Method for manufacturing a lightweight crash structure for a motor vehicle

Abstract

Method for manufacturing a lightweight crash structure (100) comprising a cross member (110) and at least two crash boxes (120) designed as thermoplastic injection-molded parts, wherein the cross member (110) is designed as a sandwich component with a shell-like front thermoplastic continuous fiber-reinforced cover layer (111) and a shell-like rear thermoplastic continuous fiber-reinforced cover layer (112) and an intermediate core layer (113) made of particle foam, comprising the steps: - material-bonding connection of the crash boxes (120) with the rear cover layer (112) by directly injection molding, welding or gluing the crash boxes (120) to this cover layer (112); - then the rear cover layer (112) is joined to the prefabricated core layer (113) and the front cover layer (111) by pressing the two cover layers (111, 112) together with the core layer (113).

Description

[0001] The invention relates to a method for producing a lightweight crash structure for a motor vehicle, which has a cross member designed as a sandwich component with a particle foam core and at least two crash boxes.

[0002] DE 10 2017 007 309 B4 describes a bumper assembly with a cross member and two crash boxes. In the event of an accident-related energy input to the cross member, the crash boxes are deformable and energy-absorbing.

[0003] DE 10 2016 012 183 B4 describes a crash structure for a vehicle, which includes, among other things, a bumper cross member and two crash boxes. The end sections of the bumper cross member are each connected to a corresponding longitudinal member of a vehicle body via a crash box. In the event of an accident, the forces generated can be absorbed by the bumper cross member, the crash boxes, and the longitudinal members through deformation of these structures. The end sections of the bumper cross member and the central section can each be designed as (metallic) extruded profiles. Extruded profiles are advantageously stable and can be manufactured easily and cost-effectively.

[0004] The closest document, DE 10 2019 113 641 A1, describes a bumper beam that extends in the vehicle's transverse direction (y-direction) and is thus a cross member. The bumper beam is designed as a sandwich component and has a front cover layer (compression band) and a rear cover layer (tension band), which are preferably made of a continuous fiber-reinforced thermoplastic. Between them is a core layer, referred to as a connecting element, which can consist of a particle foam, namely an EPP foam. The bumper beam is attached to the vehicle chassis by means of rear brackets. A method for manufacturing the bumper beam is not described.

[0005] Regarding the state of the art, reference is also made to DE 10 2016 007 371 A1, which describes a bumper cross member for a vehicle with two crash boxes protruding from the rear of the bumper cross member, connecting the cross member to the vehicle body. The crash boxes can be formed from the fiber-reinforced flat material of a one-piece blank and molded-on thermoplastic material.

[0006] The inventive method of claim 1 enables the series-production-ready production of a lightweight crash structure mentioned above, which comprises a cross member designed as a sandwich component with a particle foam core and at least two crash boxes. Additional features of the invention are set out in the dependent claims, the following description of the invention (this expressly includes features described as examples), and the drawings.

[0007] The lightweight crash structure to be manufactured comprises a cross member, in particular a bumper cross member, and at least two crash boxes, wherein the crash boxes are arranged in particular in the end sections of the cross member. The cross member is designed as a sandwich component with two thermoplastic continuous fiber-reinforced cover layers and a core layer of (thermoplastic) particle foam arranged between them. The crash boxes are designed as thermoplastic injection-molded parts and are integrally connected to the cross member. Metallic extruded profiles are therefore not provided. Significant weight and mass savings can be achieved.

[0008] This lightweight crash structure is preferably arranged at the front and / or rear of a motor vehicle, in particular a car. The cross member can absorb crash energy due to its core layer formed from particle foam. Furthermore, the cross member can divert crash energy into the crash boxes in a known manner, which then absorb crash energy through deformation. Thus, both the cross member and the crash boxes function as energy absorption elements, particularly to absorb or dampen impact energy. The crash structure can therefore also be referred to as a lightweight impact damping structure.

[0009] The lightweight crash structure is made of plastic and can only be manufactured using thermoplastics, which offers recycling advantages, among other things.

[0010] The crash boxes can be injection-molded directly onto one of the thermoplastic continuous fiber-reinforced cover layers, namely the rear cover layer, of the cross member. This means that the crash boxes are molded onto the respective continuous fiber-reinforced cover layer of the cross member during their injection-molded production. However, the crash boxes can also be first injection-molded and then welded or glued to the respective continuous fiber-reinforced cover layer of the cross member.

[0011] The crash boxes are preferably designed as honeycomb structural elements. The crash boxes can thus absorb a comparatively high amount of crash energy despite their low weight or mass. In particular, the honeycombs extend essentially perpendicular to the cross member.

[0012] The crash boxes are made of injection-molded thermoplastic material, preferably polypropylene (PP). This is preferably the same thermoplastic material used for the thermoplastic continuous fiber-reinforced cover layers of the cross member (see below), or at least a thermoplastic material compatible with it. The crash boxes are made, in particular, of fiber-reinforced thermoplastic material, i.e., reinforcing fibers, in particular short glass fibers or long glass fibers, can be admixed with the thermoplastic.

[0013] The cover layers of the cross member are made of continuous fiber-reinforced thermoplastic. This means in particular that the continuous reinforcing fibers, preferably glass fibers (continuous glass fibers), are embedded in a thermoplastic matrix, preferably polypropylene, whereby the continuous reinforcing fibers can also be combined to form a fiber fabric or the like. It is preferably provided that the cover layers of the cross member are multi-layer laminates constructed from several layers, e.g., ten to twenty layers (so-called layer structure). The layers are preferably so-called UD layers with unidirectionally aligned continuous fibers, in particular continuous glass fibers, which are available as thermoplastic (i.e., with a thermoplastic matrix) pre-impregnated UD semi-finished products. The UD layers are preferably arranged with different fiber orientations (e.g., 0°, 45°, and 90°).The continuous fiber-reinforced thermoplastic cover layers can have a preferred layer thickness of 0.5 mm to 4.0 mm.

[0014] The core layer of the cross member is made of particle foam. Similarly, the cross member can also have multiple core layers made of particle foam. A particle foam or particle foam is a foam consisting of thermoplastic foam beads bonded at their surfaces. These are preferably spherical and, in particular, closed-cell thermoplastic foam beads. The sandwich core or foam core of the cross member is formed, in particular, from a polypropylene particle foam (EPP), polystyrene particle foam (EPS), polyethylene particle foam (EPE), polyamide particle foam (E-PA), or polybutylene terephthalate particle foam (E-PBT). The sandwich core is preferably manufactured separately from a particle foam starting material in a so-called molding process, e.g., as described in DE 10 2020 106 725 A1, and then further processed (see below).The core layer of the cross member, made of particle foam, can have a preferred layer thickness of 30 mm to 60 mm.

[0015] Due to its sandwich construction with two thermoplastic continuous fiber-reinforced cover layers and a core layer of particle foam arranged between them, the cross member is very rigid despite its low weight and mass, yet still able to absorb crash energy. The rigid design of the cross member also allows for the arrangement of at least one load introduction element on the cross member for attaching a towing eye or the like. This load introduction element is preferably arranged near a crash box, in particular at a distance of ≤ 100 mm.

[0016] Furthermore, it is preferably provided that the cross member is curved and / or has angled end sections. A curvature can increase the functional rigidity and load-bearing capacity of the cross member.

[0017] The method according to the invention for producing a lightweight crash structure comprising a cross member and at least two crash boxes formed as thermoplastic injection-molded parts, wherein the cross member is formed as a sandwich component with a shell-like front thermoplastic continuous fiber-reinforced cover layer and a shell-like rear thermoplastic continuous fiber-reinforced cover layer and a core layer of particle foam arranged therebetween, comprises at least the following steps: - materially bonded connection of the crash boxes with the rear thermoplastic continuous fiber reinforced cover layer; - then the rear cover layer is firmly bonded to the prefabricated core layer made of particle foam and the front thermoplastic continuous fiber reinforced cover layer.

[0018] The method according to the invention therefore provides that the crash boxes are first connected to the rear cover layer or attached to this cover layer, namely by direct injection molding, welding, or gluing. Only then is the cross member created by connecting or joining the rear cover layer equipped with the crash boxes to the core layer and the front cover layer. This procedure can prevent damage to the core layer, formed from particle foam, due to the sometimes very high local pressures when connecting or attaching the crash boxes. During injection molding, pressures of up to 800 bar and more can occur at certain points.

[0019] The bonding or joining of the two cover layers to the core layer is achieved by pressing, creating a flat, bonded connection between the cover layers and the core layer. To create the bonded connection, heat and / or the use of an additional adhesive may be required.

[0020] As explained above, the thermoplastic continuous fiber-reinforced cover layers of the cross member can be formed as multilayer laminates. In this case, the production of the lightweight crash structure can include the following steps: - arranging blanks of a thermoplastically pre-impregnated fiber semi-finished product, in particular a thermoplastically pre-impregnated UD semi-finished product, to form a layer structure; - Pressing the layer structure, where appropriate also giving it a three-dimensional shape (e.g. curvature), and simultaneously injecting the crash boxes, in particular in a suitably designed press-injection mold; - materially bonding the rear cover layer thus produced to the prefabricated, optionally spatially shaped, in particular having its final shape, core layer and the front cover layer, for which purpose the rear cover layer provided with the crash boxes is arranged and pressed together with the core layer and a layer structure forming the front cover layer made of cuts of a thermoplastically pre-impregnated fiber semi-finished product, in particular a thermoplastically pre-impregnated UD semi-finished product, in a pressing tool, wherein a spatial shaping or deformation of the front cover layer also takes place if necessary.

[0021] The method described above specifically envisages the use of two tools, whereby the initially produced cover layer with the molded-on crash boxes is removed or demolded from the first tool (compression-injection molding tool) and then inserted into the second tool (pressing tool). In principle, however, the process can also be carried out with only one appropriately designed tool, whereby the cover layer produced in a first operation with the molded-on crash boxes remains in the tool and is pressed together with the core layer and the other cover layer in a subsequent operation.

[0022] The invention is explained in more detail below in a non-limiting manner with reference to the drawing. Fig. 1 shows the front of a motor vehicle (passenger car) with a lightweight crash structure manufactured according to the invention. Fig. 2 shows the left-hand end section of the lightweight crash structure from Fig. 1. Fig. 3 schematically illustrates an inventive production of the lightweight crash structure from Fig. 1 and Fig. 2.

[0023] In the front of the vehicle in Fig. A lightweight crash structure 100 is arranged on the front of the motor vehicle 10 indicated in Figure 1. The lightweight crash structure 100 has a bumper cross member 110 (hereinafter referred to as the cross member) and two crash boxes 120. The crash boxes 120 are arranged on the right and left sides in the end sections of the cross member 110 and are each connected to a longitudinal member 12 of the vehicle body via an impact plate 11. The cross member 110 can be curved and / or have angled end regions (see Fig. 2).

[0024] As from Fig. 2, the cross member 110 of the lightweight crash structure 100 is designed as a sandwich component, with a shell-like front cover layer 111 and a shell-like rear or rear cover layer 112, each formed from thermoplastic continuous fiber-reinforced plastic, as well as a core layer 113 made of particle foam arranged therebetween, which can also be referred to as a particle foam core. The cover layers 111, 112 are preferably multi-layer laminates. The crash box 120 is designed as a thermoplastic injection-molded part and is integrally connected to the rear cover layer 112 of the cross member 110, namely injection-molded, welded, or glued. The same applies to the right-side crash box. If the lightweight crash structure 100 is located in the rear of the vehicle, the Fig. 1 and Fig. 2 is virtually mirrored, so that the rear cover layer 112 is located in front of the front cover layer 111 in the vehicle longitudinal direction.

[0025] Fig. 3 illustrates a simplified manufacturing process for the lightweight crash structure 100. First, the crash boxes 120 are molded directly onto the rear cover layer 112, as in Fig. 3a. The cover layer 112 can be preformed. Subsequently, the rear cover layer 112 is joined by pressing to the prefabricated core layer 113 made of particle foam, which already has its final shape, and to the front cover layer 111, as shown in Fig. 3b. The front cover layer 111 can be preformed or formed during the pressing process. To avoid repetition, reference is made to the above explanations.

[0026] As also in Fig. 3, the crash boxes 120 are preferably designed as honeycomb structural elements. In particular, it is provided that the honeycombs 125 extend substantially perpendicular to the cross member 110, as shown, for example, in Fig. 3c.

[0027] The lightweight crash structure 100 can be provided as a prefabricated unit and installed in the motor vehicle 10. This also enables easy repair by replacing the entire lightweight crash structure 100. The defective lightweight crash structure 100 can then be recycled.

Claims

[1] Method for producing a lightweight crash structure (100) comprising a cross member (110) and at least two crash boxes (120) formed as thermoplastic injection-molded parts, wherein the cross member (110) is formed as a sandwich component with a shell-like front thermoplastic continuous fiber-reinforced cover layer (111) and a shell-like rear thermoplastic continuous fiber-reinforced cover layer (112) and a core layer (113) made of particle foam arranged therebetween, comprising the steps: - materially bonding the crash boxes (120) to the rear cover layer (112) by directly injection-molding, welding or gluing the crash boxes (120) to this cover layer (112); - then materially connecting the rear cover layer (112) to the prefabricated core layer (113) and the front cover layer (111) by pressing the two cover layers (111, 112) with the core layer (113). [2] Method according to claim 1, characterized by that the crash boxes (120) are designed as honeycomb structural elements. [3] Method according to one of the preceding claims, characterized by that the crash boxes (120) are made of fiber-reinforced thermoplastic material. [4] Method according to one of the preceding claims, characterized by that the thermoplastic continuous fiber reinforced cover layers (111, 112) of the cross member (110) are multi-layer laminates. [5] Method according to one of the preceding claims, characterized by that the core layer (113) of the cross member (110) formed from particle foam has a layer thickness of 30 mm to 60 mm. [6] Method according to one of the preceding claims, characterized by that the cross member (110) is curved and / or formed with angled end regions.

Images