Cartridge molding method and cartridge

Abstract

The invention provides a barrel forming method and a barrel. The barrel forming and forming method comprises the steps that a metal plate is conveyed to the position between an upper roller and a lower roller of an asynchronous rolling mill; the upper roller and the lower roller are made to rotate at different surface linear speeds, shearing deformation is generated in the thickness direction of the metal plate, and the metal plate is gradually bent to form a barrel with the preset bending curvature in the rolling process; and the cylinder is subjected to heat preservation for a preset time at a preset annealing temperature for annealing treatment, so that part of the structure of the cylinder is softened, and layered heterogeneous structures with different softening degrees and alternately distributed areas are formed in the cylinder. Shear deformation is introduced in the thickness direction of the plate through asymmetrical rolling, natural bending forming of the cylinder is achieved, the plastic deformation amount is remarkably increased, springback is reduced, and the size precision is improved; and in combination with short-time annealing, a layered heterogeneous structure is formed, the strength and plasticity are synergistically improved, meanwhile, residual stress is reduced, and the dimensional stability is improved.

Description

Technical Field

[0001] This disclosure relates to the field of metal plastic forming technology, and in particular to a forming method for a cylinder and a cylinder. Background Technology

[0002] In the aerospace and high-end equipment manufacturing fields, as launch vehicles develop towards larger and lighter designs, the performance requirements for key structural components such as the rocket body shell are constantly increasing. Ultra-large diameter, ultra-thin wall thickness (i.e., ultra-large diameter-to-thickness ratio) stainless steel thin-walled cylinders have become an important development direction in rocket structural component manufacturing due to their ability to effectively reduce structural weight and improve launch efficiency. The manufacturing of such components not only needs to meet stringent geometric dimensional accuracy requirements but also requires excellent mechanical properties and long-term dimensional stability. However, traditional cylinder manufacturing processes suffer from problems such as large springback, difficulty in controlling springback, and the inability to form solid components.

[0003] Therefore, improving the manufacturing process to ensure that the performance of thin-walled cylinders meets the requirements has become an urgent problem to be solved. Summary of the Invention

[0004] This disclosure provides a method for forming a cylindrical body and a cylindrical body.

[0005] In a first aspect, embodiments of this disclosure provide a method for forming a cylinder, comprising: conveying a metal sheet to between an upper roll and a lower roll of an asynchronous rolling mill; causing shear deformation in the thickness direction of the metal sheet by rotating the upper roll and the lower roll at different surface linear velocities, thereby gradually bending the metal sheet into a cylinder with a predetermined curvature during the rolling process; and annealing the cylinder at a preset annealing temperature for a preset time, thereby causing partial softening of the cylinder and forming a layered heterogeneous structure with alternating regions of different softening degrees inside the cylinder.

[0006] In some embodiments, the upper roll and the lower roll are rolls of the same diameter, and the speed ratio between the upper roll and the lower roll is controlled between 1.05 and 1.5.

[0007] In some embodiments, the cylinder is made to achieve a target bending curvature by adjusting the rotation speed ratio and the rolling reduction.

[0008] In some embodiments, the rolling process is a multi-pass rolling process, wherein the total thinning rate is controlled between 60% and 90%, and the single-pass reduction is controlled to be within 30% of the thinning rate per pass.

[0009] In some embodiments, the preset annealing is controlled between 600°C and 900°C, and the preset time is controlled between 5 minutes and 30 minutes.

[0010] In some embodiments, after annealing, the process further includes: air cooling the annealed cylinder to avoid generating new thermal stress and to maintain the layered heterogeneous structure already formed inside the cylinder.

[0011] In some embodiments, before conveying the metal sheet between the upper and lower rolls of an asynchronous rolling mill, the method further includes: performing a solution treatment on the metal sheet; and cooling the solution-treated metal sheet to room temperature.

[0012] In some embodiments, the method further includes: performing roll bending on the annealed cylinder, wherein the bending reduction is controlled between 1% and 5% of the total thickness.

[0013] In some embodiments, the ratio of the diameter to the wall thickness of the formed cylinder is greater than 500.

[0014] Secondly, embodiments of this disclosure provide a cylindrical body prepared by the method described in any one of the first aspects, wherein the cylindrical body has a layered heterogeneous structure with alternating regions of different softening degrees.

[0015] This disclosure utilizes asynchronous rolling principles to introduce shear deformation along the thickness of the sheet metal, enabling natural bending of the sheet into a cylindrical shape. This significantly increases plastic deformation, reduces springback, and improves dimensional accuracy. Combined with short-time annealing, a layered heterogeneous structure with alternating hard and soft layers can be formed inside the cylinder, achieving a synergistic improvement in strength and plasticity. Simultaneously, residual stress generated by asynchronous rolling is reduced, enhancing the dimensional stability and long-term reliability of the cylinder. By adjusting rolling parameters and using optional roll bending and straightening processes, the cylinder's curvature and roundness can be flexibly controlled to meet the manufacturing needs of cylinders of different specifications, achieving a high degree of integration between forming, performance control, and dimensional stability. Attached Figure Description

[0016] Figure 1 This is a flowchart of a cylindrical forming method according to an embodiment of the present disclosure.

[0017] Figure 2 This is a schematic diagram of the shape of the asynchronously rolled and bent sheet material in an embodiment of this disclosure.

[0018] Figure 3 This is a graph comparing the uniaxial tensile properties of the ordinary and heterogeneous materials in the embodiments of this disclosure. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0020] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0021] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0022] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0024] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0025] Unless otherwise specified in this disclosure, the following technical terms shall be interpreted as follows: The speed ratio refers to the ratio of the speeds of the upper and lower rolls, usually expressed as i = v2 / v1, where v1 and v2 are the speeds of the upper and lower rolls, respectively. Reduction rate refers to the percentage reduction in thickness before and after rolling; Equivalent strain is an equivalent scalar quantity that describes the degree of material deformation. Heterogeneous structures refer to microstructures with alternating soft and hard regions; Recrystallization refers to the process by which deformed metals form new grains after heating; Back stress refers to the stress generated by dislocation accumulation that hinders subsequent deformation; The diameter-to-thickness ratio refers to the ratio of the cylinder's diameter to its wall thickness; Springback refers to the shape change caused by the elastic deformation recovering after unloading; Residual stress refers to the self-balancing stress that exists within a material when there is no external load.

[0026] Thin-walled cylinders are mainly manufactured using processes such as roll forming or high-pressure spinning. Roll bending is a process that uses three- or four-roll rolling equipment to repeatedly roll sheet metal, causing it to bend and deform in the thickness direction and gradually curl into a cylindrical component. This method is mature and the equipment is simple in structure. However, for ultra-large thin-walled cylinders with a diameter-to-thickness ratio exceeding 500, the material undergoes relatively small plastic deformation in the thickness direction, making significant springback a common problem. This makes it difficult to guarantee the dimensional accuracy and roundness of the formed cylinder.

[0027] Force spinning is a process in which localized pressure is applied to a rotating blank using a spinning wheel, causing continuous plastic deformation of the material to form a rotating component. This method can achieve high forming accuracy and has been applied in the manufacturing of some aerospace structural parts. However, for ultra-large diameter cylindrical bodies, force spinning typically requires large specialized equipment and complex mold systems, resulting in high equipment investment, high manufacturing costs, and relatively low forming efficiency.

[0028] Furthermore, the aforementioned forming methods primarily focus on the geometric forming process of components, making it difficult to effectively control the microstructure of the material during the forming process, thus limiting further improvements in the material's comprehensive properties such as strength and plasticity.

[0029] The inventors discovered that roll bending primarily relies on bending deformation, with limited plastic deformation, especially under large diameter-to-thickness ratio conditions. The deformation of the sheet metal is mainly elastic, resulting in significant springback after unloading, making precise control of the cylinder curvature difficult. Secondly, this method struggles to control the material's microstructure, hindering improvements in material properties after cylinder forming; yield strength and plasticity cannot be simultaneously achieved. Thirdly, the forming process generates substantial residual stress, leading to poor dimensional stability of the cylinder and making it prone to deformation during subsequent processing or service. Due to these issues, it is impossible to simultaneously meet the requirements of high-precision forming, synergistic improvement of strength and plasticity, and residual stress control for ultra-large diameter-to-thickness ratio cylinders.

[0030] Therefore, how to provide a forming and forming integrated manufacturing method that can achieve high-precision forming of ultra-large diameter-to-thickness thin-walled cylinders and improve the material microstructure and properties has become a technical problem that urgently needs to be solved in this field.

[0031] To address the shortcomings in the forming process of thin-walled cylinders with ultra-large diameter-to-thickness ratios, this disclosure aims to solve the following technical problems: Traditional roll bending mainly relies on bending deformation. When the diameter-to-thickness ratio is large, the plastic deformation of the sheet metal is extremely small, leading to significant springback after unloading and difficulty in controlling the forming dimensional accuracy. Furthermore, uneven deformation in the thickness direction easily generates large residual stresses, affecting the dimensional stability and service reliability of the cylinder. On the other hand, although asynchronous rolling technology can introduce shear deformation into sheet metal and improve material microstructure and properties, it is mainly applied in the field of flat plate rolling and has not been effectively used for direct cylinder forming. Moreover, it lacks methods for controlling the forming curvature and has not achieved a synergistic unity between component forming and microstructure and property control. Therefore, there is an urgent need to provide a new cylinder forming method that can achieve high-precision forming while improving material strength and plasticity and reducing residual stress, thus integrating forming and performance control.

[0032] To address the problems of large springback, difficulty in controlling dimensional accuracy, and difficulty in simultaneously improving material properties during the forming process of ultra-large diameter-to-thickness thin-walled cylinders, this disclosure provides a cylinder forming method based on the principle of asynchronous rolling.

[0033] This method introduces additional shear deformation along the thickness of the metal sheet by varying the surface linear velocities of the upper and lower rolls during rolling. This causes the sheet to bend overall during rolling, gradually forming a cylindrical structure. Simultaneously, the large plastic shear deformation introduced by asynchronous rolling significantly alters the internal deformation structure of the material, providing a basis for subsequent microstructure control. Short-term annealing after asynchronous rolling constructs a heterogeneous structure with alternating soft and hard phases within the material, achieving a synergistic improvement in strength and plasticity. The annealing process reduces residual forming stress, improving the dimensional accuracy and long-term stability of the cylindrical structure.

[0034] Figure 1 This is a flowchart of a cylindrical forming method according to an embodiment of the present disclosure.

[0035] Firstly, referring to Figure 1 This disclosure provides a method for forming a cylindrical body, comprising: S11. The metal sheet is conveyed between the upper and lower rolls of the asynchronous rolling mill; S12. By causing the upper and lower rolls to rotate at different surface linear velocities, shear deformation is generated in the thickness direction of the metal sheet, causing the metal sheet to gradually bend into a cylinder with a predetermined curvature during the rolling process; and S13. Anneal the cylinder at a preset annealing temperature for a preset time to soften part of the cylinder structure and form a layered heterogeneous structure with alternating regions of different softening degrees inside the cylinder.

[0036] In this embodiment of the disclosure, the metal sheet is conveyed between the upper and lower rolls of the asynchronous rolling mill. This conveying process can be achieved by a roller conveyor or a clamping conveyor to ensure that the sheet enters the rolling area stably.

[0037] By rotating the upper and lower rolls at different surface linear velocities, shear deformation is generated in the thickness direction of the metal sheet. Specifically, due to the difference in surface linear velocity between the upper and lower rolls, the deformation of the upper and lower surfaces of the sheet is inconsistent, forming a shear strain gradient in the thickness direction, thereby introducing additional shear deformation, with an equivalent strain of 0.5-2.0. Unlike traditional roll bending, which relies solely on bending deformation, this embodiment uses a shear-dominated composite deformation mechanism to gradually bend the sheet towards the side with lower surface linear velocity during the rolling process, thereby continuously forming a cylinder with a predetermined bending curvature. This process is preferably carried out under ambient temperature conditions.

[0038] In this embodiment, the shear deformation generated during asynchronous rolling produces a strain gradient distribution along the thickness direction of the metal sheet, resulting in different strain accumulation levels in layers of different thicknesses. During subsequent annealing, regions with higher strain preferentially soften, forming areas with a higher degree of softening, while regions with lower strain maintain a relatively lower degree of softening, forming areas with a lower degree of softening. Based on this strain gradient-driven selective softening mechanism, a structure with alternating regions of different softening degrees is formed inside the cylinder.

[0039] After asynchronous rolling, the cylinder undergoes a short-time annealing treatment to induce controlled partial softening of the material's microstructure. By controlling the annealing temperature and holding time, regions with varying degrees of softening are stably maintained. Regions with higher softening degrees can be areas undergoing recovery and / or recrystallization, while regions with lower softening degrees can be deformation microstructure regions maintaining high dislocation density. The alternating distribution of regions with different softening degrees forms a layered heterogeneous microstructure. This structure facilitates a synergistic improvement in both material strength and plasticity. It should be noted that regions with higher softening degrees are referred to as soft regions, and regions with lower softening degrees are referred to as hard regions; these terms are used in this disclosure to characterize the relative relationship between material properties.

[0040] Figure 2 This is a schematic diagram illustrating the shape of the bent sheet metal after asynchronous rolling in an embodiment of this disclosure, used to explain the bending deformation state of the sheet metal during the asynchronous rolling process. From Figure 2 It can be seen that, under the condition of a difference in surface linear velocity between the upper and lower rolls, the sheet metal undergoes significant bending and exhibits a cylindrical tendency during the rolling process. This indicates that the bending forming mechanism dominated by shear deformation during asynchronous rolling can effectively achieve the self-bending forming of the sheet metal. This result shows that the forming and shaping method described in this disclosure can achieve the continuous forming process of sheet metal into a cylindrical structure without using traditional roll bending as the main forming method.

[0041] In some embodiments, the upper roll and the lower roll are rolls of the same diameter, and the speed ratio between the upper roll and the lower roll is controlled between 1.05 and 1.5.

[0042] In this embodiment, the upper and lower rolls are of the same diameter, and a stable surface linear velocity difference is formed by controlling their rotational speed ratio between 1.05 and 1.5. Within this range, sufficient shear deformation can be introduced in the thickness direction of the sheet material while avoiding material instability or surface defects, thereby achieving stable and controllable cylinder bending forming. The roll diameter can be selected according to the target cylinder diameter and the sheet material thickness.

[0043] In some embodiments, the cylinder is made to achieve a target bending curvature by adjusting the rotation speed ratio and the rolling reduction.

[0044] In this embodiment, the bending curvature of the cylinder is controlled by adjusting the rotation speed ratio and the rolling reduction. The rotation speed ratio primarily affects the degree of shear deformation in the thickness direction, while the reduction affects the overall amount of plastic deformation; the two work synergistically to control the target curvature. Furthermore, the roll diameter and friction conditions also influence the formed curvature.

[0045] In some embodiments, the rolling process is a multi-pass rolling process. The total thinning rate is controlled between 60% and 90%, and the single-pass reduction is controlled to a thinning rate of less than 30% per pass.

[0046] In this embodiment, the rolling process is a multi-pass rolling process. By gradually reducing the material through multiple passes, the total thinning rate is controlled between 60% and 90%, thereby introducing a large cumulative plastic deformation to promote the formation of subsequent heterogeneous structures. At the same time, the reduction per pass is controlled to a thinning rate of no more than 30% per pass to avoid cracking or instability of the material during rolling, thus improving the safety and stability of the process.

[0047] In some embodiments, the preset annealing is controlled between 600°C and 900°C, and the preset time is controlled between 5 minutes and 30 minutes.

[0048] In this embodiment, the annealing temperature is controlled between 600°C and 900°C, and the holding time is controlled between 5 minutes and 30 minutes. Within this temperature and time range, controlled partial recrystallization of the material can occur, thereby forming a heterogeneous structure in which recrystallized and non-recrystallized regions coexist, achieving a synergistic improvement in strength and plasticity. Simultaneously, controlling the annealing temperature near the recrystallization temperature promotes dislocation annihilation and stress relaxation; by optimizing the annealing process parameters, 70% to 90% of residual stress is reduced while maintaining strength.

[0049] The yield strength of the cylinder disclosed herein is increased by 50% to 200%, and the uniform elongation is maintained at 15% to 30%, achieving lightweight manufacturing of the cylinder, which can both form and improve material properties.

[0050] In some embodiments, after annealing, the process further includes: The annealed cylinder is air-cooled to avoid generating new thermal stress and to maintain the layered heterogeneous structure that has been formed inside the cylinder.

[0051] In this embodiment of the present disclosure, after annealing, the cylinder is air-cooled to avoid generating new thermal stress and to maintain the stability of the heterogeneous structure formed during annealing, thereby improving the dimensional stability and service reliability of the cylinder.

[0052] The disclosed cylinder exhibits improved dimensional accuracy, enhanced long-term stability, and reduced deformation during subsequent processing.

[0053] In some embodiments, before conveying the sheet metal between the upper and lower rolls of an asynchronous rolling mill, the method further includes: The metal sheet is subjected to solution treatment; Cool the solution-treated metal sheet to room temperature.

[0054] In this embodiment of the disclosure, before the metal sheet is fed into the rolling mill, the sheet is further subjected to a solution treatment and cooled to room temperature to obtain a uniform initial microstructure, which is beneficial to the subsequent shear deformation and stable formation of heterogeneous microstructure.

[0055] In some embodiments, the method further includes: The annealed cylinder is then rolled and shaped, with the shaping reduction controlled between 1% and 5% of the total thickness.

[0056] In this embodiment of the disclosure, after annealing, the cylinder can also be rolled and shaped. The shaping can be performed using a three-roll or four-roll rolling mill, by rolling with a small reduction amount to finish the cylinder. The reduction amount is controlled between 1% and 5% of the cylinder thickness, so as to improve the shape accuracy and roundness of the cylinder without significantly introducing new residual stress.

[0057] In some embodiments, the ratio of the diameter to the wall thickness of the formed cylinder is greater than 500.

[0058] In the embodiments of this disclosure, the cylindrical body with a large diameter-to-wall-thickness ratio is generally a thin-walled structure with a large diameter-to-thickness ratio. For example, when the diameter-to-wall-thickness ratio is greater than 500, in the traditional roll forming process of this type of cylindrical body, due to the small overall plastic deformation, significant springback and difficulty in controlling dimensional accuracy are likely to occur.

[0059] This disclosure further verifies its applicability under large diameter-to-thickness ratio conditions through experiments. In one embodiment, the cylinder obtained by asynchronous rolling has a diameter of approximately 600 mm and a thickness of approximately 0.58 mm, with a diameter-to-thickness ratio of approximately 1050. Experimental results show that under such ultra-large diameter-to-thickness ratio conditions, the method of this disclosure can still achieve stable forming and obtain good dimensional accuracy and mechanical properties. It is understood that the method of this disclosure is not only applicable to the above-mentioned large diameter-to-thickness ratio cylinders, but also applicable to cylinders of other size ranges.

[0060] The method disclosed herein is applicable to the forming of cylinders with different diameter-to-thickness ratios, and can still achieve stable forming even when the diameter-to-thickness ratio is large, while obtaining high dimensional accuracy and good mechanical properties. Therefore, the method disclosed herein has more significant technical advantages in the forming and performance control of thin-walled cylinders with large diameter-to-thickness ratios.

[0061] Through the above-described process, this disclosure achieves material microstructure control and performance enhancement while simultaneously forming the cylinder, achieving an integrated forming and property control effect. Compared to traditional roll bending methods, this disclosure can significantly reduce springback and improve dimensional accuracy under large plastic deformation conditions, while simultaneously enhancing material strength and plasticity, thus realizing lightweight and high-performance cylinder structures.

[0062] In this disclosure, the cylindrical body is not limited to stainless steel, but is also applicable to metallic materials that can form heterogeneous structures through asynchronous rolling and annealing, including but not limited to titanium alloys, medium-entropy alloys, and magnesium alloys. Furthermore, the cylindrical body is not limited to rocket tubes, but is also applicable to other thin-walled cylindrical structures requiring large curvature radii.

[0063] Secondly, embodiments of this disclosure provide a cylindrical body prepared by any one of the methods described above, wherein the cylindrical body has a layered heterogeneous structure with alternating recrystallized and non-recrystallized regions.

[0064] In this embodiment of the present disclosure, the interior of the cylinder forms a heterogeneous microstructure consisting of recrystallized regions and non-recrystallized regions. The recrystallized regions are fine-grained microstructures, and the non-recrystallized regions are deformed microstructures. The two are distributed alternately to form a layered structure.

[0065] The layered heterogeneous microstructure is formed by the combined effects of shear deformation introduced by asynchronous rolling and subsequent controlled annealing, with different regions exhibiting differences in grain size, dislocation density, or orientation distribution. This heterogeneous microstructure endows the cylinder with both high strength and good plasticity, increasing yield strength by 50% to 200%, maintaining uniform elongation at 15% to 30%, and exhibiting low residual stress (reduction of 70% to 90%) and good dimensional stability.

[0066] To enable those skilled in the art to more clearly understand the technical solutions provided by the embodiments of this disclosure, the technical solutions provided by the embodiments of this disclosure will be described in detail below through specific embodiments: Example 1 This embodiment provides a cylindrical forming method based on asynchronous rolling.

[0067] (1) Material preparation 304L-1 / 2H stainless steel sheet was selected as the raw material. The sheet thickness was t=4 mm, width was B=80 mm, and length was L=140 mm. Its composition (wt.%) is as follows: C 0.02, Cr 23.02, Mn 1.75, Ni 10.69, S 0.03, P 0.04, Si 0.67, with the remainder being Fe and unavoidable impurities.

[0068] The board was placed in an 1100℃ furnace for 30 minutes and then removed and cooled to room temperature with water to obtain a uniform initial structure.

[0069] It should be noted that the thickness, width and length of the plates in this disclosure can be selected according to the target cylinder size and specific application requirements, and do not constitute a limitation.

[0070] (2) Asynchronous rolling forming The sheet metal is rolled into shape using an asynchronous rolling mill with the same diameter but different speeds. The diameter of the upper and lower rolls is D=180 mm, and the speed ratio of the upper and lower rolls is 1:1.30.

[0071] The rolling process employs multi-pass deformation, with a total thinning rate of 87.5% and a single-pass reduction controlled at 0.1 mm to avoid material cracking and ensure deformation stability.

[0072] During the rolling process, due to the difference in surface linear velocity between the upper and lower rolls, significant shear deformation occurs in the thickness direction of the sheet, causing the sheet to bend towards the side with lower surface linear velocity, thus gradually forming a cylindrical structure. The equivalent strain in this process is approximately 1.2, which is significantly higher than the strain level of traditional roll bending (typically <0.1).

[0073] (3) Short-time annealing treatment The asynchronously rolled cylinder is placed in an annealing furnace and held at 700°C for 20 minutes, then air-cooled to room temperature.

[0074] After annealing, a distinct layered heterogeneous structure forms inside the cylinder: some areas undergo recrystallization, forming fine equiaxed grains with a grain size of approximately 5–10 μm (soft regions); other areas do not undergo recrystallization, retaining the deformed structure of the rolled state (hard regions); the soft and hard regions alternate, forming a stable layered structure. This structure endows the material with both high strength and good plasticity.

[0075] (4) Roll bending and shaping (optional) In this embodiment, the annealed cylinder can also be rolled and shaped. A four-roll plate rolling machine is used, and the shaping reduction is controlled to be approximately 2% of the plate thickness. After shaping, the cylinder's out-of-roundness is less than 0.3%, meeting the requirements for high-precision manufacturing.

[0076] Example 2 This embodiment uses different roller diameters and speed ratios.

[0077] Compared with Example 1, the difference in this example is that the diameter of the upper and lower rollers is 300 mm, the speed ratio i=1.25, and the other process parameters are the same. The radius of curvature of the formed cylinder is about 10 m, and the equivalent strain is about 1.5.

[0078] The results show that: By reducing the speed ratio and increasing the roll diameter, a larger radius of curvature can be obtained, thus making it suitable for forming large-size cylinders.

[0079] It should be noted that this disclosure does not limit the diameter of the cylinder. For cylinders with a large diameter-to-thickness ratio, asynchronous rolling has introduced a certain amount of plastic bending deformation, and only small deformation correction is needed to complete the final forming, effectively overcoming the problems of insufficient plastic deformation and large springback in traditional roll forming.

[0080] Example 3 This embodiment uses a different annealing process.

[0081] Compared with Example 1, the difference in this example is that the annealing temperature is 900°C, the holding time is 10 min, and the other process parameters are the same.

[0082] After annealing, the proportion of recrystallization zone increases, the material strength decreases slightly, but the plasticity is significantly improved, and the uniform elongation reaches about 35%.

[0083] Example 4 This embodiment uses a different material system.

[0084] Compared with Example 1, this example uses 316L austenitic stainless steel sheet with a thickness of t=4 mm.

[0085] The asynchronous rolling parameters were adjusted as follows: speed ratio i = 1.15, reduction rate ε = 35%; annealing temperature was 900°C, and holding time was 20 minutes.

[0086] The results show that: This method is also applicable to 316L stainless steel, and the resulting cylinder maintains good mechanical properties while possessing excellent corrosion resistance.

[0087] Comparative Example 1 Traditional roll bending is employed. A traditional three-roll roll bending method is used to form cylindrical shapes from 304 stainless steel sheets of the same specifications. The sheet thickness is t=4 mm, and the target radius of curvature is R=5 m. Roll bending process parameters: upper roller presses down, forming the shape after one roll.

[0088] The results show that: Due to the large diameter-to-thickness ratio D / t (approximately 2500), the sheet metal mainly undergoes elastic deformation during roll bending, with plastic deformation less than 0.05. After unloading, significant springback occurs, and the actual radius of curvature deviates from the target value by approximately 12%.

[0089] Meanwhile, the residual stress inside the formed cylinder is relatively large, with a maximum residual stress of about 150 MPa, and the mechanical properties of the material are not significantly improved compared with the original material.

[0090] Comparative Example 2 Material property comparison Uniaxial tensile tests were performed on the heterogeneous material (solution treatment + asynchronous rolling + annealing) and the ordinary material (solution treatment only).

[0091] The results show that: The heterogeneous material exhibits higher yield strength and better uniform elongation, demonstrating a significant synergistic improvement in strength and plasticity.

[0092] Figure 3 This is a comparison curve of the uniaxial tensile properties of the ordinary and heterogeneous materials in the embodiments of this disclosure, used to illustrate the improvement effect of the method of this disclosure on the mechanical properties of the materials. From Figure 3 It can be seen that, compared with the ordinary material, the yield strength and tensile strength of the heterogeneous material are improved, while maintaining a high uniform elongation, demonstrating a synergistic improvement in strength and plasticity. This result is consistent with the mechanical property data in the aforementioned embodiments, further verifying the effectiveness of this disclosure in obtaining a layered heterogeneous structure through "asynchronous rolling + annealing," thereby achieving integrated forming of the cylinder.

[0093] This disclosure has at least the following technical effects: This disclosure employs asynchronous rolling to achieve cylinder forming. By utilizing the surface linear velocity difference between the upper and lower rolls, shear deformation is introduced in the thickness direction of the sheet material, causing the material to bend during rolling and gradually form a cylinder. Compared to traditional roll bending, which primarily relies on bending deformation, this disclosure prioritizes shear deformation, resulting in more complete plastic deformation in the thickness direction of the sheet material. This effectively improves the overall level of plastic deformation, thus solving the problem of insufficient plastic deformation under ultra-large diameter-to-thickness ratio conditions, making the forming process more stable and controllable.

[0094] Because asynchronous rolling introduces significant plastic deformation, the proportion of elastic deformation in the material decreases, resulting in a significant reduction in springback after unloading. Therefore, this disclosure can effectively improve the curvature accuracy and forming consistency of the cylinder, solve the problem of difficult springback control in traditional roll bending, and improve the dimensional accuracy and forming stability of the cylinder.

[0095] This disclosure introduces large plastic deformation through asynchronous rolling, combined with subsequent short-time annealing, to form a layered heterogeneous structure within the material, characterized by alternating recrystallized and non-recrystallized regions. In this heterogeneous structure, the soft and hard regions work synergistically, generating a back stress strengthening effect during deformation. This improves material strength while maintaining good plasticity, achieving a synergistic enhancement of both strength and plasticity. This overcomes the limitations of traditional forming methods, which can only achieve geometric shaping and are unlikely to improve material properties. The improvement in yield strength can be verified through tensile tests in the comparative example.

[0096] By implementing controlled annealing after asynchronous rolling, dislocation annihilation and stress relaxation can be effectively promoted, thereby significantly reducing the residual stress level inside the cylinder. The reduction in residual stress improves the dimensional stability of the cylinder, reduces the risk of deformation during subsequent processing and service, and enhances the reliability of the product.

[0097] This disclosure allows for flexible control of the cylinder's bending curvature by adjusting process parameters such as the speed ratio and reduction during asynchronous rolling, thereby adapting to the manufacturing needs of cylinders of different sizes and specifications. Furthermore, an optional roll bending correction process can be incorporated to further improve the cylinder's shape accuracy without significantly introducing new residual stress. Compared to traditional roll bending methods that rely on experience-based adjustments, this disclosure offers better process controllability and repeatability.

[0098] There is a clear intrinsic link between the above-mentioned beneficial effects: The large plastic shear deformation introduced by asynchronous rolling serves as a foundation, reducing springback and improving dimensional accuracy while providing conditions for microstructure control. Short-time annealing, while reducing residual stress, forms heterogeneous structures through partial recrystallization, achieving a balance between strength and plasticity. Optional roll bending serves as a finishing method to further improve shape accuracy. The synergistic effect of these three processes integrates cylinder forming and performance control.

[0099] The cylindrical forming and shaping method disclosed herein has good engineering applicability and can be applied to the following fields: Aerospace This disclosure applies to the manufacture of thin-walled cylindrical structures with a large diameter-to-thickness ratio, such as cylindrical components in rocket structures, including but not limited to engine casings, interstage sections, and fairings. By integrating forming and performance control, structural weight can be reduced while ensuring structural strength, thereby improving launch efficiency.

[0100] Energy Equipment Field (1) Nuclear power equipment It can be used to manufacture the cylinders of key components such as reactor pressure vessels and steam generators to meet their high requirements for dimensional accuracy and material properties.

[0101] (2) Petrochemical equipment It is suitable for manufacturing the shells of large storage tanks, reaction vessels, heat exchangers and other equipment, and helps to improve the manufacturing precision and long-term reliability of the equipment.

[0102] Other applications and extensions (1) Integration with other manufacturing technologies This disclosure can be combined with welding processes (such as laser welding and friction stir welding) to manufacture large and complex structural components; it can also be combined with surface treatment technologies to obtain components with specific surface properties.

[0103] (2) Expansion of material systems This disclosure applies not only to stainless steel materials, but also to metallic materials that can form heterogeneous structures through "asynchronous rolling + annealing", including but not limited to titanium alloys, high-temperature alloys, magnesium alloys, etc., and has good versatility and promotional value.

[0104] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A method for forming a cylindrical body, comprising: The metal sheet is fed between the upper and lower rolls of the asynchronous rolling mill; By rotating the upper and lower rolls at different surface linear velocities, shear deformation is generated in the thickness direction of the metal sheet, causing the metal sheet to gradually bend into a cylinder with a predetermined curvature during the rolling process; and The cylinder is annealed at a preset annealing temperature for a preset time, causing partial softening of the cylinder and forming a layered heterogeneous structure with alternating regions of different softening degrees inside the cylinder.

2. The forming method according to claim 1, wherein, The upper roll and the lower roll are rolls of the same diameter, and the speed ratio between the upper roll and the lower roll is controlled between 1.05 and 1.

5.

3. The forming method according to claim 2, wherein, By adjusting the speed ratio and rolling reduction, the cylinder can achieve the target bending curvature.

4. The forming method according to claim 1, wherein, The rolling process is a multi-pass rolling process. The total thinning rate is controlled between 60% and 90%, and the single-pass reduction is controlled to a thinning rate of less than 30% per pass.

5. The forming method according to claim 1, wherein, The preset annealing temperature is controlled between 600°C and 900°C, and the preset time is controlled between 5 minutes and 30 minutes.

6. The forming method according to claim 1, wherein, After annealing, the process also includes: The annealed cylinder is air-cooled to avoid generating new thermal stress and to maintain the layered heterogeneous structure that has been formed inside the cylinder.

7. The forming method according to claim 1, wherein, Before conveying the metal sheet between the upper and lower rolls of the asynchronous rolling mill, the process also includes: The metal sheet is subjected to solution treatment; Cool the solution-treated metal sheet to room temperature.

8. The forming method according to claim 1 or 6, wherein, The method further includes: The annealed cylinder is then rolled and shaped, with the shaping reduction controlled between 1% and 5% of the total thickness.

9. The forming method according to claim 1, wherein, The ratio of the diameter to the wall thickness of the formed cylinder is greater than 500.

10. A cylindrical body prepared by the method according to any one of claims 1 to 9, wherein, The cylinder has a layered heterogeneous structure with alternating regions of varying softening degrees.

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