High-precision assembling method for thin-wall weak-rigidity carrier rocket box bottom force transmission structure

Abstract

The invention provides a high-precision assembly method for a thin-wall weak-rigidity carrier rocket box bottom force transfer structure, which comprises the following steps: S1, processing a scalloped segment product and a thrust flange product in parallel; s2, the scalloped segment and the thrust flange are assembled and welded in a low-stress and compression-free mode; s3, box bottom total longitudinal or circular seam assembly welding is carried out, a friction stir welding process is adopted, and box bottom welding seam phased array detection is carried out after welding; s4, performing box bottom hydraulic airtight test assessment; s5, leveling and aligning the box bottom by using a five-axis gantry mill; s6, thrust flange butt joint faces and butt joint holes are machined in a numerical control mode; s7, performing simulation trial assembly on the butt joint structure, and adjusting interference as required; and step S8, product delivery. According to the high-precision assembly method for the thin-wall weak-rigidity carrier rocket box bottom force transmission structure, precise assembly coordination of a discrete thrust flange structure is achieved, and high-precision coordination assembly of a precise installation structure on the box bottom of a large-diameter weak-rigidity tailor-welded storage box is achieved.

Description

Technical Field

[0001] The invention belongs to the field of aerospace launch vehicle production, and in particular relates to a high-precision assembly method for a thin-walled weak-rigidity launch vehicle box bottom force transmission structure. Background Art

[0002] The bottom of traditional launch vehicles is generally designed with internal pressure and does not participate in the engine force transmission. The engine force transmission is generally transmitted through a separate force transmission section. The new 5m diameter tank adopts a new bottom force transmission structure in the structural design, which transmits the engine thrust upward through the bottom ring, reduces the engine force transmission section design, and thus achieves the purpose of reducing the length of the rocket body and reducing the overall weight. The new tank bottom force transmission structure is a 6-position engine thrust flange welded to the outside of the tank bottom ring, which participates in the engine thrust transmission as the engine docking surface.

[0003] Limited by the box bottom profile structure and the engine force transmission path requirements, the thrust interface on the thrust flange adopts a wedge-shaped cross-section structure. Since the thickness of the 5m diameter box bottom ring is less than 4mm, the structural rigidity itself is weak. At the same time, the box bottom product is welded and assembled. The assembly error and welding deformation will have a great impact on the flatness of the engine docking surface and the position of the docking hole, resulting in the excessive docking accuracy between the engine and the tank, affecting the thrust control adjustment, or even failing to dock normally. The assembly coordination accuracy of the thrust flange on the weak rigidity ring is affected by many factors in the box bottom manufacturing process, and coordination and control are extremely difficult.

[0004] At present, according to the traditional tank bottom flange welding assembly method, factors such as the thrust flange assembly error, welding deformation, welding deformation of the main weld of the tank bottom, and hydraulic airtight cycle deformation will have a great impact on the docking accuracy of the final engine docking interface. The super-weak and rigid structural characteristics will have a greater impact, resulting in the engine being unable to dock normally, affecting the rocket thrust control and failing to meet the installation accuracy requirements of the new discrete thrust flange structure. Summary of the invention

[0005] In view of this, the present invention aims to propose a high-precision assembly method for a thin-walled, weak-rigidity launch vehicle tank bottom force transmission structure, so as to solve the problem that in the traditional tank bottom flange welding assembly method, factors such as the thrust flange assembly error, welding deformation, welding deformation of the main weld of the tank bottom, hydraulic airtight cycle deformation and the like will have a significant impact on the docking accuracy of the final engine docking interface, and the super-weak and rigid structural characteristics will have a greater impact, which will result in the engine being unable to dock normally, affecting the rocket thrust control, and failing to meet the requirements for the installation accuracy of the new discrete thrust flange structure.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows: The present invention provides a high-precision assembly method for a thin-walled weak-rigidity carrier rocket box bottom force transmission structure, comprising: step S1, processing a melon slice product and a thrust flange product in parallel, leaving a margin of 10 mm or more on the engine mounting surface, leaving a docking hole uncut, and processing the whole bottom; Step S2, low-stress and non-pressing assembly welding of the melon slices and the thrust flange, during the assembly process, the melon slices are first fixed before welding, the thrust flange is soaked in low-temperature liquid nitrogen, and then the thrust flange and the melon slices are assembled; when welding the thrust flange, the melon slices and the thrust flange are welded by a friction stir welding process of segmented positioning and segmented formal welding; Step S3, performing the overall longitudinal replacement or circumferential seam assembly welding of the tank bottom by using a stir friction welding process, and performing a phased array inspection of the tank bottom weld after welding; Step S4, conducting a hydraulic and airtight test on the bottom of the box to assess the quality of the weld and the sufficient deformation of the bottom of the box; Step S5, using a five-axis gantry milling machine to level and align the bottom of the box; Step S6, CNC machining the butt joint surface and the butt joint hole of the thrust flange, the CNC machining process ensures the flatness of the butt joint surface and the position of the butt joint hole; during the machining of the thrust flange parts, a margin is set in advance in the butt joint surface area for final deformation correction machining, and the thrust flange is a small diameter, strong rigidity flange without a center hole; Step S7, simulate the test assembly of the docking structure and adjust the interference as needed; Step S8, product delivery.

[0007] Furthermore, in the step S2, the melon segments that need to be subjected to stir friction welding are subjected to a pre-welding fixing treatment after processing, and then the thrust flange is assembled after being immersed in low-temperature liquid nitrogen, and then the thrust flange and the melon segments are assembled and welded without compression; the fixing treatment method includes fixing the melon segments on both sides with a drawstring and fixing the melon segments around with a melon segment pressure plate.

[0008] Furthermore, after the thrust flange and the melon slice are processed in step S2, a process of performing a pre-welding fixing treatment includes: step S201, for the thrust flange and the melon slice, the size of the opening on the melon slice is controlled according to a free tolerance of ±0.1 mm, and the thrust flange diameter is controlled according to a tolerance of (0, +0.8); Step S202, placing the melon segment into the single melon segment membrane, aligning the melon segment midline with the membrane midline of the single melon segment membrane, adjusting the melon segment large end theoretical score line, aligning the melon segment large end theoretical score line with the membrane large end theoretical score line, and the alignment error is no more than ±0.5 mm; Step S203, using melon slice drawstrings to pre-fix the melon slices on the left and right sides of the melon slices, and using melon slice pressing plates to press the edges of the melon slices tightly so that the melon slices fit the membrane tire surface.

[0009] Furthermore, the process of assembling the thrust flange after soaking it in low-temperature liquid nitrogen in step S2 includes: step S204, placing the thrust flange in a -196°C low-temperature liquid nitrogen cylinder and soaking it for 20 minutes, taking out the thrust flange after soaking and measuring the diameter of its welding edge; Step S205, assembling the thrust flange and the melon slices; assembling the thrust flange into the melon slice opening according to the engraved position, and after 5 minutes at room temperature, the thrust flange and the melon slices form a tight fit.

[0010] Furthermore, in the step S2, the process of assembling the welding thrust flange and melon slices without pressing includes: step S206, installing the melon slice pressing mechanism, connecting the melon slice pressing mechanism to the connecting blocks on both sides of the membrane tire by bolts, tightening the pressure claws, and pressing the periphery of the melon slice welding area; step S207, installing the positioning stirring head, evenly distributing four positioning small segments in the counterclockwise direction, and the length of any positioning small segment is 20-30㎜; step S208, installing the formal welding stirring head, and formally performing stir friction welding on the flange ring seam.

[0011] Furthermore, in step S207, the flange side is in a non-pressed state, and the melon slice side is pressed by a melon slice pressure plate, so that the thrust flange and the melon slice form a tight fit; in step S208, when the flange is formally welded, the flange side is in a non-pressed state.

[0012] Furthermore, in step S6, before CNC machining the thrust flange docking surface and docking hole, a special clamping tooling product is used, wherein the special clamping tooling includes an inner support block, a column, a melon-shaped pressure plate, and a clamping nut; The special clamping steps include: step S601, when clamping the ultra-weak rigid bottom of the 5m tank of the launch vehicle, first align the rotation center of the special clamping tooling, level the horizontal reference of the tooling, and fix the tooling; step S602, press and fit the inner surface of the large end of the product with the circular inner support block, and ensure that the gap between the product and the inner support block is less than 0.2mm, adjust the roundness of the large end of the bottom of the box, and level the reference line of the large end of the product; step S603, the column passes through the center hole of the product and is connected and fixed to the tooling base; step S604, the clamping nut is screwed into the thread of the column, so that the pressure plate presses the product from top to bottom to realize the constraint of the vertical freedom of the product.

[0013] Furthermore, in step S6, the assembled product is milled and the six engine docking surfaces are divided into three groups for symmetrical processing. For any engine docking surface, it is first rough-machined and then semi-finished, and then the locking nut is loosened for natural aging to further release stress.

[0014] Furthermore, the machining allowance for the rough machining is 5 mm, and the machining allowance for the semi-finishing machining is 2 mm.

[0015] Compared with the prior art, the high-precision assembly method of the thin-walled weak-rigidity carrier rocket box bottom force transmission structure of the present invention has the following advantages: (1) The flange assembly welding process of the present invention adopts liquid nitrogen low-temperature immersion combined with non-compression welding, which solves the problem of assembly preload force when the flange is not compressed, and at the same time realizes low-stress welding and reduces welding deformation.

[0016] (2) In the present invention, the stir friction welding process is used to replace the traditional fusion welding process for the longitudinal or circumferential seam assembly welding of the box bottom, which greatly reduces the heat input during the welding process and reduces deformation.

[0017] (3) The hydraulic and air-tightness test process of the box bottom in the present invention causes the box bottom to be fully deformed. There is no subsequent working condition where the internal pressure is greater than the hydraulic and air-tightness test pressure of the single bottom. There is no way or measure to reduce the deformation in this process. Combined with the deformation of the previous two links, after the hydraulic and air-tightness test, the thrust flange joint surface is processed as a whole, and the deformation left over from the previous link is corrected in a centralized manner to ensure that the accuracy of the final product meets the use requirements.

[0018] (4) The present invention as a whole achieves precise assembly and coordination of discrete thrust flange structures by innovatively optimizing the process methods and procedures and adopts a method combining low-stress welding control of the thrust flange with overall coordinated processing of the tank bottom, thereby solving the problem of high-precision coordinated assembly of precision mounting structures on the tank bottom of a large-diameter weak-rigidity tailor-made tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] In the attached picture: Figure 1 It is a schematic flow chart of a high-precision assembly method of a thin-walled weak-rigidity carrier rocket bottom force transmission structure according to an embodiment of the present invention; Figure 2 It is a detailed flow chart of step S2 in the high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to an embodiment of the present invention; Figure 3 It is a schematic diagram of melon peel opening in the high-precision assembly method of the thin-walled weak-rigidity carrier rocket box bottom force transmission structure according to an embodiment of the present invention; Figure 4 It is a cross-sectional schematic diagram of a thrust flange in a high-precision assembly method for a thin-walled weak-rigidity carrier rocket case bottom force transmission structure according to an embodiment of the present invention; Figure 5 It is a top view schematic diagram of a thrust flange in a high-precision assembly method for a thin-walled weak-rigidity carrier rocket case bottom force transmission structure according to an embodiment of the present invention; Figure 6 It is a schematic diagram of the assembly position of a single melon segment and a membrane tire in a high-precision assembly method for a thin-walled weak-rigidity carrier rocket bottom force transmission structure according to an embodiment of the present invention; Figure 7 This is a schematic diagram of tightening the melon slice pull strap and installing the melon slice pressure plate in step S2 of the high-precision assembly method for the thin-walled weak-rigidity carrier rocket box bottom force transmission structure according to an embodiment of the present invention: Figure 8 This is a schematic diagram of assembling the thrust flange and melon slices in step S2 of the high-precision assembly method for the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to an embodiment of the present invention; Fig. 9 This is a schematic diagram of pressing the melon slice side in step S2 of the high-precision assembly method for the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to an embodiment of the present invention; Fig.10 This is a schematic diagram of the positioning section during welding in step S2 of the high-precision assembly method for the thin-walled weak-rigidity carrier rocket box bottom force transmission structure according to an embodiment of the present invention; Fig.11 It is a schematic diagram of the special clamping axis side in the high-precision assembly method of the thin-walled weak-rigidity carrier rocket box bottom force transmission structure according to an embodiment of the present invention; Fig.12 It is a cross-sectional schematic diagram of a special clamping in a high-precision assembly method of a thin-walled weak-rigidity carrier rocket case bottom force transmission structure according to an embodiment of the present invention; Fig.13 This is a schematic diagram of the bottom clamping of a thin-walled, weakly rigid launch vehicle box according to an embodiment of the present invention; Fig.14 This is a schematic diagram of the processing zones of the thin-walled, weakly rigid launch vehicle box bottom according to an embodiment of the present invention.

[0021] Description of reference numerals: 1. Inner support block; 2. Column; 3. Pressure plate; 4. Pressing nut; 5. Melon slice; 6. Melon slice center line; 7. Diaphragm shape surface; 8. Melon slice theoretical scale line; 9. Diaphragm theoretical scale line; 10. Diaphragm center line; 11. Melon slice pull strap; 12. Melon slice pressure plate; 13. Thrust flange assembly. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0025] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0026] See also Figure 1 As shown, this embodiment provides a high-precision assembly method for a thin-walled weak-rigidity carrier rocket box bottom force transmission structure, including step S1, processing a melon slice product and a thrust flange product in parallel, leaving a margin of greater than or equal to 10 mm on the engine mounting surface, leaving the docking hole unmade, and making the whole bottom state; Step S2, low-stress and non-pressing assembly welding of the melon slices and the thrust flange, during the assembly process, the melon slices are first fixed before welding, the thrust flange is soaked in low-temperature liquid nitrogen, and then the thrust flange and the melon slices are assembled; when welding the thrust flange, the melon slices and the thrust flange are welded by a friction stir welding process of segmented positioning and segmented formal welding; Step S3, performing the overall longitudinal replacement or circumferential seam assembly welding of the tank bottom by using a stir friction welding process, and performing a phased array inspection of the tank bottom weld after welding; Step S4, conducting a hydraulic and airtight test on the bottom of the box to assess the quality of the weld and the sufficient deformation of the bottom of the box; Step S5, using a five-axis gantry milling machine to level and align the bottom of the box; Step S6, CNC machining the butt joint surface and the butt joint hole of the thrust flange, the CNC machining process ensures the flatness of the butt joint surface and the position of the butt joint hole; during the machining of the thrust flange parts, a margin is set in advance in the butt joint surface area for final deformation correction machining, and the thrust flange is a small diameter, strong rigidity flange without a center hole; Step S7, simulate the test assembly of the docking structure and adjust the interference as needed; Step S8, product delivery.

[0027] A discrete multi-point force transmission structure is designed on the large-diameter ultra-weak rigid welded box bottom. To achieve high-precision assembly and manufacturing, the most important thing is to control the loss of shape and position accuracy caused by deformation in each link. During the manufacturing process of this type of box bottom product, shape and position size changes will occur mainly in the three links of flange assembly welding, box bottom longitudinal or circumferential seam assembly welding, and box bottom hydraulic airtightness assessment, which will cause the engine thrust flange to deviate from the theoretical position. Corresponding control measures are formulated for the above three links that are prone to deformation.

[0028] In the flange assembly welding process, since the thrust flange has a structure without a center hole, the traditional center mandrel clamping method cannot be used for melon-shaped thrust flange welding. Therefore, a liquid nitrogen low-temperature immersion combined with non-compression welding method is proposed to solve the problem of assembly preload force in the flange non-compression state, and at the same time achieve low-stress welding and reduce welding deformation; the stir friction welding process is used to replace the traditional fusion welding process for the longitudinal or circumferential seam assembly welding of the bottom of the box, which greatly reduces the heat input during the welding process and has a small deformation; the hydraulic and airtightness test process of the bottom of the box causes the bottom of the box to be fully deformed, and there is no subsequent working condition where the internal pressure is greater than the hydraulic and airtightness test pressure of the single bottom. There is no way and measure to reduce deformation in this process. Combined with the deformation of the previous two links, the method of overall processing of the thrust flange joint surface after the hydraulic and airtightness test is adopted to centrally correct the deformation left in the above three links to ensure that the accuracy of the final product meets the use requirements. It should be noted that during the processing of the thrust flange parts, the margin needs to be set in advance in the joint surface area for the final deformation correction processing.

[0029] See also Figure 2 In step S2, a prestressed high-quality friction stir welding method is adopted, specifically, by appropriately increasing the diameter of the thrust flange welding edge, and then assembling the flange and the melon slices by the principle of thermal expansion and contraction through low-temperature liquid nitrogen immersion, and relying on the preset interaction force between the flange welding end face and the melon slice welding end face after assembly to offset the internal stress of the weld caused by the flange welding shrinkage, thereby controlling the deformation of the flange after welding; when welding the thrust flange, the high-quality assembly welding of the melon slices and the small-diameter, strong rigidity flange is completed by a friction stir welding process method of segmented positioning combined with segmented formal welding.

[0030] Specifically, in this embodiment, in step S2, the melon segments that need to be subjected to stir friction welding are subjected to pre-welding fixing treatment after processing, and then the thrust flange is assembled after being immersed in low-temperature liquid nitrogen, and then the thrust flange and the melon segments are assembled and welded without compression; the fixing treatment method includes fixing the melon segments on both sides with drawstrings and fixing the melon segments around with melon segment pressure plates.

[0031] See also Figure 6-9 , Figure 5 In the figure, melon slice 5, melon slice midline 6, membrane tire shaped surface 7, melon slice theoretical score line 8, membrane tire theoretical score line 9, membrane tire midline 10, melon slice pull strap 11, melon slice pressing plate 12. Figure 7 The position indicated by 13 is the thrust flange assembly position.

[0032] Specifically, in this embodiment, after the thrust flange and melon slices are processed in step S2, a process of fixing before welding is performed includes: step S201, for the thrust flange and melon slices, the size of the hole on the melon slice is controlled according to the free tolerance of ±0.1mm, and the thrust flange diameter is controlled according to the tolerance of (0, +0.8); step S202, placing the melon slice 5 into a single melon slice membrane, aligning the melon slice center line 6 with the membrane center line 10 of the single melon slice membrane surface 7, adjusting the theoretical mark line of the large end of the melon slice, so that the theoretical mark line of the large end of the melon slice is aligned with the theoretical mark line of the large end of the membrane surface, and the alignment error is not greater than ±0.5mm; step S203, using the melon slice pull strap 11 to pre-fix the melon slice 5 on the left and right sides of the melon slice 5, and using the melon slice pressing plate 12 to press the edges of the melon slice 5 so that the melon slice 5 fits the membrane surface 7.

[0033] See also Figure 3-5 In the embodiment, in step S201, in order to add the preset force between the melon segment flange hole and the flange welding end face, for the small diameter flange and the single melon segment, the assembly of the flange with a diameter of Φ300mm and the melon segment is taken as an example. The size of the opening on the melon segment is controlled according to the free tolerance of ±0.1mm, that is, Φ300±0.1mm, and the flange diameter is controlled according to the tolerance of (0, +0.8), that is, Φ300 (0, +0.8). The size of the flange without a center hole of the melon segment and the thrust ring is controlled, as shown in Table 1.

[0034] Table 1 Serial number Product Name Process control size 1 Melon slice opening inner diameter ΦA=300±0.1mm 2 Flange outer diameter ΦB=Φ300(0,+0.8)mm In step S203, the gap between the melon segments and the membrane tire surface is observed, and the melon segments are pre-fixed on the left and right sides of the melon segments using melon segment tie straps, and the melon segment pressing plates are used to press the edges of the melon segments to ensure that the melon segments fit the membrane tire surface. By using the method of fixing with tie straps on both sides combined with the melon segment pressing plate 12, it can be ensured that the melon segments are not deformed due to excessive welding heat during welding.

[0035] Specifically, in this embodiment, the process of assembling the thrust flange after soaking it in low-temperature liquid nitrogen in step S2 includes: step S204, placing the thrust flange in a -196°C low-temperature liquid nitrogen cylinder and soaking it for 20 minutes, taking out the thrust flange after soaking and measuring the welding edge diameter; step S205, assembling the thrust flange and the melon slice; assembling the thrust flange into the melon slice opening according to the engraved position, and after 5 minutes at room temperature, the thrust flange and the melon slice form a tight fit.

[0036] In step S203, the small diameter flange is placed in a -196°C low-temperature liquid nitrogen cylinder and soaked for 20 minutes. After soaking, the flange is taken out to measure the welding edge diameter, which is 299.7 mm. It is assembled into the melon slice opening according to the engraved line. This step is based on the principle of thermal expansion and contraction. The enlarged diameter of the flange welding area is reduced by low-temperature contraction through liquid nitrogen immersion.

[0037] The dimensional changes of the welding edge of the thrust ring flange without center hole after being immersed in liquid nitrogen are shown in Table 2.

[0038] Table 2 Serial number Product Name Outer diameter before immersion Outer diameter after immersion 1 Thrust ring flange Φ300.8mm Φ299.7mm After step S204, it can be observed that there is no gap between the flange and the melon segment annular seam, forming a tight fit with a large interference. This step relies on the principle of thermal expansion. After returning to room temperature, its diameter will gradually recover to Φ300.8mm. At this time, the melon segment will warp under the expansion state of the flange outer diameter. However, through on-site measurement, the warping amount on both sides of the melon segment is the largest, about 5mm, and the other positions are 2-3mm.

[0039] See also Fig.10 As shown, Fig.10 The thick solid line is the small positioning section during welding. Specifically, in this embodiment, in step S2, the process of assembling and welding the thrust flange and the melon slice without pressing includes: step S206, installing the melon slice pressing mechanism, connecting the melon slice pressing mechanism with the connecting blocks on both sides of the membrane tire by bolts, tightening the pressing claws, and pressing the periphery of the melon slice welding area; step S207, installing the positioning stirring head, evenly distributing the small positioning sections in four places in the counterclockwise direction, and the length of any positioning section is 20-30 mm; step S208, installing the formal welding stirring head, and formally stir friction welding the flange annular seam.

[0040] In the embodiment, the operation of step S206 can further eliminate the gap between the weld and the back welding pad. At this time, the warping of the two sides of the melon slices is the largest, about 6mm, and the other positions are 2-3mm. In step S207, it should be noted that the flange side is in a non-pressed state, and only the melon slice side is mechanically pressed, and the flange and the melon slices only rely on their large interference to maintain a tight fit. In step S208, when the flange is formally welded, the flange side is also in a non-pressed state. After welding, the warping deformation on both sides of the melon slices is measured, which is only 2-3mm, and the deformation at other positions is 1-2mm, which proves that this kind of welding shrinkage stress offsets the expansion stress between the flange and the melon slices due to the large interference, thereby controlling the deformation of the melon slices after welding with the flange to a minimum, and achieving the goal of controlling the welding deformation of the melon slices after welding with the small diameter flange.

[0041] Specifically, in this embodiment, in step S207, the flange side is in a non-pressed state, and the melon slice side is pressed by a melon slice pressure plate, so that the thrust flange and the melon slice form a tight fit; in step S208, when the flange is formally welded, the flange side is in a non-pressed state.

[0042] Specifically, in this embodiment, if Figure 11-13 As shown, in step S6, before CNC machining the thrust flange docking surface and docking hole, a special clamping tooling product is used, and the special clamping includes an inner support block 1, a column 2, a pressure plate 3, and a clamping nut 4; The special clamping steps include: step S601, when clamping the ultra-weak rigid bottom of the 5m tank of the launch vehicle, first find the rotation center of the special clamping tooling, level the horizontal reference of the tooling, and fix the tooling; step S602, press and fit the inner surface of the large end of the product with the circular inner support block 1, and ensure that the gap between the product and the inner support block 1 is less than 0.2mm, adjust the roundness of the large end of the bottom of the box, and level the reference line of the large end of the product; step S603, the column 2 passes through the center hole of the product and is connected and fixed to the tooling base; step S604, the tightening nut 4 is screwed into the thread of the column 2, so that the pressure plate 3 presses the product from top to bottom to realize the constraint of the vertical freedom of the product.

[0043] Aiming at the problem that the discrete multi-point force transmission structure at the bottom of the box is difficult to clamp and difficult to ensure the accuracy, a precision clamping and processing method is proposed, which solves the problem of product clamping and accuracy assurance and meets the high technical index requirements of the product.

[0044] Specifically, in this embodiment, in step S6, the assembled product is milled and the six engine docking surfaces are divided into three groups for symmetrical processing. For any engine docking surface, it is first rough-machined and then semi-finished, and then the locking nut 4 is loosened for natural aging to further release stress.

[0045] Specifically, in this embodiment, the machining allowance for rough machining is 5 mm, and the machining allowance for semi-finishing is 2 mm.

[0046] See also Fig.14 As shown in the figure, when the product is milled, a symmetrical processing scheme is adopted, and the six engine docking surfaces are divided into three groups for symmetrical processing to reduce the processing deformation caused by cutting force during the processing. The product milling is divided into rough, semi-finishing and finishing. After rough and semi-finishing, natural aging is performed to release stress. The processing allowance of the product docking surface is 10mm. In order to ensure the assembly accuracy requirements of the docking surface, the internal stress of the product is released in advance. The engine docking surface is subjected to regional rough processing with a processing allowance of 5mm, and then semi-finishing is performed with a processing allowance of 2mm. After the product is rough and semi-finished, the clamping nut is loosened to make the upper part of the product free, and natural aging is performed to further release stress. The processing allowance is removed to the greatest extent through rough and semi-finishing, and supplemented by natural aging, so as to fully release the residual internal stress in the material, reduce the stress release amount during the finishing process, and then reduce the processing deformation of the final product, and ensure the high precision requirements of the engine docking surface.

[0047] Through the innovative optimization of process methods and processes, and the combination of thrust flange low-stress welding control and overall coordinated processing of the tank bottom, the precise assembly and coordination of the discrete thrust flange structure is achieved, solving the problem of high-precision coordinated assembly of the precision mounting structure on the bottom of a large-diameter, weak-rigidity welded tank.

[0048] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-precision assembly method for a thin-walled, weakly rigid carrier rocket bottom force transmission structure, characterized in that: The method comprises: step S1, processing the melon slice product and the thrust flange product in parallel, leaving a margin of 10 mm or more on the engine mounting surface, and leaving the docking hole uncut and forming the product in a whole bottom state; Step S2, low-stress and non-pressing assembly welding of the melon slices and the thrust flange, during the assembly process, the melon slices are first fixed before welding, and the thrust flange is soaked in low-temperature liquid nitrogen, and then the thrust flange and the melon slices are assembled; when welding the thrust flange, the melon slices and the thrust flange are welded by a stir friction welding process of segmented positioning and segmented formal welding, and the thrust flange is a small-diameter, strong-rigidity flange without a center hole; Step S3, performing the overall longitudinal replacement or circumferential seam assembly welding of the tank bottom by using a stir friction welding process, and performing a phased array inspection of the tank bottom weld after welding; Step S4, conducting a hydraulic and airtight test on the bottom of the box to assess the quality of the weld and the sufficient deformation of the bottom of the box; Step S5, using a five-axis gantry milling machine to level and align the bottom of the box; Step S6, CNC machining the thrust flange docking surface and docking hole, the CNC machining process ensures the flatness of the docking surface and the position of the docking hole; during the machining of the thrust flange part, a margin is set in advance in the docking surface area for final deformation correction machining; Step S7, simulate the test assembly of the docking structure and adjust the interference as needed; Step S8, product delivery.

2. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 1 is characterized in that: In step S2, the melon segments that need to be subjected to friction stir welding are processed and then subjected to pre-welding fixing treatment, and then the thrust flange is assembled after being soaked in low-temperature liquid nitrogen, and then the thrust flange and the melon segments are assembled and welded without compression; the fixing treatment method includes fixing the melon segments on both sides with drawstrings and fixing the melon segments around with melon segment pressure plates.

3. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 2 is characterized in that: After the thrust flange and melon slices are processed in step S2, a process of fixing them before welding is performed, including: step S201, for the thrust flange and melon slices, the size of the hole on the melon slices is controlled according to the free tolerance of ±0.1mm, and the thrust flange diameter is controlled according to the tolerance of (0, +0.8); step S202, placing the melon slices into a single melon slice membrane, aligning the center line of the melon slice with the center line of the membrane of the single melon slice membrane surface, adjusting the theoretical mark line of the large end of the melon slice, so that the theoretical mark line of the large end of the melon slice is aligned with the theoretical mark line of the large end of the membrane surface, and the alignment error is not greater than ±0.5mm; step S203, using melon slice drawstrings to pre-fix the melon slices on the left and right sides of the melon slices, and using melon slice pressing plates to press the edges of the melon slices to fit the melon slices with the membrane surface.

4. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 2 is characterized in that: The process of assembling the thrust flange after soaking it in low-temperature liquid nitrogen in step S2 includes: step S204, placing the thrust flange in a -196°C low-temperature liquid nitrogen cylinder and soaking it for 20 minutes, taking out the thrust flange after soaking and measuring its welding edge diameter; step S205, assembling the thrust flange and the melon slice; assembling the thrust flange into the melon slice opening according to the engraved position, and after 5 minutes at room temperature, the thrust flange and the melon slice form a tight fit.

5. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 2 is characterized in that: In step S2, there is no process of pressing and assembling the thrust flange and the melon wedges for welding. The method comprises the following steps: step S206, installing a melon slice clamping mechanism, connecting the melon slice clamping mechanism to the connecting blocks on both sides of the membrane tire by bolts, tightening the pressing claws, and clamping the periphery of the melon slice welding area; step S207, installing a positioning stirring head, distributing four positioning small sections evenly in a counterclockwise direction, and the length of any positioning small section is 20-30 mm; step S208, installing a formal welding stirring head, and formally performing stir friction welding on the flange ring seam.

6. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 2 is characterized in that: In step S207, the flange side is in a non-pressed state, and the melon slice side is pressed by a melon slice pressure plate, so that the thrust flange and the melon slice form a tight fit; in step S208, when the flange is formally welded, the flange side is in a non-pressed state.

7. The high-precision assembly method for the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 1 is characterized in that: In step S6, before CNC machining the thrust flange docking surface and docking hole, a special clamping tooling product is used, wherein the special clamping tooling product includes an inner support block (1), a column (2), a pressure plate (3), and a clamping nut (4); The special clamping clamping steps include: step S601, when clamping the ultra-weak rigid box bottom of the 5m tank of the launch vehicle, first aligning the rotation center of the tooling of the special clamping, leveling the horizontal reference of the tooling, and fixing the tooling; Step S602, press and fit the inner surface of the large end of the product with the circular inner support block (1), ensure that the gap between the product and the inner support block (1) is less than 0.2mm, adjust the roundness of the large end of the bottom of the box, and level the reference line of the large end of the product; Step S603, the column (2) passes through the center hole of the product and is connected and fixed to the tooling base; Step S604, the clamping nut (4) is screwed and connected with the thread of the column (2), so that the pressure plate (3) presses the product from top to bottom, realizing the constraint of the vertical freedom of the product.

8. The high-precision assembly method for the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 7 is characterized in that: In step S6, the assembled product is milled and the six engine docking surfaces are divided into three groups for symmetrical processing. For any engine docking surface, it is first rough-machined and then semi-finished, and then the clamping nut (4) is loosened for natural aging to further release stress.

9. The high-precision assembly method of the thin-walled weak-rigidity carrier rocket bottom force transmission structure according to claim 8 is characterized in that: The machining allowance for the rough machining is 5 mm, and the machining allowance for the semi-finishing is 2 mm.

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