A device and method for ultra-low temperature forming of aluminum-lithium alloy complex curved thin-walled components

Abstract

The present invention discloses an ultra-low temperature forming device and method for a thin-walled component of an aluminum-lithium alloy with a complex curved surface, wherein the forming device comprises a cryogenic box, a control cabinet, a liquid nitrogen tank, an electromagnetic valve group, a punch, a die, a temperature detector and a pressure device, wherein the punch, the die, the temperature detector and the pressure device are arranged in the cryogenic box, and the pipeline connecting the liquid nitrogen tank and the cryogenic box is provided with an electromagnetic valve group, the electromagnetic valve group and the temperature detector are electrically connected to the control cabinet, the pressure device is arranged to press the slab between the punch and the die, and the cryogenic box is provided with a box door. The cooling device of the present invention can realize that the temperature in the range of 0 to minus 180°C remains unchanged during the forming process, and provides an ultra-low temperature energy field for the forming process, thereby greatly improving the forming ability of the aluminum-lithium alloy thin plate, making the deformation more uniform, reducing the thinning and local wrinkling during the forming process, and avoiding the rupture of the component during the forming process.

Description

Technical Field

[0001] The present invention belongs to the technical field of sheet metal forming, and specifically relates to an ultra-low temperature forming device and method for a thin-walled component with complex curved surface made of aluminum-lithium alloy. Background Art

[0002] As one of the six key technologies in aviation manufacturing, thin-walled component manufacturing has always been the focus and difficulty of aviation structural component research. Aircraft thin-walled components account for more than 50% of the total weight of the entire aircraft structure. They need to withstand complex loads and meet the service performance requirements of high reliability and long life. For fighter jets, the large-scale use of lightweight thin-walled components with excellent performance can further increase the aircraft's cruising distance and the number of bombs, and improve the combat capability of fighter jets. At the same time, the technical indicators of weight reduction in grams for civil aircraft also put forward extremely high requirements for the forming and manufacturing of their thin-walled parts. With the development of large aircraft, the requirements for thin-walled components are more stringent and the structure becomes more complex. Its thin-walled, variable curvature and defect-sensitive characteristics are more prominent, which puts extremely demanding requirements on component design and manufacturing. Among them, the integrated, high-precision and high-performance manufacturing of thin-walled components with complex curved surfaces has become a major problem facing my country in the field of thin-walled component manufacturing, which has restricted the development of my country's aviation manufacturing technology.

[0003] Compared with traditional aluminum alloys, aluminum-lithium alloys have lower density, higher specific stiffness, specific strength and fatigue resistance, and also have good corrosion resistance and high / low temperature performance. Using it to replace conventional high-strength aluminum alloys can reduce the structural mass by 10-20% and increase the stiffness by 15-20%. It is considered to be the most ideal manufacturing material for aviation thin-walled parts. Therefore, the high-precision and high-performance manufacturing of aluminum-lithium alloy complex curved thin-walled components is of great significance for reducing structural weight, increasing aircraft load and range, and improving the level of aviation technology. However, the multi-scale microstructure formed by aluminum-lithium alloy thin-walled parts during the forming and heat treatment process, including grains, subgrained structures, residual crystalline phases and multi-element precipitation phases, is difficult to control in morphology and size. In addition, the main alloying element Li, which increases material strength and reduces density, is prone to dynamic precipitation during the forming process to form a coherent δ′ phase, resulting in coplanar slip, resulting in uneven deformation and local stress concentration. These reasons lead to the wrinkling, cracking, poor dimensional accuracy, and difficult deformation control of aluminum-lithium alloy complex curved surface components during the traditional forming process, making them difficult to form.

[0004] Ultra-low temperature deformation is a new method of material plastic deformation that is currently attracting much attention. Compared with conventional (room temperature) cold deformation, the ultra-low temperature deformation temperature is extremely low, the atoms are in a low energy state, and the diffusion rate of solute elements is low, which can increase the material's work hardening ability, inhibit dynamic precipitation, and improve the material / component formability and deformation uniformity; in addition, under low temperature conditions, the matrix deformation resistance increases, and at the same time, the dynamic recovery of the alloy is greatly inhibited, which can increase the intracrystalline dislocation density and provide a driving force for the subsequent uniform dispersion precipitation of the strengthening phase. Summary of the invention

[0005] The purpose of the present invention is to provide an ultra-low temperature forming device and method for complex curved thin-walled components of aluminum-lithium alloy, so as to solve the above-mentioned problems.

[0006] To achieve the above-mentioned purpose, the present invention first discloses an ultra-low temperature forming device for complex curved thin-walled components of aluminum-lithium alloy, comprising a cryogenic box, a control cabinet, a liquid nitrogen tank, a solenoid valve group, a punch, a die, a temperature detector and a edge pressing device, wherein the punch, the die, the temperature detector and the edge pressing device are arranged in the cryogenic box, and a solenoid valve group is arranged on the pipeline connecting the liquid nitrogen tank and the cryogenic box, the solenoid valve group and the temperature detector are electrically connected to the control cabinet, the edge pressing device is arranged to press the slab between the punch and the die, and a box door is arranged on the cryogenic box.

[0007] Furthermore, it also includes an upper template installed on the upper working platform of the press and a lower template installed on the lower working platform of the press. The edge clamping device includes a edge clamping ring, a spring and a unloading screw. The lower end of the unloading screw is connected to the lower template, and the upper end is slidably connected to the upper template. The spring is sleeved on the unloading screw and is limited to between the upper template and the lower template.

[0008] Furthermore, the lower end of the unloading screw is threadedly connected to an adjusting nut, and a gasket is sleeved on the unloading screw above the adjusting nut, and the lower end of the spring is against the gasket.

[0009] Furthermore, the cryogenic box comprises an upper cryogenic box installed on the upper working platform of the press and a lower cryogenic box installed on the lower working platform of the press. The upper cryogenic box is covered on the outside of the upper template and is configured to slide along the inside of the lower cryogenic box.

[0010] Furthermore, nozzles are arranged on the walls of the upper cryogenic box and the lower cryogenic box, and the nozzles are connected to the solenoid valve group. The nozzles form a three-layer layout from top to bottom facing the upper template, the slab and the die respectively.

[0011] Furthermore, it also includes two sets of diagonally arranged guide mechanisms, the guide mechanisms include guide sleeves and guide posts, the guide sleeves are inserted into the guide holes of the upper template, the guide posts are installed on the lower template, and the guide posts are slidably connected with the guide sleeves.

[0012] Furthermore, it also includes a thermocouple that can be welded to the side of the slab, and the thermocouple is electrically connected to the control cabinet.

[0013] Furthermore, positioning pins are provided between the upper mold plate and the male mold, and between the lower mold plate and the female mold.

[0014] Then, the present invention discloses a method for ultra-low temperature forming of a thin-walled component with complex curved surface of an aluminum-lithium alloy, including the ultra-low temperature forming device for a thin-walled component with complex curved surface of an aluminum-lithium alloy as described in the above scheme, comprising the following steps:

[0015] S1, fix the upper template and the lower template to the upper and lower working platforms of the press, install the upper deep cold box and the lower deep cold box on the press, and debug the cooling device;

[0016] S2, welding a thermocouple on the side of the slab, then marking the die and placing the slab at the designated position;

[0017] S3, use a force measuring wrench to rotate the adjusting nut to adjust the preload force of the spring to a predetermined value;

[0018] S4, close the box door and start cooling. The solenoid valve group controls the liquid nitrogen tank to press liquid nitrogen into each nozzle through the pipeline. Cool until the temperature in the box measured by the temperature detector and the slab temperature measured by the thermocouple reach the preset value and then keep warm for a period of time;

[0019] S5, start the press, the working platform on the press drives the upper template and the punch to press down, the blank holder first contacts the slab, as the upper template continues to press down, the spring is compressed, so that the blank holder starts to apply a blank holder force to the slab, and when the pressing continues, the punch contacts the slab and starts to draw, and at the same time, the spring is continuously compressed, the blank holder force keeps changing, and the press continues to press down until the slab is drawn to a predetermined size;

[0020] S6, close the nozzle, reset the press, open the box door, and take out the workpiece.

[0021] Furthermore, in step S2, ultra-low temperature grease is applied to the die and the slab.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] The cooling device of the present invention can realize that the temperature in the range of 0 to minus 180°C remains unchanged during the forming process, providing an ultra-low temperature energy field for the forming process, thereby greatly improving the forming ability of the aluminum-lithium alloy sheet, making the deformation more uniform, reducing the thinning and local wrinkling during the forming process, and avoiding the rupture of the component during the forming process. The deep cold box can move with the press to reduce the heat exchange with the outside world and ensure that the mold is insulated from the outside world during the forming process. The cooling method adopts liquid nitrogen spraying, which has a faster cooling speed and a larger cooling temperature range than the traditional compression refrigeration method. At the same time, liquid nitrogen is green and environmentally friendly as a cryogenic agent, easy to obtain, and can form a certain low-temperature lubricating layer. The cooling device detects and records the pressure and flow at the nozzle in real time through the pressure gauge and flowmeter on the pipeline, and feeds back to the corresponding control system. The solenoid valve group can be controlled in real time according to the program to change the pipeline pressure and liquid nitrogen flow, and can also display the temperature inside the box and the slab and the use of liquid nitrogen. The cooling speed and the temperature during the forming process can be effectively controlled by the spray flow, pressure and slab temperature.

[0024] The present invention adopts a block-type clamping structure with adjustable clamping force, rather than a commonly used integral clamping structure with constant clamping force. Such a clamping structure can effectively control the flow of metal during the forming process, making the flow in all directions more uniform, thereby reducing the thinning rate and improving the forming performance and forming quality. The present invention adopts a spring to apply the clamping force, and is provided with an adjusting nut to change the spring preload to adjust the clamping force. This structure allows a larger setting range of the clamping force, and the clamping force continues to increase during the forming process to prevent local wrinkling. The structure is simple and easy to operate. In addition, the present invention can be directly assembled on an ordinary single-acting hydraulic press for use, without the need to modify the press, and is easy to use and low in cost.

[0025] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 It is an axonometric schematic diagram of an ultra-low temperature forming device for a thin-walled component with a complex curved surface of an aluminum-lithium alloy disclosed in a preferred embodiment of the present invention;

[0028] Figure 2 It is an axonometric schematic diagram of an ultra-low temperature forming die for a thin-walled component with complex curved surface of an aluminum-lithium alloy disclosed in a preferred embodiment of the present invention;

[0029] Figure 3 It is a top view schematic diagram of an ultra-low temperature forming die for a thin-walled component with complex curved surface of an aluminum-lithium alloy disclosed in a preferred embodiment of the present invention;

[0030] Figure 4 It is a schematic front view of a ultra-low temperature forming die for a thin-walled component with complex curved surface of an aluminum-lithium alloy disclosed in a preferred embodiment of the present invention;

[0031] Figure 5 It is the stress-strain curve of 2060 Al-Li alloy W state sample measured by tensile test at 293K and 77K.

[0032] Legend:

[0033] 1. Upper template; 2. Punch; 3. Lower template; 4. Die; 5. Slab; 6. Blank holder; 6-1. First blank holder portion; 6-2. Second blank holder portion; 6-3. Third blank holder portion; 7. Adjusting nut; 8. Spring; 8-1. First spring; 8-2. Second spring; 8-3. Third spring; 9. Unloading screw; 10. Guide mechanism; 10-1. Guide sleeve; 10-2. Guide column; 11. Lifting ear; 12. Upper deep freezer; 13. Lower deep freezer; 14. Nozzle; 15. Temperature detector; 16. Control cabinet; 17. Display; 18. Liquid nitrogen tank; 19. Solenoid valve group; 20. Pipeline; 21. Gasket; 22. Lower positioning pin; 23. Upper positioning pin; 24. Upper hexagon socket screw; 25. Lower hexagon socket screw. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0035] like Figure 1-5 As shown, the present invention discloses an ultra-low temperature forming device for a thin-walled component with a complex curved surface of an aluminum-lithium alloy, comprising an upper template 1, a lower template 3, a punch 2, a die 4, a guide mechanism 10, a lifting lug 11, a blank holder ring structure with adjustable blank holder force in blocks, and a cooling device. The upper template 1 and the lower template 3 are respectively connected to the upper and lower working planes of a press (not shown) by bolts through T-slots, the punch 2 is mounted on the upper template 1 by an upper positioning pin 23 and an upper hexagon socket screw 24, and the die 4 is positioned with the lower template 3 by a lower positioning pin 22 and a lower hexagon socket screw 25, wherein the upper positioning pin 23 and the lower positioning pin 22 play a role in precise positioning. At the same time, a lifting lug 11 for lifting is installed on the lower template 3, and the punch 2 and the die 4 are made of low-temperature-resistant mold steel that can work reliably in an ultra-low temperature environment.

[0036] In this embodiment, the blank holding ring structure with adjustable blank holding force in blocks includes: a blank holding ring 6, an adjusting nut 7, a gasket 21, a spring 8 and a discharge screw 9. The cylindrical spiral springs (the first spring 8-1, the second spring 8-2 and the third spring 8-3) of different sizes are respectively connected between the groove of the upper template 1 and the blank holding rings at different positions (the first blank holding ring part 6-1, the second blank holding ring part 6-2, and the third blank holding ring part 6-3), and different blank holding forces can be provided to different areas under the condition of the same stroke. The adjusting nut 7 is provided with a gasket 21 sleeved on the discharge screw 9, and the gasket 21 contacts the bottom end of the spring 8. The adjusting nut 7 is connected to the discharge screw 9 by threading, so as to limit the spring 8. The upper end of the discharge screw 9 is placed in the limiting hole of the upper template 1, and the lower end is connected to the blank holding ring 6 by threading. The preload force of the spring 8 is changed by rotating the adjusting nut 7, thereby changing the blank holding force of the area.

[0037] The adjusting nut 7 contacts the bottom end of the spring 8 and is connected to the unloading screw 9 by threading to limit the spring 8. The upper end of the unloading screw 9 is placed in the limiting hole of the upper template 1, and the lower end is connected to the blank holder 6 by threading. Rotating the adjusting nut 7 can change the preload force of the spring 8 to a preset value to adjust the blank holder force in this area. Specifically, the spring 8 is made of low-temperature resistant spring steel, so as to ensure that the spring 8 can work continuously and reliably in an ultra-low temperature environment.

[0038] In this embodiment, the guide mechanism 10 is composed of a guide post 10-2 and a guide sleeve 10-1, and the guide sleeve 10-1 is connected to the guide holes of the lower mold plate 3 and the upper mold plate 1 by interference fit. The guide post 10-2 is arranged diagonally to ensure the centering of the punch 2 and the die 4. Specifically, a low-temperature lubricant is provided between the guide post 10-2 and the guide sleeve 10-1 to ensure the normal operation of the guide mechanism 10 in an ultra-low temperature environment.

[0039] In this embodiment, the cooling system includes: an upper cryogenic box 12, a lower cryogenic box 13, a nozzle 14, a temperature detector 15, a control cabinet 16, a display 17, a liquid nitrogen tank 18, a solenoid valve group 19 and a low temperature resistant pipeline 20. The lower cryogenic box 13 is fixed to the lower working platform of the press, and the upper cryogenic box 12 is connected to the upper working platform of the press, and can slide relative to the lower cryogenic box 13 following the upper working platform of the press to prevent the gap between the upper and lower cryogenic boxes 13 from causing internal heat loss when the press is working. The upper cryogenic box 12 and the lower cryogenic box 13 are wrapped with stainless steel insulation materials to reduce the overall weight and effectively insulate. The lower cryogenic box 13 is provided with a box door to facilitate the placement of the slab 5. The nozzle 14 extends out from the grooves of the upper cryogenic box 12 and the lower cryogenic box 13 to ensure that the nozzle 14 does not interfere with the upper cryogenic box 12 during the operation of the press. The nozzles 14 are divided into three rows, facing the upper template 1, the slab 5 and the die 4 for cooling respectively, and are connected by the pipeline 20 buried in the upper cryogenic box 12 and the lower cryogenic box 13. The electromagnetic valve group 19 controls the liquid nitrogen tank 18 (self-pressurized) to press the liquid nitrogen into each nozzle 14 through the pipeline 20. The pipeline 20 is connected with a pressure gauge and a flow meter, which is convenient for real-time detection and recording of the pressure and flow of the nozzle 14, and feedback to the corresponding control system (in the control cabinet 16), and the pressure of the pipeline 20 and the liquid nitrogen flow can be changed in real time according to the program. Thermocouples are welded on the side of the slab 5, and the display 17 receives the temperature detector 15 and the thermocouple signals, and displays the temperature of the box and the slab 5 and the use of liquid nitrogen. The cooling speed and the temperature during the forming process can be effectively controlled by the spray flow, pressure and the temperature of the slab 5.

[0040] Then, the present invention discloses a method (forming method) of the ultra-low temperature forming device of the above-mentioned aluminum-lithium alloy complex curved surface thin-walled component, comprising the following steps:

[0041] S1, fix the upper template 1 and the lower template 3 to the upper and lower working platforms of the press through T-slots and bolts, install the upper deep cold box 12 and the lower deep cold box 13 on the press, and debug the cooling device.

[0042] S2, a thermocouple is welded to the side of the slab 5 to measure its temperature change, ultra-low temperature grease is applied to the die 4 and the slab 5, and then a line is drawn on the die 4 and the slab 5 is placed at the designated position.

[0043] S3, use a force measuring wrench to rotate the adjusting nut 7 to adjust the preload force of the spring 8 to a predetermined value.

[0044] S4, close the box door and start cooling. The solenoid valve group 19 controls the liquid nitrogen tank 18 to press the liquid nitrogen into each nozzle 14 through the pipeline 20. The pressure gauge and flow meter on the pipeline 20 record the pressure and flow of the nozzle 14 and feed back to the control system. The pressure and flow of the liquid nitrogen spray can be changed in real time according to the program to control the cooling speed. After cooling until the temperature in the box measured by the temperature detector 15 and the temperature of the slab 5 measured by the thermocouple reach the predetermined value, keep warm for a period of time.

[0045] S5, start the press, the upper working platform of the press drives the upper template 1 and the punch 2 to press down, the blank holder 6 first contacts the slab 5, as the upper template 1 continues to press down, the spring 8 is compressed, so that the blank holder 6 begins to apply a blank holder force to the slab 5, and when the press continues to go down, the punch 2 contacts the slab 5 and starts to draw, and at the same time the spring 8 is constantly compressed, the blank holder force keeps changing, and the press continues to press down until the slab is drawn to a predetermined size, and the forming is completed.

[0046] S6, close the nozzle 14, reset the press, open the box door, and take out the workpiece.

[0047] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An ultra-low temperature forming device for complex curved thin-walled components of aluminum-lithium alloy, characterized in that: The invention comprises a cryogenic box, a control cabinet (16), a liquid nitrogen tank (18), an electromagnetic valve group (19), a punch (2), a die (4), a temperature detector (15) and a press device, wherein the punch (2), the die (4), the temperature detector (15) and the press device are arranged in the cryogenic box, a electromagnetic valve group (19) is arranged on a pipeline (20) connecting the liquid nitrogen tank (18) and the cryogenic box, the electromagnetic valve group (19) and the temperature detector (15) are both electrically connected to the control cabinet (16), the press device is arranged to press a slab (5) between the punch (2) and the die (4), and a box door is arranged on the cryogenic box; the invention also comprises an upper mold plate (1) installed on the upper working platform of the press and a lower mold plate (3) installed on the lower working platform of the press, the press The edge device comprises a blank holding ring (6), a spring (8) and a discharge screw (9); the lower end of the discharge screw (9) is connected to the blank holding ring (6), and the upper end is slidably connected to the upper template (1); the spring (8) is sleeved on the discharge screw (9) and limited between the upper template (1) and the lower template (3); the lower end of the discharge screw (9) is threadedly connected to an adjusting nut (7); the discharge screw (9) is sleeved with a gasket (21) above the adjusting nut (7), and the lower end of the spring (8) is abutted against the gasket (21); cylindrical helical springs (8) of different sizes are respectively connected between the groove of the upper template (1) and the blank holding ring (6) at different positions, so that different blank holding forces can be provided to different areas under the condition of the same stroke.

2. The ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to claim 1 is characterized in that: The cryogenic box comprises an upper cryogenic box (12) installed on the upper working platform of the press and a lower cryogenic box (13) installed on the lower working platform of the press. The upper cryogenic box (12) is wrapped around the outer surface of the upper template (1) and is configured to slide along the inner surface of the lower cryogenic box (13).

3. The ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to claim 2 is characterized in that: Nozzles (14) are arranged on the walls of the upper cryogenic box (12) and the lower cryogenic box (13); the nozzles (14) are connected to the solenoid valve group (19); and the nozzles (14) form a three-layer layout from top to bottom, facing the upper mold plate (1), the slab (5), and the concave mold (4), respectively.

4. The ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to claim 2, characterized in that: It also comprises two groups of diagonally arranged guide mechanisms (10), the guide mechanisms (10) comprising guide sleeves (10-1) and guide pillars (10-2), the guide sleeves (10-1) being inserted into guide holes of the upper template (1), the guide pillars (10-2) being mounted on the lower template (3), and the guide pillars (10-2) being slidably connected to the guide sleeves (10-1).

5. The ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to claim 2, characterized in that: It also includes a thermocouple that can be welded to the side of the slab (5), and the thermocouple is electrically connected to the control cabinet (16).

6. The ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to claim 2, characterized in that: Positioning pins are provided between the upper mold plate (1) and the male mold (2), and between the lower mold plate (3) and the female mold (4).

7. A method for ultra-low temperature forming of aluminum-lithium alloy complex curved thin-walled components, comprising an ultra-low temperature forming device for aluminum-lithium alloy complex curved thin-walled components according to any one of claims 1 to 6, characterized in that: The invention comprises the following steps: S1, fixing an upper mold plate (1) and a lower mold plate (3) on the upper and lower working platforms of a press, installing an upper deep cold box (12) and a lower deep cold box (13) on the press, and debugging a cooling device; S2, welding a thermocouple on the side of a slab (5), then marking a line on a die (4) and placing the slab (5) at a designated position; S3, rotating an adjusting nut (7) with a force measuring wrench to adjust the preload force of a spring (8) to a predetermined value; S4, closing a door of the box, starting cooling, and controlling a solenoid valve group (19) to control a liquid nitrogen tank (18) to press liquid nitrogen into each nozzle (14) through a pipeline (20), and cooling the box until the temperature is measured by a temperature detector (15). After the internal temperature and the temperature of the slab (5) measured by the thermocouple have reached the predetermined value, the temperature is kept constant for a period of time; S5, the press is started, and the working platform on the press drives the upper template (1) and the punch (2) to press downward, and the pressure ring (6) first contacts the slab (5). As the upper template (1) continues to press downward, the spring (8) is compressed, so that the pressure ring (6) begins to apply a pressure force to the slab (5). When the pressure continues to be downward, the punch (2) contacts the slab (5) and begins to draw. At the same time, the spring (8) is continuously compressed, and the pressure force continuously changes. The press continues to press downward until the slab (5) is drawn to a predetermined size; S6, the nozzle (14) is closed, the press is reset, the box door is opened, and the workpiece is taken out.

8. The method for ultra-low temperature forming of aluminum-lithium alloy complex curved thin-walled components according to claim 7, characterized in that: In step S2, ultra-low temperature grease is applied to the die (4) and the slab (5).

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