Method for manufacturing a component structure from several components, component structure and vehicle

Abstract

Method for manufacturing a component structure from several components, wherein the method comprises the following steps: Hardening (S12) of a respective fiber-reinforced plastic composite material such that a respective fiber-reinforced plastic component with a plastic matrix of a certain degree of hardness is obtained, Joining (S14) the respective fiber-reinforced plastic components to form a component structure, wherein the joining (S14) comprises a structural crosslinking of at least two of the several components with a joining agent whose plastic component is also contained in the fiber-reinforced plastic composite; and Hardening (S16) of the component structure such that the respective hardness degree of the plastic matrix of each joined fiber-reinforced plastic component is increased beyond the specified hardness degree.

Description

[0001] The invention relates to a method for manufacturing a component structure, a component structure manufactured according to the method, and a vehicle that has the component structure.

[0002] It is known from the prior art to produce complex component structures for different applications from, for example, several fiber-reinforced plastic components (also referred to as fiber-reinforced plastic matrix composite components).

[0003] Such fiber-reinforced plastic components are known to be manufactured from a fiber-plastic composite material, which is a material comprising a fiber component and a plastic component.

[0004] The fiber component is formed from fibers that serve for reinforcement and stabilization. The function of the fibers is generally to increase the stiffness and strength of a component made from the fiber-reinforced plastic composite, for example, compared to a corresponding fiberless plastic component. The fibers can be separate or formed in the form of woven fabrics, so-called preforms or prewovens.

[0005] The plastic component of the fiber-reinforced plastic composite forms a plastic matrix within the fiber-reinforced plastic component. This plastic matrix surrounds the fibers, which are bound to the plastic matrix by adhesive or cohesive forces.

[0006] These fiber-reinforced plastic components are often manufactured using injection molding or injection compression molding processes.

[0007] In the case of injection molding, such a fiber-reinforced plastic component is essentially manufactured as follows: First, a fiber-containing component is placed into a cavity of a mold, the mold cavity (or cavity) serving primarily to define the external dimensions of the fiber-reinforced plastic component to be produced. Then, a plastic molding compound intended for creating the plastic matrix of the fiber-reinforced plastic component is injected into the mold, thus surrounding or infiltrating the inserted fibers, and remaining there for a specific period of time. During this specific time in the mold, the so-called residence time, a cross-linking process of the plastic molding compound occurs due to adjustable operating parameters such as the processing pressure and temperature, thereby increasing its hardness.After the curing time has elapsed, the molding compound, which is usually completely hardened and surrounds the fiber component, can be removed from the mold. The fiber-reinforced plastic component produced using this process is widely referred to as a fiber-reinforced plastic molded part, in which the now completely hardened molding compound forms a plastic matrix encasing the fibers.

[0008] The complex component structures are ultimately produced by joining, i.e., permanently connecting, usually using joining agents, such fiber-reinforced plastic components.

[0009] Among other applications, such complex component structures made of fiber-reinforced plastic components are used in the automotive industry. For example, a vehicle's passenger cell can be at least partially formed by such a complex component structure.

[0010] Other examples of complex component structures used in connection with the automotive industry are vehicle doors and the vehicle tailgate.

[0011] In connection with the use of fiber-reinforced plastic components in the automotive industry, carbon fibers, glass fibers or aramid fibers are preferably used for the fiber component and thermosets or thermoplastics for the plastic component.

[0012] Depending on the type of plastic used for the plastic component of the fiber-reinforced plastic part, the hardening of the plastic, which can be carried out in the tool during the injection molding process, varies.

[0013] Thermoset plastics are polymers that are formed from a melt or solution of components through a cross-linking reaction during a curing process. This irreversible reaction is usually caused by heating, but can also be initiated and accelerated by oxidizing agents, high-energy radiation, or the use of catalysts. Heating thermosets does not lead to plastic deformation, but merely to their decomposition.

[0014] When a thermoset is used as a molding compound, the polymers of the plastic molding compound cross-link during curing, for example, when heated, forming a solid structure, infiltrating the fiber component, and creating a solid plastic matrix. The degree of cross-linking of the plastic indicates how far the plastic matrix, and thus a fiber-reinforced plastic component, has cured.

[0015] When using a thermoplastic polymer, the polymer matrix is ​​deformable within a specific temperature range. Therefore, after curing, the fiber-reinforced polymer component can be returned to a deformable state by heating it to a temperature within this range, particularly above its glass transition temperature. Curing can then be repeated. This is possible due to the lack of cross-linking in the molecular chains, which are connected not by chemical bonds but only by intermolecular forces.

[0016] While thermoplastics have no or virtually no cross-linking points and can therefore be melted, thermosets, due to their (cross-)linking, cannot be melted and decompose after exceeding the so-called decomposition temperature (pyrolysis). Accordingly, the curing process of thermoplastic polymers differs from that of thermoset polymers.

[0017] Based on the in Fig. The flowchart shown in Figure 2 illustrates an example of a state-of-the-art method for manufacturing a component structure using a thermosetting plastic.

[0018] Initially, in a first step, S20 provides several tools, as well as at least one thermosetting plastic molding compound, for example an epoxy resin or another reactive resin, and fibers.

[0019] To manufacture the components, in a second step (S21) the fibers (as the fiber component) and the molding compound (as the plastic component) are introduced into the molds. In a further step (S22), the fiber-reinforced plastic composite is cured in the molds under pressure and heat, thus forming the fiber-reinforced plastic components. Since thermosetting plastics are heat-curing, a separate cooling phase in the molds before removal is not required.

[0020] After the components have been hardened in the molds, they are removed from the molds in the next step (S23) and each placed in a tempering oven, where they are tempered separately in a tempering step (S24), i.e., heated for an extended period. During this process, the degree of cross-linking of the molecules of the plastic component, i.e., the thermoset plastic matrix, increases.

[0021] In a further step S25, the components are then removed from the tempering furnaces and in a further step S26 each are mechanically processed separately, for example by contour cutting or the introduction of connection options, such as holes or grooves.

[0022] Finally, in joining step S27, the components are joined to form a component structure, i.e., permanently connected to one another. For this purpose, the components are typically clamped in fixtures and then joined together in a joining process. This can be a hot or cold joining process, such as welding, soldering, gluing, screwing, or riveting. This can be done using one or more joining agents. Adhesives, for example, are used as joining agents. Additionally or instead, other joining agents, such as rivets or screws, can also be used.

[0023] If necessary, for example when using an adhesive, a further process step S28 of curing the joining material follows. Depending on the adhesive used, the curing of the joining material can take place, for example, at room temperature or, in the case of epoxy resin adhesives, by heating.

[0024] Likewise, it is usually necessary, especially if individual components or the entire component structure have become distorted, to mechanically rework the assembled component structure in a further step (S29) to bring it into its final shape.

[0025] As mentioned above, the described process can lead to problems with each component, such as warping during hardening or the subsequent tempering process, due to differing expansion behavior of the fiber and plastic components. This warping can occur, meaning the component's shape or dimensions deviate from the desired form or dimensions. Machining or trimming the individual components can also cause warping. This warping can vary from component to component and generally cannot be accurately simulated or predicted in advance for all subsequent process steps, for example, to account for or fully compensate for it in the hardening tool.

[0026] Furthermore, in industrial manufacturing, several tempering furnaces are necessary for the individual components in order to shorten the production time, in order to be able to carry out the tempering process with all components required for the component structure to be created simultaneously, in order to shorten the time to carry out the manufacturing process, which is already long due to the large number of process steps.

[0027] Depending on the number of different components that make up the component structure, a variety of tools are required for manufacturing these components. For example, fixtures for clamping the components during assembly, and possibly also during tempering and machining of the individual components, may be necessary.

[0028] Furthermore, when using an adhesive that requires curing under heat, an additional heating step may need to be provided in which the adhesive is cured.

[0029] Overall, industrial manufacturing requires significant investment in tools, equipment, and energy. Furthermore, production time is long.

[0030] Patent publication DE 10 2012 031 881 A1 discloses a structural component for a motor vehicle body and a method for its manufacture. To manufacture the structural component, several fiber-reinforced plastic components are bonded together in a curing device without the use of an adhesive additive.

[0031] Further state of the art is formed by the documents EP 2 067 611 A1, EP 2 441 571 A1 and DE 10 2009 047 671 A1.

[0032] Against this background, the object of the invention is to provide an improved method for manufacturing such a component structure, enabling more efficient and precise production of the component structure; in particular, such a component structure should be manufactured with fewer individual production devices in fewer process steps, and distortion of the finished component structure should be reduced. Accordingly, an improved component structure or an improved vehicle with such a component structure should also be provided, in which distortion is reduced.

[0033] This problem is solved by a method for manufacturing a component structure according to claim 1, a component structure according to claim 5, and a vehicle according to claim 7. Further preferred embodiments are the subject of the dependent claims.

[0034] The inventive method for producing a component structure from several components includes, among other things, the following steps: Hardening of a respective fiber-reinforced plastic composite material in such a way that a respective fiber-reinforced plastic component with a plastic matrix of a specific degree of hardness is obtained, Joining the respective fiber-reinforced plastic components to form a component structure, wherein the joining comprises a structural crosslinking of at least two of the multiple components with an adhesive whose plastic component is also contained in the fiber-reinforced plastic composite; and Hardening of the component structure in such a way that the respective hardness level of the plastic matrix of each joined fiber-reinforced plastic component is increased beyond the specified hardness level. The inventive method is particularly preferably implemented in such a way that the hardening comprises hardening a respective fiber-reinforced plastic composite material in such a way that a respective fiber-reinforced plastic component with a plastic matrix with a certain degree of cross-linking is obtained. that the joining process includes joining the respective fiber-reinforced plastic components to form a component structure; and that the hardening process includes hardening the component structure in such a way that the respective degree of cross-linking of the plastic matrix of each joined fiber-reinforced plastic component is increased beyond the specified degree of cross-linking.

[0035] To carry out the process according to the invention, a molding compound as a plastic component and fibers as a fiber component are first introduced into one or more tools for producing the fiber-reinforced plastic components. The fiber-reinforced plastic composite material formed from the components is shaped in the tools and cured to a specific degree of cross-linking in order to ultimately obtain a component that is not fully cured. The step of joining the respective fiber-reinforced plastic components to form a component structure then takes place before the components thus assembled into the component structure are further cured together. After joining, the components joined to form the component structure are either fully cured, i.e.,until the degree of cross-linking of the molecules of the plastic component reaches a maximum value, or the joined components are cured further in such a way that the degree of cross-linking is increased beyond the specified degree of cross-linking.

[0036] In this way, the individual components are no longer cured separately – as in the prior art – but are joined directly to form the component structure in a single joining process without being fully cured. Only then is the entire component structure further cured in a subsequent curing step, for example, fully cured. This curing step can also include curing the joining agent used in the joining process, such as an adhesive like an epoxy resin adhesive. Thus, the inherent stiffness of the complex component structure is used to prevent, compensate for, or at least significantly reduce distortion of the components forming the component structure, and therefore of the entire component structure, during the next curing process.

[0037] Preferably, highly integrated components are used to manufacture the complex component structure. However, it is also conceivable that the component structure is formed from simple monolithic components as well as from complex, highly integrated components. Since simple monolithic components are usually more susceptible to distortion, they are preferably pressed into the desired position using clamping or holding devices before the joining process. In this way, the distortion of the assembled component structure can be reduced.

[0038] Preferably, the fiber-reinforced plastic composite from which the components are manufactured includes a thermoset as the plastic component. Thermosets, such as epoxy resins, are plastics that, unlike thermoplastics, have a lower viscosity before curing at temperatures below the desired glass transition temperature. This makes them particularly suitable for injection molding into a tool to produce a complexly shaped, for example, highly integral, component. Furthermore, thermosets are thermosetting, meaning the curing process requires only heating and no cooling phase. This allows, for example, the use of tooling for manufacturing the components that maintains a constant operating temperature throughout multiple curing processes of the corresponding fiber-reinforced plastic composites.

[0039] Since the hardening step of the component structure can be a heat curing process, it can be carried out as a tempering step in which the component structure is heated for an extended period. The changing glass transition temperature of the thermoset used during heat curing is adjusted to a value above this temperature for all components forming the component structure by selecting the appropriate temperature for the curing process. Additionally, the heat-curing adhesive is also cured during the hardening step of the component structure.

[0040] Preferably, the fiber-reinforced plastic composite material includes carbon fiber as a fiber component. Carbon fiber reinforced plastics (CFRP) exhibit high stiffness and strength after curing. Other fiber components can be used, for example, glass fiber, aramid fiber, ceramic fiber, basalt fiber, or natural fiber, as well as combinations of different fiber components.

[0041] Preferably, the respective components are manufactured using an injection molding process, in particular an RTM process (RTM = Resin Transfer Molding). In this process, the molding compound is injected by means of a piston from a usually heated pre-chamber via distribution channels into a mold cavity, i.e., a hollow space formed inside the tool according to the desired shape of the component to be molded, where it hardens under heat and pressure.

[0042] Alternatively, the components can also be manufactured by processing prepreg semi-finished products (preimpregnated fibers) consisting of continuous fibers and an uncured thermosetting plastic matrix already enclosing them, using autoclaves, i.e., special pressure vessels in which very high pressure and high temperature act on the prepreg semi-finished products.

[0043] When using an injection molding process, it is particularly preferred if the injection molding process used is a low-pressure injection molding process. This makes it possible, in particular, to inject plastic components into the respective mold at temperatures low relative to the target glass transition temperature, at which, for example, thermosets exhibit low viscosity. Due to the long manufacturing time for highly integrated components, where the plastic component must not cure too quickly (otherwise there is a risk that the mold for producing a highly integrated component cannot be filled with the required amount of plastic component), the process is particularly suitable for the production of component structures in small and medium quantities.

[0044] Alternatively, a vacuum RTM process or a high-pressure RTM process can be used, for example.

[0045] The process step of joining the components to form a component structure involves structurally crosslinking at least two of the multiple components with an adhesive whose plastic component is also present in the fiber-reinforced plastic composite. This involves crosslinking a portion of the molecules of the plastic component used to manufacture the components with the molecules of the adhesive. In this way, a component structure can be created in which the adhesive joining the components forms a common matrix structure with the components themselves. If the component structure is then hardened by tempering the entire structure, the areas where the components have been joined can also exhibit the same glass transition temperature.

[0046] If the joining material requires hardening, the component structure is preferably placed in a tempering oven as soon as the joining material is "handleable," i.e., as soon as the component structure as a whole can be moved sufficiently. Complete hardening of the joining material is not necessary; instead, it occurs in a single step along with the hardening of the entire component structure during tempering in the oven.

[0047] According to the invention, a component structure is also provided, which was manufactured according to the inventive method for producing a component structure. The properties and advantages achieved in connection with the inventive method are thus obtained in the same or a similar manner; therefore, to avoid repetition, reference is made to the preceding explanations in connection with the inventive method.

[0048] The component structure can be, in particular, a passenger cell, for example of an automobile.

[0049] Furthermore, according to the invention, a vehicle is also provided which comprises a component structure manufactured according to the inventive method. In this case as well, the properties and advantages achieved in connection with the inventive method are obtained in the same or a similar manner, which is why, to avoid repetition, reference is made to the preceding explanations in connection with the inventive method.

[0050] One embodiment of the invention is explained below with reference to the accompanying drawing. Fig. Figure 1 shows a flowchart to illustrate a method for manufacturing a component structure according to an embodiment of the invention. Fig. Figure 2 shows a flowchart to illustrate a prior art method for manufacturing a component structure.

[0051] In Fig.Figure 1 shows a method for manufacturing a component structure from several components according to an embodiment of the invention. In a setup step S10, a plurality of tools, a plastic molding compound, and fibers are provided. A tool for manufacturing a component or molded part from a fiber-reinforced plastic composite consists of at least one die, i.e., a negative of the outer shape of the component to be manufactured, which encloses a cavity, i.e., a hollow space for the component. One or more cores, for example, can be placed in the cavity as an inner form. The plastic molding compound can, in particular, be a thermosetting resin, for example, epoxy resin. The fibers can, in particular, be carbon fibers, although other fibers can also be used, depending on the requirements placed on the component to be manufactured.

[0052] The provisioning step S10 may also include the provision of further components, such as foams, which are additionally introduced into the corresponding tool to manufacture a component.

[0053] In insertion step S11, the fibers (as the fiber component) and the molding compound (as the plastic component) are introduced into the respective tools. Using these tools, and employing at least the plastic component and the fiber component, step S12 is then performed to cure the fiber-reinforced plastic composite formed by the components. This curing process results in a fiber-reinforced plastic component with a plastic matrix exhibiting a specific degree of cross-linking. In other words, step S12 involves curing the fiber-reinforced plastic composite to obtain fiber-reinforced plastic components, whereby cross-linking occurs between molecules of the plastic component such that the components are not fully cured within the tools.

[0054] For example, an injection molding process or an RTM process, particularly a low-pressure RTM process, can be used for manufacturing. In step S11, the introduction of the plastic molding compound and the fibers into the respective tools, the fibers, for example in the form of so-called preforms or prewovens, are first introduced into the cavity of the respective tool and then embedded or enclosed by the molding compound forming the plastic matrix through injection or infiltration into the respective tool, thus creating a fiber-reinforced plastic matrix composite semi-finished product. The curing step S12 involves the semi-finished products consisting of the fiber-reinforced plastic matrix composite undergoing a curing process in the respective tools under pressure and with the application of heat, so that molded parts are formed. The plastic matrix cross-links during curing.The components remain in the molds until they have cured sufficiently for the degree of cross-linking of the plastic component molecules to allow removal. At this stage, the degree of cross-linking of the plastic matrix molecules has not yet reached its maximum possible value. For example, cross-linking may be approximately 70% or 80% complete when the components are removed from the molds in the next step, S13.

[0055] In assembly step S14, the extracted fiber-reinforced plastic components are then assembled into the desired component structure. Simple components prone to warping are pressed into a desired position in holding fixtures, where they are then joined with other components.

[0056] In this exemplary embodiment, the component structure to be manufactured is a passenger cell of a vehicle.

[0057] Joining step S14 is performed without reheating the components separately. In particular, no tempering of the individual components takes place at this stage of the inventive process, where the components could be cured separately and the glass transition temperature could be set separately for each component. According to the invention, joining comprises a permanent connection of the components to form a component structure, for example, bonding. Examples not claimed include welding, soldering, screwing, riveting, etc. According to the invention, joining is carried out using an adhesive, wherein the adhesive is the material of the plastic component itself used for the fiber-matrix composite, for example, epoxy resin.

[0058] If necessary, joining step S14 also includes an initial hardening of the joining material at least to the extent that the component structure becomes "handling-capable", i.e., can be moved without or with holding devices.

[0059] In a further step (S15), the component structure is then placed as a whole, for example, in a tempering oven. This is followed by a curing step (S16) in which the degree of cross-linking of the polymer molecules is increased. This means the component structure is cured in such a way that the degree of cross-linking of the polymer matrix of each joined fiber-reinforced plastic component is increased beyond the degree of cross-linking achieved during the curing of the individual components in the molds (step S12). For example, the degree of cross-linking is increased to the maximum possible value, and the component structure is cured. The curing step (S16) can be a tempering process in which the component structure is cured and simultaneously set to a desired glass transition temperature.In this single tempering step, which requires only one tempering furnace for the production of a component structure, the joining material can also cure. The inherent rigidity of the component structure within the composite of components prevents or at least significantly reduces distortion of the components or the entire component structure. Due to less distortion and increased component integrity, and thus a smaller number of parts, subsequent process steps that may be required are also reduced, thereby lowering their costs. For example, mechanical post-processing of the component structure, if otherwise necessitated by component distortion, can be eliminated or significantly reduced.

[0060] The features disclosed in the foregoing description, in the claims and in the drawings may be essential for the realization of the invention, both individually and in any combination.

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