Ultrasonic welding quality inspection method for continuous carbon fiber reinforced thermoplastic composites

Abstract

The present invention discloses a method for ultrasonic welding quality testing of continuous carbon fiber reinforced thermoplastic composite materials. The method involves surface treating the upper and lower bonding pairs that have undergone ultrasonic direct welding, then fixing the electrodes. A signal processing terminal collects and analyzes the signals obtained from the electrodes, and compares them with typical resistance or voltage values ​​under different welding conditions to achieve ultrasonic welding quality testing. This method utilizes the inherent properties of the material to test the ultrasonic welding effect without destroying the original structure of the workpiece after welding, with low cost, convenient operation, rapidity, and accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic welding quality detection, and particularly relates to a method for detecting the ultrasonic welding quality of a continuous carbon fiber reinforced thermoplastic composite material. Background Art

[0002] Ultrasonic welding, as a highly efficient fusion joining technology, offers advantages over traditional joining processes, including extremely high production efficiency, extremely short cycle times, superior weld strength, high quality, aesthetically pleasing joints, the absence of workpiece surface pretreatment, the ability to weld dissimilar materials, ease of automated production and control, and the elimination of the need for the introduction of foreign materials such as metal mesh or metal particles at the interface. This makes it suitable for welding various thermoplastic composites. However, the areas of fiber-reinforced composites subjected to ultrasonic welding often exhibit complex mechanical and damage behaviors. To ensure the safety and reliability of the joint, a suitable weld quality testing method is urgently needed to determine whether the weld quality meets the expected standards after completion.

[0003] Existing welding quality inspection methods all have their own limitations. Performing a tensile test on a shear tensile testing machine is the most direct way to obtain the quality of the joint welding, but the tensile test will damage the weldment and cannot be used for non-destructive evaluation. Others have also adopted the method of studying welding parameters and their influence, tracking the changes in welding parameters during the welding process to infer the quality of the welding. This method is empirical and is not accurate enough for ultrasonic welding with poor repeatability and large differences between different workpieces under the same welding parameters. The idea is also relatively limited. Although technologies such as ultrasonic scanning, acoustic emission and X-ray scanning can provide detailed information on the welding interface, they are often expensive and require complex instruments. They are not suitable for large-scale online quality inspection. At present, there is a lack of a fast, direct, low-cost non-destructive quality identification method for the welding quality of welded joints. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a method for detecting the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials, which is used to solve the technical problem that the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials cannot be non-destructively detected.

[0005] The present invention adopts the following technical solutions:

[0006] A method for detecting the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials comprises the following steps:

[0007] S1. Surface treatment is performed on the upper and lower bonding couples that have been subjected to ultrasonic direct welding, and then the electrodes are fixed;

[0008] S2. Use the signal processing end to collect and analyze the resistance signal measured by the electrode, and compare it with the typical resistance size under different welding conditions to achieve ultrasonic welding quality detection.

[0009] Specifically, in step S1, the surface treatment is as follows:

[0010] Clean up excess extrusion around the weld interface of the upper and lower joint couples.

[0011] Furthermore, conductive paint is applied to the interfaces of the upper bonding couple and the lower bonding couple after cleaning excess extrusion products, and then electrodes are connected respectively.

[0012] Furthermore, the electrodes are fixedly connected to the upper bonding couple and the lower bonding couple respectively by mechanical fastening.

[0013] Specifically, in step S1, the electrodes are placed symmetrically, respectively at one end of the upper bonding pair and the lower bonding pair.

[0014] Furthermore, the electrode is copper foil with a thickness of 0.05 to 0.15 mm.

[0015] Specifically, in step S1, the matrices of the upper bonding pair and the lower bonding pair are made of continuous carbon fiber reinforced thermoplastic composite material.

[0016] Furthermore, the volume fraction of the carbon fibers in the continuous carbon fiber reinforced thermoplastic composite material accounts for 20% to 60% of the total volume of the fiber reinforced composite material.

[0017] Furthermore, the continuous carbon fiber reinforced thermoplastic composite material includes polyethylene, polyetheretherketone, polyphenylene sulfide and / or polyethylene terephthalate.

[0018] Specifically, in step S2, the actual measured signal is compared with the curve of interface resistance and welding condition to determine whether the welding is normal; the actual measured signal is compared with the curve of interface resistance and maximum load bearing to determine the load-bearing capacity of the weld joint.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] The present invention discloses a method for detecting the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials. The method utilizes the self-inductance of carbon fiber reinforced materials and takes into account the influence and differences of the microstructure of the welding interface. Even if there are tiny defects in the welding interface caused by accidental factors, they will be displayed in the resistance or voltage of the conductive network. The method has high sensitivity and is sensitive to differences in welding quality. By evaluating the resistance or voltage of the conductive network formed by the contact of the carbon fibers of the two bonding pairs during the welding process, the welding quality is evaluated and the optimization of welding parameters is guided. This is a trend in current intelligent manufacturing.

[0021] Furthermore, after welding, the heat and pressure of the weld cause the thermoplastic matrix to melt and extrude, shifting some of the fibers. Removing excess polymer exposes the fibers encased within, increasing the contact area between the sensor head and the conductive network when monitoring resistance or voltage signals.

[0022] Furthermore, conductive paint is provided between the upper bonding pair and the lower bonding pair to maximize the electrical contact between the welding interface and the copper foil and increase the stability of the conductive network.

[0023] Furthermore, the combination of the electrode and the conductive paint is replaced by a conductive glue with stronger adhesion. After cleaning the excess polymer, a layer of conductive glue can be directly applied to the cleaned interface, and the wire can be inserted into the glue layer before it solidifies. After the glue solidifies, the connection of the monitoring circuit is completed.

[0024] Furthermore, the electrodes are symmetrically arranged along the length direction of the bonding pair. This arrangement can fully reflect the characteristics of the conductive network formed by ultrasonic welding and improve monitoring accuracy.

[0025] Furthermore, copper foil is selected as the electrode, mainly taking advantage of the excellent conductivity and ductility of copper and its economical and affordable characteristics; taking into account the reliability and ductility of copper foil, the thickness of the electrode is controlled between 0.05 and 0.15 mm.

[0026] Furthermore, carbon fiber has excellent electrical conductivity, and the core of the present invention is to use the conductive network naturally formed after welding to perform interface monitoring; at the same time, carbon fiber reinforced thermoplastic composite materials have the advantages of light weight, high modulus, high strength, designability, high temperature resistance, excellent thermal stability, fatigue resistance, corrosion resistance, good processability, etc., and are widely used.

[0027] Furthermore, the volume fraction of the matrix fibers of the continuous carbon fiber reinforced thermoplastic composite material is between 20% and 60%. Too low or too high a fiber volume fraction will lead to a decrease in the performance of the bonding couple.

[0028] Furthermore, the continuous carbon fiber reinforced thermoplastic composite matrix includes common thermoplastic materials such as polyethylene, polyetheretherketone, polyphenylene sulfide and / or polyethylene terephthalate.

[0029] Furthermore, by comparing the actual measured signal with the curve of interface resistance and welding condition, it can be determined whether the welding is normal; by comparing the actual measured signal with the curve of interface resistance and maximum load bearing, the load-bearing capacity of the welding joint can be obtained.

[0030] In summary, the present invention utilizes the properties of the material itself to detect the ultrasonic welding effect without destroying the original structure of the workpiece after welding, with low cost, convenient operation, rapidity and accuracy.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the interface resistance or voltage monitoring principle of the present invention;

[0033] Figure 2 Schematic diagram of resistance distribution measured under different welding conditions;

[0034] Figure 3 Schematic diagram of resistance and maximum load under different welding conditions;

[0035] Among them: 11. Upper bonding pair; 12. Lower bonding pair; 13. Conductive network; 14. Electrode; 15. Signal processing end. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be understood that the terms "center," "longitudinal," "lateral," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," "one side," "one end," and "one side" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, in the description of the present invention, unless otherwise specified, "a plurality" means two or more.

[0038] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0039] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0040] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0041] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0042] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0043] The present invention provides a method for ultrasonic welding quality detection of continuous carbon fiber reinforced thermoplastic composite materials. After ultrasonic welding of a bonding couple, electrodes are laid at both ends of the bonding couple and connected to a signal processing end. The electrodes are in contact with a conductive network formed by the melt extrusion of a resin matrix at the interface and the mutual contact of carbon fibers during the ultrasonic welding process. This conductive network can reflect the fusion status of the welding interface, and its characteristics can be captured by the electrodes in the form of resistance or voltage and transmitted to the signal processing end for analysis. Normal welding is indicated when the resistance is less than a standard value, thereby realizing ultrasonic welding quality detection and guiding the optimization of welding parameters.

[0044] See also Figure 1 , the theoretical basis of the present invention is as follows:

[0045] The two workpieces to be welded are arranged up and down to form an upper bonding pair 11 and a lower bonding pair 12. The fibers of the lower surface of the upper bonding pair 11 and the upper surface of the lower bonding pair 12 are in contact with each other to form a conductive network 13. Electrodes 14 are respectively provided at the connection between one end of the upper bonding pair 11 and the lower bonding pair 12, and at the connection between one end of the lower bonding pair 12 and the upper bonding pair 11. The two electrodes 14 are respectively connected to the signal processing end 15 of the resistor. In the process of ultrasonic welding of carbon fiber reinforced thermoplastic composite materials, after the thinner surface of the thermoplastic matrix is ​​melted and extruded, the carbon fiber structures at the welding interface of the upper and lower workpieces come into contact, forming a conductive network. Figure 1 The conductive circuit marked in black is used to reflect the fusion of the thermoplastic matrix at the welding interface and the contact of the carbon fibers in the two joint pairs. Due to the differences in the above conditions during the welding process, the conductive network 13 formed has obvious differences and can be identified by measuring the resistance or voltage at both ends. When the measured resistance or voltage signal is less than the standard value, it is normal welding, and when it is greater than the standard value, it is over-welding or under-welding. The difference between over-welding and under-welding is more obvious. After over-welding, the composite material matrix is ​​severely extruded, while under-welding has less extrusion or no extrusion. The difference between the two can be directly distinguished with the naked eye.

[0046] The electrode 14 and the signal processing end 15 are connected by copper wires or wirelessly.

[0047] Preferably, the electrode 14 and the signal processing end 15 are connected via a Bluetooth module.

[0048] The present invention provides a method for ultrasonic welding quality detection of continuous carbon fiber reinforced thermoplastic composite materials, comprising the following steps:

[0049] S1. Surface treatment is performed on the upper and lower bonding couples 11 and 12 that have been ultrasonically directly welded, excess extrusions around the welding interface are cleaned, conductive paint is applied to the treated interface, and the electrode 14 connected to the signal processing terminal 15 is fixed.

[0050] S2. Collect and analyze the signal obtained by the electrode 14, compare it with the typical resistance or voltage under different welding conditions, and obtain the ultrasonic welding quality.

[0051] See also Figure 2 and Figure 3 , by comparing the actual measured signal with Figure 2 The curve of interface resistance and welding condition can be used to determine whether the welding is normal or not; by comparing the actual measured signal with the Figure 3The curve of the interface resistance and the maximum load can be used to determine the load-bearing capacity of the weld joint. When the current is constant, the resistance is proportional to the voltage, so the voltage detection signal is actually the resistance detection signal.

[0052] The matrix of the carbon fiber reinforced material targeted by the method of the present invention is a thermoplastic polymer material that can be repeatedly heated and melted and can flow after softening at high temperature, including but not limited to polyethylene, polyetheretherketone, polyphenylene sulfide, polyethylene terephthalate and other polymers. This is to meet the requirement that the matrix can be melted and fused during ultrasonic welding; the reinforcing fiber is a carbon fiber with good electrical conductivity and excellent performance. The two connected pairs of continuous carbon fibers will contact each other during the ultrasonic welding process to form a conductive network 13, whose resistance or voltage can reflect the connection status.

[0053] After welding is completed, under the combined action of welding heat and welding pressure, the thermoplastic matrix will melt and extrude, and some fibers will also move in conjunction. Removing excess polymer can expose the fibers wrapped in the polymer, increasing the contact area between the monitoring head and the conductive network when monitoring resistance or voltage signals. Similarly, arranging extremely thin electrodes and applying conductive paint to the electrodes and monitoring parts can also increase the electrical contact between the electrodes and the conductive network at the joint interface, avoiding the impact of poor contact between the electrodes and the conductive network on interface resistance or voltage monitoring. As an alternative, the combination of extremely thin electrodes and conductive paint can also be replaced with a conductive glue with strong adhesion. Under this solution, after cleaning the excess polymer, a layer of conductive glue can be directly applied to the cleaned interface, and the wire can be inserted into the glue layer before it solidifies. After the glue solidifies, the connection of the monitoring circuit is completed. Mechanical compression can also ensure close contact between the electrode and the conductive network.

[0054] The method of welding quality detection using the self-conductivity of carbon fiber reinforced materials described in the present invention is not limited to the connection between composite materials and composite materials, but can also be applied to the connection between composite materials and metals; similarly, the connection method adopted by the present invention is not limited to ultrasonic welding, and other fusion welding methods that use molten materials for connection, such as induction welding, resistance welding, etc., can all use the same idea of ​​the present invention to perform interface monitoring.

[0055] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0056] In Example 1 of the present invention, a continuous carbon fiber reinforced polycarbonate composite plate with a length of 101.6 mm, a width of 25.4 mm, and a thickness of 2 mm is used, wherein the volume fraction of the carbon fiber is 20% to 60%.

[0057] The present invention will be described in detail below with reference to the accompanying drawings.

[0058] Example 1

[0059] Without setting any reinforcement phase at the welding interface, the two composite plates were welded together by direct ultrasonic welding. The welding parameters of the ultrasonic welder were: welding pressure: 2 bar; welding time: 1.2 s. Based on previous experimental experience, the welded joint obtained under this welding parameter is a normal weld.

[0060] After the specimen is cooled to room temperature, remove the excess extrusion in the front and rear directions of the welding interface to expose the carbon fiber on the surface. Apply conductive silver paint on the interface after cleaning the excess mixture. The two sides of the conductive silver paint should be parallel to the length direction of the composite plate. After it solidifies, use tape to cover the 0.1mm copper foil connected to the wire on the part where the conductive silver paint is applied and fix it. Connect the two wires to the positive and negative poles of the resistance meter respectively to detect the size of the interface resistance. Figure 1 The interface resistance or voltage monitoring system shown.

[0061] After the resistance of the conductive network is measured, all welds are subjected to a tensile test on a shear tensile testing machine to obtain the maximum load they can withstand.

[0062] After repeated measurements on the test piece, it was found that the maximum conductive network resistance measured under normal welding conditions did not exceed 2.1Ω, and the maximum load it could withstand was distributed between 9.5 and 11.2MPa.

[0063] Example 2

[0064] Without setting any reinforcement phase at the welding interface, the two composite plates were welded together by direct ultrasonic welding. The welding parameters of the ultrasonic welder were: welding pressure: 2 bar; welding time: 0.8 s. Based on previous experimental experience, the welded joint obtained under such welding parameters is considered to be under-welded.

[0065] After the specimen is cooled to room temperature, remove the excess extrusion in the front and rear directions of the welding interface to expose the carbon fiber on the surface. Apply conductive silver paint on the interface after cleaning the excess mixture. The two sides of the conductive silver paint should be parallel to the length direction of the composite plate. After it solidifies, use tape to cover the 0.1mm copper foil connected to the wire on the part where the conductive silver paint is applied and fix it. Connect the two wires to the positive and negative poles of the resistance meter respectively to detect the size of the interface resistance. Figure 1 The interface resistance or voltage monitoring system shown.

[0066] After the resistance of the conductive network is measured, all welds are subjected to a tensile test on a shear tensile testing machine to obtain the maximum load they can withstand.

[0067] Repeated measurements of the specimens revealed that the conductive network resistance measured under normal welding conditions ranged from 4.9 to 11.3 Ω, and the maximum load it could withstand ranged from 4.1 to 7.6 MPa.

[0068] Example 3

[0069] Without setting any reinforcement phase at the welding interface, the two composite plates were welded together by direct ultrasonic welding. The welding parameters of the ultrasonic welder were: welding pressure: 2 bar; welding time: 1.6 s. Based on previous experimental experience, the welded joint obtained under such welding parameters is considered to be under-welded.

[0070] After the specimen is cooled to room temperature, remove the excess extrusion in the front and rear directions of the welding interface to expose the carbon fiber on the surface. Apply conductive silver paint on the interface after cleaning the excess mixture. The two sides of the conductive silver paint should be parallel to the length direction of the composite plate. After it solidifies, use tape to cover the 0.1mm copper foil connected to the wire on the part where the conductive silver paint is applied and fix it. Connect the two wires to the positive and negative poles of the resistance meter respectively to detect the size of the interface resistance. Figure 1 The interface resistance or voltage monitoring system shown.

[0071] After the resistance of the conductive network is measured, all welds are subjected to a tensile test on a shear tensile testing machine to obtain the maximum load they can withstand.

[0072] After repeated measurements of the test pieces, it was found that the conductive network resistance measured under normal welding conditions was distributed between 2.9 and 8.8 Ω, and the maximum load that could be sustained was distributed between 4.2 and 9.7 MPa.

[0073] The resistance data of each group are summarized according to the welding conditions. Figure 2 As shown in the figure, it can be seen that the conductive network resistance measured by normal welding and the other two abnormal welding methods is significantly different. Figure 3 The resistance and the maximum load that can be sustained for each group are measured by Figure 3 It can be seen that the magnitude of the post-weld interface resistance has a clear linear relationship with the maximum load it can withstand. After welding, the interface resistance can be used to preliminarily judge the weld condition. The smaller the interface resistance, the better the weld interface fusion; the larger the interface resistance, the larger the unfused area of ​​the weld interface and the worse the weld quality. This method can be used to judge weld quality by measuring the initial joint resistance.

[0074] In summary, the method for detecting the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials of the present invention has the advantages of high sensitivity, simple operation, simple materials, low cost, high efficiency and stability, no influence on the workpiece structure, and a wide range of applications. With the widespread application of ultrasonic welding of carbon fiber reinforced thermoplastic composite materials, it has broad application prospects.

[0075] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for detecting the quality of ultrasonic welding of continuous carbon fiber reinforced thermoplastic composite materials, characterized in that: The following steps are involved: S1. Surface treatment is performed on the upper and lower bonding couples that have completed ultrasonic direct welding, and then electrodes are fixed. The electrodes are symmetrically placed at one end of the upper and lower bonding couples, respectively. The electrodes are copper foils with a thickness of 0.05 to 0.15 mm. The matrix of the upper and lower bonding couples is prepared by continuous carbon fiber reinforced thermoplastic composite materials. The volume fraction of carbon fibers in the continuous carbon fiber reinforced thermoplastic composite materials accounts for 20% to 60% of the total volume of the fiber reinforced composite materials. S2. Use the signal processing end to collect and analyze the resistance signal measured by the electrode, and compare it with the typical resistance size under different welding conditions to achieve ultrasonic welding quality detection.

2. The method for detecting the ultrasonic welding quality of continuous carbon fiber reinforced thermoplastic composite materials according to claim 1, characterized in that: In step S1, the surface treatment is specifically as follows: Clean up excess extrusion around the weld interface of the upper and lower joint couples.

3. The method for detecting ultrasonic welding quality of continuous carbon fiber reinforced thermoplastic composite materials according to claim 2, characterized in that: Apply conductive paint to the interfaces of the upper and lower bonding couples after cleaning excess extrusion, and then connect the electrodes respectively.

4. The method for detecting ultrasonic welding quality of continuous carbon fiber reinforced thermoplastic composite materials according to claim 3, characterized in that: The electrodes are fixedly connected to the upper bonding couple and the lower bonding couple respectively by mechanical fastening.

5. The method for detecting ultrasonic welding quality of continuous carbon fiber reinforced thermoplastic composite materials according to claim 1, characterized in that: The continuous carbon fiber reinforced thermoplastic composite material includes polyethylene, polyetheretherketone, polyphenylene sulfide and / or polyethylene terephthalate.

6. The method for detecting ultrasonic welding quality of continuous carbon fiber reinforced thermoplastic composite materials according to claim 1, characterized in that: In step S2, the actual measured signal is compared with the curve of interface resistance and welding condition to determine whether the welding is normal; the actual measured signal is compared with the curve of interface resistance and maximum load to determine the load-bearing capacity of the weld joint.

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