A method of sealing an aircraft integral fuel tank assembly

Abstract

This application discloses a method for sealing and assembling an integral aircraft fuel tank, relating to the field of fuel tank assembly technology. The method includes: obtaining a fuel tank area component model of the target fuel tank based on a digital model of the fuel tank area's surrounding surface and a digital model of the fuel tank area structure; extracting boundary lines at the boundaries of the fuel tank area components to form a boundary line dataset; extracting boundary surfaces of the fuel tank area components near the fuel tank surface to form a boundary surface dataset; projecting the boundary line dataset of each component in the component set onto the boundary surface datasets of the remaining components to obtain a projection line dataset; concatenating the projection line dataset and the boundary line dataset to form a hole boundary line dataset, whereby the hole boundary lines enclose a boundary hole surface; comparing the area of ​​the boundary hole surface with a preset interval to obtain the leakage risk level; and adjusting the sealing strategy based on the leakage risk level.

Description

Technical Field

[0001] This application relates to the field of fuel tank assembly technology, and in particular to a method for sealing and assembling an integral aircraft fuel tank. Background Technology

[0002] Aircraft integral fuel tanks consist of components such as the fuselage frame structure, air intake, and cap, serving both fuel storage and structural load-bearing functions, and are widely used in airframe structures. Existing fuel tank sealing and assembly processes mainly include the following steps: process review and assembly process design – component manufacturing – pre-installation of structural holes – wet installation – gas / oil tightness testing. If the gas / oil tightness test fails, leak point identification and repair are required. However, in existing technologies, some structural holes in the fuel tank are difficult to detect during the process review stage. During sealing assembly, only large amounts of sealant can be used to fill these holes, resulting in poor sealing and a tendency for leakage.

[0003] Therefore, there is an urgent need for an integrated fuel tank sealing assembly method to improve the quality and efficiency of fuel tank sealing process design and enhance the overall fuel tank sealing effect. Summary of the Invention

[0004] The main objective of this application is to provide a method for sealing and assembling an integral aircraft fuel tank, which aims to solve the technical problem in the prior art that some structural holes are difficult to detect during the process review stage, and can only be filled with a large amount of sealant during sealing and assembly, resulting in poor sealing effect and easy leakage.

[0005] To achieve the above objectives, this application provides a method for sealing and assembling an integral aircraft fuel tank, comprising:

[0006] Based on the digital model of the tank area surrounding the target tank and the digital model of the tank area structure, obtain the tank area component model of the target tank.

[0007] Based on the fuel tank area component model, the boundary lines of the fuel tank area components located at the boundary are extracted to form a boundary line dataset, and the boundary surfaces of the fuel tank area components near the fuel tank surface are extracted to form a boundary surface dataset.

[0008] Based on the fuel tank area component model, obtain the component set that can form local holes, and project the boundary line dataset of each component in the component set onto the boundary surface dataset of the other components to obtain the projection line dataset.

[0009] The projection line dataset and the boundary line dataset are spliced ​​together to form the hole boundary line dataset. The hole boundary lines enclose the boundary hole surface. The area of ​​the boundary hole surface is compared with the preset interval to obtain the leakage risk level. Based on the leakage risk level, the sealing strategy is adjusted.

[0010] Optionally, the step of obtaining the fuel tank area component model of the target fuel tank based on the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure includes:

[0011] The fuel tank area part model is obtained by intersecting the digital model of the fuel tank area's surrounding surface with the digital model of the fuel tank area's structure using 3D modeling software, and then marked.

[0012] Optionally, the step of splicing the projection line dataset and the boundary line dataset to form a hole boundary line dataset, wherein the hole boundary lines enclose and form a boundary hole surface, includes:

[0013] The hole boundary lines in the hole boundary line dataset are grouped into groups, and each group of hole boundary lines constitutes a candidate hole surface. The areas of all candidate hole surfaces in the target area are compared, and the candidate hole surface with the largest area is selected as the boundary hole surface of the target area.

[0014] Optionally, the step of comparing the area of ​​the boundary hole with a preset range to obtain the leakage risk level, and adjusting the sealing strategy based on the leakage risk level, includes:

[0015] When the area of ​​the boundary hole is less than the preset range, it indicates that there is no risk of leakage, and the inside and outside of the joint are sealed.

[0016] When the area of ​​the boundary hole surface is within the preset range, it indicates a slight risk of leakage, and local glue stacking is used for sealing.

[0017] When the area of ​​the boundary hole surface is larger than the preset range, it indicates a severe leakage risk. After sealing, a plugging corner piece is installed at the boundary hole surface.

[0018] Optionally, based on the fuel tank area part model, the connection relationship between the parts in the fuel tank area is obtained, an assembly dimension chain is established, and the composition of the deviations in each assembly link is determined.

[0019] Based on the design model requirements, determine the required thickness of the sealing adhesive layer at each boundary of the overall fuel tank;

[0020] Acquire the full-process manufacturing capabilities of parts in the fuel tank area as the basis for tolerance allocation;

[0021] Based on the requirements for sealant layer thickness and the full-process manufacturing capabilities of parts in the fuel tank area, tolerances are allocated to parts processing, heat treatment, and structural assembly.

[0022] The parts in the fuel tank area are machined, heat-treated, and structurally assembled to obtain actual deviation data.

[0023] Based on actual deviation data, assess the feasibility of the overall assembly of the fuel tank and determine whether pre-treatment or tolerance allocation optimization is required.

[0024] Optionally, the full-process manufacturing capability of the fuel tank area parts includes machining accuracy of machined parts, machining accuracy of sheet metal parts, molding accuracy of composite materials, paint thickness accuracy, and assembly positioning accuracy.

[0025] Optionally, the normal pressure at the sealing interface can be obtained based on theoretical analysis and simulation calculation of the sealing interface of the overall oil tank;

[0026] The bolt preload is obtained based on the positive pressure at the sealing interface;

[0027] Based on the interaction of the bolt groups, the overall assembly sequence of the fuel tank and the bolt installation sequence are determined, and the installation sequence result is obtained;

[0028] Based on the installation sequence, the bolt installation process is monitored and controlled during the installation process;

[0029] Measure the thickness of the components and interlayer at the overall sealing interface of the fuel tank, and monitor the change in the thickness of the sealing adhesive layer;

[0030] Adjust the bolt preload according to the changes in the thickness of the sealant layer.

[0031] Optionally, based on historical leakage data from multiple integrated oil tanks, a first leakage area with a leakage frequency greater than a preset threshold is identified;

[0032] The area where the boundary hole surface is larger than the preset range is marked as the second leakage area;

[0033] The first and second leakage areas are marked as danger zones. When the overall oil tank leaks, the danger zones are investigated first.

[0034] Optionally, the step of prioritizing the inspection of the hazardous area when the overall fuel tank leaks includes:

[0035] Based on the overall assembly sequence and production cycle of the fuel tank, determine the process leak detection plan and the final leak detection plan;

[0036] If localized leakage occurs during the implementation of the leak detection plan or the final leak detection plan, trace the cause of the localized leakage, prioritize the investigation of the dangerous areas, and carry out localized repairs for the localized leakage.

[0037] Optionally, the assembly process, process leak detection, and final leak detection results of the overall fuel tank assembly are analyzed to determine whether there are defects in the tolerance allocation. If there are defects in the tolerance allocation, the processing tolerance requirements, heat treatment tolerance requirements, and structural assembly tolerance requirements are optimized.

[0038] The beneficial effects that this application can achieve are:

[0039] This application proposes a method for sealing and assembling an integral aircraft fuel tank, comprising: obtaining a fuel tank area component model of the target fuel tank based on a digital model of the fuel tank area surrounding surface and a digital model of the fuel tank area structure; extracting boundary lines at the boundaries of the fuel tank area components based on the fuel tank area component model, forming a boundary line dataset, and extracting boundary surfaces of the fuel tank area components near the fuel tank surface, forming a boundary surface dataset; obtaining a set of components capable of forming local holes based on the fuel tank area component model, projecting the boundary line dataset of each component in the component set onto the boundary surface datasets of the remaining components to obtain a projection line dataset; splicing the projection line dataset and the boundary line dataset to form a hole boundary line dataset, the hole boundary lines enclosing to form a boundary hole surface, comparing the area of ​​the boundary hole surface with a preset interval to obtain the leakage risk level, and adjusting the sealing strategy based on the leakage risk level. By identifying and reconstructing fuel tank holes, determining risk categories, and formulating disposal methods, fuel tank leakage risks can be identified and addressed in advance during the process design stage, improving the quality and efficiency of fuel tank sealing process design and saving subsequent leak detection and troubleshooting time. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall sealing assembly process of the aircraft fuel tank according to an embodiment of this application;

[0041] Figure 2 This is an exploded structural diagram of the overall fuel tank according to an embodiment of this application;

[0042] Figure 3 This is a schematic diagram of the holes in the overall fuel tank according to an embodiment of this application;

[0043] Figure 4 for Figure 3 A schematic diagram of the projection lines of a partially magnified structure in the image;

[0044] Figure 5 for Figure 3 A magnified schematic diagram of the boundary surface of the fuel tank in the image.

[0045] Figure 6 This is a schematic diagram of the overall assembly of the fuel tank according to an embodiment of this application.

[0046] The numbers on the map are:

[0047] 1-Fuel tank cap, 2-Rubber gasket, 3-First beam, 4-First frame, 5-Fuel tank bottom plate, 6-Second beam, 7-Second frame, 8-First boundary hole, 9-Second boundary hole, 10-Third boundary hole, 11-Fourth boundary hole, 12-First beam boundary line, 13-First frame boundary line, 14-Fuel tank bottom plate boundary surface, 15-First beam boundary surface, 16-First frame boundary surface, 17-First projection line, 18-Second projection line, 19-First fuel tank interface.

[0048] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0049] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0051] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0053] In existing technologies, the current fuel tank sealing assembly process mainly includes the following steps: process review and assembly process design - parts manufacturing - pre-assembly hole drilling - wet installation - gas / oil tightness testing. If the gas / oil tightness test fails, leak point identification and repair are required. In actual production, the following problems have been found in this sealing assembly process:

[0054] Some structural holes are difficult to detect during the process review stage. During sealing assembly, a large amount of sealant can only be used to fill them, resulting in poor sealing effect and easy leakage.

[0055] The overall fuel tank sealing assembly lacks a full-process control plan, focusing only on the wet installation process, but lacks control over the manufacturing precision of parts, paint thickness precision and assembly precision in the early stages. This means that the process control in the wet installation stage is often insufficient to compensate for the impact of deviations in other stages, making it difficult to eliminate leakage problems.

[0056] The lack of in-process leak detection during the assembly of integrated fuel tanks makes it difficult to detect and address leaks in advance. Current integrated fuel tank assembly processes only require gas / oil tightness testing after assembly, with repairs only carried out if leaks are found. However, in actual production, it has been found that some areas, due to poor openness, are difficult to repair after leaks are discovered, or repairs are time-consuming, affecting subsequent work. Therefore, it is necessary to conduct in-process leak detection on critical components to detect and resolve problems early.

[0057] The overall fuel tank assembly process lacks necessary iterative optimization. Currently, when a leak occurs in the overall fuel tank, the only solution is to fill the leaking area and retest to ensure it is leak-free. However, there is no in-depth analysis of the defects in the overall assembly scheme, and the entire process of overall fuel tank assembly has not been optimized from the source.

[0058] Based on the above-mentioned technical problems, the following technical solutions are proposed.

[0059] Example 1

[0060] Reference Figures 1-6 This embodiment provides a method for sealing and assembling an integral aircraft fuel tank, including the following steps:

[0061] S10. Based on the digital model of the surrounding surface of the target fuel tank and the digital model of the fuel tank area structure, obtain the fuel tank area component model of the target fuel tank.

[0062] Optionally, first collect digital models of the tank area's surrounding surface and the tank area's structure. These models should contain precise geometric shapes, dimensions, and positional relationships of each component within the tank area. The models can be sourced from manufacturer-provided design drawings or as a 3D model generated by scanning the actual tank using digital measuring equipment. The collected models are then preprocessed to check their completeness, accuracy, and for any missing or incorrect data. For example, checks should be performed to ensure surfaces are closed, and to identify any overlaps or gaps.

[0063] like Figure 2 As shown, the main components of the fuel tank structure include fuel tank cover 1, rubber gasket 2, first beam 3, first frame 4, fuel tank bottom plate 5, second beam 6, and second frame 7.

[0064] Using professional 3D modeling software (such as CATIA and SolidWorks), the digital model of the fuel tank area's surrounding surface and the structural digital model of the fuel tank area are integrated. During the integration process, it is ensured that the coordinate systems of each digital model are consistent to avoid model misalignment caused by coordinate system differences. Based on the integrated digital model, the modeling function of the software is used to generate a model of the fuel tank area components of the target fuel tank. This model should accurately reflect the actual shape, size, and assembly relationships of each component in the fuel tank area, providing accurate geometric basis for subsequent sealing assembly work. The components in the fuel tank area are then numbered.

[0065] S20. Based on the fuel tank area part model, extract the boundary lines of the fuel tank area parts located at the boundary to form a boundary line dataset, and extract the boundary surfaces of the fuel tank area parts near the fuel tank surface to form a boundary surface dataset.

[0066] Optionally, the parts in the fuel tank area identified in step S10 are processed one by one according to their numbers; the boundary lines of the parts in the fuel tank area are extracted to establish a boundary line dataset, and the boundary surfaces of the parts in the fuel tank area that are close to the outer surface of the fuel tank are extracted to form a boundary surface dataset.

[0067] During boundary line extraction, based on the generated fuel tank area part model, the software's boundary extraction tool is used to extract the boundary lines of the parts located at the boundaries. During extraction, it is necessary to carefully identify the boundary features of the parts to ensure that the extracted boundary lines are complete and accurate, without omitting any important boundary information. The extracted boundary lines are then classified and organized according to certain rules, such as by part name, location, or boundary type. The classified boundary lines are then compiled into a boundary line dataset, and each boundary line in the dataset is given a unique identifier for subsequent querying and management.

[0068] During boundary surface extraction, the software's functionality is also used to extract the boundary surfaces of the parts in the fuel tank area that are close to the fuel tank surface. When extracting the boundary surfaces, it is necessary to consider the actual shape and characteristics of the fuel tank surface to ensure that the extracted boundary surfaces accurately reflect the contact between the parts and the fuel tank surface.

[0069] For example, Figure 4 As shown, for the first beam 3, the boundary line and the boundary surface of the first beam 3 are extracted; for the first frame 4, the boundary line and the boundary surface of the first frame 4 are extracted; and for the fuel tank bottom plate 5, the boundary surface of the fuel tank bottom plate 5 is extracted.

[0070] S30. Based on the fuel tank area component model, obtain the component set that can form a local hole. Project the boundary line dataset of each component in the component set onto the boundary surface dataset of the other components to obtain the projection line dataset.

[0071] Optionally, a more in-depth analysis of the fuel tank area component model can be conducted, using the software's assembly analysis function to identify sets of components that can form localized holes. When determining these sets, factors such as the assembly relationships between components, the formation mechanism of the holes, and sealing requirements need to be considered. For example, some components may form tiny gaps or holes during assembly; if these holes are not properly sealed, they may lead to fuel tank leakage. Detailed records should be kept of the identified sets of components, including their names, numbers, quantities, and assembly order. Simultaneously, each set of components should be assigned a unique identifier for differentiation and management in subsequent operations.

[0072] During the projection process: For each part in the part set, its boundary line dataset is projected onto the boundary surface datasets of the remaining parts. During projection, a suitable projection direction and method need to be selected to ensure the accuracy and reliability of the projection results. For example, the optimal projection direction can be determined based on the relative positions and assembly relationships between parts, ensuring that the projection lines accurately reflect the relative positional relationships between part boundaries and boundary surfaces. The projection lines generated during the projection process are then organized and optimized, removing duplicate or invalid lines to ensure the simplicity and effectiveness of the projection line dataset. The organized projection lines are then combined into a projection line dataset, and relevant attribute information, such as the projection source part and the projection target boundary surface, is added to each projection line in the dataset.

[0073] For example, Figure 4 As shown, three parts are selected: the first beam 3, the first frame 4, and the fuel tank bottom plate 5. The first projection line 17 is formed by projecting the boundary line of the first frame 4 onto the boundary surface of the fuel tank bottom plate 5, and the second projection line 18 is formed by projecting the boundary line of the first frame 4 onto the boundary surface of the first beam 3.

[0074] S40. The projection line dataset and the boundary line dataset are spliced ​​together to form the hole boundary line dataset. The hole boundary lines enclose the boundary hole surface. The area of ​​the boundary hole surface is compared with the preset interval to obtain the leakage risk level. Based on the leakage risk level, the sealing strategy is adjusted.

[0075] Optional, such as Figure 2 As shown, the overall fuel tank frame mainly consists of the first beam 3, the second beam 6, the first frame 4, the second frame 7, and the fuel tank base plate 5, all made of aluminum alloy. The interfaces between the parts are sealed with HM112 sealant, with a theoretical thickness of 0.1mm. The fuel tank cap 1 is made of carbon fiber epoxy resin composite material, and is sealed with a gasket 2 made of HM112 with a thickness of 1.2mm. This embodiment only addresses the control of the sealant at the frame interfaces. Figure 3 As shown, Figure 3The two figures below are enlarged structural diagrams of the figure above. The locations of the holes are illustrated as follows: the first boundary hole 8 is a depression type, and there are also second boundary holes 9, third boundary holes 10, and fourth boundary holes 11.

[0076] Optional, such as Figure 4 As shown, Figure 4 for Figure 3 This is an enlarged view of the diagram in the lower left corner. The boundary line of the first frame 4, the first projection line 17, and the second projection line 18 enclose a region, which is the boundary hole surface. The boundary hole surface is the opening surface of the boundary hole.

[0077] Optionally, the projection line dataset and the boundary line dataset can be stitched together. During the stitching process, it is necessary to ensure that the data format and coordinate system are consistent between the different datasets to avoid stitching errors. Software data stitching tools can be used to connect the projection lines and boundary lines according to certain rules and algorithms to form a complete hole boundary line dataset. The stitched hole boundary line dataset should be verified and checked to see if the hole boundary lines are closed, and whether there are gaps or overlaps. If problems are found, the dataset should be adjusted and corrected promptly. The boundary hole surface is formed by enclosing the hole boundary lines. The area of ​​the boundary hole surface is accurately calculated using the software's area calculation function. The calculated boundary hole surface area is compared with a preset range. The preset range is determined comprehensively based on factors such as aircraft fuel tank design requirements, sealing material performance, and actual usage experience, and is used as a reference range to assess the degree of hole leakage risk.

[0078] In this embodiment, during the structural manufacturability review stage, a fuel tank boundary hole reconstruction algorithm is developed through secondary development of 3D modeling software. This algorithm uses digital means to identify the characteristics of fuel tank structural boundary holes, calculate their area, assess their impact on fuel tank leakage, and provide targeted solutions. This allows for the early identification and mitigation of leakage risks before manufacturing.

[0079] Optionally, the basic meanings of some terms involved in the above technical solutions are explained as follows:

[0080] Fuel tank area enclosure surface digital model: refers to a three-dimensional digital model used to describe the outer enclosure surface of the aircraft's fuel tank area. This model is typically used to define the location and shape of the fuel tank within the aircraft structure.

[0081] Fuel tank area structural digital model: refers to a detailed three-dimensional digital model describing the internal structure of the aircraft's fuel tank area. It includes all the parts and components inside the fuel tank and their interrelationships.

[0082] Fuel tank area component model: Based on the fuel tank area bounding surface digital model and the fuel tank area structural digital model, the three-dimensional model representing each specific component in the fuel tank area is obtained through operations such as intersection calculation.

[0083] Boundary lines: In a 3D model, boundary lines refer to the edge contour lines of a part or component, used to define its shape and boundaries.

[0084] Boundary surface: In a 3D model, the boundary surface refers to the surface of a part or component, which defines the shape of the part or component and its contact surface with other parts or components.

[0085] Projection line dataset: A collection of data obtained by projecting the boundary line dataset of one part onto the boundary surface datasets of other parts. These projection lines are used to analyze the relative positions and possible contact surfaces between parts.

[0086] Hole Boundary Line Dataset: Composed of the projection line dataset and the boundary line dataset, this set of line data describes the boundaries of holes. These lines enclose and form the boundary hole surface.

[0087] Boundary hole surface: A closed curved surface formed by the boundary line of the hole, representing the holes or gaps that may exist in the fuel tank area.

[0088] Assembly dimensional chain: A chain-like structure formed by the interrelationships and transmission paths between the dimensions of various parts during the assembly process. It is used to analyze dimensional deviations and cumulative effects during assembly.

[0089] Tolerance allocation: Based on design requirements and manufacturing capabilities, the tolerance of the overall assembly is allocated to various stages such as parts processing, heat treatment, and structural assembly to ensure the accuracy and quality of the final assembly.

[0090] Full-process manufacturing capability: refers to the various capabilities that a part possesses throughout the entire manufacturing process from raw materials to finished products, including machining accuracy of machined parts, machining accuracy of sheet metal parts, molding accuracy of composite materials, paint layer thickness accuracy, and assembly positioning accuracy.

[0091] Normal pressure at the sealing interface: The pressure perpendicular to the sealing surface generated at the sealing interface due to bolt preload or other external forces. It is one of the important factors in ensuring the sealing effect.

[0092] Bolt group interaction: When multiple bolts are connected simultaneously, the interaction and influence between the individual bolts. This interaction affects the overall assembly sequence and the bolt installation order.

[0093] Historical leakage data refers to records and data of past aircraft fuel tank leaks, including information such as the location, cause, and frequency of the leaks. This data is used to analyze and predict future leakage risks.

[0094] In-process leak detection and final leak detection: These are detection plans developed during and after assembly to check for leaks in the fuel tank. In-process leak detection typically involves multiple checks during assembly, while final leak detection involves a comprehensive inspection after assembly is complete.

[0095] Example 2

[0096] Reference Figures 1-6 The first embodiment of this application provides a method for sealing and assembling an integral aircraft fuel tank, including the following steps:

[0097] S10. Based on the digital model of the surrounding surface of the target fuel tank and the digital model of the fuel tank area structure, obtain the fuel tank area component model of the target fuel tank.

[0098] Optionally, the step of obtaining the fuel tank area part model of the target fuel tank based on the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure includes:

[0099] The fuel tank area part model is obtained by intersecting the digital model of the fuel tank area's surrounding surface with the digital model of the fuel tank area's structure using 3D modeling software, and then marked.

[0100] Specifically, before performing the intersection operation, ensure that the coordinate systems of the digital model of the tank area's surrounding surface and the digital model of the tank area's structure are consistent. If the two digital models have different coordinate systems, the software's coordinate system transformation function needs to be used to transform the coordinate system of one digital model to the same coordinate system as the other. In the 3D modeling software, select an appropriate intersection operation tool. Different software may have different names and operation methods for the intersection operation function, such as the "Boolean Operation - Intersection" function in CATIA.

[0101] When performing the intersection operation, the digital model of the tank area's surrounding surface is used as the object to be intersected, and the digital model of the tank area's structure is used as the object to be intersected. During the operation, the software calculates the intersection line, intersection surface, and other features based on the geometric shapes and topological relationships of the two digital models. Closely monitor the progress and results of the intersection operation. If any errors or anomalies occur, promptly check the geometric shapes and topological relationships of the digital models, as well as the accuracy of the coordinate system and positioning.

[0102] S20. Based on the fuel tank area part model, extract the boundary lines of the fuel tank area parts located at the boundary to form a boundary line dataset, and extract the boundary surfaces of the fuel tank area parts near the fuel tank surface to form a boundary surface dataset.

[0103] S30. Based on the fuel tank area component model, obtain the component set that can form a local hole. Project the boundary line dataset of each component in the component set onto the boundary surface dataset of the other components to obtain the projection line dataset.

[0104] S40. The projection line dataset and the boundary line dataset are spliced ​​together to form the hole boundary line dataset. The hole boundary lines enclose the boundary hole surface. The area of ​​the boundary hole surface is compared with the preset interval to obtain the leakage risk level. Based on the leakage risk level, the sealing strategy is adjusted.

[0105] Optionally, the step of concatenating the projection line dataset and the boundary line dataset to form a hole boundary line dataset, whereby the hole boundary lines enclose and form the boundary hole surface, includes:

[0106] S401. Group the hole boundary lines in the hole boundary line dataset into groups. Each group of hole boundary lines constitutes a candidate hole surface. Compare the areas of all candidate hole surfaces in the target area and select the candidate hole surface with the largest area as the boundary hole surface of the target area.

[0107] Specifically, the grouping criteria are determined by considering the assembly relationships and structural characteristics of the parts in the fuel tank area. For example, for the boundary lines of holes formed by adjacent parts, if they are close in spatial position and their orientation conforms to the logic of hole formation, they can be considered as a group of candidate boundary lines.

[0108] Examine the topological relationships between the boundary lines of the holes, such as whether they are connected, intersect, or share endpoints. Use topology analysis tools in 3D modeling software to quickly identify the connections between boundary lines. If multiple boundary lines are connected by endpoints and form a closed or semi-closed region, they can be grouped together. For example, at the connection point of a fuel tank, several boundary lines may be distributed around a potential hole area; topology analysis can group them together.

[0109] Optionally, the step of comparing the area of ​​the boundary hole with a preset range to obtain the leakage risk level, and adjusting the sealing strategy based on the leakage risk level, includes:

[0110] S410. When the area of ​​the boundary hole surface is less than the preset range, it indicates that there is no risk of leakage, and the inside and outside of the joint are sealed.

[0111] S420. When the area of ​​the boundary hole surface is within the preset range, it indicates a slight risk of leakage, and a local glue-stacking method is used for sealing.

[0112] S430. When the area of ​​the boundary hole surface is greater than the preset range, it indicates a severe leakage risk. After sealing, a plugging corner piece is installed at the boundary hole surface.

[0113] Specifically, the setting of the preset range needs to refer to the technical requirements for air / oil tightness and the test results, and is related to parameters such as the type of sealant, the test pressure, and the pressure holding time.

[0114] For example, the preset range can be 15-50. The degree of leakage risk is classified according to the size and area of ​​the boundary voids:

[0115] when In this case, S represents the area of ​​the boundary hole surface, indicating that there is no risk of leakage and no additional treatment is required. The seal inside and outside the seam can be performed according to the normal procedure.

[0116] when At this time, it indicates a slight risk of leakage, and localized glue application is used for sealing.

[0117] when When this indicates a high risk of leakage, additional plugging plates are added to seal the holes before sealing.

[0118] Assume that the area of ​​the fuel tank hole at this point is 10. The sealing performance can be ensured by normal sealing inside and outside the seam and pre-filling with depression.

[0119] The above-mentioned technical solutions mainly involve the identification and handling of fuel tank leakage risk characteristics.

[0120] Optionally, the steps for determining the manufacturing and assembly accuracy of parts with specific adhesive layer thickness requirements are as follows:

[0121] S501. Assembly Dimension Chain Establishment: Based on the fuel tank area component model, obtain the connection relationships between the components in the fuel tank area, establish the assembly dimension chain, and determine the composition of deviations in each assembly stage. Based on the overall fuel tank structure and the connection relationships between components, establish the assembly dimension chain, clarifying the composition of deviations in each stage and the rules governing deviation transmission.

[0122] Specifically, the assembly dimension chain is established, such as... Figure 5 As shown, Figure 5 for Figure 3 The structural diagram is located in the lower left corner. The following explanation uses the interface of the oil tank formed by the web of the first beam 3 and the flange of the first frame 4 as an example:

[0123]

[0124] In the formula: n represents the actual thickness of the sealant. Indicates the theoretical thickness of the sealant. This indicates the positioning deviation of the first beam. This indicates the machining deviation of the web surface of the first beam. This indicates the positioning deviation of the first frame. This indicates the machining deviation of the first frame edge strip surface. This indicates the deviation in paint layer thickness.

[0125] S502. Determine the theoretical thickness of the sealant: Based on the design model requirements, determine the required thickness of the sealant layer at each boundary of the overall fuel tank.

[0126] Optionally, the theoretical thickness of the sealant can be determined based on the design model requirements. .

[0127] S503. Determine the manufacturing capabilities of each stage: Obtain the full-process manufacturing capabilities of the fuel tank area parts as the basis for tolerance allocation; the full-process manufacturing capabilities of the fuel tank area parts include the machining accuracy of machined parts, the machining accuracy of sheet metal parts, the molding accuracy of composite materials, the paint layer thickness accuracy, and the assembly positioning accuracy.

[0128] Optionally, both the first beam 3 and the first frame 4 are CNC machined parts with the following machining accuracy levels: machining deviation of ribs and flanges -0.2mm~0.1mm; machining deviation of web plate -0.25mm~0.1mm; positioning accuracy of metal structure ±0.1mm; paint layer thickness 0.03±0.005mm.

[0129] S504, Tolerance Allocation and Assembly Compensation: Tolerance Allocation and Assembly Compensation: Based on the requirements for the thickness of the sealant layer and the full-process manufacturing capabilities of the parts in the fuel tank area, the tolerance is allocated to the parts processing, heat treatment and structural assembly.

[0130] First, based on the sealant thickness requirements and the manufacturing capabilities of each stage, tolerances are allocated to parts processing, thermal surface painting, and structural assembly. Some areas have higher tolerance requirements, but the manufacturing or assembly precision cannot meet these requirements; these areas require additional assembly compensation.

[0131] Optionally, the design requires a sealant layer thickness of 0.1mm, meaning that a 0.1mm gap must be maintained after each part is positioned. Considering the assembly dimensional chain model and manufacturing capabilities, the calculated gap range after assembly is -0.70mm to +0.37mm, with positive values ​​indicating interference. The calculation results show that current manufacturing capabilities cannot guarantee the sealant layer thickness solely from a tolerance allocation perspective; therefore, assembly compensation (grinding or adding shims) is necessary to address this issue. In cases of gaps, the shim thickness is 0-0.6mm; in cases of interference, the grinding amount is 0-0.47mm.

[0132] S505, Process Measurement: Perform parts machining, heat treatment and structural assembly on the parts in the oil tank area to obtain actual deviation data;

[0133] During the selected processes, such as parts processing and surface painting, the assembly contact surfaces are measured and virtually assembled to assess assembly gaps and pre-treatment is performed. Actual measurements revealed that the web surface deviation of beam 1 was -0.1mm, the paint layer thickness was 0.025mm, and the measured deviation of the beam 1 locator was +0.05mm; the edge strip surface deviation of frame 1 was +0.05mm, the paint layer thickness was 0.02mm, and the measured deviation of the locator was -0.05mm.

[0134] S506, Virtual Assembly: Based on actual deviation data, assess the feasibility of assembling the entire fuel tank and determine whether pre-treatment or tolerance allocation optimization is required. Areas with significant interference need to be ground in advance, and areas with large gaps need to be shimmed in advance.

[0135] Optionally, virtual assembly is performed based on the measurement results of step S505. It is found that after assembly, a gap of 0.005mm will theoretically be generated between the contact surfaces, which is less than the 0.1mm required for assembly. Therefore, it is determined that the metal structure of frame 1 edge strip is ground to 0.05mm and the web of beam 1 is ground to 0.045mm to ensure that the sealant thickness is 0.1mm after assembly.

[0136] In the above technical solution, the thickness of the adhesive layer is used as the control target, and the deviation transmission law is obtained through assembly dimension chain modeling. The system analyzes the manufacturing accuracy of each link such as parts manufacturing, heat treatment and structural assembly, and ensures that the gap formed after assembly is the same as the thickness of the adhesive layer through tolerance allocation and assembly compensation, so that the oil tank boundary does not need to be ground or shimmed.

[0137] Optional steps for inspection and control during the assembly process include:

[0138] S601. Based on the theoretical analysis and simulation calculation of the sealing interface of the overall oil tank, the normal pressure of the sealing interface is obtained;

[0139] S602. Obtain the bolt preload based on the positive pressure at the sealing interface;

[0140] S603. Based on the interaction of the bolt groups, determine the overall assembly sequence of the fuel tank and the bolt installation sequence to obtain the installation sequence result;

[0141] S604. Based on the installation sequence, monitor and control the bolt installation process during installation;

[0142] S605. Measure the thickness of the components and interlayer of the overall sealing interface of the fuel tank, and monitor the change in the thickness of the sealing adhesive layer.

[0143] S606. Adjust the bolt preload according to the changes in the thickness of the sealant layer.

[0144] Specifically, the purpose of inspection and control during the assembly process is to homogenize assembly stress and interface stress. The sealing mechanism of the fuel tank interface mainly involves the elastic deformation of the sealant layer under the action of bolt preload, resulting in compression at the interface and forming positive pressure. When the interface positive pressure is greater than the internal pressure of the fuel tank, the fuel tank remains sealed; otherwise, the fuel tank leaks. Therefore, the design of the fastener installation sequence needs to combine theoretical analysis and simulation calculations to determine the positive pressure at the sealing interface, thereby calculating the bolt preload, and then designing the fastener installation sequence, component connection sequence, and multiple tightening process scheme through the interaction of bolt groups.

[0145] Based on the fastener installation process design, the bolt tightening process is monitored and controlled during assembly, including preload, torque, and stress and strain in key areas. If the bolts deviate from the design values, tightening tools are used to control them in a timely manner.

[0146] Measure the thickness of the sealing interface components and the interlayer thickness, monitor changes in the adhesive layer thickness, and take preventative measures (identify the adhesive layer thickness and adjust the bolt preload). The sealant is still in the curing process during tightening; therefore, the adhesive layer thickness needs to be monitored during and after tightening. Adjust the bolt preload based on changes in the adhesive layer thickness during curing to ensure the sealant layer thickness meets design requirements.

[0147] For example: The overall oil tank connection uses 5mm diameter bolts with a rated torque of 4Nm and a design preload of 5kN. The compressive stress generated at the sealing interface is approximately 0.063MPa. According to the air / oil tightness test requirements, the internal pressure of the oil tank during the air / oil tightness test is 0.04MPa, which theoretically meets the sealing requirements. Based on the bolt connection experiment, the cap bolts are tightened using a cross-tightening method with a torque of 4Nm; after the sealant has fully cured, they are tightened again with the same process parameters as the first time. For fasteners on a straight edge, they are tightened sequentially from the middle to both sides with a torque of 4Nm; after the sealant has fully cured, they are tightened again with the same process parameters as the first time.

[0148] Use an electric tightening shaft to install bolts, use the sensor built into the electric tightening shaft to monitor the tightening torque, use a pressure sensor or ultrasonic sensor to monitor the preload value, and use a 3D-DIC device to measure the strain field around the bolt.

[0149] The thickness of the sealing structure interlayer is measured using a 3D-DIC device. The thickness of the sealing layer is calculated by inversely from the thickness of the interlayer, without considering the change in the thickness direction of the metal material. If the thickness is too small, the preload is reduced appropriately, and if the thickness is too large, the preload is increased appropriately.

[0150] In the above technical solution, the overall oil tank sealing assembly process is monitored and controlled in real time. By designing the bolt tightening process, the preload in key areas is determined. Through the monitoring and control of the assembly process, the preload and the thickness of the sealing adhesive layer are dynamically adjusted to ensure the sealing effect of the oil tank boundary, thus achieving pre-control and process control.

[0151] Optional steps in developing the overall fuel tank process leak detection and final leak detection process plan include:

[0152] S701. Based on historical leakage data of multiple integrated fuel tanks, identify the first leakage area where the leakage frequency exceeds a preset threshold. Specifically, if multiple integrated fuel tanks are of the same model, historical leakage data of the same type of integrated fuel tank is obtained to predict the most likely location of leakage. The preset threshold can be manually set according to actual usage requirements.

[0153] Through structural analysis and historical fault analysis, the following methods were employed. First, by analyzing the overall fuel tank structure and calculating boundary voids, areas with high risk of leakage at the tank boundaries were identified and designated as the primary targets for process leak detection. Furthermore, by statistically analyzing multiple leakage faults, areas with high leakage frequency were also identified and designated as the primary targets for process leak detection. This process effectively determined the risk areas.

[0154] S701. Mark the area where the boundary hole surface is larger than the preset interval as the second leakage area;

[0155] S701. Mark the first and second leakage areas as danger zones. When the entire oil tank leaks, prioritize checking the danger zones.

[0156] When the entire fuel tank leaks, the first steps to check the hazardous areas include:

[0157] S7011. Determine the process leak detection plan and the final leak detection plan based on the assembly sequence and production cycle of the overall fuel tank.

[0158] First, determine the leak detection methods to be used at each stage, including differential pressure leak detection, helium mass spectrometry positive / negative pressure leak detection, etc. Second, determine the timing of leak detection, specifying which parts should be tested during wet installation and at what assembly state the entire tank should be tested for final leak detection.

[0159] S7012. If local leakage occurs during the implementation of the process leak detection plan or the final leak detection plan, trace the cause of the local leakage, prioritize the investigation of the dangerous area, and carry out local repairs for the local leakage.

[0160] If local leakage is found during the process of leak detection, first determine the leakage area and identify whether it is a fastener leakage, assembly interface leakage, sunken area leakage, or sealing gasket 2 detachment, etc. Then, perform local repairs for the specific leakage situation, and perform leak detection again after repair until there is no leakage.

[0161] After the overall fuel tank structure is assembled, an air / oil tightness test is conducted according to the design requirements. If all tests pass, the sealing performance meets the standards. If local leakage is found during the leak detection process, the leakage area is first determined, and it is determined whether it is a fastener leak, an assembly interface leak, a sunken area leak, or a detached sealing gasket. Then, local repairs are carried out for the specific leakage situation. After repair, the leak detection operation is carried out again until there is no leakage.

[0162] Specifically, examples are given below:

[0163] Risk area identification: Based on the analysis of the fuel tank structure and historical failure analysis, the risk area for fuel tank leakage is the sealing boundary formed by the frame beam and the bottom plate 5 of the fuel tank.

[0164] Determine the leak detection plan: Based on the risk areas, set process leak detection requirements. Use helium mass spectrometry positive pressure leak detection method at the sealing boundary formed by the frame beam and the bottom plate 5 of the fuel tank to detect leaks at the sealing boundary and fasteners. After the overall fuel tank assembly is completed, perform gas / oil tightness testing.

[0165] Leakage detection results analysis and local repair: During the process leak detection, a bolt was found to be leaking. After removing the bolt and reinstalling it in a wet manner, a local leak detection was performed again, and the leakage problem was eliminated.

[0166] After the fuel tank structure was assembled, air / oil tightness testing and local repairs were performed: The air tightness test required an air pressure of 0.04 MPa, a pressure holding time of 3 hours, and a pressure drop not exceeding 200 Pa; the oil tightness test required fuel filling to 70% of the volume, an air pressure of 0.04 MPa, a pressure holding time of 4 hours, and no leakage. During the oil tightness test, leakage was found in the contact area between the first frame 4 flange and the first beam 3 web. After resealing the external joint of this area, the leakage problem was eliminated.

[0167] Optional steps for the design and iterative optimization of the overall fuel tank manufacturing and assembly process include:

[0168] The assembly process, process leak detection, and final leak detection results of the overall fuel tank assembly are analyzed to determine whether there are defects in the tolerance allocation. If there are defects in the tolerance allocation, the processing tolerance requirements, heat treatment tolerance requirements, and structural assembly tolerance requirements are optimized.

[0169] Tolerance index optimization and decomposition: The overall fuel tank assembly process and leak detection results are analyzed to identify the shortcomings in tolerance allocation. Based on this, the tolerance requirements for parts processing, hot surface painting, and assembly are optimized to achieve the optimization and decomposition of tolerance index.

[0170] Assembly process optimization includes: positioning method, assembly sequence, small components, and attitude adjustment method. First, optimize the part positioning method to ensure a reasonable dimensional chain transfer length and stable, controllable, and sufficiently small assembly errors. Second, optimize the part assembly sequence to improve assembly efficiency and reduce worker workload while ensuring sealing assembly quality. Third, consider assembling some parts into small components first to improve local sealing assembly quality and shorten assembly time. Finally, for fuel tanks in the fuselage or wing-fuselage mating area, it may be necessary to optimize the attitude adjustment method, gap distribution, and structural assembly stress to ensure the sealing assembly quality of the fuel tank area.

[0171] Examples are given below:

[0172] Tolerance index optimization and decomposition: During the assembly process, the contact surfaces of the first frame 4 and the first beam 3 of the metal parts need to be ground. The labor intensity of the workers is high, the flatness of the ground surface is poor, and there is a risk of leakage. Therefore, the contact positions of the first frame 4 and the first beam 3 will be processed with negative tolerance to ensure that no interference occurs at this point.

[0173] In this embodiment, the previous method of controlling sealing quality solely through the adhesive application process is extended to the entire sealing assembly process. This includes identifying and addressing tank pores and leakage risks, designing component manufacturing and assembly precision to meet adhesive thickness requirements, monitoring and controlling the assembly process, developing process leak detection and final leak detection solutions, and designing and iteratively optimizing the overall tank assembly process. This achieves full-process control over the entire tank manufacturing and assembly. By monitoring and controlling the bolt connection process and sealant thickness throughout the entire process, the accuracy of key physical quantities is ensured, thereby guaranteeing the tank's sealing performance. Leakage faults can be detected and addressed early, saving subsequent leak detection and troubleshooting time. By analyzing the sealing assembly process and leak detection results, reverse process analysis is performed to summarize the areas that need optimization in component manufacturing, heat treatment, and structural assembly. Through iterative optimization, the overall tank sealing assembly quality is continuously improved.

[0174] The above are merely preferred embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made based on the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A method for sealing and assembling an integral aircraft fuel tank, characterized in that, include: Based on the digital model of the tank area surrounding the target tank and the digital model of the tank area structure, obtain the tank area component model of the target tank. Based on the fuel tank area component model, the boundary lines of the fuel tank area components located at the boundary are extracted to form a boundary line dataset, and the boundary surfaces of the fuel tank area components near the fuel tank surface are extracted to form a boundary surface dataset. Based on the fuel tank area component model, obtain the component set that can form local holes, and project the boundary line dataset of each component in the component set onto the boundary surface dataset of the other components to obtain the projection line dataset. The projection line dataset and the boundary line dataset are spliced ​​together to form the hole boundary line dataset. The hole boundary lines enclose the boundary hole surface. The area of ​​the boundary hole surface is compared with the preset interval to obtain the leakage risk level. Based on the leakage risk level, the sealing strategy is adjusted. The step of comparing the area of ​​the boundary hole with a preset range to obtain the leakage risk level, and adjusting the sealing strategy based on the leakage risk level, includes: When the area of ​​the boundary hole is less than the preset range, it indicates that there is no risk of leakage, and the inside and outside of the joint are sealed. When the area of ​​the boundary hole surface is within the preset range, it indicates a slight risk of leakage, and local glue stacking is used for sealing. When the area of ​​the boundary hole surface is larger than the preset range, it indicates a severe leakage risk. After sealing, a plugging corner piece is installed at the boundary hole surface.

2. The aircraft integral fuel tank sealing assembly method as described in claim 1, characterized in that, The step of obtaining the fuel tank area component model of the target fuel tank based on the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure includes: The fuel tank area part model is obtained by intersecting the digital model of the fuel tank area's surrounding surface with the digital model of the fuel tank area's structure using 3D modeling software, and then marked.

3. The aircraft integral fuel tank sealing assembly method as described in claim 1, characterized in that, The step of stitching the projection line dataset and the boundary line dataset together to form the hole boundary line dataset, and the hole boundary lines enclosing the boundary hole surface, includes: The hole boundary lines in the hole boundary line dataset are grouped into groups, and each group of hole boundary lines constitutes a candidate hole surface. The areas of all candidate hole surfaces in the target area are compared, and the candidate hole surface with the largest area is selected as the boundary hole surface of the target area.

4. The aircraft integral fuel tank sealing assembly method as described in claim 1, characterized in that, Also includes: Based on the fuel tank area component model, obtain the connection relationship between the fuel tank area components, establish the assembly dimension chain, and determine the composition of the deviation of each assembly link. Based on the design model requirements, determine the required thickness of the sealing adhesive layer at each boundary of the overall fuel tank; Acquire the full-process manufacturing capabilities of parts in the fuel tank area as the basis for tolerance allocation; Based on the requirements for sealant layer thickness and the full-process manufacturing capabilities of parts in the fuel tank area, tolerances are allocated to parts processing, heat treatment, and structural assembly. The parts in the fuel tank area are machined, heat-treated, and structurally assembled to obtain actual deviation data. Based on actual deviation data, assess the feasibility of the overall assembly of the fuel tank and determine whether pre-treatment or tolerance allocation optimization is required.

5. The aircraft integral fuel tank sealing assembly method as described in claim 4, characterized in that, The full-process manufacturing capabilities for fuel tank area parts include machining accuracy of machined parts, sheet metal parts, composite material molding accuracy, paint layer thickness accuracy, and assembly positioning accuracy.

6. The aircraft integral fuel tank sealing assembly method as described in claim 4, characterized in that, Also includes: Based on theoretical analysis and simulation calculation of the sealing interface of the overall oil tank, the normal pressure of the sealing interface is obtained; The bolt preload is obtained based on the positive pressure at the sealing interface; Based on the interaction of the bolt groups, the overall assembly sequence of the fuel tank and the bolt installation sequence are determined, and the installation sequence result is obtained; Based on the installation sequence, the bolt installation process is monitored and controlled during the installation process; Measure the thickness of the components and interlayer at the overall sealing interface of the fuel tank, and monitor the change in the thickness of the sealing adhesive layer; Adjust the bolt preload according to the changes in the thickness of the sealant layer.

7. The aircraft integral fuel tank sealing assembly method as described in claim 4, characterized in that, Based on historical leakage data from multiple integrated fuel tanks, the first leakage area with a leakage frequency exceeding a preset threshold is identified. The area where the boundary hole surface is larger than the preset range is marked as the second leakage area; The first and second leakage areas are marked as danger zones. When the overall oil tank leaks, the danger zones are investigated first.

8. The method for sealing and assembling an integral aircraft fuel tank as described in claim 7, characterized in that, When the overall fuel tank leaks, the step of prioritizing the inspection of the hazardous area includes: Based on the overall assembly sequence and production cycle of the fuel tank, determine the process leak detection plan and the final leak detection plan; If localized leakage occurs during the implementation of the leak detection plan or the final leak detection plan, trace the cause of the localized leakage, prioritize the investigation of the dangerous areas, and carry out localized repairs for the localized leakage.

9. The method for sealing and assembling an integral aircraft fuel tank as described in claim 1, characterized in that, The assembly process, process leak detection, and final leak detection results of the overall fuel tank assembly are analyzed to determine whether there are defects in the tolerance allocation. If there are defects in the tolerance allocation, the processing tolerance requirements, heat treatment tolerance requirements, and structural assembly tolerance requirements are optimized.

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