Method for connecting carbon fiber thermoplastic composite panels and connection structure

Abstract

The application provides a connecting method and connecting structure of carbon fiber thermoplastic composite plate, which comprises the following steps: preparing a vertical fiber composite sheet by using carbon fiber and polyaryletherketone resin; cutting the fiber composite sheet into a required size to obtain a vertical fiber interlayer; fixing a first carbon fiber thermoplastic composite plate to be connected on an anvil of a welding machine, placing the vertical fiber interlayer at the center of a welding area, overlapping a second carbon fiber thermoplastic composite plate to be connected on the welding area of the first carbon fiber thermoplastic composite plate, and fixing the second carbon fiber thermoplastic composite plate to be connected on the anvil; applying a welding pressure and displacement load perpendicular to a plate contact surface above the welding area of the second carbon fiber thermoplastic composite plate by using an ultrasonic welding head; performing pressure holding and solidification on the welding joint by using an electrode pair after welding; and then unloading to complete the welding. The application improves the welding quality of the ultrasonic welding of the carbon fiber thermoplastic composite.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of material joining and manufacturing technology, specifically to a joining method and joining structure applicable to a carbon fiber thermoplastic composite sheet. Background Technology

[0002] Carbon fiber thermoplastic composites (CFRP) have garnered widespread attention for their application in aircraft structures due to their superior strength, stiffness, weight ratio, and cost-effective manufacturing process. However, welding CFRP has remained a technical challenge. Traditional welding methods such as laser welding and resistance welding are unsuitable for CFRP welding, necessitating the search for new welding technologies. Ultrasonic welding, as a highly efficient, clean, and low-cost welding technology, is increasingly being applied to CFRP welding. The technical principle of ultrasonic welding is primarily based on the vibrational energy of ultrasound. When ultrasound acts on the CFRP material, it generates high-frequency vibrations of tens of thousands of times per second. This vibrational energy is transmitted to the weld area through the upper workpiece. Due to the high acoustic impedance at the weld area, i.e., the interface between the two welded parts, localized high temperatures are generated, causing the resin on the two contact surfaces to melt rapidly. During the melting process, a certain pressure is applied, fusing the two sheets into one. After the ultrasound stops, the pressure is maintained for a few seconds to allow solidification, forming a strong weld and completing the welding process.

[0003] In ultrasonic welding, a thin pure resin energy-conducting rib is usually placed between the contact surfaces of two plates to transmit and concentrate vibration energy, thereby improving welding efficiency and quality. The principle is that the ultrasonic welding head applies high-frequency vibration to the workpiece, causing the material (mainly resin) to generate heat through friction, melt and flow, and finally solidify together to achieve welding. However, due to the relatively low strength and stiffness of the resin material itself, it is prone to failure when subjected to load due to shear failure of the resin matrix at the weld joint interface. Summary of the Invention

[0004] Considering that ultrasonic welding of thermoplastic composite materials mainly relies on the melting and flow of resin-based materials to form a connection with low joint strength, this invention proposes a method of adding a layer of composite material structure containing vertical fibers between the contact surfaces of the plates before ultrasonic welding. This allows the vertical fibers to be inserted between the upper and lower plates when the resin melts, thereby improving the tensile / peel strength of the ultrasonic welded joint of thermoplastic composite materials.

[0005] Specifically, the first aspect of the present invention provides a method for joining carbon fiber thermoplastic composite material sheets, comprising the following steps: S1. A vertical fiber composite sheet is prepared using carbon fiber and polyaryletherketone resin, wherein the fiber direction of the vertical fiber composite sheet is parallel to the thickness direction of the carbon fiber thermoplastic composite plate to be joined. S2. Cut the vertical fiber composite sheet prepared in S1 into the required size to obtain a vertical fiber sandwich. In the cut vertical fiber sandwich, the fibers are parallel to the thickness direction of the carbon fiber thermoplastic composite sheet to be connected. S3. Fix the first carbon fiber thermoplastic composite material plate to be connected on the anvil of the welding machine, place the vertical fiber sandwich layer obtained in S2 in the center of the welding area, overlap the welding area of ​​the second carbon fiber thermoplastic composite material plate to be connected with the welding area of ​​the first carbon fiber thermoplastic composite material plate, and fix it on the anvil. S4. Apply welding pressure and displacement load perpendicular to the contact surface of the plate directly above the area to be welded on the second carbon fiber thermoplastic composite plate in step S3 using an ultrasonic welding head. After welding, allow the electrode to hold pressure and solidify the weld joint, then unload to complete the welding.

[0006] As a further explanation of the present invention, step S1 specifically includes: S101. Impregnate the carbon fiber bundles in polyether ketone resin to fully wet the carbon fibers and form a prepreg. S102. The prepreg is laid out in one direction and placed in an autoclave for heating and pressing to form the vertical fiber composite material sheet.

[0007] As a further explanation of the present invention, in step S2, a water-cooled diamond saw is used to cut the vertical fiber composite material sheet prepared in S1 into the required size.

[0008] As a further explanation of the present invention, step S3 specifically includes: S301. Place the first carbon fiber thermoplastic composite plate to be joined with the welding area facing upwards directly below the ultrasonic welding head and fix it on the anvil. S302. Place the vertical fiber sandwich obtained in S2 at the center of the area to be welded in the first carbon fiber thermoplastic composite plate; S303. The second carbon fiber thermoplastic composite plate to be connected is overlapped with the welding area of ​​the first carbon fiber thermoplastic composite plate facing downwards, and fixed on the anvil.

[0009] As a further explanation of the present invention, in step S4, the welding process adopts a displacement control strategy, the welding displacement is perpendicular to the thickness of the fiber interlayer, and the welding pressure is 500N~2000N.

[0010] As a further explanation of the present invention, in step S4, the vibration amplitude of the displacement load is 25~100um, and it is unloaded after being held under a force of 1500N for 4s.

[0011] A second aspect of the present invention provides a connection structure for carbon fiber thermoplastic composite material sheets, wherein the connection structure is a vertical fiber composite material sheet made of carbon fiber and polyaryletherketone resin, and the fiber direction of the vertical fiber composite material sheet is parallel to the thickness direction of the carbon fiber thermoplastic composite material sheet to be connected.

[0012] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: 1. The present invention uses a vertical fiber structure to replace the energy-conducting rib for welding, which significantly improves the tensile / peel strength and effectively improves the welding quality of ultrasonic welding of carbon fiber thermoplastic composite materials.

[0013] 2. Compared with traditional energy-conducting rib welding, the present invention does not present significant difficulties in material preparation, nor does it increase the workload before welding, but it significantly improves the welding strength. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. It should be understood that the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention, wherein: Figure 1 This is a schematic diagram of the vertical fiber sandwich structure in an embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram of ultrasonic welding provided for an embodiment of the present invention.

[0016] In the picture: 1-Servo device; 2-Ultrasonic electrode; 3-First carbon fiber thermoplastic composite plate; 4-External ultrasonic signal source; 5-Anvil; 6-Vertical fiber sandwich; 61-Carbon fiber; 7-Second carbon fiber thermoplastic composite plate; 8-Thin plate. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0018] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0019] Currently, in ultrasonic welding of thermoplastic composites, the main method to enhance welding quality is to use a resin film with the same resin matrix as the sheet material to make energy-conducting ribs and place them between the welding interfaces to improve welding quality. The principle is that the ultrasonic welding head applies high-frequency vibration to the workpiece, causing the material (mainly resin) to generate heat through friction, melt and flow, and finally solidify together to achieve welding. However, due to the relatively low strength and stiffness of the resin material itself, it is prone to failure when subjected to load due to the shear failure of the resin matrix at the welding joint interface.

[0020] This invention primarily utilizes the significantly higher strength of carbon fiber compared to resin by placing a vertical fiber interlayer within the weldable plates to improve the welding quality of ultrasonic welding. The vertical fiber interlayer is composed of the same resin matrix and fibers as the plates to be welded, with the fiber direction perpendicular to the plate. During ultrasonic welding, the interlayer structure and the upper and lower welding surfaces melt, allowing the vertical fibers to insert into the melted area of ​​the plate, thereby increasing the load-bearing capacity of the weld joint.

[0021] The technical solution of the present invention will be described in detail below: This invention provides a method for joining carbon fiber thermoplastic composite sheets, comprising the following steps: S1. A vertical fiber composite sheet is prepared using carbon fiber and polyaryletherketone resin (PAEK). The fiber direction of the vertical fiber composite sheet is parallel to the thickness direction of the carbon fiber thermoplastic composite plate to be joined. S2. Cut the fiber composite material sheet prepared in S1 into the required size to obtain a vertical fiber sandwich, as shown in the schematic diagram below. Figure 1 As shown, the fibers in the cut vertical fiber sandwich are parallel to the thickness direction of the carbon fiber thermoplastic composite material plate to be connected. S3. Fix the first carbon fiber thermoplastic composite plate to be connected on the anvil of the welding machine, place the vertical fiber sandwich layer obtained in S2 in the center of the welding area, overlap the welding area of ​​the second carbon fiber thermoplastic composite plate to be connected with the welding area of ​​the first carbon fiber thermoplastic composite plate, and fix it on the anvil. S4. Apply welding pressure and displacement load perpendicular to the contact surface of the plate directly above the area to be welded on the second carbon fiber thermoplastic composite plate in step S3 using an ultrasonic welding head. After welding, allow the electrode to hold pressure and solidify the weld joint, then unload to complete the welding.

[0022] Specifically, step S1 is as follows: S101. Impregnate the carbon fiber bundles in polyether ketone resin to fully wet the carbon fibers and form a prepreg. S102. The prepreg is laid out in one direction and placed in a hot autoclave for heating and pressing to form a vertical fiber composite sheet.

[0023] Specifically, in step S2, a water-cooled diamond saw is used to cut the vertical fiber composite sheet prepared in S1 into the required size.

[0024] Specifically, step S3 is as follows: S301. Place the first carbon fiber thermoplastic composite plate to be joined with the welding area facing upwards directly below the ultrasonic welding head and fix it on the anvil. S302. Place the vertical fiber sandwich obtained in S2 at the center of the area to be welded in the first carbon fiber thermoplastic composite plate. S303. The second carbon fiber thermoplastic composite plate to be connected is overlapped with the welding area of ​​the first carbon fiber thermoplastic composite plate with the welding area facing down, and fixed on the anvil.

[0025] The schematic diagram of ultrasonic welding is as follows: Figure 2 As shown, the ultrasonic electrode 2 is installed below the servo device 1 and connected to an external ultrasonic signal source 4, so that the welding area of ​​the first carbon fiber thermoplastic composite plate 3 faces upwards, and then it is fixed on the anvil 5. The vertical fiber sandwich 6 is placed in the center of the welding area of ​​the first carbon fiber thermoplastic composite plate 3, and the welding area of ​​the second carbon fiber thermoplastic composite plate 7 is placed downwards and overlapped with the welding area of ​​the first carbon fiber thermoplastic composite plate 3. A thin plate 8 is also provided on the anvil 5, which can support the second carbon fiber thermoplastic composite plate 7, so that the welding surfaces of the first carbon fiber thermoplastic composite plate 3 and the second carbon fiber thermoplastic composite plate 7 maintain good parallelism before the electrodes contact.

[0026] Specifically, in step S4, the welding process adopts a displacement control strategy, with the welding displacement being the thickness of the fiber interlayer perpendicular to the welding displacement, and the welding pressure being 500N~2000N.

[0027] Specifically, in step S4, the vibration amplitude of the displacement load is 25~100um, and it is unloaded after being held under a force of 1500N for 4s.

[0028] This invention employs a novel CFRP ultrasonic welding structure, comprising a carbon fiber laminate and a vertical fiber interlayer. The vertical fibers are placed between the contact surfaces of the lap joint to improve the ultrasonic welding quality. The vertical fiber interlayer is composed of the same resin matrix and fibers as the plates to be welded, with the fiber direction perpendicular to the contact surfaces of the plates. During ultrasonic welding, the resin in the interlayer structure and the upper and lower welding surfaces melts through welding, allowing the vertical fibers to insert into the melted area of ​​the plate, thereby improving the load-bearing capacity of the weld joint.

[0029] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for joining carbon fiber thermoplastic composite sheets, characterized in that, Includes the following steps: S1. A vertical fiber composite sheet is prepared using carbon fiber and polyaryletherketone resin, wherein the fiber direction of the vertical fiber composite sheet is parallel to the thickness direction of the carbon fiber thermoplastic composite plate to be joined. Step S1 specifically involves: S101. Impregnate the carbon fiber bundles in polyether ketone resin to fully wet the carbon fibers and form a prepreg. S102. The prepreg is laid out in one direction and placed in an autoclave for heating and pressing to form the vertical fiber composite material sheet. S2. Cut the vertical fiber composite sheet prepared in S1 into the required size to obtain a vertical fiber sandwich. In the cut vertical fiber sandwich, the fibers are parallel to the thickness direction of the carbon fiber thermoplastic composite sheet to be connected. S3. Fix the first carbon fiber thermoplastic composite material plate to be connected on the anvil of the welding machine, place the vertical fiber sandwich layer obtained in S2 in the center of the welding area, overlap the welding area of ​​the second carbon fiber thermoplastic composite material plate to be connected with the welding area of ​​the first carbon fiber thermoplastic composite material plate, and fix it on the anvil. S4. Apply welding pressure and displacement load perpendicular to the contact surface of the plate directly above the area to be welded on the second carbon fiber thermoplastic composite plate in step S3 using an ultrasonic welding head. The welding process adopts a displacement control strategy. The welding displacement is perpendicular to the thickness of the fiber interlayer. The welding pressure is 500N~2000N. After welding, the electrode is held under pressure to solidify the weld joint, and then unloaded to complete the welding. During ultrasonic welding, the resin of the sandwich structure and the upper and lower welding surfaces is melted through welding, allowing vertical fibers to be inserted into the melting area of ​​the plate.

2. The method according to claim 1, characterized in that, In step S2, a water-cooled diamond saw is used to cut the vertical fiber composite material sheet prepared in S1 into the required size.

3. The method according to claim 1, characterized in that, Step S3 specifically involves: S301. Place the first carbon fiber thermoplastic composite plate to be joined with the welding area facing upwards directly below the ultrasonic welding head and fix it on the anvil. S302. Place the vertical fiber sandwich obtained in S2 at the center of the area to be welded in the first carbon fiber thermoplastic composite plate; S303. The second carbon fiber thermoplastic composite plate to be connected is overlapped with the welding area of ​​the first carbon fiber thermoplastic composite plate with the welding area facing downwards, and fixed on the anvil.

4. The method according to claim 1, characterized in that, In step S4, the vibration amplitude of the displacement load is 25~100㎛, and it is unloaded after being held under a force of 1500N for 4s.

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