Frame truss type thin-walled cylinder section welding deformation control method

Abstract

The invention provides a frame-truss type thin-walled cylinder section welding deformation control method which comprises the following steps: carrying out a stringer welding test on an aluminum alloy test plate to obtain a position and posture set of a wall plate after stringer welding; the method comprises the following steps: performing deformation analogue simulation on welding of a 1 / 4 cylinder section wallboard and a stringer, and determining an optimal welding sequence according to a wallboard deformation trend and a free end warping amount which are obtained after simulation; according to the simulation analysis result, the curvature radius is actively adjusted when the wallboard is formed, so that reverse pre-deformation compensation is implemented; a flexible positioning clamp is used for conducting self-adaptive positioning on the stringer so as to dynamically adjust the assembling gap between the stringer and the wall plate; and after the stringer is positioned on the wall plate, transverse pressure friction stir welding is conducted on the stringer. The stability and accuracy of the welding process can be effectively improved, the machining requirement for welding of the carrier rocket storage tank is met, the machining quality and the working efficiency are effectively improved, and the manufacturing cost is effectively controlled.

Description

Technical Field

[0001] This application belongs to the field of welding technology for frame-girder thin-walled cylindrical sections, and particularly relates to a method for controlling welding deformation of frame-girder thin-walled cylindrical sections. Background Technology

[0002] Aluminum alloy reinforced structural panels are widely used in the structure of launch vehicle propellant tanks. They are key load-bearing structural components, accounting for the largest proportion of the entire propellant tank, approximately 60% or more. Their structural form and manufacturing technology have a crucial impact on the overall launch performance, weight, and production efficiency of the rocket body.

[0003] In my country, the rigid structural panels of carrier rockets are mainly machined from aluminum alloy sheets using large five-axis CNC machine tools. Roughing uses large-diameter tools to efficiently remove excess material, while finishing uses small-diameter tools to ensure contour accuracy and form the ribs and web structure. Although milling can meet the requirements of existing models, it is best suited for products with a rib height to skin thickness ratio (rib height ratio). Thin-walled machining with a low rib height ratio is prone to deformation due to residual stress release or cutting force. Further increasing the rib height ratio can lead to problems such as forming cracks, increased structural weight, and further reduction in material utilization. Moreover, high-precision machining requires frequent tool changes, resulting in high costs.

[0004] With the development of my country's launch vehicle industry, more stringent requirements have been placed on the overall performance of rocket components, including reliability, lightweight design, and low cost. Existing manufacturing processes can no longer meet these requirements, becoming a bottleneck affecting the progress of model development. Due to limitations in my country's current manufacturing capabilities, the initial development of the launch vehicle propellant tank section wall panels still employed milling technology, which revealed the following problems: (1) When the rib height ratio is greater than 8, the product is very prone to cracking during the molding process, which leads to a decrease in product quality and reliability; (2) In order to meet manufacturing requirements, the product adopts a design that increases the thickness of the skin to reduce the rib height ratio, resulting in a significant increase in weight; (3) After the rib height ratio increases, the utilization rate of the original process materials is less than 15%, and the production cycle and manufacturing cost increase by more than 100%. (4) Increased skin thickness leads to poor forming curvature, and the roundness of the cylinder section after welding does not meet the requirements for section docking. Summary of the Invention

[0005] In view of this, this application aims to propose a method for controlling welding deformation of frame-girder thin-walled cylindrical sections to solve at least one of the above-mentioned problems.

[0006] To achieve the above objectives, the technical solution of this application is implemented as follows: This application provides a method for controlling welding deformation of a frame-girder type thin-walled cylindrical section, including: By conducting stringer welding experiments on aluminum alloy test plates, the pose set of the wall panels after stringer welding was obtained; Deformation simulation was performed on the welding of 1 / 4 section wall panels and stringers. The optimal welding sequence was determined based on the deformation trend of the wall panels and the warping of the free ends obtained after the simulation. Based on the simulation analysis results, the radius of curvature is actively adjusted during the forming of the wall panel to implement reverse pre-deformation compensation; The stringers are adaptively positioned using a flexible positioning fixture to dynamically adjust the assembly gap between the stringers and the wall panel; After the stringers are positioned on the wall panel, they are subjected to transverse pressure stir friction welding.

[0007] Furthermore, the optimal welding sequence is a method of simultaneously welding from the middle to both ends symmetrically.

[0008] Furthermore, the formula for correcting the radius of curvature is as follows: In the formula, Represents the theoretical radius of curvature. This represents the correction factor. Indicates the amount of warpage at the free end of the wall panel. Indicates the arc length of the wall panel. This represents the corrected actual radius of curvature.

[0009] Furthermore, the flexible positioning fixture includes a base, a support frame, and a pneumatic gripper unit; The support frame is mounted on the base, and a space is reserved between the support frame and the base for the passage of the stringers and wall panels; The pneumatic gripper units are multiple and symmetrically arranged on the support frame. The pneumatic gripper units are controlled to dynamically constrain the position of the stringers.

[0010] Furthermore, the pressure applied by the pneumatic gripper unit located in the middle is greater than the pressure applied by the pneumatic gripper units located at both ends.

[0011] Furthermore, the pneumatic gripper unit includes grippers, a vacuum suction cup, and a cylinder; The pressure claw is rotatably mounted on the support frame, the output shaft end of the cylinder is connected to the pressure claw, the vacuum suction cup is embedded in the head of the pressure claw, and the vacuum suction cup is connected to the vacuum air source device through a connecting pipe.

[0012] Furthermore, a five-axis CNC gantry system is used to perform transverse pressure friction stir welding on the stringers, and the shoulder of the stirring head is a convex concentric circle structure.

[0013] Compared with the prior art, the welding deformation control method for frame-girder thin-walled cylindrical sections described in this application has the following advantages: (1) By predicting the welding deformation of the wall panel stringers, a precise mathematical relationship between welding shrinkage and geometric compensation is established, transforming the deformation control mode from "passive resistance" to "active guidance". (2) At the same time, it overturns the traditional assembly logic of plate-fixed truss and abandons the scheme of relying on large, strong, and complex tooling to constrain the wall panel. It can be achieved simply by fixing the truss, which greatly reduces the tooling cost. (3) The use of horizontal pressure friction stir welding can effectively compensate for workpiece geometric deviations and thermal deformation, improve joint quality and reliability, and greatly improve work efficiency. Attached Figure Description

[0014] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart illustrating a method for controlling welding deformation of a frame-girder type thin-walled cylindrical section according to an embodiment of this application. Figure 2 This is a schematic diagram of the stringer welding constraint position as described in the embodiments of this application; Figure 3 This is a schematic diagram of the welding deformation of the wall panel stringers as described in an embodiment of this application; Figure 4 This is a schematic diagram of displacement constraint during the welding process described in the embodiments of this application; Figure 5 This is a schematic diagram of the welding process described in the embodiments of this application; Figure 6 This is a schematic diagram of the extraction path described in the embodiments of this application; Figure 7 This is a schematic diagram of the radial deformation of the stringers and wall panels after welding, as described in the embodiments of this application. Figure 8 This is a schematic diagram of the pre-deformation of the cylinder wall plate according to an embodiment of this application; Figure 9 This is a schematic diagram of the stringer positioning fixture described in an embodiment of this application.

[0015] Explanation of reference numerals in the attached figures: 1-Wall panel; 2-Stringer; 3-Base; 4-Support frame; 5-Pressure claw; 6-Vacuum suction cup; 7-Cylinder. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] This embodiment uses a 5mm thick, 2000mm high cylindrical section wall panel of a certain launch vehicle as an example. The section consists of 4 wall panels. Each section wall panel is first welded with 16 stringers by friction stir welding. The stringers are 2.8mm thick.

[0019] Please see Figure 1 As shown, this embodiment provides a method for controlling welding deformation of a frame-girder type thin-walled cylindrical section, which specifically includes the following steps: Step S101: By conducting stringer welding tests on aluminum alloy test plates, the pose set of the wall panels after stringer welding is obtained.

[0020] Specifically, in this embodiment, stringer welding is performed on a 300mm×2000mm×5mm 2219 aluminum alloy flat plate to obtain the pose set of the wall panel after stringer welding. The stringer constraint positions are as follows: Figure 2 As shown, the transverse (X), longitudinal (Z), and thickness (Y) displacements of the test plate were measured after welding. The results indicate that the main deformation mode of the thin-walled local cylinder is displacement in the Y direction, with a maximum displacement of 1.73 mm, which is a typical out-of-plane deformation. The deformation trend increases the curvature of the test plate. Figure 3 As shown.

[0021] Step S102: By performing deformation simulation on the welding of 1 / 4 section wall panel and stringers, the optimal welding sequence is determined based on the deformation trend of the wall panel and the warping of the free end obtained after simulation.

[0022] Specifically, in this embodiment, based on the deformation data of the wall panel after welding a single stringer, a deformation simulation analysis is conducted using a 1 / 4-section cylindrical wall panel assembly model with welds on 16 stringers. The displacement constraint during the welding process is a three-point constraint, only constraining the rigid body rotation, such as... Figure 4As shown, the welding deformation of the wall panel in a free state is simulated. This embodiment discusses three welding schemes for the stringers and wall panels: Scheme 1 is a single-pass sequential welding from one end to the other; Scheme 2 is symmetrical welding from both ends to the middle simultaneously; and Scheme 3 is symmetrical welding from the middle to both ends simultaneously. A schematic diagram of the process is shown below. Figure 5 As shown, Figure 6 The path in the code is used to extract the radial deformation of the final result and compare the differences between the various schemes.

[0023] Welding simulation based on the theory of inherent strain assumes that welding stress and deformation are caused by inherent strain. Therefore, residual stress and welding deformation can be obtained by loading the inherent strain generated during the welding process into the welded structure. For the state after welding, the inherent strain is the welding residual plastic strain.

[0024] In the formula, Indicates inherent strain; This indicates residual plastic strain from welding.

[0025] To facilitate finite element analysis, the inherent strain value is usually obtained by integration to obtain the inherent deformation value. The inherent deformation consists of 6 components. Considering that the inherent deformation component in thickness has a very small impact on stress deformation, it is usually ignored in practical applications. The calculation methods for the inherent deformation in the transverse and longitudinal directions are as follows: In the formula, , These represent the inherent contraction in the horizontal and vertical directions, respectively. , These represent the inherent bending in the transverse and longitudinal directions, respectively. , These represent the transverse and longitudinal residual plastic strains, respectively. Indicates plate thickness or wall thickness. Indicates the direction of perpendicular welding. Indicates the thickness direction. Indicates the direction of the weld; Among the inherent deformation components, the shrinkage component corresponds to the integral value of the plastic strain in the corresponding direction of the joint cross-section divided by the plate thickness or wall thickness, representing the average shrinkage over the wall thickness; while the bending component represents the difference in shrinkage over the wall thickness. For example, the angular deformation of a butt joint plate is the transverse inherent bending in the inherent deformation components. By convention, a negative value of the inherent shrinkage component corresponds to compressive plastic deformation, and a positive value corresponds to tensile plastic deformation; while a negative value of the inherent bending component corresponds to the shrinkage of the outer wall being less than that of the inner wall, and a positive value indicates that the shrinkage of the outer wall is greater than that of the inner wall.

[0026] Figure 7 The diagram shows the radial orientation of all weld passes after completion for the three welding schemes. The results indicate that the deformation patterns of the three schemes are consistent, with the free end warping upwards. The deformation mechanism is mainly caused by longitudinal shrinkage of the weld, resulting in deflection. Table 1 shows a comparison of welding deformation for different welding sequences. The numerical differences between Scheme 1 and Scheme 2 are not significant, while the radial deformation of Scheme 3 is significantly smaller than that of Schemes 1 and 2. Therefore, Scheme 3 is the recommended welding sequence. Step S103: Based on the simulation analysis results, actively adjust the radius of curvature during the panel forming process to implement reverse pre-deformation compensation.

[0027] Specifically, in this embodiment, based on the warping deformation of the free end of the wall panel after welding of 1 / 4 of the wall panel and 16 stringers obtained from simulation analysis, the radius of curvature is actively adjusted during the wall panel forming process to implement reverse pre-deformation compensation. The compensated wall panel is as follows: Figure 8 As shown, the formula for correcting the radius of curvature is as follows: In the formula, Represents the theoretical radius of curvature. This represents the correction factor. Indicates the amount of warpage at the free end of the wall panel. Indicates the arc length of the wall panel. This represents the corrected actual radius of curvature.

[0028] The stringers are welded to the wall panel in a pre-deformed state. During the welding process, the thermal shrinkage force drives the wall panel to naturally spring back to the theoretical radius of curvature. This method controls welding deformation at the source, eliminating the limitations of traditional methods that rely on tooling constraints or post-weld alignment, reducing equipment costs while improving manufacturing efficiency.

[0029] Step S104: Use a flexible positioning fixture to adaptively position the stringers to dynamically adjust the assembly gap between the stringers and the wall panel.

[0030] Specifically, in this embodiment, traditional processes require complex tooling to simultaneously constrain the wall panel and stringers. This embodiment designs a flexible adaptive positioning fixture for the stringers, such as... Figure 9 As shown, the traditional rigid positioning of wall panels and stringers is transformed into stringer positioning + wall panel self-adaptation through the positioning strategy of "stringer-controlled plate".

[0031] In some embodiments, the flexible positioning fixture includes a base 3, a support frame 4, and a pneumatic gripper 5 unit; The support frame 4 is mounted on the base 3, and a space is reserved between the support frame 4 and the base 3 for the truss 2 and the wall panel 1 to pass through. There are multiple pneumatic pressure claw 5 units, which are symmetrically arranged on the support frame 4. The movement of the pneumatic pressure claw 5 units is controlled to dynamically constrain the position of the stringer 2.

[0032] Among them, the pneumatic pressure claw 5 unit includes pressure claw 5, vacuum suction cup 6 and cylinder; The pressure claw 5 is rotatably mounted on the support frame 4. The output shaft end of the cylinder is connected to the pressure claw 5. The vacuum suction cup 6 is embedded in the head of the pressure claw 5 and is connected to the vacuum air source device through a connecting pipe.

[0033] Specifically, in this embodiment, the clamp has a nonlinear gradient force application function. This embodiment uses 20 independent pneumatic pressure claws 5 units. By adjusting the pressure, the pressure in the middle is greater than that at both ends. Combined with real-time thermo-mechanical coupling control, it actively counteracts welding shrinkage stress. Secondly, it has a gap adaptive dynamic adjustment function. The axial position of the pressure claw 5 can be dynamically adjusted according to the assembly gap between the stringer 2 and the wall panel 1 to ensure that the assembly gap between the stringer 2 and the wall panel 1 is not greater than 0.1mm. It also has a quick assembly function for stringers 2. Each pressure claw 5 has a vacuum suction cup 6 embedded in its head. When the stringer 2 is powered on, it is attracted. After the welding of a single stringer 2 is completed, the pneumatic pressure claw 5 automatically releases the pressure, the vacuum suction cup 6 is powered off and detaches from the stringer 2, and then the crane lifts the wall panel 1 and moves it to the next stringer 2 welding position, which greatly shortens the assembly cycle of a single stringer 2.

[0034] Step S105: After positioning the stringers on the wall panel, perform transverse pressure friction stir welding on the stringers.

[0035] Specifically, in this embodiment, after the stringers are positioned on the wall panel, a five-axis CNC gantry system is used to perform transverse pressure friction stir welding on the stringers. The shoulder of the stirring head has an outwardly convex concentric circle structure. During welding, the inclination angle of the stirring head is set to 1.5°, the welding pressure is set to 12kN, the stirring needle penetration depth is 4mm, the spindle speed is 400r / min, and the welding speed is 130mm / min. This welding method has the following technical features: (1) Effectively compensate for workpiece geometric deviations and thermal deformation. During the welding process, the stirring head is dynamically maintained to apply constant axial pressure to the welding interface through a closed-loop pressure control system, ensuring the consistency of penetration depth and weld width when encountering deviations in the geometric shape (such as curvature) or thermal deformation of the stringer surface in the welding travel direction.

[0036] (2) Improve joint quality and reliability. During transverse pressure welding, stable thermo-mechanical coupling conditions can be ensured. Constant axial pressure results in small fluctuations in frictional heat power and more stable heat input. Constant shoulder indentation depth promotes uniform plastic rheology.

[0037] (3) Improve work efficiency and automation compatibility. The constant pressure value not only adapts to stringers with different curvatures, reducing manual intervention time by 80%, but also allows the plastic material to gather towards the center during the welding process of the concentric circle structure stirring head, thickening the weld and preventing flash, which can improve weld performance and save the time of grinding flash.

[0038] This embodiment establishes a precise mathematical relationship between welding shrinkage and geometric compensation by predicting the welding deformation of the wall panel stringers, transforming the deformation control mode from "passive resistance" to "active guidance." Simultaneously, it overturns the traditional assembly logic of determining stringers based on plates, abandoning the scheme of relying on large, rigid, and complex tooling to constrain the wall panels. This can be achieved simply by fixing the stringers, greatly reducing tooling costs. Furthermore, this embodiment employs transverse pressure friction stir welding, which can effectively compensate for workpiece geometric deviations and thermal deformation, improve joint quality and reliability, and significantly enhance work efficiency.

[0039] The welding deformation control method for frame-girder thin-walled cylindrical sections described in this application can effectively improve the stability and accuracy of the welding process, meet the processing requirements of rocket propellant tank welding, effectively improve processing quality and work efficiency, and effectively control manufacturing costs.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0041] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A method for controlling welding deformation of a frame-truss type thin-walled cylindrical section, characterized in that, include: By conducting stringer welding experiments on aluminum alloy test plates, the pose set of the wall panels after stringer welding was obtained; Deformation simulation was performed on the welding of 1 / 4 cylindrical section wall panels and stringers. The optimal welding sequence was determined based on the deformation trend of the wall panels and the warping of the free ends obtained after the simulation. Based on the simulation analysis results, the radius of curvature is actively adjusted during the forming of the wall panel to implement reverse pre-deformation compensation; The stringers are adaptively positioned using a flexible positioning fixture to dynamically adjust the assembly gap between the stringers and the wall panel; After the stringers are positioned on the wall panel, they are subjected to transverse pressure friction stir welding.

2. The method according to claim 1, characterized in that: The optimal welding sequence is to weld symmetrically from the middle to both ends of the edge simultaneously.

3. The method according to claim 1, characterized in that, The formula for correcting the radius of curvature is as follows: In the formula, Represents the theoretical radius of curvature. This represents the correction factor. Indicates the amount of warpage at the free end of the wall panel. Indicates the arc length of the wall panel. This represents the corrected actual radius of curvature.

4. The method according to claim 1, characterized in that: The flexible positioning fixture includes a base, a support frame, and a pneumatic gripper unit; The support frame is mounted on the base, and a space is reserved between the support frame and the base for the passage of the stringers and wall panels; The pneumatic gripper units are multiple and symmetrically arranged on the support frame. The pneumatic gripper units are controlled to dynamically constrain the position of the stringers.

5. The method according to claim 4, characterized in that: The pressure applied by the pneumatic gripper unit located in the middle is greater than the pressure applied by the pneumatic gripper units located at both ends.

6. The method according to claim 4, characterized in that: The pneumatic gripper unit includes grippers, a vacuum suction cup, and a cylinder; The pressure claw is rotatably mounted on the support frame, the output shaft end of the cylinder is connected to the pressure claw, the vacuum suction cup is embedded in the head of the pressure claw, and the vacuum suction cup is connected to the vacuum air source device through a connecting pipe.

7. The method according to claim 1, characterized in that: The stringers are subjected to transverse pressure friction stir welding using a five-axis CNC gantry system, and the shoulder of the stirring head is a convex concentric circle structure.

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