Large high-strength cylinder ring structure ultra-low temperature medium pressure forming method and die

Abstract

This invention discloses a method and mold for cryogenic pressure forming of a large, high-strength cylindrical ring structure, relating to the field of metal sheet forming technology. The forming method includes: Step 1, determining the initial dimensions of the cylindrical ring blank and the required forming temperature based on the shape, size, and performance indicators of the target cylindrical ring structure; Step 2, cutting the flat plate, rolling and welding it into a straight-walled cylindrical ring blank; Step 3, placing the cylindrical ring blank in a mold, filling the space between the cylindrical ring blank wall and the mold with a cryogenic medium and applying pressure, causing the cylindrical ring blank to undergo plastic deformation under cryogenic conditions until it adheres to the mold surface, thus obtaining a cylindrical ring structure with weld seam reinforcement consistent with the base material. The solution provided by this invention can improve the performance and manufacturing efficiency of large cylindrical ring structures and reduce manufacturing costs.

Description

Technical Field

[0001] This invention relates to the field of metal sheet forming technology, and in particular to a method and mold for forming large, high-strength cylindrical ring structures under cryogenic medium pressure. Background Technology

[0002] Thin-walled curved ring components are a typical type of thin-walled structure in the aerospace field, such as rocket fuel tank sections, tank bottom conical rings, and aircraft nacelle skin. These thin-walled curved components are large in size and thin in wall thickness; a tank bottom conical ring with a diameter of several meters may have a wall thickness of only a few millimeters. With the development of next-generation rockets towards reusability and commercialization, stainless steel is gradually becoming the main material for rocket body structures, comparable to aluminum alloys, resulting in even thinner component walls; for example, the wall thickness of a 4-meter diameter rocket tube ring is less than 2 millimeters. Even more significantly, the bottom ring-like thin-walled structures are often ellipsoidal or spherical surfaces of revolution. The integral forming of such high-strength, large-scale thin-walled tube ring structures is extremely difficult.

[0003] Currently, existing processes are forced to adopt a technical route of forming multiple pieces separately and then welding them together to manufacture large cylindrical thin-walled curved parts. For example, aluminum alloy cylindrical sections are first formed into 3 to 5 fan-shaped wall plates, and then longitudinally stirred and friction-welded into cylindrical sections; stainless steel box bottom rings are first formed into 12 to 24 petals from hard stainless steel, and then assembled and welded into a ring. The larger the ring size, the more petals are required. The pre-forming and then welding technology route faces numerous challenges: ① High precision requirements for part forming; existing processes often struggle to achieve precise forming of hardened segments, necessitating selective welding and assembly in subsequent stages; ② Weak weld performance, high residual stress, and poor consistency; while each part has reached the material's maximum service performance, welding heat input is unavoidable. This leads to a significant reduction in weld performance and irreparable welding defects. Furthermore, it generates thermal stress and redistributes residual stress from hardened alloy forming, resulting in poor dimensional consistency and difficulty in achieving efficient assembly of subsequent system-level components. It also easily leads to dimensional changes during service due to residual stress release and phase transformation; ③ Long cycle time and high cost; the weld is a spatial curve, and the forming, selection, assembly, and welding of numerous parts result in a very long manufacturing cycle for the entire cylindrical ring component. Welding a single ring often takes several days or even dozens of days, etc. There is an urgent need to develop high-performance, low-cost, and high-efficiency manufacturing technologies for high-strength, large-scale, thin-walled cylindrical ring structures. Summary of the Invention

[0004] The purpose of this invention is to provide a method and mold for forming large, high-strength cylindrical ring structures under cryogenic medium pressure, so as to solve the problems existing in the prior art, improve the performance and manufacturing efficiency of large cylindrical ring structures, and reduce manufacturing costs.

[0005] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for cryogenic pressure forming of a large, high-strength cylindrical ring structure. The method involves forming a straight-walled cylindrical ring blank, formed by rolling and welding a flat plate, into a high-strength cylindrical ring structure with weld seams that are uniformly reinforced with the base material. The method includes: Step 1: Determine the initial dimensions of the cylinder ring blank and the required forming temperature based on the shape, size, and performance indicators of the target cylinder ring structure; Step 2: After the flat plate is cut, it is rolled and welded into a straight-walled cylindrical ring blank; Step 3: Place the cylindrical ring blank in the mold, fill the space between the cylindrical ring blank wall and the mold with a low-temperature medium and apply pressure to cause the cylindrical ring blank to undergo plastic deformation under ultra-low temperature conditions until it adheres to the mold surface, thereby obtaining a cylindrical ring structure in which the weld seam is reinforced in the same way as the base material.

[0006] Preferably, in step two, the shape of the blank near the weld zone is set to a configuration that is inwardly contracted relative to the blanks in other areas in the circumferential direction, so that the deformation obtained by the weld zone in the subsequent forming process is greater than that of other areas.

[0007] Preferably, in step three, the high-pressure cryogenic medium filled between the wall of the cylindrical ring blank and the mold is one or more of liquid argon, liquid nitrogen, or liquid helium, or a gas-liquid mixture thereof, and the forming temperature is -196°C to 25°C.

[0008] Preferably, in step three, the pressure is increased by controlling the filling amount of the high-pressure cryogenic medium and utilizing the vaporization of the medium; or the medium pressure is increased to a set value by using a cryogenic pump.

[0009] Preferably, the cylindrical ring blank is made of aluminum alloy, hard stainless steel, or solution-treated stainless steel; the welding method in step two is one of friction stir welding, laser welding, argon arc welding, resistance welding, or submerged arc welding.

[0010] Preferably, the cylindrical ring blank is a straight-walled cylindrical or conical shape; the cylindrical ring structure is a straight cylindrical structure or a conical curved surface structure.

[0011] The present invention also provides a mold for implementing step three of the method described above.

[0012] Preferably, the die includes a face mold, an inner cylinder mold, an end shrinking mold, an end restraining mold, and a sealing element; the inner wall shape of the face mold matches the outer shape of the target cylindrical ring structure; the inner cylinder mold is disposed inside the face mold, forming an annular space between them to accommodate the cylindrical ring blank; the end shrinking mold is annular and divided into multiple segments, each segment of which is radially movable and disposed at the end of the cylindrical ring blank; the end restraining mold is connected to the upper mold base, and its lower end engages with the end shrinking mold through a wedge-shaped structure; the sealing element is disposed between the cylindrical ring blank and the die to form a seal; when the end restraining mold moves downward, it pushes the end shrinking mold radially toward the axis through the wedge-shaped structure, pressing and engaging the end of the cylindrical ring blank onto the inner cylinder mold, thus establishing a sealed cavity between the inner wall of the cylindrical ring blank and the outer wall of the inner cylinder mold together with the sealing element; when the end restraining mold moves upward, the end shrinking mold can move radially away from the axis, releasing the pressure on the end of the cylindrical ring blank.

[0013] Preferably, the outer wall of the inner cylinder mold is provided with a convex ring, and the inner wall of the end shrinkage mold is provided with a corresponding groove. The end seal is achieved by the cooperation of the convex ring and the groove to press the cylinder ring blank.

[0014] Preferably, the sealing element is an annular sealing ring, which is disposed between the outer wall of the inner cylinder mold and the cylinder ring blank.

[0015] Preferably, the inner wall of the end constraint mold is a conical surface with the same taper as the cylindrical ring blank, and the outer wall of the inner cylinder mold is a conical surface with the same taper as the cylindrical ring blank. When the end constraint mold moves downward, its inner wall cooperates with the outer wall of the inner cylinder mold to clamp the large end of the cylindrical ring blank.

[0016] Preferably, an annular cooling cavity is formed between the inner wall of the mold and the cylindrical ring blank, the cooling cavity being filled with a low-temperature medium at atmospheric pressure; an inlet / outlet for the low-temperature medium at atmospheric pressure is provided at the upper part or top of the cooling cavity, the inlet / outlet for filling the low-temperature medium into the cooling cavity and discharging the low-temperature medium outward during the deformation of the cylindrical ring blank toward the target cylindrical ring structure.

[0017] The present invention achieves the following technical effects compared to the prior art: This invention employs a "first roll and weld into a cylinder, then form at ultra-low temperature" technical approach, transforming the complex spatial curved welds of traditional processes into simple planar straight or oblique welds. This significantly reduces welding difficulty and time, increasing welding efficiency from one piece every few days to several pieces per day. More importantly, because welding is performed on a flat or simply curved blank, welding defects are easier to detect and repair, avoiding the difficulty of handling welding defects after forming. In the subsequent high-pressure, low-temperature medium pressure forming process, the cylindrical ring blank undergoes uniform deformation under biaxial tensile stress. The weld zone and the base material zone simultaneously undergo ultra-low temperature deformation strengthening, thus eliminating the problem of the weld becoming a weak point in performance in traditional processes and achieving consistent enhancement of the weld and base material properties.

[0018] Furthermore, the cylindrical ring blank in this invention is made of hard stainless steel. Although the weld softens after welding, the weld area with lower yield strength deforms first during forming, resulting in a larger cumulative deformation. Simultaneously, by reducing the circumferential dimension of the weld joint area, the weld gains greater deformation space in terms of geometry. These two factors work synergistically to achieve sufficient deformation strengthening of the weld with relatively small overall deformation, realizing consistent enhancement of the weld and base material properties. This approach avoids the drawback of soft materials requiring large deformation for strengthening, making engineering implementation more convenient. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the cylindrical ring blank.

[0021] Figure 2 This is a schematic diagram of the mold in the open state.

[0022] Figure 3 This is a schematic diagram of the mold in the closed state in some embodiments. In this case, the mold surface is not provided with an inlet / outlet for the normal pressure cryogenic medium. After the high pressure cryogenic medium is filled into the sealed cavity between the cylindrical ring blank and the inner cylinder mold, the cylindrical ring blank undergoes partial plastic deformation.

[0023] Figure 4 This is a schematic diagram of the mold in the closed state in some embodiments. The mold surface is provided with an inlet and outlet of a low-temperature medium at atmospheric pressure. The space between the mold surface and the cylindrical ring blank is filled with a low-temperature medium at atmospheric pressure. The cylindrical ring blank has not yet undergone plastic deformation. The low-temperature medium at atmospheric pressure is used to pre-cool the cylindrical ring blank.

[0024] Figure 5 In order to be in Figure 4 Based on the state shown, after filling the sealed cavity between the cylindrical ring blank and the inner cylinder mold with a high-pressure cryogenic medium, a structural diagram of the cylindrical ring blank undergoing partial plastic deformation is presented.

[0025] Figure 6 In order to be in Figure 5 Based on the state shown, the pressure of the high-pressure cryogenic medium is further increased to make the cylindrical ring blank completely adhere to the mold surface and complete the final forming structure diagram.

[0026] Figure 7 This is a schematic diagram of the target cylindrical ring structure.

[0027] Figure 8 This is a partial structural diagram of the weld zone of the cylindrical ring blank and the circumferential contour of the inner wall of the mold.

[0028] Figure 9 This is a schematic diagram of the numerical simulation model.

[0029] Figure 10 This is a schematic diagram of the equivalent strain distribution after the cylindrical ring is formed.

[0030] Figure 11 The graph shows the relationship between the room temperature yield strength of 304 stainless steel at different temperatures and degrees of deformation.

[0031] In the figure: 1-Cylinder ring blank; 2-Weld; 3-Lower mold base; 4-Shaped mold; 5-End shrinkage mold; 6-Sealing element; 7-Inner cylinder mold; 8-End constraint mold; 9-Upper mold base; 10-Ambient pressure cryogenic medium; 11-High pressure cryogenic medium; 12-Target cylinder ring structure; 13-Ambient pressure cryogenic medium inlet and outlet; 14-High pressure cryogenic medium inlet and outlet. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide a method and mold for forming large, high-strength cylindrical ring structures under cryogenic medium pressure, so as to solve the problems existing in the prior art, improve the performance and manufacturing efficiency of large cylindrical ring structures, and reduce manufacturing costs.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] The following is combined with Figures 1-11 The following describes embodiments of the present invention.

[0036] Example 1 This invention provides a method for cryogenic pressure forming of a large, high-strength cylindrical ring structure, comprising: Step 1: Based on the shape, size, and performance indicators of the target cylindrical ring structure 12, determine the initial dimensions of the cylindrical ring blank 1 and the required forming temperature; that is, based on the ultra-low temperature deformation strengthening mechanical model of the aluminum alloy material or the ultra-low temperature phase transformation strengthening mechanical model of the stainless steel material (i.e., the variation law of material strength and plasticity with temperature and deformation), and combined with the deformation distribution simulation analysis of the target shape of the cylindrical ring, back-calculate the degree of deformation required for different regions of the cylindrical ring to achieve the target performance and the corresponding optimal ultra-low temperature cooling temperature, and back-calculate the initial diameter and wall thickness of the straight or conical blank required for forming the cylindrical ring based on the required degree of deformation.

[0037] Step one above can be further specified as follows: Strain calculation for each deformation zone: Based on the target shape of the cylindrical ring and the principles of constant volume and plate and shell forming theory, the strain distribution during the forming process is analyzed to obtain the theoretical deformation degree of each region. A refined numerical model is established using finite element software (such as Abaqus), taking into account actual factors such as wall thickness reduction and friction, to simulate the forming process of the cylindrical ring, correct and output the actual deformation degree distribution of the profile region.

[0038] Establish the relationship between "deformation degree-temperature-strength" of materials: Through tensile tests of wide plates at different temperatures (room temperature to -196℃) and different pre-deformation amounts, test the strength and elongation of the specimens at the service temperature, construct a performance database of materials, and clarify the minimum cryogenic cooling temperature required to achieve the target performance at each deformation degree.

[0039] Inverse process parameter determination: Based on the deformation degree and material property database of each region obtained from the comprehensive numerical simulation, and according to the target performance indicators of the cylindrical ring surface region (such as room temperature yield strength ≥1000MPa), the required minimum cryogenic cooling temperature is derived; at the same time, the corresponding diameter change degree is determined according to the required deformation degree. In engineering, cooling is usually uniformly controlled according to the lowest temperature of the most stringent region.

[0040] To facilitate understanding, the forming of stainless steel cylindrical rings will be used as an example, as follows: 1- Calculation of strain distribution in each deformation zone: The strain distribution after the cylindrical ring is qualitatively determined through mechanical analysis to serve as a criterion for setting the cryogenic cooling temperature. Based on sheet metal forming theory, thin film stress theory, and the principle of constant volume, during cylindrical ring forming, the central region of the cylindrical ring blank 1 undergoes bulging deformation, expanding its circumferential dimension and experiencing tensile stress. The cylindrical ring has a large thickness-to-diameter ratio, with axial strain essentially zero, and the circumferential strain is opposite in magnitude to the thickness strain.

[0041] Circumferential strain Calculation based on the change in perimeter before and after deformation: (1); in, D 0 D is the diameter before forming, and D is the diameter after forming; Thick strain Calculations are based on changes in wall thickness before and after deformation: (2); Where t is the wall thickness of the formed cylindrical ring. t 0 The thickness of the cylindrical ring blank 1 before forming; From this, the equivalent strain of the cylindrical ring component at different height positions can be obtained: (3); Given a fixed size of the cylindrical ring, the initial diameter and wall thickness of the cylindrical ring blank 1 can be calculated by considering the profile dimensions and deformation at different height positions of the cylindrical ring part. (4); (5); Considering that the mechanical analysis did not take wall thickness reduction into account, numerical simulation was used to further correct and optimize the strain distribution and the initial diameter and wall thickness of the cylindrical blank after it was formed into a cylindrical ring. Commercial simulation software such as Abaqus, Ansys, and Dynaform can be used for numerical simulation. Taking the numerical simulation of the strain distribution of a 6.5m diameter stainless steel cylindrical ring as an example: the numerical simulation was performed using the Abaqus 6.14 software platform, using a 1 / 4 model. The cylindrical ring blank 1 was a three-dimensional deformable body, divided into 4 layers of hexahedral structure mesh along the thickness direction, with a mesh size of 30mm; the die 4 was a discrete rigid body, divided into hexahedral free meshes, with a mesh size of 30mm; the contact relationship between the die 4 and the cylindrical ring blank 1 was a surface-to-surface adaptive contact, with a penalty function in the tangential direction, and a friction coefficient of 0.12; the material properties of the cylindrical ring blank 1 were 304 stainless steel stress-strain relationship; the forming force was linearly proportionally applied to 3MPa through a pressure load. It should be noted that the two ends of the cylindrical ring blank 1 are fixed with end face constraints to prevent the blank from displacing along the axial direction and thus failing to achieve the target strengthening degree.

[0042] 2-Relationship between deformation, temperature, and strength: Tensile tests were conducted on wide plates at different temperatures to obtain specimens with varying degrees of deformation. Single tensile specimens were then cut from these pre-deformed wide plate specimens. The specimens were prepared according to the national standard (GB / T228.1-2021). The yield strength, tensile strength, and elongation, among other mechanical properties, were tested at the corresponding service temperatures to establish the relationship between the degree of deformation, deformation temperature, and strength. For example, to obtain the relationship between the degree of deformation, deformation temperature, and strength of a 2mm thick solution-treated 304 stainless steel plate: the tensile specimen width was 10mm and the length was 70mm; the deformation temperatures were 25℃ and -196℃; the corresponding degrees of deformation were 12.5%, 25%, and 50%; the width of the mechanical property test specimen was 5mm and the length was 30mm. The room temperature yield strength relationship of 304 stainless steel at different temperatures and degrees of deformation is shown in the attached figure. Figure 11 .

[0043] 3-Setting the ultra-low temperature cooling temperature: Combining the strain distribution of the cylindrical ring forming process obtained from mechanical analysis and numerical simulation calculations with the deformation temperature-deformation degree-strength relationship of the slab, and based on the required strength performance indicators for the cylindrical ring profile region, the cryogenic cooling temperature for cylindrical ring blank 1 is comprehensively determined. Taking a 304 stainless steel cylindrical ring with a diameter of 6.5m and a wall thickness of 2mm as an example, the room temperature yield strength of the entire cylindrical ring region needs to be greater than 1000MPa. Based on the strain distribution calculated by numerical simulation (see attached...),... Figure 2 It can be seen that the strain in the profile region is 0.19; according to the room temperature yield strength relationship of 304 stainless steel under different temperatures and deformation degrees ( Figure 11 As can be seen, to achieve a yield strength of over 1000 MPa at room temperature, the deformation zone of the profile needs to be cooled to below -180°C. Considering engineering control and stability, the temperature of the cylindrical ring billet 1 is usually controlled by cooling to the lowest possible temperature. Furthermore, based on the target deformation level to be achieved, the billet diameter is calculated to be 5.5 μm.

[0044] Step 2: After cutting the flat plate, roll and weld it into a straight-walled cylindrical ring blank 1.

[0045] Step 3: Place the cylindrical ring blank 1 in the mold, fill the space between the wall of the cylindrical ring blank 1 and the mold with high pressure low temperature medium 11 and apply pressure to make the cylindrical ring blank 1 plastically deform under ultra-low temperature conditions until it adheres to the mold surface, and obtain a cylindrical ring structure in which the weld 2 is reinforced in the same way as the base material.

[0046] The term "straight wall" refers to the fact that the generatrix of the cylindrical billet is straight, meaning that the wall of the billet presents a straight profile in the axial section without bending or curvature changes.

[0047] This embodiment adopts a technical route of "first rolling and welding into a cylinder, then forming at ultra-low temperature," transforming the complex spatial curve weld 2 in the traditional process into a simple planar straight or oblique weld 2. This significantly reduces the welding difficulty and time, increasing welding efficiency from one piece every few days to several pieces per day. More importantly, because welding is performed on a flat or simple curved blank, welding defects are easier to detect and repair, avoiding the predicament of difficult-to-handle welding defects after forming (flat state: the blank has no or only very small residual stress. During repair welding, the thermal stress generated by the welding heat input can be freely released without causing blank deformation. After forming: the blank has undergone plastic deformation, and there is a large amount of residual stress inside. During repair welding, the welding heat input will break the original stress balance, causing uncontrollable deformation of the blank, and may even scrap the already formed parts). In the subsequent high-pressure low-temperature medium 11 pressure forming process, the cylindrical ring blank 1 undergoes uniform deformation under bidirectional tensile stress. The weld area and the base material area simultaneously undergo ultra-low temperature deformation strengthening, thereby eliminating the problem that the weld 2 becomes a weak link in the traditional process and realizing the consistent enhancement of the performance of the weld 2 and the base material.

[0048] In some embodiments, the pressure range of the high-pressure cryogenic medium 11 is 0.1MPa to 120MPa, for example, it can be 0.1MPa, 120MPa, 100MPa, 80MPa, 60MPa, 20MPa, 10MPa, 1MPa, etc.

[0049] In some embodiments, in step two, the blank shape near the weld zone is configured to be inwardly contracted relative to the blanks in other areas in the circumferential direction, so that the deformation of the weld zone during subsequent forming is greater than that of other areas, such as... Figure 8 As shown, the circumferential profile of the surface is the profile of the inner wall of the mold 4.

[0050] This embodiment modifies the geometry of the weld zone blank, making its circumferential dimension smaller than that of the adjacent base material zone. Therefore, during the subsequent high-pressure cryogenic medium 11 pressure forming process, when the cylindrical ring blank 1 expands outwards, the weld zone, which was originally contracting inwards, must undergo a greater tensile deformation than the base material zone to adhere to the mold surface. Based on the strengthening principle that "the greater the deformation, the more significant the strengthening effect" of metallic materials under cryogenic conditions, the weld zone receives more substantial strengthening due to the greater deformation, thus compensating for the inherent performance degradation of the weld heat-affected zone and ultimately achieving consistent enhancement of the weld 2 and the base material's properties. This technique can be achieved simply by adjusting the blanking or pre-bending process, without increasing additional costs, and is easy to implement.

[0051] The specific methods for achieving greater deformation in the weld zone are not limited to the "inwardly contracting configuration" described in this embodiment. For example, by changing the material thickness of the weld zone, it can generate greater strain under the same pressure. Furthermore, the inwardly contracting configuration is not limited to a flat plate shape; it can also be an arc shape, a broken line shape, or other geometric shapes that can reduce the circumferential dimension of the weld zone, as long as the weld zone can achieve a greater deformation than the base material zone during the forming process.

[0052] In some embodiments, in step three, the high-pressure cryogenic medium 11 filled between the wall of the cylindrical ring blank 1 and the mold is one or more of liquid argon, liquid nitrogen or liquid helium, and the forming temperature is -196°C to 25°C.

[0053] The high-pressure cryogenic medium 11 is not limited to liquid argon, liquid nitrogen, or liquid helium; a mixture of the above media or a gas-liquid mixture formed by the vaporization of the medium can also be used. The forming temperature can be optimized according to the specific material. In addition, if room-temperature deformation strengthening can meet the design performance indicators, forming can also be carried out at room temperature, in which case the medium can be one of emulsion, water, compressed air, or nitrogen.

[0054] In some embodiments, in step three, pressurization is achieved by controlling the filling amount of the high-pressure cryogenic medium 11 and utilizing the vaporization of the medium; or the medium pressure is increased to a set value by using a cryogenic pump.

[0055] This embodiment provides two media pressurization methods, which can be flexibly selected according to site conditions and equipment configuration. The media vaporization pressurization method controls the filling amount of the high-pressure cryogenic medium 11, utilizing the pressure increase generated by the natural vaporization of the medium within the sealed cavity to achieve the forming pressure. This method has advantages such as no need for pressurization equipment, low medium loss, and suitability for on-site forming, making it particularly suitable for the on-site forming of ultra-large cylindrical ring components. The cryogenic pump pressurization method allows for precise control of the medium pressure, with a wide pressure adjustment range, suitable for applications requiring high forming accuracy. Both methods ensure that the cylindrical ring blank 1 receives sufficient forming pressure under cryogenic conditions, allowing it to precisely conform to the mold surface.

[0056] Pressurization methods can also be combined. For example, initial pressurization can be achieved by first vaporizing the medium, followed by precise pressure adjustment using a cryogenic pump; or multiple cryogenic pumps can be connected in parallel to achieve rapid pressure build-up at high flow rates. The set value of the pressurization pressure can be optimized according to material properties, wall thickness, and structural dimensions. For thin-walled structures, a lower forming pressure can be used; for thick-walled or complex curved surface structures, a higher forming pressure is required.

[0057] In some embodiments, the cylindrical ring blank 1 is made of aluminum alloy, hard stainless steel or solution-treated stainless steel; the welding method in step two is one of friction stir welding, laser welding, argon arc welding, resistance welding or submerged arc welding.

[0058] This embodiment specifies the applicable material types and welding methods.

[0059] In some examples, the cylindrical ring blank 1 is preferably hard stainless steel. Although the weld softens after welding, during the pressure forming process in the high-pressure low-temperature medium 11, as the medium pressure gradually increases, the weld area with lower yield strength enters the plastic deformation stage first, while the base material area with higher yield strength deforms later. This temporal difference of "weld deformation first, base material deformation later" results in the weld area obtaining a greater cumulative deformation than the base material area during the forming process. According to the strengthening law of metallic materials under ultra-low temperature conditions, "the greater the deformation, the more significant the strengthening effect," the weld area obtains more sufficient strengthening due to the greater plastic deformation, thereby compensating for the inherent defect of performance degradation in the weld heat-affected zone and ultimately achieving consistent enhancement of the weld and base material properties.

[0060] Building upon this foundation, this example further incorporates billet size optimization design—by reducing the circumferential dimension of the weld joint area, the weld seam achieves greater deformation space in terms of geometry. This design synergizes with the aforementioned differences in material yield strength: on the one hand, the material property differences ensure preferential weld seam deformation; on the other hand, the geometric design amplifies the amount of weld seam deformation. The combined effect of these two factors allows for sufficient deformation strengthening of the weld area even with relatively small overall deformation. This technique of "achieving full-area reinforcement with relatively small overall deformation" avoids the drawback of requiring large deformations for strengthening large cylindrical ring structures using soft materials, significantly reducing forming difficulty and making engineering implementation more convenient and reliable.

[0061] In some embodiments, the ring structure is a cylindrical structure or a conical curved surface ring structure.

[0062] This embodiment clarifies the structural form of the final product. The cylindrical structure (i.e., a constant-diameter cylindrical section) is suitable for typical structures such as rocket tube sections and aircraft fuselages. Its blank is a straight cylinder, and the forming process mainly involves circumferential expansion deformation, making the forming process relatively simple. The conical curved surface ring structure (i.e., a conical curved surface ring with a variable diameter and a curved generatrix) is suitable for variable cross-section structures such as rocket box bottom conical rings and transition sections. Its blank is a conical cylinder, and the forming process involves both circumferential expansion and axial deformation. While the forming difficulty is higher, the material utilization rate is also higher. Both structures can be integrally formed using the method of this embodiment, avoiding the problems of numerous welds, poor precision, and long cycle times caused by welding multiple segments in traditional processes.

[0063] The method of this embodiment can also be applied to other thin-walled structures of revolution, such as ellipsoidal heads, spherical box bottoms, and complex generatrix curved surface structures. For non-rotating irregular cylindrical ring structures, the same method can be used to achieve forming through reasonable design of the mold surface. For cylindrical ring structures with local reinforcing ribs or bosses, the flat plate can be locally thickened before rolling and welding, or locally reinforced after forming, all of which do not depart from the protection scope of this invention.

[0064] Example 2 The present invention also provides a mold for implementing step three of the method in Embodiment 1. The mold includes a profile mold 4, an inner cylinder mold 7, an end shrinkage mold 5, an end constraint mold 8, and a sealing element 6; the inner wall shape of the profile mold 4 matches the outer shape of the target cylindrical ring structure 12; the inner cylinder mold 7 is disposed inside the profile mold 4, forming an annular space between the inner and outer cylinder molds to accommodate the cylindrical ring blank 1; the end shrinkage mold 5 is annular and divided into multiple segments, each segment of the end shrinkage mold 5 being radially movable at the end of the cylindrical ring blank 1; the end constraint mold 8 is connected to the upper mold base 9, and its lower end is connected to the end shrinkage mold 5 via... The inclined wedge structure is used for the fit; the sealing element 6 is set between the cylindrical ring blank 1 and the mold to form a seal; when the end constraint mold 8 moves downward, the inclined wedge structure pushes the end shrinking mold 5 to move radially toward the axis, pressing the end of the cylindrical ring blank 1 and biting it on the inner cylinder mold 7, together with the sealing element 6 to establish a sealing cavity between the inner wall of the cylindrical ring blank 1 and the outer wall of the inner cylinder mold 7; when the end constraint mold 8 moves upward, the end shrinking mold 5 can move radially away from the axis, releasing the pressure on the end of the cylindrical ring blank 1.

[0065] This embodiment details the specific structure and working principle of the mold. An annular space is formed between the profile mold 4 and the inner cylinder mold 7 to accommodate the cylindrical ring blank 1 and define its final shape. The end shrinking mold 5 adopts a multi-lobed structure, allowing independent radial movement to accommodate cylindrical ring blanks 1 of different diameters, and is easy to install and disassemble. The end restraining mold 8 and the end shrinking mold 5 are fitted with a wedge-shaped inclined surface. When the end restraining mold 8 moves downward, the inclined surface converts the vertical motion into radial motion, pushing the end shrinking mold 5 to contract towards the axis, pressing the end of the blank onto the inner cylinder mold 7. Firstly, this embodiment utilizes the matching of the end shrinking mold 5 and the end restraining mold 8 to achieve self-sealing of the large-size conical cylinder end, reducing the sealing difficulty. Secondly, since the sealing cavity is annular, the radial components of the high-pressure medium cancel each other out, and the press only needs to overcome the axial component. Because the sealing area is concentrated at the end of the blank, the axial projection area is small, and the end reaction force is significantly reduced. There is no need for a large-tonnage, large-table press. A small-tonnage press or mechanism with a large table can be used to form ultra-large diameter cylindrical ring structures, which significantly reduces equipment investment. The larger the diameter of the conical ring, the more obvious the advantages.

[0066] The number of segments in the end shrinkage mold 5 can be selected according to the diameter of the cylindrical ring. The larger the diameter, the more segments there are, to ensure that the radial movement of each segment is flexible and reliable. The inclination angle of the inclined wedge structure can be optimized according to the required radial stroke and clamping force, generally from 30° to 60°.

[0067] In some embodiments, the inner wall of the end constraint mold is a conical surface with the same taper as the cylindrical ring blank 1, and the outer wall of the inner cylinder mold is a conical surface with the same taper as the cylindrical ring blank 1. When the end constraint mold moves downward, its inner wall cooperates with the outer wall of the inner cylinder mold to clamp the large end of the cylindrical ring blank 1.

[0068] In this embodiment, the inner wall of the end constraint mold 8 and the outer wall of the inner cylinder mold 7 form a conical surface with the same taper as the cylindrical ring blank 1. The two work together to form an annular gap that is larger at the top and smaller at the bottom. During forming, the large end of the blank is firmly clamped, the amount of material added is effectively controlled, and the controllability of the wall thickness reduction rate is improved.

[0069] In some embodiments, such as Figures 4-6 As shown, an annular cooling cavity is formed between the inner wall of the mold and the cylindrical ring blank 1. The cooling cavity is used to fill the cavity with atmospheric pressure cryogenic medium 10. An atmospheric pressure cryogenic medium inlet / outlet 13 is provided at the upper part or top of the cooling cavity. The atmospheric pressure cryogenic medium inlet / outlet 13 is used to fill the cavity with atmospheric pressure cryogenic medium 10 and to discharge the atmospheric pressure cryogenic medium 10 outward during the deformation of the cylindrical ring blank 1 toward the target cylindrical ring structure.

[0070] In this embodiment, an annular cooling cavity is formed between the inner wall of the mold 4 and the cylindrical ring billet 1, which can be pre-filled with a normal pressure low temperature medium 10 to achieve simultaneous cooling of the inner and outer walls of the billet. This solves the problem that the billet is difficult to cool down quickly in the initial stage and ensures the full play of the ultra-low temperature "double enhancement effect".

[0071] Of course, in some examples, such as Figure 3 As shown, the inlet / outlet 13 for the cryogenic medium at atmospheric pressure may not be required.

[0072] In some embodiments, the outer wall of the inner cylinder mold 7 is provided with a convex ring, and the inner wall of the end shrinkage mold 5 is provided with a corresponding groove. The end seal is achieved by the cooperation of the convex ring and the groove to press the cylinder ring blank 1.

[0073] This embodiment incorporates a convex ring and groove fitting design in the end sealing structure. When the end constraint mold 8 descends and pushes the end shrinking mold 5 to shrink radially, the groove on the inner wall of the end shrinking mold 5 and the convex ring on the outer wall of the inner cylinder mold 7 interlock, clamping the end of the cylindrical ring blank 1 between them to form a labyrinth-type sealing structure. This design has the following technical effects: First, the interlocking of the convex ring and groove increases the length and tortuosity of the sealing path, significantly improving sealing reliability and preventing leakage even under high-pressure media; second, the interlocking of the convex ring and groove provides positioning, ensuring that the end of the blank does not move axially during the forming process, thus improving forming accuracy.

[0074] The cross-sectional shape of the convex ring and the groove is not limited to rectangle; it can be trapezoidal, arc-shaped, or triangular to achieve better sealing and positioning. There can be one or more convex rings; multiple convex rings can form multiple seals, further improving sealing reliability. The fit between the convex ring and the groove can be a clearance fit or an interference fit, depending on the material properties and sealing requirements. Furthermore, an elastic sealing layer (such as a rubber coating or PTFE coating) can be applied to the surface of the convex ring or groove to compensate for manufacturing errors and improve sealing adaptability.

[0075] In some embodiments, the sealing element 6 is an annular sealing ring disposed between the outer wall of the inner cylinder mold 7 and the cylinder ring blank 1.

[0076] In this embodiment, an annular sealing ring is used as the sealing element 6, which is placed between the outer wall of the inner cylinder mold 7 and the inner wall of the cylinder ring blank 1. This sealing ring is compressed while the end shrinkage mold 5 presses against the end of the blank, forming a reliable radial seal. The annular sealing ring has the following advantages: firstly, it has a simple structure, is easy to install, and is inexpensive; secondly, it has high sealing reliability and can maintain good elasticity and sealing performance even in ultra-low temperature environments; and thirdly, different materials of sealing rings can be selected according to the type of medium and pressure level, making it highly adaptable. The sealing scheme of this embodiment complements the end convex ring groove seal, together forming a double-sealing structure at the end, ensuring the integrity of the sealed cavity under the action of ultra-low temperature and high pressure media.

[0077] The material of the sealing ring should be selected based on the high-pressure, low-temperature medium 11 and the operating temperature: for liquid nitrogen media, cryogenic materials such as polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PTFE) can be used; for liquid helium media, metal sealing rings (such as copper gaskets or stainless steel gaskets) can be used to ensure sealing reliability at extremely low temperatures. The number of sealing rings can be one or more, and multiple sealing rings connected in series can form a multi-layer seal. Alternatively, the sealing element 6 can also adopt a non-ring structure, such as a gasket, sealing strip, or liquid sealant, all of which can achieve similar sealing effects.

[0078] Specific Implementation Method 1: Stainless Steel Rocket Box Bottom Ring. The material is 3 / 4 hard 304 stainless steel, with a plate thickness of 2.5mm; the ring has a large end diameter of 7.5m and a small end diameter of 7.0m, and the generatrix of the profile is elliptical with a major axis radius of 3.75m and an axis-to-length ratio of 1.6. The ellipse has a column section with a height of 100mm; the cylindrical ring blank is a conical cylinder with a large end diameter of 7.8m and a small end diameter of 6.8m, which is formed by laser welding after rolling 6 fan-shaped plate blanks into cones; the forming temperature is -120℃, and the cryogenic medium is liquid nitrogen.

[0079] Specific Implementation Method Two: Stainless Steel Rocket Launcher Section. The material is solution-treated 301 stainless steel with a plate thickness of 2.0 mm; the section is a 6.5 m diameter cylinder with a height of 1.2 m; the section blank is a straight cylinder with a diameter of 5.5 m, which is rolled into a circle by a long plate and then argon-arc welded; the circumferential dimension after the straight cylinder butt joint is reduced by folding the edge, so that the weld seam undergoes a deformation of more than 10% relative to other base material areas during the subsequent forming process; the forming temperature is -160℃, and liquid nitrogen is simultaneously introduced into the outer wall and inner wall cavity of the straight cylinder.

[0080] Specific Implementation Method 3: Aluminum Alloy Rocket Box Bottom Ring. The material is 2219-T4 aluminum alloy, with a plate thickness of 16mm; the ring has a large end diameter of 5m and a small end diameter of 4.2m, and the generatrix of the profile is a circle with a radius of 2.5m, with a column section 100mm high on the circle; the cylindrical ring blank is a conical cylinder with a large end diameter of 5.3m and a small end diameter of 4m, formed by conical rolling of three fan-shaped plate blanks followed by friction stir welding; the forming temperature is room temperature, and the medium is an emulsion. After the ring is formed, artificial aging is used to further improve the strength of the component.

[0081] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for cryogenic pressure forming of a large, high-strength cylindrical ring structure, characterized in that: The process involves shaping a straight-walled cylindrical ring blank, which is then rolled and welded from a flat plate, into a high-strength cylindrical ring structure with weld seams that are uniformly reinforced with the base material. Specific steps include: Step 1: Determine the initial dimensions of the cylinder ring blank and the required forming temperature based on the shape, size, and performance indicators of the target cylinder ring structure; Step 2: After the flat plate is cut, it is rolled and welded into a straight-walled cylindrical ring blank; Step 3: Place the cylindrical ring blank in the mold, fill the space between the cylindrical ring blank wall and the mold with a low-temperature medium and apply pressure to cause the cylindrical ring blank to undergo plastic deformation under ultra-low temperature conditions until it adheres to the mold surface, thereby obtaining a cylindrical ring structure in which the weld seam is reinforced in the same way as the base material.

2. The forming method according to claim 1, characterized in that: In step two, the shape of the blank near the weld zone is set to be inwardly contracted relative to the blanks in other areas in the circumferential direction, so that the deformation of the weld zone is greater than that of other areas in the subsequent forming process.

3. The forming method according to claim 1, characterized in that: In step three, the high-pressure cryogenic medium filled between the wall of the cylindrical ring blank and the mold is one or more of liquid argon, liquid nitrogen or liquid helium or a gas-liquid mixture thereof, and the forming temperature is -196°C to 25°C.

4. The forming method according to claim 1, characterized in that, In step three, the pressure is increased by controlling the filling amount of the high-pressure cryogenic medium and utilizing the vaporization of the cryogenic medium; or the medium pressure is increased to a set value by using a cryogenic pump.

5. The forming method according to claim 1, characterized in that, The cylindrical ring blank is made of aluminum alloy, hard stainless steel, or solution-treated stainless steel; the welding method in step two is one of friction stir welding, laser welding, argon arc welding, resistance welding, or submerged arc welding.

6. The forming method according to claim 1, characterized in that, The cylindrical ring blank is a straight-walled cylindrical or conical shape; the cylindrical ring structure is a straight cylindrical structure or a conical curved surface structure.

7. A mold, characterized in that, This is used to implement step three of the method described in any one of claims 1-6.

8. The mold according to claim 7, characterized in that, include: The inner wall shape of the mold is matched with the outer shape of the target cylindrical ring structure; The inner cylinder mold is set inside the mold surface, forming an annular space between it and the mold surface to accommodate the cylindrical ring blank; The end shrinkage mold is annular and divided into multiple segments, with each segment of the end shrinkage mold being radially movable and disposed at the end of the cylindrical ring blank; The end constraint mold is connected to the upper mold base, and its lower end is engaged with the end shrinkage mold through a wedge-shaped structure. And sealing elements, which are placed between the cylindrical ring blank and the mold to form a seal; When the end constraint mold moves downward, the inclined wedge structure pushes the end shrinkage mold to move radially toward the axis, pressing and engaging the end of the cylindrical ring blank onto the inner cylinder mold. Together with the sealing element, it establishes a sealed cavity between the inner wall of the cylindrical ring blank and the outer wall of the inner cylinder mold. The sealed cavity is used to fill with a high-pressure, low-temperature medium. When the end constraint mold moves upward, the end shrinkage mold can move radially away from the axis, releasing the pressure on the end of the cylindrical ring blank.

9. The mold according to claim 8, characterized in that, The inner wall of the end constraint mold is a conical surface with the same taper as the cylindrical ring blank, and the outer wall of the inner cylinder mold is a conical surface with the same taper as the cylindrical ring blank. When the end constraint mold moves downward, its inner wall cooperates with the outer wall of the inner cylinder mold to clamp the large end of the cylindrical ring blank.

10. The mold according to claim 8, characterized in that, An annular cooling cavity is formed between the inner wall of the mold and the cylindrical ring blank, and the cooling cavity is used to fill the cavity with a normal pressure cryogenic medium. The upper part or top of the cooling cavity is provided with a normal pressure cryogenic medium inlet and outlet, which are used to fill the cavity with cryogenic medium and discharge the cryogenic medium outward during the deformation of the cylindrical ring blank toward the target cylindrical ring structure.

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