Double-process multi-pass oxygen-controlled processing method and die for difficult-to-deform alloy plate

Abstract

This invention discloses a dual-process, multi-pass controlled oxidation processing method and mold for difficult-to-deform alloy plates, belonging to the field of metal material hot working technology. The method includes configuring original process parameters, blank blanking, grinding and polishing, multi-pass processing and forming, workpiece process flow decision-making, and part finishing and finished product inspection. The multi-pass processing and forming includes alternating oxygen-controlled pre-forming and vacuum hot straightening. Oxygen-controlled pre-forming includes: pre-forming the plate to the target shape of the current pass using a uniform forming device within the range of room temperature to service temperature. Vacuum hot straightening includes: placing the pre-formed part in a straightening mold, closing the mold, drawing a vacuum, and performing high-temperature stress relaxation straightening within the stress relaxation temperature range to eliminate springback. This method, through the alternating execution of oxygen-controlled pre-forming and vacuum hot straightening, real-time data feedback correction, and the establishment of a forming feedback channel, effectively reduces the degree of material oxidation, improves forming accuracy and stability, optimizes plate utilization, and enhances the service performance and surface quality of parts.

Description

Technical Field

[0001] This invention relates to the field of hot working technology of metal materials, and in particular to a dual-process, multi-pass controlled oxidation processing method and mold for difficult-to-deform alloy plates. Background Technology

[0002] Difficult-to-deform alloy sheets, due to their unique properties such as lightweight yet high strength, corrosion resistance, and creep resistance, are widely used in aerospace, military, and other fields with extremely high requirements for lightweighting, high reliability, and adaptability to extreme environments, such as aircraft skin and rocket engine casings. With continuous technological advancements, the application range of difficult-to-deform alloy sheets continues to expand, making them a key material in modern high-end manufacturing. However, the forming and processing of difficult-to-deform alloy sheets faces numerous challenges. Due to their high hardness, low plasticity, and anisotropy, difficult-to-deform alloy sheets need to be slowly formed at high temperatures. This not only increases the forming difficulty but also leads to severe oxidation of parts during high-temperature forming. How to control oxidation at low cost and high quality while ensuring forming quality has become a critical problem that the aerospace industry urgently needs to solve.

[0003] Currently, the commonly used forming methods for difficult-to-deform alloy sheets in industry mainly include superplastic forming and thermo-assisted forming. While superplastic forming can achieve complex shapes, it typically requires temperatures above 900 degrees Celsius and an inert gas atmosphere, resulting in extremely slow forming speeds and high energy consumption. Furthermore, the molds must be made of expensive, high-temperature resistant materials, and the choice of forming materials is limited, making it suitable only for certain fine-grained superplastic alloys. Thermo-assisted forming, on the other hand, requires high temperatures and a vacuum or protective atmosphere to suppress material oxidation. The molds also need to be coated with a lubricating layer to prevent adhesion to the sheet metal. This forming method demands extremely strict temperature control; uneven heating or temperature fluctuations during forming can severely affect the forming results. Its equipment structure is complex, and the forming cost is high, making it primarily suitable for forming high-value-added parts. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-process, multi-pass controlled oxidation processing method and mold for difficult-to-deform alloy plates, in order to solve the above-mentioned technical problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy plates includes the following steps:

[0007] By analyzing sheet metal samples and using simulation forming, a forming feedback channel is established to obtain material property parameters for each pass, and the number of processing passes is determined based on the simulation results.

[0008] The blanking dimensions were optimized based on the simulation results, and the surface and edges of the slab were polished to eliminate stress concentration sources.

[0009] The process alternately performs oxygen-controlled preforming and vacuum thermal straightening. The oxygen-controlled preforming includes: preforming the sheet metal to the target shape of the current pass using a uniform forming device in the range of room temperature to service temperature. The vacuum thermal straightening includes: placing the preformed part in a vacuum thermal straightening mold, closing the mold and drawing a vacuum or closing the mold and constraining it, and then placing it in a vacuum heating furnace and drawing a vacuum. High-temperature stress relaxation straightening is performed in the stress relaxation temperature range to eliminate springback.

[0010] Real-time acquisition of actual processing data is fed back to the simulation model to dynamically correct subsequent pass parameters, thereby improving processing accuracy and stability.

[0011] After the final part undergoes heat treatment and surface finishing, and passes inspection, a process database is established to provide processing and forming parameter references for subsequent processing of different shapes of the same difficult-to-deform alloy sheet.

[0012] Furthermore, the oxygen-controlled preforming includes:

[0013] After preforming, an anti-oxidation coating is sprayed onto the surface of the slab;

[0014] Pre-forming is performed using uniform forming equipment;

[0015] The forming temperature was determined through oxidation weight gain tests and simulation analysis, and it does not exceed the material's service temperature.

[0016] Furthermore, the uniform forming equipment is at least one of a plate rolling machine, a spinning machine, a multi-point forming press, or a single-point forming equipment.

[0017] Furthermore, the vacuum thermal straightening includes: using a mold cast from vermicular graphite cast iron or medium silicon molybdenum ductile iron, closing the mold at room temperature and evacuating it, then heating it to the stress relaxation temperature. The stress relaxation temperature and time are determined based on high-temperature tensile stress relaxation experiments and simulation forming.

[0018] Furthermore, the alternating oxygen-controlled preforming and vacuum hot straightening are performed in a multi-pass cycle. The non-final pass uses room temperature preforming and vacuum heating furnace straightening, while the final pass uses service temperature preforming and vacuum hot straightening molds in conjunction with vacuum heating furnace straightening.

[0019] Furthermore, in the process of establishing a forming feedback channel through plate sampling analysis and simulation forming simulation, the simulation forming simulation includes: iterative simulation pass by pass, with the effective forming and stress relaxation results of the previous pass serving as the input for the simulation of the next pass, and the deviation between the simulation results of the last pass and the target shape being within the effective forming limit and crack limit range.

[0020] A vacuum hot straightening mold for dual-process multi-pass controlled oxidation processing of difficult-to-deform alloy plates is provided, for performing the dual-process multi-pass controlled oxidation processing method for difficult-to-deform alloy plates described in any of the above-mentioned methods. The vacuum hot straightening mold includes: an inner straightening mold with an inner surface straightening support, an inner screw-in sealing port, and a conical inner sealing boss; an outer straightening mold with an outer surface straightening support, an outer screw-in threaded hole coaxial with the inner screw-in sealing port, and a conical outer sealing groove; a screw-in vacuum extraction pipe connected to the outer screw-in threaded hole via a screw-in thread, and having a vacuum extraction hole inside; and a straightening mold locking screw for locking the inner straightening mold and the outer straightening mold together; wherein the conical inner sealing boss and the conical outer sealing groove cooperate to form a vacuum sealing structure.

[0021] Furthermore, the inner and outer orthopedic molds are made of vermicular graphite cast iron or medium silicon molybdenum ductile iron.

[0022] Furthermore, the screw-in vacuum extraction tube is made of high-temperature nickel-based alloy, and the screw-in thread of the extraction tube is vacuum-sealed with the external screw-in threaded hole.

[0023] Furthermore, the profiles of the inner surface straightening support and the outer surface straightening support are determined according to the shape of the corresponding pass part and corrected by thermal expansion simulation.

[0024] Compared with the prior art, the present invention discloses at least the following beneficial effects:

[0025] This invention discloses a dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy sheets. By alternately executing controlled oxygen pre-forming and vacuum hot straightening, the oxidation level of the material during forming is effectively controlled, ensuring the service performance and surface quality of the parts. Controlled oxygen pre-forming is performed within the range of room temperature to service temperature, avoiding rapid oxidation of the material at high temperatures. Vacuum hot straightening further reduces oxidation by vacuuming after mold closing at room temperature, avoiding the high-temperature pressure forming requirements of traditional processing methods. The straightening mold can be made of vermicular graphite cast iron or medium-silicon molybdenum ductile iron, reducing mold material costs while further increasing mold lifespan. Simultaneously, this method improves forming accuracy and stability by real-time acquisition of actual processing data and feedback to the simulation model, dynamically correcting subsequent pass parameters, reducing error accumulation, and ensuring that the final part's shape and size are closer to the target shape. Furthermore, by establishing a forming feedback channel to obtain material property parameters for each pass and determining the number of processing passes based on simulation results, the blanking size is optimized, improving material utilization and reducing production costs. Finally, heat treatment and surface finishing further enhance the performance and surface quality of the parts, ensuring they meet usage requirements. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of the processing method of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the vacuum thermal straightening mold of the present invention;

[0029] Figure 3 For the present invention Figure 2 A magnified view of a section at point A in the middle;

[0030] In the diagram: 1. Inner straightening mold; 2. Straightening mold locking screw; 3. Outer straightening mold; 4. Difficult-to-deform alloy sheet material processing part; 5. Screw-in vacuum extraction pipe; 101. Inner surface straightening support; 102. Inner screw-in sealing port; 103. Conical inner sealing boss; 301. Outer surface straightening support; 302. Outer screw-in threaded hole; 303. Conical outer sealing groove; 501. Extraction pipe screw-in thread; 502. Vacuum extraction hole. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] On the one hand:

[0033] Reference Figure 1 As shown in the figure, the present invention provides a dual-process multi-pass controlled oxidation processing method for difficult-to-deform alloy plates, including five stages: original process parameter configuration, slab blanking, grinding and polishing, multi-pass processing and forming, workpiece process flow decision, part finishing and finished product inspection. Each stage includes different steps and process details.

[0034] In this embodiment, configuring the original process parameters is the first step in the dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy plates. Its key feature is the establishment of a forming feedback channel between plate sampling analysis and simulated forming. Simulated forming parameters are obtained through plate sampling analysis; the forming pass is determined based on the simulation results; and relevant experimental tests are conducted in conjunction with the simulation parameters required for different passes to further refine the simulated forming process.

[0035] In one specific embodiment, taking three-pass forming as an example, the configuration of the original process parameters includes the following steps:

[0036] Step S101, Original slab forming parameter detection:

[0037] The first pass involves determining the optimal forming temperature through oxidation weight gain experiments, or, depending on the actual forming method, selecting a forming temperature between room temperature and service temperature. Tensile tests and three-point bending tests are then conducted to obtain the material properties required for the first pass simulation analysis. Following this, high-temperature tensile stress relaxation experiments are performed to determine the time and temperature required for stress relaxation under strain.

[0038] Second pass: Perform further tensile and three-point bending tests after the first pass stress relaxation to obtain the material properties required for the second pass simulation analysis. The temperature and time for stress relaxation in the second pass can be referenced from the parameters of the first pass.

[0039] The third pass: referring to the simulation parameters obtained from the second pass, the final pass is used to conduct microstructure control experiments to optimize the performance of the formed parts.

[0040] Step S102: Simulation and estimation of processing passes:

[0041] The first stage of simulation involves obtaining the forming limits of the original slab in the first pass. A simulation forming model is constructed based on the actual forming method. The sheet metal module of 3D modeling software such as NX is used for unfolding and layout to obtain the slab dimensions. The simulation forming temperature is a selected temperature between room temperature and service temperature. The degree of deformation is controlled by adjusting the simulation analysis process using simulation software such as ABAQUS to obtain the limiting shape at which cracks appear in the original slab in the first pass. It should be understood that the sheet metal module of 3D modeling software such as NX is specifically designed for sheet metal processing. Using the sheet metal module of NX, the forming parts of difficult-to-deform alloy sheet are unfolded and laid out to obtain the slab model required for simulation and the blanking dimensions required for processing. In the second stage, based on the results of the first stage and actual forming problems, the simulation analysis process is adjusted to correct the effective forming limits of the original slab in the first pass. A stress relaxation simulation analysis process is added, with the required temperature and time obtained from the high-temperature tensile stress relaxation experiment in the first pass. Finally, the effective forming and stress relaxation results of the original slab in the first pass are output for the forming simulation of the second pass.

[0042] The second-pass simulation uses the forming limit of the first pass as a reference, and the effective forming and stress relaxation results of the first pass as input. Combined with the actual forming method of the second pass, various parameters are adjusted, and the effective forming and stress relaxation results of the second pass are output for the forming simulation of the third pass.

[0043] The third simulation pass is essentially the same as the second. After completion, the target shape model is imported into the simulation analysis software and compared with the effective forming and stress relaxation results of the third pass. Based on the results, a decision is made on whether to add more processing passes or use the third pass forming as the final output.

[0044] Step S103, Parameter detection and correction for different passes:

[0045] The third forming pass is used as the final output. The criterion for judgment is whether the shape deviation between the effective forming and stress relaxation results of the third forming pass simulation analysis and the target shape model is within the effective forming limit and crack shape limit of the first pass. If the shape deviation is within the range, it is considered the final forming pass. Based on the analysis results of the final forming pass, the parameters of different passes are further optimized and adjusted to obtain the processing passes and parameters in the actual forming process, providing reference guidance for subsequent actual forming.

[0046] In this embodiment, the blank blanking, grinding, and polishing is the second step in the dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy plates. Its key feature is the optimization of blanking dimensions through simulated forming, coupled with pre-forming treatment of the blank surface and edges to prevent stress concentration fractures caused by surface and edge unevenness, thereby enhancing the bond between the plate and the anti-oxidation coating.

[0047] In one specific embodiment, the blank cutting, grinding, and polishing includes the following steps:

[0048] Step S201: Overall board planning, layout, cutting, and blanking:

[0049] Based on the simulation of the first stage of the first processing pass S102, the blank size obtained is used to plan the layout of the difficult-to-deform alloy sheet. The blanking method can be selected according to the material properties, sheet thickness and forming accuracy requirements, such as laser blanking, wire cutting blanking, water jet blanking, etc., to obtain the blank required for forming.

[0050] Step S202: Grinding and polishing the slab surface and edges:

[0051] Surface grinding and polishing: To prevent cracking during the forming process, surface micro-cracks and hardened layers need to be removed. After surface treatment, the forming process is stable, rebound deviation can be controlled, forming quality is improved, the bond between the sheet and the anti-oxidation coating is enhanced, and oxidation during forming and straightening is reduced. The actual treatment method can be selected according to the actual situation. The effect is judged visually; the surface should be uniform, flat, and free of obvious scratches and pits.

[0052] Edge grinding and polishing: To ensure a continuous and stable forming process, it is necessary to remove edge burrs and edge defects generated during the blanking process to avoid breakage of the sheet material due to edge defects during forming. The actual treatment method can be selected according to the actual situation. The effect is judged visually, and the edges should be free of obvious protrusions, depressions or micro-cracks.

[0053] In this embodiment, multi-pass forming is the third step in the dual-process multi-pass controlled oxidation processing method for difficult-to-deform alloy sheets. Its key feature is the combination of controlled oxygen pre-forming within the room temperature to service temperature range and vacuum thermal straightening within the stress relaxation temperature range. The controlled oxygen pre-forming process uses uniform forming equipment to form the difficult-to-deform alloy sheet, while the vacuum thermal straightening process uses a straightening mold that is closed at room temperature and then vacuumed before high-temperature stress relaxation straightening. This effectively avoids oxidation caused by large-area contact with the external environment before mold closure in conventional high-temperature forming processes, further preventing the oxide scale generated before mold closure from being difficult to remove under pressure, thus optimizing the dimensional accuracy and service performance of the parts.

[0054] In one specific embodiment, the multi-pass forming process mainly includes two different processes: oxygen-controlled preforming from room temperature to service temperature (process one) and vacuum thermal straightening with high-temperature stress relaxation after vacuuming following room temperature mold closing (process two).

[0055] Step S301: Oxygen-controlled preforming:

[0056] Optimal forming temperature: The optimal forming temperature was selected from the range of room temperature to service temperature through oxidation weight gain experiments and simulation analysis, which meets the requirements of minimizing oxidation during processing and achieving the desired final shape.

[0057] Processing methods: Various uniform forming equipment can be selected, such as plate rolling machines, spinning machines, multi-point forming presses, and single-point forming equipment, to complete the processing of most shapes. Plate rolling machines and multi-point forming presses are suitable for pre-forming large-size curved surfaces; spinning machines are suitable for pre-forming complex cylindrical structures; multi-point forming presses and single-point forming equipment are suitable for different sheet metal forming or special shape pre-forming.

[0058] Taking three-pass forming as an example, oxygen-controlled preforming (process one) from room temperature to service temperature includes the following steps:

[0059] In the first pre-forming stage of Process 1, taking the multi-point forming press in conjunction with offline heating of the sheet metal as an example, an anti-oxidation coating is sprayed onto the surface of the difficult-to-deform alloy sheet metal blank after the surface and edges of the blank have been polished with S202. The difficult-to-deform alloy sheet metal blank and the multi-point forming auxiliary forming sheet metal blank are simultaneously heated to the service temperature of the difficult-to-deform alloy sheet metal blank in an induction heating furnace. The heated difficult-to-deform alloy sheet metal blank metal blank and the multi-point forming auxiliary forming sheet metal blank are placed on the multi-point forming press and simultaneously deformed to the simulated and estimated first-stage shape. The first-stage pre-formed difficult-to-deform alloy sheet metal blank is taken out. After the first-stage pre-formed difficult-to-deform alloy sheet metal blank is cooled to room temperature, some springback occurs.

[0060] In the second pre-forming stage of process one, taking the multi-point forming press forming at room temperature as an example, after the first-order workpiece, which has undergone stress relaxation and forming performance treatment, cools to room temperature, the first-order workpiece is taken out from the first-order hot straightening mold. After covering the first-order workpiece with a multi-point forming auxiliary forming plate, it is placed on the multi-point forming press and simultaneously deformed to the simulated and estimated second-order shape. The second-order workpiece, which is difficult to deform alloy plate pre-formed in the second stage of process one, is taken out. After the second-order workpiece cools to room temperature, it will show partial springback again.

[0061] In the third pre-forming stage of process one, taking single-point forming equipment at room temperature as an example, after the second-stage workpiece, which has undergone stress relaxation and forming performance treatment, cools to room temperature, the second-stage workpiece is removed from the second-stage hot straightening mold. After fixing the second-stage workpiece, the single-point forming equipment is used to perform the final forming stage on the second-stage workpiece. This forming stage needs to be combined with the simulation analysis of the final forming stage to ensure that the dimensional deviation range of the third-stage workpiece after forming springback is controlled within the effective forming limit of the original slab obtained by the simulation-predicted processing stage S102 and the shape limit range of the original slab where cracks occur.

[0062] Step S302: Vacuum thermal straightening:

[0063] The straightening mold is cast from low-cost, high-temperature resistant materials such as vermicular graphite cast iron and medium-silicon molybdenum ductile iron. Vacuum environment construction can be achieved using a vacuum heating furnace in conjunction with a standard straightening mold, a vacuum hot straightening mold in conjunction with a standard heating furnace, or a vacuum hot straightening mold in conjunction with a vacuum heating furnace, to further control oxidation.

[0064] Taking three-pass forming as an example, vacuum thermal straightening (process two) with stress relaxation during mold closing includes the following steps:

[0065] The first stage of process two, hot straightening, uses a vacuum heating furnace in conjunction with a standard straightening mold as an example. The straightening mold is cast from a low-cost, high-temperature resistant material, with relatively low dimensional accuracy requirements. The springback-prone workpiece is placed in the hot straightening mold and locked with threads, causing elastic deformation and restoring it to its pre-formed shape. The locked assembly is then placed in a vacuum heating furnace, evacuated, and heated. Based on parameters obtained from the first stage of high-temperature tensile stress relaxation experiments and simulation analysis, stress relaxation and forming performance treatments are applied to the workpiece.

[0066] The second stage of hot straightening in process two uses a vacuum hot straightening mold in conjunction with a conventional heating furnace as an example. The mold material is the same as that in the first stage of hot straightening. The mold is closed using a room temperature threaded locking method. After vacuuming, it is placed in a conventional heating furnace for heating and straightening. During the locking process, the workpiece undergoes elastic deformation and returns to its pre-formed shape. Afterward, stress relaxation and forming performance treatment are performed.

[0067] The third pass of process two involves hot straightening, taking a vacuum hot straightening mold in conjunction with a vacuum heating furnace as an example. Since the final workpiece shape is consistent with the final formed shape, the dimensions of the final pass vacuum hot straightening mold should be designed according to the final dimensions of the formed part. The mold should be modified based on the dimensional accuracy requirements and the thermal expansion simulation analysis of the mold material to meet the dimensional accuracy requirements of the formed part. The mold is closed using a room temperature threaded locking method, and after vacuuming, it is placed in a vacuum heating furnace for further vacuuming and heating for straightening.

[0068] In this embodiment, the workpiece process flow decision is the fourth step in the dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy plates. Its key feature is its integration with the simulation process, feeding data from the actual processing back into the simulated forming process. During processing, the processing method is further refined based on actual processing conditions, improving the processing details for different processing passes.

[0069] In this embodiment, the finished product inspection after part finishing is the fifth step in the dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy plates. This step includes two stages: part performance adjustment and finishing, and finished product inspection and process optimization. Specifically:

[0070] Step S501: Part performance adjustment and finishing:

[0071] By using a final straightening die to heat-treat parts formed from difficult-to-deform alloy sheets, the service performance of the parts can be improved. After performance treatment, surface treatments such as sandblasting, pickling, alkaline chipping, and laser cleaning can be used to improve the surface quality of the parts.

[0072] Step S502: Finished part inspection and process optimization:

[0073] By comparing the final formed part with the target requirements, the process details can be further optimized. At the same time, a corresponding database can be formed in combination with the forming process to guide the processing of different shapes of the same difficult-to-deform alloy sheet.

[0074] The above embodiments provide a dual-process, multi-pass controlled oxidation processing method for difficult-to-deform alloy sheets. This method combines controlled oxidation pre-forming and vacuum hot straightening processes to control the oxidation of the formed parts. Simultaneously, a multi-pass step-by-step forming method is employed to regulate the dimensional accuracy and microstructure of the formed parts. Controlled oxidation pre-forming, depending on the desired forming shape, typically uses uniform forming equipment such as plate rolling machines, spinning machines, multi-point forming presses, and single-point forming equipment to pre-form the difficult-to-deform alloy sheets from room temperature to service temperature. This process fully utilizes the overall plasticity of the difficult-to-deform alloy sheets while significantly reducing oxidation during forming. It avoids the need for vacuum or protective atmosphere forming environments, thereby further reducing forming costs and the requirements for forming equipment. The vacuum hot straightening process, considering the stress conditions during straightening, typically uses molds cast from low-cost, high-temperature resistant materials such as vermicular graphite cast iron or medium-silicon molybdenum ductile iron to hot straighten the difficult-to-deform alloy sheets. By combining oxygen-controlled preforming and vacuum thermal straightening, the requirements for the high-temperature mechanical properties of the mold can be reduced, and the range of mold materials can be expanded. This reduces the cost of mold processing materials and extends the mold's service life, ultimately achieving low-cost, high-quality controlled oxidation processing of difficult-to-deform alloy sheet parts.

[0075] On the other hand:

[0076] Reference Figure 2 and Figure 3 As shown, this embodiment of the invention provides a vacuum hot straightening mold for dual-process multi-pass controlled oxidation processing of difficult-to-deform alloy plates, used to perform the dual-process multi-pass controlled oxidation processing method for difficult-to-deform alloy plates described in any of the above claims, and is particularly suitable for processing Ti2AlNb conical guide tube structure parts. The vacuum hot straightening mold includes an inner straightening mold 1, a straightening mold locking screw 2, an outer straightening mold 3, a difficult-to-deform alloy plate processing part 4, and a screw-in vacuum extraction pipe 5.

[0077] The inner straightening mold 1 includes an inner surface straightening support 101, an inner screw-in sealing port 102, and a conical inner sealing boss 103. The inner surface straightening support 101 is determined based on the inner surface shape of the part 4 processed from difficult-to-deform alloy sheet in different processing passes. For the final straightening pass, the inner surface straightening support 101 typically requires high dimensional accuracy, necessitating simulation analysis to predict and correct for the thermal expansion effects of the inner straightening mold 1. The inner screw-in sealing port 102 must be aligned with the outer straightening mold 3. The conical inner sealing boss 103 is typically located at the edge of the inner straightening mold 1, and its overall structure is a conical boss, which, while ensuring mold closing positioning, further improves the vacuum sealing performance of the mold.

[0078] The outer straightening mold 3 includes an outer surface straightening support 301, an outer screw-in threaded hole 302, and a conical outer sealing groove 303. The outer surface straightening support 301 is determined based on the outer surface shape of the part 4 processed from difficult-to-deform alloy sheet metal in different processing passes. For the final straightening pass, the outer surface straightening support 301 typically requires high dimensional accuracy and needs to be synchronized with the inner straightening mold 1 through simulation analysis to predict and correct the thermal expansion effect of the outer straightening mold 3. The outer screw-in threaded hole 302 needs to be aligned with the inner screw-in sealing port 102. Typically, the inner straightening mold 1 and the outer straightening mold 3 are locked together using straightening mold locking screws 2 before unified drilling to ensure the normal use of the screw-in vacuum extraction pipe 5. The conical outer sealing groove 303 is usually located at the edge of the outer straightening mold 3. Its overall structure is a conical groove, used to cooperate with the conical inner sealing boss 103, ensuring mold positioning while further improving the vacuum sealing performance of the mold.

[0079] The inner straightening mold 1 and the outer straightening mold 3 are cast from low-cost, high-temperature resistant materials such as vermicular graphite cast iron and medium-silicon molybdenum ductile iron. Further processing of the molds is possible based on the required forming precision. By employing a dual-process, multi-pass controlled oxidation machining method, based on stress analysis, mold costs can be reduced while effectively ensuring mold lifespan and precision, achieving low-cost, high-precision, and stable hot straightening of difficult-to-deform alloy plates.

[0080] The screw-in vacuum extraction tube 5 includes a screw-in thread 501 and a vacuum extraction port 502. The screw-in vacuum extraction tube 5 can be machined from a high-temperature nickel-based alloy. Compared to the traditional welded vacuum extraction tube's cross-stamped sealing method, the screw-in sealing method achieves a better sealing effect and also allows the screw-in vacuum extraction tube 5 to be reused. By drilling holes of the same model for vacuum heat-forming dies of different passes, dies of different passes can be adapted.

[0081] The above embodiments provide a vacuum thermal straightening mold for dual-process, multi-pass controlled oxidation processing of difficult-to-deform alloy sheets. Taking a conical structure as an example, vacuum thermal straightening molds for other structures can be derived by modifying the inner and outer surface straightening support shapes according to the conical structure vacuum thermal straightening mold. Regarding the mold closing method, a room temperature environment threaded locking method is used for mold closing, followed by vacuuming and then heating for straightening. Compared to traditional forming methods, which typically require constructing a large-scale vacuum or inert gas protective environment at high temperatures before pressure closing, the sheet material is in extensive contact with the external environment at high temperatures before mold closing, and the resulting oxide scale is difficult to remove after mold closing and pressure. This processing method, through controlled oxygen pre-forming followed by room temperature environment threaded locking for mold closing, not only avoids the high cost and difficulty of constructing complex protective environments and forming conditions at high temperatures, but also suppresses part oxidation with higher quality and lower cost, significantly improving processing efficiency and part quality. Furthermore, when processing large-sized parts, it can reduce the demand on equipment functions, expand the range of equipment selection, and further reduce part processing costs.

[0082] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to relevant parts and specific embodiments.

[0083] Example 1:

[0084] Taking the conical guide tube structure as an example, the difficult-to-deform alloy plate selected in this embodiment is a 1.1mm thick Ti2AlNb plate with a nominal composition of Ti-22Al-24.5Nb-0.5Mo (at.%).

[0085] The Ti2AlNb conical guide tube structure component in this embodiment is obtained through the following process:

[0086] Step 1: An oxidation weight gain experiment was conducted on the Ti2AlNb sheet to effectively suppress its oxidation during the forming process. Based on the experimental results, 700℃ was selected as the preset forming temperature for the Ti2AlNb conical guide tube structure part.

[0087] Step 2: The forming limits and plastic deformation capacity of the Ti2AlNb sheet were evaluated and tested at room temperature and a preset forming temperature. Based on the shape analysis of the Ti2AlNb conical guide tube structure part, its processing method was determined to be roll forming. The evaluation and testing experiments included tensile tests, three-point bending tests, and curling tests at different temperatures. These experiments were used to obtain the material properties required for simulation analysis.

[0088] Step 3: A vacuum stress relaxation experiment was conducted on the Ti2AlNb plate, and the required time and temperature for stress relaxation were found to be 2400 seconds and 970℃, respectively. Considering the temperature fluctuations in actual processing, it was initially determined that the Ti2AlNb conical guide tube should be subjected to vacuum stress relaxation at 970℃ for 1 hour.

[0089] Step 4: Based on the processing parameters obtained from the experiment, a four-roll bending machine was selected to roll-bend the Ti2AlNb sheet. Through processing simulation analysis and rolling experiment results, it was found that it was impossible to form the Ti2AlNb conical guide tube structure part in one pass at room temperature; although it was possible to form it in one pass at the preset forming temperature, the forming process was highly volatile, easily leading to breakage of the Ti2AlNb sheet. To effectively control forming stability and suppress oxidation, it was decided to use room temperature forming and vacuum hot straightening for the first pass.

[0090] Step 5: Based on the results of the first-pass simulation analysis, supplement the relevant experiments for the second-pass forming and straightening process. Some second-pass simulation parameters can be referenced from the first-pass experimental results.

[0091] Step 6: Use the simulation results of the first-pass room temperature forming and vacuum thermal straightening as input for the second-pass forming simulation. Combine the experimental data supplemented in Step 5 to further revise the simulation parameters and model of the second-pass forming and straightening, and then perform the simulation analysis of the second pass.

[0092] Step 7: Import the Ti2AlNb conical guide tube structure part model into the simulation analysis software and compare the simulation results of the second forming and straightening process with the target shape model. It was determined that the shape deviation between the effective forming and stress relaxation results of the second simulation analysis and the target shape model can be effectively controlled within the effective forming limit and the shape limit where cracks appear of the original slab.

[0093] Step 8: After further optimization of the processing method for the Ti2AlNb conical guide tube structure parts, it was finally determined that a two-pass processing method would be adopted. The first pass forming process is room temperature roll bending, and the straightening process is vacuum heating furnace straightening; the second pass forming process is 700℃ roll bending, and the straightening process is vacuum hot straightening mold combined with vacuum heating furnace straightening.

[0094] Step 9: Based on the blanking dimensions determined by simulation analysis, laser blanking is performed on the 1.1mm thick Ti2AlNb plate, and its surface and edges are polished to ensure that the surface is free of scratches and pits, and the edges are free of uneven defects or micro-cracks.

[0095] Step 10: Using a four-roll bending machine, set the processing parameters according to the estimated shape for the first pass and roll-bend the Ti2AlNb sheet at room temperature. After room temperature pre-forming, the Ti2AlNb sheet will spring back, requiring vacuum heat straightening. Since the first pass is not the final processing pass, the dimensional accuracy requirements are lower. The edges of the Ti2AlNb sheet formed in the first pass are welded together with internal supports and external clamps. Then, an anti-oxidation coating is sprayed onto the surface of the Ti2AlNb sheet, and then, using simplified mold constraints at room temperature, it is placed in a vacuum furnace for the first straightening pass. Based on the actual straightening situation, the stress relaxation parameters are adjusted to high-temperature vacuum stress relaxation at 970℃ for 2.5 hours.

[0096] Step 11: After the first pass of straightening is completed, wait for the vacuum heating furnace to cool down to 700℃, release the gas, and then remove the Ti2AlNb conical guide tube first-order workpiece. Place it into a four-roll plate rolling mill for the second pass of forming. This second pass of forming needs to be combined with the simulation analysis of the final pass of forming to ensure that the dimensions of the second-order workpiece after springback are basically consistent with the target shape. The deviation range should be controlled within the effective forming limit of the Ti2AlNb plate and the shape limit range where cracks may occur.

[0097] Step 12: Place the Ti2AlNb sheet formed in the second pass into a vacuum thermal straightening mold, close the mold using a room temperature threaded locking method, and evacuate the mold using a screw-in vacuum extraction tube. Then, place it in a vacuum heating furnace for further vacuuming and heating to straighten the sheet. During the locking process, the Ti2AlNb sheet will undergo a small amount of elastic deformation, returning to the target shape and dimensions. Afterwards, stress relaxation and forming performance treatment are performed on the Ti2AlNb conical guide tube structure part. After cooling to room temperature, its shape and dimensions are completed.

[0098] Step 13: Compare and analyze the formed Ti2AlNb conical guide tube structure part with the target shape. The Ti2AlNb conical guide tube structure part processed using a dual-process, multi-pass controlled oxidation method on difficult-to-deform alloy sheets has a uniform surface and a low degree of oxidation. Compared with traditional superplastic forming and heat-assisted forming of difficult-to-deform alloy sheets, this method effectively controls the oxidation of difficult-to-deform alloy sheets while reducing forming costs.

[0099] Step 14: After inspection and judgment, the surface of the Ti2AlNb conical guide tube structure part meets the surface quality requirements and does not require surface treatment such as pickling, alkaline degradation, or laser cleaning. Based on this dual-process, multi-pass controlled oxidation part processing method, a corresponding database is formed for processing guidance of different shapes of the same Ti2AlNb sheet.

[0100] Example 2:

[0101] Taking the TC4 fuselage skin structure parts as an example, this embodiment optimizes the hot pressing forming process of the TC4 fuselage skin structure using a dual-process, multi-pass controlled oxidation part processing method with difficult-to-deform alloy sheet. The difficult-to-deform alloy sheet selected in this embodiment is the same type as the fuselage skin, a 0.8mm thick TC4 cold-rolled sheet with a thickness tolerance of ±0.03mm. Based on a proportionally scaled-down TC4 fuselage skin structure, the existing hot pressing forming process verification mold is used, and the optimized processing procedure is as follows:

[0102] Step 1: Based on the existing hot pressing process parameters, conduct room temperature tensile tests and three-point bending tests on 0.8mm thick TC4 cold-rolled sheet to obtain the material properties required for the first simulation analysis at room temperature.

[0103] Step 2: Based on the final shape of the TC4 fuselage skin, a multi-point forming press is used to pre-form the 0.8mm thick TC4 cold-rolled sheet. After the first simulation analysis, it is concluded that the TC4 fuselage skin structural parts can be processed in one pass using a process of room temperature oxygen-controlled pre-forming combined with high temperature vacuum heat straightening.

[0104] Step 3: Use a multi-point forming press to bend and deform the 0.8mm thick TC4 cold-rolled sheet into a predetermined shape. After pre-deformation, place the partially springbacked TC4 cold-rolled sheet forming part on a hot pressing forming process verification mold, and close the mold at room temperature.

[0105] Step 4: After closing the mold at room temperature, evacuate the vacuum hot press furnace. Then, using the existing parameters of the hot pressing process, heat the mold and the molded part to 750°C and perform stress relaxation treatment at this temperature for 1 hour. After cooling to room temperature, remove the molded part.

[0106] By optimizing the hot pressing process using a dual-process, multi-pass controlled oxidation machining method with difficult-to-deform alloy sheets, the resulting scaled-down TC4 fuselage skin structure parts offer the following advantages: Firstly, by avoiding direct contact between the difficult-to-deform alloy sheets and the external environment at high temperatures, oxidation of the formed parts is effectively suppressed. Secondly, it avoids the problem of oxide scale generated before mold closing being difficult to remove under stress during stress relaxation after mold closing, which is a significant drawback. This not only improves the service life of the mold but also reduces the difficulty of subsequent oxide scale treatment on the parts' surface, further ensuring the stability and precision of the forming process.

[0107] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0108] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of controlled oxidation processing of a difficult-to-deform alloy sheet in a two-process, multi-pass mode, characterized in that, The method comprises the following steps: a forming feedback channel is established by plate sampling analysis and simulation forming simulation, material attribute parameters of each pass are obtained, and the number of processing passes is determined based on the simulation results; the blanking size is optimized based on the simulation results, and the surface and edge of the slab are polished to eliminate stress concentration sources; alternately performing oxygen-controlled preforming and vacuum heat straightening, the oxygen-controlled preforming comprising: in the room temperature to service temperature interval, using a uniform forming device to preform the plate to the target shape of the current pass; the vacuum heat straightening comprising: placing the preformed part in the straightening die, closing the die and vacuumizing, high-temperature stress relaxation straightening in the stress relaxation temperature interval to eliminate springback; real-time collection of actual processing data is fed back to the simulation model, and the subsequent pass parameters are dynamically corrected; the final part is subjected to heat treatment and surface finishing, and the process database is established after detection.

2. The dual process multi-pass oxygen managed processing method of a less deforming alloy sheet of claim 1 wherein, The oxygen-controlled preforming comprises: spraying an anti-oxidation coating on the surface of the slab after preforming; using a uniform forming device to perform forming processing; the forming temperature is determined by oxidation weight gain test and does not exceed the service temperature of the material.

3. The dual process multi-pass oxygen managed processing of a less deforming alloy sheet of claim 2 wherein, The uniform forming device uses at least one of a plate rolling machine, a spinning machine, a multi-point forming press or a single-point forming device.

4. The dual process multi-pass oxygen managed processing of sheets of a difficult-to- form alloy of claim 1 wherein, The vacuum heat straightening comprises: using a die cast with vermicular graphite cast iron or medium silicon molybdenum nodular cast iron, closing the die at room temperature and vacuumizing, and then heating to the stress relaxation temperature, the stress relaxation temperature and time being determined based on high-temperature tensile stress relaxation experiment and simulation forming simulation.

5. The dual process multi-pass oxygen managed processing of a less deforming alloy plate of claim 1 wherein, The alternately performing oxygen-controlled preforming and vacuum heat straightening uses multi-pass cycle processing, the non-final pass uses room temperature preforming and vacuum heat straightening furnace straightening, and the final pass uses service temperature preforming and vacuum heat straightening die combined with vacuum heat straightening furnace straightening.

6. The dual process multi-pass oxygen managed processing of sheets of a difficult-to- form alloy of claim 1 wherein, In the step of establishing a forming feedback channel by plate sampling analysis and simulation forming simulation, the simulation forming simulation comprises: iterative simulation of each pass, the effective forming and stress relaxation results of the previous pass being used as the input of the simulation of the next pass, and the deviation of the simulation results of the last pass from the target shape being within the effective forming limit and the crack limit.

7. A vacuum hot straightening die for a double process multi-pass controlled oxidation processing of a difficult-to-deform alloy sheet for performing the double process multi-pass controlled oxidation processing method of any one of claims 1 to 6, characterized by, It comprises: an inner straightening die (1) provided with an inner surface straightening support (101), an inner side screw-in sealing port (102) and a conical inner side sealing boss (103); an outer straightening die (3) provided with an outer surface straightening support (301), an outer side screw-in threaded hole (302) coaxial with the inner side screw-in sealing port (102) and a conical outer side sealing groove (303); a screw-in type vacuum air exhaust pipe (5) connected to the outer side screw-in threaded hole (302) through a pipe screw-in thread (501) and provided with a vacuum air exhaust hole (502) inside; a straightening die locking screw (2) for locking the inner straightening die (1) and the outer straightening die (3); wherein the conical inner side sealing boss (103) and the conical outer side sealing groove (303) cooperate to form a vacuum sealing structure.

8. The vacuum hot straightening die for a double process multi-pass controlled oxidation processing of a non-deformable alloy sheet according to claim 7, characterized by The inner straightening die (1) and the outer straightening die (3) are made of vermicular graphite cast iron or medium silicon molybdenum nodular cast iron.

9. The vacuum hot straightening die for a dual process multi-pass controlled oxidation processing of a non-deformable alloy sheet according to claim 7, characterized by, The screw-in type vacuum air exhaust pipe (5) is made of high-temperature nickel-based alloy, and the pipe screw-in thread (501) is in vacuum sealing cooperation with the outer side screw-in threaded hole (302).

10. The vacuum hot straightening die for a double process multi-pass controlled oxidation processing of a non-deformable alloy sheet according to claim 7, characterized by The inner surface orthopedic support (101) and the outer surface orthopedic support (301) are shaped according to the shape of the corresponding pass part and are corrected by thermal expansion simulation.

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