DE102014014787A1 - A method for producing a preform from at least two fiber layers, and apparatus for forming at least two fiber layers into a preform - Google Patents

Abstract

A method is proposed for producing a preform from at least two fiber layers (3, 5) with the following steps: arranging a separating element (11, 13) between a first fiber layer (3) and a second fiber layer (5), and reshaping the fiber layers ( 3, 5) to the preform.

Description

The invention relates to a method for producing a preform according to claim 1 and to an apparatus for forming at least two fiber layers into a preform according to claim 6.

Methods and devices of the type discussed here are known. In particular, in the automotive industry increasingly components made of fiber-reinforced plastic are used as body parts, which are both lightweight and very durable. This fiber layers are produced as semi-finished textile products and typically provided with a binder. The fiber layers are superimposed to form a multi-layer textile semi-finished product and draped or reshaped into a three-dimensional preform. Typically, the binder fixes the individual layers so that the preform holds its geometry. Subsequently, a thermoplastic or thermosetting consolidation takes place, wherein a fiber-reinforced plastic part is formed from the preform, for example, by resin infusions and curing. In particular, in the manufacture of preforms with high shape complexity may occur forming errors, which reduce the quality of the fiber composite component made therefrom. Such shaping errors may be, in particular, wrinkles, fiber displacements or bulges of reinforcing fiber bundles. In order to reduce such errors, it is known to locally incise semi-finished fiber products prior to reshaping and / or to set a voltage locally by means of segmented hold-downs during the reshaping.

The invention has for its object to provide a method which allows a further reduction of molding errors in multi-layer preforms. The invention is further based on the object to provide a device which also allows a further reduction of such errors in shaping multilayer preforms.

The object is achieved by providing a method with the steps of claim 1. In the process, a preform made of at least two fiber layers is produced by arranging a separating element between a first fiber layer and a second fiber layer. The fiber layers are formed into the preform. In the context of the invention, it has been recognized that the main cause of shaping errors when draping multilayer structures is to be seen in an interaction of the different fiber layers with one another or with one another. In this case comes as an effective system a discontinuous architecture of the fiber layers, the normal and membrane stresses acting during forming, as well as locally divergent deformation mechanisms, such as a shearing and fiber intake of the fiber layers in question. The arrangement of the separating element between the fiber layers whose interaction is prevented. In this case, the separating element is preferably arranged in a catchment area of the fiber layers, from which material of the fiber layers is drawn into a forming area during the forming process. The separator significantly reduces stiction in the draw-in area because a static coefficient of friction between a fiber layer and the separator is less than a static coefficient of friction between the fiber layers. In addition, the form-related interaction of the fiber layers is decoupled, allowing an undamaged entry into the forming area.

As a separating element, a metallic sheet is preferably used, which preferably has a central recess which engages around the forming area. The fiber layers are thus formed in the region of the central recess, while the catchment area is provided around the central recess, in that the fiber layers are separated from one another by the separating element.

Preferably, in the context of the method, a preform is produced from more than two fiber layers, with a separating element being particularly preferably arranged between each two adjacent fiber layers, so that therefore also a plurality of separating elements is used. It is possible for a separating element to be arranged as a cover or floor element above and / or below a fiber layer stack.

The method can be used in various applications for the production of preforms or fiber composite structures, in particular in a multiplicity of different production methods, wherein the method is particularly preferred for producing a preform for a subsequent resin infiltration in the course of a RTM process (Resin Transfer Molding) with subsequent curing, for the transformation of organic sheets, in the context of hybrid hot pressing, wet pressing, in particular with Duromermatrix, and / or for the compression molding of hybrid semi-finished products is used.

In any case, two dominant shaping errors are reduced in the process, namely wrinkling and / or fiber transverse displacement or fiber bulging. The method is easy to implement, especially in forming intended for forming presses, whereby a tact time-oriented and cost-effective design is possible.

At least one of the fiber layers is preferably formed as a knitted fabric, knitted fabric, fabric, scrim or in another way. Such a fiber layer can be formed from individual fibers and / or fiber bundles, so-called rovings. Particularly preferably, the fiber layer comprises glass fibers, natural fibers, synthetic fibers, carbon fibers, steel fibers and / or other suitable fibers or fiber bundles.

An embodiment of the method is preferred, which is characterized in that an intake of the fiber layers during forming is controlled by means of a hold-down device. In this case, the hold-down device has a plurality of actuators, wherein the individual actuators are controlled separately. In this way it is possible to control the material intake largely and thus also to counter a high shape complexity. In particular, the feed direction of the material in the forming area can be controlled by the active and separately controllable actuators. As a result, a material flow and thus also a shear pattern distribution is preferably actively controllable in each fiber layer. The achievable shaping complexity can be further increased.

It is possible that - seen from the central recess of the separating element - are provided radially outside of the separating element separate hold-down and / or manipulators with which local membrane stress in the semifinished fiber can be changed. In this case, it is possible for the membrane stresses to be changed by the hold-downs themselves and / or by the displaceable manipulators arranged in front of or behind the hold-downs. Alternatively or additionally, it is possible that vertically displaceable clamping elements are provided, which are displaceable parallel to a Hauptumformrichtung. It is possible that the clamping elements follow during the forming of the local forming movement. In this way, the accuracy of the shaping can be further increased.

An embodiment of the method is also preferred in which the fiber layers are locally cut during the forming, in order to be able to partially reduce membrane stresses and to prevent shaping errors.

In particular, an embodiment of the method is preferred in which, alternatively or additionally, piezoactuators are used as actuators, which are arranged on the separating element in a segmented arrangement. In this case, the separator is partially bent by driving the piezo actuators. The segmented arrangement of the piezoactuators - in particular around the central recess around - results in hold-down segments, wherein the separating element is bent locally by driving the piezoactuators, which in turn locally in the region of an active hold-down segment retaining forces in the fiber layers can be introduced. In this way, the material feeder can be controlled locally as needed. Preferably, the separating element between the segment-like around the central recess arranged around piezoelectric actuators is cut, so quasi Niederhalterzungen are formed, which are bent by driving the piezo actuators.

If more than two fiber layers and thus more than one separating element is used, a material flow and thus also a shear pattern distribution of each individual layer and also over the entire layering can be actively controlled, in particular by position-selective actuation of the piezoactuators. This allows a particularly accurate deformation without deformation and an increase in the shaping complexity by full control of the material feed in all layers and in all directions within a layer.

An embodiment of the method is also preferred, which is characterized in that the piezo actuators are used as sensors for detecting shaping errors during forming. In particular, by selecting suitable, sensitive ceramics for the piezo actuators, it is possible to use these as a sensor and to detect normal forces on the piezo actuators during the forming. These normal forces can be evaluated, whereby shaping errors and in particular a wrinkle formation can be determined. Using this information, it is possible to provide a self-regulating system, the piezo actuators actively responding to shaping errors that form on the basis of the detected normal forces. In this way, a feedback is implemented, so that the material flow or material intake is locally adjustable as needed.

It is also preferred an embodiment of the method, which is characterized in that the piezo actuators - especially during the forming - are excited high frequency oscillating. In particular, by means of suitable function generators, it is possible to stimulate the piezo actuators high-frequency vibrations. As a result, the friction between the individual fiber layers is further reduced, so that they can slide together without error formation. Particularly preferably, the high-frequency excitation of actually intended to influence the influence of material control of the piezo actuators is superimposed. In this way, at the same time the friction between the fiber layers can be additionally reduced and the material influence can be controlled locally as needed.

The object is also achieved by providing a device for forming at least two fiber layers into a preform with the features of claim 6. The device is in particular set up for Carrying out a method according to one of the previously described embodiments. It has an upper tool and a lower tool, wherein the upper tool and the lower tool together include a cavity for forming the fiber layers. In particular, the upper tool and the lower tool are displaceable relative to each other in an open position and in a closed position, wherein the cavity is closed by relative displacement of the upper tool and the lower tool from the open position to the closed position, wherein the fiber layers are formed. The device has a separating element which is set up for arrangement between the fiber layers during the forming. This results in the advantages that have already been explained in connection with the method.

In one embodiment of the device, it is possible that the lower tool is arranged fixed in space, wherein the upper tool is held displaceable. In another embodiment, it is possible that the upper tool is arranged fixed in space, wherein the lower tool is held displaceable. It is also an embodiment possible in which both the upper tool and the lower tool are held displaceable and mutually displaceable away from each other or away.

The device preferably has a plurality of separating elements. In particular, it is possible that the number of separating elements varies with the number of fiber layers to be formed. At least a number n-1 of separating elements is preferably provided for a number n of fiber layers, so that between each two fiber layers a separating element can be arranged. It is also possible that in each case a separating element is arranged as a cover or floor element above and / or under a fiber layer stack / are.

An embodiment of the device is preferred, which is characterized in that one of the tool parts, namely the upper tool or the lower tool, is segmented, so that this tool part has a plurality of locally differently formed Drapierstempeln, which are preferably sequentially and independently displaced. In this way, the forming can be carried out locally controlled, wherein the material feed is controlled locally by the sequential displacement of the various Drapierstempel. Particularly preferably, the draping punches are designed as tool segments of the upper tool. In this case, a displacement angle is preferably adjustable independently of each other Drapierstempel for each Drapierstempel.

An embodiment of the method is also preferred, which is characterized in that the separating element is sheet-shaped. It can be positioned in this way simple and space-saving, especially without applying, between the fiber layers. Preferably, the separating element is designed as a metallic sheet.

In a preferred embodiment of the device it is provided that the separating element has a central recess for a passage of the upper tool and / or the lower tool. During the reshaping, the upper tool and / or the lower tool is / are thus displaced through the recess, wherein the fiber layers are reshaped in the region of the central recess. The central recess thus defines a forming area in which the fiber layers are reshaped. Outside the forming area, the individual fiber layers are separated from one another by the at least one separating element.

An exemplary embodiment of the device is also preferred, which is characterized in that segment-like, separately controllable piezoactuators are arranged around the central recess. Quasi hold-down segments are formed on the separator by the arrangement of the piezo actuators, said segments can be bent separately by the piezo actuators to locally control the material feeder in the forming area, in particular to specify a feed direction.

Preferably, the separating element on incisions between the piezo actuators, which separate the segments from each other and quasi form hold-down tongues, which are locally deformable by driving the piezo actuators, in particular bendable.

A preferred embodiment of the device has a cutting device, by means of which local cuts can be introduced into at least one fiber layer in order to relieve the fiber layers locally during forming, in particular to be able to relieve stresses. This can be used as a further degree of freedom to avoid shaping errors.

Finally, an embodiment of the device is preferred, which is characterized in that a control device is provided, which is operatively connected to the piezo actuators to their control. Preferably, the control unit is also connected to the piezo actuators in such a way that they can be used as sensors for detecting shaping errors during forming. In this case, by means of acting as sensors piezo actuators in particular Normal voltages detectable from which information about resulting molding errors can be obtained. In this case, the control unit is preferably designed as a closed control system for controlling the material intake by means of the voltage input detected via the piezoactuators.

The control unit is also preferably designed as a function generator or has a function generator, wherein it is set up for the high-frequency oscillating excitation of the piezo actuators. This excitation is preferably the actual, the influencing of the material intake serving control of the piezo actuators superimposed. Due to the high-frequency excitation of the piezo actuators and thus also of the separating element, a friction between the fiber layers separated by the separating element can be further reduced.

The description of the method on the one hand and the device on the other hand are to be understood as complementary to each other. Features of the device that have been explained explicitly or implicitly in connection with the method are preferably individually or combined with one another Features of a preferred embodiment of the device. In particular, the device is preferably characterized by at least one feature that is caused by at least one method step of the method. Method steps which have been described explicitly or implicitly in connection with the apparatus are preferably individually or combined with one another method steps of a preferred embodiment of the method. The method is preferably characterized by at least one method step, which is caused by at least one feature of the device.

The invention will be explained in more detail below with reference to the drawing. Showing:

1 a schematic representation of an embodiment of an apparatus for forming at least two fiber layers into a preform, and

2 a schematic representation of a separating element of the device according to 1 ,

1 shows a schematic representation of an embodiment of a device 1 for producing a preform from at least two fiber layers, in which case a first fiber layer 3 and a second fiber layer 5 are shown. The device 1 has an upper tool 7 and a lower tool 9 on, which are shown here in an open position. The upper tool 7 and the lower tool 9 are displaceable relative to each other in a closed position, whereby in the embodiment shown here, the upper tool 7 in a recess of the lower tool 9 engages, creating a cavity for the deformation of the fiber layers 3 . 5 is closed. This will be the fiber layers 3 . 5 partially pulled into the cavity and draped or reshaped in this.

Between the fiber layers 3 . 5 Here is a first separator 11 arranged, which is designed as a metal sheet. In the illustrated embodiment is above the second fiber layer 5 a second separating element 13 it being possible for it to be above the second separating element 13 another, not shown fiber layer is arranged. Alternatively, it is possible that as many separators 11 . 13 like fiber layers 3 . 5 are provided. In this case, preferably a lowermost fiber layer, here the first fiber layer 3 , directly on the lower tool 9 on, with a top fiber layer, here the first fiber layer 5 is covered by acting as a cover element separating element. It is also possible that under the fiber layer stack, here below the first fiber layer 3 , a separating element is arranged as a bottom element.

The separating elements 11 . 13 each have a central recess 15 on, which is set up for a penetration of the upper tool 7 , Thus defines the central recess 15 a radially arranged therein within the forming area by the fiber layers 3 . 5 be formed when closing the mold cavity.

Around the central recess 15 around are segmented piezo actuators 17 arranged, of which the sake of clarity here only one with the reference numeral 17 is marked. Due to their segment-like arrangement form the piezo actuators 17 Hold-down segments off. They are separately controllable, so that the separating elements 11 . 13 locally in the area of controlled piezo actuators 17 are bendable, which in turn holding forces on the fiber layers 3 . 5 can be exercised. As a result, a material feed into the mold cavity locally by appropriate control of the piezo actuators 17 controllable.

Preferably the device 1 a control unit 19 on, with the piezo actuators 17 is operatively connected, which here schematically only for a piezo actuator 17 is shown. Here is the control unit 19 Set up for local and separate control of the piezo actuators 17 and thus for controlling the material intake of the fiber layers 3 . 5 into the works train cavity. The control device is preferred 19 also set up to use the piezo actuators 17 as sensors, so in the controller 19 a regulation of the material intake via the voltage input in the extent used as sensors piezo actuators 17 can be realized.

Furthermore, the control unit 19 Preferably, at least one function generator, which is set up for high-frequency oscillating excitation of the piezo actuators 17 , this excitation in particular the actual control of the piezo actuators 17 for the purpose of controlled material intake is superimposed.

Using the dividers 11 . 13 is a friction between adjacent fiber layers 3 . 5 can be reduced during forming, whereby the friction due to high-frequency excitation of the piezo actuators 17 can still be reduced. At the same time is the collection of fiber layers 3 . 5 using a through the piezo actuators 17 realized hold-down device 21 controllable or controllable, so that molding errors during forming by controlled material intake and locally variable material stresses within the fiber layers 3 . 5 can be avoided.

2 shows a schematic representation of a separating element, for example, the first separating element 11 the device 1 , Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. The separating elements 11 . 13 are preferably identical. Therefore, everything related to 2 for the first separator 11 is executed, preferably also for the second separating element 13 , The central recess 15 is here preferably circular, wherein the piezo actuators 17 here circular - in particular at equal angular intervals - around the central recess 15 are arranged around. Of course, other forms are for the central recess 15 and accordingly also other, in particular also irregular, arrangements of the piezo actuators 17 possible, wherein these embodiments can be adapted in particular to a specific application or a specific forming task.

It turns out that the separating element 11 preferably cuts 23 of which, for the sake of clarity, here only one with the reference numeral 23 is marked. In this way, quasi-hold down tongues 25 formed by driving the piezo actuators 17 can be bent, causing local hold down forces in the fiber layers 3 . 5 can be introduced.

Due to the arrangement of the piezo actuators 17 and especially through the cuts 23 Niederhaltesegmente be formed, of which for clarity here delimited by dotted lines L and the reference numeral 27 is marked. In particular, these hold-down segments 27 enable a defined, locally controlled material feed into the mold cavity.

The method described is suitable both for forming fiber layers into a preform and for converting preimpregnated semi-finished products into fiber composite structures. Overall, it turns out that by using the method and the device 1 in a particularly efficient manner shaping errors in the manufacture of multilayer preforms are avoidable.

Claims (10)

Process for producing a preform from at least two fiber layers ( 3 . 5 ), with the following steps: arranging a separating element ( 11 . 13 ) between a first fiber layer ( 3 ) and a second fiber layer ( 5 ), and forming the fiber layers ( 3 . 5 ) to the preform. A method according to claim 1, characterized in that a collection of the fiber layers ( 3 . 5 ) during forming by means of a hold-down device ( 21 ), wherein the hold-down device ( 21 ) has a plurality of actuators, wherein the individual actuators are driven separately. Method according to one of the preceding claims, characterized in that as actuators piezo actuators ( 17 ) are used on the separating element ( 11 . 13 ) are arranged in a segmented arrangement, wherein the separating element ( 11 . 13 ) in areas by controlling the piezo actuators ( 17 ) is bent. Method according to one of the preceding claims, characterized in that the piezo actuators ( 17 ) can be used as sensors for detecting forming errors during forming. Method according to one of the preceding claims, characterized in that the piezo actuators ( 17 ) are driven high frequency swinging. Contraption ( 1 ) for forming at least two fiber layers ( 3 . 5 ) to a preform, in particular for carrying out a method according to one of claims 1 to 5, with an upper tool ( 7 ) and a lower tool ( 9 ), which together form a cavity for reshaping the fiber layers ( 3 . 5 ), and with at least one separating element ( 11 . 13 ), which is arranged for arrangement between the fiber layers ( 3 . 5 ) during forming. Contraption ( 1 ) according to claim 6, characterized in that the separating element ( 11 . 13 ) sheet-shaped, preferably formed as a metallic sheet. Contraption ( 1 ) according to one of claims 6 and 7, characterized in that the separating element ( 11 . 13 ) a central recess ( 15 ) for a penetration of the upper tool ( 7 ) and / or the lower tool ( 9 ) having. Contraption ( 1 ) according to one of claims 6 to 8, characterized in that around the central recess ( 15 ) Segment-like separately controllable piezo actuators ( 17 ) are arranged. Contraption ( 1 ) according to one of claims 6 to 9, characterized by a control device ( 19 ), with the piezo actuators ( 17 ) is operatively connected to the control and preferably to their use as sensors for detecting deformation errors during forming.

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