A method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding

Abstract

The present invention discloses a method for connecting the face and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding. By designing and constructing an energy-guiding structure suitable for connecting the face and core of the honeycomb on the surface of a composite panel, combined with ultrasonic welding process control, a high-strength connection between the thermoplastic composite honeycomb and the panel is achieved. The present invention aims at the problems of narrow process window, low connection strength, small effective contact area of ​​the face and core, buckling and collapse of the honeycomb wall, and deformation of the panel due to secondary heating in the existing honeycomb sandwich structure face and core connection technology in the process of connecting thermoplastic composite honeycombs and thermoplastic composite panels. On the basis of solving the problems of building the energy-guiding structure on the surface of the composite panel and designing the process for connecting the face and core of the sandwich structure, the present invention realizes the efficient and rapid preparation of a thermoplastic composite honeycomb sandwich structure with lightweight, high strength and recyclable characteristics.

Description

Technical Field

[0001] The invention belongs to the technical field of composite honeycomb sandwich structures and connections, and in particular relates to a surface-core interface connection method of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding. Background Art

[0002] Honeycomb sandwich structure is a sandwich composite material composed of a honeycomb core layer and upper and lower panels. Among them, the upper and lower panels bear the in-plane load of the structure, and the honeycomb core connected to them plays a role in supporting and resisting out-of-plane compression and shear loads, while improving the overall bending stiffness and deformation resistance of the structure, making it have multifunctional properties such as heat insulation, sound insulation, and wave absorption. At present, honeycomb sandwich structures such as aluminum honeycomb / aluminum panel, aluminum honeycomb / fiber reinforced epoxy panel, paper honeycomb / fiber reinforced epoxy panel have been widely used in aerospace, rail transportation, and automotive industries. However, with the continuous improvement of the service requirements of various equipment such as aircraft, high-speed trains, and new energy vehicles, metal honeycombs such as aluminum honeycombs have low specific strength and specific stiffness, significant thermal expansion, insufficient wet-heat aging and weathering stability of paper honeycombs, and poor recyclability of thermosetting composite sandwich structures such as epoxy. Problems have gradually been exposed, which has put forward new demands for the development of honeycomb sandwich structures that are both lightweight, high-strength, high-stiffness and recyclable.

[0003] Thermoplastic composites have excellent mechanical properties, high damage tolerance and recyclability. The new all-thermoplastic composite honeycomb made of continuous carbon fiber and glass fiber reinforced thermoplastic composites has a specific stiffness of about 2-3 times higher than that of aluminum honeycomb, and a specific strength of about 4-5 times higher. In addition, in the process of composite surface and core of all-thermoplastic composite honeycomb sandwich structure, the connection problem of heterogeneous interface can be avoided by using the same resin matrix, further improving the connection strength of honeycomb surface and core.

[0004] In the prior art, the connection between the honeycomb core and the panel is mainly in the form of brazing or gluing. The former is mainly used for the composite between the metal honeycomb core and the metal panel, and is not suitable for the connection between the composite honeycomb and the panel; the latter relies on the flow and solidification of the thermosetting structural adhesive film to promote the formation of adhesive between the honeycomb wall and the panel to achieve the surface core bonding. For thermoplastic honeycombs, panels and adhesive films, they will soften rapidly when heated to a temperature near the melting point of the resin, leaving a narrow process window for hot pressing and compounding the surface core. Excessive heat input can easily cause the honeycomb core to soften and collapse, and the panel to delaminate internally, affecting the dimensional accuracy of the sandwich structure and causing internal defects, increasing the energy consumption of the preparation process. In addition, due to the high viscosity of the thermoplastic resin itself, the narrow process window will also make it difficult to form adhesive retention when connecting the surface core, and the connection form is only line-surface contact, which reduces the effective bonding area and ultimately limits the further improvement of the surface core bonding strength.

[0005] Comparative document 202211732666.7 "A continuous fiber reinforced thermoplastic composite honeycomb sandwich structure, preparation device and preparation method" proposed for the first time that sandwich structures can be prepared by ultrasonic welding and energy-guiding structures based on thermoplastic resin materials, and proposed the use of the same isosceles right-angled triangle energy-guiding structure as the corrugated board welding in the honeycomb core to weld the panel and the core material, and finally hope to prepare a sandwich structure. However, in the actual operation process, it was found that the panel covered with energy-guiding structures will cause energy to be quickly transferred along the energy-guiding structure when connected to the core material, and the resin cannot effectively form glue after climbing the wall; thin-walled honeycombs below 2mm will also buckle under pressure, resulting in insufficient melting at the connection, frequently causing welding defects; the isosceles right-angled triangle energy-guiding structure with a vertex angle of 90 degrees cannot meet the connection requirements of all resin systems. Summary of the invention

[0006] The present invention aims to solve the technical problems mentioned in the background technology and provides a method for connecting the surface core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding to improve the interface bonding strength between the thermoplastic composite honeycomb and the thermoplastic composite panel.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A method for connecting the face and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding, comprising the following steps:

[0009] S1. Cutting the fiber-reinforced thermoplastic composite material sheet and the thermoplastic honeycomb core material to a target size to obtain a fiber-reinforced thermoplastic composite panel and a thermoplastic honeycomb core, and cleaning the surfaces of the fiber-reinforced thermoplastic composite panel and the thermoplastic honeycomb core;

[0010] S2. Determine characteristic parameters of the special-shaped energy-guiding structure on the surface of the fiber-reinforced thermoplastic composite panel according to the characteristics of the thermoplastic honeycomb core;

[0011] S3, designing a metal mold according to characteristic parameters of the special-shaped energy guiding structure, and molding the special-shaped energy guiding structure on one side of the fiber reinforced thermoplastic composite panel;

[0012] S4. Fix the thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel in an ultrasonic welding machine, fit one side of the thermoplastic honeycomb core with the side of the fiber reinforced thermoplastic composite panel with a special-shaped energy guiding structure, set welding process parameters and start the welding program to complete the welding of one side of the thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel; then fit the other side of the thermoplastic honeycomb core with the side of another fiber reinforced thermoplastic composite panel with a special-shaped energy guiding structure, fix them in an ultrasonic welding machine, set welding process parameters and start the welding program to complete the welding of both side surfaces of the thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel to obtain a thermoplastic composite honeycomb sandwich structure.

[0013] To optimize the technical solution, the present invention is further improved as follows:

[0014] The fiber reinforced thermoplastic composite panel in S1 is a flat panel or a curved panel; the reinforcement material of the fiber reinforced thermoplastic composite panel is one of carbon fiber, glass fiber, aramid fiber or a combination of at least two of them; the structural form of the reinforcement is chopped fiber, unidirectional continuous fiber or continuous fiber fabric; the resin matrix of the fiber reinforced thermoplastic composite panel is one of polyethylene, polypropylene, polyamide, polycarbonate, polyetherimide, polyphenylene sulfide, polyetherketoneketone, polyetheretherketone or a mixture of at least two of them; the honeycomb shape in the thermoplastic honeycomb core is hexagonal, quadrilateral or circular; the honeycomb compression strength is higher than 1MPa; the honeycomb wall thickness is 0.5mm-4mm; the honeycomb side length is 3mm-10mm; the honeycomb material is thermoplastic resin or fiber reinforced thermoplastic composite material, and the type of the resin matrix is ​​consistent with the resin matrix type of the fiber reinforced thermoplastic composite panel.

[0015] The special-shaped energy guiding structure is configured as a groove-type energy guiding structure or an array-type energy guiding structure. For a planar honeycomb core with a wall thickness of less than 2 mm, a groove-type energy guiding structure is adopted; for a planar honeycomb core or a curved honeycomb core with a wall thickness of ≥2 mm, an array-type energy guiding structure is adopted; the groove-type energy guiding structure is composed of a first guiding strip having a configuration adapted to the honeycomb shape of the thermoplastic honeycomb core, the first guiding strip is composed of two parallel bar units, the extension direction of the bar units is consistent with the extension direction of the first guiding strip, groove ridges are formed between the bar units, when the thermoplastic honeycomb core contacts with the groove-type energy guiding structure, the honeycombs of the thermoplastic honeycomb core are located in the groove ridges, the array-type energy guiding structure is composed of a second guiding strip having a configuration adapted to the honeycomb shape of the thermoplastic honeycomb core, the second guiding strip is composed of a plurality of array units, each array unit is formed with a raised unit ridge, the extension direction of the unit ridge is different from the extension direction of the second guiding strip, when the thermoplastic honeycomb core contacts with the array-type energy guiding structure, the honeycombs of the thermoplastic honeycomb core contact with the unit ridges.

[0016] The cross-sectional shape of the first guide bar and the array unit is triangular or semicircular. When the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core is less than 250°C, the first guide bar or array unit with a semicircular cross-sectional shape is adopted. When the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core is ≥250°C, the first guide bar or array unit with a triangular cross-sectional shape is adopted.

[0017] The properties of the thermoplastic honeycomb core in S2 include honeycomb core wall thickness, edge length, out-of-plane curvature, and heat deformation temperature.

[0018] The characteristic parameters of the slot-type energy guiding structure in S2 include slot width, slot wall width, slot ridge height, slot depth, semicircular energy guiding structure radius and triangular energy guiding structure top angle α; the characteristic parameters of the array-type energy guiding structure include array unit width, array unit depth, array unit height, semicircular energy guiding structure radius and triangular energy guiding structure top angle α.

[0019] The vertex angle α of the triangular energy-guiding structure is determined according to the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core. When the melting point is 250-300°C, the vertex angle α is 120-100°; when the melting point is 300-350°C, the vertex angle α is 100-80°; when the melting point is 350-400°C, the vertex angle α is 80-60°

[0020] In S3, the particle size of the resin powder used to melt and construct the special-shaped energy-guiding structure is 1 / 13 to 1 / 15 of the honeycomb wall thickness of the thermoplastic honeycomb core, the molding setting temperature is 105% to 110% of the melting point of the selected resin powder, the heat preservation and pressure holding time is 5-25 minutes, and the cooling rate is 10 to 60°C / min.

[0021] The welding process parameters in S4 include welding power of 800-2000W, welding pressure of 0.1-0.6MPa, vibration time of 0.6-1.5s, holding time of 0.8-3.0s, and amplitude of 15-25μm.

[0022] The ultrasonic welding machine comprises a welding bottom mold and an ultrasonic welding head. The thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel are placed between the welding bottom mold and the ultrasonic welding head for welding. The ultrasonic welding head has a curvature consistent with the side to be welded of the thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel; the welding bottom mold has a curvature consistent with the non-welding side of the thermoplastic honeycomb core and the fiber reinforced thermoplastic composite panel.

[0023] The present invention aims to solve the problems of low connection strength and small effective contact area of ​​the face core in the process of connecting thermoplastic composite honeycombs and thermoplastic composite panels in the existing face-core connection technology of honeycomb sandwich structures such as aluminum honeycombs and paper honeycombs. The present invention proposes a face-core interface connection and reinforcement method for thermoplastic composite honeycomb sandwich structures that meets various application requirements of the aerospace, rail transit and automotive industries. Through ultrasonic welding and special energy guidance, a stable, efficient and low-energy local heat source is introduced into the T-joint, solving the problems of narrow temperature window, poor processability and low interface peeling strength in traditional face-core hot-melt bonding. Compared with the prior art, the present invention has the following specific advantages:

[0024] (1) Based on the structural similarity and compatibility principle of polymer materials, the incompatibility and heterogeneous interface bonding problems caused by polarity differences between thermoplastic resins and thermosetting resins are avoided, and the bonding strength between the honeycomb core and the panel is improved;

[0025] (2) Through the special panel surface structure design, the ultrasonic energy is concentrated along the honeycomb thin wall, achieving the glue retention effect of the honeycomb wall T-type connection joint, increasing the effective contact area between the honeycomb core and the panel, and improving the fracture toughness of the surface-core connection interface;

[0026] (3) Compared with the existing ultrasonic joining process, an energy-guiding structure design scheme for the face-core joining process is proposed for the first time around thin / thick-walled honeycombs and curved honeycomb structures. For thin-walled honeycombs below 2 mm, the welding area is fixed by a groove structure to prevent local buckling caused by welding pressure. For thick-walled honeycombs above 2 mm, the size of the guiding structure is reduced and its distribution is optimized to reduce the rapid energy conduction loss caused by the guiding structure. For materials with different melting temperature ranges, the size, shape, angle, height, depth, array density of the energy-guiding structure and various welding process parameters including power, pressure, time and amplitude are designed in detail to solve the problem of rapid energy dissipation caused by full energy guidance.

[0027] (4) Compared with the face-core bonding method using thermosetting structural adhesive film, this method does not require a long curing process, which improves the connection efficiency and reduces the energy loss during the connection process; the honeycomb, panel and interface adhesive layers use the same thermoplastic resin, making the structure more recyclable. The application of this technology in the engineering field will also effectively reduce carbon emissions in the production process of honeycomb sandwich structures and improve resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of connecting a thermoplastic composite material panel and a thermoplastic honeycomb core according to the present invention;

[0029] Figure 2 It is a schematic diagram of the special-shaped energy guide structure of the present invention;

[0030] Figure 3 It is a schematic diagram of characteristic parameters of the special-shaped energy-guiding structure of the present invention;

[0031] Figure 4 It is a schematic diagram of a metal mold for constructing an energy-guiding structure according to the present invention;

[0032] Figure 5 It is a schematic diagram of the process of ultrasonically connecting a thermoplastic composite panel and a thermoplastic honeycomb core according to the present invention;

[0033] Figure 6 It is a schematic diagram of the thermoplastic honeycomb sandwich structure after connection according to the present invention.

[0034] The markings in the accompanying drawings are: 1. Fiber reinforced thermoplastic composite panel; 2. Thermoplastic honeycomb core; 3. Planar honeycomb core; 4. Groove-type energy guiding structure; 5. Array-type energy guiding structure; 6. Curved honeycomb core; 7. Groove ridge; 8. Array unit; 9. Semicircular cross-section guiding structure; 10. Triangular cross-section guiding structure; 11. Vertex angle α; 12. Metal mold; 13. Resin powder; 14. Ultrasonic welder; 15. Welding bottom mold; 16. Ultrasonic welding head; 17. Resin glue retention area. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0036] The present invention provides a method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding. The method comprises the following steps:

[0037] Step 1: Cutting of panels and honeycomb core

[0038] According to the size of the workpiece, the fiber reinforced thermoplastic composite panel 1 and the thermoplastic honeycomb core 2 with the same length and width and the same curvature are cut respectively, and after removing the cutting burrs, the surface impurities and oil stains of the panel are cleaned with ethanol solution.

[0039] Step 2: Design of energy-directing structure

[0040] The basic configuration of the energy guiding structure is designed according to the honeycomb core curvature and honeycomb wall thickness selected in step 1: for a planar honeycomb core 3 with a wall thickness of less than 2 mm, a groove-type energy guiding structure 4 is preferred; for a planar honeycomb core with a wall thickness of ≥ 2 mm, an array-type energy guiding structure 5 is preferred, and the shape and size of the array are consistent with the shape and size of the honeycomb holes; for a curved honeycomb core 6, an array-type energy guiding structure is preferred, and the shape and size of the array are consistent with the vertical projection of the honeycomb holes on the curved surface.

[0041] According to the type and softening point of the thermoplastic resin matrix in the selected panel and honeycomb core, the cross-sectional characteristics of the groove ridge 7 or array unit 8 in the energy guiding structure are designed: for thermoplastic resin systems with a melting point below 250°C, a semicircular cross-sectional guiding structure 9 is preferred; for thermoplastic resin systems with a melting point above 250°C, a triangular cross-sectional guiding structure 10 is preferred.

[0042] The specific basis for determining the characteristic parameters of the trough-type energy-guiding structure and the array-type energy-guiding structure is shown in Table 1.

[0043] Table 1 Characteristic size parameters of energy-directing structures

[0044]

[0045]

[0046] The vertex angle α11 is determined according to the melting point of the thermoplastic resin system, see Table 2.

[0047] Table 2 Determination basis of vertex angle α angle parameters

[0048] Melting point / ℃ α / ° 250～300 120～100 300～350 100～80 350～400 80～60

[0049] Step 3: Construction of energy-directing structure

[0050] According to the design parameters of the special-shaped energy-guiding structure determined in step 2, a metal mold 12 with the same size characteristics is processed. For the inner circle and the outer circle of the curved honeycomb sandwich structure, metal molds with different out-of-plane curvatures should be designed respectively. Spray the mold cavity with a release agent and fill the gap with the same type of resin powder 13 as the resin matrix selected in step 1 and compact it. The particle size of the resin powder is preferably t / 13 to t / 15; place the panel cut in step 1 between the upper and lower molds of the metal mold and place them together in a hot press, set the temperature to 105% to 110% of the melting point of the selected resin, close the mold and keep the temperature and pressure for 5-25 minutes to fully melt the resin powder; turn off the heating and control the cooling rate to 10 to 60°C / min to cool the panel to the glass transition temperature of the resin (T g ) below to complete the consolidation and construction of the energy-guiding structure.

[0051] Step 4: Connect the panel to the honeycomb core interface

[0052] Align the honeycomb wall with the energy-guiding structure on the panel surface, place it in the welding bottom mold 15 of the ultrasonic welder 14 and fix it, set the welding pressure, vibration time, holding time, amplitude and other process parameters according to the type of resin, and the preferred welding parameters of the typical thermoplastic resin system are shown in Table 3; install an ultrasonic welding head 16 that is consistent with the curvature of the panel and the honeycomb core, start the vibration program, melt the energy-guiding structure, form a resin glue retention area 17 in the face core area, and then cool and consolidate to complete the welding of the honeycomb core and one side panel; repeat the above process to complete the welding of the honeycomb core and the other side panel, and realize the face core connection of the honeycomb sandwich structure.

[0053] Table 3 Typical thermoplastic resin system honeycomb core welding process parameters

[0054]

[0055]

[0056] Example 1

[0057] This embodiment is a glass fiber reinforced polypropylene honeycomb sandwich structure for an impact-resistant bottom guard plate of a new energy vehicle, and the surface-core connection method thereof is as follows:

[0058] Step 1: Cut a glass fiber reinforced polypropylene honeycomb plate with a side length of 6 mm, a wall thickness of 1 mm, and a size of 3000*3000*10 mm, and two glass fiber reinforced polypropylene composite material flat plates with a size of 3000*3000*1 mm, use ethanol to decontaminate their surfaces, and clean the cutting burrs around them.

[0059] Step 2: Design a slot-type energy guide structure based on a flat plate component with a honeycomb wall thickness of 1 mm. Considering that the thermal deformation temperature of glass fiber reinforced polypropylene composite materials is about 170-180°C, a semicircular cross-section guide structure is selected to design the key parameters of the slot-type energy guide structure: d 1 1mm, d 2 0.3mm, h 2 is 2mm, r is 0.5mm.

[0060] Step three, according to the design parameters of step two, construct an energy-guiding structure on the surface of the glass fiber reinforced polypropylene composite material flat plate. First, process a metal flat plate with the same size as the energy-guiding structure in step two, and spray a release agent on its surface; after spraying, fill the processed groove with polypropylene powder with a particle size of 0.075mm (200 mesh); place the glass fiber reinforced polypropylene composite material flat plate obtained by cutting in step one on the mold, set the vulcanizer temperature to 185℃, the curing pressure to 0.2MPa, and keep the temperature and pressure for 15min; control the cooling rate to 10℃ / min; take it out when the temperature drops below 80℃; repeat the above process to complete the construction of the energy-guiding structure on the surface of another panel.

[0061] Step 4: align the honeycomb wall of the glass fiber reinforced polypropylene honeycomb obtained by cutting in step 1 with the groove ridge of the groove-type energy guide structure constructed in step 3, and fix them in the bottom mold of the ultrasonic welder; set the welding power to 800W, the welding pressure to 500N, the vibration time to 0.6s, the holding time to 0.8s, and the amplitude to 15μm; select a planar ultrasonic welding head, start the welding program, and after the vibration is completed, the honeycomb core is partially connected to one side of the panel. By adjusting the position of the welding head, repeat the above process to complete the connection between the single side of the honeycomb core and the entire panel; remove the connected structural parts, flip them over and fix them in the bottom mold of the welder, repeat the above welding process to complete the connection between the other side of the honeycomb core and the panel.

[0062] Example 2

[0063] A carbon fiber reinforced polyetheretherketone honeycomb sandwich structure facing the reflective surface of a satellite or other spacecraft antenna, wherein the surface-core connection method is as follows:

[0064] Step 1: Cut a piece of carbon fiber reinforced polyetheretherketone curved honeycomb core panel with a neutral surface outer curvature radius of 5000mm, an inner diameter of 1000mm, a wall thickness of 2mm, and a height of 40mm; cut two pieces of carbon fiber reinforced polyetheretherketone composite material curved panels with a diameter of 1000mm, a thickness of 1mm, and neutral surface outer curvature radii of 5020mm and 4080mm respectively; use ethanol to decontaminate the surface and clean the cutting burrs around.

[0065] Step 2: Design an array energy guide structure based on the honeycomb wall thickness of 2 mm and the curved surface component. Considering that the thermal deformation temperature of carbon fiber reinforced polyetheretherketone composite material is greater than 380°C, a triangular cross-section guide structure is selected, and the vertex angle α is designed to be 60°; Design the key parameters of the slot energy guide structure: d 3 2mm, d 4 4mm, h 3 It is 1.7mm.

[0066] Step three, according to the design parameters of step two, construct an energy-guiding structure on the surface of the curved panel of carbon fiber reinforced polyetheretherketone composite material. First, process a metal mold that is consistent with the panel curvature and energy-guiding structure size in step two, and spray a release agent on its surface; after spraying, fill the processed groove with polyetheretherketone powder with a particle size of 0.15mm (100 mesh); place the carbon fiber reinforced polyetheretherketone composite material panel cut in step one on the mold, set the vulcanizer temperature to 400℃, the curing pressure to 0.6MPa, and keep the temperature and pressure for 25min; control the cooling rate to 20℃ / min; take it out when the temperature drops below 143℃; repeat the above process to complete the construction of the energy-guiding structure on the surface of another panel.

[0067] Step 4, align the honeycomb wall of the carbon fiber reinforced polyetheretherketone honeycomb obtained by cutting in step 1 with the top of the array unit of the array energy guiding structure constructed in step 3, place it in the bottom mold of the ultrasonic welding machine and limit its in-plane freedom by fixing it on all sides; set the welding power to 2000W, the welding pressure to 1800N, the vibration time to 1.5s, the holding time to 2.0s, and the amplitude to 35μm; select an ultrasonic welding head with equal curvature, start the welding program, and after the vibration is completed, the honeycomb core is partially connected to one side of the panel, and by adjusting the position of the welding head, repeat the above process to complete the connection between the single side of the honeycomb core and the entire panel; remove the connected structural parts, flip them over and fix them in the bottom mold of the welding machine, repeat the above welding process to complete the connection between the other side of the honeycomb core and the panel.

[0068] Example 3 - Performance Test

[0069] The thermoplastic composite honeycomb sandwich structures prepared in Example 1 and Example 2 were subjected to a roller peeling performance test and a plane tensile performance test, and compared with the honeycomb sandwich structures prepared in a conventional hot pressing process. The results are shown in Table 4.

[0070] Table 4 Test results of surface-core bonding performance of sandwich structure in the embodiment

[0071]

[0072] It can be seen from Table 4 that the face-core interface performance of the honeycomb sandwich structure prepared by the embodiment of the present invention is significantly better than that of the traditional hot-pressed face-core composite process.

[0073] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding, characterized in that: The following steps are involved: S1, cutting the fiber-reinforced thermoplastic composite material plate and the thermoplastic honeycomb core material to a target size to obtain a fiber-reinforced thermoplastic composite material panel (1) and a thermoplastic honeycomb core (2), and cleaning the surfaces of the fiber-reinforced thermoplastic composite material panel (1) and the thermoplastic honeycomb core (2); S2. Determining characteristic parameters of the special-shaped energy-guiding structure on the surface of the fiber-reinforced thermoplastic composite panel (1) according to the characteristics of the thermoplastic honeycomb core (2); S3, designing a metal mold (12) according to characteristic parameters of the special-shaped energy guiding structure, and molding the special-shaped energy guiding structure on one side of the fiber-reinforced thermoplastic composite panel (1) with the metal mold (12); S4, fix the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1) in an ultrasonic welding machine (14), fit one side of the thermoplastic honeycomb core (2) with the side of the fiber-reinforced thermoplastic composite panel (1) having a special-shaped energy-guiding structure, set welding process parameters and start the welding program to complete the welding of one side of the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1); then fit the other side of the thermoplastic honeycomb core (2) with the side of another fiber-reinforced thermoplastic composite panel (1) having a special-shaped energy-guiding structure, fix them in an ultrasonic welding machine (14), set welding process parameters and start the welding program to complete the welding of the two side surfaces of the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1), and obtain a thermoplastic composite honeycomb sandwich structure; The special-shaped energy guiding structure is configured as a groove-type energy guiding structure or an array-type energy guiding structure. For a planar honeycomb core with a wall thickness of less than 2 mm, a groove-type energy guiding structure (4) is adopted; for a planar honeycomb core or a curved honeycomb core with a wall thickness of ≥ 2 mm, an array-type energy guiding structure (5) is adopted; the groove-type energy guiding structure (4) is composed of a first guiding strip having a configuration adapted to the honeycomb shape of the thermoplastic honeycomb core (2); the first guiding strip is composed of two parallel bar units, the extension direction of the bar units is consistent with the extension direction of the first guiding strip, groove ridges (7) are formed between the bar units, and the thermoplastic honeycomb core (2) is provided with a plurality of guide strips. When the thermoplastic honeycomb core (2) contacts the groove-type energy guiding structure (4), the honeycombs of the thermoplastic honeycomb core (2) are located in the groove ridges (7); the array-type energy guiding structure (5) is composed of a second guiding strip having a configuration adapted to the honeycomb shape of the thermoplastic honeycomb core (2); the second guiding strip is composed of a plurality of array units (8); each array unit (8) is formed with a raised unit ridge; the unit ridge extends in a direction different from that of the second guiding strip; and when the thermoplastic honeycomb core (2) contacts the array-type energy guiding structure (5), the honeycombs of the thermoplastic honeycomb core (2) contact the unit ridges.

2. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 1, characterized in that: The fiber reinforced thermoplastic composite panel (1) in S1 is a flat panel or a curved panel; The reinforcement material of the fiber-reinforced thermoplastic composite panel (1) is one of carbon fiber, glass fiber, aramid fiber, or a combination of at least two of them; the structural form of the reinforcement is chopped fiber, unidirectional continuous fiber, or continuous fiber fabric; the resin matrix of the fiber-reinforced thermoplastic composite panel (1) is one of polyethylene, polypropylene, polyamide, polycarbonate, polyetherimide, polyphenylene sulfide, polyetherketoneketone, polyetheretherketone, or a mixture of at least two of them; the honeycomb shape in the thermoplastic honeycomb core (2) is hexagonal, quadrilateral, or circular; the honeycomb compression strength is higher than 1MPa; the honeycomb wall thickness is 0.5mm-4mm; the honeycomb side length is 3mm-10mm; the honeycomb material is a thermoplastic resin or a fiber-reinforced thermoplastic composite material, and the type of the resin matrix is ​​consistent with the type of the resin matrix of the fiber-reinforced thermoplastic composite panel (1).

3. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 2, characterized in that: The cross-sectional shape of the first guide bar and the array unit (8) is triangular or semicircular. When the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core (2) is less than 250° C., the first guide bar or the array unit (8) with a semicircular cross-sectional shape is adopted. When the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core (2) is greater than or equal to 250° C., the first guide bar or the array unit (8) with a triangular cross-sectional shape is adopted.

4. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 3, characterized in that: The properties of the thermoplastic honeycomb core (2) in S2 include honeycomb core wall thickness, side length, out-of-plane curvature and thermal deformation temperature.

5. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 4, characterized in that: The characteristic parameters of the slot-type energy guiding structure (4) in S2 include slot width, slot wall width, slot ridge height, slot depth, semicircular energy guiding structure radius and triangular energy guiding structure top angle α, and the characteristic parameters of the array-type energy guiding structure (5) include array unit width, array unit depth, array unit height, semicircular energy guiding structure radius and triangular energy guiding structure top angle α.

6. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 5, characterized in that: The vertex angle α of the triangular energy guide structure is determined according to the melting point of the thermoplastic composite material used in the thermoplastic honeycomb core (2). When the melting point is 250-300°C, the vertex angle α is 120-100°; when the melting point is 300-350°C, the vertex angle α is 100-80°; when the melting point is 350-400°C, the vertex angle α is 80-60°.

7. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 6, characterized in that: In S3, the particle size of the resin powder used for melting and constructing the special-shaped energy-guiding structure is 1 / 13 to 1 / 15 of the honeycomb wall thickness of the thermoplastic honeycomb core (2), the molding setting temperature is 105% to 110% of the melting point of the selected resin powder, the heat preservation and pressure holding time is 5 to 25 minutes, and the cooling rate is 10 to 60°C / min.

8. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 7, characterized in that: The welding process parameters in S4 include welding power of 800~2000W, welding pressure of 0.1~0.6MPa, vibration time of 0.6~1.5s, holding time of 0.8~3.0s, and amplitude of 15~25μm.

9. The method for connecting the surface and core of a thermoplastic composite honeycomb sandwich structure based on ultrasonic welding according to claim 8, characterized in that: The ultrasonic welding machine (14) comprises a welding bottom mold (15) and an ultrasonic welding head (16); the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1) are placed between the welding bottom mold (15) and the ultrasonic welding head (16) for welding; the ultrasonic welding head (16) has a curvature consistent with the side of the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1) to be welded; and the welding bottom mold (15) has a curvature consistent with the non-welding side of the thermoplastic honeycomb core (2) and the fiber-reinforced thermoplastic composite panel (1).

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