High-precision forming processing method for U-shaped copper shield of large steam turbine generator

Abstract

The invention discloses a high-precision forming machining method for a U-shaped copper shield of a large steam-turbine generator, and relates to the technical field of large steam-turbine generator manufacturing. The high-precision forming machining method comprises the steps that the copper shield is split into a plurality of copper plates, and weld joints keep away from functional structure holes; friction stir welding tailor welding is adopted, and an N-1 advanced machining strategy is matched to reserve a matched machined part so as to guarantee the circumferential size precision; machining allowance is reserved on the blank, surface precision cutting is used for replacing compression molding, and welding stress and wave degree are eliminated; a basic hole is drilled in advance to serve as an absolute reference original point for functional hole machining; and a special tool is adopted for rigid protection in the whole process. Welding defects and stress concentration can be effectively eliminated, the flatness of the copper shielding surface is improved, precise attachment with the pressing ring is achieved, the problems of too high temperature rise and potential difference ignition are solved, meanwhile, the machining precision of the functional structure hole is guaranteed, the rejection rate is reduced, and the method is suitable for high-precision manufacturing of the large steam turbine generator stator end magnetic flux leakage shielding part.

Description

Technical Field

[0001] This invention relates to the field of large steam turbine generator manufacturing technology, and more specifically to a high-precision forming and processing method for U-shaped copper shields of large steam turbine generators. This method solves the deformation problem of thin-walled copper shields by optimizing the welding layout, improving the welding method and introducing precision cutting. Background Technology

[0002] In the manufacturing process of large steam turbine generators, the problem of magnetic leakage at the stator core ends has always been a key factor affecting generator performance and safety. To prevent localized high temperatures or overheating of the stator core retaining ring, a copper shield (electrical shield) is usually installed on the outside of the retaining ring. The copper shield uses its internal eddy currents to prevent magnetic leakage from entering the inner circle of the retaining ring, thus dispersing the concentrated magnetic leakage at the inner circle of the retaining ring through a "blocking" method. At the same time, to avoid sparks caused by potential differences between the copper shield and the retaining ring, the two must be reliably fixed or have good contact. In addition, to reduce the temperature rise of the copper shield, functional structural holes such as ventilation holes, structural components, and temperature sensing element mounting holes are also machined on the copper shield.

[0003] However, due to the large size and thinness of copper shielding plates, the unfolded dimensions often exceed the maximum size of copper plates available on the market. Currently, the commonly used processing method in the industry is "large plate welding + molding," and the specific operation process and existing problems are as follows: 1. Welding process The largest available copper plate is selected as the base material. Then, one or two supplementary plates are welded together according to the size requirements of the copper shielding to form a complete copper shielding blank. Traditional fusion welding processes, such as manual arc welding and gas shielded welding, are mainly used in the welding process. The problems encountered are as follows: ① Numerous physical defects: When welding thin copper plates using traditional fusion welding processes, the high thermal conductivity of copper causes rapid heat loss during welding, leading to excessively fast cooling of the weld joint and defects such as porosity and cracks. Furthermore, the welding process is prone to "insufficient filler" in the weld, meaning the weld metal is not fully filled, affecting the weld's strength and sealing. Once weld defects are discovered, the thin and large area of ​​the copper shield makes high-temperature repair welding highly susceptible to secondary deformation, making the defects even more difficult to repair. This, in turn, increases the product scrap rate, production costs, and production cycle.

[0004] ② Stress concentration problem: During the welding process, welding stress will inevitably be generated at the weld. When the weld is close to the location of the functional structure hole to be processed later, the cutting action during the processing of the functional structure hole will further aggravate the stress concentration at the weld, which can easily lead to weld cracking and seriously affect the structural integrity of the copper shield.

[0005] 2. Compression molding process The welded copper shielding blank is directly placed into a mold for compression molding. Compression molding mainly uses the pressure of the mold to give the copper shielding blank a certain shape and dimensional accuracy. The following problems exist: ① Poor flatness: The molding process cannot completely eliminate the original waviness of the board material. Due to the large size and thickness of the copper shield, the stress on different parts of the board is uneven during the molding process, which can easily lead to extremely poor flatness of the copper shield surface after molding. This insufficient flatness will cause the copper shield and the pressure ring to not be able to fit tightly together, resulting in obvious gaps.

[0006] ② Difficulty in guaranteeing dimensional accuracy: During the molding process, factors such as mold wear and material elastic deformation can affect the dimensional accuracy of the copper shield. Moreover, due to the complex shape of the copper shield, a large amount of subsequent processing is required after molding to meet design requirements, increasing processing difficulty and cost.

[0007] 3. Overall processing effect and impact ①Ventilation: such as Figure 2 As shown, if the surface flatness of the copper shield is poor and there are gaps between it and the mating surface of the pressure ring, the axial airflow from the pressure ring will escape through these gaps, failing to effectively cool the outer surface of the copper shield and causing excessive temperature rise. Excessive temperature rise not only affects the performance and service life of the copper shield itself but may also have thermal effects on other components of the generator, reducing the overall reliability of the generator.

[0008] ② Potential difference sparking: Poor contact between the copper shield and the pressure ring can cause a potential difference. During generator operation, this potential difference may lead to sparks, threatening the safe operation of the generator. Once sparking occurs, it may cause serious malfunctions such as hydrogen explosion, or even cause the generator to shut down, resulting in huge economic losses.

[0009] ③ Risk of machining chain breakage: Due to the poor quality of the weld seams and the inability to achieve precise leveling through molding, the cutting tools are easily impacted at weld defects during subsequent machining of functional structural holes, leading to tool damage or decreased machining accuracy. Furthermore, the increased risk of cracking at defects in the functional structural holes severely impacts the stability and reliability of the entire machining chain. Summary of the Invention

[0010] To overcome the shortcomings of the existing technology, this invention discloses a high-precision forming method for U-shaped copper shields of large steam turbine generators. The purpose of this invention is to solve the problems of numerous physical defects, stress concentration, poor flatness, difficulty in ensuring dimensional accuracy, ventilation issues, potential difference arcing, and processing chain breakage inherent in the existing "large plate welding + molding" process. This invention is applied to the manufacturing of leakage magnetic shielding components at the ends of stator cores of large steam turbine generators. Through a systematic combination of processes including stress-optimized layout design, friction stir welding, surface finishing with reserved allowance, reference hole positioning, and full-cycle tooling protection, high-precision forming of thin-walled copper shields is achieved.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator, comprising: Stress-optimized layout design: Based on the fact that the position of the weld seam on the copper shield avoids the functional structural holes on the copper shield, the copper shield is divided into multiple copper plates, and multiple copper plate blanks with reserved processing allowances are obtained according to the division result. High-quality precision welding: Multiple copper plate blanks are spliced ​​together using friction stir welding to obtain copper shielding blanks. During the welding process, an "N-1" pre-processing strategy is adopted to ensure the overall circumferential dimensional accuracy. At the same time, welding quality control is carried out during the welding process, and reference holes are drilled in the copper shielding blanks. Precision surface reconstruction machining: The copper shielding blank with reserved machining allowance is subjected to surface finishing to eliminate welding residual stress and material waviness. After finishing, surface treatment is performed. Reference error-proof positioning: A positioning system is established based on the reference hole, and functional structural holes are machined on the copper shield after precision surface reconstruction based on the positioning system; Full-cycle rigid protection: Special tooling is used to rigidly constrain the copper shield throughout the entire process of welding, processing, transportation and storage to prevent radial deformation.

[0012] Preferably, the stress-optimized layout design includes: Split Planning: Based on the final size and shape of the copper shield, and combined with the largest copper plate specifications available on the market, the copper shield will be split into 3-4 copper plates. During the splitting process, the location of the functional structure holes in subsequent processing will be fully considered. Through detailed design calculations and simulation analysis, it will be ensured that the weld seam location completely avoids the functional structure holes. Layout optimization: After determining the splitting scheme, the layout of each copper plate is designed, including the relative position and splicing sequence of the copper plates to reduce welding deformation and residual stress; at the same time, the texture direction of the copper plates is considered to make the texture direction consistent at the splicing points to improve welding quality and the overall performance of copper shielding.

[0013] Preferably, in the stress-optimized layout design, the functional structural holes include ventilation holes, structural component and temperature measuring element connection holes; stress simulation is performed on different splitting schemes using finite element analysis software, and the splitting method with the most uniform stress distribution and the least impact on the functional structural holes is selected.

[0014] Preferably, in the high-quality precision welding, the parameter control of the friction stir welding process includes: stirring head rotation speed, welding speed, and pressure. The “N-1” pre-processing strategy is as follows: reserve one copper plate as a size matching part, first complete the welding of the remaining copper plates according to the design requirements, after the welding is completed, measure and inspect the dimensions of the welded part, and according to the measurement results, precisely process the reserved matching part to make it perfectly match the welded part, and ensure the ultimate closure of the overall circumferential dimensions.

[0015] Preferably, in the high-quality precision welding, the welding quality control includes: during the welding process, using an infrared thermal imager to monitor the temperature distribution of the welding area to ensure that the welding temperature is within a reasonable range; using ultrasonic testing technology to perform non-destructive testing on the weld joint to promptly detect and address welding defects; and after welding is completed, performing mechanical property tests on the weld joint, including tensile and bending tests, to ensure that the strength and toughness of the weld joint meet the design requirements.

[0016] Preferably, in the precision surface reconstruction process, the reserved machining allowance is 2-3 mm / m, which is determined according to the dimensional accuracy requirements of the copper shield and the welding deformation. The surface finishing process includes: after welding, the welded parts are installed on a high-precision CNC machining center, and surface finishing is performed using multi-axis linkage machining technology; by precisely controlling the movement trajectory and cutting parameters of the tool, residual welding stress and material waviness are eliminated, so that the copper shielding surface achieves extremely high flatness and smoothness; during the processing, online measurement technology is used to detect the processed surface in real time, and the processing parameters are adjusted in a timely manner according to the detection results to ensure processing quality.

[0017] Preferably, in the precision surface reconstruction process, the surface treatment includes: after the surface finishing is completed, polishing and passivation surface treatment are performed on the copper shield surface to further improve the surface smoothness and corrosion resistance, and ensure that the copper shield and the pressure ring can achieve precise bonding.

[0018] Preferably, in the reference error-proof positioning, in order to address the problem that the weld seam disappears after surface finishing and cannot be avoided when drilling holes, horizontal or vertical reference holes are pre-drilled on the copper shield blank. The position of the reference hole is reasonably selected according to the structural characteristics of the copper shield and the distribution of functional structural holes, so as to ensure that the reference hole can serve as the absolute reference origin for the processing of functional structural holes.

[0019] Preferably, in the reference error-proof positioning, a high-precision positioning system is established based on a preset reference hole; when machining functional structural holes, the positioning system is used to accurately position the machining equipment to ensure the positional and dimensional accuracy of the functional structural holes; at the same time, an error-proof design is adopted to monitor the reference hole in real time during the machining process. When the position of the reference hole is found to be offset, the machining is stopped and adjusted to avoid machining errors.

[0020] Preferably, in the full-cycle rigid protection, the special tooling includes welding tooling, processing tooling, transfer tooling, and storage tooling; The welding fixture is a radial constraint fixture, used to fix the copper plate on the fixture to prevent the copper plate from undergoing radial deformation due to thermal stress during the welding process. The machining fixture is used to precisely position the copper shield on the precision machining equipment and provide stable support to prevent the copper shield from vibrating and deforming due to cutting forces during the machining process, while also having good heat dissipation performance. The transfer fixture is used to safely and reliably transfer the copper shield from one process to another, avoiding collisions and damage during the transfer process; The storage fixture is used to provide a stable and dry storage environment for the copper shield, preventing the copper shield from deformation and corrosion due to moisture and oxidation.

[0021] Preferably, the high-precision forming and processing method for the U-shaped copper shield of the large steam turbine generator is applied to the manufacturing of the leakage magnetic shield at the end of the stator core of the large steam turbine generator. Through a systematic combination of stress-optimized layout design, friction stir welding, surface finishing with reserved allowance, reference hole positioning, and full-cycle tooling protection, the high-precision forming of the thin-walled copper shield is achieved, solving the problems of multiple physical defects, stress concentration, poor flatness, difficulty in ensuring dimensional accuracy, ventilation, potential difference arcing, and processing chain breakage that exist in the traditional welding and molding process.

[0022] The beneficial effects of this invention are: 1. Significantly improved structural reliability: Friction stir welding completely solves the problems of porosity and cracks in fusion welding, and the weld hole avoidance design improves structural strength and greatly reduces the scrap rate.

[0023] 2. Electrical and ventilation performance meets standards: The extremely high surface flatness enables precise bonding between the copper shield and the pressure ring, effectively preventing axial air leakage, controlling temperature rise, and completely eliminating the potential for arcing due to potential difference.

[0024] 3. Precise and controllable machining accuracy: The combination of preset reference holes and precision machining ensures the coordinate accuracy of ventilation holes and temperature measuring element holes, improving the overall assembly quality.

[0025] 4. High overall economic benefits: Although the processing steps are increased, the total life cycle cost is significantly reduced by lowering the scrap rate, shortening the construction period, and extending the service life of the motor. Attached Figure Description

[0026] Figure 1 This is a logic block diagram of the high-precision forming and processing method for the U-shaped copper shield of a large steam turbine generator according to the present invention; Figure 2 This is a schematic diagram of the copper shielding pressure ring assembly of the present invention; Figure 3 This is a schematic diagram of the disassembly of the copper shielding welding of the present invention; in the diagram, numbers 1-3 indicate the numbers of the copper plates obtained after disassembly; Figure 4 For the present invention Figure 3 The copper plates numbered 1-3 were obtained from the splitting process; Figure 5 This is a schematic diagram of the copper shielding machining allowance of the present invention; Figure 6 For the present invention Figure 5 AA section view in the image. Detailed Implementation

[0027] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention.

[0028] A high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator, such as Figure 1 As shown, it includes: 1. Stress optimization layout design Split Planning: Based on the final size and shape of the copper shield, and considering the largest copper plate specifications available on the market, the copper shield will be split into 3-4 copper plates. During splitting, the locations of functional structural holes for subsequent processing will be fully considered. Through detailed design calculations and simulation analysis, it will be ensured that the welding positions completely avoid functional structural holes such as ventilation holes, structural component mounting holes, and temperature sensing element connection holes. For example, stress simulations of different splitting schemes will be performed using finite element analysis software to select the splitting method with the most uniform stress distribution and the least impact on functional structural holes.

[0029] Layout optimization: After determining the splitting scheme, the layout of each copper plate is designed. The relative positions and splicing order of the copper plates are rationally arranged to reduce welding deformation and residual stress. At the same time, the grain direction of the copper plates is considered, striving to ensure that the grain direction at the splicing points is consistent, thereby improving welding quality and the overall performance of the copper shielding.

[0030] Taking the copper shield of a generator as an example, four copper plates are welded together, such as... Figure 3 and 4 As shown.

[0031] 2. High-quality precision welding implementation Welding process selection: Friction stir welding (FSW) is introduced. This process has advantages such as solid-state bonding, low thermal distortion, and high precision, making it very suitable for splicing thin-walled copper shielding. Compared with traditional fusion welding, friction stir welding does not produce molten metal, avoiding defects such as porosity and cracks, and effectively ensuring welding quality.

[0032] The "N-1" pre-processing strategy: During the welding process, an "N-1" pre-processing strategy is adopted. This means reserving one copper plate as a dimensional matching part, and welding the remaining copper plates according to the design requirements first. During welding, welding parameters such as stirring head speed, welding speed, and pressure are strictly controlled to ensure the quality of the weld joint. After welding, the welded parts are dimensionally measured and inspected. Based on the measurement results, the reserved matching part is precisely machined to ensure a perfect fit with other welded parts, guaranteeing the ultimate closure of the overall circumferential dimensions.

[0033] Welding quality control: During the welding process, real-time monitoring technology is used to monitor welding quality. For example, infrared thermal imagers are used to monitor the temperature distribution in the welding area to ensure that the welding temperature is within a reasonable range; ultrasonic testing technology is used to perform non-destructive testing on the weld joint to promptly detect and address welding defects. After welding is completed, mechanical property tests, such as tensile and bending tests, are performed on the weld joint to ensure that the strength and toughness of the weld joint meet design requirements.

[0034] 3. Precision surface reconstruction machining Allowance for machining: Changing the traditional practice of not machining the surface, sufficient machining allowance is reserved at the blank stage according to design requirements. The size of the machining allowance should be reasonably determined based on factors such as the dimensional accuracy requirements of the copper shield and the welding deformation, and is generally reserved at 2-3mm / m.

[0035] Surface Finishing: After welding, the welded parts are mounted on a high-precision CNC machining center, where multi-axis machining technology is used for surface finishing. By precisely controlling the tool's movement trajectory and cutting parameters, residual welding stress and material waviness are completely eliminated, resulting in extremely high flatness and smoothness on the copper shielding surface. During processing, online measurement technology is used to monitor the machined surface in real time, and machining parameters are adjusted promptly based on the monitoring results to ensure processing quality.

[0036] Taking the copper shield of a generator as an example, the machining allowance is as follows: Figure 5 and 6 As shown.

[0037] Surface treatment: After the surface finishing is completed, the copper shield surface is subjected to appropriate surface treatment, such as polishing and passivation, to further improve the surface smoothness and corrosion resistance, and ensure that the copper shield and the pressure ring can achieve precise bonding.

[0038] 4. Application of benchmark error-proofing positioning technology Pre-drilled reference holes: To address the issue of welds "disappearing" after surface finishing, making it impossible to avoid drilling around the welds, 1-2 horizontal or vertical reference holes of 10mm are pre-drilled on the blank. The location of the reference holes should be rationally selected based on the structural characteristics of the copper shield and the distribution of functional structural holes, ensuring that the reference holes can serve as the absolute reference origin for machining the functional structural holes.

[0039] Positioning System Establishment: A high-precision positioning system is established based on preset reference holes. When machining functional structural holes, the positioning system is used to precisely position the machining equipment, ensuring the positional and dimensional accuracy of the functional structural holes. Simultaneously, an error-proofing design is adopted, with real-time monitoring of the reference holes during machining. If any deviation in the reference hole's position is detected, machining is immediately stopped and adjusted to avoid machining errors.

[0040] 5. Rigid protection measures throughout the entire life cycle Welding fixture design: During the welding process, a dedicated radial center constraint fixture is designed to fix the copper plate to the fixture and prevent radial deformation of the copper plate due to thermal stress during welding. The fixture should have sufficient rigidity and strength to withstand the heat and stress during the welding process. At the same time, the fixture design should facilitate the installation and removal of the copper plate to improve welding efficiency.

[0041] Machining Fixture Design: During precision machining, a dedicated machining fixture is designed based on the shape and size characteristics of the copper shield. The fixture should accurately position the copper shield on the machining equipment and provide stable support to prevent vibration and deformation caused by cutting forces during machining. Simultaneously, the fixture should have good heat dissipation performance to promptly dissipate the heat generated during machining, preventing deformation of the copper shield due to temperature rise.

[0042] Design of Transfer and Storage Fixtures: Dedicated transfer and storage fixtures should be designed for the transfer and storage of copper shielding. The transfer fixtures should be able to safely and reliably transfer the copper shielding from one process to another, avoiding collisions and damage during transfer. The storage fixtures should provide a stable and dry storage environment for the copper shielding, preventing deformation and corrosion due to moisture, oxidation, or other factors.

[0043] The key innovations of this invention are as follows: 1. Stress layout optimization of multi-plate welding: By splitting the copper shield into 3-4 pieces for welding and accurately calculating to ensure that the weld avoids the functional structural holes, the risk of weld cracking due to stress concentration during processing is effectively reduced, ensuring the structural integrity of the shield.

[0044] 2. High-precision applications of friction stir welding: Utilizing the unique solid-state bonding characteristics of friction stir welding, near-defect-free welding results are achieved in thin-walled copper shielded splicing. Simultaneously, an "N-1" pre-processing strategy is employed, reserving space for additional machining components to ensure precise closure of the overall circumferential dimensions, meeting high-precision machining requirements.

[0045] 3. Surface finishing replaces compression molding: Abandoning the traditional compression molding method, machining allowance is reserved on the blank after welding. Through precision surface cutting, residual welding stress and material waviness are completely eliminated, so that the surface of the shielding part achieves extremely high flatness and smoothness, and achieves precise fit with the pressure ring.

[0046] 4. Reference hole positioning technology: To address the issue of welds being invisible after surface finishing, 1-2 horizontal or vertical reference holes of 10mm are pre-drilled on the blank to provide an absolute reference origin for the subsequent processing of functional structure holes, ensuring processing accuracy.

[0047] 5. Full-cycle tooling protection: Throughout the entire process of welding, processing, transportation and storage, special radial center constraint tooling is used to effectively prevent the thin-walled copper shield from radial deformation under stress release or gravity, ensuring stable product quality.

[0048] Compared with the closest existing technology (traditional "large plate welding + molding" process), the high-precision forming method for large steam turbine generator U-shaped copper shields provided by this invention has the following advantages: ① Significantly improves structural reliability Eliminating welding defects: The solid-state joining process of friction stir welding (FSW) avoids physical defects such as porosity, cracks, and "missing material" in welds that are common in traditional fusion welding. The quality of the welded joint is stable and reliable, which greatly reduces the product scrap rate.

[0049] Avoid stress concentration cracking: Through stress optimization layout design, the location of the weld seam is completely avoided from functional structural holes such as ventilation holes, structural components and temperature measuring element connection holes, which effectively prevents the stress concentration of the weld seam from being aggravated by the cutting action during subsequent processing, eliminates the risk of weld seam cracking, and ensures the structural integrity of the copper shield.

[0050] Full-cycle dimensional stability: Through full-cycle rigid protection of welding fixtures, machining fixtures and transfer and storage fixtures, the thin-walled copper shield is effectively prevented from radial deformation under stress release or gravity, ensuring the dimensional stability of the product in each process.

[0051] ② Achieve excellent electrical and ventilation performance Completely solves the temperature rise problem: "Leave-in cutting" replaces traditional molding, and the material waviness is completely eliminated through precision surface cutting, so that the copper shield surface achieves extremely high flatness and smoothness, realizing precise fit with the stator core pressure ring, effectively preventing axial wind from leaking from the mating gap, significantly reducing the temperature rise of the copper shield, and extending the service life of the generator.

[0052] Eliminating the risk of arcing due to potential difference: The tight contact between the copper shield and the pressure ring eliminates the potential difference between them, avoiding sparks caused by poor contact during operation, fundamentally eliminating the risk of safety accidents such as hydrogen explosion, and improving the operational safety of the generator.

[0053] ③ Improve machining accuracy and assembly quality Ensuring the positional accuracy of functional structural holes: By pre-drilling reference holes as the absolute reference origin, the positioning problem caused by the "disappearance" of welds after surface finishing is solved, ensuring the coordinate accuracy of functional structural holes such as ventilation holes and temperature measuring element fitting holes, and improving the overall assembly quality.

[0054] Achieving precise circumferential closure: Adopting the "N-1" advance processing strategy, reserving matching parts, and performing precise matching processing based on actual welding measurement results, so that the overall circumferential dimensions reach the ultimate closure, meeting the requirements of high-precision assembly.

[0055] ④ Reduce overall costs and improve economic efficiency Reduce scrap rate and rework cost: The high-quality splicing and controllable surface finishing of friction stir welding significantly reduce product scrap caused by welding defects and excessive deformation, thereby reducing raw material waste and rework time.

[0056] Shorten the production cycle: Compared with the cumbersome process of repeated welding repairs and extensive finishing after molding due to welding defects in traditional processes, the process path of this invention is clear and controllable, and the processing efficiency is higher, which is conducive to shortening the generator manufacturing cycle.

[0057] Extending motor lifespan: By improving temperature rise and eliminating the risk of sparking, the failure rate of the generator during operation is reduced, the number of maintenance downtimes is reduced, the total life cycle cost is significantly reduced, and the overall economic benefits are improved.

[0058] ⑤ Expand the scope of application of the process The method of this invention breaks through the market's copper plate specification limitations by welding multiple plates together, enabling the manufacture of ultra-large copper shielding components. Furthermore, by reserving machining allowances and precision cutting, it can flexibly adapt to design requirements of different precision levels, and has good process versatility and promotional value.

[0059] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalents or substitutions are all included within the scope defined by the claims of the present invention.

Claims

1. A high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator, characterized in that, include: Stress-optimized layout design: Based on the fact that the position of the weld seam on the copper shield avoids the functional structural holes on the copper shield, the copper shield is divided into multiple copper plates, and multiple copper plate blanks with reserved processing allowances are obtained according to the division result. High-quality precision welding: Multiple copper plate blanks are spliced ​​together using friction stir welding to obtain copper shielding blanks. During the welding process, an "N-1" pre-processing strategy is adopted to ensure the overall circumferential dimensional accuracy. At the same time, welding quality control is carried out during the welding process, and reference holes are drilled in the copper shielding blanks. Precision surface reconstruction machining: The copper shielding blank with reserved machining allowance is subjected to surface finishing to eliminate welding residual stress and material waviness. After finishing, surface treatment is performed. Reference error-proof positioning: A positioning system is established based on the reference hole, and functional structural holes are machined on the copper shield after precision surface reconstruction based on the positioning system; Full-cycle rigid protection: Special tooling is used to rigidly constrain the copper shield throughout the entire process of welding, processing, transportation and storage to prevent radial deformation.

2. The high-precision forming and processing method for a large steam turbine generator U-shaped copper shield according to claim 1, characterized in that, The stress optimization layout design includes: Split Planning: Based on the final size and shape of the copper shield, and combined with the largest copper plate specifications available on the market, the copper shield will be split into 3-4 copper plates. During the splitting process, the location of the functional structure holes in subsequent processing will be fully considered. Through detailed design calculations and simulation analysis, it will be ensured that the weld seam location completely avoids the functional structure holes. Layout optimization: After determining the splitting scheme, the layout of each copper plate is designed, including the relative position and splicing sequence of the copper plates to reduce welding deformation and residual stress; at the same time, the texture direction of the copper plates is considered to make the texture direction consistent at the splicing points to improve welding quality and the overall performance of copper shielding.

3. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the stress optimization layout design, the functional structural holes include ventilation holes, structural components, and temperature measuring element connection holes; stress simulation is performed on different splitting schemes using finite element analysis software, and the splitting method with the most uniform stress distribution and the least impact on the functional structural holes is selected.

4. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the high-quality precision welding process, the parameter control of friction stir welding includes: stirring head rotation speed, welding speed, and pressure. The "N-1" pre-processing strategy is as follows: reserve one copper plate as a size matching part, first complete the welding of the remaining copper plates according to the design requirements, after the welding is completed, measure and inspect the dimensions of the welded part, and according to the measurement results, precisely process the reserved matching part to make it perfectly match the welded part, and ensure the ultimate closure of the overall circumferential dimensions.

5. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the high-quality precision welding, the welding quality control includes: during the welding process, using an infrared thermal imager to monitor the temperature distribution of the welding area to ensure that the welding temperature is within a reasonable range; using ultrasonic testing technology to perform non-destructive testing on the weld joint to promptly detect and address welding defects; and after welding is completed, performing mechanical property tests on the weld joint, including tensile and bending tests, to ensure that the strength and toughness of the weld joint meet the design requirements.

6. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the precision surface reconstruction process, the reserved machining allowance is 2-3 mm / m, which is determined according to the dimensional accuracy requirements of the copper shield and the welding deformation. The surface finishing process includes: after welding, the welded parts are installed on a high-precision CNC machining center, and surface finishing is performed using multi-axis linkage machining technology; by precisely controlling the movement trajectory and cutting parameters of the tool, residual welding stress and material waviness are eliminated, so that the copper shielding surface achieves extremely high flatness and smoothness; during the processing, online measurement technology is used to detect the processed surface in real time, and the processing parameters are adjusted in a timely manner according to the detection results to ensure processing quality.

7. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the precision surface reconstruction process, the surface treatment includes: after the surface finishing is completed, the copper shield surface is polished and passivated to further improve the surface smoothness and corrosion resistance, and ensure that the copper shield and the pressure ring can achieve precise bonding.

8. The high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the aforementioned reference error-proof positioning, to address the issue of weld seams disappearing after surface finishing, making it impossible to avoid drilling through the weld seams, horizontal or vertical reference holes are pre-drilled on the copper shield blank. The position of the reference holes is rationally selected based on the structural characteristics of the copper shield and the distribution of functional structural holes, ensuring that the reference holes can serve as the absolute reference origin for processing the functional structural holes.

9. A high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the aforementioned reference error-proof positioning, a high-precision positioning system is established based on a preset reference hole. When machining functional structural holes, the positioning system is used to accurately position the machining equipment to ensure the positional and dimensional accuracy of the functional structural holes. At the same time, an error-proof design is adopted to monitor the reference hole in real time during the machining process. When a deviation in the position of the reference hole is detected, machining is stopped and adjustments are made to avoid machining errors.

10. A high-precision forming and processing method for a U-shaped copper shield of a large steam turbine generator according to claim 1, characterized in that, In the aforementioned full-cycle rigid protection, the special tooling includes welding tooling, machining tooling, transfer tooling, and storage tooling; The welding fixture is a radial constraint fixture, used to fix the copper plate on the fixture to prevent the copper plate from undergoing radial deformation due to thermal stress during the welding process. The machining fixture is used to precisely position the copper shield on the precision machining equipment and provide stable support to prevent the copper shield from vibrating and deforming due to cutting forces during the machining process, while also having good heat dissipation performance. The transfer fixture is used to safely and reliably transfer the copper shield from one process to another, avoiding collisions and damage during the transfer process; The storage fixture is used to provide a stable and dry storage environment for the copper shield, preventing the copper shield from deformation and corrosion due to moisture and oxidation.

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