A method of induction welding of thermoplastic composites based on magnetic concentrators

Abstract

The application provides a thermoplastic composite material induction welding method based on a magnetic concentrator, comprising the following steps: preparing a thermoplastic laminated plate, cutting and then polishing, cutting a thermoplastic resin film with the same resin matrix, placing the polished thermoplastic laminated plate and the thermoplastic resin film in a single lap joint form on a to-be-welded area, fixing in an induction welding device, installing a magnetic concentrator above the composite material on the side far from an induction coil and applying pressure, controlling induction welding parameters to realize welding of the composite material plate, continuously maintaining pressure after welding until the material is cooled and then unloading, and completing induction welding of the thermoplastic composite material. The application uses a permanent magnet as the magnetic concentrator to improve the temperature of the center point of the welding interface and increase the effective welding area, can effectively alleviate the problems of too low temperature in the center area of the induction welding interface or overheating at the edge, and obviously improves the mechanical properties of the thermoplastic composite material welding joint.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material welding method, and particularly relates to a thermoplastic composite material induction welding method based on a magnetic concentrator. BACKGROUND

[0002] Carbon fiber reinforced thermoplastic composite materials have the characteristics of short forming cycle, high production efficiency, re-melting forming and weldability, and are widely used in the fields of aerospace and the like. Induction welding has the characteristics of precise welding area, strong flexibility and non-contact welding, and can avoid the problems of stress concentration and weight increase in traditional mechanical connection, the mismatch between adhesive and thermoplastic resin with weak polarity and poor environmental adaptability in adhesive connection, stress concentration and electrochemical corrosion caused by the residual resistance wire in the welding interface in resistance welding, and the limitation of ultrasonic welding which is not suitable for large-area or special-shaped structural parts. Therefore, induction welding is considered to be one of the most promising thermoplastic composite material connection technologies.

[0003] However, the temperature non-uniformity of the induction welding surface of the carbon fiber reinforced thermoplastic composite material is extremely strong, and the phenomenon of excessively low center temperature or excessively high edge region temperature is prone to occur, which seriously affects the quality and strength of the welding interface, and has become a key problem restricting the further application of induction welding technology.

[0004] Therefore, a thermoplastic composite material induction welding method based on a magnetic concentrator is provided. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a thermoplastic composite material induction welding method based on a magnetic concentrator to solve the problems in the background art.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a thermoplastic composite material induction welding method based on a magnetic concentrator, comprising the following steps:

[0007] S1, laminating a prepreg stack according to a layup scheme on the surface of a mold, and curing and forming the prepreg stack under the influence of curing and forming factors to complete the preparation of a thermoplastic laminate;

[0008] S2, cutting and polishing the thermoplastic laminate;

[0009] S3, cutting a thermoplastic resin film of the same resin matrix, and the cutting area size corresponds to the area size of the welding joint region;

[0010] S4, placing the polished thermoplastic laminate and the thermoplastic resin film in a single lap joint form in the welding region, and fixing them in an induction welding device;

[0011] S5, install the magnetic concentrator above the composite material on the side far from the induction coil, apply pressure, control the induction welding parameters to realize welding of the composite material plate, and after the welding is completed, continue to apply pressure until the material cools down and then unload, to complete the induction welding of the thermoplastic composite material;

[0012] S6, use a universal testing machine to test the single lap tensile shear of the welded thermoplastic composite material, and check the welding strength of the welded joint.

[0013] As a further description of the application, the resin matrix of the thermoplastic laminated plate 3 is polyphenylene sulfide PPS, polyether ketone PEK, polyether ether ketone PEEK, polyether ketone ketone PEKK or polyether imide PEI.

[0014] As a further description of the application, the thermoplastic laminated plate in S2 needs to be cleaned and dried after polishing, specifically, after cleaning the surface impurities with anhydrous ethanol, it is placed in an oven for drying or naturally air-dried, and the cut thermoplastic resin film in S3 needs to be cleaned and dried, specifically, after cleaning the surface impurities with anhydrous ethanol, it is placed in an oven for drying or naturally air-dried.

[0015] As a further description of the application, the thermoplastic resin film in S4 is placed between the two thermoplastic laminated plates to be welded and is fixed by a supporting structure.

[0016] As a further description of the application, the magnetic concentrator is cylindrical, the diameter of the magnetic concentrator is smaller than the diameter of the induction coil, the induction coil is placed directly below the magnetic concentrator, and the line connecting the centers of the induction coil and the magnetic concentrator is perpendicular to the thermoplastic laminated plate.

[0017] Compared with the prior art, the application has the following advantages:

[0018] The application uses a permanent magnet as a magnetic concentrator, then prepares a thermoplastic composite panel, and finally places the magnetic concentrator on the side of the composite material far from the induction coil for induction welding, to obtain a thermoplastic composite welding member. The permanent magnet is used as a magnetic concentrator to improve the temperature of the center point of the welding interface and increase the effective welding area, which can effectively alleviate the problem of too low temperature in the center area of the induction welding interface or overheating at the edge, significantly improve the mechanical properties of the thermoplastic composite material, and in the application, a thermoplastic resin film with the same resin matrix is added in the middle of the welding joint to improve the glue content of the welding interface, thereby enhancing the welding quality. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of induction welding of the application;

[0020] Figure 2 is a forming process curve of the composite material in the embodiment of the application;

[0021] Figure 3 Schematic diagram of mechanical properties of induction welded joints with and without magnetic concentrators in an embodiment of the present invention;

[0022] Description of reference numerals:

[0023] 1-magnetic concentrator; 2-support structure; 3-thermoplastic laminate; 4-induction coil; 5-thermoplastic resin film. DETAILED DESCRIPTION

[0024] 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 the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] Examples, such as Figure 1 As shown, the present invention provides a technical solution: a thermoplastic composite induction welding method based on a magnetic concentrator, comprising the following steps:

[0026] S1. Laying the prepreg stack on the mold surface according to the layup plan, curing and shaping it under the influence of curing and molding factors to complete the preparation of the thermoplastic laminate 3. The resin matrix of the thermoplastic laminate 3 is polyphenylene sulfide (PPS), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), or polyetherimide (PEI);

[0027] S2, cutting the thermoplastic laminate 3 and polishing it. After polishing, it needs to be cleaned and dried. Specifically, it is washed with anhydrous ethanol to remove surface impurities, and then placed in an oven for drying or air drying.

[0028] S3. Cut the thermoplastic resin film 5 with the same resin matrix to an area corresponding to the area of ​​the welded joint. The cut thermoplastic resin film 5 needs to be cleaned and dried, specifically by cleaning with anhydrous ethanol to remove surface impurities, and then drying in an oven or air-drying.

[0029] S4. Place the polished thermoplastic laminate 3 and the thermoplastic resin film 5 in the area to be welded in a single overlapped manner and fix them in an induction welding device. Specifically, the thermoplastic resin film 5 is placed between the two thermoplastic laminates 3 to be welded and fixed using a support structure 2.

[0030] S5, install the magnetic concentrator 1 above the composite material on the side away from the induction coil 4, apply pressure, control the induction welding parameters to realize the welding of the composite material plate, the magnetic concentrator 1 is a cylindrical permanent magnet, the diameter of the magnetic concentrator 1 is smaller than the diameter of the induction coil 4, the induction coil 4 is placed directly below the magnetic concentrator 1, the line connecting the center of the induction coil 4 and the center of the magnetic concentrator 1 is perpendicular to the thermoplastic laminated plate 3, after welding, continue to apply pressure until the material cools down and then unload, complete the induction welding of the thermoplastic composite material;

[0031] S6, use a universal testing machine to test the single lap tensile shear of the welded thermoplastic composite material, and check the welding strength of the welded joint.

[0032] Experimental example, taking carbon fiber reinforced thermoplastic composite induction welding as an example, CF / PEEK,

[0033] S1, cut the prepreg into 300mm*300mm, then wrap it with high-temperature release cloth coated with release agent, lay it on the surface of the mold, and place it in the hot press together, refer to the specified curing process system, such as Figure 2 , cure in a high-temperature and high-pressure environment, after cooling and pressure relief, take out the thermoplastic composite laminated plate 3 together with the mold.

[0034] S2, cut the thermoplastic laminated plate 3 to 25mm*150mm using a cutting machine, and polish the surface with sandpaper to remove the release agent on the surface, then clean it with anhydrous ethanol to remove surface impurities, and then put it in an oven to dry or air dry.

[0035] S3, cut the PEEK resin film to 25mm*25mm, and clean it with anhydrous ethanol to remove surface impurities, then put it in an oven to dry or air dry.

[0036] S4, fix the thermoplastic composite laminated plate 3 prepared in S2 and the thermoplastic resin film 5 prepared in S3 in a single lap form using high-temperature resistant adhesive tape, place it in the welding area, and fix it with supporting material 2, which is mica sheet, which is also conducive to heat dissipation on the surface of the composite material.

[0037] S5, fix the magnetic concentrator 1 above the composite material on the side away from the induction coil 4, as shown in Figure 1 , and apply pressure. Ensure the same welding parameters, realize the welding of the composite material plate under the conditions of adding and not adding the magnetic concentrator, after welding, continue to apply pressure until the material cools down and then unload, complete the induction welding of the thermoplastic composite material;

[0038] S6, using a universal testing machine to test the thermoplastic composite material welding sample welded in S5 for single lap tensile shear, to check the welding strength of the welding joint, as shown in Figure 3

[0039] The results show that the highest strength of the welding joint after adding the magnetic concentrator can reach 37.75Mpa, which is increased by 36.65% compared with the welding joint without adding the magnetic concentrator.

[0040] It should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or action from another, and do not necessarily require or imply that there is any such actual relationship or order between these entities or actions. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0041] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.​

Claims

1. A method for induction welding of thermoplastic composite materials based on a magnetic concentrator, characterized in that: The following steps are involved: S1, laying the prepreg stack on the mold surface according to the lay-up plan, and solidifying and forming it under the influence of the curing and molding factors to complete the preparation of the thermoplastic laminate (3); S2, cutting the thermoplastic laminate (3) and then grinding it; S3, cutting the thermoplastic resin film (5) of the same resin matrix, wherein the cutting area corresponds to the area of ​​the welding joint; S4, placing the polished thermoplastic laminate (3) and the thermoplastic resin film (5) in a single overlapped manner in the area to be welded, and fixing them in an induction welding device; S5. Install the magnetic concentrator (1) above the composite material on the side away from the induction coil (4), apply pressure, control the induction welding parameters to achieve welding of the composite material plate, and maintain the pressure after welding until the material cools down and then unload to complete the induction welding of the thermoplastic composite material, wherein the magnetic concentrator (1) is a cylindrical permanent magnet, the diameter of the magnetic concentrator (1) is smaller than the diameter of the induction coil (4), the induction coil (4) is placed directly below the magnetic concentrator (1), and the line connecting the center of the induction coil (4) and the center of the magnetic concentrator (1) is perpendicular to the thermoplastic laminate (3); S6. Use a universal testing machine to perform a single lap tensile shear test on the completed thermoplastic composite material weld to check the welding strength of the welded joint.

2. The induction welding method for thermoplastic composite materials based on a magnetic concentrator according to claim 1, characterized in that: The resin matrix of the thermoplastic laminate (3) is polyphenylene sulfide (PPS), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK) or polyetherimide (PEI).

3. The induction welding method for thermoplastic composite materials based on a magnetic concentrator according to claim 1, characterized in that: The thermoplastic laminate (3) in S2 needs to be cleaned and dried after polishing, specifically by using anhydrous ethanol to remove surface impurities, and then placing it in an oven for drying or air drying. The cut thermoplastic resin film (5) in S3 needs to be cleaned and dried, specifically by using anhydrous ethanol to remove surface impurities, and then placing it in an oven for drying or air drying.

4. The induction welding method for thermoplastic composite materials based on a magnetic concentrator according to claim 1, characterized in that: The thermoplastic resin film (5) in S4 is placed between two thermoplastic laminates (3) to be welded and fixed by a support structure (2).

5. The induction welding method for thermoplastic composite materials based on a magnetic concentrator according to claim 1, characterized in that: The curing molding factors are temperature, time and pressure.

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