Implant materials for induction welding of thermoplastic composites, their preparation methods and applications

Abstract

This invention belongs to the field of materials science and engineering technology, and relates to an implant material for induction welding of thermoplastic composite materials, its manufacturing method, and its application. The implant material includes a heating element, which is a single continuous metal foil with a thickness ≤0.05mm. The manufacturing method involves covering the upper and lower sides of the heating element with thermoplastic resin material and then hot-pressing it to obtain the implant material. The application involves using the implant material for induction welding of thermoplastic composite materials. This invention uses a single continuous metal foil as the heating element, eliminating inter-wire contact resistance, and deriving 100% of the heat from the Joule heating of the metal body, thus increasing the heating rate and shortening the welding time. Simultaneously, it reduces the amount of heating element used, lowers the weight of the weld joint, and improves the flexibility of the implant material, adapting to the welding requirements of complex curved surfaces.

Description

Technical Field

[0001] This invention belongs to the field of materials science and engineering technology, and relates to an implant material for induction welding of thermoplastic composite materials, its preparation method and application. Background Technology

[0002] Taking advantage of the ability of thermoplastic composite matrices to be repeatedly heated, melted, cooled, and solidified, induction welding technology has gradually replaced traditional joining and assembly techniques such as riveting, screwing, and gluing. Its basic principle is as follows: an alternating current is passed through an induction coil to generate an alternating magnetic field, which in turn induces alternating eddy currents in the closed conductive circuit within the workpiece to be welded. Heating is achieved through the Joule effect of these eddy currents. For carbon fiber reinforced thermoplastic composites, existing technologies often employ self-induction welding, relying on the induced eddy currents generated in the alternating magnetic field within the closed conductive circuit formed by the carbon fibers themselves.

[0003] However, the surface of the workpiece closer to the induction coil is more strongly affected by the magnetic field and generates more intense heat. Often, before the resin on the welding surface has fully melted, the surface of the workpiece has already experienced localized overheating or even charring, resulting in defects inside the workpiece. This damages both the appearance of the welded joint and its mechanical properties. Even with heat dissipation methods such as air cooling or heat-conducting plates, the heating area will be dispersed and energy loss will increase, making it impossible to achieve rapid and continuous induction welding of large-sized components.

[0004] To address the issues of uneven heat distribution and insufficient heating of the welding surface in self-induction welding, existing technologies have further proposed using metal materials as implanted heating elements, placing them on the welding surface to achieve directional energy concentration, with metal mesh as the main component, as disclosed in patent CN113043604B and the literature (Modeling and experimental investigation of induction welding of thermoplastic composites and comparison with other welding processes [J]. SAGE Publications, 2016 (21)).

[0005] However, metal mesh is a woven structure of metal wires, which has contact resistance between the wires, resulting in serious energy loss, low actual heating efficiency, long welding time, and production efficiency that cannot meet the requirements of high-efficiency composite material bonding. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and to provide an implant material for induction welding of thermoplastic composite materials, its preparation method and application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An implant material for induction welding of thermoplastic composites includes a heating element and a thermoplastic resin layer covering its surface. The heating element is a monolithic continuous metal foil with a thickness ≤0.05 mm.

[0009] This invention reveals that the fundamental reason for the severe energy loss in existing technologies using metal mesh as heating elements is that the metal mesh, being a woven structure of metal wires, exhibits inter-wire contact resistance, which accounts for more than 50% of the total resistance. This invention directly uses a single, continuous metal foil as the heating element, eliminating inter-wire contact resistance. 100% of the heat comes from the Joule heating of the metal itself, resulting in no additional losses, effectively increasing the heating rate and shortening the welding time.

[0010] Existing technologies, such as the literature (Modeling and experimental investigation of induction welding of thermoplastic composites and comparison with other welding processes [J]. SAGE Publications, 2016 (21)), generally believe that increasing the thickness of the heating element to reduce resistance is a reasonable direction for improving the heating rate. Therefore, existing technologies often control the thickness of the heating element to above 0.05 mm in order to achieve a higher heating rate. A larger thickness of the heating element will cause a series of problems, such as excessive heating element usage, excessive weight of the welded joint, and poor flexibility of the implanted material that cannot adapt to the welding requirements of complex curved surfaces, etc.

[0011] However, this invention unexpectedly discovered that when the heating element is a single continuous metal foil, reducing the thickness is actually more beneficial for increasing the heating rate. The specific principle is: Joule heat per unit time (Q=I 2 The generation efficiency of Rt is dominated by eddy current density, which is (current per unit cross-sectional area, A / mm²). 2 The eddy current density is inversely proportional to the material thickness; the smaller the thickness, the greater the eddy current density, the higher the Joule heat, and the higher the heating rate. Therefore, this invention controls the thickness of the heating element to ≤0.05mm to solve the problems of using large-thickness heating elements in the prior art while ensuring excellent heating rate.

[0012] As a preferred technical solution:

[0013] As described above, for an implant material used in induction welding of thermoplastic composites, the thickness of the heating element is ≤0.012mm. When the thickness of the heating element is ≤0.012mm, the Joule heating efficiency is significantly enhanced, the induction heating rate is higher, and the welding time is further shortened.

[0014] As described above, for an implant material used in induction welding of thermoplastic composites, the heating element is made of copper, stainless steel, iron, aluminum, nickel, titanium, silver, or gold; the thermoplastic resin layer is made of polyethylene (PE), polypropylene (PP), polyamide (PA), polystyrene (PS), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polyphenylene ether (PPO / PPE), polyether ether ketone (PEEK), polysulfone (PSF / PSU), polyphenylene sulfide (PPS), or polyarylether ether ketone (PAEK); the thickness of the implant material used for induction welding of thermoplastic composites is 5-30 times the thickness of the heating element.

[0015] As described above, in an implant material for induction welding of thermoplastic composite materials, the heating element undergoes surface treatment to improve surface roughness and / or introduces active groups on the surface, thereby improving the interfacial bonding strength between the heating element and the thermoplastic resin layer. The improvement effect on interfacial bonding strength is more significant when both surface roughness and surface active groups are introduced.

[0016] As described above, the implant material for induction welding of thermoplastic composite materials employs a single or combination of laser treatment, plasma treatment, chemical treatment, anodizing treatment, surface grafting treatment, and sandblasting treatment for surface treatment.

[0017] The laser processing parameters include: a processing frequency of 20kHz, a processing speed of 250-1000mm / s, and a processing number of 1-5 times;

[0018] The process parameters for plasma treatment include: nozzle diameter of 30-80 mm, treatment time of 10-200 s, distance between workpiece and nozzle of 5-20 mm, and gas flow rate of 500-700 L / h.

[0019] The process parameters for chemical treatment include: the concentration of the treatment solution (nitric acid solution, sulfuric acid solution, hydrochloric acid solution or hydrogen peroxide solution, etc.) is 10-40wt%, the treatment temperature is 50-90℃, and the treatment time is 5-40min;

[0020] The process parameters for anodizing include: an electrolyte concentration of 2-20 wt% (oxalic acid solution, sulfuric acid solution, phosphoric acid solution, or acid mixture, etc.), a voltage of 10-400 V, and a current density of 5-20 mA / cm². 2The oxidation time is 15 min to 10 h;

[0021] The process parameters for surface grafting treatment include: the concentration of the treatment solution (silane coupling agent solution, polyaryletherketone solution, polyimide solution, polyamic acid solution, etc.) is 0.25-2.0wt%, and the treatment time is 5-30min;

[0022] The process parameters for sandblasting include: abrasive type of quartz sand, corundum, white corundum or glass microspheres, abrasive particle size of 240-800 mesh, sandblasting pressure of 0.1-0.4MPa, nozzle diameter of 20-40mm, spray angle of 30-60°, spray distance of 150-250mm, nozzle scanning path overlap rate of 0%-75%, and moving speed of 100-200mm / s.

[0023] As described above, an implant material for induction welding of thermoplastic composite materials has multiple through holes in the overall area of ​​the heating element, and the internal space of the through holes is completely filled with thermoplastic resin; the total area of ​​all through holes is 16.6%-62.8% of the area of ​​the heating element.

[0024] This invention improves the interfacial bonding between the heating element and the thermoplastic resin layer by creating through holes on the surface of the heating element, allowing thermoplastic resin to fill the through holes and form an interlocking effect, thereby enhancing the mechanical properties of the welded joint.

[0025] The through-holes on the metal foil can be distributed in various ways, including uniform array distribution, staggered array distribution, gradient or functionalized distribution (along the transverse, longitudinal, and radial directions), cluster distribution, and combinations of the above distributions. The through-holes can be uniformly distributed in an array, or a non-uniformly distributed topological pattern can be designed according to the magnetic induction intensity requirements. By changing the conductive paths in different areas of the metal foil, the flow path and density distribution of the induced eddy currents are adjusted, thereby optimizing the heat distribution of the heating element and making the welding surface of the workpiece to be welded more uniformly heated. This not only improves the welding rate but also avoids defects such as overheating decomposition of thermoplastic resin and internal porosity, significantly improving the quality of the welded joint.

[0026] As described above, the implant material for induction welding of thermoplastic composite materials has through holes in the shape of circles, rectangles, rhombuses, or ellipses; the diameter of the circle is 0.5-5 mm; the length and width of the rectangle are 0.5-5 mm; the major axis of the ellipse is 1.2-3 times the minor axis, and the minor axis is 0.5-5 mm; the edge distance between two adjacent through holes is 0.38-1.91 mm.

[0027] The present invention also provides a method for preparing an implant material for induction welding of thermoplastic composite materials as described in any of the preceding claims, wherein a thermoplastic resin material (thermoplastic resin film or thermoplastic resin powder) is covered on the upper and lower sides of a heating element and then hot-pressed to obtain the implant material for induction welding of thermoplastic composite materials.

[0028] As a preferred technical solution:

[0029] As described above, in a method for preparing an implant material for induction welding of thermoplastic composite materials, hot pressing is performed in a mold or between hot rollers. The hot pressing temperature is 115.7%-121.2% of the melting point of the thermoplastic resin material, and the hot pressing pressure is 0.4-1.2 MPa. When hot pressing is performed using a mold, the hot pressing time is 8-20 min. When hot pressing is performed using hot rollers, the hot roller linear speed is 1-6 m / min.

[0030] The present invention also provides a method for induction welding of thermoplastic composite materials. First, the implant material is cut to an appropriate size according to the process requirements. Then, the cut implant material is laid between the welding surfaces of two workpieces to be welded (i.e., the welding surfaces of the two workpieces are respectively attached to the implant material) and induction heating is performed. Both workpieces to be welded are thermoplastic composite materials, or one thermoplastic composite material and one thermosetting composite material. The implant material is an implant material for induction welding of thermoplastic composite materials as described in any of the above claims.

[0031] The process parameters of induction heating (such as frequency, current of induction coil, working distance of induction coil), welding method (spot welding or continuous welding), and welding pressure are all adjusted according to the molding and processing temperature of the matrix resin contained in the implanted material or thermoplastic composite workpiece.

[0032] Beneficial effects:

[0033] (1) The present invention uses a single continuous metal foil as a heating element, with no contact resistance between wires, and the heat comes 100% from the Joule heat of the metal body, which improves the heating rate and shortens the welding time; at the same time, it reduces the amount of heating element, reduces the weight of the welded joint, improves the flexibility of the implanted material, and adapts to the welding requirements of complex curved surfaces.

[0034] (2) The present invention uses through holes set in the entire area of ​​the heating element to design a non-uniformly distributed topological pattern according to the magnetic induction intensity requirements, adjust the flow path and density distribution of the induced eddy current, make the welding surface of the workpiece to be welded more uniformly heated, avoid defects such as overheating decomposition of thermoplastic resin and porosity, and improve the welding rate.

[0035] (3) The present invention significantly improves the interface bonding effect by surface treatment of heating element (single or combined methods such as laser treatment and plasma treatment) and through hole interlocking (the internal space of through hole is completely filled with thermoplastic resin layer), so that the fracture mode of welded joint changes from metal-resin interface debonding to metal body fracture or composite material workpiece delamination and fracture failure, thereby improving the joint's resistance to shearing and peeling.

[0036] (4) The implant material of the present invention is compatible with a variety of thermoplastic resins and corresponding composite materials. The quality of the welded joint is stable and reliable, and there is no scorching phenomenon. It solves the problems of dispersed heating zone and large energy loss in traditional self-induction welding, and meets the needs of rapid and continuous induction welding of large-size components. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the preparation process of the implant material in Example A1; wherein, 1-heating element, 2-thermoplastic resin material, 3-implant material;

[0038] Figure 2 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B1;

[0039] Figure 3 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B2;

[0040] Figure 4 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B3;

[0041] Figure 5 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B4;

[0042] Figure 6 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B5;

[0043] Figure 7 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B6;

[0044] Figure 8 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B7;

[0045] Figure 9 This is a schematic diagram showing the shape and size of the heating element and the shape, size, and distribution of its through holes in Example B8;

[0046] Figure 10The curves showing the temperature and heating rate changes of the implanted material during the induction welding process in Example B2 are shown.

[0047] Figure 11 This is a cloud map showing the temperature distribution of the welding plane during the induction welding process of the implanted material in Example B2 (corresponding to the maximum temperature difference test within the plane). Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0050] Melting point: Tested according to GB / T 19466.3-2004 standard.

[0051] Curing temperature: Tested according to ASTM D3418-21 standard.

[0052] Thermal degradation temperature: Tested according to GB / T 33047.1-2025 standard.

[0053] Maximum temperature difference in the plane: The surface temperature field of the implanted material is monitored in real time using an infrared thermal imager; the emissivity and focal length of the thermal imager are calibrated according to the surface characteristics of the implanted material to ensure a clear observation plane; the infrared thermal imager continuously acquires thermal radiation signals at a frame rate of 30Hz and converts them into temperature data; when the average temperature of the monitored area reaches the welding molding temperature of the corresponding resin system, the highest and lowest temperatures in the target area are extracted and the difference is calculated, which is the maximum temperature difference in the sample welding plane; the welding molding temperature is consistent with the hot pressing molding temperature of the implanted material in the corresponding embodiment, which is the process setting temperature above the resin melting point and below the thermal degradation temperature; it should be noted that the through-hole area filled with resin is not included in the data statistics of the maximum temperature difference in the plane.

[0054] Maximum heating rate: Pre-arrange insulated micro-K or E type thermocouples at the target monitoring points within the sample welding plane (specifically, such as...). Figure 10As shown, a micro K-type or E-type thermocouple is placed in the center of the implant material surface, sandwiched between the two parts to be welded, ensuring that the thermocouple tip is in close contact with the sample measurement point. During induction welding, the thermocouple leads are led out and connected to the data acquisition module and recording system. The sampling frequency of the acquisition system is 30Hz. The data acquisition module can be configured in two ways: a multi-channel inspection instrument with a paperless recorder, or directly connected to a computer. The system converts the thermoelectric potential signal into temperature data and records the temperature change curve completely. The instantaneous heating rate is obtained by differentiating the temperature curve, and the maximum value is taken as the highest heating rate of the sample implant material during the test.

[0055] Single lap shear strength of the joint: According to ASTM D 5868-01(2023) standard, the sample was prepared as a standard single lap structure by induction welding. Tensile load was applied to the sample at a constant loading rate of 13 mm / min until the sample joint failed. The maximum load at the failure fracture of the sample was recorded, and the single lap shear strength of the sample joint was calculated in combination with the lap area. In order to reduce random errors, at least 5 parallel samples were tested under the same set of process parameters. The arithmetic mean of multiple test results was used as the final result of the sample joint shear strength under the process conditions.

[0056] Single lap shear strength CV value: According to ASTM D 5868-01(2023) standard, single lap shear tests were conducted on three groups of specimens prepared under the same process conditions to obtain the shear strength data corresponding to each sample. The average shear strength (μ) and standard deviation (σ) were calculated based on the test data, and the CV value was calculated according to the following formula:

[0057] .

[0058] Welding rate: After the sample completes the single lap shear test, the cross-section of the welded joint of the fractured sample is photographed using an image acquisition device. ImageJ software is used to process and analyze the macroscopic image of the cross-section, distinguishing and labeling the welded area and the total lap area within the cross-section, and quantifying the area area by pixel ratio; the welding rate (η) is calculated using the following formula:

[0059] .

[0060] In the formula, η is the weld success rate (%) of the sample joint. The sample welding area (mm) 2 ), where 𝐴 is the overlap area of ​​the sample (mm). 2 ).

[0061] Post-weld thickness change rate: The thickness of the sample before and after induction welding was measured using a contact thickness gauge or a non-contact optical testing method (DIC). The post-weld thickness change rate (δ) was calculated using the following formula:

[0062] .

[0063] In the formula, δ is the thickness change rate after welding (%), h is the thickness of the sample after welding (mm), and h0 is the thickness of the sample before welding (mm).

[0064] Porosity: After induction welding is completed, CNC machining is used to sample the joint area of ​​the sample, and the sampling range completely includes the induction welding interface of the sample; porosity is tested according to GB / T 3365-2008 standard.

[0065] Whether the joint surface is burnt: After the sample welding process is completed, the surface condition of the sample joint is determined by visual inspection. The sample is placed in a uniform lighting environment, and the sample weld and adjacent areas are observed with the naked eye or a magnifying glass. If the sample surface shows abnormal colors such as dark brown, charred black, or discolored dark spots, or if there are dents, bubbles, carbonized particles, or a significant decrease in surface smoothness, it can be determined that the sample joint area has overheating and burning problems.

[0066] It should be noted that the parameter ranges described in this invention (such as process parameters for various surface treatment methods, hot pressing temperature, hot pressing pressure, hot pressing time, etc.) are effective implementation ranges summarized from a large number of preliminary variable screening experiments (covering different heating element materials, resin materials, through-hole topologies, surface treatment parameter combinations, and hot pressing and welding process parameters). In the following embodiments, only the core variables are specifically adjusted to verify the core innovation of this invention; this design is not intended to limit the scope of protection of this invention. Those skilled in the art can adjust any parameter based on the parameter ranges defined in this invention to achieve similar efficient heating and high-quality welding effects, and these adjustments do not exceed the scope of protection defined by the claims of this invention.

[0067] Example A1

[0068] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0069] (1) Preparation of materials;

[0070] Heating element: a single continuous metal foil, 0.012mm thick, made of copper;

[0071] Thermoplastic resin material: thermoplastic resin film, made of PEEK, with a melting point of 343℃;

[0072] Workpiece A to be welded: CF / PEEK (carbon fiber / polyether ether ketone) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0073] Workpiece B to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0074] (2) Perform surface treatment on the heating element;

[0075] The surface treatment adopts laser processing. The relevant process parameters are as follows: 355nm ultraviolet laser, spot diameter of 20μm, laser power of 3W, processing frequency of 20kHz, scanning speed of 800mm / s, scanning pattern of intersecting grid with grid line spacing of 0.1mm, and processing times of 3 times.

[0076] (3) Preparation of implant materials;

[0077] like Figure 1 As shown, after covering the upper and lower sides of the heating element 1 with thermoplastic resin material 2, it is placed in a mold for hot pressing to obtain the implant material 3; wherein, the hot pressing temperature is 400℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 20min.

[0078] The thickness of the implant material was 0.36 mm.

[0079] (4) Induction welding;

[0080] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 275A, welding pressure of 1.5MPa, and welding time of 6s.

[0081] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 10℃, and the highest heating rate was 5000℃ / s. After induction welding, the single lap shear strength of the joint was 35MPa, the CV value of the single lap shear strength of the joint was 6%, the welding rate was 100%, the thickness change rate after welding was 1.2%, the porosity was 1.0%, and there was no scorching on the joint surface.

[0082] Example A2

[0083] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0084] (1) Preparation of materials;

[0085] Heating element: a single continuous metal foil, 0.012mm thick, made of 304 stainless steel;

[0086] Thermoplastic resin material: thermoplastic resin film, made of PPS, with a melting point of 280℃;

[0087] Workpiece A to be welded: CF / PPS (carbon fiber / polyphenylene sulfide) laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, PPS melting point is 280℃;

[0088] Workpiece B to be welded: CF / PPS laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, PPS melting point is 280℃;

[0089] (2) Perform surface treatment on the heating element;

[0090] The surface treatment adopts plasma treatment. The relevant process parameters are: nozzle diameter is 50mm, treatment time is 100s, distance between workpiece and nozzle is 13mm, working gas is atmospheric gas, and gas flow rate is 600L / h.

[0091] (3) Preparation of implant materials;

[0092] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 330℃, the hot pressing pressure is 0.8MPa, and the hot pressing time is 12min.

[0093] The thickness of the implant material was 0.26 mm.

[0094] (4) Induction welding;

[0095] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 250kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 250A, welding pressure of 1.0MPa, and welding time of 5s.

[0096] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 10℃, and the highest heating rate was 5500℃ / s. After induction welding, the single lap shear strength of the joint was 30MPa, the CV value of the single lap shear strength of the joint was 7%, the welding rate was 100%, the thickness change rate after welding was 1.0%, the porosity was 1.5%, and there was no scorching on the joint surface.

[0097] Example A3

[0098] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0099] (1) Preparation of materials;

[0100] Heating element: a single continuous metal foil, 0.012mm thick, made of silver;

[0101] Thermoplastic resin material: thermoplastic resin film, made of LM-PAEK (low melting point polyaryletherketone), with a melting point of 305℃;

[0102] Workpiece A to be welded: CF / LM-PAEK (carbon fiber / low melting point polyaryletherketone) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, LM-PAEK melting point is 305℃;

[0103] Workpiece B to be welded: CF / LM-PAEK (carbon fiber / low melting point polyaryletherketone) laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, LM-PAEK melting point is 305℃;

[0104] (2) Perform surface treatment on the heating element;

[0105] The surface treatment adopts a chemical treatment method, and the relevant process parameters are: the concentration of the treatment solution (hydrogen peroxide aqueous solution) is 15wt%, the treatment temperature is 60℃, and the treatment time is 20min;

[0106] (3) Preparation of implant materials;

[0107] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 360℃, the hot pressing pressure is 1MPa, and the hot pressing time is 15min.

[0108] The thickness of the implant material was 0.3 mm.

[0109] (4) Induction welding;

[0110] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 300A, welding pressure of 1.2MPa, and welding time of 5s.

[0111] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 10℃, and the highest heating rate was 5000℃ / s. After induction welding, the single lap shear strength of the joint was 35MPa, the CV value of the single lap shear strength of the joint was 6%, the welding rate was 100%, the thickness change rate after welding was 1.1%, the porosity was 1.2%, and there was no scorching on the joint surface.

[0112] Example A4

[0113] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0114] (1) Preparation of materials;

[0115] Heating element: a single continuous metal foil, 0.012 mm thick, made of titanium;

[0116] Thermoplastic resin material: thermoplastic resin powder, material is PA66, melting point is 255℃;

[0117] Workpiece A to be welded: CF / PA66 (carbon fiber / polyamide 66) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PA66 has a melting point of 255℃;

[0118] Workpiece B to be welded: GF / PA66 (glass fiber / polyamide 66) laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PA66 has a melting point of 255℃;

[0119] (2) Perform surface treatment on the heating element;

[0120] The surface treatment adopts sandblasting. The relevant process parameters are as follows: the abrasive type is glass microspheres, the abrasive particle size is 400 mesh, the sandblasting pressure is 0.2MPa, the nozzle diameter is 20mm, the spray angle is 45°, the spray distance is 150mm, the nozzle scanning path overlap rate is 50%, and the moving speed is 150mm / s.

[0121] (3) Preparation of implant materials;

[0122] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 295℃, the hot pressing pressure is 0.7MPa, and the hot pressing time is 8min.

[0123] The thickness of the implant material was 0.12 mm.

[0124] (4) Induction welding;

[0125] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 200kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 210A, welding pressure of 0.8MPa, and welding time of 5s.

[0126] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 8℃, and the highest heating rate was 5000℃ / s. After induction welding, the single lap shear strength of the joint was 28MPa, the CV value of the single lap shear strength of the joint was 6%, the welding rate was 100%, the thickness change rate after welding was 2%, the porosity was 1.8%, and there was no scorching on the joint surface.

[0127] Example A5

[0128] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0129] (1) Preparation of materials;

[0130] Heating element: a single continuous metal foil, 0.012 mm thick, made of nickel;

[0131] Thermoplastic resin material: thermoplastic resin powder, made of PMMA, with a melting point of 150℃;

[0132] Workpiece A to be welded: CF / PMMA (carbon fiber / polymethyl methacrylate) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PMMA melting point is 150℃;

[0133] Workpiece B to be welded: CF / EP (carbon fiber / epoxy resin) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, EP curing temperature is 130℃, EP thermal degradation temperature is 330℃;

[0134] (2) Perform surface treatment on the heating element;

[0135] The surface treatment adopts a surface grafting treatment method. The relevant process parameters are as follows: the concentration of the treatment solution (composed of silane coupling agent KH-570, ethanol, water and glacial acetic acid, with a volume ratio of ethanol to water of 95:5 and a pH value of 4.5) is 1wt% (the concentration here refers to the concentration of silane coupling agent KH-570 in the treatment solution), and the treatment time is 15min.

[0136] (3) Preparation of implant materials;

[0137] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 180℃, the hot pressing pressure is 0.7MPa, and the hot pressing time is 8min.

[0138] The thickness of the implant material was 0.12 mm.

[0139] (4) Induction welding;

[0140] The implant material is applied between the welding surfaces of workpiece A and workpiece B to be welded and induction heating is performed. The relevant process parameters are: frequency 175kHz, 2.5-turn planar disc coil with outer diameter the same as the workpiece width, inner diameter 6mm, wire diameter 4mm, spacing between coil and implant material 4.6mm, coil current 170A, welding pressure 0.8MPa, and welding time 7s.

[0141] Tests show that during induction welding, the maximum temperature difference in the plane of the implanted material is 5℃, and the highest heating rate is 4500℃ / s. After induction welding, the single lap shear strength of the joint is 25MPa, the CV value of the single lap shear strength of the joint is 8%, the welding rate is 100%, the thickness change rate after welding is 1.5%, the porosity is 2%, and there is no scorching phenomenon on the joint surface.

[0142] Example A6

[0143] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0144] (1) Preparation of materials;

[0145] Heating element: a single continuous metal foil, 0.012mm thick, made of aluminum;

[0146] Thermoplastic resin material: thermoplastic resin film, made of polypropylene (PP), with a melting point of 165℃;

[0147] Workpiece A to be welded: GF / PP (glass fiber / polypropylene) laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PP melting point is 165℃;

[0148] Workpiece B to be welded: GF / PP laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PP melting point is 165℃;

[0149] (2) Perform surface treatment on the heating element;

[0150] The surface treatment uses anodizing, with the following process parameters: electrolyte (phosphoric acid aqueous solution) concentration of 12wt%, voltage of 25V, and current density of 10mA / cm³. 2 The oxidation time was 15 min, the electrolyte temperature was 25℃, the electrode distance was 10 cm, and the anode-cathode area ratio was 1.5:1.

[0151] (3) Preparation of implant materials;

[0152] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed between hot rollers for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 200℃, the hot pressing pressure is 0.4MPa, and the hot roller linear speed is 1.5m / min.

[0153] The thickness of the implant material was 0.06 mm.

[0154] (4) Induction welding;

[0155] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 275kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width, an inner diameter of 6mm, a wire diameter of 4mm, a distance of 4.6mm between the coil and the implant material, a coil current of 120A, a welding pressure of 0.6MPa, and a welding time of 6s.

[0156] Tests show that during induction welding, the maximum temperature difference in the plane of the implanted material is 5℃, and the highest heating rate is 4000℃ / s. After induction welding, the single lap shear strength of the joint is 25MPa, the CV value of the single lap shear strength of the joint is 8%, the welding rate is 100%, the thickness change rate after welding is 1.7%, the porosity is 2%, and there is no scorching phenomenon on the joint surface.

[0157] Example A7

[0158] A thermoplastic composite material induction welding method, which differs from Example A1 only in that the thickness of the heating element is 0.05 mm.

[0159] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 6℃, and the highest heating rate was 800℃ / s. After induction welding, the single lap shear strength of the joint was 22MPa, the CV value of the single lap shear strength of the joint was 12%, the welding rate was 55%, the thickness change rate after welding was 2.2%, the porosity was 2.6%, and there was no scorching on the joint surface.

[0160] Example A8

[0161] A thermoplastic composite material induction welding method, which differs from Example A1 only in that the thickness of the heating element is 0.06 mm.

[0162] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 4℃, and the highest heating rate was 500℃ / s. After induction welding, the single lap shear strength of the joint was 18MPa, the CV value of the single lap shear strength of the joint was 15%, the welding rate was 35%, the thickness change rate after welding was 2.4%, the porosity was 3.2%, and there was no scorching on the joint surface.

[0163] Comparing Examples A7 and A8 with Example A1, it can be seen that when the thickness of the heating element used is 0.012 mm, the Joule heating efficiency is significantly enhanced, the induction heating rate is higher, the thermoplastic resin is fully melted and flowed under the same induction welding process parameters, the joint welding rate is significantly improved, and defects such as pores and bubbles are suppressed or fully discharged, resulting in a significant reduction in post-weld thickness change and porosity in the welded area. The welded joint exhibits excellent single lap shear performance.

[0164] Example A9

[0165] A thermoplastic composite material induction welding method, which differs from Example A1 only in that: in step (2), after laser treatment of the heating element, surface grafting treatment is also performed. The relevant process parameters of the surface grafting treatment are: the concentration of the treatment solution (prepared by diluting the polyimide solution of American Macquarie Company with product number HP-1632 with deionized water to the target concentration) is 1wt%, and the treatment time is 15min.

[0166] Tests show that during induction welding, the maximum temperature difference in the plane of the implanted material is 10℃, and the highest heating rate is 5000℃ / s. After induction welding, the single lap shear strength of the joint is 38MPa, the CV value of the single lap shear strength of the joint is 3%, the welding rate is 100%, the thickness change rate after welding is 1.2%, the porosity is 0.2%, and there is no scorching phenomenon on the joint surface.

[0167] Comparing Example A9 with Example A1, it can be seen that after composite surface treatment, the single lap shear strength of the joint increased from 35MPa to 38MPa, while the porosity decreased from 1.0% to 0.2%. This indicates that when surface roughness is increased and surface-active groups are introduced, the effect of improving the interfacial bonding strength is more significant.

[0168] Comparative Example A1

[0169] A thermoplastic composite material induction welding method, which differs from Example A1 only in that: the heating element is a metal mesh (the metal mesh material is the same as in Example A1, the metal wire diameter is the same as the foil thickness in Example A1, and the metal mesh weaving parameters are: plain weave, square mesh, and 60 mesh).

[0170] Tests show that during induction welding, the maximum temperature difference in the plane of the implanted material is 15℃, and the highest heating rate is 1000℃ / s. After induction welding, the single lap shear strength of the joint is 24MPa, the CV value of the single lap shear strength of the joint is 12%, the welding rate is 65%, the thickness change rate after welding is 2.2%, and the porosity is 2.8%.

[0171] Compared to Example A1, Comparative Example A1 showed a significant decrease in the maximum heating rate, single lap shear strength, and weld ratio, while the post-weld thickness change rate, maximum in-plane temperature difference, joint shear strength CV value, and weld area porosity significantly increased. This is because the warp and weft weave structure of the metal mesh introduces inter-filament contact resistance, resulting in less induced heat generation per unit time, which is mainly concentrated at the warp and weft interlacing points. This significantly reduces effective heating efficiency. Furthermore, the concentration of heat generation at the warp and weft interlacing points and the poorer in-plane thermal conductivity further exacerbate the uneven temperature distribution on the welding surface, leading to insufficient melting and wetting of the thermoplastic resin. Ultimately, this results in a comprehensive decline in welding efficiency, weld area, and joint performance. In contrast, Example A1 exhibits uniform bulk Joule heating, resulting in higher heating efficiency and a more even distribution. This allows for uniform and complete melting of the thermoplastic resin on the welding surface, preventing the formation of defects such as pores, thereby improving the weld joint's ability to transfer and withstand loads.

[0172] Example B1

[0173] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0174] (1) Preparation of materials;

[0175] Heating element: A single continuous metal foil, 0.012mm thick, made of copper, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 2 As shown;

[0176] Thermoplastic resin material: thermoplastic resin film, made of PEEK, with a melting point of 343℃;

[0177] Workpiece A to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0178] Workpiece B to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0179] (2) Preparation of implant materials;

[0180] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 400℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 20min.

[0181] The thickness of the implanted material is 0.36 mm;

[0182] (3) Induction welding of thermoplastic composite materials;

[0183] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 275A, welding pressure of 1.5MPa, and welding time of 4s.

[0184] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 10℃, and the highest heating rate was 7000℃ / s. After induction welding, the single lap shear strength of the joint was 38MPa, the CV value of the single lap shear strength of the joint was 5%, the welding rate was 100%, the thickness change rate after welding was 1.2%, the porosity was 1.0%, and there was no scorching on the joint surface.

[0185] Example B2

[0186] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0187] (1) Preparation of materials;

[0188] Heating element: A single continuous metal foil, 0.012mm thick, made of copper, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 3 As shown;

[0189] Thermoplastic resin material: thermoplastic resin film, made of PEEK, with a melting point of 343℃;

[0190] Workpiece A to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0191] Workpiece B to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0192] (2) Preparation of implant materials;

[0193] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 400℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 20min.

[0194] The thickness of the implanted material is 0.36 mm;

[0195] (3) Induction welding of thermoplastic composite materials;

[0196] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 275A, welding pressure of 1.5MPa, and welding time of 5s.

[0197] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 8℃, and the highest heating rate was 6500℃ / s. After induction welding, the single lap shear strength of the joint was 40MPa, the CV value of the single lap shear strength of the joint was 4%, the welding rate was 100%, the thickness change rate after welding was 1.2%, the porosity was 0.8%, and there was no scorching on the joint surface.

[0198] In this embodiment, the temperature and heating rate change curves of the implanted material during the induction welding process are as follows: Figure 10 As shown, the temperature distribution of the welding plane and the test cloud of the maximum temperature difference within the plane are as follows. Figure 11 As shown.

[0199] Example B3

[0200] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0201] (1) Preparation of materials;

[0202] Heating element: A single continuous metal foil, 0.012mm thick, made of copper, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 4 As shown;

[0203] Thermoplastic resin material: thermoplastic resin film, made of PEEK, with a melting point of 343℃;

[0204] Workpiece A to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0205] Workpiece B to be welded: CF / PEEK laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PEEK melting point is 343℃;

[0206] (2) Preparation of implant materials;

[0207] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 400℃, the hot pressing pressure is 1.2MPa, and the hot pressing time is 20min.

[0208] The thickness of the implanted material is 0.36 mm;

[0209] (3) Induction welding of thermoplastic composite materials;

[0210] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width, an inner diameter of 6mm, a wire diameter of 4mm, a distance of 4.6mm between the coil and the implant material, a coil current of 275A, a welding pressure of 1.5MPa, and a welding time of 7s.

[0211] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 7℃, and the highest heating rate was 5200℃ / s. After induction welding, the single lap shear strength of the joint was 43MPa, the CV value of the single lap shear strength of the joint was 3%, the welding rate was 100%, the thickness change rate after welding was 1.2%, the porosity was 0.6%, and there was no scorching on the joint surface.

[0212] Example B4

[0213] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0214] (1) Preparation of materials;

[0215] Heating element: A single continuous metal foil, 0.012mm thick, made of 304 stainless steel. The entire area has multiple through-holes. The shape and size of the heating element, as well as the shape, size, and distribution of the through-holes, are as follows: Figure 5 As shown;

[0216] Thermoplastic resin material: thermoplastic resin powder, material is PPS, melting point is 280℃;

[0217] Workpiece A to be welded: CF / PPS laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, PPS melting point is 280℃;

[0218] Workpiece B to be welded: CF / PPS laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, PPS melting point is 280℃;

[0219] (2) Preparation of implant materials;

[0220] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 330℃, the hot pressing pressure is 0.8MPa, and the hot pressing time is 12min.

[0221] The thickness of the implanted material is 0.26 mm;

[0222] (3) Induction welding of thermoplastic composite materials;

[0223] The implant material is applied between the welding surfaces of workpiece A and workpiece B to be welded and induction heating is performed. The relevant process parameters are: frequency 250kHz, 2.5-turn planar disc coil with outer diameter the same as the workpiece width, inner diameter 6mm, wire diameter 4mm, spacing between coil and implant material 4.6mm, coil current 250A, welding pressure 1.0MPa, and welding time 4s.

[0224] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 7℃, and the highest heating rate was 6500℃ / s. After induction welding, the single lap shear strength of the joint was 33MPa, the CV value of the single lap shear strength of the joint was 5%, the welding rate was 100%, the thickness change rate after welding was 1.0%, the porosity was 1.2%, and there was no scorching on the joint surface.

[0225] Example B5

[0226] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0227] (1) Preparation of materials;

[0228] Heating element: A single continuous metal foil, 0.012mm thick, made of silver, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 6 As shown;

[0229] Thermoplastic resin material: thermoplastic resin powder, material is LM-PAEK (low melting point polyaryletherketone), melting point is 305℃;

[0230] Workpiece A to be welded: CF / LM-PAEK laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, LM-PAEK melting point is 305℃;

[0231] Workpiece B to be welded: CF / LM-PAEK laminate, unidirectional carbon fiber reinforced composite material, quasi-isotropic symmetrical layup, LM-PAEK melting point is 305℃;

[0232] (2) Preparation of implant materials;

[0233] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 360℃, the hot pressing pressure is 1MPa, and the hot pressing time is 15min.

[0234] The thickness of the implant material is 0.3 mm;

[0235] (3) Induction welding of thermoplastic composite materials;

[0236] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 300kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width and an inner diameter of 6mm, wire diameter of 4mm, spacing between the coil and the implant material of 4.6mm, coil current of 300A, welding pressure of 1.2MPa, and welding time of 4s.

[0237] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 6℃, and the highest heating rate was 5800℃ / s. After induction welding, the single lap shear strength of the joint was 40MPa, the CV value of the single lap shear strength of the joint was 4%, the welding rate was 100%, the thickness change rate after welding was 1.1%, the porosity was 0.8%, and there was no scorching on the joint surface.

[0238] Example B6

[0239] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0240] (1) Preparation of materials;

[0241] Heating element: A single continuous metal foil, 0.012mm thick, made of titanium, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 7 As shown;

[0242] Thermoplastic resin material: thermoplastic resin powder, material is PA66, melting point is 255℃;

[0243] Workpiece A to be welded: CF / PA66 laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PA66 has a melting point of 255℃;

[0244] Workpiece B to be welded: GF / PA66 laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PA66 has a melting point of 255℃;

[0245] (2) Preparation of implant materials;

[0246] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 295℃, the hot pressing pressure is 0.7MPa, and the hot pressing time is 8min.

[0247] The thickness of the implanted material is 0.12 mm;

[0248] (3) Induction welding of thermoplastic composite materials;

[0249] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 200kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width, an inner diameter of 6mm, a wire diameter of 4mm, a distance of 4.6mm between the coil and the implant material, a coil current of 210A, a welding pressure of 0.8MPa, and a welding time of 4.5s.

[0250] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 5℃, and the highest heating rate was 5400℃ / s. After induction welding, the single lap shear strength of the joint was 30MPa, the CV value of the single lap shear strength of the joint was 5%, the welding rate was 100%, the thickness change rate after welding was 2.0%, the porosity was 1.4%, and there was no scorching on the joint surface.

[0251] Example B7

[0252] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0253] (1) Preparation of materials;

[0254] Heating element: A single continuous metal foil, 0.012mm thick, made of nickel, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 8 As shown;

[0255] Thermoplastic resin material: thermoplastic resin film, made of PMMA, with a melting point of 150℃;

[0256] Workpiece A to be welded: CF / PMMA laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, PMMA has a melting point of 150℃;

[0257] Workpiece B to be welded: CF / EP (carbon fiber / epoxy resin) laminate, carbon fiber fabric reinforced composite material, symmetrical orthogonal layup, EP curing temperature is 130℃, EP thermal degradation temperature is 330℃;

[0258] (2) Preparation of implant materials;

[0259] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed in a mold for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 180℃, the hot pressing pressure is 0.7MPa, and the hot pressing time is 8min.

[0260] The thickness of the implanted material is 0.12 mm;

[0261] (3) Induction welding of thermoplastic composite materials;

[0262] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 175kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width, an inner diameter of 6mm, a wire diameter of 4mm, a distance of 4.6mm between the coil and the implant material, a coil current of 170A, a welding pressure of 0.8MPa, and a welding time of 6s.

[0263] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 3℃, and the highest heating rate was 4900℃ / s. After induction welding, the single lap shear strength of the joint was 30MPa, the CV value of the single lap shear strength of the joint was 6%, the welding rate was 100%, the thickness change rate after welding was 1.5%, the porosity was 1.2%, and there was no scorching on the joint surface.

[0264] Example B8

[0265] A method for induction welding of thermoplastic composite materials, the specific steps of which are as follows:

[0266] (1) Preparation of materials;

[0267] Heating element: A single continuous metal foil, 0.012mm thick, made of aluminum, with multiple through holes throughout. The shape and size of the heating element, as well as the shape, size, and distribution of the through holes, are as follows: Figure 9 As shown;

[0268] Thermoplastic resin material: thermoplastic resin film, made of PP, with a melting point of 165℃;

[0269] Workpiece A to be welded: GF / PP laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PP melting point is 165℃;

[0270] Workpiece B to be welded: GF / PP laminate, glass fiber fabric reinforced composite material, symmetrical orthogonal layup, PP melting point is 165℃;

[0271] (2) Preparation of implant materials;

[0272] After covering the upper and lower sides of the heating element with thermoplastic resin material, it is placed between hot rollers for hot pressing to obtain the implant material; wherein, the hot pressing temperature is 200℃, the hot pressing pressure is 0.4MPa, and the hot roller linear speed is 1.5m / min.

[0273] The thickness of the implanted material is 0.06 mm;

[0274] (3) Induction welding of thermoplastic composite materials;

[0275] The implant material is applied between the welding surfaces of workpieces A and B to be welded and induction heating is performed. The relevant process parameters are: frequency 275kHz, 2.5-turn planar disc coil with an outer diameter the same as the workpiece width, an inner diameter of 6mm, a wire diameter of 4mm, a distance of 4.6mm between the coil and the implant material, a coil current of 120A, a welding pressure of 0.6MPa, and a welding time of 4s.

[0276] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 5℃, and the highest heating rate was 4800℃ / s. After induction welding, the single lap shear strength of the joint was 30MPa, the CV value of the single lap shear strength of the joint was 6%, the welding rate was 100%, the thickness change rate after welding was 1.7%, the porosity was 1.2%, and there was no scorching on the joint surface.

[0277] Example B9

[0278] A thermoplastic composite material induction welding method, which differs from Example B1 only in that the thickness of the heating element is 0.05 mm.

[0279] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 7℃, and the highest heating rate was 1300℃ / s. After induction welding, the single lap shear strength of the joint was 28MPa, the CV value of the single lap shear strength of the joint was 8%, the welding rate was 90%, the thickness change rate after welding was 1.6%, the porosity was 1.7%, and there was no scorching on the joint surface.

[0280] Example B10

[0281] A thermoplastic composite material induction welding method, which differs from Example B1 only in that the thickness of the heating element is 0.06 mm.

[0282] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 6℃, and the highest heating rate was 950℃ / s. After induction welding, the single lap shear strength of the joint was 25MPa, the CV value of the single lap shear strength of the joint was 9%, the welding rate was 70%, the thickness change rate after welding was 2.0%, the porosity was 2.2%, and there was no scorching on the joint surface.

[0283] Comparing Examples B9, B10 and B1, it can be seen that when the thickness of the heating element used is 0.012 mm, the Joule heating efficiency is significantly enhanced, the induction heating rate is higher, the thermoplastic resin is fully melted and flowed under the same induction welding process parameters, the joint welding rate is significantly improved, and defects such as pores and bubbles are suppressed or fully discharged, resulting in a significant reduction in post-weld thickness change and porosity in the welded area. The welded joint exhibits excellent single lap shear performance.

[0284] Comparative Example B1

[0285] A thermoplastic composite material induction welding method, which differs from Example B1 only in that: the heating element is a metal mesh (the metal mesh material is the same as in Example B1, the metal wire diameter is the same as the foil thickness in Example B1, and the metal mesh weaving parameters are: plain weave, square mesh, and 60 mesh).

[0286] Tests show that during induction welding, the maximum temperature difference in the plane of the implanted material is 15℃, and the highest heating rate is 1000℃ / s. After induction welding, the single lap shear strength of the joint is 22MPa, the CV value of the single lap shear strength of the joint is 15%, the welding rate is 65%, the thickness change rate after welding is 2.2%, and the porosity is 3.0%.

[0287] Compared to Example B1, Comparative Example B1 showed a significant decrease in the maximum heating rate, single lap shear strength, and weld ratio, while the post-weld thickness change rate, maximum in-plane temperature difference, joint shear strength CV value, and weld area porosity significantly increased. This is because the warp and weft weave structure of the metal mesh introduces inter-filament contact resistance, resulting in less induced heat generation per unit time, which is mainly concentrated at the warp and weft interlacing points. This significantly reduces effective heating efficiency. Furthermore, the concentration of heat generation at the warp and weft interlacing points and the poorer in-plane thermal conductivity further exacerbate the uneven temperature distribution on the welding surface, leading to insufficient melting and wetting of the thermoplastic resin. Ultimately, this results in a comprehensive decline in welding efficiency, weld area, and joint performance. In contrast, Example B1 exhibits uniform bulk Joule heating, resulting in higher heating efficiency and a more even distribution. This allows for uniform and complete melting of the thermoplastic resin on the welding surface, preventing the formation of defects such as pores, thereby improving the weld joint's ability to transfer and withstand loads.

[0288] Example C1

[0289] A thermoplastic composite material induction welding method differs from Example B1 only in that: before preparing the implant material, the heating element is also surface-treated in the same way as in Example A1.

[0290] Tests showed that during induction welding, the maximum temperature difference in the plane of the implanted material was 10℃, and the highest heating rate was 7000℃ / s. After induction welding, the single lap shear strength of the joint was 43MPa, the CV value of the single lap shear strength of the joint was 3%, the welding rate was 100%, the thickness change rate after welding was 1.2%, the porosity was 0.5%, and there was no scorching on the joint surface.

[0291] As can be seen from the various embodiments of the present invention, within the entire parameter configuration range of the present invention, during the induction welding process, the maximum in-plane temperature difference of the implant material used for induction welding of thermoplastic composite materials is ≤10℃, and the maximum heating rate range is 500-7000℃ / s; after induction welding, the single lap shear strength range of the joint is 18-43MPa, the coefficient of variation of the single lap shear strength of the joint is ≤15%, the welding rate range is 35%-100%, the thickness change rate after welding is ≤2.4%, the porosity is ≤3.2%, and there is no scorching phenomenon on the surface of the welded joint prepared by all schemes.

[0292] The most preferred configuration of this invention is as follows: using a single continuous metal foil with a thickness ≤0.012mm as the heating element; based on this, through holes can be opened on the surface of the heating element or surface treatment can be used to strengthen the interface bonding, depending on actual needs. With this preferred configuration, various performance characteristics are further improved: the highest heating rate range of the implanted material is 4000-7000℃ / s, the single lap shear strength range of the joint is 25-43MPa, the coefficient of variation of the single lap shear strength of the joint is ≤8%, the welding rate stably reaches 100%, the post-weld thickness change rate is ≤2%, and the porosity is ≤2%.

[0293] As can be seen from the above, the implant material prepared by the method of the present invention has high interfacial strength, and the energy can be concentrated and evenly distributed on the welding surface. When the joint is subjected to shear load and peel load, the stress can be completely transferred to the composite material workpiece body. The joint fracture mode changes from the interface debonding between the metal and the resin to the fracture of the metal body, the delamination of the composite material workpiece, or the fracture of the composite material workpiece body. It can realize high-strength, high-performance, and high-quality induction welding of thermoplastic composite materials.

[0294] It should be noted that in practical applications, the two optimization designs mentioned above (i.e., opening through holes on the surface of the heating element and using surface treatment to strengthen the interface bonding) can be used simultaneously. Surface treatment is used to strengthen the interface bonding, and the through hole structure forms mechanical interlocking and optimizes the temperature field distribution. The superposition of these multiple effects can further improve the comprehensive performance of the implanted material and the overall quality of the welded joint.

Claims

1. An implant material for induction welding of thermoplastic composite materials, comprising a heating element and a thermoplastic resin layer covering its surface, characterized in that, The heating element is a single continuous metal foil with a thickness of ≤0.05mm.

2. The implant material for induction welding of thermoplastic composite materials according to claim 1, characterized in that, The thickness of the heating element is ≤0.012mm.

3. The implant material for induction welding of thermoplastic composite materials according to claim 1, characterized in that, The heating element is made of copper, stainless steel, iron, aluminum, nickel, titanium, silver, or gold; the thermoplastic resin layer is made of polyethylene, polypropylene, polyamide, polystyrene, polyethylene terephthalate, polymethyl methacrylate, polycarbonate, polyphenylene ether, polyether ether ketone, polysulfone, polyphenylene sulfide, or polyarylether ketone; the thickness of the implant material used for induction welding of thermoplastic composite materials is 5-30 times the thickness of the heating element.

4. An implant material for induction welding of thermoplastic composite materials according to claim 1, characterized in that, The heating element undergoes surface treatment to improve surface roughness and / or introduce active groups on the surface, thereby enhancing the interfacial bonding strength between the heating element and the thermoplastic resin layer.

5. An implant material for induction welding of thermoplastic composite materials according to claim 4, characterized in that, Surface treatment employs a single method or a combination of methods from laser treatment, plasma treatment, chemical treatment, anodizing treatment, surface grafting treatment, and sandblasting treatment.

6. An implant material for induction welding of thermoplastic composite materials according to claim 1, characterized in that, The heating element has multiple through holes, and the internal space of the through holes is completely filled with thermoplastic resin; the total area of ​​all through holes is 16.6%-62.8% of the area of ​​the heating element.

7. An implant material for induction welding of thermoplastic composite materials according to claim 6, characterized in that, The through-hole can be circular, rectangular, rhomboid, or elliptical; the diameter of the circular hole is 0.5-5mm; the length and width of the rectangular hole are 0.5-5mm; the major axis of the elliptical hole is 1.2-3 times the minor axis, and the minor axis is 0.5-5mm; the edge distance between two adjacent through-holes is 0.38-1.91mm.

8. A method for preparing an implant material for induction welding of thermoplastic composite materials as described in any one of claims 1 to 7, characterized in that, After covering the upper and lower sides of the heating element with thermoplastic resin material, hot pressing is performed to obtain the implant material for induction welding of thermoplastic composite materials.

9. A method for preparing an implant material for induction welding of thermoplastic composite materials according to claim 8, characterized in that, Hot pressing is performed in a mold or between hot rollers. The temperature of hot pressing is 115.7%-121.2% of the melting point of the thermoplastic resin material, and the pressure of hot pressing is 0.4-1.2 MPa. When hot pressing is performed using a mold, the hot pressing time is 8-20 min. When hot pressing is performed using hot rollers, the linear speed of the hot rollers is 1-6 m / min.

10. A method for induction welding of thermoplastic composite materials, wherein an implant material is laid between the welding surfaces of two workpieces to be welded and induction heated, characterized in that, The implant material is an implant material for induction welding of thermoplastic composite materials as described in any one of claims 1 to 7.

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