Method for manufacturing a vehicle structure

Abstract

Method for manufacturing a vehicle support structure (10), in particular a passenger cell, comprising the steps: - Providing a single or multi-part core (11), - Creating a fiber structure by wrapping the core (11) with reinforcing fibers (12), wherein the reinforcing fibers (12) are only placed on predetermined areas of an outer surface (13) of the core (11), - Applying pressure and / or temperature to the fiber structure to cure a matrix surrounding the reinforcing fibers, wherein the core (11) represents the final contour of the vehicle structure (10), wherein, prior to wrapping the core (11), at least one insert (14) is placed on or in a predetermined area of ​​the core (11) in which the core (11) remains free of reinforcing fibers.

Description

[0001] The present invention relates to a method for manufacturing a vehicle structure (vehicle support structure) according to the preamble of claim 1.

[0002] To reduce the overall weight of motor vehicles, which typically consist largely of metallic components, replacing metal materials with plastics has become standard practice. Current body designs made of fiber-reinforced plastics are usually hand-laminated or semi-automatically laminated in small batches. They typically consist of impregnated or technical textiles that are cured in an autoclave.

[0003] To achieve the production volumes required for mass production, pre-cut fabrics or woven materials are used, which are infiltrated by wet pressing or in the resin transfer molding (RTM) process, brought into their final geometric shape, and then cured. The individual shell elements produced in this way are then generally joined to form a complete car body by bonding.

[0004] Furthermore, the winding process is known for the production of hollow profiles. This process is also used, among other things, to manufacture pressure tanks in the aerospace industry, whereby one or more fiber rovings are wound over a plastic or metal body, the so-called liner. US Patent 6,206,458 B1 discloses a vehicle structure in which fibers are wound onto a base body and then bonded to it.

[0005] However, the vehicle structures known from the prior art have the disadvantage that the shell elements or hollow profiles are individually joined together to form the vehicle structure. At these joints, there are abrupt changes in strength and stiffness, so that the material properties of the overall structure vary considerably or even decrease.

[0006] Document EP 1 134 069 A1 discloses a fiber-reinforced plastic structure with a hollow profile, wherein the structure is a fiber-reinforced plastic structure with a hollow profile having at least one opening and a main body part having an internal cavity with a maximum width greater than the maximum width of the aforementioned opening(s), the main body part being made of fiber-reinforced plastic wherein the reinforcing fiber has been impregnated with synthetic resin, and furthermore, the main body part having a solid body with a non-revolutionary shape, wherein the internal maximum width (F) of the cavity is at least 0.5 m and the ratio (F / f) of the inner maximum width (F) of the cavity to the maximum width (f) of the aforementioned opening(s) is in the range of 1.1 to 500, and furthermore the aforementioned main body section is designed as an integral construction in which its entirety essentially has no areas that are connected to each other.

[0007] Document DE 600 14 937 T2 discloses a method for forming a reinforced node structure, comprising the placement of a cored reinforcement of constant cross-section in and along the grooves of a node tool and over the nodes thereof by repeated passes along the grooves to at least partially fill the grooves, closing the tool and hardening resin applied around the reinforcement.

[0008] Document DE 10 2011 114 389 A1 discloses a method for producing a shell-shaped hollow body made of fiber-reinforced plastic, wherein in a first step a self-contained hollow body made of fiber-reinforced plastic is produced and in a second step this is separated into several shell-shaped hollow bodies.

[0009] Document DE 10 2014 206 904 A1 discloses a method for producing a fiber-reinforced molded component using a fillable hollow mold core, comprising the following steps: providing the hollow mold core; filling the hollow mold core with a magnetrheological fluid; providing a magnetic field in at least one part of the hollow mold core to cause the fluid to solidify; applying a fiber arrangement to at least that part of the hollow mold core.

[0010] Starting from this prior art, the present invention aims to provide a method for manufacturing a vehicle support structure that overcomes the disadvantages of the prior art. A particular objective of the invention is to provide a method for manufacturing a vehicle support structure characterized by the most homogeneous possible distribution of its mechanical properties.

[0011] This problem is solved by the features of claim 1. The dependent claims describe advantageous embodiments of the invention. To solve this problem, the invention proposes a method for manufacturing a vehicle support structure. For this purpose, a one- or multi-part core is first provided, and a fiber structure is created by wrapping the core with reinforcing fibers. During the wrapping of the core, the reinforcing fibers are laid only on predetermined areas of an outer surface of the core. Preferably, the reinforcing fibers are wound as a roving around the core in a load-oriented manner, whereby the fiber orientation is possible in various directions from -90° to +90°.In other words, in predetermined areas of the core's surface, the reinforcing fibers are positioned and aligned so that, in the event of a crash load on the vehicle's load-bearing structure, they can absorb the maximum forces in the longitudinal direction of the fibers. The reinforcing fibers, or rovings, can be wound over any geometric shape, laid down with a predefined fiber tension. In a first embodiment of the invention, the reinforcing fibers can be pre-impregnated with a resin material. According to a second embodiment of the invention, the rovings are wound onto the core in a dry state and then impregnated with a matrix. In both embodiments, after the fiber structure, which is formed from wound fibers, has been created, it is subjected to pressure and / or temperature, thus curing the matrix surrounding the reinforcing fibers. The outer shape of the core, or...The liner essentially corresponds to the final contour of the finished vehicle structure. "Essentially" in this context means that after the matrix has cured, no further forming steps are necessary that would alter the geometry of the vehicle structure. Of course, cutouts can still be made in the vehicle's load-bearing structure by trimming, milling, or drilling. This process offers the advantage of producing a one-piece vehicle load-bearing structure without any joints, such as adhesives, rivets, screws, or the like, and is therefore characterized by high strength and stiffness. The core is preferably mounted to rotate and / or pivot and is rotated and / or pivoted about at least one axis during the wrapping with reinforcing fibers.This allows the core to be pivoted during fiber placement to achieve the most precise placement possible while maintaining a predetermined fiber tension. Thus, the fibers applied to the core by one or more ring winding heads or one or more winding heads can be positioned precisely in the predetermined areas. The number of rotational or pivoting axes therefore determines the fiber placement accuracy and, consequently, the quality of the vehicle's load-bearing structure. To enable the wrapping of vehicle load-bearing structures with complex geometries, tests have shown that pivoting the core around four axes is optimal. Placement accuracy can be further increased, for example, by robot-assisted placement guidance of the ring winding heads or winding heads.

[0012] Before the core is wound, at least one insert is placed on or within a predetermined area of ​​the core. This insert prevents reinforcing fibers from being laid in this second predetermined area. The insert thus acts as a barrier for predetermined areas that should remain free of reinforcing fibers. When the reinforcing fibers are laid, this insert is not covered by the fibers. Areas that should remain free of reinforcing fibers include, in particular, window openings, doors, connection points, and other penetrations that should remain unobstructed in the fiber structure to be created.

[0013] The core is rotatably mounted in areas that remain free of reinforcement. In other words, inserts are used that are themselves rotatably mounted. By placing these inserts in the predetermined areas of the core that are to remain free of reinforcing fibers, the core can also rotate around the axis of rotation of the respective insert. This offers the advantage that, after removing the inserts, no additional steps are necessary to remove the mountings for the axes of rotation from the core or the resulting fiber structure.

[0014] According to a first embodiment of the invention, the core can be removed from the fiber structure after the fiber structure has been subjected to pressure and / or temperature. The core can be made of a thermoplastic or a foam, serving as a lost-wax mold, and is removed from the fiber structure after the matrix has cured. Alternatively, the core can also be made of a multi-material mix with thermoplastic and heat-insulating foam or a honeycomb structure and remain in the finished vehicle support structure.

[0015] The resulting fiber structure can be single- or multi-layered. This offers the advantage that by repeatedly unwinding reinforcing fibers onto the core, local reinforcements with ideal material usage are created at predetermined points in the fiber structure.

[0016] Furthermore, an inner part can be applied to the generated fiber structure in a predetermined area, and the fiber structure with the inner part attached to it can be wrapped with further reinforcing fibers.

[0017] A spacer, such as a honeycomb core, can be used as the inner component. Suitable core materials include honeycomb cores, aramid honeycombs, and similar materials.

[0018] Preferably, the inner part is applied to the already resin-impregnated fiber structure. When the fiber structure is subjected to pressure and / or heat to cure the matrix material, the material of the inner part bonds with the matrix material. In a subsequent step, the cured fiber structure with the attached inner part is wrapped with further reinforcing fibers. Alternatively, before curing, the uncured fiber structure with the attached inner part is wrapped with fibers. During subsequent curing, the material of the inner part bonds with the resin of the fibers that form the fiber structure and simultaneously with the individual fibers that wrap the fiber structure and the inner part. Thus, the finished vehicle support structure has a sandwich-like structure.This sandwich construction can be complete, so that the entire vehicle support structure is designed as a sandwich, or only partially in certain areas where appropriate material properties are required.

[0019] Furthermore, a vehicle structure, in particular a passenger cell, is revealed, featuring a fiber structure made of wound reinforcing fibers, with the vehicle's load-bearing structure being formed in one piece. As mentioned above, a one-piece vehicle load-bearing structure offers advantages in that no joints are necessary, resulting in higher strength and stiffness values ​​throughout the entire vehicle structure. In addition, weight and cost savings are achieved by eliminating the joining connections.

[0020] Furthermore, the vehicle structure can be multi-layered, at least in sections, with an inner layer of fiber-reinforced plastic and an outer layer of fiber-reinforced plastic, with an inner part arranged between the two layers.

[0021] Preferably, the inner part can be designed as a honeycomb core.

[0022] The advantages of the invention are summarized below. The inventive method allows the reinforcing fibers to be wound onto the core with a load-optimized fiber orientation, resulting in a design and construction that is very suitable for fiber composites, compared to the quasi-isotropic structure known from the prior art through the use of preforms. Furthermore, the use of sewing threads or support fibers, as required in the processing of non-woven fabrics, can be eliminated. The inventive method is a highly continuous process in which very few individual parts need to be joined, thus requiring significantly less fiber material. This allows the manufacturing process to be streamlined and a very high weight saving of up to 50% compared to the current state of the art to be achieved.

[0023] Constructing the vehicle's load-bearing structure as a sandwich component offers the advantage of a stiffer structure due to an increased area moment of inertia. Additional noise and thermal insulation can be achieved through the inner layer, or by selecting a suitable core material. Because of the higher area moments of inertia and the improved mechanical properties achievable with sandwich construction, the amount of fiber in the outer layers can be reduced. Using lighter core materials results in further weight savings.

[0024] The wound structure results in less waste overall compared to lamination and pressing processes. The fiber-reinforced composite design is achieved through the use of unidirectional and virtually endless fibers laid in the direction of the load.

[0025] Vehicle load-bearing structures within the meaning of this invention are, in particular, passenger cells. Naturally, such passenger cells can also include additional longitudinal and transverse beams to which chassis and drive components, as well as other body elements, are attached. The core of the invention is the concept of constructing this vehicle load-bearing structure in one piece, i.e., using a monocoque design. A monocoque is generally understood to be a single-piece, usually hollow, body. In contrast to a traditional frame construction made of individual profiles or tubes, the flat shells of the monocoque can absorb higher forces, thus enabling high rigidity at a low mass. This allows for the dissipation of higher forces and energy levels, especially in the event of a crash.

[0026] In sandwich construction as defined in this invention, materials with different properties are combined in layers to form a component or semi-finished product. Sandwich construction is a form of lightweight construction in which the components consist of load-bearing, rigid outer layers spaced apart by a relatively soft, usually lightweight core material or inner section. Components manufactured using sandwich construction exhibit high stiffness at a low weight. The core material can be made of various materials, most commonly paper honeycomb, rigid foam, mineral wool, or balsa wood. The core material transfers shear forces to the outer layers and supports them. Fiber-reinforced composites are preferably used as the outer layers.

[0027] The reinforcing fibers can be organic or inorganic. For example, the reinforcing fibers can be carbon fibers. These, together with the polymer matrix, form a carbon fiber reinforced plastic, also known as CFRP (carbon fiber reinforced plastic). The corresponding FRP component is then a CFRP component. The reinforcing fibers can also be glass fibers, for example. These, together with the polymer matrix, form a glass fiber reinforced plastic, also known as GFRP. The corresponding FRP component is then a GFRP component. However, the invention is not limited to this, and the reinforcing fibers can also be, for example, aramid fibers, polyester fibers, nylon fibers, polyethylene fibers, PMMA fibers, basalt fibers, boron fibers, ceramic fibers, silica fibers, steel fibers, and / or natural fibers.

[0028] The material of the polymer matrix may consist of one or more thermoplastic polymers (thermoplastics) and / or thermosetting polymers (thermosets). Fiber-reinforced polymers with a thermoplastic matrix have the advantage that they can be subsequently reshaped or welded. Suitable thermoplastic polymers include, for example, polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polysulfone (PSU), polyetherimide (PEI), and / or polytetrafluoroethylene (PTFE). Fiber-reinforced polymers with a thermosetting matrix cannot be reshaped after the matrix has cured or crosslinked. They advantageously have a wide temperature range. This is especially true for heat-curing systems that are cured at high temperatures. Fiber-reinforced polymers with a thermosetting matrix usually exhibit the highest strengths. Examples of thermosetting polymers or matrices include:The following resins are used: epoxy resin (EP), unsaturated polyester resin (UP), vinyl ester resin (VE), phenol-formaldehyde resin (PF), diallyl phthalate resin (DAP), methacrylate resin (MMA), polyurethane (PUR), amino resins, melamine resin (MF / MP) and / or urea resin (UF).

[0029] The invention is explained in more detail below with reference to the description of the figures. The figures, the claims, and the description include a multitude of features that a person skilled in the art would also consider in other combinations to adapt the invention to corresponding applications.

[0030] It shows in schematic form: Fig. 1 the inventive process

[0031] In Fig.Figure 1 shows two spool stands 22 from which reinforcing fibers are unwound. These are passed through an impregnation bath 21, in which the individual fibers are coated with a matrix material. In a felting section 20, the pre-impregnated fibers are compressed into a fiber bundle or roving 12 or a reinforcing fiber 12. The reinforcing fiber 12 is guided over a thread loop 23 and laid onto a core 11. The thread loop 23 can be guided by a robot.

[0032] The reinforcing fibers 12 are deposited in predetermined areas of a core 11. The core 11 is shown here, by way of example and without limitation, in the form of a body shell of the well-known BMW Isetta model. The reinforcing fibers 12 are deposited in predetermined areas of the core. In these areas, the fiber structure 10 to be produced is intended to exhibit high mechanical properties. Therefore, the reinforcing fibers 12 are deposited in a load-path-oriented manner, with the reinforcing fibers 12 being deposited only in predetermined areas. Such areas include, for example, the course of the lower and / or upper A-pillar, the B-pillar, the C-pillar, and the roof side frame. In the area of ​​the underbody or roof, the reinforcing fibers 12 can follow longitudinal or transverse struts as well as diagonally running load paths. During the wrapping with reinforcing fibers 12, the core 11 is rotatably mounted about pivot axes a.These axes of rotation a can, for example, pass through the inserts 14. The inserts 14 cover areas that are to remain free of reinforcing fibers, in particular door and window openings as well as functional connection points. Of course, the core 11 can also be rotatably mounted about an axis of rotation a' that does not pass through an insert 14. In this case, the core 11 is rotatably mounted via a joint. This joint must be removed from the core 11 after completion of the fiber structure.

Claims

[1] Method for manufacturing a vehicle support structure (10), in particular a passenger cell, comprising the steps: - Providing a single or multi-part core (11), - Creating a fiber structure by wrapping the core (11) with reinforcing fibers (12), wherein the reinforcing fibers (12) are only placed on predetermined areas of an outer surface (13) of the core (11), - Applying pressure and / or temperature to the fiber structure to cure a matrix surrounding the reinforcing fibers, wherein the core (11) represents the final contour of the vehicle structure (10), wherein, prior to wrapping the core (11), at least one insert (14) is placed on or in a predetermined area of ​​the core (11) in which the core (11) remains free of reinforcing fibers. [2] Method according to claim 1, characterized by, that the core (11) is rotatably and / or pivotably mounted and is rotated and / or pivoted about at least one axis (a) during the application of the reinforcing fibers. [3] Method according to claim 2, characterized by , that the rotatable mounting of the core (11) takes place in areas of the core (11) that remain free of reinforcing fibers. [4] Method according to any one of claims 2 to 3, characterized by , that the rotatable mounting of the core (11) is achieved by applying at least one rotatably mounted insert (14). [5] Method according to any one of the preceding claims, characterized by , that the core (11) is removed from the fiber structure after the reinforcing fibers (12) are subjected to pressure and / or temperature. [6] Method according to any one of the preceding claims, characterized by that the fiber structure is formed in one or more layers. [7] Method according to any one of the preceding claims, characterized by, that at least on a predetermined area of ​​the fiber structure an inner part is applied and the fiber structure with the inner part arranged on it is wrapped with reinforcing fibers. [8] Method according to any one of the preceding claims, characterized by that the inner part is designed as a spacer, in particular as a honeycomb core.

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