Aluminum-lithium alloy thin-walled part forming method and device

Abstract

The present invention belongs to the technical field of sheet metal forming, and specifically relates to a method and device for forming thin-walled aluminum-lithium alloy parts. The forming method comprises the following steps: pre-treating the aluminum-lithium alloy sheet metal, performing a solid solution quenching treatment on the sheet metal at a temperature not higher than a preset temperature K1; performing a solid solution quenching treatment on the sheet metal using a super-low temperature forming device, wherein the forming temperature during the super-low temperature forming treatment is lower than ‑180°C, to obtain a thin-walled part preform; performing a secondary solid solution quenching on the thin-walled part preform at a temperature not higher than a preset temperature K1; performing a stress aging treatment on the thin-walled part preform after the secondary solid solution quenching at a preset temperature K2 using a stress aging device, and then demolding to obtain an aluminum-lithium alloy thin-walled part. A super-low temperature forming device and a stress aging device for use in the forming method are also provided. The above method and device can realize high-precision and high-performance forming and manufacturing of complex aluminum-lithium alloy thin-walled parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of sheet metal forming, and in particular relates to a method and device for forming thin-walled aluminum-lithium alloy parts. Background Art

[0002] Thin-walled components account for over 50% of an aircraft's structural weight, and new forming and manufacturing technologies have long been a key area of ​​research for aircraft structures. Lightweight, high-precision manufacturing of thin-walled components is key to reducing aircraft weight and improving their efficiency, enabling lower fuel consumption, longer range, and significant economic benefits. Aircraft thin-walled components are subject to complex aerodynamic loads during flight, and their shapes tend to be more integrated, complex, and large-scale, with more prominent features such as non-uniform wall thickness and variable curvature. These components place high demands on forming accuracy, reliability, and service life, posing significant challenges to forming and manufacturing.

[0003] Compared to traditional aluminum alloys, aluminum-lithium alloys not only offer the advantages of low density, high elastic modulus, high specific strength, and high specific stiffness, but also possess a low fatigue crack growth rate and excellent high- and low-temperature performance. Using this material in place of traditional aluminum alloys can reduce component weight by 10-20% and increase component stiffness by 10-20%, making it a key development direction for thin-walled component material selection.

[0004] However, aluminum-lithium alloy sheet metal has poor formability, and traditional forming processes such as deep drawing and stamping are prone to cracking, making it difficult to produce complex aluminum-lithium alloy thin-walled parts. Recent studies have found that the plasticity of quenched aluminum-lithium alloy can be significantly improved under extreme low-temperature conditions, with its elongation increasing by 30-60% compared to that at room temperature.

[0005] During the previous research and development process, the applicant invented a low-temperature forming device and method for complex curved thin-walled components of aluminum-lithium alloy (CN110722043A). The forming device includes a cryogenic box, a control cabinet, a liquid nitrogen tank, a solenoid valve group, a punch, a die, a temperature detector, and a pressure device. The punch, die, temperature detector, and pressure device are arranged in the cryogenic box. The solenoid valve group is provided on the pipeline connecting the liquid nitrogen tank and the cryogenic box. The solenoid valve group and temperature detector are both electrically connected to the control cabinet. The pressure device is configured to press the sheet between the punch and die. The cryogenic box is provided with a door. However, during the heat treatment process, due to the low stiffness of the thin-walled parts, large warping deformation is easily generated. This has become a difficult problem that needs to be solved urgently to restrict the high-precision forming and manufacturing of aluminum-lithium alloy thin-walled parts. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a method and device for forming aluminum-lithium alloy thin-walled parts that can achieve high-precision and high-performance forming and manufacturing of complex aluminum-lithium alloy thin-walled parts.

[0007] In order to solve the above technical problems, the technical solution proposed by the present invention is: a method for forming an aluminum-lithium alloy thin-walled part, comprising the steps of:

[0008] Pre-treat the aluminum-lithium alloy plate and perform a solid solution quenching treatment on the plate at a temperature not higher than the preset temperature K1;

[0009] The sheet metal is subjected to ultra-low temperature forming treatment by adopting an ultra-low temperature forming device to obtain a thin-walled preform;

[0010] Performing secondary solution quenching on the thin-walled preform at a temperature not higher than a preset temperature K1;

[0011] The thin-walled part preform after secondary solution quenching is subjected to stress aging treatment at a preset temperature K2 using a stress aging device and then demolded to obtain an aluminum-lithium alloy thin-walled part.

[0012] In one embodiment, the preset temperature K1 is 515° C.±3° C., the heating and holding time of the first solution quenching is not less than 1 hour, and the heating and holding time of the second solution quenching is not less than 1 hour.

[0013] In one embodiment, in a single solution quenching treatment, after heating and holding, the plate is transferred to a cooling medium for quenching, and the transfer process takes less than 10 seconds.

[0014] In one embodiment, the forming temperature in the ultra-low temperature forming process is lower than -180°C, and the ultra-low temperature forming process is completed within 30 minutes.

[0015] In one embodiment, the preset temperature K2 is 165° C.±3° C., and the stress aging treatment time is not less than 40 hours.

[0016] In one embodiment, during the primary solution hardening treatment and the secondary solution hardening treatment, the distance between the edge of the plate and the heating furnace wall is 100 mm to 120 mm, and the distance between the edge of the plate and the furnace door is 250 mm to 300 mm.

[0017] In one embodiment, the ultra-low temperature forming process of the sheet material using the ultra-low temperature forming device includes:

[0018] Fix the upper and lower templates of the ultra-low temperature forming device to the working platform of the press, connect the liquid nitrogen tank to the liquid nitrogen nozzle, and debug the cooling device;

[0019] Mark the die and place the sheet in the corresponding position, spraying low-temperature lubricant on the surface of the sheet;

[0020] Open the valve of the liquid nitrogen tank, use the liquid nitrogen nozzle to transport liquid nitrogen to each nozzle, and then cool it to the predetermined temperature and keep it warm;

[0021] Start the press, and the downward pressure of the press drives the blank holder to press down. When the pressure of the blank holder reaches the preset value, the pressure of the blank holder is maintained unchanged. The press continues to press down until the plate is stretched to the predetermined size. Close the liquid nitrogen valve, lift the blank holder, and remove the formed part after demoulding to obtain a thin-walled prefabricated blank.

[0022] In one embodiment, the thin-walled part is a multi-step ultra-deep thin-walled part.

[0023] Based on the same inventive concept, a cryogenic forming device for the above-mentioned aluminum-lithium alloy thin-walled part forming method is also provided, the cryogenic forming device comprising:

[0024] The double-action press comprises an upper die plate mounted on the upper working platform of the press and a lower die plate mounted on the lower working platform of the press, a punch fixed to the bottom of the upper die plate, and a die fixed to the top of the lower die plate, a blank holder is provided between the punch and the die, and positioning pins are provided between the upper die plate and the punch, and between the lower die plate and the die; guide pins and guide sleeves are inserted into the upper and lower die plates for use in conjunction with each other;

[0025] The cooling device includes a liquid nitrogen tank, a solenoid valve group, a control cabinet, a liquid nitrogen nozzle and a nozzle, and the liquid nitrogen is transported to each nozzle through the liquid nitrogen nozzle.

[0026] Based on the same inventive concept, a stress aging device for the above-mentioned aluminum-lithium alloy thin-walled part forming method is also provided, characterized in that the stress aging device includes a stress aging die and a stress aging punch used in conjunction with each other, at least one of the stress aging die and the stress aging punch is provided with a fixing plate and a lifting lug, and the fixing plate is provided with a screw. A device for forming aluminum-lithium alloy thin-walled parts,

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention can realize the forming and manufacturing of complex aluminum-lithium alloy thin-walled parts through low-temperature forming, and the use of low temperature greatly improves the shaping of aluminum-lithium alloy plates, makes deformation more uniform, and reduces the cracking and wrinkling of components during the forming process. Through subsequent stress aging, high-density dislocations in the forming process promote stress relaxation and dense precipitation of complex aluminum-lithium alloy thin-walled parts, and utilizes the stress relaxation phenomenon and aging strengthening characteristics of metal materials to improve the forming accuracy and mechanical properties of complex aluminum-lithium alloy thin-walled parts. In addition, the uniform and dense dislocations produced by low-temperature forming contribute to stress relaxation and aging strengthening, further improving the forming accuracy and mechanical properties of components, and realizing high-precision and high-performance forming and manufacturing of complex aluminum-lithium alloy thin-walled parts, providing support for aircraft structure weight reduction. The device of the present application is simple, and a double-acting press and a forming device can be used. Low-temperature forming can be achieved by simply arranging liquid nitrogen pipelines. It is low-cost, easy to implement, and easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Schematic diagram of the structure of a cryogenic forming device according to one embodiment;

[0030] Figure 2 Schematic diagram of the structure of a cryogenic forming device according to one embodiment;

[0031] Figure 3 Schematic diagram of the structure of a stress aging device according to one embodiment;

[0032] Figure 4 A schematic diagram of a forming method for thin-walled aluminum-lithium alloy parts is shown;

[0033] Figure 5 Schematic diagram of coordinate deviation between a thin-walled part after secondary solution quenching and stress aging treatment according to the present application and a standard thin-walled part.

[0034] Figure numerals: 1. Upper template; 2. Upper punch; 3. First hexagon socket screw; 4. Lower punch; 5. Guide sleeve; 6. Second hexagon socket screw; 7. Boss; 8. Guide column; 9. Plate; 10. Third hexagon socket screw; 11. Fourth hexagon socket screw; 12. Lower template; 13. First lifting ear; 14. Liquid nitrogen nozzle; 15. Locating pin; 16. Die; 17. Locating pin; 18. Pressure ring; 19. Liquid nitrogen tank; 20. Solenoid valve group; 21. Control cabinet; 22. Screw; 23. Fixed plate; 24. Second lifting ear; 25. Multi-step ultra-deep thin-walled part; 26. Stress aging die; 27. Stress aging punch. DETAILED DESCRIPTION

[0035] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0038] See also Figure 1-5 , a method for forming an aluminum-lithium alloy thin-walled part in one embodiment, comprising the steps of:

[0039] S10. Pre-treat the aluminum-lithium alloy plate and perform a solid solution quenching treatment on the plate at a temperature not higher than a preset temperature K1.

[0040] Specifically, step S10 includes the steps of:

[0041] S11: Provide aluminum-lithium alloy plates, process them according to size requirements, and remove sharp edges and burrs from the processed aluminum-lithium alloy plates.

[0042] Specifically, the original plate in this embodiment is 2060-T8E30, and laser cutting is used for processing, so that plates that meet the size and precision requirements can be obtained more quickly and accurately, and the processed plates are cleared of sharp edges and burrs. All dimensions in this embodiment are examples for the convenience of explanation and should not be understood as limitations of the present invention.

[0043] S12: Heat the aluminum-lithium alloy plate to a preset temperature K1 and maintain the temperature for no less than a preset time of 1 hour; wherein the preset temperature K1 is 515°C ± 3°C. Preferably, to ensure uniform heating during the heating process, the plate is placed approximately 100 mm to 120 mm from the furnace wall and approximately 250 mm to 300 mm from the furnace door. The plate is heated to 515°C and then maintained at this temperature for 1 hour.

[0044] S13: Quench the heated aluminum-lithium alloy plate in a cooling medium for a transfer time less than T2. ​​After the holding period, quench the plate for a transfer time of 10 seconds. Wipe the surface of the plate clean of moisture. By controlling the transfer time, natural aging can be prevented from degrading component performance.

[0045] In one embodiment, the thin-walled part is a multi-step ultra-deep thin-walled part. The processing and forming precision of multi-step ultra-deep thin-walled parts is higher, and the method and device of the present application can be effectively applied to the processing and forming of multi-step ultra-deep thin-walled parts.

[0046] S20, performing ultra-low temperature forming treatment on the plate using an ultra-low temperature forming device to obtain a thin-walled preform.

[0047] Among them, ultra-low temperature means that the temperature is lower than -180℃ during the forming process.

[0048] Step S20 specifically includes the following steps:

[0049] S21: Fix the upper and lower templates of the ultra-low temperature forming device to the working platform of the press, connect the liquid nitrogen tank to the liquid nitrogen nozzle, and debug the cooling device;

[0050] S22: Fix the low-temperature thermocouple on the surface of the plate, draw a line on the die and place the plate in the designated area, then spray low-temperature lubricant on both surfaces of the plate;

[0051] S23: Open the valve of the liquid nitrogen tank to start cooling. The solenoid valve group controls the liquid nitrogen tank to transport liquid nitrogen to each nozzle through the pipeline. After cooling until the temperature of the plate measured by the thermocouple reaches the predetermined value, keep it warm for a period of time.

[0052] S24: Start the press, the blank holder working platform of the press drives the blank holder ring downward, the blank holder ring contacts the sheet first, and as the upper template continues to press downward, the pressure of the blank holder ring on the sheet continues to increase. When the pressure of the blank holder ring reaches a predetermined value, the blank holder ring pressure is maintained at a fixed value, and the punch working platform starts to press downward, driving the punch to press downward. The press continues to press until the sheet is stretched to a predetermined size. After reaching the predetermined size, the liquid nitrogen valve is closed, the blank holder ring is lifted, and then the punch is lifted to remove the formed part.

[0053] S25: Close the valve of the liquid nitrogen tank, reset the press, take out the workpiece, and obtain the formed thin-walled part.

[0054] Preferably, the quenched sheet should be low-temperature formed within 30 minutes.

[0055] By controlling the forming time, the mechanical properties of the component can be prevented from being reduced.

[0056] S30, performing secondary solution quenching on the thin-walled part preform at a temperature not higher than a preset temperature K1;

[0057] Specifically, step S30 includes the following steps:

[0058] S31: heating the formed thin-walled preform to a preset temperature K1 and keeping the temperature for no less than a preset time T1;

[0059] The preset temperature K1 is 515℃±3℃, T1 is 1h. In order to ensure the uniformity of heating during the heating process, the thin-walled preform is placed about 100mm~120mm away from the furnace wall and about 250~300mm away from the furnace door. The plate is heated to 515℃ and then kept warm for 1h.

[0060] S32: quenching the heated aluminum-lithium alloy plate in a cooling medium, wherein the transfer time is less than T2;

[0061] After the insulation is completed, the plate is quenched, and the transfer time T2 is 10s. After the quenching is completed, the moisture on the surface of the preform is wiped clean and stress aging is carried out within 30 minutes. By controlling the forming time, the mechanical properties of the component are prevented from being reduced.

[0062] S40, using a stress aging device to perform stress aging treatment on the thin-walled part preform after secondary solution quenching at a preset temperature K2, and then demolding to obtain an aluminum-lithium alloy thin-walled part.

[0063] S41: placing the thin-walled preform after secondary solution quenching between a stress aging punch and a stress aging die, heating them together to a preset temperature K2, and keeping the temperature for not less than a preset time T2;

[0064] Specifically, the preset temperature K2 is 165°C ± 3°C, and the preset time T2 is 40 hours. To ensure uniform heating during the heating process, the stress aging device is placed approximately 100mm to 120mm from the furnace wall and approximately 250mm to 300mm from the furnace door. The stress aging device and the thin-walled preform are heated to 165°C and then kept at this temperature for 40 hours.

[0065] S42: Demolding multi-step ultra-deep thin-walled parts after stress aging.

[0066] The manufacturing method of multi-step ultra-deep thin-walled parts of aluminum-lithium alloy aircraft cabin doors in one embodiment has higher forming capability than the traditional deep drawing process, better performance and precision after forming, and can reduce the scrap rate. The thin-walled parts obtained by low-temperature forming and stress aging process have better mechanical properties and shape accuracy. The performance of multi-step ultra-deep thin-walled parts at different sampling positions (6 sampling positions) are shown in the following table. According to the table below, the multi-step ultra-deep thin-walled parts obtained by the method and device of the present application have high tensile strength, high yield strength, good elongation, and the relevant performance of each position is well balanced. And according to Figure 5 From the schematic diagram of coordinate deviation between thin-walled parts after secondary solution quenching and stress aging treatment according to the present application and standard thin-walled parts, it can be seen that after stress aging treatment, the coordinate deviation between thin-walled parts and standard thin-walled parts is significantly reduced. Therefore, it can be seen that the geometric accuracy of thin-walled parts can be improved after secondary solution quenching and stress aging treatment according to the present application.

[0067] Table 1 Performance of multi-step ultra-deep thin-walled parts at different sampling positions

[0068]

[0069] Based on the same inventive concept, a cryogenic forming apparatus for the above-described aluminum-lithium alloy thin-walled part forming method is also provided. The cryogenic forming apparatus comprises a double-action press, comprising an upper die plate 1 mounted on the upper working platform of the press, a lower die plate 12 mounted on the lower working platform of the press, an upper punch 2 and a lower punch 4 fixed to the bottom of the upper die plate, and a die 16 fixed to the top of the lower die plate 12. A blank holder 18 is provided between the punch 2 and the die 16, and positioning pins 17 are provided between the upper die plate 1 and the punch 2, and between the lower die plate 12 and the die 16. Guide posts 8 and guide sleeves 5 are inserted into the upper and lower die plates 1 and 12 for use therewith. The upper punch 2 is connected to the upper die plate 1 by a first hexagon socket head screw 3, and the upper punch 2 and the lower punch 4 are connected by a second hexagon socket head screw 6. The upper punch 2 and the lower punch 4 are mounted to the upper die plate 1 by a third hexagon socket head screw 10. The die 16 is mounted to the lower die plate 12 by a fourth hexagon socket head screw 11. The guide posts 8 and guide sleeves 5 provide precise positioning. The lower mold plate 12 is equipped with a first lifting lug 13 for hoisting. The upper punch 2, lower punch 4, and die 16 are all made of cryogenically resistant mold steel capable of operating under ultra-low temperature conditions. The cooling system includes a liquid nitrogen tank 19, a solenoid valve assembly 20, a control cabinet 21, a liquid nitrogen nozzle, and nozzles. Liquid nitrogen is delivered to each nozzle through the liquid nitrogen nozzle.

[0070] Based on the same inventive concept, a stress aging device for use in the aforementioned aluminum-lithium alloy thin-walled part forming method is also provided. The device comprises a stress aging die 26 and a stress aging punch 27, each of which is provided with a fixing plate 23 and a second lug 24. The fixing plate 23 is provided with a screw 22. The stress aging die 26 and the punch 27 are closed together using the preload force exerted by the screw 22 on the pressure plate 23, thereby achieving stress aging treatment. The device has a simple structure and is easy to use.

[0071] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention can realize the forming and manufacturing of complex aluminum-lithium alloy thin-walled parts through low-temperature forming, and the use of low temperature can greatly improve the shaping of aluminum-lithium alloy plates, make deformation more uniform, and reduce the cracking and wrinkling of components during the forming process. Through subsequent stress aging, high-density dislocations in the forming process promote stress relaxation and dense precipitation of complex aluminum-lithium alloy thin-walled parts, and utilize the stress relaxation phenomenon and aging strengthening characteristics of metal materials to improve the forming accuracy and mechanical properties of complex aluminum-lithium alloy thin-walled parts. In addition, the uniform and dense dislocations produced by low-temperature forming are conducive to stress relaxation and aging strengthening, further improving the forming accuracy and mechanical properties of components, realizing high-precision and high-performance forming and manufacturing of complex aluminum-lithium alloy thin-walled parts, and providing support for aircraft structure weight reduction. The device of the present application is simple, and can utilize a double-acting press and a forming device, combined with a simple liquid nitrogen pipeline layout to achieve low-temperature forming. It has low cost, is easy to implement, and is easy to realize industrial production.

Claims

1. A method for forming an aluminum-lithium alloy thin-walled part, characterized in that: Including steps: Pre-treat the aluminum-lithium alloy plate and perform a solid solution quenching treatment on the plate at a temperature not higher than the preset temperature K1; The sheet is subjected to ultra-low temperature forming treatment using an ultra-low temperature forming device, wherein the forming temperature is lower than -180°C, to obtain a thin-walled preform; Performing secondary solution quenching on the thin-walled preform at a temperature not higher than a preset temperature K1; The thin-walled preform after secondary solution quenching is subjected to stress aging treatment at a preset temperature K2 by using a stress aging device, and then demoulded to obtain an aluminum-lithium alloy thin-walled part; The preset temperature K1 is 515°C ± 3°C, the heating and holding time for the first solid solution quenching is not less than 1 hour; the heating and holding time for the second solid solution quenching is not less than 1 hour; In a single solution quenching treatment, after heating and holding, the plate is transferred to a cooling medium for quenching, and the transfer process takes less than 10 seconds; Ultra-low temperature forming process is completed within 30 minutes; The preset temperature K2 is 165°C ± 3°C, and the stress aging treatment time is not less than 40 hours; In the primary solution hardening treatment and the secondary solution hardening treatment, the distance between the edge of the plate and the heating furnace wall is 100 mm to 120 mm, and the distance from the edge of the plate to the furnace door is 250 mm to 300 mm.

2. The method for forming an aluminum-lithium alloy thin-walled part according to claim 1, wherein: The ultra-low temperature forming process of the sheet material using an ultra-low temperature forming device includes: Fix the upper and lower templates of the ultra-low temperature forming device to the working platform of the press, connect the liquid nitrogen tank to the liquid nitrogen nozzle, and debug the cooling device; Mark the die and place the sheet in the corresponding position, spraying low-temperature lubricant on the surface of the sheet; Open the valve of the liquid nitrogen tank, use the liquid nitrogen nozzle to transport liquid nitrogen to each nozzle, and then cool it to the predetermined temperature and keep it warm; Start the press, and the downward pressure of the press drives the blank holder to press down. When the pressure of the blank holder reaches the preset value, the pressure of the blank holder is maintained unchanged. The press continues to press down until the plate is stretched to the predetermined size. Close the liquid nitrogen valve, lift the blank holder, and remove the formed part after demoulding to obtain a thin-walled prefabricated blank.

3. The method for forming an aluminum-lithium alloy thin-walled part according to claim 1, wherein: The thin-walled part is a multi-step ultra-deep thin-walled part.

4. An ultra-low temperature forming device for the aluminum-lithium alloy thin-walled part forming method according to any one of claims 1 to 3, characterized in that: The ultra-low temperature forming device comprises: The double-action press comprises an upper die plate mounted on the upper working platform of the press and a lower die plate mounted on the lower working platform of the press, a punch fixed to the bottom of the upper die plate, and a die fixed to the top of the lower die plate, a blank holder is provided between the punch and the die, and positioning pins are provided between the upper die plate and the punch, and between the lower die plate and the die; guide pins and guide sleeves are inserted into the upper and lower die plates for use in conjunction with each other; The cooling device includes a liquid nitrogen tank, a solenoid valve group, a control cabinet, a liquid nitrogen nozzle and a nozzle, and the liquid nitrogen is transported to each nozzle through the liquid nitrogen nozzle.

5. A stress aging device for the aluminum-lithium alloy thin-walled part forming method according to any one of claims 1 to 3, characterized in that: The stress aging device comprises a stress aging die and a stress aging punch that are used in conjunction with each other. At least one of the stress aging die and the stress aging punch is provided with a fixing plate and a lifting lug, and the fixing plate is provided with a screw.

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