Abstract:
A laying head for manufacturing a three-dimensional preform includes an inlet configured to feed in a plurality of dry rovings. A fiber conveying device simultaneously and mutually-independently conveys, in a fiber supplying direction, the rovings fed-in via the inlet. An outlet is arranged downstream of the fiber conveying device in the fiber supplying direction and simultaneously lays the plurality of rovings on a workpiece carrier to manufacture the three-dimensional preform. A fiber-cutting device is disposed downstream of the fiber conveying device and upstream of the outlet in the fiber supplying direction and cuts the rovings. A nozzle applies a medium onto the rovings. A slit-shaped through gap of the nozzle has a height is equal to the height of the dry rovings in the thickness direction plus a margin that is sufficiently small so as to cause the medium to be forcibly embedded into the dry rovings.

Description:
CROSS-REFERENCE 
     This application is the U.S. national stage of International Application No. PCT/EP2013/001056 filed on Apr. 10, 2013, which claims priority to German patent application no. 10 2012 007 439.5 filed on Apr. 13, 2012. 
     TECHNICAL FIELD 
     The present invention relates to a laying head and to an apparatus and a method for manufacturing a three-dimensional preform for a structural component from a fiber composite material. 
     RELATED ART 
     A laying head, an apparatus and a method for manufacturing a three-dimensional preform for a structural component from a fiber composite material are known from WO 2011/128110 A1. Reference is made to the description of the prior art and the technical background on pages 1 to 3 of this printed publication. It is taught in the printed publication how a plurality of dry rovings can be supplied to a laying head and can be laid on a corresponding three-dimensional workpiece carrier for forming a three-dimensional preform, in order to manufacture a structural component preform for a structural component made of fiber composite materials. 
     In this respect, so-called rovings are the starting material, as in the present application. A roving is a yarn that is comprised of a plurality of filaments made of the fiber material, which one could characterize as the actual fibers. Carbon fibers, glass fibers, aramid fibers, etc. are preferably used as fiber composite materials. Such a roving can be comprised of several, such as e.g., 8 or 10, filaments up to some 10,000 or more filaments. A 50 k roving is comprised, for example, of 50,000 filaments. 
     In the present application, the term fiber indicates a roving except when reference is explicitly made to individual filaments. 
     WO 2011/128110 A1 discloses the fixing of the beginnings and ends of the rovings at the edge of the workpiece carrier using adhesive. 
     Further devices and methods for attaching or embedding adhesive onto or into rovings are known from WO 2009/077581 A2, EP 2 433 784 A1, WO 2009/158262 A1 and US 2011/0083605 A1. 
     SUMMARY 
     In view of the above-noted problems, improved techniques for fixing the rovings and for applying media such as adhesive, binders, impregnating resins and the like are disclosed herein. 
     In one aspect of the present teachings, a laying head for manufacturing a three-dimensional preform includes an inlet configured to feed in a plurality of dry rovings. A fiber conveying device simultaneously and mutually-independently conveys, in a fiber supplying direction, the rovings fed-in via the inlet. An outlet is arranged downstream of the fiber conveying device in the fiber supplying direction and simultaneously lays the plurality of rovings on a workpiece carrier to manufacture the three-dimensional preform. A fiber-cutting device is disposed downstream of the fiber conveying device and upstream of the outlet in the fiber supplying direction and cuts the rovings. A nozzle applies a medium onto the rovings. A slit-shaped through gap(s) of the nozzle has/have a height is equal to the height of the dry rovings in the thickness direction plus a margin that is sufficiently small so as to cause the medium to be forcibly embedded (impregnated, permeated, introduced, penetrated) into the dry rovings. 
     In particular, it is made possible to impregnate a medium into the rovings by using a nozzle, i.e. to not only apply the medium, such as an adhesive, a binder or a resin onto a roving from the outside, but also to permeate the roving with the medium. 
     This makes possible a fixing of the to-be-laid fiber set or rovings in the fixing area of the workpiece carrier with a low cutting waste. 
     The process stability can be enhanced because all filaments are embedded in adhesive/binder/resin at the ends of the corresponding rovings, and thereby cannot be moved unexpectedly somewhere else. 
     In a preferred embodiment, the segments of the rovings impregnated with adhesive can be centrally severed at the end of a laying path such that the adhering portion for the end fixing of the rovings of the current laying path and the adhering portion for the start fixing of the next laying path are simultaneously obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will be apparent from the description of embodiments referring to the drawings. 
         FIG. 1 a    shows a schematic view of a robot with a laying head, roving bobbins and a workpiece carrier, and  FIG. 1 b    shows a view of the front end of the robot with a laying head during the laying of a fiber set onto the workpiece carrier. 
         FIG. 2 a    shows a view of a workpiece carrier, and in  FIGS. 2 b , 2 c  and 2 d    show fiber layers laid on the workpiece carrier. 
         FIG. 3 a    shows a perspective view of a portion of a laying head according to a first embodiment, and  FIG. 3 b    shows a side view of a portion of the laying head. 
         FIG. 4 a    shows a schematic perspective view of a nozzle according to one embodiment of the present teachings,  FIG. 4 b    shows a perspective schematic view of a rear portion of the nozzle of  FIG. 4 a   , and  FIG. 4 c    shows a front view of the portion of  FIG. 4   b.    
         FIG. 5 a    shows a front view of the nozzle of  FIG. 4 a   ,  FIG. 5 b    shows a top view of the nozzle of  FIG. 5 a   , and the upper portion of  FIG. 5 c    shows a side view of the nozzle of  FIG. 5 a    the lower portion of  FIG. 5 c    shows an enlarged view of the above portion surrounded with a dashed line. 
         FIG. 6 a    shows a schematic illustration of an impregnated roving before it is cut and  FIG. 6 b    shows the impregnated roving after it has been cut. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 a  and 1 b    schematically show a robot  10 , to which a laying head  20  is attached. A workpiece carrier  40  is held on a support  15  for the workpiece carrier. It is schematically shown that the laying head  20  is configured to simultaneously lay a fiber set  30  made of plural rovings onto the workpiece carrier  40 . In  FIG. 1 a   ), 5 bobbins  51  of a fiber supplying mechanism  50  are shown, onto which the fibers (rovings)  33  are wound and from where they are supplied to the laying head  20  via the fiber supplying mechanism  50 . In  FIG. 1 b   ), only 4 rovings are schematically shown. The fiber set  30  can comprise a plurality n of rovings, where n=2, 3 . . . , wherein n=8 or n=16 or n=32 are presently preferred. 
     The arrangement serves to manufacture a three-dimensional preform for a structural component made of a fiber composite material having a multi-layer, multi-axial fiber architecture (MAFA) similar to a multi-axial fabric (MAF). 
     The fiber supplying mechanism  50  preferably includes a fiber guiding mechanism, which is preferably configured in the manner that is shown in FIGS. 12, 13 of WO 2011/128110 A1 and is described with respect to these figures. 
     According to one embodiment, the workpiece carrier  40  has a workpiece forming area  41  and an edge-fixing area  42 , as shown in  FIG. 2 a   ). The workpiece forming area  41  corresponds to the desired three-dimensional shape of the preform. The edge-fixing area  42  serves to fix the rovings  33  in the edge area of the workpiece carrier  40 . 
     In  FIG. 2 b   ), the workpiece carrier is shown with a first fiber layer  31   a , which has been laid on the workpiece carrier in a first orientation (=axial direction). As indicated in  FIG. 2 b   ), the fiber layer  31   a  is comprised of rovings  33  that have been laid in this axial direction. In  FIG. 2 c   ), the same workpiece carrier  40  is shown, on which a second fiber layer  31   b  has been laid over the first fiber layer  31   a . The fibers of the second fiber layer  31   b  have an orientation of −45 degrees relative to the orientation of the first fiber layer  31   a . It is shown in  FIG. 2 d   ) how a third fiber layer  31   c  has been laid over the second fiber layer  31   b , wherein it has been laid only on a part of the workpiece carrier  40 . The third layer  31   c  has an orientation of +45 degrees relative to the first layer and thus of 90 degrees relative to the second layer  31   b . The three layers  31   a  to  31   c  form a multi-layer, multi-axial fiber architecture (MAFA)  31 . 
     Again referring to  FIG. 1 a   ), it can be recognized that the laying head  20  has an inlet  20   e , via which the dry rovings  33  are supplied to the laying head. The laying head  20  further has an outlet  20   a , from which the rovings  33  are output for laying onto the workpiece carrier  40 , wherein a pressing roller  20   r  is arranged at the output  20   a , using which the outputted rovings  33  can be pressed, if necessary, against the workpiece carrier  40 . In  FIG. 1 a   ), a fiber supplying direction V for the direction of the conveying or feeding of the rovings  33  is indicated. A fiber conveying device  20   f  is provided downstream of the inlet  20   e  of the laying head  20  in the fiber supplying direction V. This fiber conveying device can be implemented, for example, by a conveying unit as described in US 2009/0229760 A1. In principle, such a fiber supply according to the Eytelwein principle is known. As for the rest concerning the fiber conveying device, reference is made to the above-mentioned US 2009/0229760 A1 and the above-mentioned WO 2011/128110 A1. 
     A fiber treatment unit  20   b  is schematically shown in  FIG. 1 a   ) downstream of the fiber conveying device  20   f  in the fiber supplying direction V. This fiber treatment unit  20   b  will be described in more detail in the following with reference to  FIGS. 3 a   ) and  b ). In  FIG. 3 a   ), the portion  20   b  of the laying head for guiding and treatment of the rovings  33  or Ri, Rj, respectively, is shown in a perspective view in the supply direction V downstream of the fiber conveying device  20   f  until the pressing roller  20   r . In  FIG. 3 b   ), the same segment  20   b  of the interior of the laying head  20  is schematically shown in a side view. In the depicted embodiment of the laying head, the rovings  33  supplied via the inlet  20   e  into the laying head  20  are divided into two groups of rovings Ri (i=1, 3, 5 . . . ) and Rj (=2, 4, 6 . . . ). Group Ri includes the even-numbered rovings  33  and group Rj includes the odd-numbered rovings  33 . In the depicted embodiment, n=16, such that 8 rovings are present in group Ri (I=1, . . . 15) and 8 rovings are present in group Rj (j=2, . . . 16). Groups Ri and Rj are guided and treated on two separated paths P 1  and P 2 . 
     The division into the two groups and into the separate paths P 1  and P 2  is not necessary. A single path without division could be present, too. On the other hand, a plurality of more than two groups and paths could be implemented as well. 
     The treatment unit  20   b  for path P 1  will be described in the following. The description applies in an analogous manner for path P 2 . The reference numerals indicated with i for path P 1  have a j instead of an i for path P 2 . 
     The rovings  33 , Ri are conveyed by the fiber conveying device  20   f  in the fiber supplying direction V and arrive downstream at a nozzle  22 ,  22   i  for applying and embedding a medium M into the rovings, which will be described in more detail hereinafter. The nozzle is adapted for applying a medium (adhesive, binder, resin, and the like) in such a manner that the medium is applied onto both sides of the rovings and is embedded (is impregnated) into the rovings. This applying and embedding on both sides can be done continuously or clocked in sections. 
     In the following, a corresponding description is provided for the case, in which the medium is a so-called Hot-Melt Adhesive. Such a Hot-Melt Adhesive is adhesive above a predetermined temperature and is not adhesive below the predetermined temperature (hereinafter indicated as the adhering temperature) but is still elastic over a significant temperature range. 
     When using such a Hot-Melt Adhesive, it is preferred that a cooling device  23 ,  23   i  for cooling the rovings having the applied and embedded adhesive to below the adhering temperature is provided downstream of the nozzle  22  in the supplying direction V. 
     In the treatment unit  20   b  of the embodiment shown in  FIG. 3 , an intermediate conveying device  24 ,  24   i  is preferably provided downstream of the nozzle  22  in the supplying direction V, when the cooling device  23  is present, then preferably downstream of the cooling device  23 . The intermediate conveying device serves to reliably convey the rovings downstream of the nozzle  22 . A fiber-cutting device  21 ,  21   i  is provided downstream of the nozzle  22  in the supplying direction V and, when the cooling device  23  and/or the intermediate conveying device  24  is present, then preferably downstream of these devices. The fiber-cutting device  21  is adapted to cut the rovings. Reference is made to FIG. 9 of WO 2011/128110 A1 and the corresponding description with regard to concrete embodiments of the fiber-cutting device. 
     As was already explained above, a pressing roller  20   r  is arranged at the outlet  20   a  of the laying head  20 . A heating device  25 ,  25   i   1 ,  25   i   2  is provided upstream of the pressing roller  20   r  and downstream of the fiber cutting device  21 ,  21   i  in the supplying direction V. In the depicted embodiment, the heating device  25   i  includes two elements indicated with  25   i   1  and  25   i   2 . The first element  25   i   1  provided closer to the pressing roller  25   r  in the supplying direction V is an end-heater that serves to again heat the adhesive applied onto and embedded into the rovings  33 Ri above the adhering temperature (e.g., 100° C.). The second element  25   i   2  is a heater for maintaining a predetermined temperature (e.g., 70° C.) of the rovings (temperature holding heater). 
     When the rovings  33 Ri have been cut by the fiber cutting device  21 ,  21   i , the end of the rovings  33 Ri positioned upstream of the cutting plane can thus include adhesive. In order to prevent this adhesive from cooling down too far below the adhering temperature, this portion of the rovings can be kept at a temperature below, but close to, the adhering temperature by using the temperature-holding heater  25   i   2 . 
     The laying head  20  and the robot  10  as well as the individual components of the laying head  20  are controlled by a not-shown control device. 
     The workpiece carrier  40  is shown in  FIG. 3  as a planar workpiece carrier. This serves merely for simplification of the illustration. 
     In the following, the design of the nozzle  22 ,  22   i ,  22   j  will be described in more detail with reference to  FIGS. 4 and 5 . 
     In  FIG. 4 a   ), a perspective view of the nozzle  22  is shown in a schematic illustration. A roving  33  is supplied in the supplying direction V into the nozzle  22  via a guiding path  22   b  formed on a protrusion  22 P, which guiding path  22   b  is planar in the depicted embodiment. The medium (e.g., adhesive) M is supplied via an opening provided on the upper side. In  FIG. 4 a   ), the body of the nozzle  22  downstream of the protrusion is shown as being comprised of four parts  22 - 1  to  22 - 4 , which are held together by screws (not shown). This can also be easily recognized in the side view of  FIG. 5 c   ). In  FIGS. 4 b   ) and  c ), only the rear portion is shown. A coordinate system l-d-b is introduced to describe the formation of the nozzle  22  and the adaptation to the feeding-through of the rovings  33 , in which coordinate system axis l points in the longitudinal direction of the rovings  33 , which corresponds to the supplying direction V, direction d points in the direction of the thickness of the rovings, and direction b points in the direction of the width of the rovings. As can be easily recognized in  FIGS. 4 b   ),  c ) and  5   a ) to  c ), the nozzle  22  has a slit  22   s  that is adapted in its height and width to the dimensions of the to-be-fed-through rovings  33 . The height s in direction d of the slit corresponds to the height of the rovings  33  with a predetermined margin. The slit  22   s  thus extends in a slit plane l-b with a height s in the thickness direction perpendicular to the slit plane l-b. The determination of the margin will be explained in the following. The width of the slit  22   s , which is not provided with a reference numeral, corresponds to the width of the rovings with a like-wise predetermined margin. 
     The nozzle has a channel system  22   k  that feeds two dispensers  22   v  with the medium M supplied via the inlet  22   e . In case of the Hot-Melt Adhesive, the same is supplied via the inlet  22   e  at a pressure of, for example, 50 bar. 
     One dispenser  22   v  is respectively provided in the nozzle  22  above and below the feed-through slit  22   s . An adhesive applier formed as a nozzle gap  22   d  leads from the dispenser  22   v  located above the feed-through slit  22   s  to the feed-through slit. The nozzle gap  22   d  preferably has the width of the slit  22   s . In the same manner, an adhesive applier formed as a nozzle gap  22   d  leads from the dispenser  22   v  located below the feed-through slit  22   s  to the same. 
     When the medium M is supplied accordingly, it is thus applied to the upper side and to the lower side of a fed-through roving  33  via the nozzle gap  22   d . By moving the roving in supplying direction V, it can be applied, in accordance with the controlled supply, section-wise or clocked or continuously. 
     In order to not only apply the adhesive onto the roving but also to impregnate it into the roving, the dimensions of the feed-through slit  22   s  are adapted in accordance with the dimensions of the roving and the nature of the adhesive or of another medium as well as the supply pressure. 
     An impregnation is thereby made possible without a redirection of the rovings perpendicular to the supplying direction V. Furthermore, it is made possible to stop the adhesive application in a defined manner. An interruption of the adhesive supply by closing a valve leads to a loss of pressure and thus to an abrupt end of the application. 
     For a typical Hot-Melt Adhesive having an adhering temperature of approx. 150° C. and a supply pressure of approx. 50 bar, a margin of 0.05 to 0.1 mm can be selected for a 50 k roving having a 12 mm width and a thickness of approx. 0.3 mm to 0.35 mm in order to not only apply the Hot-Melt Adhesive onto the roving, but to also embed the same into the roving, i.e. in order to impregnate the same. In such a case, the height of the slit  22   s  is thus, e.g., 0.4 mm. The open width w of the gap  22   d  falls then in the range of 0.025 to 1 mm, thus, e.g., 0.05 mm. 
     Assisting measures such as a light combing of the rovings directly before the medium supply or the like are possible for the assistance (see also the fiber preparation described in WO 2011/128110 A1). In general, for rovings having widths in the range of 5 to 100 mm and thicknesses in the range of 0.2 to 0.6 mm, the margin should be in the range of 0.025 to 0.2 mm in the height direction d and/or in the width direction b. 
     For a roving and material combination, in which the impregnating is easy, a single feed-through slit can be provided for all or plural rovings of one supply path P 1 , P 2 . It is, however, preferable to provide a separate feed-through slit  22   s  per individual roving. 
     In particular, adhesives that are suitable for the start and end fixation of the fiber layers  31   a, b, c  or their intermediate fixation, such as, for example, adhesives based on EVA or polyolefin or epoxy, are possibilities as the media. Binders and resins also are possibilities as the media. In this respect, binders are used to apply the dry rovings with binder when laying the same, in order to obtain an easily-manageable, dry (e.g. including no resin) preform and to avoid a slippage of the fibers during preform manufacturing. The application and embedding of resin can be used so that the resin does not have to be embedded into the preform in a process subsequent to the formation of the preform, but rather the impregnation with the resin occurs directly when laying the fibers (Online-Prepregging). If plural media should be applied, a separate nozzle  22  for each medium can be provided in each path P 1 , P 2 . 
     With respect to the binders and the resin, it noted that the application in the laying head  20 , in particular with the described nozzle  22 , makes possible the handling of dry rovings from the bobbin until downstream of the fiber conveying device in the laying head  20  and thus high velocities, etc. 
     The described laying head or an apparatus for manufacturing a three-dimensional preform for a structural member made of a fiber composite material using such a laying head can thus be used with a method of the type described in WO 2011/128110 A1 in a very advantageous manner and can further improve the same. 
     In particular, a further improvement of a method for manufacturing a preform for a structural member from a fiber composite material is made possible, in which the fixation of the end portions of the rovings on both sides of a cutting can be achieved in a very advantageous manner. 
     This will be explained with reference to a case, in which dry rovings are laid on the workpiece carrier  40 . A roving  33  is, as can be seen in  FIG. 6 a   ), coated over a predetermined length l with the medium M, which is a Hot-Melt Adhesive in this case, and is eventually impregnated. The length l shown in  FIG. 6 a   ) includes at least the predetermined lengths l 1  and l 2  shown in  FIG. 6 b   ), i.e. l≧l 1 +l 2 . The roving  33  is cut by the fiber cutting device  21  at a position determined such that, after the performance of the cutting along the cutting plane S, the end  33   e  can be fixed at the end of a laying path in the edge-fixing area with the adhesive M over the first predetermined length l 1 . On the other side of the cut S, the adhesive M is present with the second predetermined length l 2  at the downstream front end of the remaining portion of the roving  33 , with which the roving  33  can be fixed on the workpiece carrier  40  at the beginning of the laying of the next laying path. 
     In general, this is not limited to an edge fixation but can also be applied in an analogous manner to the application of intermediate reinforcements or the like. 
     In the described embodiment the nozzle gaps end on one line relative to the supplying direction. Alternatively, they could also be offset in the supplying direction V. The nozzle gaps are preferably formed in a linear manner. Alternatively, holes arranged in a linear manner or in a matrix are possible as the outlet of the media applicator  22   d . The downstream lip of the nozzle gap  22   d  can be formed protruding into the slit  22   s , in order to perform a scraping (wiping) function. 
     The design of the nozzle  22  with the four parts  22 - 1  to  22 - 4  makes it possible to provide the nozzle gap  22   d  and the slit  22   s  at the front faces of the four parts, which enables a simple manufacturing. 
     It is explicitly emphasized that the individual elements and method steps which have been described are also disclosed separately as independent subject-matters. For example, the configuration of the nozzle  22  is independent of the precise configuration of the laying head or of the placement within a laying head. The method described with respect to  FIG. 6  also can generally be implemented without the laying head and/or the described nozzle. The same applies in an analogous manner to the other described elements and method steps such as the heating device, the cooling device, the division of the paths, etc. 
     In the above-described embodiment, the medium such as, e.g., the adhesive is applied to and embedded into the rovings on both sides. The construction of the nozzle has been adapted in a corresponding manner. Alternatively, it is possible to achieve an application and embedding of the medium onto and into the rovings  33  with a single-sided media supply, as described hereinafter. The previous approaches to applying media such as adhesive, binder, resin have, in essence, taught a type of contact-less or pressure-less application. The above-described nozzle results in that the medium is not only brought into contact with the rovings but is also pressed into the roving. This can also be achieved with a single-sided media supply, i.e. in case, e.g., only the upper nozzle  22   d  in  FIGS. 4, 5  is present, in case the medium is nevertheless pressed under pressure into the roving. This is achieved by having a type of counter bearing present on the other side of the roving, i.e. the opposite side of the feed-through slit  22   s , so that the medium is pressed under pressure into the roving. To promote the impregnation, in particular in the case of a single-sided media supply, it is preferable to reduce the area density of the roving. This can be achieved, for example, by combing, spreading or other known measures for reducing the area density. In the present application, a single-sided or two-sided application refers to the width sides of the roving, i.e. to the sides extending in the plane l-b in  FIG. 4 b   ). 
     It is explicitly stated that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure as well as for the purpose of restricting the claimed invention independent of the composition of the features in the embodiments and/or the claims. It is explicitly stated that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure as well as for the purpose of restricting the claimed invention, in particular as limits of value ranges.