A method of manufacturing at least a part of a wind turbine shell

Abstract

The present disclosure relates to a method of manufacturing at least a part of a shell of a wind turbine blade The method comprising the steps of: impregnating fabrics of fibres with a curable matrix to provide a plurality of pre-pregs, the plurality of pre-pregs comprising at least a first pre-preg and a second pre-preg; providing a shell mould having a shell layup area; placing the first pre-preg at the shell layup area; locally applying heat to the first pre- preg and / or to the second pre-preg; compressing the second pre-preg onto the first pre-preg at the shell layup area to consolidate the first pre-preg and the second pre-preg such that the first pre-preg and the second pre-preg form a skin laminate; cooling the first pre-preg and / or the second pre-preg of the skin laminate; and heating the shell mould to cure the curable matrix of the pre-pregs of the skin laminate.

Description

[0001] A METHOD OF MANUFACTURING AT LEAST A PART OF A WIND TURBINE SHELL

[0002] Technical field

[0003] The present invention relates to a method of manufacturing at least a part of a wind turbine shell. The invention further relates to a robot system for manufacturing at least a part of a wind turbine shell, and a wind turbine blade comprising a shell.

[0004] Background of the invention

[0005] As a part of the worldwide transition to renewable energy, the is generally a demand for efficient production of wind turbines. In particular, the blades of the wind turbine are crucial to manufacture accurately and efficiently to ensure that the wind turbines can stably deliver energy for years to come once erected.

[0006] Conventionally, wind turbine blades are typically manufactured by either vacuum assisted resin transfer moulding (VARTM) or by pre-preg technology.

[0007] In vacuum assisted resin transfer moulding, the components of a blade of a wind turbine are placed in a shell mould, the components are encapsulated in a vacuum bag, and a matrix comprising a resin is transferred to the components inside the vacuum bag held by the shell mould. The resin cures, for example at elevated temperatures, to thereby provide, e.g., a shell of a blade of a wind turbine.

[0008] Alternatively pre-preg technology is utilized. Here, fabrics of fibres are impregnated with a matrix comprising a resin prior to placement in the shell mould, thereby providing one or more pre-pregs. These are then placed in the shell mould together with other components of the blade. Fixation is applied to ensure that the components, particularly the pre-pregs, stay fixed. Such fixation may for example be a vacuum bag or clamping means. When the components are fixed, the pre-pregs are cured, for example at elevated temperatures.

[0009] For pre-pregs, conventional manufacturing significantly restrains the variety of matrixes which can viably be used. In particular, some matrixes may complicate handling and laying the pre-pregs, and such matrices are thus generally avoided. Further, conventional manufacturing approaches suffer from the risk of components displacing relatively to each other or wrinkling prior to fixation and curing, and require the use of consumables such as vacuum bags, resin inlet channels, a distribution mesh, and sealant between vacuum bag and the shell mould.

[0010] Moreover, there is a general need to avoid potential structural weaknesses in wind turbine blades since these are challenging to address once the blade is in operation.

[0011] Hence, there is a need for manufacturing methods in which a greater variety of matrixes can viably be used. Further, there is a need for manufacturing methods in which risk of displacement or wrinkling is reduced. Moreover, there is a need for manufacturing methods where the need for consumables is reduced. Additionally, there is a general need for manufacturing methods which avoid potential structural weaknesses in wind turbine blades.

[0012] Summary of the invention

[0013] On the above background, it is an object of preferred embodiments of the invention to provide a method of manufacturing which allows a greater variety of matrices to be used for pre-pregs. It is further an object of some embodiments of the invention to provide manufacturing of a part of a wind turbine shell in which risk of displacement or wrinkling is reduced, and / or in which the need for consumables is reduced. Further, it is an object of some embodiments of the invention to avoid potential structural weaknesses in wind turbine blades.

[0014] A first aspect of the present disclosure relates to a method of manufacturing at least a part of a shell of a wind turbine blade, the method comprising the steps of: impregnating fabrics of fibres with a curable matrix to provide a plurality of prepregs, the plurality of pre-pregs comprising at least a first pre-preg and a second pre-preg, wherein the curable matrix comprises at least a curable resin; providing a shell mould having a shell layup area; placing the first pre-preg at the shell layup area; locally applying heat to the first pre-preg and / or to the second pre-preg; compressing the second pre-preg onto the first pre-preg at the shell layup area to consolidate the first pre-preg and the second pre-preg such that the first prepreg and the second pre-preg form a skin laminate; cooling the first pre-preg and / or the second pre-preg of the skin laminate; and heating the shell mould to cure the curable matrix of the pre-pregs of the skin laminate.

[0015] The provision of locally applying heat to a pre-preg prior to consolidation with another prepreg may allow a greater variety of matrices to be efficiently used for production of wind turbine blades.

[0016] Conventionally, viscous matrices are typically not used. Pre-pregs impregnated with viscous matrices can be complicated to handle and lay. For example, two such pre-pregs might not consolidate well with each other. Further, in case a highly viscous matrix is employed, the pre-preg may even exhibit a degree of stiffness potentially leading to imperfect shape-wise adherence of the pre-preg to the shell mould. Generally, such viscosities may, for example, be an inherent property of the curable matrix, arise from cross-linking of the curable resin by a curing agent such as a room temperature curing agent, or some combination thereof.

[0017] Thus, even though it can in principle be possible to use a viscous curable matrix, such matrices are generally avoided due to the manufacturing complications which arise.

[0018] However, by locally applying heat to the first pre-preg and / or to the second pre-preg, the viscosity of the curable matrix impregnating the pre-preg can be locally reduced, such that a portion of the pre-preg may consolidate well with another pre-preg, and such that its shapewise adherence to the shell mould is improved. As a result, a greater variety of matrices can viably be used for manufacturing parts of shells of wind turbine blades

[0019] In turn, pre-pregs with curable matrices having a greater viscosity may have provide a reduced risk of displacement or wrinkling and thereby a reduced need for fixation prior to curing, for example in case the greater viscosity arises from cross-linking of the curable resin by a curing agent such as a room temperature curing agent.

[0020] Note however that the present disclosure is not limited to curable matrices of a particular viscosity. The present aspect may, irrespective of the properties of the curable matrix, generally improve consolidation of pre-pregs, reduce the risk of displacement and wrinkling, reduce the need for consumable, or any combination thereof.

[0021] During the step of heating the shell mould, the shell mould may for example be heated to at least 80 degrees Celsius, for example at least 100 degrees Celsius, such as at least 120 degrees Celsius. Thereby, a cure onset temperature can be reached, for example a cure onset temperature of a latent curing agent.

[0022] According to examples of the present disclosure, the step of locally applying heat to the first pre-preg and / or the second pre-preg is performed by non-contact heating.

[0023] In contrast to non-contact heating, the step of heating the shell mould provides heat to the pre-pregs by contact heating via a surface contact between the shell mould and at least one pre-preg. Non-contact heating may for example be provided using an infrared lamp or a hot air source.

[0024] According to examples of the present disclosure, the step of locally applying heat provides the first pre-preg and / or the second pre-preg with an elevated surface temperature resulting from the step of locally applying heat to the first pre-preg and / or to the second pre-preg.

[0025] According to examples of the present disclosure, the step of compressing the second prepreg onto the first pre-preg is performed while the first pre-preg and / or the second pre-preg has an elevated surface temperature resulting from the step of locally applying heat to the first pre-preg and / or to the second pre-preg.

[0026] It is primarily important to raise the surface temperature, since it is the properties at the surface of the pre-preg which determines its ability to consolidate with another pre-preg. Further, since it is not desirable to promote full curing of the curable matrix (for example, as during the step of heating the shell mould to cure the curable matrix), it is desirable to primarily elevate the surface temperature.

[0027] According to examples of the present disclosure, heat transfer occurs between the first prepreg and the second pre-preg due to the elevated surface temperature during the step of compressing the second pre-preg onto the first pre-preg.

[0028] According to examples of the present disclosure, the elevated surface temperature reduces a viscosity of the curable matrix of the first pre-preg and / or the second pre-preg. According to examples of the present disclosure, the step of cooling the first pre-preg and / or the second pre-preg shifts the temperature of the first pre-preg and / or the second pre-preg from the elevated temperature towards an ambient temperature.

[0029] According to examples of the present disclosure, the step of cooling the first pre-preg and / or the second pre-preg increases a viscosity of the curable matrix of the pre-pregs of the skin laminate.

[0030] According to examples of the present disclosure, the step of heating the shell mould is performed after the step of cooling the first pre-preg and / or the second pre-preg.

[0031] According to examples of the present disclosure, the curable matrix of the first pre-preg and / or the second pre-preg is in a semi-solid state prior to the step of locally applying heat, wherein the curable matrix at a surface of the first pre-preg and / or the second pre-preg is processed into a liquid state by the step of locally applying heat.

[0032] According to examples of the present disclosure, heating is applied to an area of at most 5 square meters in the step of locally applying heat to the first pre-preg and / or to the second pre-preg, for example at most 4 square meters, for example at most 3 square meters, for example at most 2 square meters, for example at most 1 square meter, such as at most 0.8 square meters.

[0033] According to examples of the present disclosure, heating is applied to an area which substantially extends the width of the second pre-preg in the step of locally applying heat.

[0034] According to examples of the present disclosure, heating is applied to a given area for at most 30 seconds during the step of locally applying heat, for example for at most 20 seconds, for example for at most 15 seconds, such as for at most 10 seconds.

[0035] According to examples of the present disclosure, the step of heating the shell mould is performed without vacuum bagging of the shell mould and / or without applying pressure to fixate a central portion of the skin laminate.

[0036] According to examples of the present disclosure, the central portion extends at least 30 percent of the chord of the manufactured blade, for example at least 50 percent of the chord, for example at least 70 percent of the chord, such as at least 90 percent of the chord. Optionally, fixation, such as clamping means, may be provided at the edges of the shell moulds, where pre-pregs of the skin laminate are more susceptible to displacement or wrinkling due to the typical upright orientation of the shell mould at the edges. Thereby, the shell mould can be heated without applying pressure to fixate a central portion of the skin laminate.

[0037] According to examples of the present disclosure, the plurality of pre-pregs further comprises a third pre-preg, wherein the method further comprises the steps of: locally applying heat to the second pre-preg and / or the third pre-preg; compressing the third pre-preg onto the second pre-preg at the shell layup area to consolidate the second pre-preg and the third pre-preg such that the first pre-preg, the second pre-preg, and the third pre-preg form the skin laminate; and cooling the second pre-preg and / or the third pre-preg of the skin laminate.

[0038] According to the present disclosure, any number of pre-pregs may be sequentially heated and compressed onto one another at the shell layup area.

[0039] According to examples of the present disclosure, the method further comprises placing core material and / or one or more spar caps onto the skin laminate at the shell layup area, wherein the method further comprises the steps of: impregnating further fabrics of fibres with a further curable matrix to provide an auxiliary plurality of auxiliary pre-pregs, the auxiliary plurality of pre-pregs comprising at least a first auxiliary pre-preg and a second auxiliary pre-preg, wherein the further curable matrix comprises at least a further curable resin; placing the first auxiliary pre-preg onto the core material and / or the one or more spar caps at the shell layup area; locally applying heat to the first auxiliary pre-preg and / or to the second auxiliary pre-preg; compressing the second auxiliary pre-preg onto the first auxiliary pre-preg at the shell layup area to consolidate the first auxiliary pre-preg and the second auxiliary pre-preg such that the first auxiliary pre-preg and the second-auxiliary pre-preg form an auxiliary skin laminate; and cooling the first auxiliary pre-preg and / or the second auxiliary pre-preg of the auxiliary skin laminate.

[0040] According to the present disclosure, the skin laminate may also be referred to as a first skin laminate or an outer skin laminate. The auxiliary skin laminate may also be referred to as a second skin laminate or an inner skin laminate. In the manufactured wind turbine blade, the outer skin laminate thereby constitutes the outer skin of the wind turbine blade, and the inner skin laminate constitutes the inner skin of the blade.

[0041] Examples of the present disclosure can thereby involve placement of several skin laminates, for example two skin laminates, for example such that these two skin laminates sandwich the core material and / or one or more spar caps.

[0042] The further fabrics of fibre and the further curable matrix of the auxiliary pre-pregs can typically be substantially identical to the fabrics of fibre and the curable matrix of the prepregs. Resulting, the pre-pregs can be substantially similar to the auxiliary pre-pregs.

[0043] However, alternatively, the further fabrics of fibre and / or the further curable matrix can also be different to the fabrics of fibre and the curable matrix. This can, for example, be used to provide the inner and outer skin of the wind turbine blade with different properties or be used to provide the skin laminate and the auxiliary skin laminate with different cure progression properties. Different cure progression properties can, for example, be relevant since the time from placement to curing is different for the pre-pregs and the auxiliary pre-pregs. In particular, the pre-pregs are typically placed before the auxiliary pre-pregs, but the pre-pregs and the auxiliary pre-pregs are cures simultaneously in a single step of heating the shell mould. Different cure progression properties can, for example, also be relevant since the first-laid skin laminate typically has to carry a larger weight while in the shell mould then the auxiliary skin laminate. This larger weight can arise from core material and / or one or more spar caps as well as the auxiliary skin laminate. Finally, different cure progression properties can be relevant in relation to reducing the risk of thermal exotherm run away. According to examples of the present disclosure, the step of heating the shell mould is a step of heating the shell mould to cure the curable matrix of the pre-pregs of the skin laminate and to cure the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate.

[0044] In other words, the step of heating the shell mould is a single heating step which substantially simultaneously cures the resin of the pre-pregs of the skin laminate and the further resin of the auxiliary pre-pregs in the auxiliary skin laminate.

[0045] According to examples of the present disclosure, the curable matrix comprises a room temperature curing agent for the curable resin.

[0046] The provision of a curable matrix comprising a room temperature curing agent, for example such that the curable matrix has cure progression at an ambient temperature, may ensure that laid pre-pregs are fixed already prior to curing the curable matrix by heating. In particular, this may reduce the need for additional fixation required while fully curing the prepregs by heating the shell mould. That is, according to preferable examples of the present disclosure, the need for consumables such as vacuum bagging may be reduced. Further, the fixation provided by the room temperature curing agent may reduce the risk of pre-pregs displacing or wrinkling prior to or during curing.

[0047] Generally, the curing properties of the curable resin in combination with the room temperature curing agent can be quantified in terms of a specific pot life of the curable matrix, or a specific gel time of pre-preg impregnated with the curable matrix.

[0048] According to examples of the present disclosure, the room temperature curing agent for the resin provides cure progression to the curable matrix at an ambient temperature.

[0049] The ambient temperature may, for example, be the temperature of the shell mould without actively heating the shell mould, or it may be an air temperature measured, e.g., at a distance between 0.5 meter and 1 .0 meter from the skin laminate. The ambient temperature may also be a room temperature.

[0050] According to examples of the present disclosure, the ambient temperature is in the range from 15.0 degrees Celsius to 30.0 degrees Celsius, for example from 18.0 degrees Celsius to 27.0 degrees Celsius, for example from 20.0 degrees Celsius to 25.0 degrees Celsius. The room temperature curing agent can be further quantified in terms of a temperature range at which it provides cure progression, i.e., an ambient temperature as exemplified above.

[0051] According to examples of the present disclosure, the curable matrix has a characteristic glass-transition temperature at a point in time within a time span extending from the step of providing the curable matrix to the step of placing the one or more pre-pregs, wherein the characteristic glass-transition temperature is: in a range from 8.0 degrees Celsius to 23.0 degrees Celsius, for example in a range from 9.0 degrees Celsius to 20.0 degrees Celsius, such as in a range from 10.0 degrees Celsius to 17.0 degrees Celsius; and / or in a range from 3.0 Kelvin to 20.0 Kelvin below a temperature of the shell mould after the step of placing the one or more pre-pregs and prior to the step of heating the shell mould, for example in a range from 5.0 Kelvin to 18.0 Kelvin, such as in a range from 7.0 Kelvin to 15.0 Kelvin.

[0052] The glass-transition temperature of a material characterizes the range of temperatures over which a glass transition occurs, the glass transition being a gradual and reversible transition in amorphous materials from a hard solid-like state to a viscous or rubbery state as temperature is increased.

[0053] When the pre-pregs are placed, the curable matrix with a low viscosity may result in displacement or wrinkling of the pre-pregs prior to or during curing, whereas a curable matrix which is too viscous may provide insufficient consolidation between the separate pre-pregs.

[0054] In general terms, in the context of the present disclosure, it is thus advantageous to provide a curable matrix having a glass-transition temperature which is slightly below room temperature, or alternatively, slightly below the temperature of the shell mould. More specifically, it is advantageous to provide a curable matrix having a characteristic glasstransition temperature in the ranges exemplified above. This can ensure that the viscosity of the curable matrix neither displaces nor wrinkles the pre-pregs, while consolidation between pre-pregs is weakened minimally. Note that although a characteristic glass-transition temperature as exemplified above may provide a consolidation between pre-pregs which is weakened minimally, the consolidation between pre-pregs may nevertheless optionally be improved by, e.g., compression of prepregs and / or local heating.

[0055] Due to the presence of a room temperature curing agent, the curable matrix may cure progress over time, which in turn can shift the glass-transition temperature upwards as the curable resin begins to at least partially cross-link by the room temperature curing agent. The relevant point in time for characterization of the glass-transition temperature to potentially ensure adequate placement, resistance to wrinkling and / or consolidation properties, is within the time span extending from the step of providing the curable matrix to the step of placing the one or more pre-pregs, preferably during the step of placing the one or more pre-pregs.

[0056] The glass-transition temperature of a material can be measured by differential scanning calorimetry. Here, the difference in the amount of heat required to increase the temperature of a sample and a reference is measured as a function of temperature. When a material transitions in phase, the amount of heat required to increase the temperature of that material (i.e. , the heat capacity) can change. Accordingly, a glass transition may be observed.

[0057] In practice, the heat flow required to increase the temperature does not exhibit a sharp temperature transition, but instead a gradual change across a temperature range. In such a situation, the glass-transition temperature may be defined or determined by an inflection point of a heat flow as a function of temperature. The inflection point is a point at which the curvature changes sign, and the curvature can be calculated as the second derivative. The heat flow typically exhibits a change from negative curvature to positive curvature as a function of temperature as the temperature is increased across the glass transition temperature.

[0058] The characteristic glass-transition temperature of the curable matrix can also be quantified according to ISO 11357-2:2020.

[0059] According to examples of the present disclosure, the curable matrix of the one or more prepregs is semisolid prior to placing the one or more pre-pregs.

[0060] Generally, a substance in a semisolid state is a highly viscous substance, for example, the substance may have both properties of a solid and a liquid. More specifically, in the context of the present disclosure, the terminology of a substance being in a semisolid state may be quantified in terms of a glass-transition temperature of the substance. For example, if the glass-transition temperature of the substance is between 0.0 Kelvin and 20.0 Kelvin below the temperature of the substance, then the substance is in a semisolid state, for example if the glass-transition temperature of the substance is between 5.0 Kelvin and 15.0 Kelvin below the temperature of the substance.

[0061] Typically, a substance in a semisolid state shares the properties of solids in that they have the ability to support their own weight and hold their shapes, however they also share the properties of liquids in that the shape may be conformed to another shape upon applying pressure or heat to it and it may also flow under pressure or heat.

[0062] In the context of the present disclosure, the above descriptions of a substance in a semisolid state may be applied to the curable matrix when it has not yet cured, for example cured to a gel state or a solid state.

[0063] According to examples of the present disclosure, the curable matrix has a pot life of at most 24 hours at the ambient temperature, for example at most 16 hours, for example at most 12 hours, for example at most 8 hours, such as at most 6 hours.

[0064] In the context of the present disclosure, the pot life is defined as the duration of time (at ambient or room temperature) between providing the curable matrix (for example, by mixing at least the curable resin and the room temperature curing agent) and the time at which the curable matrix reaches a gel state.

[0065] In a gel state, the cross-linking density is sufficiently great that the curable matrix is not liquid and does not liquify at elevated temperatures, such as temperatures significantly greater than the glass-transition temperature.

[0066] Preferably, due to the presence of the room temperature curing agent in the curable matrix comprising the curable resin, there is a short pot life at room temperature. This curing agent ensures that under ambient conditions, cross-linking of the curable resin occurs, which in turn provides a short pot life.

[0067] A pot life as exemplified above (for example at most 24 hours) is short compared to the pot life of matrices used in conventional pre-pregs for wind turbines. This ensures that after the pre-pregs have been placed, the pre-pregs proceed to cure progress relatively quickly, thereby fixating the pre-pregs relative to the shell mould. Thereby, the manufacturing method can quickly proceed to the step of heating the shell mould to cure the curable matrix without a lengthy waiting time prior to the step of heating the shell mould.

[0068] The pot life of the curable matrix can also be quantified according to ISO 10364:2015.

[0069] According to examples of the present disclosure, the curable matrix has a pot life of at least 2 hours at the ambient temperature, for example at least 4 hours, for example at least 5 hours, such as at least 6 hours.

[0070] According to examples of the present disclosure, the curable matrix has a pot life in a range from 4 hours to 24 hours at the ambient temperature, for example in a range from 5 hours to 16 hours, such as in a range from 6 hours to 12 hours.

[0071] A lower boundary to the pot life as exemplified above may ensure that pre-pregs can be placed and / or compressed efficiently before significant cure progression has occurred.

[0072] According to examples of the present disclosure, the one or more pre-pregs impregnated with the curable matrix have a gel time of at most 24 hours at the ambient temperature, for example a gel time of at most 16 hours, for example at most 12 hours, for example at most 8 hours, such as at most 6 hours.

[0073] The properties of the curable matrix due to the presence of a room temperature curing agent can also be quantified in terms of the gel time of the pre-pregs.

[0074] In comparison to conventional pre-pregs used to manufacture wind turbine blades, the prepregs according to the present disclosure have a short gel time. This ensures that after the pre-pregs have been placed, the pre-pregs proceed to cure progress relatively quickly, thereby fixating pre-pregs relatively to the shell mould. Thereby, the manufacturing method can quickly proceed to the step of heating the shell mould to cure the curable matrix without a lengthy waiting time prior to the step of heating the shell mould.

[0075] The gel time of a pre-preg can be quantified according to ISO 15040:1999. This standard specifies that the gel time is measured by placing specimens of a pre-preg in a heated- platen press which is heated to a cure temperature. In the context of the present disclosure, the curable matrix may both have cure progression at room temperature, and latent cure progression at an elevated temperature. When testing the gel time at ambient temperature according to the present disclosure, the relevant temperature to perform the measurement at is a room temperature or an ambient temperature, such as a temperature in the range from 15.0 degrees Celsius to 30.0 degrees Celsius, for example from 18.0 degrees Celsius to 27.0 degrees Celsius, for example from 20.0 degrees Celsius to 25.0 degrees Celsius.

[0076] The ISO standard further suggests that pre-pregs are usually stored at a low temperature, and that a sealed package of pre-pregs are warmed up to ambient temperature before taking the sample. Pre-pregs according to the present disclosure are not necessarily stored at a low temperature. For example, the one or more pre-pregs can be placed in the shell layup area within a short duration (For example, within 2 hours, within 4 hours, or within 8 hours) of actually providing the curable matrix by mixing the curable resin and the room temperature curing agent. Thus, in case the pre-pregs are not stored at a low temperature, the gel time can be measured from the time at which the curable matrix is provided (at an ambient temperature), since substantial cure progression may start from this point onward. Specimens of the one or more pre-pregs should then be placed in the heated-platen press in which the measurement according to ISO 15040:1999 is to be performed within 1 hour of providing the curable matrix.

[0077] According to examples of the present disclosure, the epoxy equivalent weight (EWW) of the curable matrix is between 300 and 500 (g / Eq).

[0078] The unit of the epoxy equivalent weight is the weight of the uncured resin in grams which contains the equivalent of one mole of an epoxy group. .

[0079] An epoxy equivalent weight in the above-exemplified range may provide the curable matrix with curing properties adequate to ensure fixation with reduced consumables and / or without displacement or wrinkling.

[0080] According to examples of the present disclosure, the curable resin may be an oligomer, a pre-polymer or a polymer.

[0081] According to examples of the present disclosure, the curable resin comprises an epoxide group.

[0082] According to examples of the present disclosure, the curable resin comprises an epoxy resin. According to examples of the present disclosure, the epoxy resin is an aromatic epoxy resin or a non-aromatic epoxy resin.

[0083] According to examples of the present disclosure, the epoxy resin is selected from the group comprising diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol B, and combinations thereof.

[0084] According to examples of the present disclosure, the room temperature curing agent is an amine curing agent.

[0085] According to examples of the present disclosure, the amine curing agent is selected from the group comprising aromatic amines, cycloaliphatic amines, aliphatic amines.

[0086] According to examples of the present disclosure, the curable matrix preferably comprises a) one or more curable epoxy resins and b) at least one room temperature curing agent.

[0087] According to examples of the present disclosure, the curable matrix further comprises a catalyst, such as urone, for example in case the curable matrix comprises a latent curing agent.

[0088] The aspects of the present disclosure identifies that the use of room temperature curable resins in the specific context of wind turbine manufacturing can be advantageous.

[0089] Generally, a ‘curable resin’ refers to a resin which is curable, i.e., is capable of hardening with or without an additive or other agent, such as a hardening or curing agent. More specifically, curing is a chemical process that produces toughening or hardening of a polymer material by cross-linking / polymerization of polymer chains through e.g., a condensation reaction or by the use of their reactive groups such as amine / epoxy etc.

[0090] The curable resin may also be a ‘hybrid resin’, i.e., may also comprise a curing agent as part of the polymer itself.

[0091] The term ‘curing agent’ refers to a substance that is able to participate in the chemical reaction between the oligomer, pre-polymer and polymer, to achieve the polymerisation process and to provide a hardened material. Preferably, the curing agent is a room temperature curing agent, i.e., the curing agent forms a copolymer with the curable resin at room temperatures, thus forming a partially cured resin that starts solidifying at room temperature. An exemplary curing agent is T-403 from Huntsman Corporation.

[0092] The room temperature curing agent may be an amine curing agent, such as polyfunctional primary amines that undergo an addition reaction with the epoxide group to form a hydroxyl group and a secondary amine. The secondary amine may further react with an epoxide to form a tertiary amine and an additional hydroxyl group. The amine may be an aliphatic, cycloaliphatic or aromatic amine or a combination thereof.

[0093] The curable matrix may comprise 20-40% by dry weight curing agent in the final curable matrix composition by total weight of the total combined amount of the curable resin and curing agent(s), such as 20-40% by dry weight room temperature curing agent. As another example, the curable matrix comprises 2-10% by dry weight latent curing agent (such as MCA10 from Alzchem) and 10-20% by dry weight room temperature curing agent in the final curable matrix composition by total weight of the total combined amount of the curable resin and curing agent.

[0094] The curable resin may further comprise curing catalysts, additives, thickeners and / or antisettling agents.

[0095] As a specific example, the curable matrix can be based on a semisolid epoxy with epoxy equivalent weight of 300 g / Eq, and Polyetheramine-T403 and / or MCA10.

[0096] The aspects disclosed herein are not limited to using pre-pregs each comprising the same composition of curing agents. For example, a first sub-set of pre-pregs may comprise a room temperature curing agent, and a second sub-set of pre-pregs comprise a room temperature curing agent and a latent curing agent, wherein the relative dry weight of the room temperature curing agent is greater in each pre-preg of the first sub-set than in the second sub-set.

[0097] Thereby, the composition of the skin laminate(s) can be tailored to improve its curing properties. For example, a relatively large concentration of the room temperature curing agent throughout the skin laminate may increase the risk of thermal exotherm run away. On the other hand, a relatively large concentration of the latent curing agent throughout the skin laminate may increase the risk of wrinkling and displacement. Furthermore, heat from the shell mould is transferred less efficiently to (auxiliary) pre-pregs which are separated from the shell mould, for example by core material. Thereby, in some preferable embodiments, the relative dry weight of the room temperature curing agent is greater in the auxiliary prepregs of the auxiliary skin laminate than in the pre-pregs of the skin laminate. Alternatively or additionally, in some preferable embodiments, the relative dry weight of latent curing agent is greater in the pre-pregs of the skin laminate than in the auxiliary pre-pregs of the auxiliary skin laminate.

[0098] Here, the relative dry weight of a curing agent in a pre-preg may be understood as the dry weight of that curable agent relative to the total weight of the total combined amount of the curable resin and curing agents, preferably from a pre-preg sample of a skin laminate, the pre-preg sample preferable comprising an evenly-sized portion of each pre-preg of a skin laminate (for example a 10cm by 10cm portion of each pre-preg of a skin laminate).

[0099] According to examples of the present disclosure, the method comprises a step of cure progressing the curable matrix of the pre-pregs of the skin laminate, wherein the step of cure progressing the curable matrix is performed prior to and separately from the step of heating the shell mould, wherein the step of cure progressing the curable matrix fixates the prepregs of the skin laminate relative to the shell mould.

[0100] Preferably, this cure progression is performed at the ambient temperature. However, alternatively, the cure progression in the step of fixating the one or more pre-pregs may also be performed at a temperature of the shell mould which is slightly elevated, for example at a temperature in the range from 20.0 degrees Celsius to 40.0 degrees Celsius, for example in the range from 25.0 degrees Celsius to 35.0 degrees Celsius. Thereby, the cure progression can be accurately controlled, for example to minimize the influence of temperature fluctuations of the surroundings.

[0101] By fixating the one or more pre-pregs of the skin laminate relatively to the shell mould by cure progression, the need for further fixation means such as vacuum consumables is reduced.

[0102] According to examples of the present disclosure, the method further comprises a step of cure progressing the further curable matrix of the auxiliary skin laminate, wherein the step of cure progressing the further curable matrix is performed prior to and separately from the step of heating the shell mould, wherein the step of cure progressing the further curable matrix fixates the auxiliary pre-pregs of the auxiliary skin laminate relative to the shell mould. According to examples of the present disclosure, the step of cure progressing the curable matrix and / or the step of cure progressing the further curable matrix is / are performed at room temperature.

[0103] According to examples of the present disclosure, the step of cure progressing the curable matrix and the step of cure progressing the further curable matrix are performed at least partially simultaneously, and / or at least partly simultaneous with the step of cooling the first pre-preg and / or the second pre-preg.

[0104] According to examples of the present disclosure, the step of cure progressing the curable matrix processes the curable matrix into a partially cured stage, wherein the step of heating the shell mould processes the curable matrix into a fully cured stage.

[0105] According to examples of the present disclosure, the step of cure progressing the further curable matrix processes the further curable matrix into a partially cured stage, wherein the step of heating the shell mould processes the further curable matrix into a fully cured stage.

[0106] In the context of the present invention, cure progressing may also be referred to as hardening. Similarly cure progressed may be referred to as hardened.

[0107] As an example, the curable matrix comprises the curable resin and at least one curing agent. A curing agent of the at least one curing agent may for example be a roomtemperature curing agent. The room-temperature curing agent may harden / cure progress the curable matrix of the pre-pregs of the skin laminate subsequent to forming the skin laminate to thereby fixate the pre-pregs of the skin laminate relative to the shell mould prior to performing the step of heating the shell mould.

[0108] According to examples of the present disclosure, the method comprises a step of hardening the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate, wherein the step of hardening the further curable matrix is performed prior to and separately from the step of heating the shell mould, wherein the step of hardening the further curable matrix fixates the auxiliary pre-pregs of the auxiliary skin laminate relative to the shell mould.

[0109] As for the curable matrix, the further curable matrix may comprise a further curable resin and at least one further curing agent. A curing agent of the at least one further curing agent may for example, be a further room-temperature curing agent. The further room-temperature curing agent may harden the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate subsequent to forming the auxiliary skin laminate to thereby fixate the auxiliary pre-pregs of the auxiliary skin laminate relative to the shell mould prior to performing the step of heating the shell mould.

[0110] According to examples of the present disclosure, the curable matrix comprises a latent curing agent.

[0111] According to examples of the present disclosure, the latent curing agent comprises dicyandiamide and an accelerator such as urone or a derivative thereof.

[0112] According to examples of the present disclosure, the curable matrix is cured primarily by cross-linking of the curable resin by the latent curing agent in the step of heating the shell mould.

[0113] According to examples of the present disclosure, the cure progression in the step of fixating the one or more pre-pregs processes the curable matrix into a semi-solid state or, preferably, a gel state.

[0114] According to examples of the present disclosure, the heating of the shell mould processes the curable matrix into a solid state.

[0115] According to examples of the present disclosure, the cure progression of the curable matrix during the step of fixating the one or more pre-pregs is primarily obtained by at least partial cross-linking of the curable resin by the room-temperature curing agent for the curable resin.

[0116] According to examples of the present disclosure, the step of fixating the one or more prepregs is performed at the ambient temperature.

[0117] According to examples of the present disclosure, the step of heating the shell mould is initiated after the curable matrix of the pre-pregs of the skin laminate has hardened from a fluid state to a gel state during the step of cure progressing the curable matrix, and optionally wherein the step of heating the shell mould is initiated before the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate has hardened from a fluid state to a gel state. By initiating heating of the shell mould after the curable matrix of the pre-pregs has hardened from a fluid state to a gel state, the risk of wrinkling or displacement of pre-pregs may be reduced.

[0118] The risk of wrinkling or displacement can generally be lower for auxiliary pre-pregs of the auxiliary skin laminate. Thereby, the step of heating the shell mould may, optionally, be initiate before the further curable matrix of the auxiliary pre-pregs has hardened from a fluid state to a gel state, thereby potentially improving time efficiency of the method.

[0119] According to examples of the present disclosure, the step of heating the shell mould to cure the curable matrix comprises at first heating sub-step and a second heating sub-step subsequent to the first heating sub-step, wherein the first heating sub-step is associated with a first heating trajectory of the shell mould and the second heating sub-step is associated with a second heating trajectory of the shell mould, wherein the first heating trajectory has a first average temperature and the second heating trajectory has a second average temperature greater than the first average temperature, wherein the second heating sub-step is initiated after the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate has hardened from a fluid state to a gel state.

[0120] The first and the second heating trajectories refer to the temperature trajectories by which heating of the shell mould is controlled.

[0121] The provision of a second heating trajectory having an average temperature which is greater than that of a first heating trajectory may potentially ensure that the temperature-dependent viscosity of curable matrices impregnating pre-pregs does not decrease too much during the initial portion of the heating phase, thereby in turn reducing the risk of wrinkling and / or displacement. After the further curable matrix has hardened to a gel state, the second heating trajectory having a greater average temperature can be initiated.

[0122] As an example of heating trajectories, the first heating trajectory is a linearly increasing temperature, and the second heating trajectory is a constant temperature. The first heating temperature may for example linearly increase from room temperature to 100 degrees, for example in a first duration having an extension from 0.5 hour to 5 hours, and the second heating temperature may for example be a constant temperature at 100 degrees, for example in a second duration having an extension between 0.5 hours and 5 hours.

[0123] However, alternatively, the first heating trajectory may also be at a constant temperature, or have a non-linear trajectory. The second heating trajectory may also have any linear trajectory, or a non-linear trajectory.

[0124] In practice, the exact trajectories and durations can be adjusted based on the composition of the curable matrix, for example depending on one or more curing agents of the curable matrix. This composition typically affects the amount of heat or the temperatures required across some duration of time to reach a gel state, for example by cross-linking of a curable resin by a latent and / or a non-latent curing agent.

[0125] Typically, the first heating trajectory can be selected so as to ensure that no pre-pregs of the shell being manufactured wrinkles or displaces during this first heating trajectory, and the second heating trajectory can be selected to lie above a cure onset temperature of a latent curing agent.

[0126] According to examples of the present disclosure, the first heating trajectory of the first heating sub-step provides an amount of heat to the auxiliary pre-pregs of the auxiliary skin laminate which maintains these auxiliary pre-pregs in a fixated state until the further curable matrix has hardened from a fluid state to a gel state.

[0127] According to examples of the present disclosure, during the step of heating the shell mould, curing of the curable matrix of the pre-pregs of the skin laminate, and optionally curing of the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate, primarily occurs during the second heating sub-step.

[0128] According to examples of the present disclosure, an amount of heat added locally to the first pre-preg and / or the second pre-preg is greater in the step of heating the shell mould than during the step of locally applying heat to the first pre-preg and / or the second pre-preg so as to maintain the curable matrix of the first pre-preg and the second pre-preg in a non-gel state during the step of locally applying heat.

[0129] This may ensure that the curable matrix does not cure while applying local heating when compressing the pre-pregs. In practice, the local heating is typically performed on a time scale of seconds or tens of seconds, whereas shell mould heating may typically be performed on time scales of hours.

[0130] According to example of the present disclosure, the first pre-preg and / or the second prepreg is placed to extend along a chordwise direction of the shell mould.

[0131] A chordwise extension of pre-pregs may allow a generally more systematic placement of the pre-pregs, which in turn may simplify robot integration, for example such that a robot system places pre-pregs.

[0132] According to examples of the present disclosure, the second pre-preg is gradually compressed onto the first pre-preg along a chordwise direction of the shell mould.

[0133] Such compression may for example be performed using a compaction roller which gradually rolls along the chordwise direction of the shell mould while applying pressure on top of the second pre-preg to compress it onto the first pre-preg.

[0134] According to examples of the present disclosure, the second pre-preg is cut into a first portion and a second portion after the first portion of the second pre-preg has been compressed onto the first pre-preg along an entire chordwise extent of the shell mould, wherein the second portion of the second pre-preg is subsequently compressed onto a further shell layup area neighbouring the shell layup area.

[0135] Thereby, a generally more systematic placement of the pre-pregs, which in turn may simplify robot integration, may be allowed. Further, cutting a pre-preg into a first portion and a second portion with an adequate cutting angle without loss of material is simplified when the pre-pregs are placed along the chordwise direction.

[0136] According to examples of the present disclosure, the first portion is gradually compressed onto the first pre-preg along a first direction, and the second portion is gradually compressed onto the further shell layup area in a second direction opposite the first direction.

[0137] This may simplify systematic placement of the pre-pregs, which in turn may simplify robot integration, for example such that a robot system places pre-pregs. In particular, a potentially reduced amount of pre-preg material is wasted in the region of the material at which the cut is performed. According to examples of the present disclosure, the each pre-preg of the plurality of prepregs has an upper width of 1300 mm, for example an upper width of 1000 mm, for example an upper width of 700 mm, such as an upper width of 500 mm.

[0138] This enables the pre-pregs to properly conform to the shape of the shell mould. A narrow pre-preg further simplifies local heating and / or compression of one pre-preg onto another.

[0139] According to examples of the present disclosure, compression of pre-pregs is performed using a compaction roller.

[0140] The fabric of fibres may for example be 600-1000 gsm biax glass fibre fabric.

[0141] According to examples of the present disclosure, the steps of impregnating fabrics of fibres and placing one or more pre-pregs are performed at the same manufacturing site.

[0142] According to examples of the present disclosure, the curable matrix is a thermosetting matrix and / or the curable resin is a thermosetting resin.

[0143] A thermosetting matrix is a matrix which can be irreversibly hardened from a soft solid or viscous liquid. Such irreversible hardening may be curing of the matrix through heating. Such properties contrasts the properties of a thermoplastic material, which is a (polymer) material that becomes pliable or mouldable at a certain elevated temperature and solidifies upon cooling.

[0144] A second aspect of the present disclosure relates to a robot system for manufacturing at least a part of a shell of a wind turbine blade, the robot system comprising: one or more robot arms; a compaction roller arranged at a robot end effector of one of the one or more robot arms; a material spool holding a pre-preg and arranged to feed the pre-preg to the compaction roller; a digital storage medium comprising robot instructions for applying the prepreg to a shell layup area of a shell mould via the one or more robot arms; a heat source for locally heating a part of the pre-preg and / or for locally heating the shell layup area; and a robot controller system which upon execution of the robot instructions controls the one or more robot arms to locally heat a part of a first pre-preg and / or a second pre-preg via the heat source and to compress the second prepreg onto the first pre-preg at the shell layup area via the compaction roller.

[0145] Conventional pre-preg technology in relation to manufacturing of wind turbine require human labour. In particular, fixation of pre-pregs and other components are typically performed manually.

[0146] Since the provisions of the present disclosure can reduce the need for fixation of pre-pregs, this may in turn allow a full or almost full automation of wind turbine blade manufacturing. Hence, a room temperature curing agent synergistically compliments a robot system for manufacturing at least a part of a wind turbine shell.

[0147] According to examples of the present disclosure, the robot system comprises a pre-preg, the pre-preg comprising fabrics of fibres impregnated with a curable matrix, the curable matrix comprising at least a curable resin.

[0148] According to examples of the present disclosure, the curable matrix comprises a room temperature curing agent for the curable resin.

[0149] According to examples of the present disclosure, the pre-preg is laid down by one robot arm, and while another robot arm applies the compaction roller.

[0150] According to examples of the present disclosure, the robot instructions is configured such that execution of the robot instructions controls the one or more robot arms to compress the pre-preg onto the shell layup area along a chordwise direction of the shell mould.

[0151] According to examples of the present disclosure, the robot system further comprises a cutting tool configured to cut the pre-preg into a first portion and a second portion, wherein the robot instructions are further configured such that execution of the robot instructions controls the cutting tool to cut the pre-preg when the first portion has been compressed onto the shell layup area along an entire chordwise extent of the shell mould. The robot instructions may further be configured such that execution of the robot instructions controls the robot arm to subsequently compress the second portion onto a further shell layup area neighbouring the shell layup area.

[0152] According to examples of the present disclosure, the heat source is a non-contact heatsource, such as an infrared lamp or a hot air source.

[0153] According to examples of the present disclosure, the robot system is configured to manufacture a part of a wind turbine shell according to the manufacturing method of the first aspect. In particular, the robot system may be configured to place the one or more pre-pregs in the shell layup area to form a skin laminate as described in relation to the first aspect.

[0154] According to examples of the present disclosure, the robot system comprises the shell mould, the shell mould comprising heating means for curing the curable matrix of the prepregs.

[0155] According to examples of the present disclosure, the robot system is configured to heat the shell mould via the heating means to thereby cure the curable matrix.

[0156] A third aspect of the present disclosure relates to a wind turbine blade comprising a shell, wherein at least a part of the shell has been manufactured according to the first aspect of the present disclosure.

[0157] The manufacturing process according to the first aspect may provide a novel consolidation composition of a cured matrix and fabrics of fibres in the shell of the wind turbine blade which is not possible to define other than in terms of a process of manufacture. The manufacturing process may further provide a novel consolidation between the laminate layers of the shell of the wind turbine which is not possible to define other than in terms of a process of manufacture.

[0158] A fourth aspect of the present disclosure relates to a horizontal axis wind turbine comprising wind turbine blades, each of the wind turbine blades comprising a shell wherein at least a part of the shell has been manufactured according to the first aspect of the present disclosure.

[0159] The manufacturing process according to the first aspect provides a novel composition of a cured matrix and fabrics of fibres in the shell of the wind turbine blade which is not possible to define other than in terms of a process of manufacture. The manufacturing process may further provide a novel consolidation between the laminate layers of the shell of the wind turbine which is not possible to define other than in terms of a process of manufacture.

[0160] Brief description of the

[0161] Embodiments of the invention will now be further described by reference to the accompanying drawings, in which:

[0162] Fig. 1 illustrates method steps according to examples of the present disclosure,

[0163] Fig. 2 illustrates a shell mould and a first pre-preg to be placed in the shell mould,

[0164] Fig. 3 illustrates locally applying heat and compression of a second pre-preg onto a first prepreg, for example to form a skin laminate,

[0165] Fig. 4 illustrates placement of core material and spar caps in a shell mould,

[0166] Fig. 5 illustrates placement of auxiliary pre-pregs in a shell mould,

[0167] Fig. 6a-c schematically illustrate cure progressions in terms of viscosity and heating according to examples of the present disclosure,

[0168] Fig. 7 illustrates a robot system according to examples of the present disclosure,

[0169] Fig. 8 illustrates a robot arm comprising a heat source and a compaction roller for compressing a pre-preg onto a shell layup area of a shell mould; and

[0170] Fig. 9 illustrates main structural components of an exemplary horizontal-axis wind turbine comprising three separate wind turbine blades.

[0171] Detailed description of the drawings

[0172] It should be understood that the detailed description and specific examples, while indicating embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description. Fig. 1 illustrates method steps S1-S7 according to examples of the present disclosure. The exemplary method is a method of manufacturing at least a part of a shell of a wind turbine blade. Typically, most of the shell, i.e., both the leeward portion and windward portion of the shell, can be manufacturing according to the disclosed method, but the method can also be applied to manufacture a sub-portion of the shell of the blade.

[0173] In a first step S1 of the method, fabrics of fibres are impregnated with the curable matrix to provide a plurality of pre-pregs. The plurality of pre-pregs comprises at least a first pre-preg and a second pre-preg. The plurality of pre-pregs may be provided onto a material spool from which the pre-pregs are cut as individual portions of the material on the spool. The curable matrix comprises at least a curable resin. Typically, the curable matrix further comprises one or more curing agents, for example at least a room temperature curing agent and / or a latent curing agent.

[0174] The fabrics of fibres may for example be 800 gsm biaxial glass fibre fabric.

[0175] The impregnation may for example be performed, in a hot melt process, by pulling the fabrics of fibres through an impregnation unit hosting the curable matrix, for example onto a material spool. Generally, various conventional impregnation methods may be applied.

[0176] In another step S2 of the method, a shell mould having a shell layup area is provided. The shell mould may, for example, be a shell mould for a leeward shell of a wind turbine blade or a shell mould for a windward shell of a wind turbine blade. Alternatively, the shell mould can be a shell mould for the entire blade or a shell mould for a sub-portion of the blade.

[0177] The shell layup area can be any inner area or inner sub-area of the shell mould.

[0178] In another step S3 of the method, the first pre-preg is placed in the shell layup area. This first pre-preg can, for example, be placed manually or by a robot arm.

[0179] In another step S4 of the method, heat is locally applied to the first pre-preg and / or the second pre-preg. This preferably reduces a viscosity of a surface of the pre-preg onto which the local heat is applied.

[0180] In another step S5 of the method, the second pre-preg is compressed onto the first pre-preg at the shell layup area to consolidate the first pre-preg and the second pre-preg such that the first pre-preg and the second pre-preg form a skin laminate. The first pre-preg and the second pre-preg are compressed such that the surface of the first pre-preg and / or the second pre-preg to which local heat is applied becomes a contact surface between the first pre-preg and the second pre-preg subsequent to the step of compressing the second prepreg onto the first pre-preg. Further, the contact between the first pre-preg and the second pre-preg may transfer heat from the surface of to which local heat is applied to another surface of the other pre-preg, thereby further consolidating the two pre-pregs.

[0181] In another step S6 of the method, the first pre-preg and / or the second pre-preg of the skin laminate are cooled. Preferably, this step is implemented by passive cooling, although active cooling can in principle be applied.

[0182] In another step S7 of the method, the shell mould is heated to cure the curable matrix of the skin laminate. This heating may be implemented by any conventional heating process, for example by electrical heating of the shell mould.

[0183] The method may optionally include further method steps, such as a step of cure progressing the curable matrix of the pre-pregs of the skin laminate to fixate the pre-pregs of the skin laminate relative to the shell mould, a step of placing core material and / or one or more spar caps onto the skin laminate, a step of placing one or more auxiliary pre-pregs onto the core material and / or the one or more spar caps, or any combination thereof.

[0184] After the curable matrix of the one or more pre-pregs of the skin laminate has been cured, the manufactured part of the shell can be combined with other components to provide at wind turbine blade comprising the manufactured part of the shell. Such other components may be other shell components, shear webs or other reinforcement structures, external components such as vortex generators, sensors, lightning conductors, etc.

[0185] Fig. 2 illustrates a shell mould 21 and a first pre-preg 20a to be placed in the shell mould 21. The figure provides a cross-sectional view transversal relative to the longitudinal direction of the eventually manufactured wind turbine blade.

[0186] The shell mould 21 has a shell layup area 22 on its inner surface.

[0187] According to example of the present disclosure, the first pre-preg 20a is placed onto the shell layup area 22 of the shell mould 21 , as also indicated in the figure by an arrow. The first pre-preg 20a can be placed manually, autonomously by a robot system, or by a robot system which is manually assisted. Fig. 3 illustrates locally applying heat and compression of a second pre-preg 20b onto a first pre-preg 20a, for example to form a skin laminate.

[0188] The illustrated shell mould 21 is similar to the one illustrated in Fig. 2. However, in Fig. 3, the first pre-preg has already been placed onto the shell layup area 22 of the shell mould 21.

[0189] Further, in Fig. 3, a second pre-preg 20b is illustrated. This second pre-preg 20b Is compressed onto the first pre-preg 20a by using a compaction roller 23. The compaction roller can be a soft cylinder of low surface tension plastic rotatably mounted to a shaft.

[0190] To compress the second pre-preg 20b onto the first pre-preg 20a, the compaction roller 23 applies a pressure onto the shell mould 21 while it rolls across the shell mould 21 to thereby gradually compress the second pre-preg 20b onto the first pre-preg 20a along a chordwise direction of the shell mould 21. In the present illustration, the compaction roller 23 is gradually rolled while applying pressure from the left-hand side of the illustration to the righthand side of the illustration, corresponding to the compaction roller 23 being gradually rolled while applying pressure from the leading edge to the trailing edge of the eventually manufactured blade.

[0191] Further, Fig. 3 also illustrates a heat source 24 which applies heat 25 to the first pre-preg 20a, thereby locally applying heat.

[0192] By locally applying heat, the viscosity of the curable matrix at the surface of the pre-preg 20a is reduced. When the second pre-preg 20b is brought into contact with the first pre-preg 20a, the surface of the second pre-preg 20b may also be heated by heat transfer from the surface of the first pre-preg 20a, thereby in turn also reducing the viscosity of the curable matrix at the surface of the second pre-preg 20b. The reduced viscosity of the curable matrix at the surface of the first pre-preg 20a and / or at the surface of the second pre-preg 20b can provide an improved consolidation of the two pre-pregs 20a, 20b.

[0193] The heat-source 24 preferably moves along with the compaction roller 23, for example along the chordwise direction.

[0194] Alternatively or additionally, the heat source 24 can apply heat to the second pre-preg 20b, in particular to a surface of the second pre-preg 20b which is to contact the first pre-preg 20a upon compression of the first pre-preg 20a onto the second pre-preg 20b. Fig. 4 illustrates placement of core material 27 and spar caps 26 in a shell mould 21. The core material 27 and the spar caps 26 are placed onto the skin laminate 28 formed by one or more pre-pregs previously placed onto the shell layup area of the shell mould 21.

[0195] In the present example, two spar caps 26 are placed first onto the skin laminate 28, followed by placement of the core material 27 with respect to the spar caps 26 already placed.

[0196] Fig. 5 illustrates placement of auxiliary pre-pregs 29a, 29b in a shell mould. These auxiliary pre-pregs 29a, 29b are preferably placed in a manner similar to the placement of the already placed pre-pregs of the (outer) skin laminate 28. Hence, the placement of one or more of the auxiliary pre-pregs 29a, 29b can involve compression and / or local heating.

[0197] Fig. 6a-c schematically illustrate cure progressions in terms of viscosity and heating according to examples of the present disclosure.

[0198] Fig. 6a schematically illustrates one example. The horizontal axis of the figure indicates time, and the vertical axis indicates viscosity. A vertical position towards the bottom of the figure indicates a fluid with low viscosity, whereas a vertical position towards the top of the figure indicates a highly viscous fluid or semisolid, a gel, or a solid depending on exact position.

[0199] The figure illustrates a pre-preg viscosity 30 of a pre-preg impregnated by a curable matrix according to the present disclosure.

[0200] Initially, the pre-preg is held at a constant temperature, and resultingly, its viscosity is substantially constant.

[0201] Just prior to placement of the pre-preg, local heating 35 is applied to the pre-preg, thereby temporarily reducing the pre-preg viscosity 30. This pre-preg is then compressed onto another pre-preg in accordance with the present disclosure. The pre-preg is then cooled passively, which in turn increases the pre-preg viscosity 30 towards the level it was at prior to local heating 35.

[0202] Finally, shell mould heating is initiated at a shell mould heating onset 34 indicated by a vertical line. Heating of the shell mould, and thus of the pre-preg, initiates two processes. Firstly, the heating of the shell mould tends to decrease the viscosity of the matrix of the pre-preg, since the curable matrix has a temperature-dependent viscosity. However, secondly, the heating also triggers curing of the matrix of the pre-preg once a cure onset temperature is reached, which tends to increase viscosity. As a result, after the shell mould heating onset 34, the pre-preg viscosity 30 initially decreases. As the resin is gradually cross-linked in the curing process, the pre-preg viscosity 30 eventually starts to rise after the initial decrease. When a relatively large fraction of the resin is cross-linked, the viscosity increases sharply, and the pre-preg is cured.

[0203] Fig. 6b schematically illustrates another example of cure progression, once again with the horizontal axis indicative of time and the vertical axis indicative of viscosity.

[0204] Further, the figure indicates a gel transition 33 by a horizontal line. Below this gel transition 33, a given substance is in a semisolid or fluid state, and above this gel transition 33, the substance is in a gel state or a solid state.

[0205] Additionally, the figure also indicates a creep viscosity 37 by a horizontal line. Above the line of the creep viscosity 37, a given substance is in a highly viscous state or a semisolid state, and a pre-preg impregnated with a curable matrix of such a state will thereby tend not to displace or wrinkle once placed. However, such a highly viscous state may consolidate less efficiently than a fluid state of low viscosity.

[0206] In comparison with the example of cure progression illustrated in Fig. 6a, the example illustrated in Fig. 6b relates to a pre-preg as well as an auxiliary pre-preg which are both impregnated with a curable matrix comprising a curable resin and a room temperature curing agent for the curable resin.

[0207] To provide a better understanding of the aspects of the present disclosure, exemplary cure progression of a conventional pre-preg is also presented in Fig. 6b in terms of a conventional pre-preg viscosity 32 illustrated by a dashed line. As also explained in relation to Fig. 6a, when the conventional pre-preg has been laid, its viscosity 32 is substantially constant for a period of time, as indicated by a horizontal portion to the left-hand side of the dashed line. Shell mould heating is initiated at a shell mould heating onset 34 indicated by a vertical line. This initially decreases the viscosity of the curable matrix of the pre-preg, but as the resin is cross-linked, the viscosity increases sharply. Thereby, the gel transition 33 is eventually crossed by the conventional pre-preg viscosity 32. Returning to aspects introduced in the present disclosure, Fig. 6b illustrates a pre-preg viscosity 30 and an auxiliary pre-preg viscosity 31 of pre-pregs impregnated by a curable matrix comprising a room temperature curing agent.

[0208] In contrast to the conventional pre-preg viscosity 32, the pre-preg viscosity 30 and the auxiliary pre-preg viscosity 31 gradually increase prior to the shell mould heating onset 34. This is due to cure progression of the curable matrix by cross linking of the curable resin by the room temperature curing agent.

[0209] In the present example, the auxiliary pre-preg viscosity 31 is shifted in time relative to the pre-preg viscosity 30. This can arise if the room temperature curing agent has been added to provide the curable matrix of the pre-preg before the further room temperature curing agent has been added to provide the further curable matrix of the auxiliary pre preg. As a result, cure progression of the curable matrix of the pre-preg is initiated earlier than cure progression of the further curable matrix of the auxiliary pre-preg.

[0210] Fig. 6b further illustrates local heating 35, 36 of both the pre-preg and the auxiliary pre-preg. As also explained in relation to Fig. 6a, local heating 35 is applied to the pre-preg just prior to placement of the pre-preg to temporarily reduce the pre-preg viscosity 30 and the auxiliary pre-preg viscosity 31 , respectively.

[0211] In this particular example, the pre-preg viscosity 30 is reduced such that the curable matrix transitions from a semisolid state to a fluid state across the creep viscosity 37. As a result, the curable matrix of the pre-pregs consolidates more efficiently, for example such that the pre-preg and its curable matrix can consolidate efficiently with another pre-preg which has already been laid.

[0212] In a similar manner, just prior to placement of the auxiliary pre-preg, local heating 36 of the auxiliary pre-preg is applied to temporarily reduce the auxiliary pre-preg viscosity 31 , thereby improving consolidation.

[0213] In the present example, the pre-preg viscosity 30 crosses the gel transition 33 prior to the shell mould heating onset 34. Hence, once heating of the shell mould starts, the decrease in viscosity exhibited by the conventional pre-preg viscosity 32 is substantially absent. That is, once a gel state has been reached by the curable matrix, the substance is less susceptible to a decrease in viscosity due to heating. As a result, the pre-preg may be fixated relative to the shell mould with reduced or without external fixation means such as clamps or vacuum bagging.

[0214] The pre-preg is part of an outer skin laminate while the auxiliary pre-preg is part of an inner skin laminate. Accordingly, the pre-preg generally has to carry a larger weight during curing than the auxiliary pre-preg. Hence, the auxiliary pre-preg viscosity 31 does not necessarily need to reach the gel transition 33 prior to the shell mould heating onset 34. Even though the auxiliary pre-preg viscosity 31 does exhibit a decrease once heating is initiated, the cure progression which have already occurred may suffice to fixate the auxiliary pre-preg. By initiating shell mould heating before the auxiliary pre-preg has reached the gel transition 31 , the manufacturing method becomes more time-efficient. However, alternatively, it can also be advantageous to let the auxiliary pre-preg viscosity 31 reach the gel transition 33 prior to the shell mould heating onset 34 to further improve fixation.

[0215] Note that the illustrated time scales are not to scale. The local heating 35, 36 may typically be on performed on time scales of seconds or tens of seconds, whereas shell mould heating may typically be performed on time scales of hours.

[0216] Fig. 6c illustrates an exemplary heating trajectory 38 of the shell mould. The vertical axis indicates temperature of the shell mould, and, as for Figs. 6a-b, the horizontal axis is indicative of time. Prior to the shell mould heating onset 34, the shell mould heating trajectory lies at a substantially constant temperature.

[0217] After the onset 34, the trajectory is partitioned into a first heating sub-step 41 and a second heating sub-step 42. In the first heating sub-step 41 , the average temperature is lower than in the second heating sub-step 42. Due to the lower heating in the first heating sub-step 41 , the initial decrease in viscosity after the shell mould heating onset 34 is reduced, thereby reducing the risk of wrinkling and displacement of pre-pregs.

[0218] After sufficient cross-linking of the curable resin of the curable matrix, preferably after the auxiliary pre-preg viscosity 31 has at least reached the gel transition 33, the second heating sub-step is initiated. After the second heating sub-step 42, the curing is complete and the shell mould heating is terminated.

[0219] During the curing process, cross-linking of the curable matrix may be exothermic. Thus, note that the exemplary shell mould heating trajectory 38 of Fig. 6c indicates the temperature trajectory by which heating of the shell mould is controlled. In practice, at least the pre-pregs may exhibit a more uneven heating trajectory and may even reach temperatures higher than those of the shell mould.

[0220] Fig. 7 illustrates a robot system 51 according to examples of the present disclosure.

[0221] The illustrated robot system 51 comprises two robot arms 47, each comprising a robot end effector. A compaction roller 23 is attached at the end effector of at least one of the robot arms 47. A heat source 24 is attached at the end effector of another robot arm 47.

[0222] The robot system 51 further comprises a shell mould 21 , which the robot arms 47 are arranged next to. Exemplary shell layup areas 22a, 22b are indicated in the figure.

[0223] Each robot arm 47 is attached to a translational stage 48 which is configured to translate the relevant robot arm 47 along the lengthwise direction relative to the eventually manufactured wind turbine blade.

[0224] The system 51 also comprises a pre-preg comprising a fabric of fibres impregnated by a curable matrix. The curable matrix comprises a curable resin. This pre-preg is held by a material spool (not shown) arranged to feed the pre-preg to the compaction roller 23.

[0225] The robot system 51 further comprises a digital storage medium 49 comprising robot instructions for the robot arms 47, and a robot control system 50. The robot control system 50 is communicatively connected to at least one of the robot arms 47. The robot control system 50 may be implemented by one or more separate robot controllers for the separate robot arms 47.

[0226] Upon execution of the robot instructions of the digital storage medium 49 by the robot control system 50, the robot control system 50 controls the robot arms 49 to locally heat a first prepreg and / or a second pre-preg via the heat source, and to compress the second pre-preg onto the first pre-preg at one of the shell layup areas 22a, 22b via the compaction roller.

[0227] Fig. 8 illustrates a robot arm 47 comprising a compaction roller 23 for compressing a prepreg 20 onto a shell layup area of a shell mould 21.

[0228] Further, for this exemplary robot arm 47, a material spool 43, a feeder 46, a cutter 45, and a heat source 24 are also arranged at the robot end effector of the robot arm 47. The material spool 43 holds the pre-preg. In other examples, the material spool can be arranged separately from the robot end effector. For example, the material spool may be held by another robot arm.

[0229] The feeder 46 feeds the pre-preg to the compaction roller 23. The cutter 45 is arranged to cut the pre-preg, for example when the pre-preg has been laid across the entire chordwise direction (of the eventually manufactured blade) at a section of the shell mould 21.

[0230] The robot arm 47 is attached to a translational stage 48, which is configured to translate the robot arm 47 along the lengthwise and chordwise direction relative to eventually manufactured blade.

[0231] In other examples, a secondary compaction roller may also be arranged at the robot end effector of the robot arm, for example to facilitate detachment of the pre-preg from the (first) compaction roller 23.

[0232] In some examples, the compaction roller 23 is cooled by an air cooler to discharge heat picked up from the pre-preg 20 due to local heating. This can also facilitate detachment of the pre-preg from the compaction roller 23.

[0233] Fig. 9 illustrates main structural components of an exemplary horizontal-axis wind turbine 1 comprising three wind turbine blades 7 constituting the rotor 4 of the wind turbine 1. The wind turbine 1 comprises a tower 2 and a nacelle 3 mounted at top of the tower 2. The rotor 4 is operatively coupled to a generator 5 within the nacelle 3 via a drive train (not shown) for converting mechanical kinetic energy harvested from the wind into electrical energy. In addition to the generator 5, the nacelle 3 may house additional components required to operate and optimize the performance of the wind turbine 1. The tower 2 supports the load presented by the nacelle 3, the rotor 4, and other wind turbine components within the nacelle 3.

[0234] The rotor 4 includes a central hub 6 and three elongated wind turbine blades 7 extending radially outward from the central hub 6, i.e. , longitudinally in a lengthwise direction, from a root section of the blades 7 at the hub 6 to a tip section of the blades. In operation, the blades 7 are configured to interact with the passing air flow to produce lift that causes the central hub 6 to rotate about the longitudinal axis of the rotor 4. Wind speed in excess of a minimum level will activate the rotor 4 and allow it to rotate within a plane substantially perpendicular to the direction of the wind. The rotation is converted to electric power by the generator 5 and is usually supplied to the utility grid.

[0235] The three separate blades 7 of the wind turbine 1 may be manufactured according to the manufacturing procedures presented in the present disclosure. Various versions and elements of the invention have been exemplified for the purpose of clarification rather than limitation. Well-known details of methods and systems have been omitted to not obscure the content of the disclosure with redundancy. Various elements and features of the invention and this disclosure may be combined in any way possible within the scope of the claims.

Claims

CLAIMS1. A method of manufacturing at least a part of a shell of a wind turbine blade, the method comprising the steps of: impregnating fabrics of fibres with a curable matrix to provide a plurality of prepregs, the plurality of pre-pregs comprising at least a first pre-preg and a second pre-preg, wherein the curable matrix comprises at least a curable resin; providing a shell mould having a shell layup area; placing the first pre-preg at the shell layup area; locally applying heat to the first pre-preg and / or to the second pre-preg; compressing the second pre-preg onto the first pre-preg at the shell layup area to consolidate the first pre-preg and the second pre-preg such that the first prepreg and the second pre-preg form a skin laminate; cooling the first pre-preg and / or the second pre-preg of the skin laminate; and heating the shell mould to cure the curable matrix of the pre-pregs of the skin laminate.

2. A method according to claim 1 , wherein the step of heating the shell mould is performed without vacuum bagging of the shell mould and / or without applying pressure to fixate a central portion of the skin laminate.

3. A method according to any of the preceding claims, wherein the plurality of pre-pregs further comprises a third pre-preg, wherein the method further comprises the steps of: locally applying heat to the second pre-preg and / or the third pre-preg; compressing the third pre-preg onto the second pre-preg at the shell layup area to consolidate the second pre-preg and the third pre-preg such that the first pre-preg, the second pre-preg, and the third pre-preg form the skin laminate; andcooling the second pre-preg and / or the third pre-preg of the skin laminate.

4. A method according to any of the preceding claims, wherein the method further comprises placing core material and / or one or more spar caps onto the skin laminate at the shell layup area, wherein the method further comprises the steps of: impregnating further fabrics of fibres with a further curable matrix to provide an auxiliary plurality of auxiliary pre-pregs, the auxiliary plurality of pre-pregs comprising at least a first auxiliary pre-preg and a second auxiliary pre-preg, wherein the further curable matrix comprises at least a further curable resin; placing the first auxiliary pre-preg onto the core material and / or the one or more spar caps at the shell layup area; locally applying heat to the first auxiliary pre-preg and / or to the second auxiliary pre-preg; compressing the second auxiliary pre-preg onto the first auxiliary pre-preg at the shell layup area to consolidate the first auxiliary pre-preg and the second auxiliary pre-preg such that the first auxiliary pre-preg and the second-auxiliary pre-preg form an auxiliary skin laminate; and cooling the first auxiliary pre-preg and / or the second auxiliary pre-preg of the auxiliary skin laminate.

5. A method according to claim 4, wherein the step of heating the shell mould is a step of heating the shell mould to cure the curable matrix of the pre-pregs of the skin laminate and to cure the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate.

6. A method according to any of the preceding claims, wherein the method comprises a step of cure progressing the curable matrix of the pre-pregs of the skin laminate, wherein the step of cure progressing the curable matrix is performed prior to and separately from the step of heating the shell mould, wherein the step of cure progressing the curable matrix fixates the pre-pregs of the skin laminate relative to the shell mould.

7. A method according to claim 6 when it is dependent on claim 4 or 5, wherein the step of heating the shell mould is initiated after the curable matrix of the pre-pregs of the skin laminate has hardened from a fluid state to a gel state during the step of cure progressing the curable matrix, and optionally wherein the step of heating the shell mould is initiated before the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate has hardened from a fluid state to a gel state.

8. A method according to any of claims 6-7, wherein the step of heating the shell mould to cure the curable matrix comprises at first heating sub-step and a second heating sub-step subsequent to the first heating sub-step, wherein the first heating sub-step is associated with a first heating trajectory of the shell mould and the second heating sub-step is associated with a second heating trajectory of the shell mould, wherein the first heating trajectory has a first average temperature and the second heating trajectory has a second average temperature greater than the first average temperature, wherein the second heating sub-step is initiated after the further curable matrix of the auxiliary pre-pregs of the auxiliary skin laminate has hardened from a fluid state to a gel state.

9. A method according to claim 8, wherein the first heating trajectory of the first heating substep provides an amount of heat to the auxiliary pre-pregs of the auxiliary skin laminate which maintains these auxiliary pre-pregs in a fixated state until the further curable matrix has hardened from a fluid state to a gel state.

10. A method according to any of the preceding claims, wherein the curable matrix has a characteristic glass transition temperature at a point in time within a time span extending from the step of impregnating the fabrics of fibres to the step of compressing the second prepreg onto the first pre-preg, wherein the characteristic glass transition temperature is: in a range from 8.0 degrees Celsius to 23.0 degrees Celsius, for example in a range from 9.0 degrees Celsius to 20.0 degrees Celsius, such as in a range from 10.0 degrees Celsius to 17.0 degrees Celsius; and / orin a range from 3.0 Kelvin to 20.0 Kelvin below an ambient temperature, for example in a range from 5.0 Kelvin to 18.0 Kelvin, such as in a range from 7.0 Kelvin to 15.0 Kelvin.11 . A method according to any of the preceding claims, wherein an amount of heat added locally to the first pre-preg and / or the second pre-preg is greater in the step of heating the shell mould than during the step of locally applying heat to the first pre-preg and / or the second pre-preg so as to maintain the curable matrix of the first pre-preg and the second pre-preg in a non-gel state during the step of locally applying heat.

12. A method according to claim 1 , wherein the second pre-preg is gradually compressed onto the first pre-preg along a chordwise direction of the shell mould.

13. A method according to any of the preceding claims, wherein compression of pre-pregs is performed using a compaction roller.

14. A method according to any of the preceding claims, wherein the curable matrix is a thermosetting matrix.

15. A robot system for manufacturing at least a part of a shell of a wind turbine blade, the robot system comprising: one or more robot arms; a compaction roller arranged at a robot end effector of one of the one or more robot arms; a material spool holding a pre-preg and arranged to feed the pre-preg to the compaction roller; a digital storage medium comprising robot instructions for applying the prepreg to a shell layup area of a shell mould via the one or more robot arms; a heat source for locally heating a part of the pre-preg and / or for locally heating the shell layup area; anda robot control system which upon execution of the robot instructions controls the one or more robot arms to locally heat a part of a first pre-preg and / or a second pre-preg via the heat source and to compress the second pre-preg onto the first pre-preg at the shell layup area via the compaction roller.

16. A robot system according to claim 15, wherein the robot system comprises the shell mould, the shell mould comprising heating means for curing the curable matrix of the prepregs.

17. A wind turbine blade comprising a shell, wherein at least a part of the shell has been manufactured according to any of claims 1-14.

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