Abstract:
A method for manufacturing a rotor blade for a wind turbine is provided. The method includes: a) arranging a first layup of fiber material inside a mold, the first layup corresponding to an airfoil of the rotor blade, b) arranging a second layup of fiber material on a core member before and/or after arranging the core member in the mold, the second layup including the core member corresponding to a web of the rotor blade, the core member comprising a recess configured to ensure a smooth transfer of loads into and out of the web, and c) curing a resin impregnating the fiber material of the first and second layup to form the rotor blade. The method is advantageous in that there is no need anymore to machine the recess into the cured web, thus saving man power and avoiding waste.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of European Application No. EP14158529 filed Mar. 10, 2014, incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to a method for manufacturing a rotor blade for a wind turbine. 
       BACKGROUND OF INVENTION 
       [0003]    Modern wind turbine rotor blades are built from fiber-reinforced composites combined with core members, such as balsa wood or plastic foam. 
         [0004]    For example, EP 2 123 431 A1 describes a method for manufacturing a rotor blade using a vacuum assisted resin transfer molding (VARTM)-process. In a first step of the manufacturing process, fiber material is laid onto a lower part and an upper part of a mold, respectively. The fiber material is secured in place by vacuum applied from beneath. Then, mold cores are covered in vacuum bags and are placed in the lower part of the mold together with a web (also known as shear web). Next, the upper part of the mold, together with the fiber material, is turned 180 degrees about its longitudinal axis and put into place so that the mold is closed. In a further step, vacuum is applied to the space between the mold cores and the mold. Then, resin is injected. When the resin has set, the mold cores are removed, the mold is opened and the cured blade is removed from the mold. 
         [0005]    The webs typically employed in the process are manufactured in a separate process. According to said separate process, plywood plates are covered with a fiber material. The fiber material is injected with a resin. Once the resin has set, the cured web comprising a fiber reinforced resin and a plywood core can be taken out of a corresponding mold. 
         [0006]    For some applications, the webs are required to have a recess at one end. The recess is configured to ensure a smooth transfer of loads into and out of the rotor blade, i.e. the recess avoids stress concentrations due to abrupt changes in the geometry. The recess is machined into said end of the web. In this process about 60-100 kg of web material need to be removed which requires substantial manpower and causes waste. 
       SUMMARY OF INVENTION 
       [0007]    One objective of the present invention is to provide an improved method for manufacturing a rotor blade for a wind turbine. 
         [0008]    Accordingly, a method for manufacturing a rotor blade for a wind turbine is provided. The method comprises: arranging a first layup of fiber material inside a mold, the first layup corresponding to an airfoil of the rotor blade, b) arranging a second layup of fiber material on a core member before and/or after arranging the core member in the mold, the second layup including the core member corresponding to a web of the rotor blade, the core member comprising a recess configured to ensure a smooth transfer of loads into and out of the web, and c) curing a resin impregnating the fiber material of the first and second layup to form the rotor blade. 
         [0009]    The method is advantageous in that there is no need anymore to machine the recess into the cured web, thus saving man power and avoiding waste. Rather, the recess is provided in the core member, and the dry or wetted (i.e. impregnated with resin) and therefore flexible second fiber layup is provided so as to follow the geometry of the recess. For example, the core member may be comprised of wood or plastic foam, e.g. polyvinyl chloride (PVC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or polyurethane (PU). Both materials may easily be provided with the recess. For example, the core member may be machined, in particular sawed, to have the required shape. Or, in the case of foam in particular, the core member may be cast in the desired shape having the recess. Further, the core member may comprise of a plurality of core elements which can be connected in manner to form the desired shape. 
         [0010]    The fiber material used for the first and second layup may comprise fiber material of different shapes and composition. For example, the fiber material may comprise a layup of fibers, rovings, a fiber mat, a fiber fabric, woven fibers or a fiber felt. The fibers may be arranged unidirectionally, in a biax-configuration or in any other configuration. The fibers may comprise glass fibers, carbon fibers and/or aramid fibers, for example. The fiber material may be supplied in a pre-impregnated state (so called prepreg material) or in an unimpregnated state. In the latter case, the fiber material is impregnated with a resin before step (c). For example, the resin may be injected into the fiber material in a resin transfer molding (RTM) or vacuum-assisted resin transfer molding (VARTM)-process. In a VARTM process for example, the first and second layup comprising the fiber material as well as the core member are covered in a vacuum bag. In a further step, vacuum is applied to the region between the vacuum bag and the mold. Then, resin is injected in said region. After the resin has set or has been cured—typically by the addition of external heat—, the vacuum bag and/or the mold is removed and the final rotor blade is obtained. Of course, when using a prepreg material there is no need to inject the fibers material with resin. 
         [0011]    Generally speaking, the mold may be an open or a closed mold. For example, the mold may comprise one or more parts, in particular a lower part and an upper part. 
         [0012]    “Uncured” herein refers to the resin not being hardened and/or cross-linked at all or not to a substantial extent. “Cured” or “set” refers to the resin being hardened and/or cross-linked to an extent where a shape of the fiber-reinforced resin will not or not significantly change anymore. 
         [0013]    Examples of a resin which may be used for impregnating the fiber material are epoxy, polyester, vinylester or any other suitable thermoplastic or duroplastic material. 
         [0014]    By the step of arranging the second layup of fiber material on the core member before “and” after arranging the core member in the mold it is meant that first portions of the second layup are laid on the core member before arranging the core member in the mold and second portions of the second layup are laid on the core member after arranging the core member in the mold. Arranging the second layup on the core member before arranging the core member in the mold may ease the layup process due to improved accessibility. 
         [0015]    According to a further embodiment, the core member having the recess may already comprise a cured fiber-reinforced plastic material before step b). In this case, the second layup forms an additional layer of fiber material on the core member. 
         [0016]    The fiber material of the first and/or second layup in step a) or b) may be dry or wet. 
         [0017]    “Layup” herein is defined as one or more layers of fiber material. 
         [0018]    “a)”, “b)” and “c)” are not to imply a fixed order of the method steps. Rather, the steps a) to c) may be carried out in a different order where appropriate in the mind of the skilled person. 
         [0019]    According to a further embodiment, the recess has a parabolic or semicircular shape. 
         [0020]    These shapes result in web tips tapering out towards the root of the blade. This improves the load transfer into and out of the web. 
         [0021]    According to a further embodiment, the core member comprises at least two interlocked elements. 
         [0022]    Interlocking is advantageously achieved by the at least two elements engaging each other, or by providing a third element engaging both elements simultaneously. Standard raw material, e.g. wooden plates, may be used. In particular, the interlocked elements may each be made of a single ply wood plate. Further, the core member may be assembled on site, i.e. at or in the mold. 
         [0023]    According to a further embodiment, the two interlocked elements comprise a tongue-and-groove joint and/or are simultaneously engaged by a locking element. 
         [0024]    According to a further embodiment, the core member comprises a base section and two tip sections, the base section and the two tip sections at least partially defining the recess, wherein the two tip sections are interlocked with the base section. 
         [0025]    Thus, the recess may be obtained in an easy manner. Further, this allows the two tip sections to be mounted to the base section at different stages of the manufacturing process, for example. 
         [0026]    According to a further embodiment, the core member and/or the at least two interlocked elements are made of wood and/or foam. 
         [0027]    For example plywood, PET or PU may be used. 
         [0028]    According to a further embodiment, the core member and/or the at least two interlocked elements are made of a planar material. 
         [0029]    This corresponds well with the planar shape of the web. 
         [0030]    According to a further embodiment, step b) comprises fastening layers of fiber material of the second layup to the core member by use of staples. 
         [0031]    Movement or dislocation of the layers relative to the core member or core element may thus be prevented. Further, the core member or core elements can be prepacked with fiber material and easily transported to the site of the mold. 
         [0032]    According to a further embodiment, step b) comprises covering tip sections of the core member defining the recess at least partially by layers of fiber material extending beyond a respective tip section. 
         [0033]    The layers may extend beyond the tip section in a sideways and/or longways direction of the tip section. This reduces the risk of delamination at the respective tips of the web from the inner surface of the airfoil. 
         [0034]    According to a further embodiment, one of the at least two interlocked elements is covered with the fiber material outside the mold and the other one of the at least two interlocked elements is covered with the fiber material inside the mold. 
         [0035]    This offers a process with high flexibility. 
         [0036]    According to a further embodiment, wherein the one of the at least two interlocked elements covered with layers of the second layup outside the mold is a tip section of the core member. 
         [0037]    It may be advantageous to mount the top tip section only after having arranged the base section and the lower tip section as well as a core member supporting the same inside the mold. 
         [0038]    According to a further embodiment, wherein step b) comprises arranging at least one support element between the core member and the first and/or second layup. 
         [0039]    The support element may lend support to the core member and/or to the fiber material. 
         [0040]    According to a further embodiment, the at least one support element has a groove receiving a corresponding edge of the core member. 
         [0041]    The at least one support element may have a triangular cross-section with the groove formed into its tip portion. 
         [0042]    According to a further embodiment, further core members are arranged inside the mold to either side of the core member for supporting the same. 
         [0043]    According to a further embodiment, the tip section and/or a corresponding support element are only interlocked with the base section after the further core members are arranged inside the mold. 
         [0044]    “Wind turbine” presently refers to an apparatus converting the wind&#39;s kinetic energy into rotational energy, which may again be converted to electrical energy by the apparatus. 
         [0045]    Further possible implementations or alternative solutions of the invention also encompass combinations—that are not explicitly mentioned herein—of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    Further objects, features and advantages of the present invention become apparent from the subsequent description and depending claims, taken in conjunction with the accompanying drawings, in which: 
           [0047]      FIG. 1  is a perspective view of a wind turbine according to an one embodiment; 
           [0048]      FIG. 2  shows a perspective view of a root end of a rotor blade according to an embodiment; 
           [0049]      FIG. 3  shows a perspective view of a core member used to manufacture a web of the rotor blade of  FIG. 2 ; 
           [0050]      FIG. 4  is a perspective view of tip section of the core member of  FIG. 3 ; 
           [0051]      FIG. 5  shows a section view from a VARTM-process according to an embodiment of a method for manufacturing the rotor blade of  FIG. 2 ; 
           [0052]      FIG. 6  is an enlarged view VI from  FIG. 3 , wherein the view VI also corresponds to a section along section line VI-VI in  FIG. 3  when the core member is arranged inside the mold; and 
           [0053]      FIG. 7  shows a flowchart in accordance with an embodiment of a method for manufacturing a component for a wind turbine. 
       
    
    
       [0054]    In the Figures, like reference numerals designate like or functionally equivalent elements, unless otherwise indicated. 
       DETAILED DESCRIPTION OF INVENTION 
       [0055]      FIG. 1  shows a wind turbine  1  according to an embodiment. 
         [0056]    The wind turbine  1  comprises a rotor  2  connected to a generator (not shown) arranged inside a nacelle  3 . The nacelle  3  is arranged at the upper end of a tower  4  of the wind turbine  1 . 
         [0057]    The rotor  2  comprises three blades  5 . Rotors  2  of this kind may have diameters ranging from, for example, 30 to 160 meters. The blades  5  are subjected to high wind loads. At the same time, the blades  5  need to be lightweight. For these reasons, blades  5  in modern wind turbines  1  are manufactured from fiber-reinforced composite materials. Therein, glass fibers are generally preferred over carbon fibers for cost reasons. In addition, the blades  5  each comprise one or more core members made of a light material to reduce the weight of the blades  5 . The core members also lend support to a fiber layup during manufacturing of the blades  5  as well as during operation of the wind turbine  1 . 
         [0058]      FIG. 2  shows a perspective view of a root end  6  of one of the blades  5  from  FIG. 1 . 
         [0059]    The blade  5  comprises a shell or airfoil  7  enclosing a space  8 . A web  9  inside the space  8  extends in the longitudinal direction of the blade  5 . The web  9  is connected along opposite edges  10 ,  11  to the inside surface  12  of the airfoil  7 . 
         [0060]    The web  9  has a recess  13  formed in its end facing towards blade root. The recess  13  has a parabolic shape defined by a base section  14  and tip sections  15 ,  16  tapering down from the base section  14  towards inner surface  12 . 
         [0061]    While the airfoil  7  is advantageously made from a fiber-reinforced plastic material and, as the case may be, various coatings, the web  9  comprises a fiber-reinforced plastic material and a core member arranged within the fiber-reinforced plastic material. 
         [0062]      FIG. 3  illustrates a core member  17  which may be used in a VARTM-process to produce the web  9 . 
         [0063]    The core member  17  comprises a number of releasably interlocked elements, for example a base section  18 , tip sections  19 ,  20  and a further base section  21 . The sections  18 ,  19 ,  20  and  21  are made from plywood plates, i.e. plates comprising a number of wooden layers glued together, by cutting or other material removal operations. Having separate elements or sections  18 ,  19 ,  20  and  21  allows the raw plates to be of a standard size simplifying storage and manufacturing. Also, having separate elements or sections  18 ,  19 ,  20  and  21  may simplify assembly of the core member  17  in- or outside a mold used in the VARTM-process. 
         [0064]    The section  18 ,  19  and  20  are shaped so as to define a parabolic recess  22 , the tip sections  19 ,  20  tapering down from the base section  18 . The tip sections  18 ,  19  may form a tongue-and-groove joint  23  with the base section  18 , respectively. In particular, the tongue and groove may respectively have curved shape as indicated in  FIG. 3 . 
         [0065]    The base section  18  may be connected to the further base section  21  by locking elements  24 . The locking elements  24  may have a U-shape, each locking element  24  being engaged with both sections  18 ,  21 . 
         [0066]    Other ways of connecting the various elements or sections  18 ,  19 ,  20  and  21  may be used instead. For example screws or glue may be used. 
         [0067]    In another embodiment, the entire core member  17  (or some of its elements or sections) is made of plastic foam, e.g. PET or PU. 
         [0068]    Further,  FIG. 3  illustrates in dashed lines support elements  25 ,  26  and  27 , which are associated with the sections  20 ,  18  and  21  respectively and extend along respective upper and lower edges  28 ,  29  of the core member  17 . The support elements associated with the upper edge  28  is not shown in  FIG. 3  for reasons of clarity. 
         [0069]    Each support element  25 ,  26  and  27  has a substantially triangular cross-section  30  comprising an upper groove  31 , in which a respective edge (corresponding to the edge  29 ) of the sections  20 ,  18  and  21  is engaged. Curved sides  32 ,  33  of the support elements  25 ,  26  and  27  lend support to a fiber layup as will be explained hereinafter. 
         [0070]      FIG. 4  illustrates the tip section  20  and the support element  25  from  FIG. 3  as well as a layup  34  of fiber material. 
         [0071]    For example, the layup  34  may comprise a plurality of fiber mats  35 , the fiber mats  35  overlapping one another at least partially. Each fiber mat  35  may comprise rovings in crisscross arrangement. The fiber mats  35  extend beyond the tip section  20  in a sideways direction Y and a longways direction X in order to reduce the risk of delamination from the inner surface  12  of the airfoil  7 , cf.  FIG. 2 . 
         [0072]    The fiber mats  35  are attached to the tip section  20  by staples  36  using a staple gun (not shown). Yet, other ways of fastening the fiber mats  35  to the tip section  20  are also possible. The staples  36  are driven so deeply into the wood of the tips section  20  that they do not damage a vacuum bag employed in the VARTM-process described hereinafter. 
         [0073]    The tip section  20  including the (dry) layup  34  and, as the case may be, the support element  25  may be prepacked and delivered to a mold  40  shown in  FIG. 5 . In fact, the entire core  17  may, as a whole or each section  18 ,  19 ,  20 ,  21  separately, be prepacked with a (dry) layup  34  and delivered to the mold  40 . 
         [0074]      FIG. 5  shows the mold  40  in a cross-section, and  FIG. 6  illustrates an enlarged region VI from  FIG. 5 . Also, it is referred to  FIG. 7  illustrating a flow diagram of the VARTM-process now described. 
         [0075]    The mold  40  may be a closed mold comprising a lower and an upper half  37 ,  38 . In the beginning, the upper half  38  is positioned next to the lower half  37  and turned by 180 degrees compared to  FIG. 5 . A layup  39  of fiber material, comprising for example fiber mats as shown in  FIG. 4 , is created on the lower and upper half  37 ,  38  respectively. Then, vacuum is applied underneath a respective layup  39 . To this end, a suction pump  41  ( FIG. 6 ) may create a vacuum between an outermost layer  42  of the layup  39  and an inside mold surface  43 . The outermost layer  42  may have a lower air permeability then layers  44  underneath layer  42 . This step of creating a layup  39  in the mold  40  is illustrated by step S 2  in  FIG. 7 . The layup  39  comprises dry fibers. According to another embodiment, pre-impregnated fibers may be used. 
         [0076]    In step S 3 , the core member  17  is, as a whole or each section  18 ,  19 ,  20 ,  21  separately, arranged inside the lower half  37  of the mold  40  on top of the layup  39 . If the sections  18 ,  19 ,  20 ,  21  are brought into the mold  40  separately, they are connected to one another by means of the tongue-and-groove joints  23  and/or the locking elements  24  inside the mold  40 , otherwise they are connected outside the mold  40 . 
         [0077]    The core member  17 , as a whole or each section  18 ,  19 ,  20 ,  21  separately, may at the point of arranging them on the layup  39  be covered by the layup  34 . Or, the “bare” core member  17  is arranged inside the mold  40  and then the layup  34  is arranged on the core member  17 . Portions of the layup  34  covering the base section  18  as well as parts of the recess  22  is shown in dashed lines in  FIG. 6 . Providing the layup  39  on the core member  17  before arranging the core member  17  inside the mold  40  is indicated by step S 1 . Step S 4  indicates an embodiment where the layup  39  is provided on the core member  17  after arranging the same inside the mold  40 . 
         [0078]    According to a further embodiment, the sections  18 ,  20  and  21  are covered with the layup  39  inside the mold  40 , and the tip section  22  is prepacked as described in connection with  FIG. 4 . The step of prepacking is indicated by step S 1 ′ in  FIG. 7 . 
         [0079]    Though, before arranging the core member  17  or the sections  18 ,  20  and  21 , the support elements  25 ,  26  and  27  should be positioned on the layup  39 . The edge  29  of the core member  17  is then brought into engagement with the groove  31  in each of the support elements  25 ,  26  and  27 . 
         [0080]    Next, core members  45  are wrapped into a vacuum bag  46 , respectively. Then, the core members  45  are arranged in the hollow spaces left and right of the core member  17  as shown in  FIG. 6 . This corresponds to step S 5  in  FIG. 7 . 
         [0081]    In the case of having only a prepacked upper tip section  19 , this tip section  19  is now connected to the base section  18  by means of the tongue-and-groove joint  23  in step S 6 . In any case, the support elements  25 ′ (other support elements not shown) are now placed at the top, and the groove  31 ′ is brought into engagement with the edge  28  of the core member  17 . 
         [0082]    In a further step, the mold  40  is closed by turning the upper half  38  by 180 degrees and placing it on top of the lower half  37 . In this manner, the layup  39  comes to lie against the support elements  25 ′ as well as the layup  34 . 
         [0083]    Then, vacuum is applied to a space  47  between the vacuum bags  46  and the respective mold surfaces  43 . In step S 7  ( FIG. 7 ), the resin is injected into the space  47  and the mold  40  is heated in order to cure the resin. If prepreg material is used, the step of injecting the resin is not required. 
         [0084]    Now, the mold  40  is opened and the mold cores  45  are removed. The cured rotor blade  5  may then be taken out of the lower half  37  of the mold  40 . The resin reinforced by the layup  39  corresponds to the airfoil  7 , the resin reinforced by the layup  34  and including the core member  17  corresponds to the web  9 . 
         [0085]    It will be noted that the web  9  produced in this manner has the parabolic recess  13  shown in  FIG. 2 , and no removal of material is required. 
         [0086]    Although the present invention has been described in accordance with preferred embodiments, it is obvious for a person skilled in the art that modifications are possible in all embodiments.