Airplane integral fuel tank sealing assembly method

Abstract

The invention discloses an aircraft integral fuel tank sealing assembly method, and relates to the technical field of fuel tank assembly. The invention provides an aircraft integral fuel tank sealing assembly method which comprises the steps that a fuel tank area part model of a target fuel tank is obtained according to a fuel tank area surrounding surface mathematical model and a fuel tank area structural mathematical model of the target fuel tank; boundary lines of the oil tank area parts at the boundary are extracted to form a boundary line data set, and boundary surfaces of the oil tank area parts close to the oil tank surface are extracted to form a boundary surface data set; projecting the boundary line data set of each part in the part set to the boundary surface data sets of other parts to obtain a projection line data set; the projection line data set and the boundary line data set are spliced to form a hole boundary line data set, a boundary hole surface is defined by hole boundary lines, the area of the boundary hole surface is compared with a preset interval, the leakage risk degree is obtained, and the sealing strategy is adjusted based on the leakage risk degree.

Description

Technical Field

[0001] The present application relates to the technical field of fuel tank assembly, and in particular to a sealing assembly method for an integral fuel tank of an aircraft. Background Art

[0002] An aircraft's integral fuel tank, comprised of components such as the fuselage frame, air intake, and cover, combines oil storage and structural load-bearing functions, making it widely used in aircraft structures. Existing fuel tank sealing and assembly processes primarily involve the following steps: process review and assembly process design - component manufacturing - structural pre-assembly and hole making - wet installation - and air / oil tightness testing. Failure to pass the air / oil tightness test requires leak identification and repair. However, existing techniques for filling certain structural holes in fuel tanks are difficult to detect during the process review phase, requiring the use of large amounts of sealant during sealing and assembly. This results in poor sealing and is prone to leaks.

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

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

[0005] To achieve the above objectives, the present application provides a method for sealing and assembling an integral fuel tank of an aircraft, comprising: Obtaining a parts model of the fuel tank area of ​​the target fuel tank according to the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure of the target fuel tank; Extracting boundary lines of the fuel tank area parts at the boundaries according to the fuel tank area parts model to form a boundary line dataset, and extracting boundary surfaces of the fuel tank area parts close to the fuel tank surface to form a boundary surface dataset; According to the parts model of the fuel tank area, a set of parts that can form a local hole is obtained, and the boundary line dataset of each part in the part set is projected onto the boundary surface datasets of the remaining parts to obtain a projection line dataset; The projection line dataset and the boundary line dataset are spliced ​​together to form a 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.

[0006] Optionally, the step of obtaining a part model of the fuel tank area 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 of the target fuel tank includes: Based on the 3D modeling software, the oil tank area part model is obtained by performing intersection operation on the oil tank area enclosing surface digital model and the oil tank area structure digital model, and then marked.

[0007] Optionally, the step of combining the projection line dataset and the boundary line dataset to form a hole boundary line dataset, and enclosing the hole boundary lines to form a boundary hole surface, includes: The hole boundary lines in the hole boundary line dataset are grouped into groups. 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.

[0008] Optionally, the step of comparing the area of ​​the boundary hole with a preset interval to obtain a leakage risk level, and adjusting the sealing strategy based on the leakage risk level includes: When the area of ​​the boundary hole surface is smaller than the preset interval, it indicates that there is no leakage risk and the seam inside and outside is sealed; When the area of ​​the boundary hole surface is within the preset range, it indicates a slight leakage risk and is sealed by local glue stacking; When the area of ​​the boundary hole surface is larger than the preset range, it indicates a risk of severe leakage. A plugging corner piece is set at the boundary hole surface to block it and then seal it.

[0009] Optionally, based on the fuel tank area parts model, the connection relationship between the fuel tank area parts is obtained, the assembly dimension chain is established, and the deviation composition of each assembly link is determined; Determine the thickness requirements of the sealant layer at each boundary of the entire fuel tank according to the design digital model requirements; Obtain the full-process manufacturing capabilities of fuel tank area parts as the basis for tolerance allocation; Based on the sealant layer thickness requirements and the full-process manufacturing capabilities of the fuel tank area parts, tolerances are allocated to parts processing, heat treatment and structural assembly; Perform parts processing, heat treatment and structural assembly on the fuel tank area parts to obtain actual deviation data; Based on the actual deviation data, the feasibility of the overall tank assembly is evaluated to determine whether preliminary treatment or tolerance allocation optimization is needed.

[0010] Optionally, the full-process manufacturing capabilities of the fuel tank area parts include machining parts processing accuracy, sheet metal parts processing accuracy, composite material molding accuracy, paint layer thickness accuracy and assembly positioning accuracy.

[0011] Optionally, based on theoretical analysis and simulation calculation of the sealing interface of the entire oil tank, the positive pressure of the sealing interface is obtained; Obtain the bolt preload force based on the positive pressure of the sealing interface; According to the interaction of the bolt groups, the assembly sequence of the entire tank and the bolt installation sequence are determined to obtain the installation sequence result; Monitor and control the bolt installation process during the installation process based on the installation sequence results; Measure the thickness of the oil tank's overall sealing interface parts and interlayer thickness, and monitor changes in the sealant layer thickness; Adjust the bolt pre-tightening force according to the change in the thickness of the sealant layer.

[0012] Optionally, based on historical leakage data of a plurality of integral fuel tanks, a first leakage area having a leakage frequency greater than a preset threshold is obtained; Marking the area where the boundary hole surface is larger than the preset interval as the second leakage area; The first leakage area and the second leakage area are marked as dangerous areas. When the entire oil tank leaks, the dangerous areas are checked first.

[0013] Optionally, when the integral fuel tank leaks, the step of prioritizing checking the dangerous area includes: Determine the process leak detection plan and final leak detection plan based on the assembly sequence and production cycle of the entire fuel tank; 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, give priority to checking the dangerous area, and perform local repairs for the local leakage.

[0014] 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.

[0015] Beneficial effects that this application can achieve: The present invention provides a method for sealing an integral aircraft fuel tank, comprising: obtaining a tank area part model of a target tank based on a digital model of the tank area enclosing surface and a digital model of the tank area structure; extracting boundary lines of the tank area parts located at the boundary of the target tank based on the tank area part model to form a boundary line dataset; extracting boundary surfaces of the tank area parts close to the tank surface to form a boundary surface dataset; obtaining a set of parts that can form a local hole based on the tank area part model; projecting the boundary line dataset of each part in the part set onto the boundary surface datasets of the remaining parts to obtain a projection line dataset; concatenating the projection line dataset with the boundary line dataset to form a hole boundary line dataset, enclosing the hole boundary lines to form a boundary hole surface; comparing the area of ​​the boundary hole surface with a preset interval to determine the leakage risk level; and adjusting the sealing strategy based on the leakage risk level. By identifying and reconstructing tank holes, determining risk categories, and formulating treatment methods, the risk of fuel tank leakage can be identified and treated in advance during the process design phase, thereby improving the quality and efficiency of the tank sealing process design and saving subsequent leak detection and troubleshooting time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the overall sealing assembly process of an aircraft fuel tank according to an embodiment of the present application; Figure 2 This is a schematic diagram of the exploded structure of the integral fuel tank according to an embodiment of the present application; Figure 3 A schematic diagram of the holes of the integral fuel tank according to an embodiment of the present application; Figure 4 for Figure 3 Schematic diagram of the local enlarged structure projection line; Figure 5 for Figure 3 Schematic diagram of the locally enlarged structural tank boundary surface; Figure 6 This is an overall schematic diagram of the fuel tank assembly according to an embodiment of the present application.

[0017] The numbers in the figure are: 1-Fuel tank cover, 2-Rubber pad, 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.

[0018] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] 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 position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0021] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0022] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0023] The existing fuel tank seal assembly process primarily includes the following steps: process review and assembly process design - parts manufacturing - structural pre-assembly and hole making - wet installation - and air / oil tightness testing. Failure to pass the air / oil tightness test requires leak identification and repair. In actual production, this seal assembly process has the following problems: 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 assembly, which results in poor sealing effect and is prone to leakage. The overall fuel tank seal assembly lacks a full-process control solution, focusing only on the wet installation process. However, there is a lack of control over the initial parts manufacturing accuracy, paint layer thickness accuracy, and assembly accuracy. As a result, process control during the wet installation phase is often insufficient to compensate for the impact of deviations in other stages, making it difficult to eliminate leakage. The lack of in-process leak detection during the assembly of integral fuel tanks makes it difficult to detect and address leaks in advance. The current process for integral fuel tank assembly only requires an air / oil tightness test after assembly, with leaks repaired if found. However, in actual production, it has been found that some areas lack accessibility, making leaks difficult to repair or time-consuming, impacting subsequent work. Therefore, it is necessary to conduct in-process leak detection in key areas to detect and troubleshoot problems in advance.

[0024] The overall fuel tank assembly process lacked necessary iterative optimization. When a leak occurred, the system simply filled the leaking area and retested it to confirm it was leak-proof. However, no in-depth analysis of the overall assembly plan flaws was conducted, and the entire process was not optimized from the outset.

[0025] Based on the above technical problems, the following technical solutions are proposed.

[0026] Example 1 Reference Figures 1-6 This embodiment provides a method for sealing and assembling an integral fuel tank of an aircraft, comprising the following steps: S10. Obtain a fuel tank area component model of the target fuel tank based on the fuel tank area enclosing surface digital model and the fuel tank area structure digital model of the target fuel tank.

[0027] Optionally, first collect digital models of the target tank's tank area's enclosing surfaces and the tank area's structural design. These models should include the precise geometry, dimensions, and relative positions of each component within the tank area. The digital models can be sourced from manufacturer-provided design drawings or generated as 3D models by scanning the actual tank using digital measurement equipment. The collected digital models are pre-processed to check for completeness, accuracy, and any missing or inaccurate data. For example, check to see if the surfaces in the model are closed, overlapped, or have gaps.

[0028] like Figure 2 As shown, the main parts of the fuel tank structure include the fuel tank cover 1, the rubber pad 2, the first beam 3, the first frame 4, the fuel tank bottom plate 5, the second beam 6 and the second frame 7.

[0029] Using professional 3D modeling software (such as CATIA or SolidWorks), integrate the digital model of the tank area's enclosure with the digital model of the tank area's structure. During the integration process, ensure the coordinate systems of the various models are consistent to avoid model misalignment caused by coordinate system differences. Based on the integrated digital model, the software's modeling capabilities are used to generate a component model of the target tank's tank area. This model should accurately reflect the actual shape, dimensions, and assembly relationships of each component in the tank area, providing an accurate geometric basis for subsequent sealing and assembly work. The components in the tank area are then numbered.

[0030] S20. Based on the fuel tank area part model, extract the boundary lines of the fuel tank area parts at the boundary to form a boundary line dataset; extract the boundary surfaces of the fuel tank area parts close to the fuel tank surface to form a boundary surface dataset.

[0031] Optionally, the fuel tank area parts identified in step S10 are processed one by one according to their numbers; the boundary lines of the fuel tank area boundary parts are extracted to establish a boundary line data set, and then the boundary surfaces of the fuel tank boundary parts close to the outer surface of the fuel tank are extracted to form a boundary surface data set.

[0032] When extracting boundaries, the software's boundary extraction tools are used based on the generated fuel tank area part model to extract the boundary lines of the parts located at the tank area. During the extraction process, the boundary features of the parts must be carefully identified to ensure that the extracted boundary lines are complete and accurate, without missing any important boundary information. The extracted boundary lines are classified and organized according to specific rules, such as by part name, location, or boundary type. These classified boundary lines are then organized into a boundary line dataset, and a unique identifier is assigned to each boundary line in the dataset to facilitate subsequent querying and management.

[0033] When extracting the boundary surface, the software also uses its capabilities to extract the boundary surface where the fuel tank part approaches the tank surface. When extracting the boundary surface, the actual shape and characteristics of the tank surface must be considered to ensure that the extracted boundary surface accurately reflects the contact between the part and the tank surface.

[0034] 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; for the fuel tank bottom plate 5, the boundary surface of the fuel tank bottom plate 5 is extracted.

[0035] S30. According to the fuel tank area part model, a part set that can form a local hole is obtained, and a boundary line dataset of each part in the part set is projected onto the boundary surface datasets of the remaining parts to obtain a projection line dataset.

[0036] Optionally, conduct an in-depth analysis of the fuel tank area part model and, using the software's assembly analysis capabilities, identify the set of parts that can form the localized hole. When determining the set of parts, consider factors such as the assembly relationship between parts, the mechanism of hole formation, and sealing requirements. For example, certain parts may form tiny gaps or holes during assembly. If these holes are not properly sealed, they can cause fuel tank leakage. Detailed records are kept for the identified set of parts, including information such as part name, number, quantity, and assembly order. Each set of parts is assigned a unique identifier to facilitate differentiation and management in subsequent operations.

[0037] During the projection process: For each part in the parts collection, its boundary line dataset is projected onto the boundary surface datasets of the remaining parts. During the projection process, it is necessary to select an appropriate projection direction and projection method to ensure the accuracy and reliability of the projection results. For example, the optimal projection direction can be determined based on the relative position and assembly relationship between the parts so that the projection line can truly reflect the relative position relationship between the part boundary and the boundary surface. The projection lines generated during the projection process are sorted and optimized, and duplicate or invalid projection lines are removed to ensure the simplicity and effectiveness of the projection line dataset. The sorted projection lines are combined into a projection line dataset, and relevant attribute information is added to each projection line in the dataset, such as the projection source part, the projection target boundary surface, etc.

[0038] For example, Figure 4 As shown, three parts, the first beam 3, the first frame 4 and the fuel tank bottom plate 5, are selected. 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.

[0039] S40: splicing the projection line dataset and the boundary line dataset to form a hole boundary line dataset. The hole boundary lines enclose a boundary hole surface. Comparing the area of ​​the boundary hole surface with a preset interval to obtain a leakage risk degree, and adjusting the sealing strategy based on the leakage risk degree.

[0040] Optional, such as Figure 2 As shown, the overall fuel tank frame is mainly composed of the first beam 3, the second beam 6, the first frame 4, the second frame 7 and the fuel tank bottom plate 5, all of which are made of aluminum alloy. The interface between each part is sealed with HM112 sealant, with a theoretical thickness of 0.1mm. The fuel tank cover 1 is made of carbon fiber epoxy resin composite material and is sealed with a rubber gasket 2, which is made of HM112 and has a thickness of 1.2mm. This embodiment only controls the sealant at the frame interface. Figure 3 As shown, Figure 3The two figures in the lower row are partial enlarged structural diagrams of the figure in the upper row. The positions of the holes are schematically explained: the first boundary hole 8 is a sunken type, and the second boundary hole 9, the third boundary hole 10 and the fourth boundary hole 11 are also formed.

[0041] Optional, such as Figure 4 As shown, Figure 4 for Figure 3 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 an envelope area, which is the boundary hole surface. The boundary hole surface is the hole opening of the boundary hole.

[0042] Optionally, the projection line dataset and the boundary line dataset can be spliced ​​together. During the splicing process, the data formats and coordinate systems of the different datasets must be consistent to avoid splicing errors. The software's data splicing tools can be used to connect the projection lines and boundary lines according to specific rules and algorithms to form a complete hole boundary line dataset. The spliced ​​hole boundary line dataset is verified and inspected to ensure that the hole boundary lines are closed and that there are no gaps or overlaps. If any issues are found, the dataset is adjusted and corrected promptly. The boundary hole surface is formed by enclosing the hole boundary lines. The area calculation function in the software is used to accurately calculate the area of ​​the boundary hole surface. The calculated boundary hole surface area is compared with a preset range. The preset range is determined based on factors such as the design requirements of the aircraft fuel tank, the properties of the sealing material, and actual usage experience, and serves as a reference range for assessing the risk of hole leakage.

[0043] In this example, during the structural processability review phase, secondary development of 3D modeling software was used to develop a fuel tank boundary hole reconstruction algorithm. This algorithm digitally identifies the characteristics of the tank structure boundary holes, calculates their area, and assesses their impact on tank leakage. A targeted solution is then developed, identifying and addressing leakage risks before manufacturing.

[0044] Optionally, the basic meanings of some terms involved in the above technical solution are explained as follows: Fuel tank area surface model: A three-dimensional digital model describing the external surface of an aircraft's fuel tank area. This model is typically used to define the position and shape of the fuel tank within the aircraft structure.

[0045] Fuel tank area structural model: This refers to a detailed three-dimensional digital model that describes the internal structure of the aircraft fuel tank area. It includes the various parts and components inside the tank and their interrelationships.

[0046] Fuel tank area part model: A three-dimensional model representing each specific part in the fuel tank area, obtained based on the digital model of the fuel tank area's enclosing surface and the digital model of the fuel tank area's structure, through operations such as intersection calculations.

[0047] Boundary line: In a 3D model, a boundary line refers to the edge outline of a part or component, which is used to define its shape and boundary.

[0048] Boundary surface: In a 3D model, a boundary surface refers to the surface of a part or component, which defines the shape of the part or component and the contact surface with other parts or components.

[0049] Projection line dataset: A dataset obtained by projecting a part's boundary line dataset onto the boundary surface datasets of other parts. These projection lines are used to analyze the relative positions and possible contact surfaces between parts.

[0050] Hole boundary line dataset: A collection of line data describing the hole boundaries, composed of a projection line dataset and a boundary line dataset. These lines enclose the hole boundary surface.

[0051] Boundary hole surface: A closed surface formed by the hole boundary line, representing the holes or gaps that may exist in the fuel tank area.

[0052] Assembly Dimension Chain: The chain structure formed by the relationship between the dimensions of each part and the transfer path during the assembly process. It is used to analyze dimensional deviations and cumulative effects during the assembly process.

[0053] Tolerance allocation: Based on design requirements and manufacturing capabilities, the tolerance of the overall assembly is allocated to each link such as part processing, heat treatment and structural assembly to ensure the accuracy and quality of the final assembly.

[0054] Full-process manufacturing capability: refers to the various capabilities possessed by parts throughout the entire manufacturing process from raw materials to finished products, including machining accuracy of machined parts, sheet metal parts, composite material molding accuracy, paint layer thickness accuracy, and assembly positioning accuracy.

[0055] Sealing interface positive pressure: The pressure perpendicular to the sealing surface generated on the sealing interface due to bolt preload or other external forces. It is one of the important factors to ensure the sealing effect.

[0056] Bolt group interaction: When multiple bolts are connected simultaneously, the interaction and influence between the individual bolts will affect the overall assembly sequence and the bolt installation sequence.

[0057] Historical leakage data: This refers to records and data on past aircraft fuel tank leaks, including information such as the location, cause, and frequency of leaks. This data is used to analyze and predict future leakage risks.

[0058] In-process leak testing and final leak testing: These are testing plans developed during and after assembly to detect leaks in fuel tanks. In-process leak testing typically involves multiple tests during assembly, while final leak testing involves a comprehensive test after assembly.

[0059] Example 2 Reference Figures 1-6 The first embodiment of the present application provides a method for sealing and assembling an integral fuel tank of an aircraft, comprising the following steps: S10. Obtain a fuel tank area component model of the target fuel tank based on the fuel tank area enclosing surface digital model and the fuel tank area structure digital model of the target fuel tank.

[0060] Optionally, the step of obtaining a part model of the fuel tank area of ​​the target fuel tank according to the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure of the target fuel tank includes: Based on the 3D modeling software, the oil tank area part model is obtained by performing intersection operation on the oil tank area enclosing surface digital model and the oil tank area structure digital model, and then marked.

[0061] Specifically, before performing the intersection operation, ensure that the coordinate systems of the digital model of the tank area's enclosing surface and the digital model of the tank area's structure are consistent. If the coordinate systems of the two digital models are different, use the software's coordinate system conversion function to convert the coordinate system of one digital model to the same coordinate system as the other. In the 3D modeling software, select the appropriate intersection operation tool. Different software may have different intersection operation function names and operation methods, such as the "Boolean Operation - Intersect" function in CATIA.

[0062] When performing an intersection calculation, the digital model of the tank area's enclosing surface is used as the intersection object, and the digital model of the tank area's structure is used as the intersection object. During the calculation, the software calculates features such as the intersection lines and surfaces based on the geometry and topological relationships of the two digital models. Pay close attention to the progress and results of the intersection calculation. If errors or anomalies occur, promptly check the geometry and topological relationships of the digital models, as well as the coordinate system and positioning.

[0063] S20. Based on the fuel tank area part model, extract the boundary lines of the fuel tank area parts at the boundary to form a boundary line dataset; extract the boundary surfaces of the fuel tank area parts close to the fuel tank surface to form a boundary surface dataset.

[0064] S30. According to the fuel tank area part model, a part set that can form a local hole is obtained, and a boundary line dataset of each part in the part set is projected onto the boundary surface datasets of the remaining parts to obtain a projection line dataset.

[0065] S40: splicing the projection line dataset and the boundary line dataset to form a hole boundary line dataset. The hole boundary lines enclose a boundary hole surface. Comparing the area of ​​the boundary hole surface with a preset interval to obtain a leakage risk degree, and adjusting the sealing strategy based on the leakage risk degree.

[0066] Optionally, the step of concatenating the projection line dataset and the boundary line dataset to form a hole boundary line dataset, and enclosing the hole boundary lines to form a boundary hole surface, includes: S401. Group the hole boundary lines in the hole boundary line data set 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.

[0067] Specifically, the grouping criteria are determined based on the assembly relationships and structural characteristics of the fuel tank area parts. For example, if the boundary lines of holes formed by adjacent parts are close in spatial position and their orientation conforms to the logic of hole formation, they can be considered as candidate boundary lines for a group.

[0068] Examine the topological relationships between hole boundary lines, such as whether they are connected, intersecting, or share endpoints. Use topological analysis tools in 3D modeling software to quickly identify the connectivity between boundary lines. If multiple boundary lines are connected by endpoints and form a closed or semi-closed area, they can be grouped together. For example, at the joint of a fuel tank, several boundary lines may be distributed around a potential hole area. Topological relationship analysis can help group these together.

[0069] Optionally, the steps of comparing the area of ​​the boundary hole with a preset interval to obtain a leakage risk level, and adjusting the sealing strategy based on the leakage risk level include: S410: When the area of ​​the boundary hole surface is smaller than the preset interval, it indicates that there is no leakage risk, and sealing is performed inside and outside the seam.

[0070] S420: When the area of ​​the boundary hole surface is within the preset range, indicating a slight leakage risk, local glue stacking is used for sealing.

[0071] S430: When the area of ​​the boundary hole surface is larger than the preset range, indicating a risk of severe leakage, a plugging corner piece is set at the boundary hole surface to plug and seal it.

[0072] Specifically, the setting of the preset interval needs to refer to the air / oil tightness technical requirements and test results, and is related to parameters such as the type of sealant, test pressure, and pressure holding time.

[0073] For example, the preset interval can be 15-50 The leakage risk level is divided according to the size of the boundary hole surface: when In the formula, S represents the area of ​​the boundary hole surface, indicating that there is no leakage risk. No additional treatment is required, and the seam inside and outside can be sealed according to the normal process; when When the leakage is slight, it indicates a risk of leakage. In this case, local glue stacking is used for sealing. when When the hole is blocked, it indicates a risk of severe leakage. In this case, add a plugging corner piece to block the hole and then seal it.

[0074] Assume that at this time, the area of ​​the tank hole is 10 The sealing can be ensured by normal sealing inside and outside the seam and pre-filling the depression.

[0075] The above technical solutions mainly focus on identifying the risk characteristics of fuel tank leakage and formulating treatment plans.

[0076] Optionally, the steps for determining the manufacturing and assembly accuracy of parts based on the glue layer thickness requirement are as follows: S501. Establishing an assembly dimension chain: Based on the fuel tank area part model, obtain the connection relationships between the fuel tank parts, establish an assembly dimension chain, and determine the deviation composition of each assembly link. Based on the overall fuel tank structure and the connection relationships between the parts, establish an assembly dimension chain, and clarify the deviation composition and deviation transmission rules of each link.

[0077] Specifically, the assembly dimension chain is established, such as Figure 5 As shown, Figure 5 for Figure 3 The structure diagram at the lower left of the figure is shown. Taking the oil tank interface formed by the web of the first beam 3 and the flange of the first frame 4 as an example, the following is explained:

[0078] Where: n represents the actual thickness of the sealant, Indicates the theoretical thickness of the sealant. Indicates the positioning deviation of the first beam, Indicates the processing deviation of the web surface of the first beam, Indicates the first frame positioning deviation, Indicates the processing deviation of the first frame edge strip. Indicates the paint layer thickness deviation.

[0079] S502. Determine theoretical sealant thickness: Determine the thickness requirements of the sealant layer at each boundary of the entire fuel tank according to the design digital model requirements; Optional, according to the design model requirements, the theoretical thickness of the sealant .

[0080] S503. Determine the manufacturing capabilities of each link: 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 processing accuracy of machined parts, sheet metal parts, composite material molding accuracy, paint layer thickness accuracy, and assembly positioning accuracy.

[0081] Optionally, the first beam 3 and the first frame 4 are both CNC machined parts, and the machining accuracy levels are as follows: rib and edge processing deviation -0.2mm~0.1mm; web processing deviation -0.25mm~0.1mm; metal structure positioning accuracy ±0.1mm, paint layer thickness 0.03±0.005mm.

[0082] S504, tolerance allocation and assembly compensation: Tolerance allocation and assembly compensation: Based on the sealant layer thickness requirements and the full-process manufacturing capabilities of the fuel tank area parts, the tolerance is allocated to parts processing, heat treatment and structural assembly.

[0083] First, based on sealant thickness requirements and the manufacturing capabilities of each link, tolerances are allocated to parts processing, hot-dip painting, and structural assembly. Some areas require higher tolerances, but manufacturing or assembly accuracy cannot meet these requirements, requiring additional assembly compensation.

[0084] Alternatively, the design requires a sealant layer thickness of 0.1mm, meaning a 0.1mm clearance must be maintained after all parts are positioned. Combining the assembly dimension chain model with manufacturing capabilities, the calculated post-assembly clearance range is -0.70mm to +0.37mm, with positive values ​​indicating interference. The calculations indicate that current manufacturing capabilities cannot guarantee this sealant thickness solely through tolerance allocation, so assembly compensation (grinding or adding shims) is necessary to address this issue. In the case of a gap, the shim thickness is 0-0.6mm, while in the case of interference, the grinding allowance is 0-0.47mm.

[0085] S505, process measurement: perform parts processing, heat treatment and structural assembly on the parts in the fuel tank area to obtain actual deviation data; During part processing and surface painting, the assembly contact surfaces were measured and virtually assembled to assess assembly clearances and implement pre-emptive measures. 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 positioner was +0.05mm. The flange surface deviation of Frame 1 was +0.05mm, the paint layer thickness was 0.02mm, and the measured deviation of the positioner was -0.05mm.

[0086] S506, Virtual Assembly: Based on actual deviation data, the feasibility of the overall tank assembly is assessed to determine whether preliminary treatment or tolerance allocation optimization is needed. Areas with large interference require pre-grinding, and areas with large gaps require pre-shielding.

[0087] Optionally, virtual assembly is performed based on the measurement results of step S505, and it is found that theoretically a gap of 0.005mm will be generated between the contact surfaces after assembly, which is less than the 0.1mm required for assembly. Therefore, it is determined to grind the metal structure of the frame 1 edge strip by 0.05mm and the web of beam 1 by 0.045mm to ensure that the sealant thickness is 0.1mm after assembly is completed.

[0088] In this technical solution, the adhesive layer thickness is the control target, and the deviation transmission law is derived through assembly dimension chain modeling. The system analyzes the manufacturing accuracy of each step, including part manufacturing, heat treatment, and structural assembly. Through tolerance allocation and assembly compensation, the gap formed after assembly is guaranteed to be consistent with the adhesive layer thickness, eliminating the need for grinding or padding the fuel tank boundary.

[0089] Optionally, the assembly process detection and control steps include: S601. Based on theoretical analysis and simulation calculation of the sealing interface of the entire oil tank, obtain the positive pressure of the sealing interface; S602. Obtaining a bolt preload force based on the positive pressure at the sealing interface; S603: Determine the assembly sequence of the entire fuel tank and the bolt installation sequence based on the interaction between the bolt groups, and obtain an installation sequence result; S604. Monitor and control the bolt installation process during the installation process according to the installation sequence result. S605: Measure the thickness of the fuel tank's overall sealing interface parts and the thickness of the interlayer, and monitor changes in the thickness of the sealant layer; S606. Adjust the bolt pre-tightening force according to the change in the thickness of the sealant layer.

[0090] Specifically, the purpose of assembly process monitoring and control is to homogenize assembly stress and interface stress. The sealing mechanism of the fuel tank interface is primarily due to the elastic deformation of the sealant layer under the action of bolt preload, which creates extrusion at the interface and forms a positive pressure. When the positive interface pressure exceeds the internal tank pressure, the tank remains sealed; otherwise, the tank leaks. Therefore, the design of the fastener installation sequence requires a combination of theoretical analysis and simulation calculations to determine the positive pressure at the sealing interface, from which the bolt preload can be calculated. The fastener installation sequence, the part connection sequence, and the multiple tightening process plan can then be designed based on the interaction of the bolt group.

[0091] According to the fastener installation process design results, the bolt tightening process is monitored and controlled during the assembly process, including preload force, torque and stress and strain in key areas. If it deviates from the design value, it will be controlled in time through the tightening tool.

[0092] Measure the thickness of the sealing interface components and the interlayer thickness, monitor changes in the adhesive layer thickness, and take preemptive action (identify adhesive layer thickness and adjust bolt preload). The sealant is still in the process of vulcanization during tightening, so the adhesive layer thickness needs to be monitored during the vulcanization process (during and after tightening). Adjust the bolt preload based on changes in adhesive layer thickness during vulcanization to ensure the sealant layer thickness meets design requirements.

[0093] For example, the integral fuel tank connection uses 5mm diameter bolts with a rated torque of 4Nm and a designed preload of 5kN. The compressive stress generated at the sealing interface is approximately 0.063MPa. According to air / oil tightness testing requirements, the internal pressure of the tank is 0.04MPa, which theoretically meets the sealing requirements. Based on experimental research on bolted connections, the cover bolts are tightened using a cross-tightening method with a torque of 4Nm. After the sealant is fully cured, they are re-tightened, using the same process parameters as the first tightening. For fasteners on a straight edge, tighten from the center to the sides with a torque of 4Nm. After the sealant is fully cured, they are re-tightened, using the same process parameters as the first tightening.

[0094] Use an electric tightening spindle to install the bolts, use the electric tightening spindle's built-in sensor 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.

[0095] Use 3D-DIC equipment to measure the thickness of the interlayer of the sealing structure, without considering the directional change of the thickness of the metal material. The thickness of the sealant layer is calculated based on the interlayer thickness. If the thickness is too small, the preload force should be appropriately reduced, and if the thickness is too large, the preload force should be appropriately increased.

[0096] In the above technical solution, the overall fuel tank sealing assembly process is monitored and controlled in real time. By designing the bolt tightening process, the pre-tightening force in the key area is clearly defined. Through monitoring and control of the assembly process, the pre-tightening force and the thickness of the sealant layer are dynamically adjusted to ensure the sealing effect of the fuel tank boundary, thereby achieving pre-control and process control.

[0097] Optional steps for leak detection of the entire fuel tank and formulation of the final leak detection process plan include: S701. Based on historical leakage data of multiple integral fuel tanks, obtain a first leakage area with a leakage frequency greater than a preset threshold. Specifically, the multiple integral fuel tanks are of the same model. By obtaining historical leakage data of the same integral fuel tank, the most likely leakage location is predicted. The preset threshold can be manually set according to actual usage requirements.

[0098] Through structural analysis and historical fault analysis, we first analyze the overall tank structure and calculate the boundary holes to identify areas with a high risk of leakage. These areas are then used as the primary targets for leak detection. Furthermore, we analyze leak failures across multiple aircraft to identify areas with the highest leakage frequency, which are also used as the primary targets for leak detection. This helps identify risk areas.

[0099] S701, marking an area where the boundary hole surface is larger than a preset interval as a second leakage area; S701. Mark the first leakage area and the second leakage area as dangerous areas. When the entire fuel tank leaks, the dangerous areas are checked first.

[0100] When a leak occurs in the entire fuel tank, prioritize steps to check the hazardous area, including: S7011. Determine the process leak detection plan and final leak detection plan based on the assembly sequence and production cycle of the entire fuel tank; 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, clarifying which parts should be leak tested during wet installation and at what assembly state the entire fuel tank should be finalized for leak detection.

[0101] S7012. If local leakage occurs during the execution of the process leak detection plan or the final leak detection plan, trace the cause of the local leakage, give priority to checking the dangerous area, and perform local repairs for the local leakage.

[0102] If local leakage is found during the process leak detection, first determine the leakage area and judge whether it is fastener leakage, assembly interface leakage, sinking area leakage or debonding of sealing gasket 2, etc. Secondly, perform local repairs for specific leakage situations, and perform leak detection again after repair until there is no leakage.

[0103] After the overall tank structure is assembled, an air / oil tightness test is carried out according to the design requirements. If all the tests pass, it indicates that the sealing meets the standards. If local leakage is found during the process of leak detection, the leakage area is first determined to determine whether it is a fastener leakage, assembly interface leakage, sinking area leakage or debonding of the sealing gasket 2, etc. Secondly, local repairs are carried out for specific leakage situations. After the repairs, the leak detection operation is carried out again until there is no leakage.

[0104] Specifically, the following examples are given: Identify risk areas: Based on the analysis of the fuel tank structure and historical faults, the fuel tank leakage risk area is the sealed boundary formed by the frame beam and the fuel tank bottom plate 5.

[0105] Determine a leak detection plan: Based on the risk areas, set process leak detection requirements. Use helium mass spectrometry positive pressure leak detection at the sealing boundary formed by the frame beam and the tank floor 5 to test for leaks along the sealing boundary and fasteners. After the entire tank is assembled, perform an air / oil tightness test.

[0106] Analysis of process leak detection results and local repair: During the process leak detection, a bolt was found to be leaking. The bolt was removed and reinstalled wet. After reinstallation, local leak detection was performed again and the leakage problem was eliminated.

[0107] After the tank structure is assembled, air and oil tightness testing and local repairs are performed: The air tightness test requires an air pressure of 0.04 MPa, a pressure hold time of 3 hours, and a pressure drop of no more than 200 Pa. The oil tightness test requires filling the tank to 70% of its volume with oil, an air pressure of 0.04 MPa, a pressure hold time of 4 hours, and no leakage. During the oil tightness test, leakage was discovered at the contact area between the first frame flange 4 and the first beam 3 web. After resealing the area, the leakage problem was eliminated.

[0108] Optional steps for designing and iteratively optimizing the overall fuel tank manufacturing and assembly process include: 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.

[0109] Tolerance index optimization and re-decomposition: Analyze the overall fuel tank assembly process and leak detection results, sort out the deficiencies in tolerance allocation, and on this basis optimize the parts processing tolerance requirements, hot plate painting tolerance requirements and assembly tolerance requirements to achieve optimization and re-decomposition of tolerance indicators.

[0110] Assembly process optimization: positioning method, assembly sequence, small components, and attitude adjustment method. First, optimize the part positioning method to ensure that the dimensional chain transfer length is reasonable and the assembly error is stable, controllable, and sufficiently small. Second, optimize the part assembly sequence to improve assembly efficiency and reduce worker labor while ensuring the quality of the sealed assembly. Third, consider the process method of assembling some parts into small components to improve the quality of local sealed assembly and shorten assembly time. Finally, for the fuel tanks in the fuselage or wing-body joint area, it may be necessary to optimize the attitude adjustment method, optimize the gap distribution and structural assembly stress, and ensure the quality of the sealed assembly in the tank area.

[0111] The following are examples: Tolerance index optimization and re-decomposition: During the assembly process, the contact surface between the first frame 4 and the first beam 3 of the metal parts needs to be polished. This is labor-intensive for workers, and the polishing flatness is poor, posing a risk of leakage. Therefore, the contact position between the first frame 4 and the first beam 3 is subsequently processed with a negative tolerance to ensure that there is no interference.

[0112] In this embodiment, the previous process of controlling the sealing quality solely through the gluing process is expanded to include the entire sealing assembly process, including operations such as identifying holes in the tank and addressing leakage risks, designing the precision of parts manufacturing and assembly based on the glue layer thickness requirements, monitoring and controlling the assembly process, developing a process plan for leak detection and final leak detection, and designing and iteratively optimizing the overall tank assembly process, thereby achieving full process control of the entire tank manufacturing and assembly process. By monitoring and controlling the bolt connection process and sealant thickness throughout the entire process, the accuracy of key physical quantities is guaranteed, thereby ensuring the sealing of the tank. Leakage faults can be discovered and addressed in advance, saving subsequent leak detection and troubleshooting cycles. By analyzing the sealing assembly process and leak detection results, a reverse process analysis is performed to summarize the areas that need to be optimized in parts manufacturing, heat treatment, and structural assembly. Through iterative optimization, the overall tank sealing assembly quality is continuously improved.

[0113] The above are only preferred embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for sealing and assembling an integral fuel tank of an aircraft, characterized in that: include: Obtaining a parts model of the fuel tank area of ​​the target fuel tank according to the digital model of the fuel tank area surrounding surface and the digital model of the fuel tank area structure of the target fuel tank; Extracting boundary lines of the fuel tank area parts at the boundaries according to the fuel tank area parts model to form a boundary line dataset, and extracting boundary surfaces of the fuel tank area parts close to the fuel tank surface to form a boundary surface dataset; According to the parts model of the fuel tank area, a set of parts that can form a local hole is obtained, and the boundary line dataset of each part in the part set is projected onto the boundary surface datasets of the remaining parts to obtain a projection line dataset; The projection line dataset and the boundary line dataset are spliced ​​together to form a 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.

2. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 1, wherein: The step of obtaining the fuel tank area part model of the target fuel tank based on the fuel tank area enclosing surface digital model and the fuel tank area structure digital model of the target fuel tank includes: Based on the 3D modeling software, the oil tank area part model is obtained by performing intersection operation on the oil tank area enclosing surface digital model and the oil tank area structure digital model, and then marked.

3. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 1, wherein: The step of splicing the projection line dataset and the boundary line dataset to form a hole boundary line dataset, and enclosing the hole boundary lines to form a boundary hole surface, includes: The hole boundary lines in the hole boundary line dataset are grouped into groups. 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 method for sealing and assembling an integral fuel tank of an aircraft according to claim 1, wherein: The step of comparing the area of ​​the boundary hole with the preset interval 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 surface is smaller than the preset interval, it indicates that there is no leakage risk and the seam inside and outside is sealed; When the area of ​​the boundary hole surface is within the preset range, it indicates a slight leakage risk and is sealed by local glue stacking; When the area of ​​the boundary hole surface is larger than the preset range, it indicates a risk of severe leakage. A plugging corner piece is set at the boundary hole surface to block it and then seal it.

5. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 1, wherein: Also includes: According to the parts model of the fuel tank area, the connection relationship between the parts in the fuel tank area is obtained, the assembly dimension chain is established, and the deviation composition of each assembly link is determined; Determine the thickness requirements of the sealant layer at each boundary of the entire fuel tank according to the design digital model requirements; Obtain the full-process manufacturing capabilities of fuel tank area parts as the basis for tolerance allocation; Based on the sealant layer thickness requirements and the full-process manufacturing capabilities of the fuel tank area parts, tolerances are allocated to parts processing, heat treatment and structural assembly; Perform parts processing, heat treatment and structural assembly on the fuel tank area parts to obtain actual deviation data; Based on the actual deviation data, the feasibility of the overall tank assembly is evaluated to determine whether preliminary treatment or tolerance allocation optimization is needed.

6. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 5, wherein: The full-process manufacturing capabilities of 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.

7. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 5, wherein: Also includes: Based on the theoretical analysis and simulation calculation of the sealing interface of the entire oil tank, the positive pressure of the sealing interface is obtained; Obtain the bolt preload force based on the positive pressure of the sealing interface; According to the interaction of the bolt groups, the assembly sequence of the entire tank and the bolt installation sequence are determined to obtain the installation sequence result; Monitor and control the bolt installation process during the installation process based on the installation sequence results; Measure the thickness of the oil tank's overall sealing interface parts and interlayer thickness, and monitor changes in the sealant layer thickness; Adjust the bolt pre-tightening force according to the change in the thickness of the sealant layer.

8. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 5, wherein: Obtaining a first leakage area having a leakage frequency greater than a preset threshold value based on historical leakage data of a plurality of integral fuel tanks; Marking the area where the boundary hole surface is larger than the preset interval as the second leakage area; The first leakage area and the second leakage area are marked as dangerous areas. When the entire oil tank leaks, the dangerous areas are checked first.

9. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 8, wherein: The step of preferentially checking the dangerous area when the integral oil tank leaks includes: Determine the process leak detection plan and final leak detection plan based on the assembly sequence and production cycle of the entire fuel tank; 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, give priority to checking the dangerous area, and perform local repairs for the local leakage.

10. The method for sealing and assembling an integral fuel tank of an aircraft according to claim 1, wherein: 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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