Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly ("directly driven") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

In order to extract more energy from the wind, the size of the rotor diameter is increased by increasing the dimensions of the wind turbine blades. The larger size of the blades introduces higher physical loads into the blade and related components. Wind turbine rotor blades generally comprise a body shell formed by two shell halves made of a composite material e.g. glass fiber reinforced composites.

The body shell is relatively lightweight and has structural properties that are not designed to withstand the bending moments and other loads acting on the blade during operation. To improve the structural properties of the rotor blade such as stiffness and strength, the blade is generally reinforced with structural components, e.g. one or more spar caps at the suction and pressure side of the blade with a shear web connecting them. Such a spar cap may also be called a "main laminate" or a "spar cap laminate" of a wind turbine blade. These terms may be used interchangeably throughout the present disclosure.

Spar caps and other composites can be manufactured using several materials such as glass fiber composites and carbon fiber composites. Modern spar caps are generally manufactured using pultruded plates. Pultruded plates are generally bonded together in a resin infused process to form a composite part such as spar cap.

<CIT> discloses fluid transfer and evacuation structures formed in a vacuum bag operable for use in vacuum-assisted resin transfer molding, debulking, compaction, or similar processes. Fiber rovings represent an interesting alternative to pultruded composites due to a reduced material cost. Further, the use of fiber rovings allows for a more tailored fiber placement than when using pultrusion plates.

In order to achieve a high-quality end product, it is important for fibers to stay in their correct position after placement in the mold. Rovings in particular are less stable than e.g. fiber pultrusion plates, i.e. rovings tend to accumulate on portions of the mold surface with a reduced local slope. Restraining the displacement of the fibers laid in a mold surface is a challenging task. Known approaches to limit the displacement of fiber mats or rovings include the use of vacuum systems. These systems generally use a vacuum bag surrounding the fiber rovings and mold surface during roving placement. Further, these systems require the use of placement heads working under vacuum conditions for laying rovings. Vacuum conditions may be difficult to maintain in such large and multi-component systems with moving parts and openings for feeding the rovings. To assure vacuum is maintain during composite manufacturing these vacuum systems require frequent maintenance. Further, such systems are relatively complex and have poor versatility.

The present disclosure provides examples of systems and methods that at least partially overcome some of the drawbacks of existing approaches.

In a first aspect, a mold assembly for manufacturing composite parts comprising fibers and resin is provided as defined in claim <NUM>.

According to this first aspect, the mold assembly allows laying fibers (e.g. rovings) in a mold, while at the same time it restrains the movement of the laid fibers. This is achieved by maintaining a certain tension on the pliable sheet, which can be achieved by locally opening and closing the pliable sheet. Further, the mold assembly restrains the displacement of the fibers in a passive manner, i.e. the mold assembly does not require activation to restrain the displacement of the fibers. Besides, the fact that the pliable sheet is configured to be opened and closed locally allows introducing fibers of different dimensions into a space delimited by the mold and the pliable sheet. Additionally, this mold assembly reduces maintenance and other expenses associated with systems based on the use of vacuum.

In another aspect but not according to the invention, a placement head for laying fibers is provided. The placement head is configured for laying fibers on a mold through a pliable sheet. The placement head comprises a guide element and a shoe. The guide element is configured to guide the fibers to a mold; and the shoe is configured to contact the pliable sheet. Further, the shoe is also configured to open and close the pliable sheet locally. Thus, the shoe defines an open area in the pliable sheet through which the fibers are laid in the mold.

According to this aspect, the placement head allows opening and closing the pliable sheet and provides an open area to lay further fibers without substantially modifying the overall tension in the pliable sheet. Thus, the placement head promotes an efficient laying process wherein portions of the fibers that are not below the placement head are substantially unaffected by the addition of material.

In yet another aspect, a method for manufacturing a composite part comprising fibers and resin is provided as defined in claim <NUM>. The method comprises laying fibers in a mold. Besides, the method comprises covering the laid fibers and the mold with a pliable sheet to restrain movement of the laid fibers. Additionally, the method includes at least partially uncovering the laid fibers or the mold; and laying additional fibers.

According to this aspect, the method allows laying fibers in a mold and restrain the movement of the same in a simple and yet reliable manner. Besides, the method allows the further laying of fibers without substantially affecting the positioning of the previously laid fiber. This may be performed at a plurality of instances, i.e. to provide several layers of fibers at different locations in the mold. This method reduces the complexity of known approaches considerably and makes the manufacturing process more efficient. Further, since even rovings can be efficiently used and these can be tailored at will, the method promotes the manufacture of more tailored composite parts.

Throughout this disclosure, the terms "pultruded composites", "pultruded plates", "pultrusions" or similar terms are generally used to define reinforced materials (e.g. fibers or woven or braided strands) that are impregnated with a resin and pulled through a heated die such that the resin cures.

The term "roving" is generally used to define any fibrous or filamentous structure such as a yarn, i.e. monofilament yarn or multifilament yarn, in which the fiber(s)/filament(s) run at least a portion of the whole length of the structure. Further, such fibrous or filamentous structure may be pre-impregnated with a resin, such as a thermoplastic polymer resin. Additionally, the fibrous or filamentous structure may be a woven fiber with filaments orientated in more than one direction, such as a biaxial fiber.

A "fiber mat" may herein be regarded as a piece of cloth or fabric comprising fibers. The fibers may have a variety of different orientations e.g. the fiber mats may be uniaxial, biaxial, multi-axial or different. The fibers may be woven with different types of weaves or may be unwoven. The fiber mats may comprise fibers in other arrangements, i.e. stitched fibers, flattened strands with adhesives to improve fiber mat integrity, and others.

Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

<FIG> illustrates a conventional modern upwind wind turbine <NUM> 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>.

The wind turbine blade <NUM> comprises a blade shell comprising two blade shell parts or half shells, a first blade shell part <NUM> and a second blade shell part <NUM>, typically made of fiber-reinforced polymer. The wind turbine blade <NUM> may comprise additional shell parts, such as a third shell part and/or a fourth shell part. The first blade shell part <NUM> is typically a pressure side or upwind blade shell part. The second blade shell part <NUM> is typically a suction side or downwind blade shell part. The first blade shell part <NUM> and the second blade shell part <NUM> are fastened together with adhesive, such as glue, along bond lines or glue joints <NUM> extending along the trailing edge <NUM> and the leading edge <NUM> of the blade <NUM>. Typically, the root ends of the blade shell parts <NUM>, <NUM> has a semi-circular or semi-oval outer cross-sectional shape.

<FIG> is a schematic diagram illustrating a cross sectional view of an exemplary wind turbine blade <NUM>, e.g. a cross-sectional view of the airfoil region of the wind turbine blade <NUM>. The wind turbine blade <NUM> comprises a leading edge <NUM>, a trailing edge <NUM>, a pressure side <NUM>, a suction side <NUM> a first spar cap <NUM>, and a second spar cap <NUM>. The wind turbine blade <NUM> comprises a chord line <NUM> between the leading edge <NUM> and the trailing edge <NUM>. The wind turbine blade <NUM> comprises shear webs <NUM>, such as a leading edge shear web and a trailing edge shear web. The shear webs <NUM> could alternatively be a spar box with spar sides, such as a trailing edge spar side and a leading edge spar side. The spar caps <NUM>, <NUM> may comprise carbon fibers while the rest of the shell parts <NUM>, <NUM> may comprise glass fibers.

<FIG> is a schematic diagram illustrating an exemplary mold system for molding a blade shell of a wind turbine blade. The mold system <NUM> comprises a first mold <NUM> and a second mold <NUM>. The first mold <NUM> is configured for manufacturing a first blade shell part of a wind turbine blade, such as an upwind shell part of the wind turbine blade (forming the pressure side). The second mold <NUM> is configured for manufacturing a second blade shell part of the wind turbine blade, such as a downwind shell part of the wind turbine blade (forming the suction side). The mold system <NUM> also comprises mold surfaces <NUM>, <NUM> for depositing fibers.

<FIG> schematically illustrates a perspective view of a portion of a mold assembly <NUM> for manufacturing composite parts according to one example. The composite parts comprise fibers <NUM> and resin to bond the fibers <NUM> together. The mold assembly <NUM> comprises a mold surface <NUM> and a pliable sheet <NUM>. The mold surface <NUM> extends in a longitudinal direction and in a transverse direction. Further, the mold surface defines lateral end walls <NUM> that delimit the mold surface <NUM> in the transverse direction.

The pliable sheet <NUM> is configured to be connected to the mold surface <NUM> between the lateral end walls <NUM>. The pliable sheet <NUM> is configured to be opened and closed locally so that the fibers <NUM> can be laid in the mold. Additionally, the pliable sheet <NUM> is also configured to restrain movement of the laid fibers <NUM>.

Opening and closing "locally" is to be understood herein that only a portion of the pliable sheet is opened at the same time, and not over the entire length of the pliable sheet. a local opening at any given moment may extend over less than <NUM>% of the total length of the mold, and optionally less than <NUM>% or less than <NUM>% or less than <NUM>% of the total length of the mold.

As illustrated in <FIG>, the pliable sheet <NUM> may be connected to the mold surface <NUM> at or near a top part of the mold surface <NUM> or in a lower part of the mold surface <NUM> depending on the specifications of the composite part. In <FIG>, the connection between the pliable sheet <NUM> and the mold surface <NUM> has been illustrated with a broken line.

In the illustrated example, rovings <NUM> are used as fiber material. Rovings <NUM> are more easily moved than other fiber materials after their placement in the mold. With examples of the present disclosure, rovings <NUM> can be effectively used. Rovings used in this manner can provide a significant cost reduction and offers possibilities of tailoring the strength and stiffness to a large extent.

In the present example, when the height of the layers of rovings <NUM> exceeds the height at which the pliable sheet <NUM> is connected to the mold surface <NUM>, the pliable sheet <NUM> will exert a pressure on the laid rovings <NUM> towards the mold surface <NUM>. This pressure promotes a secure placement of the rovings <NUM> and reduces the risk of fiber misalignment or motion during manufacturing. Further, as the pliable sheet <NUM> can be opened locally, additional rovings <NUM> may be laid, without substantially reducing the overall pressure acting on the majority of the rovings <NUM>. When opening the pliable sheet locally, significant movement of the rovings may still be avoided, along the entire length of the mold or almost the entire length of the mold.

In examples, the pliable sheet <NUM> at least partially seals the mold surface <NUM>. This may allow using the pliable sheet <NUM> as an interface for a vacuum system to infuse the rovings <NUM> with the resin, specifically after all rovings have been positioned in the mold. Further, the pliable sheet <NUM> may be made of an elastic material. More specifically, the pliable sheet may comprise synthetic rubbers, and more specifically it may comprise ethylene and/or propylene.

Besides, the pliable sheet <NUM> comprises a mechanism allowing locally opening and closing the pliable sheet such as e.g. a zip lock <NUM>, a hook and loop fastener <NUM> (e.g. Velcro ™) or a zipper <NUM> extending along a longitudinal direction of the mold surface. Combinations of the aforementioned elements are also possible, as schematically illustrated in <FIG>. In some examples, the pliable sheet <NUM> may comprise a plurality of said elements or combinations of the same, as for example <NUM> or more zippers, specifically <NUM> of more zippers and more specifically <NUM> or more zippers.

In some examples, the pliable sheet <NUM> may comprise at least one opening <NUM> configured to introduce resin into a space delimited by the pliable sheet <NUM> and the mold surface <NUM>. In examples, the openings <NUM> may be configured to be connected to a vacuum system to infuse resin, e.g. in a VARTM process (Vacuum Assisted Resin Transfer Molding).

In other examples, a vacuum bag may be used to infuse resin to the rovings <NUM>. In this case, the vacuum bag may be laid on top of the pliable sheet (if this is sufficiently permeable) or it may be laid directly on top of the rovings <NUM>.

<FIG> illustrates a cross-section of another example of a mold assembly <NUM> according to the present disclosure. Note that the mold assembly <NUM> in <FIG> has been illustrated with a rounded mold surface <NUM>, but other types of mold surfaces <NUM> could also be employed. Similarly, the pliable sheet <NUM> may be connected to the mold surface at different heights. In fact, in examples, the connection between the pliable sheet <NUM> and the mold surface <NUM> may be configured to be displaced along the surface of the mold surface, i.e. using guides or other connection means. This enables maintaining a certain level of pressure acting on the fibers <NUM> during the manufacturing process, e.g. as the height of the rovings increases the connection point between the pliable sheet <NUM> and the mold surface <NUM> may be displaced to compensate the increase in height of the fibers <NUM>. Note that for illustrative purposes the fibers <NUM> do not reach the heigh of the pliable sheet <NUM> in the figure. Further, the fibers <NUM> in this example are woven fibers, i.e. uniaxial or biaxial fiber mats, extending within a 2D plane. Other types of fibers, as for example fiber yarns extending substantially in only one dimensions or fiber pultrusions could also be employed.

As illustrated, the pliable sheet <NUM> may comprise a zipper <NUM> to locally open and close the pliable sheet <NUM>. Depending on specifications of the composite part to be manufactured, the zipper <NUM> may be orientated at an angle relative to the longitudinal direction of the mold surface <NUM>. Thus, the fibers <NUM> may be laid at an angle and the mechanical properties of the composite part may be tailored. The fibers <NUM> may comprise glass fiber, carbon fiber, aramid fibers and others suitable fibers. Further, the fibers <NUM> may comprise fibers that have been previously impregnated with resin, such as prepregs comprising fibers impregnated with epoxy resin, polyester resin, vinylester resin or other suitable resins.

The zipper <NUM> of the pliable sheet <NUM> comprises a chain and two sliders arranged in a head-to-head configuration (also known as O-type configuration). This configuration of the sliders allows creating an open area between the sliders, with one of them opening the chain and the other one of them closing the chain. This feature will be discussed in more detail in relation with <FIG>. Note that a similar effect could also be achieved with other type of openable connections such as zip-locks and hook and loop fasteners.

<FIG> schematically shows a mold assembly <NUM> comprising a placement head <NUM> according to an example of the present disclosure. The placement head <NUM> is illustrated in combination with a zipper <NUM> comprising a chain <NUM> and two sliders <NUM>, <NUM>. The placement head <NUM> of the mold assembly may be configured for connecting with the two sliders <NUM>, <NUM> so that one slider <NUM> opens the chain <NUM>, and the other slider <NUM> closes the chain <NUM> as the placement head moves. Thus, an open area <NUM> to access the mold or mold surface <NUM> between the two sliders <NUM>, <NUM> can be defined. Additionally, the placement head <NUM> may also be configured for laying the fibers <NUM> through said open area <NUM> and along the longitudinal direction. Note that if the motion of the placement head <NUM> is reverse, the opening and closing of the chain <NUM> would be performed by the other slider <NUM>, <NUM>.

In another aspect, <FIG> also discloses a placement head <NUM> according to an example of the present disclosure. The placement head <NUM> is configured for laying fibers <NUM> in a mold (not illustrated) through a pliable sheet <NUM>. The placement head <NUM> comprises a guide element <NUM> and a shoe <NUM>. The guide element <NUM> is configured to guide the fibers in a mold (not illustrated). The shoe <NUM> is configured to contact the pliable sheet <NUM>. Further, the shoe <NUM> is also configured to open and close the pliable sheet <NUM> locally. Thus, the shoe <NUM> defines an open area <NUM> through which the fibers are laid in the mold. The placement head <NUM> in <FIG> has been illustrated with broken lines not to obstruct the view of the zipper <NUM> below.

The fibers <NUM> may be particularly rovings or fiber mats.

The shoe <NUM> may include fastening elements to connect with the sliders <NUM>, <NUM> of the zipper <NUM>. The fastening elements may be configured to connect with sliders of a zip-lock, or it may include other type of connections configured to open and close a hook and loop type fastener. The shoe <NUM> may be dimensioned such as to allow fibers <NUM> of different widths to pass through the open area <NUM>, i.e. woven fibers extending within a 2D plane, fiber yarns extending along a longitudinal direction, or other type of fibers.

In <FIG>, the guide element <NUM> has been illustrated as a closed duct through which the fibers are fed to the mold, but other type of guide elements may be also employed for this task. Additionally, the guide element <NUM> may include a drive that controls the amount or number of fibers that is laid in the mold during the displacement of the placement head <NUM> along the mold surface.

<FIG> is a flow diagram of a method <NUM> for manufacturing a composite part comprising fibers <NUM> and resin according to the present disclosure. The method <NUM> comprises, at block <NUM>, laying fibers <NUM> in a mold <NUM>. Further, the method <NUM> also comprises, at block <NUM>, covering the laid fibers <NUM> and the mold surface <NUM> with a pliable sheet <NUM> to restrain movement of the laid fibers <NUM>. Besides, the method <NUM> also comprises, at block <NUM>, at least partially uncovering the laid fibers <NUM> or the mold surface <NUM> and laying <NUM> additional fibers <NUM>.

In some examples, the pliable sheet <NUM> used in method <NUM> may be at least partially openable. Further, the step <NUM> of at least partially uncovering the laid fibers <NUM> or the mold surface <NUM> may comprise opening at least a portion of the pliable sheet <NUM> locally for the laying <NUM> of the additional fibers <NUM>. Besides, the opening of at least a portion of the pliable sheet <NUM> may be performed at least partially automatically, i.e. by sliding at least one slider <NUM>, <NUM> of the zipper <NUM> or the zip-lock <NUM> using a placement head <NUM> or other automatic systems.

In examples, laying <NUM> fibers <NUM>, and covering <NUM> the laid fibers <NUM> and the mold surface <NUM> is performed using a placement head <NUM>. Further, the placement head <NUM> may also perform the subsequent opening a portion of the pliable or sheet <NUM> (or uncovering <NUM> the laid fibers <NUM>) and laying <NUM> additional fibers <NUM>.

Additionally, the pliable sheet <NUM> may be made of an elastic material such as the length of the pliable sheet <NUM> may be modified when the pliable sheet <NUM> exerts pressure against the fibers <NUM>.

In further examples, the method <NUM> further comprises at least partially sealing off the laid fibers <NUM> and infusing the laid fibers <NUM> with resin. The sealing off and the infusing may be performed using the pliable sheet <NUM>. This allows maintaining pressure always acting on the fibers, e.g. rovings and considerably reduces the risk of misalignment before resin infusion. The infusion of resin may include one of resin injection and applying vacuum, e.g. in a VARTM process (Vacuum Assisted Resin Transfer Molding).

Note that some of the technical features described in relation with the mold assembly <NUM> and placement head <NUM> may be included in the method <NUM> for manufacturing a composite part, and vice versa.

Claim 1:
A method (<NUM>) for manufacturing a composite part comprising fibers (<NUM>) and resin, the method (<NUM>) comprising:
laying (<NUM>) fibers (<NUM>) in a mold;
covering (<NUM>) the laid fibers (<NUM>) and a mold surface (<NUM>) with a pliable sheet (<NUM>) to restrain movement of the laid fibers (<NUM>);
at least partially uncovering (<NUM>) the laid fibers (<NUM>) in the mold; and
laying (<NUM>) additional fibers (<NUM>).