Arc-shaped cover, integrated press bending forming method and application thereof

Abstract

This invention belongs to the field of aerospace structural component manufacturing technology, specifically relating to an arc-shaped cap and its integrated bending forming method and application. The integrated bending forming method includes the following steps: S1, blanking to obtain a cap plate blank or cap frame blank; S2, milling to machine the external dimensions and hole positions before bending, obtaining a flat, non-arc semi-finished product; S3, bending, placing the flat semi-finished product between the punch and die of a bending die, and applying pressure to press it into an arc-shaped part with a predetermined curvature; S4, stress-relieving treatment of the bent arc-shaped part to eliminate its internal residual stress; S5, shaping, bending and shaping again to stabilize its curvature shape, obtaining the final arc-shaped cap product. This invention effectively solves the problem of springback during sheet metal bending by introducing a combination of bending die design, graded pressure control, and stress-relieving and shaping processes, ensuring the accuracy of the final product's curvature and external dimensions.

Description

Technical Field

[0001] This invention relates to an arc-shaped cap and its integral bending forming method and application, belonging to the field of aerospace structural component manufacturing technology. Background Technology

[0002] Low Earth orbit (LEO) plays a vital role in emergency rescue, aviation and maritime communications, and navigation and positioning, but its capacity is limited. Currently, major spacefaring nations are actively developing LEO constellations, which involves the networking and launch of a large number of LEO satellites. The large number of LEO satellite launches and the tight deployment window place high demands on the launch vehicle's large-scale launch capabilities and launch economy.

[0003] The access cover is a functional structural component on the surface of a launch vehicle, used for the maintenance, repair, or replacement of onboard equipment. In existing technology, the access cover is typically composed of a cover plate and a cover frame riveted together using hinges, and then riveted to the rocket body. The cover plate and cover frame are often formed using a five-axis CNC machine tool. Because this structural component needs to maintain consistency with the rocket body's shape, it is characterized by its thinness (below 10mm) and curvature (φ3350~φ3811mm), resulting in significant material removal during processing and requiring consideration of stress release, making the forming process complex. Furthermore, this processing method results in substantial raw material loss; for example, when the required product thickness is 7mm, 35mm or even thicker sheet metal is actually required, leading to low processing efficiency and high manufacturing costs.

[0004] Therefore, how to improve manufacturing efficiency and reduce manufacturing costs while ensuring the performance of the rocket body inspection port cover is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing an arc-shaped cap and its integral bending forming method and application.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides an integral bending forming method for an arc-shaped cap, the cap comprising a cap plate and a cap frame, comprising the following steps: S1. Cutting: Select a plate of predetermined thickness according to the arc-shaped unfolded size of the cover and cut it to obtain a cover plate blank or cover frame blank. S2. Milling: The cover plate blank or the cover frame blank is milled to produce the external dimensions and hole positions before bending, and to obtain a flat semi-finished product without curvature. S3. Pressing and bending: The flat semi-finished product is placed between the punch and the die of the pressing and bending mold, and pressure is applied to press it into an arc-shaped part with a predetermined curvature. S4. Stress relief: The curved part after bending is subjected to stress relief treatment to eliminate its internal residual stress. S5. Shaping: The stress-relief arc-shaped part is placed in the bending mold and bent again to stabilize its arc shape and obtain the final arc-shaped cap.

[0007] Based on the above technical solution, the present invention can also be improved as follows: Furthermore, in step S3, the springback compensation amount corresponding to the cover plate or cover frame is first obtained through finite element analysis, and then corrected through process verification test to obtain the springback compensation amount. Based on the springback compensation amount, the required bending die profile is designed.

[0008] Furthermore, in step S3, the bending is carried out in a graded pressure application method. First, pressure is applied to press the flat semi-finished product to a pre-pressure angle so that the material initially fits the bending mold. After holding the pressure for a period of time, pressure is applied again until the bending mold is completely closed.

[0009] Furthermore, in step S3, the applied pressure is 2500 kg to 5000 kg, the pre-compression angle is 10° to 20°, and the pressure holding time is 2 min to 5 min.

[0010] Furthermore, in step S4, the stress relief treatment adopts natural aging treatment, and the aging time is 120h to 168h.

[0011] Furthermore, in step S5, the pressure applied during the calibration is 2500 kg to 5000 kg; the pressure holding time is 2 min to 5 min.

[0012] Furthermore, in step S1, the predetermined thickness of the selected board material is 1.1 to 1.2 times the thickness of the final product.

[0013] Furthermore, in step S2, a vacuum suction cup is used to fix the cover plate blank or the cover frame blank.

[0014] Secondly, the present invention provides an arc-shaped cap, which is manufactured using the integral bending forming method of the arc-shaped cap described above.

[0015] Thirdly, the present invention provides an application of the arc-shaped cover as described above for use in the inspection port of a launch vehicle body.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The solution of the present invention can directly use a sheet material with a thickness close to that of the final product for processing. Compared with the prior art, which uses a sheet material with a thickness several times that of the final product, the utilization rate of raw materials is greatly improved and the material cost is reduced.

[0017] This invention replaces the complex five-axis CNC machine tool machining process with flat plate milling and bending forming. Flat plate milling is simple to clamp and fast to process, while bending forming can be completed in one step or in several steps, which greatly shortens the single-piece processing cycle and can increase production efficiency by more than 100%.

[0018] This invention effectively solves the problem of springback in sheet metal bending by introducing a combination of bending die design, graded pressure control, and stress relief and shaping processes, thus ensuring the accuracy of the curvature and dimensions of the final product.

[0019] The overall process of this invention is simplified, the requirements of CNC machine tools for CNC processes are reduced, and the amount of processing is less; the bending process can be continuously batch processed after trial processing and adjustment of the appropriate springback compensation amount according to different batches of raw materials, thus shortening the overall processing time and the total processing time for multiple batches. Attached Figure Description

[0020] Figure 1 A schematic diagram of the bending die for the lid cover; Figure 2 A schematic diagram of the punch structure of the bending die for the lid cover plate; Figure 3 This is a graph showing the change in the dimensions of key points in the axial direction of the cover plate arrow body of Example 1 as a function of natural aging time. Figure 4 This is a graph showing the change in the dimensions of key points in the axial direction of the cover frame arrow body as a function of natural aging time in Example 2.

[0021] The reference numerals in the attached diagram are as follows: 1. Cavity; 2. Punch; 3. Groove; 4. Cavity surface; 5. Punch surface. Detailed Implementation

[0022] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0023] Example 1 This embodiment provides an integral bending forming method for an arc-shaped cover for a launch vehicle body inspection port. The cover includes a cover plate and a cover frame. The cover plate and cover frame are bent using the same processing steps. The integral bending forming method of the present invention is described below using the bending forming of the cover plate as an example, specifically including the following steps: S1. Material feeding: Based on the arc-shaped unfolded dimensions of the target cover plate, its outline dimensions in the planar state are obtained using calculation or drawing software. In this embodiment, the cover plate is 2.5mm thick, has an arc of φ3811mm, and has a 4.5mm thick reinforcing rib, resulting in an outline dimension of 485mm×485mm in the planar state.

[0024] Based on the dimensions of the cover plate, an 8mm thick aluminum alloy sheet is selected (the target thickness of the finished product is 7mm, taking into account the subsequent processing allowance). The sheet is cut using laser cutting to obtain a cover plate blank whose shape and size match the outline dimensions of the cover plate in the planar state of the target cover.

[0025] S2, Milling: The cover plate blank obtained in step S1 is placed on the worktable of a three-axis CNC machine tool and fixed using a vacuum chuck. Since the cover plate blank is flat, the vacuum chuck ensures its flatness and stability. The required outline, hole positions, and other features are then machined. After machining, a flat, non-curved semi-finished cover plate is obtained. At this point, the hole positions can be deburred and chamfered.

[0026] S3, bending: Mold preparation: A bending mold is used for processing. The bending mold is designed and manufactured according to the final curvature of the target cap plate, such as... Figure 1 and Figure 2 As shown, the bending die includes a punch 2 and a die 1. The punch 2 has a groove 3 for avoiding the reinforcing rib. The opposing surfaces of the punch 2 and the die 1 are the punch surface 5 and the die surface 4, respectively. To solve the springback problem after bending the aluminum alloy sheet, springback compensation is implemented when designing the punch surface 5 and the die surface 4 of the bending die. Specifically, the bending process is simulated using finite element analysis software. In this embodiment, Abaqus software is used, and at least three batches of process verification tests are conducted to obtain the curvature deviation compensation amount of the batch of 8mm thick aluminum alloy sheets after bending to the target curvature R.

[0027] Specifically, in this embodiment, the curvature R of the cover plate is φ3811mm (i.e., the diameter of the circle corresponding to the curvature R of the cover plate is 3811mm). The compensation amount after bending this batch of 8mm thick aluminum alloy sheet to the target curvature R is 11mm. The curvature of the bending die is adjusted to be slightly larger than the target curvature R. For example, the edge curvature of the bending die is adjusted to R' (R' = R - curvature deviation compensation amount, i.e., the edge curvature diameter of the bending die is reduced by 11mm compared to the curvature diameter of the target cover plate). In this embodiment, R' is φ3800mm. By applying a larger bending deformation to the sheet material through the bending die, it is ensured that after the cover plate is bent, the sheet material springs back, and its final curvature can be restored to the target curvature.

[0028] Staged Pressing: Place the flat semi-finished product obtained in step S2 onto the punch 2. During placement, ensure that the reinforcing rib structure on the back of the cover plate aligns with the corresponding groove 3 on the punch 2 to avoid damaging the reinforcing rib and ensure forming accuracy. Start the press and adopt the staged pressing process. First, the press drives the die 1 downward. After contacting the flat semi-finished product, reduce the loading speed and apply a pre-pressure of 2500 kg to press the flat semi-finished product to a pre-pressure angle of 15°. This pre-pressure angle refers to the angle between the end of the plate and the horizontal plane, and makes the plate initially fit against the punch surface 5 and the die surface 4. Hold the pressure at this position for 2 minutes. Then, apply the final pressure of 5000 kg to completely close the punch 2 and die 1, pressing the flat semi-finished product into its final shape. After holding the pressure for 5 minutes, the press returns, obtaining an arc-shaped part with a predetermined curvature, which is then removed.

[0029] Establish a database: Test and record the mechanical properties (yield strength 367 MPa, tensile strength 466 MPa, elongation after fracture 20.5%) of this batch of aluminum alloy sheets and their corresponding springback compensation. Enter the above data into the database. In the future, when using raw materials of the same grade, batch, or with similar properties, the compensation values ​​in the database can be directly retrieved for mold design and process parameter setting, reducing repeated experiments.

[0030] S4, Stress Relief: After bending in step S3, the arc-shaped component is placed on a dedicated shelf to avoid stacking and compression. Natural aging is then performed at room temperature (25℃) to release residual stress generated during bending. The arc-shaped component is placed vertically, i.e., along the axial direction of the arrow body to which the cap will be installed, to reduce the impact of its own weight on stress release. The aging time is 120h–168h, determined experimentally. Multiple arc-shaped component test samples were used. At 72 hours, 120 hours, and two months of aging, the critical dimensions of the arc-shaped component (i.e., the distance between the critical hole positions and the center point on the cap plate) were measured using a coordinate measuring machine. The results are shown in Table 1 below. Figure 3 As shown.

[0031] Table 1. Key Dimension Data After Different Aging Treatment Times in Example 1

[0032] In the table, the positive and negative signs of the data only represent the position of the site relative to the center point of the cover plate. For example, positive is upward and negative is downward, positive is left and negative is right.

[0033] The test results show that the dimensions of the arc-shaped component in this embodiment have stabilized after 120 hours of aging treatment, and there were no significant changes in the subsequent two tests. Therefore, this embodiment determines the natural aging time to be 120 hours.

[0034] S5, School Type: After natural aging, the product may experience slight secondary deformation or springback due to partial release of residual stress. To eliminate this effect, a reshaping process is performed. The product is then placed back into the bending die used in step S3. A second bending reshaping is performed on the product with a pressure of 2500 kg. After holding the pressure for 5 minutes, the product is removed. After this reshaping, the curvature shape of the product is finally stabilized, and the dimensional accuracy meets the design requirements.

[0035] After completing steps S1 to S5 above, a finished cover plate that can be used as an arc-shaped opening cover for the launch vehicle body can be obtained.

[0036] Example 2 This embodiment provides an integral bending forming method for an arc-shaped cover for a launch vehicle body inspection port. This embodiment is an integral bending forming method for the cover frame, and its processing steps are similar to the cover plate forming method in Embodiment 1, the difference being the adjustment of the following parameters: In step S1, the cover frame has a plate thickness of 4mm and a 6mm thick reinforcing rib. Its outline dimensions in the planar state are 539mm×538.9mm. Based on the dimensions of the target cover plate, an aluminum alloy plate with a thickness of 12mm is selected (the target thickness of the finished product is 10mm, taking into account the subsequent processing allowance).

[0037] In step S3, the curvature R of the cover frame is φ3808mm. Based on the curvature deviation compensation amount of the batch of 10mm thick aluminum alloy sheet after bending to the target curvature R (after simulation and verification, the curvature deviation compensation amount in this embodiment is 20mm), the curvature of the bending die is adjusted to R' as φ3788mm.

[0038] The pressure was first applied at 3000 kg and held for 2.5 min. The final pressure was the same as in Example 1.

[0039] Establish a database: Record the mechanical properties of this batch of aluminum alloy sheets (yield strength 372 MPa, tensile strength 472 MPa, elongation after fracture 19%) and their corresponding springback compensation.

[0040] In step S5, the calibration pressure is 3000 kg.

[0041] The time limit for this embodiment is determined in the same way as in Embodiment 1, and the results are shown in Table 2 below. Figure 4 As shown.

[0042] Table 2 Key Dimension Data after Different Aging Processing Times in Example 2

[0043] The test results show that the dimensions of the arc-shaped component in this embodiment have stabilized after 120 hours of aging treatment, and there were no significant changes in the subsequent two tests. Therefore, this embodiment determines the natural aging time to be 120 hours.

[0044] In this embodiment, the curvature of the cover frame product is inspected using a curvature gauge to ensure a tight fit, which cannot be achieved by using a 0.2mm thick feeler gauge. A coordinate measuring machine is then used to verify that the product meets the dimensional tolerance requirements, thus determining that the product is qualified.

[0045] Comparative Example 1 Machining scheme for the arrow body inspection port cover frame: Use 35mm thick aluminum alloy sheet. First, level the sheet surface and machine countersunk holes. Use bolts to fix the raw material to the CNC machine tool fixture. Roughly machine both sides, leaving a 1.5mm machining allowance on each side. Then, age the product for 7 days. After aging, finish both sides. During the finishing process, grooves are machined on the material edge to release machining stress.

[0046] The processing cycle of this comparative example is long and the material utilization rate is low. In addition, due to the complex clamping, stress deformation may occur if the clamping process is not well controlled, which may easily lead to the deviation of the finished product size. The table below shows the coordinate measuring machine data of the cover frame of this comparative example.

[0047] Table 3 Key Dimension Data of Finished Product (Comparative Example 1)

[0048] Comparison of the data results from the above embodiments and comparative examples shows that the present invention achieves springback compensation by pre-adjusting the curvature of the bending die, combined with natural aging to stabilize dimensions, and finally obtains the finished product through calibration. The dimensions of each key point are stably within the nominal tolerance range. Compared with traditional machining methods, the method of the present invention shortens the processing cycle, improves material utilization, and provides better dimensional stability of the processed cap. It can effectively avoid stress deformation problems during processing and meet the precision requirements of the launch vehicle body for the arc-shaped cap. The arc-shaped cap obtained by the present invention can be applied to the maintenance opening position of the launch vehicle body. The arc-shaped structure fits the shape of the rocket body, meeting the usage requirements.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integrally bending an arc-shaped cap, the cap comprising a cap plate and a cap frame, characterized in that, Includes the following steps: S1. Cutting: Select a plate of predetermined thickness according to the arc-shaped unfolded size of the cover and cut it to obtain a cover plate blank or cover frame blank. S2. Milling: The cover plate blank or the cover frame blank is milled to produce the external dimensions and hole positions before bending, and to obtain a flat semi-finished product without curvature. S3, bending: The flat semi-finished product is placed between the punch (2) and the die (1) of the bending die, and pressure is applied to press it into an arc-shaped part with a predetermined curvature; S4. Stress relief: The curved part after bending is subjected to stress relief treatment to eliminate its internal residual stress. S5. Shaping: The stress-relief arc-shaped part is placed in the bending mold and bent again to stabilize its arc shape and obtain the final arc-shaped cap.

2. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S3, the springback compensation amount corresponding to the cover plate or cover frame is first obtained through finite element analysis, and then corrected through process verification test to obtain the springback compensation amount. The required bending die profile is designed based on the springback compensation amount.

3. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S3, the bending is carried out in a graded pressure application method. First, pressure is applied to press the flat semi-finished product to the pre-pressure angle so that the material initially fits the bending mold. After holding the pressure for a period of time, pressure is applied again until the bending mold is completely closed.

4. The integral bending forming method for the arc-shaped cap according to claim 3, characterized in that, In step S3, the applied pressure is 2500 kg to 5000 kg, the pre-pressure angle is 10° to 20°, and the pressure holding time is 2 min to 5 min.

5. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S4, the stress relief treatment adopts natural aging treatment, and the aging time is 120h to 168h.

6. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S5, the pressure applied during the calibration is 2500 kg to 5000 kg; the pressure holding time is 2 min to 5 min.

7. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S1, the predetermined thickness of the selected board material is 1.1 to 1.2 times the thickness of the final product.

8. The integral bending forming method for the arc-shaped cap according to claim 1, characterized in that, In step S2, a vacuum suction cup is used to fix the cover plate blank or the cover frame blank.

9. An arc-shaped cap, characterized in that, It is manufactured using the integral bending forming method of the arc-shaped cap as described in any one of claims 1 to 8.

10. An application of the arc-shaped cap as described in claim 9, characterized in that, Used for inspection ports on the rocket body.

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