ES3009366T3 - Reinforcement thermoplastic-based fibre-metal laminate composite frame and manufacturing method thereof - Google Patents

Abstract

This patent application provides a thermoplastic metal-fiber reinforcing composite frame (22), which constitutes an optimal compositional solution for the construction of a lightweight structure. This patent application also describes the manufacturing process of said reinforcing composite frame. The reinforcing composite frame (22) described herein is suitable for any lightweight component, preferably for automotive and aerospace components. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Metal and fiber-reinforced laminated composite frame based on thermoplastic and its manufacturing method

Technical field

This application relates to a reinforcing composite frame for any lightweight application component, preferably for automotive and aerospace components, and to the manufacturing process of said reinforcing composite frame.

Background of the technique

The quest for lightweight structures has driven the advancements and commercial use of composite materials. The high strength-to-weight ratio of composite materials is highly dependent on the lamination direction of the fibers, and this characteristic quickly begins to be lost as the fibers deviate from the loading direction to include more trans-isotropic behavior (bulk strength).

Among the early proponents of hybrid fiber-metal materials and their use as aerospace-grade materials was the TU Delft, where Schijve et al. (EP-A-0056289) described a composite laminate consisting of multiple layers of metal foils and fiber layers bonded together using an adhesive. The metal foils are made of aluminum alloys and are proposed to have a thickness of 0.25–1.00 mm, with the fiber/adhesive layer sandwiched between the metal foils. The laminated structure was proposed to be a suitable material for aircraft skins.

However, in certain examples (such as highly loaded joints), the overall increase (in all directions) in strength through the addition of multiple layers increases the volume of the structure and the weight of the component, thus defeating the purpose of using composite materials to achieve “high strength-to-weight ratio” gains. Patent EP-1801428 claims to provide a solution to this problem by proposing the use of metal reinforcements in highly loaded joint areas, particularly mechanically fastened joints, since a virgin CFRP composite is susceptible to delamination around the fixing holes. The metal reinforcements (layers) are inserted while laying the multiple layers of a composite panel (or beam) such that the fibers of the panel area (non-bonded area) are continuous across the entire joint area, meaning that the increase in thickness of the joint area is the same as the thickness of said reinforcements.

For large-scale production and cost-effectiveness, low cycle times are essential. Patent US-4,390,489 established the basic concept for the rapid manufacture of a multi-material layered structure. It proposed forming a metal/reinforced thermoplastic layer using a rapid stamping process, where the metal layer acts as a holding support and provides structural integrity during heating, before forming complex three-dimensional shapes. WO 96/31667 describes a fiber-reinforced thermoplastic frame with metal plate-like attachments.

Current technique and general methodology include the addition of composite layers in the critical load path of a component. The general practice is to include multiple layers of fiber/polymer composite in a single direction (UD) or in varying directions to improve planar strength in all directions. To reduce weight, each layer can be custom-cut by laser to add holes or perforations of the desired shape. However, this laminate philosophy of constructing each layer as a closed surface geometry leaves some discontinuous fibers in each layer that do not contribute to the overall strength and stiffness of the material, but instead contribute to the apparent mass.

Summary

The present invention relates to a reinforcing composite frame (22) comprising:

at least one set of layers, wherein each set of layers comprises:

a first layer comprising at least one first prepreg strip (11) having a first orientation; a second layer comprising at least one second prepreg strip (12) having a second orientation arranged at an angle between 0° and 180° with respect to each of the first prepreg strips (11), wherein each of the second prepreg strips (12) is fixed to each of the first prepreg strips (11) in at least one intersection zone (A); and

a third layer comprising a metal sheet (13) at each intersection (A);

wherein each prepreg strip (11, 12) comprises unidirectional thermoplastic fiber.

In one embodiment, each metal sheet (13) is on top of each second prepreg strip (12) in each intersection zone (A) or between each first (11) and second (12) prepreg strips in each intersection zone (A).

In one embodiment, each of the second prepreg strips (12) intercepts each of the first prepreg strips (11), forming an angle of 0° and 180° between them, preferably an angle of 90°.

In one embodiment, the composite further comprises a discontinuous prepreg layer (14) subsequently disposed at each end of each metal sheet (13).

The present invention also relates to a process for producing the reinforcing composite frame (22) comprising the steps of:

- placing a reinforcing frame (22) comprising at least one set of layers as described above, wherein the process for producing a set of layers comprises:

placing a first layer in an orientation, wherein the first layer comprises at least a first strip of prepreg (11);

placing a second layer on the first layer, wherein the second layer comprises at least one second prepreg strip (12) arranged at an angle between 0 and 180° with respect to the orientation of the at least one first prepreg strip (11), wherein at least one second prepreg strip (12) of the second layer is adhered to the top of each prepreg strip (11) of the first layer at at least one intersection (A); and placing a third layer comprising a metal foil (13) over each intersection (A);

wherein each prepreg strip (11, 12) comprises unidirectional thermoplastic fibers.

In one embodiment, each metal sheet (13) is placed in a different orientation than each metal sheet (13) of the subsequent set of layers, forming a staggered position of the metal sheets (13).

In one embodiment, each metal sheet (13) has a size between 5 and 15% different from each metal sheet (13) of the subsequent set of layers, forming a staggered position.

In one embodiment, each metal sheet (13) is placed either on top of each second prepreg strip (12) at each intersection area (A) or between each first (11) and second (12) prepreg strips at each intersection area (A).

In one embodiment, each of the second prepreg strips (12) intercepts each of the first prepreg strips (11), forming an angle of 0° and 180° between them, preferably an angle of 90°.

In one embodiment, a layer of discontinuous prepreg (14) is subsequently placed at each end of each metal sheet (13), depending on the disparity between the thickness of the prepreg and the metal sheet (13).

In one embodiment, a bulk part (23) made of lightweight moldable material selected from thermoplastic sheets or short fiber composite mats, or manufactured by injection molding using thermoplastic pellets, is overmolded onto the top of the frame (22), resulting in a reinforced part (24).

Detailed Description

This patent application provides a laminated composite frame made of metal and thermoplastic-based reinforcing fiber, which is an optimal compositional solution for constructing a lightweight structure. This patent application also provides the manufacturing process for said reinforcing frame.

For a high volume production application, a bulk part (23) made of lightweight moldable material selected from thermoplastic sheets or short fiber composite mats, or made by injection molding using thermoplastic pellets, is overmolded on top of the frame (22) to give a reinforced part (24). It is proposed that the reinforcing frame be made of a unidirectional (UD) fiber composite. The arrangement of the reinforcing frame (22) is the focus of this invention. Furthermore, an addition of metal layers at the intersection areas is proposed to benefit the fixing hole behavior. The invention also proposes a method of laying down the metal layers.

In a primary embodiment of the present patent application, disclosed herein is a reinforcing composite framework comprising multiple layers of unidirectional thermoplastic prepreg, wherein each prepreg layer is placed on top of one another and arranged in an intersecting pattern such that each layer has an orientation arranged at an angle between 0 and 180°, preferably 90° to the subsequent layer, thereby forming a mesh-like structure or framework, wherein a smaller metal/metal foil layer is placed after each intersection of prepreg layers to reinforce those areas that are more prone to multidirectional stresses. In a preferred embodiment, the reinforcing framework disclosed herein is a mesh-like structure. The prepreg layers comprise any fibers suitable for composite construction, e.g., glass, carbon, or aramid fibers. The metal layers comprise at least one of aluminum alloy, steel and magnesium alloy, preferably thin sheets (0.05 to 2.00 mm) of aluminum alloy.

The present invention proposes that the layers comprising the composite reinforcement frame be arranged in a modular manner, where each strip of unidirectional prepreg runs the entire length or width of the piece to be reinforced and creates intersection zones, thus creating an interlaced mesh form. Referring to Figure 1 which describes the simplest embodiment of the present invention, i.e. a ply module, and to Figure 2 which describes a reinforcement frame comprising multiple ply modules, there is described herein a reinforcement frame (22) comprising at least one ply module of unidirectional composite plies arranged in an alternating succession of at least a first strip of prepreg composite (11) having a first orientation and at least one second strip of prepreg composite (12) having a second orientation arranged at an angle between 0 and 180°, preferably 90°, with respect to the first prepreg strips (11) which cross and contact each other in at least one intersection area (A), and at least one metal foil (13) placed in the at least one intersection area (A), either between each first strip of prepreg (11) and subsequently each second strip of prepreg (12) or on top of each intersection between each first strip of prepreg (11) and each second strip of prepreg (12). According to the present application, and for the sake of clarity, the invention described herein refers to “layer module” or “layer assembly” which can be used interchangeably and are best defined as an assembly of 3 layers where a first layer comprises at least a first prepreg strip (11) having a first orientation (and parallel to each other in case of at least two first prepreg strips (11)), a second layer comprising at least a second prepreg strip (12) having an orientation arranged at an angle between 0 and 180° with respect to the first orientation, where each of the second prepreg strips (12) is fixed to each of the first prepreg strips (11) in at least one intersection zone (A), a third layer comprising a metal foil (13) in each intersection zone (A) either between each first (11) and second (12) prepreg strips or on top of said first (11) and second (12) prepreg strips, wherein a reinforced frame (22) may comprise as many layer modules as possible. as needed.

In one embodiment, and when referring to a 2D plane, the prepreg strips having a first orientation (11) could be understood as substantially horizontal strips and the prepreg strips having a second orientation (12) could be understood as substantially vertical strips (fig. 1c).

Although a manual layup could be performed on a flat surface (2D plane) in the context of the present invention, a preferred embodiment (Figure 7) is to use an automated tape (prepreg strip) layup method where the laminate is prepared such that two tape layup heads place the first (horizontal) prepreg strips (12) followed by three tape layup heads placing the second (vertical) strips (11), followed by the placement of a metal foil (13) at each intersection area (A), and these three steps are repeated until the desired thickness of the composite strips is achieved. Again, it is important to emphasize that the terms vertical and horizontal serve to give a positional reference relative to the 2D plane where the layers are being laminated.

Figure 10 shows further examples, where a bulk part (23) is supported by a reinforcing frame (22) made of mesh-like unidirectional composite strips (11, 12) as well as metal sheets (13) for reinforcing the intersection areas (A). The alternating layers at the intersection areas are firmly bonded during co-forming and a molded reinforcing frame (22) behaves as a cohesive structure rather than a group of thick strips.

In another main embodiment of the present patent application, there is provided herein a process for producing said reinforcement frame (22) which includes the addition of metallic layers. The placement of the metallic layer during the lamination is of primary importance. In one example, according to Figure 5, the reinforcement frame (22) comprises three-layer modules (and an additional layer of first prepreg strips (11)), i.e. a total of 4 layers of first prepreg strips (11) and 3 layers of second prepreg strips (12) with metallic foils (13) at each intersection area (A). All of the first prepreg strips (11) run lengthwise, while the second prepreg strips (12) have a dimension equal to or greater than the total width of the final component (24) and run widthwise. The laminate also comprises one metallic foil (13) at each intersection (A) per layer module. In this example, metal sheets (13) are placed on top of each of the second prepreg strips (12). After another set of first prepreg strips (11) and another set of second prepreg strips (12) are placed, the next set of metal sheets (13) placed is 5 to 15% (preferably 10%) smaller in size compared to the metal sheets (13) of the previous layer module. This size difference allows for a staggered position when centered across the intersection area. Similarly, a third layer of metal sheet (13) is placed after another set of first (11) and second (12) prepreg strips. From a top-to-bottom perspective, the top metal sheets (13) are smaller in size compared to both metal layers below them and allow all of the metal layers to be placed in a staggered manner.

In an embodiment best illustrated by Figures 6a and 6b, every third layer constitutes both a metal layer and a prepreg layer. The first prepreg strip (11) of the first layer module is placed, followed by metal foils (13) in the intersection area. Two discontinuous prepreg strips (14) are placed adjacent to the metal foil (13), which is followed by a second prepreg strip (12). This set of 3 layers is repeated on the lower assembly (subsequent layer module). In the subsequent layer module, the metal foil is placed in an orientation that is orthogonal to the metal foil of the previous layer module. These two layer modules are then repeated, in which the respective metal layers are placed in a slightly staggered position with respect to the metal layers of the previous layer modules. The two staggered positions are within 5 to 15% of the length of the metal foils. This arrangement of a 6-layer assembly is repeated 2 more times, each time orienting the metal layer perpendicular to the direction of the preceding metal layer. Optionally, a strip of prepreg (11) is placed on top of the laminate.

Brief description of the drawings

For a better understanding of this application, figures representing preferred forms of implementation are attached in the annex, which, however, are not intended to limit the technique described herein.

Figure 1a shows a layer module, where the layer of the first prepreg strip (11) is placed and then the layer of the second prepreg strip (12) is placed on top of the layer of the first prepreg strip (11), so that both layers are perpendicular to each other.

The layer module consists of a third layer of metal foil (13) placed in each intersection area of the two layers of prepreg strips (11, 12).

Figure 1b shows the layer module from the front view.

Figure 1c shows the layer module from below, with the metal foil (13) hidden behind the 2 prepreg layers (11, 12).

Figures 2a and 2b show the stacking of multiple layer modules on top of each other to form a thicker composite structure.

Figure 3 shows a single-layer module comprising a layer of multiple first prepreg strips (11) and a layer of multiple second prepreg strips (12), producing a large mesh-like structure.

Figure 4 shows an embodiment of the proposed invention, where the reinforcing frame (22) has a cylindrical shape ending in a hemispherical shape.

Figure 5 shows another embodiment of the application in an intersection area on multiple layer modules stacked on top of each other.

Figure 6a shows another embodiment of the same application where each layer module further comprises discontinuous prepreg strips (14) arranged as a continuation of each metal sheet (13).

Figure 6b shows, in three-dimensional perspective, the same embodiment as Figure 6a.

Figure 7 shows a non-molded (flat) reinforcement frame (22).

Figure 8 shows the reinforcing composite frame (22) as molded into the shape of a bulk piece, achieved after a forming process.

Figure 9 shows the schematic view of a bulk part (23) that needs reinforcement. It also shows fixing holes (16) where the intersection areas (A) of the reinforcement frame (22) will be.

Figure 10 shows the bulk piece (23) and the reinforcing frame (22) together, as intended in accordance with the presently described invention.

Description of the achievements

Preferred embodiments of the present application will now be described in detail with reference to the accompanying drawings. However, they are not intended to limit the scope of this application.

The present patent application describes a reinforcing composite material frame (22) comprising: at least one set of layers, wherein each set of layers comprises:

a first layer comprising at least one first prepreg strip (11) having a first orientation; a second layer comprising at least one second prepreg strip (12) having a second orientation arranged at an angle between 0 and 180° with respect to each of the first prepreg strips (11), wherein each of the second prepreg strips (12) is fixed to each of the first prepreg strips (11) in at least one intersection area (A); and

a third layer comprising a metal sheet (13) at each intersection (A);

wherein each strip of prepreg (11, 12) comprises unidirectional thermoplastic fiber.

In one embodiment, each metal sheet (13) is either on top of each second prepreg strip (12) in each intersection area (A) or between each first (11) and second (12) prepreg strips in each intersection area (A).

In one embodiment, each of the second prepreg strips (12) intersects each of the first prepreg strips (11), forming an angle of 0° and 180° between them, preferably an angle of 90°.

The present patent application also describes the production process of the reinforcing composite frame as defined above, wherein the process comprises:

- the placement of a reinforcing frame (22) comprising at least one set of layers as described above, wherein the process of producing a set of layers comprises:

placing a first layer in an orientation, wherein the first layer comprises at least a first strip of prepreg (11);

placing a second layer on the first layer, wherein the second layer comprises at least one second prepreg strip (12) arranged at an angle between 0 and 180° with respect to the orientation of the at least one first prepreg strip (11), wherein at least one second prepreg strip (12) of the second layer is adhered to the top of each prepreg strip (11) of the first layer at at least one intersection (A); and placing a third layer comprising a metal foil (13) over each intersection (A);

wherein each prepreg strip (11, 12) comprises unidirectional thermoplastic fibers.

In one embodiment, each metal sheet (13) is placed in a different orientation than each metal sheet (13) of the subsequent layer set, forming a staggered position of the metal sheets (13).

In another embodiment, each metal sheet (13) is 5 to 15% different in size than each metal sheet (13) of the subsequent layer set, forming a staggered position.

In one embodiment, each metal sheet (13) is placed either on each second prepreg strip (12) in each intersection zone (A) or between each first (11) and second (12) prepreg strips in each intersection zone (A).

In one embodiment, each of the second prepreg strips (12) intercepts each of the first prepreg strips (11), forming an angle of 0° and 180° between them, preferably an angle of 90°.

In one embodiment, a discontinuous prepreg layer (14) is subsequently placed at each end of each metal layer, depending on the disparity between the thickness of the prepreg and the metal sheet (13).

Of course, this description is in no way limited to the embodiments presented herein, and anyone with a reasonable understanding of the subject matter can provide many possibilities for modifying it without departing from the general idea defined by the claims. The preferred embodiments described above can obviously be combined with one another. The following claims define the preferred implementations in more detail.

Claims (11)

1. A reinforcing composite frame (22) characterized in that it comprises: at least one set of layers, wherein each set of layers comprises: a first layer comprising at least one first prepreg strip (11) having a first orientation; a second layer comprising at least one second prepreg strip (12) having a second orientation arranged at an angle between 0° and 180° with respect to each of the first prepreg strips (11), wherein each of the second prepreg strips (12) is fixed to each of the first prepreg strips (11) in at least one intersection zone (A); and a third layer comprising a metal sheet (13) at each intersection (A); wherein each strip of prepreg (11, 12) comprises unidirectional thermoplastic fiber. 2. The reinforcing composite frame (22) according to the preceding claim, wherein each metal sheet (13) is located either above each second prepreg strip (12) in each intersection zone (A) or between each first (11) and second (12) prepreg strips in each intersection zone (A). 3. The reinforcing composite frame (22) according to any of claims 1 or 2, wherein each of the second prepreg strips (12) intercepts each of the first prepreg strips (11), forming an angle between them of 0° and 180°, preferably an angle of 90°. 4. The reinforcing composite frame (22) according to any one of claims 1 to 3, further comprising a discontinuous prepreg layer (14) subsequently disposed at each end of each metal sheet (13). 5. Process for producing the reinforcing composite frame (22) as defined in any of the preceding claims, characterized in that the process comprises the steps of: - placing a reinforcing frame (22) comprising at least one set of layers as defined in any of the preceding claims, wherein the method for producing a set of layers comprises: placing a first layer in an orientation, wherein the first layer comprises at least a first strip of prepreg (11); placing a second layer on the first layer, wherein the second layer comprises at least one second prepreg strip (12) arranged at an angle between 0 and 180° with respect to the orientation of the at least one first prepreg strip (11), wherein at least one second prepreg strip (12) of the second layer is adhered to the top of each prepreg strip (11) of the first layer at at least one intersection (A); and placing a third layer comprising a metal foil (13) over each intersection (A). 6. The process according to claim 5, wherein each metal sheet (13) is placed in a different orientation than each metal sheet (13) of the subsequent set of layers, forming a staggered position of the metal sheets (13). 7. The process according to any of claims 5 or 6, wherein each metal sheet (13) has a size between 5 and 15% different from each metal sheet (13) of the subsequent set of layers, forming a staggered position. 8. The process according to any one of claims 5 to 7, wherein each metal sheet (13) is placed either on each second strip of prepreg (12) in each intersection area (A) or between each first (11) and second (12) strips of prepreg in each intersection area (A). 9. The process according to any one of claims 5 to 8, wherein the angle from 0° to 180° at the intersection between each second prepreg strip (12) and each first prepreg strip (11) is preferably an angle of 90°. 10. The process according to any one of claims 5 to 9, wherein a discontinuous prepreg layer (14) is subsequently placed at each end of each metal sheet (13), depending on the disparity between the thickness of the prepreg and the metal sheet (13). 11. A reinforced part (24) comprising a block part (23) made of lightweight moldable material selected from thermoplastic sheets or short fiber composite mats, or manufactured by injection molding using thermoplastic pellets, characterized in that said block part (23) is overmolded on top of a reinforcing frame, as defined in any one of claims 1 to 4.