A method of superplastic expansion forming

Abstract

This invention relates to a superplastic expansion forming method, belonging to the field of superplastic forming technology. It solves the problem in existing technologies where the shape and size of superplastic formed parts are determined by the internal cavity of the mold, and a single mold can only form parts of one size. The superplastic expansion forming method of this invention includes the following steps: A. Establishing a table showing the relationship between piston displacement and sheet metal shape; B. Preparing for superplastic expansion forming; C. Superplastic expansion forming; D. Completing superplastic forming. The forming method of this invention can control a first actuator to push or pull a first actuator rod, which in turn pushes or pulls a piston, causing the piston to move towards the upper or lower end of a pressure regulating cylinder. This forces the protective gas in the first pressure chamber to the upper cavity, or the protective gas in the second pressure chamber to the lower cavity, thereby changing the shape of the sheet metal and performing superplastic forming.

Description

Technical Field

[0001] This invention relates to the field of superplastic forming technology, and more particularly to a superplastic expansion forming method. Background Technology

[0002] When metals and alloys are stretched under certain microstructure, deformation temperature, and strain rate conditions, they can exhibit exceptionally high elongation, exceeding 200%, with very low deformation resistance. This phenomenon is called superplasticity. Titanium alloys have poor machinability, making it difficult to form parts with complex shapes. However, they possess superplasticity under specific conditions, and this property has led to the development of superplastic forming, a near-net-shape forming process.

[0003] Currently, superplastic forming uses pneumatic forming in the superplastic state of the material. The shape and size of the part are determined by the internal cavity of the mold, and one mold can only form a part of one size. For parts with similar shapes but different sizes, such as spherical or arched parts with the same diameter but different heights, superplastic forming requires multiple molds, making the process cumbersome and costly.

[0004] Based on this, the present invention proposes a method for superplastic expansion forming to solve the above problems. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a superplastic expansion forming method to solve the problem in the prior art that the shape and size of superplastic formed parts are determined by the inner cavity of the mold, and a set of molds can only form parts of one size.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] A superplastic expansion forming method, utilizing a superplastic expansion forming apparatus, the forming method comprising the following steps:

[0008] A. Develop a table showing the relationship between piston displacement and sheet metal shape;

[0009] B. Prepare for superplastic expansion molding;

[0010] C. Superplastic expansion molding;

[0011] D. Complete superplastic forming.

[0012] Further, in step A, a table relating piston displacement to sheet shape is created, including calculating the real-time volume of the upper and lower cavities at all time steps, creating a volume data table for each time point and the upper and lower cavities, and inputting it into the controller.

[0013] Furthermore, step A, developing a table showing the relationship between piston displacement and sheet shape, also includes establishing a table showing the relationship between piston displacement and the volume changes of the upper and lower cavities.

[0014] Furthermore, step A, "developing a table relating piston displacement to sheet shape," also includes establishing such a table.

[0015] Further, step B, preparing for superplastic expansion molding, includes mold assembly, mold closing, and applying contact surface loads to the mold.

[0016] Furthermore, the contact surface load is 3 MPa.

[0017] Furthermore, step B, preparing for superplastic expansion molding, also includes connecting the piston to the lower end of the pressure regulating cylinder to minimize the volume of the second pressure chamber and fix the position of the piston.

[0018] Furthermore, step B, preparing for superplastic expansion molding, also includes: opening the first and third air valves and setting the second air valve to the overflow protection state, opening the air supply unit, and filling the first and second air passages with protective gas.

[0019] Furthermore, the critical pressure of the second air valve is set to 0.4 MPa, and the air pressure of the first air passage and the second air passage is set to 0.3 MPa.

[0020] Furthermore, the material of the sheet metal is TC4 titanium alloy.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The forming method of the present invention can control the peripheral part of the sheet to extend into the annular cavity, thereby making the peripheral part of the sheet thinner, and when the sheet is superplastically formed, the thickness of the sheet after forming can be more uniform.

[0023] (2) The forming method of the present invention can control the first actuator to push or pull the first actuator rod, thereby pushing or pulling the piston, so that the piston moves to the upper or lower end of the pressure regulating cylinder, thereby pressing the protective gas of the first pressure chamber to the upper forming cavity, or pressing the protective gas of the second pressure chamber to the lower forming cavity, thereby changing the shape of the sheet material.

[0024] (3) The forming method of the present invention uses a worm gear pair of forming device mounted on the first actuating rod. The motor is connected to the worm and the controller respectively. The controller can control the motor to rotate so as to drive the worm. The worm can drive the worm wheel to rotate and drive the first actuating rod to move, thereby driving the piston.

[0025] (4) The worm gear pair of the forming device used in the forming method of the present invention has a self-locking function and a reduction ratio greater than 40, which ensures the self-locking and driving of the first actuating rod;

[0026] (5) The second actuator of the forming device used in the forming method of the present invention has the same structure as the first actuator, the second actuator rod has the same structure as the first actuator rod, and the change rate of the volume of the first pressure chamber and the second pressure chamber is the same; and compared with setting a single actuator, the two actuators improve the driving force on the piston and the degree of self-locking. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a flowchart illustrating the forming method;

[0029] Figure 2 This is a schematic diagram of the overall structure of the forming device of the present invention;

[0030] Figure 3 This is a schematic diagram of the overall structure of the forming unit;

[0031] Figure 4 This is a schematic diagram of the overall structure of the forming unit in Example 4.

[0032] Figure label:

[0033] 1-Forming unit; 2-Air supply unit; 3-Controller; 4-First air passage; 5-Exhaust air passage; 6-Second air passage; 7-Pressure regulating cylinder; 8-Piston; 11-Upper mold; 12-Lower mold; 13-First air port; 14-Second air port; 15-Upper cavity; 16-Lower cavity; 17-Annular die; 18-Lower punch; 21-First air valve; 22-Second air valve; 23-Third air valve; 31-First pressure gauge; 32-Second pressure gauge; 71-First pressure chamber; 72-Second pressure chamber; 81-First actuating rod; 82-Second actuating rod; 100-Sheet metal. Detailed Implementation

[0034] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0035] Example 1

[0036] A specific embodiment of the present invention, such as Figure 1 As shown, a superplastic expansion forming method (hereinafter referred to as the forming method) is disclosed, which uses a forming device to perform superplastic expansion processing on sheet 100.

[0037] The forming method includes the following steps:

[0038] Step 1: Develop a table showing the relationship between piston 8 displacement and sheet metal 100 shape, including the following sub-steps:

[0039] Step 11: Output the node coordinates of the 100 deformable mesh elements of the sheet metal.

[0040] The superplastic expansion process of sheet metal 100 was simulated using finite element simulation software, and the coordinates of the deformed mesh element nodes of sheet metal 100 were output according to the time step.

[0041] Preferably, MARC finite element simulation software is used, with a time step of once every 10 seconds.

[0042] Step 12: Construct a 3D model of the sheet metal deformed by 100mm.

[0043] Based on the coordinates of the deformed sheet metal mesh elements at each time step, reverse modeling is performed to construct a 3D model of the deformed sheet metal 100.

[0044] Preferably, HyperMesh software is used for reverse modeling.

[0045] Step 13: Compile a volume data table for each time point and for the upper cavity 15 and the lower cavity 16.

[0046] Based on the three-dimensional deformation model of sheet metal 100, a solid model of the forming cavity of forming unit 1 is constructed. The volume change state of the forming cavity solid is calculated, that is, the real-time volume of the upper cavity 15 and the lower cavity 16 at all time steps. A volume data table for each time point and the upper cavity 15 and the lower cavity 16 is formulated and input into controller 3.

[0047] Step 14: Establish a table showing the relationship between the displacement of piston 8 and the volume changes of upper cavity 15 and lower cavity 16.

[0048] The volume of the upper cavity 15 is V1, the volume of the lower cavity 16 is V2, the volume of the first pressure chamber 71 is V3, and the volume of the second pressure chamber 72 is V4; the reading of the first pressure gauge 31 is P1, and the reading of the second pressure gauge 32 is P2.

[0049] When piston 8 moves towards one end of the first pressure chamber 71, the total volume V1+V3 of the first air passage 4 (i.e., the upper cavity 15 and the first pressure chamber 71) decreases, and the reading P1 of the first pressure gauge 31 increases; the total volume V2+V4 of the second air passage 6 (i.e., the lower cavity 16 and the second pressure chamber 72) increases, and the reading P2 of the second pressure gauge 32 decreases, creating a pressure difference on both sides of the sheet 100, causing superplastic expansion of the sheet 100. The changes in volume of the first pressure chamber 71 and the second pressure chamber 72 can be calculated based on the area S of one side of piston 8 and the displacement h of piston 8.

[0050] ΔV3=-h·S

[0051] ΔV4=-ΔV3

[0052] Based on the pressure P1 measured by the first pressure gauge 31 and the pressure P2 measured by the second pressure gauge 32 before and after the piston 8 moves, and the protective gas equation pV = nRT, where n represents the amount of gas, R represents the gas constant, and T represents the thermodynamic temperature of the gas, the volume changes of the first gas path 4 and the second gas path 6 can be calculated, namely ΔV1 + ΔV2 and ΔV3 + ΔV4. Subtracting the volume changes of the first pressure chamber 71 and the second pressure chamber 72, ΔV3 and ΔV4, gives the volume changes of the upper cavity 15 and the lower cavity 16, ΔV1 and ΔV2. Thus, the relationship between the displacement h of the piston 8 and the volume changes of the upper cavity 15 and the lower cavity 16, ΔV1 and ΔV2, is established.

[0053] ΔV1=-h·S

[0054] ΔV2=-ΔV1

[0055] Step 15: Establish a table showing the relationship between piston 8 displacement and sheet metal 100 shape.

[0056] Calculate the volumes of the upper cavity 15 and the lower cavity 16 based on the shape of the sheet metal 100, create a table showing the correspondence between the shape of the sheet metal 100 and the volumes of the upper cavity 15 and the lower cavity 16, and store it in the controller 3. Based on the table showing the relationship between the displacement of the piston 8 and the volume changes of the upper cavity 15 and the lower cavity 16, calculate the table showing the relationship between the displacement of the piston 8 and the shape of the sheet metal 100, and store it in the controller 3.

[0057] Step 2: Prepare for superplastic expansion molding, including the following sub-steps:

[0058] Step 21: Install and close the mold, and apply load to the mold.

[0059] Place the sheet metal 100 between the upper mold 11 and the lower mold 12, close the second air valve 22 and the third air valve 23, fill the lower cavity 16 with protective gas, and press the upper mold 11 and the lower mold 12 together.

[0060] Preferably, the material of the sheet metal 100 is TC4 titanium alloy. The load on the contact surface between the lower mold 12 and the sheet metal 100 is 3 MPa.

[0061] Step 22: Zeroing and adjusting pressure regulating cylinder 7

[0062] Connect piston 8 to the lower end of pressure regulating cylinder 7 to minimize the volume of the second pressure chamber 72 and fix the position of piston 8.

[0063] Step 23: Connect the gas line

[0064] Connect the first air passage 4, the exhaust air passage 5, and the second air passage 6, and connect the first air pressure gauge 31, the second air pressure gauge 32, the first air valve 21, the third air valve 23, and the second air valve 22 to the controller 3.

[0065] Step 24: Inflate the air passageway

[0066] Open the first air valve 21 and the third air valve 23 and set the second air valve 22 to the overflow protection state. Open the air supply unit 2 and fill the first air passage 4 and the second air passage 6 with protective gas.

[0067] Preferably, the critical pressure of the second air valve 22 is set to 0.4 MPa, and the air pressure in the air passage is set to 0.3 MPa.

[0068] Step 3: Superplastic expansion pre-stretching

[0069] Heat the forming unit 1 to 920℃ and hold for 10-60 minutes. Set the air supply pressure of the air supply unit 2 to 1MPa and pressurize the forming unit 1. When the values ​​of the first air pressure gauge 31 and the second air pressure gauge 32 are stable and the readings are the same, turn off the air supply unit 2, and close the first air valve 21 and the third air valve 23, so that the upper forming cavity 15 and the first pressure cavity 71 form a sealed space, and the lower forming cavity 16 and the second pressure cavity 72 form another sealed space.

[0070] The control program in controller 3 calculates the displacement h of piston 8 based on the relationship table between piston 8 displacement and sheet 100 shape, forming a piston displacement-time curve throughout the superplastic forming process. It outputs a signal to control piston 8 to move towards the lower end of pressure regulating cylinder 7, and calculates the volume change of upper cavity 15 and lower cavity 16 in real time based on the pressure changes measured by first pressure gauge 31 and second pressure gauge 32, thereby adjusting the displacement speed of piston 8 in real time, thus achieving the purpose of pre-extending the peripheral parts of sheet 100.

[0071] Step 4: Superplastic expansion molding

[0072] The output signal controls the piston 8 to move towards the upper end of the pressure regulating cylinder 7, and calculates the volume change of the upper cavity 15 and the lower cavity 16 in real time based on the pressure change measured by the first pressure gauge 31 and the second pressure gauge 32, thereby adjusting the displacement speed of the piston 8 in real time, thus realizing the control of superplastic expansion forming.

[0073] In a specific forming process, at 300s, V1 = 36549mm 3 Simulation calculations show that V1 = 39012 mm at 310 s. 3 ΔV1=2463mm 3 According to ΔV1=-ΔV3=h·S, where S is the bottom area of ​​the first pressure chamber 71, which is 2827mm². 2The calculated displacement of piston 8 within 10 seconds (300s-310s) is h = 0.87mm. Controller 3 controls the piston displacement within 10 seconds based on the pressure output signals measured by the first and second pressure gauges 31 and 32, adjusting the piston's moving speed in real time to maintain the pressure p1 of the first pressure gauge 31 and the pressure p2 of the second pressure gauge 32 satisfying p1-p2 = 1MPa. The actual piston displacement within 300s-310s is h = 0.86mm, and the actual change in volume of the upper cavity 15 is 2431mm. 3 Within the allowable error range of the expected volume change (2463±50mm) 3 ).

[0074] Step 5: Complete superplastic forming

[0075] Open the first air valve 21, the third air valve 23, and the second air valve 22 to purge the protective gas from the first air passage 4, the second air passage 6, and the exhaust air passage 5. Start forming unit 1, remove sheet metal 100, and superplastic forming is complete.

[0076] Example 2

[0077] Another specific embodiment of the present invention, such as Figure 2 As shown, a superplastic expansion forming apparatus (the forming apparatus of Example 1) is disclosed to implement the forming method of Example 1. It includes a forming unit 1, an air supply unit 2 and a controller 3. The forming unit 1 and the air supply unit 2 are respectively connected to the controller 3. The controller 3 controls the air supply unit 2 to supply air to the forming unit 1 to inflate the sheet material 100 into shape.

[0078] Preferably, the forming unit 1 includes an upper mold 11 and a lower mold 12. The upper mold 11 and the lower mold 12 are disposed in the forming unit 1, and the sheet metal 100 is placed between the upper mold 11 and the lower mold 12. The lower mold 12 includes a forming cavity, which is a hollow part of the lower mold 12. The opening of the hollow part faces the upper mold 11, and the sheet metal 100 can be blown into the forming cavity of the lower mold 12 for forming.

[0079] Preferably, the upper mold 11 is provided with a first air port 13, and the lower mold 12 is provided with a second air port 14. The first air port 13 is connected to the air supply unit 2 via a controller 3. The controller 3 controls the air supply unit 2 to supply air into the upper mold 11 through the first air port 13, inflating the sheet metal 100 into shape. The protective gas in the forming cavity is discharged through the second air port 14. During the superplastic expansion forming process, the forming cavity is divided into two parts by the sheet metal 100. The forming cavity between the sheet metal 100 and the upper mold 11 is the upper forming cavity 15, and the forming cavity between the sheet metal 100 and the lower mold 12 is the lower forming cavity 16. The upper forming cavity 15 is connected to the first air port 13, and the lower forming cavity 16 is connected to the second air port 14.

[0080] Preferably, the gas supply unit 2 is a high-pressure gas cylinder, and the pressure of the protective gas inside the high-pressure gas cylinder is ≥1 MPa, and the protective gas is argon.

[0081] Preferably, the forming apparatus of the present invention further includes a gas path assembly, which includes a first gas path 4 and an exhaust gas path 5. One end of the first gas path 4 is connected to a first air port 13, and the other end is connected to the air supply unit 2. One end of the exhaust gas path 5 is connected to a second air port 14, and the other end is open. The first gas path 4 is used to transmit protective gas to the upper forming cavity 15, and the exhaust gas path 5 is used to discharge protective gas from the lower forming cavity 16.

[0082] Preferably, the first air passage 4 is equipped with a first pressure gauge 31 and a first air valve 21. The first pressure gauge 31 is positioned between the first air port 13 and the first air valve 21, and both the first pressure gauge 31 and the first air valve 21 are connected to the controller 3. The first pressure gauge 31 is used to measure the air pressure in the first air passage 4 and send the pressure reading to the controller 3. The controller 3 can adjust the opening of the first air valve 21, thereby controlling the air intake of the first air passage 4. The controller 3 can also close the first air valve 21, thereby closing the first air passage 4.

[0083] Preferably, the exhaust air passage 5 is provided with a second air valve 22. The controller 3 can adjust the opening of the second air valve 22 to control the air output of the exhaust air passage 5. The controller 3 can also close the second air valve 22 to close the exhaust air passage 5.

[0084] Preferably, the second air valve 22 is an overflow exhaust valve, which can be set to an overflow protection state and a critical pressure. When the air pressure in the exhaust air passage 5 is higher than the critical pressure, the second air valve 22 can be automatically opened, and the exhaust air passage 5 is opened to release pressure, preventing damage to the forming unit 1; the second air valve 22 can also be opened or closed to open or close the exhaust air passage 5.

[0085] Preferably, the gas path assembly further includes a second gas path 6. One end of the second gas path 6 is connected to the second gas port 14, and the other end is connected to the gas supply unit 2. The second gas path 6 is used to deliver protective gas to the downward cavity 16.

[0086] Preferably, the second air passage 6 is equipped with a second pressure gauge 32 and a third air valve 23. The second pressure gauge 32 is positioned between the second air port 14 and the third air valve 23, and both the second pressure gauge 32 and the third air valve 23 are connected to the controller 3. The second pressure gauge 32 is used to measure the air pressure in the second air passage 6 and send the pressure reading to the controller 3. The controller 3 can adjust the opening of the third air valve 23, thereby controlling the air output of the second air passage 6. The controller 3 can also close the third air valve 23, thereby closing the second air passage 6.

[0087] Preferably, the forming apparatus of the present invention further includes a pressure regulating unit, which includes a pressure regulating cylinder 7 and a piston 8, with the piston 8 disposed inside the pressure regulating cylinder 7. The two ends of the pressure regulating cylinder 7 are respectively connected to the first air passage 4 and the second air passage 6, with the end connected to the first air passage 4 being the upper end and the end connected to the second air passage 6 being the lower end.

[0088] Preferably, the pressure regulating cylinder 7 includes a cylinder cavity, which is divided into two parts by the piston 8. The part of the cylinder cavity connected to the first air passage 4 is the first pressure chamber 71, and the part of the cylinder cavity connected to the second air passage 6 is the second pressure chamber 72. The protective gas in the first pressure chamber 71 can be transferred to the upper cavity 15 through the first air passage 4, and the protective gas in the second pressure chamber 72 can be transferred to the lower cavity 16 through the second air passage 6. The piston 8 can move to one end or the other end of the pressure regulating cylinder 7, thereby changing the volume of the first pressure chamber 71 and the second pressure chamber 72.

[0089] Preferably, in order to drive the piston 8, the forming apparatus of the present invention further includes an actuation assembly, which includes a first actuating rod 81 and a first actuator (not shown in the figure). One end of the first actuating rod 81 passes through the side wall of the upper end of the pressure regulating cylinder 7 and is connected to one end of the piston 8. The other end of the first actuating rod 81 is connected to the first actuator, which is connected to the controller 3. The controller 3 can control the first actuator to push or pull the first actuating rod 81, thereby pushing or pulling the piston 8, causing the piston 8 to move towards the upper or lower end of the pressure regulating cylinder 7, thereby pressing the protective gas in the first pressure chamber 71 into the upper forming cavity 15, or pressing the protective gas in the second pressure chamber 72 into the lower forming cavity 16, thereby changing the shape of the sheet metal 100.

[0090] Preferably, the first actuator is a hydraulic cylinder or an electric cylinder, which pushes or pulls the first actuating rod 81. Alternatively, the first actuator includes a worm gear pair and a motor. The worm gear pair is mounted on the first actuating rod 81, and the motor is connected to both the worm and the controller 3. The controller 3 controls the motor to rotate, thereby driving the worm. The worm drives the worm wheel to rotate, which in turn drives the first actuating rod 81 to move, thus driving the piston 8. The worm gear pair has a self-locking function and a reduction ratio greater than 40, ensuring self-locking and driving of the first actuating rod 81.

[0091] Preferably, the actuation assembly further includes a second actuating rod 82 and a second actuator (not shown in the figure). One end of the second actuating rod 82 passes through the side wall of the lower end of the pressure regulating cylinder 7 and is connected to the other end of the piston 8. The other end of the second actuating rod 82 is connected to the second actuator, which is connected to the controller 3. The second actuator has the same structure as the first actuator. The second actuating rod 82 has the same structure as the first actuating rod 81, and the rate of change of the volume of the first pressure chamber 71 and the second pressure chamber 72 is the same. Moreover, compared to setting a single actuator, two actuators improve the driving force on the piston 8 and the self-locking firmness.

[0092] In the superplastic forming process, the thickness of the center part of the sheet 100 is usually less than that of the periphery. Therefore, a pre-forming operation can be performed on the sheet 100 to pre-extend the periphery of the sheet 100, making the periphery thinner than the center part.

[0093] Preferably, such as Figure 3 As shown, the upper mold 11 is a circular upper mold, and the sheet metal 100 is a circular plate-shaped sheet metal. The upper mold 11 includes an annular cavity 17, which is disposed on the outer wall of the upper mold 11 that contacts the sheet metal 100. The annular cavity 17 is an annular groove, and the opening of the annular groove faces the sheet metal 100. The peripheral part of the sheet metal 100 can extend into the annular cavity 17, thereby making the peripheral part of the sheet metal 100 thinner. When the sheet metal 100 is superplastic formed, the thickness of the sheet metal 100 after forming can be more uniform.

[0094] Preferably, the annular cavity die 17 is concentric with the upper die 11, and the center of the sheet metal 100 is circular and concentric with both the sheet metal 100 and the upper die 11.

[0095] Preferably, to prevent the sheet metal 100 from clogging the first air port 13 during the extension of the upper die 11 and the annular die 17, the opening of the first air port 13 in the upper cavity 15 is provided on the annular die 17. Multiple first air ports 13 are provided, allowing for more complete and uniform extension and deformation of the sheet metal 100 during preforming.

[0096] Compared to existing technologies, in this embodiment, the controller 3 can control the first actuator to push or pull the first actuator rod 81, thereby pushing or pulling the piston 8, causing the piston 8 to move towards the upper or lower end of the pressure regulating cylinder 7, thus pressing the protective gas in the first pressure chamber 71 into the upper cavity 15, or pressing the protective gas in the second pressure chamber 72 into the lower cavity 16, thereby changing the shape of the sheet metal 100; the worm gear pair is mounted on the first actuator rod 81, and the motor is connected to the worm and the controller 3 respectively. The controller 3 can control the motor to rotate, thereby driving the worm, which can drive the worm wheel to rotate, and drive the first actuator rod 81 to move, thereby driving the piston 8; the worm gear pair has a self-locking function, and The reduction ratio is greater than 40, ensuring the self-locking and driving of the first actuator 81; the second actuator has the same structure as the first actuator, the second actuator 82 has the same structure as the first actuator 81, and the volume change rate of the first pressure chamber 71 and the second pressure chamber 72 is the same; and compared with setting a single actuator, the two actuators improve the driving force and self-locking firmness of the piston 8; the annular die 17 is an annular groove, the opening of the annular groove faces the sheet metal 100, and the peripheral part of the sheet metal 100 can extend into the annular die 17, thereby making the peripheral part of the sheet metal 100 thinner, and when the sheet metal 100 is superplastic formed, the thickness of the sheet metal 100 after forming can be more uniform.

[0097] Example 3

[0098] In another specific embodiment of the forming method of the present invention, the sheet 100 is subjected to superplastic expansion forming using a forming device. Based on embodiment 1, steps 3: superplastic expansion pre-extension and step 4: superplastic expansion forming are improved.

[0099] Step 3: Superplastic expansion pre-stretching

[0100] The driving mechanism drives the lower punch 18 to press the sheet metal 100 towards the upper die 11, squeezing the peripheral part of the sheet metal 100 into the annular die 17. The peripheral part of the sheet metal 100 extends into the annular die 17, making the peripheral part of the sheet metal 100 thinner.

[0101] Step 4: Superplastic expansion molding

[0102] Heat the forming unit 1 to 920℃ and hold for 10-60 minutes. Set the air supply pressure of the air supply unit 2 to 1MPa and pressurize the forming unit 1. When the values ​​of the first air pressure gauge 31 and the second air pressure gauge 32 are stable and the readings are the same, turn off the air supply unit 2, and close the first air valve 21 and the third air valve 23, so that the upper forming cavity 15 and the first pressure cavity 71 form a sealed space, and the lower forming cavity 16 and the second pressure cavity 72 form another sealed space.

[0103] The control program in controller 3 calculates the displacement h of piston 8 based on the relationship table between piston 8 displacement and sheet 100 shape, forming a piston displacement-time curve throughout the superplastic forming process. It outputs a signal to control piston 8 to move towards the upper end of pressure regulating cylinder 7, and calculates the volume change of upper cavity 15 and lower cavity 16 in real time based on the pressure change measured by first pressure gauge 31 and second pressure gauge 32, thereby adjusting the displacement speed of piston 8 in real time and realizing superplastic expansion forming control.

[0104] Example 4

[0105] Another specific embodiment of the forming apparatus of the present invention (the forming apparatus of embodiment 3), such as Figure 4 As shown, the lower mold 12 has been improved based on Example 2.

[0106] Preferably, the lower die 12 is provided with a lower punch 18 and a driving mechanism (not shown in the figure). The lower punch 18 is connected to the driving mechanism, and the driving mechanism is connected to the lower die 12. The driving mechanism can drive the lower punch 18 to extrude the sheet metal 100 towards the upper die 11 and extrude the peripheral part of the sheet metal 100 into the annular die 17. The peripheral part of the sheet metal 100 can extend into the annular die 17, thereby making the peripheral part of the sheet metal 100 thinner. When the sheet metal 100 is superplastic formed, the thickness of the sheet metal 100 after forming can be more uniform.

[0107] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for superplastic expansion molding, characterized in that, Using a superplastic expansion molding device, The superplastic expansion forming device includes a forming unit (1), a pressure regulating cylinder (7) and a piston (8). The forming unit (1) includes an upper mold (11) and a lower mold (12). A sheet metal (100) is placed between the upper mold (11) and the lower mold (12). An annular cavity (17) is provided on the outer wall of the upper mold (11) that contacts the sheet metal (100). The opening of the annular cavity faces the sheet metal (100). A lower punch (18) and a driving mechanism are provided on the lower mold (12). The lower punch (18) is connected to the driving mechanism, and the driving mechanism is connected to the lower mold (12). The forming method includes the following steps: A. Develop a table showing the relationship between piston (8) displacement and sheet metal (100) shape; B. Prepare for superplastic expansion molding; Superplastic expansion pre-extension: The driving mechanism drives the lower punch (18) to extrude the sheet metal (100) towards the upper die (11), and squeezes the peripheral part of the sheet metal (100) into the annular die (17). The peripheral part of the sheet metal (100) extends into the annular die (17), making the peripheral part of the sheet metal (100) thinner. C. Superplastic expansion molding; D. Complete superplastic forming.

2. The superplastic expansion forming method according to claim 1, characterized in that, Step A involves creating a table showing the relationship between the piston (8) displacement and the sheet metal (100) shape, including calculating the real-time volume of the upper cavity (15) and the lower cavity (16) at all time steps, creating a table of volume data for each time point and the upper cavity (15) and the lower cavity (16), and inputting it into the controller (3).

3. The superplastic expansion forming method according to claim 2, characterized in that, Step A, establishing the relationship table between piston (8) displacement and sheet (100) shape, also includes establishing the relationship table between piston (8) displacement and upper cavity (15) and lower cavity (16) volume change.

4. The superplastic expansion forming method according to claim 3, characterized in that, Step A, "Formulating the relationship table between piston (8) displacement and sheet (100) shape", also includes establishing the relationship table between piston (8) displacement and sheet (100) shape.

5. The superplastic expansion forming method according to claim 1, characterized in that, Step B, preparing for superplastic expansion molding, includes loading and closing the mold, and applying contact surface load to the mold.

6. The superplastic expansion forming method according to claim 5, characterized in that, The contact surface load is 3 MPa.

7. The superplastic expansion forming method according to claim 6, characterized in that, Step B, preparing for superplastic expansion molding, also includes connecting the piston (8) to the lower end of the pressure regulating cylinder (7) to reduce the volume of the second pressure chamber (72) to the minimum and fix the position of the piston (8).

8. The superplastic expansion forming method according to claim 7, characterized in that, Step B, preparing for superplastic expansion molding, further includes: opening the first gas valve (21) and the third gas valve (23) and setting the second gas valve (22) to the overflow protection state, opening the gas supply unit (2), and filling the first gas path (4) and the second gas path (6) with protective gas.

9. The superplastic expansion forming method according to claim 8, characterized in that, The critical pressure of the second air valve (22) is set to 0.4 MPa, and the air pressure of the first air passage (4) and the second air passage (6) is set to 0.3 MPa.

10. The superplastic expansion forming method according to claim 1, characterized in that, The material of the plate (100) is TC4 titanium alloy.

Images