Patent Description:
Climate change has created an urgent need for sustainable energy, putting the spotlight on wind power as a cost-effective and clean energy source. Wind turbines typically comprise a tower, generator, gearbox, nacelle, and one or more rotor blades, which capture kinetic energy of wind using known airfoil principles. With increasing energy demand, modern wind turbines can have power ratings of above <NUM> MW and may have rotor blades that exceed <NUM> meters in length.

Wind turbine rotor blades are typically made from a fibre-reinforced polymer material, comprising a pressure side shell half and a suction side shell half, also called blade halves. The cross-sectional profile of a typical blade includes an airfoil for creating an air flow leading to a pressure difference between both sides. The resulting lift force generates torque for producing electricity.

The shell halves of rotor blades are often manufactured using blade moulds. First, a blade gel coat or primer is applied to the mould. Subsequently, fibre reinforcement and/or fabrics are placed into the mould followed by resin infusion. A vacuum is typically used to draw epoxy resin material into a mould. Alternatively, prepreg technology can be used in which a fibre or fabric pre-impregnated with resin forms a homogenous material which can be introduced into the mould. Several other moulding techniques are known for manufacturing wind turbine blades, including compression moulding and resin transfer moulding. The shell halves are assembled by being glued or bolted together substantially along a chord plane of the blade.

In such blade manufacturing processes, the use of preforms has become increasingly important. A preform is a shaped arrangement of fibres, such as multiple layers thereof, which has been bound and/or consolidated for later use as part of the fibre lay-up in the blade mould. The rationale for using preforms for blade manufacturing is to reduce cycle time in the blade mould. In addition, using preforms may reduce the number of required repairs due to the pre-consolidated structure of the preforms. As blade lengths increase, using preforms for blade lay-up adds efficiency and precision.

Typically, multiple preforms will be used in manufacturing a wind turbine blade. This usually requires large space for manufacturing and for storing the preforms. In addition, the manufacturing of preforms of different shapes and sizes can be time-consuming and expensive. Providing moulds for manufacturing preforms can be tedious and costly, which applies even more if preforms of various shapes and curvatures are required.

In addition, a typically wind turbine blade contains various parts of complex geometry and/or materials which a different from the classic fibre laminate used for a major part of a blade shell. When using such parts in combination with fibre preforms, even more complex geometries are required, which will vary between preforms depending on their placement location in the blade mould.

From <CIT> it is known to provide shell halves of a wind turbine blade with a root end insert comprising a plurality of fastening members which are embedded between outer fibre layers and inner fibre layers of the shell. These fastening members are accessible from the root end of the shell part so that the wind turbine blade may be mounted to the hub of a wind turbine. In this process, a mounting plate can be used to facilitate integration of the fastening members, wherein a plurality of bushings are provided on the mounting plate, alternating with wedge-shaped inserts. After completing the manufacturing process, the mounting plate of the root end assembly can be removed, and the remaining part constitutes a root end insert for attachment to the hub.

<CIT> relates to a mould part for manufacturing at least a root section of a wind turbine blade and adapted for use via mould inlays; paragraph [<NUM>]. <FIG> shows a side view of a lay-up in the mould part witha mould inlay <NUM> arranged on the mould surface <NUM> of the mould part <NUM>; [<NUM>]. An outer fibre skin <NUM> comprising a number of fibre layers is arranged on top of the mould inlay <NUM> and the mould surface <NUM>. Fastening members <NUM> in form of bushings for fastening the blade to the hub of a wind turbine as well as possible intermediate inserts are arranged on top of the outer fibre skin <NUM>. Finally, an inner fibre skin <NUM> comprising a number of fibre layers is arranged on top of the bushings <NUM> and the possible intermediate inserts; [<NUM>].

When including such root end inserts and other parts, like core material in the blade mould, precise geometry control of the various required fibre preforms becomes challenging.

It is therefore a first object of the present invention to provide a more cost-efficient way of manufacturing preforms for wind turbine blade parts.

It is a further object of the present invention to provide a more flexible and simple mode of manufacturing such preforms.

It is another object of the present invention to provide an improved preform mould assembly for forming preforms having varying shapes and sizes.

It is another object of the present invention to provide an improved method of manufacturing a wind turbine blade using multiple preforms which are to be arranged at different locations within the blade mould.

The present invention addresses one or more of the above-discussed objects by providing a method of manufacturing a preform for a wind turbine blade according to the subject-matter of the independent claim <NUM>.

It was found that this method allows for the manufacturing of preforms which can be used in the subsequent blade manufacturing process, particularly in regions where uneven or complex geometries need to be covered with fibre material. This applies in particular to the blade root end when a root end assembly is to be inserted, or toward the chordwise centre of the shell half where typically core material is to be sandwiched between fibre layers. Thus, by using a mould inlay comprising a tapered edge, preforms can be obtained that compensate for such uneven or complex geometries at their bottom surface. This was found to substantially reduced wrinkle formation while laying preforms in the blade mould. In particular when making the mould inlay(s) a permanent part of the preform mould for a standardized manufacturing process this results in substantial reduction of manufacturing cost.

Preferably, the preform to be manufactured by the present method is a consolidated arrangement of material comprising fibres, such as glass fibres, and a binding agent. The preform will typically be used for manufacturing a blade half of a wind turbine blade, such as a suction side shell half or a pressure side shell half. The preforms can be used in a subsequent blade moulding process as part of the fibre lay-up in the blade mould, such as a blade half mould. The preforms manufactured according to the present invention can be placed within the root region of a blade mould, thus constituting part of the root laminate. The root region may correspond to a region of the blade having a substantially circular or elliptical cross-section. However, the preforms could also be used for other parts and regions of a wind turbine blade, such as trailing edge or leading edge reinforcements or adhesive flanges. Alternatively, the preforms could be used for a full blade layup, or the central load carrying laminates as the main laminate.

The preform mould used in the method of the present invention may be of a type comprising one or more support elements and a plurality of strip members arranged on the one or more support elements. Preferably, each of the strip members comprises a top surface extending between a first lateral edge and an opposing second lateral edge, a groove extending along the first lateral edge, a tongue extending along the second lateral edge, and a sealing member arranged in the groove, wherein the strip members are arranged in juxtaposition, and wherein the tongue of a strip member is fixed, preferably releasably fixed, within the groove of an adjacent strip member, preferably such that the tongue abuts the sealing member, the respective top surfaces of the strip members forming a moulding surface for moulding the preform.

In some embodiments, the mould surface of the preform mould has a length of between <NUM> and <NUM> meters. In other embodiments, the mould surface of the preform mould has a width of <NUM>-<NUM> meters. In some embodiments, the preform mould has a height of between <NUM> and <NUM> meters. The mould surface of the preform mould may have a moulding surface area of between <NUM> and <NUM> square meters, such as between <NUM> and <NUM> square meters, preferably between <NUM> and <NUM> square meters. In a preferred embodiment, the mould surface is substantially gas tight.

In some embodiments, each preform mould has a length-width ratio of at least <NUM>:<NUM>. In other embodiments, each preform mould has a length-width ratio of at least <NUM>:<NUM>, such as at least <NUM>:<NUM>. In a preferred embodiment, each preform mould has a length-width ratio of at least <NUM>:<NUM>. In some embodiments, each preform mould has a length-width ratio of up to <NUM>:<NUM>.

In a preferred embodiment, each of the preforms obtainable by the preform mould of the present invention is configured to form a blade section starting from the root end of the wind turbine blade. Thus, preferably each of the preforms obtainable by the preform mould of the present invention is configured to be arranged at the root end of the blade mould. Most preferably, the preform obtainable using the preform mould of the present invention is configured to form a subsection of the root section extending from the root end of the blade together with other subsections of the root section equally extending from the root end of the blade.

In some embodiments, the preform moulds of the present invention comprise a mould surface configured for the manufacturing of respective subsections of a wind turbine blade, each subsection extending from the root end of the wind turbine blade. In some embodiments, the preform mould has a concave, or inwardly curved, mould surface. In a particularly preferred embodiment, the preform mould has an elongate mould surface with a length which is at least double, preferably at least five times, its width. The longitudinally extending lateral edges of the said mould surface, such as a left lateral edge and an opposing right lateral edge, extend in the length direction of the preform mould.

The step of fastening a first mould inlay to a first portion of the mould surface preferably comprises bonding the first mould inlay to the mould surface using an adhesive. The first mould inlay has an outer surface, which typically faces upward when the mould inlay is fastened to the preform mould, and an inner surface, which typically faces downward when the mould inlay is fastened to the preform mould, wherein the inner surface of the first mould inlay faces the first portion of the mould surface. It is preferred that the first portion of the mould surface extends from one of the two lengthwise ends of the preform mould surface, preferably along substantially the entire width of the mould surface, for a length of at least <NUM>%, more preferably at least <NUM>%, most preferably at least <NUM>% of the length of the preform mould surface.

In a preferred embodiment, the mould surface comprises a front edge, a rear edge, and two lateral edges each extending between the front edge and the rear edge, wherein said first portion of the mould surface extends along the front edge of the mould surface. In some embodiments, the extent of the mould surface can be delimited by one or more vacuum profiles which are fastened to the mould surface, typically extending parallel to the lateral edges of the mould surface. The fibre material is then preferably arranged in between the two opposing vacuum profiles. During the subsequent step of applying negative pressure, air can be advantageously withdrawn from the mould cavity via the vacuum profiles. In some embodiments, the first mould inlay is arranged in between a first and a second vacuum profile, said vacuum profiles extending in the length direction of the preform mould, wherein preferably the first mould inlay extends over the entire width in between the vacuum profiles.

At least part of the perimeter of the first mould inlay has a tapered edge. As used herein the term "perimeter" means the circumference or outer boundary of the mould inlay, i.e. its edges which extend between the outer (top) surface and the inner (bottom) surface of the inlay. Typically, the perimeter of the mould inlay consists of four edges, at least one of which is a tapered edge. Preferably, the first and second mould inlays have a substantially cuboid shape. Preferably, the first and second mould inlays have a substantially cuboid shape with four edges, wherein at least one of the four edges is a tapered edge. In a preferred embodiment, each mould inlay is shaped as a substantially flat cuboid having a height which is not more than <NUM>% of its length or width, with a least one tapered edge.

In the step of laying a fibre material and a binding agent on the mould surface and on the first mould inlay, the fibre material is typically placed on the outer surface (top surface) of the first mould inlay and on the surrounding mould surface. The fibre laying step will typically comprise the use of one or more fibre lay-up devices.

The fibre material and the binding agent can be preferably covered with a vacuum bag, such as a disposable vacuum bag or single-use vacuum bag for providing a vacuum chamber that allows consolidation of the fibre material of the preform. To form the moulding cavity, the periphery of the vacuum bag can be sealed to the mould, preferably by using a sealant tape, e.g. comprising a double sided adhesive, such as tacky tape.

Vacuum or negative pressure is then applied to the fibre material and binding agent, preferably via one or more vacuum profiles, for consolidating the preform.

The step of applying heat to the consolidated fibre material and binding agent to form the preform is preferably carried out using one or more heating devices, such as an oven. The heating temperature is preferably between <NUM> and <NUM>, such as <NUM>-<NUM>.

The binding agent can be applied to the fibre material during layup on the preform mould. In other embodiments, the binding agent is applied to the fibre material prior to the layup of the fibre material. Such binding agent is preferably present in an amount of <NUM>-<NUM> wt% relative to the weight of the fibre material. The binding agent may also be present in an amount of <NUM>-<NUM> gram per square meter of glass surface. In other embodiments, the binding agent may be present in an amount of <NUM>-<NUM> gram per square meter of glass surface.

Typically, the fibre material is placed successively onto the moulding surface together with the binding agent. The fibre material may comprise glass fibres, carbon fibres or a combination thereof. According to a preferred embodiment of the method, a glass fibre material is placed onto the mould surface, such as multiple layers of glass fibre material. The fibre material may advantageously be brought into contact with a binding agent before or during the fibre lay-up.

In another embodiment, the fibre material may include fibre rovings, such as glass fibre rovings. The lay-up process may include placing multiple single roving bundles into the mould, the roving bundles being preferably aligned unidirectionally. In a preferred embodiment, multiple layers of fibre rovings or roving bundles are successively placed onto each preform mould.

The binding agent may also be present in an amount of <NUM>-<NUM>, preferably <NUM>-<NUM>, gram per square meter of fibre surface. In preferred embodiments, the binding agent is present in an amount of <NUM>-<NUM> wt%, preferably <NUM>-<NUM> wt%, relative to the weight of the fibre material. Advantageously, the binding agent is a thermoplastic binding agent. The binding agent may comprise a polyester, preferably a bisphenolic polyester.

In a preferred embodiment, a heating step is carried out during or after applying negative pressure to the fibre material and binding agent, wherein heating of the fibre material and the binding agent takes place at a temperature of between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

An example of a suitable binding agent is a polyester marketed under the name NEOXIL <NUM>. Examples include NEOXIL <NUM> PMX, NEOXIL <NUM> KS <NUM> and NEOXIL <NUM> HF 2B, all manufactured by DSM Composite Resins AG. Another example is a polyester resin marketed under the name C. FILCO® <NUM> FPG <NUM>, which is a bisphenolic unsaturated polyester resin in powder form. Preferably, the binding agent is a polyester, preferably a bisphenolic polyester. In other embodiments, the binding agent is a hotmelt adhesive or based on a prepreg resin. In some embodiments, the preform comprises an epoxy material.

According to another embodiment, the binding agent is a thermoplastic binding agent. Typically, the fibre material comprises fibre rovings which are at least partially joined together by means of the binding agent by thermal bonding. In a preferred embodiment, the binding agent is a binding powder, such as a thermoplastic binding powder.

In one embodiment, the preforms of the present invention essentially consist of the fibre material and the binding agent. This means that the preforms contain no more than <NUM> wt%, preferably not more than <NUM> wt% or not more than <NUM> wt%, of material other than fibre material and binding agent relative to the total weight of the preform. According to another embodiment, the preform consists of the fibre material and the binding agent.

In another embodiment, the fibre material used for the preforms of the present invention essentially consists of glass fibres. This means that the fibre material contains not more than <NUM> wt%, preferably not more than <NUM> wt% or not more than <NUM> wt%, of material other than glass fibres relative to the total weight of the fibre material. According to another embodiment, the fibre material consists of glass fibres.

In one embodiment, the binding agent is present in an amount of <NUM>-<NUM> wt% relative to the weight of the fibre material. According to another embodiment, the melting point of the binding agent is between <NUM>° and <NUM>, preferably between <NUM> and <NUM>. According to another embodiment, the binding agent comprises a polyester, preferably a bisphenolic polyester.

In one embodiment of the present invention, each preform essentially consists of the fibre material and the binding agent. According to another embodiment, the fibre material comprises fibre rovings, preferably glass fibre rovings. In other embodiments, the fibre material may comprise carbon fibres or a hybrid material. According to another embodiment, the fibre material comprises a fibre fabric, such as a fibre mat. In another embodiment, a preform may further comprise at least one fibre fabric such as a fibre mat. Fibre rovings may be arranged on top and/or below such fabric.

In a preferred embodiment, the preforms manufactured according to the afore-mentioned method are used as part of the root region of a wind turbine blade, such as the root laminate. The root region may extend up to <NUM> meters, such as up to <NUM> meters, from the root end of the blade, as seen in its longitudinal direction. In other embodiments, the root region may extend to the shoulder of the blade +/- <NUM> meters. However, the preforms could also be used for other parts and regions of a wind turbine blade. In other embodiments, the preforms manufactured according to the afore-mentioned method are used over a length of <NUM>-<NUM>% of the total blade length. In another embodiment, the preforms manufactured according to the afore-mentioned method are used in a region of the blade extending between its root end and a shoulder of the blade.

In a preferred embodiment, the method further comprises fastening a second mould inlay to a second portion of the mould surface, the second portion being different from the first portion of the mould surface, the second mould inlay having an outer surface and an inner surface, wherein the inner surface of the second mould inlay faces the second portion of the mould surface, and wherein at least part of the perimeter of the second mould inlay has a tapered edge, wherein the laying step comprises laying a fibre material and a binding agent on the mould surface, on the first mould inlay, and on the second mould inlay. It is preferred that the first portion and the second portion of the mould surface constitute not more than <NUM>% of the entire mould surface, preferably <NUM>-<NUM>%, most preferably <NUM>-<NUM>% of the entire mould surface.

In a preferred embodiment, the first mould inlay is spaced apart from the second mould inlay. It is particularly preferred that the first mould inlay is arranged at the first lengthwise end of the preform mould, and that the second mould inlay is arranged at the second lengthwise end of the preform mould. Preferably, the first mould inlay is arranged such that its tapered end faces towards the second mould inlay. It is also preferred that the first mould inlay extends over the width of the mould surface, whereas the second mould inlay extends over only part of the width of the mould surface.

In a preferred embodiment, the first mould inlay is spaced apart from the second mould inlay by a distance of at least <NUM>, such as at least <NUM>, as measured along the longitudinal axis of the mould surface. In a preferred embodiment, said second portion of the mould surface extends along at least part of the rear edge of the mould surface, and preferably along at least part of one of the lateral edges of the mould surface.

According to the invention, the longitudinal axis of the first mould inlay is substantially perpendicular to the longitudinal axis of the mould surface. Thus, the first mould inlay may be oriented substantially transverse to the length of the mould surface of the preform mould.

According to the invention, the longitudinal axis of the second mould inlay is substantially parallel to the longitudinal axis of the mould surface. Thus, the second mould inlay may be oriented substantially along the length of the mould surface of the preform mould.

In a preferred embodiment, the first and/or the second mould inlay are permanently fastened to the mould surface, preferably using an adhesive. In a preferred embodiment, the first and/or the second mould inlay are substantially planar or substantially plate-shaped.

In a preferred embodiment, the tapered edge of the first and/or the second mould inlay is uniformly linearly tapered, e.g. tapering from a point maximum thickness of the mould inlay linearly to a point of minimum thickness.

In a preferred embodiment, the perimeter of the first mould inlay comprises a front edge, a rear edge, and two side edges, wherein the rear edge is a tapered edge, preferably wherein the front edge and the two side edges are substantially straight edges. Similarly, in a preferred embodiment, the perimeter of the second mould inlay comprises a front edge, a rear edge, and two side edges, wherein the front edge and one of the side edges are tapered edges, preferably wherein the rear edge and the other side edge are substantially straight edges.

In some embodiments, at least a portion of the perimeter of the mould inlays has a contoured or stepped edge.

The first and/or the second mould inlay can be made of a polymer material. In a preferred embodiment, the first and/or the second mould inlay are made of a foam material, such as a polymer foam, e.g. a polyurethane foam.

In a preferred embodiment, the tapered edge of the first and/or the second mould inlay is formed as a wedge-shaped part. In a preferred embodiment, the first and/or second mould inlay has a thickness of <NUM>-<NUM>, preferably <NUM>-<NUM>, tapering to less than <NUM> at the respective tapered edge.

In another aspect, the present invention relates to a mould assembly according to the subject-matter of the independent claim <NUM>.

In another aspect, the present invention relates to a method of manufacturing a shell part of a wind turbine blade, the method comprising the steps of.

wherein the second set of preforms comprises a plurality of preforms manufactured according to the method of the present invention.

The root end assembly is preferably a substantially semi-circular arrangement comprising a plurality of embedded fastening members, preferably bushings, arranged along a substantially semi-circular path, the fastening members being arranged to receive root bolts for fixing the blade to a hub of a wind turbine blade. The root end assembly preferably comprises a wedge-shaped or tapered part at its distal end, i.e. at the end pointing towards the tip end of the blade.

In a preferred embodiment, each of the plurality of preforms comprises a top surface and an opposing bottom surface, wherein the bottom surface comprises a cavity with one or more chamfered portions. Said cavity with one or more chamfered portions is advantageously formed in the preform manufacturing method by use of the mould inlays(s) as discussed above.

In a preferred embodiment, the method further comprises the steps of placing a core material on top of at least part of the first set of preforms, and arranging the second set of preforms on top of the root end assembly, the core material and the first set of preforms. The core material may comprise balsa wood or a foam material.

In some embodiments, each bushing may be embedded in a respective root inserts surrounding the bushing. In some embodiments, spacer elements, such as spacer elements with a butterfly-shaped cross section may be arranged in between neighbouring bushings along the substantially semi-circular path.

In some embodiments, the method of manufacturing a wind turbine blade part may involve arranging preforms in a prefab mould with subsequent infusing of resin and curing for manufacturing sub parts for later blade assembly. In some embodiments, the wind turbine blade part is a root laminate, a main laminate or a part thereof. In another embodiment, the blade part is a blade half.

Typically, the resin infusion step comprises vacuum assisted resin transfer moulding. In a preferred embodiment, the resin dissolves the binding agent of the preform. Other embodiments involve chemical binding, for example for epoxy or thermoset resins.

The resin for injecting the preform during the manufacturing of wind turbine blade parts, such as a root laminate, may be an epoxy, a polyester, a vinyl ester or another suitable thermoplastic or duroplastic material. In other embodiments, the resin may be a thermosetting resin, such as epoxy, vinyl ester or polyester, or a thermoplastic resin, such as nylon, PVC, ABS, polypropylene or polyethylene.

The fastening members of the root end insert are preferably adapted for incorporation within the root end of the shell part or shell half. In a preferred embodiment, the fastening members are bushings, preferably bushings with an inner thread. The bushings usually have a generally hollow cylindrical body. The fastening members are preferably accessible from the end of the wind turbine blade shell so that the fastening members in the final wind turbine blade can be used to mount the root end of the wind turbine blade to the hub of a wind turbine. The root end insert may further advantageously comprise a number of intermediate retaining inserts arranged between fastening members, said retaining inserts preferably comprising a wedge-shaped section for being arranged in between upper and lower fibre layers or plies of the shell part. Thereby, the fastening members and the retaining inserts may together form a root end insert that is embedded in the entire cross-section of the blade root end, thus forming a substantially circular insert in the finished wind turbine blade shell. The intermediate inserts and the fastening members preferably comprise lateral sides that abut each other.

According to an advantageous embodiment, the root end assembly further comprise wedge-shaped extension members arranged in longitudinal extension of the fastening members, tapering towards their distal end. The wedge-shaped extension member may for instance be made of foamed polymer or balsa-wood. The wedge-shaped extension member is preferably arranged such that it has the thickest part proximal to the end of the fastening member, and the thinnest part distal to the end of the fastening member. This ensures that the root end assembly has a gradual transition to the outer and inner fibre layers, in turn ensuring that the blade root does not have a steep or discontinuous stiffness transition.

The wedge-shaped extension members may thus provide for a gradual stiffness transition in the longitudinal direction of the finished wind turbine blade shell.

The present disclosure relates to a preform obtainable by the aforedescribed method of manufacturing a preform. Preferably, the preform comprises a top surface and an opposing bottom surface, wherein the bottom surface comprises a cavity with one or more chamfered portions. Said cavity with one or more chamfered portions is advantageously formed in the preform manufacturing method by use of the mould inlays(s) as discussed above. The top surface of the preform will usually face upwards in the preform mould, and the bottom surface of the preform will usually face downwards in the preform mould.

The present disclosure also relates to a blade part obtainable by the method of manufacturing a wind turbine blade part.

It will be understood that any of the embodiments and features described above in relation to the method of manufacturing a preform for a wind turbine blade likewise apply to the moulding assembly, to the method of manufacturing a blade part, and to the preform, as such, of the present invention, and vice versa.

As used herein, the term "wt%" means weight percent. The term "relative to the weight of the fibre material" means a percentage that is calculated by dividing the weight of an agent, such as a binding agent, by the weight of the fibre material. As an example, a value of <NUM> wt% relative to the weight of the fibre material corresponds to <NUM> of binding agent per kilogram of fibre material.

As used herein, the term "longitudinal" means an axis or direction running substantially parallel to the maximum linear dimension of the element in question, for example a preform mould.

<FIG> illustrates a conventional modern upwind wind turbine according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> furthest from the hub <NUM>.

<FIG> shows a schematic view of an embodiment of a wind turbine blade <NUM> according to the invention. The wind turbine blade <NUM> has the shape of a conventional wind turbine blade and comprises a root region <NUM> closest to the hub, a profiled or an airfoil region <NUM> furthest away from the hub and a transition region <NUM> between the root region <NUM> and the airfoil region <NUM>.

<FIG> and <FIG> depict parameters which are used to explain the geometry of the wind turbine blade according to the invention. <FIG> shows a schematic view of an airfoil profile <NUM> of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile <NUM> has a pressure side <NUM> and a suction side <NUM>, which during use - i.e. during rotation of the rotor - normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil <NUM> has a chord <NUM> with a chord length c extending between a leading edge <NUM> and a trailing edge <NUM> of the blade. The airfoil <NUM> has a thickness t, which is defined as the distance between the pressure side <NUM> and the suction side <NUM>. The thickness t of the airfoil varies along the chord <NUM>. The deviation from a symmetrical profile is given by a camber line <NUM>, which is a median line through the airfoil profile <NUM>. The median line can be found by drawing inscribed circles from the leading edge <NUM> to the trailing edge <NUM>. The median line follows the centres of these inscribed circles and the deviation or distance from the chord <NUM> is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord <NUM> and the suction side <NUM> and pressure side <NUM>, respectively.

Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position df of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line <NUM>, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position dp of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

<FIG> shows other geometric parameters of the blade. The blade has a total blade length L. As shown in <FIG>, the root end is located at position r = <NUM>, and the tip end located at r = L. The shoulder <NUM> of the blade is located at a position r = Lw, and has a shoulder width W, which equals the chord length at the shoulder <NUM>. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius ro and a minimum inner curvature radius ri, which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Δy, which corresponds to the out of plane deflection from a pitch axis <NUM> of the blade.

<FIG> is a schematic perspective drawing of a known preform mould <NUM>. The preform mould <NUM> comprises a support element <NUM> and nine strip members 88a-i arranged on the support element <NUM>. Each of the strip members 88a-i has a top surface <NUM>. Together, the top surfaces of the respective strip members form a moulding surface <NUM> for moulding a preform for a rotor blade moulding process. The moulding surface <NUM> extends between a left edge <NUM>, a right edge <NUM>, a rear edge <NUM> and a front edge <NUM>. <FIG> illustrates another embodiment of a preform mould <NUM> comprising a support element a plurality of strip members <NUM> arranged on the support element to form a moulding surface <NUM> for moulding a preform for a rotor blade moulding process. As seen in <FIG>, the mould surface <NUM> is an elongate mould surface with a length which is more than five times its width.

As illustrated in <FIG>, the manufactured preforms 98a, 98b, 98c can be laid up in a blade mould <NUM> to form part of a wind turbine blade, such as the root laminate. It is particularly preferred that the preforms manufactured according to the present invention are used for a blade section starting from the root end of the blade, such as the root region. The preforms 98a, 98b, 98c are arranged in the blade mould cavity <NUM>, usually together with additional fibre material <NUM>. Typically, the layup process also includes placing a core material <NUM>, such as balsawood or foam, on top of, and/or underneath the fibre preforms. Then, resin is infused to the blade mould cavity <NUM>, which is subsequently cured or hardened in order to form the blade part, such as a blade half.

<FIG> shows a known root end arrangement inserted at the root end during manufacturing of a wind turbine blade shell half <NUM>. In the moulding process, typically an outer skin <NUM> is formed of one or more layers of fibre material, and then a root end assembly <NUM> is placed on top of the outer skin <NUM> at the root end of the blade mould <NUM>. Then, an inner skin <NUM> formed of one or more layers of fibre material is placed on top of the root end assembly <NUM> and the outer skin <NUM>. Typically, such root end assemblies comprise a plurality of root inserts <NUM> each comprising one or more bushings <NUM> for receiving bolts to fasten the blade to the turbine hub. The root inserts <NUM> or bushings <NUM> are usually spaced apart by spacers or retaining members <NUM> along the semi-circular path at the root end of the blade. Also, as seen in <FIG>, such root end assemblies usually have a substantially wedge shaped part that tapers in a direction towards the tip end of the blade.

The preforms manufactured according to the method of the present invention are meant to address some the challenges with these known methods of manufacturing a wind turbine shell half, in particular concerning regions such as the wedge-shaped part of the root end assembly. The preforms of the present invention are particularly suitable for forming at least part of said inner skin <NUM> shown in <FIG>.

<FIG> illustrate a mould assembly <NUM> and a method of manufacturing a preform <NUM> for a wind turbine blade according to the present invention. The method comprises providing a preform mould <NUM> which has a mould surface <NUM>. The mould surface comprises a front edge <NUM>, a rear edge <NUM>, and two lateral edges <NUM>, <NUM> each extending between the front edge and the rear edge. The mould surface <NUM> for moulding the preform <NUM> may further be defined by vacuum profiles <NUM>, which are used to apply negative pressure to the fibre material in the latter steps of the method. As seen in <FIG>, a first mould inlay <NUM> is fastened to a first portion <NUM> of the mould surface, the first mould inlay <NUM> having an outer surface <NUM> and an inner surface <NUM>. The inner surface of the first mould inlay <NUM> faces the first portion <NUM> of the mould surface. Said first portion <NUM> of the mould surface extends preferably along the front edge <NUM> of the mould surface. The longitudinal axis L1 of the first mould inlay <NUM> is substantially perpendicular to the longitudinal axis Lm of the mould surface, as seen in <FIG>.

Similarly, a second mould inlay <NUM> is fastened to a second portion <NUM> of the mould surface, the second mould inlay <NUM> having an outer surface <NUM> and an inner surface <NUM>, wherein the inner surface of the second mould inlay <NUM> faces the second portion of the mould surface. The longitudinal axis L2 of the second mould inlay <NUM> is substantially parallel to the longitudinal axis Lm of the mould surface. At least part of the perimeter of the first mould inlay <NUM> has a tapered edge <NUM>. Also, at least part of the perimeter of the second mould inlay <NUM> has a tapered edge <NUM>, <NUM>. This is best seen in the cross sectional view of first mould inlay <NUM> in <FIG>, taken along the line a-a' in <FIG>, and in the cross sectional views of the second mould inlay in <FIG>, taken along the lines b-b' and c-c' in <FIG>. The first mould inlay <NUM> is spaced apart from the second mould inlay <NUM>.

The perimeter of the first mould inlay <NUM> comprises a front edge <NUM>, a rear edge <NUM>, and two side edges <NUM>, <NUM>, wherein the rear edge <NUM> is a tapered edge; see <FIG>. By contrast, the front edge <NUM> and the two side edges <NUM>, <NUM> are substantially straight edges. The first mould inlay <NUM> of such shape is preferably used for providing preforms with a cavity in their lower surface for providing space for a root end assembly, as discussed above. As for second mould inlay <NUM>, its perimeter comprises a front edge <NUM>, a rear edge <NUM>, and two side edges <NUM>, <NUM>, wherein the front edge <NUM> and one of the side edges <NUM> are tapered edges, wherein the rear edge and the other side edge are substantially straight edges. The cavity imparted to the preform by the second mould inlay is preferably used for accommodating a core material, as discussed above.

As seen in <FIG>, subsequently a fibre material <NUM> and a binding agent is laid on the mould surface <NUM>, on the first mould inlay <NUM>, and on the second mould inlay <NUM>. Preferably, a vacuum bag can be placed over the fibre lay up and over the vacuum profiles <NUM>, subsequently applying negative pressure to the fibre material and binding agent for consolidating the fibre material. Finally heat is applied to the consolidated fibre material and binding agent to form the preform.

The resulting shape of the preform is illustrated in the perspective views of <FIG>, as seen from the top, and in <FIG>, as seen from the bottom. The preform <NUM> comprises a top surface <NUM> and an opposing bottom surface <NUM>, wherein the bottom surface <NUM> comprises a first cavity <NUM> with chamfered portion <NUM>, and a second cavity <NUM> with chamfered portions <NUM>, <NUM>. When being placed in the blade mould, the first cavity <NUM> of the preform <NUM> is preferably located above the root end assembly of the blade. The second cavity <NUM> is preferably located above a core material of the blade.

The method of manufacturing a shell part of a wind turbine blade of the present invention is further illustrated in the schematic end views of <FIG>, which show a blade mould <NUM> as seen from the root end thereof. As seen in <FIG>, a first set of preforms 130a-e are arranged at respective positions P1-P2 along the circumference of the semi-circular or oval root end of the blade mould. Then a root end assembly <NUM>, preferably comprising a plurality of root inserts, is placed on top of at least part of the first set of preforms 130a-e, <FIG>. The root end assembly preferably comprises a plurality of root inserts and/or a plurality of bushings configured to receive a root bolt, wherein the root inserts and/or bushings are arranged at the root end of the blade mould along a substantially semi-circular radial path, as seen in <FIG> and <FIG>.

Subsequently, a second set of preforms <NUM> are placed on top of the root inserts and on top of the first set of preforms, further towards the tip end of the blade mould. The second set of preforms <NUM> comprises a plurality of preforms manufactured according to the method of the present invention, i.e. comprising one or more of the above-discussed cavities. Then a resin is infused into the blade mould <NUM>, and the resin is cured in order to form the blade part, i.e. the shell half in the illustrated embodiment.

Claim 1:
A method of manufacturing a preform (<NUM>) for a wind turbine blade, the method comprising the steps of
providing a preform mould (<NUM>) comprising a mould surface (<NUM>),
fastening a first mould inlay (<NUM>) to a first portion (<NUM>) of the mould surface, the first mould inlay (<NUM>) having an outer surface (<NUM>) and an inner surface (<NUM>), wherein the inner surface of the first mould inlay (<NUM>) faces the first portion of the mould surface, and wherein at least part of the perimeter of the first mould inlay (<NUM>) has a tapered edge (<NUM>),
laying a fibre material (<NUM>) and a binding agent on the mould surface (<NUM>) and on the first mould inlay (<NUM>),
applying negative pressure to the fibre material and binding agent for consolidating the fibre material, and
applying heat to the consolidated fibre material and binding agent to form the preform.
wherein the method further comprises fastening a second mould inlay (<NUM>) to a second portion (<NUM>) of the mould surface, the second mould inlay (<NUM>) having an outer surface (<NUM>) and an inner surface (<NUM>), wherein the inner surface of the second mould inlay (<NUM>) faces the second portion of the mould surface, and wherein at least part of the perimeter of the second mould inlay (<NUM>) has a tapered edge (<NUM>, <NUM>) wherein the laying step comprises laying a fibre material (<NUM>) and a binding agent on the mould surface (<NUM>), on the first mould inlay (<NUM>), and on the second mould inlay (<NUM>),
wherein the longitudinal axis (L1) of the first mould inlay (<NUM>) is substantially perpendicular to the longitudinal axis (Lm) of the mould surface, and wherein the longitudinal axis (L2) of the second mould inlay (<NUM>) is substantially parallel to the longitudinal axis (Lm) of the mould surface.