Large box bottom and forming method thereof

Abstract

The invention discloses a large-scale box bottom and a forming method thereof, and relates to the field of rocket structure manufacturing, the large-scale box bottom comprises a bottom cover and a plurality of ring sections, the plurality of ring sections are stacked in sequence, every two adjacent ring sections are fixedly sealed, and the outer side edge of one ring section located at the end is fixedly connected with the side edge of the bottom cover in a sealed mode. The large box bottom forming method comprises the steps that a large box bottom is designed into a bottom cover and a plurality of ring section structures; designing a flat plate circular ring blank according to the structural size of the bottom cover, and forming the flat plate circular ring blank into the bottom cover; a corresponding conical ring blank is designed according to the structural size of each ring section, and then the conical ring blanks are formed into the ring sections; and the bottom cover and the multiple ring sections are sequentially spliced, installed and fixed to a girth welding tool, the butt joint areas of every two adjacent ring sections are welded in the circumferential direction, the tail end of the ring section located on the top and the butt joint area of the bottom cover are welded in the circumferential direction, and the large box bottom is obtained. The welding seam performance is good, the production efficiency is high, and the manufacturing cost is low.

Description

Technical Field

[0001] This invention relates to the field of rocket structure manufacturing technology, and in particular to a large box bottom and its forming method. Background Technology

[0002] In the aerospace field, the diameter of rocket bodies continues to increase. As the main structure of a rocket, the fuel tank accounts for 80% of its dry weight. The fuel tank is generally composed of components such as the front and rear tank bottoms, cylindrical sections, and short shells. It not only undertakes the function of fuel storage, but also needs to withstand complex loads such as internal pressure, axial pressure, vibration, and impact, which directly determines the reliability of rocket operation.

[0003] The exponential increase in rocket body diameter presents numerous challenges to rocket structure design and manufacturing, with the fabrication of the large fuel tank bottom being one of the core difficulties. The large tank bottom has a semi-ellipsoidal curved surface structure, characterized by its ultra-large diameter and ultra-thin walls. The wall thickness of a 5m-class aluminum alloy tank bottom is only a few millimeters, while that of a 10m-class stainless steel tank bottom is less than 4mm. These defects make the tank highly susceptible to instability and wrinkling during the overall forming process. Furthermore, the poor formability of the rocket body structural materials and the deep cavities of the structure further increase the risk of cracking during the forming process.

[0004] like Figure 1 As shown, the existing manufacturing process for large rocket bottoms generally involves forming multiple circular segments and top cover segments separately before welding them together. This manufacturing method has several inherent drawbacks: First, the large number of segments results in a lengthy welding cycle, typically requiring dozens of days to complete the manufacturing of a single bottom segment; second, welding after forming causes a significant loss of weld performance, and the welding process is prone to deformation and weight gain; third, the large number of welds not only reduces the reliability of the bottom structure but also puts enormous pressure on weld evaluation for reusable rockets, making it difficult to meet the development requirements of low cost, high efficiency, and high reliability for rockets.

[0005] Therefore, there is an urgent need to design a technical solution that has good weld performance, high production efficiency, and low manufacturing cost. Summary of the Invention

[0006] The purpose of this invention is to provide a large box bottom and its forming method to solve the problems existing in the prior art, which has good weld performance, high production efficiency and low manufacturing cost.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for forming a large box bottom, which is designed as an integral ring structure. After forming the integral ring segment from a flat welded blank, it is then circumferentially welded to form the large box bottom, including the following steps: S1 features a large box bottom designed as a bottom cover and multiple ring-shaped structures. S2, Design a flat circular blank according to the structural dimensions of the bottom cover, and form the flat circular blank into a bottom cover; S3, Design the corresponding conical ring blank according to the structural dimensions of each ring segment, and then form the conical ring blank into a ring segment; S4. The bottom cover and multiple ring segments are sequentially spliced ​​and fixed to the circumferential welding fixture. The docking areas of two adjacent ring segments are welded along the circumferential direction, and the end of the top ring segment is welded to the docking area of ​​the bottom cover along the circumferential direction to obtain a large box bottom.

[0008] In one embodiment, the bottom cover is integrally formed from a flat circular blank through a deep drawing or bulging process. The flat circular blank is a single circular blank or a circular blank formed by welding together multiple strip blanks. The weld seam of the weld is reinforced in the same way as the base material during forming.

[0009] In one embodiment, the ring segment is integrally formed from a conical ring blank through an expansion, widening, or narrowing process. The conical ring blank comprises multiple arc-shaped blanks connected end to end in sequence, which are formed by rolling a flat plate into a cone and then fixing and welding them together. The weld seam of the weld is reinforced in the same way as the base material during forming.

[0010] In one embodiment, the surface of the mating area between adjacent ring segments or between a ring segment and the bottom cover is designed as a transition surface. After welding along the circumferential direction, the transition surface is locally expanded or rolled to the actual surface to enhance the circumferential weld, and the entire bottom of the box reaches a high strength level.

[0011] In one embodiment, the radial arc length of the transition surface is 0.5% to 25% smaller than the radial arc length of the actual surface.

[0012] In one embodiment, the temperature during the molding process is room temperature to -196°C.

[0013] In one embodiment, the bottom cover and the ring segment are made of aluminum alloy, solution-treated stainless steel, or hard stainless steel.

[0014] In one embodiment, the welding process is one of friction stir welding, laser welding, argon arc welding, and electron beam welding.

[0015] The present invention also provides a large box bottom manufactured based on the above-described large box bottom forming method, comprising a bottom cover, the bottom cover being a spherical or ellipsoidal conical bottom, the projection of which on a virtual horizontal plane is a circular structure; and at least one ring segment, wherein when there is one ring segment, the outer side of the ring segment is fixedly and sealed to the side of the bottom cover; when there are multiple ring segments, the multiple ring segments are stacked sequentially, adjacent two ring segments are fixedly and sealed to each other, and the outer side of the top ring segment is fixedly and sealed to the side of the bottom cover.

[0016] In one embodiment, both the bottom cover and the ring segment are integrally formed structures.

[0017] The present invention achieves the following technical effects compared to the prior art: This invention designs the large box bottom as a single-piece bottom cover and a ring structure consisting of two or more sequentially spliced ​​segments, significantly reducing the number of welds. This not only improves reliability but also greatly reduces the need for repeated rocket weld evaluation. The invention involves welding circular or conical ring blanks in a flat state before forming, transforming spatially curved longitudinal welds into planar straight welds. This simplifies clamping, increases welding speed and efficiency, and significantly shortens the manufacturing cycle and reduces manufacturing costs. Furthermore, through ultra-low temperature phase transformation strengthening, the weld and base material are uniformly reinforced during the forming process, achieving a weld joint coefficient of over 1.0, avoiding the significant performance degradation of welds after forming. Through the design of the butt joint surface structure and local bulging, this invention can also synergistically strengthen the circumferential seam without structurally reinforcing it, significantly improving the reliability and lightweighting of the large box bottom. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the bottom of a melon-shaped welded box in the prior art; Figure 2 This is an exploded view of the bottom of a large box in one or more embodiments of the present invention; Figure 3 This is a schematic diagram of a large box bottom structure in one or more embodiments of the present invention; Figure 4 This is a schematic diagram of another structure of the large box bottom in one or more embodiments of the present invention; Figure 5 This is a schematic diagram of the flat ring blank structure of a large box bottom in one or more embodiments of the present invention. Figure 6 This is a schematic diagram of the conical ring blank structure of a large box bottom in one or more embodiments of the present invention.

[0020] In the diagram: 1-Lobe; 2-Welder; 3-Bottom cover lobe; 4-Circumferential weld; 5-Longitudinal weld; 6-Bottom cover; 7-Straight seam on flat plate; 8-First ring segment; 9-Second ring segment; 10-Large box bottom; 11-Flat circular ring blank; 12-Conical ring blank. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The purpose of this invention is to provide a large box bottom and its forming method to solve the problems existing in the prior art, which has good weld performance, high production efficiency and low manufacturing cost.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] The large box has a semi-ellipsoidal curved bottom structure with an extremely large diameter and extremely thin walls, such as... Figure 1 As shown, the existing manufacturing process for the bottom of a rocket box typically involves forming multiple annular segments 1 and bottom cover segments 3 separately, and then welding them together using a welder 2. This process suffers from numerous problems, including a large number of segments 1, a long assembly and welding cycle, and welding after forming. It also results in numerous circumferential welds 4 and longitudinal welds 5, leading to performance losses, welding deformation and weight gain, and low reliability. This makes it difficult to meet the development requirements of low-cost, high-efficiency, and reusable rockets. To address this issue, this invention provides a large bottom box, as shown in the reference... Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the large box bottom 10 includes a bottom cover 6 and at least one ring segment. The bottom cover 6 and the ring segment are made of aluminum alloy, solution-treated stainless steel, or hard stainless steel. The number of ring segments is flexibly designed according to the size and specifications of the large box bottom 10. The bottom cover 6 is a spherical or ellipsoidal conical bottom, and the projection of the bottom cover 6 on the virtual horizontal plane is a circular structure. When there is one ring segment, the outer edge of the ring segment is fixedly and sealed to the side edge of the bottom cover 6. When there are multiple ring segments, the multiple ring segments are stacked sequentially, and adjacent ring segments are fixedly and sealed. The outer edge of the ring segment at the end is fixedly and sealed to the side edge of the bottom cover 6. The connection method is welding, and after welding, a circumferential weld 4 is formed. Figure 2 and Figure 3As shown, in one embodiment, there are two ring segments, namely a first ring segment 8 and a second ring segment 9. The first ring segment 8 is located between the bottom cover 6 and the second ring segment 9, and is welded by a welder 2 to form a large box bottom 10. The present invention designs the large box bottom 10 as an integrally formed bottom cover 6 and a ring structure of two or more segments spliced ​​together in sequence, which greatly reduces the number of welds, not only improving reliability, but also greatly reducing the evaluation work of repeated rocket welds. The present invention welds the large box bottom 10 from the blank of the flat plate structure into a flat circular ring blank 11 or a conical ring blank 12 before forming it, which not only transforms the spatial curved longitudinal weld into a planar straight weld, but also simplifies clamping, increases welding speed and efficiency, and greatly shortens the manufacturing cycle and reduces manufacturing costs. Through ultra-low temperature phase transformation strengthening, the weld and the base material are strengthened in a consistent manner during the forming process, and the weld joint coefficient reaches more than 1.0, avoiding the problem of a significant reduction in weld performance after forming and then welding. The present invention can also enhance the circumferential weld 4 by designing the surface structure of the docking area and local bulging, without the need to structurally reinforce the circumferential weld 4, thus significantly improving the reliability and lightweight level of the large box bottom 10.

[0025] In one embodiment, both the bottom cover 6 and the ring segment are integrally formed structures; straight seam splicing is performed in the state of a flat plate or conical ring to form a preform blank, and the preform blank is then subjected to cryogenic forming to obtain an integral bottom cover 6 and ring segment with weld seams consistent with the base material. The number of ring segments is designed according to the principle of minimizing the width of the industrial plate and the circumferential weld seams 4.

[0026] In another embodiment, the bottom cover 6 is made of a flat circular ring blank 11, which includes a flat strip blank and two flat side blanks. The flat strip blank has two symmetrically arranged smooth arc-shaped sides, and two symmetrical strip-shaped sides are provided between the two smooth arc-shaped sides. One side of the flat side blank has an arc-shaped structure, and the other side has a linear structure. The linear structure is fixedly and sealed to an adjacent strip-shaped side of the flat strip blank by welding, and the weld joint forms a flat straight seam 7. The ring segment is made of a conical ring blank 12, which includes multiple arc-shaped blanks connected end to end in sequence. Adjacent arc-shaped blanks are fixedly and sealed to each other by welding, and the weld joint forms a flat straight seam 7.

[0027] The present invention also provides a method for forming a large box bottom 10, comprising the following steps: The large box bottom 10 is designed as a bottom cover 6 and multiple ring segments; the number of ring segments is designed according to the principle of minimizing the width of the industrial plate and the number of circumferential welds 4. For example, for box bottoms with a diameter of 5-6m, the bottom cover 6 and one ring segment are two-segment structures; for box bottoms with a diameter of 7-8m, the bottom cover 6 and one ring segment are three-segment structures. Figure 2 and Figure 3As shown, the two ring segments are the first ring segment 8 and the second ring segment 9; the bottom of the 9-10m diameter box consists of a bottom cover 6, which is a three- or four-segment structure with two or three ring segments. The bottom cover 6 has a diameter of 3-6m and an axial height of 0.3-1.5m for the ring segments. The plates used to make the bottom cover 6 and the ring segments are aluminum alloy, solution-treated or hardened stainless steel.

[0028] Based on the structural dimensions of the bottom cover 6, a flat strip blank and two flat side blanks are designed and welded together to form a flat circular ring blank 11. The flat circular ring blank 11 is then formed into the bottom cover 6 within a set temperature range. The welding process is one of friction stir welding, laser welding, argon arc welding, or electron beam welding. The set temperature range during the forming process is room temperature to -196℃. Multiple arc-shaped blanks are designed according to the structural dimensions of each ring segment. After the multiple arc-shaped blanks are cut and rolled, they are welded together to form a conical ring blank 12. The phase transformation strengthening effect is utilized within a set temperature range. Then, the conical ring blank 12 is expanded into a ring segment through ultra-low temperature. The set temperature range during the forming process is room temperature to -196℃. The bottom cover 6 and multiple ring segments are sequentially spliced ​​and fixed to the circumferential welding fixture. The mating areas of two adjacent ring segments are welded along the circumferential direction, and the end of one ring segment located at the end is welded to the mating area of ​​the bottom cover 6 along the circumferential direction to obtain a large box bottom 10. In one embodiment, the surface at the mating area between the bottom cover 6 and the ring segment, and between the ring segment and the adjacent ring segment, is designed as a transition surface. After welding along the circumferential direction, the transition surface is locally bulged or rolled to the actual surface. The radial arc length of the transition surface is 0.5% to 25% less than that of the actual surface. The transition surface with the circumferential weld 4 is locally bulged at ultra-low temperature to the final surface to achieve consistent reinforcement of the circumferential weld 4, thereby obtaining a large box bottom 10 with full reinforcement of the surface area.

[0029] Example 1 In this embodiment, the sheet metal for the bottom cover 6 and the ring segment is T4 temper 2219 aluminum alloy. The large box bottom 10 is designed with a diameter of 5m and is made of a two-section structure consisting of a bottom cover 6 and a ring segment. The bottom cover 6 has a diameter of 4.2m, and the welding method for the connection area is stir welding. The forming method of the large box bottom 10 in this embodiment includes the following steps: The large box bottom 10 is designed as a two-section structure consisting of a bottom cover 6 and a ring segment.

[0030] Based on the structural dimensions of the bottom cover 6, a flat strip blank and two flat side blanks are designed and welded together to form a flat ring blank 11. The flat ring blank 11 is integrally formed into the bottom cover 6 by deep drawing or bulging within a set temperature range. In one embodiment, the flat ring blank is a single integral circular blank, or a circular blank formed by welding together multiple strip blanks. The weld seam is reinforced in the same way as the base material during forming. Multiple arc-shaped blanks are designed according to the structural dimensions of each ring segment. After the multiple arc-shaped blanks are cut and rolled, they are sequentially welded together to form a conical ring blank 12. Utilizing the phase transformation strengthening effect within a set temperature range, the conical ring blank 12 is then integrally formed into a ring segment through bulging, widening, or narrowing processes. The set temperature range during the forming process is room temperature to -196℃. In one embodiment, the conical ring blank includes multiple arc-shaped blanks that are sequentially connected end to end. After being rolled into a cone shape by a flat plate, they are fixedly welded together to form a conical ring blank. The weld seam of the weld is reinforced in the same way as the base material during forming. The bottom cover 6 and the ring segment are sequentially spliced ​​and fixed to the circumferential welding fixture. The joint area between the end of the ring segment and the bottom cover 6 is welded along the circumferential direction to obtain the large box bottom 10. Finally, the box bottom is further strengthened by artificial aging. This invention uses industrially produced naturally aged plates (T4 state, solution quenched, naturally placed) for splicing and forming, and then artificially aging them, avoiding the problem of abnormal grain growth in the weld caused by solution quenching after splicing.

[0031] Example 2 In this embodiment, the plates used to make the bottom cover 6 and the ring section are solution-treated stainless steel. The diameter of the large box bottom 10 is designed to be 6.5m. It is made of a two-section structure consisting of a bottom cover 6 and a ring section. The bottom cover 6 has a diameter of 5.5m. The welding method is laser welding, and the forming method is the same as in Embodiment 1.

[0032] Example 3 In this embodiment, the base plate 6 and the ring segment are made of hardened stainless steel. The diameter of the large box bottom 10 is designed to be 7.5m. It is made of a three-section structure consisting of one base plate 6 and two ring segments. The base plate 6 has a diameter of 4.5m and a transition surface design. The welding method for the butt joint area is laser welding. The forming method of the large box bottom 10 in this embodiment includes the following steps: The large box bottom 10 is designed as a bottom cover 6 and two ring-shaped structures.

[0033] Based on the structural dimensions of the bottom cover 6, a flat strip blank and two flat side blanks were designed and welded together to form a flat circular ring blank 11. The flat circular ring blank 11 was then drawn into the bottom cover 6 at an ultra-low temperature. Multiple arc-shaped blanks are designed according to the structural dimensions of each ring segment. After the multiple arc-shaped blanks are cut and rolled, they are welded together to form a conical ring blank 12. The phase transformation strengthening effect within a set temperature range is utilized, and the conical ring blank 12 is then expanded into a ring segment through ultra-low temperature expansion. The set temperature range during the forming process is room temperature to -196℃. The bottom cover 6 and two ring segments are sequentially spliced ​​and fixed to the circumferential welding fixture. The mating areas of the two adjacent ring segments are welded along the circumferential direction, and the end of one ring segment located at the end is welded to the mating area of ​​the bottom cover 6 along the circumferential direction to obtain a large box bottom 10. The surface at the mating area between the bottom cover 6 and the ring segment, and between the ring segment and the adjacent ring segment, is designed as a transition surface. The radial arc length of the transition surface is 0.5% to 25% less than the actual surface. The transition surface with the circumferential weld 4 is locally cryogenically expanded to the final surface to achieve consistent reinforcement of the circumferential weld 4, resulting in a large box bottom 10 with full reinforcement of the surface area.

[0034] Example 4 In this embodiment, the plates used for the bottom cover 6 and the ring segments are made of stainless steel. The diameter of the large box bottom 10 is designed to be 10m. It is made of a four-segment structure consisting of one bottom cover 6 and three ring segments. The bottom cover 6 has a diameter of 5.0m. The welding method for the butt joint area is argon arc welding. The specific steps of the forming method of the large box bottom 10 in this embodiment are the same as those in Embodiment 3.

[0035] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for forming the bottom of a large box, characterized in that, According to the overall ring structure design, after the flat welded blank is formed into an integral ring segment, it is circumferentially welded into a large box bottom, including the following steps: S1 features a large box bottom designed as a single-piece bottom cover and multiple ring-shaped structures. S2, Design a flat circular blank according to the structural dimensions of the bottom cover, and form the flat circular blank into a bottom cover; S3, Design the corresponding conical ring blank according to the structural dimensions of each ring segment, and then form the conical ring blank into a ring segment; S4, the bottom cover and multiple ring segments are sequentially spliced ​​and fixed to the circumferential welding fixture, the docking areas of two adjacent ring segments are welded along the circumferential direction, and the end of the top ring segment is welded to the docking area of ​​the bottom cover along the circumferential direction to obtain a large box bottom; The bottom cover is integrally formed from a flat circular blank through deep drawing or bulging processes. The flat circular blank is a single piece or a circular blank welded from flat pieces. The ring segment is integrally formed from a conical ring blank through bulging, widening, or narrowing processes.

2. The method for forming a large box bottom according to claim 1, characterized in that: The conical ring blank comprises multiple arc-shaped blanks connected end to end in sequence. The blanks are formed by rolling flat plates into cones and then fixing and welding them together. The weld seam of the weld is reinforced in the same way as the base material during forming.

3. The method for forming a large box bottom according to claim 1, characterized in that: The surface of the mating area between adjacent ring segments or between a ring segment and the bottom cover is designed as a transition surface. After welding along the circumferential direction, the transition surface is locally expanded or rolled to the actual surface.

4. The method for forming a large box bottom according to claim 3, characterized in that: The radial arc length of the transition surface is 0.5% to 25% smaller than the radial arc length of the actual surface.

5. The method for forming a large box bottom according to claim 1, characterized in that: The temperature during the forming process is from room temperature to -196℃.

6. The method for forming a large box bottom according to claim 1, characterized in that: The bottom cover and ring section are made of aluminum alloy, solution-treated stainless steel, or hard stainless steel.

7. The method for forming a large box bottom according to claim 1, characterized in that: The welding process is one of friction stir welding, laser welding, argon arc welding, or electron beam welding.

8. A large box bottom manufactured based on the large box bottom forming method according to any one of claims 1 to 7, characterized in that: The device includes a bottom cover, which is a spherical or ellipsoidal conical bottom and its projection on a virtual horizontal plane is a circular structure; and at least one ring segment, wherein when there is one ring segment, the outer side of the ring segment is fixedly and sealed to the side of the bottom cover; when there are multiple ring segments, the multiple ring segments are stacked sequentially, and adjacent two ring segments are fixedly and sealed to each other, and the outer side of the top ring segment is fixedly and sealed to the side of the bottom cover.

9. The large box bottom according to claim 8, characterized in that: Both the bottom cover and the ring section are integrally formed structures.

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