High-frequency resistance welding method for transformer

Abstract

The invention relates to a high-frequency electric resistance welding method for a transformer, and relates to the technical field of metal welding. A layer of self-reaction soldering paste is applied to the to-be-welded surface of the coil or the iron core to serve as a middle layer; and performing high-frequency resistance welding after mounting and positioning. The self-reaction soldering paste is the technical core of the invention and is composed of a powder mixture containing a solid chemical reducing agent and nano metal particles and an organic carrier. Under excitation of welding heat, the solid chemical reducing agent is subjected to an in-situ chemical reaction, and metal oxides on a welding interface are effectively removed; and meanwhile, the low-melting-point nano metal particles are rapidly melted, the purified clean interface is filled, and a compact metallurgical bonding layer is formed. Through the synergistic effect of chemical purification and physical filling, a defect-free welding joint is obtained, the welding joint has excellent mechanical strength and extremely low contact resistance, the process window is remarkably widened, and the reliability of the welding process is improved.

Description

Technical Field

[0001] This application relates to the field of metal welding technology, and in particular to a high-frequency resistance welding method for transformers. Background Technology

[0002] Transformers are core components in power systems and electronic equipment, and the welding quality during their manufacturing process directly affects the product's performance and long-term reliability. High-frequency resistance welding, due to its advantages such as rapid heating, small heat-affected zone, and high degree of automation, is used for connecting components such as transformer coils and cores. However, existing high-frequency resistance welding technology still faces some inherent drawbacks in practical applications.

[0003] During welding, the instantaneous high temperatures inevitably cause severe oxidation on the metal surface. This oxide layer, formed before metal fusion, is a brittle phase that remains at the welding interface, hindering direct diffusion and bonding between metal atoms. This oxide inclusion not only becomes a source of cracks but also leads to the formation of micropores at the interface, severely weakening the mechanical bonding strength of the weld joint and significantly reducing the reliability and durability of the connection.

[0004] From an electrical performance perspective, the metal oxide layer remaining at the interface is typically a poor conductor or even an insulator. Its presence is equivalent to introducing an unnecessary and inconsistent resistance into the conductive path, significantly increasing the transformer's contact resistance during operation, leading to unnecessary power loss and localized overheating. This unstable, high-resistance interface severely impacts the transformer's energy transfer efficiency and long-term operational stability.

[0005] Furthermore, existing high-frequency resistance welding processes suffer from poor stability and an extremely narrow process window. Weld quality is highly sensitive to factors such as the initial surface condition of the workpiece and minute fluctuations in welding parameters. To barely achieve acceptable weld points, extremely stringent process control is required, which not only increases production costs but also makes it difficult to guarantee consistent product quality in mass production. This process uncertainty leads to low production yields, hindering the widespread application of high-frequency resistance welding technology in the manufacturing of high-performance transformers. Summary of the Invention

[0006] The purpose of this application is to provide a high-frequency resistance welding method for transformers, which solves the technical problem in the existing high-frequency resistance welding process for transformers that micro-defects are generated due to easy oxidation of the welding interface, resulting in a decrease in the mechanical and electrical properties of the joint and a narrow process window.

[0007] This application provides a high-frequency resistance welding method for transformers, comprising the following steps:

[0008] S1. Pre-treatment step: Clean and dry the surfaces of the transformer coils and cores to be welded. This step aims to provide a clean substrate surface for subsequent processes.

[0009] In some preferred embodiments, the pretreatment step specifically includes: first, mechanically grinding or sandblasting the surface to be welded to remove macroscopic oxide layers and contaminants. Then, ultrasonically cleaning the workpiece in an organic solvent to further remove microscopic grease and impurities. In a more specific embodiment, the organic solvent used is acetone or anhydrous ethanol, and the ultrasonic cleaning time is 10-15 minutes. Finally, the cleaned surface is dried for subsequent use.

[0010] S2. Application step: Apply a self-reactive intermediate layer formed by self-reactive solder paste to at least one pretreated workpiece surface.

[0011] In one specific embodiment, the self-reactive solder paste comprises, by total mass, 60-80 wt% of a powder mixture and 20-40 wt% of an organic carrier. The powder mixture consists of a solid chemical reducing agent and nano-metal particles, wherein the mass ratio of the solid chemical reducing agent to the nano-metal particles is 1:2-5.

[0012] In some preferred embodiments, the solid chemical reducing agent is selected from at least one of cuprous formate or cuprous oxalate.

[0013] In some preferred embodiments, the nano-metal particles are core-shell nanoparticles with size effects, for example, silver-coated copper nanoparticles.

[0014] In some preferred embodiments, the organic carrier is a system comprising terpineol and ethyl cellulose. In a more specific embodiment, the organic carrier is prepared by slowly dissolving 10-15 wt% ethyl cellulose in terpineol and magnetically stirring for 2-4 hours until a uniform, transparent, viscous solution is formed. The self-reactive solder paste is prepared by adding the powder mixture to the prepared organic carrier and homogenizing it using a planetary ball mill at 200-400 rpm for 2-4 hours until a uniform, non-agglomerated paste is formed. The function of the organic carrier is to provide suitable viscosity and rheological properties for the powder mixture, facilitating its application.

[0015] In one specific implementation, the application step is performed by micro-dispensing or screen printing to form a uniform intermediate layer film with a thickness of 5-20 μm on the workpiece surface.

[0016] S3. Positioning Step: Install and precisely align the transformer coil and core with the self-reactive intermediate layer applied on the workbench of the welding equipment to ensure that the areas to be welded are aligned.

[0017] S4. Welding Steps: High-frequency resistance welding is performed on the positioned transformer coils and core. This step is crucial for achieving the synergistic effect of chemical reaction and physical fusion.

[0018] In one specific implementation, the welding current frequency of high-frequency resistance welding is set to 500-800kHz, and the welding time is set to 100-500ms.

[0019] In welding step S4, the instantaneous Joule heat generated by the high-frequency current causes the temperature of the welding interface to rise rapidly within milliseconds. This rapid heating process not only melts the metal, but more importantly, it precisely triggers the pre-programmed chemical and physical processes within the self-reactive intermediate layer.

[0020] First, when the interface temperature reaches the initial decomposition temperature of the solid chemical reducing agent, it undergoes an in-situ decomposition reaction, instantly generating a highly active reducing atmosphere at the welding interface. This process is designed to occur before the surface of the base materials such as transformer coils and cores reaches a molten state, thereby completely reducing microscopic oxides that were present before welding or newly formed in the early stage of heating, forming an oxide-free, extremely clean metal contact interface.

[0021] Secondly, the chemical reaction kinetics of the self-reactive intermediate layer are designed to be matched with the heating process of high-frequency resistance welding. By controlling the type and characteristics of the reducing agent, its reaction rate peak occurs within the optimal time window before the base material melts, ensuring the high efficiency and timeliness of the in-situ purification effect.

[0022] Finally, on a clean interface, the nano-metal particles with low melting point effect preferentially melt and fill all micro gaps, followed by the melting of the base material surface. The two work together to produce a full metallurgical reaction, thereby forming a dense welded joint with no oxide inclusions and high bonding strength.

[0023] Through the precise coupling and synergistic effect of the above-mentioned chemical reaction and physical fusion process in time and space, the present invention fundamentally solves the inherent contradiction of the difficulty in balancing high temperature and oxidation in traditional welding processes.

[0024] In summary, this application includes at least one of the following beneficial technical effects:

[0025] 1. This application introduces a self-reactive intermediate layer at the welding interface. The built-in solid chemical reducing agent undergoes an in-situ chemical reaction under welding heat, fundamentally eliminating the brittle oxide layer that hinders direct metal bonding. Simultaneously, the molten filling effect of the nano-metal particles ensures a dense and defect-free weld structure. This synergistic effect of chemical purification and physical filling allows the final weld joint to avoid oxide inclusions and porosity defects common in traditional processes, thus achieving a high-strength and reliable connection.

[0026] 2. This application effectively improves the electrical performance of transformer welded joints, achieving low and stable contact resistance. The key lies in the in-situ purification function of the self-reactive intermediate layer, which completely eliminates oxides at the interface that act as high-resistance barriers. Based on this, the dense fusion layer formed by metal nanoparticles constructs an uninterrupted conductive path, significantly reducing scattering and loss during electron transport, thus ensuring the long-term efficient operation of the transformer.

[0027] 3. This application introduces a self-reactive intermediate layer, giving the welding process a self-regulating characteristic. The chemical reaction of the intermediate layer is precisely triggered by the welding heat, actively compensating for minor differences in the workpiece surface condition and exhibiting greater tolerance to fluctuations in process parameters. This inherent fault-tolerant mechanism reduces the stringent requirements on equipment control precision, resulting in a significant improvement in the consistency of welding results and the yield rate of finished products. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0029] This application will be further described in detail below.

[0030] Example 1

[0031] See appendix Figure 1 This embodiment provides a high-frequency resistance welding method for transformers, and the specific steps are as follows:

[0032] Step 1: Preprocessing

[0033] T2 type oxygen-free copper transformer coil and DT4C type electrical pure iron core were selected as the workpieces to be welded. First, the area to be welded was sandblasted. Then, the workpieces were placed in an ultrasonic cleaner containing analytical grade acetone and cleaned for 12 minutes. Finally, the surface of the workpieces was dried with high-purity nitrogen and placed in a desiccator for later use.

[0034] Step 2: Preparation and application of self-reactive solder paste

[0035] S1. Preparation of organic carrier: In a glove box, 12.5 wt% ethyl cellulose was added to terpineol and magnetically stirred for 3 hours to obtain a uniform and viscous organic carrier.

[0036] Solder paste preparation: Accurately weigh cuprous formate powder and silver-coated copper nanoparticles to a mass ratio of 1:3.5. Add the powder mixture to the organic carrier prepared in step (1) so that the total mass of the powder mixture accounts for 70 wt% of the total mass of the solder paste. Grind the mixture in a planetary ball mill at 300 rpm for 3 hours to obtain a uniform self-reactive solder paste.

[0037] S2. Application: Using a micro-dispensing system, the prepared self-reactive solder paste is uniformly applied to the surface of the coil to be soldered, forming an intermediate layer with a thickness of 12μm.

[0038] S3: Installation Positioning

[0039] The coil coated with the intermediate layer and the iron core are mounted on a special fixture of the high-frequency resistance welding machine and aligned using a CCD vision system to ensure precise alignment of the welding parts.

[0040] S4: High-frequency resistance welding

[0041] Set the welding parameters as follows: welding current frequency 650kHz, welding time 300ms, electrode pressure 200N. Start the welding program and complete the welding.

[0042] Example 2

[0043] See appendix Figure 1 This embodiment provides a high-frequency resistance welding method for transformers, including the following steps:

[0044] S1: Preprocessing

[0045] After sandblasting the workpieces to be welded, they are ultrasonically cleaned in anhydrous ethanol for 10 minutes, and then dried for later use.

[0046] S2: Preparation and application of self-reactive solder paste

[0047] (1) Preparation of organic carrier: 10 wt% ethyl cellulose was added to terpineol and magnetically stirred for 2 hours.

[0048] (2) Solder paste preparation: Accurately weigh cuprous oxalate powder and silver-coated copper nanoparticles to a mass ratio of 1:2. Add the powder mixture to the organic carrier so that the total mass of the powder mixture accounts for 60 wt% of the total mass of the solder paste. Grind the mixture in a planetary ball mill at 200 rpm for 2 hours.

[0049] (3) Application: Using screen printing technology, the solder paste is applied to the surface of the iron core to be soldered to form an intermediate layer with a thickness of 5μm.

[0050] S3: Installation Positioning

[0051] Same as Example 1.

[0052] S4: High-frequency resistance welding

[0053] Set the welding parameters as follows: welding current frequency 500kHz, welding time 100ms, electrode pressure 100N. Start the welding program and complete the welding.

[0054] Example 3

[0055] See appendix Figure 1 This embodiment provides a high-frequency resistance welding method for transformers, including the following steps:

[0056] S1: Preprocessing

[0057] After sandblasting the workpiece, place it in acetone for ultrasonic cleaning for 15 minutes, then blow it dry and set it aside for use.

[0058] S2: Preparation and application of self-reactive solder paste

[0059] (1) Preparation of organic carrier: 15wt% of ethyl cellulose was added to terpineol and magnetically stirred for 4 hours.

[0060] (2) Solder paste preparation: Accurately weigh cuprous formate powder and silver-coated copper nanoparticles to a mass ratio of 1:5. Add the powder mixture to the organic carrier so that the total mass of the powder mixture accounts for 80 wt% of the total mass of the solder paste. Grind the mixture in a planetary ball mill at 400 rpm for 4 hours.

[0061] (3) Application: Using a micro-dispensing system, solder paste is applied to the surface of the coil to be soldered to form an intermediate layer with a thickness of 20 μm.

[0062] S3: Installation Positioning

[0063] Same as Example 1.

[0064] S4: High-frequency resistance welding

[0065] Set the welding parameters as follows: welding current frequency 800kHz, welding time 500ms, electrode pressure 300N. Start the welding program and complete the welding.

[0066] Comparative Example 1:

[0067] The difference compared to Example 1 is that in the preparation of the self-reactive solder paste, the total mass of the powder mixture accounts for 50 wt% of the total mass of the solder paste, and the remainder is an organic carrier.

[0068] Comparative Example 2:

[0069] The difference compared to Example 1 is that in the preparation of the self-reactive solder paste, the mass ratio of cuprous formate powder to silver-coated copper nanoparticles is 1:1.

[0070] Comparative Example 3:

[0071] Compared with Example 1, the difference is that the applied intermediate layer does not contain a solid chemical reducing agent (cuprous formate) and is composed only of silver-coated copper nanoparticles and an organic carrier, wherein the mass of the silver-coated copper nanoparticles accounts for 70 wt% of the total mass of the solder paste.

[0072] Comparative Example 4:

[0073] Compared with Example 1, the difference is that the applied intermediate layer does not contain nano-metal particles (silver-coated copper nanoparticles), but is composed only of cuprous formate powder and organic carrier, wherein the mass of cuprous formate accounts for 70 wt% of the total mass of solder paste.

[0074] Comparative Example 5:

[0075] Compared with Example 1, the difference is that the first pretreatment step is omitted, that is, the self-reactive solder paste is applied directly to the surface of the workpiece in its original state without sandblasting and ultrasonic cleaning.

[0076] Comparative Example 6:

[0077] Compared with Example 1, the difference is that no self-reactive intermediate layer is used at all, and high-frequency resistance welding is performed directly on the transformer coil and core after the first step of pretreatment.

[0078] Test Example 1: Mechanical Property Testing of Welded Joints

[0079] Experimental steps:

[0080] This test aims to quantitatively evaluate the mechanical bonding strength of transformer welded joints prepared using different methods. The testing equipment is a microcomputer-controlled universal testing machine. The specific testing steps are as follows: Welded samples prepared according to Examples 1-3 and Comparative Examples 1-6 are taken out and fixed on the special fixture of the testing machine, ensuring that the direction of the tensile force is parallel to the weld interface. The testing machine is set to apply a tensile-shear load to the sample at a constant tensile rate of 1 mm / min until the joint fractures. The testing machine system automatically records the load-displacement data throughout the process, and the maximum load value recorded before fracture is taken as the tensile-shear strength of the sample. The above test is repeated for 10 samples in each group, and the final result is the arithmetic mean.

[0081] The experimental data are shown in Table 1:

[0082] Table 1: Comparison of tensile and shear strength of welded joints

[0083] Sample group Average tensile shear strength (N) Example 1 452.8 Example 2 418.3 Example 3 437.1 Comparative Example 1 209.5 Comparative Example 2 181.4 Comparative Example 3 32.7 Comparative Example 4 94.2 Comparative Example 5 155.6 Comparative Example 6 No valid connection was formed

[0084] Experimental conclusion:

[0085] As shown in Table 1, the welded samples prepared using the methods described in Examples 1-3 of this invention exhibit significantly higher tensile and shear strengths than all comparative sample samples, demonstrating excellent mechanical bonding performance. Specifically, the sample strengths of Examples 1-3 are consistently above 410 N, proving that the method of this invention can achieve reliable and high-strength welding within the defined composition and process parameter ranges, demonstrating good process robustness. In contrast, the tensile and shear strengths of all comparative sample samples show a significant decrease, and as shown in Comparative Example 6, effective connections cannot be formed under conventional processes.

[0086] Comparing the results of Example 1 with those of Comparative Examples 3 and 4 clearly reveals the core technical mechanism of the method of the present invention. In Comparative Example 3, the removal of cuprous formate, a solid chemical reducing agent, from the intermediate layer resulted in a sharp drop in tensile shear strength to 32.7 N. This indicates that during the rapid heating process of welding, without timely removal of interface oxides through in-situ chemical reaction, an effective metallurgical bond cannot be formed, severely weakening the joint strength. Similarly, in Comparative Example 4, the removal of nano-metal particles from the intermediate layer resulted in a strength of only 94.2 N. This demonstrates that simple interface purification is insufficient to guarantee a high-strength connection; rapid melting, wetting, and filling of the purified interface by low-melting-point metal particles are necessary to ensure the formation of a dense, defect-free weld. Therefore, the precise synergy between the in-situ purification effect of the solid chemical reducing agent and the melting and filling effect of the nano-metal particles constitutes the fundamental reason why the present invention obtains a high-strength joint.

[0087] Further analysis of Comparative Examples 1 and 2 shows that even when both key components are present, their synergistic effect is significantly reduced if their ratio deviates from the range defined in this invention, resulting in insufficient joint strength. Comparative Example 5 demonstrates that a thorough pretreatment step is a necessary prerequisite for ensuring the optimal performance of the self-reactive intermediate layer, and a clean initial surface is the foundation for achieving efficient in-situ chemical reactions. Finally, the complete failure of Comparative Example 6, from the opposite perspective, confirms that the technical solution proposed in this invention—applying a self-reactive intermediate layer between workpieces to be welded—is an innovative and effective approach to solving the high-frequency resistance welding problems of such materials.

[0088] Test Example 2: Electrical Performance Test of Welded Joints

[0089] Experimental steps:

[0090] This test aims to accurately measure the interfacial contact resistance of welded joints prepared using different methods to evaluate their conductivity. The testing equipment is a micro-ohmmeter, and the four-probe method is used to eliminate interference from lead resistance. The specific test steps are as follows: Welded samples prepared according to Examples 1-3 and Comparative Examples 1-6 are taken out respectively. Two current probes and two voltage probes of the micro-ohmmeter are applied to both sides of the welded area, ensuring that the voltage probes are located inside the current probes. A stable DC current is applied through the welded joint, while simultaneously measuring the voltage drop between the voltage probes and automatically calculating the contact resistance value. The above test is repeated for 10 samples in each group, and the final result is the arithmetic mean.

[0091] The experimental data are shown in Table 2:

[0092] Table 2: Comparison of contact resistance of welded joints

[0093] Sample group Average contact resistance (μΩ) Example 1 18.7 Example 2 23.4 Example 3 20.1 Comparative Example 1 88.9 Comparative Example 2 105.2 Comparative Example 3 6730 Comparative Example 4 345.6 Comparative Example 5 258.1 Comparative Example 6 open circuit

[0094] Experimental conclusion:

[0095] The experimental data in Table 2 clearly show that the welded joints prepared using the methods described in Examples 1-3 of this invention have extremely low contact resistances, significantly better than all comparative examples. The resistance values ​​of Examples 1-3 are all below 25Ω, proving that within the scope of this invention, electrical connections with excellent conductivity can be stably obtained. In stark contrast, the contact resistances of all comparative examples are several times or even orders of magnitude higher, and some even fail to form a conductive path under the conditions of Comparative Example 6, directly demonstrating the significant progress of this invention in improving the electrical performance of welding.

[0096] The core technical effects of this invention can be verified through the failure mechanisms of Comparative Examples 3 and 4. Comparative Example 3, lacking a solid chemical reducing agent in its intermediate layer, exhibits a contact resistance as high as 6730 μΩ, more than three hundred times that of Example 1. This irrefutably proves that metal oxides are the culprit behind the formation of high-resistance interfaces. The in-situ chemical reaction designed in this invention can create a highly active reducing atmosphere at the welding interface, effectively removing the oxide layer that acts as an insulator, thus clearing the way for smooth electron transport. Meanwhile, Comparative Example 4, lacking nano-metal particles in its intermediate layer, also exhibits a resistance as high as 345.6 μΩ, indicating that even with a clean interface, without sufficient metal molten filling, the resulting micropores will severely hinder conductive pathways and increase electron scattering.

[0097] Furthermore, the results of Comparative Examples 1 and 2 reveal the importance of precise control over the proportions of each component. Inappropriate proportions can disrupt the synchronicity of the chemical reaction and physical filling process, leading to incomplete interface cleanup or insufficient filling, thereby increasing contact resistance. The results of Comparative Example 5 emphasize the necessity of the pretreatment step; contaminants at the initial interface can interfere with the in-situ chemical reaction, resulting in a decline in the quality of the final electrical connection. Finally, the open-circuit results of Comparative Example 6 fundamentally demonstrate that without the introduction of the self-reactive intermediate layer described in this invention, conventional high-frequency resistance welding cannot form reliable electrical connections in such applications, thus highlighting the necessity and inventiveness of the technical solution of this invention.

[0098] Test Example 3: Microscopic Morphology and Defect Analysis of Weld Interface

[0099] Experimental steps:

[0100] This test aims to directly verify the effect of the method of this invention in improving the quality of weld interfaces and eliminating defects through microscopic observation. The testing equipment is an electron microscope with an energy dispersive spectroscopy (EDS) analyzer. The specific testing steps are as follows: One typical sample was taken from each of the samples prepared in Example 1, Comparative Example 3, Comparative Example 5, and Comparative Example 6, and a cross-section was sampled along the center of the weld using a precision metallographic cutting machine. The samples were then cold-mounted in resin, followed by coarse and fine grinding using an automatic metallographic grinding and polishing machine with sandpaper of different grits, and finally fine polished with diamond polishing paste until a smooth, scratch-free mirror surface was obtained. The prepared metallographic samples were placed in the sample chamber of the scanning electron microscope and evacuated to a high vacuum. First, the weld interface was located under low magnification, and then gradually magnified to 500-2000x to observe and photograph the microscopic morphology of the interface area. Finally, at typical interface locations, line scanning or point analysis was performed using EDS to determine the elemental distribution of the interface area, especially the oxygen content.

[0101] The experimental data are shown in Table 3:

[0102] Table 3: Microscopic Analysis Results of Welding Interface

[0103] Sample group Interface micromorphology observation Main EDS energy spectrum findings in the interface region Example 1 The interface is tightly bonded, forming a continuous metallurgical bonding zone, free of pores, cracks, or inclusions. The interface mainly consists of matrix metal elements, while the oxygen element signal is extremely weak, close to the detection background value. Comparative Example 3 The interface exhibits a clear, continuous gray layered structure with visible microcracks in some areas. The gray layered structure region shows an extremely strong oxygen peak, proving that it is a metal oxide layer. Comparative Example 5 The interface is discontinuous, with visible scattered non-metallic inclusions and micropores. In addition to metallic elements, carbon, sulfur, and other pollutant elements were also detected in the inclusion area. Comparative Example 6 The interface gaps are huge, with only localized point-like fusion and most areas unbonded. The edges of the fused zones have a loose oxide layer. The oxygen signal is very strong throughout the entire interface area, especially at the edge of the fusion zone.

[0104] Experimental conclusion:

[0105] The above results intuitively reveal the superiority of the technical solution of this invention. Table 3 shows that only the sample using the method of Example 1 formed an ideal welding interface, achieving a seamless metallurgical bond between its coil and core, without any macroscopic or microscopic defects. Conversely, all comparative sample interfaces exhibited severe defects, such as oxide inclusions, voids, and even large areas of unbonded surfaces. This explains, from a microstructural perspective, the fundamental reason for their poor performance in mechanical and electrical property tests.

[0106] The core technical mechanism described in this invention is most strongly demonstrated through a direct comparison between Example 1 and Comparative Example 3. Comparative Example 3 simply removed the solid chemical reducing agent from the self-reactive solder paste, resulting in the formation of a visible, continuous oxide layer at its interface. EDS analysis further confirmed the enrichment of oxygen in this layer, irrefutably demonstrating that metal oxidation is unavoidable under the instantaneous high-temperature environment of high-frequency resistance welding. It is precisely the solid chemical reducing agent introduced in this invention that, through in-situ chemical reaction during the welding process, promptly removes these newly formed, harmful oxides, thus creating the prerequisite for the formation of pure metal-metal direct bonds.

[0107] Finally, comparing Example 1 with Comparative Examples 5 and 6 fully demonstrates the necessity and synergistic effect of the entire process flow of the present invention. Comparative Example 6 completely omits the intermediate layer, resulting in severe interface oxidation and almost no bonding, which conversely proves that introducing a functional intermediate layer is the fundamental way to solve this welding problem. Comparative Example 5, omitting the pretreatment step and using complete self-reactive solder paste, still exhibits defects at the interface due to initial contaminants. This illustrates that a clean initial surface combined with a powerful self-reactive intermediate layer achieves highly reliable and high-performance welding.

[0108] Test Example 4: Welding Process Stability and Pass Rate Test

[0109] Experimental steps:

[0110] This test aims to evaluate the process reliability and finished product yield of the method of the present invention under continuous production conditions. The test was conducted on an automated welding workstation to simulate a batch production environment. The specific test steps are as follows: The process flow of the welding workstation was set to the schemes described in Examples 1-3, Comparative Examples 5 and 6, respectively. For each scheme, 100 samples were continuously welded. After each sample was welded, it was quickly inspected according to two standards: 1) visual inspection, checking for obvious spatter, cracks or structural misalignment in the weld joint; 2) electrical continuity test, using the resistance setting of a multimeter to test whether the weld joint is conductive. Only samples that pass both the visual inspection and the electrical continuity test are recorded as qualified products. Finally, the number of qualified products under each scheme is counted, and the pass rate is calculated.

[0111] The experimental data are shown in Table 4:

[0112] Table 4: Comparison of Welding Process Stability and Pass Rate

[0113] Sample group Total number of welds Qualified quantity Pass rate (%) Example 1 100 99 0.99 Example 2 100 98 0.98 Example 3 100 99 0.99 Comparative Example 5 100 67 0.67 Comparative Example 6 100 2 0.02

[0114] Experimental conclusion:

[0115] The test results in Table 4 strongly demonstrate that the method of the present invention has extremely high process stability and production reliability. The samples using the methods described in Examples 1-3 all achieved a pass rate of 98% or higher, indicating that the technical solution of the present invention has a wide process window and excellent anti-interference ability, fully meeting the requirements of industrial mass production. In stark contrast, the pass rates of Comparative Examples 5 and 6 were extremely low, especially Comparative Example 6, where the traditional method almost failed to produce qualified products. This highlights the significant breakthrough of the present invention in process implementation.

[0116] The reason this invention achieves such high process stability lies in the fact that the introduction of a self-reactive intermediate layer fundamentally alters the physicochemical process of welding. In traditional processes (such as Comparative Example 6), weld quality is extremely sensitive to minute differences in oxidation on the workpiece surface and slight temperature fluctuations; any minor disturbance can lead to weld failure, resulting in an extremely narrow process window. However, the self-reactive intermediate layer designed in this invention, under the stimulation of welding heat, can spontaneously undergo "in-situ purification" and "melt filling," a process characterized by self-regulation and fault tolerance. It can proactively create ideal welding conditions within milliseconds, thereby greatly reducing the dependence on precise control of external process parameters, widening the process window, and ensuring a high degree of consistency in welding results.

[0117] Comparing the results of Example 1 with those of Comparative Example 5 further clarifies the synergistic effect of each step in the complete technical solution of this invention. Although Comparative Example 5 used a self-reactive intermediate layer, its yield rate dropped significantly to 67% due to the omission of the pretreatment step. This indicates that macroscopic contaminants on the initial surface consume part of the effectiveness of the self-reactive intermediate layer, interfering with its function. This demonstrates that a clean initial substrate combined with an intermediate layer possessing strong in-situ reactive capabilities is essential to ensure the ultimate reliability of the welding process. Therefore, it is through the organic combination of the pretreatment step and the application of the self-reactive intermediate layer that this invention overcomes the inherent defects of traditional processes, achieving stable, reliable, and high-yield welding production.

[0118] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A high frequency resistance welding method of a transformer, characterized by, The method comprises the following steps: S1, pretreatment: cleaning and drying the surface of the transformer coil and core to be welded; S2, applying: applying a self-reacting intermediate layer formed by a self-reacting soldering paste on at least one surface after pretreatment, wherein the self-reacting soldering paste contains the following components by total mass: 60-80wt% of a powder mixture; 20-40wt% of an organic carrier; wherein the powder mixture contains a solid-state chemical reducing agent and nano-metal particles, and the mass ratio of the solid-state chemical reducing agent to the nano-metal particles is 1:2-5; S3, positioning: installing and positioning the transformer coil and core to which the self-reacting intermediate layer is applied; S4, welding: high-frequency resistance welding of the positioned transformer coil and core, and the heat generated by the high-frequency resistance welding initiates a chemical reaction of the self-reacting intermediate layer to purify the welding interface in situ and realize fusion connection of the transformer coil and core.

2. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The chemical reaction kinetics of the self-reacting intermediate layer matches the temperature rising process in step S4, so that the initial decomposition temperature of the chemical reaction is lower than the melting point of the transformer coil and core, and the rate peak of the chemical reaction appears before the surface of the transformer coil and core reaches the molten state.

3. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The solid-state chemical reducing agent contained in the self-reacting soldering paste is at least one of cuprous formate or cuprous oxalate.

4. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The nano-metal particles contained in the self-reacting soldering paste are core-shell structure nano-particles.

5. A method of high frequency resistance welding of a transformer according to claim 4, characterised in that, The core-shell structure nano-particles are specifically silver-coated copper nano-particles.

6. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The organic carrier contained in the self-reacting soldering paste contains terpineol and ethyl cellulose.

7. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The applying step in S2 is carried out by micro-dispensing or screen printing to form the self-reacting intermediate layer with a thickness of 5-20µm.

8. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The parameter setting of the high-frequency resistance welding in the welding step S4 is as follows: the welding current frequency is 500-800kHz, and the welding time is 100-500ms.

9. A method of high frequency resistance welding of a transformer according to claim 1, characterized in that, The pretreatment step in S1 specifically comprises: mechanical polishing or sandblasting treatment on the surface to be welded; then, ultrasonic cleaning of the surface with an organic solvent.

10. A method of high frequency resistance welding a transformer according to claim 9, characterised in that, The ultrasonic cleaning uses acetone or anhydrous ethanol as the organic solvent, and the cleaning time is 10-15 minutes.

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