A method for integrally forming a large-size thin-walled ring shell

Abstract

The present invention belongs to the field of metal forming and manufacturing technology, and discloses a method for integrally forming a large-sized thin-walled ring shell. A straight cylindrical billet with a cross-sectional shape similar to that of the target ring shell part is used as a blank. The cross-sectional shape changes little during the subsequent forming process, effectively avoiding the risk of large deformation and cracking caused by drastic changes in the cross section. The integral ring shell obtained by the forming method of the present invention has only one circumferential weld and one radial weld. If these two welds are located in the process section area that can be removed, the target part without welds can be obtained after removing the process section. The forming method of the present invention adopts a local hot air expansion forming method. During a single local forming, plastic deformation occurs only in the high-temperature area constrained by the mold. After multiple local hot air expansion forming, parts that meet the requirements in all areas can be obtained. The forming method of the present invention can obtain two open-section ring shell parts or multiple segmented ring shell parts at a time, significantly improving material utilization while improving production efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of metal forming and manufacturing, and particularly relates to an integral forming method of a large-size thin-walled ring shell. Background Art

[0002] Thin-walled annular shells are annular shell components with a wall thickness to radial radius ratio of less than 1 / 20. Large-scale thin-walled annular shell components have important applications in aerospace, petrochemical, energy, and water conservancy, primarily including aircraft engine inlet lips, launch vehicle fuel tanks, petrochemical equipment, and transportation pipelines. Due to their specialized applications, large-scale thin-walled annular shell components often operate under complex loads such as high temperature, high pressure, high strength, and severe corrosion [Development and Challenges of Forming and Manufacturing Technology for Large Thin-Walled Rotational Curved Surface Components in Aerospace. Zhang Hongrui. 2022. Research on a CNC Machining Process for Thin-Walled Shell Parts. Liu Zhigang. 2016]. Furthermore, large-scale thin-walled annular shell components typically exhibit large curvature, large size, and a large drawing ratio. These characteristics place high demands on form accuracy, wall thickness uniformity, and performance. Driven by the urgent need for industrial technological development, the aerospace, petrochemical, and other fields are showing a trend toward integrated, lightweight, precise, and low-damage manufacturing. At the same time, with the global energy shortage and lack of raw materials, countries are prompted to continuously develop and research, seeking new plastic forming processes and methods that can save energy and materials.

[0003] Currently, large-scale thin-walled annular shells are primarily manufactured by stamping the shells into segments and then welding them together to form a monolithic component. This involves dividing the shell into two or more sectors, forming them separately, and then assembling them using welding [Development and Challenges of Manufacturing Technology for Forming Large Thin-Walled Rotational Curved Surface Components in Aerospace. Zhang Hongrui, 2022]. Thin-walled annular shells produced using current manufacturing processes suffer from numerous welds, leading to poor surface quality, low dimensional accuracy, structural defects at the welds, and decreased mechanical properties. To mitigate the effects of excessive welds, monolithic annular shells are required. However, the deformation associated with forming large-scale thin-walled annular shells from sheet metal often exceeds the sheet metal's forming limit, making it impossible to achieve monolithic formation of large-scale thin-walled annular shells using traditional sheet metal stamping methods.

[0004] In recent years, researchers have conducted research on integral forming methods such as integral deep drawing and integral superplastic forming [A forming method for a superplastic forming die for an aircraft inlet lip. Zhu Li. 2018. An integral forming die and forming method for an aircraft engine annular lip. Li Kui. 2019]. Both integral deep drawing and integral superplastic forming require large-scale dies and large-scale forming equipment, which are costly and inefficient. When large-scale thin plates undergo plastic deformation, they are very sensitive to thickness deviations and are prone to defects such as severe local wall thinning. At the same time, in order to alleviate forming defects, it is necessary to adopt a large-area blanking method and add a large number of process sections. The resulting formed part needs to remove the blanking area and process sections, resulting in serious waste of raw materials.

[0005] In summary, to eliminate the adverse effects of excessive welds on large, thin-walled ring shells, such as poor surface quality, low dimensional accuracy, structural defects, and loss of mechanical properties, there is an urgent need for monolithic large-scale thin-walled ring shells. However, the traditional forming methods for forming monolithic large-scale thin-walled ring shells place extremely high demands on mold size and equipment capacity, and are also prone to defects such as wrinkling and cracking. Therefore, a new monolithic forming method for large, thin-walled ring shells is needed. Summary of the Invention

[0006] The present invention proposes a new method for integrally forming a large-sized thin-walled ring shell in order to solve the problems existing in the existing large-sized thin-walled ring shell forming method, such as many welds, reduced microstructure and mechanical properties, large forming mold size, high equipment requirements, and low material utilization rate.

[0007] The technical solution of the present invention:

[0008] A method for integrally forming a large-sized thin-walled ring shell, comprising the following steps:

[0009] Step 1: Analyze the target part features and determine the forming plan and blank size

[0010] The target part's characteristics are analyzed to determine the required cross-sectional shape and dimensions of the tube blank. The impact of welds on the tube blank's bending process is analyzed, and welds are placed in locations that are most beneficial for part forming. For closed-cross-section annular shells (i.e., those with a closed cross-section obtained without cutting or radially cut), welds should be placed in locations with minimal deformation to avoid weld failure and improve material formability, or in locations subject to minimal stress during service to improve part performance. For open-cross-section annular shells (i.e., those with an open cross-section obtained by circumferential cutting), two open annular shells can be butted together to form a closed annular shell, with welds placed in the butt joint area on either the inside or outside of the shells. Simulations are then used to predict the generation and distribution of wrinkling defects during each forming step. The shape, dimensions, and forming process parameters of the tube blank and preforms are then optimized based on the simulation results. The axial welds and wrinkling defects of the tube blank are placed in the process section, and after forming, the process section containing the welds and wrinkles is removed, resulting in an open thin shell that meets the shape and dimension requirements.

[0011] Step 2: Prepare a cylinder with a straight axis

[0012] Based on the analysis results from step one, the material and dimensions of the slab are determined, and the slab is then coiled and welded into a tube. Depending on the part requirements, the tube's cross-section can be circular, elliptical, or racetrack-shaped. Other processes can also be used to prepare the desired tube in this step.

[0013] Step 3: bending the straight tube blank so that its two ends are butted together and welding them into a closed annular preform;

[0014] Step 4: Hot air bulging of the ring-shaped preform by local mold constraint

[0015] The annular preform obtained in step 3 is placed in a local constrained bulging mold for hot air bulging. During the forming process, the partially unformed areas of the annular preform, such as bends and wrinkles, are bulged and formed under the action of high temperature and high pressure, while the remaining unformed areas do not undergo plastic deformation due to the low temperature.

[0016] Step 5: Rotary progressive hot air expansion of the ring shell;

[0017] The partially formed annular preform obtained in step 4 is rotated by a certain angle, and the locally constrained hot air bulging is continued according to step 4; the local hot air bulging step is repeated until all regions of the annular shell meet the design requirements;

[0018] Step 6: Remove the process section to obtain the target part

[0019] According to the characteristics of the target part, an integral annular shell part can be obtained without cutting, or two open-section annular shell parts can be obtained by cutting along the annular direction, or a segmented closed-section annular shell part can be obtained by cutting along the radial direction, or a segmented open-section annular shell part can be obtained by combining cutting along the annular direction and the radial direction.

[0020] The beneficial effects of the present invention are:

[0021] 1. The large-size thin-walled ring shell integral forming method of the present invention uses a straight cylindrical blank with a cross-sectional shape similar to the cross-sectional shape of the target ring shell part as the blank. The cross-sectional shape changes little during the subsequent forming process, effectively avoiding the risk of large deformation and cracking caused by drastic changes in the cross-sectional shape.

[0022] Second, the present invention's method for integrally forming a large-scale, thin-walled annular shell produces a single, single circumferential weld and a single radial weld. If these two welds are located within a removable process section, the resulting weld-free component can be obtained after the section is removed. Compared to conventional methods, this eliminates the multiple welds between thin-walled annular shell components in tailor-welded structures, effectively improving the serviceability of thin-walled annular shell components.

[0023] Third, the present invention's integral forming method for large-scale, thin-walled ring shells utilizes localized hot air bulging. During a single localized forming operation, plastic deformation occurs only in the high-temperature area constrained by the mold. Multiple localized hot air bulging operations yield a part that meets requirements in all areas. The required molds and equipment are compact, resulting in low cost, high efficiency, simple operation, and high forming precision.

[0024] 4. The large-size thin-walled annular shell integral forming method of the present invention can obtain two open-section annular shell parts or multiple segmented annular shell parts at one time, thereby significantly improving material utilization while increasing production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart for integrally forming a large-sized thin-walled ring shell according to the present invention.

[0026] Figure 2 Schematic diagram of the metal sheet of the present invention being rolled and welded into a straight tube blank and the typical cross-sectional shape of the tube blank, wherein (a) is a schematic diagram of the original sheet structure, (b) is a schematic diagram of the tube blank structure after rolling and welding, (c) is a schematic diagram of the circular cross-sectional structure of the tube blank, (d) is a schematic diagram of the elliptical cross-sectional structure of the tube blank, and (e) is a schematic diagram of the runway-shaped cross-sectional structure of the tube blank.

[0027] Figure 3 Schematic diagram of the straight tube blank bent into an annular preform according to the present invention, wherein (a) is a schematic diagram of the tube blank structure before bending, (b) is a schematic diagram of the tube blank structure after bending, and (c) is a schematic diagram of the tube blank structure after welding.

[0028] Figure 4Schematic diagram of the progressive hot air bulging forming of a metal ring according to the present invention (the solid line represents the formed area, and the dotted line represents the unformed area).

[0029] Figure 5 It is a schematic diagram of the metal ring progressive hot air bulging forming device of the present invention.

[0030] Figure 6 Schematic diagrams of metal ring cutting according to the present invention, wherein (a) is a schematic diagram of the structure of an open-section ring shell obtained by cutting along the circumferential direction, (b) is a schematic diagram of the structure of a segmented closed-section ring shell obtained by cutting along the radial direction, and (c) is a schematic diagram of the structure of an open-section ring shell obtained by combining cutting along the circumferential and radial directions.

[0031] In the figure: 1 original plate, 2 tube blank after coiling and welding, 3 circular section, 4 elliptical section, 5 runway section, 6 tube blank before bending, 7 tube blank after bending, 8 tube blank after welding, 9 hot air expansion forming mold, 10 upper mold of hot air expansion forming mold, 11 mold heating device, 12 lower mold of hot air expansion forming mold, 13 air pressure controller, 14 compressed air source, 15 cutting along the circumferential direction to obtain an open-section ring shell part, 16 cutting along the radial direction to obtain a segmented closed-section ring shell part, 17 combined cutting along the circumferential and radial directions to obtain a segmented open-section ring shell part. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0033] Example 1

[0034] Step 1: Analyze the target part characteristics and determine the forming strategy and blank dimensions. Analyze the target part characteristics to determine the required cross-sectional shape and dimensions of the tube blank. The impact of welds during tube blank bending must be analyzed, and welds should be placed in locations that are most beneficial for part forming. For closed-cross-section annular shells (i.e., those with a closed cross-section obtained without cutting or by radial cutting), welds should be placed in locations with minimal deformation to avoid weld failure and improve material forming properties. Alternatively, welds should be placed in locations with minimal stress during service to improve part performance. For open-cross-section annular shells (i.e., those with an open cross-section obtained by circumferential cutting), two open annular shells can be butted together to form a closed annular shell, with welds placed in the butt joint area on either the inner or outer sides of the shells. Simulations are then used to predict the generation and distribution of wrinkling defects during each forming step. Based on these simulation results, the shape, dimensions, and forming process parameters of the tube blank and preforms are further optimized. Axial welds and wrinkling defects in the tube blank are placed in the process section. After forming, the process section containing the welds and wrinkles is removed, resulting in an open, thin shell that meets the required shape and dimensions.

[0035] Step 2: Prepare a tube blank with a straight axis. Based on the analysis results from Step 1, determine the material and dimensions of the slab, and then coil and weld the slab into a tube blank. Depending on the part requirements, the cross-section of the tube blank can be circular, elliptical, or racetrack-shaped. Other processes can also be used to prepare the desired tube blank in this step.

[0036] Step 3: bend the straight tube blank so that its two end surfaces are butted together and welded to form a closed annular preform.

[0037] Step 4: Hot air bulging of the ring-shaped preform using a localized mold constraint. The ring-shaped preform obtained in Step 3 is placed in a localized mold constraint for hot air bulging. During the forming process, the partially under-formed areas of the ring-shaped preform, such as bends and wrinkles, are bulged and formed under the action of high temperature and high pressure. The remaining unformed areas, due to the low temperature, do not undergo plastic deformation.

[0038] Step 5: Rotational and progressive hot air bulging of the ring shell. Rotate the partially formed annular preform obtained in step 4 by a certain angle and continue to perform local constrained hot air bulging according to step 4. Repeat the local hot air bulging steps to achieve progressive hot air bulging until all areas of the ring shell meet the design requirements.

[0039] Step 6: Cut off the process section to obtain the target part. According to the characteristics of the target part, the whole ring shell part can be obtained without cutting; or Figure 6 As shown in a, an open cross-section ring shell is obtained by cutting along the circumferential weld position; or as shown in Figure 6 As shown in b, the closed cross-section shell parts are obtained by cutting along the radial weld position, or as shown in Figure 6 As shown in c, a segmented open cross-section annular shell is obtained by combined cutting along the circumferential direction and the radial direction.

[0040] Advantages of Example 1: (1) The method of bending the plate into a tube can be used to effectively reduce the degree of material deformation when forming thin-walled ring shell parts by specially designing the cross-sectional shape and size of the straight tube blank, thereby reducing the risk of wrinkling and cracking; (2) The weld of the coiled straight tube blank can be cut off as a process section, which significantly reduces the weld length and can improve the service performance and stability of thin-walled ring shell parts; (3) The method of circular ring progressive hot air expansion forming is adopted, and the overall closed tube blank is used as the original blank. Loading is done from the inside. The closed tube blank itself can balance the load, and only a local constraint mold is required. Therefore, no overall mold or large equipment is required during the entire forming process. (4) The overall forming method is adopted, and cutting is performed after forming. According to the part requirements, two open-section ring shell parts or multiple segmented ring shell parts can be obtained at one time, with high forming efficiency and low cost.

[0041] Example 2

[0042] Combine Figure 2b Note that in step 2, the cross-sectional shape of the straight tube blank can be determined according to the part requirements, and can be circular, elliptical, racetrack, etc. The other steps are the same as in embodiment 1.

[0043] Advantages of Example 2: Rolling is used to form the fillet, and parts with different cross-sectional shapes can be formed according to part requirements. The forming method is simple, easy to implement, and has high forming efficiency.

[0044] Example 3

[0045] Combine Figure 2 a Note that in step 2 and step 3, laser welding (TIG) can be used to weld the cylinder and the ring obtained in step 3 and step 5. The other steps are the same as those in Example 1.

[0046] Advantages of Example 3: (1) Laser welding is used, which has a small laser spot diameter, high precision, and low heat input. Therefore, the heat-affected zone, post-weld deformation, and residual stress are all smaller than those of arc welding, making it suitable for high-precision welding applications. (2) The resulting weld seam of the thin-walled annular shell parts is of high quality and better suited to extreme service environments such as aerospace and petrochemical industries. (3) The laser beam can be transmitted via optical fiber, which is highly flexible and convenient for integration into finished products with automated equipment.

[0047] Example 4

[0048] Combine Figure 4 Note that in steps 4 and 5, a suitable hot forming temperature is selected for hot bulging according to the different materials of the thin-walled ring shell, such as titanium alloy, aluminum alloy, etc. The other steps are the same as those in Example 1.

[0049] Advantages of Example 4: It is difficult to accurately form the commonly used materials for thin-walled annular shell parts, such as aluminum alloy and titanium alloy, at room temperature. Therefore, a hot forming method is adopted, which reduces the deformation resistance of the metal, increases the elongation, and improves the forming accuracy.

[0050] Example 5

[0051] Combine Figure 4 、 5 In steps 4 and 5, the mold is heated to 300-550°C using an induction heater or electric heating rod, and a high-pressure gas pump introduces 0.1-15 MPa of high-pressure gas into the part through the medium channel for hot air bulging. The other steps are the same as in Example 1.

[0052] Advantages of Example 5: (1) Using gas for bulging allows for uniform pressure to be applied throughout the part, and the gas pressure varies little with cavity shape, making internal pressure control more accurate. (2) The required high-pressure gas source can be pressurized by absorbing air from a high-pressure pump station, making it easy to obtain and inexpensive. (3) Maintaining the temperature and pressure for a period of time at high temperature and high pressure facilitates the control of the microstructure and properties of the formed part.

[0053] Example 6

[0054] Combine Figure 2 A and 3 illustrate that in steps 1, 2, and 3, for closed-cross-section annular shell components, the side surfaces of the tube blank are subjected to significant forces during bending. Therefore, the weld seam during coil welding can be reserved at the top or bottom of the tube blank to reduce weld stress, prevent weld failure, and improve formability. The remaining steps are the same as in Example 1.

[0055] Advantages of Example 6: The position of the weld during forming is designed in advance according to the part requirements to reduce the stress on the weld and avoid weld failure, thereby reducing the forming difficulty and improving the forming performance.

Claims

1. A method for integrally forming a large-sized thin-walled ring shell, characterized in that: Here are the steps: Step 1: Analyze the target part features and determine the forming plan and blank size First, perform feature analysis on the target part to determine the cross-sectional shape and size of the required tube blank; When the tube blank is bent into shape, the influence of the weld needs to be analyzed, and the weld needs to be placed in the position that is most favorable for the part forming. The position of the weld can be divided into two situations: the first is for closed cross-section annular shell parts, that is, annular shell parts with a closed cross-section obtained without cutting or by radial cutting. The weld should be placed in a position with small deformation or a position with small stress during service. The second is for open cross-section annular shell parts, that is, parts with an open cross-section obtained by circumferential cutting. It can be considered to butt two open annular shells to form a closed annular shell, and place the weld in the butt area on the inside or outside of the annular shell according to the requirements of the target part. Finally, the generation and distribution of wrinkle defects during the forming process were predicted through simulation. Based on the simulation results, the shape, size, and forming process parameters of the tube blank and each preform were further optimized. The axial weld seam and wrinkle defects of the tube blank were placed in the process section. After forming, the process section with the weld seam and wrinkles was removed, thus obtaining a thin-walled annular shell that met the shape and size requirements. Step 2: Prepare a cylinder with a straight axis According to the analysis results of step 1, the material and size of the slab are determined, and the slab is rolled and welded into a straight tube; Step 3: bending the straight tube blank so that its two ends are butted together and welding them into a closed annular preform; Step 4: Hot air bulging of the ring-shaped preform by local mold constraint The annular preform obtained in step 3 is placed in a partially constrained bulging die for hot air bulging; during the forming process, the partially under-formed area of ​​the annular preform is bulged under the action of high temperature and high pressure, while the remaining unformed areas do not undergo plastic deformation due to the low temperature; Step 5: Rotary progressive hot air bulging of the ring shell The partially formed annular preform obtained in step 4 is rotated by a certain angle, and the locally constrained hot air bulging is continued according to step 4; the local hot air bulging step is repeated until all regions of the annular shell meet the design requirements; Step 6: Remove the process section to obtain the target part According to the characteristics of the target part, an integral annular shell part can be obtained without cutting, or two open-section annular shell parts can be obtained by cutting along the annular direction, or a segmented closed-section annular shell part can be obtained by cutting along the radial direction, or a segmented open-section annular shell part can be obtained by combining cutting along the annular direction and the radial direction.

2. The method for integrally forming a large-sized thin-walled ring shell according to claim 1, characterized in that: In step 2, the cross section of the straight tube blank is circular, elliptical or racetrack-shaped.

Images