An ultrasonic welding method for fiber-reinforced thermosetting composite materials

Abstract

This invention discloses an ultrasonic welding method for fiber-reinforced thermosetting composite materials, belonging to the field of ultrasonic welding. The joints welded using this ultrasonic welding method exhibit excellent mechanical properties, avoiding drilling damage and structural weight increase, as well as the disadvantages of surface pretreatment and long curing times required for adhesive bonding. During the surface plasticization process of the fiber-reinforced thermosetting composite material, the use of a mesh-like pure glass fiber cloth ensures that one side of the pure glass fiber cloth is tightly bonded to the prepreg during hot pressing, gradually embedding itself into the fibers of the softened resin to form a pinning effect, while the other side retains a large number of gaps to allow the thermoplastic resin to flow between the gaps during co-curing, tightly bonding with the thermoplastic resin film and improving the compatibility between different resins. This invention eliminates the need for additional surface treatment of the thermosetting composite material and has a short welding cycle, providing a highly efficient manufacturing method for welding fiber-reinforced thermosetting composite materials.

Description

Technical Field

[0001] This invention relates to an ultrasonic welding method for fiber-reinforced thermosetting composite materials, belonging to the field of ultrasonic welding. Background Technology

[0002] Fiber-reinforced thermosetting composites are widely used in aerospace and other fields due to their high specific strength, high specific stiffness, and excellent fatigue resistance. However, the increasing application of fiber-reinforced thermosetting composites in aerospace structural materials and the growing size and complexity of components have brought challenges to composite material preparation and structural molding. Therefore, the joining and assembly process of composite materials is a crucial factor determining the service strength of the structure.

[0003] In the production and assembly of large or complex aerospace structures, the connections between components are particularly important. Traditional composite material joining technologies have some obvious shortcomings. For fiber-reinforced thermosetting composites, researchers are simultaneously exploring new and efficient mechanical joining and adhesive bonding methods while also focusing on the promising field of fusion welding. Ultrasonic welding is a commonly used welding technology in industry, known for its speed and short cycle time. Furthermore, ultrasonic welding is characterized by high efficiency, ease of automation, and suitability for mass production. Unlike induction welding and resistance welding, which require the implantation of dissimilar materials or fibers, ultrasonic welding involves laying a layer of raised or flat resin material called ultrasonic energy-conducting ribs (ED) at the welding interface, reducing potential impacts.

[0004] However, ultrasonic welding also has its limitations. One of them is that the composite matrix needs to have the property of secondary melting. When this joining technology is applied to the joining of thermosetting composites, it will cause the resin matrix to decompose. The highly cross-linked molecular structure of thermosetting polymer-based composites cannot achieve secondary melting after heating. To solve this problem, the surface of the composite material to be welded needs to be pretreated. Thermosetting composites can be transformed into a hybrid laminate with the properties of thermoplastic resin on the surface. This is done by introducing a layer of thermoplastic polymer on the surface of the thermosetting composite weldment, and then co-curing it with the thermosetting composite material. The welding strength can reach or even exceed the adhesive bonding strength. Although this method can achieve ultrasonic welding of thermosetting composite laminates, it requires that the thermoplastic film used has good compatibility with the thermosetting polymer matrix, and its application range is relatively limited. It is also complex to operate, difficult to industrialize, and not suitable for large-scale production. Summary of the Invention

[0005] To address the aforementioned technical problems, the main objective of this invention is to provide an ultrasonic welding method for fiber-reinforced thermosetting composite materials. This method involves directly co-curing a thermoplastic resin film on the surface of the thermosetting composite material using an autoclave process, and then employing ultrasonic welding technology with high welding pressure and ultrasonic amplitude to limit the range of the heat-affected zone at the interface, thereby achieving the welding of the thermosetting composite material.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] This invention discloses an ultrasonic welding method for fiber-reinforced thermosetting composite materials, comprising the following steps:

[0008] Step (1): The prepreg is laminated onto the mold surface according to the laying scheme, and cured under the influence of curing factors to prepare the thermosetting laminate; the curing factors include temperature, time and pressure.

[0009] Step (2): The mesh of pure glass fiber cloth pre-impregnated with thermoplastic resin is laid between the thermosetting laminate and the thermoplastic resin film. Then, the plasticized film and the thermosetting laminate are co-cured in an autoclave to prepare a surface-plasticized fiber-reinforced thermosetting composite laminate.

[0010] Step (3): The energy-conducting ribs are hot-pressed using wet molding technology;

[0011] Step (4): Place the fiber-reinforced thermosetting composite material plate prepared in step (2) and the energy-conducting rib prepared in step (3) in the area to be welded in a single lap joint and fix them on the anvil.

[0012] Step (5): Using an ultrasonic welding head, apply welding pressure and sinusoidal vibration displacement load perpendicular to the surface of the composite material plate directly above the welding area of ​​the second fiber-reinforced thermosetting composite material plate overlapped in step (4). Set ultrasonic welding parameters through different control methods to achieve welding of composite material plates under different working conditions. After welding, use the welding head to hold pressure on the welding area until the energy conduction rib cools down and then unload it to complete the ultrasonic welding of thermosetting composite material.

[0013] Step (6): Use a universal testing machine to perform a single lap tensile shear test on the thermosetting composite material welded specimen completed in step (5) to check the weld strength of the welded joint.

[0014] As a further improvement of the present invention, the resin matrix of the fiber-reinforced thermosetting composite material is one of epoxy resin (EP), polyimide (PI), and bismaleimide (BMI). The present invention is applicable to a variety of thermosetting composite materials.

[0015] As a further improvement of the present invention, the thermoplastic film and pure glass fiber cloth in step (2) need to be cleaned and dried before laying to avoid the introduction of impurities that may affect the welding performance. The cleaning steps are as follows: ultrasonically clean with anhydrous ethanol and acetone for 5-10 minutes respectively to remove surface impurities, and then put them into an oven to dry.

[0016] As a further improvement of the present invention, the thermoplastic resin film in step (2) is one of polyamide (PA), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), polyetherimide (PEI), polyaryletheronitrile (PEN), and polyetheretherketone (PEEK).

[0017] As a further improvement of the present invention, the material of the energy-conducting rib in step (3) is one of polyamide (PA), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), polyetherimide (PEI), polyaryletheronitrile (PEN), and polyetheretherketone (PEEK).

[0018] As a further improvement of the present invention, the thickness of the energy-conducting rib in step (3) is controlled at 0.1-0.4 mm.

[0019] As a further improvement of the present invention, the welding pressure in step (5) is 500N and 1500N respectively.

[0020] As a further improvement of the present invention, the welding amplitudes in step (5) are 25 μm and 40 μm, respectively.

[0021] As a further improvement of the present invention, the stroke control parameter in step (5) is set to 0.35 mm.

[0022] As a further improvement of the present invention, the energy control parameters in step (5) are set to 930J, 1100J and 1550J respectively.

[0023] As a further improvement of the present invention, the time control parameters of step (5) are set to 0.5s and 1.6s respectively.

[0024] Beneficial effects:

[0025] 1. The present invention discloses an ultrasonic welding method for fiber-reinforced thermosetting composite materials. The joints welded by the ultrasonic welding method for fiber-reinforced thermosetting composite materials have excellent mechanical properties (high specific stiffness / specific strength, high fatigue life, high damage tolerance, etc.), effectively avoiding the drilling damage and structural weight increase caused by mechanical connection, as well as the disadvantages of surface pretreatment and long curing time required for adhesive bonding.

[0026] 2. In order to achieve a good bonding effect at the co-curing interface, the present invention discloses an ultrasonic welding method for fiber-reinforced thermosetting composite materials. During the plasticizing process of the fiber-reinforced thermosetting composite material surface, a mesh of pure glass fiber cloth is used to ensure that one side of the pure glass fiber cloth is closely attached to the prepreg during hot pressing, gradually embedding into the fibers in the softened resin to form a pinning effect, while the other side leaves a large number of gaps so that the thermoplastic resin can flow in the gaps during co-curing and be tightly connected with the thermoplastic resin film, thereby improving the compatibility between different resins.

[0027] 3. The ultrasonic welding method for fiber-reinforced thermosetting composite materials disclosed in this invention does not require additional surface treatment of the thermosetting composite material, and has a short welding cycle, providing a high-efficiency manufacturing method for welding fiber-reinforced thermosetting composite materials. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of an ultrasonic welding method for fiber-reinforced thermosetting composite materials according to the present invention.

[0029] Figure 2 Figure 1 shows a schematic diagram of the preparation of fiber-reinforced thermosetting composite materials; Figure 2 shows a schematic diagram of unwinding the fiber prepreg; Figure 3 shows a schematic diagram of prepreg laying; Figure 4 shows a schematic diagram of placing the autoclave; Figure 5 shows a schematic diagram of hot pressing and curing; Figure 6 shows a schematic diagram of cooling and depressurizing the autoclave.

[0030] Figure 3 Figure 1 shows a schematic diagram of the surface plasticizing process of fiber-reinforced thermosetting composite materials; Figure 2 shows a schematic diagram of unwinding pure glass fiber cloth; Figure 3 shows a schematic diagram of cleaning pure glass fiber cloth; Figure 4 shows a schematic diagram of laying pure glass fiber cloth; Figure 5 shows a schematic diagram of surface plasticizing of glass fiber cloth; Figure 6 shows a schematic diagram of laying in an autoclave; Figure 7 shows a schematic diagram of hot pressing and curing of thermosetting composite materials; Figure 8 shows a schematic diagram of surface plasticizing of thermosetting composite materials; and Figure 9 shows a schematic diagram of cooling and depressurizing in an autoclave.

[0031] Figure 4 Figure 1 shows a schematic diagram of the compression molding process for energy-conducting ribs; Figure 2a shows a schematic diagram of the thermoplastic polymer material injection process; Figure 3b shows a schematic diagram of the hot pressing molding process for energy-conducting ribs.

[0032] Figure 5 Figure 1 is a schematic diagram of the ultrasonic welding process of the fiber-reinforced thermosetting composite material of the present invention; wherein Figure 2a is a schematic diagram of a single lap joint of the welded sample; and Figure 3b is a schematic diagram of the ultrasonic welding process.

[0033] In the diagram: 1—fiber prepreg, 2—mold, 3—thermosetting composite material, 4—pure glass fiber cloth roll, 5—spray gun, 6—thermoplastic film, 7—fiber-reinforced thermosetting composite material, 8—nozzle, 9—thermoplastic polymer material, 10—polymer molding mold, 11—energy-conducting rib, 12—lower welding composite plate, 13—upper welding composite plate, 14—aluminum gasket, 15—anvil, 16—ultrasonic welding head. Detailed Implementation

[0034] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate;

[0035] The existence of the described features, wholes, steps, operations, elements and / or components is permitted, but the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof is not excluded.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0039] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0040] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions:

[0041] This invention provides an ultrasonic welding method for fiber-reinforced thermosetting composite materials. The invention employs an autoclave process to directly co-cure a thermoplastic resin film on the surface of the thermosetting composite material, and then uses ultrasonic welding technology with high welding pressure and ultrasonic amplitude to limit the range of the heat-affected zone at the interface, ultimately achieving the welding of the thermosetting composite material.

[0042] As one embodiment of the present invention, the specific implementation process is as follows:

[0043] Step 1, such as Figure 2 (a) shows the fiber prepreg 1 being unwound and cut, then as shown in the diagram. Figure 2 (b) Lay the prepreg 1 on the surface of mold 2 according to the layup plan, then cover it with high-temperature resistant release cloth, release film, and vacuum bag, and then place it together with mold 2 into an autoclave. Seal the autoclave door and cure it in a high-temperature and high-pressure environment according to the specified curing process. After cooling and depressurization, open the autoclave door and take out the thermosetting composite material 3 sample together with the mold.

[0044] Step Two, as follows Figure 3 (a) The pure glass fiber cloth roll 4 is unwound and cut. Then, the cut mesh glass fiber cloth 4 is ultrasonically cleaned for 5-10 minutes with anhydrous ethanol and acetone respectively to remove surface impurities and then placed in an oven for drying.

[0045] Step 3, as follows Figure 3 (c) The mesh glass fiber cloth 4 after step two is laid on the upper surface of the thermosetting composite material 3. The thermoplastic resin is sprayed evenly on the surface of the mesh glass fiber cloth 4 using a spray gun 5. Then, the thermoplastic film is laid on the uppermost surface. Finally, the thermoplastic film 6 and the thermosetting composite material 3 are co-cured in an autoclave to prepare a surface-plasticized fiber-reinforced thermosetting composite material 7.

[0046] Step 4, as follows Figure 4 (a) shows that the molten thermoplastic polymer material 9 is injected into the polymer molding mold 10 under high pressure using nozzle 8. After the material injection is completed, the mold 10 is vacuumed and pressurized. After the material is reduced to the melting point, the molten thermoplastic polymer will rapidly solidify into energy-conducting ribs 11.

[0047] Step 5, as follows Figure 5(a) First, the energy-conducting rib 11 made in step four is placed on the interface of the welding area of ​​the lower welding composite material plate 12 processed in step three. Then, the welding area of ​​the upper welding composite material plate 13, which was also processed in step three, is overlapped on the interface of the energy-conducting rib 11, and aluminum gaskets 14 are added and fixed on the anvil 15.

[0048] Step Six, as Figure 5 (b) As shown, in step five, the ultrasonic welding head 16 applies a welding pressure perpendicular to the surface of the composite material plate 13 to be welded, and a sinusoidal vibration displacement load. Table 1 lists the welding parameters under three control modes: stroke, energy, and time. After welding, the welding head is used to maintain pressure on the welding area. After the energy-conducting rib cools down, the pressure is released to complete the ultrasonic welding of the thermosetting composite material.

[0049] Step 7: Use a universal testing machine to perform single-lap tensile shear tests on the welded thermosetting composite material specimens completed in Step 6, analyze the failure mechanism of the cross-section, and explore the optimal welding process.

[0050] Step 8: To verify the reinforcing effect of the interfacial inclusion of mesh glass fiber cloth in surface plasticization, the same welding process was used to weld the thermosetting composite material of traditional surface plasticization and the tensile strength of the welded joint was checked. The tensile strength results are shown in Table 2.

[0051] The results show that in almost every welding process, the peel strength of the welded joint can be achieved by embedding a mesh of glass fiber cloth on the plasticized surface.

[0052] Table 1 Welding process parameters for the specimens

[0053]

[0054] Table 2 Tensile strength of welded joints of specimens

[0055]

[0056]

[0057] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultrasonic welding method for fiber-reinforced thermosetting composite materials, characterized in that: Includes the following steps, Step (1): The prepreg is laminated onto the mold surface according to the layup scheme and cured under the influence of curing factors to prepare the thermosetting laminate; the curing factors include temperature, time and pressure. Step (2): The mesh of pure glass fiber cloth pre-impregnated with thermoplastic resin is laid between the thermosetting laminate and the thermoplastic resin film. Then, the thermoplastic resin film and the thermosetting laminate are co-cured in an autoclave to prepare a surface-plasticized fiber-reinforced thermosetting composite material board. Step (3): The energy-conducting ribs are hot-pressed using wet molding technology; Step (4): Place the fiber-reinforced thermosetting composite material plate prepared in step (2) and the energy-conducting rib prepared in step (3) in the area to be welded in a single lap joint and fix them on the anvil. Step (5): Using an ultrasonic welding head, apply welding pressure and sinusoidal vibration displacement load perpendicular to the surface of the composite material plate directly above the welding area of ​​the second fiber-reinforced thermosetting composite material plate overlapped in step (4). Set ultrasonic welding parameters through different control methods to achieve welding of composite material plates under different working conditions. After welding, use the welding head to hold pressure on the welding area until the energy conduction rib cools down and then unload it to complete the ultrasonic welding of thermosetting composite material. Step (6): Use a universal testing machine to perform a single lap tensile shear test on the thermosetting composite material welded specimen completed in step (5) to check the weld strength of the welded joint.

2. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: The resin matrix of the fiber-reinforced thermosetting composite material is one of epoxy resin (EP), polyimide (PI), and bismaleimide (BMI).

3. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: Before laying the thermoplastic resin film and pure glass fiber cloth in step (2), they need to be cleaned and dried to avoid impurities affecting the welding performance. The cleaning steps are as follows: use anhydrous ethanol and acetone for ultrasonic cleaning for 5-10 minutes respectively to remove surface impurities, and then put them into the oven to dry.

4. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: The thermoplastic resin film in step (2) is one of polyamide (PA), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), polyetherimide (PEI), polyaryletheronitrile (PEN), and polyetheretherketone (PEEK).

5. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: The material of the energy-conducting rib in step (3) is one of polyamide (PA), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), polyetherimide (PEI), polyaryletheronitrile (PEN), and polyetheretherketone (PEEK).

6. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: In step (3), the thickness of the energy-conducting rib is controlled at 0.1-0.4 mm.

7. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: When the welding pressure is 500N, the amplitude is 40μm, the stroke control parameter is 0.35 mm, the energy control parameter is 1500J, and the time control parameter is 1.6s.

8. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: When the welding pressure is 1500N, the amplitude is 40μm, the stroke control parameter is 0.35 mm, the energy control parameter is 930J, and the time control parameter is 0.5s.

9. The ultrasonic welding method for fiber-reinforced thermosetting composite materials as described in claim 1, characterized in that: When the welding pressure is 1500N, the amplitude is 25μm, the stroke control parameter is 0.35 mm, the energy control parameter is 1100J, and the time control parameter is 1.6s.

Images