Low stress forming of metal variable wall thickness diaphragms

Abstract

The application relates to a low-stress forming method of a metal variable-wall-thickness diaphragm, and belongs to the technical field of metal diaphragms, to solve the problems that the prior art method cannot form and manufacture the variable-wall-thickness diaphragm at one time, and the precision and quality of the diaphragm prepared by the prior art method are difficult to control. The forming method of the metal variable-wall-thickness diaphragm comprises the following steps: (a) preparing a variable-thickness circular metal diaphragm forming blank from a metal plate; and (b) sequentially performing hot pressure stretching and hot expansion stretching on the metal diaphragm blank in a mold to obtain the metal variable-wall-thickness diaphragm. The forming method has the advantages of high machining precision and high yield rate by means of simulation simulation and high-precision grinding process control.

Description

Technical Field

[0001] This invention relates to the field of metal diaphragm technology, and more particularly to a low-stress forming method for metal variable wall thickness diaphragms. Background Technology

[0002] The metal diaphragm (hereinafter referred to as the diaphragm) is the main working component of the metal diaphragm tank. The normal flipping deformation of the diaphragm according to operational requirements is a necessary condition for ensuring the reliable operation of the spacecraft. Failure of the diaphragm to flip and deform can lead to serious consequences such as spacecraft launch failure and satellite attitude adjustment failure. Therefore, it is essential to study the reliability of the effective flipping deformation of the diaphragm. Existing metal thin film manufacturing processes suffer from problems such as high processing difficulty, high cost, low precision, and incompatibility with specific field requirements.

[0003] On the one hand, traditional metal diaphragm manufacturing processes often employ multiple methods such as machining, forging, and heat treatment. However, these methods typically require multiple processing steps and complex procedures, making it difficult to control the precision and quality of the diaphragm. On the other hand, the thickness of traditional metal diaphragms is often gradually varying, making one-step manufacturing impossible. Therefore, it is necessary to develop a new metal diaphragm manufacturing process that ensures the processing precision and quality of the diaphragm while meeting the needs of specific fields. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a low-stress forming method for metal variable wall thickness films, in order to solve the problems that existing methods cannot manufacture variable wall thickness films in one step, and that the precision and quality of films prepared by existing methods are difficult to control.

[0005] In a first aspect, the present invention provides a method for forming a metal variable-wall thickness film, comprising the following steps:

[0006] (a) Forming a circular metal diaphragm blank of varying thickness from a sheet metal;

[0007] (b) The metal film blank is placed in the mold and then subjected to hot pressing and hot expansion stretching to form a metal variable wall thickness film.

[0008] Furthermore, step (a) is performed as follows:

[0009] (1) Determine the target membrane parameters;

[0010] (2) Establish a diaphragm blank model in the finite element model based on the target diaphragm parameters;

[0011] (3) Perform finite element simulation on the process of processing the diaphragm blank model into a diaphragm to obtain the model after blank deformation. Use mesh generation to track the position points of the blank after deformation and obtain the difference in thickness at different radial positions of the model after blank deformation.

[0012] (4) Compare the difference in thickness at different radial positions of the model after blank deformation with the difference in thickness at the corresponding radial position of the target diaphragm to determine the final diaphragm blank model.

[0013] (5) Based on the thickness values ​​of different radial positions of the final determined diaphragm blank model, determine the outline size of the diaphragm blank model and select the corresponding grinding roller;

[0014] (6) Provide a metal sheet and use the grinding roller described in step (5) to grind the metal sheet to obtain a metal diaphragm forming blank.

[0015] Furthermore, in step (3) or (4), the difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

[0016] Furthermore, in step (4), if the difference between the thickness of the model at different radial positions after the blank is deformed and the difference between the thickness of the target diaphragm at the corresponding radial position is -0.02 to 0.02 mm, then the diaphragm blank model established in step (2) is determined to be the final diaphragm blank model.

[0017] If the difference between the thickness of the model at different radial positions after blank deformation and the difference between the thickness of the target diaphragm at the corresponding radial position are not within the range of -0.02 to 0.02 mm, then the difference between the thickness of the model after blank deformation and the difference between the two should be corrected to satisfy -0.02 to 0.02 mm.

[0018] Furthermore, in step (6), positioning holes are machined into the metal plate to determine the fixed position of the metal plate on the rotary grinding table. One side of the metal plate is ground to obtain a flat bottom surface. The flat bottom surface is placed on the rotary grinding table and fixed by vacuum adsorption so that the metal plate is evenly attached to the rotary grinding table. The rotary grinding table is turned on to complete the grinding of the metal plate and obtain the metal film forming blank.

[0019] Furthermore, in step (6), when the metal sheet is ground on the rotary table, the thickness at different radial positions is obtained by an ultrasonic thickness gauge or a laser rangefinder.

[0020] Furthermore, in step (b), the temperature of the hot pressing stretching is 650–850°C, and the pressure is 10–2000 tons.

[0021] Furthermore, in step (b), the pressure during thermal expansion and stretching is 0.2–1 MPa, and the holding time is 30–120 min.

[0022] Secondly, the present invention provides a metal variable wall thickness film obtained by the method described.

[0023] Thirdly, the present invention provides an anti-sway energy absorption structure built into an aircraft tank, comprising a square porous grid array and the aforementioned diaphragm;

[0024] The square porous mesh array consists of multiple units arranged along the XYZ coordinates to form a porous mesh array skeleton. The square porous mesh array is composed of several mesh units, each mesh unit including an axisymmetric first sub-frame and a second sub-frame. A diaphragm is installed in the first sub-frame and the second sub-frame, respectively. The wave crest direction of the diaphragm in the first sub-frame is opposite to that of the diaphragm in the second sub-frame.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] (1) The forming method of the present invention firstly controls the process through simulation and high-precision grinding, which has the advantages of high processing accuracy and high yield. Since the diaphragm will thin during the gradual transformation process and the subsequent thermoforming process, the present invention controls the material thickness through finite element simulation technology and completes the reverse calculation of the material. This can avoid the need for secondary processing after the forming of the plate of equal thickness, so that the diaphragm has more uniform performance in the latitudinal direction, forming a structure that is thick in the middle and thin at the edges. This allows it to form a structure that becomes thinner and thicker when it is processed into a metal diaphragm, making the deformation of the metal diaphragm more uniform, achieving high precision, improving processing efficiency, and eliminating the need for turning. This method can significantly improve the qualification rate of the produced diaphragms.

[0027] (2) The anti-sway energy-absorbing composite structure of the present invention dissipates energy through the plastic deformation of the diaphragm, exhibiting a strong plastic energy dissipation effect. The hollow structure design of the grid array reduces the overall weight of the structural components. At the same time, the cross-combination design of the diaphragm can dissipate the liquid impact energy with opposite directions, achieving a good impact energy absorption effect. Therefore, the anti-sway energy-absorbing structure of the present invention has the characteristics of small weight, high impact absorption energy range, detachability, and reusability.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0029] 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.

[0030] Figure 1This is a three-dimensional structural diagram of a metal variable wall thickness film according to the present invention;

[0031] Figure 2 This is a front view of a metal variable wall thickness film according to the present invention;

[0032] Figure 3 This is a front view of a metal variable-wall thick film with raised ribs according to the present invention;

[0033] Figure 4 This is a front view of a metal variable-wall thick film with raised ribs according to the present invention;

[0034] Figure 5 This is a schematic diagram of a metal diaphragm forming blank structure according to the present invention;

[0035] Figure 6 This is a schematic diagram of a metal diaphragm forming blank structure with reinforcing ribs according to the present invention;

[0036] Figure 7 This is a front view of an apparatus for preparing a metal film blank according to the present invention;

[0037] Figure 8 This is a left view of an apparatus for preparing a metal film blank according to the present invention;

[0038] Figure 9 This is a schematic diagram showing the positional relationship between a metal diaphragm blank and a grinding roller according to the present invention;

[0039] Figure 10 This is a schematic diagram showing the positional relationship between a metal diaphragm blank with reinforcing ribs and a grinding roller according to the present invention.

[0040] Figure 11 This is a schematic diagram of a rigid-flexible composite forming mold structure according to the present invention;

[0041] Figure 12 This is a schematic diagram of a vacuum suction cup structure according to the present invention;

[0042] Figure 13 This is a schematic diagram of another rigid-flexible composite forming mold structure according to the present invention;

[0043] Figure 14 This is a schematic diagram of a finite element simulation according to the present invention;

[0044] Figure 15 This is a schematic diagram of the square porous mesh array of the present invention;

[0045] Figure 16 This is a schematic diagram of the structure of the grid unit equipped with the diaphragm according to the present invention;

[0046] Figure 17This is a cross-sectional view of the welding between the diaphragm and the support ring stop of the present invention;

[0047] Figure 18 This is a schematic diagram of the bolt connection between the grid unit, support ring, and fixing plate of the present invention;

[0048] Figure 19 This is a schematic diagram of the porous mesh array skeleton of the present invention;

[0049] Figure 20 This is a schematic diagram of the porous mesh array skeleton with membranes according to the present invention;

[0050] Figure 21 This is a schematic diagram of the four diaphragms of the present invention around the axis;

[0051] Figure label:

[0052] 1-Central flipping area, 2-Edge fixing area, 3-Protruding rib, 4-Metal diaphragm forming blank, 41-Edge part, 42-Middle part, 5-Reinforcing rib, 6-Rotating table, 7-Grinding roller, 8-Rotating shaft, 9-Spring modulator, 10-Ultrasonic vibrator, 11-Groove, 12-Upper hot-pressing stretching area, 13-Upper hot-expansion stretching area, 14-Lower hot-pressing stretching area, 15-Lower hot-expansion stretching area, 16-Air inlet, 17-Boss, 18-Concave, 19-Recess, 01-Square porous mesh array, 02-Diaphragm, 03-Support ring, 04-Fixing plate, 07-Mesh unit, 08-Slot, 09-Stop structure, 010-Through hole, 011-Main impact surface, 012-Secondary impact surface. Detailed Implementation

[0053] 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.

[0054] One specific embodiment of the present invention discloses a method for forming a metal variable wall thickness film, comprising the following steps:

[0055] (a) Forming a circular metal diaphragm blank of varying thickness from a sheet metal;

[0056] (b) The metal film blank is placed in the mold and then subjected to hot pressing and hot expansion stretching to form a metal variable wall thickness film.

[0057] Furthermore, step (a) is performed as follows:

[0058] (1) Determine the parameters of the target membrane;

[0059] (2) Establish a diaphragm blank model in the finite element model based on the target diaphragm parameters;

[0060] (3) Perform finite element simulation on the process of processing the diaphragm blank model into a diaphragm to obtain the model after the blank is deformed. Use mesh generation to track the position points of the blank after deformation and obtain the difference in thickness at different radial positions of the model after the blank is deformed.

[0061] (4) Compare the difference in thickness at different radial positions of the model after blank deformation with the difference in thickness at the corresponding radial position of the target diaphragm to determine the final diaphragm blank model.

[0062] (5) Based on the thickness values ​​of different radial positions of the final determined diaphragm blank model, determine the outline size of the diaphragm blank model and select the corresponding grinding roller;

[0063] (6) Provide a metal sheet and use the grinding roller described in step (5) to grind the metal sheet to obtain a metal diaphragm forming blank.

[0064] In one specific implementation, in step (3) or (4), the difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

[0065] In one specific implementation, in step (4), if the difference between the thickness of different radial positions of the model after blank deformation and the difference between the thickness of the radial position corresponding to the target diaphragm is -0.02 to 0.02 mm, then the diaphragm blank model established in step (2) is determined to be the final diaphragm blank model.

[0066] If the difference between the thickness of the model at different radial positions after blank deformation and the difference between the thickness of the target diaphragm at the corresponding radial position are not within the range of -0.02 to 0.02 mm, then the difference between the thickness of the model after blank deformation and the difference between the two should be corrected to satisfy -0.02 to 0.02 mm.

[0067] In one specific implementation, in step (6), positioning holes are machined into the metal plate to determine the fixed position of the metal plate on the rotary grinding table. One side of the metal plate is ground to obtain a flat bottom surface. The flat bottom surface is placed on the rotary grinding table and fixed by vacuum adsorption so that the metal plate is evenly attached to the rotary grinding table. The rotary grinding table is turned on to complete the grinding of the metal plate and obtain the metal film forming blank.

[0068] In one specific implementation, in step (6), when the metal sheet is ground on the rotary table, the thickness at different radial positions is obtained by an ultrasonic thickness gauge or a laser rangefinder.

[0069] In one specific implementation, in step (b), the temperature of the hot pressing stretching is 650–850°C, and the pressure is 10–2000 tons.

[0070] In one specific implementation, in step (b), the pressure during thermal expansion and stretching is 0.2 to 1 MPa, and the holding time is 30 to 120 min.

[0071] Another specific embodiment of the present invention discloses a metal variable wall thickness film obtained by the above method. The film is circular, and the thickness of the film gradually decreases from the center to the edge, forming a structure that is thicker in the middle and thinner at the edge. The film includes a central flipping area 1 and an edge fixing area 2. The central flipping area 1 is hemispherical, and the arc of the hemispherical arc surface is R10 to R800. The diameter of the film is 30 to 1800 mm, the height is 15 to 1200 mm, the thickness of the central flipping area 1 is 0.4 to 2 mm, and the thickness of the edge fixing area is 0.2 to 1.2 mm.

[0072] In existing technologies, diaphragms are all manufactured by hot stamping and then machining relatively thick plates. The anisotropy of the plates can cause significant flipping instability and eccentricity in the diaphragms. However, the diaphragm of this invention can effectively solve this problem. The contour formed by deformation at the pre-flipping edge weakens the existing microstructure of the plate and reduces the anisotropy of the raw material, enabling the variable wall thickness diaphragm to achieve a stable and eccentric flipping effect.

[0073] In one specific implementation, the edge fixing area is a flange structure formed by the downward indentation of the edge of the template.

[0074] In one specific embodiment, a raised rib 3 is provided on the central flipping area 1, and the cross-section of the raised rib 3 is one of a semi-circle, a rectangle, a square or a trapezoid.

[0075] Another specific embodiment of the present invention discloses a specific application of the above-mentioned metal variable wall thickness diaphragm as a diaphragm for an anti-sway energy absorption structure built into an aircraft tank.

[0076] Specifically, such as Figure 15-21 As shown, the present invention discloses an anti-sway energy absorption structure built into an aircraft storage tank, comprising a square porous mesh array 01 and a diaphragm 02;

[0077] The square porous mesh array 01 consists of multiple units arranged along the XYZ coordinates to form a porous mesh array skeleton. The square porous mesh array 01 is composed of several mesh units 07. Each mesh unit 07 includes an axisymmetric first sub-frame and a second sub-frame. A diaphragm 02 is installed in the first sub-frame and the second sub-frame, respectively. The wave crest direction of the diaphragm 02 in the first sub-frame is opposite to that of the diaphragm 02 in the second sub-frame.

[0078] Specifically, the diaphragm 02 is fixedly connected to the grid unit 07 via the support ring 03 and the fixing plate 04.

[0079] In one specific embodiment, the first and second sub-grid frames of the grid unit 07 are each provided with a recessed groove as a slot 08, and the slots 08 of the first and second sub-grid frames are oriented in opposite directions; each of the first and second sub-grid frames is equipped with a diaphragm 02, and the crests of the two diaphragms 02 are oriented in opposite directions, with the crests of the diaphragms 02 pointing towards the slot 08 of the grid unit 07. During installation, a support ring 03 is placed on the slot 08, and then a fixing plate 04 is placed on it. The slot 08, support ring 03, and fixing plate 04 are fixed by bolts.

[0080] In one specific embodiment, the support ring 03 is provided with a stop structure 09 that is welded to the diaphragm 02, and the outer arc contour of the support ring 03 is consistent with the inner contour of the diaphragm flange structure. The diaphragm 02 is disposed below the support ring 03, and the diaphragm 02 is fixedly connected to the stop structure 09 of the support ring 03. The support ring 03 is disposed above the slot 08 of the grid unit 07, and the fixing plate 04 is disposed above the support ring 03. The slot 08, the support ring 03, and the fixing plate 04 are fixed to the diaphragm 02 by bolts. The diaphragm 02 is detachably and fixedly connected in the grid unit 07.

[0081] Among them, the stop structure 09 ensures the welding strength, and the support ring 03 provides support when the diaphragm flips. The rigid grid unit 07, the support ring 03 and the flexible diaphragm work together to make the whole rigid-flexible composite structure achieve the effect of energy absorption and shock reduction.

[0082] Unlike traditional energy absorption principles, this invention is based on the principle of modal superposition. Because the impact energy varies at different locations within the tank, the corresponding diaphragm deformation responses also differ, resulting in the entire structure being in a superposition of different states. This invention uses several grid units 07 to form the entire porous grid array skeleton, fully utilizing the monostable equilibrium structure. During the plastic deformation of the metal diaphragm during flipping, no higher-order modal deformation occurs, exhibiting a strong plastic energy dissipation effect under cyclic loading of liquid sloshing impact. In other words, the nonlinear plastic response deformation of the diaphragm 02 effectively absorbs energy.

[0083] Compared with existing technologies, this invention provides a novel multi-directional coupled modal anti-sloshing energy-absorbing composite structure. Continuous impacts induce a dynamic response in this structure, enabling continuous kinetic energy absorption and reducing the peak impact value of the liquid fuel in the entire tank. This achieves energy absorption and anti-sloshing in different directions, suppressing the swirling disturbance of the liquid fuel. Under cyclic loading of liquid sloshing impacts, the structure dissipates energy through the plastic deformation of diaphragms, exhibiting a strong plastic energy dissipation effect. The hollow structure design of the grid array reduces the overall structural weight, while the cross-combination design of the diaphragms dissipates liquid impact energy in opposite directions, achieving a good impact energy absorption effect. Therefore, the anti-sloshing energy-absorbing structure of this invention features low weight, high impact absorption energy range, detachability, and reusability.

[0084] In one specific embodiment, the support ring 03 is provided with equally spaced through holes 010 near the stop structure 09.

[0085] By arranging equally spaced through holes 010 around the perimeter, the fuel in the tank can be diverted, reducing the local overload impact of propellant fuel on the diaphragm 02.

[0086] Specifically, the porous mesh array skeleton divides the square porous mesh array 01 into a main impact surface 011 and two secondary impact surfaces 012. The boundary line between the main impact surface 011 and the secondary impact surface 012 serves as the axis. Multiple diaphragms 02 around the axis have the same clockwise or counterclockwise wave crest direction. For example, Figure 20 As shown, the four diaphragms 02 around the axis point in the same direction along clockwise or counterclockwise.

[0087] The diaphragms are positioned so that the peaks point in the same direction, either clockwise or counterclockwise, creating multiple obstacles to the sloshing and swirling of the propellant fuel. All four diaphragms, whether clockwise or counterclockwise, can prevent sloshing in the same direction, thus avoiding swirling disturbances of the liquid fuel in the tank.

[0088] Specifically, the main impact surface 011 is perpendicular to the main sloshing impact direction of the liquid in the tank.

[0089] Specifically, the porous mesh array skeleton establishes XYZ coordinates with the central axis of the tank, and the central axis of the tank is perpendicular to the main impact surface 011. The square porous mesh array 01 can be arranged in the XY, XZ and YZ planes of the tank respectively.

[0090] A three-dimensional porous mesh array framework is constructed. When the liquid inside the tank sloshes and impacts, diaphragms 02 at corresponding positions dissipate the liquid vibration energy through plastic deformation. Through the flexible and coordinated deformation of numerous diaphragms in different modes, the excitation disturbance outside the aircraft tank is significantly reduced, meeting the requirements for high-level load-bearing and shock resistance.

[0091] In one specific embodiment, the planar dimensions of the grid cell 07 are (0.08-0.2)Φ×(0.04-0.1)Φ, where Φ is the equivalent diameter of the tank cross-section.

[0092] Preferably, the thickness of the grid unit 07 is determined according to the tank capacity, and is generally ≥3.2mm.

[0093] By controlling the thickness of grid cell 07, the weight of the structure can be reduced while ensuring the overall structural rigidity and strength.

[0094] Preferably, when the tank capacity is >500L, the thickness of the grid unit 07 is ≥4.2mm; when the tank capacity is >800L, the thickness of the grid unit 07 is ≥5.4mm; and when the tank capacity is >1000L, the thickness of the grid unit 07 is ≥7.8mm.

[0095] Setting a lower limit on the thickness of grid cell 07 is to ensure the rigidity of the anti-sway device when the tank volume increases.

[0096] Preferably, the grid unit 07 is made of high-strength and high-toughness alloy by machining.

[0097] In one specific embodiment, the anti-sway energy-absorbing structure built into the aircraft tank also includes a bolt assembly, wherein bolt mounting holes are provided on the slot 08, the support ring 03 and the fixing plate 04, and the bolt mounting holes are adapted to the bolts.

[0098] Preferably, the number of bolt connections on one side of the grid unit 07 is ≥6.

[0099] Compared with existing technologies, the use of threaded mechanical fitting instead of traditional welding allows for convenient and quick replacement of damaged diaphragms and support rings 03, enabling the overall structure to be disassembled and reused, thus improving the service life of the overall anti-sway energy-absorbing structure and reducing maintenance costs.

[0100] Preferably, the fixing plate 04 and the slot 08 of the grid unit 07 are interference-fitted to provide a certain structural preload.

[0101] like Figure 1-13 As shown, in a specific embodiment of the present invention, a metal film forming blank prepared by the above method is disclosed. The blank is a circle composed of a middle part 42 and an edge part 41. The thickness of the blank 4 gradually decreases from the center to the edge, forming a structure that is thick in the middle and thin at the edge. The diameter of the blank is 50 to 2000 mm, the thickness of the middle part 42 is 0.5 to 2.2 mm, and the thickness of the edge part 41 is 0.3 to 1.4 mm.

[0102] The metal diaphragm forming blank of the present invention is configured with a structure that is thick in the middle and thin at the edges, which allows it to form a structure that varies in thickness when it is processed into a metal diaphragm. This results in more uniform deformation of the metal diaphragm, enabling high precision, improving processing efficiency, and eliminating the need for turning. This structure can significantly improve the yield rate of the produced diaphragms.

[0103] In one specific embodiment, at least one circumferential reinforcing rib 5 is provided on the middle part 42, and the cross-section of the reinforcing rib 5 is one of a semi-circle, a rectangle, a square or a trapezoid.

[0104] In one specific embodiment, the width of the reinforcing rib 5 is 0.5-4 mm, the thickness is 0.5-3 mm, and the number of reinforcing ribs 5 is 1-4.

[0105] It should be noted that the width of the reinforcing rib 5 refers to its length in the longitudinal direction of the sphere, and the thickness refers to its length in the normal direction of the sphere.

[0106] In one specific embodiment, the reinforcing rib 5 is a reinforcing material formed by adding silicon carbide particles or carbon nanotubes to the metal as additives.

[0107] Specifically, the billet is one or more of stainless steel, aluminum, aluminum alloy, titanium, or titanium alloy.

[0108] Based on step (a) above, the present invention also discloses a method for processing the above-mentioned metal diaphragm forming blank, comprising the following steps:

[0109] (1) Determine the parameters of the target membrane;

[0110] (2) Establish a diaphragm blank model in the finite element model based on the target diaphragm parameters;

[0111] (3) Perform finite element simulation on the process of processing the diaphragm blank model into a diaphragm to obtain the model after the blank is deformed. Use mesh generation to track the position points of the blank after deformation and obtain the difference in thickness at different radial positions of the model after the blank is deformed.

[0112] (4) Compare the difference in thickness at different radial positions of the model after blank deformation with the difference in thickness at the corresponding radial position of the target diaphragm to determine the final diaphragm blank model.

[0113] (5) Based on the thickness values ​​of different radial positions of the final determined diaphragm blank model, determine the outline size of the diaphragm blank model and select the corresponding grinding roller;

[0114] (6) Provide a metal sheet and use the grinding roller described in step (5) to grind the metal sheet to obtain a metal diaphragm forming blank.

[0115] Compared with existing technologies, the processing method of the metal diaphragm forming blank of the present invention, firstly through simulation and high-precision grinding process control, has the advantages of high processing accuracy and high yield. Since the diaphragm will thin during the gradual transformation process and subsequent thermoforming process, the present invention controls the material thickness through finite element simulation technology and completes the reverse calculation of the material. This avoids the need for secondary processing after the forming of the uniform thickness plate, resulting in a more uniform performance of the diaphragm in the latitudinal direction.

[0116] In one specific implementation, in step (2), finite element simulation is carried out by modeling and simulation using commercial software such as Abaqus and Ansys, or by directly building a model using commercial software such as UG, ProE, and Solidworks.

[0117] Specifically, finite element simulation uses the diaphragm flipping pressure difference system parameters to determine material profile, pre-flipped radius, spherical radius, straightness angle, and wall thickness conditions at different locations to establish the model. It should be noted that all the above finite element simulations are performed using existing technical methods.

[0118] In one specific implementation, in step (3) or (4), the difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

[0119] In one specific implementation, in step (4), if the difference between the thickness of different radial positions of the model after blank deformation and the difference between the thickness of the radial position corresponding to the target diaphragm is -0.02 to 0.02 mm, then the diaphragm blank model established in step (2) is determined to be the final diaphragm blank model.

[0120] If the difference between the thickness of the model at different radial positions after blank deformation and the difference between the thickness of the target diaphragm at the corresponding radial position are not within the range of -0.02 to 0.02 mm, then the difference between the thickness of the model after blank deformation and the difference between the two should be corrected to satisfy -0.02 to 0.02 mm.

[0121] It should be noted that in step (5), the outline dimensions of the grinding roller 7 refer to the length of the grinding roller 7 and its diameter at different radial positions. The outline dimensions of the diaphragm blank model refer to the radius of the diaphragm blank model and its thickness at different radial positions. Specifically, the deviation between the length of the grinding roller 7 and the radius of the diaphragm blank model is ±0.01mm, and the deviation between the diameter of the grinding roller at different radial positions and the thickness of the diaphragm blank model at different radial positions is ±0.01mm.

[0122] In one specific implementation, in step (6), positioning holes are machined into the metal plate to determine the fixed position of the metal plate on the rotary grinding table. One side of the metal plate is ground to obtain a flat bottom surface. The flat bottom surface is placed on the rotary grinding table and fixed by vacuum adsorption so that the metal plate is evenly attached to the rotary grinding table. The rotary grinding table is turned on to complete the grinding of the metal plate and obtain the metal film forming blank.

[0123] In one specific implementation, in step (6), when the metal sheet is ground on the rotary table 6, the thickness at different radial positions is obtained by an ultrasonic thickness gauge or a laser rangefinder.

[0124] It should be noted that the rotary grinding table includes a rotary table 6 and grinding rollers 7. A vacuum suction cup is fixed on the rotary table 6, such as... Figure 12 As shown. The vacuum suction cup is equipped with multiple holes for vacuuming. When the rotary table 6 is turned on, it drives the metal sheet to rotate evenly, while the grinding roller 7 also rotates. During the rotation process, micro-cuts are performed sequentially. The grinding process is a line contact process, grinding is performed on the raised areas, and the metal sheet with gradually changing wall thickness is ground as it is gradually lowered.

[0125] A specific embodiment of the present invention, such as Figure 7-10 As shown, an apparatus for preparing the aforementioned metal diaphragm blank is disclosed, comprising a rotary table 6 for placing a circular metal diaphragm blank and a grinding roller 7 for grinding the metal diaphragm blank. The grinding roller 7 is located above the rotary table 6, and the axial direction of the grinding roller 7 is consistent with the radial direction of the rotary table 6, so that the metal diaphragm blank is subjected to both axial and radial grinding forces when the grinding roller 7 is pressed down. The axial length of the grinding roller 7 is not less than the diameter of the metal diaphragm blank. When the grinding roller 7 is pressed down, the metal diaphragm blank is subjected to grinding forces from the middle to the edge simultaneously.

[0126] Compared with existing technologies, the apparatus for preparing metal diaphragm blanks of the present invention has strong versatility, and a single unit can prepare diaphragms with different gradients. It is also flexible and highly adjustable. Compared with existing technologies, it moves the material removal process forward, avoiding dimensional errors and product damage caused by subsequent machining deformation. Furthermore, it can remove material with little or no stress, thus obtaining more accurate sheet blank thicknesses. Moreover, the ultrasonic-assisted vibration reduces internal stress in the material, resulting in low deformation and high precision after grinding.

[0127] In one specific embodiment, the diameter of the grinding roller 7 increases linearly or non-linearly from the inside to the outside along the radial direction of the rotary table 6, so that the grinding thickness of the metal diaphragm forming blank decreases linearly or non-linearly from the inside to the outside.

[0128] In one specific embodiment, the rotating platform 6 is circular.

[0129] In one specific embodiment, the grinding roller 7 includes a rotating shaft 8, the grinding roller 7 rotates around the rotating shaft 8, and the length of the rotating shaft 8 along the radial direction of the rotating table 6 is greater than the length of the grinding roller 7 along the radial direction of the rotating table 6.

[0130] In one specific embodiment, a through hole is provided at one end of the rotating shaft 8 near the center of the rotating platform 6, and a spring modulator 9 is fixedly installed in the through hole.

[0131] It should be noted that the purpose of the above-mentioned setting is that the large-diameter grinding roller 7 has relatively weak rigidity in the middle. Through the structural setting of the present invention, when the rotary table 6 rotates, the grinding roller 7 also rotates around the rotation axis, and the downward flexible force can be adjusted by the spring modulator 9.

[0132] In one specific embodiment, an ultrasonic vibrator 10 is fixedly connected to one end of the rotating shaft 8 away from the center of the rotating table. The ultrasonic vibrator 10 adjusts the grinding pressure of the vibrator by adjusting the ultrasonic frequency and amplitude, which is especially suitable for grinding powder materials with strong viscosity such as pure titanium, thereby controlling the grinding accuracy.

[0133] In a specific implementation, such as Figure 10 As shown, the grinding roller 7 is provided with a groove 11 corresponding to the reinforcing rib.

[0134] Specifically, in step (b), the metal film blank is placed in the mold and then subjected to hot pressing and thermal expansion stretching to form a metal variable wall thickness film.

[0135] To achieve hot pressing and thermal expansion stretching of metal film blanks, this invention also discloses a rigid-flexible composite forming mold. The mold is used to prepare metal variable wall thickness films, such as the aforementioned metal variable wall thickness films. The rigid-flexible composite forming mold includes an upper mold and a lower mold. The upper mold consists of an upper hot pressing stretching area 12 located at the edge and an upper thermal expansion stretching area 13 located in the middle. The lower mold consists of a lower hot pressing stretching area 14 located at the edge and a lower thermal expansion stretching area 15 located in the middle. After the upper mold and the lower mold are closed, the upper thermal expansion stretching area 13 and the lower thermal expansion stretching area 15 form a thermally expanded mold cavity. The lower thermal expansion stretching area 15 is provided with an air inlet 16.

[0136] Compared with the prior art, the rigid-flexible composite forming mold of the present invention can use different loading methods for different areas of the same blank. The edge fixing area 2 of the diaphragm is hot-pressed and stretched into shape by the upper hot-pressing stretching area 12 and the lower hot-pressing stretching area 14, forming a circular arc area with a large precision dimension. When the upper and lower molds are in rigid contact with a certain pressure, a sealed cavity is formed. The metal diaphragm forming blank 4 at the corresponding positions of the upper hot-expansion stretching area 13 and the lower hot-expansion stretching area 15 can be blown upward by the action of high-pressure gas, so that the metal diaphragm forming blank 4 is attached to the upper hot-expansion stretching area 13, completing the reverse contour forming of the central area and obtaining the overall diaphragm structure. A set of molds and a blank can achieve rigid-flexible composite forming in different areas.

[0137] In one specific embodiment, the upper hot-press stretching region 12 is provided with a ring of protrusions 17, and the lower hot-press stretching region 14 is provided with a recess 18 corresponding to the protrusions 17, forming a folded structure of the edge fixing region 2 of the diaphragm.

[0138] In one specific embodiment, the distance between the upper thermal expansion stretching region 13 and the lower thermal expansion stretching region 15 gradually increases from the outside to the inside, so that the metal film forming blank 4 in contact with this part is subjected to both vertical thermal pressure and thermal expansion stretching force.

[0139] In one specific embodiment, the upper thermal expansion stretching region 13 is further provided with a plurality of recesses 19, such as... Figure 13 As shown, the recessed portion 19 is provided corresponding to the reinforcing rib 5 on the blank, and is used to form the rib in the diaphragm.

[0140] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0141] Example 1

[0142] This embodiment discloses a metal diaphragm forming blank, such as Figure 5 As shown, the blank is a titanium alloy, and the metal diaphragm forming blank 4 is a circle composed of a middle part 42 and an edge part 41. The thickness of the metal diaphragm forming blank 4 gradually decreases from the center to the edge, forming a structure that is thick in the middle and thin at the edge. In this embodiment, the diameter of the metal diaphragm forming blank 4 is 50 mm, the thickness of the thickest part of the middle part 42 is 0.5 mm, and the thickness of the thinnest part of the edge part 41 is 0.15 mm, as an example for explanation. Specifically, the distribution of the diaphragm thickness can be calculated and determined based on the overall axial height of the diaphragm and the finite element simulation results.

[0143] Example 2

[0144] The metal diaphragm forming blank in this embodiment is the same as that in Embodiment 1, except that, as Figure 6 As shown, two circumferential reinforcing ribs 5 are provided on the middle part 42. In this embodiment, the number of reinforcing ribs is explained by taking two as an example, but it is not limited to two. It can be set according to actual needs. In this embodiment, the cross-section of the reinforcing rib is rectangular, with a width of 3mm and a height of 2mm.

[0145] Specifically, in this embodiment, the reinforcing rib 5 is made of silicon carbide particles as an additive, which are added to the metal.

[0146] Example 3

[0147] A method for processing a metal diaphragm forming blank according to Embodiment 1 or 2 includes the following steps:

[0148] (1) Determine the target membrane parameters: The target membrane parameters are: pre-flanged edge R3mm, spherical radius R156mm, and the pre-flanged edge and the spherical surface are kept tangent.

[0149] (2) Modeling was performed using UG. Specifically, a diaphragm blank model was established in the finite element model based on the target diaphragm parameters. The diameter of the diaphragm blank model ranged from 350mm (including the allowance for the positioning holes), and the wall thickness increased from 0.55mm to 0.75mm. The wall thickness of the diaphragm blank model ranged from 0.55mm at the edge to 0.75mm at the center.

[0150] (3) Perform finite element simulation on the process of processing the diaphragm blank model into a diaphragm to obtain the model after the blank is deformed. Use mesh generation to track the position points of the blank after deformation and obtain the difference in thickness at different radial positions of the model after the blank is deformed. The difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

[0151] (4) Compare the difference in thickness at different radial positions of the model after blank deformation with the difference in thickness at the corresponding radial position of the target diaphragm to determine the final diaphragm blank model. The difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

[0152] If the difference between the thickness of the model at different radial positions after the blank is deformed and the difference between the thickness of the target diaphragm at the corresponding radial position is -0.02 to 0.02 mm, then the diaphragm blank model established in step (2) is determined to be the final diaphragm blank model.

[0153] If the difference between the thickness of the model at different radial positions after blank deformation and the difference between the thickness of the target diaphragm at the corresponding radial position are not within the range of -0.02 to 0.02 mm, then the difference between the thickness of the model after blank deformation and the difference between the two should be corrected to satisfy -0.02 to 0.02 mm.

[0154] (5) Based on the thickness values ​​of different radial positions of the final determined diaphragm blank model, determine the outline size of the diaphragm blank model and select the corresponding grinding roller 7;

[0155] The outline dimensions of the grinding roller 7 refer to its length and diameter at different radial positions. The outline dimensions of the diaphragm blank model refer to its radius and thickness at different radial positions. Specifically, this means that the deviation between the length of the grinding roller 7 and the radius of the diaphragm blank model is ±0.01mm, and the deviation between the diameter of the grinding roller at different radial positions and the thickness of the corresponding radial positions of the diaphragm blank model is ±0.01mm.

[0156] (6) Provide a metal sheet, process the metal sheet to make positioning holes, determine the fixed position of the metal sheet on the rotary grinding table, grind one side of the metal sheet, the grinding amount is not less than the wall thickness tolerance of the sheet, generally not more than 0.4mm, to obtain a flat bottom surface, the range of which is determined according to the diameter of the diaphragm blank sheet, place the flat bottom surface on the rotary grinding table, fix it by vacuum adsorption, so that the metal sheet is evenly attached to the rotary grinding table, turn on the rotary grinding table, and the grinding roller 7 in step (5) grinds the sheet to obtain the metal diaphragm forming blank.

[0157] The finite element simulation diagram in this embodiment is as follows: Figure 14 As shown.

[0158] Example 4

[0159] This embodiment provides an apparatus for preparing the metal film blank of Example 1, such as... Figure 7-9 As shown, it includes a rotary table 6 for placing a circular metal diaphragm forming blank and a grinding roller 7 for grinding the metal diaphragm forming blank. The grinding roller 7 is located above the rotary table 6, and the axial direction of the grinding roller 7 is consistent with the radial direction of the rotary table 6, so that the metal diaphragm forming blank 4 is subjected to both axial and radial grinding forces when the grinding roller 7 is pressed down. The axial length of the grinding roller 7 is not less than the diameter of the metal diaphragm forming blank 4. When the grinding roller 7 is pressed down, the metal diaphragm forming blank 4 is subjected to grinding forces from the middle to the edge at the same time.

[0160] Specifically, the diameter of the grinding roller 7 increases linearly from the inside to the outside along the radial direction of the rotary table 6, causing the grinding thickness of the metal film forming blank 4 to decrease linearly from the inside to the outside. The rotary table 6 is circular, and the grinding roller 7 includes a rotating shaft 8 around which it rotates. The length of the rotating shaft 8 along the radial direction of the rotary table 6 is greater than the length of the grinding roller 7 along the radial direction of the rotary table 6.

[0161] In a further preferred embodiment, a through hole is provided at the end of the rotating shaft 8 near the center of the rotating table 6, and a spring modulator 9 is fixedly installed in the through hole. An ultrasonic vibrator 10 is fixedly connected at the end of the rotating shaft 8 away from the center of the rotating table 6, and the ultrasonic vibrator 10 can control the grinding accuracy.

[0162] Example 5

[0163] The apparatus for preparing the metal film forming blank of Example 2 in this embodiment is the same as that in Example 4, except that, as Figure 10 As shown, the grinding roller 7 is provided with a groove 11 corresponding to the reinforcing rib 5.

[0164] Example 6

[0165] This embodiment describes a metal variable-wall thickness film, such as... Figure 1 and 2 As shown, the diaphragm is circular, and its thickness gradually decreases from the center to the edge, forming a structure that is thicker in the middle and thinner at the edges. The diaphragm includes a central flipping area 1 and an edge fixing area 2. The flipping area 1 is hemispherical, with an arc of R150 on its curved surface. The diameter of the diaphragm is R150mm, and its height is 70mm. The thickest part of the central flipping area 1 is 1mm, and the thinnest part of the edge fixing area 2 is 0.5mm. The edge fixing area 2 is a flanged structure formed by the downward indentation of the diaphragm edge.

[0166] Example 7

[0167] The metal variable-wall thick film in this embodiment is the same as that in Embodiment 6, except that, as Figure 3-4 As shown, a rib 3 is provided on the central flipping area 1, and the cross-section of the rib 3 is rectangular.

[0168] Example 8

[0169] like Figure 11As shown, this embodiment of a rigid-flexible composite forming mold is used for forming the metal variable wall thickness film described in Embodiment 6. It includes an upper mold and a lower mold. The upper mold consists of an upper hot-pressing stretching area 12 located at the edge and an upper hot-expansion stretching area 13 located in the middle. The lower mold consists of a lower hot-pressing stretching area 14 located at the edge and a lower hot-expansion stretching area 15 located in the middle. After the upper mold and the lower mold are closed, the upper hot-expansion stretching area 13 and the lower hot-expansion stretching area 15 form a hot-expansion mold cavity. The lower hot-expansion stretching area 15 is provided with an air inlet 16.

[0170] Specifically, the upper hot-pressing stretching region 12 is provided with a ring of bosses 17, and the lower hot-pressing stretching region 14 is provided with a recess 18 corresponding to the bosses 17. The distance between the upper hot-expansion stretching region 13 and the lower hot-expansion stretching region 15 gradually increases from the outside to the inside, so that the film blank in contact with this part is subjected to both vertical hot pressure and hot expansion stretching force.

[0171] Example 9

[0172] The rigid-flexible composite molding die in this embodiment is the same as that in Embodiment 8, except that, as Figure 13 As shown, the upper thermal expansion stretching area is also provided with two recesses 19, which are provided in correspondence with the ribs 3 on the blank.

[0173] Example 10

[0174] The method for forming a metal variable wall thickness film according to this embodiment includes the following steps:

[0175] (a) Metal film forming blanks were prepared using the method of Example 3;

[0176] (b) The metal film forming blank is placed in the mold of Example 8. The metal film forming blank 4 is placed between the upper mold and the lower mold. When the upper mold and the lower mold are closed by pressure, the upper hot-pressing stretching area 12 and the lower hot-pressing stretching area 14 squeeze the metal film forming blank 4 to form the edge fixing area 2. The mold cavity is formed between the upper hot-expansion stretching area 13 and the lower hot-expansion stretching area 15. High-pressure nitrogen is introduced through the air inlet 16 to blow the metal film forming blank 4 upward, so that the metal film forming blank 4 is attached to the upper hot-expansion stretching area 13, completing the reverse forming contour of the central area and obtaining the overall metal variable wall thickness film structure.

[0177] The hot pressing and stretching temperature is 650–850℃, the pressure is 10–2000 tons, the pressure during hot expansion stretching is 0.2–1 MPa, and the holding time is 30–120 min.

[0178] The diaphragm prepared in this embodiment has a surface accuracy of ±0.5mm and a wall thickness accuracy of ±0.03mm.

[0179] Example 11

[0180] The forming method of the metal variable wall thickness diaphragm with ribs in this embodiment is the same as that in Embodiment 10. The difference is that the mold used in Embodiment 9 is adopted to obtain the diaphragm with ribs 3. The surface accuracy of the diaphragm prepared in this embodiment is ±0.5mm and the wall thickness accuracy is ±0.03mm.

[0181] Example 12

[0182] like Figure 15-21 As shown, this embodiment discloses an anti-sway energy absorption structure built into an aircraft tank, including a square porous mesh array 01 and a metal variable wall thickness diaphragm 02 prepared in Example 10; the square porous mesh array 01 consists of multiple units, arranged along the XYZ coordinates to form a porous mesh array skeleton; the square porous mesh array 01 is composed of several mesh units 07, each mesh unit 07 including an axisymmetric first sub-frame and a second sub-frame, and a diaphragm 02 is installed in the first sub-frame and the second sub-frame respectively, the wave crest direction of the diaphragm 02 in the first sub-frame being opposite to the wave crest direction of the diaphragm 02 in the second sub-frame.

[0183] Specifically, the diaphragm 02 is fixedly connected to the grid unit 07 via a support ring 03 and a fixing plate 04. Each of the first and second sub-grid frames of the grid unit 07 has a recessed groove as a slot 08, with the slots 08 of the first and second sub-grid frames facing opposite directions. Each of the first and second sub-grid frames is fitted with a diaphragm 02, the crests of which face opposite directions, with the crests of the diaphragm 02 pointing towards the slot 08 of the grid unit 07. The support ring 03 is placed in the slot 08, and then the fixing plate 04 is placed thereon. The slots 08, support ring 03, and fixing plate 04 are secured to the diaphragm 02 by bolts.

[0184] In a further embodiment, the support ring 03 is provided with a stop structure 09 that is welded to the diaphragm 02, and the outer arc contour of the support ring 03 is consistent with the inner contour of the diaphragm flange structure. The diaphragm 02 is located below the support ring 03, and the diaphragm 02 is fixedly connected to the stop structure 09 of the support ring 03. The support ring 03 is located above the slot 08 of the grid unit 07, and the fixing plate 04 is located above the support ring 03. The slot 08, the support ring 03, and the fixing plate 04 are fixed to the diaphragm 02 by bolts. The diaphragm 02 is detachably and fixedly connected in the grid unit 07. The fixing plate 04 and the slot 08 of the grid unit 07 are interference-fitted.

[0185] Specifically, the support ring 03 has equally spaced through holes 010 near the stop structure 09. The porous mesh array skeleton divides the square porous mesh array 01 into a main impact surface 011 and two secondary impact surfaces 012. The boundary line between the main impact surface 011 and the secondary impact surface 012 serves as the axis. Multiple diaphragms 02 around the axis have the same clockwise or counterclockwise wave crest direction. For example, Figure 20 As shown, the four diaphragms 02 around the axis point in the same direction along clockwise or counterclockwise.

[0186] The main impact surface 011 is perpendicular to the main sloshing impact direction of the liquid in the tank. The porous mesh array skeleton establishes XYZ coordinates with the central axis of the tank, which is perpendicular to the main impact surface 011. The square porous mesh array 01 can be arranged in the XY, XZ and YZ planes of the tank respectively.

[0187] The planar dimensions of the grid unit 07 are (0.08-0.2)Φ×(0.04-0.1)Φ, where Φ is the equivalent diameter of the tank cross-section.

[0188] Specifically, the anti-sway energy-absorbing structure built into the aircraft storage tank also includes a bolt assembly. The slot 08, support ring 03 and fixing plate 04 are provided with bolt mounting holes, and the bolt mounting holes are adapted to the bolts.

[0189] Experiments revealed that adding the anti-sway device of this embodiment to the Flying Chess storage tank produced the effects of energy dissipation and changed the flow field structure, thereby reducing the total kinetic energy of the system.

[0190] 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 low-stress forming method for a metal variable-wall thickness film, characterized in that, Includes the following steps: (a) Forming a circular metal diaphragm blank of varying thickness from a sheet metal; The specific operation of step (a) is as follows: (1) Determine the target membrane parameters; (2) Establish a diaphragm blank model in the finite element model based on the target diaphragm parameters; (3) Perform finite element simulation on the process of processing the diaphragm blank model into a diaphragm to obtain the model after blank deformation. Use mesh generation to track the position points of the blank after deformation and obtain the difference in thickness at different radial positions of the model after blank deformation. (4) Compare the difference in thickness at different radial positions of the model after blank deformation with the difference in thickness at the corresponding radial position of the target diaphragm to determine the final diaphragm blank model; (5) Based on the thickness values ​​of different radial positions of the final determined diaphragm blank model, determine the outline size of the diaphragm blank model and select the corresponding grinding roller; (6) Provide a metal sheet and use the grinding roller described in step (5) to grind the metal sheet to obtain a metal diaphragm forming blank; The diameter of the grinding roller increases linearly or non-linearly from the inside to the outside along the radial direction of the rotary table, so that the grinding thickness of the metal diaphragm forming blank decreases linearly or non-linearly from the inside to the outside. The blank is a circle consisting of a middle part and an edge part. The thickness of the blank gradually decreases from the center to the edge, forming a structure that is thick in the middle and thin at the edge. The diameter of the blank is 50~2000mm, the thickness of the middle part is 0.5~2.2mm, and the thickness of the edge part is 0.3~1.4mm; (b) The metal film blank is placed in a mold and then subjected to hot pressing and hot expansion stretching to form a metal variable wall thickness film. The mold includes an upper mold and a lower mold. The upper mold consists of an upper hot-pressing stretching area located at the edge and an upper hot-expansion stretching area located in the middle. The lower mold consists of a lower hot-pressing stretching area located at the edge and a lower hot-expansion stretching area located in the middle. After the upper mold and the lower mold are closed, the upper hot-expansion stretching area and the lower hot-expansion stretching area form a hot-expansion mold cavity. The lower hot-expansion stretching area is provided with an air inlet. The upper hot-press stretching area is provided with a ring of protrusions, and the lower hot-press stretching area is provided with a concave platform corresponding to the protrusions, forming a flange structure for the edge fixing area of ​​the film. The distance between the upper thermal expansion stretching region and the lower thermal expansion stretching region gradually increases from the outside to the inside, so that the metal film forming blank in contact with this part is subjected to both vertical thermal pressure and thermal expansion stretching force.

2. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (3) or (4), the difference in thickness at different radial positions refers to the difference in thickness between any two contour lines spaced 5 mm apart.

3. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (4), if the difference between the thickness of different radial positions of the model after blank deformation and the difference between the thickness of the corresponding radial position of the target diaphragm is -0.02~0.02mm, then the diaphragm blank model established in step (2) is determined to be the final diaphragm blank model. If the difference between the thickness of the model at different radial positions after blank deformation and the difference between the thickness of the target diaphragm at the corresponding radial position are not within the range of -0.02 to 0.02 mm, then the difference between the thickness of the model after blank deformation and the difference between the two should be corrected to satisfy -0.02 to 0.02 mm.

4. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (6), positioning holes are machined into the metal plate to determine the fixed position of the metal plate on the rotary grinding table. One side of the metal plate is ground to obtain a flat bottom surface. The flat bottom surface is placed on the rotary grinding table and fixed by vacuum adsorption so that the metal plate is evenly attached to the rotary grinding table. The rotary grinding table is turned on to complete the grinding of the metal plate and obtain the metal film forming blank.

5. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (6), when the metal sheet is ground on the rotary table, the thickness at different radial positions is obtained by an ultrasonic thickness gauge or a laser rangefinder.

6. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (b), the temperature of hot pressing and stretching is 650~850℃ and the pressure is 10~2000 tons.

7. The low-stress forming method for a metal variable-wall thickness film according to claim 1, characterized in that, In step (b), the pressure during thermal expansion and stretching is 0.2~1MPa, and the holding time is 30~120min.

8. A metal variable-wall thickness film obtained by the method according to any one of claims 1-7.

9. A built-in anti-sway energy-absorbing structure for an aircraft storage tank, characterized in that, The anti-sway energy-absorbing structure includes the metal variable-wall thick film and the square porous grid array as described in claim 8; The square porous mesh array consists of multiple units arranged along the XYZ coordinates to form a porous mesh array skeleton. The square porous mesh array is composed of several mesh units, each mesh unit including an axisymmetric first sub-mesh frame and a second sub-mesh frame. A diaphragm is installed in the first sub-mesh frame and the second sub-mesh frame respectively. The wave crest direction of the diaphragm in the first sub-mesh frame is opposite to that of the diaphragm in the second sub-mesh frame.

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