An ultrasonic welding method, assembly

Abstract

The present invention provides an ultrasonic welding method and an assembly, relating to the technical field of materials, to solve the technical problems of poor weldability and low connection strength of thermosetting composites. The ultrasonic welding method includes: disposing a layer of thermoplastic film on the surface of the thermosetting composite to be welded, and the surface of the thermoplastic film facing away from the thermosetting composite has periodically alternating recessed portions, wherein the thickness of the thermoplastic film is 0.05 mm to 0.5 mm, and the depth of the recessed portion is 0.01 mm to 0.09 mm; abutting the surface of the other workpiece to be welded against the surface of the thermoplastic film having the recessed portions; and performing ultrasonic welding on the two workpieces. The ultrasonic welding method of the present invention is used for welding between two workpieces, wherein at least one of the workpieces is a thermosetting composite, and welding can be performed without using energy guiding ribs. Not only is the connection strength high, but the welding time is short, and thermal degradation of the thermosetting composite can be effectively avoided.

Description

Technical Field

[0001] The present disclosure relates to the field of materials, and particularly to an ultrasonic welding method and an assembly. Background Art

[0002] In the fields of aerospace, energy power, and transportation, thermosetting materials such as epoxy resins are widely used as matrix materials for most carbon fiber reinforced composite materials due to their good mechanical properties, corrosion resistance, and heat resistance. However, at present, it is difficult to fabricate large-sized and complex-shaped thermosetting composite components in one step, and two components need to be joined.

[0003] Since thermosetting composites are difficult to directly complete the connection by ultrasonic welding once they are formed, the ultrasonic welding in the prior art requires the use of energy guiding ribs, which requires a long welding time and high welding energy, and it is difficult to avoid the thermal degradation of the thermosetting matrix. Moreover, the weld seams are difficult to be evenly distributed and the weld strength is not high. Summary of the Invention

[0004] The purpose of the present invention is to provide an ultrasonic welding method and an assembly to solve the technical problems of poor weldability and low connection strength of thermosetting composites.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] An embodiment of the present invention provides an ultrasonic welding method for welding between two workpieces, wherein at least one of the workpieces is a thermosetting composite. The ultrasonic welding method includes:

[0007] Providing a layer of thermoplastic film on the surface of the thermosetting composite to be welded, the surface of the thermoplastic film facing away from the thermosetting composite has periodically alternating recesses, wherein the thickness of the thermoplastic film is 0.05 mm to 0.5 mm, and the depth of the recesses is 0.01 mm to 0.09 mm;

[0008] Bringing the surface of the other workpiece to be welded into contact with the surface of the thermoplastic film having the recesses;

[0009] Performing ultrasonic welding on the two workpieces.

[0010] According to at least one embodiment of the present disclosure, the recesses have openings on the surface of the thermoplastic film, the size of the openings is 0.5 mm to 1 mm, and the distance between adjacent two recesses is 0.1 mm to 1 mm.

[0011] According to at least one embodiment of the present disclosure, the cross-sectional shape of the recesses is one of a triangle, a pentagon, a hexagon, a circle, and an ellipse.

[0012] According to at least one embodiment of the present disclosure, the material of the thermoplastic film includes a high-performance semi-crystalline material or an amorphous material, wherein the high-performance semi-crystalline material includes one of polyether ether ketone, polyphenylene sulfide, polyarylether ketone, and polyether ketone ketone; or,

[0013] the amorphous material includes one of polyetherimide and polyethersulfone resin.

[0014] According to at least one embodiment of the present disclosure, the other workpiece is one of a thermoplastic composite or a thermosetting composite;

[0015] When the other workpiece is a thermosetting composite, a layer of the thermoplastic film is provided on each of the welding surfaces of the two thermosetting composites, and the surface of each thermoplastic film facing away from the corresponding thermosetting composite has the periodic and alternating recesses.

[0016] According to at least one embodiment of the present disclosure, providing a layer of thermoplastic film on the welding surface of the thermosetting composite, and the surface of the thermoplastic film facing away from the thermosetting composite has periodic and alternating recesses, includes:

[0017] structuring the thermoplastic film to obtain a thermoplastic film with the recesses, and combining the thermoplastic film with the recesses with the thermosetting composite through co-curing; or,

[0018] combining the thermoplastic film with the thermosetting composite through co-curing, and then structuring the surface of the thermoplastic film to obtain a thermoplastic film with the recesses.

[0019] According to at least one embodiment of the present disclosure, when the material of the thermoplastic film is a high-performance semi-crystalline material, before combining with the thermosetting composite, the bonding surface between the thermoplastic film and the thermosetting composite is subjected to one or more of ultraviolet irradiation, plasma, and laser surface treatment.

[0020] According to at least one embodiment of the present disclosure, the welding surfaces of the two workpieces are a planar structure or a curved surface structure.

[0021] According to at least one embodiment of the present disclosure, the matrix material of the thermosetting composite includes one of epoxy resin, vinyl resin, unsaturated polyester resin, phenolic resin, and polyurethane resin;

[0022] the fiber reinforcing phase of the thermosetting composite 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.

[0023] Compared with the prior art, the ultrasonic welding method of the present invention applies a thermoplastic film on the surface of the thermosetting composite, and the surface of the thermoplastic film facing away from the thermosetting composite has periodically alternating recesses. The thickness of the thermoplastic film is 0.05 mm to 0.5 mm, and the depth of the recesses is 0.01 mm to 0.09 mm. It can achieve the welding of the thermosetting composite and other composites without energy guiding ribs. At the same time, the joint has a very high joint strength. The periodically alternating recesses on the thermoplastic film can improve the fluidity of the resin at the weld, shorten the welding time, avoid the thermal degradation of the thermosetting composite, increase the continuous welding speed, and greatly improve the welding efficiency. The present invention controls the depth of the recesses to be 0.01 mm to 0.09 mm. When the depth is too large, the molten resin at the weld is at a small distance from the surface of the thermosetting composite, and the heat is transferred to the thermosetting composite, resulting in local overheating degradation and thus reducing the strength of the welding joint. When the depth of the recesses is too small, the decrease in the fluidity of the resin at the weld leads to a decrease in the weld uniformity, a decrease in the weld strength, an extension of the welding time, and a decrease in the welding efficiency.

[0024] Another object of the present invention is to further provide an assembly, including two workpieces, at least one of the workpieces being a thermosetting composite, and the two workpieces are connected together by the above welding method.

[0025] Compared with the prior art, the assembly of the present invention has the following advantages:

[0026] The assembly and the above ultrasonic welding method have the same advantages as those compared with the prior art, and will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings illustrate exemplary embodiments of the present disclosure and, together with the description thereof, are used to explain the principles of the present disclosure. These drawings are included to provide a further understanding of the present disclosure, and the drawings are included in this specification and form a part of this specification.

[0028] Figure 1 It is a schematic diagram of the layup of prepreg and structured thermoplastic film in the co-curing molding process according to an embodiment of the present disclosure.

[0029] Figure 2 It is a schematic diagram of the structure of a workpiece with a structured thermoplastic film on its surface according to an embodiment of the present disclosure.

[0030] Figure 3 is Figure 2 a schematic cross-sectional structure diagram of

[0031] Figure 4 It is a schematic diagram of the layup of prepreg and thermoplastic film in the co-curing molding process according to another embodiment of the present disclosure.

[0032] Figure 5 It is a schematic diagram of the surface thermoplastic film structuring treatment of a thermosetting composite according to an embodiment of the present disclosure.

[0033] Figure 6 It is a schematic diagram of a workpiece with a structured thermoplastic film on the surface according to another embodiment of the present disclosure.

[0034] Figure 7 is Figure 6 a schematic cross-sectional structure diagram of

[0035] Figure 8 It is a schematic diagram of the structuring of a thermoplastic film according to an embodiment of the present disclosure, where a is a triangle, b is a hexagon, and c is a circle.

[0036] Figure 9 It is a schematic diagram of ultrasonic spot welding of a workpiece to be welded with a planar structure according to an embodiment of the present disclosure.

[0037] Figure 10 It is a schematic diagram of ultrasonic continuous welding of a workpiece to be welded with a planar structure according to an embodiment of the present disclosure.

[0038] Figure 11 It is a schematic diagram of ultrasonic continuous welding of a workpiece to be welded with a curved surface structure according to an embodiment of the present disclosure. Specific Embodiments

[0039] The present disclosure will be further described in detail below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant content and do not limit the present disclosure. Additionally, it should be noted that for the convenience of description, only parts related to the present disclosure are shown in the drawings.

[0040] It should be noted that, without conflict, the embodiments in the present disclosure and the features in the embodiments can be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and embodiments. For those conditions not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0041] Please refer to Figures 1-11 As shown, an embodiment of the present invention provides an ultrasonic welding method for welding thermosetting composites. By introducing a structured thermoplastic film on the surface of the thermosetting composite, the weldability of the thermosetting composite is realized, effectively avoiding surface damage and thermal degradation of the composite, and significantly improving the fluidity and uniformity of the weld resin, and enhancing the strength of the welded joint of the thermosetting composite.

[0042] It can be understood that the welding method of the present invention can weld two thermosetting composite workpieces, and is also applicable to the welding between a thermosetting composite and a thermoplastic composite. When both workpieces are thermosetting composites, a layer of the above-mentioned structured thermoplastic film is provided on the welding surfaces of the two thermosetting composites, and the surface of each thermoplastic film facing away from the corresponding thermosetting composite has periodically alternating recesses.

[0043] The thickness of the above-mentioned surface-structured thermoplastic film is 0.05 - 0.5 mm, optionally 0.1 - 0.35 mm, and further optionally 0.15 - 0.3 mm. The material of the thermoplastic film includes high-performance semi-crystalline materials or amorphous materials. Among them, high-performance semi-crystalline materials include, but are not limited to, thermoplastic resins such as polyether ether ketone (abbreviated as PEEK), polyphenylene sulfide (abbreviated as PPS), polyaryletherketone (abbreviated as PAEK), polyether ketone ketone (abbreviated as PEKK), etc.; and amorphous materials include, but are not limited to, thermoplastic resins such as polyetherimide (abbreviated as PEI) and polyethersulfone resin (abbreviated as PES).

[0044] In some embodiments, for the amorphous thermoplastic film, there can be interdiffusion at the interface with the thermosetting composite matrix resin to form a network interface layer structure, and the interfacial bonding between the two is relatively strong, so there is no need for additional surface treatment. For the thermoplastic film of high-performance semi-crystalline materials, before co-curing and molding with the thermosetting composite, it is first necessary to undergo surface treatment processes such as ultraviolet irradiation, plasma treatment, and laser surface treatment to improve the surface activity of the thermoplastic film, thereby enhancing the interfacial bonding between it and the thermosetting composite.

[0045] In an optional embodiment, in the step of setting a thermoplastic film on the welding surface of the thermosetting composite, and the surface of the thermoplastic film facing away from the thermosetting composite has periodically alternating recesses, first, the thermoplastic film is structured, and then the thermoplastic film with recesses is combined with the thermosetting composite through co-curing. Please refer to Figures 1-3 as shown:

[0046] S101. The thermoplastic film is structured by methods such as hot pressing, rolling, or laser engraving to obtain a hollow mesh thermoplastic film 2. The structure on the surface of the thermoplastic film is periodically alternating recesses or hollow meshes.

[0047] S102. The structured thermoplastic film 2 is applied to the surface of the multi-layer thermosetting composite prepreg 1, and laying is carried out by manual, mechanical assistance, or fully automatic methods.

[0048] S103. Adopt one of the molding processes such as prepreg hot pressing molding, vacuum-assisted resin infusion molding, and resin transfer molding. After extracting the air and volatiles in the system, a welded composite workpiece 3 with a surface-applied structured thermoplastic film 2 and a thickness of 0.5 - 3.0 mm is obtained through co-curing under certain temperature and pressure conditions.

[0049] In another alternative embodiment, in the step of providing a thermoplastic film on the surface of the thermosetting composite to be welded, and the surface of the thermoplastic film facing away from the thermosetting composite has periodically alternating recesses, first, the thermoplastic film is combined with the thermosetting composite through co-curing, and then the surface of the thermoplastic film is structured to obtain a thermoplastic film with recesses. Please refer to Figures 4-7 as shown:

[0050] S101. Apply a planar thermoplastic film 4 on the surface of a multi-layer thermosetting composite prepreg 1, and perform layering by manual, mechanical assistance, or fully automatic methods.

[0051] S102. Adopt one of the molding processes such as prepreg hot pressing molding, vacuum-assisted resin infusion molding, and resin transfer molding. After extracting the air and volatiles in the system, a welded composite workpiece 3 with a surface-applied thermoplastic film 4 and a thickness of 0.5 - 3.0 mm is obtained through co-curing under certain temperature and pressure conditions.

[0052] S103. Structure the thermoplastic film on the surface of the composite to be welded by methods such as hot pressing, rolling, or laser engraving, to obtain a welded composite workpiece 3 with a thermoplastic film 6 having recesses on the surface.

[0053] The forms of the structured thermoplastic film obtained above are diverse. Exemplarily, for the cross-section of the recess or the hollow mesh hole, the cross-section is in the direction parallel to the plane of the thermoplastic film, and the shapes include triangle, pentagon, hexagon, circle, ellipse, or can also be a complex polygon. Exemplarily, please refer to Figure 8 the shapes of a - c in. The size of its cross-sectional base, or the size of the opening of the recess on the surface of the thermoplastic film is 0.5 mm - 1 mm. Here, the size can be the diameter of a circle, or the side length of a polygon, or the major axis of an ellipse, or the maximum width of a complex shape, optionally 0.65 mm - 0.95 mm, and further optionally 0.75 mm - 0.85 mm; the spacing between two adjacent recesses is 0.1 mm - 1 mm, that is, the shortest spacing between two adjacent recesses is 0.1 mm - 1 mm, optionally 0.2 mm - 0.7 mm, and further optionally 0.3 mm - 0.5 mm.

[0054] It should be noted that the above thermosetting composite materials can be any composite materials with a thermosetting resin as the matrix material. Exemplarily, the matrix materials include, but are not limited to, thermosetting resins such as epoxy resins, vinyl resins, unsaturated polyester resins, phenolic resins, and polyurethane resins. The fiber reinforcement phase in the thermosetting composite materials includes, but is not limited to, carbon fibers, graphite fibers, glass fibers, ceramic fibers, boron fibers, polyamide fibers, polyethylene fibers, PBO fibers, polyester fibers, and natural fibers, etc. The thermosetting composite materials adopt one of the molding processes such as prepreg molding, vacuum-assisted resin infusion molding, and resin transfer molding. Under different molding process conditions, a layer of thermoplastic resin film, exemplarily carbon fiber, needs to be applied on the surface of the fiber layup.

[0055] The ultrasonic welding method of the embodiment of the present invention is applicable not only to the welding surfaces of two workpieces being planar structures but also to the welding between the welding surfaces of two workpieces being curved surface structures. Exemplarily, the thermosetting composite material to be welded is fixed on the support anvil by a fixture, and the ultrasonic welding head is placed above the overlapping area of the composite material to be welded, contacting the composite material to be welded and applying a pre-pressure of 200 - 500 N. A welding pressure perpendicular to the overlapping interface and in the range of 500 - 2000 N is applied under the conditions of an amplitude of 20 - 100 μm and a frequency of 15 - 50 kHz. After reaching the preset stop condition, the ultrasonic spot welding of the area to be welded is completed, or, while the ultrasonic welding head starts to vibrate, it moves along the welding direction at a speed of 10 - 30 mm / s, and the ultrasonic continuous welding of the overlapping area to be welded is completed after reaching the preset stop condition.

[0056] In the above welding method, when the composite material to be welded is a planar structure, the contact surface between the welding head and the composite material to be welded is planar. When the composite material to be welded is a complex curved surface structure, the contact surface between the welding head and the composite material to be welded is a curved surface.

[0057] For the ultrasonic welding method of thermosetting composite materials with a planar structure welding surface, please refer to Figures 9-10 as shown, where Figure 9 is ultrasonic spot welding, Figure 10 is ultrasonic continuous welding. The specific method includes:

[0058] S201. Apply the structured thermoplastic film 6 on the surface of the upper workpiece 8 of the thermosetting composite material, and apply the structured thermoplastic film 6 on the surface of the lower workpiece 10 of the thermosetting composite material.

[0059] S202. Place the flat contact surface ultrasonic welding head 7 above the overlapping area of the composite material to be welded. Fix the lower workpiece 10 on the planar support anvil 12 by a fixture, contact the upper workpiece 8 and apply a pre-pressure of 200 - 500 N.

[0060] S203. Apply a welding pressure perpendicular to the lap interface of the area to be welded under certain amplitude and frequency conditions. Among them, the amplitude is 20 - 100 μm, the frequency is 15 - 50 kHz, and the welding pressure is 500 - 2000 N.

[0061] S204. Complete spot welding after reaching the preset stop condition ( Figure 9 ); or, while the welding head 7 starts to vibrate, move along the welding direction of the lap area at a speed of 10 - 30 mm / s, and complete ultrasonic continuous welding after reaching the preset stop condition ( Figure 10 ).

[0062] S205. After completing the ultrasonic welding of the lap area, lift the welding head 7, and repeat the above steps to complete the connection of the joints of the planar structure thermosetting composite material.

[0063] For the ultrasonic welding method of the thermosetting composite material with a curved surface welding surface, please refer to Figure 11 as shown. The specific method includes:

[0064] S201. Apply a structured thermoplastic film 6 on the surface of the upper workpiece 14 of the thermosetting composite material to be welded on the curved surface, and apply a structured thermoplastic film 6 on the surface of the lower workpiece 15 of the thermosetting composite material to be welded on the curved surface.

[0065] S202. Place the curved contact surface ultrasonic welding head 13 above the lap area of the composite material to be welded. Fix the lower workpiece 15 of the thermosetting composite material to be welded on the curved surface on the curved surface support anvil 16 with a fixture, and contact the upper workpiece 14 of the thermosetting composite material to be welded on the curved surface and apply a pre - pressing pressure of 200 - 500 N.

[0066] S203. Apply a welding pressure perpendicular to the lap interface of the area to be welded under certain amplitude and frequency conditions. Among them, the amplitude is 20 - 100 μm, the frequency is 15 - 50 kHz, and the welding pressure is 500 - 2000 N.

[0067] S204. While the curved contact surface ultrasonic welding head 13 starts to vibrate, move along the welding direction of the lap area at a speed of 10 - 30 mm / s, and complete the ultrasonic continuous welding of the lap area to be welded after reaching the preset stop condition.

[0068] S205. After completing the ultrasonic welding of the lap area of the workpiece to be welded, lift the ultrasonic welding head, and repeat the above steps to complete the connection of the joints of the thermosetting composite material with a curved surface structure.

[0069] The following gives examples of several ultrasonic welding methods, and selects representative welded assemblies for performance analysis.

[0070] Testing method: Test the single-lap shear strength of the welded joints obtained in this embodiment according to the method disclosed in GB / T 33334-2016. Take 5 groups of specimens at different positions of the weld seam to obtain the average shear strength.

[0071] Example 1

[0072] This embodiment provides a method for applying a thermoplastic film with recessed parts on the surface of a thermosetting composite workpiece, specifically including:

[0073] (1) Irradiate the surface of the polyetheretherketone thermoplastic film with high-intensity ultraviolet light. The thickness of the polyetheretherketone thermoplastic film is 0.25 mm.

[0074] (2) Cut the polyetheretherketone thermoplastic film and the T300 carbon fiber-reinforced epoxy prepreg into 50 cm × 50 cm. Use a mechanical assistance method to lay the polyetheretherketone thermoplastic film and the prepreg. Among them, the prepreg is laid in 8 layers in total, and the polyetheretherketone thermoplastic film is placed on the top layer.

[0075] (3) Use an autoclave molding process to prepare the workpiece to be welded. Connect the vacuum pipeline and lock the autoclave door to evacuate the air and volatile components in the system. Heat up to 80 °C at a rate of 1 °C / min, keep it warm for 30 min, then continue to heat up to 120 °C, apply a pressure of 0.5 MPa while keeping it warm for 120 min to complete the co-curing process. Subsequently, cool down to room temperature at a rate of 1 °C / min and take out the workpiece to obtain a workpiece to be welded with a thickness of 2 mm and a polyetheretherketone thermoplastic film applied on the surface.

[0076] (4) Perform a structuring process on the polyetheretherketone thermoplastic film on the surface of the workpiece to be welded through a hot pressing mold to obtain a workpiece to be welded with a thermoplastic film having periodically alternating quadrilateral recessed parts. Among them, the size of the quadrilateral recessed part is 1 × 1 mm, the height from the bottom surface to the top convex of the film is 0.05 mm, and the spacing is 0.2 mm.

[0077] Example 2

[0078] This embodiment provides a method for applying a thermoplastic film with hollow mesh on the surface of a thermosetting composite workpiece, specifically including:

[0079] (1) Use a polyetherimide thermoplastic film with a thickness of 0.25 mm, and no additional surface treatment is required before co-curing.

[0080] (2) Perform a structuring process on the PEI thermoplastic film through laser engraving to obtain a PEI thermoplastic film with periodically alternating hollow quadrilateral meshes. Among them, the size of the hollow mesh of the PEI thermoplastic film is 1 × 1 mm, and the mesh spacing is 0.2 mm.

[0081] (3) Cut the PEI thermoplastic film with hollow quadrilateral mesh holes and the T300 carbon fiber reinforced epoxy prepreg into 50 cm × 50 cm. Apply a release agent on the surfaces of the upper and lower templates, and use a mechanical assistance method to lay the PEI thermoplastic film with hollow quadrilateral mesh holes and the prepreg, ensuring that each layer is laid flat. Among them, a total of 8 layers of carbon fiber reinforced epoxy prepreg are laid, and the PEI thermoplastic film with hollow quadrilateral mesh holes is placed on the top layer.

[0082] (4) Use an autoclave molding process to prepare the workpiece to be welded. Connect the vacuum pipeline and lock the autoclave door to evacuate the air and volatile components in the system. Heat up at a rate of 1 °C / min to 80 °C, keep it warm for 30 min, then continue to heat up to 120 °C, and apply a pressure of 0.5 MPa while keeping it warm for 120 min to complete the co-curing process. Subsequently, cool down to room temperature at a rate of 1 °C / min and take out the workpiece to obtain a workpiece to be welded with a thickness of 2 mm and a PEI thermoplastic film with hollow quadrilateral mesh holes applied on the surface.

[0083] Example 3

[0084] The ultrasonic welding method provided in this example specifically includes:

[0085] (1) Based on the method in the above Example 1, both workpieces are carbon fiber reinforced epoxy composites, and at least on the welding areas of the two workpieces, PEEK thermoplastic films with periodically alternating quadrilateral recesses are applied.

[0086] (2) Please refer to Figure 9 As shown, fix the lower workpiece above the flat-structured support anvil with a fixture, place the flat-contact surface ultrasonic welding head above the overlapping area of the workpieces to be welded, contact the upper surface of the upper workpiece and apply a pre-pressure of 300 N.

[0087] (3) Under the conditions of an amplitude of 86.2 μm and a frequency of 20 kHz, apply a welding pressure of 1000 N perpendicular to the overlapping interface. After the flat-contact surface ultrasonic welding head reaches the preset trigger condition, start the ultrasonic spot welding process.

[0088] (4) When the flat-contact surface ultrasonic welding head reaches the preset stop condition, stop moving and lift it up.

[0089] Example 4

[0090] The ultrasonic continuous welding method provided in this example specifically includes:

[0091] (1) Based on the method in the above Example 1, both workpieces are carbon fiber reinforced epoxy composites, and at least on the welding areas of the two workpieces, PEEK thermoplastic films with periodically alternating quadrilateral recesses are applied.

[0092] (2) Please refer toFigure 10 As shown, the lower workpiece is fixed above the flat-structured support anvil by a fixture, and the flat-contact surface ultrasonic welding head is placed above the overlapping area of the workpiece to be welded, contacting the upper surface of the upper workpiece and applying a pre-pressure of 300 N.

[0093] (3) Under the conditions of an amplitude of 86.2 μm and a frequency of 20 kHz, a welding pressure of 1000 N perpendicular to the overlapping interface is applied. After the flat-contact surface ultrasonic welding head reaches the preset trigger condition, it moves along the welding direction above the overlapping area at a speed of 20 mm / s, and the ultrasonic continuous welding process is started.

[0094] (4) When the flat-contact surface ultrasonic welding head reaches the preset stop condition, it stops moving and lifts up.

[0095] Example 5

[0096] The ultrasonic continuous welding method for the curved surface structure to-be-welded surface provided in this example specifically includes:

[0097] (1) Based on the method in the above Example 1, both workpieces are carbon fiber reinforced epoxy composites, and the to-be-welded surfaces are both curved surface structures. A PEEK thermoplastic film with periodically alternating quadrilateral depressions is applied at least in the to-be-welded areas of the two workpieces.

[0098] (2) Please refer to Figure 11 As shown, the lower workpiece is fixed above the curved surface structure support anvil by a fixture, and the curved-contact surface ultrasonic welding head is placed above the overlapping area of the workpiece to be welded, contacting the upper surface of the upper workpiece and applying a pre-pressure of 400 N.

[0099] (3) Under the conditions of an amplitude of 86.2 μm and a frequency of 20 kHz, a welding pressure of 1500 N perpendicular to the overlapping interface is applied. After the curved-contact surface ultrasonic welding head reaches the preset trigger condition, it moves along the welding direction above the overlapping area at a speed of 20 mm / s, and the ultrasonic continuous welding process is started.

[0100] (4) When the curved-contact surface ultrasonic welding head reaches the preset stop condition, it stops moving and lifts up.

[0101] Comparative Example 1

[0102] The difference between the ultrasonic welding method provided in this example and that in Example 3 is:

[0103] In step (1), an unstructured PEEK thermoplastic film with a thickness of 0.25 mm is applied to the to-be-welded surfaces of the two workpieces.

[0104] Comparative Example 2

[0105] The difference between the ultrasonic welding method provided in this example and that in Example 3 is:

[0106] In step (1), a PEEK film with periodically alternating quadrilateral depressions is applied to the welding surfaces of the two workpieces, and the depth of the depressions is 0.20 mm.

[0107] Comparative Example 3

[0108] The ultrasonic welding method provided in this example is different from that in Example 3 in that:

[0109] In step (1), based on the method in Example 2, both workpieces are carbon fiber reinforced epoxy composites, and a PEEK thermoplastic film with periodically alternating hollowed-out quadrilateral meshes is applied at least in the welding areas of the two workpieces.

[0110] Comparative Example 4

[0111] The ultrasonic welding method provided in this example is different from that in Example 3 in that:

[0112] In step (1), the thickness of the PEEK thermoplastic film with periodically alternating quadrilateral depressions is 0.6 mm.

[0113] Comparative Example 5

[0114] The ultrasonic welding method provided in this example is different from that in Example 4 in that:

[0115] In step (1), an unstructured PEEK thermoplastic film is applied to the welding surfaces of the two workpieces, and the thickness of the PEEK thermoplastic film is 0.25 mm.

[0116] Comparative Example 6

[0117] The ultrasonic welding method provided in this example is different from that in Example 4 in that:

[0118] In step (1), a PEEK film with periodically alternating quadrilateral depressions is applied to the welding surfaces of the two workpieces, and the depth of the depressions is 0.2 mm.

[0119] Comparative Example 7

[0120] The ultrasonic welding method provided in this example is different from that in Example 4 in that:

[0121] In step (1), based on the method in Example 2, both workpieces are carbon fiber reinforced epoxy composites, and a PEEK thermoplastic film with periodically alternating hollowed-out quadrilateral meshes is applied at least in the welding areas of the two workpieces.

[0122] Comparative Example 8

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

[0124] In step (1), an unstructured PEEK thermoplastic film is applied to the welding surfaces of the two workpieces, and the thickness of the PEEK thermoplastic film is 0.25 mm.

[0125] Comparative Example 9

[0126] The ultrasonic welding method provided in this embodiment is different from that in Embodiment 5 in that:

[0127] In step (1), a PEEK film with periodically alternating quadrilateral recesses is applied to the welding surfaces of the two workpieces, and the depth of the recesses is 0.2 mm.

[0128] Comparative Example 10

[0129] The ultrasonic welding method provided in this embodiment is different from that in Embodiment 5 in that:

[0130] In step (1), based on the method in Embodiment 2, both workpieces are carbon fiber reinforced epoxy composites, and a PEEK thermoplastic film with periodically alternating hollow quadrilateral meshes is applied at least in the welding areas of the two workpieces.

[0131] The shear strength of the welded joints of the embodiments and comparative examples is given below. Please refer to Table 1.

[0132] Table 1 Shear strength of welded joints

[0133]

[0134]

[0135] As can be seen from the differences between Comparative Example 1 and Embodiment 3 in Table 1, when the thermoplastic film introduced on the surface of the thermosetting composite is not structured, the average shear strength is reduced compared to the thermoplastic film with recesses on the surface, and the welding time is prolonged. This may be because with a flat thermoplastic film, the reduction in the fluidity of the weld resin leads to a decrease in the weld uniformity. At the same time, the prolonged welding time will cause thermal degradation of the thermosetting composite, thereby reducing the joint strength. The differences between Comparative Example 5 and Embodiment 4, and the differences between Comparative Example 8 and Embodiment 5 show that for continuous welding with a planar structure and continuous welding with a curved surface structure, the shear strength of the welded joints using a flat-structured thermoplastic film is lower than that of the embodiments with a recessed structure in the present invention.

[0136] From the differences between Comparative Example 2 and Example 3, it can be seen that when the depth of the recessed part of the thermoplastic film, that is, the protrusion height, exceeds the depth range of the recessed part of the thermoplastic film of the present invention, the strength of ultrasonic welding is significantly reduced. This is because when the depth of the recessed part of the thermoplastic film is too deep, the bottom surface of the recessed part is at a small distance from the surface of the corresponding thermosetting composite material, and the melted resin at the weld will transfer heat to the thermosetting composite material, resulting in local overheating and degradation, thus significantly reducing the shear strength of the welded joint. At the same time, the ultrasonic welding time is also significantly increased, and the efficiency is significantly decreased, further leading to local overheating of the thermosetting composite material and reducing the shear strength of the joint. As can be seen from Table 1, the differences between Comparative Example 6 and Example 4, and the differences between Comparative Example 9 and Example 5 indicate that for continuous welding with a planar structure and continuous welding with a curved surface structure, the shear strength of the welded joint of the structured thermoplastic film with a deeper recessed part is lower than that of the recessed part structure depth adopted in the present invention. This further illustrates that the depth range of the recessed part of the thermoplastic film in this application has a better welding effect.

[0137] From the differences between Comparative Example 3 and Example 3, compared with the alternately regular recessed parts of the present invention, the thermoplastic film with a hollow mesh structure has a significantly reduced shear strength of the welded joint, while the ultrasonic welding time is significantly increased. When using the thermoplastic film with a hollow mesh structure for ultrasonic welding, the melted resin at the weld directly contacts the surface of the thermosetting composite material, and when the heat is transferred to its surface, it causes local overheating and degradation, thus reducing the shear strength of the joint. And because the depth of the hollow mesh structure is equal to the thickness of the thermoplastic film, the melted resin at the weld needs to first fill the hollow mesh structure, thus increasing the welding time, and the extension of the welding time will increase local overheating and cause thermal degradation of the thermosetting composite material. As can be seen from Table 1, the differences between Comparative Example 7 and Example 4, and the differences between Comparative Example 10 and Example 5 indicate that for continuous welding with a planar structure and continuous welding with a curved surface structure, it also shows that for the thermoplastic film with a hollow mesh structure, when the heat of the melted resin is directly transferred to the surface of the thermosetting composite material, it causes local overheating and degradation, reducing the shear strength of the joint.

[0138] From the differences between Comparative Example 4 and Example 3, when the thickness of the structured thermoplastic film is too thick, under the displacement mode condition of ultrasonic welding, the welding time is not significantly increased, but the shear strength of the welded joint is significantly reduced. This is because the too thick thermoplastic film will cause a great decrease in the mechanical properties of the welding layer of the thermoplastic film itself, and the structural integrity of the welded joint - composite material is relatively poor, ultimately resulting in a reduction in the connection strength of the welded joint.

[0139] As described above, in the ultrasonic welding method of the present invention, the surface structure of the thermoplastic film enables it to have a good drainage effect after uniform melting. While the fluidity of the thermoplastic resin between the workpieces to be welded is improved, the welding time is significantly shortened, the better process window is expanded, and the thermal degradation of the thermosetting composite can be effectively inhibited. Thus, high-efficiency spot welding and continuous welding of complex structure welding joints between the composites to be welded can be realized without energy guiding ribs, and better welding joint strength and uniform weld thickness can be obtained.

[0140] In the description of this specification, the description with reference to terms such as "one embodiment / way", "some embodiments / ways", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / way or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments / ways or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments / ways or examples described in this specification and the features of different embodiments / ways or examples.

[0141] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of this application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0142] Those skilled in the art should understand that the above embodiments are only for clearly explaining the present disclosure and not for limiting the scope of the present disclosure. For those skilled in the art, other changes or modifications can 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, characterized in that, For welding between two workpieces, where at least one of the workpieces is a thermosetting composite, the ultrasonic welding method includes: Providing a layer of thermoplastic film on the surface of the thermosetting composite to be welded, the surface of the thermoplastic film facing away from the thermosetting composite having periodically alternating recesses, wherein the thickness of the thermoplastic film is 0.25 mm and the depth of the recesses is 0.05 mm; Bringing the surface of the other workpiece to be welded into contact with the surface of the thermoplastic film having the recesses; Performing ultrasonic welding on the two workpieces; the recesses have openings on the surface of the thermoplastic film, the size of the openings being 0.5 mm to 1 mm, and the distance between adjacent two of the recesses being 0.1 mm to 1 mm; The material of the thermoplastic film includes a high-performance semi-crystalline material or an amorphous material, wherein the high-performance semi-crystalline material includes one of polyether ether ketone, polyphenylene sulfide, polyarylether ketone, and polyether ketone ketone; or, The amorphous material includes one of polyetherimide and polyethersulfone resin.

2. The welding method according to claim 1, wherein The cross-sectional shape of the recesses is one of triangle, pentagon, hexagon, circle, and ellipse.

3. The welding method according to claim 1, characterized in that, The other workpiece is one of a thermoplastic composite or a thermosetting composite; When the other workpiece is a thermosetting composite, a layer of the thermoplastic film is provided on the surfaces of both of the thermosetting composites to be welded, and the surfaces of each of the thermoplastic films facing away from the corresponding thermosetting composites have the periodically alternating recesses.

4. The welding method according to any one of claims 1 to 3, characterized in that, The step of providing a layer of thermoplastic film on the surface of the thermosetting composite to be welded, the surface of the thermoplastic film facing away from the thermosetting composite having periodically alternating recesses, includes: Structuring the thermoplastic film to obtain a thermoplastic film having the recesses, and bonding the thermoplastic film having the recesses to the thermosetting composite by co-curing; or, Bonding the thermoplastic film to the thermosetting composite by co-curing, and then structuring the surface of the thermoplastic film to obtain a thermoplastic film having the recesses.

5. The welding method according to claim 4, characterized in that, When the material of the thermoplastic film is a high-performance semi-crystalline material, before bonding to the thermosetting composite, the bonding surface between the thermoplastic film and the thermosetting composite is treated by one or more of ultraviolet irradiation, plasma, and laser surface treatment.

6. The welding method according to claim 4, wherein, The welding surfaces of the two workpieces are of a planar structure or a curved surface structure.

7. The welding method according to claim 4, characterized in that, The matrix material of the thermosetting composite includes one of epoxy resin, vinyl resin, unsaturated polyester resin, phenolic resin, and polyurethane resin; The fiber reinforcing phase of the thermosetting composite 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.

8. A combination body, characterized in that, Including two workpieces, at least one of the workpieces being a thermosetting composite, and the two workpieces being connected together by the welding method according to any one of claims 1-7.

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