Transformer terminal welding process

Abstract

The invention discloses a transformer terminal welding process, which relates to the technical field of transformer terminals, and comprises the following steps: placing a stainless steel band on the upper surface of an aluminum foil, placing a copper-aluminum composite plate on the lower surface of the aluminum foil, and enabling the aluminum surface of the copper-aluminum composite plate to be in contact with the aluminum foil, then the stainless steel band, the aluminum foil and the copper-aluminum composite plate are welded together through spot welding; the copper terminal strip is attached to the copper face of the copper-aluminum composite board, and the surface of the copper terminal strip is heated through an oxygen-propane welding torch; adding a tin wire in a gap between the edge of the copper terminal strip and the copper-aluminum composite plate, and welding through an oxygen-propane welding torch; if the edge of the copper terminal strip is a bent edge, the edge does not need to be welded, high-strength and high-reliability welding of copper and aluminum dissimilar materials is achieved, the performance of the transformer terminal is remarkably improved, the service life of the transformer terminal is remarkably prolonged, and the transformer terminal is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of transformer terminal technology, and more specifically to a transformer terminal welding process. Background Technology

[0002] A transformer is a device that uses the principle of electromagnetic induction to change voltage, current, and waveform. Transformers play a crucial role in power electronic systems. They mainly consist of an iron core, coils, and corresponding fasteners. During coil fabrication, the quality of terminal soldering can significantly impact product performance.

[0003] In existing technologies, terminals are mostly welded using copper terminal blocks with copper foil or aluminum terminals with aluminum foil. However, some customers specifically require copper for the wiring connections. From a cost perspective, copper foil is more expensive than aluminum foil, and aluminum foil can also meet the customer's performance requirements. Therefore, the copper terminal block with aluminum foil is used for welding. However, since the melting point of copper is much higher than that of aluminum, aluminum melts first during direct welding, but copper has not reached its melting point. This results in a loose weld, which can easily lead to problems such as incomplete welding, cracks, and insufficient strength, thereby affecting the electrical performance and service life of the transformer. Summary of the Invention

[0004] The present invention aims to solve the problem of poor welding strength between copper terminal blocks and aluminum foil in transformer terminals in the prior art.

[0005] To address the above problems, this invention provides a transformer terminal welding process, comprising the following steps: S1. Place the stainless steel strip on the upper surface of the aluminum foil, place the copper-aluminum composite plate on the lower surface of the aluminum foil and make the aluminum side of the copper-aluminum composite plate contact the aluminum foil, and then weld the stainless steel strip, aluminum foil and copper-aluminum composite plate together by spot welding. S2. Attach the copper terminal block to the copper surface of the copper-aluminum composite plate and heat the surface of the copper terminal block using an oxygen-propane welding torch; S3. Add tin wire to the gap between the edge of the copper terminal block and the copper-aluminum composite plate and weld it with an oxygen-propane welding torch; if the edge of the copper terminal block is a bent edge, then the edge does not need to be welded.

[0006] The transformer terminal welding process provided by this invention has, but is not limited to, the following beneficial effects compared to existing technologies: In the transformer terminal welding process of this invention, stainless steel strip, aluminum foil, and copper-aluminum composite plate are first welded together by spot welding. The aluminum surface of the copper-aluminum composite plate contacts the aluminum foil, achieving fusion between the aluminum materials and avoiding insufficient welding strength caused by unmelted copper. The stainless steel strip serves as a reinforcing layer, improving the mechanical strength and stability of the spot-welded area. Subsequently, heating with an oxygen-propane welding torch promotes better adhesion of subsequent solder. Solder wire is then added to the edges of the copper terminal block and welded to the aluminum foil, thereby welding the copper terminal block to the copper surface of the copper-aluminum composite plate, further enhancing the overall structural sealing and mechanical integrity. This process achieves high-strength, high-reliability welding of dissimilar copper and aluminum materials, significantly improving the performance and lifespan of transformer terminals, and is suitable for industrial production.

[0007] Furthermore, in S1, welding is performed by an electric welding machine, and the interlocking gap between the upper and lower welding heads of the electric welding machine conforms to: C=(0.85-0.9)H; where C is the interlocking gap between the upper and lower welding heads, and H is the superimposed thickness of the stainless steel strip, aluminum / copper foil, and copper-aluminum composite plate.

[0008] Specifically, this gap range ensures uniform distribution of welding pressure, avoiding material crushing due to excessive pressure or incomplete welding due to insufficient pressure; moreover, an appropriate gap facilitates the concentration of current through the welding area, improving spot welding efficiency and quality consistency.

[0009] It is important to note that before using the spot welding machine, you need to check whether the circuit and water circuit of the spot welding machine are normal, confirm that there is no water leakage at the welding head, and check whether the upper and lower welding heads are oxidized. If there is oxidation, the oxide layer needs to be ground off. Before welding, test the engagement of the upper and lower welding heads to confirm that the engagement gap between the upper and lower welding heads meets the above requirements.

[0010] Furthermore, the diameter of the upper welding head is 5-8mm.

[0011] Specifically, the upper welding head with a diameter of 5-8mm provides a suitable welding area, ensuring that the weld spot is of uniform size, neither too small to cause insufficient strength nor too large to cause an expansion of the heat-affected zone; this diameter range is conducive to concentrated current transmission, reducing energy loss and improving spot welding efficiency and weld spot quality.

[0012] Furthermore, in S1, the spot welding operation method is as follows: the upper welding head is placed above the stainless steel strip, and the lower welding head is placed below the copper-aluminum composite plate. The upper and lower welding heads are first pressed together before being energized for spot welding. After the power is turned off, the pressure is released and the welding points are separated to form a weld.

[0013] Specifically, firstly, pressure is applied to ensure close contact of the materials, and when electricity is applied, the current passes through evenly to form a strong weld point; after power is cut off, pressure is released to prevent the weld point from cracking or the materials from sticking together, which can improve the welding quality.

[0014] Furthermore, the spot welding time is 1 second; the indentation area is 19 mm²; and the welding current is positively correlated with the aluminum foil thickness: when the aluminum foil thickness is 0.6-0.9 mm, the welding current is 25-30 A; when the aluminum foil thickness is 0.9-1.1 mm, the welding current is 30-35 A; when the aluminum foil thickness is 1.1-1.4 mm, the welding current is 35-40 A; and when the aluminum foil thickness is 1.4-1.7 mm, the welding current is 40-50 A.

[0015] Specifically, the 1-second welding time ensures controllable heat input, avoiding overheating or lack of fusion; the range of weld diameter and crater area ensures sufficient mechanical strength and conductive area; the welding current increases with the thickness of the aluminum foil, ensuring that materials of different thicknesses can obtain appropriate penetration depth and weld quality, avoiding welding defects caused by insufficient or excessive current.

[0016] Furthermore, after all spot welding is completed, check whether all weld points on the copper-aluminum composite plate meet the requirements of being regularly round, having a diameter of ≥5mm, and having no chipping at the spot weld. If not, the weld point is unqualified and needs to be re-spot welded until it meets the requirements.

[0017] Specifically, visual and dimensional inspections ensure that each solder joint meets design requirements, eliminating potential defects; non-conforming solder joints are immediately reprocessed, preventing defect accumulation and subsequent process failures, thus improving product pass rate; this inspection process is easy to implement, suitable for quality control systems, and enhances process traceability.

[0018] Furthermore, the solder joints are arranged in rows and columns, with a center-to-center distance of 15mm between two adjacent rows and a center-to-center distance of 20mm between two adjacent columns.

[0019] Specifically, the uniform distribution of weld points reduces local stress concentration and improves the fatigue strength and overall stability of the welded joint.

[0020] Furthermore, the thickness of the stainless steel strip is 0.5 mm.

[0021] Specifically, a 0.5mm thick stainless steel strip provides sufficient rigidity and support to prevent deformation of aluminum foil or composite sheets during spot welding; moreover, this thickness balances thermal conductivity and mechanical strength, avoiding overheating or energy loss during welding.

[0022] Furthermore, in S2, the method for heating the surface of the copper terminal block with the oxygen-propane welding torch is as follows: attach and fix the copper surface of the copper-aluminum composite plate to the copper terminal block, aim the nozzle of the oxygen-propane welding torch at the upper center position of the copper terminal block, adjust the flame of the propane welding torch, and use the inner flame of the neutral flame to heat the copper terminal block. During the heating process, move the oxygen-propane welding torch at a constant speed along the length of the base material to be welded, and the heating time is 5-10 seconds.

[0023] Specifically, the neutral flame has a stable inner flame temperature and low oxidizing properties, preventing copper from oxidizing or overheating; uniform movement ensures even heating; and the heating time of 5-10 seconds, based on the material's heat capacity design, ensures that the copper terminal block reaches the appropriate welding temperature, thus improving welding quality.

[0024] Further, in S3, the welding method is as follows: after heating, the solder wire is fed from the gap between the edge of the copper terminal block to be welded and the copper-aluminum composite plate, and the solder wire is heated using an oxygen-propane welding torch. The feeding speed is consistent with the moving speed of the oxygen-propane welding torch. The molten solder produced by the melting of the solder wire flows into the gap between the copper terminal block and the copper-aluminum composite plate to complete the welding. Finally, the solder wire is removed and the oxygen-propane welding torch is removed.

[0025] Specifically, the synchronous feeding of wire and oxygen-welding torch ensures that the molten solder continuously and evenly fills the gaps, avoiding incomplete penetration or solder nodules; the operation sequence of removing wire first and then moving torch reduces porosity and cold shuts, improving the density and appearance quality of the weld; this welding step ensures the sealing and mechanical connection between the terminal block and the edge of the copper-aluminum composite plate, enhancing the overall structural reliability. Attached Figure Description

[0026] The invention will now be further described with reference to the accompanying drawings.

[0027] Figure 1 This is a schematic diagram of spot welding in step S1 of the transformer terminal welding process in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the oxy-propane welding in step S2 of the transformer terminal welding process in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the neutral flame temperature distribution during oxy-propane welding in step S2 of the transformer terminal welding process in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of step S3 in the transformer terminal welding process of Embodiment 1 of the present invention. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0029] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0030] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0033] It should be noted that in the following embodiments and comparative examples, the welding machine was inspected before use. The inspection method was as follows: check whether the circuit and water circuit of the spot welding machine were normal, confirm that there was no water leakage at the welding head, and check whether the upper and lower welding heads were oxidized. If there was oxidation, the oxide layer needed to be polished clean. Before welding, the upper and lower welding heads were tested to confirm that the interlocking gap between the upper and lower welding heads was C, where C=(0.85-0.9)H; where C is the interlocking gap between the upper and lower welding heads, and H is the superimposed thickness of the stainless steel strip, aluminum foil and copper-aluminum composite plate.

[0034] It should be noted that in the following examples and comparative examples, the propane welding torch must be tested for its injection performance and airtightness before ignition, and ignition can only proceed if the test is passed.

[0035] Example 1

[0036] This embodiment discloses a transformer terminal welding process, including the following steps: S1. A piece with a thickness of 0.5mm and a size of 60mm... A 310mm stainless steel strip is placed in two layers of 0.8mm thick, 60mm wide strips. The top surface of a 315mm thick aluminum foil is coated with a 0.5mm thick foil of 70mm size. A 310mm copper-aluminum composite plate (T2 / 1060A) is placed on the lower surface of the aluminum foil, with the aluminum side of the plate in contact with the foil. The gap between the upper and lower welding heads of the welding machine is adjusted to 2.288mm, and the diameter of the upper welding head is 6mm. The upper welding head is positioned above the stainless steel strip, and the lower welding head is positioned below the copper-aluminum composite plate. The upper and lower welding heads are first pressed together before energizing for spot welding. The pressure is released and the welding points are separated after the power is turned off, forming a weld point. The welding time is 1 second, and the indentation area is 19mm². 2 The welding current is 45A; thus, the stainless steel strip, aluminum foil, and copper-aluminum composite plate are welded together; the resulting weld points are distributed in rows and columns, with a center-to-center distance of 15mm between adjacent rows and 20mm between adjacent columns; after all spot welding is completed, check whether all weld points on the copper-aluminum composite plate meet the requirements of being regularly round, having a diameter of ≥5mm, and having no chipping at the spot weld. If not, the weld point is considered unqualified and must be re-spot welded until the requirements are met. S2. Attach the copper surface of the copper-aluminum composite plate to the copper terminal block and fix it with pliers. Point the nozzle of the propane welding torch at the middle position above the copper terminal block, turn on the propane adjustment handwheel, ignite the propane and immediately turn on the oxygen adjustment handwheel. Use the inner flame of the neutral flame to heat the copper terminal block. During the heating process, move the welding torch at a constant speed along the length of the base material to be welded. The heating time is 8 seconds. S3. After heating, feed the solder wire through the gap between the edge of the copper terminal block to be welded and the copper-aluminum composite plate, and heat the solder wire with a propane torch. The feeding speed is the same as the moving speed of the propane torch. The molten solder produced by the melting of the solder wire flows into the interlocking gap between the copper terminal block and the aluminum foil to complete the welding. Finally, remove the solder wire and remove the propane torch to obtain the transformer terminal.

[0037] Example 2

[0038] Compared with Example 1, the only difference is that in step 1: the meshing gap between the upper and lower welding heads of the welding machine is adjusted to 2.21mm; other steps and conditions remain the same, and finally the transformer terminal is obtained.

[0039] Example 3

[0040] Compared with Example 1, the only difference is that in step 1: the meshing gap between the upper and lower welding heads of the welding machine is adjusted to 2.34mm; other steps and conditions remain the same, and finally the transformer terminal is obtained.

[0041] Example 4

[0042] Compared with Example 1, the only difference is that in step 1, the welding current is 40A; the other steps and conditions remain the same, and the transformer terminal is finally obtained.

[0043] Example 5

[0044] Compared with Example 1, the only difference is that in step 1, the welding current is 50A; the other steps and conditions remain the same, and the transformer terminals are finally obtained.

[0045] Comparative Example 1

[0046] This comparative example discloses a transformer terminal welding process, including the following steps: S1. Using the same copper terminal block and aluminum foil as in Example 1, align the copper terminal block with the edge of the aluminum foil, press it down with a pressure plate, and then heat it with an oxygen-propane welding torch. Point the nozzle of the propane welding torch at the middle position above the copper terminal block, turn on the propane adjustment handwheel, ignite the propane, and immediately turn on the oxygen adjustment handwheel. Use the inner flame of the neutral flame to heat the copper terminal block. During the heating process, move the welding torch at a constant speed along the length of the base material to be welded. The heating time is 8 seconds. S2. After heating, feed the solder wire from the edge of the copper terminal block to be welded and heat the solder wire with a propane torch. The feeding speed is the same as the moving speed of the propane torch. The molten solder produced by the melting of the solder wire flows into the interlocking gap between the copper terminal block and the aluminum foil to complete the welding. Finally, remove the solder wire and then remove the propane torch to obtain the transformer terminal.

[0047] Comparative Example 2

[0048] Compared with Example 1, the only difference is that the heating operation of the copper terminal block in step 2 is omitted, while the other steps and conditions remain the same, and the transformer terminals are finally obtained.

[0049] The transformer terminals prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to strength performance tests. The peel strength between the copper terminal block and the aluminum foil, the solder joint qualification rate, and the solder joint penetration were tested. The test methods were as follows: Peel strength: Refer to the peel strength test requirements in GB / T2790-1995 and the power industry standard DL / T1315-2013 "Technical Conditions for Connecting Terminals for Transformers"; Solder joint pass rate: Inspect each solder joint on the copper-aluminum composite plate and record the shape (whether it is a regular circle), diameter (measure the diameter of the largest outer circle of the solder joint), and whether there are any chips / cracks / pores. Solder joints with a diameter ≥ 5mm, regular shape without obvious distortion, and no visible chips / cracks / pores are considered qualified; otherwise, they are considered unqualified.

[0050] Solder penetration depth: 5% of the solder joints of each group of transformer terminals are randomly selected and the cross-section of the solder joints is observed using a metallographic microscope (50x magnification); the penetration depth is ≥0.3mm (not less than 40% of the aluminum foil thickness) to ensure complete fusion between aluminum materials.

[0051] The test results are listed in Table 1, as follows: Table 1

[0052] Analysis of the data in Table 1 shows that the peel strength of the transformer terminals prepared in Examples 1-5 is significantly higher than that of Comparative Examples 1-2. This indicates that the transformer terminals prepared using the welding process of the present invention have superior welding strength. At the same time, compared with Comparative Example 1, the increase in peel strength of Comparative Example 2 is significantly greater than the increase in peel strength of Examples 1-5 compared with Comparative Example 2. This indicates that step S1 in the present invention plays a crucial role in improving peel strength.

[0053] Meanwhile, the weld qualification rate of Examples 1-5 and Comparative Example 2 all reached 100%, and the average weld penetration depth all reached more than 0.4 mm, which shows that the spot welding process of the present invention can achieve high-quality welding effect.

[0054] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A transformer terminal welding process, characterized in that, Includes the following steps: S1. Place the stainless steel strip on the upper surface of the aluminum foil, place the copper-aluminum composite plate on the lower surface of the aluminum foil and make the aluminum side of the copper-aluminum composite plate contact the aluminum foil, and then weld the stainless steel strip, aluminum foil and copper-aluminum composite plate together by spot welding. S2. Attach the copper terminal block to the copper surface of the copper-aluminum composite plate and heat the surface of the copper terminal block using an oxygen-propane welding torch; S3. Add tin wire to the gap between the edge of the copper terminal block and the copper-aluminum composite plate and weld it with an oxygen-propane welding torch; if the edge of the copper terminal block is a bent edge, then the edge does not need to be welded.

2. The transformer terminal welding process according to claim 1, characterized in that, In S1, welding is performed by an electric welding machine. The interlocking gap between the upper and lower welding heads of the electric welding machine conforms to the following: C=(0.85-0.9)H; where C is the interlocking gap between the upper and lower welding heads, and H is the superimposed thickness of the stainless steel strip, aluminum / copper foil, and copper-aluminum composite plate.

3. The transformer terminal welding process according to claim 2, characterized in that, The diameter of the upper welding head is 5-8mm.

4. The transformer terminal welding process according to claim 2, characterized in that, In S1, the spot welding operation method is as follows: the upper welding head is placed above the stainless steel strip, and the lower welding head is placed below the copper-aluminum composite plate. The upper and lower welding heads are first pressed and engaged before the power is applied for spot welding. After the power is turned off, the pressure is released and the welding points are separated to form a weld.

5. The transformer terminal welding process according to claim 4, characterized in that, The spot welding time is 1 second; the crater area is 19 mm. 2 The welding current is positively correlated with the aluminum foil thickness: when the aluminum foil thickness is 0.6-0.9mm, the welding current is 25-30A; when the aluminum foil thickness is 0.9-1.1mm, the welding current is 30-35A; when the aluminum foil thickness is 1.1-1.4mm, the welding current is 35-40A; and when the aluminum foil thickness is 1.4-1.7mm, the welding current is 40-50A.

6. The transformer terminal welding process according to claim 5, characterized in that, After all spot welding is completed, check whether all the welds on the copper-aluminum composite plate meet the requirements of being regularly round, having a diameter of ≥5mm, and having no chipping at the spot weld. If they do not meet the requirements, the weld is unqualified and needs to be re-spot welded until it meets the requirements.

7. The transformer terminal welding process according to claim 4, characterized in that, The solder joints are arranged in rows and columns, with a center-to-center distance of 15mm between adjacent rows and a center-to-center distance of 20mm between adjacent columns.

8. The transformer terminal welding process according to claim 1, characterized in that, The thickness of the stainless steel strip is 0.5 mm.

9. The transformer terminal welding process according to claim 1, characterized in that, In S2, the method for heating the surface of the copper terminal block with the oxygen-propane welding torch is as follows: attach and fix the copper surface of the copper-aluminum composite plate to the copper terminal block, aim the nozzle of the oxygen-propane welding torch at the middle position above the copper terminal block, adjust the flame of the propane welding torch, and use the inner flame of the neutral flame to heat the copper terminal block. During the heating process, move the oxygen-propane welding torch at a constant speed along the length of the base material to be welded, and the heating time is 5-10 seconds.

10. The transformer terminal welding process according to claim 9, characterized in that, In S3, the welding method is as follows: after heating, the solder wire is fed from the gap between the edge of the copper terminal block to be welded and the copper-aluminum composite plate, and the solder wire is heated using an oxygen-propane welding torch. The feeding speed is the same as the moving speed of the oxygen-propane welding torch. The molten solder produced by the melting of the solder wire flows into the gap between the copper terminal block and the copper-aluminum composite plate to complete the welding. Finally, the solder wire is removed and the oxygen-propane welding torch is removed.

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