DE102014014788A1 - Method and device for producing a preform from at least two fiber layers - Google Patents

Abstract

The invention relates to a method for producing a preform from at least two fiber layers (3, 5), comprising the following steps: arranging a separating element (11, 13, 37) between a first fiber layer (3) and a second fiber layer (5), forming the Fiber layers (3, 5) to form a preform, wherein the separating element (11, 13, 37) has a plurality of piezo actuators (17), which are excited to oscillate.

Description

The invention relates to a method for producing a preform from at least two fiber layers according to claim 1 and to an apparatus for forming at least two fiber layers into a preform according to claim 5.

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 into a multi-layer textile semifinished 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 infusion 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. When forming a multi-layer textile semifinished product, the additional problem arises of a relative displacement between the different fiber layers. These rub against each other, whereby friction-induced damage to the fiber layers and / or the tissues can occur.

The invention has for its object to provide a method and an apparatus in which the disadvantages mentioned do not occur.

The object is achieved by providing the subject matters of the independent claims. Advantageous embodiments emerge from the subclaims.

The object is achieved in particular by providing a method for producing a preform from at least two fiber layers, which has the following steps: A separating element is arranged between a first fiber layer and a second fiber layer. The fiber layers are formed into a preform, wherein the separating element - in particular by means of a plurality of piezo actuators, which preferably has the separating element - is excited to vibrate. The arrangement of the separating element between the fiber layers, a friction occurring between them can be reduced during the forming. It shows that a coefficient of static friction between a fiber layer and the separating element is less than a static coefficient of friction between the fiber layers. In addition, a form-related interaction of the fiber layers is decoupled, which allows a largely undamaged entry into the forming area. In addition, however, the excitation of the piezo actuators leads to vibrations that these vibrations transmitted to the separating element. In this case, the separating element is bent in particular locally and vibrated, whereby the friction between the individual fiber layers is further reduced. In this way, an easier sliding of the fiber layers relative to each other can be ensured.

Preferably, the piezo actuators are excited high frequency oscillating. In particular, by means of suitable function generators, it is possible to stimulate the piezo actuators high-frequency oscillations.

As a separating element, a metallic sheet is preferably used. Alternatively or additionally, it is also possible for a separating element to be used which has plastic, in particular carbon-fiber-reinforced plastic, or consists of plastic, in particular of carbon-fiber-reinforced plastic. Fiber-reinforced plastics have a lower coefficient of thermal expansion than metals, which is why the use of such a fiber-reinforced plastic separating element is more advantageous than the use of a separating element, which is designed as a metal sheet. The separating element preferably has a preforming recess, in particular a central one, which defines a forming area. The fiber layers are deformed in the region of the preforming recess, while a feed zone is provided around the preforming recess, in which 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 one separating element being particularly preferably arranged between each two adjacent fiber layers, so that a plurality of separating elements is used. It is possible for a separating element to be arranged above and / or below a fiber layer stack as a cover and / or floor element. In particular, it is possible that under the fiber layer stack a support plate is arranged, which may have larger dimensions than the other separating elements and this may extend beyond the circumference. The support plate serves for a simplified handling of the fiber layer stack.

The process can be used in various applications for the production of preforms or fiber composite structures, In particular, in a variety of different manufacturing processes, the method particularly preferred for producing a preform for subsequent resin infiltration in the course of a RTM process (Resin Transfer Molding) with subsequent curing, for forming organo sheets, in the context of hybrid hot pressing, wet pressing, in particular with Duromermatrix, and / or for compression molding of hybrid semi-finished products is used. In the context of the method, the semi-finished fiber product, in particular the fiber layer stack, is particularly preferably infiltrated with a resin-hardener mixture, which is subsequently cured.

In the context of the method, in particular two dominant shaping errors are reduced, namely a wrinkling and / or a fiber transverse displacement or Faserausbeulung. 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 any other suitable manner. Such a fiber layer can be formed from individual fibers and / or from 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 a separating element is used on which the piezo actuators are arranged in a segmented arrangement, wherein the separating element is bent in regions by controlling the piezo actuators. Due to the segmented arrangement of the piezoelectric actuators, in particular around the central preforming recess, segments that are excited locally to vibrations result, wherein the separating element can be locally excited by activating the piezoactuators to oscillate. The piezo actuators are preferably controlled separately. By a different control of different piezo actuators, the vibration excitation can be controlled locally as needed.

Particularly preferred is a separating element is used, which is cut between the segment-like around the central Vorformausnehmung arranged around piezo actuators, so quasi tongues are formed, which can be largely excited separately by driving the piezo actuators to vibrate.

An embodiment of the method is also preferred, which is characterized in that a retraction of the fiber layers during forming is controlled by means of a hold-down device, wherein the hold-down device has a plurality of local clamping elements as actuators. Preferably, the local clamping elements are controlled separately from each other and are also preferably driven separately from each other. In this way it is possible to largely control a material feed of the fiber layers during forming and thus also to counter a high shape complexity. In particular, a feed direction of the material of the fiber layers in the forming area can be controlled via the active and separately controllable, local clamping elements. 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 Vorformausnehmung of the separating element - are provided radially outwardly of the separating element separate hold-down and / or manipulators with which locally membrane stresses 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.

By the local clamping elements tensile forces and / or holding forces are introduced locally in a fiber layer during the transformation. However, during the forming process, these are partly converted into normal forces, which then act on an adjacent fiber layer. These normal forces result in a relative movement of the fiber layers to increased friction and thus damage to the fiber layers, provided that exceed the normal forces to some extent. For example, it is possible for fibers to be pulled apart or sheared. In that regard, there is a conflict of interest: To avoid wrinkling, tensile forces must be exerted by the local clamping elements. However, these lead to the formation of normal forces that damage the fiber layers during forming. In the present embodiment of the method, however, this is largely reduced or completely avoided by locally inducing the at least one separating element to vibrate with the aid of the piezoactuators, so that the friction between adjacent fiber layers is reduced.

The local clamping elements are preferably arranged in segments around the central preforming recess. In this way, a collection of fiber layers during forming can be controlled locally as needed particularly efficient.

An embodiment of the method is preferred in which the piezoactuators are used as actuators of the hold-down device, in particular as local clamping elements. In this case, the separator is partially bent by driving the piezo actuators. The preferred segmented arrangement of the piezoactuators - in particular around the central preforming recess - results in hold-down segments, wherein the separating element is bent locally by driving piezoactuators, which in turn can be introduced locally in the region of an active hold-down retaining forces in the fiber layers. In this way, the material feeder can be controlled locally as needed. The previously described tongues, which preferably has the separating element, then serve as hold-down tongues, which are bent by activating the piezoactuators.

If more than two fiber layers and thus also more than one separating element is used, a material flow and therefore also a shear pattern distribution of each individual layer can be actively controlled even over the entire layering, in particular by a 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.

The piezo actuators are preferably driven to exercise their hold-down function with a DC voltage. This can be superimposed to exercise the vibration-stimulating function of the piezo actuators with a - especially high-frequency - AC voltage. In this way, it is simple and also cost-effective to represent both the hold-down function as well as the vibration excitation function by the same elements. In particular, one and the same piezo actuators can be used on the one hand for clamping and on the other hand for introducing vibrations.

Alternatively or additionally, it is preferably provided that at least one local clamping element has a tie rod as an actuating element. The mechanism of action lies in an off-center introduction of a tensile force in the plane, which results in a bend and thus in a clamping. The local clamping element can be controlled by means of the tie rod independent of the control of the piezo actuators. This embodiment has the further advantage that greater clamping forces can be exerted via the tie rod than is possible with currently known piezo actuators. The tie rod is preferably connected to the separating element, in particular adhesively bonded to the separating element. As an actuating device preferably a pneumatic is used, which - mediated by the tie rod - initiates tensile and / or holding forces in the separating element. When exercising the tensile forces, the separating element bends. In particular, the tie rod is preferably connected to a tongue of the separating element, in particular glued to a tip of a tongue of the separating element. If a tensile force is then introduced into the tie rod, the tongue is bent, in particular in the region of its tip, so that clamping forces can be introduced into a fiber layer arranged below the separating element.

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 in which the fiber layers are locally cut during the forming, in order to partially reduce membrane stresses and to prevent shaping errors can.

The object is also achieved by providing a device which is adapted for forming at least two fiber layers into a preform. Preferably, the device is set up to carry out a method according to one of the previously described embodiments. The device has an upper tool and a lower tool, which together enclose a cavity for forming the fiber layers. Furthermore, a device for heating the layers and thus for binder activation is provided. In addition, the device has at least one separating element which is arranged to be arranged between the Fiber layers during forming. In particular, the upper tool and the lower tool are displaceable relative to one another 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 reshaped. The separating element has a plurality of piezoactuators which can be excited to oscillate. By the separating element and in particular by the piezo actuators, the advantages that have already been explained in connection with the method. The piezo actuators are preferably separately controllable.

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 metallic sheet as the separating element. The separating element can be positioned in this way simple and space-saving, in particular without applying, between the fiber layers. Alternatively or additionally, it is possible for the device to have a separating element which comprises plastic, in particular carbon-fiber-reinforced plastic, or consists of plastic, in particular of carbon-fiber-reinforced plastic. This has weight advantages compared to a separator, which is designed as a metallic sheet.

Preferred is an embodiment of the device in which the piezo actuators are embedded or embedded in the separator. In this case, each piezoactuator is formed at most flush with a surface of the separating element, or it is geodetically lower than this surface, so that no piezoelectric actuator protrudes beyond the surface of the separating element. As a result, the low-friction sliding of the fiber layers on the separating element is not impaired by disturbing geometries of the piezo actuators.

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. In particular, it is possible that a support plate is arranged below the fiber layer stack, which preferably projects beyond the separating elements of the device along a circumferential line, wherein it has larger dimensions than the separating elements. The support plate serves for easier handling of the fiber layer stack.

An exemplary embodiment of the device is also preferred, which is characterized in that the separating element has a preforming recess, wherein it preferably has a plurality of tongues projecting radially inwards - towards the preforming recess.

The preforming recess serves in particular 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 preforming recess, wherein the fiber layers are reshaped in the region of the preforming recess. This thus defines a forming area in which the fiber layers are formed. Outside the forming area, the individual fiber layers are separated from one another by the at least one separating element.

The tongues preferably surround the preforming recess in a segmental manner. Preferably, the piezo actuators are arranged on the tongues. In particular, it is possible that at least one piezoelectric actuator is arranged on each tongue. In this way, it is very easy to influence the friction between the fiber layers locally as needed around the Vorformausnehmung by appropriate control of the piezo actuators.

The piezo actuators are preferably embedded in the associated tongue and / or embedded. In this way, a low-friction sliding of the fiber layers can be ensured on the tongues, wherein the piezo actuators do not protrude beyond a surface of the tongues, so that no interference contours are present by the piezo actuators. For this purpose, reference is also made to the above remarks on the embedded in the separator / embedded piezo actuators.

In a preferred embodiment of the device it is provided that more than one piezoelectric actuator is arranged on one and the same tongue of the separating element. This makes it possible to achieve greater vibration amplitudes of the tongues and thus to reduce the friction between the fiber layers even more. Particularly preferred is a device in which two piezo actuators per tongue are provided.

The tongues are preferably formed by the separating element has cuts between the piezo actuators, whereby segments separated from each other and the tongues are formed. These tongues are locally deformable by driving the piezo actuators and in particular excited to vibrate.

In a preferred embodiment, 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.

An exemplary embodiment of the device is also preferred, which is characterized in that it has a hold-down device which is set up in order to control an intake of the fiber layers during forming. The hold-down device preferably has a plurality of local clamping elements. These are preferably individually controllable separately, wherein they preferably surround the Vorformausnehmung segment-like or segmentally arranged around the Vorformausnehmung around. In one embodiment, it is possible that the piezo actuators - in particular together with the tongues - form the local clamping elements. Alternatively or additionally, it is possible that a local clamping element has a tie rod as an actuating element. This device allows for the first time a single-layer-specific hold down of the individual layers. In this connection, reference is made to the above description of the method.

An embodiment of the device is also preferred, which is characterized in that the device has a strut element holding the edge at least one separating element. In this way, bending of the semifinished fiber product with the at least one separating element can be avoided in particular. In particular, when a larger number of separators are stacked with fiber layers interposed therebetween, the fiber layer stack may become heavy. In order then to avoid bending of the fiber layer stack and thus an unwanted deformation of the fiber layers under the weight of the fiber layer stack and in particular under the weight of the separating elements, the fiber layer stack must be stiffened. This is preferably achieved by the edge-mounted strut element.

The bracing element preferably has an attack element for a gripper. Additionally or alternatively, the bracing element preferably has a support or clamping region for a support plate of the fiber layer stack. Using the gripper and / or by means of the support or clamping area a particularly simple handling of the fiber layer stack is possible.

In a preferred embodiment, the bracing element is formed circumferentially, so that it surrounds the fiber layer stack on the supply side. In particular, the bracing element is preferably designed as a frame, in particular as a frame, which receives the fiber layer stack. The attack element is preferably designed as a strut. This is a particularly simple and inexpensive embodiment of the strut element.

In particular, a transport of a fiber layer stack is possible via the bracing element, in which case the individual fiber layers have variable outer contours. It is therefore possible first to cut the individual fiber layers and then to layer. These can vary in their outer contour, which takes into account a direction-dependent intake behavior during forming of the semifinished fiber product. Furthermore, the bracing element acts as a stiffening edge for simplified handling and for fixing the separating elements against displacement.

Preferably, an insertion strut is provided on the stiffening element, which is arranged at an angle different from 180 ° to a main plane of the fiber layer stack, preferably at an angle of 45 °. The insertion strut can be used to guide the insertion of the fiber layer stack in the device.

Preferably, the device for accurate positioning of the fiber layer stack at least one stop and / or at least one mandrel, wherein the fiber layer stack abuts when correctly positioned with the bracing and / or the support plate and / or at least one separating element on the at least one stop, and / or where he is plugged with a recess on the at least one standing mandrel. In this way, the fiber layer stack can be aligned with high precision relative to the device. Particularly preferably, the lower tool has at least one stop and / or at least one standing mandrel.

Due to the stiffening of the fiber layer stack by means of the bracing element is a rapid removal of the fiber layer stack, which would otherwise be flexible soft - especially via an ejector - possible. This makes it possible, in particular, to remove the fiber layer stack in a not yet fully hardened binder state and to allow it to cure in air outside the device. This in turn leads in particular to cycle time savings.

An exemplary embodiment of the device is also preferred, which is characterized in that the separating element has at least one joint, in particular at least one hinge, wherein at least two parts of the separating element are pivotable relative to one another about an axis determined by the hinge, preferably by the hinge are. This allows in a particularly favorable manner, a pre-bending of the fiber layer stack on the provided by the hinge or hinge kinematics of the separating element. This is particularly advantageous for complex geometries which are to be formed by reshaping the fiber layer stack. In particular, a degree of deformation of the fiber layer stack in the tool is reduced by approaching the final contour via the possible pre-bending.

An embodiment of the device is also preferred, which is characterized in that the separating element is formed at least in two parts. In this case, it is preferable to provide a closing mechanism, in particular a material, positive or non-positive closure mechanism, for connecting and disconnecting at least two subelements of the separating element. It is then possible to divide the separator to remove the preformed preform, whereby the preform can be removed very easily without using a cutting tool.

Alternatively, however, it is possible for the preform to be cut out of the stacked separating elements, in particular along an edge of the preforming recess.

An embodiment of the device is also preferred, which is characterized by a control device which is operatively connected to the piezoactuators for their - in particular local and separate - control. Preferably, the control unit with the piezo actuators is also operatively connected to their use as sensors for detecting deformation errors during forming.

Furthermore, it is possible to actively temper the intermediate sheets (for example via resistive heating of the carbon fibers, if carbon fiber reinforced plastic sheets are used as composite intermediate sheets). As a result, a cooling of the binder during transport can be reduced. In addition, a sticking of a thermoplastic binder to the intermediate plates can be avoided in this way.

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. Procedural steps that have been described explicitly or implicitly in connection with the device are preferably individually or combined with each other 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;

2 a schematic detail of embodiments of a separating element;

3 a schematic representation of another embodiment of a separating element;

4 a schematic representation of two further embodiments of the device, and

5 a schematic representation of an embodiment of the method.

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, not shown, 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 preferably formed 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.

In another preferred embodiment, 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. Particularly preferred here is a support plate is arranged, which the separating elements 11 . 13 projected circumferentially in a preferred embodiment and allows for simplified handling of the fiber layer stack.

But it is also possible that a support plate is arranged under a serving as a bottom element separating element, wherein also in this case, the support plate preferably projects beyond the partition elements circumferentially. In both of the aforementioned embodiments, it is also possible that the support plate has the same dimensions as the separating elements, so that it does not extend beyond this circumference.

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

The separating elements 11 . 13 each have a plurality of piezo actuators 17 which are excitable to swing. Here are the piezo actuators 17 preferably in segments around the preforming recess 15 arranged around. For better clarity, here is only a piezo actuator with the reference numeral 17 characterized. By the excitation of the piezo actuators 17 To preferably high-frequency vibrations, a friction between the fiber layers 3 . 5 be reduced. Furthermore, the segment-like arranged piezo actuators form 17 prefers hold-down segments.

The piezo actuators 17 are preferably separately and individually controllable, so that the separating elements 11 . 13 locally in the area of actuated 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 in particular for local, separate vibration excitation of the separating elements 11 . 13 and also preferably for local and separate control of the material intake of the fiber layers 3 . 5 into the tool cavity.

In a preferred embodiment, the controller is 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 adapted to the vibration excitation of the piezo actuators 17 , in particular for the high-frequency vibration excitation of the same. This excitation can in particular control the piezo actuators 17 be superimposed for the purpose of a controlled material intake. Here are the piezo actuators 17 through the control unit 19 preferably with a DC voltage controllable to hold down forces in the fiber layers 3 . 5 being initiated by the control unit 19 preferably be driven with an alternating voltage to be excited to vibrations and thereby the separating elements 11 . 13 vibrate locally. In this case, the AC voltage can preferably be superimposed on the DC voltage.

The separating elements 11 . 13 preferably have a plurality of radially inwardly to the preforming 15 towards protruding tongues, of which here for the sake of clarity, only one with the reference numeral 21 is marked. In particular, the separating elements 11 . 13 preferably cuts 23 on, of which the sake of clarity here also only one with the reference numeral 23 is marked. The tongues 21 be between the cuts 23 educated. Preference is given to every tongue 21 at least one piezo actuator 17 assigned, with the tongues 21 through the piezo actuators 17 on the one hand bent and on the other hand can be vibrated. The tongues 21 act as a kind of hold-down tongues, through which locally hold down forces in the fiber layers 3 . 5 can be introduced. In this respect, through the tongues 21 on the one hand and the piezo actuators 17 on the other hand, a hold-down device 25 educated. The piezo actuators act here 17 - especially together with the tongues 21 - Preferably as a local clamping elements of the hold-down device 25 ,

2 shows two schematic detail representations of two embodiments of a separating element. Here are the different separating elements 11 . 13 a fiber layer stack preferably formed identically, so that it suffices here, hereinafter on the first separator 11 remedy. Of course, it is also possible to use differently shaped separating elements in a fiber layer stack.

2a) shows a detailed view of the separating element 11 , in particular a region of a tongue 21 , It turns out that exactly one piezoelectric element is here 17 the tongue 21 is assigned, wherein the piezoelectric element 17 in the tongue 21 embedded or embedded. The piezo element protrudes 17 at no point over a surface 27 of the separating element 11 In addition, so that no interference contours are formed, which is a collection of fiber layers 3 . 5 could disturb. It also shows that the separating element 11 Zuführausnehmungen 29 , in particular in the form of grooves, in which - in particular electrical - supply lines to the piezoelectric element 17 can be arranged. Here are the Zuführausnehmungen 29 configured such that the supply lines to the piezoelectric element 17 not over the surface 27 protrude.

2 B) shows a schematic detail of a further embodiment of the separating element 11 , It is provided that exactly two piezo actuators 17 the tongue 21 are assigned, with both piezo actuators 17 in the previously related to 2a) way described in the tongue 21 are embedded so that they do not have the surface 27 protrude. Accordingly, here are Zuführausnehmungen 29 provided, in which - in particular electrical - supply lines to the piezo elements 17 can be arranged in a way that also the supply lines do not over the surface 27 protrude. Sturgeon contours, which a material intake of the fiber layers 3 . 5 could be so completely avoided.

The assignment of a plurality of piezo actuators 17 to a tongue 21 of the separating element 11 has the advantage that larger vibration amplitudes can be achieved than with exactly one piezo actuator 17 the case is.

3 shows a further embodiment of a separating element 11 , Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. Again, it is clear in the plan view shown on the left that a plurality of tongues 21 , of which the sake of clarity, only one with the reference numeral 21 is characterized, the Vorformausnehmung 15 engages segmentally, with each tongue 21 a piezo actuator 17 is assigned, for the sake of clarity, only a piezoelectric actuator with the reference numeral 17 is marked. In addition, however, in this embodiment, a hold-down device 25 provided at which selected local clamping elements 31 a tie rod 33 have as an actuating element. In particular, four here, in each case in two mutually perpendicular directions opposite, local clamping elements 31 one tie rod each 33 as an actuating element.

In a right area of 3 is a detail sectional view of such a local clamping element 31 shown. It turns out that the tie rod 33 with a tip 35 the local clamping element 31 forming tongue 21 is glued. By means of a pneumatic device (not shown), a tensile force, schematically indicated here by F, in the tie rod may be preferred 33 be initiated, causing the tip 35 the tongue 21 - in 3 - is shifted downwards. In this way, a clamping force in a below the separating element 11 arranged fiber layer 3 . 5 be initiated. It is particularly possible by means of the tie rod 33 apply greater clamping forces than with currently known piezo actuators 17 is possible. In this embodiment, moreover, a function separation of the friction reduction by means of vibration excitation of the tongue 21 through the piezo actuator 17 on the one hand and the hold-down function by means of the tie rod 33 on the other hand. While in this case, the clamping force serving the hold-down function alone on the tie rod 33 is applied, the piezo actuator 17 preferably excited only by means of an AC voltage to vibrate, whereby the friction between the tongue 21 and its associated fiber layer is reduced.

4 shows a schematic sectional view of two embodiments of a fiber layer stack of the device 1 , Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description.

Here, a fiber layer stack is shown, which is the first fiber layer 3 , the second fiber layer 5 , the first separating element 11 between the fiber layers 3 . 5 and the second separator 13 having as cover element. In addition, serving as a bottom element, third separating element 37 intended. This is here on a support plate 39 on.

It is one of the dividers 11 . 13 . 37 holding strut element 41 provided, which is in particular circumferential and preferably frame-shaped, wherein it is the separating elements 11 . 13 . 37 and thus surrounds the fiber layer stack and a relative displacement of the separating elements 11 . 13 . 37 relative to each other and thus also relative to the fiber layers 3 . 5 in particular by means of a - preferably circumferential - stop edge 43 prevented. The bracing element 41 also has an attack element 45 - Here in the form of a radially projecting strut - on, wherein on the attack element 45 a gripper can handle the handling of the fiber ply stack. In this case, the gripper may be formed in a particularly simple and cost-saving manner as a finger gripper or magnetic gripper.

The bracing element 41 also has an insertion strut 47 preferably at an angle different from 180 ° relative to the separating elements 11 . 13 . 37 is oriented, in particular at an angle of 45 °. In this case, the preferably circumferential insertion strut forms 47 an insertion bevel, with which the fiber layer stack exact position on the lower tool 9 can be arranged. In addition, this preferably has at least one mandrel, preferably in a positioning recess in the strut element 41 , the support plate 39 and / or at least one separating element 11 . 13 . 37 intervenes.

It shows 4a) an embodiment in which the support plate 39 larger dimensions than the separating elements 11 . 13 . 37 so that it survives on the periphery. It is preferred in the area of the attack element 45 in the bracing element 41 clamped.

4b) shows an embodiment in which the support plate 39 has the same dimensions as the separating elements 11 . 13 . 37 , This is the support plate 39 and thus the entire fiber layer stack on the bracing element 41 on. It is possible that the bracing element 41 with the support plate 39 is firmly connected, for example, by welding, gluing, soldering, screwing, riveting, or in any other suitable manner. Also a one-piece design of the bracing element 41 with the support plate 39 is possible.

The baffle 39 preferably has as well as the separating elements 11 . 13 . 37 a Vorformausnehmung through which in particular the upper tool 7 can grab.

An embodiment is possible in which the third separating element 37 is not provided, in which case a lowermost fiber layer, here the first fiber layer 3 , directly on the support plate 39 is arranged.

The bracing element 41 causes a stiffening of the fiber layer stack, so that bending of the stack and thus an unwanted deformation of the fiber layers 3 . 5 avoided under the weight of the stack.

5 shows a schematic representation of an embodiment of the method for producing a preform from at least two fiber layers. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. In a first step S1, cutting of fiber layers takes place, it being possible in this case in particular to cut the different fiber layers with different geometry and / or different dimensions in order to take account of a material infeed that varies over the fiber layers during the forming process.

The cut fiber layers are stacked in a second step S2, wherein between the fiber layers separator elements are inserted, preferably from a separate separator stack 49 be taken. The handling of the separating elements, the fiber layers and also the finally formed fiber layer stack 51 is preferably done by means of a robot 53 , The fiber layer stack S1 is formed by alternately forming a separator from the separator stack 49 and a fiber layer from a cutting table 55 is removed.

The fiber ply stack is finally made by the robot 53 , the preferred vacuum gripper or needle gripper for the handling of the individual fiber layers, as well as mechanical grippers, in particular finger grippers or magnetic grippers for the handling of the entire fiber layer stack 51 has, in a heating station 57 shifted, where in a third step S3, a heating of the fiber layer stack 51 takes place, in particular to make the - preferably thermoplastic - binder, with which the fiber layers are provided, soft or liquid.

It is possible that the heating in a separate heating station 57 he follows. In particular, it is possible that the device 1 has an inlet area, which serves as a heating station 57 is formed, wherein the device 1 also a curing area 59 in which the fiber layer stack 51 finally draped, thus three-dimensionally shaped, wherein the binder in the curing area 59 at least partially cured.

Alternatively, it is possible that the heating takes place only in the actual forming tool, in which case no inlet area or no separate heating station 57 is provided. In this case, the actual forming tool, thus the device 1 , temperature controlled.

The fiber layer stack 51 can in the inlet area, especially in the heating station 57 , resistive, inductive, in a continuous furnace, heated by hot air, by radiant heat and / or by contact with at least one heating element.

In particular, it is possible for the heating station 57 having a lower and an upper heating plate. The upper heating plate may for example have an infrared heater. The lower heating plate preferably comprises a plurality of in particular honeycomb-shaped heating elements, which are preferably separately electrically heated. In this way it is possible to different areas of the fiber layer stack 51 to heat differently.

In the case of the use of carbon fiber-reinforced fiber layers, in particular of CFRP fabrics, as fiber mats, the heating can be carried out by applying a voltage to the CFRP fabric. Alternatively, heating wires to which a voltage is applied may be integrated in the fiber layers.

The heating station 57 is preferably thermal from the curing area 59 separated so that this one of the temperature of the heating station 57 may have different, in particular lower temperature, in which a binder is curable.

The fiber layers preferably have both a locally applied thermoset and a thermoplastic binder. In this case, the forming preferably takes place in a device which has a heatable forming tool, wherein the forming takes place in two stages. In this case, the thermosetting binder is cured in a first heating stage, wherein a pre-deformation of the fiber layers is fixed. In the second heating step, the thermoplastic binder is preferably liquefied and then solidified. In this case, a fixation of the final deformation of the semifinished fiber product takes place.

In any case, in a fourth step S4, the fiber layer stack is preferred 51 in the device 1 draped, formed in a heated state and then cooled, so that the binder of the fiber layers solidifies. Subsequently, the draped fiber layer stack 51 or the preform - preferably by means of an ejector - from the device 1 taken.

In a fifth step S5, the preform is then separated from the separating elements.

It is possible according to a first embodiment of the method that this by means of a cutting tool 61 from the preforming recess 15 the separating elements 11 . 13 . 37 is cut out. The cutting tool cuts 61 preferably at an edge of the preforming recess 15 along.

Alternatively, it is possible that separators 11 be used, which is formed at least in two parts, wherein the example shown below, the first separating element 11 a first subelement 63 and a second subelement 65 having. The two subelement 63 . 65 can be taken apart to remove the preform.

It is a locking mechanism 67 provided for connecting and disconnecting the sub-elements 63 . 65 is set up. This has here two pivotable locking arms, wherein a first locking arm 69 on the first subelement 63 pivotally hinged, with a second locking arm 71 on the second subelement 65 is hinged pivotally. The locking arms cooperate with locking bolts, in which case a first locking bolt 73 firmly on the second subelement 65 is arranged, wherein a second locking pin 75 firmly on the first subelement 63 is arranged. Behind the locking arms 69 . 71 their respective assigned locking pin 73 . 75 in a first pivotal position in a locking manner, the two sub-elements 63 . 65 firmly arranged together in the closed state. To the two sub-elements 63 . 65 It is possible to separate the locking arms 69 . 71 to relocate to a second, open pivot position, in which they the locking bolt 73 . 75 do not back up. The two subelements 63 . 65 can then be taken apart or separated from each other. In this way, it is very easy and without cutting possible, the preform of the separating elements 11 to separate.

Overall, it is found that by means of the device and the method, a low-friction, low-deformation, reproducible and simple production of a preform from a plurality of fiber layers by forming is possible.

Claims (10)

Process for producing a preform from at least two fiber layers ( 3 . 5 ), comprising the following steps: arranging a separating element ( 11 . 13 . 37 ) between a first fiber layer ( 3 ) and a second fiber layer ( 5 ), - reshaping the fiber layers ( 3 . 5 ) to a preform, wherein the separating element ( 11 . 13 . 37 ) a plurality of piezo actuators ( 17 ), which are excited to vibrate. Method according to claim 1, characterized in that a separating element ( 11 . 13 . 37 ) on which the piezo actuators ( 17 ) are arranged in a segmented arrangement. Method according to one of the preceding claims, characterized in that a collection of the fiber layers ( 3 . 5 ) during forming by means of a hold-down device ( 25 ), wherein the hold-down device ( 25 ) a plurality of local clamping elements ( 31 ), wherein the individual, local clamping elements ( 31 ) preferably be controlled separately. Method according to one of the preceding claims, characterized in that the piezo actuators ( 17 ) as local clamping elements ( 31 ), and / or that at least one local clamping element ( 31 ) a tie rod ( 33 ) As an actuating element. Device for producing a preform by forming at least two fiber layers ( 3 . 5 ), in particular for carrying out a method according to one of claims 1 to 4, 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 . 37 ), which is arranged for arrangement between the fiber layers ( 3 . 5 ) during the forming, wherein the separating element ( 11 . 13 . 37 ) a plurality of piezo actuators ( 17 ), which are excitable to vibrations. Contraption ( 1 ) according to claim 5, characterized in that the separating element ( 11 . 13 . 37 ) a preforming recess ( 15 ), wherein a plurality of radially inwardly to the Vorformausnehmung ( 15 ) protruding tongues ( 21 ), wherein the tongues ( 21 ) the preforming recess ( 15 ) preferably surrounded in segments. Contraption ( 1 ) according to one of claims 5 and 6, characterized in that the device ( 1 ) a hold-down device ( 25 ), wherein the hold-down device ( 25 ) a plurality of local clamping elements ( 31 ) having. Contraption ( 1 ) according to one of claims 5 to 7, characterized in that the device ( 1 ) the at least one separating element ( 11 . 13 . 37 ) edge-holding strut element ( 41 ), wherein the strut element ( 41 ) preferably an attack element ( 45 ) for a gripper. Contraption ( 1 ) according to one of claims 5 to 8, characterized in that the separating element ( 11 . 13 . 37 ) has at least one joint, wherein at least two parts of the separating element about an axis determined by the hinge are pivotable relative to each other. Contraption ( 1 ) according to one of claims 5 to 9, characterized in that the separating element ( 11 . 13 . 37 ) is formed at least in two parts, wherein a locking mechanism ( 67 ) for connecting and disconnecting at least two subelements ( 63 . 65 ) of the separating element ( 11 . 13 . 37 ) is provided.

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