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: providing a curable matrix, said curable matrix comprising a curable resin and a room temperature curing agent for said curable resin; impregnating fabrics of fibres with said curable matrix to provide one or more pre-pregs; providing a shell mould having a shell layup area; placing the one or more pre- pregs in the shell layup area to form a skin laminate; and heating the shell mould to cure the curable matrix of the one or more pre-pregs of the skin laminate. The disclosure further relates to a wind turbine blade and a robot system for manufacturing at least a part of a shell of a wind turbine blade.

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 part of the worldwide transition to renewable energy, there 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 via consumable resin inlets 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 is via a vacuum bag. When the components are fixed, the pre-pregs are cured, typically at elevated temperatures.

[0009] Both of these conventional approaches have various strengths and disadvantages. A common disadvantage is that a significant number of consumables are required, in particular the vacuum bag required in vacuum assisted resin transfer moulding or used for fixation of pre-pregs. Further, manufacturing of shells of wind turbines may require additional consumables such as resin inlet channels, a distribution mesh, and sealant between vacuum bag and the shell mould.

[0010] Further, both conventional manufacturing approaches suffer from the risk of components displacing relatively to each other or wrinkling prior to fixation and curing.

[0011] Hence, there is a need for manufacturing methods which reduced the need of consumables during manufacture of wind turbine blades, and a need for methods which reduce the risk of components displacing or wrinkling prior to fixation and curing.

[0012] Summary of the invention

[0013] On the above background, it is an object of preferred embodiments of the invention to provide a manufacturing method which reduces the need of consumables during the manufacture of wind turbine blades. It is further an object of some embodiments of the invention to reduce the risk of components displacing or wrinkling prior to or during fixation and curing.

[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: providing a curable matrix, said curable matrix comprising a curable resin and a room temperature curing agent for said curable resin; impregnating fabrics of fibres with said curable matrix to provide one or more pre-pregs; providing a shell mould having a shell layup area; placing the one or more pre-pregs in the shell layup area to form a skin laminate; and heating the shell mould to cure the curable matrix of the one or more pre-pregs of the skin laminate.

[0015] The provision of a curable matrix comprising a curable resin and a room temperature curing agent for the curable resin, for example such that the curable matrix has cure progression at an ambient temperature, can ensure that laid pre-pregs are fixed in position prior to and during curing the curable matrix by heating. In particular, this can reduce the need for any additional fixation while fully curing the pre-pregs 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 can reduce the risk of pre-pregs displacing or wrinkling prior to or during curing.

[0016] According to typical examples, the curable matrix cure progresses at least partially prior to the step of heating the shell mould. Thus, after placing the one or more pre-pregs, the curable matrix may cure progress to be processed into a partially cured stage. In this stage, the curable matrix may, for example, be in a semisolid state where the curable resin is highly viscous or a gel state. Hence, in a partially cured stage, the components may stay in place, even when heated to fully cure the curable matrix.

[0017] The curable matrix may further comprise an additional curing agent, such as a latent curing agent which cures at elevated temperatures. Thereby, the room temperature curing agent can ensure that the curable matrix cure progresses to a state in which it fixates the prepregs, while the latent curing agent ensures that the curable matrix cure progresses to a fully cured state capable of fulfilling the mechanical requirements with regards to strength required for a wind turbine blade in operation.

[0018] Note that heating the shell mould to cure the curable matrix can temporarily decrease the viscosity of the curable matrix before it cures. Hence, conventional pre-pregs not comprising a room temperature curing agent are typically insufficient to ensure that the pre-pregs are properly fixated prior to and during heating of the shell mould.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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).

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The characteristic glass-transition temperature of the curable matrix can also be quantified according to ISO 11357-2:2020.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The pot life of the curable matrix can also be quantified according to ISO 10364:2015.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] According to examples of the present disclosure, the epoxy equivalent weight (EWW) of the curable matrix is between 300 and 500 (g / Eq).

[0054] 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.

[0055] 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.

[0056] According to examples of the present disclosure, the curable resin may be an oligomer, a pre-polymer or a polymer.

[0057] According to examples of the present disclosure, the curable resin comprises an epoxide group.

[0058] 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.

[0059] 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.

[0060] According to examples of the present disclosure, the room temperature curing agent is an amine curing agent.

[0061] According to examples of the present disclosure, the amine curing agent is selected from the group comprising aromatic amines, cycloaliphatic amines, aliphatic amines.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The curable resin may also be a ‘hybrid resin’, i.e., may also comprise a curing agent as part of the polymer itself.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The curable resin may further comprise curing catalysts, additives, thickeners and / or antisettling agents.

[0071] 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, optionally, MCA10.

[0072] According to examples of the present disclosure, the method comprises a step of fixating the one or more pre-pregs of the skin laminate relatively to the shell mould by cure progression of the curable matrix, wherein the step of fixating the one or more pre-pregs is performed prior to and separately from the step of heating the shell mould.

[0073] Preferably, the cure progression in the step of fixating the one or more pre-pregs 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. By fixating the one or more pre-pregs of the skin laminate relatively to the shell mould, the need for further fixation means such as vacuum consumables is reduced.

[0074] 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 of the one or more pre-pregs into a partially cured stage, wherein the step of heating the shell mould processes the curable matrix of the one or more pre-pregs into a fully cured stage.

[0075] In the context of the present disclosure, cure progression or cure progressing may also be referred to as hardening. Similarly, cure progressed may be referred to as hardened.

[0076] In the fully cured stage, the crosslink density increases to its maximum and the system reaches the end of the chemical reaction.

[0077] According to examples of the present disclosure, the curable matrix further comprises a latent curing agent.

[0078] According to examples of the present disclosure, the latent curing agent comprises dicyandiamide and an accelerator such as urone or a derivative thereof.

[0079] 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.

[0080] 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.

[0081] According to examples of the present disclosure, the heating of the shell mould processes the curable matrix into a solid state.

[0082] 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.

[0083] According to examples of the present disclosure, the step of fixating the one or more prepregs is performed at the ambient temperature. 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.

[0084] 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.

[0085] 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.

[0086] According to examples of the present disclosure, the one or more pre-pregs comprises at least a first pre-preg and a second pre-preg, wherein the step of placing the one or more pre-pregs comprises the steps of: placing the first pre-preg at the shell layup area; and 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 the skin laminate.

[0087] Consolidation of the pre-pregs may be improved by compressing the pre-pregs onto one another. This compression is preferably performed separately from applying, e.g., vacuum bagging or clamps to ensure that the components are fixed during heating of the shell mould. Instead, the compression is preferably performed in relation to placement of the prepregs. The second pre-preg may for example be placed onto the first pre-preg by compressing it onto the first pre-preg, for example by using a compaction roller.

[0088] According to examples of the present disclosure, the method comprises the steps of: locally applying heat to the first pre-preg and / or the second pre-preg, wherein the step of locally applying heat is performed prior to the step of compressing the second pre-preg onto the first pre-preg; and cooling the first pre-preg and / or the second pre-preg of the skin laminate, wherein the step of cooling the first pre-preg and / or the second pre-preg is performed prior to the step of heating the shell mould.

[0089] Consolidation of the pre-pregs may be improved by locally applying heat. By locally raising the temperature, the viscosity of the curable matrix decreases which improves consolidation between the pre-pregs. When one pre-preg is heated and brought into contact with another pre-preg, some of the heat may be transferred to this other pre-preg, thereby reducing the viscosity of the curable matrix of both pre-pregs, which further improves consolidation.

[0090] Typically, the cooling of the first pre-preg and / or the second pre-preg occurs passively after the local heating has terminated. Thereby, viscosity is raised again, enhancing fixation of the pre-pregs.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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. 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.

[0096] 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 the ambient temperature.

[0097] According to examples of the present disclosure, the curing of the curable resin of the prepregs of the skin laminate is by applying at least a second predetermined temperature.

[0098] According to examples of the present disclosure, the curable matrix of first pre-preg and 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] According to examples of the present disclosure, the one or more 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, wherein the step of cooling the second pre-preg and / or the third pre-preg is performed prior to the step of heating the shell mould.

[0104] According to the present disclosure, any number of pre-pregs may be sequentially heated and compressed onto one another at the shell layup area.

[0105] According to examples of the present disclosure, the method further comprises placing a 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 one or more auxiliary pre-pregs, wherein the further curable matrix comprises a further curable resin and a further room temperature curing agent for said further curable resin; and placing the one or more auxiliary pre-pregs onto the core material and / or the one or more spar caps at the shell layup area to form an auxiliary skin laminate.

[0106] 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.

[0107] 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. 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.

[0108] 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.

[0109] 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 resin of the pre-pregs of the skin laminate and to cure the further curable resin of the auxiliary pre-pregs of the auxiliary skin laminate.

[0110] According to examples of the present disclosure, the one or more auxiliary pre-pregs comprises at least a first auxiliary pre-preg and a second auxiliary pre-preg, wherein the step of placing the one or more auxiliary pre-pregs comprises the step of: placing the first pre-preg onto the core material and / or the one or more spar caps at the shell layup area; and 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 the auxiliary skin laminate.

[0111] According to examples of the present disclosure, the method comprises the steps of: locally applying heat to the first auxiliary pre-preg and / or the second auxiliary pre-preg, wherein the step of locally applying heat to the first auxiliary pre-preg and / or the second auxiliary pre-preg is performed prior to the step of compressing the second auxiliary pre-preg onto the first auxiliary pre-preg; and cooling the first auxiliary pre-preg and / or the second auxiliary pre-preg of the auxiliary skin laminate, wherein the step of cooling the auxiliary first pre-preg and / or the second auxiliary pre-preg is performed prior to the step of heating the shell mould.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] The first and the second heating trajectories refer to the temperature trajectories by which heating of the shell mould is controlled.

[0117] 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.

[0118] 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. 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.

[0119] 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.

[0120] 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.

[0121] According to example of the present disclosure, the one or more pre-pregs are placed to extend along a chordwise direction of the shell mould. 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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. According to examples of the present disclosure, compression of pre-pregs is performed using a compaction roller.

[0130] The fabric of fibres may for example be 600-1000 gsm biax glass fibre fabric.

[0131] 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.

[0132] According to examples of the present disclosure, the curable matrix is a thermosetting matrix and / or the curable resin is a thermosetting resin.

[0133] 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.

[0134] A second aspect of the present disclosure relates to a robot system for manufacturing at least a part of a wind turbine shell, 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 pre-preg comprising a fabric of fibres impregnated by a curable matrix, the curable matrix comprising a curable resin and a room temperature curing agent for the curable resin; a material spool holding the 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; and a robot control system which upon execution of the robot instructions controls the one or more robot arms to place the pre-preg onto the shell layup area via the compaction roller.

[0135] 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.

[0136] Since the provision of a curable matrix comprising a room temperature curing agent 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.

[0137] According to examples of the present disclosure, the robot system further comprises a heat source for locally heating a part of the pre-preg and / or for locally heating the shell layup area.

[0138] 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.

[0139] According to examples of the present disclosure, the pre-preg may be laid down by one robot arm, and while another robot arm applies the compaction roller.

[0140] According to examples of the present disclosure, the robot instructions may further be 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.

[0141] According to examples of the present disclosure, the robot system may further comprise 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. 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] A fourth aspect of the present disclosure relates to a pre-preg, the pre-preg comprising a fabric of fibres and a curable matrix impregnating the fabric of fibres, wherein the curable matrix comprises a curable resin and a room temperature curing agent for the curable resin.

[0147] The pre-preg of the fourth aspect can be a pre-preg as described in relation to the first aspect. For example, the curable matrix may have a characteristic glass temperature 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. For example, the curable matrix has a pot life as exemplified in relation to the first aspect. For example, the pre-preg has a gel time as exemplified in relation to the first aspect.

[0148] A fifth 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.

[0149] 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.

[0150] Brief of the

[0151] Embodiments of the invention will now be further described by reference to the accompanying drawings, in which:

[0152] Fig. 1 illustrates method steps according to examples of the present disclosure,

[0153] Fig. 2 illustrates a shell mould and a pre-preg to be placed in the shell mould,

[0154] Fig. 3a-c illustrate various examples of placing an additional pre-preg in a shell mould, for example to form a skin laminate,

[0155] Fig. 4 illustrates placement of core material and spar caps in a shell mould,

[0156] Fig. 5 illustrates placement of auxiliary pre-pregs in a shell mould,

[0157] Fig. 6a-c schematically illustrate cure progressions in terms of viscosity and heating according to examples of the present disclosure,

[0158] Fig. 7 illustrates a robot system according to examples of the present disclosure,

[0159] Fig. 8 illustrates a robot arm comprising a compaction roller for compressing a pre-preg onto a shell layup area of a shell mould; and

[0160] Fig. 9 illustrates main structural components of an exemplary horizontal-axis wind turbine comprising three separate wind turbine blades.

[0161] Detailed description of the drawings 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.

[0162] Fig. 1 illustrates method steps S1-S5 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.

[0163] In a first step S1 , a curable matrix is provided. The curable matrix comprises a curable resin and a room temperature curing agent for the curable resin. Hence, the curable matrix may cure progress at room temperature primarily by cross-linking of the curable resin by the room temperature curing agent. Preferably, at room temperature conditions, the curable matrix progresses to a partially cured stage. The curable matrix can then be cured to a fully cured stage later in the manufacturing process.

[0164] In another step S2 of the method, fabrics of fibres are impregnated with the curable matrix to provide one or more pre-pregs. The fabrics of fibres are impregnated before they are placed in the shell layup area, i.e., they are pre-impregnated.

[0165] The fabrics of fibres may for example be 800 gsm biaxial glass fibre fabric.

[0166] These one or more pre-pregs may optionally be wound onto a material spool from which the pre-pregs can be drawn and cut.

[0167] 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.

[0168] In another step S3 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.

[0169] The shell layup area can be any inner area or inner sub-area of the shell mould. In another step S4 of the method, the one or more pre-pregs are placed in the shell layup area to form a skin laminate. In case several pre-pregs are used, they may be stacked onto each other. The pre-pregs may be placed by means of compression. Further, prior to placing one pre-preg onto another pre-preg, one of these pre-pregs may be heated locally to improve consolidation.

[0170] In another step S5 of the method, the shell mould is heated to cure the curable matrix of the one or more pre-pregs of the skin laminate. This heating may be implemented by any conventional heating process, for example by electrical heating of the shell mould.

[0171] The method may optionally include further method steps, such as a step of fixating the prepregs of the skin laminate by cure progression, a step of locally applying heat, 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.

[0172] 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.

[0173] Fig. 2 illustrates a shell mould 21 and a 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.

[0174] The shell mould 21 has a shell layup area 22 on its inner surface.

[0175] According to example of the present disclosure, the 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 pre-preg can be placed manually, autonomously by a robot system, or by a robot system which is manually assisted.

[0176] Fig. 3a-c illustrate various examples of placing an additional pre-preg 20b in a shell mould 21 , for example to form a skin laminate. Fig. 3a illustrates a shell mould 21 similar to the one illustrated in Fig. 2. However, in Fig. 3a, a first pre-preg 20a has already been placed onto the shell layup area 22 of the shell mould 21.

[0177] A second pre-preg 20b is also illustrated. It is placed onto the first pre-preg 20a at the shell layup area 22 of the shell mould 21 as indicated in the figure by an arrow. The second prepreg 20b may be placed in a manner similar to how the first pre-preg 20a is placed, or it may involve different or additional actions in comparison with the placement of the first pre-preg 20a.

[0178] Fig. 3b also illustrates a shell mould 21 similar to the one illustrated in Fig. 2 and placement of a second pre-preg 20b. However, in comparison with Fig. 3a, Fig. 3b further illustrates that the second pre-preg is compressed onto the first pre-preg by using a compaction roller 23. The compaction roller can be a soft cylinder of low surface tension plastic rotatably mounted to a shaft.

[0179] To compress the second pre-preg onto the first pre-preg, 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 right-hand 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.

[0180] Fig. 3c illustrates a situation similar to that illustrated in Fig. 3b, but additionally illustrates a heat source 24 which applies heat 25 to the first pre-preg 20a, thereby locally applying heat.

[0181] 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.

[0182] The heat-source 24 preferably moves along with the compaction roller 23, for example along the chordwise direction. 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.

[0183] 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.

[0184] 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.

[0185] Fig. 5 illustrates placement of auxiliary pre-pregs 29a, 29b in a shell mould. These auxiliary pre-pregs 29a, 29b are typically 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.

[0186] Fig. 6a-c schematically illustrate cure progressions in terms of viscosity and heating according to examples of the present disclosure.

[0187] 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 a semisolid, a gel, or a solid depending on exact position. A gel transition 33 is indicated 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.

[0188] To provide a better understanding of the aspects of the present disclosure, exemplary cure progression of a conventional pre-preg is discussed in the following.

[0189] The cure progression of a conventional pre-preg is illustrated in terms of a conventional prepreg viscosity 32 illustrated by a dashed line. When a 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. Heating of the shell mould, and thus of the conventional pre-preg, initiates two processes. Firstly, the heating of the shell mould tends to decrease the viscosity of the matrix of the prepreg, since the matrix has a temperature-dependent viscosity. However, secondly, the heating also triggers curing of the matrix of the conventional 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 conventional pre-preg viscosity 32 initially decreases. As the resin is gradually cross-linked in the curing process, the conventional pre-preg viscosity 32 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 gel transition is crossed by the conventional pre-preg viscosity.

[0190] Returning to the aspects introduced in the present disclosure, Fig. 6a 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.

[0191] 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.

[0192] 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.

[0193] Further, 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.

[0194] 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 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.

[0195] 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.

[0196] In comparison with Fig. 6a, Fig. 6b further illustrates local heating 35, 36 and a creep viscosity 37 indicated 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 prepreg 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.

[0197] 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. In this particular example, the 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.

[0198] 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.

[0199] As for Fig. 6a, the trajectory of a conventional pre-preg viscosity 32 is illustrated for comparison in Fig. 6b.

[0200] 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. 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] Fig. 7 illustrates a robot system 51 according to examples of the present disclosure.

[0205] 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. Other robot arms of the system may also comprise a compaction roller, but may alternatively comprise additional or other robot tools, such as a separate heating source for applying local heat.

[0206] 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.

[0207] 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 of the eventually manufactured wind turbine blade. 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 and a room temperature curing agent for the curable resin. This pre-preg is held by a material spool (not shown) arranged to feed the pre-preg to the compaction roller 23.

[0208] 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.

[0209] 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 place the pre-preg onto a shell layup area 22a, 22b.

[0210] 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.

[0211] 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.

[0212] The material spool 43 holds the pre-preg. In other examples, the material spool can be arranged separately from the robot end effector.

[0213] 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.

[0214] 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.

[0215] 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. 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.

[0216] 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.

[0217] 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.

[0218] The three separate blades 7 of the wind turbine 1 may be manufactured according to the manufacturing procedures presented in the present disclosure.

[0219] 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: providing a curable matrix, said curable matrix comprising a curable resin and a room temperature curing agent for said curable resin; impregnating fabrics of fibres with said curable matrix to provide one or more pre-pregs; providing a shell mould having a shell layup area; placing the one or more pre-pregs in the shell layup area to form a skin laminate; and heating the shell mould to cure the curable matrix of the one or more pre-pregs of the skin laminate.

2. A method according to claim 1 , wherein the room temperature curing agent for the resin provides cure progression to the curable matrix at an ambient temperature, wherein 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.

3. 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 providing the curable matrix to the step of placing the one or more prepregs, 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 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.

4. A method according to any of the preceding claims, wherein 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.

5. A method according to any of the preceding claims, wherein 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.

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

7. A method according to claim 6, wherein the cure progression of the curable matrix during the step of fixating the one or more pre-pregs is by at least partial cross-linking of the curable resin by the room-temperature curing agent for the curable resin.

8. A method according to any of the preceding claims, 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.

9. A method according to any of the preceding claims, wherein the one or more pre-pregs comprises at least a first pre-preg and a second pre-preg, wherein the step of placing the one or more pre-pregs comprises the steps of: placing the first pre-preg at the shell layup area; and 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 the skin laminate.

10. A method according to claim 9, wherein the method comprises the steps of: locally applying heat to the first pre-preg and / or the second pre-preg, wherein the step of locally applying heat is performed prior to the step of compressing the second pre-preg onto the first pre-preg; and cooling the first pre-preg and / or the second pre-preg of the skin laminate, wherein the step of cooling the first pre-preg and / or the second pre-preg is performed prior to the step of heating the shell mould.

11. A method according to any of the preceding claims, wherein the method further comprises placing a 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 one or more auxiliary pre-pregs, wherein the further curable matrix comprises a further curable resin and a further room temperature curing agent for said further curable resin; and placing the one or more auxiliary pre-pregs onto the core material and / or the one or more spar caps at the shell layup area to form an auxiliary skin laminate.

12. A method according to claim 11 , wherein the one or more auxiliary pre-pregs comprises at least a first auxiliary pre-preg and a second auxiliary pre-preg, wherein the step of placing the one or more auxiliary pre-pregs comprises the step of: placing the first pre-preg onto the core material and / or the one or more spar caps at the shell layup area; and 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 the auxiliary skin laminate.

13. A method according to claim 12, wherein the method comprises the steps of: locally applying heat to the first auxiliary pre-preg and / or the second auxiliary pre-preg, wherein the step of locally applying heat to the first auxiliary pre-preg and / or the second auxiliary pre-preg is performed prior to the step of compressing the second auxiliary pre-preg onto the first auxiliary pre-preg; and cooling the first auxiliary pre-preg and / or the second auxiliary pre-preg of the auxiliary skin laminate, wherein the step of cooling the auxiliary first pre-preg and / or the second auxiliary pre-preg is performed prior to the step of heating the shell mould.

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 pre-preg comprising a fabric of fibres impregnated by a curable matrix, the curable matrix comprising a curable resin and a room temperature curing agent for the curable resin; a material spool holding the 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; and a robot control system which upon execution of the robot instructions controls the one or more robot arms to place the pre-preg onto 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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