DE102014018801B4 - Method and device for producing a fiber preform - Google Patents

Abstract

Method for producing a fixed fiber preform (10), wherein a fiber bundle (8) is applied to a core (12) and / or introduced into a mold, and the fiber bundle (8) immediately before and / or during and / or immediately after application or an electric current is applied to the core (12) or into the mold, in order to bring about thermal heating in conjunction with a plastic to fix the fiber preform (10) by means of a fixing device (20), wherein the fixing device (20) a sliding surface for applying a pressure to the fiber bundle (8) and at least two electrodes (24), wherein current is applied to the fiber bundle (8) via the electrodes (24), characterized in that the electrodes (24) form the fiber bundle (8) 8) immediately after the introduction of the current and / or during the introduction of the current and / or before the introduction of the current with a defined force (F) against the core (12) and un Press d / or the mold, wherein the sliding surface and the electrodes (24) are integrally and rigidly arranged on the fixing device (20).

Description

The present invention relates to an apparatus and a method for producing and fixing a fiber preform.

Fiber preform is understood to mean a fiber packet which already has the form of a component or whose fibers are shaped accordingly. The fiber preform is also referred to below as preform.

Today's components made of carbon fiber reinforced plastics are often produced from pre-impregnated semi-finished products, so-called prepregs, or from dry / binder semi-finished fiber products, which are then impregnated with resin. If dry / binded semifinished fiber products are used, a fiber preform or preform is usually first produced from these semifinished fiber products, that is to say an optionally dry fiber package which already anticipates the later form of the component. Also impregnated fiber packages can be used for this purpose. In this sense, the semi-finished fiber products or the textile precursors, such as fabric or scrim, assembled and then brought by reorientation and reshaping (draping) of the fiber structure in the desired shape (preform). A fabric is a fabric made, for example, on a weaving machine of two preferably orthogonal thread systems (weft and warp); a scrim consists of several fiber layers, which are deposited in different directions on each other and, for example, connected to each other with thin holding threads. The fixation of preforms can be done with the help of a binder system. The binder systems used are usually thermosets or thermoplastic substances which are applied, for example, in powder form and in a relatively small amount, for example in the range from 2 to 5 percent by weight, to the semifinished product and activated under the influence of temperature or by increasing the temperature. In addition to defining the fiber orientation, the binder systems can be used to fix the preforms in a compacted state. The preform fixing thus causes a more punctual or flat (depending on the manufacturing process), loose fixation of the fiber composite or its shape, so to speak, a pre-fixation. Such a fixed preform can then be stacked and stored for example before further processing. The final fiber-plastic composite is then prepared by impregnating the fixed preform with a predetermined amount of a matrix (for example, based on the component between 25 and 85 volume percent) and then allowing the matrix portion to set.

In the prior art preform fixing processes, the activation of the binder is usually accomplished by heating the preform by means of, for example, a laser diode, an infrared radiator or hot air (e.g., in a convection oven or with a hot air dryer). A major disadvantage of these prior art methods is that they either overheat the preform mainly on the material surface too much, the energy transfer or consumption is very high or that they called the preform tool, hereinafter also referred to as core or mold , so that it requires a longer heating phase for a homogeneous temperature distribution. For this reason, the cycle times in the prior art preform production are relatively long. In most cases, the known fixing methods have a flat and inhomogeneous heat formation range, high energy consumption and thermal losses during heat transfer. In addition, the required large installation space, the high investment costs and the high construction costs are disadvantageous. Such factors lead in particular to limited integration possibilities in automated manufacturing processes. The application of the compression force must be done separately and for configuration reasons in series to the heating area. Free spaces for the formation of undesirable temperature gradients arise from this. The quality of the textile preform can be visually monitored in real time during the manufacturing process only with increased effort.

DE 10 2008 028 441 A1 discloses a method for producing an annular preform from fibrous semifinished product, comprising winding a semifinished product provided as a band on a winding core, wherein the winding takes place substantially in the circumferential direction of the winding core on a contoured lateral surface of the winding core, so that successive wound tape layers substantially in the axial direction completely overlap, and that during winding the individual band layers, viewed in the cross section, are deformed in adaptation to the lateral surface contour.

DE 10 2008 019 147 A1 discloses a method for producing fiber preforms for composite components by applying a plurality of dry fiber rovings independently of one another. Even in spatially uneven contours directly complex geometries can be produced flexibly and inexpensively.

EP 2 821 201 A1 discloses a semi-finished fiber tempering device and a method for controlling the temperature of fiber preforms, wherein by means of two electrodes, a current flow through a plurality Fiber semi-finished layers is produced for tempering.

DE 10 2011 102 950 A1 discloses a laying head, a laying line and a method for depositing fiber arrangements for the production of textile preforms, which at least partially consist of carbon fibers. The laying head has at least one fiber feeding device, a depositing roller and a heating device for heating a thermally activatable binder for fixing the textile preform. The laying head comprises two contact surfaces which are contacted by the fiber feed device fed through the laying head to the depositing roller by the fiber feed device, wherein the two contact surfaces are electrically conductively designed as a pair of electrodes and connected to a power source, wherein the electrically conductive carbon fibers of the fiber arrangement between the Electrode pair form a heating section of the laying head, which provides the heating device of the laying head.

DE 10 2011 054 287 A1 discloses a method and an apparatus for producing a plastic molded part from a flat semifinished product by means of a hot forming process in which the semifinished product is transported by means of a gripper from a storage location into a pressing tool having a shape of the plastic molded part forming tool parts, fixed to the pressing tool and under heating by a pressing operation of the pressing tool is brought into shape, wherein the semifinished product is provided during its production as a polymer material with electrically conductive additives and controlled by the pressing process by resistance heating of the electrically conductive additives to a predetermined temperature.

DE 10 2012 019 915 A1 discloses a method for providing a fiber preform intended for producing a fiber composite component in a molding tool, in which a flat fiber material blank is transported to the molding tool. The transport takes place by means of a transport device, wherein a heating of the fiber material blank is effected by an electrical energization of the fiber material blank during transport.

Out DE 103 53 070 A1 It is known to apply an electric current to a fiber preform in order to achieve heating by utilizing the limited electrical conductivity of carbon fibers, which serves to fix a fiber preform.

The object of the present invention is to provide a method and a device, with the help of which the activation of the binder in the fiber preform can take place in a significantly shortened period of time and thus the clock frequency of the preforming process can be significantly increased. The heating method is carried out with reduced heat affected zones and with a predetermined force application.

This object is solved by the subject of claim 1 and the subject of the independent claim. Advantageous developments are the subject of the respective dependent claims.

In a method for producing a fixed fiber preform, a fiber bundle is applied to a core and / or introduced into a mold. The fiber bundle is flowed through in sections immediately before and / or during and / or immediately after application or introduction onto the core or into the mold, in order to fix the fiber preform by thermal heating in conjunction with a plastic, in particular a binder effect by means of a fixing device. This process utilizes the step of depositing a respective portion of the fiber bundle to heat precisely that portion so as to activate plastic to fix the fiber bundle in its shape. This plastic can be a thermoplastic, which is melted and dimensionally stable after cooling. The thermoplastic can be supplied as a powder or nonwoven. Also can be used as a binder, a thermoset, which cures irreversibly by the thermal activation. Since only a small portion of the preform is heated and cured, a rapid heating with a low use of energy is possible. In addition, this step is practically possible at the same time as creating the geometry of the fiber preform. It is with the method in particular a winding, a fabric with weft and warp fibers or, for example, a clutch produced.

• - Das direkte Aufheizen des Preforms führt zu einem sehr schnellen Aufheizen desselben innerhalb von wenigen Sekunden.
• - Eine Erwärmung des Preform-Werkzeugs findet kaum statt.
• - Im Gegensatz zu herkömmlichen Methoden, wo Werkzeugkomponenten zusammen mit dem Preform erwärmt werden und vor dem nächsten Zyklus wieder heruntergekühlt werden müssen, sind mit der vorgestellten Methodik kurze Taktzeiten des Preform-Prozesses möglich. Es können also höhere Preform-Stückzahlen pro Zeiteinheit hergestellt werden.

The device or the corresponding method allows a number of advantages:

• - The direct heating of the preform leads to a very rapid heating of the same within a few seconds.
• - Heating of the preform tool hardly takes place.
• - In contrast to conventional methods, where tool components are heated together with the preform and have to be cooled down again before the next cycle, the presented methodology allows short cycle times of the preform process. It can therefore be produced higher preform quantities per unit time.

A fixing device preferably has electrodes and current is applied to the fiber bundle via the electrodes. Accordingly, the current flows through the conductive fibers. As a result, the heat is generated directly in the (carbon) fibers, which is ideal for fixation.

In particular, the fixing device presses the fiber bundle against the core and / or the mold immediately after the introduction of the current and / or during the introduction of the current and / or before the introduction of the current with a defined force. The method step of pressing is essential for achieving a secure connection between the fiber strand and the substrate as well as a targeted fiber volume content. Since this step is combined with the fixing, results in an efficient procedure. The case that happens immediately after or before the introduction of the pressure of the pressure, for example, is given if there is a two processes also sometimes done at the same time. In particular, the aforementioned immediacy is given if the time interval between the introduction of the current and the pressing of the fiber bundle is less than 1 second, since within this period, a curing of the plastic does not occur or is completed.

In a subsequent method step, the fixed fiber preform can be processed further by supplying plastic to a fiber composite plastic component. If prepregs are processed, they harden directly into their final state and require no further processing step. The fixed dry preforms may then be impregnated with a predetermined amount of a matrix, generally 25 to 85 percent by volume, based on the final component, for the production of the final component, and then set for curing.

In the fixing method, in particular, a binder substance is supplied, which preferably contains or consists of a thermoplastic copolyamide. The binder substance can also contain or consist of an epoxy resin, preferably based on bisphenol A. The fibers may be wrapped with the binder. In the method, impregnated fibers, ie in particular fibers impregnated or wetted with a curable thermosetting resin, can also be fed to a fixing device, and the fixing device at least partially cures the curable resin.

Preferably, an electrical measurement variable, such as a voltage or a current can be measured, and it can be judged depending on this measurement variable whether the method is carried out correctly. As an alternative to voltage or current, a capacitance can also be measured. Depending on the measurement result, the execution of the method can be terminated or a corresponding warning issued. Also, fractures in the fiber material can be detected.

An apparatus for producing a fiber preform comprises a core and / or a mold, which is usable for shaping the fiber preform, and a positioning device for positioning a fixing device relative to the core and / or the mold. With at least two electrodes, current can be brought to an electrically conductive fiber or a fiber bundle. Since the said positioning is relative, in appropriate embodiments optionally the core and / or the mold or the fixing device can be arranged stationary.

In particular, the electrodes and a sliding surface for applying a pressure to the fiber bundle can be arranged integrally and rigidly on the fixing device. The sliding surface may also comprise a sliding roller, which is mounted rotatably mounted on the fixing device.

• 1 eine Wickelvorrichtung zur Aufbringung eines Faserbündels auf einen Kern,
• 2 eine Detailansicht der Wickelvorrichtung gemäß 1 mit einer Fixiervorrichtung,
• 3 eine Ansicht der Unterseite der Fixiervorrichtung,
• 4 eine perspektivische Ansicht der Fixiervorrichtung,
• 5 eine Seitenansicht der Fixiervorrichtung,
• 6 einen Längsschnitt in der y-z-Ebene durch die Fixiervorrichtung,
• 7 eine alternative Ausführungsform der Fixiervorrichtung und
• 8 eine Ausgestaltung der Fixiervorrichtung mit einer gesonderten Andruckrolle oder -walze.

In the following, a preferred embodiment of the invention is explained in more detail with reference to schematic representations. Show it:

• 1 a winding device for applying a fiber bundle to a core,
• 2 a detailed view of the winding device according to 1 with a fixing device,
• 3 a view of the underside of the fixing device,
• 4 a perspective view of the fixing device,
• 5 a side view of the fixing device,
• 6 a longitudinal section in the yz plane through the fixing device,
• 7 an alternative embodiment of the fixing device and
• 8th an embodiment of the fixing device with a separate pinch roller or roller.

1 schematically shows the structure of a winding machine. It drives a drive device 14 a drive shaft 15 which, in turn, has a core 12 connected, so the core 12 is rotatable about its longitudinal axis. From a storage drum, not shown, an endless fiber, in particular a carbon fiber strand of the winding machine is provided. The carbon fiber strand is in particular a fiber bundle 8th with a variety of individual fibers. Further, the force F _fiber shown, which is applied to a straight-rolling of the fiber bundle 8th to the core 12 sure. With the speed v _fiber the fiber bundle is fed for processing.

2 shows the detail of the fixing device according to 1 in a rotated view, wherein in both figures the identical coordinate system is used. It is shown that the fiber bundle 8th is supplied and first still a distance to the core 12 Has. The rotation of the nucleus in the connection with a pressure of the force F radially on the core 12 causes the fiber bundle 8th directly and without gaps to the core 12 invests. The application of compressive force enables the secure connection between fiber and substrate and a high fiber volume content to be achieved. A high fiber volume content gives the finished component a high load capacity. This is especially true when several fiber bundles are wound in the later loading direction and on top of each other. The distance of the fiber filaments is determined by the contact pressure F reduced. Due to the rotation of the core 12 the fixing device moves at the speed v relative to the corresponding surface of the core 12 , The fixture may also be pivotally mounted about its vertical axis to follow fiber strands in the machining orientation angle.

2 also shows two electrodes 24 the fixing device 20 , which are marked with the symbols + and -. The structure of the fixing device 20 is in the 3 to 6 shown. The underside of the fixing device 20 (please refer 3 ) has the two spaced electrodes 24 on, which can be acted upon by a wiring, not shown, with a voltage. The distance between the electrodes is 5 mm in the x-direction and the width in the y-direction is 20 mm. Especially if the fiber bundle 8th Spreading a large width can be helpful. In preferred embodiments, the spacing of the electrodes is between 2 mm and 2 cm. The width may preferably be between 5 and 30 mm. The electrodes 24 are on a main body of the fixing device 20 attached, which is tubular. This tube shape causes the outer geometry of the fixing device 20 is rounded so that the fiber bundle is a smooth sliding surface over which it can slide, so as to the desired position on the core 12 to be led. In the free interior of the tube form sensors, such as a thermal sensor may be arranged, which measures the temperature, so as to readjust the voltage on the electrodes if necessary. On the side of the fixing device which is spaced apart from the electrodes, there is first a force transmitter 36 arranged. This can be a hydraulic or pneumatic cylinder, so as to achieve a desired pressure F the fixing device to the fiber bundle 8th and therefore also to the core 12 to effect. There are also two guide rods 38 shown, which ensure that the fixing device is not about its own axis, ie the longitudinal axis Kraftübertragers 36 of the turn can. By an adjusting device, not shown, it is ensured that the required angular orientation of the fixing device 20 opposite the core 12 and the fiber bundle 8th is adjustable.

The fixation is performed as follows. First, the in 1 provided structure described. The following is the fiber bundle 8th to the core 12 guided and aligned with the fixing device in position and against the core 12 pressed. The self-rotation of the core 12 causes the fiber bundle to remain in position. In addition, via the electrodes 24 an electrical voltage in the fiber bundle 8th initiated. The fiber bundle is preferably made of carbon fibers. Carbon fibers are known to be electrically conductive and have a resistance of 1.6 10 ^-5 ohm m, or 16 ohms mm ² / m in other words, where the millimeter refers to the cross-section and the meter refers to the measured span. These resistance values result in the required voltage and the required current, depending on the geometry and distance of the electrodes.

The fiber bundles may be, for example, impregnated fibers. Impregnated fibers are fibers which have been impregnated with a thermosetting thermosetting resin such as epoxy resin. The curing of the resin is possible via a thermal initialization. From the electrodes 24 the current transfers to the fiber bundle 8th and heats it locally, so that the curing reaction is started. Meanwhile, the fiber bundle 8th stored at its desired location. If already a layer of fibers on the core 12 is wound, so join the individual fiber bundles and form after curing a solidified solid structure, which is already characterized as a finished component and requires no further processing step.

Alternatively, the fiber bundles may be dry / necked fibers. These are fibers that may optionally be coated with a dry or powdered binder or that are not coated. The binder may be a solid, thermoplastic copolyamide or a bisphenol A-based liquid epoxy resin. The binder present on the fibers or embedded in the fiber bundle can be activated thermally and can be activated via the already described current flow. Alternatively, with uncoated fibers, a binder may be on the fiber bundle shortly before the electrical heating of the fiber bundle 8th or to the core 12 be supplied. Even semi-dry fibers can be used accordingly.

At the in 2 the embodiment shown, the fixation, ie the heating is practically simultaneously with the deposition of the fiber bundle 8th performed on the core. Alternatively, in 7 an embodiment of the fixing device 20 shown the two electrodes 24 , (marked with + and -) and which are connected to each other via an electrically insulating support, not shown. Here, a case is shown that fixing is performed immediately before dropping. That is, the heat is introduced immediately before depositing and due to the delayed curing of the binder or plastic, the fiber can still be brought in their desired position. Alternatively, the fixing may also be performed immediately after the fiber bundle has been deposited on the core. (not shown). It is advantageous for the present invention that a direct temporal and / or spatial reference to the placement of the respective fiber bundle in the mold (or on the core 12 ) takes place with the fixing. At this time, the position of the fiber bundle is defined exactly by the guides in the position. So it is sufficient to heat a relatively small volume. This is a well-controlled process that can be performed without an additional and time-consuming / energy-consuming additional processing step, as it can be integrated directly into the laying of the fiber bundle.

It is necessary for the invention, no core is wound on. Alternatively, the fibers can also be placed in a mold.

It can optionally be over the electrodes 24 Measured current can be measured. Also, the voltage drop of the electrodes or the capacity built up there can be measured. On the basis of one or more of these measured values, it can first be determined whether sufficient thermal activation has taken place. Also provides such a reading for the state of the fiber bundle. For example, fiber breaks can be detected.

Strengths / benefits of the invention include reduced heat losses (to the environment), high heat build-up speed, local heat generation, in-situ detection of the quality state of processed fiber bundle semi-finished products, extremely compact device construction space combining heat build-up and compression area, and simple and cost-effective investment / construction; Maintenance for the implementation of the system. Furthermore, the device principle can be adapted flexibly, so that various freedom of design allows practical application to different processes.

The application described above is for manufacturing processes with continuous fibers, such. For example, braiding, wrapping and spreading technology, Automated Fiber Placement (AFP) and Dry Fiber Placement (DFP) are extremely interesting. This benefits in particular from the installation space and the execution of a preforming step, due to the complexity of the component geometries as well as the own processing path of the individual fiber bundles. The construction of the device described makes it possible, in conjunction with compressed air cylinders, to set different pressure forces. Preforming (also called preforming) of predefined sections is made possible by the installation of the components on a separate drive or by the feed of the component to be processed, as long as a safe electrical power supply is available. In this respect, the number of preform components required depends on the process and component, since they are used specifically for single or multiple fiber strands. For manufacturing processes in which multilayer fiber preforms and not individual fiber bundles are heated and compressed, the design of the preform components can be adapted in shape and size as needed without affecting the actual operating principle (sufficient inter-layer contact between the fiber strands over the wall thickness of the Preform provided). Is the preforming step for z. B. a Drapierprozess desired, the electrodes are to be selectively positioned in sections on the mold. It is the aim of a planar heating of the semifinished product. The type of compression force to be applied subsequently depends on the selected draping process. The objective is to integrate the electropreforming method in process chains, mainly to reduce accelerated heat transfer processes, and to improve preform quality.

In the embodiment according to 8th It is shown that the process of applying force to the fiber bundle 8th can be separated from the electrodes 24 , In this sense, it is shown that the roller 40 with a force Fwauf the molding or core 12 is pressed. In addition, there are the electrodes 24 on a support that supports the electrodes with an electrode force (not labeled) against the fiber bundle 8th suppressed. The electrode force may be smaller than the roller force _FW be, so that the fiber bundle 8th is not damaged by the electrodes. In this sense, an embodiment is shown here in which the fiber bundle 8th immediately before and during and immediately after application or application to the core 12 with an electric current flowing through it. Via a resilient suspension (not shown) from the electrodes 24 to the roller 40 can be caused that the roll force Fw and electrode force are in a desired relationship to each other.

LIST OF REFERENCE NUMBERS

8th

fiber bundles

10

Fiber preform

12

core

14

driving device

15

drive shaft

20

fixing

24

electrodes

30

Positioning device

36

Power transformer

38

guide

40

roller

F

contact force

v

feed rate

Claims (7)

Method for producing a fixed fiber preform (10), wherein a fiber bundle (8) is applied to a core (12) and / or introduced into a mold, and the fiber bundle (8) immediately before and / or during and / or immediately after application or an electric current is applied to the core (12) or into the mold, in order to bring about thermal heating in conjunction with a plastic to fix the fiber preform (10) by means of a fixing device (20), wherein the fixing device (20) a sliding surface for applying a pressure to the fiber bundle (8) and at least two electrodes (24), wherein current is applied to the fiber bundle (8) via the electrodes (24), characterized in that the electrodes (24) form the fiber bundle (8) 8) immediately after the introduction of the current and / or during the introduction of the current and / or before the introduction of the current with a defined force (F) against the core (12) u Press the mold with the sliding surface and the electrodes (24) integrally and rigidly attached to the fixing device (20). Method according to Claim 1 , characterized in that the fixed fiber preform (10) is further processed in a subsequent process step by supplying plastic to a plastic component. Method according to one of the preceding claims, characterized in that a binder substance is supplied, which contains in particular a thermoplastic copolyamide, such as preferably a copolyamide adhesive nonwoven or consists thereof and / or that the binder substance contains an epoxy resin based on bisphenol A or from it consists. Method according to one of the preceding claims, characterized in that impregnated fibers, ie in particular impregnated with a hardenable resin or wetted fibers are fed to a fixing device, and the fixing device hardens the curable resin at least partially. Method according to one of the preceding claims, characterized in that an electrical measurement variable, such as a voltage or a current is measured and is judged depending on this measurement, whether the method is performed properly. Apparatus for making a fiber preform (10) comprising a core (12) and / or a mold suitable for molding the fiber preform (10), and a positioning device (30) for positioning a fixing device (20) relative to the core (12) and / or the mold, wherein the fixing device (20) has a sliding surface for applying a pressure to the fiber bundle (8) and at least two electrodes (24) for applying electric current to an electrically conductive fiber or a fiber bundle (8) characterized in that the electrodes (24) are adapted to cause the fiber bundle (8) to deflect against the fiber bundle (8) immediately after introduction of the stream and / or during introduction of the stream and / or prior to introduction of the stream with a defined force (F) Core (12) and / or to press the mold, wherein the sliding surface and the electrodes (24) are integrally and rigidly arranged on the fixing device (20). Device according to Claim 6 , characterized in that the force application takes place via a rigidly sliding or always rolling cylinder.

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