An ultrasonic head for ultrasonic welding of thermoplastic composite material without energy guide ribs and a welding method thereof

Abstract

The application relates to an ultrasonic head for thermoplastic composite material ultrasonic welding without energy guide ribs and a welding method thereof, and belongs to the technical field of fiber-reinforced thermoplastic composite material welding. The application solves the technical problem that a uniform stress field distribution and a uniform temperature field distribution cannot be realized by using a traditional ultrasonic welding mechanism. The working surface of the ultrasonic head is square, a plurality of rectangular grooves with the same size are arranged at the edges of each side of the working surface, and a ring-shaped groove is arranged at the center position of the working surface. The welding method is as follows: the ultrasonic head is installed, and the plate materials to be welded are overlapped; the ultrasonic welding is carried out by starting the welding equipment. The ultrasonic head is subjected to the slotting treatment on the traditional rectangular working surface, so that the base resin can be uniformly fused in the welding process of the composite material without the energy guide ribs, the operation is simple, the cost is low, and the quality of the thermoplastic composite material ultrasonic spot welding joint is improved. The application is used for ultrasonic welding of thermoplastic composite materials.

Description

Technical Field

[0001] This invention relates to the field of welding technology for fiber-reinforced thermoplastic composite materials. Background Technology

[0002] The superior performance advantages of composite materials have enabled their continuous technological development in the aerospace industry, leading to their widespread application in aviation, automotive, shipbuilding, and electronic devices. Compared to traditional materials, their high specific strength, high specific stiffness, high corrosion resistance, and high fatigue resistance significantly extend the service life of vehicles, improve fuel efficiency, and reduce operating costs. Because the one-time molding process for large composite structural components is complex and costly, welding is typically used to assemble these large components. Compared to riveting and adhesive bonding, welding does not damage the surface of the structural component and requires no complex surface treatment, offering advantages such as speed, high productivity, low cost, and environmentally friendly production. Among these, ultrasonic welding, as a fast, efficient, and environmentally friendly welding method, is a major research direction in composite material welding technology.

[0003] Traditional ultrasonic spot welding machines for composite materials without energy-conducting ribs typically use ultrasonic heads larger than the welding area, with rectangular or circular contact surfaces with the composite material plate. This design ensures a tight bond between the ultrasonic head and the composite material plate during welding, allowing ultrasonic vibrations and sound fields to be transmitted unimpeded in a direction perpendicular to the surface to be welded, thus improving the stability of the welding process and ultrasonic energy efficiency. However, fracture tests of the composite welded joints reveal that uneven welding heat generation caused by uneven interfacial stress distribution and heat accumulation results in temperatures in the central and edge regions of the composite material joint interface being significantly higher than in the region between the center and edges during ultrasonic spot welding. This localized overheating caused by uneven heat generation significantly affects the joint fracture mode, thereby impairing the joint's mechanical properties and severely damaging its strength, failing to meet the strength requirements of industrial production.

[0004] It is evident that the existing ultrasonic spot welding mechanism cannot achieve uniform internal stress distribution and uniform temperature field distribution, which leads to uneven fusion and low connection strength of the joint. Summary of the Invention

[0005] This invention addresses the technical problem of uneven resin fusion and low joint strength caused by the inability to achieve uniform stress and temperature field distribution during traditional ultrasonic welding, which is a consequence of traditional ultrasonic welding mechanisms. It provides an ultrasonic head and welding method for ultrasonic welding of thermoplastic composite materials without conductive ribs. This invention improves the stress field distribution in composite material joints through the design of the ultrasonic head structure.

[0006] An ultrasonic head for ultrasonic welding of thermoplastic composite materials without conductive ribs is disclosed. The working surface of the ultrasonic head is square. Several rectangular grooves of the same size are formed at the edge of each side of the working surface, and the spacing between the rectangular grooves on the same edge is equal. An annular groove is formed at the center of the working surface. A concentric circular groove is formed inside the annular groove. The outer diameter of the annular groove is 20-60% of the side length of the working surface. The depths of the rectangular groove, the annular groove, and the concentric circular groove are all 0.5 mm to 2.0 mm.

[0007] Furthermore, the number and spacing of rectangular grooves on each side are equal.

[0008] Furthermore, the ultrasonic head is made of titanium alloy or high-strength tool steel.

[0009] Furthermore, the size of the ultrasonic head's working surface completely covers the area to be welded.

[0010] Furthermore, the length of each rectangular groove is 2.0~4.0mm and the width is 0.5~2.0mm.

[0011] Furthermore, the annular groove is a circular ring or a polygonal ring, and the width of the annular groove is 1.0 mm to 3.0 mm;

[0012] The diameter of the concentric circular grooves is 2~6mm.

[0013] After the ultrasonic head is grooved, the working surface is sanded with sandpaper to ensure it is flat and smooth, and then ultrasonically cleaned with organic solvents such as acetone or alcohol to remove oil and impurities from the surface.

[0014] The welding method for an ultrasonic head used in ultrasonic welding of thermoplastic composite materials without energy-conducting ribs is carried out according to the following steps:

[0015] 1. Install the ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs on the ultrasonic welding equipment and set the welding working parameters;

[0016] 2. Place the two thermoplastic composite material sheets to be welded on the welding platform in an overlapping manner;

[0017] 3. Start the ultrasonic welding equipment with the ultrasonic head installed in step one, press down the ultrasonic head and make it contact the upper thermoplastic composite material plate that was overlapped in step two, and perform ultrasonic welding.

[0018] Fourth, after the welding in step three is completed, stop the ultrasonic vibration, maintain pressure, and lift the ultrasonic head after cooling. Then remove the ultrasonic head from the ultrasonic welding equipment to complete the process.

[0019] Furthermore, the welding process parameters set in step one are as follows: welding pressure of 1.0 MPa to 3.0 MPa, welding energy of 800 J to 1600 J, and ultrasonic vibration amplitude of 60 μm to 100 μm.

[0020] Furthermore, in step two, the surfaces are cleaned with acetone before the two thermoplastic composite material sheets to be welded are overlapped.

[0021] Furthermore, in step four, the welded joint is allowed to cool naturally to room temperature.

[0022] This invention performs a grooving process on a traditional rectangular working surface ultrasonic head, which improves the stress field distribution in composite material joints and enables the matrix resin to fuse evenly during the welding process of composite materials without energy-conducting ribs. The operation is simple and the cost is low, thereby improving the quality of ultrasonic spot welded joints of thermoplastic composite materials.

[0023] This invention first involves designing a square titanium alloy ultrasonic head that can completely cover the overlapping area of ​​the parts to be connected, based on the dimensions of the parts to be connected. Then, rectangular grooves are cut at equal intervals along the edges of the square ultrasonic head. A circular groove is cut at the center of the ultrasonic head. After the grooving process, the surface of the ultrasonic head is polished and cleaned with sandpaper and acetone, and the ultrasonic head is then assembled into a composite material ultrasonic spot welding machine. After an ultrasonic sound emission test, the ultrasonic spot welding process of the resin-based composite material can be carried out.

[0024] In traditional flat-faced ultrasonic welding, ultrasonic energy and pressure are concentrated at the center and edges of the overlap area during welding. This results in a significantly higher shear strain rate and frictional heat generation rate in these areas compared to other regions, creating a "thermal ring" or "center overheating" phenomenon. This uneven temperature distribution leads to uneven melting of the matrix resin. The central or edge areas experience thermal degradation due to excessively high temperatures, while the intermediate transition area may suffer from insufficient fusion due to inadequate temperature, ultimately severely affecting the overall mechanical properties of the joint.

[0025] This invention effectively solves this problem by creating grooves on the working surface of the ultrasonic head. Its mechanism of action is as follows: 1. The grooves transform the originally continuous, flat contact surface into a discontinuous contact surface composed of multiple independent "protrusions." Under welding pressure, stress concentrates in these protrusion areas, and ultrasonic energy is primarily transferred to the welding interface through these protrusions. This changes the energy input from "surface input" to "multi-point array input," avoiding excessive energy concentration at the center and edges. 2. The annular groove in the central region significantly reduces the energy input density in that area, fundamentally suppressing overheating and thermal degradation at the center point. The rectangular grooves at the edges effectively alleviate energy accumulation in the edge areas, preventing overheating caused by edge effects. 3. Due to the more uniform temperature field, the matrix resin throughout the welding interface can achieve synchronous and sufficient melting and molecular chain diffusion, resulting in a more uniform fracture pattern and a significantly improved weldability, thereby enhancing the overall strength and reliability of the joint.

[0026] Beneficial effects of this invention:

[0027] 1. The cost of grooving ultrasonic heads is low, the manufacturing process is simple, and the materials are readily available;

[0028] 2. It can improve the stress field distribution in the spot weld joint of composite materials;

[0029] 3. It can make the welding temperature field distribution more uniform and reduce local overheating during the welding process;

[0030] 4. It can improve the uniformity of resin flow and fusion in welded joints, thereby increasing the weldability of the joints;

[0031] 5. The mechanical properties of the joint can be significantly improved compared to joints obtained by ultrasonic head welding with traditional structures;

[0032] 6. Applicable to ultrasonic welding processes of composite materials without energy-conducting ribs.

[0033] This invention is used for ultrasonic welding of thermoplastic composite materials. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the ultrasonic head described in Example 1;

[0035] Figure 2 This is a photograph of the ultrasonic head described in Example 1;

[0036] Figure 3 This is a comparison chart of the mechanical test results of the welded joints obtained in Example 1 and the control group of Example 1;

[0037] Figure 4 Comparison of the fracture surfaces of the welded joints obtained in Example 1 and the control group of Example 1;

[0038] Figure 5 This is a comparison chart of the mechanical test results of the welded joints obtained in Example 2 and the control group of Example 2. Detailed Implementation

[0039] Specific Implementation Method 1: This implementation method provides an ultrasonic head for ultrasonic welding of thermoplastic composite materials without conductive ribs. The working surface of the ultrasonic head is square. Several rectangular grooves of the same size are formed at the edge of each side of the working surface, and the spacing between the rectangular grooves on the same edge is equal. An annular groove is formed at the center of the working surface, and a concentric circular groove is formed inside the annular groove. The outer diameter of the annular groove is 20-60% of the side length of the working surface. The depths of the rectangular groove, the annular groove, and the concentric circular groove are all 0.5 mm to 2.0 mm.

[0040] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the spacing between the rectangular grooves on each side is equal. Everything else is the same as in Specific Implementation Method One.

[0041] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the ultrasonic head is made of titanium alloy or high-strength tool steel. Everything else is the same as in Specific Implementation Method One or Two.

[0042] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the size of the working surface of the ultrasonic head completely covers the area to be welded. Everything else is the same as in Specific Implementation Methods One to Three.

[0043] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the length of each rectangular groove is 2.0~4.0mm and the width is 0.5~2.0mm. Everything else is the same as in Specific Implementation Methods One to Four.

[0044] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the annular groove is a circular ring or a polygonal ring, and the width of the annular groove is 1.0 mm to 3.0 mm;

[0045] The diameter of the concentric circular groove is 2~6mm. Other aspects are the same as in any of the specific embodiments one to five.

[0046] Specific Implementation Method Seven: This implementation method provides a welding method for an ultrasonic head used in ultrasonic welding of thermoplastic composite materials without energy-conducting ribs. The method is carried out according to the following steps:

[0047] 1. Install the ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs on the ultrasonic welding equipment and set the welding working parameters;

[0048] 2. Place the two thermoplastic composite material sheets to be welded on the welding platform in an overlapping manner;

[0049] 3. Start the ultrasonic welding equipment with the ultrasonic head installed in step one, press down the ultrasonic head and make it contact the upper thermoplastic composite material plate that was overlapped in step two, and perform ultrasonic welding.

[0050] Fourth, after the welding in step three is completed, stop the ultrasonic vibration, maintain pressure, and lift the ultrasonic head after cooling. Then remove the ultrasonic head from the ultrasonic welding equipment to complete the process.

[0051] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the welding process parameters set in step one are: welding pressure of 1.0 MPa to 3.0 MPa, welding energy of 800 J to 1600 J, and ultrasonic vibration amplitude of 60 μm to 100 μm. Everything else is the same as in Specific Implementation Method Seven.

[0052] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Seven or Eight in that: in step two, the surface is cleaned with acetone before the two thermoplastic composite material sheets to be welded are overlapped. Everything else is the same as in Specific Implementation Method Seven or Eight.

[0053] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Seven to Ninety-One in that: in step four, the welded joint is allowed to cool naturally to room temperature. Everything else is the same as in Specific Implementation Methods Seven to Ninety-One.

[0054] The scope of this invention is not limited to the above-described embodiments; a combination of one or more specific embodiments can also achieve the purpose of the invention.

[0055] Example 1:

[0056] The thermoplastic composite sheets to be welded consist of two glass fiber reinforced polyphenylene sulfide (GF / PPS) composite sheets, each measuring 100 mm × 25 mm × 2 mm. The overlapping surfaces (overlap size 25 mm × 25 mm) are cleaned with acetone.

[0057] Ultrasonic head fabrication: A square ultrasonic head with a working surface of 25 mm × 25 mm was fabricated using TC4 titanium alloy. Grooving was performed on its working surface: multiple rectangular grooves were evenly distributed along the edges of each of the four sides. Each rectangular groove was 3.0 mm long, 2.0 mm wide, and 0.5 mm deep, with a groove spacing of 2.0 mm. A circular groove with an outer diameter of 12 mm, a width of 2.0 mm, and a depth of 0.5 mm was created at the center of the working surface. Inside the circular groove, a concentric circular groove with a diameter of 4 mm and a depth of 0.5 mm was created. The completed ultrasonic head is shown in the image below. Figure 2As shown.

[0058] The ultrasonic head was installed on the ultrasonic welding machine and the ultrasonic sound generation was adjusted. The welding parameters were set as follows: welding pressure 2.0 MPa, welding energy 1200 J, and vibration amplitude 80 μm.

[0059] Example 1 Control Group:

[0060] Using a conventional flat ultrasonic head with an ungrooved working surface of 25 mm × 25 mm, another set of GF / PPS composite material joints was welded as a control group using the welding process and welding parameters of Example 1.

[0061] The welded joints of Example 1 and the control group were subjected to tensile shear strength tests, and the fracture patterns after the tensile shear tests were compared and observed.

[0062] The mechanical test results are as follows: Figure 3 As shown, the joint welded using a conventional flat ultrasonic head in the control group of Example 1 had an average tensile shear strength of 10.5 MPa, while the joint welded using the slotted ultrasonic head described in this invention had an average tensile shear strength of 14.1 MPa, which is 39.0% higher than that of the conventional ultrasonic head.

[0063] Its fracture surface comparison diagram is as follows Figure 4 As shown, the fracture surface of a conventional ultrasonic head exhibits obvious characteristics of overheating and degradation in the center and edge regions, and insufficient fusion in the middle region; while the joint welded using the special ultrasonic head described in this invention shows uniform fusion at the connection interface and no obvious overheating phenomenon.

[0064] Example 2:

[0065] The difference between this embodiment and the previous one is that the thermoplastic composite material sheet to be welded is carbon fiber reinforced polyetheretherketone (CF / PEEK), and the welding parameters are set as follows: welding pressure 2.5 MPa, welding energy 1600 J, and vibration amplitude 80 μm. Everything else is the same as in Embodiment 1.

[0066] Another control group for Example 2 was set up: a conventional flat ultrasonic head with an ungrooved surface of 25 mm × 25 mm was used to weld another set of CF / PEEK composite material joints as a control group using the welding process and welding parameters of Example 2.

[0067] The tensile-shear strength results of the joint obtained in this embodiment are as follows: Figure 5 As shown in the figure, when using a traditional ultrasonic head for welding (rectangular working surface), the joint strength is 14.8 MPa. The joint strength obtained by using a slotted special ultrasonic head for welding is significantly improved to 17.9 MPa, which is 20.9% higher than that of the traditional ultrasonic head.

Claims

1. An ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs, characterized in that... The working surface of the ultrasonic head is square. Several rectangular grooves of the same size are made at the edge of each side of the working surface, and the spacing between the rectangular grooves on the same edge is equal. An annular groove is made at the center of the working surface, and a concentric circular groove is made inside the annular groove. The outer diameter of the annular groove is 20-60% of the side length of the working surface. The depth of the rectangular groove, the annular groove and the concentric circular groove are all 0.5 mm to 2.0 mm. The length of each rectangular groove is 2.0~4.0mm, and the width is 0.5~2.0mm; The annular groove is a circular or polygonal ring, and the width of the annular groove is 1.0 mm to 3.0 mm. The diameter of the concentric circular grooves is 2~6mm.

2. The ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 1, characterized in that... The spacing between the rectangular grooves on each side is equal.

3. The ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 1, characterized in that... The ultrasonic head is made of titanium alloy or high-strength tool steel.

4. The ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 1, characterized in that... The working surface of the ultrasonic head completely covers the area to be welded.

5. The welding method of the ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs as described in claim 1, characterized in that... This method is performed in the following steps:

1. Install the ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs on the ultrasonic welding equipment and set the welding working parameters; 2. Place the two thermoplastic composite material sheets to be welded on the welding platform in an overlapping manner; 3. Start the ultrasonic welding equipment with the ultrasonic head installed in step one, press down the ultrasonic head and make it contact the upper thermoplastic composite material plate that was overlapped in step two, and perform ultrasonic welding. Fourth, after the welding in step three is completed, stop the ultrasonic vibration, maintain pressure, and lift the ultrasonic head after cooling. Then remove the ultrasonic head from the ultrasonic welding equipment to complete the process.

6. The welding method of an ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 5, characterized in that... The welding process parameters set in step one are: welding pressure of 1.0 MPa to 3.0 MPa, welding energy of 800 J to 1600 J, and ultrasonic vibration amplitude of 60 μm to 100 μm.

7. The welding method of an ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 5, characterized in that... Step two involves cleaning the surface with acetone before overlapping the two thermoplastic composite material sheets to be welded.

8. The welding method of an ultrasonic head for ultrasonic welding of thermoplastic composite materials without energy-conducting ribs according to claim 5, characterized in that... Step 4: Allow the welded joint to cool naturally to room temperature.

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