Ultrasonic welding method and assembly with controllable interface structure

Abstract

The present invention provides an ultrasonic welding method and assembly with controllable interface structure, which relates to the field of material technology, and aims to solve the technical problems of uneven welds and low strength in ultrasonic welding between thermoplastic composite materials. The ultrasonic welding method comprises: co-consolidating and forming a layer of film on the surface to be welded of each workpiece, wherein the material of the film is a continuous fiber reinforced thermoplastic composite material, and the thickness of the film is 0.05mm to 0.5mm; abutting the surfaces to be welded of the two workpieces with the film; and ultrasonically welding the two workpieces. The ultrasonic welding method with controllable interface structure of the present invention is used for welding between two thermoplastic composite workpieces. It is particularly suitable for high-quality and high-efficiency welding of thermoplastic composite workpieces to be welded with complex curved surface structures.

Description

Technical Field

[0001] The present disclosure relates to the field of materials, and in particular to an ultrasonic welding method and assembly with controllable interface structure. Background Art

[0002] Fiber-reinforced thermoplastic composites have broad application prospects in aerospace and other fields due to their outstanding mechanical properties, heat resistance, corrosion resistance and recyclability. It is generally difficult to use thermoplastic composites to prepare complex structures and large-sized workpieces, which require separate processing before connection.

[0003] In the prior art, when conventional ultrasonic welding technology is used to connect thermoplastic composite materials, ultrasonic continuous welding of complex curved workpieces is prone to uneven weld distribution and strength, resulting in local unwelded areas and local stress concentration, and the efficiency is relatively low. The use of energy-conducting ribs requires the application of tiny surface protrusions between the composite workpieces to be welded, which results in complex processing technology and is prone to damage to the composite surface structure. In addition, the melting uniformity of the energy-conducting ribs is poor, which is prone to uneven welds and strength. Summary of the invention

[0004] The purpose of the present invention is to provide an ultrasonic welding method and assembly with controllable interface structure to solve the technical problems of ultrasonic welding between thermoplastic composite materials, uneven welds and low strength.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] An embodiment of the present invention provides an ultrasonic welding method with controllable interface structure, which is used for welding two thermoplastic composite workpieces. The ultrasonic welding method comprises:

[0007] A layer of film is co-consolidated on each of the workpiece surfaces to be welded, wherein the film is made of a continuous fiber reinforced thermoplastic composite material and has a thickness of 0.05 mm to 0.5 mm;

[0008] Abutting the surfaces of two workpieces to be welded having the films;

[0009] The two workpieces are ultrasonically welded.

[0010] According to at least one embodiment of the present disclosure, the two workpieces are made of the same material, and the ratio of the volume fraction of the fibers in the weld formed by the membrane to the volume fraction of the fibers in the workpieces is (0.9-1.1):1.

[0011] According to at least one embodiment of the present disclosure, the matrix material in the film or the workpiece includes one of polyetheretherketone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetherimide, and polyethersulfone resin; and / or,

[0012] The fiber reinforcement phase in the film and the workpiece includes one of carbon fiber, basalt fiber, aramid fiber, graphite fiber, glass fiber, ceramic fiber, boron fiber, polyamide fiber, polyethylene fiber, PBO fiber, polyester fiber and natural fiber.

[0013] According to at least one embodiment of the present disclosure, the co-consolidation forming a layer of film on each of the workpiece surfaces to be welded comprises applying the film on the surface of an unconsolidated prepreg layer used to form the workpiece, and forming the film by a co-consolidation process; or,

[0014] The prepreg layup used to form the workpiece is consolidated into the workpiece, and the film is applied to the surface of the workpiece by a co-consolidation process.

[0015] According to at least one embodiment of the present disclosure, the thickness of the workpiece to which the film is applied is 0.5 mm to 3.0 mm.

[0016] According to at least one embodiment of the present disclosure, a matrix phase of the film is the same as a matrix phase of the workpiece.

[0017] According to at least one embodiment of the present disclosure, the welding surfaces of the two workpieces are planar structures or curved structures. Further, the welding surfaces of the workpieces are curved structures of large-sized aviation-grade thermoplastic composite materials.

[0018] According to at least one embodiment of the present disclosure, when the welding surfaces of the two workpieces are planar structures, the pre-pressing pressure of the ultrasonic welding is 100N to 500N;

[0019] The amplitude of the ultrasonic welding is 20 μm to 100 μm, the frequency is 10 kHz to 50 kHz, and the welding pressure is 400 N to 2000 N; or,

[0020] When the welding surfaces of the two workpieces are curved structures, the pre-pressing pressure of the ultrasonic welding is 200N to 500N;

[0021] The amplitude of the ultrasonic welding is 30 μm to 100 μm, the frequency is 15 kHz to 50 kHz, and the welding pressure is 500N to 2000N.

[0022] According to at least one embodiment of the present disclosure, when the welding surfaces of the two workpieces are planar structures, the welding speed of the ultrasonic welding is 10 mm / s to 40 mm / s;

[0023] When the welding surfaces of the two workpieces are curved structures, the welding speed of the ultrasonic welding is 10 mm / s to 30 mm / s.

[0024] Compared with the prior art, the ultrasonic welding method of the present invention applies a layer of continuous fiber reinforced thermoplastic film on the surface of the thermoplastic composite, and the thickness of the continuous fiber reinforced thermoplastic film is 0.05mm to 0.5mm, which can realize the welding between two thermoplastic composite workpieces without energy-conducting ribs, and the joint has a very high joint strength. In the ultrasonic welding method of the present invention, the fiber volume fraction, morphology and distribution of the continuous fiber reinforced thermoplastic film are controllable; the application of the continuous fiber reinforced thermoplastic film can play a role in melting and uniform distribution of the interfacial thermoplastic resin during welding and improving the integrity of the welding joint-composite structure, weld uniformity, and performance stability. High-quality and high-efficiency continuous ultrasonic welding of thermoplastic composite workpieces with flat and complex curved structures to be welded can be achieved without energy-conducting ribs.

[0025] Another object of the present invention is to provide a combination, including two workpieces, both of which are made of thermoplastic composite materials, and the two workpieces are connected together by the above-mentioned welding method.

[0026] Compared with the prior art, the combination of the present invention has the following advantages:

[0027] The advantages of the combination and the above-mentioned ultrasonic welding method over the prior art are the same, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings illustrate exemplary embodiments of the present disclosure and together with the description serve to explain the principles of the present disclosure. These drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification.

[0029] Figure 1 Schematic diagram of the layering of prepreg and film in the co-curing molding process according to an embodiment of the present disclosure.

[0030] Figure 2 Schematic diagram of a workpiece structure having a film on its surface according to an embodiment of the present disclosure.

[0031] Figure 3 It is a schematic diagram of ultrasonic spot welding of a planar structure workpiece to be welded according to an embodiment of the present disclosure.

[0032] Figure 4 It is a schematic diagram of ultrasonic continuous welding of a planar structure workpiece to be welded according to an embodiment of the present disclosure.

[0033] Figure 5It is a schematic diagram of ultrasonic continuous welding of a workpiece with a curved surface structure to be welded according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] The present disclosure is further described in detail below in conjunction with the accompanying drawings and implementations. It is understood that the specific implementations described herein are only used to explain the relevant content, rather than to limit the present disclosure. It should also be noted that, for ease of description, only the parts related to the present disclosure are shown in the accompanying drawings.

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0036] See also Figure 1-Figure 5 As shown, an embodiment of the present invention provides an ultrasonic welding method with controllable interface structure, which is used for welding between two thermoplastic composite workpieces. By introducing a continuous fiber reinforced thermoplastic film on the surface of the two thermoplastic composite workpieces, the welding between the thermoplastic composite workpieces is achieved, which is particularly suitable for high-quality, high-efficiency ultrasonic spot welding and continuous welding of large-sized and complex-shaped aviation-grade thermoplastic composite materials. Compared with traditional ultrasonic welding methods, such as welding with flat energy-conducting ribs, the uniformity of flow under pressure after melting is relatively poor, the thickness of the weld and its uniformity are difficult to control, the difference between the weld and the composite structure is large, and the uniformity of the performance of the weld and the composite itself is poor, which is difficult to apply to ultrasonic welding of large-sized and complex-structured workpieces. The present invention uses a continuous fiber reinforced thermoplastic composite film to make the weld evenly distributed and have higher strength, and is also applicable to workpieces with complex shapes.

[0037] It can be understood that the materials of the two workpieces are the same or different. By controlling the fiber volume fraction and fiber morphology of the continuous fiber reinforced thermoplastic composite film, the weld between the two workpieces in ultrasonic welding can be controllable. For example, in the weld formed by the continuous fiber reinforced thermoplastic composite film between the two workpieces, the ratio of the volume fraction of the fiber to the volume fraction of the fiber in the workpiece is (0.9-1.1):1, optionally (0.95-1.07):1, and optionally (0.97-1.05):1. By actively regulating the volume fraction of the fiber in the weld, the integration of the workpiece and the joint is achieved, the interface uniformity is effectively improved, and it is beneficial to expand the process window during ultrasonic continuous welding, thereby obtaining a better weld joint strength. For example, the volume fraction of the fiber in the weld can be controlled to be the same as the volume fraction of the fiber in the workpiece. For example, the fiber volume fraction of the workpiece is 35%-55%, and the fiber volume fraction of the membrane is controlled at 20%-30%. After the membranes on the two workpieces are welded, the fiber volume fraction in the weld is consistent or similar to the fiber volume fraction in the workpiece. For example, the fiber volume fractions in the workpiece and the weld are both 45%, 50% or 55%.

[0038] In some embodiments, the resin material in the film and the workpiece can be thermoplastic resins such as polyetheretherketone (abbreviated as PEEK), polyphenylene sulfide (abbreviated as PPS), polyaryletherketone (abbreviated as PAEK), polyetherketoneketone (abbreviated as PEKK), polyetherimide (abbreviated as PEI) and polyethersulfone resin (abbreviated as PES). Exemplarily, the resin material of the above-mentioned film and the workpiece is selected as the same resin, or a compatible resin, and there is a good interface bonding between the two to increase the integration of the two workpieces and the weld. The fiber-reinforced phase in the film and the workpiece includes but is not limited to one of carbon fiber, basalt fiber, aramid fiber, graphite fiber, glass fiber, ceramic fiber, boron fiber, polyamide fiber, polyethylene fiber, PBO fiber, polyester fiber and natural fiber. Exemplarily, the fiber-reinforced phase of the above-mentioned film and the workpiece is the same fiber.

[0039] In some embodiments, the continuous fiber reinforced thermoplastic film is applied to the surface of the thermoplastic composite workpiece by a forming process such as a vacuum bagging process, an autoclave forming process, or a compression molding process.

[0040] For example, see Figure 1 As shown, a layer of continuous fiber reinforced thermoplastic composite film 2 is applied to the surface of the unconsolidated carbon fiber reinforced thermoplastic resin layer 1, so that the continuous fiber reinforced thermoplastic composite film 2 is applied to the surface of the thermoplastic composite workpiece 3 by co-consolidation. This method is simple in process, but the thickness of the continuous fiber reinforced thermoplastic composite film 2 will be correspondingly reduced during the preparation process. Please refer to Figure 2As shown, after the co-consolidation process is completed, the thickness of the thermoplastic composite workpiece 3 to be welded with the continuous fiber reinforced thermoplastic composite film applied on the surface obtained by demolding is 0.5-3.0 mm.

[0041] In another optional embodiment, the carbon fiber reinforced thermoplastic composite prepreg layer is first consolidated to prepare a thermoplastic composite workpiece 3, and then a layer of continuous fiber reinforced thermoplastic composite film 2 is applied to the surface of the thermoplastic composite workpiece 3 through a co-consolidation process. This method can reduce the pressure during the preparation process, thereby improving the thickness uniformity of the thermoplastic composite film. The film finally obtained covers the thermoplastic composite workpiece to be welded with a thickness of 0.5 to 3.0 mm in the area to be welded.

[0042] In some implementations, the surfaces to be welded of the two workpieces of the embodiment of the present invention may be a planar structure or a large-sized curved structure with a complex shape. There are various welding methods for welding surfaces of different shapes.

[0043] For example, ultrasonic spot welding and continuous welding methods for flat thermoplastic composite parts include: Figure 3-Figure 4 As shown, the upper workpiece 5 and the lower workpiece 6 are both planar thermoplastic composite workpieces, the support platform is a planar structure, and the ultrasonic welding head is a planar surface.

[0044] S101. Based on the co-consolidation molding method in the above technical solution, a continuous fiber reinforced thermoplastic composite film 7 with a controllable fiber volume fraction is applied on the surface of the upper workpiece 5, and a continuous fiber reinforced thermoplastic composite film 8 with a controllable fiber volume fraction is applied on the surface of the lower workpiece 6.

[0045] S102, fix the upper workpiece 5 and the lower workpiece 6 on the support platform 9, place the ultrasonic welding head 10 above the areas to be welded of the two workpieces, apply pressure perpendicular to the areas to be welded without energy guiding ribs, and the pre-compression pressure is 100-500N.

[0046] S103, setting corresponding ultrasonic welding displacement parameters according to the fiber volume fraction and target volume fraction of the thermoplastic composite film. Perform spot welding under certain amplitude and frequency conditions, such as Figure 3 As shown, or the ultrasonic horn 10 starts to vibrate and moves along the welding direction at a certain speed to perform continuous ultrasonic welding, such as Figure 4 As shown, the amplitude is 20-100 μm, the frequency is 10-50 kHz, the welding pressure is 400-2000 N, and the welding speed is 10-40 mm / s.

[0047] S104, after reaching the preset stop condition, lift the ultrasonic welding head and repeat the above steps to complete ultrasonic spot welding or continuous welding, so that the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 0.9 to 1.1.

[0048] Ultrasonic spot welding and continuous welding methods for curved thermoplastic composite workpieces include: Figure 5 As shown, the upper workpiece 5 and the lower workpiece 6 are both curved thermoplastic composite workpieces, the support platform is a curved structure, and the ultrasonic welding head is an arc welding head.

[0049] S101. Based on the co-consolidation molding method in the above technical solution, a continuous fiber reinforced thermoplastic composite film 7 with a controllable fiber volume fraction is applied on the surface of the upper workpiece 5, and a continuous fiber reinforced thermoplastic composite film 8 with a controllable fiber volume fraction is applied on the surface of the lower workpiece 6.

[0050] S102, fix the upper workpiece 5 and the lower workpiece 6 on the support platform 9, place the ultrasonic welding head 10 above the areas to be welded of the two workpieces, apply pressure perpendicular to the areas to be welded without energy guiding ribs, and the pre-compression pressure is 200-500N.

[0051] S103, setting corresponding ultrasonic welding displacement parameters according to the fiber volume fraction and target volume fraction of the thermoplastic composite film. Under certain amplitude and frequency conditions, the ultrasonic welding head 10 starts to vibrate and moves along the welding direction at a certain speed to perform continuous ultrasonic welding, such as Figure 5 As shown, the amplitude is 30-100 μm, the frequency is 15-50 kHz, the welding pressure is 500-2000 N, and the welding speed is 10-30 mm / s.

[0052] S104, after reaching the preset stop condition, lift the ultrasonic welding head, and repeat the above steps to complete the ultrasonic continuous welding, so that the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 0.9 to 1.1.

[0053] Several examples of ultrasonic welding methods are given below, and representative welded assemblies are selected for performance analysis.

[0054] Test method: The single lap shear strength of the welded joint was tested according to the method disclosed in GB / T33334-2016. Five groups of specimens were taken at different positions of the weld to obtain the average shear strength value.

[0055] Example 1

[0056] This embodiment provides a method for co-consolidation molding of a continuous fiber reinforced thermoplastic composite film and a thermoplastic composite workpiece, which specifically includes:

[0057] (1) A T700 continuous carbon fiber reinforced polyetherimide (PEI) membrane with a thickness of 0.25 mm was used, wherein the fiber volume fraction was 25%. The PEI membrane and the T700 carbon fiber reinforced PEI prepreg were precut into a uniform size of 50 cm×50 cm, wherein the fiber volume fraction of the prepreg was 50%.

[0058] (2) A release agent is applied to the upper and lower mold surfaces, and the PEI thermoplastic composite film and PEI prepreg are laid using a mechanically assisted method so that each layer can be laid flat. A total of 8 layers of PEI prepreg are laid, and the PEI film is placed on the top layer.

[0059] (3) The workpiece to be welded was prepared by autoclave molding process. The vacuum pipeline was connected and the autoclave was sealed to extract the air and volatiles. The temperature was raised to 250°C at a rate of 8°C / min, kept at this temperature for 30 minutes, then raised to 300°C, kept at this temperature for 120 minutes while applying a pressure of 2.5 MPa, then raised to 320°C, kept at this temperature for 60 minutes while maintaining a pressure of 2.5 MPa. Finally, the temperature was lowered to room temperature at a rate of 5°C / min to complete the co-consolidation process, and a workpiece to be welded with a thickness of 2 mm and a PEI film applied on the surface was obtained.

[0060] Example 2

[0061] This embodiment provides a method for co-consolidation molding of a discontinuous short fiber reinforced thermoplastic composite film and a workpiece, which specifically includes:

[0062] (1) A T700 short carbon fiber reinforced polyetherimide (PEI) membrane with a thickness of 0.25 mm was used, wherein the carbon fiber was a T700 short fiber with a length of 0.5 mm and a fiber volume fraction of 25%. The PEI membrane and the T700 carbon fiber reinforced PEI prepreg were precut into a uniform size of 50 cm × 50 cm. The fiber volume fraction of the prepreg was 50%.

[0063] (2) A release agent is applied to the upper and lower mold surfaces, and the PEI thermoplastic composite film and PEI prepreg are laid using a mechanically assisted method so that each layer can be laid flat. A total of 8 layers of PEI prepreg are laid, and the PEI film is placed on the top layer.

[0064] (3) The workpiece to be welded was prepared by autoclave molding process. The vacuum pipeline was connected and the autoclave was sealed to extract the air and volatiles. The temperature was raised to 250°C at a rate of 8°C / min, kept at this temperature for 30 minutes, then raised to 300°C, kept at this temperature for 120 minutes while applying a pressure of 2.5 MPa, then raised to 320°C, kept at this temperature for 60 minutes while maintaining a pressure of 2.5 MPa. Finally, the temperature was lowered to room temperature at a rate of 5°C / min to complete the co-consolidation process, and a workpiece to be welded with a thickness of 2 mm and a PEI film applied on the surface was obtained.

[0065] Example 3

[0066] The ultrasonic spot welding method provided in this embodiment specifically includes:

[0067] (1) Based on the method in the above-mentioned embodiment 1, the two workpieces are made of the same material and both have a layer of continuous carbon fiber reinforced PEI film co-cured, and the surfaces of the two workpieces are degreased using isopropyl alcohol.

[0068] (2) The upper and lower workpieces are fixed on the anvil supported by the planar structure by a clamp, and the flat contact surface ultrasonic welding head is placed above the overlap area of ​​the workpieces to be welded. A pre-compression pressure of 300N is applied perpendicular to the area to be welded without energy guiding ribs.

[0069] (3) Under the conditions of amplitude 86.2 μm and frequency 20 kHz, a welding pressure of 1200 N was applied perpendicular to the lap joint interface. After the flat contact surface ultrasonic welding head reached the preset trigger condition, the ultrasonic spot welding process was started.

[0070] (4) The flat contact surface ultrasonic welding head reaches the preset stop condition, stops moving and lifts up. The ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0071] Example 4

[0072] The ultrasonic continuous welding method provided in this embodiment specifically includes:

[0073] (1) Based on the method in the above-mentioned embodiment 1, the two workpieces are planar structures, made of the same material and both have a co-cured layer of T700 continuous carbon fiber reinforced PEI film, and the surfaces of the two workpieces are degreased using isopropyl alcohol.

[0074] (2) Please refer to Figure 4 As shown, the upper and lower workpieces are fixed above the planar structure support anvil by a clamp, the flat contact surface ultrasonic welding head is placed above the overlapping area of ​​the workpieces to be welded, and a pre-stressing pressure of 300N perpendicular to the area to be welded is applied through the pre-stressing module 11 without energy guiding ribs.

[0075] (3) Under the conditions of amplitude 86.2 μm and frequency 20 kHz, a welding pressure of 1200 N was applied perpendicular to the lap joint interface, and the welding speed was 30 mm / s. After the flat contact surface ultrasonic welding head reached the preset trigger condition, the ultrasonic continuous welding process was started.

[0076] (4) A pressure of 1000 N is applied to the welded area by the pressure holding module 12 to complete the ultrasonic continuous welding of the workpiece to be welded. After the planar ultrasonic horn 10 reaches the preset stop condition, the ultrasonic horn is lifted. The ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0077] Example 5

[0078] The ultrasonic continuous welding method provided in this embodiment specifically includes:

[0079] (1) Based on the method in the above-mentioned embodiment 1, the two workpieces are curved structures, made of the same material and both have a co-cured layer of T700 continuous carbon fiber reinforced PEI film, and the surfaces of the two workpieces are degreased using isopropyl alcohol.

[0080] (2) Please refer to Figure 5 As shown, the upper and lower workpieces are fixed above the curved surface structure support anvil by a clamp, and the curved contact surface ultrasonic welding head is placed above the overlapping area of ​​the workpieces to be welded. In the absence of energy guiding ribs, a pre-stressing pressure of 300N perpendicular to the area to be welded is applied through the pre-stressing module 11.

[0081] (3) Under the conditions of amplitude 86.2 μm and frequency 20 kHz, a welding pressure of 1500 N was applied perpendicular to the lap joint interface, and the welding speed was 20 mm / s. After the curved contact surface ultrasonic welding head reached the preset trigger condition, the ultrasonic continuous welding process was started.

[0082] (4) A pressure of 1000 N is applied to the welded area by the pressure holding module 12 to complete the ultrasonic continuous welding of the workpiece to be welded. After the curved ultrasonic welding head reaches the preset stop condition, the ultrasonic welding head is lifted. The ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0083] Comparative Example 1

[0084] The ultrasonic welding method provided in this comparative example is different from that in Example 3 in that:

[0085] After ultrasonic spot welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.2.

[0086] Comparative Example 2

[0087] The ultrasonic welding method provided in this comparative example is different from that in Example 3 in that:

[0088] After ultrasonic spot welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 0.8.

[0089] Comparative Example 3

[0090] The ultrasonic welding method provided in this comparative example is different from that in Example 3 in that:

[0091] In step (1), no fiber reinforcement phase is introduced, and only a PEI film of the same thickness is solidified on the workpiece surface.

[0092] Comparative Example 4

[0093] The ultrasonic welding method provided in this comparative example is different from that in Example 3 in that:

[0094] In step (1), in the fiber-reinforced PEI membrane, the continuous carbon fiber reinforcement phase is replaced by chopped carbon fibers using the method of Example 2, wherein the length of the short carbon fibers is 0.5 mm. After the ultrasonic spot welding is completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.0.

[0095] Comparative Example 5

[0096] The ultrasonic welding method provided in this comparative example is different from that in Example 3 in that:

[0097] In step (1), the carbon fiber reinforced PEI film has a plurality of rectangular mesh shapes, the mesh size is 3 mm, and the carbon fiber reinforced PEI film is placed between the two workpieces without being solidified on the workpieces. By adjusting the displacement mode of ultrasonic welding, the same weld thickness is obtained, and the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0098] Comparative Example 6

[0099] The ultrasonic welding method provided in this comparative example is different from that in Example 4 in that:

[0100] After ultrasonic welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.2.

[0101] Comparative Example 7

[0102] The ultrasonic welding method provided in this comparative example is different from that in Example 4 in that:

[0103] After ultrasonic welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 0.8.

[0104] Comparative Example 8

[0105] The ultrasonic welding method provided in this comparative example is different from that in Example 4 in that:

[0106] In step (1), no fiber reinforcement phase is introduced, and only a PEI film of the same thickness is solidified on the workpiece surface.

[0107] Comparative Example 9

[0108] The ultrasonic welding method provided in this comparative example is different from that in Example 4 in that:

[0109] In step (1), in the fiber-reinforced PEI membrane, the continuous carbon fiber reinforcement phase is replaced by chopped carbon fibers using the method of Example 2, wherein the length of the short carbon fibers is 0.5 mm. After ultrasonic welding is completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.0.

[0110] Comparative Example 10

[0111] The ultrasonic welding method provided in this comparative example is different from that in Example 4 in that:

[0112] In step (1), the carbon fiber reinforced PEI film has a plurality of rectangular mesh shapes, the mesh size is 3 mm, and the carbon fiber reinforced PEI film is placed between the two workpieces without being solidified on the workpieces. By adjusting the displacement mode of ultrasonic welding, the same weld thickness is obtained, and the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0113] Comparative Example 11

[0114] The ultrasonic welding method provided in this comparative example is different from that in Example 5 in that:

[0115] After ultrasonic welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.2.

[0116] Comparative Example 12

[0117] The ultrasonic welding method provided in this comparative example is different from that in Example 5 in that:

[0118] After ultrasonic welding, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 0.8.

[0119] Comparative Example 13

[0120] The ultrasonic welding method provided in this comparative example is different from that in Example 5 in that:

[0121] In step (1), no fiber reinforcement phase is introduced, and only a PEI film of the same thickness is solidified on the workpiece surface.

[0122] Comparative Example 14

[0123] The ultrasonic welding method provided in this comparative example is different from that in Example 5 in that:

[0124] In step (1), in the fiber-reinforced PEI membrane, the continuous carbon fiber reinforcement phase is replaced by chopped carbon fibers using the method of Example 2, wherein the length of the short carbon fibers is 0.5 mm. After ultrasonic welding is completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece is 1.0.

[0125] Comparative Example 15

[0126] The ultrasonic welding method provided in this comparative example is different from that in Example 5 in that:

[0127] In step (1), the carbon fiber reinforced PEI film has a plurality of rectangular mesh shapes, the mesh size is 3 mm, and the carbon fiber reinforced PEI film is placed between the two workpieces without being solidified on the workpieces. By adjusting the displacement mode of ultrasonic welding, the same weld thickness is obtained, and the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction is 1.0.

[0128] The shear strength of the welded joints of the embodiments and comparative examples are given below. Please refer to Table 1.

[0129] Table 1 Shear strength of welded joints

[0130]

[0131] Please refer to Table 1. From the difference between Comparative Example 1 and Example 3, it can be seen that when the fiber volume fraction of the weld is too much greater than the fiber volume fraction of the workpiece, the weld uniformity is relatively poor, a higher stress concentration is generated locally, and the fibers at the weld are locally damaged. This causes the strength of the weld joint to decrease. When the fiber volume fraction of the weld is too small less than the fiber volume fraction of the workpiece, such as in Comparative Example 2, since the weld width between the two workpieces is relatively large, the lower welding displacement setting causes the resin at the weld to not be fully melted and extruded, resulting in a large number of defects at the weld, which causes the strength of the weld joint to decrease. The comparison between Comparative Examples 6-7 and Example 4, and the difference between Comparative Examples 11-12 and Example 5 also confirms that for continuous welding of planar structures and continuous welding of curved structures, the ratio of the weld fiber volume fraction to the workpiece fiber volume fraction after welding is not within the scope of the embodiments of the present invention, and the strength of the joint will be reduced.

[0132] It can be seen from Comparative Examples 3, 8, and 13 that when only PEI resin film is used, that is, no fiber reinforcement phase is introduced into the thermoplastic film, under the same displacement ultrasonic welding mode conditions, the final joint strength is much smaller than that of the PEI film introduced with a continuous fiber reinforcement phase.

[0133] It can be seen from comparative examples 4, 9, and 14 that when fiber-reinforced PEI resin film is used, after chopped fibers are used instead of continuous fibers, due to the irregular distribution of short carbon fibers, a large number of pore defects and stress concentration are easily generated at both ends of the short carbon fibers during the resin extrusion process. At the same time, compared with the regular arrangement of continuous fibers, local agglomeration is prone to occur, which is not conducive to improving the strength of the welded joint.

[0134] It can be seen from comparative examples 5, 10, and 15 that when using mesh thermoplastic composite energy conductors, compared with the fiber-reinforced composite membrane of the embodiment of the present application, the uniformity and stability of resin extrusion in the process of achieving the target welding displacement are reduced, so the uniformity of the fiber volume fraction at the weld is poor, and local stress concentration is more likely to occur. At the same time, the molten resin at the weld quickly transfers heat to the surface of the thermoplastic composite workpiece, resulting in the melting of the composite surface and the exposure and deformation of the fibers. As a result, the joint strength of the mesh thermoplastic composite membrane is much lower than the joint strength of the fiber-reinforced thermoplastic composite membrane without a mesh structure under the same conditions.

[0135] From the above, it can be seen that in the ultrasonic welding method of the present invention, the continuous fiber reinforced thermoplastic film has a good drainage effect after uniform melting, and by controlling the fiber volume content, the joint-composite workpiece is integrated, thereby realizing spot welding and continuous welding of complex curved surface structure welding joints between thermoplastic composite materials to be welded without energy guiding ribs, and obtaining better welding joint strength and uniform weld thickness.

[0136] In the description of this specification, the description with reference to the terms "one embodiment / method", "some embodiments / methods", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments / methods or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.

[0137] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0138] Those skilled in the art should understand that the above embodiments are only for the purpose of clearly illustrating the present disclosure, and are not intended to limit the scope of the present disclosure. For those skilled in the art, other changes or modifications may be made based on the above disclosure, and these changes or modifications are still within the scope of the present disclosure.

Claims

1. An ultrasonic welding method with controllable interface structure, characterized in that: For welding between two thermoplastic composite workpieces, the ultrasonic welding method comprises: A layer of film is co-consolidated on each of the workpiece surfaces to be welded, wherein the film is made of a continuous fiber reinforced thermoplastic composite material and has a thickness of 0.05 mm to 0.5 mm; Abutting the surfaces of two workpieces to be welded having the films; Performing ultrasonic welding on the two workpieces; The two workpieces are made of the same material, and the ratio of the volume fraction of the fibers in the weld formed by the membrane to the volume fraction of the fibers in the workpieces is (0.9-1.1):

1.

2. The welding method according to claim 1, characterized in that: The matrix material in the film and the workpiece includes one of polyetheretherketone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetherimide and polyethersulfone resin; and / or, The fiber reinforcement phase in the film and the workpiece includes one of carbon fiber, basalt fiber, aramid fiber, graphite fiber, glass fiber, ceramic fiber, boron fiber, polyamide fiber, polyethylene fiber, PBO fiber, polyester fiber and natural fiber.

3. The welding method according to claim 1 or 2, characterized in that: The co-consolidation forming of a layer of film on each of the workpiece surfaces to be welded comprises applying the film on the surface of an unconsolidated prepreg layer used to form the workpiece, and forming the film by a co-consolidation process; or, The prepreg layup used to form the workpiece is consolidated into the workpiece, and the film is applied to the surface of the workpiece by a co-consolidation process.

4. The welding method according to claim 3, characterized in that: The thickness of the workpiece to which the film is applied is 0.5 mm to 3.0 mm.

5. The welding method according to claim 3, characterized in that: The matrix phase of the film is the same as the matrix phase of the workpiece.

6. The welding method according to claim 3, characterized in that: The welding surfaces of the two workpieces are planar structures or curved structures.

7. The welding method according to claim 6, characterized in that: When the welding surfaces of the two workpieces are planar structures, the pre-compression pressure of the ultrasonic welding is 100N to 500N; The amplitude of the ultrasonic welding is 20 μm to 100 μm, the frequency is 10 kHz to 50 kHz, and the welding pressure is 400 N to 2000 N; or, When the welding surfaces of the two workpieces are curved structures, the pre-compression pressure of the ultrasonic welding is 200N to 500N; The amplitude of the ultrasonic welding is 30 μm to 100 μm, the frequency is 15 kHz to 50 kHz, and the welding pressure is 500N to 2000N.

8. The welding method according to claim 7, characterized in that: When the welding surfaces of the two workpieces are planar structures, the welding speed of the ultrasonic welding is 10 mm / s to 40 mm / s; When the welding surfaces of the two workpieces are curved structures, the welding speed of the ultrasonic welding is 10 mm / s to 30 mm / s.

9. A combination, characterized in that: It comprises two workpieces, both of which are made of thermoplastic composite materials, and the two workpieces are connected together by the welding method according to any one of claims 1 to 8.

Images