Method for manufacturing a hollow component from fiber-reinforced plastic

Abstract

Method for producing a hollow component (5) made of fiber-reinforced plastic, which comprises the following process steps: - an assembly step in which a multi-part core (1, 1a) is built up from a plurality of core elements (2a-2f, 3, 4a, 4b), wherein at least one rigid core element (2a-2f, 4a, 4b) is provided, wherein the rigid core element (2a-2f, 4a, 4b) expands more with increasing temperature and shrinks more with decreasing temperature than the hollow component (5), and the remaining core element (3) expands less than or in the same way as the hollow component (5) with increasing temperature and shrinks less than or in the same way as the hollow component (5) with decreasing temperature; - an application step in which reinforcing fibers are applied to the multi-part core (1, 1a); - an embedding step in which the reinforcing fibers are embedded in a matrix material made of plastic to form the hollow component (5), wherein the core (1, 1a) is brought to an increased temperature in or before the embedding step so that the stiff core element (2a-2f, 4a,4b) expands more than the remaining core element (3); - a removal step prior to which the core (1, 1a) is cooled in such a way that the rigid core element (2a-2f, 4a, 4b) shrinks more than the hollow component (5), thereby releasing the rigid core element (2a-2f, 4a, 4b) from its seat in the hollow component (5) and allowing the rigid core element (2a-2f, 4a, 4b) to be removed from the hollow component (5) without damage, and at least the remaining core element (3), which is at least free of play in the hollow component (5) and therefore cannot be removed without damage or forms a targeted reinforcement of the hollow component, remains in the hollow component (5); and - a final step in which the process is completed, with the remaining core element (3) remaining in the hollow component (5) beyond the final step.

Description

[0001] The present invention relates to a method for producing a hollow component made of fiber-reinforced plastic.

[0002] Fiber-reinforced plastics are increasingly being used in automotive construction, and hollow components are also being made from these fiber-reinforced plastics.

[0003] In the production of such hollow components, cores are used that define the contour of the hollow component and are braided with reinforcing fibers, for example. The reinforcing fibers are then embedded in a matrix material, and the core is optionally removed to form the hollow component.

[0004] In view of the large-scale production required in automotive engineering, easy-to-handle, rigid cores must be used, for example for braiding the core or applying the reinforcing fibers, which can be easily and stably held by gripper systems.

[0005] For example, aluminum cores are used, which are removed from the hollow component after the reinforcing fibers have been embedded. However, these cores can only be used for components with simple geometries, as otherwise the core cannot be removed again to produce the hollow component.

[0006] On the other hand, washable core systems such as salt or sand cores are used to make the cores removable in complex geometries. However, these core systems are complex to manufacture and very costly, making them unsuitable for large-scale production.

[0007] Furthermore, blow mold cores are used to produce hollow components with complex geometries, such as undercuts or branches, which collapse after the reinforcing fibers have been embedded in the matrix material and are removed from the hollow component.

[0008] Fig. Figure 5 shows a cross-sectional view of a blow mold core 8 before it is braided with reinforcing fibers. The blow mold core 8 is filled with air and held by grippers 7. As can be seen, the blow mold core offers little resistance to deformation and therefore must be supported at additional positions not shown. Furthermore, the gripper(s) 7 provided for holding the blow mold core 8 must be configured so that they do not damage the blow mold core. These problems occur particularly with large blow mold cores and / or those with thin walls. Therefore, blow mold cores with a wide variety of cross-sections and wall thicknesses are difficult to handle, especially in automated manufacturing processes.

[0009] In addition, blow mold cores cannot be reused directly after removal from the hollow component, but usually have to be melted down and remanufactured first.

[0010] Ultimately, none of the cores mentioned are used in the corresponding manufacturing processes in such a way that the cores also perform other functions in addition to determining the contour of the hollow component.

[0011] Patent publication DE 10 2009 051 459 A1 discloses a method for producing a fiber composite component having a hollow profile. In this method, several fiber layers are wound over a single- or multi-part core in a radial braiding process, then synthetic resin is injected, for example, and the core is partially removed if necessary. At least one preferably metallic reinforcement insert is integrated into the fiber composite component at at least one load-critical location. This reinforcement insert is designed either as a lost core or as an inserted reinforcement insert and is positioned, for example, by magnetic force.

[0012] Further prior art is represented by the documents DE 601 04 574 T2, DE 698 07 545 T2, DE 10 2009 058 487 A1 and CH 509 870 A.

[0013] Against this background, the object of the invention is to propose an easily manageable manufacturing method with which hollow components with different requirements and / or complex geometries can be manufactured from fiber-reinforced plastics.

[0014] The object is achieved by a method for producing a hollow component made of fiber-reinforced plastic according to claim 1. A preferred embodiment of the method according to the invention is the subject of the dependent claim.

[0015] The invention is defined by the claims, with aspects of the invention being set forth below.

[0016] According to one aspect of the invention, a method for producing a hollow component made of fiber-reinforced plastic comprises in particular the following method steps: - a construction step in which a multi-part core is constructed from a plurality of core elements, wherein at least one rigid core element is provided, wherein the rigid core element expands more with increasing temperature and shrinks more with decreasing temperature than the hollow component, and the remaining core element expands less than or in the same way as the hollow component with increasing temperature and shrinks less than or in the same way as the hollow component with decreasing temperature; - an application step in which reinforcing fibres are applied to the multi-part core; - an embedding step in which the reinforcing fibers are embedded in a plastic matrix material to form the hollow component, the core being brought to an elevated temperature in or before the embedding step so that the rigid core element expands more than the remaining core element; - a removal step, prior to which the core is cooled in such a way that the rigid core element shrinks more than the hollow component, thereby releasing a seat of the rigid core element in the hollow component and removing the rigid core element from the hollow component in a non-destructive manner, and at least the remaining core element, which is seated in the hollow component at least without play and therefore cannot be removed non-destructively or forms a targeted reinforcement of the hollow component, remains in the hollow component; and - a final step in which the process is concluded, with the remaining core element remaining in the hollow component beyond the final step.

[0017] According to one aspect of the invention, for example, it is a method for producing a fiber-reinforced hollow component that has at least one component section with a complex geometry, such as an undercut, a branch, a junction, or a connecting element. Such a hollow component can be, for example, a bend, a force introduction element, or a hollow profile.

[0018] Due to the multi-part nature of the core and the retention of one of the core elements according to the invention, hollow components with complex geometries can be manufactured, with, for example, a section with a simple geometry being realized by the rigid core element and a section with a complex geometry being realized by the remaining core element. Due to the multi-part nature, the core can also be constructed in different ways depending on the geometry of the hollow component to be produced.

[0019] According to one aspect of the invention, for example, it further relates to a method for producing a fiber-reinforced hollow component that is to be specifically reinforced at a specific section. In this regard, in the removal step, the rigid core element is removed from the hollow component, with the remaining core element remaining specifically at a specific section of the hollow component, where it forms a reinforcement of the hollow component. The specific section can be any section of the hollow component.

[0020] If, for example, it is determined during the design and dimensioning of the hollow component that a section does not have sufficient stability for a specific application, the remaining core element can be taken into account in the design / construction and the multi-part core can be constructed in the assembly step in such a way that in the removal step the remaining core element remains on the section and forms the targeted reinforcement there.

[0021] According to one aspect of the invention, the entire production of the hollow component can be simplified in that inserts or stiffening elements may not have to be integrated into the hollow component in the application or embedding step.

[0022] According to one aspect of the invention, the method can be carried out and easily handled by providing at least one rigid core element, particularly in the manufacture of hollow components in automated large-scale production. This is because the provision of at least one rigid core element with sufficient flexural rigidity and pressure resistance allows the multi-part core to be securely held and the risk of damage to the rigid core element by a gripper to be reduced. Thus, rigid core elements that are easy to handle, for example, by automated grippers, can be used to manufacture hollow components with complex component geometries and specific requirements.

[0023] Furthermore, the use of the rigid core element makes it very easy to ensure good and high compressive strength of the multi-part core, at least in certain sections. With the rigid core element correctly positioned, this leads to a good wall thickness distribution of the plastic matrix embedding the reinforcing fibers. This increases the mechanical properties of the complex hollow component and reduces its complexity.

[0024] In addition, the easy handling of the core elements allows for reduced cycle times in the production of fiber-reinforced hollow components.

[0025] By retaining one of the numerous core elements as intended, specific sections, such as branches of the hollow component, can be deliberately reinforced, or the torsional rigidity of the hollow component can be deliberately increased. In general, local reinforcements can be easily implemented without the need for additional plant technology or process steps.

[0026] The cross-sectional shape of the rigid core element can be any desired shape. Furthermore, the rigid core element(s) can have draft angles. The remaining core element is preferably made of a lightweight material, such as foam, structural foam, or plastic, to minimize the impact on the desired lightweight properties of the hollow component. For targeted reinforcement, the remaining core element can also preferably be made of metal.

[0027] By removing the rigid core element, additional weight can be saved - compared to a one-piece foam core that remains completely in the hollow component.

[0028] The reinforcing fibers used in the application step can be, for example, carbon fibers, glass fibers or aramid fibers, which are applied to the core as long or continuous fibers or in the form of woven or non-woven fabrics.

[0029] In the embedding step, the reinforcing fibers are impregnated with a plastic matrix material after the application step. This can be achieved, for example, by placing the core containing the reinforcing fibers into a mold cavity and injecting the plastic matrix material into the cavity (low-pressure / high-pressure process). Alternatively, the reinforcing fibers can be impregnated with the plastic matrix material prior to the application step.

[0030] The plastic matrix material is then cured to form the hollow component and forms the matrix of the reinforcing fibers.

[0031] According to one aspect of the invention, the process is carried out as a resin injection process (resin transfer molding) or as a resin infusion process (resin infusion).

[0032] In a preferred embodiment of the method, the core is held at least on the rigid core element in the application step and / or in the embedding step.

[0033] This offers the advantage that the multi-part core can be easily guided through the process using automated robotic or gripping systems, without, for example, being plastically deformed or damaged. Furthermore, the risk of core collapse, as is the case with prior art blow molding cores, is prevented by the use of the rigid core element. This also eliminates the need for additional support of the core from the inside, for example, when inserting the core from one side into a braiding system to perform the application step.

[0034] Preferably, the core is held exclusively on the rigid core element.

[0035] This preferred embodiment of the method is particularly suitable for the production of hollow components in large-scale production using robot or gripping systems.

[0036] By reducing the effort required for core handling, the complexity of the manufacturing process can be reduced while simultaneously increasing production speed, leading to increased economic efficiency.

[0037] The method provides that in the assembly step, the multi-part core is constructed from the plurality of core elements such that the plurality of core elements are detachably connected to one another and in the removal step, the rigid core element or a plurality of rigid core elements of the plurality of core elements is / are detached from the remaining core element and removed from the hollow component.

[0038] The detachable connection of the core elements can be established, in particular, via a plug-in mechanism, an adhesive connection, a screw connection, or a press connection. The detachable connection is preferably established such that the core elements form a flush transition to one another. Particularly preferably, an additional seal is provided between the core elements to prevent the plastic matrix material from penetrating between the core elements during the embedding step—which can lead to problems during the demolding step.

[0039] In the case of adhesive bonding, an adhesive is used that sufficiently holds the core elements together in the application step and the embedding step and can be easily released in the removal step, for example by shear stress.

[0040] Due to the detachable connection, especially between the remaining core element and the rigid core element(s) to be removed, the assembly step and the removal step can be carried out easily.

[0041] The core elements, especially the rigid core elements, can be designed as identical parts using the modular principle. Furthermore, connecting elements, transition pieces, or adapter parts can be available using the modular principle, thus expanding the possibilities of a modular design of the multi-part core.

[0042] The process is easy to handle due to the modular design of the multi-part core and can be adapted quickly and cost-effectively to the hollow components to be manufactured and their geometries.

[0043] In the method, at least the rigid core element(s) is / are removed non-destructively in the removal step.

[0044] Non-destructive removal enables the reuse of the corresponding core elements. In particular, the non-destructively removable core elements are advantageously made of rigid materials so that they will not be damaged even by repeated handling by a robot or gripping system used in mass production. Stable and rigid materials for the manufacture of the removable rigid core elements are preferably metals, especially aluminum or magnesium.

[0045] The use of reusable, rigid core elements and the possibility of a modular core design can reduce process costs, increase productivity and promote sustainability.

[0046] The method provides that in the assembly step, the multi-part core is constructed in such a way that the rigid core element or the rigid core elements to be removed in the removal step expand more with increasing temperature and shrink more with decreasing temperature than the hollow component, and the core is brought to an elevated temperature in or before the embedding step and is cooled after the embedding step in or before the removal step in such a way that the rigid core element or the core elements to be removed shrink more than the hollow component and as a result the rigid core element(s) become loose from the hollow component.

[0047] Temperature fluctuations can occur due to process factors. For example, when using a thermoplastic matrix material, it is applied to the reinforcing fibers at elevated temperatures before / during the embedding step and then cooled to cure. This necessary temperature fluctuation can be exploited to achieve the aforementioned expansion / shrinkage behavior. Alternatively, the multi-part core can be heated and cooled in additional heating and cooling steps.

[0048] To achieve the expansion and shrinkage behavior, for example, the rigid core elements to be removed are made of a material that has a thermal expansion coefficient that leads to a greater expansion and shrinkage behavior of the rigid core elements than that of the hollow component.

[0049] In particular, the materials used for the rigid core elements mentioned above, i.e. aluminum or magnesium, have such a thermal expansion coefficient.

[0050] In contrast, a firm, at least play-free connection between the core element, which remains in the hollow component as intended, and the hollow component is advantageous.

[0051] Therefore, the method provides that in the assembly step, the multi-part core is constructed in such a way that the core element, which remains in the hollow component as intended in the removal step, expands less than or in the same way as the hollow component with increasing temperature and shrinks less than or in the same way as the hollow component with decreasing temperature, and the core is brought to an elevated temperature in or before the embedding step and is cooled after the embedding step in or before the removal step, whereby the remaining core element sits in the hollow component at least without play.

[0052] Before the removal step, the plastic matrix material, as already mentioned, is brought to an elevated temperature and then cured, which leads to the expansion / shrinkage behavior.

[0053] By realizing the expansion and shrinkage behavior mentioned above, the remaining core element does not detach from the hollow component during cooling, but remains in the hollow component without any play.

[0054] Depending on the thermal expansion and shrinkage behavior of the remaining core element and the hollow component, a press fit of the remaining core element in the hollow component can also be created.

[0055] Advantageously, the remaining core element is made of a material having a thermal expansion coefficient that results in the remaining core element exhibiting the same or weaker expansion and shrinkage behavior than that of the hollow component.

[0056] Finally, the method provides that in the assembly step, the multi-part core is constructed in such a way that the remaining core element, after the removal step, sits in a section of the hollow component which forms a connection point, a node point or a force introduction point.

[0057] This means that stiffeners and local reinforcements can be formed at connection points without additional plant technology and / or without further process steps.

[0058] In the following, preferred embodiments of the method according to the invention are explained with reference to the attached figures. Fig. 1a shows a construction step of a multi-part core used in the method according to the invention; Fig. Figure 1b shows a fully assembled core after the assembly step; Fig. Figure 1c shows a sectional view of a hollow component containing the multi-part core after the embedding step; Fig. Figure 1d shows the removal step in which stiff core elements are removed from the hollow component; Fig. Figure 1e shows a cross-sectional view of the finished hollow component with a remaining core element; Fig. 2 shows a possibility of connecting individual core elements; Fig. Figure 3 shows another multi-part core used in the method according to the invention; Fig. Figure 4 shows a sectional view of a rigid core element held by a gripper; and Fig. Figure 5 shows the state of the art or a sectional view of a blow mold core held by a gripper.

[0059] The process of the invention is shown schematically in the Fig. 1a to 1e explained.

[0060] Fig. Figure 1a shows a construction step of the method according to the invention, in which a multi-part core 1 is constructed from a plurality of core elements, for example, round or square in cross-section. Specifically, the core 1 is constructed from four identical rigid core elements 2a-2d, a core element 3 that remains in the ultimately produced hollow component 5 as intended, and two optional rigid core end elements 4a, 4b, which serve to form flanges on the ultimately produced hollow component 5.

[0061] The four preferably identical core elements 2a-2d and the core end elements 4a, 4b can be removed non-destructively from the ultimately produced hollow component 5, as will be explained below.

[0062] The removable core elements 2a-2d and the core end elements 4a, 4b are preferably made of a rigid material such as aluminum or magnesium.

[0063] The core element 3 remaining as intended is preferably made of a lightweight structural foam, which only slightly influences the desired lightweight construction properties of the hollow component 5 to be produced.

[0064] Furthermore, the removable core elements 2a-2d and the core termination elements 4a, 4b can be derived from a modular kit (not shown), which provides various core elements, such as identical parts. This allows for simple and rapid adaptation of the core to be assembled using the method according to the invention.

[0065] Fig. Figure 1b shows the multi-part, fully assembled core 1 after the assembly step. The connection between the core elements is designed to be detachable to enable later easy and non-destructive removal of the core elements 2a-d and the core end elements 4a, 4b.

[0066] The detachable connection can be made, for example, by a Fig. 2 shown plug-in system can be realized. As shown by the core elements 2a to 2c in Fig. 2, the individual core elements 2a to 2c have male and female connecting sections which enable the core elements to be plugged into one another and / or screwed together.

[0067] The remaining core element 3 preferably has a female connecting portion in the structural foam on each side facing the removable core elements 2c and 2d.

[0068] Preferably, the surfaces of all core elements are flush when assembled, i.e., the core elements merge seamlessly into one another. This allows a virtually continuous surface of the core 1 to be achieved, which leads to increased quality of the hollow component 5.

[0069] Returning to Fig. 1b, a reinforcing fiber is applied to the thus constructed or assembled multi-part core 1 in a subsequent application step, for example, by winding a continuous fiber or a fiber fabric around the core 1. The fibers can be, for example, a carbon fiber or a glass fiber.

[0070] In an embedding step of the method according to the invention, the reinforcing fiber is embedded in a thermosetting or thermoplastic matrix material to produce the hollow component 5. This can be done by applying the reinforcing fiber to the core 1 in a state impregnated with the matrix material, or by impregnating the reinforcing fiber already applied to the core 1 with the matrix material.

[0071] After curing of the plastic matrix material, the hollow component 5 is dimensionally stable, with the multi-part core 1 still being located in the hollow component 5.

[0072] According to the invention, it is preferably provided that the core 1 is held on the rigid core end elements 4a, 4b during the application and embedding steps.

[0073] Fig. Figure 1c shows a sectional view of the multi-part core 1 and the hollow component 5 after the application and embedding step.

[0074] This is followed by a removal step of the method according to the invention, in which the removable core elements 2a - 2d of the core 1 are removed from the hollow component 5. This step is shown in Fig. 1d. As can be seen from this figure, the rigid core elements 2a-2d and core termination elements 4a, 4b are separated from each other, for example, by loosening the plug-in connection or screw connection, and pulled out of the hollow component. The rigid core elements 2a-2d and the core termination elements 4a, 4b can thus be removed from the hollow component 5 without causing any damage and can subsequently be reused without major effort.

[0075] The core element 3 is located in a bend or a curved section of the hollow component 5 and for this reason cannot be removed from the hollow component 5 without being damaged, which is why it remains in the hollow component 5 and forms a targeted, local stiffening.

[0076] In the previously explained method, all core elements are preferably heated to a higher temperature before or during the embedding step and cooled again after the embedding step. This results in the core elements expanding with increasing temperature and shrinking with cooling. The core elements 2a to 2d and the core end elements 4a, 4b to be removed are preferably designed such that they shrink more during cooling than the hollow component 5. This loosens their fit within the hollow component 5, making the removal step easier.

[0077] The remaining core element 3 is preferably designed such that its thermal expansion and shrinkage behavior is opposite. This means that the core element 3 remaining as intended shrinks less or to the same extent as the hollow component 5 and therefore sits at least play-free in the hollow component 5 after cooling.

[0078] Before the process is completed, further processing steps, not shown, can be carried out on the hollow component 5, such as drilling holes.

[0079] The method is concluded in a final step, which may, for example, consist in the finished hollow component 5 being removed from a device carrying out the removal step.

[0080] Fig. Figure 1e shows a cross-sectional view of the finished hollow component 5, in which the remaining core element 3 is located after the final step. The core element 3, which remains as intended, serves as reinforcement in the illustrated hollow component 5. In particular, the reinforcement of the curvature can result in increased rigidity of the hollow component 5.

[0081] With reference to Fig. 3 explains a preferred variant of the multi-part core provided for carrying out the method according to the invention.

[0082] Fig. Figure 3 shows a multi-part core 1a, which is composed of three different core elements 2e, 2f, and 3. The core elements 2e and 2f are advantageously made of rigid materials, such as aluminum or magnesium, and the remaining core element 3 is made of a structural foam.

[0083] In contrast to the Fig. 1a-1e, this variant does not contain any core termination elements. In addition, the cores shown in Fig. 1a-1e shown core elements 2a to 2c are realized by a single core element 2e.

[0084] As can be understood from the previous description, rigid core elements can also be used to manufacture hollow components with a complex structure due to the multi-part nature of the core and their detachability from the remaining core element 3. Furthermore, the process can also be carried out in large-scale production because the multi-part core with its rigid core elements offers a good engagement point for robot and gripper systems. Fig. 4 shows an example of a sectional view of the rigid core element 2f before reinforcing fibers are applied to the core 1a in the application step.

[0085] The core element 2f is held by gripper 7. Due to the sufficiently high flexural rigidity and compressive strength of the core element 2f, correspondingly applied forces can be absorbed. Additional support points for the core element 2f, especially on its inner side, are unnecessary.

[0086] The features and method steps disclosed in the above description, in the drawings and in the claims can be combined with one another.

Claims

[1] Method for producing a hollow component (5) made of fiber-reinforced plastic, which comprises the following process steps: - a construction step in which a multi-part core (1, 1a) is constructed from a plurality of core elements (2a-2f, 3, 4a, 4b), wherein at least one rigid core element (2a-2f, 4a, 4b) is provided, wherein the rigid core element (2a-2f, 4a, 4b) expands more with increasing temperature and shrinks more with decreasing temperature than the hollow component (5), and the remaining core element (3) expands less than or in the same way as the hollow component (5) with increasing temperature and shrinks less than or in the same way as the hollow component (5) with decreasing temperature; - an application step in which reinforcing fibers are applied to the multi-part core (1, 1a); - an embedding step in which the reinforcing fibers are embedded in a plastic matrix material to form the hollow component (5), wherein the core (1, 1a) is brought to an elevated temperature in or before the embedding step so that the rigid core element (2a-2f, 4a, 4b) expands more than the remaining core element (3); - a removal step, before which the core (1, 1a) is cooled such that the rigid core element (2a-2f, 4a, 4b) shrinks more than the hollow component (5), thereby releasing a seat of the rigid core element (2a-2f, 4a, 4b) in the hollow component (5) and removing the rigid core element (2a-2f, 4a, 4b) from the hollow component (5) in a non-destructive manner, and at least the remaining core element (3), which sits in the hollow component (5) at least without play and therefore cannot be removed non-destructively or forms a targeted reinforcement of the hollow component, remains in the hollow component (5); and - a final step in which the process is concluded, wherein the remaining core element (3) remains in the hollow component (5) beyond the final step. [2] Method according to claim 1, wherein the core (1, 1a) is held / supported at least on the rigid core element (2a-2f, 4a, 4b) in the application step and / or in the embedding step.

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