Resistance welding method of thermoplastic composite material and implementation device

Abstract

The invention belongs to the technical field of material processing engineering, and relates to a resistance welding method for a thermoplastic composite material and an implementation device. According to the method, an implantation layer is clamped between two to-be-welded parts, pricking needles of a pricking electrode array are used for pricking the implantation layer from top to bottom and are electrified after making contact with a conductive core layer, and resistance welding is achieved; the acupuncture electrode array adopts a special arrangement mode, so that the current can be uniformly distributed, and the stable introduction and connection of the current are ensured by optimizing the pricking needle structure. The device comprises a power supply, an insulating bottom plate, an insulating force application block, an acupuncture electrode array and a pressurizing device, and is simple in structure and convenient to operate. Compared with the prior art, the method has the advantages of being uniform in current distribution, stable in connection, low in preparation cost and high in welding quality, and is suitable for connection of thermoplastic composite materials in the fields of aerospace, automobile manufacturing, electronics and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of material processing engineering, and relates to a resistance welding method of a thermoplastic composite material and an implementation device. Background Art

[0002] Thermoplastic composites have been widely used in aerospace, automobile manufacturing, electronics and other fields due to their light weight, high strength and recyclability. Resistance welding, as an efficient and environmentally friendly connection method, is particularly suitable for the connection of thermoplastic composites. However, the resistance welding process of thermoplastic composites faces many challenges, one of which is how to achieve uniform input of current and stable connection in the implant layer.

[0003] In the process of resistance welding, the implant layer serves as a medium for current transmission, and its preparation process and electrode connection method are crucial. At present, the preparation of the implant layer usually adopts the melt impregnation method or the suspension impregnation method, so that the resin matrix is ​​impregnated with the conductive core layer such as metal or carbon fiber to form a well-impregnated implant layer. However, during the preparation process, the good impregnation of the conductive core layer often conflicts with the stable connection of the electrode clamping device, because the resin needs to apply greater pressure and fluidity when impregnating the conductive core layer, which may cause the electrode clamping area to be covered by the resin, thereby affecting the stable transmission of the current.

[0004] In order to solve this problem, the existing electrode connection methods mainly include the following:

[0005] 1. Direct clamping with metal sheets (usually copper sheets): For example, patent application CN109822910A processes the electrode clamping area after the implantation layer is prepared, so that the conductive core layer is exposed, and then uses metal sheets to clamp and realize electrode connection. However, this method requires further processing of the heating element, and the electrode clamping area of ​​the treated heating element is uneven, and there is an obvious problem of uneven current distribution. For another example, patent application CN111086224A prepares the heating element by three hot pressings, and hot presses the metal sheet on the conductive core layer to realize electrode connection. However, this method is first of all cumbersome and requires three hot pressing steps to realize the current introduction of the heating element; secondly, during the second hot pressing process, the molten resin at high temperature escapes to the surroundings, and it is impossible to reserve the area not covered by the resin matrix; thirdly, in the third hot pressing, if there is no bonding of the resin matrix, it is difficult for the metal sheet to cover the conductive core layer. If there is too much resin, the conductive core layer and the metal sheet will be separated by the resin, affecting the conductive performance.

[0006] 2. Use conductive products to process the connection parts before clamping: For example, patent application CN116685009A uses conductive glue to process again on the basis of using metal sheets for clamping, which greatly improves the efficiency and uniformity of current input. However, this method requires multi-step processing of the heating element (removing excess resin from the electrode clamping area and coating with conductive glue), and the conductive glue used is expensive and takes a long time to cure. For another example, patent application CN117295194A uses a needle-punched array structure to create through holes on the electrode side of the heating element, and then uses conductive silver paste to coat and cure to form electrodes. However, when using conductive silver paste to treat the electrode connection area, the conductive silver paste also has the defects of being expensive and taking a long time to cure, and it cannot be reused after curing.

[0007] In summary, the existing resistance welding method of thermoplastic composite materials has many shortcomings in the electrode connection method, and a new electrode connection method is urgently needed to achieve uniform input and stable connection of current in the implant layer, while reducing the preparation cost and improving the welding quality. Summary of the invention

[0008] The purpose of the present invention is to solve the problems existing in the prior art and to provide a resistance welding method and an implementing device for thermoplastic composite materials.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A resistance welding method for thermoplastic composite materials, wherein an implant layer covers the overlap of two front and rear parts to be welded, and the left and right ends of the implant layer are exposed outside the area to be welded, and then the needles of the left and right needle electrode arrays are inserted from top to bottom into the left and right ends of the implant layer respectively, so that the needles are in contact with the conductive core layer in the implant layer, and then the electricity is continuously supplied, so that the resistance welding of the thermoplastic composite material is realized;

[0011] The needles in the acupuncture electrode array are arranged in a matrix, with the row direction parallel to the front-to-back direction. The needles in two adjacent rows are offset by D1 / 2 along the row direction, and D1 is the center distance between two adjacent needles in the same row. This arrangement enables the acupuncture electrode array to evenly cover the target area. The value range of D1 is 0.2-10mm, the distance D2 between the centers of two adjacent rows of needles along the column direction is 0.1-10mm, and the diameter d of the needles is 0.1-5mm.

[0012] At present, there are three main types of conductive core materials used for resistance welding, namely, macroscopically conductive and thermally anisotropic materials (CF-type heating elements, including CF fabrics and CF unidirectional tapes), conductive and thermally isotropic materials (stainless steel mesh), and conductive networks composed of conductive particles (conductive particle resin films). In the actual resistance welding process, affected by the welded parts and welding tooling, the needle structure of the acupuncture electrode array cannot completely penetrate the implant layer to form an electrode connection, and only the needle tip part contacts the conductive core layer to form a conductive path. Therefore, the diameter d of the needle should not be too large, otherwise it will affect the acupuncture arrangement density and further affect the conductive efficiency. The value is preferably 0.1-5mm.

[0013] Under the condition that the diameter d of the needle is determined, in order to make the entire conductive core layer in the implant layer contact the acupuncture electrode as much as possible to achieve uniform current distribution, the needles need to be densely arranged, that is, D1 is equal to the acupuncture diameter d. Under this condition, the integration of the needles and the pinhole substrate is difficult to achieve. In order to achieve the same current input uniformity effect when the needles are densely arranged, the densely arranged needle structure is divided into multiple rows, D2 (0.1-10mm) is reserved between two adjacent rows, the value range of D1 is 0.2-10mm, and the needles of two adjacent rows are staggered by D1 / 2 along the row direction. Through such a staggered multi-row needle array structure, the conductive core layer is guaranteed to be in direct contact with the electrode in the same axial direction, and the stable introduction and uniform distribution of current in the implant layer are achieved.

[0014] As the preferred technical solution:

[0015] In the resistance welding method of a thermoplastic composite material as described above, the exposed length of the needle is h=2×D3+T+α, D3 is the distance between the upper surface or lower surface of the implant layer and the conductive core layer, T is the thickness of the conductive core layer, and α is 0.1-0.3 mm.

[0016] In the resistance welding method of a thermoplastic composite material as described above, the sharpening angle θ of the needle tip is 20-60°, and θ is closely related to the magnitude of the force required for the needle to penetrate the implant layer. The smaller θ is, the smaller the force required for the needle to penetrate the implant layer. The force required for the needle to penetrate the implant layer is mainly limited by the force that the cylinder can provide. The greater the force that the cylinder can provide, the larger its cylinder diameter. The position in the tooling does not allow the existence of a cylinder with a cylinder diameter that is too large, so θ is 20-60°.

[0017] In the resistance welding method of a thermoplastic composite material as described above, the needle-piercing electrode array is composed of a flat bottom plate (the material is the same as that of the pinhole substrate), a pinhole substrate (the material is copper, stainless steel, aluminum and other metal materials with good conductivity) and a needle (the material is carbon steel, stainless steel and other metals with high hardness and good conductivity), the pinhole substrate and the needle are both located below the flat bottom plate, the pinhole substrate is fixedly connected to the flat bottom plate, the needle tip of the needle faces downward, and the needle tail is embedded in the pinhole substrate.

[0018] In the resistance welding method of a thermoplastic composite material as described above, the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded is 1-2 mm, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded is 1-2 mm; the left and right ends of the implanted layer are completely located directly below the area where the needles of the two needle-punctured electrode arrays are located.

[0019] In the above-mentioned resistance welding method of a thermoplastic composite material, the steps of preparing the implant layer are as follows:

[0020] (1) In a mold, a thermoplastic resin (materials including but not limited to PEEK, PEKK, PPS, PEI, PA, PP, etc., in the form of film or powder) is covered on the upper and lower sides of a conductive core layer (carbon fiber cloth / stainless steel mesh or other materials that can be used for heating), and then the semi-finished product is obtained by the first hot pressing;

[0021] (2) In the mold, after the thermoplastic resin is covered on the upper and lower sides of the semi-finished product, a second hot pressing is performed. After the mold is cooled to below 50°C, the pressure can be released, the mold is removed from the press, the mold is opened, and the implant layer is taken out. After that, the tool can be used to cut it into the corresponding size according to the size of the welding area for subsequent welding;

[0022] The temperature of each heat pressing is higher than the melting temperature of the thermoplastic resin and lower than the decomposition temperature of the thermoplastic resin.

[0023] The first hot pressing can make the conductive core layer well impregnated, and the second hot pressing can build a resin-rich layer in the welding area, thus eliminating the need to add a thick insulating layer. If only one hot pressing is performed, the temperature and pressure of the hot pressing need to be increased to make the conductive core layer well impregnated, but this will cause serious overflow and fail to build a resin-rich layer. If the temperature and pressure of the hot pressing are reduced, the conductive core layer cannot be well impregnated.

[0024] In the resistance welding method of a thermoplastic composite material as described above, the temperature of each hot pressing is 30-50°C higher than the melting temperature of the thermoplastic resin, so that the fluidity of the thermoplastic resin is moderate and the conductive core layer can be better impregnated; during the first hot pressing, the pressure is maintained at 1.5-2MPa for 30-35min, and then at 5-6MPa for 15-20min; during the second hot pressing, the pressure is maintained at 2-3MPa for 20-30min.

[0025] In the resistance welding method of a thermoplastic composite material as described above, during the continuous power-on process, the temperature difference of the area to be welded does not exceed 40°C; after the continuous power-on ends, the welding rate of the welded joint is higher than 90%, and the welding strength is 18-30MPa.

[0026] The present invention also provides a device for implementing a resistance welding method of a thermoplastic composite material as described in any one of the above items, comprising a power source, an insulating base plate, an insulating force block arranged directly above the insulating base plate, two acupuncture electrode arrays, and a pressurizing device;

[0027] The two acupuncture electrode arrays are distributed on the left and right sides of the insulating force block, and both are connected to the power supply at the same time; the pressure device is used to apply downward pressure to the insulating force block and the two acupuncture electrode arrays.

[0028] As the preferred technical solution:

[0029] The device as described above, the pressurizing device comprises two insulating connecting blocks, two metal rods, a metal plate, two metal knobs, a No. 2 cylinder, and a No. 1 cylinder;

[0030] The two insulating connection blocks are respectively located directly above the two acupuncture electrode arrays and are fixedly connected thereto; the two metal rods are respectively located directly above the two insulating connection blocks and are fixedly connected thereto; after the two metal rods simultaneously pass through the metal plate from bottom to top, they are respectively connected to two metal knobs, and the metal knobs are used to fix the metal rods to the metal plate; the metal plate is provided with metal guide rails for the two metal rods to move in the left and right directions;

[0031] Cylinder No. 2 is located directly above the insulating force block;

[0032] The metal plate is a rectangular plate, and there are four No. 1 cylinders, which are located at the four corners of the metal plate. This ensures that the force provided by the four No. 1 cylinders can cover the force required for the needles of the acupuncture electrode array to penetrate the implant layer, and through the mutual cooperation of the four cylinders, the metal plate is evenly stressed, thereby ensuring that the forces on the two acupuncture electrode arrays are the same.

[0033] Beneficial effects:

[0034] (1) The resistance welding method of the present invention ensures direct contact between the conductive core layer and the electrode by optimizing the arrangement of the needle electrode array and the needle structure, thereby achieving uniform input and stable connection of current in the implant layer. It has significant technical advantages and application prospects in the field of resistance welding of thermoplastic composite materials.

[0035] (2) The device of the present invention has a simple structure and is easy to operate. It does not require complicated post-processing of the welded parts, thus reducing the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the three-dimensional structure of the welding device;

[0037] Figure 2 is a schematic diagram of the three-dimensional structure of the acupuncture electrode array;

[0038] Figure 3 is a schematic diagram of the side structure of the acupuncture electrode array;

[0039] Figure 4 is a schematic diagram of the structure of the needle;

[0040] Figure 5 Schematic diagram of the top view of the acupuncture electrode array;

[0041] Figure 6 It is a schematic diagram of assembling the implant layer and the parts to be welded on the welding device;

[0042] Figure 7 is an infrared temperature measurement data diagram (∆ in the diagram indicates the location where the highest temperature occurs); wherein a corresponds to Example 1, b corresponds to Example 5, and c corresponds to Example 7;

[0043] Figure 8 Schematic diagram of semi-finished product;

[0044] Fig. 9 is a schematic diagram of the implantation layer;

[0045] Among them, 1-No. 1 cylinder, 2-No. 2 cylinder, 3-metal plate, 4-metal guide rail, 5-metal knob, 6-metal rod, 7-insulating connecting block, 8-implantation layer, 9-acupuncture electrode array, 10-insulating force block, 11-parts to be welded, 12-insulating base plate, 13-flat base plate, 14-pinhole substrate. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0047] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0048] Maximum temperature difference in the area to be welded: firstly, evenly arrange multiple K-type thermocouples at different positions in the area to be welded and connect them to the data recorder. Start the data recorder to monitor the temperature changes in the area to be welded in real time. Then, through experimental comparison, determine the two temperature measuring points (the lowest temperature point and the highest temperature point) in the area to be welded. Then, place the K-type thermocouples at the two temperature measuring points in the area to be welded, record the temperature data of the two temperature measuring points during the welding process, use the absolute value of the data difference between the two temperature measuring points at the same time to represent the temperature difference of the welding interface, and record the maximum temperature difference in the area to be welded during the welding process.

[0049] Welding strength (single lap shear strength): Tested according to ASTM-D5868 standard, use a metal aluminum reinforcement sheet (size: length × width × height = 25.4mm × 50mm × 2mm) to stick it on the end of the weldment (i.e. the weldment to be welded after resistance welding), and then use a universal testing machine to perform a single lap shear strength test at a tensile speed of 13mm / min. Take 5 parallel samples to repeat the test and take the average value.

[0050] Welding rate of welded joints: After the welded parts are pulled apart using a universal testing machine, the cross-sectional morphology is photographed using a high-definition camera. The images are imported into the image analysis tool to calculate the number of pixels in the unwelded area (denoted as ) and the number of pixels in the entire welding area (denoted as ), and then calculate the welding rate of the welded joint according to the following formula :

[0051] .

[0052] like Figure 1 As shown, the welding device used in the following embodiments includes a power source, an insulating base plate 12, an insulating force block 10, two acupuncture electrode arrays 9 and a pressurizing device;

[0053] The insulating force block 10, two acupuncture electrode arrays 9 and the pressurizing device are simultaneously arranged directly above the insulating bottom plate 12;

[0054] Two acupuncture electrode arrays 9 are distributed on the left and right sides of the insulating force-applying block 10, and both are connected to a power source at the same time;

[0055] like Figure 2 and Figure 3 As shown, the acupuncture electrode array 9 is composed of a plane bottom plate 13, a pinhole substrate 14 and a needle. The pinhole substrate 14 and the needle are both located below the plane bottom plate 13. The pinhole substrate 14 is fixedly connected to the plane bottom plate 13 by M4 screws. The needle tips of the needles face downward, and the needle tails are embedded in the pinhole substrate 14.

[0056] like Figure 5 As shown, the needles in the acupuncture electrode array 9 are arranged in a matrix, the row direction is parallel to the front-back direction, the center distance between two adjacent needles in the same row is recorded as D1, the needles in two adjacent rows are offset by D1 / 2 along the row direction, and the distance between the centers of the needles in two adjacent rows along the column direction is recorded as D2; Figure 4 As shown in FIG. 1 , the diameter of the needle is denoted as d, and the sharpening angle of the needle tip is denoted as θ; Figure 3 As shown, part of the length of the needle is exposed below the pinhole substrate 14, and the exposed length of the needle is recorded as h;

[0057] The pressurizing device includes two insulating connecting blocks 7, two metal rods 6, a metal plate 3, two metal knobs 5, a No. 2 cylinder 2, and a No. 1 cylinder 1;

[0058] Two insulating connection blocks 7 are respectively located directly above the two acupuncture electrode arrays and are fixedly connected thereto; two metal rods 6 are respectively located directly above the two insulating connection blocks 7 and are fixedly connected thereto; after the two metal rods 6 simultaneously pass through the metal plate 3 from bottom to top, they are respectively connected to two metal knobs 5, and the metal knobs 5 are used to fix the metal rods 6 to the metal plate 3; the metal plate 3 is provided with a metal guide rail 4 for the two metal rods 6 to move in the left and right directions;

[0059] The No. 2 cylinder 2 is located directly above the insulating force block 10, and the two are fixedly connected;

[0060] The metal plate 3 is a rectangular plate, and there are four No. 1 cylinders 1, which are located at the four corners of the metal plate 3;

[0061] like Figure 1 and Figure 6 As shown, before using the welding device to perform resistance welding on the thermoplastic composite material, first overlap the two parts to be welded 11 on the insulating bottom plate 12 in the front-to-back direction, and make the overlap of the two parts to be welded 11 located in the area to be welded, and then cover the overlap of the two parts to be welded 11 with the trimmed implant layer 8, and make the left and right ends of the implant layer 8 exposed outside the area to be welded;

[0062] Subsequently, the positions of the two acupuncture electrode arrays 9 are adjusted by the metal guide rails 4 so as to be aligned with the left and right ends of the implanted layer 8 that are exposed outside the area to be welded (the left and right ends of the implanted layer 8 are completely located directly below the areas where the needles of the two acupuncture electrode arrays 9 are located);

[0063] Then start the No. 2 cylinder 2 to apply downward pressure to the insulating force block 10, so that the welded part 11 is in good contact with the implant layer 8. At the same time, start the four No. 1 cylinders 1 to apply downward pressure to the two puncture electrode arrays 9, so that the parts of the needles of the two puncture electrode arrays 9 exposed under the pinhole substrate 14 can completely penetrate into the left and right ends of the implant layer 8.

[0064] In the following embodiments, the manufacturer information of the thermoplastic resin, the conductive core layer and the parts to be welded has no significant effect on the maximum temperature difference of the welding area, the welding rate of the welding joint and the welding strength, so it will not be described in detail below.

[0065] In the following embodiments, the dimensions of the parts to be welded are 101.6 mm×25.4 mm×2 mm (length×width×height).

[0066] Example 1

[0067] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0068] (1) Preparation of raw materials;

[0069] Thermoplastic resin: PEEK;

[0070] Conductive core layer: CF satin fabric, thickness 0.1mm;

[0071] Parts to be welded: CF / PEEK composite material, CF volume fraction is 60%;

[0072] (2) preparing an implant layer;

[0073] (2.1) In the mold, after the thermoplastic resin is covered on the upper and lower sides of the conductive core layer, the temperature is controlled to 390°C, and hot pressing is first performed at 2MPa and maintained for 35 minutes, and then hot pressing is performed at 6MPa and maintained for 20 minutes to obtain a semi-finished product (such as Figure 8 As shown in the figure), the distance between the upper surface and the lower surface of the semi-finished product and the conductive core layer is 0.01 mm;

[0074] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot press at 360°C and 3MPa and maintain the pressure for 30 minutes. After the mold cools to 50°C, release the pressure, open the mold, and take out the implant layer (such as Fig. 9 shown);

[0075] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.1 mm;

[0076] (3) Resistance welding;

[0077] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously supplied for 30 seconds at a total input current of 20A to achieve resistance welding of the thermoplastic composite material; wherein, the parameters related to the welding device are: D1 is 2mm, D2 is 2mm, d is 1mm, θ is 45°, and h is 0.5mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 1.5mm.

[0078] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 30°C; after the continuous power-on ends, the welding rate of the welding joint is 90% and the welding strength is 30MPa.

[0079] Comparative Example 1

[0080] A resistance welding method for thermoplastic composite materials is basically the same as that in Example 1, except that D1 is 7 mm, D2 is 7 mm, and d is 6 mm.

[0081] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 60°C; after the continuous power-on ends, the welding rate of the welded joint is 80% and the welding strength is 20MPa.

[0082] Compared with Example 1 and Comparative Example 1, the maximum temperature difference in the area to be welded is significantly increased, and the welding rate and welding strength of the welding joint are significantly reduced. This is because when the spacing between two adjacent needles in the same row and the spacing between two adjacent rows of needles in the acupuncture electrode array are the same, the larger needle diameter reduces the number of needles that can be arranged on the implant layer of the same area, and the acupuncture arrangement density is reduced, resulting in fewer conductive paths, and the conduction of current in the conductive core layer is hindered, and it cannot be effectively distributed evenly in the implant layer, so that the heat received by various parts of the area to be welded is uneven, which leads to a significant increase in the maximum temperature difference of the area to be welded during continuous power-on. At the same time, due to poor current conduction, the welding joint cannot obtain sufficient and uniform heat for sufficient welding, which reduces the welding rate of the welding joint, and due to insufficient and uneven heat at the welding joint, a good connection structure cannot be formed, which leads to a significant reduction in welding strength.

[0083] Comparative Example 2

[0084] A resistance welding method for thermoplastic composite materials is basically the same as that in Example 1, except that D2 is 11 mm.

[0085] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 40°C; after the continuous power-on ends, the welding rate of the welding joint is 85% and the welding strength is 27MPa.

[0086] Compared with Example 1, the maximum temperature difference in the area to be welded in Comparative Example 2 is significantly increased, and the welding rate and welding strength of the welding joint are significantly reduced. This is because in Comparative Example 2, D2 increases, that is, the distance between the needles in the same row of the positive and negative electrodes becomes larger, and the resistance increases accordingly. The current will be conducted from the positive electrode to the negative electrode along the path with the smallest resistance (that is, the needles closer to the positive and negative electrodes), while the area far away from these needles has a larger resistance, a smaller current, and a lower temperature, resulting in a significant increase in the maximum temperature difference in the area to be welded. In addition, this uneven current distribution and temperature distribution causes different degrees of melting of the resin matrix in different parts of the welding area, and the area with lower temperature is not enough to fully melt the resin matrix, which leads to a decrease in the welding rate of the joint and a corresponding decrease in the welding strength.

[0087] Comparative Example 3

[0088] A resistance welding method for thermoplastic composite materials is basically the same as that in Example 1, except that D1 is 11 mm.

[0089] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 60°C; after the continuous power-on ends, the welding rate of the welding joint is 80% and the welding strength is 20MPa.

[0090] Compared with Example 1, the maximum temperature difference in the area to be welded in Comparative Example 3 is significantly increased, and the welding rate and welding strength of the welding joint are significantly reduced. This is because the center distance between adjacent needles in the same row is too wide, resulting in a relatively reduced number of needles that can be arranged in a row of the same length, a reduced needle arrangement density, fewer conductive paths, and obstructed conduction of current in the conductive core layer. It cannot be effectively distributed evenly in the implant layer, resulting in uneven heat received by various parts of the area to be welded, and thus the maximum temperature difference in the area to be welded is significantly increased during continuous power-on. At the same time, due to poor current conduction, the welding joint cannot obtain sufficient and uniform heat for sufficient welding, which reduces the welding rate of the welding joint, and due to insufficient and uneven heat at the welding joint, a good connection structure cannot be formed, so the welding strength is significantly reduced.

[0091] Comparative Example 4

[0092] A resistance welding method for thermoplastic composite materials is basically the same as that of Example 1, except that the needles in two adjacent rows in two needle electrode arrays are completely aligned.

[0093] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 45°C; after the continuous power-on ends, the welding rate of the welding joint is 83% and the welding strength is 25MPa.

[0094] Compared with Example 1, the maximum temperature difference of the area to be welded in Comparative Example 4 is significantly increased, and the welding rate and welding strength of the welding joint are significantly reduced. This is because when the needles of two adjacent rows in the two acupuncture electrode arrays are completely aligned, the conductive core layer area between the adjacent needles will reduce the effective distribution of the current due to the concentration of the current path, resulting in a reduction in the heat generated in these areas, forming a "temperature cold zone". This local temperature reduction not only increases the maximum temperature difference of the entire area to be welded, but also due to the uneven current conduction, the welding joint cannot obtain sufficient and uniform heat to ensure good welding. Therefore, the welding rate of the welding joint decreases, and due to insufficient and uneven heat distribution, it is difficult to form a good connection structure, resulting in a significant reduction in welding strength.

[0095] Example 2

[0096] A resistance welding method for a thermoplastic composite material is basically the same as that of Example 1, except that: Step (2) is: in a mold, after covering the upper and lower sides of a conductive core layer with a thermoplastic resin, controlling the temperature to 360° C., first hot pressing and holding the pressure at 1 MPa for 35 min, and then hot pressing and holding the pressure at 3 MPa for 20 min to obtain an implant layer; the upper and lower surfaces of the implant layer are both 0.1 mm apart from the conductive core layer.

[0097] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 30°C; after the continuous power-on ends, the welding rate of the welding joint is 90% and the welding strength is 25MPa.

[0098] Example 3

[0099] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0100] (1) Preparation of raw materials;

[0101] Thermoplastic resin: PEKK;

[0102] Conductive core layer: CF satin fabric, thickness 0.1mm;

[0103] Parts to be welded: CF / PEKK composite material, with a CF volume fraction of 60%;

[0104] (2) preparing an implant layer;

[0105] (2.1) In a mold, after covering the upper and lower sides of the conductive core layer with thermoplastic resin, the temperature is controlled to 400°C, and hot pressing is first performed at 2 MPa and maintained for 35 minutes, and then hot pressing is performed at 6 MPa and maintained for 20 minutes to obtain a semi-finished product, wherein the distance between the upper surface and the lower surface of the semi-finished product and the conductive core layer is 0.01 mm;

[0106] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot pressing is performed at 370°C and 3MPa and the pressure is maintained for 30 minutes. After the mold is cooled to 50°C, the pressure is released, the mold is opened, and the implant layer is taken out;

[0107] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.1 mm;

[0108] (3) Resistance welding;

[0109] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously turned on for 30 seconds at a total input current of 20A to achieve resistance welding of the thermoplastic composite material; among which, the parameters related to the welding device are: D1 is 2mm, D2 is 1mm, d is 1mm, θ is 45°, and h is 0.5mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 1.5mm.

[0110] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 30°C; after the continuous power-on ends, the welding rate of the welded joint is 92% and the welding strength is 30MPa.

[0111] Example 4

[0112] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0113] (1) Preparation of raw materials;

[0114] Thermoplastic resin: PPS;

[0115] Conductive core layer: CF unidirectional tape, thickness 0.1mm;

[0116] Parts to be welded: CF / PPS composite material, CF volume fraction is 60%;

[0117] (2) preparing an implant layer;

[0118] (2.1) In a mold, after covering the upper and lower sides of the conductive core layer with thermoplastic resin, the temperature is controlled to 330°C, and hot pressing is first performed at 2 MPa and maintained for 35 minutes, and then hot pressing is performed at 6 MPa and maintained for 20 minutes to obtain a semi-finished product, wherein the distance between the upper and lower surfaces of the semi-finished product and the conductive core layer is 0.01 mm;

[0119] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot pressing is performed at 300°C and 3MPa and the pressure is maintained for 30 minutes. After the mold is cooled to 50°C, the pressure is released, the mold is opened, and the implant layer is taken out;

[0120] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.1 mm;

[0121] (3) Resistance welding;

[0122] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously supplied for 25 seconds at a total input current of 20A to achieve resistance welding of the thermoplastic composite material; wherein, the parameters related to the welding device are: D1 is 1mm, D2 is 0.5mm, d is 0.5mm, θ is 45°, and h is 0.5mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 1.5mm.

[0123] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 28°C; after the continuous power-on ends, the welding rate of the welding joint is 92% and the welding strength is 27MPa.

[0124] Example 5

[0125] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0126] (1) Preparation of raw materials;

[0127] Thermoplastic resin: PEI;

[0128] Conductive core layer: CNT particle composite film, thickness 0.2mm;

[0129] Parts to be welded: GF / PEI composite material, GF volume fraction is 60%;

[0130] (2) preparing an implant layer;

[0131] (2.1) In a mold, after covering the upper and lower sides of the conductive core layer with thermoplastic resin, the temperature is controlled to 390°C, and hot pressing is first performed at 1.8 MPa and maintained for 30 minutes, and then hot pressing is performed at 5.5 MPa and maintained for 18 minutes to obtain a semi-finished product, wherein the distance between the upper surface and the lower surface of the semi-finished product and the conductive core layer is 0.01 mm;

[0132] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot pressing is performed at 350°C and 2.5 MPa and the pressure is maintained for 25 minutes. After the mold is cooled to 50°C, the pressure is released, the mold is opened, and the implant layer is removed;

[0133] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.05 mm;

[0134] (3) Resistance welding;

[0135] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously supplied for 30 seconds at a total input current of 20A to achieve resistance welding of the thermoplastic composite material; wherein, the parameters related to the welding device are: D1 is 0.2mm, D2 is 0.2mm, d is 0.1mm, θ is 60°, and h is 0.6mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 1mm.

[0136] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 40°C; after the continuous power-on ends, the welding rate of the welding joint is 90% and the welding strength is 20MPa.

[0137] Example 6

[0138] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0139] (1) Preparation of raw materials;

[0140] Thermoplastic resin: PA;

[0141] Conductive core layer: 400 mesh stainless steel mesh, thickness 0.2mm;

[0142] Parts to be welded: GF / PA composite material, GF volume fraction is 60%;

[0143] (2) preparing an implant layer;

[0144] (2.1) In a mold, after covering the upper and lower sides of the conductive core layer with thermoplastic resin, the temperature is controlled to 280°C, and hot pressing is first performed at 1.5 MPa and maintained for 30 minutes, and then hot pressing is performed at 5 MPa and maintained for 15 minutes to obtain a semi-finished product, wherein the distance between the upper surface and the lower surface of the semi-finished product and the conductive core layer is 0.01 mm;

[0145] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot pressing is performed at 260°C and 2MPa and the pressure is maintained for 20 minutes. After the mold is cooled to 50°C, the pressure is released, the mold is opened, and the implant layer is taken out;

[0146] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.05 mm;

[0147] (3) Resistance welding;

[0148] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously turned on for 30 seconds at a total input current of 15A to achieve resistance welding of the thermoplastic composite material; among which, the parameters related to the welding device are: D1 is 5mm, D2 is 5mm, d is 2.5mm, θ is 30°, and h is 0.4mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 2mm.

[0149] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 20°C; after the continuous power-on ends, the welding rate of the welding joint is 95% and the welding strength is 20MPa.

[0150] Example 7

[0151] A resistance welding method for thermoplastic composite materials, the specific steps are as follows:

[0152] (1) Preparation of raw materials;

[0153] Thermoplastic resin: PP;

[0154] Conductive core layer: 400 mesh stainless steel mesh, thickness 0.2mm;

[0155] Parts to be welded: GF / PP composite material, GF volume fraction is 60%;

[0156] (2) preparing an implant layer;

[0157] (2.1) In a mold, after covering the upper and lower sides of the conductive core layer with thermoplastic resin, the temperature is controlled to 230°C, and hot pressing is first performed at 1.5 MPa and maintained for 30 minutes, and then hot pressing is performed at 5 MPa and maintained for 15 minutes to obtain a semi-finished product, wherein the distance between the upper surface and the lower surface of the semi-finished product and the conductive core layer is 0.01 mm;

[0158] (2.2) In the mold, after covering the upper and lower sides of the semi-finished product with thermoplastic resin, hot pressing is performed at 210°C and 2MPa and the pressure is maintained for 20 minutes. After the mold is cooled to 40°C, the pressure is released, the mold is opened, and the implant layer is taken out;

[0159] The distance between the upper surface and the lower surface of the prepared implant layer and the conductive core layer is 0.05 mm;

[0160] (3) Resistance welding;

[0161] After the implant layer and the two parts to be welded are assembled on the welding device, the power is continuously turned on for 30 seconds at a total input current of 13A to achieve resistance welding of the thermoplastic composite material; among which, the parameters related to the welding device are: D1 is 10mm, D2 is 10mm, d is 5mm, θ is 20°, and h is 0.4mm; the distance between the right edge of the pinhole substrate of the left needle-punctured electrode array and the area to be welded, and the distance between the left edge of the pinhole substrate of the right needle-punctured electrode array and the area to be welded are both 2mm.

[0162] The test shows that during the continuous power-on process, the maximum temperature difference in the area to be welded is 25°C; after the continuous power-on ends, the welding rate of the welding joint is 94% and the welding strength is 18MPa.

[0163] In order to intuitively analyze the temperature distribution characteristics of the implant layer during the welding process, an infrared thermal imager was set up 1m above the implant layer and kept vertically aligned during the welding process. The infrared thermal imager was started to record temperature data. When the infrared thermal imager detected that the highest temperature in the area to be welded was close to the melting temperature of the thermoplastic resin, the power supply was immediately cut off and the recording of temperature data was stopped to obtain the infrared thermal image. Figure 7 The infrared thermal imaging results of Example 1, Example 5 and Example 7 show that the maximum temperature difference in the area to be welded does not exceed 40°C, which is significantly improved compared to the temperature difference (over 70°C) caused by the traditional welding method.

Claims

1. A resistance welding method for thermoplastic composite materials, characterized in that: After the implant layer covers the overlap of the front and rear parts to be welded, and the left and right ends of the implant layer are exposed outside the area to be welded, the needles of the left and right needle electrode arrays are inserted into the left and right ends of the implant layer from top to bottom, respectively, so that they are in contact with the conductive core layer in the implant layer, and then continuously energized, thereby realizing resistance welding of the thermoplastic composite material; The needles in the acupuncture electrode array are arranged in a matrix, with the row direction parallel to the front-to-back direction. The needles in two adjacent rows are offset by D1 / 2 along the row direction. D1 is the center distance between two adjacent needles in the same row, and the value range of D1 is 0.2-10mm. The distance D2 between the centers of two adjacent rows of needles along the column direction is 0.1-10mm, and the diameter d of the needles is 0.1-5mm.

2. The resistance welding method of a thermoplastic composite material according to claim 1, characterized in that: The exposed length of the needle is h=2×D3+T+α, D3 is the distance between the upper surface or the lower surface of the implant layer and the conductive core layer, T is the thickness of the conductive core layer, and α is 0.1-0.3 mm.

3. The resistance welding method of a thermoplastic composite material according to claim 1, characterized in that: The sharpening angle θ of the needle tip is 20-60°.

4. The resistance welding method of a thermoplastic composite material according to claim 1, characterized in that: The acupuncture electrode array consists of a planar bottom plate, a pinhole substrate and acupuncture needles. The pinhole substrate and the acupuncture needles are both located below the planar bottom plate. The pinhole substrate is fixedly connected to the planar bottom plate. The needle tips of the acupuncture needles face downward, and the needle tails are embedded in the pinhole substrate.

5. The resistance welding method of a thermoplastic composite material according to claim 4, characterized in that: The distance between the right edge of the pinhole substrate of the left acupuncture electrode array and the area to be welded is 1-2 mm, and the distance between the left edge of the pinhole substrate of the right acupuncture electrode array and the area to be welded is 1-2 mm; The left and right ends of the implant layer are completely located directly below the areas where the needles of the two acupuncture electrode arrays are located.

6. The resistance welding method of a thermoplastic composite material according to claim 1, characterized in that: The steps for preparing the implant layer are as follows: (1) In a mold, after the thermoplastic resin is covered on the upper and lower sides of the conductive core layer, a first hot pressing is performed to obtain a semi-finished product; (2) In the mold, after the thermoplastic resin is covered on the upper and lower sides of the semi-finished product, a second hot pressing is performed. After the mold is cooled, the pressure can be released, the mold can be opened, and the implant layer can be taken out; The temperature of each heat pressing is higher than the melting temperature of the thermoplastic resin and lower than the decomposition temperature of the thermoplastic resin.

7. The resistance welding method of a thermoplastic composite material according to claim 6, characterized in that: The temperature of each hot pressing is 30-50°C higher than the melting temperature of the thermoplastic resin; during the first hot pressing, the pressure is maintained at 1.5-2MPa for 30-35min, and then at 5-6MPa for 15-20min; during the second hot pressing, the pressure is maintained at 2-3MPa for 20-30min.

8. A resistance welding method for thermoplastic composite materials according to any one of claims 1 to 7, characterized in that: During the continuous power-on process, the temperature difference in the area to be welded does not exceed 40°C; after the continuous power-on ends, the welding rate of the welded joint is higher than 90%, and the welding strength is 18-30MPa.

9. A device for implementing a resistance welding method of a thermoplastic composite material as claimed in any one of claims 1 to 8, characterized in that: It comprises a power source, an insulating base plate (12), an insulating force-applying block (10) arranged directly above the insulating base plate (12), two acupuncture electrode arrays, and a pressurizing device; The two acupuncture electrode arrays are distributed on the left and right sides of the insulating force application block (10), and both are connected to a power source at the same time; the pressure device is used to apply downward pressure to the insulating force application block (10) and the two acupuncture electrode arrays.

10. The device according to claim 9, characterized in that The pressurizing device comprises two insulating connecting blocks (7), two metal rods (6), a metal plate (3), two metal knobs (5), a No. 2 cylinder (2), and a No. 1 cylinder (1); The two insulating connection blocks (7) are respectively located directly above the two acupuncture electrode arrays and are fixedly connected thereto; the two metal rods (6) are respectively located directly above the two insulating connection blocks (7) and are fixedly connected thereto; after the two metal rods (6) simultaneously pass through the metal plate (3) from bottom to top, they are respectively connected to the two metal knobs (5), and the metal knobs (5) are used to fix the metal rods (6) to the metal plate (3); the metal plate (3) is provided with a metal guide rail (4) for the two metal rods (6) to move in the left-right direction; The No. 2 cylinder (2) is located directly above the insulating force block (10); The metal plate (3) is a rectangular plate, and there are four No. 1 cylinders (1) in total, which are respectively located at the four corners of the metal plate (3).

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