Hollow rivet for joining composite and metal

Abstract

A hollow rivet for joining composite materials and metals has a rivet head with several wedge-shaped structures and a hollow rivet body. The wedge-shaped structures have countersunk holes at their centers for accommodating debris and connecting to a vacuum system. The hollow structure includes an upper, uniform cross-section portion and a lower, variable cross-section portion. This invention enables integrated drilling and riveting of composite materials and metals, significantly simplifying the process, improving production efficiency, and providing high joint strength.

Description

Technical Field

[0001] This invention relates to a technology in the field of machining, specifically a hollow rivet for connecting composite materials and metals. Background Technology

[0002] Existing composite material and metal joining technologies suffer from several drawbacks: when using riveting technology, there are problems such as high riveting force, easy damage to the surface around the hole, high riveting noise, and low efficiency; when using joining technologies such as riveting and puckering that require pre-made through holes, it is often difficult to completely guarantee their sealing performance, and joint performance is easily degraded in humid or corrosive environments; in addition, debris from pre-made through holes cannot be discharged into the profile structure, which may cause safety and noise problems during service. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes a hollow rivet for connecting composite materials and metals, which enables integrated drilling and riveting of composite materials and metals, significantly simplifying the process, improving production efficiency, and providing high joint strength.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a hollow rivet for connecting composite materials and metals, wherein the rivet head has several wedge-shaped structures and the rivet body is a hollow structure.

[0006] The wedge-shaped structure has a countersunk hole at its center for accommodating debris and connecting to the vacuum system.

[0007] The hollow structure is used to discharge debris generated during the process, and specifically includes: a constant cross-section portion at the top and a variable cross-section portion at the bottom.

[0008] The cross-section of the uniform section is circular or cross-shaped.

[0009] The variable cross-section portion is a cone shape that gradually expands outward.

[0010] The hollow rivet has a cross-shaped groove structure at its tail.

[0011] This invention relates to a riveting and welding equipment based on the above-mentioned hollow rivet, comprising: a rivet driving device and a negative pressure device for in-situ removal of debris, wherein: the rivet driving device is in contact with the wedge-shaped structure of the hollow rivet, and the negative pressure device is connected to the cavity formed by the interior of the rivet driving device, the interior of the hollow rivet, and the plate to be processed, thereby generating negative pressure to draw out debris from the riveting and welding joint.

[0012] The negative pressure device is implemented by a vacuum pump, a filter, or a hollow motor integrated with a rivet drive device.

[0013] Technical effect

[0014] This invention employs rivets with circumferentially distributed grooves and a bottom cross-shaped groove structure. During friction riveting, the composite material plate is cut and drilled while the axial riveting force is reduced. The hollow rivet structure connects the composite material and the metal, facilitating the removal of debris from the joint structure and preventing it from adhering to the rivet / metal plate interface during the riveting process, thus avoiding a decrease in joint strength. Simultaneously, the hollow rivet structure facilitates the collection and cleaning of debris, preventing it from remaining in the joint structure and causing abrasive wear during subsequent service. This invention solves the problems of complex processes and lengthy cycles in existing composite material and metal joining processes, simplifying the original multi-step processes of hole making, adjustment, drilling, and connection into a single step, significantly reducing the manufacturing cycle of dissimilar material structures and equipment. Attached Figure Description

[0015] Figure 1 This is a three-dimensional structural diagram of the hollow rivet in Example 1;

[0016] In the figure: 1. Wedge-shaped structure at the top of the rivet head; 2. Countersunk hole in the middle of the rivet head; 3. Cylindrical surface structure of the rivet through hole; 4. Cross-shaped groove structure distributed along the circumference; 5. Arc-shaped surface structure at the bottom of the rivet leg; 6. Cross-shaped groove structure at the bottom of the rivet leg.

[0017] Figure 2 This is a cross-sectional schematic diagram of the hollow rivet in Example 1;

[0018] Figure 3 for Figure 2 Top view;

[0019] Figure 4 for Figure 2 Bottom view;

[0020] Figure 5 This is a cross-sectional topography of the welded joint in Example 1;

[0021] In the picture: 7 hollow rivet, 8 composite material plate, 9 metal plate.

[0022] Figure 6 This is a three-dimensional structural diagram of the hollow rivet in Example 2;

[0023] In the diagram: a cylindrical surface structure with 10 rivet through holes;

[0024] Figure 7 This is a schematic cross-sectional view of the hollow rivet in Example 2;

[0025] Figure 8 This is a cross-sectional view of the welded joint in Example 2;

[0026] In the picture: 11 hollow rivets;

[0027] Figure 9 This is a flowchart of the riveting and welding process for Example 1;

[0028] Figure 10 This is a schematic diagram of the joint cross-sectional morphology in an embodiment;

[0029] Figure 11 This is a schematic diagram of the load-displacement curve for an example.

[0030] In the diagram: 101 drive shaft, 102 pressure sleeve, 103 hollow rivet, 104 composite material plate, 105 metal plate, 106 support structure, 107 negative pressure device, 108 composite material debris. Detailed Implementation

[0031] Example 1

[0032] like Figures 1-4 As shown, this embodiment relates to a hollow rivet used to connect composite materials and metals, with a plurality of wedge-shaped structures 1 on the rivet head and a hollow rivet body.

[0033] The wedge-shaped structure 1 on the upper part of the rivet head transmits torque during the riveting and welding process. In order to prevent it from softening and failing during the connection process, and to achieve a good solid-state connection with the lower plate, the hardness of the rivet material is usually required to be 0.8 to 1.0 times the hardness of the metal plate to be connected.

[0034] The rivet cap has a countersunk hole 2 at its center for accommodating fiber debris and connecting to a vacuum system. The radius R1 of the countersunk hole 2 and the outer diameter R of the rivet cap satisfy the following condition: R1≤0.5R.

[0035] The height h of the countersunk hole 2 and the height H of the rivet head satisfy the condition: 0 ≤ h < 0.6H. When the thickness T1 of the composite material plate is ≤ 2 mm, there are fewer chips, and the cleaning and collection work is carried out after the riveting and welding process, so the countersunk hole structure is not required. When the thickness T1 of the composite material plate is > 2 mm, in order to avoid too many chips flowing out between the drive head and the rivet head and affecting the joint forming, the countersunk hole structure is required.

[0036] The hollow structure nail body has a cross-shaped groove structure 4 along the circumferential direction in the middle for discharging fiber debris, and a cylindrical surface structure 3 is provided between adjacent cross-shaped groove structures 4 to further optimize the fiber debris discharge effect and to cut the composite material.

[0037] The diameter R3 of the cylindrical surface structure satisfies: L4 < R3 < L3, where L3 is the length from the edge of the groove to the center, and L4 is the width of the cross-shaped groove.

[0038] The length L3 from the edge to the center of the cross-shaped groove structure 4 satisfies: L3≤R2-0.25mm, where the outer diameter R2 of the rivet leg satisfies: R2≤R1.

[0039] The hollow rivets are typically made of the same alloy as the underlying metal sheet to ensure the quality of the joint and the connection effect.

[0040] like Figure 2 As shown, in this embodiment, the total length of the hollow rivet body is L = L1 + L2, where: t i L1 represents the thickness of the i-th composite material layer, n represents the number of composite material layers, and L2 represents the length of the conical cross-section.

[0041] The length of the hollow structure is H+L1-h.

[0042] The angle at the tip of the rivet leg in the conical variable cross-section section Where: K is the material hardness correction factor, with a recommended value range of [-0.4, -0.2]. The value of the tension angle α can usually be selected based on the fiber strength and layup method of the composite material. Generally, the higher the fiber strength and the more complex the layup, the smaller the tension angle α should be.

[0043] The bottom arc surface structure 5 of the rivet leg is used to cut the composite material. The angle β between the projection of the arc surface of the rivet leg and the horizontal direction affects the cutting effect of the rivet on the composite material plate. Its value range is usually [0°, 10°].

[0044] The cross-shaped groove structure 6 at the bottom of the rivet leg is used to cut the composite material. The width of the groove at the bottom of the rivet leg is the same as the width of the cross groove L4. To ensure the stability of the cutting edge at the bottom of the rivet, its height is usually 0.1-0.5 times the length of the rivet leg L2, and is adjusted according to the rivet's lightweight requirements.

[0045] Through specific experiments, carbon fiber composite plate with grade T300 and a thickness of 4.0mm was used as the upper connecting part, and stainless steel plate with grade 301L-HT and a thickness of 3.0mm was used as the lower connecting part. The contact surface between the carbon fiber composite plate and the stainless steel plate is a smooth surface, and there is no need to clean the surface of the connecting parts before riveting and welding.

[0046] The rivet head has a height of 2.0 mm and a diameter of 10.0 mm. Six wedge-shaped structures 1 are distributed at equal angles along the outer circumference. The wedge-shaped structures have a height of 1.2 mm and mesh with the end of the drive shaft to achieve axial and rotational movement.

[0047] In this embodiment, the thickness T1 of the carbon fiber composite plate is greater than 2mm. To prevent carbon fiber chips from flowing out between the drive head and the nail head during the riveting process, a countersunk hole needs to be machined, wherein the diameter of the countersunk hole is 5.0mm and the depth is 1.0mm.

[0048] The cylindrical surface of the rivet through hole is coaxial with the countersunk hole, and its diameter is 2.0mm.

[0049] The total length of the rivet leg is 7.0 mm, with the upper part of the rivet leg being 4.0 mm long, consistent with the thickness of the carbon fiber composite plate, and the lower part being 3.0 mm long. This lower part is consumed during the riveting and welding process, forming a solid-state connection with the stainless steel plate. Furthermore, the outer diameter of the rivet leg is 4.5 mm.

[0050] The tip of the rivet is connected to the cylindrical surface of the rivet through hole, with an angle α = 20° and a fillet radius R = 1 mm at the connection point.

[0051] The rivet has four through slots evenly distributed along its inner circumference, each 2.0 mm long and 1 mm wide. These slots, along with the cylindrical surface of the rivet through hole and the tip of the rivet, act as cutting edges to cut the carbon fiber composite material.

[0052] The included angle β of the rivet leg arc surface is 3°, and the width of the groove at the bottom of the rivet leg is 1.0 mm and the height is 0.3 mm.

[0053] In this embodiment, the hollow rivet is made of SUS304 stainless steel. The rivet is cold-forged and EDM (Electrical Discharge Machining). The EDM dimensional tolerance is ±0.05mm, and the other tolerances are ±0.1mm.

[0054] like Figure 9 As shown, this embodiment relates to a riveting and welding process based on the above-mentioned hollow rivets, including:

[0055] In the first stage, carbon fiber composite plates and stainless steel plates are stacked in sequence and the upper and lower plates are fixed by pressing sleeves. The pressing force is controlled by a pair of springs. A hollow ring support is placed in the area where the bottom of the stainless steel plate is coaxial with the drive rod to simulate the riveting and welding of a closed profile structure.

[0056] In Phase Two, the hollow rivet engages with the drive head, feeds at low speed to the upper surface of the carbon fiber composite, and makes stable contact. Simultaneously, this point is used as the zero point of the riveting process, the riveting process parameters are input, and then the riveting is performed.

[0057] In stage three, the hollow rivet pierces the upper carbon fiber composite plate at a rotational speed of 2400 rpm and a feed rate of 2 mm / s. Under the cutting action of the rivet, the carbon fiber composite plate is cut into carbon fiber fragments. The generated carbon fiber fragments are removed by a vacuum device to prevent heat accumulation. The feed displacement in this stage is slightly greater than the thickness of the upper carbon fiber composite plate to ensure that the carbon fiber composite plate in the area projected axially by the rivet leg is completely removed.

[0058] In stage four, the hollow rivet continues to advance downwards by 3mm at a rotation speed of 1800rpm and a feed rate of 8mm / s. After the rivet contacts the lower stainless steel plate, the friction between the two generates heat, softening the rivet leg and the upper surface of the plate. Under the combined action of axial force and the reaction force of the bottom stainless steel plate, the softened material forms a flash in the radial direction. The material flowing inwards squeezes out the remaining carbon fiber debris and fills the cavity.

[0059] In stage five, the hollow rivet is fed until the lower surface of the rivet head contacts the upper surface of the carbon fiber composite plate. At this point, the drive rod stops rotating and feeding, but remains tightly engaged with the rivet. After maintaining a constant axial pressure for 5 seconds, composite debris is sucked away by the negative pressure device through the hollow structure of the rivet, preventing residue. The drive rod then retracts upward, completing the riveting process.

[0060] Compared with traditional solid riveting and rivet riveting processes, this embodiment significantly simplifies the connection process and improves connection efficiency. The time for single-point connection is reduced from 3-5 minutes to 7.4 seconds. In this embodiment, the lower stainless steel plate has no through holes, and the hollow rivet is in close contact with the carbon fiber plate, greatly improving the joint sealing performance. In this embodiment, a solid-phase connection interface with a microstructure is formed between the hollow rivet and the stainless steel plate. At the same time, the rivet leg sidewall and rivet head structure mechanically lock the carbon fiber composite plate, ultimately obtaining a riveted welded joint with excellent mechanical properties. In a tensile-shear test conducted at room temperature, compared with a rivet joint with an outer diameter of 4.8 mm, the peak tensile-shear force of the riveted welded joint in this embodiment is increased from 5.2 kN to 8.2 kN.

[0061] Example 2

[0062] like Figures 6-7 As shown, this example relates to a hollow rivet for connecting composite materials and metal. Compared with Example 1, the hollow rivet structure of this example is simpler. The rivet head is provided with several wedge-shaped structures 1, the rivet center is provided with a through hole 10, and the conical variable cross section and the bottom groove of the rivet leg for circumferential cutting are retained.

[0063] The wedge-shaped structure 1 on the upper part of the rivet head transmits torque during the riveting and welding process. In order to prevent it from softening and failing during the connection process, and to achieve a good solid-state connection with the lower plate, the hardness of the rivet material is usually required to be 0.8 to 1.0 times the hardness of the metal plate to be connected.

[0064] The cylindrical surface structure 10 with rivet through holes is used as a channel for the discharge of fiber debris, and the inner diameter R3 of its central part usually satisfies: 0.5R2≤R3<R2.

[0065] The hollow rivets are typically made of the same alloy as the underlying metal sheet to ensure the quality of the joint and the connection effect.

[0066] In this embodiment, the total length of the hollow rivet body is L = L1 + L2, where L1 satisfies: t i Let be the thickness of the i-th composite material layer, and n be the number of composite material layers.

[0067] The hollow structure includes: a cross-shaped constant cross-section portion at the top with a length of H+L1-h, and a conical variable cross-section portion at the bottom with a length of L2.

[0068] The angle α at the tip of the rivet leg in the conical cross-section portion satisfies the following condition. Where K is the material hardness correction factor, and the recommended value range is [-0.4, -0.2]. The value of the tension angle α can usually be selected according to the fiber strength and layup method of the composite material. Generally, the higher the fiber strength and the more complex the layup, the smaller the tension angle α should be.

[0069] The outer diameter R2 of the hollow rivet usually satisfies: 0.5R≤R2<R.

[0070] In this embodiment, the width L4 of the groove at the bottom of the hollow rivet leg satisfies: 0.2≤L4<0.5R2. To ensure the stability of the cutting edge at the bottom of the rivet, its height is usually 0.1-0.5 times the length L2 of the rivet leg, and is adjusted according to the rivet's lightweight requirements.

[0071] Through specific experiments, carbon fiber composite plate with grade T300 and a thickness of 4.0mm was used as the upper connecting part, and stainless steel plate with grade 301L-HT and a thickness of 3.0mm was used as the lower connecting part. The contact surface between the carbon fiber composite plate and the stainless steel plate is a smooth surface, and there is no need to clean the surface of the connecting parts before riveting and welding.

[0072] The rivet head has a height of 2.0 mm and a diameter of 10.0 mm. Six wedge-shaped structures 1 are distributed at equal angles along the outer circumference. The wedge-shaped structures have a height of 1.2 mm and mesh with the end of the drive shaft to achieve axial and rotational movement.

[0073] The diameter of the cylindrical surface of the rivet through hole is 4.0 mm.

[0074] The total length of the rivet leg is 7.0 mm, with the upper part of the rivet leg being 4.0 mm long, consistent with the thickness of the carbon fiber composite plate, and the lower part being 3.0 mm long. This lower part is consumed during the riveting and welding process, forming a solid-state connection with the stainless steel plate. Furthermore, the outer diameter of the rivet leg is 6.4 mm.

[0075] The conical surface of the rivet is connected to the cylindrical surface of the rivet through hole, with an angle α = 20° and a fillet radius R = 1mm at the connection.

[0076] The hollow rivet in this embodiment is made of SUS304 stainless steel. The rivet is cold-forged and machined, with a dimensional tolerance of ±0.1mm.

[0077] like Figure 9 As shown, the riveting and welding process involved in this embodiment is the same as that in the previous embodiment, including:

[0078] In the first stage, carbon fiber composite plates and stainless steel plates are stacked in sequence and the upper and lower plates are fixed by pressing sleeves. The pressing force is controlled by a pair of springs. A hollow ring support is placed in the area where the bottom of the stainless steel plate is coaxial with the drive rod to simulate the riveting and welding of a closed profile structure.

[0079] In Phase Two, the hollow rivet engages with the drive head, feeds at low speed to the upper surface of the carbon fiber composite, and makes stable contact. Simultaneously, this point is used as the zero point of the riveting process, the riveting process parameters are input, and then the riveting is performed.

[0080] In stage three, the hollow rivet penetrates the upper carbon fiber composite plate at a rotational speed of 3600 rpm and a feed rate of 1 mm / s. Under the cutting action of the rivet, the carbon fiber composite plate is cut into carbon fiber fragments. The generated carbon fiber fragments are removed by a vacuum device to prevent heat accumulation. The feed displacement in this stage is slightly greater than the thickness of the upper carbon fiber composite plate to ensure that the carbon fiber composite plate in the area projected axially by the rivet leg is completely removed.

[0081] In stage four, the hollow rivet continues to advance downwards by 3mm at a rotation speed of 2400rpm and a feed rate of 6mm / s. After the rivet contacts the lower stainless steel plate, the friction between the two generates heat, softening the rivet leg and the upper surface of the plate. Under the combined action of axial force and the reaction force of the bottom stainless steel plate, the softened material forms a flash in the radial direction. The material flowing inwards squeezes out the remaining carbon fiber debris and fills the cavity.

[0082] In stage five, the hollow rivet is fed until the lower surface of the rivet head contacts the upper surface of the carbon fiber composite plate. At this point, the drive rod stops rotating and feeding, but remains tightly engaged with the rivet. After maintaining a constant axial pressure for 5 seconds, composite debris is sucked away by the negative pressure device through the hollow structure of the rivet, preventing residue. The drive rod then retracts upward, completing the riveting process.

[0083] Compared with traditional solid riveting and pull riveting processes, this embodiment significantly simplifies the connection process and improves connection efficiency. The time required for a single-point connection is reduced from 3-5 minutes to 9.5 seconds. In this embodiment, the lower stainless steel plate has no through holes, and the hollow rivets are in close contact with the carbon fiber plate, greatly improving the joint's sealing performance. This embodiment uses hollow rivets to form a solid-phase connection interface with a microstructure with the stainless steel plate, while the rivet leg sidewalls and rivet head structure mechanically lock the carbon fiber composite plate, ultimately obtaining a welded joint with excellent mechanical properties. The joint cross-sectional morphology is as follows... Figure 10 As shown. Tensile-shear tests were conducted at room temperature, and the load-displacement curves are as follows. Figure 11 As shown, compared with the rivet joint with an outer diameter of 4.8mm, the peak shear force of the riveted welded joint in this embodiment is increased from 5.2kN to 10.6kN.

[0084] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A hollow rivet for connecting composite materials and metal, characterized in that, The nail head has several wedge-shaped structures, and the nail body is a hollow structure; The hollow structure includes: a constant cross-section portion at the top and a variable cross-section portion at the bottom; The wedge-shaped structure has a countersunk hole at its center for accommodating debris and connecting to the vacuum system; The variable cross-section portion is a cone shape that gradually expands outward; The conical rivet leg tip angle Where: K is the material hardness correction coefficient and its value ranges from -0.4 to -0.

2. The length of the conical deformed cross section; The hollow rivet has a cross-shaped groove structure at its tail; The radius of the countersunk hole and The outer diameter of the rivet head meets the following requirements: The height of the countersunk hole Height of the rivet head satisfy: ; A cylindrical surface structure is provided between adjacent cross-shaped groove structures to further optimize fiber debris discharge and cut the composite material. The diameter of this cylindrical surface structure is... satisfy: ,in: The length from the edge of the groove to the center. The width of the cross-shaped groove; The length from the edge to the center of the cross-shaped groove structure satisfy: Among them: outer diameter of rivet leg satisfy: .

2. The hollow rivet for connecting composite materials and metal according to claim 1, characterized in that, The constant cross-section portion is circular or cross-shaped.

3. A riveting and welding device based on the hollow rivet described in claim 1 or 2, characterized in that, include: The rivet driving device and the negative pressure device for in-situ removal of debris are provided, wherein: the rivet driving device is in contact with the wedge-shaped structure of the hollow rivet, and the negative pressure device is connected to the cavity formed by the interior of the rivet driving device, the interior of the hollow rivet, and the plate to be treated, and the debris is drawn out from the riveting joint by generating negative pressure.

4. A riveting and welding process based on the hollow rivet described in claim 1 or 2, characterized in that, include: In the first stage, carbon fiber composite plates and stainless steel plates are stacked in sequence and the upper and lower plates are fixed by pressing sleeves. The pressing force is controlled by a pair of springs. A hollow ring support is placed in the area where the bottom of the stainless steel plate is coaxial with the drive rod to simulate the riveting and welding of the closed profile structure. In the second stage, the hollow rivet engages with the drive head and is fed at low speed to the upper surface of the carbon fiber composite material and makes stable contact. At the same time, the contact point is used as the zero point position of the riveting and welding program, the riveting and welding process parameters are input, and then the riveting and welding is carried out. In stage three, the hollow rivet is inserted into the upper carbon fiber composite plate at a rotation speed of 3600 rpm and a feed speed of 1 mm / s. Under the cutting action of the rivet, the carbon fiber composite plate is cut into carbon fiber fragments. The generated carbon fiber fragments are removed by a vacuum device to avoid heat accumulation. The feed displacement in this stage is slightly greater than the thickness of the upper carbon fiber composite plate to ensure that the carbon fiber composite plate in the axial projection area of ​​the rivet leg is completely removed. In stage four, the hollow rivet continues to feed downwards by 3mm at a rotation speed of 2400rpm and a feed speed of 6mm / s. After the rivet contacts the lower stainless steel plate, the friction between the two generates heat, softening the rivet leg and the upper surface of the plate. Under the combined action of axial force and reaction force of the bottom stainless steel plate, the softened material forms a flash in the radial direction. The material flowing inward squeezes out the remaining carbon fiber debris and fills the cavity. In stage five, the hollow rivet is fed until the lower surface of the rivet head contacts the upper surface of the carbon fiber composite plate. At this time, the drive rod stops rotating and feeding, but still maintains a tight engagement with the rivet. After maintaining a constant axial pressure for 5 seconds, the composite debris is sucked away by the negative pressure device through the hollow structure of the rivet to avoid residue. The drive rod is then retracted upwards, and the riveting is completed.

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