Method for manufacturing a fibre plastic composite material

Abstract

Method for producing a fibre plastic composite with a defined fibre orientation, wherein continuous fibres or long fibres are oriented and wrapped with a matrix, characterized by the following steps: (a) providing a mould comprising at least one flow channel, (b) introducing continuous fibres or long fibres into the at least one flow channel, (c) positioning and orienting the continuous fibres or long fibres in the at least one flow channel by a pressure gradient in the flow channel, (d) wrapping the continuous fibres or long fibres with a matrix.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing a fiber plastic composite having continuous fibers or long fibers. Furthermore, the present invention relates to a processing tool comprising a mold and at least one flow channel embedded into the mold. BACKGROUND

[0002] Fiber plastic composites having continuous fibers or long fibers have very good mechanical properties. In particular, the good ratio of strength and stiffness to density makes this material an ideal lightweight construction material.

[0003] Since the production of such fiber plastic composites having continuous fibers or long fibers is complex and time-consuming and the fibers used are often expensive, fiber plastic composites are currently only used in high-tech areas.

[0004] Fiber composites are anisotropic in their mechanical properties, wherein the mechanical properties are naturally greatest along the fiber direction. Deviations from this fiber direction result in significantly poorer properties.

[0005] In conventional production methods, the continuous fibers or long fibers are laid in the component at a fixed fiber angle. Since the stress state in complex components is multiaxial and the properties of the fibers are anisotropic, the composite is constructed from a plurality of different layers having different fiber angles, which composite is referred to as a "constant stiffness design". This, however, results in the properties specific to the fibers not being fully utilized.

[0006] Recent production methods attempt to avoid this disadvantage by purposefully orienting the fibers along the load direction ("variable stiffness design"). With this production method it is possible to bend the fibers and it is not necessary to force them to be straight in the component any more. This load-compliant orientation of the fibers results in significantly fewer fibers having to be used in order to achieve the same material properties along the load direction, whereby mass and costs can be saved.

[0007] Manufacturing methods for fibre plastic composites with a targeted orientation of the fibres in the load direction and with continuous or long fibres are known and have been applied in industry. So-called Tailored Fibre Placement applies individual fibre tows to a base layer by means of a stitching technique. With this, an arbitrary fibre orientation can be achieved. Tailored Patch Placement places fibre cutouts onto a base layer with the aid of a robot. The fibres are no longer continuous as a result of this process, but can likewise be placed in a complex orientation. In addition to these methods, there are other methods which place fibres according to the load flow or according to other design criteria, usually with the aid of a robot. These methods are characterised by the highest material effect and the least waste. However, the manufacture of the structure is very time-consuming and it is not possible to manufacture components for the mass market.

[0008] DE 10 2007 054 424 A1 describes a method for manufacturing a fibre plastic composite, in which fibres are blown into a mould. The fibre direction is determined by the blowing direction of the nozzle and can only be varied accordingly within a narrow range.

[0009] In DE 10 2010 045 428 B4, a method for manufacturing a fibre plastic composite is described, in which fibres are transported to the processing site by means of an air flow. The transport takes place through a transport channel, in which a matrix resin is added during the transport of the fibres. Further processing and shaping takes place by means of conventional manufacturing methods.

[0010] EP 1 177 871 B1 describes fibre spraying, in which fibres are applied to an open tool mould by means of an undirected air flow. Precise positioning of the fibres in the open mould is not possible.

[0011] DE 10 2016 103 979 A1 describes a method for manufacturing a structural hollow component and the structural hollow component itself. The method is characterised in that a washable mandrel is wound with fibres and, in the bore in the mandrel, fibres are produced which create a strut in the hollow component, the fibres being positioned by means of a needle or by means of an air flow.

[0012] With regard to the manufacturing method, the prior art known today basically shows that the fibres are blown into a channel or, generally, into a mould cavity; with this, only special hollow components can be manufactured and not components with a defined fibre orientation. SUMMARY

[0013] The methods used to date for producing fiber composite plastics with fibers oriented purposefully in the direction of the load are based on the (temporally) costly laying concept or on the geometrically inaccurate and limited to one direction blowing-in method.

[0014] The object of the present application is therefore to provide a method for producing a fiber composite plastic which allows a purposeful orientation of the fibers in the direction of the load, if necessary also with a curvature, and enables a short production time.

[0015] The object is achieved by a method for producing a fiber plastic composite material with a defined fiber orientation, in which continuous fibers or long fibers are oriented and wrapped with a matrix, characterized by the following steps:

[0016] a) providing a mold comprising at least one flow channel,

[0017] b) introducing continuous fibers or long fibers into the at least one flow channel,

[0018] c) positioning the continuous fibers or long fibers in the at least one flow channel by a pressure gradient in the flow channel, and

[0019] d) wrapping the continuous fibers or long fibers with a matrix.

[0020] In DE 10 2010 045 428 B4 a channel is described, but this channel is only used for providing and preparing a composite material which can then be processed using conventional methods. The present application enables a precise positioning of the fibers in the mold using the respective channel.

[0021] The mold-related channel is responsible for the fiber orientation. By means of the flow channel the precise position of the continuous fibers or long fibers in the later fiber plastic composite material is determined, which is usually a semi-finished product. The flow channel can extend linearly, however the flow channel can preferably have an arbitrarily complex shape. Particularly preferably, the flow channel is at least simply curved.

[0022] In an embodiment variant it is provided that the continuous fibers or long fibers are positioned in the flow channel by a fluid flow.

[0023] The fluid flow for positioning the fibers is generated by a pressure gradient in the respective flow channel. This pressure gradient can be generated, for example, by a relative overpressure on the inflow side of the fluid or by a relative underpressure on the outflow side of the fluid or by both. The fluid is usually air, but can also be an inert gas or a noble gas. It is also possible to use an evaporated liquid as a fluid. The fluid can be temperature-regulated or not.

[0024] In the simplest case, the continuous fibers or long fibers relate to simple fiber tows consisting only of reinforcing fibers. Preferably, the continuous fibers or long fibers are hybrid fiber tows, i.e. fiber tows consisting of reinforcing fibers and a matrix material, particularly preferably are mixed yarns, i.e. fiber tows consisting of reinforcing fibers and plastic fibers as matrix material.

[0025] The long fiber or filament yarns either comprise pure continuous fibers or bundled long fibers or comprise a composite structure consisting of fibers and a matrix, wherein the matrix can preferably be present in the form of a polymer fiber, a polymer powder or a resin. The reinforcing fibers can comprise carbon fibers, glass fibers, aramid fibers, other polymer fibers, metal fibers and ceramic fibers as well as natural fibers.

[0026] Alternatively, the long fibers or filament yarns can also be introduced for other purposes. The long fibers or filament yarns may, for example, serve a decorative purpose. An alternative embodiment provides that the long fibers or filament yarns are introduced for thermal purposes. In these embodiments, the introduction of the long fibers or filament yarns is not limited to a reinforcing effect only. Combinations of these functions are, of course, also conceivable.

[0027] The mold mostly has mold halves. The contact surface between the mold halves can be flat or present in a complex curvature. If the contact surface is flat, semi-finished products are usually produced with the method, which should be reshaped in a further step and wrapped with a matrix. If the reinforcement in the later component is only in two dimensions, only a wrapping is necessary. If the contact surface is curved, the degree of deformation for the later component can be reduced therewith or the reinforcing geometry for the component can also be produced directly. In the latter case only a wrapping is necessary.

[0028] The wrapping refers to the embedding of the fibers into the matrix, wherein the wrapping can be only punctiform or over a large area. The wrapping serves to reinforce the fiber tows against one another or to fix them on a base layer. The fixing can be carried out directly in the mold. For this purpose, a heated stamp can reinforce the fiber tows against one another or fix them on a base layer by applying pressure. Alternative possibilities for reinforcement are pressurized air, suction by means of a vacuum or a flexible tube, which is located in the channel and is inflated. Depending on the matrix material used, heating is necessary.

[0029] In another variant, the method is integrated directly in an injection molding process, a pressing process, a thermoforming process or another processing process. The reinforcement of the positioned fibers is carried out directly in the process, for example by filling the component contour with injection molding material.

[0030] The wrapping can also take place outside the mold. To this end, the flat gripper can electrostatically, pneumatically, by means of negative pressure or by adhesive clamping and transport the fiber tows oriented by the flow channel of the mold to the wrapping station. There, the fiber tows are consolidated with one another or, in addition, on a base layer.

[0031] Preferably, all steps (providing a mold; introducing continuous or long fibers into a flow channel; positioning the continuous or long fibers in the flow channel by a pressure gradient in the flow channel; and wrapping the continuous or long fibers with a matrix) are carried out in one mold.

[0032] The base layer can itself be a semifinished product in the form of a film or a plate. Preferably, a film is used, which ensures good adhesion to the matrix material. Here, only exemplarily listed: If a hybrid yarn with a PP matrix is used, it is advisable to use a film or a plate made of PP as a base layer. If a hybrid yarn with a PA6 matrix is used, a metal plate with a corresponding adhesive or a pre-impregnation with a PA6 matrix can be used. Furthermore, the base layer can already be a three-dimensional structure, which is reinforced by fiber attachment.

[0033] In another aspect, the application relates to a processing tool for the production of fiber composite materials, comprising a mold and at least one flow channel embedded in the mold, wherein the flow channel is equipped with at least one fluid nozzle, wherein the fluid nozzle has a fiber reservoir for continuous or long fibers.

[0034] The flow channel preferably has at least one bend in its shape. The flow channel determines the flow direction and thus the orientation of the fiber tows in the semifinished product or component.

[0035] The mold preferably comprises two mold halves, i.e. an upper and a lower part. The flow channel can be machined into the lower part or into the upper part or into both the upper and lower part. Not only one single flow channel but also multiple flow channels can be machined in one mold, which supply fiber tows.

[0036] In one embodiment variant, it is provided that the mold has two mold halves, wherein the flow channel is formed by the two mold halves.

[0037] The contact surface between the half-moulds can constitute a flat surface or be present in a complex curvature. If the contact surface is a flat surface, it is preferred to produce the semi-finished product with the mould, which must be shaped and wrapped in a further step. If the reinforcement in the later component is only two-dimensional, only wrapping is necessary. If the contact surface is a curved surface, it is thereby possible to reduce the degree of deformation for the later component or to directly produce the reinforcement geometry for the component. In the latter case, only wrapping is necessary.

[0038] It is preferably provided that the mould has a plurality of flow channels and that the supply takes place through one or more stationary nozzles. The nozzles only move away from the contact surface normaUy in order to provide the possibility of cutting off the fibres.

[0039] As a material for the mould, steel, aluminium and other metals can be used. EquaUy, plastics can be the mould material. It is also possible that one of the two mould parts is the base layer itself, which is described later, or can also be a flat clamp for taking up the positioned fibre tows.

[0040] The cross-section of the channels can have any shape. Thus, the channels can have a circular, rectangular or further shape. The only criterion is that its cross-sectional area is equal to or (preferably) greater than the cross-sectional area of the stationary component parts of the fibre tows.

[0041] In another aspect, the present application relates to a processing tool for a plastics processing apparatus, comprising a mould and at least one flow channel embedded into the mould, wherein the flow channel is equipped with a fluid nozzle. It is preferably provided that the plastics processing apparatus is an injection moulding machine. BRIEF DESCRIPTION OF DRAWINGS

[0042] The present application is explained in more detail below by means of examples and the attached drawings.

[0043] Figure 1 Schematically shown is the lower part of a mould with flow channels.

[0044] Figure 2 Schematically shown is the lower part of a mould according to Figure 1 together with the transparently shown upper part of the mould and the nozzle equipped to the flow channel.

[0045] Figure 3 Shown is a mould according to Figure 2 together with the nozzle and the continuous fibres.

[0046] Figure 4 Shown is a base layer with laid continuous fibres.

[0047] Figure 5 Schematically shown is the entire construction of a processing tool according to the present application for a plastics processing apparatus. DETAILED DESCRIPTION

[0048] The method according to the application and the processing tool according to the application are shown by means of the figures. Since the figures are associated with the method steps, all figures are jointly described. In Figure 3 A processing tool is shown in

[0049] For example, each flow channel 10 is equipped with a fluid nozzle 12, wherein the fluid nozzle has a fiber reserve for continuous fibers.

[0050] For the method according to the application for producing a fiber plastic composite with continuous fibers or long fibers, a mold with half-molds is first provided, which half-molds comprise at least one flow channel. In Figure 1 Three flow channels 10 are shown in the example, which are additionally curved differently. The second half-mold 3 is now positioned onto the first half-mold 4 and the nozzles 12 are placed Figure 2 The continuous fibers or long fibers are then introduced into the flow channels via the nozzles. The continuous fibers are positioned in the flow channels by means of a pressure gradient. Figure 3 The upper half-mold can also be a plastic base layer, for example, so that the continuous fibers are positioned on the base layer in the mold by means of, for example, embossing.

[0051] The fibers used in the method are provided by means of the nozzles. The fiber sections that are to be positioned in the mold are in the nozzles in the reserve, which are tightly closed with respect to the environment. The channels are supplied by means of the nozzles. If a pressure gradient is produced, the nozzles and the mold are tightly closed apart from the inflow openings and the outflow openings in order to produce the desired fluid flow in the mold channels. If the fibers are positioned well in the mold, the nozzles are lifted from the mold and the fiber strands between the mold and the nozzles are broken off. The breaking off can be carried out not only mechanically but also by cutting off, for example, by means of heat.

[0052] The reworking of the produced semifinished product can be carried out by injection molding. The semifinished product can be acted upon by injection molding in an already reshaped mold and thus any desired component can be produced.

[0053] In Figure 5A processing tool 1 for carrying out the method according to the application is shown in Fig. 1. The processing tool comprises a mold 2 having two mold halves 3, 4, an upper mold half 3 and a lower mold half 4. Embedded in the mold 2 is a flow channel 10. The flow channel is formed in the lower mold half 4. The flow channel 10 is equipped with a fluid nozzle 12, wherein the fluid nozzle 12 has a fiber reservoir 14 for continuous fibers 16 in the form of fiber tows. At the inlet 18 of the fluid nozzle 12 there is a pressure pi, which is higher than the pressure p2 in the flow channel 10. By the pressure gradient Δp = pi - p2 thus created, the continuous fibers 16 are introduced into the flow channel 10.

Claims

1. A method for manufacturing a fiber-reinforced plastic composite material having a defined fiber orientation, wherein, Orienting continuous fibers (16) or long fibers and encapsulating them with a matrix, characterized by the following steps: a) Provide a mold (2) including at least one flow channel (10), b) Introduce continuous fibers (16) or long fibers into the at least one flow channel (10). c) Positioning and orienting the continuous fiber (16) or long fiber in the at least one flow channel (10) by means of a pressure gradient (Δp) in the flow channel (10). d) Oriented continuous fibers (16) or long fibers are supplied to a packaging station outside the mold via a flat clamp, wherein the flat clamp electrostatically, pneumatically, by means of negative pressure, or by adhesion holds the continuous fibers (16) or long fibers and supplies them to the packaging station. e) Using a matrix to encapsulate continuous fibers (16) or long fibers.

2. The method according to claim 1, characterized in that, The continuous fiber (16) or long fiber is positioned in the flow channel (10) by the fluid flow.

3. The method according to claim 1 or claim 2, characterized in that, Fiber orientation is fixed on the carrier substrate either inside or outside the mold (2).

4. The method according to claim 1 or claim 2, characterized in that, The continuous fiber (16) or long fiber is introduced into multiple flow channels (10).

5. A processing tool (1), the processing tool comprising a mold (2) and at least one flow channel (10) embedded in the mold (2), wherein, Each flow channel (10) is provided with at least one fluid nozzle (12), wherein the fluid nozzle (12) has a fiber reserve (14) for continuous fibers (16) or long fibers, wherein a wrapping station and a flat clamp are provided for clamping the continuous fibers (16) or long fibers oriented in the mold, wherein the flat clamp is designed to clamp the oriented continuous fibers (16) or long fibers electrostatically, pneumatically, by means of negative pressure or by adhesion.

6. The processing tool according to claim 5, characterized in that, The mold (2) has two half molds (3, 4), wherein the flow channel (10) is formed by the two half molds (3, 4).

7. The processing tool according to claim 5 or claim 6, characterized in that, The at least one flow channel (10) specifies the orientation of continuous fibers (16) or long fibers from the fiber reserve (14).

8. The processing tool according to claim 5 or 6, characterized in that, The mold (2) has multiple flow channels (10).

9. The processing tool according to claim 5 or 6, characterized in that, At least one flow channel (10) is equipped with a pump.

10. The processing tool according to claim 8, characterized in that, The fluid nozzle (12) has a motion unit and can move from one flow channel (10) to the next flow channel (10).

11. The machining tool according to claim 9, characterized in that, The fluid nozzle (12) has a motion unit and can move from one flow channel (10) to the next flow channel (10).

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