Interference mounted pull-in light weight fastener and method of manufacture

Abstract

The application discloses an interference installation pull-in type light fastener and a manufacturing method thereof, and belongs to the technical field of aviation fasteners. The fastener comprises a fastening main body and a pull-in core rod. The fastening main body comprises a nut, an interference shaft section and a locking shaft section. The interiors of the interference shaft section and the locking shaft section are hollow structures. The outer diameter of the interference shaft section is larger than that of the locking shaft section. One end of the pull-in core rod is connected with the nut, and the other end of the pull-in core rod is extended out of the locking shaft section to form a free end. An annular cavity is formed between the pull-in core rod and the interference shaft section. There is a weak link on the pull-in core rod in the interference shaft section. The application has the advantages of simple structure, convenient installation, stable and reliable installation, high assembly efficiency, reduced redundant structure weight under the premise of ensuring the connection strength and the anti-loosening performance, weight reduction compared with traditional high locking bolts of the same specification, remarkable light weight characteristics, and the ability to meet the multiple requirements of high strength, high reliability and light weight of fasteners in the aviation field.

Description

Technical Field

[0001] This invention relates to an interference-installed pull-in lightweight fastener and its manufacturing method, belonging to the field of aerospace fastener technology. Background Technology

[0002] Fasteners are one of the main connection methods for aircraft structural components. They are mainly used for connecting load-bearing structural parts of aircraft. As the most widely used basic mechanical components, their demand is generally very large. Currently, most fasteners used in civil aircraft are high-tightness bolts.

[0003] For example, Chinese utility model patent CN203230706U discloses a pull-out type high-tightness bolt, which includes a bolt head, a screw, a pull rod, and a break. The screw includes a stud section and a threaded section. The stud section has a smooth surface. The screw is connected to the pull rod through the break. The pull rod is located at the tail of the screw and is connected to the screw through the break. The pull rod has external threads on its surface. The assembly process is as follows: the threaded pull rod is pulled or pulled, creating a high interference fit between the stud section of the screw and the mounting hole. The high-tightness bolt is pulled into the mounting hole by pulling or pulling until the bolt head contacts the fastened component. When the tension reaches a certain level, the pull rod and the screw break at the break. During the tightening process of the high-tightness bolt's locking nut and the threaded section of the screw, because of the high interference fit between the stud section and the mounting hole of the fastened component, the traditional anti-rotation internal hexagonal groove at the tail end of the high-tightness bolt is unnecessary.

[0004] The aforementioned high-tightness bolts can be pulled apart by a pull-out method to achieve the installation and positioning of the high-tightness bolts. Utilizing the interference fit between the stud section and the mounting hole, the installed high-tightness bolts can simultaneously withstand longitudinal and lateral loads, exhibiting strong anti-loosening capabilities. However, as a product widely used in aircraft, especially commercial aircraft with a cumulative flight time of 60,000-80,000 hours, 40,000-60,000 takeoffs and landings, and a design life of 20-30 years, the weight requirement throughout the aircraft's life cycle is the lighter the better. As fasteners used extensively in aircraft, not only are good locking performance required, but also higher demands are placed on their lightweight design. Although with the increasing application of composite materials in the aerospace field, slotted bushings or press-fit bushings are used for connections, the installation methods of slotted bushings or press-fit bushings are prone to causing scratches and delamination of the composite materials in aircraft, affecting the safety and economy throughout the aircraft's life cycle. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an interference-installed pull-in lightweight fastener and its manufacturing method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: An interference-mounted pull-in lightweight fastener includes a fastening body and a pull-in mandrel disposed on the fastening body. The fastening body includes a nut, an interference shaft section and a locking shaft section. The interference shaft section and the locking shaft section are both hollow structures. The outer diameter of the interference shaft section is larger than the outer diameter of the locking shaft section. One end of the pull-in mandrel is connected to the nut, and the other end extends out of the locking shaft section to form a free end. An annular cavity is formed between the pull-in mandrel and the interference shaft section. A weak point is provided on the pull-in mandrel located in the interference shaft section.

[0007] The beneficial effects of this invention are as follows: After assembly, the fastener has a hollow structure, which significantly reduces the overall weight of the fastener compared to traditional solid aerospace fasteners, meeting the lightweight requirements throughout the aircraft's life cycle. Furthermore, the fastener retains an interference mounting structure, allowing for installation by pulling down weak points. The outer diameter of the interference shaft is larger than that of the locking shaft and also larger than the diameter of the mounting hole, thus creating the required interference fit. The assembly process is smooth and efficient. After installation, the interference shaft and mounting hole form an interference fit, capable of simultaneously withstanding longitudinal and lateral loads, and exhibiting strong anti-loosening capabilities. Compared to existing slotted bushings and press-fit bushings, the installation process of this fastener does not cause scratches or delamination damage to the aircraft's composite material structure, ensuring the aircraft's structural safety and improving the safety and economy throughout the aircraft's life cycle. In summary, this invention has a simple structure, is easy to install, and the entire installation process is stable and reliable with high assembly efficiency. While ensuring connection strength and anti-loosening performance, it reduces unnecessary structural weight and achieves weight reduction compared to traditional high-tightening bolts of the same specifications. It has significant lightweight characteristics and can meet the multiple requirements of the aerospace field for fasteners in terms of high strength, high reliability and lightweight.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the pull-in mandrel includes a mandrel connecting shaft section, a mandrel traction shaft section, and a mandrel guide shaft section disposed between the mandrel connecting shaft section and the mandrel traction shaft section. The interference shaft section has an interference shaft inner hole, the locking shaft section has a locking shaft inner hole, the mandrel connecting shaft section is located in the interference shaft inner hole, the mandrel guide shaft section is adapted to the locking shaft inner hole, and the mandrel traction shaft section extends out of the fastening body for traction or pulling.

[0010] The beneficial effects of adopting the above-mentioned further solution are that the pull-in mandrel adopts a segmented structure. The mandrel connecting shaft section is used to connect with the fastening body, specifically to the nut of the fastening body. The mandrel traction shaft section is used for traction or pulling. The mandrel guide shaft section can achieve guidance and adaptation when pulling and traction to pull in the mandrel, ensuring that the pull-in mandrel always moves along the axial direction of the mounting hole, avoiding the mandrel deflection during the pulling process and causing the fastener to shift, thus ensuring the smoothness of the pull-in installation. The pull-in mandrel of this fastener plays a traction and positioning role during the installation process. After installation, it can be pulled out and removed from the fastening body as a whole, without leaving it inside the fastening body. The assembled fastening body is a hollow structure, which reduces the overall weight of the fastener while ensuring connection strength and reliability, thereby meeting the lightweight requirements of the aerospace field.

[0011] Furthermore, the outer diameter of the mandrel guide shaft section is greater than the outer diameter of the mandrel connecting shaft section; and / or the outer diameter of the mandrel guide shaft section is greater than the outer diameter of the mandrel traction shaft section.

[0012] The beneficial effects of adopting the above-mentioned further solutions are that the outer diameter of the mandrel guide shaft section can be adapted to the inner hole of the locking shaft, which can fully enhance the guiding effect of the guide structure, reduce the probability of mandrel deflection during traction or pulling, and improve the stability of the fastener pulling and installation process; the outer diameter of the mandrel connecting shaft section and / or mandrel traction shaft section is smaller than the outer diameter of the mandrel guide shaft section, which can also avoid unnecessary friction between the mandrel connecting shaft section and / or mandrel traction shaft section and the inner hole of the locking shaft of the locking shaft section, reduce the resistance during the pulling and pulling of the mandrel, and make the pulling operation smoother and less strenuous.

[0013] Furthermore, the diameter of the inner hole of the interference shaft is larger than the diameter of the inner hole of the locking shaft.

[0014] The beneficial effects of adopting the above-mentioned further solution are that the mandrel guide shaft section can cooperate with the inner hole of the locking shaft for guidance, the inner hole of the interference shaft provides a space for the mandrel connecting shaft section, the mandrel connecting shaft section is located in a large space in the inner hole of the interference shaft and will not interfere with the inner hole of the interference shaft. In addition, the inner hole of the interference shaft and the inner hole of the locking shaft form a stepped hole, which facilitates the weight reduction of fasteners.

[0015] Furthermore, the pulled-in mandrel has a stepped shaft structure.

[0016] The beneficial effects of adopting the above-mentioned further solution are that the stepped shaft structure has low processing difficulty, makes it easy to ensure the dimensional accuracy of each shaft segment, and can also meet the functional requirements of each shaft segment. It can be adapted to the stepped hole of the fastening body, making the pulling or pulling process of the pulled mandrel more stable and meeting the assembly requirements of the fastener.

[0017] Furthermore, a first axial transition chamfer is provided between the mandrel connecting shaft segment and the mandrel guide shaft segment; and / or a second axial transition chamfer is provided between the mandrel guide shaft segment and the mandrel traction shaft segment.

[0018] The beneficial effects of adopting the above-mentioned further solution are that the transition chamfer can reduce the stress concentration at the joint of each shaft segment, improve the overall structural strength of the pull-in mandrel, avoid the pull-in mandrel from breaking at the joint of the shaft segment during the pulling process, reduce the scraping when the pull-in mandrel enters the inner hole of the fastener body, avoid scratching the inner hole wall of the fastener body, ensure the smoothness of the assembly process, and improve the installation accuracy of the fastener.

[0019] Furthermore, the pull-in mandrel is provided with external threads and / or radial holes for traction or pull-out docking.

[0020] The advantages of adopting the above-mentioned further solutions are that only external threads can be provided, which are located on the outer surface of the mandrel traction shaft section of the pull-in mandrel. The external threads can be used for quick threaded connection of traction tools, facilitating the rapid assembly and docking of the pull-in mandrel. Alternatively, only radial holes can be provided, located at the free end of the mandrel traction shaft section of the pull-in mandrel. The radial holes can be connected and adapted by inserting pins, resulting in higher traction assembly efficiency. Of course, the pull-in mandrel can also have both external threads and radial holes, allowing for the selection of appropriate methods for traction connection with the pull-in mandrel based on site conditions. This improves the adaptability of the pull-in mandrel, making traction and pulling operations more flexible and convenient, and adapting to different site assembly requirements.

[0021] Furthermore, the nut has a flat head or countersunk head structure.

[0022] The advantages of adopting the above-mentioned further solutions are that a suitable nut structure can be selected according to the hole structure of the fastening mounting hole. The inner side of the flat-head nut is flush with the fastened part, which is easy to process and suitable for working conditions with sufficient installation space and low requirements for assembly thickness. The countersunk nut can be sunk into the mounting hole of the fastened part. After assembly, the outer side of the nut is flush with the outer surface of the fastened part and will not protrude from the surface of the fastener, thus not affecting subsequent assembly and surface appearance. It is suitable for application scenarios that require assembly flatness. It can be flexibly selected according to the installation requirements of the fastened part, thereby improving the applicability of the fastener.

[0023] Furthermore, the weak link is the annular groove, and the groove cross-section of the annular groove is a semi-circular structure.

[0024] The advantages of adopting the above-mentioned further solution are that the annular groove structure is easy to process, it is easy to control the cross-sectional dimensions of the weak link, ensure the consistency of the fracture position, the stress distribution of the semi-circular groove is uniform, it can avoid the abnormal stress concentration in the groove leading to accidental fracture, and ensure that the pulled mandrel always breaks at the preset annular groove position after the pull-out operation, thus meeting the usage requirements.

[0025] This invention also relates to a method for manufacturing an interference-installed pull-in type lightweight fastener, the specific steps of which are as follows: S1. Prepare the fastening body blank and the pull-in mandrel blank respectively; S2. Process the fastening body blank and the pull-in mandrel blank respectively to form the fastening body semi-finished product and the pull-in mandrel semi-finished product; The fastening body semi-finished product has a hollow structure and includes a fastening cap end, which has an annular inner bevel. The semi-finished mandrel pull-in includes a large cylindrical section, a mandrel connecting shaft section, a mandrel traction shaft section, and a mandrel guide shaft section set between the mandrel connecting shaft section and the mandrel traction shaft section, which are integrally structured. The large cylindrical section has an annular outer bevel on the side near the mandrel connecting shaft section, and the slope of the annular outer bevel is adapted to the annular inner bevel. It also includes weak points located on the mandrel connecting shaft section; S3. Insert the pull-in mandrel semi-finished product into the fastening body semi-finished product, and weld the outer annular bevel and the inner annular bevel together by inertial friction welding to form a lightweight fastener semi-finished product. S4. The large cylindrical section of the lightweight fastener semi-finished product is machined into a nut, and the lightweight fastener semi-finished product is formed into an interference installation pull-in type lightweight fastener as described above.

[0026] The preparation method of the fastening body blank and the drawn-in mandrel blank in step S1 above is forging.

[0027] The beneficial effects of this invention are as follows: by processing the fastener into two parts, the fastening body and the pull-in mandrel, separately and then welding them together, the overall processing difficulty is reduced; the two parts are fixed by inertial friction welding, resulting in high welding strength; the outer and inner annular bevels match, ensuring accurate and stable connection between the two parts, while also meeting the operational requirements of pull-in interference installation; the overall manufacturing process is simple and efficient, and the finished fastener's structural strength meets the usage requirements. Compared with the processing of integrated fasteners, it significantly reduces material costs and processing losses. The finished fastener is easy to assemble and has high installation efficiency. The assembled fastening body has a hollow structure, reducing excess structural weight and achieving fastener lightweighting, thus meeting the multiple requirements of the aerospace field for fasteners in terms of high strength, high reliability, and lightweight. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 2 This is a cross-sectional structural diagram of Embodiment 1 of the present invention; Figure 3 This is a three-dimensional structural diagram of Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the assembly and pull-out mandrel state structure of Embodiment 1 of the present invention; Figure 5 for Figure 4 A magnified view of point A in the image; Figure 6 This is a schematic diagram of the fastener and locking nut mating state in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 8 This is a schematic diagram of the assembly process structure of Embodiment 2 of the present invention; Figure 9 for Figure 8 A magnified view of a section at point B in the middle; Figure 10 This is a schematic diagram of the structure of the fastening body semi-finished product of the present invention; Figure 11 This is a schematic diagram of the structure of the pull-in mandrel semi-finished product of the present invention; Figure 12 This is a structural schematic diagram of the present invention, showing the state of the semi-finished mandrel being inserted into and fastened to the main semi-finished product, and the state of the outer end face of the nut being flat.

[0029] In the diagram, 100 is the fastening body; 101 is the nut; 102 is the interference shaft section; 103 is the locking shaft section; 104 is the inner hole of the interference shaft; 105 is the inner hole of the locking shaft; 106 is the assembly chamfer; 107 is the rounded corner structure; 108 is the annular inner bevel; 200 is the pulled-in mandrel; 201 is the mandrel connecting shaft section; 202 is the mandrel guide shaft section; 203 is the mandrel traction shaft section; 204 is the radial hole; 205 is the first shaft transition chamfer; 206 is the second shaft transition chamfer; 207 is the weak link; 208 is the large cylindrical section; 209 is the annular outer bevel; 300 is the locking nut; 301 is the annular flexible link; 302 is the screwing structure; 303 is the outer end face of the nut; 400 is the first fastened component; 500 is the second fastened component. Detailed Implementation

[0030] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0031] Example 1 like Figures 1-6As shown, an interference-mounted pull-in lightweight fastener includes a fastening body 100 and a pull-in mandrel 200 disposed on the fastening body 100. The fastening body 100 includes a nut 101, an interference shaft section 102, and a locking shaft section 103. The interference shaft section 102 and the locking shaft section 103 are both hollow structures. The outer diameter of the interference shaft section 102 is larger than the outer diameter of the locking shaft section 103. One end of the pull-in core rod 200 is connected to the nut 101, and the other end extends out of the locking shaft section 103 to form a free end. An annular cavity is formed between the pull-in core rod 200 and the interference shaft section 102. A weak link 207 is provided on the pull-in core rod 200 located in the interference shaft section 102.

[0032] The locking shaft section 103 is provided with external threads.

[0033] The pull-in mandrel 200 includes a mandrel connecting shaft section 201, a mandrel traction shaft section 203, and a mandrel guide shaft section 202 disposed between the mandrel connecting shaft section 201 and the mandrel traction shaft section 203. The interference shaft section 102 has an interference shaft inner hole 104, and the locking shaft section 103 has a locking shaft inner hole 105. The mandrel connecting shaft section 201 is located inside the interference shaft inner hole 104. The mandrel guide shaft section 202 is adapted to the locking shaft inner hole 105. The mandrel traction shaft section 203 extends out of the fastening body 100 for traction or pulling. The pull-in mandrel 200 adopts a segmented structure. The mandrel connecting shaft section 201 is used to connect with the fastening body 100, specifically to the nut 101 of the fastening body 100. The mandrel traction shaft section 203 is used for traction or pulling. The mandrel guide shaft section 202 can achieve guidance and adaptation when pulling and traction pulling in the mandrel 200, ensuring that the pull-in mandrel 200 always moves along the axial direction of the mounting hole, avoiding the pull-in mandrel 200 from deflecting and causing the fastener to shift during the pulling process, and ensuring the smoothness of the pull-in installation. The pull-in mandrel 200 of this fastener plays a traction and positioning role during the installation process. After the installation is completed, it can be pulled out and removed from the fastening body 100 as a whole, without leaving it inside the fastening body 100. The assembled fastening body 100 is a hollow structure, which reduces the overall weight of the fastener while ensuring connection strength and reliability, thereby meeting the lightweight requirements of the aerospace field.

[0034] The pull-in mandrel 200 is connected to the nut 101 through the weak link 207.

[0035] The outer diameter of the mandrel guide shaft section 202 is larger than the outer diameter of the mandrel connecting shaft section 201; and / or the outer diameter of the mandrel guide shaft section 202 is larger than the outer diameter of the mandrel traction shaft section 203. The outer diameter of the mandrel guide shaft section 202 can be adapted to the inner hole 105 of the locking shaft, which can fully enhance the guiding effect of the guide structure, reduce the probability of deviation when the mandrel 200 is pulled in during traction or pulling, and improve the stability of the fastener pulling in and installing process; the outer diameter of the mandrel connecting shaft section 201 and / or the mandrel traction shaft section 203 is smaller than the outer diameter of the mandrel guide shaft section 202, which can also avoid unnecessary friction between the mandrel connecting shaft section 201 and / or the mandrel traction shaft section 203 and the inner hole 105 of the locking shaft section 103, reduce the resistance during the pulling in of the mandrel 200, and make the pulling in operation smoother and less strenuous.

[0036] The diameter of the inner hole 104 of the interference shaft is larger than the diameter of the inner hole 105 of the locking shaft. The mandrel guide shaft section 202 can cooperate with the inner hole 105 of the locking shaft for guidance. The inner hole 104 of the interference shaft provides a receiving space for the mandrel connecting shaft section 201. The mandrel connecting shaft section 201 is located in the large space within the inner hole 104 of the interference shaft and will not interfere with the inner hole 104 of the interference shaft. In addition, the inner hole 104 of the interference shaft and the inner hole 105 of the locking shaft form a stepped hole, which facilitates the weight reduction of fasteners.

[0037] The pull-in mandrel 200 has a stepped shaft structure. The stepped shaft structure of the pull-in mandrel 200 is easy to process, makes it easy to ensure the dimensional accuracy of each shaft segment, and can also meet the functional requirements of each shaft segment. It can be adapted to the stepped hole of the fastening body 100, making the traction or pulling process of the pull-in mandrel 200 more stable and meeting the assembly requirements of the fastener.

[0038] A first axial transition chamfer 205 is provided between the mandrel connecting shaft section 201 and the mandrel guide shaft section 202; and / or a second axial transition chamfer 206 is provided between the mandrel guide shaft section 202 and the mandrel traction shaft section 203. The transition chamfer can reduce stress concentration at the joint of each shaft section, improve the overall structural strength of the pull-in mandrel 200, avoid the pull-in mandrel 200 from breaking at the joint of the shaft section during the pulling process, and also reduce the scraping when the pull-in mandrel 200 enters the inner hole of the fastening body 100, avoid scratching the inner hole wall of the fastening body 100, ensure the smoothness of the assembly process, and improve the installation accuracy of the fastener.

[0039] The pull-in mandrel 200 is provided with external threads and / or radial holes 204 for traction or pull-out docking. It can be provided with only external threads, which are located on the outer surface of the mandrel traction shaft section 203 of the pull-in mandrel 200. These external threads can be used for quick threaded connection to traction tools, facilitating rapid assembly and docking of the pull-in mandrel 200. Alternatively, it can be provided with only radial holes 204, which are through holes located at the free end of the mandrel traction shaft section 203 of the pull-in mandrel 200. These radial holes 204 can be connected and adapted using a pin insertion method, resulting in higher traction assembly efficiency. Alternatively, the pull-in mandrel 200 can have both external threads and radial holes 204 simultaneously. The appropriate method can be selected for traction connection with the pull-in mandrel 200 based on the site conditions, improving the adaptability of the pull-in mandrel 200 and making traction and pull-out operations more flexible and convenient, adapting to different site assembly needs.

[0040] The nut 101 has a flat head structure. A suitable nut structure can be selected according to the hole structure of the fastening mounting hole. The inner surface of the flat head nut 101 is flush with the fastened part, which is easy to process and suitable for working conditions with sufficient installation space and low requirements for assembly thickness.

[0041] The weak point 207 is an annular groove, and the groove has a semi-circular cross-section. The annular groove structure is easy to manufacture, making it easy to control the cross-sectional dimensions of the weak point 207, ensuring the consistency of the fracture location. The stress distribution of the semi-circular groove is uniform, which can avoid abnormal stress concentration in the groove and prevent accidental fracture. This ensures that the pulled-in mandrel 200 always breaks at the preset annular groove position after the pull-out operation, meeting the usage requirements.

[0042] An assembly chamfer 106 is provided between the interference shaft section 102 and the locking shaft section 103. This chamfer can guide the fastener when it is inserted into the mounting hole, preventing the interference shaft section 102 from getting stuck in the mounting hole, reducing assembly difficulty, preventing sharp edges from scratching the inner wall of the mounting hole of the fastened component, ensuring assembly accuracy, and improving the smoothness of the assembly process.

[0043] The inner surface of the flat-head nut 101 and the interference axis segment 102 are smoothly transitioned by a rounded corner structure 107. This transition can be strengthened by cold extrusion, improving the fatigue performance at this point.

[0044] Example 2 like Figures 7-9As shown, the nut 101 has a countersunk head structure. A suitable nut structure can be selected based on the hole structure of the fastening mounting hole. The countersunk nut 101 can be recessed into the mounting hole of the fastened component. After assembly, the outer surface of the nut 101 is flush with the outer surface of the fastened component and will not protrude from the surface of the fastened component, thus not affecting subsequent assembly or surface appearance. This design is suitable for application scenarios requiring flatness during assembly and can be flexibly selected according to the installation needs of the fastened component, thus expanding the applicability of the fastener.

[0045] The inner surface of the countersunk nut 101 and the interference shaft section 102 are smoothly transitioned by a rounded corner structure 107, which meets the installation requirements of the countersunk hole while improving the fatigue resistance at this point. The rest of the structure is the same as in Embodiment 1, and will not be described in detail here.

[0046] During assembly, the fastener of the present invention has its pull-in mandrel 200 passed through the mounting holes of the first fastened component 400 and the second fastened component 500. Since the fastening body 100 is interference-fitted with the first fastened component 400 and the second fastened component 500, an external thread or radial hole 204 is used to connect the pulling tool to the mandrel traction shaft section 203 of the pull-in mandrel 200. The pull-in mandrel 200 is pulled backward, and the locking shaft section 103 of the fastener passes through the mounting hole. It is tightened until the end face of the fastener nut 101 fits against the connection point of the first fastened component 400. Finally, the pull-in mandrel 200 is broken and removed at the weak point 207.

[0047] The fastener can then be locked via the locking shaft section 103. The locking shaft section 103 has external threads. Screw the locking nut 300 onto the locking shaft section 103 of the fastener and tighten the locking nut 300 until the tightening force reaches the required value. At this point, the tightening structure 302 on the locking nut 300, such as the hexagonal structure, will disengage from the locking nut 300. The locking nut 300 has an annular flexible link 301. The locking nut 300 will disengage at the position of the annular flexible link 301, completing the entire tightening process.

[0048] If necessary, after the fastener assembly is completed, the part where the nut 101 is disconnected from the pull-in mandrel 200 can be machined with a milling cutter to form a flat end face. The outer end face 303 of the locking nut 300 can also be ground flat, which reduces the weight of the fastener product while ensuring the consistency of quality after assembly.

[0049] like Figures 10-12 As shown, the present invention also relates to a method for manufacturing an interference-installed pull-in type lightweight fastener, the specific steps of which are as follows: S1. Prepare the fastening body blank and the pull-in mandrel blank respectively; S2. Process the fastening body blank and the pull-in mandrel blank respectively to form the fastening body semi-finished product and the pull-in mandrel semi-finished product; The fastening body semi-finished product has a stepped hollow structure. The fastening body semi-finished product includes a fastening cap end, which is provided with an annular inner bevel 108. The semi-finished mandrel pull-in includes a large cylindrical section 208 with an integral structure, a mandrel connecting shaft section 201, a mandrel traction shaft section 203, and a mandrel guide shaft section 202 disposed between the mandrel connecting shaft section 201 and the mandrel traction shaft section 203. The large cylindrical section 208 has an annular outer bevel 209 on the side near the mandrel connecting shaft section 201, and the slope of the annular outer bevel 209 is adapted to the slope of the annular inner bevel 108. It also includes a weak link 207 located on the mandrel connecting shaft section 201; S3. Insert the pull-in mandrel semi-finished product into the fastening body semi-finished product, and weld the annular outer bevel 209 and the annular inner bevel 108 together by inertial friction welding to form a lightweight fastener semi-finished product. S4. The large cylindrical section 208 of the lightweight fastener semi-finished product is machined into a nut 101, and the lightweight fastener semi-finished product is formed into an interference installation pull-in type lightweight fastener as described above.

[0050] In step S1 above, the preparation method for the fastening body blank and the drawn-in mandrel blank is forging.

[0051] The fastening body blank can be made of titanium alloy forging; the inner hole and outer dimensions of the fastening body blank are machined and precision machined. If there is an external thread on the locking shaft section 103, the thread rolling blank diameter needs to be machined and the external thread is rolled or twisted at the thread rolling blank diameter to form a fastening body semi-finished product. The mandrel blank can be made of titanium alloy forging; the mandrel blank is machined to its external dimensions. If the mandrel 200 has external threads, the thread rolling blank diameter needs to be machined, and the external threads are rolled or twisted at the thread rolling blank diameter to form a semi-finished mandrel. Assembly: First, inertial friction welding is used to weld the drawn-in mandrel semi-finished product and the fastening body semi-finished product into a whole; second, the assembly is subjected to solution treatment and aging heat treatment to homogenize the material and improve its mechanical properties; third, the protruding part at the connection between the drawn-in mandrel semi-finished product and the fastening body semi-finished product is removed by turning to make the outer end face of the nut 101 flat; fourth, the outer circle of the fastening body part of the assembly is precision ground to ensure its dimensions and to ensure the interference fit with the mounting hole; fifth, the transition of the rounded corner structure 107 of the fastening body part of the assembly is cold extruded and strengthened by cold extrusion process to improve fatigue resistance and obtain this lightweight fastener.

[0052] The lightweight fastener can also be surface-treated with aluminum or molybdenum disulfide to improve the lubrication between it and the fastened parts, or reduce the risk of potential corrosion, making it easier to insert the lightweight fastener into the mounting hole.

[0053] After the product is assembled and installed, the pull-in mandrel 200 is pulled off at the weak point 207 where it is connected to the fastening body 100. The bottom of the inner hole can be flattened by using an end milling tool to make the break point flat, thereby reducing the risk of stress concentration, reducing the weight of the fastener product, and ensuring the consistency of quality after assembly.

[0054] This invention reduces the overall processing difficulty by processing the fastener into two parts, a fastening body 100 and a pull-in mandrel 200, separately and then welding them together. Inertial friction welding is used to fix the two parts together, resulting in high welding strength. The annular outer bevel 209 and the annular inner bevel 108 fit together, ensuring accurate and stable connection between the two parts, while also meeting the operational requirements of pull-in interference installation. The overall manufacturing process is simple and efficient, and the finished fastener's structural strength meets usage requirements. Compared to processing integrated fasteners, it significantly reduces material costs and processing losses. The finished fastener is easy to assemble and has high installation efficiency. The assembled fastening body 100 has a hollow structure, reducing unnecessary structural weight and achieving fastener lightweighting. This meets the multiple requirements of the aerospace field for fasteners, including high strength, high reliability, and lightweight design.

[0055] 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

1. An interference-mounted pull-in lightweight fastener, comprising a fastening body (100) and a pull-in mandrel (200) disposed on the fastening body (100), characterized in that, The fastening body (100) includes a nut (101), an interference shaft section (102), and a locking shaft section (103). The interference shaft section (102) and the locking shaft section (103) are both hollow structures. The outer diameter of the interference shaft section (102) is larger than the outer diameter of the locking shaft section (103). One end of the pull-in mandrel (200) is connected to the nut (101), and the other end extends out of the locking shaft section (103) to form a free end. An annular cavity is formed between the pull-in mandrel (200) and the interference shaft section (102). A weak link (207) is provided on the pull-in mandrel (200) located in the interference shaft section (102).

2. The interference-installed pull-in lightweight fastener according to claim 1, characterized in that, The pull-in mandrel (200) includes a mandrel connecting shaft section (201), a mandrel traction shaft section (203), and a mandrel guide shaft section (202) disposed between the mandrel connecting shaft section (201) and the mandrel traction shaft section (203). The interference shaft section (102) is provided with an interference shaft inner hole (104), and the locking shaft section (103) is provided with a locking shaft inner hole (105). The mandrel connecting shaft section (201) is located inside the interference shaft inner hole (104). The mandrel guide shaft section (202) is adapted to the locking shaft inner hole (105). The mandrel traction shaft section (203) extends out of the fastening body (100) for traction or pulling.

3. The interference-installed pull-in lightweight fastener according to claim 2, characterized in that, The outer diameter of the mandrel guide shaft section (202) is greater than the outer diameter of the mandrel connecting shaft section (201); and / or the outer diameter of the mandrel guide shaft section (202) is greater than the outer diameter of the mandrel traction shaft section (203).

4. The interference-installed pull-in lightweight fastener according to claim 2, characterized in that, The diameter of the inner hole (104) of the interference shaft is larger than the diameter of the inner hole (105) of the locking shaft.

5. The interference-installed pull-in lightweight fastener according to claim 2, characterized in that, The pull-in mandrel (200) has a stepped shaft structure.

6. The interference-installed pull-in lightweight fastener according to claim 2, characterized in that, A first axial transition chamfer (205) is provided between the mandrel connecting shaft section (201) and the mandrel guide shaft section (202); and / or a second axial transition chamfer (206) is provided between the mandrel guide shaft section (202) and the mandrel traction shaft section (203).

7. The interference-mounted pull-in lightweight fastener according to any one of claims 1-6, characterized in that, The pull-in mandrel (200) is provided with external threads and / or radial holes (204) for traction or pull-out docking.

8. The interference-mounted pull-in lightweight fastener according to any one of claims 1-6, characterized in that, The nut (101) has a flat head or a countersunk head structure.

9. The interference-mounted pull-in lightweight fastener according to any one of claims 1-6, characterized in that, The weak link (207) is the annular groove, and the groove cross-section of the annular groove is a semi-circular structure.

10. A method for manufacturing an interference-installed pull-in type lightweight fastener, characterized in that, The specific steps are as follows: S1. Prepare the fastening body blank and the pull-in mandrel blank respectively; S2. Process the fastening body blank and the pull-in mandrel blank respectively to form the fastening body semi-finished product and the pull-in mandrel semi-finished product; The fastening body semi-finished product is a hollow structure, including a fastening cap end, which has an annular inner bevel (108). The semi-finished mandrel pull-in includes a large cylindrical section (208) with an integral structure, a mandrel connecting shaft section (201), a mandrel traction shaft section (203), and a mandrel guide shaft section (202) set between the mandrel connecting shaft section (201) and the mandrel traction shaft section (203). The large cylindrical section (208) has an annular outer bevel (209) on the side near the mandrel connecting shaft section (201). The slope of the annular outer bevel (209) is adapted to that of the annular inner bevel (108). It also includes a weak link (207) located on the mandrel connecting shaft section (201); S3. Insert the pull-in mandrel semi-finished product into the fastening body semi-finished product, and make the annular outer bevel (209) and the annular inner bevel (108) welded together by inertial friction to form a lightweight fastener semi-finished product. S4. The large cylindrical section (208) of the lightweight fastener semi-finished product is processed into a nut (101), and the lightweight fastener semi-finished product is formed into an interference-installed pull-in type lightweight fastener as described in any one of claims 1-9.

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