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

Abstract

The invention belongs to the technical field of plate forming, and particularly relates to an aluminum-lithium alloy thin-wall part forming method and device. The forming method comprises the steps that an aluminum-lithium alloy plate is pretreated, and primary solid solution quenching treatment is conducted on the plate at the temperature not higher than the preset temperature K1; an ultralow-temperature forming device is adopted for conducting ultralow-temperature forming treatment on the plate, the forming temperature in the ultralow-temperature forming treatment is lower than-180 DEG C, and a thin-wall part preformed blank is obtained; carrying out secondary solid solution quenching on the thin-wall part preformed blank at the temperature not higher than the preset temperature K1; and a stress aging device is adopted for conducting stress aging treatment on the thin-wall part preformed blank obtained after secondary solid solution quenching at the preset temperature K2, demolding is conducted, and the aluminum-lithium alloy thin-wall part is obtained. The invention further provides an ultralow-temperature forming device and a stress aging device used in the forming method. By means of the method and device, high-precision and high-performance forming manufacturing of the complex aluminum-lithium alloy thin-wall part can be achieved.

Description

Technical Field

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

[0002] Thin-walled components account for more than 50% of the weight of aircraft structures, and new forming and manufacturing technologies have always been the focus of research on aircraft structural parts. Lightweight and high-precision manufacturing of thin-walled components is the key to reducing the weight and improving the efficiency of aircraft structures, which can achieve lower fuel consumption and longer range, bringing significant economic benefits. Aircraft thin-walled components are subject to complex aerodynamic loads during flight, and their shapes tend to be integrated, complex, and large-scale. Characteristics such as non-uniform wall thickness and variable curvature are more prominent, which puts forward high requirements on forming accuracy, reliability, and service life, and poses severe challenges to forming and manufacturing.

[0003] Compared with traditional aluminum alloys, aluminum-lithium alloys not only have the advantages of low density, high elastic modulus, high specific strength and high specific stiffness, but also have the characteristics of low fatigue crack growth rate, good high temperature and low temperature performance, etc. Using this material to replace traditional aluminum alloys can reduce the weight of parts by 10~20% and increase the stiffness by 10~20%, which is an important development direction for the selection of materials for thin-walled components.

[0004] However, the forming ability of aluminum-lithium alloy sheets is poor, and the traditional forming and manufacturing processes such as deep drawing and stamping are prone to cracking, making it difficult to prepare complex aluminum-lithium alloy thin-walled parts. In recent years, studies have found that the plasticity of quenched aluminum-lithium alloys can be significantly improved under low temperature extreme conditions, and its elongation can be increased by 30~60% compared with the elongation under room temperature.

[0005] In 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), in which 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, and the pipeline connecting the liquid nitrogen tank and the cryogenic box is provided with a solenoid valve group. The solenoid valve group and the temperature detector are electrically connected to the control cabinet. The pressure device is set to press the plate between the punch and the die, and the cryogenic box is provided with a box door. However, during the heat treatment process, due to the low stiffness of thin-walled parts, large warping deformation is easily generated, which has become a 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: Pre-treating the aluminum-lithium alloy plate, and performing a solid solution quenching treatment on the plate at a temperature not higher than a preset temperature K1; The sheet is subjected to ultra-low temperature forming treatment by using an ultra-low temperature forming device 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 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.

[0008] In one embodiment, the preset temperature K1 is 515°C ± 3°C, the heating and insulation time of the first solution quenching is not less than 1 hour, and the heating and insulation time of the second solution quenching is not less than 1 hour.

[0009] In one embodiment, in a solution quenching treatment, after heating and heat preservation, the plate is transferred to a cooling medium for quenching, and the transfer process time is less than 10 seconds.

[0010] 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.

[0011] In one embodiment, the preset temperature K2 is 165°C±3°C, and the stress aging treatment time is not less than 40h.

[0012] In one embodiment, 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 furnace door is 250 mm to 300 mm.

[0013] In one embodiment, the ultra-low temperature forming process of the sheet material using the 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, spray low-temperature lubricant on the surface of the sheet; Open the valve of the liquid nitrogen tank, use the liquid nitrogen nozzle to transport the liquid nitrogen to each nozzle, and perform low-temperature insulation after cooling the temperature to the predetermined value; Start the press, and the downward pressure of the press drives the blank holder ring to press down. When the pressure of the blank holder ring reaches the preset pressure value, the pressure of the blank holder ring is maintained unchanged. The press continues to press down until the plate is stretched to the preset size, close the liquid nitrogen valve, lift the blank holder ring, and take out the formed part after demolding to obtain a thin-walled preform.

[0014] In one embodiment, the thin-walled part is a multi-step ultra-deep thin-walled part.

[0015] Based on the same inventive concept, there is also provided an ultra-low temperature forming device for the aluminum-lithium alloy thin-walled part forming method as described above, the ultra-low temperature forming device comprising: The double-action press comprises an upper mold plate installed on the upper working platform of the press and a lower mold plate installed on the lower working platform of the press, a punch fixed on the bottom of the upper mold plate, and a die fixed on the top of the lower mold plate, a blank holder ring is arranged between the punch and the die, and positioning pins are arranged between the upper mold plate and the punch, and between the lower mold plate and the die; guide pillars and guide sleeves for matching use are inserted on the upper mold plate and the lower mold plate; The cooling device comprises a liquid nitrogen tank, a solenoid valve group, a control cabinet, a liquid nitrogen nozzle and a nozzle, and liquid nitrogen is transported to each nozzle through the liquid nitrogen nozzle.

[0016] 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 comprises 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 ear, and a screw is provided on the fixing plate. A device for forming aluminum-lithium alloy thin-walled parts, 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, reduce the cracking and wrinkling of components during the forming process, and promote stress relaxation and dense precipitation of complex aluminum-lithium alloy thin-walled parts through subsequent stress aging. The stress relaxation phenomenon and aging strengthening characteristics of metal materials are used 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 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

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0018] Figure 1This is a schematic structural diagram of an ultra-low temperature forming device according to one embodiment; Figure 2 This is a schematic structural diagram of an ultra-low temperature forming device according to one embodiment; Figure 3 It is a schematic structural diagram of a stress aging device according to one embodiment; Figure 4 A schematic diagram of a forming method for an aluminum-lithium alloy thin-walled part; 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.

[0019] 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. fixing plate; 24. second lifting ear; 25. multi-step ultra-deep thin-walled parts; 26. stress aging die; 27. stress aging punch. DETAILED DESCRIPTION

[0020] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional 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.

[0022] 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.

[0023] See also Figure 1-5 , a method for forming an aluminum-lithium alloy thin-walled part in one embodiment, comprising the steps of: S10, pre-treating the aluminum-lithium alloy plate, and performing a solid solution quenching treatment on the plate at a temperature not higher than a preset temperature K1.

[0024] Specifically, step S10 includes the steps of: 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.

[0025] 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 free of sharp edges and burrs. All dimensions in this embodiment are examples for the convenience of explanation and are not to be construed as limitations of the present invention.

[0026] S12: Heat the aluminum-lithium alloy plate to a preset temperature K1 and keep it warm for no less than a preset time of 1 hour; wherein the preset temperature K1 is 515°C±3°C. Preferably, in order to ensure uniform heating during the heating process, the plate is placed about 100mm~120mm away from the furnace wall and about 250~300mm away from the furnace door, and the plate is heated to 515°C and kept warm for 1 hour.

[0027] S13: Quench the heated aluminum-lithium alloy plate in a cooling medium, and the transfer time is less than T2. ​​After the insulation is completed, the plate is quenched, and the transfer time T2 is 10s. After the quenching is completed, wipe off the moisture on the surface of the plate. By controlling the transfer time, natural aging is prevented from reducing the performance of the component.

[0028] 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.

[0029] S20, using an ultra-low temperature forming device to perform ultra-low temperature forming treatment on the plate to obtain a thin-walled preform.

[0030] Among them, ultra-low temperature means that the temperature is lower than -180℃ during the forming process.

[0031] Step S20 specifically includes the following steps: S21: Fix the upper template and the lower template 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; 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, and then spray the low-temperature lubricant on both surfaces of the plate; 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 a predetermined value, keep it warm for a period of time; S24: Start the press, the press working platform of the press drives the press ring downward, the press ring contacts the sheet first, and as the upper mold plate continues to press downward, the pressure of the press ring on the sheet increases continuously. When the pressure of the press ring reaches a predetermined value, the pressure of the press ring is maintained unchanged, the punch working platform starts to press downward, drives the punch downward, and the press continues to press until the sheet is stretched to a predetermined size. When the predetermined size is reached, the liquid nitrogen valve is closed, the press ring is lifted, and then the punch is lifted to take out the formed part; S25: Close the valve of the liquid nitrogen tank, reset the press, take out the workpiece, and obtain the formed thin-walled part.

[0032] Preferably, the quenched sheet should be low temperature formed within 30 minutes.

[0033] By controlling the forming time, the mechanical properties of the component can be prevented from being reduced.

[0034] S30, performing secondary solution quenching on the thin-walled preform at a temperature not higher than a preset temperature K1; Specifically, step S30 includes the following steps: S31: heating the formed thin-walled preform to a preset temperature K1 and keeping the temperature for no less than a preset time T1; 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 kept warm for 1h.

[0035] S32: quenching the heated aluminum-lithium alloy plate in a cooling medium, wherein the transfer time is less than T2; After the insulation is completed, the plate is quenched, and the transfer time T2 is 10s. After the quenching, 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.

[0036] 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.

[0037] 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; Specifically, the preset temperature K2 is 165°C ± 3°C, and the preset time T2 is 40h. In order to ensure the uniformity of heating during the heating process, the stress aging device is placed about 100mm~120mm away from the furnace wall and about 250~300mm away from the furnace door. The stress aging device and the thin-walled preform are heated to 165°C and then kept warm for 40h.

[0038] S42: Demolding multi-step ultra-deep thin-walled parts after stress aging.

[0039] Compared with the traditional deep drawing process, the method for manufacturing multi-step ultra-deep thin-walled parts of an aluminum-lithium alloy aircraft cabin door in one embodiment has a higher forming ability, 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 the thin-walled parts after secondary solid solution quenching and stress aging treatment according to the present application and the standard thin-walled parts, it can be seen that after stress aging treatment, the coordinate deviation between the thin-walled parts and the standard thin-walled parts is significantly reduced. Therefore, it can be seen that the geometric accuracy of the thin-walled parts can be improved after secondary solid solution quenching and stress aging treatment according to the present application.

[0040] Table 1 Performance table of multi-step ultra-deep thin-walled parts at different sampling positions

[0041] Based on the same inventive concept, a super low temperature forming device for the above-mentioned aluminum-lithium alloy thin-walled part forming method is also provided, the super low temperature forming device comprising: a double-acting press, comprising an upper die plate 1 installed on the upper working platform of the press and a lower die plate 12 installed on the lower working platform of the press, a punch upper 2 fixed to the bottom of the upper die plate, a punch lower 4, 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; the upper die plate 1 and the lower die plate 12 are plugged with guide pins 8 and guide sleeves 5 for use; wherein the punch upper 2 is connected to the upper die plate 1 by a first hexagon socket screw 3, the punch upper 2 and the punch lower 4 are connected by a second hexagon socket screw 6, and are installed on the upper die plate 1 by a third hexagon socket screw 10. The die 16 is installed on the lower die plate 12 by a fourth hexagon socket screw 11, wherein the guide pins 8 and the guide sleeves 5 play a role in precise positioning. At the same time, the lower mold plate 12 is provided with a first lifting lug 13 for lifting, and the upper punch 2, the lower punch 4 and the concave mold 16 are all made of low-temperature resistant mold steel that can work under ultra-low temperature conditions. The cooling device includes a liquid nitrogen tank 19, a solenoid valve group 20, a control cabinet 21, a liquid nitrogen nozzle and a nozzle, and liquid nitrogen is transported to each nozzle through the liquid nitrogen nozzle.

[0042] Based on the same inventive concept, a stress aging device for the aluminum-lithium alloy thin-walled part forming method as described above is also provided, the stress aging device comprises a stress aging die 26 and a stress aging punch 27 used in conjunction with each other, at least one of the stress aging die 26 and the stress aging punch 27 is provided with a fixing plate 23 and a second lug 24, and the fixing plate 23 is provided with a screw 22. The stress aging die 26 and the punch 27 are molded together by the pre-tightening force of the screw 22 acting on the pressure plate 23, so that stress aging treatment can be achieved. The structure is simple and easy to use.

[0043] 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, reduce the cracking and wrinkling of components during the forming process, and promote stress relaxation and dense precipitation of complex aluminum-lithium alloy thin-walled parts through subsequent stress aging. The stress relaxation phenomenon and aging strengthening characteristics of metal materials are used 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 use a double-acting press and a forming device, combined with a simple liquid nitrogen pipeline layout to achieve low-temperature forming, with low cost, convenient implementation, and easy to realize industrial production.

Claims

1. A method for forming an aluminum-lithium alloy thin-walled part, characterized in that: Includes steps: Pre-treating the aluminum-lithium alloy plate, and performing a solid solution quenching treatment on the plate at a temperature not higher than a preset temperature K1; The sheet is subjected to ultra-low temperature forming treatment by using an ultra-low temperature forming device, wherein the forming temperature during the ultra-low temperature forming treatment is lower than -180°C, and a thin-walled preform is obtained; Performing secondary solution quenching on the thin-walled preform at a temperature not higher than a preset temperature K1; 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.

2. The method for forming an aluminum-lithium alloy thin-walled part according to claim 1, characterized in that: The preset temperature K1 is 515°C ± 3°C, the heating and insulation time of the first solution quenching is not less than 1 hour, and the heating and insulation time of the second solution quenching is not less than 1 hour.

3. The method for forming an aluminum-lithium alloy thin-walled part according to claim 2, characterized in that: In a single solution quenching treatment, after heating and heat preservation, the plate is transferred to the cooling medium for quenching, and the transfer process time is less than 10s.

4. The method for forming an aluminum-lithium alloy thin-walled part according to claim 3, characterized in that: The ultra-low temperature forming process is completed within 30 minutes.

5. The aluminum-lithium alloy thin-walled part forming method according to claim 1, characterized in that: The preset temperature K2 is 165°C±3°C, and the stress aging treatment time is not less than 40h.

6. The method for forming an aluminum-lithium alloy thin-walled part according to claim 1, characterized in that: In the primary solution quenching treatment and the secondary solution quenching 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 furnace door is 250 mm to 300 mm.

7. The method for forming an aluminum-lithium alloy thin-walled part according to claim 1, characterized in that: The ultra-low temperature forming process of the sheet material using the 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, spray low-temperature lubricant on the surface of the sheet; Open the valve of the liquid nitrogen tank, use the liquid nitrogen nozzle to transport the liquid nitrogen to each nozzle, and perform low-temperature insulation after cooling the temperature to the predetermined value; Start the press, and the downward pressure of the press drives the blank holder ring to press down. When the pressure of the blank holder ring reaches the preset pressure value, the pressure of the blank holder ring is maintained unchanged. The press continues to press down until the plate is stretched to the preset size, close the liquid nitrogen valve, lift the blank holder ring, and take out the formed part after demolding to obtain a thin-walled preform.

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

9. An ultra-low temperature forming device for the aluminum-lithium alloy thin-walled part forming method according to any one of claims 1 to 8, characterized in that: The ultra-low temperature forming device comprises: The double-action press comprises an upper mold plate installed on the upper working platform of the press and a lower mold plate installed on the lower working platform of the press, a punch fixed on the bottom of the upper mold plate, and a die fixed on the top of the lower mold plate, a blank holder ring is arranged between the punch and the die, and positioning pins are arranged between the upper mold plate and the punch, and between the lower mold plate and the die; guide pillars and guide sleeves for matching use are inserted on the upper mold plate and the lower mold plate; The cooling device comprises a liquid nitrogen tank, a solenoid valve group, a control cabinet, a liquid nitrogen nozzle and a nozzle, and liquid nitrogen is transported to each nozzle through the liquid nitrogen nozzle.

10. A stress aging device for the aluminum-lithium alloy thin-walled part forming method according to any one of claims 1 to 8, characterized in that: The stress aging device comprises a stress aging die and a stress aging punch which are used together. At least one of the stress aging die and the stress aging punch is provided with a fixing plate and a lifting ear, and a screw is provided on the fixing plate.

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