Manufacturing a pre-bent wind turbine blade with a pre-cured SPAR cap

Abstract

A method of manufacturing a pre-bent wind turbine blade (10, 82) with the steps of providing a shell mould (70, 71) and a spar cap mould (50, 51). The shell mould defines at least part of an airfoil shape in the chordwise direction (18) and defines a first pre-bend shape along a longitudinal direction (17). The spar cap mould defines at least part of substantially the same airfoil shape in the chordwise direction as the shell mould, and a second shape in the longitudinal direction. The second shape exhibits less pre-bend compared to the first pre-bend shape. Then, a first fibre material (67, 70) is arranged, infused, and cured in the spar cap mould. The cured spar cap (60, 61) is moved to a shell mould, and deformed from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell mould under the influence of gravity.

Description

[0001] MANUFACTURING A PRE-BENT WIND TURBINE BLADE WITH A PRE-CURED SPAR CAP

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method of manufacturing a pre-bent wind turbine blade using a pre-cured spar cap.

[0004] BACKGROUND

[0005] Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having a rotatable hub with one or more wind turbine blades. The wind turbine blades capture kinetic energy of wind using known airfoil principles. The wind turbine blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the wind turbine blades to a gearbox or, if a gearbox is not used, directly to the generator.

[0006] The wind turbine blades generally include a suction side shell and a pressure side shell each moulded in a dedicated shell mould and typically formed using moulding processes that are bonded together at bond lines along the leading and trailing edges of the blade. Further, the pressure and suction shells are relatively lightweight and have structural properties (e.g., stiffness, buckling resistance and strength) which are not configured to withstand the bending moments and other loads exerted on the wind turbine blade during operation. Thus, to increase the stiffness, buckling resistance and strength of the wind turbine blade, the body shell is typically reinforced using one or more structural components (e.g. opposing spar caps with a shear web configured therebetween) that engage the inner pressure and suction side surfaces of the shell halves. The spar caps and / or shear web may be constructed of various materials, including but not limited to glass fibre laminate composites and / or carbon fibre laminate composites.

[0007] Wind turbine blades typically have a pre-bend in the flap-wise direction to ensure that the wind turbine blade does not strike the tower under loading. However, modern wind turbine blades can exceed 100 metres and even a modest pre-bend of the tip of the blade can involve that the tip of the mould is located multiple storeys above the root of the blade. Thus, as blades are increasingly getting longer, the amount of pre-bend is increasingly limited by the interior height of the blade manufacturing factory. This height difference further entails that extensive scaffolding is required to ensure a safe work platform and further ties up the scarce space of the factory which could be put to productive uses such as manufacturing on multiple storeys. SUMMARY

[0008] On this background, it may be seen as an object of the present disclosure to provide a method of manufacturing a pre-bent wind turbine blade that at least mitigates some of the above-mentioned drawbacks and, e.g., efficiently utilises the factory volume, improves worker safety, and improves quality while reducing cost. Another object of the present disclosure is to provide an efficiently produced wind turbine blade. One or more of these objects may be met by aspects of the present disclosure as described in the following.

[0009] A first aspect of this disclosure relates to a method of manufacturing a pre-bent wind turbine blade extending in a longitudinal direction (L), a chordwise direction (C), and a height direction (H), comprising the steps of:

[0010] - providing: o a shell mould for moulding a shell part of the pre-bent wind turbine blade, the shell mould extending along the longitudinal direction and the chordwise direction, wherein the shell mould defines at least part of an airfoil shape in the chordwise direction and defines a first pre-bend shape along the longitudinal direction, and o a spar cap mould for moulding a spar cap of the pre-bent wind turbine blade, the spar cap mould extending along the longitudinal direction and the chordwise direction, wherein the spar cap mould defines at least part of substantially the same airfoil shape in the chordwise direction as the shell mould, and wherein the spar cap mould defines a second shape in the longitudinal direction, wherein the second shape exhibits less pre-bend compared to the first pre-bend shape;

[0011] - arranging a first fibre material in the spar cap mould;

[0012] - infusing a first resin into the spar cap mould;

[0013] - causing or allowing the first resin to cure to obtain the cured spar cap having the at least part of substantially the same airfoil shape in the chordwise direction and having the second shape in the longitudinal direction;

[0014] - arranging a second fibre material and the cured spar cap in the shell mould; and

[0015] - deforming the cured spar cap from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell mould under the influence of gravity.

[0016] The method of manufacturing a pre-bent wind turbine blade offers several notable advantages. Firstly, the need for scaffolding adjacent to the spar cap mould can be reduced or even eliminated. This reduction or elimination of work at height significantly reduces the risks associated with worker accidents and injuries in the manufacturing process. Furthermore, during the layup step, material can be more precisely placed due to reduced height difference, resulting in a reduced defect risk. Additionally, it provides better control over fibre, e.g. pultrusion stack placement and resin infusion, ensuring a more consistent and reliable infusion. One of the most compelling advantages is that the inventors found that an estimated 20-30% cost reduction as well as a faster cycle time in spar cap production can be achieved. Moreover, this manufacturing method optimizes factory floor space utilization. By eliminating the need for scaffolding, it reduces the space required for manufacturing, thus allowing the accommodation of other essential processes or additional production lines. In line with space efficiency, the method may also reduce the factory's required height. Lower ceilings can translate to reduced construction costs for the manufacturing facility, making it more cost-effective to build and maintain. Finally, a cured spar cap exhibiting less prebend may also ease recycling and reuse of the spar cap material for new wind turbine blades since the spar cap material may more easily conform to a new blade shape.

[0017] In the context of the present disclosure, the "substantially same airfoil shape in the chordwise direction" of the spar cap mould compared to that of the shell mould is understood to mean that the spar cap mould is designed to ensure that the airfoil shape of the resulting cured spar cap approximates the airfoil shape of the shell mould. In a practical setting, the wind turbine blade may, in addition to pre-bend, also involve a twist (i.e. chordwise cross-sections are rotated along the longitudinal direction). To account for such a twist and ensure a snug fit of the cured spar cap in the shell mould, the twist of the spar cap mould may be designed to locally deviate slightly from the twist of the shell mould.

[0018] Additionally or alternatively, the method may further comprise the steps of:

[0019] - infusing a second resin into the shell mould; and

[0020] - causing or allowing the second resin to cure to co-embed the cured spar cap and the second fibre material in the second resin to obtain the shell part with the cured spar cap embedded therein.

[0021] Advantageously, the infusion of a second resin into the shell mould and its subsequent curing serves to co-embed the cured spar cap and the second fibre material in the second resin, creating a shell part with the spar cap embedded within. This process enhances the structural integrity of the blade and may ensure a good and reliable connection between the cured spar cap and the second fibre material.

[0022] Additionally or alternatively, the shell mould may instead be a shell cradle and the step of arranging the second fibre material and the cured spar cap in the shell cradle may comprise:

[0023] - providing the second fibre material as a part of a cured fairing part on a surface of the shell cradle, and arranging the cured spar cap on the cured fairing part so that the cured spar cap deforms from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell cradle under the influence of gravity, and preferably adhering the cured spar cap to the cured fairing part to obtain the shell part.

[0024] As an alternative to co-embedding the cured spar cap and second fibre material, the cured spar cap may instead be adhered to an already pre-cured fairing part. Thus, the fairing part can be moulded separately from the spar cap, potentially allowing parallel production of these elements to reduce the cycle time. In the present disclosure, a distinction is made between a "mould" and a "cradle" in that the former allows the performance of a vacuum assisted resin transfer infusion process while this may not be case for the latter which is only required to support the cured fairing part.

[0025] Additionally or alternatively, the method may further comprise performing finishing steps to obtain the pre-bent wind turbine blade comprising the shell part.

[0026] Advantageously, the inclusion of finishing steps in the manufacturing process may ensure that the pre-bent wind turbine blade is of the highest quality and ready for use in a wind turbine. These steps may include griding edges, applying paint or gelcoat, final inspections, quality control checks, and any necessary adjustments to ensure the blade meets all necessary specifications and standards.

[0027] Additionally or alternatively, the first pre-bend shape of the shell mould may involve that the tip end of the shell mould is displaced from the root end of the shell mould along a height direction (H), which is preferably perpendicular to the longitudinal direction (L) and / or chordwise direction (C), by a first pre-bend distance (Di). Further, the second shape of the spar cap mould may involve that the tip end of the shell mould is displaced from the root end of the shell mould by a second distance (D2) along the height direction (H), wherein the second distance is less than the first pre-bend distance. The second distance may be, with increasing preference, at most 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or 0% of the first pre-bend distance.

[0028] Advantageously, the displacement of the tip end of the shell mould from the root along the height direction by a first pre-bend distance and the displacement of the tip end of the shell mould from the root by a second distance, which is less than the first pre-bend distance, allow for a cost-efficient manufacturing of the spar cap for the pre-bent blade. This pre-bend is critical in ensuring that long blades do not strike the tower under loading, especially with modern wind turbine blades that can exceed 100 metres in length. The lower pre-bend of the spar cap mould also allows for the spar cap to be manufactured in a factory or a section of the factory with a lower ceiling height, reducing construction costs and optimizing factory floor space utilisation. Further, by varying the second distance to be a certain percentage of the first pre-bend distance, an increasingly flat spar cap can be provided providing increasing benefits in lowering scaffolding height and work height with the associated benefits described above. Additionally or alternatively, the second shape of the spar cap mould may be substantially flat along the height direction.

[0029] Advantageously, this embodiment simplifies the manufacturing process and reduces the likelihood of defects. A substantially flat spar cap mould may allow for a more consistent fibre placement in the spar cap mould, which may ensure a robust spar cap that can reinforce the shell part of the blade. Further, the required ceiling height is minimised leading to improve factory space utilisation.

[0030] Additionally or alternatively, the second shape of the spar cap mould may lie substantially within a plane extending in the longitudinal and chordwise directions. In other words, the root end of the spar cap may be located at substantially the same height as the tip end of the spar cap.

[0031] Additionally or alternatively, the second shape of the spar cap mould may curve in the chordwise direction. In other words, the second shape of the spar cap mould may be substantially bananashaped in the plane extending in the longitudinal and chordwise directions. Accordingly, the tip end of the spar cap may be offset in the chordwise direction compared to the root end of the spar cap.

[0032] This curvature in the chordwise direction may advantageously increase the drapability of the spar cap on the mould surface of the shell mould which can curve in the height direction (i.e. to form a prebend), twist about the longitudinal direction, and curve in the chordwise direction (i.e. to form a sweep).

[0033] It will be appreciated that such a banana-shape can be obtained by cutting and draping conventional fibre mats accordingly but also by using partial or full length pultrusions. The inventors have found that residual tensile stresses of conventional straight pultrusions are symmetric across a crosssection perpendicular to the longitudinal direction with the greatest residual tensile stresses found greatest at the longitudinal edges thereof. This is thought to be due to higher friction through the die at these locations during the pultrusion process. A banana-shape can thus be obtained by removing, e.g. by cutting or grinding, a longitudinal slice of material at one of the longitudinal edges with the result that the residual tensile stresses now are asymmetric resulting in the pultrusion curving in the chordwise direction. Another option would be to increase the pulling forces in the tows of fibre reels going into one side of the pultrusion die. Thus, the residual tensile stresses would also be asymmetric leading a banana-shape.

[0034] Additionally or alternatively, the second shape of the spar cap mould may be straight along the longitudinal direction.

[0035] Additionally or alternatively, the second shape may form a substantially straight line, preferably in the plane extending in the longitudinal and chordwise directions. Advantageously, a straight spar cap mould is particularly simple to handle and allows the use of straight pultrusion planks without any modification. Thus, a straight spar cap mould may allow for a more consistent and reliable fibre arrangement, ensuring a high-quality spar cap.

[0036] Additionally or alternatively, the method may further comprise a step of applying a moulding pressure, preferably a negative relative pressure, prior to and / or during the step of infusing the second fibre material and the cured spar cap with a second resin so as to further deform the cured spar cap to the first pre-bend shape of the shell mould. The moulding pressure may preferably be applied during a vacuum assisted resin transfer process.

[0037] Advantageously, the application of a moulding pressure, preferably a negative relative pressure, prior to and / or during the infusion step, further deforms the cured spar cap to match the pre-bend shape of the shell mould. This process not only enhances the structural integrity of the blade but also reduces or even eliminates any gaps present between the cured spar cap and the second fibre material to improve the fibre ratio of the resulting shell part.

[0038] Additionally or alternatively, the step of arranging the second fibre material and the cured spar cap in the shell mould may include arranging an exterior side of the cured spar cap on a third fibre material, and optionally so that, during the step of deforming of the cured spar cap from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell mould under the influence of gravity, the third fibre material swells to at least partially fill one or more gaps between an exterior side of the cured spar cap and an upper surface of the second fibre material. Additionally, the third fibre material may be a substantially non-stitched fibre material, for example a powder bound fibre material, such as a chopped strand mat and / or a continuous filament mat; a veil, such as a polyester veil, a glass veil and / or a carbon veil; or a combination of a powder bound fibre material and a veil.

[0039] Advantageously, the third fibre material increases the fibre ratio of the resulting wind turbine blade by reducing or even avoiding resin pools between the cured spar cap and the second fibre material.

[0040] Additionally, the third fibre material may comprise a root side edge, a tip side edge, a leading side edge, and a trailing side edge, wherein:

[0041] - optionally the root side edge of the third fibre material is located closer to the root end of the shell mould than the root end of the cured spar cap, and / or

[0042] - optionally the tip side edge of the third fibre material is located closer to the tip end of the shell mould than the tip end of the cured spar cap, and / or

[0043] - optionally the leading side edge of the third fibre material is located closer to the leading side edge of the shell mould than the leading side edge of the cured spar cap, and / or optionally the trailing side edge of the third fibre material is located closer to the trailing side edge of the shell mould than the trailing side edge of the cured spar cap.

[0044] Advantageously, the positioning of the third fibre material's edges closer to the respective edges of the shell mould than those of the cured spar cap may ensure that the third fibre material covers most if not all of the exterior side of the cured spar cap leading to further reducing or avoiding resin pools and thus an increased fibre ratio.

[0045] Additionally or alternatively, the third fibre material may have a length in the longitudinal direction and a width in the chordwise direction, wherein:

[0046] - optionally the length of the third fibre material is equal to or greater than the length of the cured spar cap, and / or

[0047] - optionally the width of the third fibre material is equal to or greater than the width of the cured spar cap.

[0048] Advantageously, the third fibre material's length and width being equal to or greater than those of the cured spar cap may ensure that the entire exterior surface of the cured spar cap is covered by the third fibre material leading to further reducing or avoiding resin pools and thus an increased fibre ratio.

[0049] Additionally or alternatively, the third fibre material may cover one or more distinct and separate regions of the exterior side of the cured spar cap, and optionally the third fibre material may cover at most partially the exterior side of the cured spar cap. In other embodiments, the third fibre material may cover the entirety of the exterior side of the cured spar cap.

[0050] Advantageously, this method of selectively covering distinct regions of the exterior side of the cured spar cap with a third fibre material allows for targeted application of the third fibre material, thus, only arranging the third fibre material in regions that exceed a gap tolerance. This selective coverage also optimizes the use of materials, reducing waste and potentially lowering manufacturing costs.

[0051] Additionally or alternatively, the method may further comprise a step of sliding the third fibre material in between the exterior side of the cured spar cap and the second fibre material. This step may preferably be performed after the step of arranging the second fibre material and the cured spar cap in the shell mould.

[0052] Advantageously, the step of sliding the third fibre material between the exterior side of the cured spar cap and the second fibre material allows for precise placement of this reinforcing material. This ensures that the third fibre material is positioned exactly where it is needed to absorb excessive gap dimensions that would otherwise lead to unacceptable resin pools. Additionally or alternatively, the first resin may be the same as or, preferably, be different from the second resin. Preferably, the first resin is an epoxy resin. The second resin may be a polyester resin. However, the resin types may vary according to the specific circumstances, including but not limited to the material selection for the first and second fibre material.

[0053] Advantageously, the ability to use the same or different resins for the first and second infusions provides flexibility in the manufacturing process. This allows for the selection of resins based on their specific properties, such as curing time, strength, flexibility, cost, and environmental impact. For example, a stronger, more durable resin could be used for the first resin to enhance the structural integrity of the final composite, while a faster curing resin could be used for the second resin to speed up the manufacturing process.

[0054] Additionally or alternatively, the first fibre material may be the same as or, preferably, be different from the second fibre material. Additionally or alternatively, the plurality of pultrusions and / or the plurality of fibrous layers comprises glass fibres, carbon fibres, or a combination thereof. For example, the first fibre material may comprise or consist essentially of a carbon fibre composite material, and the second fibre material may comprise or consist essentially of a glass fibre composite material.

[0055] Advantageously, the ability to use the same or different fibre materials for the first and second arrangements provides flexibility in the manufacturing process. This allows for the selection of fibre materials based on their specific properties, such as strength, stiffness, weight, cost, and environmental impact. For example, a strong but flexible fibre material could be used for the first arrangement to facilitate the deformation of the spar cap, while a lighter and highly drapable fibre material could be used for the second arrangement to ease the shell layup.

[0056] Advantageously, the use of glass fibres, carbon fibres, or a combination thereof in the pultrusions and / or fibrous layers allows for the creation of a composite material with superior properties. Glass fibres are relatively inexpensive, lightweight, and provide good strength and stiffness, making them a popular choice for wind turbine blades. Carbon fibres, while more expensive, provide even greater strength and stiffness and can be used in critical areas of the blade or in blades designed for high- performance applications.

[0057] Additionally or alternatively, the first fibre material and / or the second fibre material may comprise or consist essentially of a plurality of pultrusions and / or a plurality of fibrous layers. For example, the first fibre material may preferably comprise or consist essentially of a plurality of pultrusions, and the second fibre material may preferably comprise or consist essentially of a plurality of fibrous layers. Advantageously, the use of a plurality of pultrusions and / or fibrous layers in the first and / or second fibre materials allows for the creation of a multi-layered composite structure. This structure can provide superior strength and stiffness compared to a single layer of material, while still maintaining a relatively low weight. The use of pultrusions, which are continuous, aligned fibres embedded in a resin matrix, can further enhance the strength and stiffness of the blade. The ability to use a variety of fibrous layers, including unidirectional fibre mats, multidirectional fibre mats, or a combination thereof, provides additional flexibility in the manufacturing process and allows for the optimization of the blade's properties based on the specific requirements of its intended application.

[0058] Additionally, the plurality of fibrous layers may be uncured, pre-preg, pre-cured, or a combination thereof. Preferably, the second fibre material may comprise or consist essentially of a plurality of uncured fibrous layers.

[0059] Advantageously, the use of uncured, pre-preg, or pre-cured fibrous layers provides flexibility in the manufacturing process. Uncured fibrous layers can be shaped and formed as needed before being infused with resin and cured, allowing for precise shaping of the blade. Pre-preg fibrous layers, which are pre-impregnated with resin, can simplify the manufacturing process and ensure a consistent, high-quality infusion. Pre-cured fibrous layers, which have already been infused with resin and cured, can provide additional strength and stiffness to the blade.

[0060] Additionally or alternatively, the plurality of fibrous layers may comprise unidirectional fibre mats, multidirectional, e.g. biaxial, fibre mats, or a combination of unidirectional and multidirectional, e.g. biaxial, fibre mats. Preferably, the second fibre material may comprise or consist essentially of a plurality of multiaxial fibre mats, which are preferably uncured during the arrangement thereof in the shell mould.

[0061] Advantageously, the use of unidirectional and / or multidirectional fibre mats allows for the optimization of the blade's properties based on the specific requirements of its intended application. Unidirectional fibre mats, in which the far majority or even all fibres are aligned in the same direction, provide high strength and stiffness in that direction, making them ideal for areas of the blade that are subject to high loads in a specific direction. Multidirectional fibre mats, in which fibres are aligned in multiple directions, provide good strength and stiffness in more directions, making them ideal for areas of the blade that are subject to complex multidirectional loads.

[0062] Advantageously, the first fibre material preferably comprises or consists essentially of a plurality of pultrusions, and the second fibre material preferably comprises or consists essentially of a plurality of uncured fibrous layers, such as multidirectional, e.g. biaxial or triaxial, fibre mats. A second aspect of the present disclosure relates to a pre-bent wind turbine blade obtainable by a method according to the first aspect of the present disclosure.

[0063] A third aspect of the present disclosure relates to a pre-bent wind turbine blade defining a first prebent shape along a longitudinal direction and comprising a shell part and a pre-cured spar cap, wherein the pre-cured spar cap comprises or consists essentially of a composite material including a cured first resin, wherein the shell part comprises a cured second resin, wherein the pre-cured spar cap comprises a relaxed shape and a prestressed shape along the longitudinal direction, wherein the spar cap is embedded in the cured second resin in the stressed shape so as to follow the first pre-bent shape, and wherein the spar cap has a second shape in the relaxed state exhibiting less pre-bend compared to the first pre-bend shape.

[0064] Additionally, the cured second resin may be cured after the cured first resin. The cured second resin may preferably be different from the cured first resin.

[0065] A fourth aspect of the present disclosure relates to a kit of parts for manufacturing a pre-bent wind turbine blade, the kit of parts comprising:

[0066] - a shell mould extending along a longitudinal direction (L) and along a chordwise direction (C), wherein the shell mould defines at least part of an airfoil shape in the chordwise direction and defines a first pre-bend shape along the longitudinal direction, and

[0067] - a spar cap mould extending along the longitudinal direction and the chordwise direction, wherein the spar cap mould defines at least part of substantially the same airfoil shape in the chordwise direction as the shell mould, and wherein the spar cap mould defines a second shape in the longitudinal direction, wherein the second shape exhibits less pre-bend compared to the first pre-bend shape.

[0068] Additionally, the second shape of the spar cap mould may be substantially flat along a height direction.

[0069] A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects of this disclosure and embodiments thereof.

[0070] BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Embodiments of this disclosure will be described in more detail in the following with regard to the accompanying figures. The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Fig. 1 is a schematic perspective view of a wind turbine.

[0072] Fig. 2 is a schematic perspective view of a wind turbine blade for a wind turbine as shown in Fig. 1.

[0073] Fig. 3A is a schematic cross-sectional view in the chord-height plane of a layup in a spar cap mould.

[0074] Fig. 3B is a cross-sectional view in the longitudinal-height plane of a first embodiment of the layup shown in Fig. 3A.

[0075] Fig. 3C is a cross-sectional view in the longitudinal-height plane of a second embodiment of the layup shown in Fig. 3A.

[0076] Fig. 4A is a schematic view in the longitudinal-height plane of a cured spar cap resulting from the first embodiment of the layup shown in Fig. 3B prior to being arranged in shell mould.

[0077] Fig. 4B is a schematic view in the longitudinal-height plane of the cured spar cap of Fig. 4A after being arranged in shell mould.

[0078] Fig. 5A is a schematic view in the longitudinal-height plane of a cured spar cap resulting from the second embodiment of the layup shown in Fig. 3C prior to being arranged in shell mould.

[0079] Fig. 5B is a schematic view in the longitudinal-height plane of the cured spar cap of Fig. 5A after being arranged in shell mould.

[0080] DETAILED DESCRIPTION

[0081] In the following figure description, the same reference numbers refer to the same elements and may thus not be described in relation to all figures.

[0082] Fig. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called "Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft which may include a tilt angle of a few degrees. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8.

[0083] Fig. 2 shows a schematic view of an exemplary wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade extending in a longitudinal direction L between a root end 17 and a tip end 15. The blade 10 comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The airfoil region 34 includes a tip region 36 closest to the tip end 15. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub 8, and a trailing edge 20 facing the opposite direction of the leading edge 18. The blade 10 comprises a first shell part 24 and a second shell part 26 joined together at the leading edge 18 and the trailing edge 20.

[0084] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root region 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord C extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord C decreases with increasing distance r from the hub. A shoulder 38 of the blade 10 is defined as the position where the blade 10 has its largest chord length. The shoulder 38 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

[0085] It should be noted that the chords of different sections of the blade do not lie in a common plane since the blade is curved (i.e. pre-bent) and may also be twisted, thus providing the chord plane with a correspondingly curved and optionally twisted course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0086] A method of manufacturing such a pre-bent wind turbine blade 10 as shown in Figs. 1-2 according to the present disclosure is now described. As described above, the blade 10 extends in the longitudinal direction L and the chordwise direction C. The blade 10 further extends in a height direction H, which extends between the first and second shell parts 24, 26 normally at the thickest point thereof. The blade 10 is pre-bent which is generally defined as the tip end 15 of the blade 10 being at an elevated point compared to the root end 17 of the blade 10 in the height direction. A conventional prebend is often in around 4% - 6% of the blade length. Thus for a blade length of a 100 metres, the prebend is normally around 4-6 metres.

[0087] First, a shell mould 70 as shown in Figs. 4A-4B and 5A-5B, and a spar cap mould 50 as shown in Figs. 3A-3C are provided. The shell mould 70 is for moulding a shell part 80, such as the first shell part 24 or the second shell part 26 of the pre-bent wind turbine blade 10. The shell mould 70 extends along the longitudinal direction L and the chordwise direction C. The shell mould 70 defines at least part of an airfoil shape in the chordwise direction C corresponding to the airfoil shape of the finished shell part 80 and thus the wind turbine blade 10. The spar cap mould 50 is for moulding a spar cap of the shell part 80, e.g. the first or second shell part. The spar cap mould 50 also extends along the longitudinal direction L between a root end 51 and a tip end 52 and along the chordwise direction C between a leading side edge 53 and a trailing side edge 54. The spar cap mould 50 defines at least part of substantially the same airfoil shape in the chordwise direction C as the shell mould 70. However, it is appreciated that the spar cap mould 50 is designed to ensure that the airfoil shape of the resulting cured spar cap 60 approximates the airfoil shape of the shell mould 70. In a practical setting, the wind turbine blade 10 may, in addition to prebend, also include a twist about the longitudinal direction L (i.e. chordwise cross-sections are rotated along the longitudinal direction). To account for such a twist and ensure a snug fit of the cured spar cap 60 in the shell mould 70, the spar cap mould can be designed to locally deviate slightly from the shell mould 70. Furthermore, to ensure an improved drapability on the moulding surface 75 of the shell mould 70, which is double curved surface, of the cured spar cap 60, which is a flattened profile, the spar cap mould 50 may additionally curve in the chordwise direction (i.e. in a sweep direction).

[0088] Turning to Figs. 3A-3C, a first fibre material 67 for forming the spar cap is then arranged in the spar cap mould 50 on the moulding surface 55 thereof. In this embodiment, the first fibre material 67 is a stack of pultrusion planks extending substantially along the full length of the resulting spar cap, i.e. from a root end 51 to a tip end 52 of the spar cap mould 50. The pultrusion planks may also be full width, i.e. extending from the leading edge side 53 to the trailing edge side 54 of the spar cap mould 50, but would most advantageously be partial width, i.e. a plurality of planks arranged side- by-side in the chordwise direction, to provide an easier handling and improved drapability. A first resin (not shown) is then infused into the spar cap mould in a vacuum assisted resin transfer infusion process, and the first resin is allowed to cure to obtain the cured spar cap 60 having the at least part of substantially the same airfoil shape in the chordwise direction as shown in Fig. 3A. In the longitudinal direction L, the cured spar cap 60 has a second shape which is either a substantially flat shape as shown in Fig. 3B or a pre-bend shape as shown in Fig. 3C. After curing, the cured spar cap 60 can then be demoulded and prepared for inclusion into the shell mould. The cured spar cap 60 then extends in the longitudinal direction L from a root end 61 to a tip end 62, in the chordwise direction C from a leading edge side 63 to a trailing edge side 64, and in the height direction H from an interior side 65 to an exterior side 66.

[0089] As best seen in Figs. 4A and 5A, a second fibre material 87 is arranged on a moulding surface 75 of the shell mould 70. The second fibre material 87 is for forming the exterior surface of the wind turbine blade 10, these may also be referred to as skin layers forming the exterior side 86 of the shell part 80. In the present disclosure, the second fibre material 87 is glass fibre mats, preferably biaxial. But this material selection may vary widely and may for example also be provided as carbon fibre mats. In other embodiments, the second fibre material 87 may form part of a pre-cured fairing part to which the cured spar cap 60 is adhered. Notably, the shape of the cured spar cap 60 in its relaxed state differs from the shape of the shell mould 70 along the longitudinal direction L. The shell mould 70 further defines a first pre-bend shape along the longitudinal direction L involving the tip end 72 of the shell mould 70 being displaced from the root end 71 of the shell mould 70 along the height direction (H) by a first pre-bend distance Di. As shown in Figs. 3B-3C, the spar cap mould 50 defines a second shape in the longitudinal direction L involving that the tip end 52 of the shell mould 70 is displaced from the root end 51 of the shell mould by a second distance D2 along the height direction H. As best illustrated in Figs. 4A and 5A, the second distance D2 is less than the first pre-bend distance Di. Although not shown in Fig. 4A, the second distance D2 is substantially zero since the cured spar cap 60 is substantially flat, i.e. without pre-bend. Turning to Fig. 5A, in this embodiment, the cured spar cap 60 does exhibit some prebend which is however less than the prebend of shell mould. This is illustrated by the second distance D2 being less (approximately 25% of) than the first pre-bend distance Di.

[0090] In any case, the cured spar cap 60 is lowered onto the second fibre material 87 resting on the moulding surface 75 of the shell mould 70. Once the cured spar cap 60 makes contact with the second fibre material 87 and the shell mould 70, the cured spar cap 60 starts to deform due to gravity. Since the stiffness of the cured spar cap 60 is calibrated to the prebend of the shell mould 70, the cured spar cap 60 deforms until substantially assuming the pre-bend shape of the shell mould 70 as shown in Figs. 4B and 5B. A second resin material is then infused into the shell mould 70 in another resin transfer infusion process and subsequently cured to obtain the shell part 80. The shell part thus extends in the longitudinal direction L from a root end 81 to a tip end 82, in the chordwise direction C from a leading edge side (not shown) to a trailing edge side (not shown), and in the height direction H from an interior side 85 to the exterior side 86.

[0091] During the resin transfer infusion process, a negative relative moulding pressure, i.e. a vacuum pressure, is applied. This moulding pressure further deforms the cured spar cap to substantially the first pre-bend shape of the shell mould 70. Optional finishing steps such as grinding edges, applying gelcoat or paint can then be performed. The process is repeated with another shell mould for the opposite shell part. Then the two shell parts are joined, typically along the leading edge sides and trailing edge sides defining the leading 18 and trailing edge 20 to obtain the wind turbine blade 10.

[0092] Although not shown in the figures, the present disclosure also envisages that, if for any reason the desired gap tolerances between the exterior side 66 of the cured spar cap 60 and the second fibre material 87 are exceeded, a third fibre material can be arranged within this gap. During resin infusion, the third fibre material swells up to absorb the gap dimensions and thus increases the fibre ratio of the shell part. The third fibre material is a non-stitched fibre material, for example a powder bound fibre material (e.g. a chopped strand mat and / or a continuous filament mat), a veil (e.g. a polyester veil, a glass veil and / or a carbon veil), or a combination of a powder bound fibre material and a veil. Generally, stitched fibre materials do not swell to a significant degree due to the stitching. The gap may, for example, only be present in certain regions, e.g. as identified by a visual inspection. In such a case, the third fibre material would be only arranged in these identified regions, for example, by sliding the third fibre material in between the cured spar cap and the second fibre material at the identified regions. In other embodiments, the third fibre material may comprise a larger footprint than the cured spar cap. For example, a root side edge of the third fibre material is located closer to the root end 71 of the shell mould 70 than the root end 61 of the cured spar cap 60, and a tip side edge of the third fibre material is located closer to the tip end 72 of the shell mould

[0093] 70 than the tip end 62 of the cured spar cap 60, a leading side edge of the third fibre material is located closer to a leading side edge of the shell mould 70 than a leading side edge of the cured spar cap 60 and a trailing side edge of the third fibre material is located closer to a trailing side edge of the shell mould 70 than the trailing side edge of the cured spar cap 60. In other words, the length of the third fibre material is greater than the length of the cured spar cap 60, and the width of the third fibre material is greater than the width of the cured spar cap 60.

[0094] LIST OF REFERENCES

[0095] 2 wind turbine 72 tip end

[0096] 4 tower 75 moulding surface

[0097] 6 nacelle 80 shell part

[0098] 8 hub 81 root end

[0099] 10 blade 82 tip end

[0100] 13 shell 85 interior side

[0101] 14 blade tip 86 exterior side

[0102] 15 tip end 87 second fibre material

[0103] 16 blade root L longitudinal direction

[0104] 17 root end C chordwise direction

[0105] 18 leading edge H height direction

[0106] 20 trailing edge Di first prebend distance

[0107] 24 first shell part D? second distance

[0108] 26 second shell part

[0109] 30 root region

[0110] 32 transition region

[0111] 34 airfoil region

[0112] 36 tip region

[0113] 38 shoulder

[0114] 50 spar cap mould

[0115] 51 root end

[0116] 52 tip end

[0117] 53 leading side edge

[0118] 54 trailing side edge

[0119] 55 moulding surface

[0120] 60 cured spar cap

[0121] 61 root end

[0122] 62 tip end

[0123] 63 leading side edge

[0124] 64 trailing side edge

[0125] 65 interior side

[0126] 66 exterior side

[0127] 67 first fibre material

[0128] 70 shell mould

[0129] 71 root end

Claims

CLAIMS1. A method of manufacturing a pre-bent wind turbine blade extending in a longitudinal direction (L), a chordwise direction (C), and a height direction (H), comprising the steps of:- providing: o a shell mould for moulding a shell part of the pre-bent wind turbine blade, the shell mould extending along the longitudinal direction and the chordwise direction, wherein the shell mould defines at least part of an airfoil shape in the chordwise direction and defines a first pre-bend shape along the longitudinal direction, and o a spar cap mould for moulding a spar cap of the pre-bent wind turbine blade, the spar cap mould extending along the longitudinal direction and the chordwise direction, wherein the spar cap mould defines at least part of substantially the same airfoil shape in the chordwise direction as the shell mould, and wherein the spar cap mould defines a second shape in the longitudinal direction, wherein the second shape exhibits less pre-bend compared to the first pre-bend shape;- arranging a first fibre material in the spar cap mould;- infusing a first resin into the spar cap mould;- causing or allowing the first resin to cure to obtain the cured spar cap having the at least part of substantially the same airfoil shape in the chordwise direction and having the second shape in the longitudinal direction;- arranging a second fibre material and the cured spar cap in the shell mould; and- deforming the cured spar cap from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell mould under the influence of gravity.

2. A method according to claim 1, further comprising:- infusing a second resin into the shell mould; and- causing or allowing the second resin to cure to co-embed the cured spar cap and the second fibre material in the second resin to obtain the shell part with the cured spar cap embedded therein.

3. A method according to claim 1, wherein the shell mould is instead a shell cradle, and wherein the step of arranging the second fibre material and the cured spar cap in the shell cradle comprises:- providing the second fibre material as a part of a cured fairing part on a surface of the shell cradle, and arranging the cured spar cap on the cured fairing part so thatthe cured spar cap deforms from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell cradle under the influence of gravity; and- preferably adhering the cured spar cap to the cured fairing part to obtain the shell part.

4. A method according to any one of the previous claims, further comprising performing finishing steps to obtain the pre-bent wind turbine blade comprising the shell part.

5. A method according to any one of the previous claims, wherein the first pre-bent shape of the shell mould involves the tip end of the shell mould being displaced from the root end of the shell mould along a height direction (H), preferably being perpendicular to the longitudinal direction (L) and / or chordwise direction (C), by a first pre-bend distance (Di), and wherein the second shape of the spar cap mould involves the tip end of the shell mould being displaced from the root end of the shell mould by a second distance (D?) along the height direction (H), wherein the second distance is less than the first pre-bend distance.

6. A method according to claim 5, wherein the second distance is, with increasing preference, at most 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or 0% of the first pre-bend distance.

7. A method according to any one of the previous claims, wherein the second shape of the spar cap mould is substantially flat along the height direction.

8. A method according to any one of the previous claims, wherein the second shape of the spar cap mould curves in the chordwise direction.

9. A method according to any one of the claims 1-7, wherein the second shape of the spar cap mould is straight along the longitudinal direction.

10. A method according to any one of the previous claims, wherein the method further comprises applying a moulding pressure, preferably a negative relative pressure, prior to and / or during the step of infusing the second fibre material and the cured spar cap with a second resin so as to further deform the cured spar cap to the first pre-bend shape of the shell mould, wherein the moulding pressure is preferably applied in a vacuum assisted resin transfer process.

11. A method according to any one of the previous claims, wherein the step of arranging the second fibre material and the cured spar cap in the shell mould includes arranging an exteriorside of the cured spar cap on a third fibre material, and optionally so that, during the step of deforming of the cured spar cap from the second shape along the longitudinal direction to substantially the first pre-bend shape of the shell mould under the influence of gravity, the third fibre material swells to at least partially fill one or more gaps between an exterior side of the cured spar cap and an upper surface of the second fibre material.

12. A method according to claim 11, wherein the third fibre material comprises a root side edge, a tip side edge, a leading side edge, and a trailing side edge, wherein: optionally the root side edge of the third fibre material is located closer to the root end of the shell mould than the root end of the cured spar cap; and / or optionally the tip side edge of the third fibre material is located closer to the tip end of the shell mould than the tip end of the cured spar cap; and / or optionally the leading side edge of the third fibre material is located closer to the leading side edge of the shell mould than the leading side edge of the cured spar cap; and / or optionally the trailing side edge of the third fibre material is located closer to the trailing side edge of the shell mould than the trailing side edge of the cured spar cap.

13. A method according to any one of claims 11-12, wherein the third fibre material has a length in the longitudinal direction and a width in the chordwise direction, wherein: optionally the length of the third fibre material is equal to or greater than the length of the cured spar cap; and / or optionally the width of the third fibre material is equal to or greater than the width of the cured spar cap.

14. A method according to any one of claims 11-13, wherein the third fibre material covers one or more distinct and separate regions of the exterior side of the cured spar cap, and optionally the third fibre material covers at most partially the exterior side of the cured spar cap.

15. A method according to any one of claims 11-14, further comprising a step of sliding the third fibre material in between the exterior side of the cured spar cap and the second fibre material, preferably after the step of arranging the second fibre material and the cured spar cap in the shell mould.

16. A method according to any one of claims 11-15, wherein the third fibre material is a nonstitched fibre material, for example a powder bound fibre material, such as a chopped strandmat and / or a continuous filament mat; a veil, such as a polyester veil, a glass veil and / or a carbon veil; or a combination of a powder bound fibre material and a veil. .

17. A method according to any one of the previous claims when dependent at least on claim 2, wherein the first resin is the same as or, preferably, different from the second resin.

18. A method according to any one of the previous claims, wherein the first fibre material is the same as or, preferably, different from the second fibre material.

19. A method according to any one of the previous claims, wherein the first fibre material and / or the second fibre material comprises a plurality of pultrusions and / or a plurality of fibrous layers.

20. A method according to claim 19, wherein the plurality of fibrous layers is uncured, pre-preg, pre-cured, or a combination thereof.

21. A method according to any one of claims 19-20, wherein the plurality of pultrusions and / or the plurality of fibrous layers comprises glass fibres, carbon fibres, or a combination thereof.

22. A method according to any one of claims 19-21, wherein the plurality of fibrous layers comprises unidirectional fibre mats, multidirectional, e.g. biaxial, fibre mats, or a combination of unidirectional and multidirectional, e.g. biaxial, fibre mats.

23. A method according to any one of the previous claims, wherein the first fibre material preferably comprises or consists essentially of a plurality of pultrusions, and the second fibre material preferably comprises or consists essentially of a plurality of uncured fibrous layers, such as multidirectional, e.g. biaxial or triaxial, fibre mats.

24. A pre-bent wind turbine blade obtainable by a method according to any one of the previous claims.

25. A pre-bent wind turbine blade defining a first pre-bend shape along a longitudinal direction and comprising a shell part and a pre-cured spar cap, wherein the pre-cured spar cap comprises or consists essentially of a composite material including a cured first resin, wherein the shell part comprises a cured second resin, wherein the pre-cured spar cap comprises a relaxed shape and a prestressed shape along the longitudinal direction, wherein the spar cap is embedded in the cured second resin in the stressed shape so as to follow the first pre-bent shape, and wherein the spar cap has a second shape in the relaxed state exhibiting less pre-bend compared to the first pre-bend shape.

26. A pre-bent wind turbine blade according to claim 25, wherein the cured second resin is cured after the cured first resin, the cured second resin preferably being different from the cured first resin.

27. A kit of parts for manufacturing a pre-bent wind turbine blade, the kit of parts comprising: - a shell mould extending along a longitudinal direction (L) and along a chordwise direction (C), wherein the shell mould defines at least part of an airfoil shape in the chordwise direction and defines a first pre-bend shape along the longitudinal direction; and- a spar cap mould extending along the longitudinal direction and the chordwise direction, wherein the spar cap mould defines at least part of substantially the same airfoil shape in the chordwise direction as the shell mould, and wherein the spar cap mould defines a second shape in the longitudinal direction, wherein the second shape exhibits less pre-bend compared to the first pre-bend shape.

28. A kit of parts according to claim 27, wherein the second shape of the spar cap mould is substantially flat along a height direction.

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