Method for assembling and defect control of 5m diameter tank closure ring joint friction stir welding

Abstract

The application provides a 5m diameter storage tank sealing ring gap friction stir welding assembly and defect control method, which comprises the following steps: calculating the inner surface diameter of the tank bottom welding area; measuring the assembly gap of the connection surface of the storage tank and the supporting ring; assembling an auxiliary operation platform under the frame and hoisting it to the tank bottom; assembling a detachable inner supporting mechanism under the frame; assembling the detachable inner supporting mechanism with the mandrel, hoisting the whole to the tank bottom feeding mechanism and positioning and assembling; pushing the tank bottom and the inner supporting mechanism to the ring holding mechanism by the tank bottom feeding mechanism, and entering the welding position; controlling the butt joint gap of the weld by the milling light flat method; aligning and adjusting the detachable inner supporting mechanism and the center of the weld by the line marking method; supporting the supporting block until the inner surface diameter of the storage tank is expanded; eliminating the tire gap between the welding backing plate and the product and the misaligned edges of the weld assembly. The application has the beneficial effects that the 5m diameter storage tank sealing ring gap friction stir welding assembly and defect control method improves the assembly precision and the welding quality.

Description

Technical Field

[0001] This invention belongs to the aerospace field, and in particular relates to a flexible assembly and defect control method for sealing circumferential seam friction stir welding in the vertical mode of a 5m diameter storage tank. Background Technology

[0002] The new generation of launch vehicles is characterized by its ultra-long length, large thickness, and novel structure. The propellant tanks have a diameter of 5 meters and significant weld thickness, all employing a double-chamber, common-bottom structure. Currently, the manufacturing process for the 5-meter diameter propellant tanks utilizes a traditional horizontal assembly method combined with TIG welding for the tank sealing circumferential seam. However, when assembling the inner support in the horizontal position, the inner support mandrel undergoes bending deformation due to gravity, resulting in poor overall coordination and linkage between the inner support segments. This affects the pre-welding assembly accuracy of the sealing tank. Furthermore, traditional welding processes inevitably introduce certain welding defects (such as porosity, slag inclusions, and microcracks) and residual welding stress, significantly reducing the mechanical properties of the weld and causing substantial welding deformation, making it difficult to guarantee the propellant tank's dimensional and positional dimensions. Therefore, the production of 5-meter diameter propellant tanks still has significant room for optimization in terms of welding assembly and welding processes. For this type of novel 5m diameter storage tank, a research and development production model combining vertical assembly with friction stir welding has been proposed. In the vertical friction stir welding manufacturing of the storage tank, the assembly of the tank sealing circumferential seam presents the greatest difficulty and welding risk. After the sealing circumferential seam is welded, the storage tank becomes a closed box, requiring the internal supports to be disassembled into individual parts. Due to the confined space, the internal supports are designed to be detachable, resulting in weak overall interlocking and linkage between the internal support blocks, leading to low assembly accuracy. Theoretically, relying on the internal support mechanism to provide sufficient support force can ensure the product fits snugly against the rigid support plate. However, in actual engineering applications, influenced by factors such as the upstream process cylinder section profile and assembly conditions, misalignment and non-fitting of the product with the rigid support plate are inevitable, severely affecting weld quality. Summary of the Invention

[0003] In view of this, the present invention aims to propose a flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank to solve the problem of low assembly accuracy of the existing storage tank circumferential seam assembly.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank includes the following steps:

[0006] S1. Calculate the diameter of the inner surface of the welding area at the bottom of the box;

[0007] S2. Hoist the bottom assembly of the tank assembly downwards to the bottom loading mechanism and measure the assembly gap between the tank and the support ring connection surface.

[0008] S3. The auxiliary operation platform is assembled under the frame and hoisted into the bottom of the box;

[0009] S4. Assemble a detachable inner support mechanism under the frame, and ensure that both the inner and outer support blocks are in a retracted state;

[0010] S5. After the detachable inner support mechanism and mandrel are assembled under the frame, they are hoisted to the bottom loading mechanism of the box as a whole and positioned for assembly.

[0011] S6. An umbrella-shaped support leveling method is adopted to keep the inner and outer support blocks of the detachable inner support mechanism level as a whole.

[0012] S7. The bottom feeding mechanism pushes the bottom of the box and the inner support mechanism into the ring clamping mechanism, and enters the welding position.

[0013] S8. The gap between weld joints is controlled by milling and smoothing method;

[0014] S9. Use the engraving marking method to align the detachable internal support mechanism with the weld center.

[0015] S10. Extend the support block until the diameter of the inner surface of the storage tank is increased by 2mm.

[0016] S11. Eliminate the gap between the welding backing plate and the product and the misalignment of the weld assembly.

[0017] Furthermore, the method for calculating the inner surface diameter of the bottom welding area in S1 is as follows: the outer surface circumference L1 of the bottom welding area and the outer surface circumference L2 of the cylindrical section welding area are measured respectively, and the thickness δ of the bottom welding area is measured. During the cylindrical section welding production process, the blanking size of the wall panel is controlled so that L2 is 3~5mm smaller than L1. Therefore, during the vertical sealing box circumferential seam assembly welding, the bottom welding area size data is used as the support assembly reference to calculate the inner surface diameter D1 of the bottom welding area, that is, D1=L1 / π-2δ.

[0018] Furthermore, the auxiliary operating platform in S3 includes several profile frames and several foldable aluminum cover plates, which are connected in an interlocking manner to form a ring structure. A support rod is installed in the middle of the bottom of each profile frame, and a support plate is installed at the other end of the support rod. Several support plates form a ring structure. Each profile frame has feet installed at its bottom for height adjustment. The part of the feet that contacts the inner surface of the box bottom is made of rubber material, and the shape of the feet is a contoured arc surface to ensure surface contact with the box bottom.

[0019] Furthermore, the detachable inner support mechanism in S4 includes an inner support mandrel and support blocks. The first end of the inner support mandrel is circumferentially hinged to 24 supporting beams. A leveling support rod is movably installed below each supporting beam. The other ends of several leveling support rods are circumferentially hinged to the second end of the inner support mandrel. A scale is provided above each supporting beam to indicate the support capacity of the support blocks. A horizontal tensioner is installed between two adjacent supporting beams. A support block is fixedly installed at the end of each supporting beam. The outer edge of each support block... Welded pads are provided at each edge. The support blocks are divided into inner support blocks and outer support blocks, which are staggered. A guide plate is provided below each support block. A spiral force-adding push rod is installed above the support beam connecting the inner support block, and the spiral force-adding push rod is fixedly connected to the inner support block. Several tightening bolts are also installed on each inner support block, and the force-applying position of the tightening bolts is on the load-bearing protrusion of the outer support block. The outer support block and the inner support mandrel are also connected by the outer support block support rod, and the 12 outer support block support rods are circumferentially hinged to the inner support mandrel.

[0020] Furthermore, the specific method for controlling the weld gap using the milling and smoothing method in S8 is as follows: before the cylinder section and the bottom of the box are joined, the end face of the welding area of ​​the cylinder section and the end face of the welding area of ​​the bottom of the box are milled and smoothed using the milling shaft of the equipment. After milling, the end face of the welding area of ​​the cylinder section and the bottom of the box are 25~30mm away from the pressure plates of the upper and lower clamping ring mechanism, respectively. Aluminum chips are cleaned and the oxide film in the welding area is polished.

[0021] Furthermore, the method of aligning the detachable inner support mechanism with the weld center using the engraving marking method in S9 is as follows: taking the end face of the welding area of ​​the cylinder section as a reference, a full circle of assembly position lines is drawn on the inner surface of the welding area at a distance of 45mm from the end face. The upper clamping ring mechanism descends synchronously with the cylinder section to align and verify the cylinder section with the bottom of the box. The docking gap is measured and can be controlled within 0.3mm. By controlling the lifting mechanism of the bottom loading mechanism, the axial height of the detachable inner support mechanism is adjusted so that the upper surface of the welding pad is aligned with the assembly position line on the inner surface of the welding area of ​​the cylinder section, thereby achieving the alignment of the center of the welding pad with the center of the weld.

[0022] Furthermore, the method for extending the support blocks in S10 until the inner surface diameter of the storage tank is increased by 2mm is as follows: Adjust the length of the outer support block support rod to extend the outer support blocks symmetrically. Use a ruler to ensure that the extension amount of each outer support block is consistent. At this time, the extension diameter D of the outer support block is the inner surface diameter D1 of the bottom welding area of ​​the tank. Use the set spiral force push rod to extend the inner support blocks symmetrically in the same way. Use a ruler to ensure that the extension amount of each inner support block is consistent. At this time, the extension diameter D of the inner support block is also the inner surface diameter D1 of the bottom welding area of ​​the tank. Push out the tightening bolts on both sides of the inner support block evenly. The outer support block continues to move outward along the slide between the support blocks and tightens. Simultaneously adjust the spiral force push rod of the inner support block to make the inner support block move outward synchronously until the inner surface diameter of the storage tank is increased by 2mm. After extension, the extension diameter D of the inner and outer support blocks is D1+2. The gap between the support block pad and the inner surface of the storage tank is controlled within 0.2mm.

[0023] Furthermore, in S11, the method to eliminate the gap between the pad of the inner support block and the tank and the misalignment of the weld assembly is to simultaneously reduce the clamping diameter of the upper and lower clamping rings by 0.5mm.

[0024] Compared with existing technologies, the flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank described in this invention has the following advantages:

[0025] (1) The flexible assembly method of friction stir welding for sealing circumferential seam of 5m diameter storage tank described in this invention has achieved a breakthrough from scratch in the precise assembly and control process of the internal support of the detachable interlocking structure of the sealing circumferential seam of the 5m diameter ultra-long and thick common bottom storage tank of the launch vehicle in the vertical mode. It also provides an effective solution for achieving efficient and high-quality friction stir welding production of sealing circumferential seam of 5m diameter storage tank and improves the assembly accuracy.

[0026] (2) The flexible assembly method of friction stir welding for sealing ring seam of 5m diameter storage tank described in this invention achieves strong rigidity assembly and tightening of sealing ring seam. After assembly, the radial expansion of the welding area of ​​storage tank can be increased by 2mm. The assembly roundness is ≤±0.8mm, the butt gap is ≤0.3mm, the assembly misalignment is ≤0.5mm, and the tire gap is ≤0.2mm. The assembly qualification rate is increased to 100%.

[0027] Another objective of this invention is to propose a defect control method for friction stir welding of the sealing circumferential seam of a 5m diameter storage tank, in order to solve the problems of welding defects and residual stress, significant loss of mechanical strength of the weld, and large welding deformation of the product when welding the circumferential seam of the storage tank using traditional fusion welding process.

[0028] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0029] A method for controlling defects in the friction stir welding of the circumferential seam of a 5m diameter storage tank sealing joint includes the following steps:

[0030] T1. First, perform segmented positioning welding, then perform full-circle positioning welding to initially fix the assembly state of the full-circle seam.

[0031] T2. Perform deep tack welding to further fix the assembly state;

[0032] T3. Perform pre-welding to form a complete closed extrusion mold between the stirring head and the backing plate, and achieve a certain degree of weld penetration;

[0033] T4. The retractable welding uses a retractable stirring head. During the welding end stage, the stirring pin is retracted at a uniform speed to eliminate keyhole defects.

[0034] Furthermore, the specific method for performing segmented positioning welding followed by full-circumference positioning welding in T1 is as follows: First, segmented positioning welding is performed using a positioning stirring head with a needle length of 2-3mm. 8-12 segments are welded, with each segment having a weld length of 300-400mm. Areas with misaligned assembly are given priority for positioning, and areas with poor assembly quality are fixed in their state. Then, full-circumference positioning welding is performed. The stirring head is the same as in the segmented positioning welding, with a welding angle of 358°. A 2° angle is left unwelded for positioning the seam during near-thinning friction stir welding with a retractable stirring needle, thus initially fixing the assembly state of the entire circumferential seam.

[0035] Compared with existing technologies, the defect control method for friction stir welding of the circumferential seam of a 5m diameter storage tank described in this invention has the following advantages:

[0036] (1) The method for controlling defects in friction stir welding of the circumferential seam of the 5m diameter storage tank described in this invention reduces the generation of internal defects in the weld and increases the weld pass rate to 100%. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 This is a flowchart of the flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to an embodiment of the present invention;

[0039] Figure 2 A schematic diagram of the existing 5m diameter common-bottom vertical tank body circumferential seam friction stir welding system;

[0040] Figure 3 This is a schematic diagram of the auxiliary operation platform described in an embodiment of the present invention;

[0041] Figure 4This is a schematic diagram of the detachable internal support mechanism described in an embodiment of the present invention;

[0042] Figure 5 for Figure 4 Enlarged view of section A in the middle;

[0043] Figure 6 This is a diagram showing the state of the inner and outer support blocks as described in an embodiment of the present invention.

[0044] Figure 7 This is a schematic diagram of the assembly state of the detachable inner support mechanism frame according to an embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram of the axial height adjustment of the detachable inner support mechanism and the synchronous clamping of the upper and lower clamping mechanisms according to an embodiment of the present invention;

[0046] Figure 9 This is a flowchart of the method for controlling defects in the friction stir welding of the circumferential seam of a 5m diameter storage tank according to an embodiment of the present invention;

[0047] Figure 10 This is a schematic diagram of a single positioning weld as described in an embodiment of the present invention;

[0048] Figure 11 This is a schematic diagram of deep positioning welding according to an embodiment of the present invention;

[0049] Figure 12 This is a schematic diagram of the pre-welding process described in an embodiment of the present invention;

[0050] Figure 13 This is a schematic diagram of the retractable stirring welding described in an embodiment of the present invention.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1-Auxiliary operating platform; 11-Profile frame; 12-Foldable aluminum cover plate; 13-Foot; 14-Support rod; 2-Detachable internal support mechanism; 21-Internal support mandrel; 22-Support square beam; 23-Screw force-increasing push rod; 24-Scale; 25-External support block support rod; 26-Leveling support rod; 27-Internal support block; 28-External support block; 281-External support block load-bearing boss; 29-Horizontal tensioner; 210-Welding pad; 211-Tightening bolt; 3-Box bottom assembly; 4-Lifting machine; 5-Equipment mandrel; 6-Cylinder section; B-Cylinder section full circle assembly position line. Detailed Implementation

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0055] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0056] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0057] In the vertical configuration, the assembly of the sealing circumferential seam of the 5m diameter launch vehicle propellant tank is carried out on a vertical friction stir welding system for the circumferential seam. This system mainly consists of a frame body, equipment base, bottom loading mechanism, cylinder section loading mechanism, upper clamping ring mechanism, lower clamping ring mechanism, lifting mechanism, and hoisting mechanism. This 5m diameter common-bottom propellant tank vertical circumferential seam friction stir welding system is existing technology. To facilitate understanding, the positional relationships of the system are briefly described below: the cylinder section loading mechanism and the bottom loading mechanism are symmetrically installed above the equipment base, with the frame body installed in the middle. From top to bottom, the frame body is equipped with the lifting mechanism, hoisting mechanism, upper clamping ring mechanism, and lower clamping ring mechanism.

[0058] The sealing circumferential seam of the container is the last circumferential weld of the storage tank. Before assembly and welding, the already welded container part is moved upward by the lifting mechanism, and the six cylindrical sections to be connected are moved into the upper clamping ring mechanism. Then, the bottom of the container to be welded is hoisted onto the bottom loading mechanism, and the assembled auxiliary operating platform and detachable inner support mechanism are hoisted into the bottom loading mechanism. The bottom loading mechanism lifts the bottom of the container and the detachable inner support mechanism into the lower clamping ring mechanism for the alignment, assembly and welding of the sealing circumferential seam.

[0059] A flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank, such as... Figures 1 to 8 As shown, it includes the following steps:

[0060] S1. Measure the perimeter L1 of the outer surface of the bottom welding area and the perimeter L2 of the outer surface of the cylindrical section welding area, and the thickness δ of the bottom welding area. During the production of the cylindrical section 6, by controlling the blanking size of the wall panel, L2 is made 3~5mm smaller than L1. Therefore, when assembling and welding the vertical sealing box circumferential seam, the bottom welding area size data is used as the support assembly reference to calculate the inner surface diameter D1 of the bottom welding area, i.e., D1=L1 / π-2δ.

[0061] S2. Hoist the bottom assembly 3, with its convex spherical surface pointing downwards, onto the support ring of the bottom loading mechanism, and connect and fix it. Measure the assembly gap between the bottom assembly 3 and the support ring; the gap should be less than 0.2mm, and locally no more than 0.5mm. The bottom assembly 3 is an existing structure. The support ring of the bottom loading mechanism is annular, and has several weight-reducing holes evenly distributed on it.

[0062] S3. The auxiliary operation platform 1 is assembled under the frame and hoisted into the bottom of the box as a whole. The other end of the support rod 14 is screwed and fixed to the spindle of the bottom loading mechanism.

[0063] The auxiliary operating platform 1 allows operators to install and debug the detachable internal support mechanism inside the tank in vertical mode, improving the convenience of operation inside the tank. The auxiliary operating platform is assembled under the frame 1, and after assembly, it is hoisted to the working position. After welding, it is disassembled into parts inside the tank and transported out through the tank's manhole flange. The auxiliary operating platform 1 includes several profile frames 11 and several foldable aluminum cover plates 12, which are interlocked to form a ring structure. A support rod 14 is installed in the middle of the bottom of each profile frame 11, and a support plate is installed at the other end of the support rod 14. Several support plates form a ring structure. Each profile frame 11 has adjustable feet 13 at its bottom. The contact part between the feet 13 and the inner surface of the tank bottom is made of rubber to avoid scratching the tank. The shape of the feet 13 is a contoured arc surface to ensure surface contact with the tank bottom.

[0064] S4. Assemble the detachable inner support mechanism 2 under the frame, ensuring that both the inner and outer support blocks are in a retracted state. Use a ruler to ensure that the retraction amount of all outer support blocks is consistent. To ensure that the inner and outer support blocks extend evenly during subsequent assembly and to prevent some inner support blocks from failing to extend properly due to pressure from adjacent outer support blocks, the sides of the inner and outer support blocks should be in close contact.

[0065] The detachable inner support mechanism 2 includes an inner support spindle 21, support beams 22, a spiral force-adding push rod 23, a scale 24, an outer support block support rod 25, a leveling support rod 26, an inner support block 27, an outer support block 28, a horizontal tensioner 29, a welding pad 210, and a tightening bolt 211. The first end of the inner support spindle 21 is circumferentially hinged with 24 support beams 22. A leveling support rod 26 is movably installed below each support beam 22. Several leveling support rods... The other end of each of the 26 is circumferentially and uniformly hinged to the second end of the inner support mandrel 21. Each support beam 22 is equipped with a scale 24 above it. The scale 24 is used to measure the support amount of the inner support block 27 and the outer support block 28. A horizontal tensioner 29 is installed between two adjacent support beams 22. By adjusting the length of the horizontal tensioner 29, the circumferential position of the beam where the inner support block is located is adjusted, eliminating the gap between the inner and outer support blocks, so that the inner and outer support blocks are in a state of close contact with each other. A support block is fixedly installed at the end of each supporting beam 22. Each support block has a welding pad 210 at its outer edge. The support blocks are inner support block 27 and outer support block 28, and the inner support block 27 and outer support block 28 are staggered. A guide plate is provided below each support block. The guide plate restricts the circumferential freedom of the support block while ensuring sliding along the diameter 22 of the supporting beam. A spiral force-adding push rod 23 is installed above each supporting beam 22 connected to the inner support block 27, and the spiral force-adding push rod 23 is fixedly connected to the inner support block 27. In order to achieve strong rigid support of the detachable inner support mechanism 2 and prevent the support block from retracting under the action of upsetting force during friction stir welding, the detachable inner support mechanism 2 further enhances the interlocking rigidity of the inner support block 27 and outer support block 28 after they are extended by tightening the bolts 211. Each inner support block 27 is also equipped with several tightening bolts 211, the force application position of the tightening bolts 211 is on the load-bearing boss 281 of the outer support block; preferably, each inner support block 27 is also equipped with several four tightening bolts 211 and two disassembly auxiliary bolts; the outer support block 28 and the inner support spindle 1 are also connected by outer support block support rods 25, and the 12 outer support block support rods 25 are circumferentially and evenly hinged to the inner support spindle 1. Before the support operation of the inner support blocks 27 and outer support blocks 28, the levelness is adjusted by adjusting the leveling support rods 26 to ensure radial support. The inner support blocks 27 and outer support blocks 28 are supported by the support beam 22 and can slide radially on the support beam 22. When the support blocks are extended, the extension diameter is determined by the scale 24. The outer support block 28 provides support force during pre-tensioning through the outer support block support rod 25, and the inner support block 27 provides support force through the spiral force-increasing push rod 23. After both the inner and outer support blocks are extended, the support force is increased through the tightening bolt 211 to achieve strong rigidity tightening. The welding pad 210 is 90mm wide. The shape of the welding pad is divided into upper and lower parts with the center as the dividing line. The upper part is a straight structure, and the lower part is an arc structure that is consistent with the inner surface of the welding area on the bottom side of the box. When assembling the support, it can be tightly fitted to the welding areas on the sides of the cylinder section 6 and the welding area on the bottom side of the box, respectively.The detachable inner support mechanism 2 adopts a self-locking design concept. After being tightened, the 12 inner support blocks 27 and the 12 outer support blocks 28 can fit together to form a rigid whole, which can withstand the upsetting force of the welding spindle.

[0066] S5. After the detachable inner support mechanism 2 and the equipment spindle 5 are assembled under the frame, they are hoisted as a whole onto the spindle of the bottom loading mechanism. The detachable inner support mechanism 2 is quickly positioned and assembled through the guide device on the spindle, and the detachable inner support mechanism 2 and the equipment spindle are reliably fixed by bolt connection.

[0067] S6. To ensure that the welding pad 210 and the inner surface of the tank welding area are in surface contact after the detachable inner support mechanism 2 is tightened and force is applied, and to avoid the detachable inner support mechanism 2 from tilting, an umbrella-shaped support leveling method is adopted: Since one end of the leveling support rod 26 is connected to the square beam 22 and the other end is connected to the inner support mandrel 21, by adjusting the leveling support rod 26 and cooperating with the level, the inner and outer support blocks are kept horizontal as a whole, preventing the support blocks from tilting down or tilting up.

[0068] S7. The bottom feeding mechanism pushes the bottom of the box and the detachable inner support mechanism 2 into the clamping ring mechanism and enters the welding position, so that the axial distance between the bottom end face of the storage box to be welded and the pressure plate of the lower clamping ring pressing mechanism is 25~30mm. The lower clamping ring pressing mechanism is pre-clamped to ensure that the pressure plate and the storage box are tightly fitted, and the local fitting gap is no more than 0.2mm.

[0069] S8. The gap between weld joints is controlled by milling and smoothing. Before the cylinder section 6 is aligned with the bottom of the box, the end face of the welding area of ​​the cylinder section 6 and the end face of the welding area of ​​the bottom of the box are milled and smoothed by the milling shaft of the equipment. After milling, the end face of the welding area of ​​the cylinder section 6 and the bottom of the box are 25~30mm away from the pressure plates of the upper and lower clamping ring mechanism, respectively. Aluminum chips are cleaned and the oxide film of the welding area is polished.

[0070] S9. Align the detachable inner support mechanism 2 with the weld center using a marking method. Using the end face of the welded section as a reference, mark a complete assembly position line around the inner surface of the welded area at a distance of 45mm from the end face. Figure 8 At point B, the upper clamping ring mechanism descends synchronously with the cylinder section, aligning and verifying the mating surfaces of the cylinder section and the bottom of the box. The mating gap is measured and can be controlled within 0.3mm. By controlling the lifting mechanism of the mandrel of the bottom loading mechanism, the axial height of the detachable inner support mechanism 2 is adjusted to align the upper surface of the welding pad with the assembly position line of the inner surface of the welding area of ​​the cylinder section, thereby aligning the center of the welding pad with the center of the weld.

[0071] S10. Adjust the length of the outer support block support rod 25 to symmetrically extend the outer support blocks 28. Use the scale 24 to ensure that the extension amount of each outer support block 28 is consistent. At this time, the extension diameter D of the outer support block 28 is the inner surface diameter D1 of the bottom welding area. Extend the inner support block 27. Because the inner support block 27 will be squeezed and hindered by the outer support block 28 before reaching the target support position, the support force needs to be increased to ensure that it is extended in place. Use the set spiral force-adding push rod 23 to extend the inner support block 27 symmetrically. Use the scale 24 to ensure that the extension amount of each inner support block 27 is consistent. At this time, the extension diameter D of the inner support block 27 is also the inner surface diameter D1 of the bottom welding area. The tightening bolts 211 on both sides of the inner support block 27 are pushed out evenly, and the outer support block 28 continues to move outward along the slide between the support blocks to tighten. The spiral force-adding push rod 23 of the inner support block is adjusted synchronously so that the inner support block 27 moves outward synchronously until the diameter of the inner surface of the storage tank is increased by 2mm. After being stretched out, the diameter of the inner and outer support blocks is D=D1+2. The gap between the support block pad 210 and the inner surface of the storage tank can be controlled within 0.2mm.

[0072] S12. Simultaneously reduce the clamping diameter of the upper and lower clamping rings by 0.5mm, with the clamping direction being... Figure 8 The arrow at point C further eliminates the gap between the welding backing plate 210 and the tank and the misalignment of the weld assembly. After assembly using this method, the roundness of the tank welding area can be controlled within ±0.8mm, the misalignment can be controlled within 0.5mm, and the overall gap between the welding backing plate 210 and the inner surface of the tank can be controlled within 0.1mm, with a local gap not exceeding 0.2mm.

[0073] The 5m diameter, thick sealing ring seam precision assembly technology in vertical mode achieves strong rigidity assembly and tightening of the sealing ring seam. After assembly, the radial expansion of the tank welding area can be increased by 2mm. The assembly roundness is ≤±0.8mm, the butt gap is ≤0.3mm, the assembly misalignment is ≤0.5mm, and the tire gap is ≤0.2mm. The assembly qualification rate is increased to 100%.

[0074] For the sealing circumferential seam of a storage tank with a diameter of 5m and a weld zone thickness of 20mm, the large diameter and thickness of the tank make the removal and repair of defects more difficult than for existing tank models. Therefore, it is essential to maximize the circumferential seam welding pass rate and ensure that the weld passes on the first attempt. To address these issues, this solution proposes a defect control approach for friction stir welding, combining primary tack welding, deep tack welding, pre-welding, and retraction welding. This approach aims to reduce internal weld defects and achieve the goal of passing the weld on the first attempt.

[0075] Methods for controlling defects in the friction stir welding of the circumferential seam of a 5m diameter storage tank, such as... Figures 9 to 13 As shown, it includes the following steps:

[0076] T1. The first positioning weld includes segmented positioning welds and full-circumference positioning welds. Segmented positioning welds are performed first, using a positioning stirring head with a needle length of 2-3mm. 8-12 segments are welded, each with a weld length of 300-400mm. Areas with misaligned assembly are given special attention, and areas with poor assembly quality are fixed to prevent deterioration during subsequent welding. Then, full-circumference positioning welds are performed, using the same stirring head as the segmented positioning welds, with a welding angle of 358°. A 2° margin is left unwelded for positioning during near-thinning friction stir welding with a retractable stirring needle, initially fixing the assembly state of the entire circumferential seam.

[0077] T2. Perform deep positioning welding using a positioning stirring head with a needle length of 8-10mm to further fix the assembly state, enhance the strength of the weld joint, improve the weld's resistance to strong upsetting force, and prevent the weld from opening during the pre-welding process.

[0078] T3. Pre-welding is performed. The shoulder of the stirring head adopts an Archimedean spiral as its structural curve, which can improve the convergence effect of the shoulder structure on the plastic metal and the stability of the welding process. This reduces the adverse effects of assembly gaps and misalignment on weld quality. The length of the stirring head needle is 0.3~0.5mm less than the actual thickness of the welding area. During the welding process, the weld can be tightly fitted with the rigid support on the back under the action of the spindle upsetting force, eliminating the phenomenon of non-fitting between the two. This allows the weld between the stirring head and the backing plate to form a complete closed extrusion mold and achieve a certain degree of penetration. Due to the influence of the assembly state, this process may produce welding defects inside the weld.

[0079] T4. Retractable welding utilizes a retractable stirring head. At the end of the welding process, the stirring pin retracts at a uniform speed, eliminating keyhole defects. The shoulder diameter of the retractable stirring head is 1-2 mm larger than that of the pre-welding stirring head, allowing burrs generated during pre-welding to be re-incorporated into the weld, reducing base metal loss. During the retractable welding stage, the weld and rigid support plate achieve a tight fit, resulting in a better assembly condition than during pre-welding. Therefore, the retractable stirring welding stage eliminates internal weld defects generated during pre-welding, yielding a complete, near-defect-free weld and achieving a successful weld in one pass.

[0080] In vertical mode, a defect control technology for 5m diameter and thick sealing box circumferential seam friction stir welding is proposed. The defect control approach of friction stir welding is proposed, which includes one-time positioning welding + deep positioning welding + pre-welding + retraction welding. This reduces the generation of internal defects in the weld and increases the weld pass rate to 100%.

[0081] This patent represents a breakthrough from scratch in the precise assembly and control process of the internal support of the detachable interlocking structure of the sealing ring seam of the vertical mode of the 5m diameter ultra-long and thick common bottom tank of my country's new generation of carrier rockets. It also provides an effective solution for achieving efficient and high-quality friction stir welding production of the sealing ring seam of the 5m diameter tank.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

A flexible assembly method for friction stir welding of the circumferential seam of a 1.5m diameter storage tank, characterized by: Includes the following steps: S1. Calculate the diameter of the inner surface of the welding area at the bottom of the box; S2. Hoist the bottom assembly of the tank assembly downwards to the bottom loading mechanism and measure the assembly gap between the tank and the support ring connection surface. S3. The auxiliary operation platform is assembled under the frame and hoisted into the bottom of the box; S4. Assemble a detachable inner support mechanism under the frame, and ensure that both the inner and outer support blocks are in a retracted state; S5. After the detachable inner support mechanism and mandrel are assembled under the frame, they are hoisted to the bottom loading mechanism of the box as a whole and positioned for assembly. S6. An umbrella-shaped support leveling method is adopted to keep the inner and outer support blocks of the detachable inner support mechanism level as a whole. S7. The bottom feeding mechanism pushes the bottom of the box and the inner support mechanism into the ring clamping mechanism, and enters the welding position. S8. The gap between weld joints is controlled by milling and smoothing method; S9. Use the engraving marking method to align the detachable internal support mechanism with the weld center. S10. Extend the support block until the diameter of the inner surface of the storage tank is increased by 2mm. S11. Eliminate the gap between the welding backing plate and the product, and the misalignment of the weld assembly; An auxiliary operating platform is used to allow operators to install and debug the detachable internal support mechanism inside the tank in vertical mode. The auxiliary operating platform is assembled under the frame and then hoisted to the working position as a whole. After welding is completed, it is disassembled into parts inside the tank and transported out of the tank through the manhole flange. The auxiliary operating platform consists of several profile frames and several foldable aluminum cover plates, which are staggered to form a ring structure. A support rod is installed in the middle of the bottom of each profile frame, and a support plate is installed at the other end of the support rod. Several support plates form a ring structure. Each profile frame is equipped with feet for height adjustment. The contact part between the feet and the inner surface of the tank bottom is made of rubber material, and the shape of the feet is a contoured arc surface.

2. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: The method for calculating the inner surface diameter of the bottom welding area in S1 is as follows: measure the outer surface circumference L1 of the bottom welding area and the outer surface circumference L2 of the cylindrical section welding area, and the thickness δ of the bottom welding area. During the cylindrical section welding process, by controlling the blanking size of the wall panel, L2 is made 3~5mm smaller than L1. Therefore, when assembling and welding the vertical sealing box circumferential seam, the bottom welding area size data is used as the support assembly reference to calculate the inner surface diameter D1 of the bottom welding area, i.e., D1=L1 / π-2δ.

3. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: The detachable inner support mechanism in S4 includes an inner support mandrel and support blocks. The first end of the inner support mandrel is circumferentially hinged to 24 supporting square beams. A leveling support rod is movably installed below each supporting square beam. The other ends of several leveling support rods are circumferentially hinged to the second end of the inner support mandrel. A scale is provided above each supporting square beam, indicating the support capacity of the support blocks. A horizontal tensioner is installed between two adjacent supporting square beams. A support block is fixedly installed at the end of each supporting square beam, and each support block has a support block at its outer edge. It is equipped with a welding backing plate, and the support blocks are divided into inner support blocks and outer support blocks, which are staggered. Each support block is equipped with a guide plate at the bottom. A spiral force-adding push rod is installed above the support beam connecting the inner support block, and the spiral force-adding push rod is fixedly connected to the inner support block. Several tightening bolts are also installed on each inner support block, and the force-applying position of the tightening bolts is on the load-bearing protrusion of the outer support block. The outer support block and the inner support mandrel are also connected by the outer support block support rod, and the 12 outer support block support rods are circumferentially hinged to the inner support mandrel.

4. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: The specific method for controlling the weld gap using the milling and smoothing method in S8 is as follows: Before the cylinder section and the bottom of the box are joined, the end face of the welding area of ​​the cylinder section and the end face of the welding area of ​​the bottom of the box are milled and smoothed using the milling shaft of the equipment. After milling, the end face of the welding area of ​​the cylinder section and the bottom of the box are 25~30mm away from the pressure plates of the upper and lower clamping ring mechanism, respectively. Aluminum chips are cleaned and the oxide film in the welding area is polished.

5. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: The method for aligning the detachable inner support mechanism with the weld center using the engraving marking method in S9 is as follows: Taking the end face of the welding area of ​​the cylinder section as a reference, a full circle of assembly position lines is drawn on the inner surface of the welding area at a distance of 45mm from the end face. The upper clamping ring mechanism descends synchronously with the cylinder section to align and verify the cylinder section with the bottom of the box. The joint gap is measured and can be controlled within 0.3mm. By controlling the lifting mechanism of the mandrel of the bottom loading mechanism, the axial height of the detachable inner support mechanism is adjusted so that the upper surface of the welding pad is aligned with the assembly position line on the inner surface of the welding area of ​​the cylinder section, thereby achieving the alignment of the center of the welding pad with the center of the weld.

6. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: The method for extending the support block in S10 until the inner surface diameter of the storage tank is increased by 2mm is as follows: Adjust the length of the outer support block support rod to symmetrically extend the outer support blocks. Use a ruler to ensure that the extension of each outer support block is consistent. At this time, the extension diameter D of the outer support block is the inner surface diameter D1 of the bottom welding area. Similarly, use the set spiral force-adding push rod to symmetrically extend the inner support blocks. Use a ruler to ensure that the extension of each inner support block is consistent. At this time, the extension diameter D of the inner support block is also the inner surface diameter D1 of the bottom welding area. Push out the tightening bolts on both sides of the inner support block evenly. The outer support block continues to move outward along the slide between the support blocks and tightens. Simultaneously adjust the spiral force-adding push rod of the inner support block to make the inner support block move outward synchronously until the inner surface diameter of the storage tank is increased by 2mm. After extension, the extension diameter D of the inner and outer support blocks is D1+2. The gap between the support block pad and the inner surface of the storage tank is controlled within 0.2mm.

7. The flexible assembly method for friction stir welding of the circumferential seam of a 5m diameter storage tank according to claim 1, characterized in that: In S11, the method to eliminate the gap between the pad of the inner support block and the tank and the misalignment of the weld assembly is to simultaneously reduce the clamping diameter of the upper and lower clamping rings by 0.5mm.

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