Composite powders and methods for ultrasonic welding of carbon fiber reinforced thermoplastic resin composites

Abstract

The present application relates to the technical field of ultrasonic welding of composite materials, and particularly relates to a composite powder and method for ultrasonic welding of carbon fiber reinforced thermoplastic resin composite materials. Specifically, the composite powder for ultrasonic welding of carbon fiber reinforced thermoplastic resin composite materials comprises two kinds of thermoplastic resin powders, A powder and B powder, wherein: the particle size D50 of the A powder and the B powder is 15-25 mu m; the A powder is a high-flowability thermoplastic resin powder, the melt flow rate MFR_A of which is greater than the melt flow rate MFR_B of the B powder, and MFR_A / MFR_B>2 is satisfied; and the mass fraction ratio of the A powder and the B powder is A powder:B powder=(60-90):(10-40) according to the total mass fraction of 100 parts.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic welding technology for composite materials, and in particular to a composite powder and method for ultrasonic welding of carbon fiber reinforced thermoplastic resin composite materials. Background Technology

[0002] Entering the 21st century, aerospace, defense, and high-end equipment manufacturing industries have placed extremely high demands on the joining technology of lightweight, high-performance composite materials. Thermoplastic composites, such as carbon fiber reinforced polyetheretherketone (CF / PEEK), have become the preferred material for critical structural components due to their excellent specific strength, fatigue resistance, and recyclability. For the manufacture of large or complex components, reliable joining technology is the core bottleneck for realizing their engineering applications.

[0003] Ultrasonic welding technology, as a highly efficient and environmentally friendly joining method, converts mechanical vibration energy into heat energy at the interface through energy-conducting ribs, causing the resin matrix to melt and then solidify, achieving a solid-body connection. This avoids the fiber cutting and stress concentration problems associated with mechanical joining, as well as the aging issues and long processing cycles of adhesive bonding. Therefore, this technology is considered an ideal solution for joining thermoplastic composite materials.

[0004] The energy-conducting rib is the core of ultrasonic welding, and its shape and performance directly determine the welding quality. Existing energy-conducting ribs mainly exist in the following two forms and have inherent defects: 1. Preformed energy-conducting ribs: These include forms such as triangular prisms, films, and non-woven fabrics. These energy-conducting ribs have the following insurmountable drawbacks: • Poor processability and high cost: Special engineering plastics, represented by PEEK, have a narrow processing window and require complex processes such as extrusion, injection molding, and hot pressing to pre-form shapes. The process is long, energy-intensive, and costly.

[0005] • Poor shape adaptability: Rigid preforms are difficult to fit perfectly with complex curved surfaces (such as the three-dimensional curved surfaces of aerospace components), resulting in uneven distribution of welding pressure and energy, which easily leads to weak connections or welding defects.

[0006] • Fragile interface fusion line: After the preformed energy-conducting rib melts, a clear "fusion line" (Knit-line) will be formed between its fusion front and the composite matrix. Due to insufficient molecular chain entanglement, this interface becomes a weak link in mechanical properties, with low joint toughness and easy interface delamination.

[0007] 2. Single-material powder energy conductor: The inventors have previously explored this area. To overcome the shape limitations of pre-formed energy conductors, existing technologies have proposed using a single type of ultrafine resin powder as the energy conductor. While this method solves the compatibility problem with complex curved surfaces, it inherently presents a fundamental mechanical contradiction: • Strength and toughness are mutually exclusive: To achieve good welding, high-flowability resin powder must be selected to ensure full melting and interface wetting. However, welds formed by such resins are often homogeneous in material, with limited fracture toughness, poor resistance to crack propagation, and the joint exhibits brittle fracture characteristics.

[0008] • Conversely, if a resin powder with high toughness and high heat resistance is selected, its fluidity is usually poor. It is difficult to completely melt and flow fully during the short ultrasonic treatment time, which can easily lead to insufficient wetting of the interface and the generation of incomplete fusion defects, which in turn greatly reduces the connection strength.

[0009] In summary, neither traditional preformed energy-conducting ribs nor emerging single-material powder energy-conducting ribs can achieve an ideal balance between high strength and high toughness in welded joints. Those skilled in the art have long faced a dilemma: pursuing strength at the expense of toughness, or pursuing toughness at the expense of strength. This core contradiction severely restricts the application of ultrasonic welding technology in load-bearing, high-reliability structural components.

[0010] Therefore, there is an urgent need in this field for a novel energy-conducting rib design concept and implementation that can fundamentally and synergistically improve the strength and toughness of welded joints, breaking through the performance bottlenecks of existing technologies. Summary of the Invention

[0011] This invention covers the following technical solutions: One aspect of the present invention relates to a composite powder for ultrasonic welding of carbon fiber reinforced thermoplastic resin composites, comprising two thermoplastic resin powders, A powder and B powder, wherein: The particle size D50 of both powder A and powder B is 15μm~25μm; • Powder A is a high-flow-rate thermoplastic resin powder, whose melt flow rate MFR_A is greater than that of powder B, and satisfies MFR_A / MFR_B > 2; Based on a total mass of 100 parts, the mass ratio of powder A to powder B is: Powder A: Powder B = (60-90): (10-40).

[0012] Another aspect of the present invention relates to an ultrasonic welding method for carbon fiber reinforced thermoplastic resin composite materials, comprising: 1) Apply the composite powder as described above 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, thus connecting the interface; During the ultrasonic vibration process, powder A preferentially melts and spreads, while powder B forms a relatively stagnant region during the melting process, thereby forming a molten bonding layer with non-uniform flow characteristics at the welding interface.

[0013] This invention introduces a composite powder energy-conducting layer composed of powder A and powder B at the ultrasonic welding interface of carbon fiber reinforced thermoplastic resin composites. Utilizing the difference in melt flowability between the two thermoplastic resin powders, it achieves effective energy concentration and synergistic control of melting behavior during the welding process. Under ultrasonic vibration, the highly fluid powder A preferentially melts and spreads at the interface, while the less fluid powder B forms a relatively stagnant region during melting, thus forming a continuous but non-uniform flow molten bonding layer at the welding interface. Through this method, the invention ensures sufficient fusion at the interface while suppressing excessive loss of molten resin, effectively improving the interface density, load-bearing capacity, and fracture toughness of the weld joint, reducing the probability of incomplete welding and brittle fracture, and exhibiting good adaptability to curved surfaces and complex three-dimensional interfaces. Attached Figure Description

[0014] 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.

[0015] Figure 1 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 1.

[0016] Figure 2 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 2.

[0017] Figure 3 Scanning electron microscopy results of the weld fracture surface after fracture in Comparative Example 3.

[0018] Figure 4 SEM images of cross-sections of BP-CN resin ultrafine powder samples with different particle sizes after testing.

[0019] Figure 5 SEM image of cross-section with A / B=80:20; ① Schematic diagram of component fracture point; ② Schematic diagram of crack deflection point.

[0020] Figure 6 The cross-section of the multiphase powder exhibits a sea-island structure; ① Schematic diagram of the "island" structure; ② Schematic diagram of the "sea" structure. Detailed Implementation

[0021] 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.

[0022] 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 and laboratory procedures related to thermoplastic composite engineering, ultrasonic welding and solid-state / fusion bonding technology, polymer materials science and rheology, powder engineering and particulate materials technology, interface and fracture mechanics, composite material joining processes and manufacturing engineering used herein are all widely used terms and routine procedures in their respective fields. To better understand this invention, definitions and explanations of relevant terms are provided below.

[0023] 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.

[0024] 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.

[0025] As used in this invention, the term "about" or "approximately" means within 20%, preferably within 10%, and more preferably within 5%, of a given value or range. It also includes specific numbers, such as about 20 including 20.

[0026] 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.

[0027] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0028] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity of 2 or more.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In this invention, the term "melt flow rate" or "MFR" is a parameter used to characterize the flowability of thermoplastic resins in the molten state, representing the mass of melt extruded through a standard capillary per unit time under specified conditions. The melt flow rate can be determined according to commonly used testing methods in the art and is used to compare the relative flowability of different resin powders in the molten state.

[0035] In this invention, powder A refers to a thermoplastic resin powder with relatively high melt flowability during welding, while powder B refers to a thermoplastic resin powder with lower melt flowability than powder A under the same welding conditions. The difference in flowability between powder A and powder B can be characterized by melt flow rate and used to achieve functional division of labor with different melting behaviors during welding.

[0036] In this invention, the term "composite powder" refers to a powder system comprising at least two thermoplastic resin powders, powder A and powder B, wherein powder A and powder B differ in melt flowability and synergistically form an energy-conducting layer or energy-conducting rib for interfacial bonding during welding. This composite powder differs from single-component resin powders and also from simple mixed powders lacking differences in melt flowability.

[0037] In this invention, the term "molten bonding layer with non-uniform flow characteristics" refers to a continuous molten layer formed at the weld interface, which exhibits differences in flow behavior between different regions at the microscale. The non-uniform flow characteristics originate from the difference in melt flowability between powder A and powder B, rather than defects caused by insufficient welding or material deficiency.

[0038] In this invention, the particle size D 50 The median particle size refers to the particle size value corresponding to 50% of the cumulative volume fraction in the powder particle size distribution, i.e., the volume median particle size. The particle size D... 50 Used 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.

[0039] 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.

[0040] In this invention, the term "preferential melting" refers to the process characteristic where, under the same ultrasonic energy input conditions, powder A softens or melts earlier than powder B and participates in interfacial spreading. This term is used to describe the relative trend of melting behavior and does not limit the absolute time sequence or melting temperature.

[0041] In this invention, the term "stagnant region" refers to a region in the molten bonding layer where the flow rate is significantly lower than that of the surrounding molten resin. The stagnant region is not entirely unmelted solid particles, but rather a region that plays a role in structural retention, energy regulation, or toughening of the molten layer during the welding process.

[0042] The first aspect of this invention relates to a composite powder for ultrasonic welding of carbon fiber reinforced thermoplastic resin composites, the composite powder comprising two thermoplastic resin powders, A powder and B powder, wherein: The particle size D50 of both powder A and powder B is 15μm~25μm; • Powder A is a high-flow-rate thermoplastic resin powder, whose melt flow rate MFR_A is greater than that of powder B, and satisfies MFR_A / MFR_B > 2; Based on a total mass of 100 parts, the mass ratio of powder A to powder B is: Powder A: Powder B = (60-90): (10-40).

[0043] Within the range of 15 μm to 25 μm, the uniformity of powder spread on the welding interface and its rapid response characteristics under ultrasonic vibration can be guaranteed; the difference in melt flow rate can form obvious differences in melt flowability during the welding process; through the above component design, the composite powder can simultaneously take into account the rapid melting and spreading of the interface and the stability of the melt structure during ultrasonic welding, providing a material basis for the subsequent formation of a melt bonding layer with non-uniform flow characteristics.

[0044] In some embodiments, powder A and powder B can be selected from various thermoplastic resin systems with reversible melting properties. Specifically, powder A and / or powder B can be selected from polyaryletherketone resins, polyphenylene sulfide resins, polyetherimide resins, polyarylethersulfone resins, polyphenylene sulfone resins, polyphenylene sulfone resins, and polyarylethernitrile ketone resins containing nitrile groups, or blends or modified systems of the above resins. These resin systems exhibit good melt stability and interfacial wetting ability under the instantaneous thermo-mechanical coupling conditions generated by ultrasonic welding, and can form an effective fusion bond with the matrix resin of carbon fiber reinforced thermoplastic resin composites.

[0045] In some preferred embodiments, the polyaryletherketone resin includes, but is not limited to, PEEK, PEKK, PEK, PEEKK and their blends or modified systems. Polyaryletherketone resins, due to their high thermal stability and good melt flow characteristics, can be used as a high-flowability component in composite powders. In a further preferred embodiment, powder A is a polyaryletherketone resin powder, and powder B is a polyaryletherketone nitrile resin powder containing nitrile groups. The nitrile-containing polyaryletherketone nitrile resin introduces polar groups into its molecular chain, which is beneficial for improving its interfacial adhesion and structure retention in the molten state. Therefore, it works synergistically with the high-flowability powder A during welding to promote the formation of a stable and continuous welding interface.

[0046] In a further embodiment, to better balance the interfacial melting and spreading capacity and the stability of the molten structure during welding, the mass ratio of powder A to powder B is preferably controlled within the range of (70-80):(20-30). By combining the highly fluid powder A with the relatively low fluid powder B in the above ratio, powder A can preferentially melt and rapidly spread on the welding interface under ultrasonic vibration. Simultaneously, the relatively stagnant region formed by powder B during melting plays a structural role in maintaining the molten layer, thereby facilitating the formation of a continuous molten bonding layer with non-uniform flow characteristics at the welding interface. Practice shows that within the above ratio range, the welding interface can effectively suppress excessive loss of molten resin while achieving full fusion, thereby improving the load-bearing capacity and fracture toughness of the welded joint.

[0047] The particle size D of powder A and powder B 50 The particle size is controlled within the range of 15 μm to 25 μm. This particle size range is beneficial for the uniform deposition of the composite powder on the welding interface and allows for rapid response and melting under ultrasonic vibration, which helps improve the consistency and continuity of interface melting. In a further preferred embodiment, the particle size D... 50 The thickness can be selected from 18 μm to 22 μm to achieve a more stable balance between powder spreadability and melting rate.

[0048] In some embodiments, the melt flow rate ratio (MFR_A / MFR_B) of powder A to powder B is preferably 3 to 6, or 3 to 5. Within this range, powder A and powder B can form a more obvious and stable difference in melt flow during welding, thereby enhancing the formation effect of the non-uniform flow melt structure and improving the overall density and mechanical property stability of the weld interface.

[0049] Another aspect of the present invention relates to an ultrasonic welding method for carbon fiber reinforced thermoplastic resin composites, the method comprising: 1) Apply the composite powder as described above 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, thus connecting the interface; During the ultrasonic vibration process, powder A preferentially melts and spreads, while powder B forms a relatively stagnant region during the melting process, thereby forming a molten bonding layer with non-uniform flow characteristics at the welding interface.

[0050] Compared to the conductive layer formed using a single resin powder, the non-uniform flow molten bonding layer formed by this invention ensures sufficient interfacial fusion while effectively suppressing excessive loss of molten resin and maintaining the structural stability of the welded area, thereby improving the interfacial density and mechanical properties of the weld joint. Through the above method, this invention can achieve stable and reliable interfacial bonding in a shorter welding time, and is suitable for ultrasonic welding of carbon fiber reinforced thermoplastic resin composites.

[0051] In some embodiments, the areal density of the energy-conducting layer formed by the composite 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] In some embodiments, the composite powder is applied to the surface of the interface to be welded by at least one of powder spreading, powder spraying, and electrostatic adsorption. These methods allow the composite powder to be uniformly distributed across the welding interface region, forming a continuous energy-conducting layer on interfaces with different morphologies. Powder spreading is suitable for planar or near-planar welding interfaces, allowing for precise control of the application area and amount of composite powder. Powder spraying facilitates rapid and uniform powder application on larger welding interfaces. Electrostatic adsorption utilizes the electrostatic interaction between the powder and the interface surface to stably adhere the composite powder to the interface surface, making it particularly suitable for curved surfaces, hyperboloids, or welding interfaces with complex three-dimensional morphologies. By employing any one or more of these powder application methods, the composite powder can form a uniformly distributed, controllable-thickness energy-conducting layer before welding, which facilitates effective energy coupling and rapid melting at the interface during subsequent ultrasonic welding, thereby improving the stability of the welding process and the consistency of the weld joint.

[0056] In some embodiments, the composite powder can be 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 composite 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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, dense molten bonding layer with non-uniform flow characteristics at the welding interface. This improves 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The embodiments of the present invention will be described in detail below with reference to the examples. It should be understood that these embodiments are only used to illustrate the technical content of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the specific experimental conditions in the following embodiments are given priority reference to the guidelines provided in this specification, or may be carried out according to generally accepted experimental manuals or conventional experimental conditions, or other experimental methods known in the art, or according to the conditions recommended by the relevant reagent or instrument manufacturers. In specific embodiments, unless otherwise specified, minor deviations within the weighing accuracy range are allowed for the measurement parameters involving raw material components; reasonable deviations due to instrument detection accuracy or operational accuracy are also allowed for parameters such as temperature and time.

[0067] 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 .

[0068] 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.

[0069] Based on the scanning electron microscope results ( Figure 1 The 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).

[0070] 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 ).

[0071] Comparative Example 3 (Single PEEK ultrafine powder energy-conducting rib) 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). 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 molten layer at the interface was continuous, uniform, and dense, and the weld area showed intact bonding. Figure 3 ).

[0072] Comparative Example 4 (Single BP-CN Ultrafine Powder Energy Conducting Rib) 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). 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)

[0073] Unless otherwise specified, the areal density of the energy-conducting layer formed at the interface by the composite powder in the following embodiments is 14 g / m². 2 .

[0074] Example 1 (Window of particle size parameters for thermoplastic resin powder) This invention provides an ultrasonic welding method for composite materials based on resin powder energy-conducting ribs. To simplify the model, a single BP-CN powder particle size is used for parameter window verification. 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 image 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 image of 20µm BP-CN particles in Comparative Example 4. 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.

[0075] Example 2 (Performance comparison experiment of multiphase powder energy conductive ribs and single-component powder energy conductive ribs) The welding surface used is a CF / PEEK laminate with dimensions of 100mm in length, 25mm in width, and 2mm in thickness.

[0076] Energy guide material: Component A: Polyarylene ether nitrile ketone ultrafine powder BP-CN (360℃ MFR=80 g / 10min), D 50 =20μm; Component B: Ultrafine powder containing biphenyl-structured polyaryletherketone (PEK-B) (360℃ MFR=30 g / 10min), D 50 =22μm.

[0077] Multiphase powder: mechanically mixed at a mass ratio of 80:20; Control 1: 100% component A; Control 2: 100% component B.

[0078] The powder must be dry to avoid moisture bubbles. Welding was performed under the following conditions: vibration frequency of 20kHz, vibration time of 3s, welding pressure of 1MPa, amplitude of 50μm, and holding time of 2s. The obtained welded joints were subjected to single lap strength testing according to ASTM D1002, and impact performance testing according to GB / T 2650-2022. The results are shown in the table below: ; Scanning electron microscopy analysis of the A / B multiphase energy-conducting rib powder clearly shows the sea-island structure described in this patent. It can be observed that the B powder, acting as an island, has undergone pull-out, cracking, crack termination, and displacement, which effectively improves the interlayer performance of the weld surface, achieves the synergistic effect of components A and B, combines the advantages of both, and simultaneously realizes high strength and high toughness.

[0079] The multiphase powder energy-conducting ribs described in this invention can simultaneously achieve high strength and high toughness. Their tensile shear strength is increased by about 29% compared to single high-toughness powder, and their impact toughness is increased by about 64% compared to single high-flowability powder, verifying the synergistic toughening and strengthening effect of the "sea-island" structure.

[0080] Example 3 (Experiment on the effect of different A:B mass ratios on welding performance) The welding surface used is a CF / PEEK laminate with dimensions of 100mm in length, 25mm in width, and 2mm in thickness.

[0081] Energy-conducting rib material: A:B = 90:10, 80:20, 70:30, 60:40 (mass ratio) The process and testing methods are the same as in Example 1, and the test results are shown in the figure below: ; The joint exhibits optimal overall mechanical properties when the A:B ratio is within the range of (80:20) to (70:30). Strength decreases significantly when the ratio is below 70:30; the preferred ratio is 80:20.

[0082] Example 4 (Process stability verification of powder placement and fixation method) The welding surface used is a CF / PEEK laminate with dimensions of 100mm in length, 25mm in width, and 2mm in thickness.

[0083] Energy guide material: Multiphase composite material with A / B ratio of 80:20 Three powder application methods are used: a) Direct application of powder: without any fixed measures.

[0084] b) Electrostatic adsorption method: Use an ion air gun to blow away the charge, then blow away the charged powder before spreading it.

[0085] c) Slight preheating method: The workpiece is heated to 150℃ (near the Tg of PEEK) by laser temperature control before powder is spread.

[0086] The process and testing methods are the same as in Example 1, and the test results are shown in the figure below: ; 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. A composite powder for ultrasonic welding of carbon fiber reinforced thermoplastic resin composites, characterized in that, The composite powder comprises two thermoplastic resin powders, A powder and B powder, wherein: • Particle size D of powder A and powder B 50 All are 15μm to 25μm; • Powder A is a high-flow-rate thermoplastic resin powder, whose melt flow rate MFR_A is greater than that of powder B, and satisfies MFR_A / MFR_B > 2; Based on a total mass of 100 parts, the mass ratio of powder A to powder B is: Powder A : Powder B = (60-90) : (10-40).

2. The composite powder according to claim 1, characterized in that, The A powder and the B powder are respectively selected from polyaryletherketone resins, polyphenylene sulfide resins, polyetherimide resins, polyarylether sulfone resins, polyphenylene sulfone resins, polyphenylene sulfone resins, polyarylether nitrile ketone resins containing nitrile groups, or blends or modified systems of the above resins. Optionally, the polyaryletherketone resins include, but are not limited to, PEEK, PEKK, PEK, PEEKK and their blends or modified systems; Optionally, powder A is a polyaryletherketone resin powder, and powder B is a polyaryletherketone resin powder containing a nitrile group.

3. The composite powder according to claim 1 or 2, characterized in that, The mass ratio of powder A to powder B is: powder A : powder B = (70-80) : (20-30).

4. An ultrasonic welding method for carbon fiber reinforced thermoplastic resin composites, characterized in that, The method includes: 1) Apply the composite powder according to any one of claims 1 to 3 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, thus connecting the interface; During the ultrasonic vibration process, powder A preferentially melts and spreads, while powder B forms a relatively stagnant region during the melting process, thereby forming a molten bonding layer with non-uniform flow characteristics at the welding interface.

5. The method according to claim 4, wherein the areal density of the energy-conducting layer formed by the composite powder at the interface is 5–20 g / m². 2 .

6. The method according to claim 5, characterized in that, The composite powder is applied to the surface of the interface to be welded by at least one of powder spreading, powder spraying, and electrostatic adsorption.

7. The method according to any one of claims 4-6, characterized in that, The composite powder can be applied to the interface to be welded and fixed by preheating.

8. The method according to claim 7, characterized in that, The interface region of the composite material is heated to a temperature range of ±10℃ from the glass transition temperature (Tg) of its matrix resin, causing slight softening of the composite powder surface and initial adhesion and fixation to the interface surface.

9. The method according to any one of claims 4-6 and 8, characterized in that, 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 their blends or modified systems.

10. The method according to any one of claims 4-6, 8, characterized in that, 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.

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