A method for manufacturing and self-heating riveting of thermoplastic composite and metal hybrid structure rivets

Abstract

The application discloses a kind of thermoplastic composite and metal mixed structure rivet's production and self-heating riveting method.The method first designs a kind of thermoplastic composite and metal mixed rivet, proposes two-step moulding method process and mould design for preparing metal and thermoplastic composite mixed structure rivet.In the preparation of rivet, the metal added has strong electromagnetic induction heating capacity, in the riveting process, using induction current to heat the rivet to working temperature and then press to complete the press riveting connection.This technology can significantly reduce the weight of metal rivet, can realize fast self-heating riveting, in addition, the heating and melting of thermoplastic composite can fill the damage of composite hole edge that may be caused by machining, at the same time, the wear and tear and electrochemical corrosion between rivet and plate are avoided, the sealing and impact shock resistance of riveting joint are improved.In addition, after riveting is completed, the reliable head formed at both ends of the rivet improves the strength and reliability of the connection, and is suitable for complex working conditions.

Description

Technical Field

[0001] This invention relates to a method for manufacturing and self-heating riveting of a thermoplastic composite material and metal hybrid structure rivet, belonging to the field of composite material and material processing and connection technology. Background Technology

[0002] Thermoplastic composites, due to their light weight, excellent mechanical properties, and chemical properties such as corrosion resistance, have widely replaced metallic materials in many aircraft components. These materials are mainly used in wing panels, stabilizers, and fuselage structures. With the increasing lightweighting of fuselage materials, fasteners are also increasingly trending towards lightweight designs. Among aircraft fastening methods, adhesive bonding suffers from reliability and airworthiness instability, while screwing is limited by its weight and tendency to loosen. Riveting technology, however, is widely used due to its maturity and ease of maintenance and inspection. Traditional metal rivet fastening suffers from problems such as galvanic corrosion, moisture corrosion, lightning strike risk, increased weight, and dimensional instability caused by differences in thermal expansion coefficients.

[0003] Carbon fiber thermoplastic composite rivets are rivets made from high-performance composite materials, possessing many advantages of composite materials. The advantages of carbon fiber thermoplastic composite rivets are: (1) High strength and rigidity: The addition of carbon fiber significantly improves the tensile and shear strength of the rivet, enabling it to withstand greater loads and making it suitable for applications subject to high forces. (2) Lightweight: Carbon fiber reinforced PEEK rivets are lighter than metal rivets, helping to reduce the overall weight of the structure, which is especially important in the aerospace and automotive industries. (3) Excellent chemical and heat resistance: For example, PEEK itself has excellent chemical corrosion resistance and high temperature resistance, which allows the rivets to be used in harsh environments, such as exposure to grease, fuel, and strong acids and alkalis. (4) Good fatigue resistance: For example, carbon fiber reinforced PEEK rivets can withstand repeated loads without easily experiencing fatigue fracture, making them suitable for applications requiring long-term reliability. (5) Low coefficient of thermal expansion: This type of rivet has a low coefficient of thermal expansion, maintaining better dimensional stability and structural integrity even in environments with large temperature fluctuations. At the same time, composite materials also have some disadvantages: (1) Difficult processing: Resin and carbon fiber are difficult to process and require special processing equipment and technology, which increases production costs. (2) Repair and recycling issues: Compared with metal materials, the repair and recycling of composite materials are more complex and difficult, and may require special methods or technologies.

[0004] Based on the analysis of the advantages and disadvantages of carbon fiber thermoplastic composite rivets, this paper proposes using thermoplastic composite and metal hybrid structure rivets as fasteners. This can significantly reduce the overall weight while allowing for better and faster processing of thermoplastic composites by induction heating the internal metal.

[0005] Induction heating technology offers advantages such as high power transmission efficiency, supporting rapid and targeted heating. Polymers have low electrical conductivity, and induction heating can rapidly heat thermoplastic composites by heating a metal induction heating medium. The heating temperature can be adjusted according to frequency, power, coil shape, and working distance. Furthermore, induction heating is feasible for assisting in the adhesion of thermoplastic composites, micro-damage recovery, component molding, and resin curing. During the heating process, the melting of the thermoplastic composite within the metal-hybrid rivet effectively fills the damage caused by machining to the connecting plates, while preventing wear and electrochemical corrosion between the rivet and the plate. In addition, this technology enhances the strength and reliability of the connection by improving the sealing and shock resistance of the riveted joint. The reliable upheads formed at both ends of the rivet after riveting, combined with the high strength and high ductility of the thermoplastic composite, provide excellent riveting performance, making this method suitable for complex working conditions.

[0006] Shandong Zhonghang Hehui Aviation Standard Parts Co., Ltd. disclosed a composite material rivet hot pressing forming device and a method for riveting composite plates using the same in its invention patent publication number CN116803665A. This method significantly reduces the overall weight of composite material components, avoids wear and electrochemical corrosion between the rivet and the hole wall of the plate, reduces the impact of the connection on the surface shape of the component, and improves the sealing performance and resistance to thermal mismatch and impact vibration of the riveted joint. After riveting, both ends of the rivet have reliable upset heads, thereby greatly improving the connection strength and reliability, and enabling it to adapt to complex working conditions.

[0007] The thermoplastic composite material used in this patent is a continuous carbon fiber reinforced PEEK thermoplastic composite rivet. Since PEEK has a high processing temperature and low thermal conductivity, a complex external heating system is required for long-term heating during the riveting process, resulting in long heating time and low riveting efficiency. In view of this, we designed a thermoplastic composite metal hybrid structure rivet that can quickly self-induction heat up to achieve rapid riveting, improve riveting efficiency, and reduce connection costs. Summary of the Invention

[0008] The technical problem to be solved by this invention is that metal rivet fastening has potential problems in the aerospace industry, including reducing composite layer damage, galvanic corrosion, moisture corrosion, lightning strike threat, weight increase, and dimensional instability due to different coefficients of thermal expansion.

[0009] To address the aforementioned problems, this invention provides a method for manufacturing and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets, comprising the following steps:

[0010] Step 1), Fabrication of rivets for a hybrid thermoplastic composite and metal structure:

[0011] Step 1.1): The thermoplastic carbon fiber prepreg is laminated and wound around a metal induction heating medium, and then placed into a rod pressing mold. The rod-shaped blank is formed by radial molding. Alternatively, the thermoplastic carbon fiber prepreg and the metal induction heating medium are laminated and molded to form a composite material and metal hybrid laminate, and then machined to form a rectangular or round rod-shaped blank.

[0012] Step 1.2): Compression molding of rivets: Place the blank in a detachable rivet compression molding mold, place a release agent between the mold and the bar to facilitate demolding, and compress to obtain a thermoplastic composite and metal hybrid structure rivet.

[0013] Step 1.3): Post-processing and heat treatment of rivets: The thermoplastic composite material and metal hybrid structure rivets are machined, the edge burrs and excess resin are ground off, and then annealing and tempering heat treatment is performed as needed.

[0014] Step 2) Self-heating riveting of thermoplastic composite and metal hybrid structure rivets:

[0015] Step 2.1): Preparation and positioning of the composite material or metal parts to be joined: Use machining to make holes in the composite material or metal sheet to be joined, and place it on the riveting platform for overlapping and positioning;

[0016] Step 2.2): Rivet clamping: Clamp the thermoplastic composite and metal hybrid structure rivets into the riveting equipment, adjust the position and direction of the rivets to ensure that the rivets are placed in the center of the induced current heating coil and that the rivets are vertically downward, in preparation for riveting;

[0017] Step 2.3): Press riveting: Start the induction current heating riveting equipment. After induction heating for 1~60s, the rivet reaches the preset temperature and automatically completes the pressing operation, pressing the rivet into the pre-made through hole of the two plates. The rivet contacts the lower die to complete the pressing until the upper plate stops moving. Maintain a constant pressure value and hold the pressure until it cools down to complete the plate connection.

[0018] Step 2.4): Inspect the riveted structure: First, visually observe the integrity and surface defects of the riveted structure, and then detect the internal defects of the riveted structure through non-destructive testing.

[0019] Preferably, in step 1.1), the raw materials for the thermoplastic carbon fiber prepreg include resin powder materials and carbon fiber raw materials.

[0020] More preferably, the resin powder material is at least one of polyamide-6, polyetheretherketone (PEEK), and polyphenylene sulfide (PPS).

[0021] More preferably, the carbon fiber raw material is at least one of unidirectional carbon fiber prepreg and carbon fiber fabric.

[0022] Preferably, in step 1.1), the specifications of the metal induction heating medium are at least one of the following: rod-shaped, layered, mesh-shaped, and granular.

[0023] Preferably, in step 1.1), the hybrid structure of the billet is an alternating layered structure; the volume percentage of carbon fiber raw material in the billet is 40%-65%.

[0024] Preferably, in step 2.3), the parameters of the induced current heating riveting equipment are adjusted according to the material and structure of the rivet. The parameters of the riveting equipment include heating power, riveting pressure, speed, and holding time.

[0025] Preferably, in step 2.3), the pressure holding time is 1-10 seconds.

[0026] Preferably, in step 2.3), the pre-drilled through holes on the two plates are reserved during the preparation of the plates or obtained by drilling. The connection method between the thermoplastic composite material and metal hybrid structure rivet and the two plates is: connecting composite material to composite material structure, composite material to metal structure, or metal to metal structure. The connection structure is lighter than the metal rivet connection, and its connection strength can exceed that of ordinary metal rivets through reasonable rivet design.

[0027] Thermoplastic composite and metal hybrid structure rivets greatly reduce the overall weight of composite material construction. When the thermoplastic composite is heated and melted, the internal resin can fill the damage to the composite material caused by machining, while also avoiding wear and electrochemical corrosion between the rivet and the sheet metal. This improves the sealing performance and impact and vibration resistance of the riveted joint. After riveting, there are reliable end caps at both ends, which improves the connection strength and reliability, and allows for use in complex working conditions.

[0028] This invention provides a thermoplastic composite material and metal hybrid structure rivet and its rapid self-heating riveting method. This thermoplastic composite material and metal hybrid structure rivet can replace metal rivets, improving stability while possessing the high modulus of composite materials, thereby increasing strength and reducing the weight of the connection structure.

[0029] Compared with existing metal rivets and riveting methods, the advantages of this invention are as follows:

[0030] (1) The specific strength of the thermoplastic composite material and metal hybrid structure rivet of the present invention is greater than that of the existing metal rivet, and the mass of the thermoplastic composite material and metal hybrid structure rivet is lighter than that of the metal rivet.

[0031] (2) It overcomes the damage between metal rivets and connecting plates, and thermoplastic composite materials can fill the machining damage on the sides of the connectors when they are heated and plasticized.

[0032] (3) The thermoplastic composite material and metal hybrid structure rivet described in this invention has a flexible design for the outer composite material and the inner induction heating medium;

[0033] (4) The riveting method uses induced current heating, which is more efficient and simpler. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the compression molding process of two types of rivets: thermoplastic composite material and metal hybrid bar stock, as provided in the embodiments.

[0035] Figure 2 A schematic diagram of the rivet forming mold provided in the embodiment;

[0036] Figure 3 A schematic diagram of a forming mold for a coiled rivet bar provided in an embodiment;

[0037] Figure 4 This is a schematic diagram of the induction heating riveting process of a thermoplastic composite material and metal hybrid structure rivet provided in the embodiment;

[0038] Figure 1-4 In the diagram, 1 represents resin powder material, 2 represents carbon fiber raw material, 3 represents metal induction heating medium, 4 represents thermoplastic composite material and metal hybrid structure rod, 5 represents induction current heating riveting equipment, 6 represents thermoplastic composite material and metal hybrid structure rivet, 7 represents detachable rod molding die, and 8 represents rivet molding die. Detailed Implementation

[0039] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0040] Example 1

[0041] Prepare a thin layer of stainless steel and carbon fiber reinforced PEEK unidirectional prepreg (Toray T800).

[0042] Carbon fiber prepreg is wound into 1 layer of stainless steel and 7 layers of prepreg; a cylindrical thermoplastic composite hybrid metal structure is formed by using a mold; the preform of the thermoplastic composite hybrid metal structure is placed in a molding mold; a release agent is applied between the mold and the preform; the hot press parameters are 390℃ / 5MPa; a thermoplastic composite and metal hybrid structure rivet is formed by hot pressing process.

[0043] The rivet is held in place by a riveting machine, while a high-frequency alternating current (220KHz, 5 turns, 220A) is passed through the coil inside the rivet gun. After 10s-30s, the rivet reaches the working temperature and is pressed into the pre-drilled hole at the joint of the composite board and the metal plate. Then, it contacts the lower die of the rivet, which has been coated with release agent, to form a head and complete the fastening.

[0044] Example 2

[0045] Prepare copper alloy thin layer and carbon fiber polyamide unidirectional prepreg (T800).

[0046] Carbon fiber polyamide unidirectional prepreg is stacked in a manner of 8 layers of prepreg and 1 layer of copper alloy to form a laminate (fiber volume fraction 60%), which is then cut into a rectangular thermoplastic composite material mixed with metal sandwich structure.

[0047] The prepared rectangular thermoplastic composite material mixed with metal sandwich structure preform is placed in a mold; a release agent is applied between the mold and the preform; the hot press parameters are 270℃ / 10MPa; the thermoplastic composite material and metal hybrid structure rivet is made by hot pressing process.

[0048] The rivet is held in place by a riveting machine, while a high-frequency alternating current is applied to the coil inside the rivet gun. After 10-60 seconds, the rivet reaches the working temperature and is pressed into the pre-drilled hole at the joint of the composite board. It then contacts the lower die of the rivet, which has been coated with release agent, to form a head and complete the fastening.

[0049] Example 3

[0050] Prepare titanium thin film and carbon fiber reinforced PEEK unidirectional prepreg (Toray T300).

[0051] A rectangular thermoplastic composite mixed metal sandwich structure was made by layering carbon fiber reinforced PEEK unidirectional prepreg with titanium alloy thin-layer layup (fiber volume fraction 60%).

[0052] The preform of the thermoplastic composite material mixed with metal sandwich structure is placed in a mold; a release agent is applied between the mold and the preform; the hot press parameters are 390℃ / 10MPa; and the thermoplastic composite material and metal hybrid structure rivet is made by hot pressing process.

[0053] The rivet is clamped by a riveting machine, and high-frequency alternating current is passed through the coil in the rivet gun. After 10-20 seconds, the rivet reaches the working temperature and is pressed into the pre-drilled hole at the joint of the composite board and the metal plate. Then, it contacts the rivet lower mold coated with release agent to form a head and complete the fastening.

[0054] Example 4

[0055] Prepare copper alloy mesh and carbon fiber polyamide unidirectional prepreg (T800).

[0056] Carbon fiber polyamide unidirectional prepreg is wound in a stacking manner of 8 layers of prepreg and 1 layer of aluminum alloy mesh (fiber volume fraction 60%) to form a cylindrical thermoplastic composite material mixed metal sandwich structure.

[0057] The pre-made cylindrical thermoplastic composite material mixed with metal sandwich structure is placed in a mold; a release agent is applied between the mold and the pre-made part; the hot press parameters are 270℃ / 10MPa; the thermoplastic composite material and metal hybrid structure rivet is made by hot pressing process;

[0058] The rivet is held in place by a riveting machine, while a high-frequency alternating current is applied to the coil inside the rivet gun. After 20-30 seconds, the rivet reaches the working temperature and is pressed into the pre-drilled hole at the joint of the composite board. It then contacts the lower die of the rivet, which has been coated with release agent, to form a head and complete the fastening.

[0059] Example 5

[0060] Prepare titanium alloy thin layers and carbon fiber reinforced PPS unidirectional prepreg (T800); lay up the carbon fiber reinforced PPS unidirectional prepreg in a stacking manner of 8 layers of prepreg and 1 layer of titanium alloy thin layer (fiber volume fraction 60%); press the laid-up thermoplastic composite metal sandwich structure in a mold using a hot press (parameters 320◦C / 5MPa) to form a thermoplastic composite metal sandwich structure plate; process and peel the composite plate to form a thermoplastic composite hybrid metal sandwich preform structure;

[0061] The preform of the thermoplastic composite material mixed with metal sandwich structure is placed in a mold; a release agent is applied between the mold and the preform; the hot press parameters are 320℃ / 10MPa; and the thermoplastic composite material and metal hybrid structure rivet is made by hot pressing process.

[0062] The rivet is held in place by a riveting machine, while a high-frequency alternating current is applied to the coil inside the rivet gun. After 20-30 seconds, the rivet reaches the working temperature and is pressed into the pre-drilled hole at the joint of the composite board. It then contacts the lower die of the rivet, which has been coated with release agent, to form a head and complete the fastening.

Claims

1. A method for fabricating and self-heating riveting of a thermoplastic composite material and metal hybrid structure rivet, characterized in that, Includes the following steps: Step 1), Fabrication of rivets for a hybrid thermoplastic composite and metal structure: Step 1.1): The thermoplastic carbon fiber prepreg is laminated and wound around a metal induction heating medium, and then placed into a rod pressing mold. The rod-shaped blank is formed by radial molding. Alternatively, the thermoplastic carbon fiber prepreg and the metal induction heating medium are laminated and molded to form a composite material and metal hybrid laminate, and then machined to form a rectangular or round rod-shaped blank. Step 1.2): Compression molding of rivets: Place the blank in a detachable rivet compression molding mold, place a release agent between the mold and the bar to facilitate demolding, and compress to obtain a thermoplastic composite and metal hybrid structure rivet. Step 1.3): Post-processing and heat treatment of rivets: The thermoplastic composite material and metal hybrid structure rivets are machined, the edge burrs and excess resin are ground off, and then annealing and tempering heat treatment is performed as needed. Step 2) Self-heating riveting of thermoplastic composite and metal hybrid structure rivets: Step 2.1): Preparation and positioning of the composite material or metal parts to be joined: Use machining to make holes in the composite material or metal sheet to be joined, and place it on the riveting platform for overlapping and positioning; Step 2.2): Rivet clamping: Clamp the thermoplastic composite and metal hybrid structure rivets into the riveting equipment, adjust the position and direction of the rivets to ensure that the rivets are placed in the center of the induced current heating coil and that the rivets are vertically downward, in preparation for riveting; Step 2.3): Press riveting: Start the induction current heating riveting equipment. After induction heating for 1~60s, the rivet reaches the preset temperature and automatically completes the pressing operation, pressing the rivet into the pre-made through hole of the two plates. The rivet contacts the lower die to complete the pressing until the upper plate stops moving. Maintain a constant pressure value and hold the pressure until it cools down to complete the plate connection. Step 2.4): Inspect the riveted structure: First, visually observe the integrity and surface defects of the riveted structure, and then detect the internal defects of the riveted structure through non-destructive testing.

2. The method for manufacturing and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 1.1), the raw materials for thermoplastic carbon fiber prepreg include resin powder materials and carbon fiber raw materials.

3. The method for manufacturing and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 2, characterized in that, The resin powder material is at least one of polyamide-6, polyetheretherketone, and polyphenylene sulfide.

4. The method for manufacturing and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 2, characterized in that, The carbon fiber raw material is at least one of unidirectional carbon fiber prepreg and carbon fiber fabric.

5. The method for fabricating and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 1.1), the specifications of the metal induction heating medium are at least one of the following: rod-shaped, layered, mesh-shaped, and granular.

6. The method for fabricating and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 1.1), the hybrid structure of the billet is an alternating layered structure; the volume percentage of carbon fiber raw material in the billet is 40%-65%.

7. The method for fabricating and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 2.3), the parameters of the induction current heating riveting equipment are adjusted according to the material and structure of the rivet. The parameters of the riveting equipment include heating power, riveting pressure, speed, and holding time.

8. The method for fabricating and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 2.3), the pressure holding time is 1-10 seconds.

9. The method for manufacturing and self-heating riveting of thermoplastic composite material and metal hybrid structure rivets as described in claim 1, characterized in that, In step 2.3), the pre-drilled through holes on the two plates are reserved during the preparation of the plates or obtained by drilling. The connection method between the thermoplastic composite material and metal hybrid structure rivet and the two plates is one of the following: connecting composite material and composite material structure, composite material and metal structure, or metal and metal structure.

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