A welding method for busbars and flexible connections

Abstract

The present application belongs to the technical field of welding, and particularly relates to a welding method for busbars and flexible connections. The method comprises the following steps: respectively performing surface cleaning on the components of the busbar to be welded and the flexible connection; assembling the first component and the second component of the busbar; fixing the assembled busbar on a clamp and setting welding parameters; performing laser welding on the weld of the busbar by using a composite laser; performing post-processing on the welded busbar; assembling the welded busbar and the flexible connection; fixing the assembled busbar and flexible connection on a clamp and setting welding parameters; and performing laser welding on the weld of the busbar and the flexible connection by using a composite laser. The welding method of the present application does not use filler metal, the joint resistance is significantly reduced, the electrical conductivity is greatly improved, the joint strength is much higher than that of brazed joints, and the mechanical performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and specifically relates to a welding method for busbars and flexible connections. Background Technology

[0002] Currently, busbars and flexible connectors are key components for the efficient transmission and distribution of electrical energy in electrical systems, and reliably connecting busbars and flexible connectors is crucial for the stable operation of electrical equipment. Copper is the most mainstream material for busbars and flexible connectors, and the connection between busbars and non-rigid flexible connectors (such as copper foil laminations and braided wires) mainly relies on traditional vacuum brazing technology.

[0003] Although brazing is widely used, its inherent technical defects are becoming increasingly apparent in actual production and operation, mainly in the following aspects: (1) The connector has high resistivity and large power loss. Brazing relies on the melting of a filler metal with a melting point lower than the base metal (such as silver-based filler metal) to fill the gap and achieve a connection. The conductivity of the filler metal itself is typically much lower than that of copper or aluminum busbars and flexible connecting materials. This results in high contact resistance at the weld joint, which generates significant Joule heating under high current conditions, causing continuous energy loss and potentially leading to localized overheating, affecting system energy efficiency and safety. Studies have shown that defects such as non-sealing of the brazed joint (e.g., voids, discontinuities, and incomplete penetration) are common in brazed joints, further deteriorating the joint's conductivity.

[0004] (2) Large heat-affected zone, resulting in deterioration of mechanical and electrical properties.

[0005] The brazing process requires heating the entire workpiece, either as a whole or over a large area, to reach the melting temperature of the brazing filler metal. This heating method generates a large heat-affected zone, which may cause annealing of the flexible connection, reducing its mechanical strength and increasing its toughness, making it prone to fatigue fracture under long-term vibration stress. Simultaneously, excessive heat may also damage the insulation layer on the surface of the busbar or flexible connection, and even alter the microstructure of the base material, adversely affecting its electrical properties.

[0006] (3) Insufficient connection strength and poor fatigue resistance

[0007] The strength of brazed joints primarily depends on the limited metallurgical bonding force between the filler metal and the base metal, as well as the small brazing area. Its bonding strength is typically lower than that of the base metal itself. Soft brazed joints have relatively low strength, generally not exceeding 70 MPa. Under harsh operating conditions involving mechanical vibration and thermal cycling (such as in new energy vehicles, electric locomotives, and frequency converters), these joints are prone to developing microcracks due to stress concentration, which gradually propagate and eventually lead to loosening or even failure, posing a risk of power outage. Furthermore, common defects in brazed joints, such as brittle phases, porosity, and cracks, can severely weaken the joint strength.

[0008] (4) The stability and consistency of the process are difficult to control.

[0009] The quality of brazing heavily depends on the operator's skill level, the selection and uniformity of the flux, and the precise control of heating temperature and time. Copper has a high thermal conductivity, resulting in rapid heat loss during heating, which easily leads to problems such as uneven temperature distribution, uneven melting of the brazing filler metal, and filler metal deviation. Defects such as incomplete filler metal filling, cold solder joints, porosity, and slag inclusions are prone to occur. These defects are difficult to detect completely during finished product inspection, posing a threat to the long-term reliability of the product and affecting the consistency between batches.

[0010] (5) There are environmental and aesthetic issues.

[0011] The flux used in brazing may generate harmful fumes, requiring corresponding ventilation and dust removal facilities, which increases environmental pressure. Furthermore, residual flux after welding needs to be cleaned, otherwise it can cause corrosion; welded joints are usually rough and irregular, affecting the product's aesthetics.

[0012] To address these issues, laser welding technology has gained increasing attention in recent years. However, copper has extremely low absorption of near-infrared fiber lasers (wavelength 1070nm), only about 4%, requiring extremely high laser power for welding. High power input easily leads to welding defects such as porosity. Copper's high thermal conductivity also makes it difficult to concentrate laser energy, resulting in low energy coupling efficiency. Therefore, simple infrared laser welding cannot meet the high-quality connection requirements of copper busbars and flexible connectors.

[0013] In recent years, the emergence of high-power blue lasers has offered new possibilities for solving the aforementioned problems. Research shows that copper absorbs over 60% of blue light at a wavelength of 455nm, far exceeding its absorption rate of approximately 5% for near-infrared light. A combined blue and infrared laser welding method can utilize copper's high absorption of blue light to achieve efficient preheating and shallow melting, while combining this with the deep-penetrating capability of infrared lasers to achieve high-quality welding.

[0014] Therefore, there is an urgent need to design a new welding method that can overcome the above-mentioned defects in brazing technology. Summary of the Invention

[0015] To address the problems existing in the prior art, the present invention provides a welding method for busbars and flexible connections, and specifically discloses the following technical solutions: A welding method for busbars and flexible connections includes the following steps: S1. Clean the workpiece: Clean the surface of the components and flexible connections of the busbar to be welded to remove oil and impurities. S2. Busbar assembly: Assemble the first and second components of the busbar. S3. Busbar welding preparation: Fix the assembled busbar on the fixture, set the deflection angle between the welding head and the vertical direction to ≥5°, and set the welding parameters; S4. Busbar welding: Laser welding of busbar weld seams is performed using a composite laser. S5. Weld treatment: Post-treatment of the busbar weld after welding; S6. Flexible connection assembly: Assemble the welded busbar with the flexible connection and fix them relatively with tooling to prevent displacement during the welding process. S7. Preparation for flexible connection welding: Fix the assembled busbar and flexible connection combination workpiece on the fixture, set the deflection angle between the welding head and the workpiece in the vertical direction to 40°~60°, and offset the actual welding point outward by a predetermined distance relative to the contact position of the busbar and the flexible connection, and set the welding parameters. S8. Flexible connection welding: Laser welding is performed on the weld seam between the busbar and the flexible connection using a composite laser.

[0016] Furthermore, in step S1, the components and flexible connections of the busbar are first cleaned with a degreasing agent, and then their surfaces are cleaned with anhydrous ethanol. The degreasing agent is pure acetone.

[0017] Furthermore, the first component of the busbar is a copper tube, and the second component of the busbar is a copper plug. In step S2, the copper plug is tightly fitted into the inside of one end of the copper tube, and then the two are fixed relative to each other using tooling.

[0018] Furthermore, in step S3, the deflection angle between the welding head and the vertical direction is 5°~8°.

[0019] Furthermore, in step S4, the busbar weld is located in the overlapping area of ​​the copper pipe and the copper plug, and the copper pipe is subjected to deep penetration welding to fix it to the copper plug.

[0020] Furthermore, in step S4, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 4500~5200W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.4~0.45mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 30~40mm / s, and defocusing amount 0~1mm.

[0021] Furthermore, in step S6, the flexible connector is a copper foil laminate or a braided wire, and the assembly method of the busbar and the flexible connector is to insert the copper tube into the through hole on the connecting plate at the end of the flexible connector.

[0022] Furthermore, in step S7, the actual welding point is offset by 0.5 mm from the outside of the contact position between the busbar and the flexible connection.

[0023] Furthermore, in step S8, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 3600~4500W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.5~0.55mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 35~40mm / s, and defocusing amount 0~1mm.

[0024] Furthermore, in step S5, the post-processing involves grinding the weld seam to make the busbar surface smooth.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. No solder filler, significantly reduced joint resistance, and greatly improved conductivity. This invention utilizes a red-blue composite laser to directly weld copper busbars to flexible connectors, eliminating the need for filler materials such as silver-based brazing filler metal and avoiding additional contact resistance introduced by the low conductivity of the brazing filler metal. The weld is a direct fusion of the base materials, resulting in a joint conductivity more closely resembling that of the base material itself. The conductivity of the weld area in the red-blue laser composite welded copper joint can reach 85.23%~90.73% of that of the base material. Compared to traditional brazed joints, this invention significantly reduces joint resistance and substantially decreases Joule heat loss under high current conditions, effectively improving the energy efficiency and safety of the electrical system.

[0026] 2. The joint strength is much higher than that of brazed joints, and the mechanical properties are excellent.

[0027] This invention achieves direct metallurgical bonding between base materials through laser deep penetration welding, resulting in a bond strength far exceeding that of brazed joints that rely on filler metal. The tensile strength of red-blue composite laser-welded copper joints can reach 254.42 MPa, significantly better than the traditional soft brazing joint's strength level of no more than 70 MPa. This high-strength joint effectively resists mechanical vibration and thermal cyclic stress, significantly reducing the risk of fatigue fracture, making it particularly suitable for demanding operating conditions such as those in new energy vehicles and electric locomotives.

[0028] 3. Small heat-affected zone and less heat accumulation greatly improve electrical and mechanical performance.

[0029] This invention utilizes the high absorption rate (>60%) of copper for blue laser light, achieving efficient energy coupling and rapid melting even at relatively low laser power. Blue light can effectively preheat and achieve shallow melting at low power, resulting in a minimal heat-affected zone. Compared to the overall heating method of brazing, the laser welding of this invention offers precise and controllable heat input, less heat accumulation, and avoids soft-joint annealing and microstructural degradation of the base material, effectively protecting the mechanical and electrical properties of the workpiece.

[0030] 4. Laser welding offers precise control, facilitates automated production, and ensures consistent product quality.

[0031] This invention employs a composite laser welding system, allowing for precise setting and repeated execution of welding parameters (power, oscillation radius, oscillation frequency, welding speed, defocusing amount, etc.). The laser welding process is unaffected by fluctuations in operator skill levels, exhibiting high process stability and excellent batch-to-batch consistency. Compared to brazing, which is heavily reliant on operator skill and process conditions, this invention is more suitable for industrial mass production, effectively ensuring product quality stability and reliability.

[0032] 5. No welding pollution, green and environmentally friendly.

[0033] This invention uses a laser as the heat source, eliminating the need for auxiliary materials such as flux. The welding process produces no harmful fumes, and there are no post-weld residues requiring cleaning, thus avoiding the corrosion problems and environmental pressures caused by flux in brazing processes. Furthermore, the weld formation is aesthetically pleasing and has a smooth surface, meeting appearance requirements without the need for complex post-weld treatment.

[0034] 6. Significantly reduces production costs

[0035] This invention eliminates the need for expensive filler materials such as silver-based brazing filler, saving material costs; it offers fast welding speed (30~40mm / s) and high efficiency, shortening the production cycle per unit; it provides good process stability, reducing scrap rate and rework costs; and it eliminates the need for auxiliary processes such as ventilation, dust removal, and post-weld cleaning, reducing equipment and manpower investment. Overall, this invention can significantly reduce the comprehensive production cost of busbar and flexible connection manufacturing. Attached Figure Description

[0036] Figure 1 This is a schematic diagram showing the positional relationship between the weld joint and the busbar during busbar welding.

[0037] Figure 2 This diagram illustrates the positional relationship between the busbar, the flexible connector, and the weld joint during flexible connector welding.

[0038] Figure 3 This is a schematic diagram of the product structure after the busbar and flexible connector have been welded together.

[0039] Figure 4 This is a front view of the product structure after the busbar and flexible connector have been welded together.

[0040] Figure 5 for Figure 4 Sectional view at point AA.

[0041] Figure 6 This is a disassembly diagram of copper pipes, copper plugs, and flexible connectors.

[0042] Among them: 1-copper pipe, 2-copper plug, 3-flexible connector, 4-welded head. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] refer to Figures 1-6 A welding method for busbars and flexible connections includes the following steps: S1. Clean the workpiece: Clean the surface of the components of the busbar to be welded and the flexible connection 3 to remove surface oil and impurities; S2. Busbar assembly: Assemble the first and second components of the busbar. S3. Busbar welding preparation: Fix the assembled busbar on the fixture, set the deflection angle between the welding head and the vertical direction to ≥5°, and set the welding parameters; S4. Busbar welding: Laser welding of busbar weld seams is performed using a composite laser. S5. Weld treatment: Post-treatment of the busbar weld after welding; S6. Flexible connection assembly: Assemble the welded busbar with flexible connection 3, and fix the two relatively with tooling to prevent displacement during the welding process. S7. Preparation for flexible connection welding: Fix the assembled busbar and flexible connection combination workpiece on the fixture, set the deflection angle between the welding head 4 and the vertical direction of the workpiece to 40°~60°, and shift the actual welding point outward by a predetermined distance relative to the contact position of the busbar and the flexible connection, and set the welding parameters. S8. Flexible connection welding: The weld between the busbar and flexible connection 3 is laser welded using a composite laser.

[0046] In this embodiment, in step S1, the components of the busbar and the flexible connection 3 are first cleaned with a degreasing agent, and then their surfaces are cleaned with anhydrous ethanol. The degreasing agent is pure acetone.

[0047] In this embodiment, the first component of the busbar is a copper pipe 1, and the second component of the busbar is a copper plug 2. In step S2, the copper plug 2 is tightly fitted into one end of the copper pipe 1, and then the two are fixed relative to each other using a tool. The tool not only prevents the copper plug 2 from shaking before welding, but also resists welding stress during the welding process to ensure the concentricity of the product.

[0048] In this embodiment, in step S3, the deflection angle between the welding head 4 and the vertical direction is 5°~8° to prevent the copper from reflecting laser light and damaging the welding equipment.

[0049] In this embodiment, in step S4, the busbar weld is located in the overlapping area of ​​the copper pipe 1 and the copper plug 2, and the copper pipe 1 is subjected to deep penetration welding to fix it to the copper plug 2.

[0050] In this embodiment, in step S4, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 4500~5200W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.4~0.45mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 30~40mm / s, and defocusing amount 0~1mm.

[0051] In this embodiment, in step S6, the flexible connection 3 is a copper foil laminate or a braided wire, and the assembly method of the busbar and the flexible connection 3 is to insert the copper tube 1 into the through hole on the connecting plate at the end of the flexible connection 3.

[0052] In this embodiment, in step S7, the actual welding point is offset by 0.5 mm from the outside of the contact position between the busbar and the flexible connection.

[0053] In this embodiment, in step S8, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 3600~4500W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.5~0.55mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 35~40mm / s, and defocusing amount 0~1mm.

[0054] In this embodiment, in step S5, the post-processing involves grinding the weld seam to make the busbar surface smooth.

[0055] In this embodiment, the laser welding equipment uses an infrared laser with a total power of ≤6000W, a blue laser of 1000W, and a composite welding head with infrared oscillation function. During welding, the tilt angle between the welding head and the vertical plane is ≥5°, the welding speed is 40~60mm / s, the defocusing amount of the near-infrared laser is 1~3mm, the oscillation radius is 0.4mm~0.6mm, and the blue light spot is 0.5~1mm. After welding, the appearance and penetration depth need to be inspected.

[0056] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A welding method for busbars and flexible connections, characterized in that, Includes the following steps: S1. Clean the workpiece: Clean the surface of the components and flexible connections of the busbar to be welded to remove oil and impurities. S2. Busbar assembly: Assemble the first and second components of the busbar. S3. Busbar welding preparation: Fix the assembled busbar on the fixture, set the deflection angle between the welding head and the vertical direction to ≥5°, and set the welding parameters; S4. Busbar welding: Laser welding of busbar weld seams is performed using a composite laser. S5. Weld treatment: Post-treatment of the busbar weld after welding; S6. Flexible connection assembly: Assemble the welded busbar with the flexible connection and fix them relatively with tooling to prevent displacement during the welding process. S7. Preparation for flexible connection welding: Fix the assembled busbar and flexible connection combination workpiece on the fixture, set the deflection angle between the welding head and the workpiece in the vertical direction to 40°~60°, and offset the actual welding point outward by a predetermined distance relative to the contact position of the busbar and the flexible connection, and set the welding parameters. S8. Flexible connection welding: Laser welding is performed on the weld seam between the busbar and the flexible connection using a composite laser.

2. The welding method for busbars and flexible connections according to claim 1, characterized in that, In step S1, the components and flexible connections of the busbar are first cleaned with a degreasing agent, and then their surfaces are cleaned with anhydrous ethanol. The degreasing agent is pure acetone.

3. The welding method for busbars and flexible connections according to claim 1, characterized in that, The first component of the busbar is a copper tube, and the second component of the busbar is a copper plug. In step S2, the copper plug is tightly fitted into one end of the copper tube, and then the two are fixed together using tooling.

4. The welding method for busbars and flexible connections according to claim 1, characterized in that, In step S3, the deflection angle between the welding head and the vertical direction is 5°~8°.

5. A welding method for busbars and flexible connections according to claim 3, characterized in that, In step S4, the busbar weld is located in the overlapping area of ​​the copper pipe and the copper plug. The copper pipe is subjected to deep penetration welding to fix it to the copper plug.

6. The welding method for busbars and flexible connections according to claim 1, characterized in that, In step S4, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 4500~5200W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.4~0.45mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 30~40mm / s, and defocusing amount 0~1mm.

7. The welding method for busbars and flexible connections according to claim 1, characterized in that, In step S6, the flexible connector is a copper foil laminate or a braided wire, and the assembly method of the busbar and the flexible connector is to insert the copper tube into the through hole on the connecting plate at the end of the flexible connector.

8. A welding method for busbars and flexible connections according to claim 1, characterized in that, In step S7, the actual welding point is offset by 0.5 mm from the outside of the contact position between the busbar and the flexible connection.

9. A welding method for busbars and flexible connections according to claim 1, characterized in that, In step S8, the composite laser includes an infrared laser and a blue laser, wherein the infrared laser power is 3600~4500W and the blue laser power is 800~900W; the welding process parameters are: oscillation radius 0.5~0.55mm, oscillation frequency 80~100Hz, spot diameter 1~1.5mm, welding speed 35~40mm / s, and defocusing amount 0~1mm.

10. A welding method for busbars and flexible connections according to claim 1, characterized in that, In step S5, the post-processing involves grinding the weld seam to make the busbar surface smooth.

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