Heating element for resistance welding of thermoplastic composite material

Abstract

The invention relates to a heating element for resistance welding of a thermoplastic composite material. The heating element comprises a heat production area, a heat conduction area and an insulating layer which are compounded together, wherein the heat production area serves as a heating body and is located at the center position; the heat conduction area is used for conducting excessive heat at the edge and is located at the edge; the insulating layers are used for preventing current shunting and blocking current and enhancing the bonding property of the heating element and the thermoplastic composite material to be welded, and are positioned on the upper side and the lower side of the heat production area; compared with the traditional heating element for the thermoplastic composite material, the heating element disclosed by the invention can effectively optimize the uniformity of heat distribution, and considers three aspects of preventing edge effect, shunting current and improving bonding property, so that the welding efficiency and the joint strength are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of thermoplastic resin-based composite materials and welding, in particular to a heating element for resistance welding of thermoplastic composite materials. Background Art

[0002] Compared with thermosetting composites, thermoplastic composites have the characteristics of high specific strength, fast molding, excellent environmental resistance, recyclability and repairability. They have become a popular new generation of lightweight materials and key strategic materials supporting the new generation of high-tech fields such as aerospace, automobile manufacturing, energy and power, transportation, national defense and military industry.

[0003] Since thermoplastic composite materials have no curing reaction during melting and solidification, and their performance is not affected by heating and the number of molding times during repeated molding, they can be connected by welding technology. Compared with mechanical connection, adhesive bonding and other welding technologies, the resistance welding equipment of thermoplastic composite materials has the advantages of simple process, no need for complicated surface cleaning, high connection efficiency and good connection quality. It has been used to connect the skin, aileron, fairing, beam rib, elevator, structural panel and other components of Airbus A320, A330, A340-600, A350XWB, A380, Fokker F50 and other models.

[0004] The main heat source of resistance welding is the resistance heat generated when the current flows through the heating element. When the interface temperature reaches the glass transition temperature of the amorphous polymer or the crystalline melting point of the semi-crystalline polymer, the thermoplastic matrix melts, the internal polymer chain activity increases, and diffuses and entangles with each other under pressure, and forms a reliable connection after cooling. Therefore, factors such as the material type, shape, size, and surface state of the heating element affect its electrical conductivity and thermal conductivity, and thus closely affect the joint performance. At present, the heating elements commonly used for resistance welding of thermoplastic composite materials include metal meshes mainly based on stainless steel meshes, carbon fiber materials, and other special heating elements.

[0005] However, due to the poor natural convection heat transfer between traditional heating elements and air, the temperature of the part exposed to the air is higher, the temperature gradient at the end of the weld is large, and the temperature of the edge area of ​​the interface is significantly higher than the inside, which produces an "edge effect", which is prone to problems such as overheating and degradation of the end, large deformation of the joint, and reduced connection strength. In addition, the current shunting caused by the contact between the heating element and the conductive reinforcement inside the thermoplastic composite material, and the bonding between the heating element and the base material interface all affect the final quality of the joint. In order to effectively solve the above problems, innovative structural design is needed to optimize heat distribution, timely evacuate the heat in the edge area, and reduce the impact of the edge effect.

[0006] Current solutions include adjusting the welding process by applying pulse voltage or linear voltage, optimizing the clamping distance, appropriately increasing the power, cooling the ends of the weldment, and reducing the length of the heating element in the joint area, but none of them designs the heating element to reduce the edge effect.

[0007] Through searching, the public literature related to the patent application of the present invention was found: High Performance Polymers, 2021, 33(8): 892-904 disclosed that Li et al. found that surface treatment methods such as sandblasting, aromatic diazo grafting, and silane grafting of heating elements can improve the bonding, and the silane grafting treatment method was preferred. The IFSS and LSS of the joint were 38 MPa and 45 MPa, respectively, which were 36% and 23% higher than those of the untreated joint, respectively. However, the problem of obvious edge effect during welding was not effectively solved.

[0008] Through searching, the published patents related to the patent application of the present invention were found: Chinese Patent Publication No.: CN110356012B discloses a method for in-situ growth of a CNT array modified metal mesh heating element, in which CNTs with good electrical and thermal conductivity and mechanical properties are prepared on the metal mesh, which improves the interface bonding strength and the heating characteristics of the metal mesh, but it is easy to cause uneven heat conduction due to the uneven arrangement of the CNT array.

[0009] In general, the above methods have their own limitations in solving edge effects, current shunting, and improving bonding, and their actual effects and applicability are limited. Developing a heating element that can effectively reduce edge effects, effectively insulate, thereby reducing current shunting, and improve bonding with the parent material is of great significance to the resistance welding technology of thermoplastic composites. Summary of the invention

[0010] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a heating element for resistance welding of thermoplastic composite materials, which can effectively optimize heat distribution, timely dissipate heat from the edge area of ​​the heating element, and reduce the influence of edge effect.

[0011] The present invention solves the technical problem by adopting the following technical solutions:

[0012] A heating element for resistance welding of thermoplastic composite materials, comprising a heat generating area, a heat conducting area and an insulating layer which are composited together;

[0013] Wherein, the heat generating area is used as a heating element, and the conductive layer of the heat generating area is a material with a high heating rate or a carbon fiber or a stainless steel mesh after surface modification;

[0014] The heat-conducting region is located on both sides of the current flow direction of the heat-generating region and is connected to the heat-generating region, and the heat-conducting region is made of a high-conductivity material;

[0015] The insulating layers are respectively located at the upper and lower sides of the heat generating area and the heat conducting area, and the insulating layers are at least one of thermoplastic resin film, insulating fiber felt, and insulating non-woven fabric.

[0016] Moreover, the high heat generation rate material is at least one of a metal mesh, a unidirectional continuous carbon fiber bundle, a carbon fiber fabric, a mixed mesh of carbon fiber filaments and metal filaments, and a mixed mesh of carbon fiber and organic fiber.

[0017] Furthermore, the surface modification is silane treatment, preparation of metal oxide coating, oxidation treatment, chemical etching or in-situ preparation of carbon nanotubes.

[0018] Moreover, when the high heat generation rate material of the heat generating area is a metal mesh, the material of the metal wire includes but is not limited to stainless steel, iron, brass, cobalt or nickel, and the diameter of the metal wire is 0.02-0.6 mm, the spacing of the metal wire is 0.04-2.5 mm, and the mesh shape of the metal wire includes but is not limited to rectangle, diamond, circle or polygon; and / or

[0019] When the high heat generation rate material in the heat generating area is a unidirectional continuous carbon fiber bundle, the specification of the carbon fiber bundle is 1 to 24K; and / or

[0020] When the high heat generation rate material of the heat generating area is carbon fiber fabric, the weaving form includes but is not limited to plain weave, twill weave, satin weave, unidirectional weave, multi-axial weave or special weave, and the surface density of the fabric is 5 to 150 g / m 2 , the carbon fiber tow specification of the fabric is 0.2~3K; and / or

[0021] When the high heat generation rate material of the heat generating area is a mixed mesh of carbon fiber and organic fiber, the surface density of the fabric is 25 to 350 g / m 2 , the specification of carbon fiber tow is 2K~13K, the organic fiber includes but is not limited to polyester, polyamide, esterimide, polypropylene, ultra-high molecular weight polyethylene, polyphenylene sulfide, polyacrylonitrile, p-benzimidazole, polybenzoxazole, poly-p-phenylene benzobisoxazole or polyphenylene pyridine diimidazole, and the direction of the carbon fiber is consistent with the direction of current and is closely combined with the heat conduction areas on both sides; and / or

[0022] When the high heat generation rate material of the heat generating area is a mixed mesh of carbon fiber filaments and metal filaments, the surface density of the fabric is 35 to 550 g / m 2 The specification of the carbon fiber tow is 0.2~3K, and the metal wire includes but is not limited to stainless steel, iron, brass, cobalt, and nickel. The direction of the carbon fiber or metal wire is consistent with the direction of the current and is tightly combined with the heat conduction areas on both sides.

[0023] Moreover, the high conductivity material of the heat conduction area is a copper mesh or an aluminum mesh;

[0024] The diameter of the metal wire of the copper mesh or aluminum mesh is 0.02-0.6 mm, and the mesh spacing of the copper mesh or aluminum mesh is 0.04-2.5 mm.

[0025] Moreover, the resistivity of the high heat generation rate material is greater than 6.0×10 -7 Ω·m, the resistivity of the high conductivity material is less than 3.0×10 -8 Ω·m.

[0026] Moreover, the metal mesh in the heat generating area has the same size as the copper mesh or aluminum mesh in the heat conducting area;

[0027] When the heat generating area is a metal mesh, the welding method between the metal mesh and the heat conducting area is resistance welding, ultrasonic welding, laser welding or brazing.

[0028] Moreover, when the heat generating area is a unidirectional continuous carbon fiber bundle, a carbon fiber fabric, a mixed mesh of carbon fiber filaments and metal filaments, or a mixed mesh of carbon fiber and organic fiber, it is connected to the heat conducting area by weaving.

[0029] Moreover, when the insulating layer is a thermoplastic resin film, its density is less than or equal to 150g / m 2 ;

[0030] When the insulating layer is an insulating fiber mat, it includes but is not limited to chopped strand mat, continuous mat, surface mat or composite mat, and the surface density is less than or equal to 150g / m 2 , fiber tow specifications are 0.2~3K;

[0031] When the insulating layer is an insulating non-woven fabric, the weaving form of the fabric includes but is not limited to plain weave, twill weave, satin weave, unidirectional weave, multi-axial weave or special weave, and the surface density is 5 to 150 g / m 2 .

[0032] Moreover, the thermoplastic matrix of the parent material and the thermoplastic resin film includes amorphous polymers: polystyrene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, polyvinyl chloride, styrene-acrylonitrile copolymer, polycarbonate, polycarbonate alloy, polyphenylene oxide, polypropylene oxide, polyetherimide, polyurethane, polysulfone, polyethersulfone, polyethersulfoneketone, polyamide-imide, polybenzimidazole, polyimide, thermoplastic polyimide;

[0033] Also included are semi-crystalline polymers: polyethylene, polyethylene terephthalate, polypropylene, high-density polyethylene, low-density polyethylene, polyamide, polycaprolactam, polyhexamethylene adipamide, polybutylene terephthalate, cross-linked polyethylene, polyoxymethylene, polyethylene terephthalate copolymer, polyvinylidene chloride, ultra-high molecular weight polyethylene, polyundecanamide, polydodecanamide, polyaromatic hydrocarbon resins, para-aromatic polyamides, polyphthalamide, polyphenylene sulfide, polytetrafluoroethylene, liquid crystal polymers, polyaryletherketone, polyetheretherketone, polyetherketoneketone, polyethernitrileketone, polyethersulfoneketone, polyethernitrilesulfone, polyethernitrile, polyaryletherketone-containing phthalazinone, polyarylethernitrileketone-containing phthalazinone, polyarylethersulfoneketone-containing phthalazinone, polyarylethernitrilesulfone-containing phthalazinone, polyoxymethylene;

[0034] The reinforcement phase includes fiber reinforcement, particle reinforcement, sheet reinforcement, fabric reinforcement, foam reinforcement, and nanoparticle reinforcement;

[0035] Wherein, when the insulating layer is a thermoplastic resin film, the material of the thermoplastic resin film is consistent with that of the thermoplastic matrix.

[0036] The advantages and positive effects of the present invention are:

[0037] 1. The present invention effectively reduces the influence of edge effect on joint performance by combining traditional heating elements with copper mesh or aluminum mesh with excellent thermal conductivity. Through optimized material combination and new structural design, the excessive resistance heat at the interface edge during resistance welding of thermoplastic composite materials is effectively dispersed, the temperature gradient at the end of the weldment is reduced, and the edge effect and the problems caused by the edge effect, such as overheating of the end, excessive surface melting and melting, large joint deformation, and reduced connection strength are effectively solved.

[0038] 2. The present invention effectively ensures the insulation between the heating element and any conductive parts at the interface during resistance welding of thermoplastic composite materials by adding an insulating layer to the heat generating area and the heat conducting area, and preparing an oxide coating on the surface of the heat generating area and the heat conducting area, thereby blocking the current shunting caused by the new conductive path generated when the heating element contacts the conductive fibers inside the weldment, and eliminating the problems of reduced current density of the heating element, insufficient heat generation, uneven interface temperature, etc. caused by current shunting, thereby improving the interface connection strength and joint performance.

[0039] 3. The present invention adds an insulating layer that is the same as or similar to the thermoplastic composite material matrix on the upper and lower sides, thereby enabling the thermoplastic matrix polymer chain to flow and diffuse better and fill the interface gap during resistance welding, thereby reducing welding defects such as holes and cracks caused by insufficient thermoplastic matrix, improving the stability, consistency and reliability of the overall structure, and extending the service life to a certain extent.

[0040] 4. The invention has a wide range of applications. It can be used for resistance welding of various types of thermoplastic resins and their composite materials, thermosetting resins and their composite materials, or one or more of them. It can also be customized according to the temperature resistance level, application environment and other conditions of different resins and their composite materials. For example, the reinforcing phases of thermoplastic composite materials or thermosetting composite materials include fibers, particles, sheets, fabrics, foams, nanoparticles, etc.; among them, the reinforcing fibers of fiber-reinforced composite materials include glass fibers, carbon fibers, graphite fibers, boron fibers, ceramic fibers, polyethylene fibers, polyamide fibers, polyester fibers, PBO fibers, natural fibers, etc.

[0041] 5. The process of the present invention has a wide range of optional parameters and a wider process window. The present invention is based on heating elements for traditional thermoplastic composite materials such as metal mesh, unidirectional carbon fiber and carbon fiber fabric. The traditional heating elements can be directly used as the heat-generating area of ​​the present invention, or they can be first treated with silane, prepared with metal oxide coating, oxidized, chemically etched, prepared in situ with carbon nanotubes (CNT) and other surface modifications, and then used as the heat-generating area of ​​the present invention. At the same time, the present invention can effectively improve production efficiency, reduce the defective rate caused by edge effects, shorten the welding cycle, and improve production efficiency and the stability of the welding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the structure of the present invention.

[0043] Figure 2 It is a schematic diagram of the structure of the heat generating area and the heat conducting area in Example 1 of the present invention.

[0044] Figure 3 Schematic diagram of the structure of the heat generating area and the heat conducting area in Example 2 of the present invention.

[0045] Figure 4 Schematic diagram of the structure of the heat generating area and the heat conducting area in Example 3 of the present invention.

[0046] Figure 5 Schematic diagram of the structure of the heat generating area and the heat conducting area in Example 4 of the present invention.

[0047] Figure 6 Schematic diagram of the structure of the heat generating area and the heat conducting area in Example 5 of the present invention.

[0048] Reference numerals

[0049] 1-1 heat generating area, 1-2 heat conducting area, 2 insulating layer, 1-21 pure copper mesh, 1-11 stainless steel mesh, 1-12 unidirectional continuous carbon fiber bundle, 1-13 plain carbon fiber fabric, 1-14 mixed mesh of carbon fiber bundle and metal wire, 1-15 mixed mesh of carbon fiber and organic fiber. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0051] A heating element for resistance welding of thermoplastic composite materials, comprising a heat generating area, a heat conducting area and an insulating layer which are composited together;

[0052] Wherein, the heat generating area is used as a heating element, and the conductive layer of the heat generating area is a material with a high heating rate or a carbon fiber or a stainless steel mesh after surface modification;

[0053] The heat-conducting region is located on both sides of the current flow direction of the heat-generating region and is connected to the heat-generating region, and the heat-conducting region is made of a high-conductivity material;

[0054] The insulating layers are respectively located at the upper and lower sides of the heat generating area and the heat conducting area, and the insulating layers are at least one of thermoplastic resin film, insulating fiber felt, and insulating non-woven fabric.

[0055] Example 1

[0056] like Figure 2 As shown, a heating element for resistance welding of thermoplastic composite materials, this embodiment uses a stainless steel mesh 1-11 treated with in-situ prepared carbon nanotubes (CNT), a pure copper mesh 1-21 and carbon fiber reinforced polyetheretherketone (not shown in the figure):

[0057] The process of preparing carbon nanotubes on the surface of stainless steel mesh by chemical vapor deposition is as follows: First, the stainless steel mesh is immersed in a 0.3 mol / L dilute sulfuric acid solution at 50°C for 30 minutes to remove impurities and oxide layers on the surface. Then the stainless steel mesh is placed in a nickel plating solution (composed of 280 g / L nickel sulfate (NiSO4), 40 g / L nickel chloride (NiCl2), and 35 g / L boric acid (H3BO3)), and nickel plating is performed at a current of 0.3A for 15 seconds as a catalyst. Finally, ethanol is selected as a carbon source, and the stainless steel mesh is placed in a chemical vapor deposition equipment for deposition at a preheating temperature of 600°C and vacuum conditions for 10 to 20 minutes. After the growth is completed, stop the gas supply, and let the sample cool naturally or actively cool to room temperature.

[0058] Among them, the heat generating area is a stainless steel mesh 1-11 treated with in-situ prepared carbon nanotubes (CNT), the metal wire diameter of the stainless steel mesh is 0.5mm, and the mesh spacing is 0.85mm. The heat conducting area is a pure copper mesh 1-21, the metal wire diameter of the copper mesh is 0.5mm, and the mesh spacing is 0.85mm. The two are connected by laser welding, and a smooth transition is ensured at the connection.

[0059] The insulating layer is consistent with the thermoplastic matrix of the material to be welded. That is, when a 3mm thick carbon fiber reinforced polyetheretherketone (CF / PEEK) material to be welded is selected, the insulating layer is a 0.1mm thick polyetheretherketone (PEEK) film with a surface density of 129g / m 2 Finally, through infrared camera observation, it was found that the heating element can effectively optimize the temperature distribution. The temperature of the heat conduction area is lower, while the temperature of the heat generation area is higher and evenly distributed, which effectively reduces the uneven temperature distribution at the interface. Further observations found that the stainless steel mesh treated with in-situ carbon nanotubes (CNT) has better wettability with the thermoplastic polyetheretherketone matrix.

[0060] Example 2

[0061] like Figure 3 As shown, a heating element for resistance welding of thermoplastic composite materials, this embodiment uses a composite unidirectional continuous carbon fiber bundle 1-12, a pure copper mesh 1-21 and carbon fiber reinforced polyetheretherketone:

[0062] Among them, the heat generating area uses unidirectional continuous carbon fiber bundles 1-12 with a specification of 10K, and the heat conducting area uses pure copper mesh 1-21. The pure copper mesh metal wire diameter of the heat conducting area is 0.5mm and the mesh spacing is 0.8mm. The two are connected by weaving to ensure a smooth transition at the connection.

[0063] The insulating layer is consistent with the thermoplastic matrix of the material to be welded. That is, when a 3mm thick carbon fiber reinforced polyetheretherketone (CF / PEEK) material to be welded is selected, the insulating layer is a 0.1mm thick polyetheretherketone (PEEK) film with a surface density of 129g / m 2 Finally, through infrared camera observation, it was found that the heating element can effectively optimize the temperature distribution. The temperature of the heat conduction area is lower, while the temperature of the heat generation area is higher and evenly distributed, which effectively reduces the uneven temperature distribution at the interface.

[0064] Example 3

[0065] like Figure 4 As shown, a heating element for resistance welding of thermoplastic composite materials, this embodiment uses a plain carbon fiber fabric 1-13, a pure copper mesh 1-21 and carbon fiber reinforced polyetheretherketone composited together:

[0066] The heat generating area is made of plain carbon fiber fabric 1-13, and the surface density of the fabric is 50g / m 2 The fiber bundle specification is 0.5K, the heat conduction area uses pure copper mesh 1-21, the pure copper mesh metal wire diameter of the heat conduction area is 0.5mm, and the mesh spacing is 0.85mm. The two are connected by ultrasonic welding to ensure a smooth transition at the connection.

[0067] The insulating layer is consistent with the thermoplastic matrix of the material to be welded. That is, when a 3mm thick carbon fiber reinforced polyetheretherketone (CF / PEEK) material to be welded is selected, the insulating layer is a 0.1mm thick polyetheretherketone (PEEK) film with a surface density of 129g / m 2 Finally, through infrared camera observation, it was found that the heating element can effectively optimize the temperature distribution. The temperature of the heat conduction area is lower, while the temperature of the heat generation area is higher and evenly distributed, which effectively reduces the uneven temperature distribution at the interface.

[0068] Example 4

[0069] like Figure 5 As shown, a heating element for resistance welding of thermoplastic composite materials, this embodiment uses a mixed mesh 1-14 of carbon fiber bundles and metal wires, a pure copper mesh 1-21 and carbon fiber reinforced polyetheretherketone:

[0070] The heat generating area is made of a mixed mesh 1-14 of carbon fiber bundles and metal wires, and the surface density of the fabric is 80g / m 2 The specification of the carbon fiber tow is 5K, and the heat conduction area uses pure copper mesh 1-21. The diameter of the pure copper mesh metal wire in the heat conduction area is 0.5mm and the mesh spacing is 0.85mm. The two are connected by weaving technology, and the direction of the carbon fiber is consistent with the direction of the current, and a smooth transition is guaranteed at the connection.

[0071] The insulating layer is consistent with the thermoplastic matrix of the material to be welded. That is, when a 3mm thick carbon fiber reinforced polyetheretherketone (CF / PEEK) material to be welded is selected, the insulating layer is a 0.1mm thick polyetheretherketone (PEEK) film with a surface density of 129g / m 2 , polyetheretherketone (PEEK) fiber was selected as the organic fiber. Finally, through infrared camera observation, it was found that the heating element can effectively optimize the temperature distribution. The temperature of the heat conduction area is lower, while the temperature of the heat generation area is higher and evenly distributed, which effectively reduces the uneven temperature distribution at the interface.

[0072] Example 5

[0073] like Figure 6 As shown, a heating element for resistance welding of thermoplastic composite materials, this embodiment uses a composite carbon fiber and organic fiber mixed mesh 1-15, a pure copper mesh 1-21 and carbon fiber reinforced polyetheretherketone:

[0074] The heat generating area is made of a carbon fiber and organic fiber mixed mesh 1-15, and the surface density of the fabric is 150g / m 2The specification of the carbon fiber tow is 1K, and the heat conduction area uses pure copper mesh 1-21. The diameter of the pure copper mesh metal wire in the heat conduction area is 0.5mm and the mesh spacing is 0.85mm. The two are connected by weaving technology, and the direction of the carbon fiber or metal wire is consistent with the direction of the current, and it is tightly combined with the heat conduction areas on both sides, and a smooth transition is guaranteed at the connection.

[0075] The insulating layer is consistent with the thermoplastic matrix of the material to be welded. That is, when a 3mm thick carbon fiber reinforced polyetheretherketone (CF / PEEK) material to be welded is selected, the insulating layer is a 0.1mm thick polyetheretherketone (PEEK) film with a surface density of 129g / m 2 , polyetheretherketone (PEEK) fiber was selected as the organic fiber. Finally, through infrared camera observation, it was found that the heating element can effectively optimize the temperature distribution. The temperature of the heat conduction area is lower, while the temperature of the heat generation area is higher and evenly distributed, which effectively reduces the uneven temperature distribution at the interface.

[0076] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A heating element for resistance welding of thermoplastic composite materials, characterized in that: It includes a heat generating area, a heat conducting area and an insulating layer which are combined together; Wherein, the heat generating area is used as a heating element, and the conductive layer of the heat generating area is a material with a high heating rate or a carbon fiber or a stainless steel mesh after surface modification; The heat-conducting region is located on both sides of the current flow direction of the heat-generating region and is connected to the heat-generating region, and the heat-conducting region is made of a high-conductivity material; The insulating layers are respectively located at the upper and lower sides of the heat generating area and the heat conducting area, and the insulating layers are at least one of thermoplastic resin film, insulating fiber felt, and insulating non-woven fabric.

2. The heating element for resistance welding of thermoplastic composite materials according to claim 1, characterized in that: The high heat generation rate material is at least one of a metal mesh, a unidirectional continuous carbon fiber bundle, a carbon fiber fabric, a mixed mesh of carbon fiber filaments and metal filaments, and a mixed mesh of carbon fiber and organic fiber.

3. The heating element for resistance welding of thermoplastic composite materials according to claim 2, characterized in that: The surface modification is silane treatment, preparation of metal oxide coating, oxidation treatment, chemical etching or in-situ preparation of carbon nanotubes.

4. The heating element for resistance welding of thermoplastic composite materials according to claim 3, characterized in that: When the high heat generation rate material of the heat generating area is a metal mesh, the material of the metal wire includes but is not limited to stainless steel, iron, brass, cobalt or nickel, and the diameter of the metal wire is 0.02-0.6 mm, the spacing of the metal wire is 0.04-2.5 mm, and the mesh shape of the metal wire includes but is not limited to rectangle, diamond, circle or polygon; and / or When the high heat generation rate material in the heat generating area is a unidirectional continuous carbon fiber bundle, the specification of the carbon fiber bundle is 1 to 24K; and / or When the high heat generation rate material of the heat generating area is carbon fiber fabric, the weaving form includes but is not limited to plain weave, twill weave, satin weave, unidirectional weave, multi-axial weave or special weave, and the surface density of the fabric is 5 to 150 g / m 2 , the carbon fiber tow specification of the fabric is 0.2~3K; and / or When the high heat generation rate material of the heat generating area is a mixed mesh of carbon fiber and organic fiber, the surface density of the fabric is 25 to 350 g / m 2 , the specification of carbon fiber tow is 2K~13K, the organic fiber includes but is not limited to polyester, polyamide, esterimide, polypropylene, ultra-high molecular weight polyethylene, polyphenylene sulfide, polyacrylonitrile, p-benzimidazole, polybenzoxazole, poly-p-phenylene benzobisoxazole or polyphenylene pyridine diimidazole, and the direction of the carbon fiber is consistent with the direction of current and is closely combined with the heat conduction areas on both sides; and / or When the high heat generation rate material of the heat generating area is a mixed mesh of carbon fiber filaments and metal filaments, the surface density of the fabric is 35 to 550 g / m 2 The specification of the carbon fiber tow is 0.2~3K, and the metal wire includes but is not limited to stainless steel, iron, brass, cobalt, and nickel. The direction of the carbon fiber or metal wire is consistent with the direction of the current and is tightly combined with the heat conduction areas on both sides.

5. The heating element for resistance welding of thermoplastic composite materials according to claim 4, characterized in that: The high conductivity material of the heat conduction area is a copper mesh or an aluminum mesh; The diameter of the metal wire of the copper mesh or the aluminum mesh is 0.02-0.6 mm, and the mesh spacing of the copper mesh or the aluminum mesh is 0.04-2.5 mm.

6. The heating element for resistance welding of thermoplastic composite materials according to claim 5, characterized in that: The resistivity of the high heat generation rate material is greater than 6.0×10 -7 Ω·m, the resistivity of the high conductivity material is less than 3.0×10 -8 Ω·m.

7. The heating element for resistance welding of thermoplastic composite materials according to claim 6, characterized in that: The metal mesh in the heat generating area has the same size as the copper mesh or aluminum mesh in the heat conducting area; When the heat generating area is a metal mesh, the welding method between the metal mesh and the heat conducting area is resistance welding, ultrasonic welding, laser welding or brazing.

8. The heating element for resistance welding of thermoplastic composite materials according to claim 7, characterized in that: When the heat generating area is a unidirectional continuous carbon fiber bundle, a carbon fiber fabric, a mixed mesh of carbon fiber filaments and metal filaments, or a mixed mesh of carbon fiber and organic fiber, it is connected to the heat conducting area by weaving.

9. The heating element for resistance welding of thermoplastic composite materials according to claim 8, characterized in that: When the insulating layer is a thermoplastic resin film, its density is less than or equal to 150g / m 2 ; When the insulating layer is an insulating fiber mat, it includes but is not limited to chopped strand mat, continuous mat, surface mat or composite mat, and the surface density is less than or equal to 150g / m 2 , fiber tow specifications are 0.2~3K; When the insulating layer is an insulating non-woven fabric, the weaving form of the fabric includes but is not limited to plain weave, twill weave, satin weave, unidirectional weave, multi-axial weave or special weave, and the surface density is 5 to 150 g / m 2 .

10. The heating element for resistance welding of thermoplastic composite materials according to claim 9, characterized in that: Thermoplastic matrices of parent materials and thermoplastic resin films include amorphous polymers: polystyrene, acrylonitrile-butadiene-styrene copolymers, polymethyl methacrylate, polyvinyl chloride, styrene-acrylonitrile copolymers, polycarbonate, polycarbonate alloys, polyphenylene oxide, polypropylene oxide, polyetherimide, polyurethane, polysulfone, polyethersulfone, polyethersulfoneketone, polyamide-imide, polybenzimidazole, polyimide, thermoplastic polyimide; Also included are semi-crystalline polymers: polyethylene, polyethylene terephthalate, polypropylene, high-density polyethylene, low-density polyethylene, polyamide, polycaprolactam, polyhexamethylene adipamide, polybutylene terephthalate, cross-linked polyethylene, polyoxymethylene, polyethylene terephthalate copolymer, polyvinylidene chloride, ultra-high molecular weight polyethylene, polyundecanamide, polydodecanamide, polyaromatic hydrocarbon resins, para-aromatic polyamides, polyphthalamide, polyphenylene sulfide, polytetrafluoroethylene, liquid crystal polymers, polyaryletherketone, polyetheretherketone, polyetherketoneketone, polyethernitrileketone, polyethersulfoneketone, polyethernitrilesulfone, polyethernitrile, polyaryletherketone-containing phthalazinone, polyarylethernitrileketone-containing phthalazinone, polyarylethersulfoneketone-containing phthalazinone, polyarylethernitrilesulfone-containing phthalazinone, polyoxymethylene; The reinforcement phase includes fiber reinforcement, particle reinforcement, sheet reinforcement, fabric reinforcement, foam reinforcement, and nanoparticle reinforcement; Wherein, when the insulating layer is a thermoplastic resin film, the material of the thermoplastic resin film is consistent with that of the thermoplastic matrix.

Images