Abstract:
In a device and method for manufacturing preforms of fiber reinforced plastic, in a first step, continuously supplied fiber layers are laterally reshaped in a predetermined manner, and the section that is obtained is curved longitudinally in a specific manner in a second step.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2010 014 704.4 filed on Apr. 12, 2010. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a device and a method for manufacturing preforms of fiber reinforced plastic. 
         [0003]    Today, glass fiber reinforced plastics (GFRP) and carbon reinforced plastics (CRP) are chosen increasingly often for use as the material for highly diverse applications. This is due to a growing demand for lightweight construction solutions. In the field of machine engineering and, in particular, aerotechnics and space engineering, and in the construction of wind power plants, highly stable and extremely lightweight solutions based on GFRP and CRP have become indispensible. 
         [0004]    The advantageous properties of these materials have also proven valuable in automotive and aircraft construction, of course. Predictions call for an increasing use of GFRP and CRP components for production of very large quantities in automotive construction in particular. 
         [0005]    In aircraft construction, which deals primarily with moving large masses, the performance of a product can be increased greatly by the use of lightweight construction solutions. For example, reducing weight can also help to minimize perpetual costs such as fuel costs. 
         [0006]    The advantage of fiber reinforced plastics is their high specific strength and stiffness combined with very low density. This is a clear advantage over metallic materials. Due to the very low density of the fibers used, and given that density of the plastics used is even lower, these lightweight construction materials are clearly superior to classically used metallic materials in terms of weight. 
         [0007]    The entire production of components made of fiber reinforced plastics is still highly manually oriented. This results in very high production costs, thereby rendering production of large quantities, let alone mass production, unaffordable at this time. Semi-automated or fully automated processes have become known only for components having very simple geometries. For example, pultrusion is used to manufacture straight shapes having a constant cross section. This is suitable for manufacturing plastic railings, plastic ladders, tent stakes, or bed frames, for example. 
         [0008]    The curved structural components required in the aircraft and automobile industries in particular can only be produced manually at this time, which is an elaborate and tedious process. It is precisely such curved parts composed of fiber reinforced plastics, which are often required for aerodynamic reasons or due to greater stiffness, that are becoming increasingly significant in the field of automobile or aircraft construction. 
         [0009]    To manufacture components having greater geometric complexity, so-called “integral components”, the desired structures composed of fiber semi-finished products such as rovings, wovens, non-wovens, fleeces, interwovens, or the like, are first draped into the desired shape. This takes place, for instance, by using a certain precut blank of the materials which are then draped around or in devices that are convex, concave, or have other three-dimensional shapes. Finally, the formed bodies, which are usually composed of a plurality of semi-finished products, are sewn together and impregnated with a plastic which sets to form the so-called matrix. 
         [0010]    The disadvantages of this manufacturing method are, in particular, the small holes produced during sewing, which can negatively affect stability, for instance, since the seams can also destroy fibers. 
         [0011]    Document EP 1 504 880 A makes known an automated process and a machine intended for use therefor, by way of which components having simpler geometric shapes, such as L, S, H, or hat shapes, can be manufactured out of prepregs in a semi-automated process. Slight curvatures can be created by tightening up the prepregs that are used in a special pressing mold during the process of manufacturing the component such that the component has a respective radius. 
         [0012]    The disadvantage of such a method is that only very slight curvatures can be produced, and only prepregs but no other types of starting materials can be used. Prepregs are expensive and they must be covered with special sheets when stored, to prevent them from sticking together. These sheets must be removed, of course, before various layers are combined. This also complicates a continuous production of components. In addition, prepregs have a limited storage life before processing, and they must be stored in cool conditions. 
         [0013]    Furthermore, the prepreg stack that was formed must be covered with other special sheets at the top and the bottom, to prevent them from sticking in the heated press. 
         [0014]    To attain a desired curvature, these sheets must be prefabricated with precisely this curvature, which also requires a considerable amount of effort. 
         [0015]    If structural components having greater complexity are required, for instance, they must be manufactured at this time as individual components having a simple geometry, which can then be combined to form the desired assembly using complex assembly processes. This production method results in very high costs, greater weight, and very long production times. 
       SUMMARY OF THE INVENTION 
       [0016]    The problem addressed by the present invention is therefore that of providing a method and a device which enable preforms and components made of fiber reinforced plastics to be manufactured more cost effectively. 
         [0017]    This problem is solved by a method for the manufacture of preforms of fiber reinforced plastic and by a device for carrying out such a method in accordance with the present invention. 
         [0018]    Using the method according to the invention for manufacturing preforms of fiber reinforced plastic, continuously supplied fiber layers are first reshaped into a predetermined cross section by way of transverse reshaping. A profile produced in this manner is then curved in a specific manner by longitudinal reshaping in a further step. 
         [0019]    The method according to the invention offers many advantages. One considerable advantage is that a structural component having high geometric complexity can be manufactured continuously and in an automated manner. The transverse reshaping into a target cross section is attained by way of reshaping using CNC-machined mold cores. In that particular case, the fiber layers are shaped around the mold cores using pressure rollers, and thereby gradually assume the desired section shape. A further advantage is that curved components can also be manufactured using the method according to the invention. It is also particularly advantageous that dry fiber material, which does not stick together and is easily stored, can also be used for this method. 
         [0020]    This applies primarily to the manufacture of complex structural components. The preforms are therefore preferably composed of at least two sections. 
         [0021]    To provide a truly continuous method which is also rapid, it is particularly preferable to manufacture at least two sections for a preform in parallel and simultaneously, and to subsequently combine them to form one component. 
         [0022]    According to preferred embodiments, the fiber layers are stored on reels or bobbins, and are delivered to the production process from a stockpiling unit. Continuous production can be ensured as a result. 
         [0023]    It is particularly preferable for necessary bobbin changes to take place automatically. However, it is feasible and possible to continuously prefabricate the fiber layers in a special production device or development unit situated upstream of the process. 
         [0024]    Dry fiber material, rovings, wovens, non-wovens, fleeces, interwovens or are preferably used as fiber layers. They are subsequently enclosed in a matrix of thermoplastic material. The plastic that is used need not always be applied to the fiber layers. For example, the fiber layers can also be fabricated using fibers sheathed in plastic. In that case, individual fibers or a certain portion of the fibers or every fiber can be sheathed separately. They can be used to manufacture a woven material or the like. It is also feasible to use thermosetting plastics for the matrix. Prepregs are already prepregnated with a binder system. 
         [0025]    To prevent any stress in the component, the fiber layers in preferred embodiments are introduced into the process relieved of strain. This strain relief can be controllable and delivers the fiber layers to the production process in an oriented and controlled manner by way of a jockey roller system or levelled rollers, for example. 
         [0026]    Particularly preferably, the fiber layers of at least one section can be set only at certain points before the transverse reshaping. This is particularly important for sections having unidirectional fiber layers that cannot be extended in the longitudinal reshaping process. Punctiform setting therefore does not take place in the region of the eventual outer radius in particular, since the fiber layers must remain mobile relative to one another for the longitudinal reshaping. 
         [0027]    The thermoplastic materials are preferably activated using a heating device. Infrared radiators are advantageous in that particular case. 
         [0028]    Particularly preferably, they can be swivelled and/or rotated in particular. It is thereby possible to prevent the material from overheating if production is delayed. This can also be accomplished by covering the radiator. 
         [0029]    Since various applications require different components having various radii, it is provided in preferred embodiments that the radius induced in the section in the longitudinal reshaping is variable. It is also feasible and reasonable to change the radius during the production of a section. 
         [0030]    According to preferred embodiments, the sections that are produced are cut directly to the desired length. Production can be interrupted briefly for this purpose, although it is also feasible in particular to provide a displaceable cutting unit which is synchronized with the production process. As a result the sections can also be cut to the desired size without interrupting production. 
         [0031]    The sections that are cut to the proper length in this manner are then, particularly preferably, transferred by a handling unit—which can be a robot—to an assembly and compacting unit. The robot can have a gripper arm comprising a vacuum device, for example, by way of which the finished sections are transported. The robot can grip components having a radius of between 1500 and 2500 mm, for example. 
         [0032]    The device according to the invention for the continuous manufacture of preforms of fiber reinforced plastic has various regions. At least one stockpiling unit is provided, in which fiber layers can be stored on reels or bobbins. At least one heating unit is provided, by way of which the fiber layers can be heated, using infrared radiators, for example. At least one transverse reshaping unit and at least one longitudinal reshaping unit are also provided. The fiber layers to be processed can be supplied continuously from the stockpiling unit. The fiber layers can be reshaped in the transverse reshaping unit into a section having a predetermined cross section. This section can then be curved in the longitudinal reshaping unit into a predetermined radius. 
         [0033]    To enable a binder system to be applied to the fiber layers if pretreated fiber layers such as prepregs are not used, a binder application module is provided according to preferred embodiments. It can be used to apply the binder system locally onto the fiber layers, although the complete fiber layers can also be provided with the binder system. The binder system can be present in powder form, for instance, and can be applied onto the fiber layers using a perforated plate and a rotating carriage. Liquid binder systems which can be applied as an aerosol using a spray head, for instance, are also feasible. 
         [0034]    Particularly preferably the device comprises at least one of the following modules: Inductor unit, binder application module, cutting unit, handling unit, and/or assembly device, 
         [0035]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  a schematic depiction of the device according to the invention, in a perspective side view; 
           [0037]      FIG. 2  a principle sketch according to  FIG. 1 , in a perspective side view; 
           [0038]      FIG. 3  a further principle sketch of the device according to the invention, in a side view; 
           [0039]      FIG. 4   a  a schematic depiction of the transverse shaping unit; 
           [0040]      FIG. 4   b  a principle sketch according to  FIG. 4   a;    
           [0041]      FIG. 5   a  a schematic depiction of the longitudinal reshaping unit, in a side view; 
           [0042]      FIG. 5   b  a schematic depiction of the longitudinal reshaping unit, in a top view; 
           [0043]      FIG. 5   c  a principle sketch of the longitudinal reshaping unit according to  FIG. 5   b;    
           [0044]      FIG. 6  a schematic depiction of a binder application module in a perspective side view; 
           [0045]      FIG. 7  an LCF section manufactured using the method according to the invention 
           [0046]      FIG. 8  a schematically depicted cross section of an LCF section of the type shown in  FIG. 7 ; and 
           [0047]      FIGS. 9   a - g  a schematic depiction of the mode of operation of the assembly/compacting unit, in cross sections. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0048]      FIG. 1  shows an embodiment of a device  1  according to the invention. The system is composed of frames made of standard profiled elements. In selecting which components to use, particular attention is given to ease of replacement, temperature resistance up to at least approximately 200° C., acetone resistance, and very gentle of handling of material during the production process. Furthermore, the entire system can be lubricant-free, and therefore no limits are placed on the material selection. 
         [0049]    The framework has a modular design, and the installations for the related functional carriers are located inside the individual frames. As a result, the system can be adapted in an optimal manner to various requirements regarding the preform that is produced, and regarding the installation site. 
         [0050]    The system shown in  FIG. 1  has a length of 8 m, a width of 2.5 m, and a height of 2 m, for example. The individual modules have a unit height of 625 mm and a unit width of 500 mm. The length of the individual modules varies depending on the unit installed, wherein the modules are provided in a grid arrangement of 125 mm in this case. 
         [0051]    The system according to the invention is used to manufacture preforms or structural elements having complex geometries in one continuous process. This is achieved by manufacturing at least two sections in the system and then assembling them to form the complex structural element. To ensure that the process is rapid and continuous, at least two sections, which can have different cross sections, of course, can be manufactured in parallel/simultaneously in the system. This is shown as an example in  FIGS. 1-3  using the three production levels  17 ,  18 ,  19  shown. 
         [0052]    The system shown in  FIG. 1  has a stockpiling unit  2  containing a total of 10 modules. In this example, each module can accommodate two bobbins  15  having fiber layers  16 . Bobbins are provided for the +/−45° and the 0° layers of the sections. The method of bobbin replacement is designed such that bobbins can be replaced as quickly and in the most user-friendly manner possible. The +/−45° layers are particularly suited for draping, since a longitudinally lying strip can be reshaped into a curve without fibers being stretched or compressed in the inner or outer radius. 
         [0053]    In each production level  17 ,  18 ,  19 , a plurality of fiber layers from different bobbins can be introduced into the production process. 
         [0054]    To ensure that material is transported without delay and in a controlled manner, it is advantageous to provide UD portions in the fiber layers. Moreover, the bobbins are advantageously designed to be braked, thereby preventing the fiber layers from being introduced too quickly. For this purpose, the bobbins have a hollow core which is clamped between two displaceable, rotatably supported conical pieces. Braking takes place by way of a spring-loaded frictional element on one of the conical pieces, for example. Other braking systems are feasible, of course, such as magnetic powder or hysteresis brakes. 
         [0055]    Every module of the stockpiling unit has at least one rotatable removal device for safely unwinding the fiber layers from the bobbin. Rollers for levelling the material processions are provided at the end of each module of stockpiling device  2 . To ensure that the material is guided in a straight manner during unwinding, insertion rings are used as shoulder rings. 
         [0056]    Another possible method for the controlled unrolling of the individual fiber layers from the bobbins is a module which is not depicted in  FIGS. 1-3 , the strain relief unit. In that particular case, permanently levelled rollers are disposed at the entrance and the exit of the module. The function of strain relief is performed by rollers disposed therebetween in a displaceable manner on common vertical guides, which function as compensation elements depending on the tensile load. The individual fiber layers are thereby prevented from travelling at different speeds. This module can also be used in addition to the braked rollers. 
         [0057]    The next module in  FIGS. 1-3  is conveyor unit  3 . It is used to bring the individual fiber layers into their correct orientation. For this purpose, set collars are provided on rotatable rollers, which guide the individual fiber layers in terms of direction and can also specify the desired material width. At the end of this module the fiber layers that are used are combined to form one stack. 
         [0058]    In  FIGS. 1-3  an additional module is installed in the lowermost level  19  of the system. Inductor unit  4  is required for a special profile property. The device according to the invention, and the method according to the invention are described with reference to a system for manufacturing a special LCF section. This LCF section (preform)  30  is described in greater detail with reference to  FIGS. 7 and 8 . A section for this preform has a C shape and comprises unidirectional fiber layers in the two reshaped flange sides. They cannot be extended in a subsequent longitudinal reshaping, i.e. when a curvature is applied to the component. Therefore, the fiber layers for the C-shaped section must not be set completely. 
         [0059]    Inductor unit  4  is required for this purpose since it can be used to locally connect the fiber layers. As a result, the individual layers can still become displaced relative to one another in the region of the eventual outer radius. The required inductors are positioned using a pneumatic gripping mechanism. 
         [0060]    The module that contains heating unit  5  is used to join the fibers layers still moving loosely on top of one another such that deviations in direction are ruled out in the subsequent transverse reshaping. In the embodiment presented here, each of the sections that are ultimately assembled to form the preform comprises unidirectional fiber layers at least on one side in the ultimate flange region. They can be heated from both sides in heating unit  5  since they are still in the flat position in heating unit  5 . Various heat sources are feasible and possible. However, infrared radiators are used in the embodiment described herein, which heat only the unidirectional layers of the fiber layer stack in the process shown here. The infrared radiators can be swivelled, preferably through an angle of approximately 90°. They can also be swivelled away at any other angle, or they can be tilted away, moved laterally outwardly, or covered by metal plates, for example. Overheating of the fiber layers can therefore be prevented if the system should come to a standstill. 
         [0061]    The heated fiber layer stacks are then pressed together using pressure rollers at desired points to form a secure composite structure. The layered structure, which is otherwise still loose, is held in the desired shape using specially shaped guides, thereby also preventing individual layers from sliding off laterally. 
         [0062]    The following module, transverse reshaping unit  6 , brings the fiber layer stack into the correct cross section. The detailed mode of operation of this module is described with reference to  FIGS. 4   a  and  4   b.    
         [0063]    The next module is a conveyor unit  7  (see  FIG. 3 ). It is responsible for transporting the material within the production process. In the embodiment described, a pair of knurled, stainless steel rollers in the region of the segment of the component conveys the strand through the system. In that particular case, one roller is driven by a frequency-dependent servo gearbox motor, and the other, as a counter-roller, is controlled in a spring-loaded or pneumatic manner. The counter-roller can also be displaced in the vertical axis, thereby enabling the conveyance process to be adjusted such that optimal straight-ahead running and stress-free transfer of the section to the subsequent longitudinal reshaping unit  8  are ensured. The process speed can also be controlled by regulating the motor of the first roller. 
         [0064]    Longitudinal reshaping unit  8  is described in detail with reference to  FIGS. 5   a - c.    
         [0065]    As soon as the sections have been curved in a predetermined manner in longitudinal reshaping unit  8 , they are cut to the desired length in the subsequent module, cutting unit  9 . In the embodiment shown here, the pneumatic feed cylinder is mechanically coupled to the cutoff wheel drive. The cutoff wheel is also pneumatically controlled. 
         [0066]    The cutting unit can be disposed on a displacement table so it can be moved to the predetermined points for cutting the sections. 
         [0067]    It is possible to stop the continuous process briefly to perform the cutting. However, it is feasible and particularly preferable for the cutting unit to be synchronized with the section feed, so that the production process need not be interrupted. In this case, the cutting unit moves on the displacement table in a synchronized manner with the section feed, thereby enabling the section to also be cut during forward motion. 
         [0068]    The final module of the machine is a handling unit  10 . It comprises a positioning device (e.g. a robot)  11  and a handling device (assembly/compacting unit). Robot  11  transfers the individual sections into assembly unit  38 , in which the sections are assembled to form the finished preform. 
         [0069]    For transferring, robot  11  uses a robot gripper  14  attached to an arm  13  which can have movable joints. The robot can also stand on a base  15 . Robot gripper  14  has individual gripping elements which have a fixed distance in the longitudinal direction and are adjustable in the transverse direction. It is therefore possible to grip sections having a certain radius of curvature using the holding force of a vacuum. In the embodiment shown here, the radius of curvature can be between 1500 mm and 2500 mm. 
         [0070]      FIGS. 4   a  and  4   b  show an embodiment of reshaping device  6 . 
         [0071]    The schematic depiction presented in  FIG. 4   a  shows various driven and non-driven pressure rollers. Some rollers  21  press vertically onto fiber layers  16 . Other rollers  22  press fiber layers  16  around a CNC-machined mold core  20 . Rollers  23  are also provided at a 90° angle relative to the original fiber layers. Rollers  21 ,  22 ,  23  can have a shape that is convex, concave, or straight. It is also possible in particular for all rollers to be adjustable into certain contact angles. All shaping elements and all conveying elements used in the system are made of stainless steel material. 
         [0072]      FIG. 4   b  shows a similar reshaping device  6  in a schematic depiction. 
         [0073]      FIGS. 5   a -c show embodiments according to the invention of longitudinal reshaping unit  7 .  FIG. 5   a  shows a module having a longitudinal reshaping device  7 , in a perspective view from the side. 
         [0074]    Longitudinal reshaping unit  7  is shown from above in  FIG. 5   b . Radiant heaters  24  can also be assigned to longitudinal reshaping unit  7 . They can also be designed to be displaceable, swivellable, or tiltable, to prevent overheating. In this case as well, shielding can be used to keep heat away from the material. Cooling also takes place in this module. It may be accelerated by introducing cold air. 
         [0075]    In the embodiment described here, a toothed belt unit conveys the section through longitudinal reshaping unit  7 . The section moves over reshaping and guiding plates  25  which, in this embodiment, can be brought into a certain radius by way of a plunger  26  which can be displaced by a spindle  27 . Spindle  27  can be used to change a specified radius during production as well, and therefore a different radius can be formed along a section. 
         [0076]    Flexible conveyor belts, which in this embodiment can adapt to the radii of curvature of the section in the range of 1500 mm to 2500 mm, grip a flange of the section on both sides. Other radii are also feasible and possible, of course. The parallel guidance also results in a large working region for set up when the system is being started up. 
         [0077]      FIG. 6  shows a binder application module  28  according to the invention, in a perspective side view. In this module, fiber layers  16  can be provided with a binder system completely or only locally. For this purpose, a rotating carriage  29 , to the underside of which a perforated plate is attached, is used to apply a powdery binder to fiber layers  16  passing through. 
         [0078]    A shaft comprising guide vanes installed on the longitudinal side is supported in rotating carriage  29  and enables the vanes to rotate when the shaft is rotated, and delivers a consistent quantity of the binder onto the perforated plate. The rotational speed of rotating carriage  29  is matched to the feed rate of fiber layers  16 , thereby ensuring that a defined quantity of the powdered binder drops through the perforated plate onto fiber layers  16 . 
         [0079]    To bond the binder to the fiber layers, radiant heaters, in particular infrared radiators  24  in this case, are assigned to binder application module  28 . 
         [0080]      FIGS. 7 and 8  show a preform  30  that can be manufactured using an embodiment according to the invention.  FIG. 7  shows a schematic depiction with lateral surfaces  32 ,  33 ,  34 , and horizontal surface  31 . 
         [0081]    The special layered structure of this structural section is shown in a section in  FIG. 8 . In that particular case, three manufactured sections  35 ,  36 ,  37  are assembled in an assembly device  38  (see  FIG. 9 ). Two sections,  35  and  36 , have an S shape, and one section  37  has a C shape. Large S section  35  lies over small S section  36  and C section  37 , and forms horizontal surface  21 . Lateral surface  34  is composed of large and small S sections  35 ,  36 , respectively, lateral surface  33  is composed of small S section  36  and C section  37 , and lateral surface  32  is composed of large S section  35  and C section  37 . 
         [0082]    By connecting the three individual sections  35 ,  36 ,  37 , a highly complex and dimensionally stable structural component is obtained. 
         [0083]      FIGS. 9   a  to  9   g  show the assembly of a preform  30  (LCF section), according to the invention, out of three sections  35 ,  36 ,  37 . 
         [0084]    An assembly unit  38  having a base plate  42  and three rigid metal molds  39 ,  40 ,  41  is provided for this purpose. Metal mold  39  is securely connected to base plate  42 . The three sections are now inserted by robot  11  one after the other into assembly unit  38 . First, C section  37  is placed onto metal mold  39  ( FIG. 9   a ). Next, small S section  36  is placed onto metal mold  40 . Metal mold  40  can be displaced on the base plate and is slid directly against the C section on metal block  40  ( FIG. 9   b, c ). 
         [0085]    Next, large S section  35  is placed onto the two sections ( FIG. 9   d ). Metal mold  41 , which is designed as a displaceable lever, is now moved next to sections  35 ,  36 ,  37  and folded down to secure sections  35 ,  36 ,  37  ( FIGS. 9   e, f ). 
         [0086]    All metal blocks  39 ,  40 ,  41  are equipped with heating cartridges and activate the binder in the fiber layers, thereby joining the sections to form a preform. A vacuum diaphragm  43  provides the required process pressure ( FIG. 9   g ). 
         [0087]    The compacting carried out in assembly unit  38  minimizes the set-up time of the actual RTM curing device. 
         [0088]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions and methods differing from the types described above. 
         [0089]    While the invention has been illustrated and described as embodied in a method and device for manufacturing preforms of fiber reinfoced plastic, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0090]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.