A kind of deep cold progressive forming process of aluminum alloy

Abstract

The present invention discloses a deep cold progressive forming process for aluminum alloys, and adopts a deep cold progressive forming device to perform deep cold progressive forming on aluminum alloy plates. The process comprises the following steps: S1, a liquid nitrogen flow automatic control system supplies liquid nitrogen, and adjusts the temperature of the liquid nitrogen storage chamber to ‑160°C; S2, performing progressive forming on the aluminum alloy plate, wherein the angle between the progressive forming tool head and the aluminum alloy plate is less than 90°, and MoS2 powder is used as a lubricant in the forming process; S3, artificial aging is performed on the formed aluminum alloy formed parts, and the temperature is 185°C and the time is 120min. The present application optimizes the deep cold progressive forming process of 2219 aluminum alloy plates, and realizes deep cold conditions under a ‑160°C environment through precise control of the deep cold temperature, so that the aluminum alloy plates have excellent forming performance.

Description

Technical Field

[0001] The invention relates to the field of plastic forming processing of metal materials, in particular to a deep cold progressive forming process of an aluminum alloy. Background Art

[0002] Aluminum alloys play an important role in the aerospace and automotive industries due to their good comprehensive mechanical properties such as light weight and high specific strength. However, with the surge in demand for high-performance, high-quality thin-walled lightweight plate components, the plastic forming problem of aluminum alloy plate components with complex shapes has become more prominent. Traditional forming processes mainly include cold forming and hot forming. Due to the poor plasticity of aluminum alloy at room temperature, the cold forming process has a high scrap rate and poor product quality. The hot forming process can significantly improve the forming plasticity, but the severe oxidation of the workpiece at high temperature leads to poor surface quality, and the energy consumption of mold heating leads to high production costs; on the other hand, the hot forming process changes the microstructure of the material, causing the alloy strength to drop sharply, requiring additional heat treatment processes for regulation, and reducing production efficiency. In addition, hot-formed structural parts also have springback phenomenon, and dimensional accuracy cannot be guaranteed.

[0003] At present, cryogenic technology has been proven to be an effective method to improve the forming performance of aluminum alloy sheets. As a face-centered cubic (FCC) metal, aluminum alloy will not undergo brittle transformation at low temperatures, and the mechanical properties of the alloy will continue to improve as the temperature decreases. Domestic and foreign researchers call the phenomenon of simultaneous improvement of strength and plasticity of aluminum alloys at low temperatures the double-increase effect, and this effect is independent of the composition of aluminum alloy materials. At present, 2 series, 6 series, 7 series and other aluminum alloys have been confirmed to have a double-increase effect at low temperatures. Cryogenic forming process is a new type of aluminum alloy sheet processing technology. It uses the double-increase effect of aluminum alloys at low temperatures to overcome the defects of traditional forming processes and provide a solution for the forming of large-scale aluminum alloy integral structure thin-walled curved surface components. For example, the deep cold bulging technology that has been successfully developed has currently trial-produced a 2219 aluminum alloy 3m-class rocket integral box bottom sample under ultra-low temperature conditions. In addition, ultra-fine-grained aluminum alloy materials can also be prepared by using the ultra-low temperature double-increase effect to solve the difficulties in the preparation of high-performance aluminum alloy materials, such as deep cold rolling, deep cold extrusion and other processes.

[0004] Incremental forming is a flexible sheet metal forming process. Based on the idea of ​​layered manufacturing, it can realize dieless processing and has broad application prospects in the field of rapid sheet metal forming. However, for low-ductility materials, it is difficult to process complex parts using traditional sheet metal incremental forming processes, and the parts often break prematurely during the forming process. Therefore, developing a new incremental forming process to improve the sheet metal forming performance has become a focus of attention. At present, there is little research on deep cold incremental forming processes, and it is difficult to improve the sheet metal forming performance. According to the data, the unique local loading method of incremental forming causes severe friction between the tool and the forming surface. The deep cold incremental forming method of completely immersing the aluminum alloy sheet in liquid nitrogen makes all conventional lubricants ineffective, resulting in serious deterioration of the forming surface, cracks and premature rupture of the parts, and finally the sheet metal forming performance is reduced. Summary of the invention

[0005] The purpose of the present invention is to provide an aluminum alloy deep cold progressive forming process in view of the deficiencies in the prior art.

[0006] To achieve the above object, the present invention adopts the following scheme:

[0007] A deep cold progressive forming process for aluminum alloys, using a deep cold progressive forming device to perform deep cold progressive forming on an aluminum alloy sheet, the deep cold progressive forming device comprising a liquid nitrogen storage chamber, a fixed pressing plate, a liquid nitrogen flow automatic control system and a cold-keeping shell, wherein the fixed pressing plate presses the aluminum alloy sheet above the liquid nitrogen storage chamber, an exhaust hole is provided on the liquid nitrogen storage chamber to maintain a stable pressure in the liquid nitrogen storage chamber, the liquid nitrogen flow automatic control system can achieve accurate regulation of the cryogenic temperature and continuous supply of liquid nitrogen, the cold-keeping shell is arranged outside the liquid nitrogen storage chamber, when liquid nitrogen is supplied in the liquid nitrogen storage chamber, the cooling medium is in direct contact with the bottom of the aluminum alloy sheet; the process comprises the following steps:

[0008] S1, the liquid nitrogen flow automatic control system supplies liquid nitrogen and adjusts the temperature of the liquid nitrogen storage chamber to -160°C;

[0009] S2, performing incremental forming on the aluminum alloy sheet, wherein the angle between the incremental forming tool head and the aluminum alloy sheet is less than 90°, and MoS2 powder is used as a lubricant during the forming process;

[0010] S3. The formed aluminum alloy parts are artificially aged at a temperature of 185°C for 120 minutes.

[0011] Furthermore, the aluminum alloy grade is 2219, the cold-insulating outer shell material is polyurethane, and the aluminum alloy sheet is solution treated before incremental forming at a temperature of 535° C. for 30 min.

[0012] Furthermore, the liquid nitrogen flow automatic control system also includes a gas circulation device, which includes a bottom air supply device and a side air supply device. The bottom air supply device is arranged at the bottom of the liquid nitrogen storage chamber, and a flared portion 1 and a closed portion 1 are arranged in the side wall of the liquid nitrogen storage chamber. The closed portion extends to the bottom of the liquid nitrogen storage chamber, and then passes through the closed portion 2 on the outside to the flared portion 2. An exhaust hole is arranged on the top of the flared portion 2. The side air supply device is arranged in the closed portion 1. The bottom air supply device transports the liquid nitrogen transported by the liquid nitrogen transport pipeline to the bottom surface of the aluminum alloy plate, and the side air supply device guides the nitrogen and / or liquid nitrogen on the bottom surface of the aluminum alloy to diffuse to the surroundings.

[0013] Furthermore, a fluid rolling tool head is used for progressive forming, a lubricant supply device is arranged in front of the fluid rolling tool head, and a heating coil is arranged at the end of the fluid rolling tool head. In step S2, during the forming process, the lubricant supply device supplies lubricant powder in real time, and the heating coil heats in real time.

[0014] Furthermore, the liquid nitrogen flow automatic control system includes a self-pressurized liquid nitrogen container, an electromagnetic switch valve, a liquid nitrogen flow meter, an opening valve, a liquid nitrogen delivery pipeline, a temperature sensor, and a PLC control host, wherein the temperature sensor adopts a K-type thermocouple, which is connected to the edge of the upper surface of the aluminum alloy plate to monitor the temperature of the aluminum alloy plate in real time.

[0015] Furthermore, the control method of the liquid nitrogen flow automatic control system is to output pressurized liquid nitrogen from the pressurized liquid nitrogen container, the solenoid valve controls the opening and closing of the liquid nitrogen delivery pipeline, and the PLC control host controls the opening of the opening valve through feedback of the flow data collected by the flow meter and the temperature data collected by the temperature sensor. When the actual temperature is higher than the target temperature, the liquid nitrogen input flow rate is increased, and when the actual temperature is lower than the target temperature, the liquid nitrogen input flow rate is reduced, ultimately achieving accurate temperature control of the aluminum alloy plate.

[0016] The advantages of the present invention compared with the prior art are: the present application optimizes the deep cold progressive forming process of 2219 aluminum alloy plates, and through precise control of the deep cold temperature, achieves deep cold conditions under a -160°C environment, so that the aluminum alloy plates have excellent forming performance.

[0017] 1. Through continuous attempts, it was found that 2219 aluminum alloy sheet has excellent forming performance under -160°C environmental conditions. Moreover, the deep cold progressive forming device in this application can achieve the effect of single-sided contact of the aluminum alloy sheet with the cooling medium, avoiding the adverse effects of immersion deep cold conditions on progressive forming.

[0018] 2. In the present application, an inclined tool head is used for progressive forming, which can significantly improve the forming limit and reduce the influence of the tool head on the aluminum alloy plate during the forming process. When a fluid rolling tool head is used, a lubricant powder supply device is arranged in the front, and a heating coil is arranged at the end of the fluid rolling tool head, which can ensure that the working oil of the fluid rolling tool head operates normally in a low-temperature environment, and the liquid state is still maintained between the ball and the tool head, thereby avoiding the problem of obstruction of the tool head movement due to low-temperature solidification. In addition, during the heating process of the heating coil, the working oil flows out of the tool head and flows on the surface of the ball until it solidifies. The lubricant powder can adhere to the liquid working oil, thereby ensuring that the lubricant powder is always filled between the ball and the aluminum alloy plate, and the lubricating effect is fully exerted. Even if the working oil solidifies after leaving the tool head, the lubricant powder is still attached. Even if the solidified working oil falls off to the area to be processed, it will not cause pure solid working oil to hinder the rolling process, thereby ensuring the surface quality of the progressively formed workpiece.

[0019] 3. In this application, the liquid nitrogen flow automatic control system can achieve precise temperature control, and combined with the gas circulation device, the accuracy and distribution uniformity of temperature control are significantly improved, and the temperature difference is reduced from ±10°C to ±3°C, ensuring a low temperature environment.

[0020] 4. The present application realizes the progressive forming of 2219 aluminum alloy plates in a -160°C environment, the forming height is increased from 14.6 mm at room temperature to 20.2 mm, and the forming limit angle is increased from 64° at room temperature to 70°, which significantly improves the surface hardness of the formed parts and significantly improves the hardness improvement efficiency of artificial aging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the deep cold progressive forming device of the present invention.

[0022] Figure 2 This is a schematic diagram of the structure of the improved fluid rolling tool head in this application.

[0023] Figure 3 This is a schematic diagram of the structure of the liquid nitrogen flow automatic control system.

[0024] Figure 4 Schematic diagram of the gas circulation device structure.

[0025] Figure 5 It is a schematic diagram of the longitudinal section of the side wall of the liquid nitrogen storage chamber.

[0026] Figure 6 This is a comparison chart of forming height and forming limit angle.

[0027] Figure 7 This is the forming specimen diagram.

[0028] Figure 8This is a comparison chart of sample surface quality.

[0029] Fig. 9 This is the fracture morphology diagram.

[0030] Reference numerals:

[0031] 1. Tool head, 1.1. Hydraulic pump, 1.2. Working oil, 1.3. Heating coil, 1.4. Ball, 1.5. Lubricant supply device, 2. Aluminum alloy plate, 3. Liquid nitrogen storage chamber, 3.1. Bottom air supply device, 3.2. Side air supply device, 3.3. Expanding part 1, 3.4. Closing part 1, 3.5. Closing part 2, 3.6. Expanding part 2, 4. Cold insulation shell, 5. Fixed pressure plate, 6. Temperature sensor, 7. PLC control host, 8. Opening valve, 9. Liquid nitrogen flow meter, 10. Solenoid switch valve, 11. Self-pressurized liquid nitrogen container, 12. Liquid nitrogen delivery pipeline. DETAILED DESCRIPTION

[0032] Example 1

[0033] A deep cold progressive forming process for aluminum alloy, using a deep cold progressive forming device to perform deep cold progressive forming on an aluminum alloy plate 2, such as Figure 1 As shown, the cryogenic incremental forming device includes a tool head 1, a liquid nitrogen storage chamber 3, a fixed pressing plate 5, a liquid nitrogen flow automatic control system and a cold-keeping shell 4, wherein the fixed pressing plate 5 presses the aluminum alloy plate 2 above the liquid nitrogen storage chamber 3, and the liquid nitrogen storage chamber 3 is provided with an exhaust hole for maintaining the pressure in the liquid nitrogen storage chamber 3 stable. The liquid nitrogen flow automatic control system can realize accurate regulation of the low temperature and continuous supply of liquid nitrogen. The cold-keeping shell 4 is arranged outside the liquid nitrogen storage chamber 3. When liquid nitrogen is supplied to the liquid nitrogen storage chamber 3, the cooling medium is in direct contact with the bottom of the aluminum alloy plate 2; the process includes the following steps:

[0034] S1, the liquid nitrogen flow automatic control system supplies liquid nitrogen and adjusts the temperature of the liquid nitrogen storage chamber to -160°C;

[0035] S2, using the tool head 1 to perform incremental forming on the aluminum alloy plate 2, wherein the angle between the tool head 1 and the aluminum alloy plate is less than 90° ( Figure 1 , 2 The figure is a schematic diagram, the angle is actually <90°), and MoS2 powder is used as a lubricant in the forming process;

[0036] S3. The formed aluminum alloy parts are artificially aged at a temperature of 185°C for 120 minutes.

[0037] The aluminum alloy grade is 2219, the cold-insulating shell 4 is made of polyurethane, and the aluminum alloy sheet 2 is subjected to a solid solution treatment at a temperature of 535° C. for 30 minutes before incremental forming.

[0038] like Figure 3 As shown, the liquid nitrogen flow automatic control system includes a self-pressurized liquid nitrogen container 11, an electromagnetic switch valve 10, a liquid nitrogen flow meter 9, an opening valve 8, a liquid nitrogen delivery pipeline 12, a temperature sensor 6, and a PLC control host 7. Among them, the temperature sensor 6 adopts a K-type thermocouple, which is connected to the edge of the upper surface of the aluminum alloy plate 2 to monitor the temperature of the aluminum alloy plate 2 in real time. A liquid level sensor can also be set in the liquid nitrogen storage chamber 3.

[0039] The control method of the liquid nitrogen flow automatic control system is as follows: the pressurized liquid nitrogen is output from the pressurized liquid nitrogen container 11, the electromagnetic switch valve 10 controls the opening and closing of the liquid nitrogen delivery pipeline 12, and the PLC control host 7 controls the opening of the opening valve 8 through the flow data collected by the liquid nitrogen flowmeter 9 and the temperature data collected by the temperature sensor 6. When the actual temperature is higher than the target temperature, the liquid nitrogen input flow rate is increased, and when the actual temperature is lower than the target temperature, the liquid nitrogen input flow rate is reduced, and finally the aluminum alloy plate 2 is accurately controlled.

[0040] like Figure 4 As shown, the liquid nitrogen flow automatic control system also includes a gas circulation device, which includes a bottom air supply device 3.1 and a side air supply device 3.2. The bottom air supply device 3.1 is arranged at the bottom of the liquid nitrogen storage chamber 3, which can be arranged above the liquid nitrogen delivery pipeline 12, or below the liquid nitrogen partition warehouse below the liquid nitrogen delivery pipeline 12. The liquid nitrogen partition warehouse can store liquid nitrogen in partitions and allow air to pass through the gaps between the partitions. Figure 4 , 5As shown, at least two opposite side walls, preferably all four side walls, of the side walls of the liquid nitrogen storage chamber 3 are configured as follows: a flaring portion 3.3 and a closing portion 3.4 are arranged on the inner side, wherein the vertical distance of the flaring portion 3.3 is greater than the vertical distance of the closing portion 3.4 (the figure is only a schematic diagram and does not represent a specific numerical relationship), the closing portion 3.3 extends to the bottom of the liquid nitrogen storage chamber 3, and is connected with the closing portion 3.5 and the flaring portion 3.6 on the outer side, the closing portion 3.5 is basically the same in structure as the closing portion 3.4, the flaring portion 3.6 is basically the same in structure as the flaring portion 3.3, an exhaust hole is arranged on the top of the flaring portion 3.6, the side air supply device 3.2 is arranged in the closing portion 3.3, the bottom air supply device 3.1 blows the liquid nitrogen transported by the liquid nitrogen transport pipeline 12 to the bottom surface of the aluminum alloy plate 2, and the side air supply device 3.2 guides the nitrogen and / or liquid nitrogen on the bottom surface of the aluminum alloy to diffuse to the surroundings. The air supply device can select an air supply fan. Through the setting of the bottom air supply device 3.1, the liquid nitrogen delivered to the liquid nitrogen storage chamber and the vaporized cryogenic gas can be quickly delivered to the bottom surface of the aluminum alloy plate 2, and then through the side air supply device 3.2, the nitrogen and / or liquid nitrogen on the bottom surface of the aluminum alloy plate 2 can be diffused to the surroundings to promote a more uniform temperature distribution. Among them, the setting of the expansion part 3.3 and the closing part 3.4 can form a faster airflow in the closing part 3.4 through the side air supply device 3.2 set in the closing part 3.4, and in the expansion part 3.3, the airflow velocity gradually increases from the bottom surface of the aluminum alloy plate 2 to the closing part 3.4, that is, the airflow velocity on the bottom surface of the aluminum alloy plate 2 is small, which can form a stable low-temperature gas distribution, and accelerate the circulation speed of the cooling gas and / or liquid, which can significantly improve the temperature control accuracy of the bottom surface of the aluminum alloy plate 2. Through the improvement of the gas circulation device, the present application can achieve a cooling temperature control accuracy of ±3°C, which can ensure the stability and reliability of the cryogenic environment. In addition, a closing portion 3.5 and a flaring portion 3.6 corresponding to the closing portion 1 3.3 and the flaring portion 1 3.4 are arranged on the middle and outer sides of the side wall of the liquid nitrogen storage chamber 3 to form opposite airflow directions. Through the arrangement of the closing portion 3.5 and the flaring portion 3.6, on the one hand, a double-layer insulation layer can be formed, and the residual cold capacity of the low-temperature gas is used to keep the liquid nitrogen storage chamber 3 cold, which can improve the utilization rate of liquid nitrogen. On the other hand, the airflow flows from the closing portion 3.5 to the flaring portion 3.6, which can slow down the nitrogen flow rate, increase the time that the nitrogen stays in the liquid nitrogen storage chamber 3, reduce the amount of liquid nitrogen used, and reduce costs.

[0041] In an optional embodiment, if Figure 2 As shown, a fluid rolling tool head is used for incremental forming. The structural schematic diagram of the fluid rolling tool head is shown in Figure 2As shown, the fluid rolling tool head controls the ultra-high pressure hydraulic working oil 1.2 through the hydraulic pump 1.1 to support the ball 1.4, so that the ball 1.4 is "suspended" on the lubricating film of the working oil 1.2, thereby achieving "frictionless" rolling. Furthermore, a lubricant supply device 1.5 is provided in front of the fluid rolling tool head, and a heating coil 1.3 is provided at the end of the fluid rolling tool head. In step S2, during the forming process, the lubricant supply device 1.5 supplies lubricant powder in real time, and the heating coil 1.3 is heated in real time.

[0042] The aluminum alloy formed parts prepared by the aluminum alloy deep cold incremental forming process carried out in Example 1 of the present application have excellent performance, and the specific results are as follows:

[0043] 1. After solution treatment at 535°C for 30 min, 2219-T4 aluminum alloy sheet with a thickness of 2 mm was subjected to deep cold incremental forming. The comparative example was incremental forming at room temperature. The other processing techniques were the same as those in the embodiment. The forming height is shown in Table 1, the hardness is shown in Table 2, and the comparison between the forming height and the forming limit angle is shown in Table 2. Figure 6 As shown in the figure, it can be seen that the forming limit angle increases from 64° at room temperature to 70°. Figure 7 As shown, Figure 7 In the figure, the upper part is a comparative example and the lower part is an embodiment.

[0044] Table 1

[0045]

[0046] Table 2

[0047]

[0048] 2. The samples of the embodiment and the comparative example were artificially aged for different lengths and their microhardness was measured. The test force was 0.49 N and the holding time was 10 s. The numerical changes of the sample hardness with increasing aging time are shown in Table 3.

[0049] Table 3

[0050]

[0051] As shown in Table 3, in the solid solution state before aging, the hardness of the -160℃ sample is 164.6HV, which is 7% higher than that of the room temperature sample. It can be seen that the 2219 sheet can be formed at low temperature to improve the hardness of the workpiece. After aging for 60 minutes, the hardness of the -160℃ sample is 186HV, an increase of 13.4%, while the increase of the room temperature sample is smaller, only 3.7%. After aging for 120 minutes, the hardness of the -160℃ sample is 203.7HV, an increase of 9.5%. At this time, the room temperature sample reaches 188.5HV, which also shows a significant increase of 18%. In the process of gradually increasing aging time, the hardness of the -160℃ sample changes little. Finally, after aging for 720 minutes, the hardness value is 203.2HV, while the hardness of the room temperature sample rises slowly after aging for 120 minutes, and finally obtains a hardness similar to that of the -160℃ sample. The hardness of the room temperature sample after 720 minutes is 202.2HV. It can be seen that the -160℃ sample achieved a higher hardness and did not change in a relatively short aging time. Therefore, when formed at -160℃, the aging power of the 2219 sample was improved.

[0052] 3. For the study of the surface quality of the sample after forming, a fluid rolling tool head comparison example was added, which used the improved fluid rolling tool head in this application for incremental forming, and the incremental forming environment was room temperature. When the conventional incremental forming tool head was used for incremental forming in the embodiment, the lubricant molybdenum disulfide powder was manually spread. The surface quality of the sample after forming in Example 1, the comparison example, and the fluid rolling tool head comparison example is as follows: Figure 8 shown. Figure 8 In the figure, the left side is the comparative sample, the middle is the embodiment sample, and the right side is the fluid rolling tool head comparative sample. Figure 8 It can be seen that the deep cold environment can improve the forming performance of aluminum alloy plates, and the surface quality of the samples is improved compared with that at room temperature. However, the embodiment still has some forming marks that have an adverse effect on the surface quality. The improved fluid rolling tool head is used for incremental forming. Compared with the surface quality of the conventional incremental forming tool head after forming at room temperature and Example 1, the improved fluid rolling tool head is used for incremental forming. The surface quality of the sample can be significantly improved. Although the fluid rolling tool head comparison example is carried out at room temperature, it proves that the fluid rolling tool head has a significant effect on improving the surface quality of incremental forming. Moreover, the lubricant is supplied by the lubricant supply device, which can improve the lubricating effect of the lubricant and ensure the surface quality after forming. When it is used for incremental forming in an environment of -160°C, heating by the heating coil can ensure the flow state of the working oil and the uniform distribution of the lubricant, thereby significantly improving the surface quality after forming under the deep cold incremental forming process.

[0053] 4. Analysis of the evolution of the sample microstructure, through SEM observation of the fracture surface of the workpiece, reveals the influence of the test temperature on the fracture mechanism. Fig. 9 Shown are the fracture morphologies of the comparative example 1 and the truncated cone specimens of the embodiment, wherein (a), (c), and (e) are comparative example 1, and (b), (d), and (f) are embodiments. The fracture morphologies of the specimens at different temperatures show obvious differences. The embodiment specimens show obvious ductile fracture characteristics, with a higher fracture morphology height, a smaller dimple size, and a denser distribution of dimples, while the fracture of the comparative example 1 specimen shows brittle fracture characteristics, with a lower morphology height and a smaller number of dimples. In addition, in the fracture morphology of the embodiment specimens, the formation of small holes can be observed on the dimple sub-boundaries, which indicates that the embodiment specimens have a higher dislocation density, reflecting that the alloy deforms more uniformly under the forming process of the present application.

[0054] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0055] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0057] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A deep cold incremental forming process for aluminum alloy, characterized in that: A cryogenic progressive forming device is used to perform cryogenic progressive forming on an aluminum alloy sheet. The cryogenic progressive forming device includes a liquid nitrogen storage chamber, a fixed pressing plate, a liquid nitrogen flow automatic control system, and a cold-keeping shell. The fixed pressing plate presses the aluminum alloy sheet against the liquid nitrogen storage chamber. An exhaust hole is provided on the liquid nitrogen storage chamber to maintain a stable pressure in the liquid nitrogen storage chamber. The liquid nitrogen flow automatic control system can achieve accurate regulation of the cryogenic temperature and continuous supply of liquid nitrogen. The cold-keeping shell is provided outside the liquid nitrogen storage chamber. When liquid nitrogen is supplied to the liquid nitrogen storage chamber, the cooling medium is in direct contact with the bottom of the aluminum alloy sheet. The process includes the following steps: S1, the liquid nitrogen flow automatic control system supplies liquid nitrogen and adjusts the temperature of the liquid nitrogen storage chamber to -160°C; S2, performing incremental forming on the aluminum alloy sheet, wherein the angle between the incremental forming tool head and the aluminum alloy sheet is less than 90°, and MoS2 powder is used as a lubricant during the forming process; S3. The formed aluminum alloy parts are artificially aged at a temperature of 185°C for 120 minutes.

2. The aluminum alloy deep cold incremental forming process according to claim 1, characterized in that: The aluminum alloy grade is 2219, the cold-insulating shell material is polyurethane, and the aluminum alloy sheet is solution treated before incremental forming at a temperature of 535°C for 30 minutes.

3. The aluminum alloy deep cold incremental forming process according to claim 1, characterized in that: The liquid nitrogen flow automatic control system also includes a gas circulation device, which includes a bottom air supply device and a side air supply device. The bottom air supply device is arranged at the bottom of the liquid nitrogen storage chamber, and a flaring portion 1 and a closing portion 1 are arranged in the side wall of the liquid nitrogen storage chamber. The closing portion 1 extends to the bottom of the liquid nitrogen storage chamber, and then reaches the flaring portion 2 through the closing portion 2 on the outside. An exhaust hole is arranged on the top of the flaring portion 2. The side air supply device is arranged in the closing portion 1. The bottom air supply device transports the liquid nitrogen transported by the liquid nitrogen transport pipeline to the bottom surface of the aluminum alloy plate, and the side air supply device guides the nitrogen and / or liquid nitrogen on the bottom surface of the aluminum alloy to diffuse to the surroundings.

4. The aluminum alloy deep cold incremental forming process according to claim 1, characterized in that: A fluid rolling tool head is used for progressive forming. A lubricant supply device is provided in front of the fluid rolling tool head, and a heating coil is provided at the end of the fluid rolling tool head. In step S2, during the forming process, the lubricant supply device supplies lubricant powder in real time, and the heating coil is heated in real time.

5. The aluminum alloy deep cold incremental forming process according to claim 1, characterized in that: The liquid nitrogen flow automatic control system includes a self-pressurized liquid nitrogen container, an electromagnetic switch valve, a liquid nitrogen flow meter, an opening valve, a liquid nitrogen delivery pipeline, a temperature sensor, and a PLC control host. The temperature sensor adopts a K-type thermocouple, which is connected to the edge of the upper surface of the aluminum alloy plate to monitor the temperature of the aluminum alloy plate in real time.

6. The aluminum alloy deep cold incremental forming process according to claim 5, characterized in that: The control method of the liquid nitrogen flow automatic control system is to output pressurized liquid nitrogen from the pressurized liquid nitrogen container, and the electromagnetic switch valve controls the opening and closing of the liquid nitrogen delivery pipeline. The PLC control host controls the opening of the opening valve through the flow data collected by the flow meter and the temperature data collected by the temperature sensor. When the actual temperature is higher than the target temperature, the liquid nitrogen input flow rate is increased, and when the actual temperature is lower than the target temperature, the liquid nitrogen input flow rate is reduced, ultimately achieving accurate temperature control of the aluminum alloy plate.

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