at the same time, the welding temperature is low when welding is just started, and the risk that the front end is not fused is caused; and the abnormity can be solved by re-welding the front part.

Description

Technical Field

[0001] The invention relates to the technical field of pole tab welding, and in particular to a laser welding method for a negative pole tab cover plate. Background Art

[0002] Lithium-ion lug cover laser welding utilizes the excellent directionality and high power density of the laser beam to work. The laser beam is focused into a very small area through an optical system, forming a heat source area with highly concentrated energy at the weld in a very short time, thereby melting the weld and forming a firm weld mark.

[0003] The patent publication number is CN113385814A, and the patent name is the laser welding method of multi-layer pole lugs, laser welding device and prior art of lithium battery, which specifically discloses "including A, arranging and fastening the multiple pole lugs of the first pole lug group and the second pole lug group in sequence, and the gap between the adjacent pole lugs of the first pole lug group and the second pole lug group is not more than 0.1mm; wherein the first pole lug group and the second pole lug group are made of different metal materials respectively; B, irradiating the welding positions of the first pole lug group and the second pole lug group with a laser beam and blowing a protective gas into the welding positions to be welded, so as to weld the multiple pole lugs of the first pole lug group and the second pole lug group into an integrated conductive structure", the above technology adopts single-layer welding and the welding power is constant power, and different welding powers are not adopted according to different positions, and there is a risk of the front end not melting in and unstable welding when low-temperature initial welding is performed.

[0004] When welding square battery assemblies, the poles are thickly contaminated, and the contaminants decompose when welding the pole ears and cover poles, which can easily form welding explosion points and cause holes; batteries with thin poles and plastic or ceramic structural parts underneath are easily welded through; in order to ensure the overcurrent capacity and internal resistance of the battery cell, it is also necessary to control the welding strength and welding area. Unstable welding seriously affects the assembly yield and production capacity. Based on this, this application proposes a negative pole ear cover laser welding method to solve the above-mentioned shortcomings. Summary of the invention

[0005] The technical problem to be solved by the present invention is: how to improve the welding stability of the negative electrode lug cover plate, reduce the proportion of poor welding, and thus improve the assembly yield and production efficiency.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A negative electrode tab cover plate laser welding method comprises the following steps:

[0008] Make the tab and the cover fit together, use a spiral welding track, and weld two layers;

[0009] The first layer of spiral welding is for the entire track of the pole ear, and the first layer of spiral welding power adopts variable power welding;

[0010] The first fifth of the second layer of spiral welding of the lug is welded, and the second layer of spiral welding power adopts constant power welding;

[0011] The spiral line density of the first layer of spiral welding is different from that of the second layer of spiral welding.

[0012] The present application adopts a spiral welding trajectory, which can provide a continuous and smooth motion path, helping to maintain a stable welding speed. This stability improves welding efficiency because the laser welding head does not need to be started and stopped frequently, reducing non-productive time; the same weld mark is welded twice, the first layer welds the entire trajectory, and the second layer welds the first fifth of the track. The density of the spiral lines of the two layers of welding trajectories is also different. The main purpose of the second layer is to modify the welding appearance. At the same time, the welding temperature is low at the beginning of welding, and there is a risk that the front end will not melt in. Re-welding the front part can now solve this abnormality.

[0013] As a further solution of the present invention: the variable power of the first layer spiral welding is divided into three stages, the welding power in the first stage is the highest, and the welding power in the second and third stages begins to decrease as the welding temperature increases.

[0014] In this application, different welding powers are used at different positions. Variable power is used for welding on the first layer. At the beginning, the temperature is low and the welding power is the highest. As the heat affected zone of welding increases, the temperature is lowered and then maintained for welding. The temperature is lowered in advance when it is about to end, and targeted welding is used to improve the welding quality.

[0015] As a further solution of the present invention: the welding power of the second layer of spiral re-welding is lower than the power of the first layer of spiral welding with the longest welding time.

[0016] The second layer of this application is welded at constant power, and the welding power is lower than the power with the longest welding time in the first section. The main purpose is to modify the appearance and solve the problem of poor welding caused by low temperature in the early stage, thereby improving the assembly yield and production efficiency.

[0017] As a further solution of the present invention: the density of the first layer of spiral welding wires is less than the density of the second layer of spiral welding wires.

[0018] As a further solution of the present invention: the distance between two adjacent spirals in the first layer of spiral welding wires is 0.2 mm-0.4 mm, and the distance between two adjacent spirals in the second layer of spiral wires is 0.15 mm-0.25 mm.

[0019] The first and second layers of this application use different spiral wire welding densities. Too high a welding density may lead to the expansion of the heat-affected zone. The heat-affected zone refers to the area where the microstructure and performance changes occur due to high temperature during the welding process. An excessively large heat-affected zone may lead to degradation of material properties, such as reduced hardness, increased brittleness, etc. The higher the welding density, the greater the welding time and material consumption, thereby reducing the welding efficiency. Therefore, while ensuring the welding quality, choosing an appropriate welding density can balance efficiency and cost.

[0020] As a further solution of the present invention: the total length of the first layer spiral welding track is 20cm-25cm, and the radius of the first layer spiral welding line is 3.5cm-4cm.

[0021] As a further solution of the present invention: the radius of the second layer spiral welding line is 4cm-4.5cm, and the total length of the second layer spiral welding track is 5cm-5.5cm.

[0022] As a further solution of the present invention: taking the base mode welding laser as an example:

[0023] The highest welding power of the first layer of spiral welding is 85%-90% of the base mold, and the welding power with the longest welding time is 65%-70% of the base mold;

[0024] The welding power of the second layer of spiral welding is 45%-50% of that of the base mold.

[0025] After the same laser is changed from a constant single-layer welding power to the above-mentioned welding, the proportion of explosion points and cold welds in the laser welding of the negative electrode tab is significantly reduced, and the melting depth and width also tend to be stable, which is a significant improvement compared with before, and the welding yield of the laser welding of the negative electrode tab cover is successfully improved.

[0026] As a further solution of the present invention: the first layer of spiral welding is welded to the inside of the cover plate pole with the highest welding power, and then the welding power gradually decreases with the increase of time.

[0027] As a further solution of the present invention: the total duration of the first layer of spiral welding is 2685ms-3000ms. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of power parameter setting for the first layer of spiral welding according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the laser welding trajectory of the first layer of the negative electrode tab cover plate in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the laser welding trajectory of the second layer of the negative electrode tab cover plate of an embodiment of the present invention;

[0031] Figure 4 This is a comparison diagram of actual detection of penetration depth and width before and after welding in an embodiment of the present invention; DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] Reference Figure 2 and Figure 3 A method for laser welding a negative electrode tab cover comprises the following steps:

[0035] S1, make the tab and the cover plate fit together, use a spiral laser welding track, and weld two layers;

[0036] It should be noted that the spiral welding trajectory provides a continuous and smooth motion path, which helps to maintain a stable welding speed; this stability improves welding efficiency because the laser welding head does not need to be started and stopped frequently, reducing non-productive time.

[0037] S2, the entire track of the first layer of spiral welding pole ear, and the first layer of spiral welding power adopts variable power welding;

[0038] It should be noted that the first layer of spiral welding adopts variable power welding, and different positions adopt different welding powers. The first layer adopts variable power welding. At the beginning of welding, the temperature is low and the welding power is the highest. As the heat affected zone of welding increases, the temperature is lowered and then maintained at this temperature for welding. The temperature is lowered in advance when it is about to end. The total length of the first layer of spiral welding track is 25cm, and the radius of the first layer of spiral welding line is 4cm.

[0039] S3, the second layer of spiral re-welding is about the first fifth of the track of the lug, and the second layer of spiral welding power adopts constant power welding.

[0040] It should be noted that the main purpose of the second layer of spiral re-welding is to modify the welding appearance. At the same time, when the first layer of spiral welding starts, the welding temperature is low and there is a risk that the front end will not melt in. Now re-welding the front part of the first layer of spiral welding can solve this abnormality. The second layer of spiral re-welding adopts constant power welding, and the welding power is lower than the power with the longest welding time in the first section. The main purpose is to modify the appearance.

[0041] Furthermore, the spiral wire density of the first layer spiral welding is different from that of the second layer spiral welding. Too high welding density may lead to the expansion of the heat affected zone. The heat affected zone refers to the area where the microstructure and performance changes occur due to high temperature during welding. An excessively large heat affected zone may cause material performance degradation, such as reduced hardness, increased brittleness, etc. The higher the welding density, the greater the welding time and material consumption, thereby reducing welding efficiency. Therefore, under the premise of ensuring welding quality, it is very important to select an appropriate welding density to balance efficiency and cost.

[0042] Furthermore, the pitch of the spiral wires of the first layer of spiral welding in the present application is 0.2 mm, and the pitch of the spiral wires of the second layer of spiral re-welding is 0.15 mm; the radius of the second layer of spiral welding wires is 4 cm, and the total length of the second layer of spiral welding tracks is 5 cm.

[0043] The specific operating principles of this application are as follows:

[0044] Reference Figure 1 The first layer of spiral welding is carried out with variable power, and the total welding time is 2685ms, in which the welding is divided into gradual in and gradual out;

[0045] Among them, when welding is performed with a 2000w base mode welding laser and the welding power is 70% of the base mode (i.e. 1400w), the welding time is the longest and plays a major welding role; the front-end welding power is relatively high, mainly because the welding temperature is relatively low at the beginning, and a higher power is required to weld into the pole lug cover plate pole. As time goes by, the heat affected zone becomes larger and larger, and the welding power gradually decreases; during the first layer of spiral welding, the welding power can reach up to 90% of the base mode (i.e. 1800w); when welding to 2545ms, the welding power gradually decreases until it is reduced to 0.

[0046] Furthermore, the second layer of spiral re-welding is welded at constant power, and the welding power is 50% of the base mold (i.e. 1000w), which modifies the welding appearance and blocks the risk of the front end welding not being melted in. The spacing of the spiral lines of the first layer of spiral welding is 0.2mm, and the spacing of the spiral lines of the second layer of spiral re-welding is 0.15mm. Since the welding density is too high, the heat affected zone may expand. The welding density used in the first layer of spiral welding is less than the welding density of the second layer of spiral re-welding, which can effectively solve the abnormal explosion point.

[0047] Through the above improvements, after the same laser changes from a constant single-layer welding power to the above welding, the proportion of laser welding explosion points and cold welds of the negative pole tab is significantly reduced, and its melting depth and width also tend to be stable (refer to Figure 4), which is significantly improved compared with the traditional welding method. The welding method of the present application successfully improves the welding yield of the negative electrode lug cover plate laser welding, wherein this embodiment 1 is the most preferred implementation method, and the following examples of the other two less preferred implementation methods are given for reference.

[0048] Example 2

[0049] The rest is the same as Example 1, except that: in Example 2, the total length of the first layer of spiral welding track is changed to 20 cm, the radius of the first layer of spiral welding line is 3.5 cm; the spacing of the first layer of spiral welding spiral lines is 0.4 mm;

[0050] The total length of the second layer spiral welding track is 5.5 cm, the radius of the second layer spiral welding line is 3.5 cm, and the spacing of the second layer spiral re-welding spiral lines is 0.25 mm; the total duration of the first layer spiral welding is 3000 ms.

[0051] During welding, a 2000W base mode welding laser is used for welding: the highest welding power of the first layer of spiral welding is 85% of the base mode, and the welding power with the longest welding time is 65% of the base mode; the welding power of the second layer of spiral welding is 45% of the base mode.

[0052] Example 3

[0053] The rest is the same as Example 1, except that: in Example 2, the total length of the first layer of spiral welding track is changed to 22.5 cm, the radius of the first layer of spiral welding line is 3.8 cm; the spacing of the first layer of spiral welding spiral lines is 0.3 mm;

[0054] The total length of the second layer spiral welding track is 5.3 cm, the radius of the second layer spiral welding line is 3.8 cm, and the spacing of the second layer spiral re-welding spiral lines is 0.2 mm; the total duration of the first layer spiral welding is 2842 ms.

[0055] During welding, a 2000W base mode welding laser is used for welding: the highest welding power of the first layer of spiral welding is 88% of the base mode, and the welding power with the longest welding time is 68% of the base mode; the welding power of the second layer of spiral welding is 48% of the base mode.

[0056] Example 4

[0057] Unlike Example 1, Example 4 adopts a traditional welding method, that is, a constant distance spiral wire is used for welding, and single-layer welding, wherein in Example 4, the spacing between two adjacent spiral welding spiral wires is 0.2 mm, the welding power adopts constant power welding, which is 70%-73% of the base mold, and the welding size is determined according to the specific design of the overcurrent capacity of the battery cell. The total length of the spiral welding track is 25 cm, and the radius of the spiral welding wire is 4 cm. Then, the depth of penetration and the width of the weld after welding in Example 4 are compared with the depth of penetration and the width of the weld after welding in Example 1, and the reference is made to the embodiment of the invention. Figure 4 The traditional constant single-layer welding has unstable penetration depth and width after welding, with an average penetration depth of 0.417 mm and an average width of 4.41 mm. However, after adopting the double-layer welding method of the present application, it can be clearly seen that the penetration depths are relatively uniform, with an average penetration depth of 0.428 mm and an average width of 4.3 mm.

[0058] Note: The standard for penetration depth is 0.15mm≤penetration depth≤0.7mm, and the standard for penetration width is ≥3.8mm.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode tab cover plate laser welding method, characterized in that: The steps include: Make the tab and the cover fit together, use a spiral welding track, and weld two layers; The first layer of spiral welding is for the entire track of the pole ear, and the first layer of spiral welding power adopts variable power welding; The first fifth of the second layer of spiral welding of the lug is welded, and the second layer of spiral welding power adopts constant power welding; The spiral line density of the first layer of spiral welding is different from that of the second layer of spiral welding.

2. A negative electrode tab cover laser welding method according to claim 1, characterized in that: The variable power of the first layer spiral welding is divided into three stages, the welding power in the first stage is the highest, and the welding power in the second and third stages begins to decrease as the welding temperature increases.

3. A negative electrode tab cover laser welding method according to claim 2, characterized in that: The welding power of the second layer of spiral re-welding is lower than the power of the first layer of spiral welding with the longest welding time.

4. The negative electrode tab cover laser welding method according to claim 1, characterized in that: The density of the first layer of spiral welding lines is less than the density of the second layer of spiral welding lines.

5. A negative electrode tab cover laser welding method according to claim 4, characterized in that: The spacing between two adjacent spirals in the first layer of spiral welding wires is 0.2 mm-0.4 mm, and the spacing between two adjacent spirals in the second layer of spiral wires is 0.15 mm-0.25 mm.

6. The negative electrode tab cover laser welding method according to claim 1, characterized in that: The total length of the first layer spiral welding track is 20cm-25cm, and the radius of the first layer spiral welding line is 3.5cm-4cm.

7. The negative electrode tab cover laser welding method according to claim 1, characterized in that: The radius of the second layer spiral welding line is 4cm-4.5cm, and the total length of the second layer spiral welding track is 5cm-5.5cm.

8. The negative electrode tab cover laser welding method according to claim 1, characterized in that: Take the base mode welding laser as an example: The highest welding power of the first layer of spiral welding is 85%-90% of the base mold, and the welding power with the longest welding time is 65%-70% of the base mold; The welding power of the second layer of spiral welding is 45%-50% of that of the base mold.

9. The negative electrode tab cover laser welding method according to claim 7, characterized in that: The first layer of spiral welding has the highest welding power when welded into the cover plate pole, and then the welding power gradually decreases as time goes by.

10. The negative electrode tab cover laser welding method according to claim 8, characterized in that: The total duration of the first layer spiral welding is 2685ms-3000ms.

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