CN115923145A

CN115923145A - Ultrasonic welding method with controllable interface structure and assembly

Info

Publication number: CN115923145A
Application number: CN202211558810.XA
Authority: CN
Inventors: 全东; 刘嘉鸣; 赵国群
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2022-12-06
Filing date: 2022-12-06
Publication date: 2023-04-07

Abstract

The invention provides an ultrasonic welding method with a controllable interface structure and a combination body, relates to the technical field of materials, and aims to solve the technical problems of uneven welding seams and low strength in ultrasonic welding between thermoplastic composite materials. The ultrasonic welding method comprises the following steps: co-consolidating and forming a film on the surface to be welded of each workpiece, wherein the film is made of a continuous fiber reinforced thermoplastic composite material and has the thickness of 0.05-0.5 mm; abutting the surfaces to be welded of the two workpieces with films; and carrying out ultrasonic welding on the two workpieces. The ultrasonic welding method with the controllable interface structure is used for welding two thermoplastic composite material workpieces. The welding head is particularly suitable for high-quality and high-efficiency welding of to-be-welded thermoplastic composite workpieces with complex curved surface structures.

Description

Ultrasonic welding method and assembly with controllable interface structure

Technical Field

The disclosure relates to the field of materials, in particular to an ultrasonic welding method and an ultrasonic welding assembly with controllable interface structures.

Background

The fiber reinforced thermoplastic composite material has outstanding mechanical property, heat resistance, corrosion resistance and can be recycled, so that the fiber reinforced thermoplastic composite material has wide application prospect in the fields of aerospace and the like. The thermoplastic composite material is used for preparing workpieces with complex structures and large sizes, is generally difficult to form, and needs to be connected after being processed in a split mode.

In the prior art, when the traditional ultrasonic welding technology is adopted to connect thermoplastic composite materials, the weld distribution and the strength are uneven easily caused during the ultrasonic continuous welding of complex curved surface workpieces, local unwelded areas are generated, local stress concentration is caused, and the efficiency is relatively low. And the mode of adopting the energy guiding rib needs to apply a surface micro-convex structure between the workpieces to be welded with the composite material, so that the processing technology is complex, the surface structure of the composite material is easy to damage, the melting uniformity of the energy guiding rib is poor, and the welding seam and the strength are easy to be uneven.

Disclosure of Invention

The invention aims to provide an ultrasonic welding method and an ultrasonic welding assembly with controllable interface structures, which aim to solve the technical problems of uneven welding seams and low strength of ultrasonic welding between thermoplastic composite materials.

In order to achieve the above purpose, the invention provides the following technical scheme:

the embodiment of the invention provides an ultrasonic welding method with a controllable interface structure, which is used for welding two thermoplastic composite material workpieces, and comprises the following steps:

co-consolidating and forming a film on the surface to be welded of each workpiece, wherein the film is made of a continuous fiber reinforced thermoplastic composite material, and the thickness of the film is 0.05-0.5 mm;

abutting the surfaces of the two workpieces to be welded with the films;

and carrying out ultrasonic welding on the two workpieces.

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 seam formed by the film to the volume fraction of the fibers in the workpieces is (0.9-1.1): 1.

According to at least one embodiment of the present disclosure, the membrane, the matrix material in the workpiece, comprises one of polyetheretherketone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetherimide, polyethersulfone resin; and/or the presence of a gas in the gas,

the membrane and the fiber reinforced phase in the workpiece comprise 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.

According to at least one embodiment of the present disclosure, the co-consolidation of a film on the surface to be welded of each workpiece comprises applying the film on the surface of an unconsolidated prepreg layer used for forming the workpiece, and forming by a co-consolidation process; alternatively, the first and second liquid crystal display panels may be,

consolidating a prepreg layup used to form the workpiece into the workpiece, applying the film to a surface of the workpiece by a co-consolidation process.

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

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

According to at least one embodiment of the present disclosure, the welding surfaces of the two workpieces are of a planar structure or a curved structure. Furthermore, the welding surface of the workpiece is a curved surface structure of a large-size aviation-grade thermoplastic composite material.

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

the amplitude of the ultrasonic welding is 20-100 μm, the frequency is 10-50 kHz, and the welding pressure is 400-2000N; alternatively, the first and second electrodes may be,

when the welding surfaces of the two workpieces are of curved surface structures, the pre-pressing pressure of the ultrasonic welding is 200N-500N;

the amplitude of the ultrasonic welding is 30-100 mu m, the frequency is 15-50 kHz, and the welding pressure is 500-2000N.

According to at least one embodiment of the present disclosure, when the welding surfaces of the two workpieces are in a planar structure, the welding speed of the ultrasonic welding is 10mm/s to 40mm/s;

when the welding surfaces of the two workpieces are of a curved surface structure, the welding speed of ultrasonic welding is 10-30 mm/s.

Compared with the prior art, the ultrasonic welding method has the advantages that the continuous fiber reinforced thermoplastic film is applied to the surface of the thermoplastic composite material, the thickness of the continuous fiber reinforced thermoplastic film is 0.05-0.5 mm, welding between two thermoplastic composite material workpieces can be realized under the condition without energy-guiding ribs, and meanwhile, the joint has high joint strength. In the ultrasonic welding method, the fiber volume fraction, the form and the 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 uniformly distributing the thermoplastic resin at the interface in the welding process and improving the strong structural integrity, the welding seam uniformity and the performance stability of the welding joint-clad material structure. The high-quality and high-efficiency continuous ultrasonic welding of the thermoplastic composite material workpiece to be welded with the plane and the complex curved surface structure under the condition without the energy guiding ribs can be realized.

The invention also provides a combination which comprises two workpieces, wherein the two workpieces are both made of thermoplastic composite materials, and the two workpieces are connected together by the welding method.

Compared with the prior art, the combination disclosed by the invention has the following advantages:

the advantages of the assembly and the above-mentioned ultrasonic welding method over the prior art are the same and are not described in detail here.

Drawings

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

FIG. 1 is a schematic illustration of the lay-up of prepregs and films in a co-cure molding process according to embodiments of the disclosure.

FIG. 2 is a schematic view of a workpiece structure having a film on a surface thereof according to an embodiment of the disclosure.

FIG. 3 is a schematic view of ultrasonic spot welding of a planar structure to-be-welded workpiece according to an embodiment of the disclosure.

FIG. 4 is a schematic illustration of ultrasonic continuous welding of a planar structure to-be-welded workpiece according to an embodiment of the disclosure.

FIG. 5 is a schematic view of ultrasonic continuous welding of a workpiece to be welded with a curved surface structure according to an embodiment of the disclosure.

Detailed Description

The present disclosure will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present disclosure. It should be further noted that, for the convenience of description, only the portions relevant to the present disclosure are shown in the drawings.

It should be noted that the embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Referring to fig. 1-5, an embodiment of the present invention provides an ultrasonic welding method with a controllable interface structure, which is used for welding two thermoplastic composite workpieces, and realizes welding between the thermoplastic composite workpieces by introducing a continuous fiber reinforced thermoplastic film on the surfaces of the two thermoplastic composite workpieces, and is particularly suitable for high-quality and high-efficiency ultrasonic spot welding and continuous welding of large-size aviation-grade thermoplastic composites with complex shapes. Compared with the traditional ultrasonic welding method, such as welding of the flat energy-conducting rib, the uniformity of the flow of the molten flat energy-conducting rib under the action of pressure is relatively poor, the thickness and uniformity of a welding seam are difficult to regulate and control, the structural difference between the welding seam and a composite material is large, the performance uniformity between the welding seam and the composite material is poor, and the welding seam and the composite material are difficult to apply to ultrasonic welding of workpieces with large sizes and complex structures.

It can be understood that the two workpieces are made of the same or different materials, and the weld joint between the two ultrasonically welded workpieces can be controllable by controlling the fiber volume fraction and the fiber morphology of the continuous fiber reinforced thermoplastic composite film, for example, in the weld joint formed by the continuous fiber reinforced thermoplastic composite film between the two workpieces, the ratio of the volume fraction of the fibers to the volume fraction of the fibers in the workpieces is (0.9-1.1): 1, optionally (0.95-1.07): 1, and further optionally (0.97-1.05): 1, and by actively regulating the volume fraction of the fibers in the weld joint, the integration of the workpieces and the joint is realized, the interface uniformity is effectively improved, the process window is favorably expanded in the ultrasonic continuous welding process, and the better strength of the welded joint is obtained. Illustratively, the volume fraction of fibers in the weld may be controlled to be the same as the volume fraction of fibers in the workpiece. For example, the fiber volume fraction of the workpieces is 35-55%, while the fiber volume fraction of the film is controlled at 20-30%, when the films on the two workpieces are welded, the fiber volume fraction in the weld is identical or similar to the fiber volume fraction in the workpieces. For example, the fiber volume fraction in the workpiece and the weld is 45%, 50%, 55%, or the like.

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

In some embodiments, the continuous fiber reinforced thermoplastic film is applied to the surface of the thermoplastic composite workpiece by one of a vacuum bagging process, an autoclave molding process, or a molding process.

For example, referring to FIG. 1, a continuous fiber reinforced thermoplastic composite film 2 is applied to the surface of an uncured carbon fiber reinforced thermoplastic resin layup 1, such that the continuous fiber reinforced thermoplastic composite film 2 is applied to the surface of a thermoplastic composite workpiece 3 by co-curing. The method has simple process, but the thickness of the continuous fiber reinforced thermoplastic composite film 2 is correspondingly reduced in the preparation process. Referring to fig. 2, after the co-consolidation process is completed, the thickness of the to-be-welded thermoplastic composite workpiece 3 with the continuous fiber reinforced thermoplastic composite film applied on the surface is 0.5-3.0 mm.

In another optional embodiment, the carbon fiber reinforced thermoplastic composite prepreg paving layer is firstly 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. The finally prepared film covers and overlaps the to-be-welded thermoplastic composite material workpiece with the thickness of 0.5-3.0 mm in the area to be welded.

In some embodiments, the surfaces to be welded of the two workpieces of the embodiment of the present invention may have a planar structure, or may have a large-sized curved structure with a complex shape. For welding surfaces of different shapes, welding methods are various.

For example, ultrasonic spot welding and continuous welding methods for flat thermoplastic composite workpieces include: referring to fig. 3-4, the upper workpiece 5 and the lower workpiece 6 are both flat thermoplastic composite workpieces, the supporting platform is a flat structure, and the ultrasonic horn is a flat surface.

S101, based on the co-consolidation forming method in the technical scheme, the continuous fiber reinforced thermoplastic composite film 7 with controllable fiber volume fraction is applied to the surface of the upper workpiece 5, and the continuous fiber reinforced thermoplastic composite film 8 with controllable fiber volume fraction is applied to the surface of the lower workpiece 6.

S102, fixing the upper workpiece 5 and the lower workpiece 6 on a support table 9, placing an ultrasonic welding head 10 above to-be-welded areas of the two workpieces, and applying pressure vertical to the to-be-welded areas under the condition of no energy guiding ribs, wherein the pre-pressing pressure is 100-500N.

S103, setting corresponding ultrasonic welding displacement parameters according to the fiber volume fraction and the target volume fraction of the thermoplastic composite film. Spot welding is performed under a certain amplitude and frequency, as shown in fig. 3, or continuous ultrasonic welding is performed while the ultrasonic horn 10 is moved in the welding direction at a certain speed while starting vibration, as shown in fig. 4. Wherein the amplitude is 20-100 μm, the frequency is 10-50 kHz, the welding pressure is 400-2000N, and the welding speed is 10-40 mm/s.

And S104, after the preset stop condition is reached, lifting the ultrasonic welding head, and repeating the steps to finish ultrasonic spot welding or continuous welding, so that the ratio of the volume fraction of the fibers of the welding seam to the volume fraction of the fibers of the workpiece is 0.9-1.1.

The ultrasonic spot welding and continuous welding method for the curved thermoplastic composite workpiece comprises the following steps: referring to fig. 5, 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 a cambered welding head.

S102, fixing the upper workpiece 5 and the lower workpiece 6 on a support table 9, placing an ultrasonic welding head 10 above to-be-welded areas of the two workpieces, and applying pressure vertical to the to-be-welded areas under the condition of no energy guiding ribs, wherein the pre-pressing pressure is 200-500N.

S103, setting corresponding ultrasonic welding displacement parameters according to the fiber volume fraction and the target volume fraction of the thermoplastic composite film. Continuous ultrasonic welding is performed while the ultrasonic horn 10 starts vibrating and moves in the welding direction at a constant speed under a constant amplitude and frequency, as shown in fig. 5. Wherein, the amplitude is 30 to 100 μm, the frequency is 15 to 50kHz, the welding pressure is 500 to 2000N, and the welding speed is 10 to 30mm/s.

And S104, after the preset stop condition is met, lifting the ultrasonic welding head, and repeating the steps to finish the ultrasonic continuous welding, so that the ratio of the volume fraction of the fibers of the welding seam to the volume fraction of the fibers of the workpiece is 0.9-1.1.

Several examples of ultrasonic welding methods are given below, and a representative post-weld assembly was selected for performance analysis.

The test method comprises the following steps: and testing the single lap shear strength of the obtained welded joint according to the method disclosed in GB/T33334-2016, and taking 5 groups of samples at different positions of a weld joint to obtain an average value of the shear strength.

Example 1

The embodiment provides a co-consolidation forming method of a continuous fiber reinforced thermoplastic composite film and a thermoplastic composite workpiece, which specifically comprises the following steps:

(1) A T700 continuous carbon fiber reinforced Polyetherimide (PEI) film with a thickness of 0.25mm was used, with a fiber volume fraction of 25%. The PEI film and the T700 carbon fiber reinforced PEI prepreg were precut to a uniform size of 50cm x 50 cm. Wherein the prepreg has a fiber volume fraction of 50%.

(2) And (3) coating a release agent on the surfaces of the upper template and the lower template, and paving the PEI thermoplastic composite film and the PEI prepreg by adopting a mechanical auxiliary method, so that each layer can be paved flatly. Wherein, 8 layers of PEI prepreg are paved and pasted together, and a PEI film is arranged on the uppermost layer.

(3) And preparing the workpiece to be welded by adopting an autoclave molding process. Connecting vacuum pipeline and sealing autoclave, and pumping out air and volatile. Heating to 250 deg.C at a speed of 8 deg.C/min, maintaining the temperature for 30min, heating to 300 deg.C, maintaining the temperature for 120min while applying 2.5MPa, heating to 320 deg.C, and maintaining the pressure for 60min while maintaining 2.5 MPa. And finally, cooling to room temperature at the speed of 5 ℃/min to finish the co-consolidation process, and preparing the workpiece to be welded, which has the thickness of 2mm and is provided with the PEI film on the surface.

Example 2

The embodiment provides a co-consolidation forming method of a discontinuous short fiber reinforced thermoplastic composite film and a workpiece, which specifically comprises the following steps:

(1) A Polyetherimide (PEI) film reinforced with T700 short carbon fibers having a thickness of 0.25mm, wherein the carbon fibers are T700 short fibers having a length of 0.5mm and the fiber volume fraction is 25%. The PEI film and the T700 carbon fiber reinforced PEI prepreg were precut to a uniform size of 50cm x 50 cm. Wherein the prepreg has a fiber volume fraction of 50%.

(3) And preparing the workpiece to be welded by adopting an autoclave molding process. Connecting vacuum pipeline and sealing autoclave, and pumping out air and volatile. Heating to 250 deg.C at a rate of 8 deg.C/min, maintaining the temperature for 30min, heating to 300 deg.C, maintaining the temperature for 120min while applying 2.5MPa pressure, heating to 320 deg.C, and maintaining the pressure for 60min while maintaining 2.5MPa pressure. And finally, cooling to room temperature at the speed of 5 ℃/min to finish the co-consolidation process, and preparing a workpiece to be welded, which is 2mm in thickness and is applied with a PEI film on the surface.

Example 3

The ultrasonic spot welding method provided by the embodiment specifically includes:

(1) Based on the method in the embodiment 1, the two workpieces are made of the same material and are both co-cured with a layer of continuous carbon fiber reinforced PEI film, and the surfaces of the two workpieces are degreased by using isopropanol.

(2) The upper workpiece and the lower workpiece are fixed above a plane structure supporting anvil block by a fixture, a flat contact surface ultrasonic welding head is arranged above a lap joint area of the workpieces to be welded, and 300N pre-pressing pressure perpendicular to the area to be welded is applied under the condition of no energy guiding rib.

(3) And applying welding pressure vertical to the lap joint interface 1200N under the conditions of amplitude of 86.2 mu m and frequency of 20kHz, and starting the ultrasonic spot welding process after the flat contact surface ultrasonic welding head reaches a preset trigger condition.

(4) And the ultrasonic welding head with the flat contact surface stops moving and is lifted when reaching the preset stop condition. Wherein the ratio of the volume fraction of the weld fibers to the volume fraction of the workpiece fibers is 1.0.

Example 4

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

(1) Based on the method in the embodiment 1, the two workpieces are of planar structures, are made of the same material, and are co-cured with a layer of T700 continuous carbon fiber reinforced PEI film, and the surfaces of the two workpieces are degreased by using isopropanol respectively.

(2) Referring to fig. 4, an upper workpiece and a lower workpiece are fixed above a planar structural support anvil by a fixture, a flat contact surface ultrasonic welding head is placed above a lap joint area of the workpieces to be welded, and a pre-pressing pressure which is perpendicular to the lap joint area of the workpieces to be welded is applied by a pre-pressing module 11 under the condition of no energy guiding rib by 300N.

(3) And applying welding pressure vertical to the 1200N of the lap joint interface under the conditions of the amplitude of 86.2 mu m and the frequency of 20kHz, wherein the welding speed is 30mm/s, and starting the ultrasonic continuous welding process after the ultrasonic welding head with the flat contact surface reaches the preset triggering condition.

(4) And applying pressure of 1000N to the area where welding is finished through the pressure maintaining module 12 to finish the ultrasonic continuous welding of the workpiece to be welded, and lifting the ultrasonic welding head after the planar ultrasonic welding head 10 reaches a preset stopping condition. Wherein the ratio of the volume fraction of the weld fibers to the volume fraction of the workpiece fibers is 1.0.

Example 5

(1) Based on the method in the embodiment 1, the two workpieces have curved surface structures, are made of the same material, and are both co-cured with a layer of T700 continuous carbon fiber reinforced PEI film, and the surfaces of the two workpieces are degreased by using isopropanol.

(2) Referring to fig. 5, an upper workpiece and a lower workpiece are fixed above a curved surface structure supporting anvil by a fixture, a curved contact surface ultrasonic welding head is arranged above an overlapping area of the workpieces to be welded, and a prepressing module 11 applies prepressing pressure perpendicular to the area to be welded by 300N under the condition of no energy guiding rib.

(3) And applying welding pressure vertical to 1500N of the lap joint interface under the conditions of the amplitude of 86.2 mu m and the frequency of 20kHz, wherein the welding speed is 20mm/s, and starting the ultrasonic continuous welding process after the curved contact surface ultrasonic welding head reaches the preset triggering condition.

(4) And applying pressure of 1000N to the area where welding is finished through the pressure maintaining module 12 to finish the ultrasonic continuous welding of the workpiece to be welded, and lifting the ultrasonic welding head after the curved surface ultrasonic welding head reaches a preset stop condition. Wherein the ratio of the volume fraction of the weld fibers to the volume fraction of the workpiece fibers is 1.0.

Comparative example 1

The ultrasonic welding method provided by this comparative example is different from that of example 3 in that:

after the ultrasonic spot welding is completed, the ratio of the fiber volume fraction of the welding seam to the fiber volume fraction of the workpiece is 1.2.

Comparative example 2

The ultrasonic welding method provided by the present comparative example is different from example 3 in that:

after the ultrasonic spot welding is completed, the ratio of the fiber volume fraction of the welding seam to the fiber volume fraction of the workpiece is 0.8.

Comparative example 3

in the step (1), the fiber reinforced phase is not introduced, and the PEI film with the same thickness is only used for curing on the surface of the workpiece.

Comparative example 4

in step (1), chopped carbon fibers were substituted for the continuous carbon fiber reinforcement phase in the fiber reinforced PEI film using the method of example 2, wherein the chopped carbon fibers had a length of 0.5mm. After the ultrasonic spot welding is completed, the ratio of the fiber volume fraction of the welding seam to the fiber volume fraction of the workpiece is 1.0.

Comparative example 5

in the step (1), the carbon fiber reinforced PEI membrane is provided with a plurality of rectangular meshes, the mesh size is 3mm, and the carbon fiber reinforced PEI membrane is arranged between two workpieces and is not solidified on the workpieces. The same welding seam thickness is obtained by adjusting the displacement mode of ultrasonic welding, and the ratio of the fiber volume fraction of the welding seam to the fiber volume fraction of the workpiece is 1.0.

Comparative example 6

The ultrasonic welding method provided by the comparative example is different from that of example 4 in that:

after the ultrasonic welding was completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece was 1.2.

Comparative example 7

after the ultrasonic welding was completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece was 0.8.

Comparative example 8

Comparative example 9

in step (1), chopped carbon fibers were substituted for the continuous carbon fiber reinforcement phase in the fiber reinforced PEI film using the method of example 2, wherein the chopped carbon fibers had a length of 0.5mm. After the ultrasonic welding was completed, the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the workpiece was 1.0.

Comparative example 10

Comparative example 11

The ultrasonic welding method provided by the comparative example is different from that of example 5 in that:

Comparative example 12

after the ultrasonic welding is completed, the ratio of the fiber volume fraction of the welding seam to the fiber volume fraction of the workpiece is 0.8.

Comparative example 13

The ultrasonic welding method provided by the present comparative example is different from example 5 in that:

Comparative example 14

in step (1), chopped carbon fibers were substituted for the continuous carbon fiber reinforcement phase in the fiber reinforced PEI film using the method of example 2, wherein the chopped carbon fibers had a length of 0.5mm. After the ultrasonic welding is finished, the ratio of the volume fraction of the fibers of the welding seam to the volume fraction of the fibers of the workpiece is 1.0.

Comparative example 15

in the step (1), the carbon fiber reinforced PEI membrane is provided with a plurality of rectangular net empty shapes, the size of the net hole is 3mm, and the carbon fiber reinforced PEI membrane is arranged between two workpieces and is not solidified on the workpieces. The same weld thickness is obtained by adjusting the displacement mode of ultrasonic welding, and the ratio of the volume fraction of the fibers in the weld to the volume fraction of the fibers in the workpiece is 1.0.

The shear strength of the welded joints of the examples and comparative examples is given below, see table 1.

TABLE 1 shear strength of welded joints

Referring to table 1, it can be seen from the difference between comparative example 1 and example 3 that when the fiber volume fraction of the weld is too large compared to the fiber volume fraction of the workpiece, the weld has relatively poor uniformity, locally generates higher stress concentration, and locally damages the fibers at the weld. Thereby causing a decrease in the strength of the welded joint. And when the fiber volume fraction of the weld is too small compared with the fiber volume fraction of the workpieces, as in comparative example 2, because the width of the weld between the two workpieces is relatively large, the resin at the weld is not sufficiently melted and extruded due to the low welding displacement setting, so that a large number of defects exist at the weld, and the strength of the welded joint is reduced. From the comparison between comparative examples 6 to 7 and example 4 and the difference between comparative examples 11 to 12 and example 5, it was also confirmed that the strength of the joint was reduced when the ratio of the fiber volume fraction of the weld to the fiber volume fraction of the work after completion of welding was outside the range of the examples of the present invention in the continuous welding of the planar structure and the continuous welding of the curved structure.

As can be seen from comparative examples 3, 8 and 13, when only PEI resin films are used, i.e., no fiber-reinforced phase is introduced into the thermoplastic film, the final joint strength is much lower than that of PEI films with continuous fiber-reinforced phase under the same displacement ultrasonic welding mode.

It can be seen from comparative examples 4, 9, and 14 that, when the fiber-reinforced PEI resin film is used, after the chopped fibers are used instead of the continuous fibers, a large number of air hole defects and stress concentrations are easily generated at both ends of the chopped carbon fibers during the resin extrusion process due to the irregular distribution of the chopped carbon fibers, and meanwhile, local agglomeration is easily generated compared with the regular arrangement of the continuous fibers, thereby being not beneficial to the improvement of the strength of the welded joint.

It can be seen from comparative examples 5, 10, and 15 that when the energy-conducting ribs of the net-shaped thermoplastic composite material are adopted, compared with the fiber-reinforced composite material film of the embodiment of the present application, the uniformity and stability of resin extrusion during the process of achieving the target welding displacement are reduced, and therefore the uniformity of the fiber volume fraction at the welding seam is poor, and local stress concentration is more easily generated. Meanwhile, the molten resin at the weld rapidly transfers heat to the surface of the thermoplastic composite workpiece, resulting in melting of the composite surface and exposure and deformation of the fibers. Therefore, the joint strength of the reticular thermoplastic composite film is far less than that of the fiber reinforced thermoplastic composite film without a mesh structure under the same condition.

According to the ultrasonic welding method, the continuous fiber reinforced thermoplastic film has a good drainage effect after being uniformly melted, and the connector-composite material workpiece is integrated by controlling the volume content of the fiber, so that the spot welding and the continuous welding of the welding connector with the complex curved surface structure between the thermoplastic composite materials to be welded are realized under the condition without energy guiding ribs, and the better welding connector strength and the uniform welding seam thickness are obtained.

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to be the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/aspects or examples and features of the various embodiments/aspects or examples described in this specification can be combined and combined by one skilled in the art without conflicting therewith.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to implicitly indicate the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

It will be understood by those skilled in the art that the foregoing embodiments are merely for clarity of illustration of the disclosure and are not intended to limit the scope of the disclosure. Other variations or modifications may occur to those skilled in the art, based on the foregoing disclosure, and are still within the scope of the present disclosure.

Claims

1. An ultrasonic welding method with controllable interface structure, which is used for welding between two thermoplastic composite workpieces, and comprises the following steps:

abutting the surfaces of the two workpieces to be welded with the films;

and carrying out ultrasonic welding on the two workpieces.

2. The welding method according to claim 1, wherein the two workpieces are made of the same material, and the ratio of the volume fraction of the fibers in the weld seam formed by the film to the volume fraction of the fibers in the workpieces is (0.9-1.1): 1.

3. The welding method of claim 1, wherein the membrane, the matrix material in the workpiece, comprises one of polyetheretherketone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetherimide, polyethersulfone resin; and/or the presence of a gas in the gas,

4. The welding method according to any one of claims 1 to 3, wherein co-consolidation of a film on the surface to be welded of each workpiece comprises applying the film to the surface of an unconsolidated prepreg layer forming the workpiece, and forming by a co-consolidation process; alternatively, the first and second electrodes may be,

5. The welding method according to claim 4, wherein the thickness of the workpiece to which the film is applied is 0.5mm to 3.0mm.

6. The welding method of claim 4, wherein the matrix phase of the film is the same as the matrix phase of the workpiece.

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

8. The welding method according to claim 7, wherein when the welding surfaces of the two workpieces are in a planar configuration, the pre-pressure of the ultrasonic welding is 100N to 500N;

the amplitude of the ultrasonic welding is 20-100 μm, the frequency is 10-50 kHz, and the welding pressure is 400-2000N; alternatively, the first and second liquid crystal display panels may be,

9. The welding method according to claim 8, wherein when the joining faces of the two workpieces are in a planar configuration, the welding speed of the ultrasonic welding is 10mm/s to 40mm/s;

10. A combination comprising two workpieces, both of which are of thermoplastic composite material, joined together by a welding process according to any one of claims 1 to 9.