Chopped fiber reinforced thermoplastic resin composite dot matrix sandwich structure and forming method thereof

Abstract

The invention provides a chopped fiber reinforced thermoplastic resin composite dot matrix sandwich structure and a forming method thereof, and belongs to the technical field of composite forming. A compression molding technology, an ultrasonic welding technology and a machining technology are combined, so that the preparation technology of the sandwich structure is further simplified, and the production efficiency is improved; through machining treatment and coating treatment of the panel and combination of ultrasonic welding, the performance of the panel is improved, and the overall stability of the sandwich structure is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material molding, and specifically discloses a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure and a molding method thereof. Background Art

[0002] The lattice structure is a new type of structure designed to meet the needs of lightweight and multifunctional engineering structures. It has the advantages of high specific stiffness, high specific strength, strong design flexibility and meeting multifunctional needs. Therefore, the lattice structure is regarded as a new generation of advanced, lightweight, ultra-tough multifunctional structure with the most application prospects.

[0003] Compared with metal materials, advanced composite materials have higher specific strength and specific stiffness, becoming the preferred material for preparing lattice structures. Fiber-reinforced resin-based composite materials have the characteristics of light weight, good mechanical properties, corrosion resistance, and high temperature resistance. Therefore, fiber-reinforced resin-based composite materials are widely used in defense, aviation, aerospace, ships, submersibles and other industries. However, the current process for preparing fiber-reinforced composite lattice sandwich structures is complex, with low production efficiency, difficult to ensure dimensional accuracy and poor surface quality; the use of ultrasonic welding alone to weld the panel and the core layer has problems such as low strength at the joint and poor overall stability of the sandwich structure. Summary of the invention

[0004] The present invention provides a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure and a molding method thereof, so as to improve the problems of low interlayer strength, low production efficiency, difficulty in ensuring dimensional accuracy and poor surface quality of the sandwich structure manufactured by the existing molding process.

[0005] The present invention provides a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, comprising two layers of panels and a lattice core layer connecting the two layers of panels; the panels and the lattice core layer are both chopped fiber reinforced thermoplastic resin composite materials, the chopped fibers are carbon fibers or glass fibers, and the thermoplastic resin is polyamide resin, polyethylene resin or polystyrene resin; the lattice core layer is a pyramid-shaped lattice core layer or a honeycomb-shaped lattice core layer; the pyramid-shaped lattice core layer includes a plurality of pyramid-shaped lattice unit cells; each pyramid-shaped lattice unit cell is an integral part composed of four rods, the top ends of the four rods are connected, the bottom ends of the four rods are located in the same plane and are arranged in a rhombus shape, and the top ends and bottom ends of the four rods are all provided with connection points; the rods in two adjacent pyramid-shaped lattice unit cells are connected to each other, and the bottom ends of the four rods are connected to each other. The bottom ends are connected by the same connection point; the honeycomb lattice core layer includes a plurality of honeycomb lattice cells; the honeycomb lattice cell is an integral piece composed of six plates, and the sides of the six plates are connected in sequence to form a hexagon; two adjacent honeycomb lattice cells are connected by the same plate; the surface where the panel is connected to the lattice core layer is the inner surface, a connection groove is provided on the inner surface, an epoxy resin layer is coated on the position of the inner surface except the connection groove, and a continuous carbon fiber layer is coated on the epoxy resin layer; for the pyramid lattice core layer, the connection groove of the panel is adapted to the connection point of the pyramid lattice core layer and is ultrasonically welded; for the honeycomb lattice core layer, the connection groove of the panel is adapted to the top and bottom surfaces of the plates in the honeycomb lattice core layer and is ultrasonically welded.

[0006] In the above-mentioned chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, the cross-sections of the rods and connection points in the pyramid-shaped lattice unit cell are circular or rectangular.

[0007] In the above-mentioned chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, the chopped fibers are carbon fibers, and the thermoplastic resin is nylon 6 resin among polyamide resins.

[0008] In the above-mentioned chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, the mass fraction of carbon fiber in the chopped fiber reinforced thermoplastic resin composite material is 10%-40%.

[0009] The present invention also provides a method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, comprising the following steps: S0, design the hot compression molding die for the panel and the lattice core layer; S1, preparing molten short fiber reinforced thermoplastic resin composite material: Thermoplastic resin pellets and continuous fibers are placed in a twin-screw extruder, the continuous fibers are cut by a cutter of the twin-screw extruder to obtain chopped fibers, the resin pellets and the chopped fibers are mixed and melted to obtain a molten chopped fiber reinforced thermoplastic resin composite material; Alternatively, the thermoplastic resin pellets and the chopped fibers are directly placed in a twin-screw extruder for mixing and melting to obtain a molten chopped fiber reinforced thermoplastic resin composite material; S2, workpiece hot molding: The molten short fiber reinforced thermoplastic resin composite material is placed in a hot compression molding die, and hot compression molding is performed by a hydraulic press, and then the hot compression molding die is cooled, and the hot compression molding die is opened after the temperature of the hot compression molding die is lowered to room temperature to obtain a panel and a lattice core layer; S3, panel machining: The inner surface of the panel is machined to make the connection groove, and the inner surface of the panel is polished; S4, coating: Apply epoxy resin and continuous carbon fiber to the inner surface of the panel except for the connection grooves, and then cure at high temperature; S5, ultrasonic welding: Ultrasonic spot welding is performed at the junction of the panel and the lattice core layer to obtain the above-mentioned chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure.

[0010] In step S2, the temperature of the hot compression molding mold is not lower than the melting temperature of the panel and the lattice core layer, and is not higher than the thermal decomposition temperature of the thermoplastic resin.

[0011] In step S4, the epoxy resin and the continuous carbon fiber are preheated and then applied.

[0012] Specifically, in step S1, the continuous fiber and the chopped fiber are carbon fibers, the thermoplastic resin pellets are nylon 6 resin in the polyamide resin, the screw speed of the twin-screw extruder is 160 rpm, and the feed rate of the twin-screw extruder is 2.5 Hz; In step S2, the temperature parameter of the mold temperature controller is set to 180°C, the temperature of the hot compression molding mold is made to reach 180°C by the mold temperature controller, the molten short fiber reinforced nylon 6 composite material is placed in the hot compression molding mold, and hot compression molding is performed by a hydraulic press. After the mold is closed, the heat and pressure are kept for 30 seconds, and then the hot compression molding mold is oil-cooled. After the hot compression molding mold is cooled to room temperature, the mold is opened to obtain a panel and a lattice core layer; In step S5, the pressure of ultrasonic welding is 0.1-0.5 MPa, the rated power of ultrasonic welding is 2.6 kW, and the rated frequency of ultrasonic welding is 20 kHz.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a molding process to compact the material inside the structure, so that the material is evenly distributed and continuously dense, overcoming the problem of low interlayer strength caused by existing molding processes (such as 3D printing technology) resulting in low overall strength of the structure. 2. The present invention is formed by a molding process, and its dimensional accuracy is guaranteed by a hot molding die, which can realize the molding of high-precision components and ensure the final surface quality of the molded components; 3. The present invention uses a one-time molding process to improve the preparation efficiency of the panel and the core layer; 4. The present invention combines ultrasonic welding with mechanical processing, and the bonding strength between the core layer and the panel is greatly improved compared with the bonding strength of ultrasonic welding alone, and the overall stability of the sandwich structure is higher; In summary, the present invention combines compression molding technology, ultrasonic welding technology and machining technology, so that the preparation process of the sandwich structure is further simplified and the production efficiency is improved; through mechanical processing and coating of the panel, combined with ultrasonic welding, not only the performance of the panel is improved, but also the overall stability of the sandwich structure is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a three-dimensional diagram (pyramid type) of a lattice sandwich structure of a chopped fiber reinforced thermoplastic resin composite material; Figure 2 for Figure 1 Side view of Figure 3 It is a three-dimensional image of the core layer of the pyramidal lattice; Figure 4 for Figure 3 A top view of Figure 5 It is a three-dimensional diagram of a lattice sandwich structure of a chopped fiber reinforced thermoplastic resin composite material (honeycomb type); Figure 6 for Figure 5 Side view of Figure 7 It is a three-dimensional picture of the honeycomb lattice core layer; Figure 8 for Figure 7 A top view of Fig. 9 A flow chart of a molding method for a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure (pyramid type); Fig.10The present invention is a flow chart of a molding method for a lattice sandwich structure of a chopped fiber reinforced thermoplastic resin composite material (honeycomb type).

[0016] In the figure: 1-panel; 2-pyramid lattice core layer; 2.1-rod; 2.2-connection point; 3-honeycomb lattice core layer; 4-epoxy resin layer; 5-continuous carbon fiber layer. DETAILED DESCRIPTION

[0017] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Example 1 The present embodiment provides a lattice sandwich structure of a chopped fiber reinforced thermoplastic resin composite material, comprising two layers of panel panels 1 and a lattice core layer connecting the two layers of panel panels 1; the panel panels 1 and the lattice core layer are both chopped fiber reinforced thermoplastic resin composite materials, the chopped fibers are carbon fibers or glass fibers, and the thermoplastic resin is polyamide resin, polyethylene resin or polystyrene resin.

[0019] The lattice core layer is a pyramid-type lattice core layer 2 or a honeycomb-type lattice core layer 3 .

[0020] The pyramid lattice core layer 2 includes a plurality of pyramid lattice cells; each pyramid lattice cell is an integral part composed of four rods 2.1, the tops of the four rods 2.1 are connected, the bottoms of the four rods 2.1 are located in the same plane and arranged in a rhombus, and the tops and bottoms of the four rods 2.1 are provided with connection points 2.2; the bottoms of the rods 2.1 in two adjacent pyramid lattice cells are connected through the same connection point 2.2. The cross-sections of the rods 2.1 and the connection points 2.2 in the pyramid lattice cell are circular or rectangular, so as to facilitate production and installation.

[0021] The honeycomb lattice core layer 3 includes a plurality of honeycomb lattice unit cells; the honeycomb lattice unit cell is an integral part composed of six plates, the sides of which are sequentially connected to form a hexagon; two adjacent honeycomb lattice unit cells are connected by the same plate.

[0022] The surface where the panel 1 is connected to the lattice core layer is the inner surface, on which a connecting groove is arranged, and on which an epoxy resin layer 4 is coated except for the connecting groove, and on which a continuous carbon fiber layer 5 is coated.

[0023] For the pyramid-type lattice core layer 2, the connection groove of the panel 1 is adapted to the connection point 2.2 of the pyramid-type lattice core layer 2 and is welded by ultrasonic wave; for the honeycomb-type lattice core layer 3, the connection groove of the panel 1 is adapted to the top and bottom surfaces of the panel in the honeycomb-type lattice core layer 3 and is welded by ultrasonic wave.

[0024] Example 2 This embodiment provides a method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, comprising the following steps: S0, design the hot compression molding mold for panel 1 and lattice core layer; S1, preparing molten short fiber reinforced thermoplastic resin composite material: Thermoplastic resin pellets and continuous fibers are placed in a twin-screw extruder, the continuous fibers are cut by a cutter of the twin-screw extruder to obtain chopped fibers, the resin pellets and the chopped fibers are mixed and melted to obtain a molten chopped fiber reinforced thermoplastic resin composite material; Alternatively, the thermoplastic resin pellets and the chopped fibers are directly placed in a twin-screw extruder for mixing and melting to obtain a molten chopped fiber reinforced thermoplastic resin composite material; S2, workpiece hot molding: Putting the molten short fiber reinforced thermoplastic resin composite material into a hot compression molding die, performing hot compression molding by a hydraulic press, and then cooling the hot compression molding die, opening the mold after the hot compression molding die is cooled to room temperature, to obtain a panel 1 and a lattice core layer; S3, panel machining: The inner surface of the panel 1 is machined to form a connection groove, and the inner surface of the panel 1 is polished; S4, coating: Apply epoxy resin and continuous carbon fiber to the inner surface of the panel 1 except the connection groove, and then cure at high temperature; S5, ultrasonic welding: Ultrasonic spot welding is performed at the junction of the panel 1 and the lattice core layer to obtain the chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure described in Example 1.

[0025] In step S2, the temperature of the hot compression molding mold is not lower than the melting temperature of the panel 1 and the lattice core layer, and is not higher than the thermal decomposition temperature of the thermoplastic resin.

[0026] In step S4, the epoxy resin and the continuous carbon fiber are preheated and then applied.

[0027] Example 3 This embodiment provides a lattice sandwich structure of a chopped fiber reinforced thermoplastic resin composite material, which is different from Embodiment 1 in that the chopped fibers are carbon fibers, the thermoplastic resin is nylon 6 resin in a polyamide resin, and the mass fraction of the carbon fibers in the chopped fiber reinforced thermoplastic resin composite material is 10%-40%.

[0028] This embodiment also provides a method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, which is different from the embodiment 2 in that: In step S1, thermoplastic resin pellets and continuous fibers are placed in a twin-screw extruder, the screw speed of the twin-screw extruder is 160 rpm, and the feed rate of the twin-screw extruder is 2.5 Hz; In step S2, the temperature parameter of the mold temperature controller is set to 180°C, the temperature of the hot compression molding mold is made to reach 180°C by the mold temperature controller, the molten short fiber reinforced nylon 6 composite material is placed in the hot compression molding mold, and hot compression molding is performed by a hydraulic press. After the mold is closed, the heat and pressure are kept for 30 seconds, and then the hot compression molding mold is oil-cooled. After the hot compression molding mold is cooled to room temperature, the mold is opened to obtain a panel and a lattice core layer; In step S5, the pressure of ultrasonic welding is 0.1-0.5 MPa, the rated power of ultrasonic welding is 2.6 kW, and the rated frequency of ultrasonic welding is 20 kHz.

[0029] Example 4 In this example, a pyramid-shaped short fiber reinforced thermoplastic resin composite material lattice sandwich structure is prepared by the molding method in Example 3 using a short fiber reinforced thermoplastic resin composite material with a carbon fiber mass fraction of 30%. The structure is compared with the pyramid-shaped short fiber reinforced thermoplastic resin composite material lattice sandwich structure prepared by 3D printing in terms of relative density, compressive strength, compressive strength ratio and production time. The results are shown in the following table.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, characterized in that: It includes two panels and a lattice core layer connecting the two panels; The panel and the lattice core layer are both short-cut fiber reinforced thermoplastic resin composite materials, the short-cut fibers are carbon fibers or glass fibers, and the thermoplastic resin is polyamide resin, polyethylene resin or polystyrene resin; The lattice core layer is a pyramid lattice core layer or a honeycomb lattice core layer; The pyramid lattice core layer includes a plurality of pyramid lattice unit cells; Each pyramid-shaped lattice unit cell is an integral part composed of four rods, the tops of the four rods are connected, the bottoms of the four rods are located in the same plane and arranged in a diamond shape, and the tops and bottoms of the four rods are provided with connection points; The bottom ends of the rods in two adjacent pyramidal lattice unit cells are connected through the same connection point; The honeycomb lattice core layer includes a plurality of honeycomb lattice unit cells; The honeycomb lattice unit cell is an integral piece consisting of six plates, and the sides of the six plates are sequentially connected to form a hexagon; Two adjacent honeycomb lattice unit cells are connected by the same plate; The surface where the panel is connected to the lattice core layer is the inner surface, a connection groove is provided on the inner surface, an epoxy resin layer is coated on the inner surface except for the connection groove, and a continuous carbon fiber layer is coated on the epoxy resin layer; For the pyramid-shaped lattice core layer, the connection grooves of the panel are adapted to the connection points of the pyramid-shaped lattice core layer and are ultrasonically welded; For the honeycomb lattice core layer, the connection grooves of the panel are adapted to the top and bottom surfaces of the panels in the honeycomb lattice core layer and are welded by ultrasonic wave.

2. The chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 1, characterized in that: The cross sections of the rods and connection points in the pyramid-shaped lattice unit cell are circular or rectangular.

3. The chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 1, characterized in that: The chopped fibers are carbon fibers, and the thermoplastic resin is nylon 6 resin among polyamide resins.

4. The chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 3, characterized in that: The mass fraction of carbon fiber in the chopped fiber reinforced thermoplastic resin composite material is 10%-40%.

5. A method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure, characterized in that: The steps include: S1, preparing molten short fiber reinforced thermoplastic resin composite material: Thermoplastic resin pellets and continuous fibers are placed in a twin-screw extruder, the continuous fibers are cut by a cutter of the twin-screw extruder to obtain chopped fibers, the resin pellets and the chopped fibers are mixed and melted to obtain a molten chopped fiber reinforced thermoplastic resin composite material; Alternatively, the thermoplastic resin pellets and the chopped fibers are directly placed in a twin-screw extruder for mixing and melting to obtain a molten chopped fiber reinforced thermoplastic resin composite material; S2, workpiece hot molding: The molten short fiber reinforced thermoplastic resin composite material is placed in a hot compression molding die, and hot compression molding is performed by a hydraulic press, and then the hot compression molding die is cooled, and the hot compression molding die is opened after the temperature of the hot compression molding die is lowered to room temperature to obtain a panel and a lattice core layer; S3, panel machining: The inner surface of the panel is machined to make connection grooves, and the inner surface of the panel is polished; S4, coating: Apply epoxy resin and continuous carbon fiber to the inner surface of the panel except for the connection grooves, and then cure at high temperature; S5, ultrasonic welding: Ultrasonic spot welding is performed at the junction of the face plate and the lattice core layer to obtain the chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure as claimed in claim 1.

6. The method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 5, characterized in that: The method also includes step S0, designing a hot compression molding mold for the panel and the lattice core layer.

7. The method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 5, characterized in that: In step S2, the temperature of the hot compression molding mold is not lower than the melting temperature of the panel and the lattice core layer, and is not higher than the thermal decomposition temperature of the thermoplastic resin.

8. The method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 5, characterized in that: In step S4, the epoxy resin and the continuous carbon fiber are preheated and then applied.

9. The method for forming a chopped fiber reinforced thermoplastic resin composite material lattice sandwich structure according to claim 5, characterized in that: In step S1, the continuous fiber and the chopped fiber are carbon fibers, the thermoplastic resin pellets are nylon 6 resin in the polyamide resin, the screw speed of the twin-screw extruder is 160 rpm, and the feed rate of the twin-screw extruder is 2.5 Hz; In step S2, the temperature parameter of the mold temperature controller is set to 180°C, the temperature of the hot compression molding mold is made to reach 180°C by the mold temperature controller, the molten short fiber reinforced nylon 6 composite material is placed in the hot compression molding mold, and hot compression molding is performed by a hydraulic press. After the mold is closed, the heat and pressure are kept for 30 seconds, and then the hot compression molding mold is oil-cooled. After the hot compression molding mold is cooled to room temperature, the mold is opened to obtain a panel and a lattice core layer; In step S5, the pressure of ultrasonic welding is 0.1-0.5 MPa, the rated power of ultrasonic welding is 2.6 kW, and the rated frequency of ultrasonic welding is 20 kHz.

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