Method for joining a metal element and a heat-cured resin element

Abstract

Method for joining a metal element (11) and a resin element (12), wherein a thermoplastic resin (50) is placed between the metal element (11) and the resin element (12), wherein the resin element is a thermo-cured resin element (12), wherein the thermo-cured resin of the thermo-cured resin element is not melted by heat, and The process is implemented by friction stir welding, in which the metal element (11) and the thermo-cured resin element (12), with the thermoplastic resin (50) placed between them, are stacked on top of each other, a rotating rotary tool (16) is pressed against the metal element (11) to generate frictional heat, thereby softening and melting the thermoplastic resin (50), and then the molten thermoplastic resin (50) solidifies to join the metal element (11) and the thermo-cured resin element (12). including friction stir welding: a first step of stacking the metal element (11) and the thermo-cured resin element (12) on top of each other with the thermoplastic resin (50) in between; and a second step of pressing the rotating tool (16) against the metal element (11) to generate frictional heat, thereby softening and melting the thermoplastic resin (50), and solidifying the molten thermoplastic resin to join the metal element (11) and the resin element (12) together, characterized by that the second step comprises an immersion / stirring process of immersing the rotary tool (16) into the metal element (11) to a depth close to an interface (13) between the metal element (11) and the thermoplastic resin (50), but not reaching it, wherein the second step comprises a preheating process of rotating the rotary tool (16), wherein only a front end of the rotary tool (16) is in contact with the surface of the metal element (11), wherein the preheating process is carried out before the immersion / stirring process, wherein during the preheating process the rotary tool (16) may only rotate under a first pressure for a first pressing time, and During the immersion / stirring process, the rotary tool (16) may only rotate for a second pressing time, which is shorter than the first pressing time, under a second pressure that is greater than the first pressure. wherein the thermoplastic resin (50) placed between the metal element (11) and the thermosetting resin element (12) has a thickness greater than 50 µm and less than or equal to 600 µm, preferably from 100 µm to 550 µm, wherein the melting point Tm (°C) of the thermoplastic polymer is 140-350°C, in particular 140-300°C, and wherein the connection temperature, which is the highest temperature of the region (112) located directly below it at an interface between the thermoplastic resin (50) and the resin element (12), is Tm - 50°C to Tm + 150°C, wherein acid-modified polyolefin, thermoplastic epoxy polymer, polyamide or vinyl acetate-containing polymer is used as the thermoplastic resin and When using acid-modified polyolefin as a thermoplastic resin (50), the joining temperature Tm to Tm + 150°C, suitable Tm + 20°C to Tm + 130°C, far more suitable T + 70°C to Tm + 120°C, When using a thermoplastic epoxy polymer as the thermoplastic resin (50), the joining temperature Tm - 50°C to Tm + 30°C is suitable, Tm - 10°C to Tm + 20°C, When using polyamide as a thermoplastic resin (50), the joining temperature is Tm + 10°C to Tm + 70°C, suitable Tm + 20°C to Tm + 60°C and When using a vinyl acetate-containing polymer as a thermoplastic resin (50), the joining temperature Tm is to Tm + 80°C.

Description

TECHNICAL AREA

[0001] The present invention relates to a method for joining a metal element and a heat-cured resin element. TECHNICAL BACKGROUND

[0002] Weight reduction is essential in various fields, such as motor vehicles, railcars, and aircraft. In the automotive sector, for example, the use of high-strength materials has contributed to reducing the thickness of steel sheets. Furthermore, aluminum alloys or even resin materials are used as alternatives to steel. In such fields, the development of technologies for joining metal and resin components plays a crucial role not only in reducing the weight of a vehicle body but also in improving the strength and stiffness of the bonded product and increasing productivity.

[0003] So far, so-called "friction stir welding" (FSW) has been proposed as a method for joining a metal element and a resin element. In friction stir welding, as in Fig. Figure 7 shows a metal element 511 and a resin element 512 stacked on top of each other, and a rotating rotary tool 516 is pressed against the metal element 511 to generate frictional heat, which melts the resin element 512. The molten resin element 512 then solidifies to join the metal element 511 and the resin element 512 together (see, for example, JP 2014-208461 A, WO 2015 / 107873 A1 or DE 112015000397 T5). However, if a thermosetting resin element is used, the resin element cannot be joined to the metal element because the thermosetting resin is not melted by the heat.

[0004] JP 2009-279858 A discloses a method for joining a metal element with a thermoplastic resin element by friction stir welding, wherein a layer of a thermoplastic resin is inserted between them.

[0005] DE 10 2013 202 583 B3 discloses a friction welding process for attaching a metal mounting bushing to a housing (thermoset resin). To improve the quality of the connection, the mounting bushing is attached to the housing using a friction welding element. The friction welding element consists of the mounting bushing to which a friction welding jacket (thermoset resin) with a radially external friction welding contour is molded. A special design of the friction welding contour creates bonding areas between the friction welding element and the housing during the friction welding process.

[0006] US 2007 / 0044406 A1 discloses a connection consisting of: at least one structural element defining first and second mating surfaces in an opposing configuration and defining an interface between them; a connection extending through the interface and connecting the first and second mating surfaces of the at least one structural element; and a thermoplastic sealant arranged in the interface, wherein the thermoplastic sealant has a melting temperature lower than the melting temperature of the at least one structural element. SUMMARY OF THE INVENTIONAL PROBLEM

[0007] In light of the foregoing background, one or more aspects of the present invention are directed to provide a method for joining a metal element and a resin element, even when a thermosetting resin element is used as the resin element. SOLUTION TO THE PROBLEM

[0008] This problem is solved by a method according to claim 1. Preferred aspects of the present invention are the subject of the dependent claims.

[0009] The present invention relates to a method for joining a metal element and a thermosetting resin element, wherein a thermoplastic resin is placed between them. ADVANTAGES OF THE INVENTION

[0010] The joining method of the present invention enables the joining of a metal element and a heat-cured resin element. ABBREVIATION OF THE DRAWINGS Fig. Figure 1 is a schematic view showing an example of part of a friction stir welding device suitable for a method of joining a metal element and a heat-cured resin element of the present invention. Fig. Figure 2 is a view showing, on an enlarged scale, a front end of an example of a rotary tool as a pressing element used in the joining method according to the invention. Fig. Figure 3 is a schematic cross-sectional view showing an example of a preheating process of the present invention. Fig. Figure 4 is a schematic cross-sectional view showing an example of an immersion / stirring process, a continuous stirring process and a holding process of the present invention. Fig. Figure 5 is a schematic view showing a method for measuring joint strength in examples. Fig. Figure 6 is a graph showing a relationship between connection temperature and the connection strength measured in examples. Fig. Figure 7 is a schematic cross-sectional view showing a method for joining a metal element and a resin element according to the prior art. DETAIL DESCRIPTION [Method for joining metal element and thermosetting resin element]

[0011] According to a method according to the invention for joining a metal element and a thermosetting resin element, the metal element and the thermosetting resin element are joined together by melting and solidifying a thermoplastic resin that is placed between the metal element and the thermosetting resin element. The thermosetting resin of the thermosetting resin element is not melted by heat in this process. The method is implemented by friction stir welding, in which the metal element and the resin element, with the thermoplastic resin placed between them, are stacked on top of each other. A rotating tool is pressed against the metal element to generate frictional heat, thereby softening and melting the thermoplastic resin. The molten thermoplastic resin then solidifies to join the metal element and the thermosetting resin element.

[0012] The inventive method for joining the metal element and the resin element using friction stir welding is described below with reference to the drawings.

[0013] It should be noted that the components shown in the drawings are merely schematic representations for the purpose of clarifying the present invention and that their appearance and dimensional relationships may differ from actual components. In this document, the directions "vertical," "horizontal," "front," and "back," used directly or indirectly in the description, correspond to the directions "vertical," "horizontal," "front," and "back" in the drawings. Unless otherwise indicated, common reference numerals denote identical elements, parts, dimensions, or regions in the drawings. [Method for joining metal element and resin element by friction stir welding]

[0014] A joining method according to the invention (friction stir welding) is described in more detail below. (1) Connecting device

[0015] Fig. Figure 1 is a schematic view showing an example of a part of a friction stir welding device suitable for the joining method according to the invention. A Fig. The friction stir welding device 1 shown is designed as a device for joining a metal element 11 and a resin element 12 by friction stir welding and comprises a cylindrical rotary tool 16 as a pressing element.

[0016] The rotary tool 16, which is driven by a (not shown) drive source to rotate about a central axis line X (in Fig. As the tool 16 rotates in the direction of arrow A1 (as shown in Figure 2), it moves downwards in the direction of arrow A2 towards a workpiece 10, which is obtained by vertically stacking the metal element 11 on the resin element 12 with a thermoplastic resin (not shown) placed between them. At this point, the turning tool 16 exerts pressure on a pressure region P (pressure region) of a surface of the metal element 11. The pressure exerted by the turning tool 16 generates frictional heat, which is transferred to the thermoplastic resin to soften and melt it. The molten resin then solidifies, thus bonding the metal element 11 and the resin element 12 together.

[0017] Fig. Figure 2 shows a front end of the rotary tool 16 at an enlarged scale. Fig. Figure 2 shows the right half of the appearance of the rotary tool 16 and the left half shows a cross-section of the rotary tool 16. As in Fig. As shown in 2, the cylindrical rotary tool 16 comprises at its front end (a lower end in Fig. 2) a journal 16a and a shoulder 16b. The shoulder 16b is a front end section of the turning tool 16, which includes a round end face of the turning tool 16. The journal 16a is a cylindrical section extending outwards from the round end face of the turning tool 16 along the central axis X of the turning tool 16 (in Fig. 2 downwards) protrudes and has a smaller diameter than the shoulder 16b. The pin 16a positions the turning tool 16 when the rotating turning tool 16 first comes into contact with the workpiece 10 and presses against it.

[0018] The material of the turning tool 16 and the dimensions of the journal and shoulder of the turning tool 16 can be determined based on the type of metal forming the metal element 11 that is to be pressed by the turning tool 16. For example, if the metal element 11 is made of an aluminum alloy, the turning tool 16 can be made of a tool steel (e.g., SKD61), the shoulder 16b can have a diameter D1 of 10 mm, and the journal 16a can have a diameter D2 of 2 mm and a projection height h of 0.5 mm. Alternatively, if the metal element 11 is made of steel, the turning tool 16 can be made of silicon nitride, polycrystalline cubic boron nitride (PCBN), or any other suitable material, the shoulder 16b can have a diameter D1 of 10 mm, and the journal 16a can have a diameter D2 of 3 mm and a projection height h of 0.5 mm.Naturally, the materials and dimensions are merely examples and not limiting. For instance, the diameter D1 of the shoulder 16b is generally 5-30 mm, preferably 5-15 mm, but is not limited to this.

[0019] A cylindrical holding tool 17, with a diameter greater than or equal to the diameter of the rotary tool 16, is arranged coaxially with and below the rotary tool 16. The holding tool 17 is moved upwards towards the workpiece 10 by the (not shown) drive source in the direction of arrow A3. At the latest when the rotary tool 16 begins to press against the workpiece 10, the upper end face of the holding tool 17 comes into contact with a bottom surface of the workpiece 10 (more precisely, a bottom surface of the resin element 12). With the workpiece 10 sandwiched between the holding tool 17 and the rotary tool 16, the holding tool 17 supports the workpiece 10 from below against the pressure exerted by the rotary tool 16 during a pressing period, e.g., during friction stir welding.Note that the holding tool 17 is not necessarily moved in the direction of arrow A3. Alternatively, the turning tool 16 can be moved in the direction of arrow A2 after the workpiece 10 has been placed on the holding tool 17.

[0020] The friction stir welding device 1 is mounted on a (not shown) drive control unit consisting of an articulated robot or any other suitable device. The drive control unit appropriately controls the coordinate positions of the rotary tool 16 and the holding tool 17, the rotational speed (rpm) of the rotary tool 16, the applied pressure (N), the pressing time (s), and any other suitable parameter. Even if this is in Fig. Not shown in Figure 1, the friction stir welding device 1 includes a holding device, such as a spacer or a clamp, for prior fixation of the workpiece 10 and limiting upward distortion of the metal element 11 when pressed against it by the rotary tool 16. (2) Thermoplastic resin

[0021] A thermoplastic resin 50 (see Fig. 3) is a so-called “adhesive interlayer” that helps to bond the metal element 11 and the resin element 12. The thermoplastic resin 50 is melted by applied heat and then cooled to solidify, thereby bonding the metal element 11 and the resin element 12 together.

[0022] The thermoplastic resin 50 can have any shape as long as it is placed between the metal element 11 and the resin element 12. For example, the thermoplastic resin can be in the form of a sheet, a coating formed on the surface of the metal element, or a coating formed on the surface of the resin element, or it can have a combination of these forms. The "sheet" is a thin, plate-shaped product that does not adhere to either the metal element or the resin element and can be purchased separately. The sheet can be formed by thermally pressing a thermoplastic resin.The “coating formed on the surface of the metal element” or the “coating formed on the surface of the resin element” is a thin film that adheres to the surface of the metal element or resin element and can be formed by applying a solution or dispersion of a thermoplastic resin to the surface and allowing the applied solution or dispersion to dry. The fact that the thermoplastic resin has “a combination of these forms” means that the thermoplastic resins are placed between the metal element 11 and the resin element 12 in the form of at least two of the forms described above. Fig. 3 is a schematic cross-sectional view along line XX and in one direction of the Fig. The arrows shown in Figure 1 illustrate an example of a preheating process of the present invention described later.

[0023] The type of thermoplastic resin is described in more detail below. Thermoplastic polymers used in the automotive industry, particularly those with a functional group, are preferred. If the thermoplastic resin placed between the metal element and the resin element has a functional group, the interaction between the thermoplastic resin and the resin element 12, as well as the interaction between the thermoplastic resin and the metal element 11, is accelerated during joining, thereby further improving the bond strength between the elements.

[0024] A functional group preferably comprising the thermoplastic polymer may be a group comprising at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a fluorine atom, and a sulfur atom. More preferably, the functional group may contain at least one oxygen atom and / or one nitrogen atom, and far more preferably, the functional group may contain at least one oxygen atom.

[0025] Non-restrictive examples of such a functional group include a carboxyl group (-COOH), a hydroxyl group (-OH), an amide group (-CO-NH-), an ester group (-CO-O-), an ether group (-O-), a thioether group (-S-), a carboxylate group (-COOR (where R is an alkyl group with 1-3 carbon atoms)), a fluorine atom (-F), a urethane group (-NH-CO-O-), and a carbonate group (-O-CO-O-). The functional group may be at least one selected from the group consisting of these groups. Preferably, the functional group may be at least one selected from the group consisting of a carboxyl group (-COOH), a hydroxyl group (-OH), an amide group (-CO-NH-), and an ester group (-CO-O-). Preferably, the functional group can be at least one selected from the group consisting of a carboxyl group (-COOH), a hydroxyl group (-OH) and an amide bonding group (-CO-NH-).Much preferably, the functional group may be at least one selected from the group consisting of a carboxyl group (-COOH) and a hydroxyl group (-OH). Most preferably, the functional group may be a carboxyl group (-COOH). The ester bonding group does not include a carboxyl group, a carboxylate group, a urethane bonding group, or a carbonate group.

[0026] The functional group described above can form at least part of a main chain and / or a side chain of the thermoplastic polymer.

[0027] The thermoplastic polymer generally has a hydrogen atom in its main chain and / or side chain in addition to the functional group described above. Thus, the hydrogen atom in the thermoplastic polymer interacts with an oxygen atom in the metal oxide on the surface of the metal element via a hydrogen bond. A thermosetting resin (to be described later), which forms the resin element, generally has a hydrogen atom and an oxygen atom. These atoms interact with the functional group of the thermoplastic polymer via a hydrogen bond. This results in the metal element 11 and the resin element 12 being bonded together.

[0028] Examples of the thermoplastic polymer with a functional group according to the invention include acid-modified polyolefin, a thermoplastic epoxy polymer, polyamide, and a vinyl acetate-containing polymer. The thermoplastic polymer does not necessarily have a functional group and can, for example, be a polyolefin. These polymers can be used individually as thermoplastic polymers, or two or more of them can be used in combination. With a view to further improving the bond strength, preferred examples of the thermoplastic polymer include acid-modified polyolefin, a thermoplastic epoxy polymer, a vinyl acetate-containing polymer, and a mixture thereof. Similarly, more preferred examples of the thermoplastic polymer include acid-modified polyolefin, a thermoplastic epoxy polymer, polyamide, and a mixture thereof.Similarly, far more preferred examples of the thermoplastic polymer include acid-modified polyolefin, a thermoplastic epoxy polymer, and a mixture thereof. Similarly, the most preferred thermoplastic polymer is acid-modified polyolefin.

[0029] Acid-modified polyolefin is a thermoplastic polymer with a carboxyl group in the side chain. "Acid-modified polyolefin" refers to polyolefin modified by acid. Non-restrictive examples of acid-modified polyolefin include a copolymer of a carboxyl-containing monomer and an olefin-based monomer. The carboxyl-containing monomer can be an unsaturated carboxylic acid with 3-8, preferably 3-6, carbon atoms (including one carbon atom in a carboxyl group). Non-restrictive examples include acrylic acid, methacrylic acid, maleic acid, fumaric acid, citraconic acid, and citraconic anhydride. The olefin-based monomer can be an unsaturated hydrocarbon with 2-8, preferably 2-4, carbon atoms. Non-restrictive examples include ethylene, propylene, and butylene.The ratio of the carboxyl group-containing monomer to the total monomer forming the acid-modified polyolefin is 10 mol% or more, in particular 10-90 mol%, preferably 30-70 mol%. Unless otherwise specified in this document, the number of carbon atoms, if present in a compound, includes the number of carbon atoms in the carboxyl group.

[0030] The thermoplastic epoxy polymer is a thermoplastic polymer with a hydroxyl group in its side chain. It is the product of a polyaddition reaction between a diepoxy compound and a diol compound. The diepoxy compound is not particularly restricted as long as it comprises two epoxy groups in a single molecule. Preferred examples of the diepoxy compound include an aromatic diepoxy compound. Non-restrictive examples of the aromatic diepoxy compound include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, brominated bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, bisphenol A AF diglycidyl ether, and 4,4'-dihydroxybiphenyl diglycidyl ether. The diol compound is not particularly restricted as long as it comprises two hydroxyl groups in a single molecule. Preferred examples of the diol compound include an aliphatic diol compound.Non-restrictive examples of aliphatic diol compounds include saturated aliphatic diol compounds with 2-6, preferably 2-4, carbon atoms. Examples include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 2,3-butanediol. The diepoxy compounds and the diol compounds can be used alone, or two or more of the same can be used in combination.

[0031] Polyamide is a thermoplastic polymer with an amino group in the main chain. Polyamide is a product of the polycondensation of a dicarboxylic acid compound and a diamine compound, or a product of ring-opening polymerization of a cyclic amino compound. The cyclic amide compound can also be used as the reactive monomer from the previous polycondensation. The dicarboxylic acid compound is not particularly restricted, as long as it comprises two carboxyl groups in a single molecule. Preferred examples of the dicarboxylic acid compound include aliphatic dicarboxylic acids and aromatic dicarboxylic acids. The aliphatic dicarboxylic acid can be a saturated dicarboxylic acid with 3-12, preferably 4-10, carbon atoms. Non-restrictive examples include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, cortic acid, azelaic acid, and sebacic acid. The aromatic dicarboxylic acid can preferably have 8-12 carbon atoms.Non-restrictive examples include terephthalic acid, isophthalic acid, and 1,8-naphthalenedicarboxylic acid. The diamine compound is not particularly restricted as long as it comprises two amino groups in a single molecule. Preferred examples of the diamine compound include aliphatic diamine and aromatic diamine. The aliphatic diamine may be saturated aliphatic diamine with 2–12, preferably 4–10, carbon atoms. Non-restrictive examples include ethylenediamine, propylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, and 2-methyl-1,5-pentanediamine. The aromatic diamine may have 6–12, preferably 6–8, carbon atoms. Non-restrictive examples include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, and metaxylylenediamine. The cyclic amide compound can contain 4-14 carbon atoms.Non-restrictive examples include ε-caprolactam, undecanlactam, and lauryllactam. The dicarboxylic acid compounds, the diamine compounds, and the cyclic amide compounds can be used alone, or two or more of the same can be used in combination. Preferred examples of polyamide include PA6, PA66, PA11, PA12, PA6T, PA9T, and MXD6.

[0032] The vinyl acetate-containing polymer is a thermoplastic polymer with an ester bonding group in the side chain. It is a copolymer of vinyl acetate and an olefin-based monomer. The olefin-based monomer can be an unsaturated hydrocarbon with 2-8, preferably 2-4, carbon atoms. Non-restrictive examples include ethylene, propylene, and butylene. The ratio of vinyl acetate to the total monomer forming the vinyl acetate-containing polymer is 10 mol% or higher, particularly 10-90 mol%, preferably 30-70 mol%.

[0033] Non-restrictive examples of polyolefin that is useful as a thermoplastic polymer include a homopolymer or copolymer of an olefin-based monomer, such as ethylene, propylene, and butylene.

[0034] With a view to further improving the bond strength, the thermoplastic polymer preferably has the functional group(s) described above in the side chain(s). More preferred examples of the thermoplastic polymer include polymers in which a monovalent functional group from the functional groups described above is directly bonded as a side chain to a carbon atom in the main chain. Non-restrictive examples of such thermoplastic polymers include acid-modified polyolefin and a thermoplastic epoxy polymer.

[0035] The relative molecular mass of the thermoplastic polymer is not particularly limited, as long as the thermoplastic polymer can be melted during joining. For example, the thermoplastic polymer can have a relative molecular mass that, according to the invention, allows the melting point to be between 140 and 350°C, and in particular between 140 and 300°C.

[0036] The thermoplastic resin may also contain, for example, a filler such as carbon fibers and glass fibers, and an additive such as a plasticizer.

[0037] The thermoplastic resin of each of the above-described shapes, which is placed between the metal element 11 and the resin element 12, has, according to the invention, a thickness greater than 50 μm and less than or equal to 600 μm, preferably from 100 μm to 550 μm. If the thermoplastic resin is too thick, it is too hard to melt and cannot contribute sufficiently to the bonding process. If the thermoplastic resin is too thin, the amount of molten thermoplastic resin is too small to contribute sufficiently to the bonding process. The thermoplastic resin can be a combination of the above-described shapes, as long as the total thickness of the thermoplastic resin falls within the range described above.

[0038] The arrangement and dimensions (except for the thickness) of the thermoplastic resin are not particularly restricted, as long as the metal element and the resin element are joined together. Generally, the thermoplastic resin 50 can be present in a region of the metal element 11 and a region of the resin element 12 that are joined together. In friction stir welding, the arrangement and dimensions (except for the thickness) of the thermoplastic resin 50 are not particularly restricted, as long as the thermoplastic resin 50 generally covers at least one region 112 directly beneath a surface 121 of the resin element 12 that faces the metal element 11.Let us assume, in detail, that the rotary tool 16 has a diameter D1, the thermoplastic resin 50 generally has a round plate with a diameter of D1 to D1 x 2, preferably D1 x 1.1 to D1 x 1.5, and is arranged such that its center is aligned with the axis of the rotary tool. The region 112 located directly below it is a region of the surface 121 of the resin element 12 facing the metal element 11, which is located directly below the rotary tool 16. (3) Metal element

[0039] The metal element 11 can consist of any metal with a higher melting point than the thermoplastic polymer that forms the thermoplastic resin 50. The following metals and alloys, commonly used in the automotive industry, are preferred: Aluminium and aluminium alloys (5000 and 6000 series); Steel; Magnesium and alloys thereof; and Titanium and alloys thereof.

[0040] The metal element 11 used in the present invention has the overall form of a substantially flat plate, as shown in Fig. Figure 1 shows, but this is not a limiting factor. The metal element 11 can have any shape, as long as at least a portion of it that overlaps with the resin element 12 has the shape of a substantially flat plate. The portion of the metal element 11 that overlaps with the resin element 12 generally has flat surfaces.

[0041] The part of the metal element 11, which is essentially in the form of a flat plate and overlaps with the resin element 12, generally has a thickness T (thickness before joining; see Fig. 3) from 0.5-4 mm, but this is not a limiting factor. (4) Resin element

[0042] Resin element 12 is a thermo-cured resin element, meaning it has been cured by heat; that is, it is a hardened product of a thermo-curable resin. "Curing" refers to the formation of a three-dimensional network structure. A "thermo-curable resin" is a resin that can be cured by heat.

[0043] Non-restrictive examples of thermosetting resins include thermosetting epoxy resins, thermosetting phenolic resins, thermosetting melamine resins, and thermosetting urea resins. For further improvement of bond strength, thermosetting epoxy resins are preferred.

[0044] The thermosetting epoxy resin contains an epoxy resin and a hardening agent.

[0045] The epoxy resin is not particularly restricted as long as it is a compound with two or more epoxy groups. Non-restrictive examples of epoxy resin include: a bifunctional glycidyl ether epoxy resin with an epoxy compound containing a bisphenyl group (such as a bisphenyl A epoxy compound, a bisphenyl F epoxy compound, a brominated bisphenyl A epoxy compound, a hydrogenated bisphenyl A epoxy compound, a bisphenyl S epoxy compound, a bisphenyl AF epoxy compound, and a biphenyl epoxy compound), a polyalkylene glycol epoxy compound, an alkylene glycol epoxy compound, an epoxy compound containing a naphthalene ring, and an epoxy compound containing a fluorene group; a multifunctional glycidyl ether epoxy resin with a phenolic novolac epoxy resin, an ortho-cresol novolac epoxy resin, a trishydroxyphenylmethane epoxy resin, and a tetraphenylolethane epoxy resin; a glycidyl ester epoxy resin of a synthetic aliphatic acid, such as dimer acid;an aromatic epoxy resin with a glycidylamino group, such as N,N,N',N'-tetraglycidyldiaminodiphenylmethane (TGDDM), tetraglycidyl-m-xylylenediamine, triglycidyl-p-aminophenol and N,N-diglycidylaniline;and an epoxy compound with a tricyclodecane ring (e.g., an epoxy compound obtained by polymerizing dicyclopentadiene and cresols (such as m-cresol) or phenols and reacting the resulting polymer with epichlorohydrin). Furthermore, an epoxy resin with a sulfur atom in the main chain, such as FLEP 10, manufactured by Toray Fine Chemicals Co., Ltd., can also be used. The epoxy resins can be used individually or two or more of the same can be combined. Of these, a bisphenol-A epoxy resin and / or a bisphenol-F epoxy resin are preferably used. The amount of the bisphenol-A epoxy resin and / or bisphenol-F epoxy resin is preferably greater than 0 parts by weight and not greater than 100 parts by weight, more preferably greater than 0 parts by weight and not greater than 70 parts by weight of the total amount of epoxy resin. In the present invention, the proportion of bisphenol-A epoxy resin and bisphenol-F epoxy resin is the amount added.

[0046] The curing agent that may be included in the thermosetting epoxy resin along with the epoxy resin may be a polyamine, an acid anhydride, or a mixture thereof. Non-restrictive examples of polyamine include: aromatic polyamines, such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, and m-xylylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and diaminodiethyldiphenylmethane; aliphatic polyamines, such as ethylenediamine, propylenediamine, butylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, trimethylhexamethylenediamine, 1,2-propanediamine, iminobispropylamine, methyliminobispropylamine, and MPMD, manufactured by DuPont Japan; N-aminoethylpiperazine; and monoamines with an ether bond in the main chain, such as 3-butoxyisopropylamine. Diamine with a polyether backbone, represented by JEFFAMINE EDR-148, manufactured by Sun Techno Chemicals Co., Ltd.; alicyclic polyamine such as isophorone diamine, 1,3-bisaminomethylcyclohexane, 1-cyclohexylamino-3-aminopropane, 3-aminomethyl-3,3,5-trimethylcyclohexylamine; diamine with a norbornane backbone, prepared by NBDA, manufactured by Mitsui Chemicals; polyamidoamine with an amino group at a terminal end of a polyamide molecule; and 2,5-dimethyl-2,5-hexamethylenediamine, menthenediamine, 1,4-bis(2-amino-2-methylpropyl)piperazine, JEFFAMINE D230 and JEFFAMINE D400 with a polypropylene glycol (PPG) backbone, manufactured by Sun Techno Chemicals Co., Ltd. Non-restrictive examples of acid anhydride include trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, nadic anhydride, methyl nadic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and dodecenyl succinic anhydride (DSA).

[0047] The thermosetting phenolic resin contains phenol and / or a derivative thereof as well as formaldehyde.

[0048] The thermosetting melamine resin contains melamine and / or a derivative thereof as well as formaldehyde.

[0049] The thermosetting urea resin contains urea and / or a derivative thereof as well as formaldehyde.

[0050] The resin element 12 has the overall shape of an essentially flat plate, as shown in Fig. Figure 1 shows that the resin element 12 can have any shape, as long as a portion of it located directly beneath the metal element 11, when the resin element 12 and the metal element 11 are stacked on top of each other, has the shape of a substantially flat plate. The portion of the resin element 12 directly beneath the metal element 11 generally has flat surfaces.

[0051] The part of the resin element 12 directly below the metal element 11 generally has a thickness T (thickness before joining; see Fig. 3) from 2-10 mm, especially 2-5 mm, but this is not a limiting factor.

[0052] The resin element 12 may also contain, for example, additives such as reinforcing fibers, a filler, a stabilizer, a flame retardant, a dye or a foaming agent.

[0053] The resin element 12 can be formed by using an autoclave, hand lamination, resin transfer molding (RTM), precision winding, or any other suitable forming process.

[0054] The resin element 12 can also be formed by injection molding or pressing a mixture of a thermosetting resin and a desired additive and holding the resulting product at a high temperature so that the product is sufficiently hardened. (5) Joining methods

[0055] The method for joining the metal element and the resin element by friction stir welding according to the present invention comprises at least the following steps.

[0056] The process comprises in detail: a first step of stacking the metal element 11 and the resin element 12 on top of each other, with the thermoplastic resin 50 placed in between; and a second step of immersing the rotating tool 16 into the metal element 11 to generate frictional heat, which softens and melts the thermoplastic resin 50, and then of solidifying the molten thermoplastic resin 50 to join the metal element 11 and the resin element 12 together.

[0057] In the first step, as in Fig. Figure 1 shows a desired connection section of the metal element 11 and a desired connection section of the resin element 12 stacked on top of each other, wherein the thermoplastic resin 50 (in Fig. (1 not shown) is placed between them.

[0058] In the second step, at least one immersion / stirring process C2 is suitably carried out, in which the rotary tool 16 is immersed in the metal element 11 to a depth that is close to an interface 13 between the metal element 11 and the thermoplastic resin 50, but does not reach it.

[0059] In the second step, prior to the immersion / stirring process C2, a preheating process C1 is appropriately carried out, in which the rotary tool 16 is rotated, whereby only the front end of the rotary tool 16 is brought into contact with the surface of the metal element 11. However, the preheating process C1 is not always necessary.

[0060] Following the immersion / stirring process C2, a continuous stirring process C3 is suitably carried out, in which the rotary tool 16, which is immersed in the metal element 11 to a depth close to the interface but not reaching it, can rotate continuously. However, the continuous stirring process C3 is not always necessary.

[0061] The processes according to the invention can be carried out by controlling the pressure (welding pressure) exerted by the rotary tool and the pressing time, or by controlling a distance traveled by the rotary tool in the pressing direction (how deep the rotary tool was immersed in the joining target after the rotary tool touched the joining target) and the duration of the travel.

[0062] These processes are described in more detail below. (Preheating process C1)

[0063] During the preheating process C1, the turning tool 16 and the holding tool 17 are brought close together, and, as described in Fig. As shown in Figure 3, the rotary tool 16 is rotated, with only the front end of the rotary tool 16 in contact with the surface (the top side in the example shown) of the metal element 11. During the preheating process C1, the rotary tool 16 is rotated under an initial pressure (e.g., 900 N) at a predetermined speed (e.g., 3000 rpm) for an initial pressing time (e.g., 1.00 s).

[0064] During the preheating process C1, the pressing action of the rotary tool 16 generates frictional heat on the surface (top side) of the metal element 11. This frictional heat is transferred internally into the metal element 11, preheating a pressure region P (the region against which the rotary tool presses) of the metal element 11 and its surroundings. This facilitates the immersion of the rotary tool 16 into the metal element 11 during the subsequent immersion / stirring process C2.

[0065] During preheating process C1, the initial pressure and pressing time are determined to ensure easy insertion of the rotary tool 16, easy softening and melting of the resin element 12, and productivity. The pressure and time values ​​can vary depending on factors such as the rotational speed of the rotary tool 16, the thickness and material of the metal element 11, or other parameters. For example, if the metal element 11 is made of an aluminum alloy and has a thickness of 1 mm or more and 2 mm or less, the initial pressure applied during preheating process C1 should be 700 N or more and less than 1200 N. The initial pressing time should be 0.5 seconds or more and less than 2.0 seconds. The rotational speed of the rotary tool should be 2000 rpm or more and 4000 rpm or less. (Immersion / stirring process C2)

[0066] In the immersion / stirring process C2, the rotary tool 16 and the holding tool 17 are brought close together, so that the rotary tool 16 is positioned as in Fig. 4A shows the immersion into the metal element 11. When the immersion / stirring process C2 follows the preheating process C1, the turning tool 16 and the holding tool 17 are brought much closer together, causing the turning tool 16 to be positioned as shown in Fig. Figure 4 shows the turning tool being immersed into the metal element 11. Thus, the turning tool 16 is immersed into the metal element 11 to a depth that is close to, but does not reach, an interface 13 between the metal element 11 and the thermoplastic resin 50. At this point, part of the metal element 11 can protrude directly below the turning tool into the (not shown) thermoplastic resin 50.

[0067] During the immersion / stirring process C2, the rotary tool 16 is rotated under a second pressure, which is greater than the first pressure (e.g. 1500 N), at a predetermined speed (e.g. 3000 rpm) for a second pressing time, which according to the invention is shorter than the first pressing time (e.g. 0.25 s).

[0068] During the immersion / stirring process C2, the pressure is greater than the pressure exerted in the preheating process C1, which allows the rotary tool 16 to be immersed in the metal element 11. In other words, the rotary tool 16 sinks deep into the metal element 11. In a suitable example, the immersion of the rotary tool 16 allows the interface 13 between the metal element 11 and the thermoplastic resin 50 to shift towards the holding tool 17 (in Fig. 4 downwards) on a part of the metal element 11 directly below the turning tool, i.e., the part directly below the turning tool projects towards the resin element 12 in the thermoplastic resin 50. This causes the thermoplastic resin to be softened and melted by the frictional heat, and the molten resin flows from directly below region 112 to a region surrounding the directly underlying region 112 on the surface 121 of the resin element 12, which faces the metal element 11. The molten resin flows in an essentially circular shape centered around the region directly below the turning tool. After the molten resin solidifies upon cooling, the metal element 11 and the thermoplastic resin 50 interact with each other over a wide region, and the thermoplastic resin 50 and the resin element 12 interact with each other over a wide region, thus bonding the metal element 11 and the resin element 12 together.

[0069] If the rotary tool 16 is plunged further into the metal element 11 (i.e., the pressure is too high and / or the pressing time is too long), the shoulder 16b of the rotary tool 16 extends beyond the interface 13. This means the rotary tool 16 penetrates the metal element 11, and an outer circumferential section of the rotary tool 16 comes into contact with the thermoplastic resin 50 and the resin element 12. This means the rotary tool 16 bores a hole into the metal element 11, leading to a failure of the connection.

[0070] In this immersion / stirring process C2, the immersion of the rotary tool 16 is therefore stopped when the shoulder 16b of the rotary tool 16 reaches a depth close to, but not reaching, the interface 13. In other words, the rotary tool 16 is immersed into the metal element 11 to a depth close to, but not reaching, the interface 13. In the subsequent continuous stirring process C3, frictional heat is thus generated at a reference position near the resin element 12, and a large amount of frictional heat is transferred to the resin element 12, thereby accelerating the softening and melting of the thermoplastic resin 50.

[0071] In the immersion / stirring process C2, the second pressure and pressing time are set so that the metal element 11 is not drilled and the rotary tool 16 is brought as close as possible to the resin element 12. The pressure and time values ​​can vary depending on, for example, the rotational speed of the rotary tool 16, the thickness and material of the metal element 11, or other parameters. For example, if the metal element 11 is made of an aluminum alloy and has a thickness of 1 mm or more and 2 mm or less, the second pressure applied in the immersion / stirring process C2 is suitable to be 1200 N or more and less than 1800 N. The second pressing time is suitable to be 0.1 seconds or more and less than 0.5 seconds. The rotational speed of the rotary tool is suitable to be 2000 rpm or more and 4000 rpm or less. (Continuous stirring process C3)

[0072] During the continuous stirring process C3, the rotary tool 16 and the receiving tool 17 are no longer brought close to each other, whereby the rotary tool 16 reaches a position where it has attained a depth close to the interface 13 but has not reached the interface (this position is hereinafter referred to as the “reference position”), as in Fig. As shown in Figure 4, the rotary tool 16 can rotate continuously. During the continuous stirring process C3, the rotary tool 16 is rotated under a third pressure, which is less than the first pressure (e.g., 500 N), at a predetermined speed (e.g., 3000 rpm) for a third pressing time, which is longer than the first pressing time (e.g., 5.75 s).

[0073] During the continuous stirring process C3, the pressure is lower than that applied in the preheating process C1 (and that applied in the immersion / stirring process C2). The rotary tool 16 is thus held almost at the reference position. Since the rotary tool 16 is allowed to rotate continuously at the reference position near the thermoplastic resin 50, a large amount of frictional heat is generated, most of which is transferred to the thermoplastic resin 50. The thermoplastic resin 50 is therefore sufficiently softened and melted in a wider region extending beyond the region directly below the pressure region P.

[0074] In the continuous stirring process C3, the third pressure and pressing time are adjusted to achieve sufficient softening and melting of the resin element 12, as described above, over a wider range and for productivity. The pressure and time values ​​can vary depending on, for example, the rotational speed of the rotary tool 16, the thickness and material of the metal element 11, or other parameters. For example, if the metal element 11 is made of an aluminum alloy and has a thickness of 1 mm or more and 2 mm or less, the third pressure applied in the continuous stirring process C3 is suitably 100 N or more and less than 700 N. The third pressing time is suitably 1.0 second or more and less than 20 seconds, particularly 3 seconds or more and 10 seconds or less. The rotational speed of the rotary tool is suitably 2000 rpm or more and 4000 rpm or less. (Holding process C4)

[0075] After the continuous stirring process C3, a holding process C4 can be executed or skipped. In the holding process C4, the rotating tool 16 can stop rotating and is held under a predetermined pressure for a predetermined time.

[0076] In the holding process C4, the rotary tool 16 can stop rotating and the stopped rotary tool 16 will remain stationary for a predetermined time as described in Fig. Figure 4 shows the tool held under a predetermined pressure. During the holding process C4, the rotary tool 16 can rotate for a fourth pressing time, which is shorter than the third pressing time and longer than the second pressing time (e.g., 5.00 s), under a fourth pressure that is greater than the third pressure and less than the second pressure (e.g., 1000 N).

[0077] During the holding process C4, the turning tool 16 can stop rotating. Therefore, no further frictional heat is generated. This means that a key operation related to friction stir welding is completed, and the cooling of the workpiece 10 begins. During the cooling of the workpiece 10, a pressure is applied that is lower than the pressure applied in the immersion / stirring process C2 and higher than the pressure applied in the continuous stirring process C3. Thus, the metal element 11 and the resin element 12 are sandwiched and clamped between the turning tool 16, which has stopped rotating, and the holding tool 17. This strengthens the adhesion between the metal element 11 and the resin element 12 during cooling, thereby improving the joint strength after cooling and solidification.

[0078] In holding process C3, the fourth pressure and pressing time are set to enhance adhesion in a region directly below the pressure region P, as described above, during cooling. The pressure and time values ​​can vary depending on, for example, the material of the metal element 11 or other parameters. For instance, if the metal element 11 is made of an aluminum alloy, the fourth pressure applied in holding process C4 is suitably 700 N or more and less than 1200 N. The fourth pressing time is suitably 1 second or more.

[0079] Assuming that in the joining process described above, the thermoplastic resin 50 has a melting point of Tm (°C), and the joining temperature is generally Tm - 50°C to Tm + 150°C. With a view to further improving the joint strength, the joining temperature, depending on the type of thermoplastic resin 50, falls within the following range according to the invention.

[0080] When using acid-modified polyolefin, the compound temperature is Tm to Tm + 150°C, suitable Tm + 20°C to Tm + 130°C, and far more suitable T + 70°C to Tm + 120°C.

[0081] When using a thermoplastic epoxy polymer, the bonding temperature is Tm - 50°C to Tm + 30°C, suitable Tm - 10°C to Tm + 20°C.

[0082] When using polyamide, the joining temperature is Tm + 10°C to Tm + 70°C, suitable Tm + 20°C to Tm + 60°C.

[0083] When using a vinyl acetate-containing polymer, the bonding temperature is Tm to Tm + 80°C.

[0084] The joining temperature is the highest temperature of the region 112 located directly below it at an interface between the thermoplastic resin 50 and the resin element 12 and can be controlled by adjusting the pressure (welding pressure) applied by the rotary tool 16, the pressing time, the rotational speed of the rotary tool 16, the distance traveled by the rotary tool 16 in the pressing direction, the travel time and the rotational speed.

[0085] In the joining method described above, the rotary tool is not moved along the surface of the metal element that is in contact with the rotary tool, and the metal element and the resin element are joined at a fixed point (spot welding). Alternatively, if the rotary tool is moved along the surface of the metal element so that the metal element and the resin element are joined along a line (weld line), it is obvious that the advantages of the present invention can also be achieved. [Example][Example 1](Metal element)

[0086] A flat plate element made of a 6000 series aluminum alloy (100 mm long x 30 mm wide x 1.2 mm thick) was used as the metal element. (Heat-cured resin element)

[0087] A bisphenol-A epoxy resin (EP-834, manufactured by Japan Epoxy Resins Co., Ltd.) and o-phenylenediam were mixed as a curing agent to create a thermosetting epoxy resin composition. The thermosetting epoxy resin composition was formed in a mold and held in the mold at 230°C to achieve sufficient curing. This resulted in the production of one resin element 12 (100 mm long x 50 mm wide x 3 mm thick). (Thermoplastic resin sheet)

[0088] A maleic acid-modified polypropylene polymer sheet (MODIC, manufactured by Mitsubishi Chemical Corporation, 500 µm thick) was used. Maleic acid-modified polypropylene was a copolymer of propylene and maleic anhydride (melting point: 143°C).

[0089] The thermoplastic resin plate was a round plate with a diameter of 12 mm and was arranged so that its center was aligned with the axis of the rotary tool. (Turning tool)

[0090] It was the in Fig. The turning tool shown in Figure 2 was used. The turning tool had a diameter D1 of 10 mm, a diameter D2 of 2 mm and a height of 0.5 mm and was made of tool steel. (Connection method)

[0091] The metal element 11 and the resin element 12 were joined together by the following procedure. First step:

[0092] The metal element 11 and the resin element 12 were stacked on top of each other, with the thermoplastic resin plate 50 as shown in Fig. 1 was shown and placed in between. Second step:

[0093] As in Fig. As shown in Figure 3, the rotary tool 16 was only allowed to rotate with the front end of the rotary tool 16 in contact with the surface of the metal element 11 (preheating process C1, welding pressure: 900 N, pressing time: 1.00 seconds, tool speed: 3000 rpm).

[0094] Then, as in Fig. Figure 4 shows that the rotary tool 16 was immersed in the metal element 11 to a depth close to an interface between the metal element 11 and the thermoplastic resin 50, but did not reach this (immersion / stirring process C2, welding pressure: 1500 N, pressing time: 0.25 seconds, tool speed: 3000 rpm).

[0095] Then, as in Fig. Figure 4 shows the rotary tool 16, which was immersed in the metal element 11 to a depth near the interface but did not reach it, rotating continuously (continuous stirring process C3, welding pressure: 500 N, pressing time: 5.75 seconds, tool speed: 3000 rpm).

[0096] Then the rotary tool 16 was withdrawn from a connected product 20 and the connected product 20 was left to cool.

[0097] In the procedure described above, the temperature of a region directly beneath the rotary tool at the interface between the thermoplastic resin plate 50 and the resin element 12 was monitored. The highest temperature, representing the bonding temperature, was 223°C.

[0098] Using the method described above, a number of bonded products were obtained in the same way, except that the bonding temperature was changed. [Example 2]

[0099] Several bonded products were obtained in the same manner as in Example 1, except that a thermoplastic resin sheet as described below was used and the bonding temperature was changed. (Thermoplastic resin sheet)

[0100] A thermoplastic epoxy polymer sheet (manufactured by Nagase ChemteX Corporation, 500 µm thick) was used as the thermoplastic resin sheet. The thermoplastic epoxy polymer had a melting point of 260°C.

[0101] The thermoplastic resin plate was a round plate with a diameter of 12 mm and was arranged so that its center was aligned with the axis of the rotary tool. [Example 3]

[0102] Several bonded products were obtained in the same manner as in Example 1, except that a thermoplastic resin sheet as described below was used and the bonding temperature was changed. (Thermoplastic resin sheet)

[0103] A polyamide polymer sheet (manufactured by Toray Plastics Precision Co., Ltd., 500 µm thick) was used as the thermoplastic resin sheet. Polyamide had a melting point of 220°C.

[0104] The thermoplastic resin plate was a round plate with a diameter of 12 mm and was arranged so that its center was aligned with the axis of the rotary tool. [Example 4]

[0105] Several compound products were obtained in the same manner as in Example 1, except that instead of using the thermoplastic resin sheet, a coating was formed by applying a thermoplastic resin solution to the metal element and drying the solution to a dry thickness of 500 µm, and that a copolymer of vinyl acetate and propylene was used as the thermoplastic resin (melting point: 165°C). [Connection strength]

[0106] As in Fig. As shown in Figure 5, a joined product consisting of the metal element 11 and the resin element 12 was placed in a holding device 100. The holding device 100 is designed to exert a downward load on the upper end of the resin element 12 when pulled downwards. The holding device 100 was fixed, and the metal element 11 was pulled upwards to apply a downward load to the upper end of the resin element 12, thereby measuring the joint strength (maximum shear stress) of the joined part without considering the strength of the base material of the resin element 12. Fig. Figure 6 shows a relationship between the connection temperature and the connection strength. COMMERCIAL APPLICABILITY

[0107] The joining method according to the invention is suitable for joining a metal element and a resin element together in various fields, for example motor vehicles, railcars, aircraft and household appliances. DESCRIPTION OF REFERENCE MARK 1 friction stir welding device 10 workpieces 11 Metal element 12 resin elements 13 Interface between metal element and thermoplastic resin 16 Rotary tool 17 Recording tool 50 Thermoplastic resin (layer) 100 Device for measuring connection strength 111 Surface of the metal element facing the resin element P Pressure region (region to be pressed) 121 Surface of the resin element facing the metal element

Claims

[1] Method for joining a metal element (11) and a resin element (12), wherein a thermoplastic resin (50) is placed between the metal element (11) and the resin element (12), wherein the resin element is a thermo-cured resin element (12), wherein the thermo-cured resin of the thermo-cured resin element is not melted by heat, and The process is implemented by friction stir welding, in which the metal element (11) and the thermo-cured resin element (12), with the thermoplastic resin (50) placed between them, are stacked on top of each other, a rotating rotary tool (16) is pressed against the metal element (11) to generate frictional heat, thereby softening and melting the thermoplastic resin (50), and then the molten thermoplastic resin (50) solidifies to join the metal element (11) and the thermo-cured resin element (12). including friction stir welding: a first step of stacking the metal element (11) and the thermo-cured resin element (12) on top of each other with the thermoplastic resin (50) in between; and a second step of pressing the rotating tool (16) against the metal element (11) to generate frictional heat, thereby softening and melting the thermoplastic resin (50), and solidifying the molten thermoplastic resin to join the metal element (11) and the resin element (12) together, characterized by , that the second step comprises an immersion / stirring process of immersing the rotary tool (16) into the metal element (11) to a depth close to an interface (13) between the metal element (11) and the thermoplastic resin (50), but not reaching it, wherein the second step comprises a preheating process of rotating the rotary tool (16), wherein only a front end of the rotary tool (16) is in contact with the surface of the metal element (11), wherein the preheating process is carried out before the immersion / stirring process, wherein during the preheating process the rotary tool (16) may only rotate under a first pressure for a first pressing time, and During the immersion / stirring process, the rotary tool (16) may only rotate for a second pressing time, which is shorter than the first pressing time, under a second pressure that is greater than the first pressure. wherein the thermoplastic resin (50) placed between the metal element (11) and the thermosetting resin element (12) has a thickness greater than 50 µm and less than or equal to 600 µm, preferably from 100 µm to 550 µm, wherein the melting point Tm (°C) of the thermoplastic polymer is 140-350°C, in particular 140-300°C, and wherein the connection temperature, which is the highest temperature of the region (112) located directly below it at an interface between the thermoplastic resin (50) and the resin element (12), is Tm - 50°C to Tm + 150°C, wherein acid-modified polyolefin, thermoplastic epoxy polymer, polyamide or vinyl acetate-containing polymer is used as the thermoplastic resin and When using acid-modified polyolefin as a thermoplastic resin (50), the joining temperature Tm to Tm + 150°C, suitable Tm + 20°C to Tm + 130°C, far more suitable T + 70°C to Tm + 120°C, When using a thermoplastic epoxy polymer as the thermoplastic resin (50), the joining temperature Tm - 50°C to Tm + 30°C is suitable, Tm - 10°C to Tm + 20°C, When using polyamide as a thermoplastic resin (50), the joining temperature is Tm + 10°C to Tm + 70°C, suitable Tm + 20°C to Tm + 60°C and When using a vinyl acetate-containing polymer as a thermoplastic resin (50), the joining temperature Tm is to Tm + 80°C. [2] Method according to claim 1, wherein the thermo-cured resin element (12) is a cured product of a thermo-curable resin. [3] Method according to one of claims 1 or 2, wherein the thermoplastic resin (50) has the form of at least one selected from the group consisting of a plate, a coating formed on a surface of the metal element (11) and a coating formed on a surface of the thermo-cured resin element (12). [4] Method according to any one of claims 1 to 3, wherein the thermoplastic resin (50) is a thermoplastic polymer with a functional group and the functional group contains at least one selected from the group consisting of an oxygen atom, a nitrogen atom, a fluorine atom and a sulfur atom. [5] Method according to claim 4, wherein the functional group is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an amide bonding group, an ester bonding group, an ether group, a thioether group, a carboxylate group, a fluorine atom, a urethane bonding group and a carbonate group. [6] Method according to any one of claims 1 to 5, wherein the thermo-cured resin element (12) consists of at least one selected from the group consisting of a thermo-curable epoxy resin, a thermo-curable phenolic resin, a thermo-curable melamine resin and a thermo-curable urea resin. [7] Method according to any one of claims 1 to 6, wherein a front end of the turning tool (16) comprising a shoulder (16b) which is a front end section, and a pin (16a) which projects outwards from the shoulder (16b) and has a smaller diameter than the shoulder (16a), and In the immersion / stirring process, the rotary tool (16) is immersed in the metal element (11) so that the shoulder (16b) of the rotary tool (16) reaches a depth that is close to, but does not reach, an interface (13) between the metal element (11) and the thermoplastic resin (50). [8] Method according to claim 7, wherein the second step continues to include a continuous stirring process in which the rotary tool (16) is allowed to rotate continuously at a depth close to the interface (13), but without reaching it, and During the ongoing stirring process, the rotary tool (16) may only rotate for a third pressing time, which is longer than the first pressing time, under a third pressure, which is smaller than the first pressure.

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