Vacuum box type friction stir welding tailor-welding tool and welding process

Abstract

The invention relates to the technical field of vacuum box manufacturing, and particularly discloses a vacuum box type friction stir welding tailor-welding tool and a welding process, and the vacuum box type friction stir welding tailor-welding tool comprises a basic splicing part, a mortise and tenon joint positioning structure, a tool locking assembly and an auxiliary function part. According to the vacuum box type friction stir welding tailor-welding tool, precise assembly with the plate gap smaller than or equal to 0.1 mm is achieved through mortise and tenon joint matching of the boss and the groove, by combining staged welding and special tool rigid constraint, a parameterization friction stir welding process is adopted for completing all-round sealing weld joints, and air tightness is verified through 1.5 MPa nitrogen water immersion detection. The problems of aging of traditional fusion welding air holes and sealing strips and waste of overall machining materials can be effectively solved, and the welding quality and the material utilization rate are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of vacuum chamber manufacturing technology, and in particular to a friction stir welding fixture and welding process for vacuum chambers. Background Technology

[0002] Aluminum alloys, due to their lightweight, high strength, excellent corrosion resistance, and fatigue resistance, have been widely used in aerospace, rail transportation, electronic equipment, and high-end manufacturing, especially in vacuum chamber components where strict requirements for structural weight and sealing performance exist, where they hold irreplaceable advantages. However, under traditional fusion welding processes, aluminum alloy welding requires the addition of additional solder and is prone to metallurgical defects such as porosity and pinholes, resulting in irregular weld formation, difficulty in controlling penetration depth, and concentrated welding heat input leading to high residual stress and severe deformation, making it difficult to meet the manufacturing requirements of high-airtightness vacuum structures. Furthermore, the mainstream manufacturing methods for existing vacuum sealing chambers still have significant limitations: while splicing fusion welding can achieve overall connection, the aforementioned welding defects make it difficult to guarantee long-term reliable airtightness; while using screw connections with sealing strips facilitates assembly, the sealing materials are prone to aging and are not resistant to high temperatures, making them unsuitable for harsh working conditions; and while overall machining can achieve a good sealing surface, it is limited by tool accessibility, making it difficult to process complex internal cavity structures, and the utilization rate of raw materials is low and the cost is high, often requiring a secondary welding and sealing of the final surface, which introduces new leakage risks.

[0003] Friction stir welding (FSW), as a solid-state joining technology, utilizes frictional heat generated between the stirring head and the workpiece to bring the material to a thermoplastic state, achieving high-quality connections without melting the base material. It boasts significant advantages such as no porosity, no cracks, low deformation, high repeatability, and no need for filler material, making it particularly suitable for manufacturing aluminum alloy vacuum chambers with stringent requirements for airtightness and structural integrity. However, applying FSW to multi-plate assembled chamber structures presents key challenges: ensuring precise alignment and tight fit of each plate during welding to avoid welding defects caused by gaps or misalignments; and existing tooling, mostly designed for flat plate butt joints, is ill-suited for the assembly and welding requirements of three-dimensional mortise and tenon structures like chambers, lacking effective constraints and positioning mechanisms for complex joint types. Therefore, there is an urgent need to develop a dedicated FSW welding tooling and supporting process for vacuum chamber components. Through reasonable structural design and process control, high-precision positioning, stable clamping, and reliable welding can be achieved, fully realizing the technological potential of FSW in the manufacturing of high-airtightness structures while also saving materials and improving production efficiency. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a vacuum chamber-type friction stir welding fixture and welding process. Through tenon and mortise positioning and rigid fixture constraints, high-precision assembly and low-deformation welding are achieved, solving the defects of traditional processes.

[0005] The technical solution of the present invention is as follows:

[0006] On one hand, a vacuum chamber-type friction stir welding fixture is provided, including basic splicing components, tenon and mortise positioning structures, fixture locking components, and auxiliary functional components. Through modular structural design and staged welding processes, a high-airtightness aluminum alloy vacuum chamber is integrally formed. The basic splicing components consist of a middle partition, side frames, an upper cover plate, and a lower cover plate. The tenon and mortise positioning structure achieves controllable micro-gap assembly with a plate joint gap not exceeding 0.1mm through the geometric fit of bosses and grooves. The fixture locking components provide rigid constraints during welding through a mechanical connection of countersunk holes and threaded holes. The auxiliary functional components include pressure testing process holes and a full-circumference continuous welding path for welding quality verification and sealing integrity assurance.

[0007] Furthermore, the intermediate partition is symmetrically provided with first bosses at both ends. The height and width of the first bosses are both equal to 0.5 times the diameter of the friction stir welding needle adapted to the vacuum chamber-type friction stir welding fixture. The intermediate partition is provided with first threaded holes on both sides for connection with the side frame welding fixture. The inner side of the side frame is provided with a first groove matching the first boss. The depth and width of the first groove are increased by 0.05mm on each side based on the corresponding size of the first boss, forming a clearance fit. The side frame is provided with a second boss in the thickness direction. The height and width of the second boss are also equal to 0.5 times the diameter of the friction stir welding needle adapted to the vacuum chamber-type friction stir welding fixture. The inner sides of the upper cover plate and the lower cover plate are provided with second grooves. The depth and width of the second grooves are increased by 0.05mm on each side based on the size of the second boss, forming a longitudinal clearance fit. The outer edges of the upper cover plate and the lower cover plate are distributed with second countersunk holes for connection with the upper and lower cover plate welding fixtures.

[0008] Specifically, the first boss and the first groove form a transverse tenon-and-mortise positioning structure for precise alignment of the middle partition and the side frame in the horizontal plane; the second boss and the second groove form a longitudinal tenon-and-mortise positioning structure for precise vertical positioning of the side frame, the upper cover plate, and the lower cover plate. The dimensional tolerances of the aforementioned bosses and grooves are controlled within ±0.02mm, and the joint gap after assembly does not exceed 0.1mm to meet the assembly accuracy requirements of friction stir welding.

[0009] The side frame welding fixture has a first countersunk hole, which corresponds to the first threaded hole on the middle partition. A countersunk head screw passes through the first countersunk hole and is screwed into the first threaded hole to press and fix the middle partition to the side frame. The upper and lower cover plate welding fixture has a second threaded hole on its side, which corresponds to the second countersunk holes on the upper and lower cover plates. A countersunk head screw passes through the second countersunk hole and is screwed into the second threaded hole to press and fix the upper and lower cover plates to the side frame. The diameter of the countersunk head screw is determined according to the plate thickness, satisfying the relationship: countersunk head screw diameter × 1.5 ≤ plate thickness ≤ countersunk head screw diameter × 2.0, applicable specifications are M3 to M6.

[0010] Furthermore, the friction stir welding path is continuously set along all the tenon and mortise joints, including four transverse joints between the middle partition and the side frame, and eight longitudinal joints between the side frame and the upper and lower cover plates, forming a closed box outline. The diameter of the welding pin is set to twice the height of the corresponding boss, and the specific selection is determined according to the type of base material: For 6061 and 6063 aluminum alloys, use T3-8W or T3-10C welding pins, with a rotation speed of 1300–1500 rpm, a feed rate of 300–350 mm / min, and a deflection of 0.2 mm; for 5A06 aluminum alloys, use T3-8W, T3-10C, or T3.5-9 welding pins, with a rotation speed of 1200–1600 rpm, a feed rate of 300–350 mm / min, and a deflection of 0.2 mm; for 5A06 / ADC12 dissimilar material butt welding, place ADC12 on the forward side, use T3-8W or T3-10C welding pins, with a rotation speed of 1300–1500 rpm, a feed rate of 300–350 mm / min, and a deflection of 0.2 mm; mm / min, pressing amount 0.2mm; for conventional 2-series, 3-series, 5-series, and 6-series aluminum alloy thick plates, T7-16 welding needles are selected, with a rotation speed of 1100 rpm, a feed speed of 300mm / min, and a pressing amount of 0.3mm.

[0011] The present invention also provides a friction stir welding process based on the above-mentioned welding fixture, specifically including the following steps:

[0012] S1: Perform CNC milling on the middle partition plate to symmetrically machine the first bosses at both ends and drill the first threaded holes on both sides; at the same time, mill the side frame to machine the first groove matching the first bosses on its inner side.

[0013] S2: Fabricate a side frame welding fixture and machine multiple first countersunk holes on its surface that correspond to the positions of the first threaded holes;

[0014] S3: Insert the first boss of the middle partition into the first groove of the side frame to complete the lateral tenon and tenon positioning; then cover the outside of the assembly with the side frame welding fixture, use the internal hexagon countersunk screw to pass through the first countersunk hole and screw into the first threaded hole, apply pre-tightening force to make the middle partition and the side frame fit tightly.

[0015] S4: Use friction stir welding equipment to weld along the joint between the middle partition and the side frame. The diameter of the welding needle is not less than twice the height of the first boss. The welding parameters are selected from the preset process parameter table according to the base material grade to ensure that the weld nugget is fully plasticized and fills the joint area.

[0016] S5: After welding is completed, remove the side frame welding fixture, and keep the middle partition and side frame assembly that have been welded together.

[0017] S6: Perform CNC milling on the upper and lower cover plates to machine a second groove on their inner side and drill a second countersunk hole around the outer edge;

[0018] S7: Perform secondary milling on the welded side frame assembly in its thickness direction to process a second boss. The height and width of the second boss are equal to 0.5 times the diameter of the friction stir welding needle adapted to the vacuum chamber type friction stir welding tool.

[0019] S8: Make a welding fixture for the upper and lower cover plates, and machine a second threaded hole on its side, the position of which corresponds to the second countersunk hole of the upper and lower cover plates.

[0020] S9: Fit the second grooves of the upper cover plate and the lower cover plate into the second protrusion of the side frame respectively to complete the longitudinal tenon and mortise positioning; then install the upper and lower cover plate welding fixture on the outside of the box, use the internal hex countersunk screw to pass through the second countersunk hole and screw into the second threaded hole to lock the upper cover plate, lower cover plate and side frame.

[0021] S10: Continuous welding is carried out along the full circumferential joint between the side frame and the upper and lower cover plates using friction stir welding equipment. The welding path covers all longitudinal joints to form a closed and sealed structure.

[0022] S11: After welding is completed, remove the welding fixtures for the upper and lower cover plates;

[0023] S12: Perform precision milling on the outer surface of the enclosure to remove countersunk hole marks left by the installation fixtures, making the surface smooth; then drill pressure test process holes in non-critical areas of the enclosure.

[0024] S13: Perform an airtightness test on the finished box: Fill the inner cavity of the box with nitrogen through the pressure test process hole to a gauge pressure of 1.5 MPa, immerse the entire box completely in the water tank, and maintain the pressure for 30 minutes. If no air bubbles escape, the box is deemed to be airtight.

[0025] In S4 and S10, the welding process adopts a constant pressure control strategy, with the pressure set to 0.2 mm or 0.3 mm. The specific value depends on the welding needle model and the thickness of the base material. At the beginning of the welding process, the needle lowering procedure is executed: the Z-axis descends to the set depth at a speed of F30 mm / min and then pauses for 3 seconds to allow the material to be fully preheated. At the end of the welding process, the needle lifting procedure is executed: the Z-axis is first raised by 0.5–1.0 mm and then quickly lifted away from the weld to avoid keyhole defects.

[0026] Furthermore, the tenon and mortise positioning structure is not limited to a rectangular cross-section; it can also employ a cylindrical boss and an annular groove, a trapezoidal boss and a matching groove, or a polygonal irregular structure, as long as the boss and groove can restrict the relative displacement of the sheet metal in three translational degrees of freedom after assembly, and the welding gap is controlled within 0.1 mm. The tooling locking assembly can also use hydraulic clamps, pneumatic pressure plates, or electromagnetic chucks to replace mechanical screw connections, but it must ensure that the clamping force provided during friction stir welding is sufficient to resist the axial force and lateral disturbance force generated by the welding spindle, preventing the sheet metal from warping or separating.

[0027] Specifically, the diameter of the pressure test process hole is Φ6–Φ10 mm, located in the non-stressed area on the top or side of the chamber, and the hole opening is equipped with a conical sealing structure to connect the airtight test connector; after the test is completed, the hole can be sealed by welding or threaded plug, without affecting the overall sealing performance of the chamber.

[0028] Compared with existing technologies, the present invention achieves the following beneficial effects:

[0029] 1. This invention controls the assembly gap of the plates to within 0.1 mm through the tenon and mortise positioning structure, avoiding defects such as incomplete penetration or flash caused by excessive gap during friction stir welding.

[0030] 2. The present invention first completes the connection between the side frame and the middle partition through a phased welding process, and then welds the upper and lower cover plates, which effectively reduces the superposition of welding residual stress and reduces overall deformation.

[0031] 3. This invention provides rigid support during the welding process through a special welding fixture, resisting the thermal-mechanical coupling effect generated by the rotation of the stirring head and the feed, ensuring the stability of the weld trajectory. At the same time, the rigid fixture effectively controls welding deformation, solving the problem of deformation in traditional fusion welding.

[0032] 4. This invention uses a design that correlates the diameter of the welding needle with the size of the boss, with the boss height being 0.5 × the diameter of the welding needle. This design ensures that the shoulder of the welding needle can completely cover the joint area, guaranteeing uniform heat input and sufficient plasticization of the weld nugget.

[0033] 5. The present invention uses a 1.5 MPa nitrogen water immersion method for airtightness testing. This pressure value is higher than the requirements of conventional vacuum applications, which verifies the sealing reliability of the weld under extreme conditions.

[0034] 6. Compared with the overall machining solution, the present invention increases the material utilization rate from less than 30% to 60%-80%, significantly reduces the cost of raw materials, and avoids the internal cavity structure being limited by the accessibility of the cutting tool.

[0035] In summary, this invention, through the synergistic effect of precise geometric positioning, rigid tooling constraints, and parametric welding processes, solves the technical challenges of positioning deviations, gap loss, welding defects, and insufficient airtightness in the splicing of aluminum alloy vacuum chambers using friction stir welding, providing a highly reliable manufacturing solution that can be industrially implemented. Compared to overall machining solutions, this invention increases material utilization from less than 30% to 60%–80%, significantly reducing raw material costs. The solid-state connection achieved through friction stir welding requires no additional solder, avoiding the risk of aging. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the milling process before friction stir welding of the middle partition plate and the side frame;

[0037] Figure 2 for Figure 1 A magnified view of a section at point A in the middle;

[0038] Figure 3 This is a schematic diagram showing the positional relationship between the middle partition and the side frame after assembly, as well as the structural diagram of the side frame welding fixture.

[0039] Figure 4 This is a schematic diagram showing the positional relationship between the side frames and the welding fixture after assembly.

[0040] Figure 5 This is a schematic diagram of the welding path for friction stir welding of the side frame;

[0041] Figure 6 A schematic diagram of the structure for removing the welding fixture for the side frame after friction stir welding of the side frame;

[0042] Figure 7 This is a schematic diagram of the milling process before friction stir welding of the upper and lower cover plates.

[0043] Figure 8 for Figure 7 A magnified view of a section at point B in the middle;

[0044] Figure 9 This is a schematic diagram of the milling process for the boss in the thickness direction of the side frame;

[0045] Figure 10 for Figure 9A magnified view of a section at point C;

[0046] Figure 11 A schematic diagram showing the structure of the welding fixture for the upper and lower cover plates and its positional relationship with the upper cover plate, lower cover plate, and side frame before assembly.

[0047] Figure 12 A schematic diagram showing the positional relationship between the welding fixture for the upper and lower cover plates and the upper cover plate, lower cover plate, and side frame after assembly.

[0048] Figure 13 This is a schematic diagram of the welding path for friction stir welding of the upper cover plate, lower cover plate, and side frame;

[0049] Figure 14 This is a structural diagram showing the structure after the welding fixtures for the upper and lower cover plates have been removed.

[0050] Figure 15 A schematic diagram of the finished structure of a vacuum sealing box after milling to remove the countersunk holes;

[0051] Figure 16 This is a cross-sectional schematic diagram of the internal structure of a vacuum sealing box;

[0052] Figure 17 This is a schematic diagram of the structure in Example 2 where a cylindrical boss and an annular groove are provided on the plate surface;

[0053] Figure 18 This is a schematic diagram of the structure in Example 3 where polygonal irregular bosses and polygonal irregular grooves are provided on the plate surface.

[0054] In the above figures, the components are labeled as follows:

[0055] 1. Middle partition plate; 2. First boss; 3. First threaded hole; 4. Side frame; 5. First groove; 6. Second boss; 7. Side frame welding fixture; 8. First countersunk hole; 9. Screw; 10. Top cover plate; 11. Second groove; 12. Second countersunk hole; 13. Bottom cover plate; 14. Upper and lower cover plate welding fixture; 15. Second threaded hole; 16. Pressure test process hole; 17. Friction stir welding path; 18. Finished vacuum sealing box. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of the invention; it is merely illustrative. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. Unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.

[0057] Example 1

[0058] This embodiment takes the manufacture of a vacuum-sealed box made of 6061 aluminum alloy plates as an example. Its overall structure consists of a middle partition 1, a side frame 4, an upper cover plate 10 and a lower cover plate 13. The solid connection of the four-sided tenon joints is completed by two-stage friction stir welding, and high-precision positioning and rigid clamping are achieved with the help of special tooling.

[0059] First, refer to Figure 1 and Figure 2 The intermediate partition 1 is CNC milled to symmetrically machine first bosses 2 at both ends. Each boss has a height and width of 3.5 mm, corresponding to half the 7 mm diameter of the selected T7-16 welding pin. Simultaneously, M5 threaded holes 3 are drilled on both sides of the intermediate partition 1 for subsequent installation of the side frame welding fixture 7. Simultaneously, the inner side of the side frame 4 is milled to machine a first groove 5 matching the first bosses 2. The groove 5 has a depth of 3.55 mm and a width of 3.6 mm, which is 0.05 mm larger on each side than the boss dimensions, forming a clearance fit. This ensures that the joint gap after assembly is controlled within 0.1 mm, meeting the assembly precision requirements of friction stir welding.

[0060] Subsequently, as Figure 3 and Figure 4 As shown, a side frame welding fixture 7 is fabricated, and multiple first countersunk holes 8 are machined on its surface, with their positions corresponding one-to-one with the first threaded holes 3 on the middle partition plate 1. The first boss 2 of the middle partition plate 1 is embedded into the first groove 5 of the side frame 4 to complete the lateral tenon and tenon positioning. Then, the side frame welding fixture 7 is covered on the outside of the assembly, and an M5 hexagon countersunk screw 9 is used to pass through the first countersunk holes 8 and screw into the first threaded holes 3. An appropriate preload is applied to make the middle partition plate 1 and the side frame 4 fit tightly to prevent misalignment or gap expansion due to thermal deformation during the welding process.

[0061] Next, as Figure 5 As shown, a friction stir welding machine was used to perform welding path 17 along the four transverse joints between the intermediate partition 1 and the side frame 4. A T7-16 welding needle (7 mm length, 16 mm shoulder diameter) was selected. The spindle speed was set to 1100 rpm, the feed rate to 300 mm / min, and the pressure drop to 0.3 mm. At the beginning of welding, a needle-down procedure was executed: the Z-axis descended at a speed of F30 mm / min to Z-7.3 mm and paused for 3 seconds to allow the material to be fully preheated and plasticized. At the end of welding, a needle-up procedure was executed: the Z-axis was first raised to Z-6 mm and held for 1 second, then quickly lifted away to Z30 mm to avoid keyhole defects. After welding, as shown... Figure 6 As shown, the side frame welding fixture 7 is removed, and the middle partition plate 1 and side frame 4 components, which have been welded together, are retained.

[0062] Before proceeding to the second stage of welding, refer to Figure 7 and Figure 8 The upper cover plate 10 and lower cover plate 13 are CNC milled to machine a second groove 11 on their inner sides, with a depth and width of 3.55 mm and 3.6 mm respectively; and a second countersunk hole 12 of Φ5.5 mm is drilled around the outer edge of the upper cover plate 10 and lower cover plate 13 for subsequent locking of the upper and lower cover plate welding fixture 14. Meanwhile, as... Figure 9 and Figure 10 As shown, the welded side frame 4 is precision milled in its thickness direction to produce a second boss 6 with a height and width of 3.5 mm, which forms a longitudinal tenon-and-mortise fit with the second groove 11.

[0063] Subsequently, as Figure 11 and Figure 12 As shown, a welding fixture 14 for upper and lower cover plates is fabricated. A second threaded hole 15 of M5 specification is machined on its side, corresponding to the second countersunk hole 12 of the upper cover plate 10 and the lower cover plate 13. The second grooves 11 of the upper cover plate 10 and the lower cover plate 13 are respectively fitted onto the second boss 6 of the side frame 4 to complete the precise vertical positioning. The welding fixture 14 for upper and lower cover plates is then installed on the outside of the box. An M5 hexagon countersunk screw 9 is passed through the second countersunk hole 12 and screwed into the second threaded hole 15 to lock the upper cover plate 10, the lower cover plate 13 and the side frame 4, ensuring that the three fit together without gaps during the welding process.

[0064] like Figure 13 As shown, the same T7-16 welding needle was used to perform full-circumference continuous friction stir welding on eight longitudinal joints between the side frame 4 and the upper cover plate 10 and the lower cover plate 13. The welding parameters were the same as in the first stage: 1100 rpm, 300 mm / min, and a downward pressure of 0.3 mm. The needle insertion and withdrawal procedures were the same to ensure that the weld nugget fully filled the joint area and formed a closed and sealed structure. After welding, as shown... Figure 14 As shown, remove the welding fixture 14 for the upper and lower cover plates.

[0065] like Figure 15 As shown, the outer surface of the housing is precision milled to remove the traces of the second countersunk hole 12 left by the installation fixture, making the surface smooth and flat. Then, Φ8 mm pressure testing process holes 16 are drilled in a non-critical area on the top of the housing, with the hole opening machined with a tapered surface for connecting the airtightness testing connector. Finally, as shown... Figure 16 As shown, the airtightness test of the finished vacuum sealing box 18 is carried out: nitrogen gas is filled into the inner cavity through the pressure test process hole 16 to a gauge pressure of 1.5 MPa, the entire box is completely immersed in the water tank, and the pressure is maintained for 30 minutes. If no bubbles escape, it is determined that the airtightness is qualified and meets the requirements for vacuum application.

[0066] Throughout the implementation process, the mortise and tenon positioning structure (first boss 2 and first groove 5, second boss 6 and second groove 11) effectively restricts the relative displacement of the plates in three translational degrees of freedom, keeping the assembly gap stably within 0.1 mm; the special welding fixture provides rigid constraints through screw 9 to resist the axial force (approximately 8–12 kN) and lateral disturbance force generated by the rotation and feeding of the stirring head, preventing warping or separation during welding; the diameter of the welding needle (7 mm) is not less than twice the height of the boss (3.5 mm), ensuring that the shoulder completely covers the joint area, the heat input is uniform, the weld nugget is fully plasticized, and there are no defects such as pores or cracks inside; the phased welding strategy first completes the connection between the side frame and the middle partition, and then welds the upper and lower cover plates, effectively reducing the superposition of residual stress and reducing the overall deformation, which is far superior to the deformation level of traditional fusion welding. Furthermore, the 6061 aluminum alloy sheet used in this embodiment has a thickness of 10 mm, which conforms to the relationship of screw diameter × 1.5 ≤ sheet thickness ≤ screw diameter × 2.0 (M5 screw diameter 5 mm, 5 × 1.5 = 7.5 mm, 5 × 2.0 = 10 mm), ensuring sufficient locking force without damaging the sheet. If applied to the butt welding of dissimilar materials 5A06 / ADC12, the ADC12 die-cast aluminum is placed on the advancing side, and a T3-10C welding pin (pin length 3 mm, shoulder 10 mm) is selected, with a rotation speed of 1300 rpm, a feed rate of 300 mm / min, and a pressing amount of 0.2 mm, which can also obtain a defect-free weld.

[0067] Example 2

[0068] Unlike Embodiment 1, this embodiment employs a mortise and tenon positioning structure with a cylindrical boss and an annular groove. For example... Figure 17 As shown, specifically, cylindrical first bosses are machined at both ends of the intermediate partition 1, and correspondingly, annular first grooves are machined on the inner side of the side frame 4; cylindrical second bosses are machined in the thickness direction of the side frame 4, and annular second grooves are machined on the inner sides of the upper cover plate 10 and the lower cover plate 13. During assembly, the fitting clearance between the cylindrical bosses and the annular grooves is controlled within 0.1 mm to restrict the relative displacement of the plate in the X, Y, and Z translational degrees of freedom. The welding process is the same as in Example 1, using T7-16 welding needles, a spindle speed of 1100 rpm, a feed rate of 300 mm / min, a pressing amount of 0.3 mm, and the needle insertion and release procedures are consistent. Testing showed that the assembly accuracy of the housing using cylindrical bosses is comparable to that using rectangular bosses, and the airtightness test was passed.

[0069] Example 3

[0070] Unlike Embodiment 1, this embodiment employs a mortise and tenon positioning structure using a polygonal irregular boss and a polygonal irregular groove. For example... Figure 18As shown, specifically, polygonal irregular bosses are provided at both ends of the middle partition, and polygonal irregular grooves are provided on the inner side of the side frame accordingly; polygonal irregular bosses are provided in the thickness direction of the side frame, and polygonal irregular grooves are provided on the inner side of the upper and lower cover plates. The tooling locking assembly adopts the same side frame welding tool 7 and upper and lower cover plate welding tool 14 as in Embodiment 2; the friction stir welding process parameters are: spindle speed 1200 rpm, welding speed 80 mm / min, downward pressure 0.2 mm, and no leakage is detected after immersion in 1.5 MPa nitrogen water after welding.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A vacuum chamber-type friction stir welding fixture, characterized in that, include: The basic splicing components consist of a middle partition (1), a side frame (4), an upper cover plate (10), and a lower cover plate (13); The tenon and mortise positioning structure includes a first boss (2) disposed at both ends of the middle partition (1), a first groove (5) disposed on the inner side of the side frame (4) and matching the first boss (2), a second boss (6) disposed in the thickness direction of the side frame (4), and a second groove (11) disposed on the inner side of the upper cover plate (10) and the lower cover plate (13) and matching the second boss (6). The first boss (2) and the first groove (5) form a transverse positioning pair, and the second boss (6) and the second groove (11) form a longitudinal positioning pair. The tooling locking assembly includes a side frame welding fixture (7) and an upper and lower cover plate welding fixture (14). The side frame welding fixture (7) is provided with a first countersunk hole (8). The middle partition plate (1) is provided with a first threaded hole (3) corresponding to the first countersunk hole (8). A screw (9) is passed through the first countersunk hole (8) and screwed into the first threaded hole (3) to press and fix it. The upper and lower cover plate welding fixture (14) is provided with a second threaded hole (15). The upper cover plate (10) and the lower cover plate (13) are provided with a second countersunk hole (12) corresponding to the second threaded hole (15). A screw (9) is passed through the second countersunk hole (12) and screwed into the second threaded hole (15) to press and fix it.

2. The vacuum chamber-type friction stir welding fixture according to claim 1, characterized in that, The height and width of the first boss (2) are both equal to 0.5 times the diameter of the friction stir welding needle adapted to the vacuum chamber type friction stir welding fixture. The depth and width of the first groove (5) are increased by 0.05 mm on one side based on the size of the corresponding first boss (2). The height and width of the second boss (6) are equal to 0.5 times the diameter of the friction stir welding needle adapted to the vacuum chamber type friction stir welding fixture. The depth and width of the second groove (11) are increased by 0.05 mm on one side based on the size of the corresponding second boss (6).

3. The vacuum chamber-type friction stir welding fixture according to claim 1, characterized in that, The diameter of the screw (9) satisfies the following relationship: screw (9) diameter × 1.5 ≤ plate thickness ≤ screw (9) diameter × 2.

0.

4. The vacuum chamber-type friction stir welding fixture according to claim 1, characterized in that, It also includes auxiliary functional components, including a pressure test process hole (16) for airtightness testing; the diameter of the pressure test process hole (16) is Φ6–Φ10 mm, located in the non-stressed area on the top or side of the box, and the orifice is provided with a conical sealing structure.

5. The vacuum chamber-type friction stir welding fixture according to claim 1, characterized in that, The cross-sectional shape of the mortise and tenon positioning structure is rectangular, cylindrical, trapezoidal, or polygonal.

6. A welding process based on the vacuum chamber-type friction stir welding fixture as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Machining the first boss (2) and the first threaded hole (3) of the middle partition plate (1), and machining the first groove (5) of the side frame (4); S2: Make a side frame welding fixture (7), which has a first countersunk hole (8) corresponding to the first threaded hole (3); S3: Assemble the middle partition (1) and the side frame (4) through the first boss (2) and the first groove (5), and lock them with the side frame welding fixture (7) and screws (9); S4: Perform friction stir welding along the joint between the middle partition (1) and the side frame (4); S5: Remove the side frame welding fixture (7); S6: Machining the second groove (11) and the second countersunk hole (12) of the upper cover plate (10) and the lower cover plate (13); S7: Machining a second boss (6) on the welded side frame (4); S8: Make a welding fixture (14) for upper and lower cover plates, which has a second threaded hole (15). S9: Assemble the upper cover plate (10), lower cover plate (13) and side frame (4) through the second boss (6) and the second groove (11), and lock them with the upper and lower cover plate welding fixture (14) and screws (9); S10: Continuous friction stir welding is performed along the entire circumferential joint between the side frame (4) and the upper cover plate (10) and the lower cover plate (13); S11: Remove the welding fixture for the upper and lower cover plates (14). S12: Mill the outer surface of the box body and drill pressure test process holes (16). S13: Fill the inner cavity of the chamber with 1.5MPa nitrogen through the pressure test process hole (16) to perform water immersion air tightness test.

7. The welding process according to claim 6, characterized in that, In steps S4 and S10, the diameter of the welding pin is not less than twice the height of the corresponding boss, and the downward pressure is 0.2mm or 0.3mm.

8. The welding process according to claim 6, characterized in that, In the initial welding stage of steps S4 and S10, the needle-down procedure is executed: the Z-axis descends to the set depth at a speed of F30 mm / min and then pauses for 3 seconds; at the end of welding, the needle-up procedure is executed: the Z-axis is first raised by 0.5–1.0 mm and then quickly lifted away from the weld.

9. The welding process according to claim 6, characterized in that, In step S13, the pressure holding time is 30 minutes. If no air bubbles escape, the airtightness is deemed acceptable.

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