Ultrasonic welding method for carbon fiber reinforced thermoplastic resin composite material

Abstract

The invention relates to the technical field of ultrasonic welding of composite materials, in particular to an ultrasonic welding method of a carbon fiber reinforced thermoplastic resin composite material. The method comprises the steps that (1) thermoplastic resin powder with the particle size D50 meeting the requirement of 15-25 microns is applied to the surface of an interface to be welded, and the thermoplastic resin powder forms an energy conduction layer on the interface; and (2) the interfaces are welded under the ultrasonic vibration effect, the energy conducting layer is melted under the ultrasonic vibration effect, and the interfaces are connected. According to the method, the non-welding defect can be remarkably reduced, the interface integrity and mechanical strength of a welding joint are improved, and the method is suitable for plane connection and ultrasonic welding of curved surface and complex three-dimensional surface structures and has the advantages of being simple in process, high in applicability and stable in connection quality.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic welding technology for composite materials, and more specifically, to an ultrasonic welding method for carbon fiber reinforced thermoplastic resin composite materials. Background Technology

[0002] Carbon fiber reinforced thermoplastic resin composites (CFRT) have been widely used in aerospace, rail transportation, automotive lightweighting, and UAV structural components due to their high specific strength, high specific modulus, good impact resistance, remeltability, repairability, and excellent recyclability. As the proportion of composite materials used in load-bearing structures continues to increase, the connection method between different components has become one of the key factors affecting the overall structural reliability and service life.

[0003] Existing methods for joining carbon fiber reinforced thermoplastic composites mainly include mechanical joining, adhesive bonding, and fusion welding. While mechanical joining facilitates assembly, it introduces stress concentration and disrupts fiber continuity, leading to a decline in the material's mechanical properties. Adhesive bonding relies heavily on surface treatment for interface quality, and its heat resistance and long-term environmental adaptability are insufficient, making it difficult to meet the requirements of high-temperature structural components. In contrast, ultrasonic welding, as a fusion bonding method without an external adhesive layer, can achieve rapid melting and solidification of the interface resin in a short time. It features high joining efficiency, stable interface performance, and good repeatability, thus becoming an important development direction for joining thermoplastic composites.

[0004] However, current ultrasonic welding of composite materials largely relies on prefabricated energy directors (EDs) to concentrate interfacial energy and promote rapid melting. Typical forms of energy directors include thermoplastic resin films, wedge-shaped ribs, three-dimensional fabrics, or non-woven fabrics. While these energy directors are effective in planar or regular surface connections, they have the following shortcomings in curved surfaces, hyperboloids, or three-dimensional interfaces with complex stepped structures: 1) It is difficult to adhere to irregular surfaces. The film or ribs are difficult to fully adhere at the interface, which can easily result in unbonded areas. 2) The shape of the energy-conducting layer is fixed and cannot automatically adapt to interface roughness and micropores at the microscale; 3) Existing energy-conducting layers require prefabrication, cutting, and positioning, which involves complex processes and high assembly precision requirements; 4) When the interface structure is complex, the ultrasonic energy is not transmitted evenly at the interface, and the melting is discontinuous, which leads to stress concentration and strength reduction in the weld. Summary of the Invention

[0005] This invention covers the following technical solutions: This invention relates to an ultrasonic welding method for carbon fiber reinforced thermoplastic resin composites, the method comprising: 1) Ensure the particle size meets D 50 A thermoplastic resin powder with a thickness of 15–25 μm is applied to the surface of the interface to be welded, so that the thermoplastic resin powder forms an energy-conducting layer at the interface. 2) The interface is subjected to ultrasonic vibration for welding, and the energy-conducting layer melts under ultrasonic vibration to connect the interface.

[0006] This invention applies a particle size that satisfies D at the interface to be welded. 50 A conductive layer is formed on 15–25 μm thermoplastic resin powder, enabling the powder to conform to the interface morphology and rapidly melt and penetrate under ultrasonic vibration. This results in a uniform, continuous, and dense resin bridging layer at the interface, achieving stable energy transfer and effective interface fusion. This significantly reduces incomplete welding defects, improves the interface integrity and mechanical strength of the welded joint, and makes the method applicable not only to planar connections but also to ultrasonic welding of curved surfaces and complex three-dimensional surface structures. It has the advantages of simple process, strong applicability, and stable connection quality. Attached Figure Description

[0007] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0008] Figure 1 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 1.

[0009] Figure 2 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 2.

[0010] Figure 3 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 3.

[0011] Figure 4 SEM images of cross-sections of BP-CN resin ultrafine powder samples with different particle sizes after testing. Detailed Implementation

[0012] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0013] Unless otherwise stated, all terms used to disclose this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance is provided below for a better understanding of the teachings of this invention. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0014] In this invention, unless otherwise stated, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the terms materials science, composite materials engineering, surface and interface chemistry, and ultrasonic welding process steps used herein are all widely used terms and conventional procedures in their respective fields. To better understand this invention, definitions and explanations of related terms are provided below.

[0015] The terms “containing,” “comprising,” and “including” as used in this invention are synonyms and are inclusive or open-ended, not excluding additional, uncited members, elements, or method steps.

[0016] In this invention, the numerical range represented by endpoints includes all numerical values ​​and fractions contained within that range, as well as the endpoints mentioned.

[0017] Furthermore, in describing representative embodiments of the invention, this specification may present the methods and / or processes of the invention as a specific sequence of steps. However, the method or process should not be limited to the specific order of the steps described herein, to the extent that the method or process does not depend on the specific order of the steps presented herein. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps presented in the specification should not be construed as a limitation of the claims. Additionally, the claims relating to the methods and / or processes of the invention should not be limited to the execution of their steps in the order they are written, and those skilled in the art will readily recognize that the sequence can be changed while still remaining within the spirit and scope of the invention.

[0018] The concentration values ​​involved in this invention include fluctuations within a certain range.

[0019] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0020] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity of 2 or more.

[0021] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0022] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" merely describe implementation methods or embodiments with better effects and should be understood not to limit the scope of protection of this invention. In this invention, terms such as "optionally," "optionally," and "optional" mean that something is optional, that is, selected from either "with" or "without" a parallel solution. If multiple "optional" statements appear in a technical solution, unless otherwise specified and without contradiction or mutual constraint, each "optional" statement is independent.

[0023] In this invention, the term "polyaryletherketone (PAEK) resin" refers to a class of thermoplastic polymers whose main chain contains aromatic rings, ether bonds, and ketone groups. Their copolymer or sequential structure can vary depending on the ratio of ketone to ether groups, chain segment regularity, and crystallinity. PAEK belongs to a family of resins, including but not limited to PEEK, PEKK, PEK, PEEKK, PEAEK, PAEK random copolymers, block copolymers, and blends or modified systems formed with other thermoplastic resins or filler systems. All of the above-mentioned PAEK systems possess reversible melting properties, high-temperature mechanical property stability, and good interfacial wetting ability, and can all be used as the matrix resin for the carbon fiber reinforced thermoplastic resin composites applicable to this invention. This invention does not limit the use of PAEK.

[0024] In this invention, the carbon fiber reinforced thermoplastic resin composite material is a resin-based composite material with reversible melting characteristics. That is, its matrix resin can transform from a solid state to a molten state under heating conditions, and then re-solidify back to a stable structure after cooling. This process can be repeated without irreversible cross-linking or degradation. Typical resins with reversible melting characteristics include polyaryletherketones, polyphenylene sulfides, polyetherimides, and polyarylsulfones. This reversible melting property allows the thermoplastic resin powder of this invention to melt under ultrasonic vibration, enabling it to contact the matrix resin and undergo melt diffusion, thereby forming a continuous interfacial bonding layer.

[0025] In this invention, the particle size D 50 The median particle size refers to the particle size value corresponding to the 50% cumulative volume fraction in the particle size distribution of thermoplastic resin powder, i.e., the volume median particle size. The particle size D... 50Used to characterize the overall size level of powder particles, it should not be interpreted as average particle size, maximum particle size, or individual particle size.

[0026] In this invention, the terms "energy-conducting layer" and "energy-conducting rib" are used interchangeably, referring to a material layer or structure disposed at the interface to be welded, capable of preferentially absorbing and concentrating energy under ultrasonic vibration. The energy-conducting layer or rib is formed by melting composite powder during the welding process, rather than a pre-prepared solid rib or thin film structure.

[0027] In this invention, the term "areal density" refers to the mass of thermoplastic resin powder applied per unit weld interface area, which can be expressed as the mass value of the thermoplastic resin powder per unit area, and is used to characterize the amount of powder applied to the energy-conducting layer.

[0028] In this invention, the term "ultrasonic welding" refers to a welding method that uses high-frequency mechanical vibration to generate frictional heat at the interface to be welded, thereby melting the thermoplastic resin at the interface and achieving a connection under pressure.

[0029] In this invention, the thermoplastic resin powder and the composite matrix resin possess melt compatibility or interfacial wetting ability. Melt compatibility refers to the ability of the two to form a certain degree of mutual dissolution or molecular chain segment diffusion in the molten state, thereby avoiding the formation of a brittle delamination layer at the interface. Interfacial wetting ability refers to the ability of the molten powder to spread and cover the surface microstructure of the carbon fiber bundles, ensuring sufficient interfacial contact area. When the powder and the matrix resin possess the aforementioned compatibility or wetting ability, the interfacial molten layer formed during ultrasonic welding can fully penetrate into the interfibers and surface micropores, and form a stable resin bridging structure after cooling, thus obtaining a continuous and dense weld interface. Therefore, reversible meltability ensures that the interface can undergo melt fusion, while melt compatibility or wetting ability ensures that the interfacial connection does not experience delamination or brittle fracture.

[0030] This invention provides an ultrasonic welding method for carbon fiber reinforced thermoplastic resin composite materials, the method comprising: 1) Ensure the particle size meets D 50 A thermoplastic resin powder with a thickness of 15–25 μm is applied to the surface of the interface to be welded, so that the thermoplastic resin powder forms an energy-conducting layer at the interface. 2) The interface is subjected to ultrasonic vibration for welding, and the energy-conducting layer melts under ultrasonic vibration to connect the interface.

[0031] During the welding process, the interface is in a localized rapid heating environment caused by ultrasonic vibration. The thermoplastic resin powder in the energy-conducting layer preferentially melts and fills the interfacial gaps, achieving wetting and penetration of the fiber bundle surface, allowing the interfacial resin to reconnect, and thus forming a continuous resin bridging layer. In this way, fusion bonding can be achieved between composite material components without relying on external adhesive layers.

[0032] Using the above method, a uniform, dense and uninterrupted bonding layer can be formed at the welding interface, significantly reducing interface defects such as incomplete welding and improving the overall connection strength and stability of the welded joint. At the same time, since the powder application method does not rely on pre-made thin film or rib structure, this method can adapt to the welding of interfaces with planar, curved and complex three-dimensional morphologies, and has the advantages of simple process, strong applicability and good repeatability.

[0033] Those skilled in the art can select thermoplastic resin powders according to the principles of the present invention, provided that: they can reversibly melt and fuse with carbon fiber reinforced thermoplastic resin composites; the melt viscosity is not so high as to prevent spreading; and they do not damage the interface or cause significant thermal decomposition. Therefore, the following can be selected: polyaryletherketone (PAEK) resins, polyphenylene sulfide (PPS) resins, polyetherimide (PEI) resins, polyarylsulfone (PSU) resins, polyphenylene sulfone (PES) resins, polyphenylene sulfone (PPSU) resins, or polyaryletherketone resins containing nitrile groups. In some preferred embodiments, the thermoplastic resin powder is a polyaryletherketone resin or a polyaryletherketone resin powder containing nitrile groups.

[0034] Polyaryletherketone resins include, but are not limited to, PEEK, PEKK, PEK, PEEKK and their blends or modified systems. Among them, PEEK is the preferred system due to its good melt flowability, thermal stability and compatibility with carbon fiber matrix.

[0035] The polyarylene ether ketone resin containing nitrile groups introduces polar –CN groups into its molecular chain, exhibiting strong polarity. These groups can form hydrogen bonds or dipole-dipole interactions with the carbon fiber surface and the composite matrix resin, thereby enhancing the wetting and spreading ability of the powder at the interface and its interfacial adhesion in the molten state. This allows for the formation of a more continuous and dense resin bonding layer at the welding interface. Furthermore, the polyarylene ether ketone resin is preferably a polyarylene ether ketone resin containing phenolphthalein. The phenolphthalein structural units can improve the rigidity and heat resistance of the resin chain, enabling it to maintain good flow-curing synergy even under the instantaneous high temperatures generated by ultrasonic welding. This facilitates rapid solidification of the welding interface after melting and the formation of a stable bridging structure, thereby improving the mechanical properties and long-term service reliability of the welded joint.

[0036] In summary, the molten layer formed at the interface by the nitrile-containing polyarylether nitrile ketone resin powder exhibits stronger interfacial bonding ability and structural stability, which can further improve the connection quality and consistency of the method of the present invention in the welding process of planar, curved, and complex three-dimensional components.

[0037] In some embodiments, the areal density of the conductive layer formed by the thermoplastic resin powder at the interface is 5–20 g / m². 2 For example, it can be 8 g / m 2 12 g / m 2 15 g / m 2 Or 18 g / m 2 By controlling the areal density within the above range, the powder can form a continuous coating while avoiding energy transfer obstruction or uneven melting due to excessive powder accumulation.

[0038] In this invention, the areal density can be calculated from the mass of powder applied to a unit area interface, and the calculation method is as follows: areal density (g / m²) 2 = m / A.

[0039] Where m is the mass of powder applied, in grams (g); A is the area of ​​the powder-covered region, in square meters (m²). 2 When the application step is carried out using a powder spreader, powder spraying device, or electrostatic spraying method, the m can be obtained by weighing the difference in mass of the substrate before and after powder application.

[0040] When the areal density is controlled as described above, the energy-conducting layer can melt rapidly under ultrasonic action and penetrate into the interfacial gap to form a continuous molten bridging layer, thereby significantly reducing the probability of unwelded areas and improving the density of the welded interface and the connection strength of the joint.

[0041] In some embodiments, the matrix resin in the composite material is selected from: polyaryletherketone (PAEK) resin, polyphenylene sulfide (PPS) resin, polyetherimide (PEI) resin, polyarylsulfone (PSU) resin, polyphenylene sulfone (PES) resin, polyphenylene sulfone (PPSU) resin, and blends or modified systems thereof.

[0042] The above-mentioned resin system can undergo reversible melting when heated. In its molten state, it has a certain chain segment diffusion ability and interface wetting ability, and can form a continuous melt connection interface with the molten layer of the thermoplastic resin powder during ultrasonic welding.

[0043] Furthermore, the aforementioned resin system is widely used in aerospace, rail transportation, and structural load-bearing components. It exhibits excellent interfacial compatibility and toughness retention with carbon fibers, and its melt viscosity characteristics are suitable for the rapid localized heating-flow-solidification process required for ultrasonic welding, ensuring the formation of a stable bonding layer at the weld interface within a short time. By selecting a matrix resin system with reversible melting and compatibility, the method of this invention can obtain uniform, dense, and reliable welded joints between composite materials of different components, thicknesses, and geometries.

[0044] In some embodiments, the thermoplastic resin powder is applied to the interface to be welded and fixed by preheating. Preferably, the interface region of the composite material can be heated to a temperature range of ±10°C from the glass transition temperature (Tg) of its matrix resin, causing slight softening of the thermoplastic resin powder surface and initial adhesion and fixation to the interface surface. Since the heating temperature does not reach the complete melting range of the resin, it will not cause changes in the interface resin structure or disturbance of fiber distribution. At the same time, it can form a uniform, continuous, and non-detachable energy-conducting layer at the interface, which is beneficial to the stable formation of the interface molten layer during subsequent ultrasonic welding.

[0045] By using the above-mentioned preheating and softening fixation method, it is possible to effectively prevent powder displacement or accumulation during the initial stage of assembly or ultrasonic vibration. At the same time, it can improve the contact area and spreading consistency between powder and interface, thereby enhancing the interface energy conduction efficiency and promoting the continuous fusion connection of the welding interface.

[0046] In another embodiment of the present invention, applying the thermoplastic resin powder to the interface surface includes: adhering the powder to the interface surface by electrostatic adsorption. Specifically, the welding area is first cleaned, and the interface surface is treated with an ion gun in neutralization mode (or a mode that generates both positive and negative ions simultaneously) to eliminate any residual electrostatic charges that may exist in the interface area, forming a stable electrically neutral surface. Subsequently, the ion gun is adjusted to "positive ion" mode or "negative ion" mode, and the welding surface is lightly swept to form a stable layer of positive or negative charge on the interface.

[0047] The formation of the powder fixation layer is based on the charge adsorption mechanism: since resin powder is a good insulator, its surface can naturally become charged when in contact with air or through friction. When the interface surface carries a charge of opposite polarity to the powder surface, the powder can be uniformly adsorbed and fixed on the interface surface under the action of charge attraction, and will not fall off due to changes in interface curvature or the direction of gravity. This allows for uniform powder application on large areas, curved surfaces, hyperboloids, and complex surfaces with local uneven textures.

[0048] This method avoids the difficulty of bonding thin film or strip-shaped conductive layers to complex surfaces, achieving powder conductive layers with easily controllable thickness and uniform distribution. It also eliminates the need for additional heating steps, simplifies the process, and can be used with automated spraying equipment. It offers advantages such as high efficiency, good interface uniformity, and remanufacturability.

[0049] In some embodiments, the surface of the interface to be welded is a non-planar structure. Preferably, it is a curved surface, a hyperboloid, a surface with varying curvature, or a complex three-dimensional surface with a stepped shape. Since the present invention uses particles with a diameter satisfying D... 50 The conductive layer is formed directly on the interface by thermoplastic resin powder with a thickness of 15–25 μm. The powder can be uniformly distributed according to the microstructure of the interface and is not limited by the pre-fabricated geometry of the conductive layer. Therefore, even if there are curvature changes, uneven morphology or stepped structure at the interface, the powder conductive layer can still achieve continuous coverage at the interface without gaps or unbonded areas caused by poor local adhesion.

[0050] Under ultrasonic vibration, the powder conductive layer can first melt in the local contact area and penetrate into the interfacial gap and fiber bundle surface, forming a continuous and dense resin bridging layer at the welding interface, thereby improving the interface integrity and connection stability of the non-planar structural connection area. Therefore, the welding method described in this invention has good applicability and process consistency in the connection of curved surfaces and complex three-dimensional structural components.

[0051] In this invention, the frequency of ultrasonic vibration can be adjusted according to the type of welding equipment, the thickness of the component, and the area of ​​the interface to be welded. Preferably, the ultrasonic vibration frequency is 15–40 kHz. Lower frequencies (e.g., 15–20 kHz) can provide a larger vibration amplitude, suitable for situations where the component size is large or the interface roughness is high; higher frequencies (e.g., 30–40 kHz) are beneficial for achieving finer energy control, suitable for structural components with thinner walls or higher requirements for interface forming quality. By controlling the frequency within the above range, it can be ensured that the interface energy-conducting layer melts rapidly under ultrasonic action without causing fiber breakage or excessive thermal deformation of the matrix, thereby obtaining a stable welding interface.

[0052] During the welding process, applying appropriate welding pressure ensures sufficient contact between the energy-conducting layer and the interface during the molten stage, and promotes the penetration of molten resin into the fiber bundle surface and interfacial micropores. Preferably, the welding pressure is 0.5–3 MPa. Too low a pressure may result in insufficient interfacial contact and inadequate molten resin spreading, forming localized unwelded areas; while too high a pressure may cause excessive extrusion of molten resin from the interface or localized compaction of the carbon fibers, affecting the continuity of the connection. Controlling the welding pressure within the above range achieves a balance between dense interfacial bonding and mechanical property stability.

[0053] In this invention, the welding time and post-weld pressure holding time can be adjusted according to the component thickness, interface size, and ultrasonic energy input rate. Preferably, the welding time is 1–5 s, and the post-weld pressure holding time is 1–5 s. The welding time controls the melting depth and melting rate of the interface energy-conducting layer; the pressure holding time is used to stabilize the interface resin during the gradual dissipation of heat, ensuring that the resin bridging layer has a uniform and continuous structure. By controlling the welding time and pressure holding time within the above ranges, incomplete melting due to insufficient welding or insufficient cooling and solidification due to insufficient pressure holding can be avoided, thereby ensuring the structural integrity and connection strength of the weld interface.

[0054] The embodiments of the present invention will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this invention, or follow experimental manuals or conventional conditions in the art, or other experimental methods known in the art, or follow the conditions recommended by the manufacturer.

[0055] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0056] Unless otherwise specified, the areal density of the energy-conducting layer formed at the interface by the composite powder in the following examples / comparative examples (except for Comparative Examples 1-2) is 14 g / m². 2 .

[0057] Comparative Example 1 (Baseline: No energy-conducting ribs) This comparative example provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs, the specific steps of which are as follows: The prepreg used was CF / PEEK (carbon fiber reinforced polyetheretherketone resin-based composite). Welding experiments were conducted using two CF / PEEK composite strips, each 100 mm long, 25 mm wide, and 2 mm thick. The vibration frequency was 20 kHz, the vibration time was 3 s, the welding pressure was 1 MPa, the amplitude was 50 μm, the holding time was 2 s, the overlap length was 12.5 mm, and the overlap width was 25 mm.

[0058] Based on the scanning electron microscope results ( Figure 1The fracture surface of the welded joint after fracture revealed a large area of ​​exposed carbon fiber bundles. The interface lacked a continuous resin melt bridging layer, and the fibers were not fully coated. Due to the absence of a conductive layer, ultrasonic energy was difficult to concentrate effectively at the interface, resulting in incomplete local melting. The interface load was primarily borne directly by the carbon fibers, ultimately leading to a typical fracture morphology of brittle fracture of numerous carbon fibers. This type of "fiber-dominated brittle fracture" significantly reduced the load-bearing capacity of the lap joint; therefore, the shear strength of this group was only 13.25 ± 0.77 MPa (the single lap strength of the obtained welded joint was tested according to ASTM D1002).

[0059] Comparative Example 2 (Control: PEEK thin film energy conductor) This comparative example provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs, the specific steps of which are as follows: The prepreg used was CF / PEEK (carbon fiber reinforced polyetheretherketone resin-based composite). Two CF / PEEK composite strips, each 100 mm long, 25 mm wide, and 2 mm thick, were used. The lower surface was covered with a 13 mm long, 26 mm wide, and 100 μm thick PEEK film. The upper surface of the strip to be welded was then overlapped onto the lower surface to form a tightly fitted lap joint. The welding process used was a vibration frequency of 20 kHz, a vibration time of 3 s, a welding pressure of 1 MPa, an amplitude of 50 μm, and a holding time of 2 s. The resulting welded joint was tested for single lap strength according to ASTM D1002, with a result of 23.52 ± 0.42 MPa. Visual inspection of the cross-section revealed only a few areas with resin loss and exposed fiber. Scanning electron microscopy analysis showed that cracks extended along the interface between the energy-conducting ribs and the CF / PEEK composite material, indicating a relatively weak weld interface. Figure 2 ).

[0060] Example 1 (PEEK ultrafine powder energy-conducting ribs) This invention provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs, the specific steps of which are as follows: The prepreg used was CF / PEEK (carbon fiber reinforced polyetheretherketone resin-based composite). First, PEEK resin ultrafine powder (D...) was prepared by high-speed pulverization. 50The powder (15–25 μm) must be dried to avoid moisture and air bubbles. Then, using two CF / PEEK composite samples (100 mm long, 25 mm wide, and 2 mm thick), a 12.5 mm long and 25 mm wide area was selected on the lower surface. The surface resin was heated to 120°C using a laser emitter to slightly melt it. Using a feeding device, ultrafine PEEK powder was spread onto the molten resin area on the lower surface. The upper surface sample to be welded was then overlapped onto the lower surface sample to form a tightly fitted lap joint. The welding process used was a vibration frequency of 20 kHz, a vibration time of 3 s, a welding pressure of 1 MPa, an amplitude of 50 μm, and a holding time of 2 s. The resulting weld joint was tested for single lap strength according to ASTM D1002, and the result was 30.38 ± 0.18 MPa. Visual inspection of the cross-section revealed that the resin fibers were fully impregnated with no exposed fibers. Scanning electron microscopy analysis showed that the resin fractured locally at the energy-conducting ribs, but the crack did not extend into the composite matrix, indicating that the resin melt layer at the interface was continuous, uniform, and dense, and the weld area was well-bonded. Figure 3 ).

[0061] Example 2 (BP-CN ultrafine powder energy-conducting ribs) This invention provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs, the specific steps of which are as follows: The prepreg used was CF / PEEK (carbon fiber reinforced polyetheretherketone resin-based composite). First, BP-CN resin ultrafine powder (D...) was prepared by high-speed pulverization. 50 The powder (15–25 μm) must be dried to avoid moisture and air bubbles. Then, using two CF / PEEK composite samples (100 mm long, 25 mm wide, and 2 mm thick), a 12.5 mm long and 25 mm wide area on the lower surface is heated to 120°C using a laser emitter to slightly melt the surface resin. Using a feeding device, BP-CN ultrafine powder is laid on the resin-molten area on the lower surface. The upper surface sample to be welded is then overlapped onto the lower surface sample to form a tightly fitted lap joint. The welding process uses a vibration frequency of 20 kHz, a vibration time of 3 s, a welding pressure of 1 MPa, an amplitude of 50 μm, and a holding time of 2 s. The resulting welded joint is tested for single lap strength according to ASTM D1002, and the result is 40.76 ± 0.20 MPa, reaching 60% of the original strength. The resin fibers were fully impregnated, with no exposed fibers. Scanning electron microscopy revealed that the crack propagated at the energy-conducting ribs without extending into the composite matrix, and the resin layer weld was uniform (see reference). Figure 4 (B)

[0062] Example 3 (BP-CN powder particle size parameter window) This invention provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs, and is used to verify the parameter window of BP-CN powder particle size. The specific steps are as follows: The prepreg used was CF / PEEK (carbon fiber reinforced polyetheretherketone resin-based composite). First, BP-CN resin ultrafine powder (D...) was prepared by high-speed pulverization. 50 =10 / 20 / 25 / 35 / 50µm) powder must be dry to avoid moisture bubbles; then, using two CF / PEEK composite samples with dimensions of 100mm long, 25mm wide, and 2mm thick, a 12.5mm long and 25mm wide area was selected on the lower surface. The surface resin was heated to 120℃ using a laser emitter to slightly melt it. Using a feeding device, BP-CN ultrafine powder was laid on the resin-molten area on the lower surface. The upper surface sample to be welded was then overlapped onto the lower surface sample to form a tightly fitted lap joint. The welding process selected was a vibration frequency of 20kHz, a vibration time of 3s, a welding pressure of 1MPa, an amplitude of 50μm, and a holding time of 2s. The resulting welded joint was tested for single lap strength according to ASTM D1002, and the results are shown in the table below: ; like Figure 4 As shown, A is a weld surface diagram of 30µm BP-CN particles. It can be observed that some BP-CN resin was not completely melted and appeared as particles on the weld surface. This incompletely melted resin caused a decrease in performance. B is a weld surface diagram of 20µm BP-CN particles in Example 2. The overall resin and fiber were fully impregnated. After fracture, exposed carbon fibers can be seen, indicating that the crack did not simply occur in the toughened resin matrix (BP-CN), but had extended into the deeper matrix (CF / PEEK). The bonding force between resins is much smaller than the bonding force between resin and fiber. The crack propagation into the matrix indicates that a deeper fracture mechanism can be reached, opening up new directions for future research.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. An ultrasonic welding method for carbon fiber reinforced thermoplastic resin composites, the method comprising: 1) Ensure the particle size meets D 50 A thermoplastic resin powder with a thickness of 15–25 μm is applied to the surface of the interface to be welded, so that the thermoplastic resin powder forms an energy-conducting layer at the interface. 2) The interface is subjected to ultrasonic vibration for welding, and the energy-conducting layer melts under ultrasonic vibration to connect the interface.

2. The method according to claim 1, wherein the thermoplastic resin powder is a polyaryletherketone resin or a polyaryletherketone resin powder containing a nitrile group; Preferably, the polyaryletherketone resin is PEEK; Preferably, the polyarylene ether nitrile ketone resin is a polyarylene ether nitrile ketone resin containing a phenolphthalein structure.

3. The method according to claim 1, wherein the areal density of the conductive layer formed by the thermoplastic resin powder at the interface is 5–20 g / m². 2 .

4. The method according to claim 1, wherein the matrix resin in the composite material is selected from: polyaryletherketone (PAEK) resin, polyphenylene sulfide (PPS) resin, polyetherimide (PEI) resin, polyarylethersulfone (PSU) resin, polyphenylene sulfone (PES) resin, polyphenylene sulfone (PPSU) resin, and blends or modified systems thereof.

5. The method according to any one of claims 1-4, wherein the thermoplastic resin powder is applied to the interface to be welded and fixed by preheating; preferably, the interface region of the composite material is heated to a temperature range of ±10°C of the glass transition temperature (Tg) of its matrix resin, so that the surface of the thermoplastic resin powder is slightly softened and initially adhered and fixed to the interface surface.

6. The method according to any one of claims 1-4, wherein applying the thermoplastic resin powder to the interface surface comprises: The powder is attached to the interface surface by electrostatic adsorption.

7. The method according to any one of claims 1-4, wherein the surface of the interface to be welded is a non-planar structure; preferably, it is a curved surface, a hyperboloid, a surface with varying curvature, or a complex three-dimensional surface with a stepped shape.

8. The method according to any one of claims 1-4, wherein the frequency of the ultrasonic vibration is 15-40 kHz.

9. The method according to any one of claims 1-4, wherein the welding pressure is 0.5 to 3 MPa.

10. The method according to any one of claims 1-4, wherein the welding time is 1-5 s and the post-weld pressure holding time is 1-5 s.

Images