A fiber reinforced composite material ultrasonic welding method and variable flexibility energy conducting rib

Abstract

The present invention belongs to the field of plastic forming and connection, and provides a fiber-reinforced composite ultrasonic welding method and variable flexibility energy conductor, including: using a thermoplastic hollow grid as a variable flexibility energy conductor for ultrasonic welding; the density of the openings of the thermoplastic hollow grid changes in a gradient from the central area to the edge area; fixing the variable flexibility energy conductor above the to-be-welded area of ​​the workpiece under the thermoplastic composite to be welded, and abutting against the welding surface of the workpiece on the thermoplastic composite to be welded; ultrasonic welding is performed on the thermoplastic composite to be welded. The present invention realizes the uniformity of heat generation, melt flow and temperature distribution at the welding interface during ultrasonic welding, and significantly improves the forming efficiency, quality and connection strength of the welding head. The present invention solves the problems of uneven heat generation and temperature distribution on the welding surface during ultrasonic welding of thermoplastic composites, which leads to local overheating decomposition or unwelded joints in the welding head.

Description

Technical Field

[0001] The invention belongs to the field of plastic molding and connection, and in particular relates to an ultrasonic welding method for fiber-reinforced composite materials and variable-flexibility energy-conducting ribs. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Thermoplastic fiber reinforced composite materials (hereinafter referred to as thermoplastic composites) have the characteristics of high fracture toughness, corrosion resistance, impact resistance and recyclability. In recent years, they have received key attention and development and application in the fields of aerospace, rail transportation, new energy vehicles and national defense. Thermoplastic composites can be connected and assembled by welding, and ultrasonic welding has the advantages of short welding time, high connection strength, green environmental protection and intelligent control, and plays an important role in the field of thermoplastic composite connection and assembly.

[0004] During the ultrasonic welding of thermoplastic composites, a pure resin structure that is the same as or compatible with the thermoplastic composite matrix resin needs to be placed in the overlap area of ​​the two workpieces, called "energy conductors". During the ultrasonic welding process, the energy conductors can concentrate most of the heat on the overlap surface of the two workpieces, and the thermoplastic resin on the overlap surface is melted by the heat, and the interface connection is achieved under a certain pressure.

[0005] For example, patent CN112026185A discloses an ultrasonic thermoplastic material welding method and energy-conducting component, and proposes that the energy-conducting ribs adopt a mesh woven structure or a mesh hollow structure, and the energy-conducting rib material is metal, thermoplastic resin or fiber-reinforced thermoplastic composite material, and emphasizes that the two structures have uniformly distributed mesh holes. However, in the process of ultrasonic welding using thin-film energy-conducting ribs and uniform grid-shaped energy-conducting ribs, there is still a significant phenomenon of uneven heat generation on the lap joint surface, with the heat generation in the center area of ​​the lap joint surface being too low and the heat generation in the edge area being too high, and even the temperature in the center area of ​​the lap joint surface being nearly 200°C higher than that in the edge area, resulting in a narrow welding process window, as well as serious problems such as overheating and decomposition of the resin in the edge area of ​​the welding surface, and unmelted resin in the center area. Summary of the invention

[0006] In view of the problems of uneven heat generation and temperature distribution on the welding surface in the current ultrasonic welding process of thermoplastic composites, which leads to local overheating decomposition or unwelded joints, the present invention provides a thermoplastic composite ultrasonic welding method, an energy guiding rib design method and its application, wherein variable flexibility energy guiding ribs are used to replace traditional film and other uniform flexibility energy guiding ribs, thereby achieving uniform heat generation, melt flow and temperature distribution on the welding interface during ultrasonic welding, and significantly improving the welding joint forming efficiency, quality and connection strength.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a method for ultrasonic welding of fiber reinforced composite materials, comprising:

[0009] Thermoplastic hollow mesh is used as flexible energy conductor for ultrasonic welding;

[0010] The density of the openings of the thermoplastic hollow grid changes gradually from the central area to the edge area;

[0011] The variable flexibility energy conductor is fixed above the to-be-welded area of ​​the lower workpiece of the thermoplastic composite material to be welded, and is abutted against the welding surface of the upper workpiece of the thermoplastic composite material to be welded;

[0012] The thermoplastic composite material to be welded is ultrasonically welded to obtain the product.

[0013] The study found that the phenomenon of uneven interface temperature during ultrasonic welding of thermoplastic composites can be explained by the interface heat generation mechanism during ultrasonic welding. Specifically, surface friction heat generation and molecular chain viscoelastic heat generation are the main heat generation mechanisms of the ultrasonic welding interface, which are calculated by formulas (1) and (2) respectively:

[0014] (1)

[0015] (2)

[0016] In the formula, Q fruc To generate heat by friction, e is the hammer correction factor, that is, the ratio of the amplitude of the workpiece thermoplastic composite material to be welded to the welding head on the thermoplastic composite material to be welded, ω is the vibration angular frequency, μ is the friction coefficient, 𝜎 yy (x) is the vertical stress on the lap joint material under ultrasonic vibration, u *(x) is the horizontal displacement of the interface, Q vis For viscoelastic heat generation, ε is the strain amplitude of the lap joint material system under ultrasonic vibration, E '' is the material loss modulus. The interface resin in the edge area of ​​the lap joint during ultrasonic weldingu *(x) is significantly higher than that in the central area, so the frictional heat generation in the edge area is higher, and the viscoelastic heat generation starts earlier, so the temperature rises faster.

[0017] In view of the above problems, the present invention proposes a design method for a variable flexibility energy guiding rib structure based on the principle of heat generation at the welding interface, so as to achieve high uniformity of heat generation and temperature distribution on the welding surface during ultrasonic welding, improve welding efficiency, and solve the technical problems currently faced by ultrasonic welding of thermoplastic composites.

[0018] The gradient change mode will affect the heat generation and temperature distribution of the welding surface. Therefore, the present invention conducts systematic research and experimental exploration on different gradient change modes and their effects. Preferably, the gradient change mode is selected from the following:

[0019] (1) The hole area remains unchanged, the hole spacing in the center area is large, and the hole spacing in the edge area is small;

[0020] (2) The hole area remains unchanged, and the hole spacing changes from large to small from the center area to the edge area;

[0021] (3) The hole spacing remains unchanged, and the single hole area changes from small to large from the center area to the edge area;

[0022] (4) The hole spacing and the single hole area change simultaneously. The hole spacing gradually decreases from the center area to the edge area, and the hole area gradually increases from the center area to the edge area of ​​the variable flexibility energy guiding rib.

[0023] Furthermore, the variable flexibility energy conductor is in the shape of a long strip, and the gradient change mode is selected from the following:

[0024] (1) The hole area remains unchanged, and the hole spacing remains unchanged in the length direction. In the width direction, the hole spacing in the center area is large, and the hole spacing in the edge area is small;

[0025] (2) The hole area remains unchanged, the hole spacing remains unchanged in the length direction, and in the width direction, the hole spacing decreases from the center area to the edge area;

[0026] (3) The hole spacing remains unchanged, the hole area remains unchanged in the length direction, and in the width direction, the hole area changes from small to large from the center area to the edge area;

[0027] (4) The hole spacing and hole area remain unchanged in the length direction. In the width direction, the hole spacing changes from large to small from the center area to the edge area, and the hole area changes from small to large from the center area to the edge area.

[0028] The hole spacing and hole area will also affect the heat generation and temperature distribution of the welding surface during ultrasonic welding. Therefore, the present invention studies the range of hole spacing and hole area. Preferably, the hole area is 0.03 mm2 -3.14 mm 2 The hole spacing is 1.0mm-2.0mm.

[0029] Ultrasonic welding conditions have a great influence on the welding strength. Only appropriate processing parameters can obtain a welding effect with a good welding surface and a large welding pull-out force. Therefore, the present invention studies the amplitude, frequency, welding pressure, pre-pressing and holding pressure, and welding speed. Preferably, the ultrasonic welding conditions are an amplitude of 20 μm-100 μm, a frequency of 10kHz-50 kHz, a welding pressure of 400 N-2000 N, a pre-pressing and holding pressure of 200 N-500 N and 300 N-1000N respectively, and a welding speed of 10 mm / s-40 mm / s.

[0030] During ultrasonic welding, the energy conductor can concentrate most of the heat on the surface of the overlapping surface of the two workpieces, the thermoplastic resin on the overlapping surface is heated and melted, and the interface connection is achieved under a certain pressure. Therefore, the material of the energy conductor is studied in the present invention. Preferably, the material of the variable flexibility energy conductor is a thermoplastic resin, and the thermoplastic resin is the same as or compatible with the matrix resin of the thermoplastic composite material to be welded.

[0031] A second aspect of the present invention provides a variable flexibility energy conductor, wherein the variable flexibility energy conductor is a thermoplastic hollow mesh, and the density of the openings of the thermoplastic hollow mesh changes gradually from the central area to the edge area;

[0032] The material of the variable flexibility energy conductor is a thermoplastic resin, and the thermoplastic resin is the same as / compatible with the matrix resin of the thermoplastic composite material to be welded.

[0033] Furthermore, the gradient change mode is selected from the following:

[0034] (1) The hole area remains unchanged, the hole spacing in the center area is large, and the hole spacing in the edge area is small;

[0035] (2) The hole area remains unchanged, and the hole spacing changes from large to small from the center area to the edge area;

[0036] (3) The hole spacing remains unchanged, and the single hole area changes from small to large from the center area to the edge area;

[0037] (4) The hole spacing and the single hole area change simultaneously. The hole spacing gradually decreases from the center area to the edge area, and the hole area gradually increases from the center area to the edge area of ​​the variable flexibility energy guiding rib.

[0038] Furthermore, the variable flexibility energy conductor is in the shape of a long strip, and the gradient change mode is selected from the following:

[0039] (1) The hole area remains unchanged, and the hole spacing remains unchanged in the length direction. In the width direction, the hole spacing in the center area is large, and the hole spacing in the edge area is small;

[0040] (2) The hole area remains unchanged, the hole spacing remains unchanged in the length direction, and in the width direction, the hole spacing decreases from the center area to the edge area;

[0041] (3) The hole spacing remains unchanged, the hole area remains unchanged in the length direction, and in the width direction, the hole area changes from small to large from the center area to the edge area;

[0042] (4) The hole spacing and hole area remain unchanged in the length direction. In the width direction, the hole spacing changes from large to small from the center area to the edge area, and the hole area changes from small to large from the center area to the edge area.

[0043] Furthermore, the hole area is 0.03 mm 2 -3.14 mm 2 The hole spacing is 1.0mm-2.0mm.

[0044] Beneficial Effects of the Invention

[0045] (1) The welding method of the present invention adopts variable flexibility energy guiding ribs to replace the uniform flexibility energy guiding ribs such as traditional thin films, thereby realizing uniform distribution of heat generation, melt flow and temperature at the welding interface during ultrasonic spot welding, especially continuous welding, and significantly improving the forming efficiency, quality and connection strength of the welding joint.

[0046] (2) The variable flexibility energy guiding ribs proposed in the present invention can effectively improve the uniformity of the structure of the welding interface and eliminate the pore defects, thereby significantly improving the connection strength of ultrasonic spot welding and continuous welding joints.

[0047] (3) The variable flexibility energy conducting ribs used in the present invention can undergo a controllable deformation process under the application of welding pressure, thereby effectively improving the viscoelastic heat generation of the welding interface, thereby shortening the welding time and improving the welding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0049] Figure 1 Schematic diagram of the typical structure of the hollow hole of the variable flexibility energy conductor; among them, A is a circular opening, B is a triangular opening, C is a semicircular opening, and D is an elliptical opening.

[0050] Figure 2 Schematic diagram of variable flexibility energy guiding ribs with varying spacing between center and edge holes for ultrasonic spot welding;

[0051] Figure 3 Schematic diagram of variable flexibility energy guiding ribs with gradually changing spacing between center and edge holes for ultrasonic spot welding;

[0052] Figure 4 A schematic diagram of a flexible energy-conducting rib with gradually changing center and edge hole sizes for ultrasonic spot welding;

[0053] Figure 5 Schematic diagram of variable flexibility energy guiding ribs with varying spacing between center and edge holes for ultrasonic continuous welding;

[0054] Figure 6 Schematic diagram of ultrasonic spot welding process of planar thermoplastic composites using variable flexibility energy directors;

[0055] Figure 7 Schematic diagram of ultrasonic continuous welding process of planar thermoplastic composites using variable flexibility energy directors;

[0056] Figure 8 Schematic diagram of the ultrasonic continuous welding process of curved thermoplastic composites using variable flexibility energy directors.

[0057] Among them, 1. the first central area; 2. the first edge area; 3. the second central area; 4. the second edge area; 5. the supporting anvil; 6. the lower workpiece of the thermoplastic composite to be welded; 7. the variable flexibility energy guiding ribs; 8. the upper workpiece of the thermoplastic composite to be welded; 9. the flat ultrasonic welding head; 10. the pre-pressing module; 11. the pressure maintaining module; 12. the curved ultrasonic welding head. DETAILED DESCRIPTION

[0058] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0059] In the following examples, the single lap shear strength of the obtained welded joints was tested according to the method disclosed in GB / T 33334-2016, and 5 groups of specimens were taken at different positions of the weld to obtain the average shear strength value.

[0060] Example 1

[0061] See also Figure 1-Figure 8As shown, the present invention provides a method for ultrasonic welding of thermoplastic composites, a method for designing variable flexibility energy conductors 7, and their applications, which realize ultrasonic welding between thermoplastic composite workpieces, and are particularly suitable for high-quality, high-efficiency ultrasonic spot welding and continuous welding of large-sized and complex-shaped aviation-grade thermoplastic composite materials. Traditional ultrasonic welding methods, such as welding with thin films or uniform hollow energy conductors, have uneven heat generation and temperature distribution at the welding interface, which leads to problems such as local overheating decomposition or unwelded joints at the welding joint, and the performance uniformity of the weld and the composite material itself is seriously compromised, limiting its engineering application. The present invention uses variable flexibility energy conductors 7 to improve the uniformity of heat generation, melt flow and temperature distribution at the welding interface, significantly improve the welding joint forming efficiency, quality and connection strength, and is more suitable for ultrasonic welding of workpieces with complex shapes.

[0062] The variable flexibility energy conductor rib 7 and the thermoplastic composite workpiece matrix resin can be high-performance resins such as polyetheretherketone (PEEK), polyetherketone (PEK), polyphenylene sulfide (PPS), low molecular weight polyaryletherketone (LM-PAEK), polyetherketoneketone (PEKK) and polyetherimide (PEI). The reinforcing phase of the thermoplastic composite workpiece is continuous fiber, the unidirectional continuous fiber arrangement direction can be the axial arrangement of the connector, and the woven continuous fiber can be common weaving methods such as plain weave, twill and satin. The reinforcing phase fiber of the thermoplastic composite workpiece can be carbon fiber, basalt fiber, aramid fiber, graphite fiber, glass fiber, ceramic fiber, boron fiber, polyamide fiber, polyethylene fiber, PBO (poly(p-phenylene benzobisoxazole)) fiber, polyester fiber and natural fiber. The thermoplastic composite workpiece is manufactured by co-consolidation process molding technology.

[0063] The surfaces to be welded of the two workpieces can be planar structures or curved surfaces with complex shapes. For example, the ultrasonic spot welding and continuous welding methods for planar thermoplastic composite workpieces include:

[0064] Step 1: Process a thermoplastic resin film with a thickness of 60 μm-400 μm into a shape Figure 1 The holes shown are circular, semicircular, elliptical, triangular, etc., with a single hole area of ​​0.03 mm 2 -3.14 mm 2 If a circular hole is used, its diameter is between 0.2 mm and 2 mm, and a thermoplastic hollow mesh is obtained as an energy conductor for ultrasonic welding. The hole making techniques that can be used include stamping, machining, hot pressing or rolling;

[0065] Step 2: The hollow variable flexibility energy guiding rib 7 for ultrasonic spot welding can be designed in the following way to achieve gradient change: (1) Keep the area of ​​the single hole unchanged, the hole spacing in the first center area 1 is large, and the hole spacing in the first edge area 2 is small, such as Figure 2As shown; (2) the area of ​​the single hole is kept unchanged, and the hole spacing changes from large to small from the first central area 1 to the first edge area 2, as shown Figure 3 As shown; (3) Keeping the hole spacing unchanged, the single hole area changes from small to large from the first central area 1 to the first edge area 2, as shown Figure 4 As shown; (4) the hole spacing and the single hole area change simultaneously, the hole spacing gradually decreases from the first central area 1 of the energy conductor rib to the first edge area 2, and the single hole area gradually increases from the first central area 1 of the variable flexibility energy conductor rib 7 to the first edge area 2;

[0066] The hollow variable flexibility energy guiding rib 7 used for ultrasonic continuous welding is usually in the shape of a long strip, and its gradient change can be achieved by: (1) keeping the area of ​​the single hole unchanged, the hole spacing in the length direction unchanged, and the hole spacing in the width direction. The second center area 3 has a large hole spacing, and the second edge area 4 has a small hole spacing, such as Figure 5 As shown; (2) the single hole area of ​​the produced hole is kept unchanged, the hole spacing in the length direction is kept unchanged, and the hole spacing in the width direction changes from large to small from the second center area 3 to the second edge area 4; (3) the hole spacing is kept unchanged, the single hole area in the length direction is kept unchanged, and the single hole area in the width direction changes from small to large from the second center area 3 to the second edge area 4; (4) the hole spacing and the single hole area are kept unchanged in the length direction, the hole spacing in the width direction changes from large to small from the second center area 3 to the second edge area 4, and the single hole area in the width direction changes from small to large from the second center area 3 to the second edge area 4.

[0067] Step 3: Fix the lower thermoplastic composite workpiece 6 to be welded above the support anvil 5, and fix the variable flexibility energy conductor 7 above the to-be-welded area of ​​the lower thermoplastic composite workpiece 6 to be welded. Abut the variable flexibility energy conductor 7 against the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and fix the upper thermoplastic composite workpiece 8 to be welded;

[0068] Step 4: Start the ultrasonic welding equipment, use the flat ultrasonic welding head 9 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite material to be welded, and perform spot welding under certain amplitude and frequency conditions, such as Figure 6 Alternatively, a certain pressure is applied to the area to be welded through the pre-pressing module 10, and the planar ultrasonic welding head 9 moves along the length direction of the area to be welded at a certain speed while vibrating, so as to perform ultrasonic continuous welding on the planar thermoplastic composite material, and use the pressure holding module 11 to assist in completing the high-quality bonding of the welding interface, as shown in FIG. Figure 7As shown. After reaching the welding stop condition, the ultrasonic equipment is turned off, and an ultrasonic spot welding joint is formed after cooling. Among them, the amplitude is 20 μm-100 μm, the frequency is 10 kHz-50 kHz, the welding pressure is 400 N-2000N, the pre-pressure and holding pressure are 200 N-500 N and 300 N-1000 N respectively, and the welding speed is 10 mm / s-40 mm / s;

[0069] For ultrasonic continuous welding of curved thermoplastic composite workpieces, such as Figure 8 Different from the above-mentioned planar ultrasonic continuous welding, the lower thermoplastic composite workpiece 6 and the upper thermoplastic composite workpiece 8 to be welded are both curved thermoplastic composite workpieces, the supporting anvil 5 is also a curved structure, and a curved ultrasonic welding head 12 is used for welding.

[0070] Embodiment 2:

[0071] This embodiment provides a method for preparing variable-flexibility energy conductors 7 for ultrasonic spot welding, which specifically includes:

[0072] (1) Use Figure 2 The structural design method of the variable flexibility energy conductor 7 is shown, and the PEI variable flexibility energy conductor 7 for ultrasonic spot welding is prepared. The hole processing shape is circular, and the diameter of the circular hole is 1.0 mm. The overall size of the variable flexibility energy conductor 7 is 12.7 mm × 25.4 mm, and the thickness of the variable flexibility energy conductor 7 is 300 μm. The variable flexibility energy conductor 7 is fixed on the processing support anvil 5.

[0073] (2) First, holes are evenly drilled in the first central region 1 (8.7 mm×21.4 mm) of the variable flexibility energy director 7 by mechanical drilling, with a hole spacing of 2.0 mm.

[0074] (3) Mechanical drilling is used to uniformly drill holes in the first edge region 2 of the variable flexibility energy guiding rib 7 with a width of 2 mm, and the hole spacing is 1.5 mm.

[0075] (4) The processed ultrasonic spot welding variable flexibility energy guiding rib 7 is removed, and is thoroughly cleaned with isopropyl alcohol and vacuum dried.

[0076] Embodiment 3:

[0077] This embodiment provides a method for preparing variable-flexibility energy conductors 7 for ultrasonic spot welding, which specifically includes:

[0078] (1) Use Figure 3The structural design method of the variable flexibility energy conductor 7 is shown, and the PEI variable flexibility energy conductor 7 for ultrasonic spot welding is prepared. The hole processing shape is circular, and the diameter of the circular hole is 1.0 mm. The overall size of the variable flexibility energy conductor 7 is 12.7 mm×25.4 mm, and the thickness of the variable flexibility energy conductor 7 is 300 μm. The variable flexibility energy conductor 7 is fixed on the processing support anvil 5.

[0079] (2) Mechanical drilling is used to uniformly drill holes in the first central region 1 (4.7 mm × 17.4 mm) of the variable flexibility energy guiding rib 7, with a hole spacing of 2.0 mm.

[0080] (3) Mechanical drilling is used to gradually drill holes in the first edge region 2 of the variable flexibility energy guiding rib 7 with a width of 3 mm, and the hole spacing gradually changes from 2.0 mm to 1.1 mm.

[0081] (4) The processed ultrasonic spot welding variable flexibility energy guiding rib 7 is removed, and is thoroughly cleaned with isopropyl alcohol and vacuum dried.

[0082] Embodiment 4:

[0083] This embodiment provides a method for preparing variable-flexibility energy conductors 7 for ultrasonic spot welding, which specifically includes:

[0084] (1) Use Figure 4 The structural design method of the variable flexibility energy conductor 7 is shown, and the PEI variable flexibility energy conductor 7 for ultrasonic spot welding is prepared. The hole processing shape is circular, and the diameter of the circular hole is 1.0 mm. The overall size of the variable flexibility energy conductor 7 is 12.7 mm × 25.4 mm, and the thickness of the variable flexibility energy conductor 7 is 300 μm. The variable flexibility energy conductor 7 is fixed on the processing support anvil 5.

[0085] (2) First, holes are evenly drilled in the first central region 1 (4.7 mm×17.4 mm) of the variable flexibility energy director 7 by mechanical drilling, with a hole spacing of 2.0 mm.

[0086] (3) Mechanical drilling is used to uniformly drill holes in the first edge region 2 of the variable flexibility energy guiding rib 7 with a width of 3 mm, and the hole size gradually changes from 1.0 mm to 1.8 mm.

[0087] (4) The processed ultrasonic spot welding variable flexibility energy guiding rib 7 is removed, and is thoroughly cleaned with isopropyl alcohol and vacuum dried.

[0088] Embodiment 5:

[0089] This embodiment provides a method for preparing variable-compliance energy conductors 7 for ultrasonic continuous welding, which specifically includes:

[0090] (1) Use Figure 5The structural design method of the variable flexibility energy conductor 7 is shown, and the PEI variable flexibility energy conductor 7 for ultrasonic continuous welding is prepared. The hole processing shape is circular, and the diameter of the circular hole is 1.0 mm. The overall size of the variable flexibility energy conductor 7 is 12.7 mm × 150 mm, and the thickness of the variable flexibility energy conductor 7 is 300 μm. The variable flexibility energy conductor 7 is fixed on the processing support anvil 5.

[0091] (2) First, holes are uniformly drilled in the second central region 3 (8.7 mm×300 mm) of the variable flexibility energy director 7 by mechanical drilling, with a hole spacing of 2.0 mm.

[0092] (3) First, mechanical drilling is used to uniformly drill holes in the second edge region 4 of the variable flexibility energy guiding rib 7 with a width of 2 mm, and the hole spacing is 1.5 mm.

[0093] (4) The processed variable-flexibility energy guiding rib 7 for ultrasonic continuous welding is removed, degreased with isopropyl alcohol and vacuum dried.

[0094] Embodiment 6:

[0095] The ultrasonic spot welding method provided in this embodiment specifically includes:

[0096] (1) Based on the method in the above-mentioned embodiment 2, a lower thermoplastic composite workpiece 6 (made of T700 carbon fiber reinforced PEI composite) with a thickness of 2.5 mm is fixed above the support anvil 5, and the PEI variable flexibility energy conductor 7 is fixed above the welding area of ​​the lower thermoplastic composite workpiece 6. The variable flexibility energy conductor 7 is abutted against the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and the upper thermoplastic composite workpiece 8 to be welded is fixed; before this, the variable flexibility energy conductor 7 and the surfaces of the two workpieces are degreased with isopropyl alcohol.

[0097] (2) Start the ultrasonic welding equipment, use the ultrasonic welding head 9 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite to be welded, perform ultrasonic spot welding under the conditions of an amplitude of 80 μm and a frequency of 20 kHz, and apply a welding pressure of 1000 N perpendicular to the lap interface. After the plane ultrasonic welding head 9 reaches the preset trigger condition, start the ultrasonic spot welding process, such as Figure 6 shown.

[0098] (3) The planar ultrasonic welding head 9 reaches the preset stop condition, stops moving and is lifted up, and an ultrasonic spot welding joint is formed after cooling. The ultrasonic welding time is 0.432 s.

[0099] The single lap shear strength of the ultrasonic spot welded joint was measured to be 39.8±0.8 MPa.

[0100] Embodiment 7:

[0101] The ultrasonic spot welding method provided in this embodiment specifically includes:

[0102] (1) Based on the method in the above-mentioned embodiment 3, a lower thermoplastic composite workpiece 6 (made of T700 carbon fiber reinforced PEI composite) with a thickness of 2.5 mm is fixed above the support anvil 5, and the PEI variable flexibility energy conductor 7 is fixed above the welding area of ​​the lower thermoplastic composite workpiece 6. The variable flexibility energy conductor 7 is abutted against the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and the upper thermoplastic composite workpiece 8 to be welded is fixed; before this, the variable flexibility energy conductor 7 and the surfaces of the two workpieces are degreased with isopropyl alcohol.

[0103] (2) Start the ultrasonic welding equipment, use the ultrasonic welding head 9 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite to be welded, perform ultrasonic spot welding under the conditions of an amplitude of 80 μm and a frequency of 20 kHz, and apply a welding pressure of 1000 N perpendicular to the lap interface. After the plane ultrasonic welding head 9 reaches the preset trigger condition, start the ultrasonic spot welding process, such as Figure 6 shown.

[0104] (3) The planar ultrasonic welding head 9 reaches the preset stop condition, stops moving and is lifted up, and an ultrasonic spot welding joint is formed after cooling. The ultrasonic welding time is 0.419 s.

[0105] The single lap shear strength of the ultrasonic spot welded joint was measured to be 40.1±0.9 MPa.

[0106] Embodiment 8:

[0107] The ultrasonic spot welding method provided in this embodiment specifically includes:

[0108] (1) Based on the method in the above-mentioned embodiment 4, a lower thermoplastic composite workpiece 6 (made of T700 carbon fiber reinforced PEI composite) with a thickness of 2.5 mm is fixed above the support anvil 5, and a PEI variable flexibility energy conductor 7 with a variable flexibility structure is fixed above the welding area of ​​the lower thermoplastic composite workpiece 6. The variable flexibility energy conductor 7 is abutted against the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and the upper thermoplastic composite workpiece 8 to be welded is fixed; before this, the variable flexibility energy conductor 7 and the surfaces of the two workpieces are degreased with isopropyl alcohol.

[0109] (2) Start the ultrasonic welding equipment, use the ultrasonic welding head 9 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite to be welded, perform ultrasonic spot welding under the conditions of an amplitude of 80 μm and a frequency of 20 kHz, and apply a welding pressure of 1000 N perpendicular to the lap interface. After the plane ultrasonic welding head 9 reaches the preset trigger condition, start the ultrasonic spot welding process, such as Figure 6 shown.

[0110] (3) The planar ultrasonic welding head 9 reaches the preset stop condition, stops moving and is lifted up, and an ultrasonic spot welding joint is formed after cooling. The ultrasonic welding time is 0.421 s.

[0111] The single lap shear strength of the ultrasonic spot welded joint was measured to be 40.3±1.2 MPa.

[0112] Embodiment 9:

[0113] The ultrasonic continuous welding method provided in this embodiment specifically includes:

[0114] (1) Based on the method in the above-mentioned embodiment 5, a lower thermoplastic composite workpiece 6 (made of T700 carbon fiber reinforced PEI composite) with a thickness of 2.5 mm is fixed above the support anvil 5, and a PEI variable flexibility energy conductor 7 with a variable flexibility structure is fixed above the welding area of ​​the lower thermoplastic composite workpiece 6. The variable flexibility energy conductor 7 is brought into contact with the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and the upper thermoplastic composite workpiece 8 to be welded is fixed; before this, the variable flexibility energy conductor 7 and the surfaces of the two workpieces are degreased with isopropyl alcohol.

[0115] (2) Start the ultrasonic welding equipment, use the pre-pressing module 10 to apply a pressure of 300 N on the area to be welded, and after the planar ultrasonic welding head 9 reaches the preset trigger condition, use the planar ultrasonic welding head 9 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite to be welded, and perform ultrasonic continuous welding under the conditions of an amplitude of 86 μm and a frequency of 20 kHz. At the same time, move along the length direction of the area to be welded at a welding speed of 20 mm / s, apply a welding pressure of 800 N perpendicular to the lap interface, and use the pressure holding module 11 to assist with a pressure of 500 N to complete the high-quality bonding of the welding interface, as shown in FIG. Figure 7 shown.

[0116] (3) The planar ultrasonic welding head 9 reaches a preset stop condition, stops moving and is lifted up, and forms an ultrasonic continuous welding head after cooling.

[0117] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 36.2±2.7 MPa.

[0118] Embodiment 10:

[0119] The ultrasonic continuous welding method provided in this embodiment specifically includes:

[0120] (1) Based on the method in the above-mentioned embodiment 5, a lower thermoplastic composite workpiece 6 (made of T700 carbon fiber reinforced PEI composite) with a thickness of 2.5 mm is fixed above the support anvil 5, and a PEI variable flexibility energy conductor 7 with a variable flexibility structure is fixed above the to-be-welded area of ​​the lower thermoplastic composite workpiece 6 with a curved surface structure. The variable flexibility energy conductor 7 is brought into contact with the welding surface of the upper thermoplastic composite workpiece 8 to be welded, and the upper thermoplastic composite workpiece 8 to be welded is fixed; before this, the variable flexibility energy conductor 7 and the surfaces of the two workpieces are degreased using isopropyl alcohol.

[0121] (2) Start the ultrasonic welding equipment, use the pre-pressing module 10 to apply a pressure of 250 N on the area to be welded, and after the curved ultrasonic welding head 12 reaches the preset trigger condition, use the curved ultrasonic welding head 12 to apply high-frequency ultrasonic vibration and downward pressure to the workpiece 8 on the thermoplastic composite to be welded, and perform ultrasonic continuous welding under the conditions of an amplitude of 86 μm and a frequency of 20 kHz. At the same time, move along the length direction of the area to be welded at a welding speed of 15 mm / s, apply a welding pressure of 600 N perpendicular to the lap interface, and use the pressure holding module 11 to assist in completing the high-quality bonding of the continuous welding interface with a pressure of 400 N. Figure 8 shown.

[0122] (3) The curved surface ultrasonic welding head 12 reaches a preset stop condition, stops moving and is lifted up, and forms an ultrasonic continuous welding head after cooling.

[0123] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 35.3±2.2 MPa.

[0124] Table 1 Single lap shear strength of ultrasonic welded joints

[0125]

[0126] Comparative Example 1:

[0127] Comparative Example 1 corresponds to Examples 6-8, and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity at the ultrasonic spot welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic spot welding method provided in this comparative example is different from that of Examples 6-8 in that:

[0128] The T700 carbon fiber reinforced PEI composite workpiece was ultrasonically spot welded using a 300 μm thick planar film PEI energy conductor. The ultrasonic welding time was 0.698 s.

[0129] The single lap shear strength of the ultrasonic spot welded joint was measured to be 35.1±2.1 MPa.

[0130] The test results show that compared with traditional film energy guiding ribs, the use of variable flexibility energy guiding ribs 7 can effectively improve the interface heat generation efficiency, temperature and structure uniformity during ultrasonic spot welding, effectively eliminate defects in welds and thermoplastic composites, and improve the quality and strength of welded joints.

[0131] Comparative Example 2:

[0132] Comparative Example 2 corresponds to Examples 6-8, and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity at the ultrasonic spot welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic spot welding method provided in this comparative example is different from that of Examples 6-8 in that:

[0133] The T700 carbon fiber reinforced PEI composite workpiece was ultrasonically spot welded using a 300 μm thick constant flexibility PEI energy conductor. The energy conductor was structured in the welding area using the perforated structure of the first central area 1. The ultrasonic welding time was 0.502 s.

[0134] The single lap shear strength of the ultrasonic spot welded joint was measured to be 37.1±1.4 MPa.

[0135] The test results show that compared with the uniformly perforated constant-flexibility energy guiding ribs, the variable-flexibility energy guiding ribs 7 with small flexibility in the center area and large flexibility in the edge area can more effectively improve the interface heat generation efficiency, temperature and structural uniformity during ultrasonic spot welding, effectively eliminate defects in the weld and the composite material, and improve the quality and strength of the welded joint.

[0136] Comparative Example 3:

[0137] Comparative Example 3 corresponds to Example 9 and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity of the ultrasonic continuous welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic continuous welding method provided in this comparative example is different from that in Example 9 in that:

[0138] The T700 carbon fiber reinforced PEI composite workpiece was ultrasonically continuously welded using a 300 μm thick planar film PEI energy conductor.

[0139] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 33.0±2.4 MPa.

[0140] The test results show that compared with traditional film energy guiding ribs, the use of variable flexibility energy guiding ribs 7 can effectively improve the interface heat generation efficiency, temperature and structural uniformity during ultrasonic continuous welding, effectively eliminate defects in welds and thermoplastic composites, and improve the quality and strength of welded joints.

[0141] Comparative Example 4:

[0142] Comparative Example 4 corresponds to Example 9 and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity of the ultrasonic continuous welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic continuous welding method provided in this comparative example is different from that in Example 9 in that:

[0143] The T700 carbon fiber reinforced PEI composite workpiece was ultrasonically continuously welded using constant flexibility PEI energy conductors with a thickness of 300 μm. In the welding area, the energy conductors were structured using the perforated structure of the second central area 3.

[0144] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 35.0±1.7 MPa.

[0145] The test results show that compared with the uniformly perforated constant-flexibility energy guiding ribs, the variable-flexibility energy guiding ribs 7 with small flexibility in the center area and large flexibility in the edge area can more effectively improve the interface heat generation efficiency, temperature and structural uniformity during ultrasonic continuous welding, effectively eliminate defects in the weld and the inside of the thermoplastic composite, and improve the quality and strength of the welded joint.

[0146] Comparative Example 5:

[0147] Comparative Example 5 corresponds to Example 10, and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity of the ultrasonic continuous welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic continuous welding method provided in this comparative example is different from that in Example 10 in that:

[0148] The curved T700 carbon fiber reinforced PEI composite workpiece was ultrasonically continuously welded using a 300 μm thick flat film PEI energy guiding rib.

[0149] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 29.7±2.7 MPa.

[0150] The test results show that compared with traditional film energy guiding ribs, the use of variable flexibility energy guiding ribs 7 can effectively improve the interface heat generation efficiency, temperature and structure uniformity during ultrasonic continuous welding of curved thermoplastic composites, effectively eliminate defects in welds and thermoplastic composites, and improve the quality and strength of welded joints.

[0151] Comparative Example 6:

[0152] Comparative Example 6 corresponds to Example 10, and is used to compare the use of variable flexibility energy conductors 7 in the present invention to achieve the improvement of heat generation, melt flow and temperature distribution uniformity of the ultrasonic continuous welding interface, thereby significantly improving the welding head forming efficiency, quality and connection strength. The ultrasonic continuous welding method provided in this comparative example is different from that in Example 10 in that:

[0153] The curved T700 carbon fiber reinforced PEI composite workpiece was ultrasonically welded using 300 μm thick constant flexibility PEI energy conductors. The energy conductors in the welding area were structured with a perforated structure in the center area.

[0154] The single lap shear strength of the ultrasonic continuous welded joint was measured to be 32.6±2.2 MPa.

[0155] The test results show that compared with the uniformly perforated constant-flexibility energy guiding ribs, the variable-flexibility energy guiding ribs 7 with small flexibility in the center area and large flexibility in the edge area can more effectively improve the interface heat generation efficiency, temperature and structural uniformity during the ultrasonic continuous welding of curved thermoplastic composites, effectively eliminate the defects in the weld and the inside of the thermoplastic composite, and improve the quality and strength of the welded joint.

[0156] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fiber reinforced composite material ultrasonic welding method, characterized in that: include: Thermoplastic hollow mesh is used as flexible energy conductor for ultrasonic welding; The density of the thermoplastic hollow grid openings changes gradually from the central area to the edge area; The variable flexibility energy conductor is fixed above the to-be-welded area of ​​the lower workpiece of the thermoplastic composite material to be welded, and is abutted against the welding surface of the upper workpiece of the thermoplastic composite material to be welded; Ultrasonic welding is performed on the thermoplastic composite material to be welded, and the result is obtained; The gradient change mode is selected from the following: (1) The hole area remains unchanged, the hole spacing in the center area is large, and the hole spacing in the edge area is small; (2) The hole area remains unchanged, and the hole spacing changes from large to small from the center area to the edge area; (3) The hole spacing remains unchanged, and the single hole area changes from small to large from the center area to the edge area; (4) The hole spacing and the single hole area change simultaneously. The hole spacing gradually decreases from the center area to the edge area, and the hole area gradually increases from the center area to the edge area of ​​the flexible energy director. The variable flexibility energy conductor is in the shape of a long strip, and the gradient change mode is selected from the following: (1) The hole area remains unchanged, and the hole spacing remains unchanged in the length direction. In the width direction, the hole spacing in the center area is large, and the hole spacing in the edge area is small; (2) The hole area remains unchanged, the hole spacing remains unchanged in the length direction, and in the width direction, the hole spacing decreases from the center area to the edge area; (3) The hole spacing remains unchanged, the hole area remains unchanged in the length direction, and in the width direction, the hole area changes from small to large from the center area to the edge area; (4) The hole spacing and hole area remain unchanged in the length direction. In the width direction, the hole spacing changes from large to small from the center area to the edge area, and the hole area changes from small to large from the center area to the edge area.

2. The fiber-reinforced composite material ultrasonic welding method according to claim 1, characterized in that: The hole area is 0.03 mm 2 -3.14 mm 2 The hole spacing is 1.0 mm-2.0 mm.

3. The method for ultrasonic welding of fiber-reinforced composite materials according to claim 1, characterized in that: The ultrasonic welding conditions are as follows: an amplitude of 20 μm-100 μm, a frequency of 10 kHz-50 kHz, a welding pressure of 400 N-2000 N, a pre-pressure and a holding pressure of 200 N-500 N and 300 N-1000 N respectively, and a welding speed of 10 mm / s-40 mm / s.

4. The method for ultrasonic welding of fiber-reinforced composite materials according to claim 1, characterized in that: The material of the variable flexibility energy conductor is a thermoplastic resin, and the thermoplastic resin is the same as / compatible with the matrix resin of the thermoplastic composite material to be welded.

5. A variable flexibility energy conductor, characterized in that: The variable flexibility energy conducting ribs are thermoplastic hollow meshes, and the density of the openings of the thermoplastic hollow meshes changes gradually from the central area to the edge area; The material of the variable flexibility energy conductor is a thermoplastic resin, and the thermoplastic resin is the same as / compatible with the matrix resin of the thermoplastic composite material to be welded; The gradient change mode is selected from the following: (1) The hole area remains unchanged, the hole spacing in the center area is large, and the hole spacing in the edge area is small; (2) The hole area remains unchanged, and the hole spacing changes from large to small from the center area to the edge area; (3) The hole spacing remains unchanged, and the single hole area changes from small to large from the center area to the edge area; (4) The hole spacing and the single hole area change simultaneously. The hole spacing gradually decreases from the center area to the edge area, and the hole area gradually increases from the center area to the edge area of ​​the flexible energy director. The variable flexibility energy conductor is in the shape of a long strip, and the gradient change mode is selected from the following: (1) The hole area remains unchanged, and the hole spacing remains unchanged in the length direction. In the width direction, the hole spacing in the center area is large, and the hole spacing in the edge area is small; (2) The hole area remains unchanged, the hole spacing remains unchanged in the length direction, and in the width direction, the hole spacing decreases from the center area to the edge area; (3) The hole spacing remains unchanged, the hole area remains unchanged in the length direction, and in the width direction, the hole area changes from small to large from the center area to the edge area; (4) The hole spacing and hole area remain unchanged in the length direction. In the width direction, the hole spacing changes from large to small from the center area to the edge area, and the hole area changes from small to large from the center area to the edge area.

6. The variable flexibility energy conductor according to claim 5, characterized in that: The hole area is 0.03 mm 2 -3.14 mm 2 The hole spacing is 1.0 mm-2.0 mm.

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