Method for joining two parts, adhesive film and use of an adhesive film

Abstract

Method for joining two joining parts (11, 12) in which the joining parts (11, 12) are bonded together by means of an adhesive material (13) provided between the joining parts (11, 12), the method comprising the following steps: - Providing a first joining part (11) and at least a second joining part (12); - Providing an adhesive material (13) which contains at least one open-pore venting textile (14a, 14b) and is provided integrally with the at least one venting textile (14a, 14b) in the form of an adhesive film (20); - Introducing the adhesive material (13) together with the open-pore venting textile (14a, 14b) between the joining parts (11, 12) in a predetermined joining zone, such that the venting textile (14a, 14b) touches the respective joining part (11, 12) with one surface side, wherein the joining zone is tempered at least in a partial area before the application of surface pressure and subsequently pressure is applied locally to the joining zone for position fixation; - Creating a vacuum setup (10) such that at least the joining zone with the open-pore venting textile (14a, 14b) is sealed vacuum-tight under the vacuum setup (10); - Evacuating the joining zone under the vacuum setup (10) including the open-pore venting textile (14a, 14b) using a vacuum pump; and - Carrying out a curing process to cure the adhesive material (13) introduced between the joining parts (11, 12), wherein, for carrying out the curing process, the adhesive material (13) is tempered by means of a tempering device only after the complete evacuation of the at least one open-pore venting textile (14a, 14b).

Description

[0001] The present invention relates to a method for joining two components, in which the components are bonded together by means of an adhesive material provided between them. The invention also relates to a film adhesive for this purpose.

[0002] Due to their high strength-to-weight ratio and stiffness, fiber-reinforced composites are virtually indispensable in the production of all kinds of components. Fiber-reinforced composites consist primarily of two essential components: a fiber material and a matrix material that embeds the fiber material. In addition, such fiber-reinforced composites may contain other components that are application-specific. In the production of fiber-reinforced composite components, the fiber material is typically formed into the desired component shape, and then the matrix material embedding the fiber material is cured. In most cases, curing is achieved through temperature and, if necessary, pressure application.During the curing process, the load-bearing fibers of the fiber material are forced into their predetermined direction and, together with the cured matrix material, form an integral unit for load transfer.

[0003] Adhesive bonding is a joining method with significant lightweight potential, not only in the production of complex fiber-reinforced composite components. Using an adhesive bond, two components are firmly and generally permanently joined at their respective joining surfaces through cohesion and / or adhesion. Further mechanical fasteners can only be dispensed with if the failure of the adhesive bond is insignificant for the operation of the underlying technical equipment. Validating the strength and durability of adhesive bonds is a key challenge for adhesive technologies, as incorrect or insufficient surface treatments, expired or improperly processed adhesives, and contamination can severely reduce bond strength.Especially in the aviation sector, in the manufacture of aircraft, particularly from fiber-reinforced composite materials, where structural components are also manufactured using adhesive bonds, it is essential that the adhesive bonds have strength and durability, as in the event of damage to such an adhesive bond, safe flight operations can no longer be guaranteed.

[0004] German patent application DE 10 2013 107 849 A1 discloses a method for producing a fiber composite structure from at least two separately manufactured fiber composite components, which are to be joined together by adhesive bonding. Two different adhesive systems are used, which are introduced into the adhesive bond in such a way that separate adhesive zones are formed from the first and second adhesive systems. In the cured state, the second adhesive system exhibits higher fracture toughness than the first adhesive system, resulting in different properties within the adhesive bond. In the area with low fracture toughness and high strength (first adhesive system), any cracks that develop can only propagate into the areas of the second adhesive zone, where the adhesive bond has high fracture toughness (tough-elastic) but reduced strength and stiffness.Cracks that form in the adhesive seam can thus be effectively limited to a local area.

[0005] From DE 10 2017 113 432 A1, a film adhesive for bonding at least two components is known, wherein the adhesive is applied in a film-like manner to a textile, planar substrate. The textile, planar substrate has at least a first section adjoining at least a second section of the substrate, wherein the substrate of the first section is materially, chemically, and / or geometrically modified compared to the substrate of the second section such that, after curing of the adhesive, the adhesive joint in the region of the first section has a mechanical property with respect to elongation at break or fracture toughness that differs from the mechanical property of the adhesive joint in the region of the second section.

[0006] Furthermore, WO 02 / 081189 A1 describes, for example, a method for joining two components, in which an adhesive material is introduced that has a textile on at least one side. The aim is to prevent air inclusions by evacuating this textile. The reinforcing material can have a ventilation structure to allow gas to escape from the laminate structure. EP 2 324 979 A1 describes a method for producing a preform using adhesive strips between different layers of fiber material, primarily for prefabricated elements. For example, DE 10 2004 002 618 A1 describes a method for laminating decorative cutouts or molded parts made of leather or similar materials, in particular vacuum-assisted lamination onto rigid, elastic, or elastically designed surfaces (using suitable intermediate layers).

[0007] Currently, thermoset matrix systems are predominantly used for the production of fiber-reinforced composite components and adhesive bonds in the aerospace industry. These systems typically require curing at elevated temperatures. During this process, the component is isolated from the atmosphere using a vacuum and often subjected to high pressure (e.g., in an autoclave). This high overpressure leads to significant compaction of the fiber layers or the adhesive layer or materials applied between two parts, as well as the formation of compressed air bubbles.

[0008] In some applications, however, the use of additional pressure is not possible or undesirable. In these applications, the component is only subjected to a vacuum during the curing of the matrix material, so that the pressure acting on the component corresponds only to the ambient pressure (1 bar). In these applications, porosity often occurs in the components or the adhesive joint.

[0009] The porosity is caused by air inclusions in the matrix system or the adhesive introduced during the impregnation or lamination process. On the one hand, the trapped air bubbles cannot be sufficiently compressed during the curing process due to the low pressure of one bar. On the other hand, applying a vacuum to the resin, which is liquid at elevated temperatures, causes resin flow and a corresponding expansion of existing air inclusions, thus enlarging the pores. When using pre-formulated adhesives, such as film adhesives, air inclusions often arise from the lamination process itself. In this process, the impregnated layers are applied one layer at a time, and large air bubbles are supposed to be removed by rolling or pressing. However, often not all air inclusions can be removed and are further trapped by the pressure.

[0010] After subsequent curing, voids form within the adhesive joint or seam, impairing the stability and strength of the bond. Especially when structurally critical components in the aerospace industry are to be joined using adhesives, a reduction in structural mechanical properties must be avoided. Currently, however, particularly when using pre-formed adhesives such as film adhesives, it cannot be reliably guaranteed that air inclusions can be prevented during the application of the adhesive.

[0011] It is therefore an object of the present invention to provide an improved method for joining two components, in particular two components made of a fiber composite material, in which the formation of structure-weakening cavities within the adhesive bond due to air inclusions can be reliably prevented.

[0012] The problem is solved by the method according to claim 1 according to the invention. Advantageous embodiments of the invention are found in the corresponding dependent claims.

[0013] According to claim 1, a method for joining two components is proposed, in which the components are to be bonded (joined) to one another by means of an adhesive material provided between them. The two components can, for example, be fiber-reinforced composite components made of a fiber-reinforced composite material, and the fiber-reinforced composite components can be in a previously cured state. It is also conceivable, of course, that one or both of the components are not yet cured, i.e., that the matrix material embedding the fiber material is not yet fully polymerized.

[0014] First, the two parts to be joined are prepared accordingly. The same applies to the adhesive material intended for use. This could, for example, be a matrix material also used in the production of fiber-reinforced composite components. In particular, it could be the same matrix material from which the parts to be joined were formed, provided they are made of a fiber-reinforced composite. Therefore, the adhesive material could be a matrix material of a fiber-reinforced composite. The adhesive materials used could, for example, be thermoplastic or thermosetting adhesives.

[0015] The adhesive is provided in such a way that it includes at least one open-pore venting textile. This open-pore venting textile is an integral component of the adhesive. The adhesive and the open-pore venting textile are provided as a single, integrated unit. The open-pore venting textile is at least partially impregnated or in contact with the adhesive.

[0016] The adhesive material, along with the open-pore venting textile, is then applied to a designated joining zone between the parts to be joined. This can be achieved, for example, by applying the adhesive material evenly to a joining surface of one of the two parts and then bringing the applied adhesive into contact with the joining surface of the other part. After this application of the adhesive material to the respective joining zone, it is present between the two parts in the designated joining zone and is intended to bond them together by curing within the designated joining zone.

[0017] According to the invention, the at least one open-pored venting textile, which is an integral part of the adhesive material, touches or contacts the respective joining part at its joining surface with a first surface area. The opposite second surface area of ​​the open-pored venting textile is wetted or contacted with the adhesive material.

[0018] The joining zone, and in particular the at least one open-pore venting textile, is now sealed vacuum-tight under a vacuum setup. A connection for a vacuum pump is located at one point within the vacuum setup to evacuate the enclosed area, especially the joining zone. A vacuum bridge is situated between the open-pore venting textile under the vacuum setup and the vacuum pump connection. This bridge prevents the vacuum cover (e.g., a vacuum film) from being compressed during the evacuation of the vacuum setup to such an extent that the open-pore venting textile could no longer be evacuated, thus preventing further air pockets from forming within the open-pore venting textile.Accordingly, the vacuum setup is created such that a vacuum bridge is formed between a vacuum pump connection and at least one open-pore venting textile, allowing continuous evacuation of the venting textile by the vacuum pump. Such a vacuum bridge can be, for example, a thin, non-compressible hose or tube. However, such a vacuum bridge can also be formed by one or more layers of a venting textile. Flow aids or peel ply can also be used, since channels always remain between individual fabric filaments (with a round cross-section) through which a vacuum bridge can be ensured.

[0019] The joining zone, and in particular the at least one open-pore venting textile, is then evacuated using the connected vacuum pump. This creates a vacuum between the first surface of the respective joining part and the adhesive material where the open-pore venting textile is located, preventing air inclusions from forming during the subsequent curing of the adhesive.

[0020] The vacuum setup can be implemented in such a way that it seals against a mold, thereby completely enclosing both parts to be joined. Alternatively, it is conceivable that the vacuum setup seals against only one of the two parts to be joined, so that at least the other part is completely enclosed within the vacuum setup. This is usually advantageous when the first part to be joined is significantly larger than the second.

[0021] The adhesive material applied between the joining parts is cured together with the open-pore venting textile in a curing process.

[0022] By providing an open-pore venting textile between the joining surface of one of the parts and the adhesive material intended for the bond, it is possible to evacuate any trapped air inclusions during the evacuation of the joining zone between the adhesive material and the joining surface of the part, thereby preventing the formation of air bubbles. Thus, the inventive method for joining two parts enables the production of non-porous bonds during curing, particularly without the need for additional pressure.

[0023] During the curing process of the adhesive, the open-pore venting textile is pressed into it before the adhesive has fully cured, thus ensuring complete contact between the adhesive and the respective joining surface. Since the venting textile is completely evacuated, the voids formed by the open-pore venting textile can be completely filled by the adhesive without any air entrapment.

[0024] The inventors discovered that, with the aid of an open-pore venting textile, the entrapment of air bubbles in the interface between the joining surface of one of the components and the adhesive can be reliably prevented without significantly impairing the adhesive's adhesion. In fact, it has been shown that, despite the presence of the open-pore venting textile, a reliable bond between the adhesive and the joining surface can still be achieved, allowing the open-pore venting textile to remain in the interface between the adhesive and the joining surface.Moreover, it has been shown that the presence of the open-pore venting textile allows the venting textile to take on further functional tasks, such as acting as a spacer or providing mechanical properties in the adhesive bond, such as crack stopping.

[0025] The inventive method is particularly suitable for repair processes when the first component is already fully cured and a smaller component is to be bonded to it. The vacuum setup is designed such that the second component to be bonded, including the adhesive layer, is completely enclosed within the vacuum setup, and the vacuum setup is then sealed off from the first component. This allows for the creation of an adhesive bond in a repair process, ensuring that no air inclusions or porosity occur in the interface between the joining surface and the adhesive material.

[0026] The advantage of the invention lies particularly in repair processes where no additional compaction (> atmospheric pressure) can be achieved using a pressure oven (autoclave).

[0027] An open-pore venting textile within the meaning of the present invention is understood in particular to be a venting textile which forms evacuable pores in the boundary layer between the joining surface and the adhesive material, which are occupied or filled by the adhesive material in a later process.

[0028] According to one embodiment, the adhesive material is provided such that an open-pore venting textile is present both between the adhesive material and the first joining part and between the adhesive material and the second joining part when the adhesive material is introduced into the joining zone. Consequently, a corresponding evacuation of the interface between the adhesive material and both joining parts is achieved by means of a corresponding open-pore venting textile.

[0029] According to the invention, the adhesive material is tempered using a temperature control device to carry out the curing process. Tempering the adhesive material typically activates it thermally, thereby initiating the chemical crosslinking reaction. This generally softens the adhesive material, ensuring that the cavities formed by the venting textile at the interface between the adhesive material and the respective joining part are completely filled by the adhesive material. Due to the vacuum created in these cavities of the venting textile, no air is trapped, thus ensuring that the bonded interface is free of porous areas. Alternatively, the entire joining zone or the entire component formed from the two joining parts can be tempered.

[0030] According to the invention, the adhesive material is tempered only after the at least one open-pore venting textile has been completely evacuated.

[0031] According to one embodiment, the vacuum assembly is placed in an autoclave, and an overpressure is generated in the area surrounding the vacuum assembly by means of the autoclave to apply surface pressure for compacting the adhesive layer. This ensures reliable contact between the adhesive material and the respective surface of the component being joined. It can also be provided that the joining zones are simultaneously heated in the autoclave.

[0032] It is advantageous if the overpressure in the surrounding area of ​​the vacuum setup is only generated after the complete evacuation of the at least one open-pored venting textile, in order to reliably avoid air inclusions in the interface.

[0033] According to a further advantageous embodiment, the adhesive material is introduced with the at least one venting textile in such a way that, before the application of surface pressure, the pores of the open-pore venting textile form a cavity between the adhesive material and the respective joining part. By tempering and evacuating the joining zone, the cavity within the pores is evacuated, whereby, due to the melting of the adhesive material, this cavity is then filled by the adhesive material, thus eliminating all air inclusions.

[0034] According to the invention, the adhesive material is provided integrally with the at least one venting textile in the form of an adhesive film.

[0035] According to the invention, the joining zone is heated at least locally within a specific area, and subsequently, local pressure is applied to the joining zone to fix its position. This allows the adhesive material to be locally bonded to the joining surface for positional fixation, thus preventing slippage of the adhesive material within the joining zone. Only after the venting textile is evacuated and the adhesive material cures is the entire adhesive layer compacted and any air inclusions within it eliminated.

[0036] According to one embodiment, the entire joining zone and / or the entire surface of one or both joining partners is covered with the open-pore venting textile.

[0037] The problem is also solved according to the invention with the adhesive film for joining two parts according to claim 12, wherein the adhesive film has an adhesive material configured to form an adhesive bond between the parts. According to the invention, at least one open-pored venting textile is arranged on the adhesive material of the adhesive film such that the venting textile is not completely saturated with the adhesive material and that the pores of the open-pored venting textile form a cavity for venting when the adhesive film is applied to the parts.

[0038] Advantageous embodiments of the adhesive film can be found in the corresponding subclaims.

[0039] The problem is also solved by using such an adhesive film for the adhesive joining of two joining parts according to claim 14.

[0040] The invention is explained in more detail using the attached figures as examples. They show: Fig. 1 - Schematic setup for joining two components before hardening; Fig. 2 - Schematic representation of a vacuum setup during or after the curing of the adhesive.

[0041] Fig. Figure 1 shows a vacuum setup 10 with which a first joining part 11 is to be joined to a second joining part 12 using an adhesive 13 in an adhesive joining process. For this purpose, a film adhesive 20 containing the adhesive 13 and an open-pore venting textile 14a and 14b is first applied to the first joining part 11. The venting textiles 14a and 14b are designed such that the adhesive 13 is located between them. Accordingly, exactly one surface of each of the venting textiles 14a and 14b is impregnated with the adhesive 13, while the other surface of each venting textile 14a and 14b is intended for contact with the respective joining part 11, 12.

[0042] After the film adhesive 20, along with the adhesive 13 and the venting textiles 14a and 14b, has been applied to the first joining part 11, the first venting textile 14a contacts both the adhesive 13 and the first joining part 11. Voids 15 form in the individual pores of the venting textile 14a, due to the fact that the adhesive 13 does not completely saturate the respective venting textile 14a, 14b.

[0043] Subsequently, the second joining part 12 is placed onto the film adhesive 20 applied to the first joining part 11, so that the second venting textile 14b now contacts not only the adhesive 13 but also the second joining part 12. Here, too, corresponding cavities 15 are formed by the pores of the venting textile 14b.

[0044] This assembly is now covered by a vacuum film 16 and sealed vacuum-tight against the first joining part 11 by means of a sealing tape 17. Furthermore, the cavity 18 formed under the vacuum film 16 is connected to a vacuum port 19, to which a vacuum pump (not shown) can be connected. This allows the vacuum cavity 18 under the vacuum film 16 to be evacuated, thereby also evacuating the joining zone covered by the film adhesive 20.

[0045] A vacuum bridge 22 is provided under the vacuum film 16 between the vacuum connection 19 and the venting textile 14a, 14b to prevent the vacuum film 16 from being pressed against the first joining part 11 in the area of ​​the vacuum bridge 22 during the evacuation of the joining zones and, in particular, the venting textile 14a, 14b. Otherwise, the venting textile might not be able to be evacuated further, and corresponding air inclusions could subsequently form at the interface. The vacuum bridge, however, ensures that the venting textile can be completely evacuated.

[0046] Now that the in Fig. Once the vacuum setup 10 shown in Figure 1 has been prepared, the vacuum cavity 18 is evacuated using a vacuum pump, in particular to evacuate the venting textile. Furthermore, the entire vacuum setup is temperature-controlled, for example with a temperature control device (not shown), so that the adhesive 13 of the adhesive layer 21 melts and becomes plastically deformable. Due to the surface pressure and the evacuation of the vacuum cavity 18, as well as the plastic deformability of the adhesive 13, the cavities 15 previously formed by the venting textile 14a, 14b are filled by the adhesive 13, while all air inclusions in the interface between a joining part 11, 12 and the adhesive layer 21 are completely evacuated due to the vacuum and the surface pressure. The resulting outcome is shown in Figure 1. Fig. 2 shown.

[0047] All pores of the venting textile 14a, 14b are completely filled by the adhesive material 13 and thus form a corresponding adhesive bond with the respective joining part 11, 12. In addition, due to the surface pressure, the adhesive layer 21 was compacted to such an extent that it was reduced to the size of the venting textiles, so that the venting textiles in this context also serve as spacers to form a defined adhesive layer thickness.

[0048] The venting textile 14a, 14b can, for example, be a knitted, woven, or nonwoven fabric. The material from which the venting textiles are formed can be designed to have additional functions. For example, the material could chemically react with the adhesive during curing, thus imparting further advantageous properties to the adhesive bond (e.g., crack-stopping properties). Alternatively, the material could partially or completely melt or merge into the adhesive during the curing reaction, so that after curing, the adhesive and the fabric of the venting textile are mixed. Furthermore, it is also conceivable that, in addition to the venting textile on one or more outer surfaces, the novel adhesive film could also have a conventional spacer fabric in the middle. Reference symbol list 10 Vacuum setup 11 first joining part 12 second joining part 13 Adhesive material 14a, 14b Ventilation textile 15 Cavity of the pores of the ventilation textile 16 vacuum film 17 Sealing tape 18 Vacuum cavity 19 Vacuum connection 20 film adhesive 21 Adhesive layer 22 Vacuum bridge

Claims

[1] Method for joining two joining parts (11, 12) wherein the joining parts (11, 12) are bonded together by means of an adhesive material (13) provided between the joining parts (11, 12), the method comprising the following steps: - Providing a first joining part (11) and at least a second joining part (12); - Providing an adhesive material (13) which contains at least one open-pore venting textile (14a, 14b) and is provided integrally with the at least one venting textile (14a, 14b) in the form of an adhesive film (20); - Introducing the adhesive material (13) together with the open-pore venting textile (14a, 14b) between the joining parts (11, 12) in a predetermined joining zone, such that the venting textile (14a, 14b) touches the respective joining part (11, 12) with one surface side, wherein the joining zone is tempered at least in a partial area before the application of surface pressure and subsequently pressure is applied locally to the joining zone for position fixation; - Creating a vacuum setup (10) such that at least the joining zone with the open-pore venting textile (14a, 14b) is sealed vacuum-tight under the vacuum setup (10); - Evacuating the joining zone under the vacuum setup (10) including the open-pore venting textile (14a, 14b) using a vacuum pump; and - Carrying out a curing process to cure the adhesive material (13) introduced between the joining parts (11, 12), wherein, for carrying out the curing process, the adhesive material (13) is tempered by means of a tempering device only after the complete evacuation of the at least one open-pore venting textile (14a, 14b). [2] Method according to claim 1, characterized by , that the adhesive material (13) is provided in such a way that an open-pore venting textile (14a, 14b) is provided both between the adhesive material (13) and the first joining part (11) and between the adhesive material (13) and the second joining part (12). [3] Method according to any one of the preceding claims, characterized by, that the vacuum setup (10) is placed in an autoclave, whereby an overpressure in the surrounding area of ​​the vacuum setup (10) is generated by means of the autoclave in order to carry out the curing process, in order to apply a surface pressure to compact the adhesive layer (21). [4] Method according to claim 3, characterized by , that the overpressure in the surrounding area of ​​the vacuum setup is only generated after the complete evacuation of the at least one open-pore venting textile (14a, 14b). [5] Method according to any one of the preceding claims, characterized by , that the adhesive material (13) is introduced with the at least one venting textile (14a, 14b) in such a way that, before evacuating the joining zone and / or carrying out the curing process, the pores of the open-pore venting textile (14a, 14b) each form a cavity (15) between the adhesive material (13) and the respective joining part (11, 12). [6] Method according to any one of the preceding claims, characterized by that the entire joining zone and / or the entire surface of one or both joining partners is covered with the open-pore venting textile. [7] Method according to any one of the preceding claims, characterized by that one or both joining parts (11, 12) are made of a fiber composite material. [8] Adhesive film (20) for joining two joining parts (11, 12), wherein the adhesive film (20) has an adhesive material (13) which is configured to be applied according to a method according to one of the preceding claims. [9] Adhesive film (20) according to claim 8, characterized by , that an open-pore venting textile (14a, 14b) is arranged on each surface side of the adhesive film (20). [10] Use of an adhesive film (20) according to one of claims 8 or 9 for the adhesive joining of two joining parts (11, 12). [11] Use according to claim 10, characterized by, that at least one joining part (11), preferably both joining parts (11, 12), are or will be manufactured.

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