Friction stir welding device and method for large-curvature thin-wall circular pipe type structure

Abstract

The invention discloses a friction stir welding device for a large-curvature thin-wall round pipe type structure, which comprises a weldment clamping tool, a clamping tool supporting mechanism, a stirring welding main shaft, a stationary shaft shoulder stirring welding stirring head and a filling stirring welding stirring head, and further discloses a using method of the device. According to the method, after the joint surfaces of the two round pipes are welded through friction stir circular seam welding of the stationary shaft shoulder, the end part of the filling rod is reserved in the keyhole for filling by using a filling friction stir welding method to finish welding, the method is a solid-phase welding method, and compared with melting welding methods such as electric arc welding and laser welding, the performance of the welded joint is better.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and relates to a friction stir welding device and method for a large-curvature thin-walled circular tube structure. Background Art

[0002] Pipeline structures are widely distributed in industries such as aerospace, rail transportation, weapons industry, home appliances, construction and shipbuilding. With the rapid development of my country's industrial manufacturing capabilities, lightweight structures, diversified functions and high-quality connection performance in various fields are the inevitable development path to improve product performance. For this reason, lightweight and high-strength alloy materials represented by aluminum alloys are increasingly used in pipelines. Among them, small deformation, near-zero defects and low stress have become the core elements of manufacturing. At present, fusion welding is mostly used in the industry for welding between conduits, but due to the process limitations of fusion welding, there are disadvantages such as poor microstructure and performance of welded joints, large residual stress and deformation, and defects that are easy to occur during the welding process, resulting in a low welding qualification rate for products and high manufacturing costs. At the same time, it also affects the sealing and service life of the pipeline structure.

[0003] Friction stir welding is a new solid-phase connection technology. Compared with traditional welding methods, this method has the advantages of low welding heat input, high joint strength coefficient, small welding deformation, simple pre-welding cleaning, and no need for protective gas and welding wire. It is particularly suitable for welding lightweight alloys with poor thermal processing performance such as aluminum alloys and magnesium alloys. However, traditional friction stir welding is only suitable for welding flat plates or large-diameter barrel butt joints. For example, in the patent application with publication number CN 115635260A, a spherical top cover is connected to a special-shaped transition ring and a tunnel flange by annular seam friction stir welding. Due to the large diameter of the weld structure (about 1000mm), the size of the stirring head is smaller than the arc trajectory of the weld, and the joint structure is similar to the flat plate butt joint, and the stirring head has a significant effect on the weld. However, since the weld trajectory of a small-diameter catheter is a large curvature arc shape, the shoulder cannot achieve effective envelopment of the weld surface during the welding process, resulting in overflow of the weld material, making it difficult to form. In addition, due to the rotation of the shaft shoulder, traditional stir friction welding generates a lot of heat, and the weld flash and joint thinning are serious. The flash treatment process after welding is cumbersome, and the joint thinning significantly reduces the bearing capacity of the weldment structure.

[0004] In static shoulder friction stir welding, the shoulder and the stirring needle of the traditional stirring head are designed separately. During the welding process, the stirring needle rotates and penetrates into the weld area of ​​the weldment for stirring welding. The shoulder does not rotate and acts on the weld position with a certain pressure. During the welding process, it slides along the weld with the stirring needle to compact the joint surface material. In this technology, the welding heat input is lower, the weld flash and thinning are small, the joint surface quality is high, and due to the independent characteristics of the shoulder, the shoulder morphology can be changed to adapt to different joint structures, so that the application scope of stirring welding is no longer limited to flat plate and quasi-flat plate butt welding.

[0005] When the friction stir welding is completed, the stirring head is separated from the weldment, leaving a keyhole at the final weld, which reduces the effective width of the weld and is a weak point in the weldment structure. At present, there is a patent document with publication number CN 106342136 B, which uses a stirring head retraction device combined with a retraction stirring head to achieve keyless friction stir welding, but the equipment structure of this method is complex, and the relative movement of the stirring needle and the peripheral structure requires very high processing and control accuracy; there is also a patent application document with publication number CN IO6584038 A, which uses laser cladding additive method to fill the keyhole after expanding the keyhole, but this method is essentially a molten heat treatment, and for some materials with poor welding performance, its mechanical properties are somewhat different from those of the solid phase method. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a friction stir welding device and method for thin-walled circular tube structures with large curvature.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A friction stir welding device for a large curvature thin-walled circular tube structure comprises a weldment clamping tool, a clamping tool support mechanism, a stirring welding spindle, a stationary shoulder stirring welding stirring head, and a filling stirring welding stirring head. The weldment clamping tool is connected to a welding positioner via a positioner turntable, the stirring welding spindle and the clamping tool support mechanism are relatively arranged on both sides of the weld position of the circular tube to be welded, and the stirring welding spindle is connected to a stationary shoulder stirring welding stirring head or a filling stirring welding stirring head.

[0009] As a preferred embodiment, the weldment clamping tool includes a chuck fixing section, an inner support section, an inner support section positioning block, a limit section and a locking nut which are assembled and fixed to the center rod in sequence. The weldment clamping tool also includes a fixing sleeve and an outer pressure hoop sleeve. The inner support section and the limit section are adjustable in axial position along the center rod, and a key block is provided on the center rod.

[0010] Further preferably, outer pressure hoop sleeves are provided on both sides of the circular tube to be welded.

[0011] Further preferably, the chuck fixing section and the limiting section are respectively connected with end fixing blocks.

[0012] As a preferred embodiment, the clamping tool support mechanism includes a strut base, a support, a lifting handwheel, a screw assembly and a roller group assembled in sequence. The upper surface of the strut base is provided with a long waist hole, the position of the support can be adjusted through the long waist hole, the height of the screw assembly is adjusted by rotating the lifting handwheel, and the roller group supports the round tube to be welded.

[0013] As a preferred embodiment, the stationary shoulder stirring welding stirring head includes a stirring needle and a stationary shoulder. The stirring needle penetrates into the joint position of the weldment at a certain rotation speed for stirring welding, and the stationary shoulder envelopes the surface of the arc weld with a certain pressure for forming. The end surface of the stirring needle is distributed with threads and truncated structures, and the end of the stationary shoulder is a curvature arc that matches the outer shape of the circular tube to be welded.

[0014] As a preferred embodiment, the filling stir welding stirring head includes a filling rod, a filling rod sleeve and a support rod. The filling rod sleeve is connected and fixed to the stirring welding main shaft. The end axial hole of the filling rod sleeve is equipped with the filling rod. The end plane of the filling rod sleeve is evenly distributed with spiral groove structures. The end of the filling rod is in the shape of a cone, and the size is consistent with the keyhole of the stirring welding weld after processing.

[0015] The present invention also discloses a method for using a friction stir welding device for a large curvature thin-walled circular tube structure, comprising the following steps:

[0016] S1. Connect the weldment clamping fixture and the positioner turntable, adjust so that the main axis of the welding positioner is coaxial with the center rod height, and tighten them; based on the length and inner diameter of the round tube to be welded, select the corresponding inner support section and end fixing block, and make the middle of the inner support section correspond to the position of the round tube joint to be welded, and then tighten it; insert the round tube to be welded, adjust the position so that the evenly distributed holes on the surface are aligned with the threaded holes of the end fixing block, and then screw it to fix it; tighten the locking nut to make the end face of the round tube joint to be welded fit tightly through the fixed sleeve to limit the section, and fix the external pressure hoop sleeves on both sides of the joint to make the inner wall of the round tube to be welded fit tightly with the inner support section;

[0017] S2. Adjust the position of the support of the clamping fixture support mechanism relative to the support rod base so that the roller group is aligned with the position of the round pipe joint to be welded and screwed and fixed; rotate the lifting handwheel to adjust the height of the screw assembly so that the roller group contacts the outer surface of the welding joint of the round pipe to be welded, and apply a certain force to achieve partial support of the weldment clamping fixture;

[0018] S3, assembling a stirring welding head for a stationary shaft shoulder that matches the outer surface contour of the round tube to be welded with a stirring welding spindle, and adjusting the stirring welding spindle so that the end arc surface of the stationary shaft shoulder corresponds to the joint surface of the round tube to be welded;

[0019] S4, prepare a welding program, so that the stirring welding main shaft and the stationary shoulder stirring welding stirring head act on the joint position of the round pipe to be welded at the set stirring needle rotation speed, welding pressure and a certain inclination angle, and then fix it; after the stirring needle acts at the welding starting position for a short time, the welding positioner and the weldment clamping tool drive the round pipe to be welded to rotate at a certain speed, and the stirring needle and the stationary shoulder continuously act on the welding joint and promote the welding of the joint surfaces of the two round pipes to be welded; after the round pipe to be welded rotates one circle, the welding positioner stops running, and the stirring welding main shaft and the stationary shoulder stirring welding stirring head withdraw from the weld to complete the welding;

[0020] S5. Process the keyhole of the weld after friction stir welding of the stationary shoulder so that its size is consistent with the cone structure at the end of the filling rod of the filling stir welding stirring head;

[0021] S6. Assemble the filling stirring welding stirring head to the stirring welding main shaft, compile the welding program, and make the stirring welding main shaft carry the filling stirring welding stirring head to accurately act on the weld keyhole position with the set rotation speed and downward pressure and then be fixed; after the high-speed rotating filling rod acts on the weld keyhole for a certain period of time, the welding positioner with the weldment clamping tooling drives the round pipe to be welded to rotate a certain angle, so that the softened end of the filling rod remains at the keyhole position for filling.

[0022] When clamping round tube weldments of different sizes, the present invention assembles matching end clamps, internal supports at joints and surface hoop assemblies, wherein the position of the internal supports is axially adjustable based on the weld position to adapt to the welding of round tubes of different lengths; a stationary shaft shoulder and a stirring needle adapted to the arc curvature and wall thickness of the round tube are used to perform friction stir ring welding on the weldment, thereby solving the problems of large differences in organizational properties, large residual stress and deformation, and low welding qualification rate in conventional fusion welding, while also avoiding the disadvantages of difficult welding forming, large weld burrs, poor weld surface quality, and significant thinning of the joint after welding in the welding process of large curvature butt joints caused by traditional stirring welding; a filling rod consistent with the material of the weldment is used, the end of which is processed to be consistent with the size of the keyhole, and the end of the filling rod is left in the keyhole for filling by filling friction stir welding. This method is a solid phase welding method, which has better performance than molten heat treatment, and has a simple structure and low equipment requirements.

[0023] The present invention has the following advantages:

[0024] (1) The present invention adopts the static shoulder friction stir welding technology to weld the large curvature circular pipe circumferential seam, avoiding the disadvantages of poor organizational performance, large residual stress and deformation, and easy defects in the welding process in the fusion welding method. It also avoids the disadvantages of difficult welding forming and significant thinning of the joint after welding in the traditional stirring welding process. It is particularly suitable for welding metals with poor thermal processing properties such as aluminum alloys and magnesium alloys or dissimilar metal joints. (2) The weldment clamping tool of the present invention can realize the clamping of the to-be-welded circular pipe structure with an inner diameter of 50 to 260 mm and a total length of 200 to 1000 mm through the optional accessories such as the inner support section, the end fixing block and the outer pressure hoop sleeve. In the case of lengthening the center rod, it can also clamp longer circular pipe structures, realizing the wide application of the tool. (3) The present invention uses a clamping tool support mechanism with controllable position and screw height to enable the roller group to support the position of the weldment joint, thereby ensuring the normal operation of the welding positioner and the welding process. (4) The present invention adopts a solid phase method of filling stir friction welding to fill the keyhole to complete the closed loop of the welding process. The equipment is simple and the solid phase method is adopted to ensure the strength of the joint. (5) The filling stir welding stirring head of the present invention has a simple structure and adopts a form of combining a filling rod sleeve and a small filling rod. It not only saves materials, but also cooperates with the microstructure of the end of the filling rod sleeve to achieve a better filling effect. In addition, the setting of the support rod can fine-tune the position of the filling rod to adapt to the welding process, and it can also facilitate the separation of the filling rod sleeve and the used filling rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of a friction stir welding device for a large curvature circular tube according to the present invention;

[0026] Figure 2 This is a schematic diagram of the weldment clamping tooling structure;

[0027] Figure 3 It is a schematic diagram of the structure of the clamping tool support mechanism;

[0028] Figure 4 It is a schematic diagram of the assembly of a stationary shoulder stir welding stirring head, a filling stir welding stirring head and a stir welding spindle;

[0029] Figure 5 It is a schematic diagram of the structure of the stirring head for stationary shoulder stirring welding;

[0030] Figure 6 Schematic diagram of the structure of the filling stir welding stirring head.

[0031] In the figure: 1. welding positioner; 2. positioner turntable; 3. round pipe to be welded; 4. weldment clamping fixture; 5. clamping fixture support mechanism; 6. stirring welding spindle; 7. stirring welding head for stationary shoulder; 8. stirring welding head for filling; 4-1. chuck fixing section; 4-2. end fixing block; 4-3. center rod; 4-4. external pressure hoop sleeve; 4-5. inner support section; 4-6. inner support section positioning block; 4-7. key block; 4-8. limiting section; 4-9. fixing sleeve; 4-10. locking nut; 5-1. support rod base; 5-2. support; 5-3. lifting handwheel; 5-4. screw assembly; 5-5. roller group; 7-1. stirring needle; 7-2. stationary shoulder; 8-1. filling rod; 8-2. support rod; 8-3. filling rod sleeve. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Example:

[0035] Taking the friction stir welding of a 2219 aluminum alloy round tube with an outer diameter of 255 mm, a wall thickness of 5 mm, and a length of 250 mm as an example, a friction stir welding device for a large curvature thin-walled round tube structure includes a weldment clamping tool 4, a clamping tool support mechanism 5, a stir welding spindle 6, a stationary shoulder stir welding stirring head 7, and a filling stir welding stirring head 8.

[0036] The weldment clamping tool 4 includes a chuck fixing section 4-1, an inner support section positioning block 4-6, an end fixing block 4-2, an inner support section 4-5, an outer pressure hoop sleeve 4-4, a center rod 4-3, a key block 4-7, a limit section 4-8, a fixing sleeve 4-9 and a locking nut 4-10. The chuck fixing section 4-1 and the center rod 4-3 are tightly screwed to the positioner turntable 2, and the inner support section 4-5 and the limit section 4-8 are adjustable along the axial position of the center rod 4-3 to adapt to the welding of the 250mm length round pipe 3 to be welded. Among them, the inner support section 4-5 can be fixed by the inner support section positioning block 4-6 after the position is determined. The end fixing block 4-2 is screwed and fixed with the chuck fixing section 4-1 and the limiting section 4-8 respectively, and is used for screwing and fastening the non-welding end face of the circular tube 3 to be welded, and limiting the rotational freedom of the weldment relative to the tooling. Its size is selected corresponding to the inner diameter of 245mm of the circular tube 3 to be welded, and cooperates with the inner support section 4-5 with an outer diameter of 245mm and the outer pressure hoop sleeve 4-4 with an inner diameter of 255mm to achieve the welding of the circular tube 3 with an outer diameter of 255mm and a wall thickness of 5mm. The limiting section 4-8 can drive the end face of the joint of the circular tube 3 to be welded to fit closely under the action of the locking nut 4-10 through the fixing sleeve 4-9, and the outer pressure hoop sleeve 4-4 acts on the outer surfaces of both sides of the weld of the circular tube 3 to be welded, so that its inner surface fits closely with the inner support section 4-5, so as to complete the clamping of the circular tube 3 to be welded. After clamping, the welding positioner 1 carries the chuck fixing section 4-1 and the center rod 4-3, and drives the tooling as a whole and the round pipe 3 to be welded to rotate around the axis through the key block 4-7 to perform the welding operation.

[0037] The clamping tool support mechanism 5 includes a support rod base 5-1, a support 5-2, a lifting handwheel 5-3, a screw assembly 5-4 and a roller group 5-5. The clamping tool support mechanism 5 is used to balance the downward pressure applied by the stirring welding spindle 7 to the weld position during welding, to avoid damage to the welding positioner 1 due to welding pressure, and to prevent the center rod 4-3 from bending under force and causing joint misalignment that affects the welding effect. The support rod base 5-1 is placed opposite the welding positioner 1 and fixed, and the remaining components are moved to adapt to the joint position of the 250mm long round tube 3 to be welded through the long waist hole on the upper surface of the support rod base 5-1 by the support 5-2. The screw assembly 5-4 is adjusted in height by rotating the lifting handwheel 5-3 until the roller group 5-5 acts on the joint surface of the round tube 3 to be welded to achieve support.

[0038] The stationary shoulder stirring welding stirring head 7 includes a stirring needle 7-1 and a stationary shoulder 7-2. The stirring needle 7-1 and the stationary shoulder 7-2 are assembled on the stirring welding spindle 6. The stirring needle 7-1 is inserted into the weld joint position at a certain rotation speed for stirring welding, and the stationary shoulder 7-2 is formed by enveloping the arc weld surface with a certain pressure. Among them, the surface of the end of the stirring needle 7-1 is distributed with spiral and truncated structures to increase the material flow at the weld, and the end of the stationary shoulder 7-2 is a curvature arc with a radius of 127.5mm, which can effectively envelop the weld joint during the welding process.

[0039] The filling stir welding stirring head 8 mainly includes a filling rod 8-1, a filling rod sleeve 8-3 and a support rod 8-2. The filling rod 8-1 is made of 2219 aluminum alloy, and the end is in a frustum shape. The size is consistent with the keyhole of the stirring welding weld after processing. By rotating the filling rod 8-1 at high speed, the outer surface of the end of the filling rod 8-1 and the inner surface of the keyhole are solid-phase connected under a certain pressure, and then remain in the hole to achieve the filling effect. The filling rod sleeve 8-3 is connected and fixed to the stirring welding main shaft 6, and the filling rod 8-1 is assembled in the end shaft hole. During the operation, the filling rod sleeve 8-3 rotates and presses down with the filling rod 8-1 to act on the keyhole of the weld. The spiral grooves evenly distributed on the end plane can gather the surface material of the weld to the central axis to enhance the filling effect. The support rod 8-2 can fine-tune the axial position of the filling rod 8-1, and it is convenient to separate the used filling rod 8-1 after the operation is completed to prepare for the next filling operation.

[0040] A method for using a friction stir welding device for a large curvature thin-walled circular tube structure, the implementation process method steps comprising:

[0041] S1: Connect the weldment clamping fixture 4 and the positioner turntable 2, adjust the main axis of the welding positioner 1 to be coaxial with the center rod 4-3, and tighten them. Optional inner support section 4-5 and end fixing block 4-2 with an outer diameter of 245mm. Insert the round tube 3 to be welded, adjust the position so that the holes evenly distributed on its surface are aligned with the threaded holes of the end fixing block 4-2, and screw them in place. Tighten the locking nut 4-10 to act on the limiting section 4-8 through the fixing sleeve 4-9 to make the end face of the joint of the round tube 3 to be welded fit tightly. Fix the outer pressure hoop sleeve 4-4 with an inner diameter of 255mm on both sides of the joint to make the inner wall of the round tube 3 to be welded fit tightly with the inner support section 4-5.

[0042] S2: Adjust the position of the support 5-2 in the clamping fixture support mechanism 5 relative to the support rod base 5-1, so that the roller group corresponds to the joint position of the round pipe 3 to be welded, and screw it in place. Rotate the lifting handwheel 5-3 to adjust the height of the screw assembly 5-4, so that the roller group 5-5 contacts the outer surface of the welding joint of the round pipe 3 to be welded, and exert a certain force to achieve partial support of the weldment clamping fixture 4.

[0043] S3: Assemble the stationary shoulder 7-2 with an end curvature arc radius of 127.5 mm and the stirring needle 7-1 on the stirring welding spindle 6. During the installation process, attention should be paid to the adjustment of the assembly orientation of the stationary shoulder 7 so that the arc surface of the end of the stationary shoulder 7 corresponds to the joint surface of the round tube 3 to be welded.

[0044] S4: Prepare a welding program so that the stirring welding spindle 6 and the stationary shoulder stirring welding stirring head 7 act on the joint position of the circular tube 3 to be welded at the set stirring needle 7-1 rotation speed, welding pressure and a certain inclination angle, and then fix it. After the stirring needle 7-1 acts briefly at the welding starting position, the welding positioner 1 and the weldment clamping fixture 4 drive the circular tube 3 to be welded to rotate at a certain speed, and the positioned stirring needle 7-1 and the stationary shoulder 7-2 continuously act on the welding joint and promote the welding of the joint surfaces of the two circular tubes 3 to be welded. After the circular tube 3 to be welded rotates one circle, the welding positioner 1 stops running, and the stirring welding spindle 6 and the stationary shoulder stirring welding stirring head 7 withdraw from the weld to complete the welding.

[0045] S5: Process the keyhole of the weld after the static shoulder is stir-fried so that its size is consistent with the cone structure at the end of the filling rod 8-1 in the filling stir welding stirring head 8.

[0046] S6: Assemble the filling stirring welding stirring head 8 on the stirring welding main shaft 6, and the filling rod is made of 2219 aluminum alloy. Prepare a welding program so that the stirring welding main shaft 6 and the filling stirring welding stirring head 8 can accurately act on the keyhole position of the weld with the set rotation speed and downward pressure and then be fixed. After the high-speed rotating filling rod 8-1 acts on the weld keyhole for a certain period of time, the welding positioner 1 and the weldment clamping fixture 4 drive the round tube 3 to be welded to rotate a certain angle, so that the softened end of the filling rod 8-1 remains at the keyhole position for filling. Finally, the weld is processed as a whole after welding, and the through holes are evenly distributed on both end faces of the round tube are cut off to complete the entire welding process.

[0047] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A friction stir welding device for thin-walled circular tubes with large curvature, characterized in that: It includes a weldment clamping tool, a clamping tool supporting mechanism, a stirring welding spindle, a stationary shoulder stirring welding stirring head, and a filling stirring welding stirring head. The weldment clamping tool is connected to the welding positioner through a positioner turntable. The stirring welding spindle and the clamping tool supporting mechanism are relatively arranged on both sides of the weld position of the circular pipe to be welded. The stirring welding spindle is connected to a stationary shoulder stirring welding stirring head or a filling stirring welding stirring head.

2. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 1, characterized in that: The weldment clamping tooling includes a chuck fixing section, an inner support section, an inner support section positioning block, a limit section and a locking nut which are assembled and fixed to the center rod in sequence. The weldment clamping tooling also includes a fixing sleeve and an outer pressure hoop sleeve. The inner support section and the limit section are adjustable in axial position along the center rod, and a key block is provided on the center rod.

3. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 2, characterized in that: External pressure hoop sleeves are arranged on both sides of the circular pipe to be welded.

4. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 2, characterized in that: The chuck fixing section and the limiting section are respectively connected with end fixing blocks.

5. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 1, characterized in that: The clamping tool support mechanism includes a support rod base, a support, a lifting handwheel, a screw assembly and a roller group assembled in sequence. The upper surface of the support rod base is provided with a long waist hole, the support can be adjusted through the long waist hole, the screw assembly is adjusted in height by rotating the lifting handwheel, and the roller group supports the round pipe to be welded.

6. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 1, characterized in that: The stationary shoulder stirring welding stirring head comprises a stirring needle and a stationary shoulder. The stirring needle penetrates into the weld joint position at a certain rotation speed for stirring welding, and the stationary shoulder envelopes the arc weld surface with a certain pressure for forming. The end surface of the stirring needle is distributed with threads and a truncated structure, and the end of the stationary shoulder is a curvature arc that matches the outer shape of the circular tube to be welded.

7. The friction stir welding device for thin-walled circular tubes with large curvature according to claim 1, characterized in that: The filling stirring welding stirring head includes a filling rod, a filling rod sleeve and a supporting rod. The filling rod sleeve is connected and fixed to the stirring welding main shaft. The end axial hole of the filling rod sleeve is equipped with the filling rod. The end plane of the filling rod sleeve is evenly distributed with spiral groove structures. The end of the filling rod is in a frustum shape, and the size is consistent with the keyhole of the stirring welding weld after processing.

8. A method for using the friction stir welding device for thin-walled circular tube structures with large curvature according to any one of claims 1 to 7, characterized in that: The steps include: S1. Connect the weldment clamping fixture and the positioner turntable, adjust so that the main axis of the welding positioner is coaxial with the center rod height, and tighten them; based on the length and inner diameter of the round tube to be welded, select the corresponding inner support section and end fixing block, and make the middle of the inner support section correspond to the position of the round tube joint to be welded, and then tighten it; insert the round tube to be welded, adjust the position so that the evenly distributed holes on the surface are aligned with the threaded holes of the end fixing block, and then screw it to fix it; tighten the locking nut to make the end face of the round tube joint to be welded fit tightly through the fixed sleeve to limit the section, and fix the external pressure hoop sleeves on both sides of the joint to make the inner wall of the round tube to be welded fit tightly with the inner support section; S2. Adjust the position of the support of the clamping fixture support mechanism relative to the support rod base so that the roller group is aligned with the position of the round pipe joint to be welded and screwed and fixed; rotate the lifting handwheel to adjust the height of the screw assembly so that the roller group contacts the outer surface of the welding joint of the round pipe to be welded, and apply a certain force to achieve partial support of the weldment clamping fixture; S3, assembling a stirring welding head for a stationary shaft shoulder that matches the outer surface contour of the round tube to be welded with a stirring welding spindle, and adjusting the stirring welding spindle so that the end arc surface of the stationary shaft shoulder corresponds to the joint surface of the round tube to be welded; S4, prepare a welding program, so that the stirring welding main shaft and the stationary shoulder stirring welding stirring head act on the joint position of the round pipe to be welded at the set stirring needle rotation speed, welding pressure and a certain inclination angle, and then fix it; after the stirring needle acts at the welding starting position for a short time, the welding positioner and the weldment clamping tool drive the round pipe to be welded to rotate at a certain speed, and the stirring needle and the stationary shoulder continuously act on the welding joint and promote the welding of the joint surfaces of the two round pipes to be welded; after the round pipe to be welded rotates one circle, the welding positioner stops running, and the stirring welding main shaft and the stationary shoulder stirring welding stirring head withdraw from the weld to complete the welding; S5. Process the keyhole of the weld after friction stir welding of the stationary shoulder so that its size is consistent with the cone structure at the end of the filling rod of the filling stir welding stirring head; S6. Assemble the filling stirring welding stirring head to the stirring welding main shaft, compile the welding program, and make the stirring welding main shaft carry the filling stirring welding stirring head to accurately act on the weld keyhole position with the set rotation speed and downward pressure and then be fixed; after the high-speed rotating filling rod acts on the weld keyhole for a certain period of time, the welding positioner with the weldment clamping tooling drives the round pipe to be welded to rotate a certain angle, so that the softened end of the filling rod remains at the keyhole position for filling.

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