Non-destructive, long-life riveting device and method using tapered washers / gradient rivets

Abstract

This invention discloses a non-destructive, long-life riveting device using a tapered washer / gradient rivet, comprising a gradient rivet, a tapered washer, a riveting die, and a component to be riveted. The gradient rivet includes a rivet head, a shank connected to the rivet head, and an upsetting head connected to the shank. The diameter of the shank is larger than the diameter of the upsetting head, and the height of the shank is the same as the thickness of the component to be riveted. The upsetting head has a circular hole coaxial with it, and the depth of the circular hole is the same as the height of the upsetting head. The tapered washer is positioned above the component to be riveted. The gradient rivet passes through the riveting hole of the component to be riveted and is riveted to the tapered washer. The head surface of the riveting die has a protruding portion, which is inserted into the circular hole of the upsetting head during installation. This invention also discloses a non-destructive, long-life riveting method using a tapered washer / gradient rivet, which significantly improves the connection life of the riveted components.

Description

Technical Field

[0001] This invention relates to the field of machining technology, and in particular to a non-destructive, long-life riveting device and method for tapered washers / gradient rivets. Background Technology

[0002] Lightweight design is one of the core technologies in aircraft manufacturing. Advanced composite materials, represented by carbon fiber reinforced resin (CFRP), possess advantages such as high strength, high modulus, ease of cutting, and ease of molding, significantly reducing aircraft weight and thus finding widespread application. The US's new generation air-to-surface cruise missile, ACMI 58-JASSM, utilizes composite materials in its wings, tail fins, air intakes, and all fuselage sections, resulting in a 30% weight reduction and a 50% cost reduction. Similarly, the Boeing 767 aircraft reduced its fuselage weight from 60 tons to 48 tons by 50% after increasing CFRP usage from 3% to 50%, a 20% reduction. Therefore, the widespread use of CFRP can generate substantial economic benefits.

[0003] Currently, the main connection methods for CFRP components are adhesive bonding, bolting, and hybrid connections. Adhesive bonding offers uniform load distribution but poor safety in case of failure, and adhesive joints are sensitive to environmental factors. Bolting is currently the most common connection method for CFRP components, offering advantages such as high reliability and high load-bearing capacity, but it is more expensive and heavier than riveting. Hybrid connections offer high strength but involve complex processes. Riveting is the most important assembly connection method for aircraft, offering significant advantages such as low cost, high reliability, and simple process, but it is prone to damaging CFRP components. Therefore, riveting is not yet widely used in the connection of CFRP components.

[0004] To address the installation damage caused by direct riveting of rivets to CFRP, invention application number 201710864649.1 discloses a novel riveting method and apparatus for aerospace hybrid composite materials. This invention features a recessed portion at the top of the rivet handle to accommodate the rivet head. Protected by the rivet handle and the composite material washer, the rivet head does not deform during riveting, improving the fatigue strength of the riveted structure and enhancing the riveting effect. However, this invention does not solve the problem of rivet deformation damaging the riveting hole wall during riveting. Patent number CN202110134494.2 discloses a non-destructive riveting apparatus and method for CFRP components. This invention uses a countersunk bushing to constrain the radial expansion of the rivet head, thus avoiding riveting damage. However, this riveting process is complex, the washer may warp during riveting, and the bushing manufacturing process requires stringent specifications, failing to improve the fatigue life of the connected components. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a non-destructive, long-life riveting device and method using tapered washers / gradient rivets. This invention employs a riveting method with trapezoidal rivets featuring tapered washers and cold-shrink interference fit, which limits the uneven deformation of the upsetting head and reduces the radial deformation of the rivet shank during the riveting process, thereby reducing riveting damage. Simultaneously, the rivet shank forms a cold-shrink interference fit with the CFRP riveting hole wall, improving fatigue life and load-bearing capacity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a non-destructive, long-life riveting device for tapered washers / gradient rivets, comprising a gradient rivet, a tapered washer, a riveting die, and a component to be riveted. The gradient rivet includes a rivet head, a rivet shank connected to the rivet head, and an upsetting head connected to the rivet shank. The diameter of the rivet shank is larger than the diameter of the upsetting head, and the height of the rivet shank is the same as the thickness of the component to be riveted. The upsetting head has a circular hole coaxial with it, and the depth of the circular hole is the same as the height of the upsetting head. The tapered washer is positioned above the component to be riveted. The gradient rivet passes through the riveting hole of the component to be riveted and is riveted to the tapered washer. The head surface of the riveting die has a protruding portion, which is inserted into the circular hole of the upsetting head during installation.

[0007] As a further improvement of the invention, the riveting device also includes a top iron located below the gradient rivet.

[0008] As a further improvement of the present invention, the thickness of the conical washer is distributed in a trapezoidal shape, and the washer is integrally formed from a perforated plate and a perforated frustum.

[0009] As a further improvement of the present invention, the nail rod section and the upsetting head section are integrally formed, and the diameter of the nail rod section forms a cold shrinkage interference fit with the riveting hole of the component to be riveted.

[0010] As a further improvement of the present invention, the diameter of the shank of the gradient rivet is 0.1%-5% larger than the diameter of the riveting hole.

[0011] As a further improvement of the present invention, the components to be riveted are a CFRP upper plate and a CFRP lower plate.

[0012] This invention also provides a non-destructive, long-life riveting method using tapered washers / gradient rivets, characterized by comprising the following steps:

[0013] Step 1: Place the CFRP upper plate and CFRP lower plate horizontally, immerse the gradient rivet in liquid nitrogen to shrink it, and then insert it into the rivet holes of the CFRP upper plate and CFRP lower plate from one side. Then hold the rivet head with the top iron. The CFRP upper plate, CFRP lower plate and rivet and the rivet are placed horizontally on the top iron.

[0014] Step 2: Place the tapered washer through the upset head section of the gradient riveting onto the CFRP upper plate;

[0015] Step 3: The surface of the moving riveting die head is brought into contact with the surface of the gradient rivet upsetting head. The protruding part of the riveting die surface is inserted into the round hole of the upsetting head section, and the riveting is performed with force. The riveting die squeezes the gradient rivet upsetting head section to complete the riveting.

[0016] This invention uses a conical washer to limit uneven upsetting of the rivet head. Simultaneously, the conical thickness of the washer prevents the washer from warping up around its edges during riveting, thus avoiding gaps between the washer and the CFRP layer and improving the riveting effect and the load-bearing capacity of the component. The diameter of the rivet shank is larger than that of the upsetting head section, reducing the radial deformation of the rivet shank and thus minimizing riveting damage to the component. The upsetting head section has a central hole, making it easier to form the upsetting head. The diameter of the gradient rivet shank section is 0.1%-5% larger than the diameter of the riveting hole, and the rivet shank section forms a cold-shrinkage interference fit with the CFRP riveting hole wall, improving the fatigue life of the component.

[0017] The beneficial effects of this invention are:

[0018] This invention utilizes a gradient rivet with a smaller upsetting head diameter than the rivet shank diameter, a rivet shank height equal to the thickness of the component to be riveted, an upsetting head with a circular hole of the same height as the upsetting head. This reduces the radial deformation of the rivet shank and solves the riveting damage problem of the CFRP riveting hole wall by using a conical washer to limit the upsetting head expansion. Furthermore, to address the issue of insufficient contact between the washer and the component surface after riveting, a conical washer with a trapezoidal thickness distribution is invented, preventing the washer from warping up around the edges and creating gaps with the CFRP layer during riveting, thus improving the riveting effect and the load-bearing capacity of the component. To reduce the difficulty of upsetting head forming, an upsetting head section with a central circular hole is invented, with the protruding part at the bottom of the riveting die inserted into the circular hole of the upsetting head section. Finally, to improve the connection fatigue life of the component, a gradient rivet liquid nitrogen cooling shrinkage method is used, forming a cold shrinkage interference fit between the rivet shank and the riveting hole wall, significantly improving the connection life of the riveted component. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the riveting device in an embodiment of the present invention;

[0020] Figure 2 This is an isometric view of the riveting device in an embodiment of the present invention;

[0021] Figure 3 This is an isometric view of the trapezoidal rivet in an embodiment of the present invention;

[0022] Figure 4 This is a cross-sectional view of the trapezoidal rivet in an embodiment of the present invention;

[0023] Figure 5This is an isometric view of the tapered washer in an embodiment of the present invention;

[0024] Figure 6 This is an isometric view of the riveted components in an embodiment of the present invention.

[0025] Figure 7 This is a comparison diagram of the fatigue life of fasteners with different interference fits in embodiments of the present invention;

[0026] Figure 8 This is a comparison diagram of the peak tensile load of the riveted specimen with washer and the specimen without washer in the embodiments of the present invention.

[0027] Figure label:

[0028] 1. Gradient rivet; 2. Conical washer; 3. Riveting die; 4. Top iron; 5. CFRP upper plate; 6. CFRP lower plate; 1.1. Rivet head; 1.2. Upsetting head section; 1.3. Rivet rod section; 1.4. Rivet round hole; 2.1. Conical washer with hole frustum; 2.2. Conical washer round hole plate. Detailed Implementation

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] Example

[0031] like Figures 1-8 As shown, in order to solve the problems of uneven deformation of the rivet rod causing damage to the wall of the riveting hole and low service life of the riveted component during the riveting process, the present invention provides a non-destructive long-life riveting device and method for CFRP component tapered washer / gradient rivet, which realizes non-destructive riveting of CFRP and improves the fatigue life and load-bearing capacity of the component.

[0032] This embodiment provides a non-destructive, long-life riveting device for CFRP components using tapered washers / gradient rivets, specifically including a gradient rivet 1, a tapered washer 2, a riveting die 3, a top iron 4, an upper CFRP plate 5, and a lower CFRP plate 6.

[0033] The gradient rivet 1 comprises a head 1.1, an upsetting section 1.2, a shank section 1.3, and a rivet hole 1.4. During installation, the bottom of the head 1.1 is in contact with the top iron, and the shank diameter is stepped. The shank section 1.3, connected to the head 1.1, has a diameter 0.1%-5% larger than the riveting hole diameter, and its height is the same as the total thickness of the CFRP upper plate 5 and CFRP lower plate 6 components to be riveted. During installation, the gradient rivet 1 passes through the riveting holes in the CFRP upper plate 5 and CFRP lower plate 6. Before installation, the gradient rivet 1 is cooled and shrunk using liquid nitrogen, causing the shank section 1.3 to interfere with the riveting hole. The upsetting section 1.2, connected to the shank section 1.3, has a diameter smaller than that of the shank section 1.3. The upsetting head section 1.2 has a round hole in the middle, and the depth of the round hole is the same as the height of the upsetting head section 1.2. During installation, the surface of the head of the riveting die 3 is in close contact with the surface of the upsetting head section 1.2, and the protruding part of the surface of the riveting die 3 is inserted into the round hole of the upsetting head section 1.2.

[0034] The conical washer 2 comprises a conical washer frustum with a hole 2.1 and a conical washer circular hole plate 2.2. The thickness of the conical washer 2 is trapezoidal. The washer is integrally formed from the conical washer frustum with a hole 2.1 and the conical washer circular hole plate 2.2. The conical washer circular hole plate 2.2 is located below the conical washer frustum with a hole 2.1. During installation, the upset head section 1.2 of the gradient rivet passes through the circular hole of the conical washer 2, and the bottom of the conical washer circular hole plate 2.2 contacts the CFRP upper plate 5. During riveting, the washer restricts the excessive expansion of the upset head section, thereby avoiding CFRP riveting damage and improving connection strength; at the same time, the conical design prevents the washer from warping upwards during riveting.

[0035] This embodiment also provides a non-destructive, long-life riveting method for CFRP components using tapered washers / gradient rivets, the specific implementation process of which includes the following steps:

[0036] Step 1: Place the CFRP upper plate 5 and CFRP lower plate 6 horizontally, immerse the gradient rivet 1 in liquid nitrogen to shrink it, and then insert it into the rivet holes of the CFRP upper plate 5 and CFRP lower plate 6 from one side. Then, hold the rivet head 1.1 with the top iron 4. The CFRP upper plate 5, CFRP lower plate 6 and gradient rivet 1 are placed horizontally on the top iron 4.

[0037] Step 2: Place the tapered washer 2 through the rivet upsetting head section 1.2 onto the CFRP upper plate 5;

[0038] Step 3: The head surface of the moving riveting die 3 is made to fit against the surface of the rivet upsetting head section 1.2. The protruding part of the surface of the riveting die 3 is inserted into the round hole of the rivet upsetting head section 1.2, and the riveting is performed with force. The riveting die 3 squeezes the end of the rivet upsetting head section 1.2 to complete the riveting.

[0039] This invention not only achieves non-destructive riveting of CFRP structures and simplifies the riveting process, but also improves the fatigue life and load-bearing capacity of components through cold shrinkage interference fit. Specifically, after the rivet is cooled in a liquid nitrogen environment and then installed into the CFRP component at room temperature, the rivet shank will form an interference fit with the wall of the riveting hole, thereby improving the riveting strength.

[0040] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A non-destructive long life riveting method of a conical washer / gradient rivet, characterized by, The application discloses a conical washer / gradient rivet non-destructive long-life riveting device, which comprises a gradient rivet, a conical washer, a rivet die and a component to be riveted. The application further discloses a method for riveting the component to be riveted. The method comprises the following steps: Step 1: horizontally placing the CFRP upper layer plate and the CFRP lower layer plate, placing the gradient rivet into liquid nitrogen for cold shrinking, placing the cold-shrunk gradient rivet into the riveting holes of the CFRP upper layer plate and the CFRP lower layer plate from one side, and placing the rivet head of the gradient rivet on the anvil, wherein the CFRP upper layer plate, the CFRP lower layer plate and the gradient rivet are horizontally placed on the anvil; Step 2: placing the conical washer on the CFRP upper layer plate through the head section of the gradient rivet; Step 3: moving the surface of the head of the rivet die to be in close contact with the surface of the head section of the gradient rivet, inserting the convex part of the surface of the head of the rivet die into the hole in the head section of the gradient rivet, applying force for riveting, and extruding the head section of the gradient rivet by the rivet die to complete riveting and forming. ​ ​ ​ ​

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