Patent Description:
Producing more power using a wind turbine under given wind conditions can be achieved by increasing the size of the blades. However, the manufacture of wind turbine blades is becoming increasingly difficult for increasing blade sizes.

It is known to pre-manufacture lengthwise blade sections (such as an inboard blade section and an outboard blade section) separately from fibre-reinforced material and glue the sections to each other. However, the gluing process has some limitations. It is, for example, an open process where the glue is applied on the surfaces to bond and, as such, it may represent a hazard for the operators. In addition, it is difficult to control the quality of the glue line.

For example, <CIT> discloses a modular wind turbine blade comprising first and second lengthwise blade sections. The first and second lengthwise blade sections are connected to each other by bonding a connecting member by means of an adhesive to the blade outside.

Further, <CIT> discloses a method and an apparatus for manufacturing composite parts, in particular sections of a fuselage for an aircraft.

Further, <CIT> discloses a method for forming composite components by disposing a composite laminate over a mandrel. The method further includes infusing the composite laminate with a resin. A gelation of the infused resin is caused by applying a first environmental condition to the composite laminate and mandrel. At least a portion of the mandrel is deformed by applying a second environmental condition to the composite laminate and mandrel. The method further includes forming a composite structure by curing the composite laminate infused with resin. The deformed mandrel is removed from the composite structure after forming the composite structure.

It is one object of the present invention to provide an improved method for manufacturing a wind turbine blade and an improved mandrel tool for joining two blade sections of a wind turbine blade.

Accordingly, a method according to claim <NUM> for manufacturing a wind turbine blade is proposed. The method comprises the steps of:.

Thus, a light-weight and at the same time strong blade section joint is provided. In particular, the strength of this laminate joint formed by resin infusion is comparable to the strength of the pristine laminate. Compared to a connection using an adhesive, the laminate joint formed by resin infusion provides a lighter and stronger blade section joint, in particular, a better weight-to-strength performance. This is because in the case of an adhesive, the weight of the adhesive is added in the bond line and the interlaminar shear strength drops as the bond line thickness increases. Further, the laminate joint formed by resin infusion avoids the problem of glue joints of having a different material in the glue than in the rest of the blade.

Furthermore, the proposed method for manufacturing a wind turbine blade allows to perform the joining process of the blade sections from inside the blade cavity. This facilitates the manufacturing process as there are joining processes, such as a web connection, which can only be performed from inside the blade cavity.

Furthermore, reducing the cross-section size of the mandrel tool allows to arrange it better and more easily inside the adjacent blade sections. In particular, it allows to better fit the mandrel tool inside cavities of respective blade sections. In particular, the mandrel tool can be arranged in the cavity of the respective blade section such that there is sufficient space between an outer surface of the mandrel tool and in inner surface of the respective blade section. For example, there is sufficient space provided to better manoeuvre and position the mandrel tool inside the cavity of the respective blade section. Further, there is, for example, sufficient space provided such that the respective blade section (e.g., its opening edge and/or its inner surface) does not interfere with the fibre lay-up arranged on the mandrel tool during the insertion process.

Further, the blade cross-section is increasing towards the blade root. Hence, when the mandrel tool is in its extended state its cross-section is also increasing towards an inboard end of the mandrel tool in order to position the fibre lay-up arranged on the mandrel tool at an inner surface of the blade sections. When arranging the mandrel tool (partly) into an inboard blade section and (partly) into an adjacent outboard blade section, it might be of advantage to insert it through the outboard end of the inboard blade section (and not through the inboard end/root portion of the inboard blade section). This is in particular the case for very long inboard sections. Reducing the cross-section size of the mandrel tool allows to better insert the mandrel tool through the outboard end of the inboard blade section despite the fact that the outboard end of the inboard section has a smaller cross-section as the inboard end of the mandrel tool in its original extended state.

The wind turbine blade is part of a rotor of a wind turbine. The wind turbine is an apparatus to convert the wind's kinetic energy into electrical energy. The wind turbine comprises, for example, the rotor having one or more of the blades connected each to a hub, a nacelle including a generator, and a tower holding, at its top end, the nacelle. The tower of the wind turbine may be connected via a transition piece to a foundation of the wind turbine, such as a monopile in the seabed.

The wind turbine blade comprises two or more blade sections dividing the blade in a lengthwise direction. In particular, the adjacent blade sections are arranged adjacent to each other in a lengthwise direction of the blade. A first one of the adjacent blade sections is, for example, an inboard blade section. The inboard blade section comprises, for example, a root section connected to the hub of the rotor. A second one of the adjacent blade sections is, for example, an outboard blade section. The outboard blade section comprises, for example, a blade tip. In addition to the described first and second blade sections, the wind turbine blade may also comprise one or more further blade sections. The one or more further blade sections may be joined with each other and/or with the described first and/or second blade sections by the same joining process by which the first blade section is joined with the second blade section.

The wind turbine blade, e.g., the root section, is, for example, fixedly connected to the hub. The wind turbine blade is, for example, directly bolted to the hub.

Alternatively, the wind turbine blade, e.g., the root section, is rotatably connected to the hub. For example, the wind turbine blade is connected to a pitch bearing of the wind turbine, and the pitch bearing is connected to the hub. The pitch bearing is configured to adjust the angle of attack of the blade according to the wind speed to control the rotational speed of the blade.

Apart from the (cylindrical) root section connected with the hub, the wind turbine blade has an aerodynamically shaped cross-section (airfoil). The wind turbine blade, i.e. each of its blade sections, comprises, for example, a pressure side (upwind side) and a suction side (downwind side). The pressure side and the suction side are connected with each other at a leading edge and a trailing edge. The pressure and suction sides and the leading and trailing edges define an interior cavity of the wind turbine blade.

Two adjacent blade sections might be arranged adjacent to each other such that the blade sections abut each other. Alternatively, there might be a small gap between the adjacent blade sections which may be filled by the (cured) joining portion.

The mandrel tool is, for example, arranged inside the adjacent blade sections by means of a lifting tool. The lifting tool is, for example, a crane or a lifting vehicle, and it allows to better arrange and position the mandrel tool.

When arranging the mandrel tool comprising the fibre lay-up inside the adjacent blade sections and then increasing the cross-section size of the mandrel tool the fibre lay-up is, in particular, arranged at an inner surface of the adjacent blade sections. For example, it is arranged at the inner surface of the adjacent blade sections such that it is overlapping with the blade sections in a joining area of the blade sections.

For example, an outer surface of the mandrel tool may reproduce (i.e. match with) the inner surface of the adjacent blade sections over the joining area of the blade sections.

The fibre lay-up includes, for example, glass fibres, carbon fibres, aramid fibres and/or natural fibres. The fibre lay-up comprises, for example, fibres in dry condition, i.e. without resin and/or pre-impregnated fibres (prepreg). The fibre lay-up includes, for example, a core material such as wood, balsa, PET foam and/or PVC foam. The core material allows to reduce the weight of the final fibre-reinforced resin laminate while maintaining a sufficient rigidity and/or strength of the blade.

The resin includes, for example, thermosets, thermoplastics, epoxy, polyurethane, vinyl ester and/or polyester.

The resin is infused and cured from inside the wind turbine blade cavity. The resin is, for example, cured by applying heat.

The fibre lay-up forms, once infused with resin and cured, a joining portion joining the blade sections inside. The cured joining portion is, in particular, a fibre-reinforced resin laminate.

The phrase "a cured joining portion joining the blade sections inside" is to say that the cured joining portion joins or connects the blade sections on their inside surfaces, i.e. surfaces of the blade sections that face an open or closed cavity within each blade section.

In step b) of the method, the cross-section size of the mandrel tool is, for example, reduced from an original cross-section size to a smaller cross-section size. In step d) of the method, the original cross-section size of the mandrel tool is, for example, re-established.

An enveloping surface of the mandrel tool (e.g., of the outer surfaces of the at least two mandrel portions) has, for example, an airfoil section. In particular, when the mandrel tool is in its original extended state - i.e. before step b) and after step d) - an enveloping surface of the mandrel tool has an airfoil section.

The cross-section of the mandrel tool in its original extended state is, thus, in particular an airfoil section. At a certain position with respect to the longitudinal length of the blade, the cross-section size of the mandrel tool is slightly smaller than a cross-section size of the manufactured blade.

The airfoil section of the enveloping surface of the mandrel tool comprises a leading edge, a trailing edge, a suction side and a pressure side. A chord length of an airfoil section is the distance between its leading edge and its trailing edge. A thickness of an airfoil section is the maximum distance between its upper and lower surfaces (its suction and pressure sides).

The mandrel tool comprises, for example, actuator means to retract and/or extend at least one of the mandrel portions.

In embodiments, the method includes, before step e), the steps of covering the fibre lay-up and the adjacent blade sections at least partially with a vacuum bag, and applying vacuum to a space covered by the vacuum bag, and wherein, in step e), the resin is infused due to the generated vacuum.

In embodiments, each of the adjacent blade sections comprises an outwardly tapered portion such that the outwardly tapered portions form a common recess. Further, the mandrel tool is arranged inside the adjacent blade sections such that the fibre lay-up is arranged in the common recess when the cross-section size of the mandrel tool is increased.

By having the outwardly tapered portions of the adjacent blade sections, the outer surfaces of the blade sections can be finished prior to the joining process.

In particular, each of the adjacent blade sections comprises at an end portion thereof an outwardly tapered portion. In particular, each of the blade sections is tapered outwardly towards a joining interface with the other blade section. Further, each of the blade sections is tapered outwardly such that each of the blade sections forms an inner recess. The inner recesses of the blade sections form a common recess when the blade sections are arranged adjacent to each other. The common inner recess is filled by the fibre lay-up when the cross-section size of the mandrel tool is increased.

Particularly, a thickness of a blade shell, beam and/or web decreases towards the interface with the other blade section to form the outwardly tapered portion. The outwardly tapered portion may, for example, be configured such that the thickness of its blade shell, beam and/or web decreases linearly towards the interface with the other blade section. The outwardly tapered portion may, for example, be configured such that the thickness of its blade shell, beam and/or web decreases stepwise or curved towards the interface with the other blade section.

In embodiments, each blade section may comprise at a certain end portion thereof two or more outwardly tapered portions. In particular, each of the two or more outwardly tapered portions of a first blade section corresponds to an outwardly tapered portion of a second blade section. Further, each of the two or more outwardly tapered portions of the first and second blade sections form a common recess.

According to an embodiment, the cross-section size of the mandrel tool is reduced by reducing a height of the mandrel tool and/or a width of the mandrel tool.

A height of the mandrel tool is, for example, a thickness of an airfoil section of the mandrel tool. A width of the mandrel tool is, for example, a chord length of the airfoil section of the mandrel tool.

For example, the at least two mandrel portions comprise at least one upper mandrel portion. Further, the height of the mandrel tool is reduced by retracting the at least one upper mandrel portion towards the frame (and towards a lower mandrel portion).

For example, the at least two mandrel portions comprise at least one trailing edge mandrel portion. Further, the width of the mandrel tool is reduced by retracting the at least one trailing edge mandrel portion towards the frame (and towards a leading edge mandrel portion).

According to a further embodiment, the method includes, during step b) or between step b) and step c) the step of folding the fibre lay-up inwards.

By folding the fibre lay-up inwards, the behaviour of the fibre lay-up during reducing the cross-section size of the mandrel tool, inserting it and increasing its cross-section size again can be better controlled. For example, one or more folds of the fibre lay-up extending along the longitudinal direction of the mandrel tool can be generated in a controlled manner. Hence, undesired folds and dislocations of the fibre lay-up during or after reducing the cross-section size of the mandrel tool can be avoided. Further, an interference of the fibre lay-up with the blade sections during inserting the mandrel tool is reduced.

The fibre lay-up is, for example, folded inwards at the leading edge, the trailing edge or an upper side (pressure side) of the mandrel tool.

According to a further embodiment, the mandrel tool comprises at least one gap extending along a longitudinal direction of the mandrel tool and arranged, as seen in cross-section, between two adjacent mandrel portions, and wherein the fibre lay-up is folded inwards into the at least one gap.

Having the gap and folding the fibre lay-up inwards into the gap allows to even better control the arrangement of the fibre lay-up during retracting and expanding the mandrel tool.

According to a further embodiment, the fibre lay-up is tensioned during and/or after folding it inwards.

Tensioning the fibre lay-up during and/or after folding it inwards allows to even better control the arrangement of the fibre lay-up during retracting, inserting and expanding the mandrel tool.

The fibre lay-up is, for example, tensioned during step b), c) and/or d).

The fibre lay-up is, for example, tensioned by gravity and/or an applied tensioning force.

For example, when reducing the mandrel tool in height, a fold of the fibre lay-up may hang downward into a gap between two upper mandrel portions and is tensioned due to gravity.

For example, when reducing the mandrel tool in height and/or width, a pushing and/or pulling force may be applied to the fibre lay-up pushing and/or pulling it inwards towards the frame.

According to a further embodiment, the method includes, after step a) and before step b) the step of fixing at least one moveable longitudinal member to the mandrel tool such that it is arranged along the longitudinal direction of the mandrel tool and outside the at least one gap, and wherein the fibre lay-up is folded inwards by moving the at least one longitudinal member into the at least one gap.

The at least one longitudinal member is, for example, a bar. One or more longitudinal members are, for example, fixed to the mandrel tool at the leading edge and/or at the trailing edge.

The at least one longitudinal member may be used for tensioning the fibre-lay by pushing the fibre lay-up inwards.

In embodiments, the method includes, after step c), a step of dismounting and removing the at least one moveable longitudinal member from the mandrel tool.

According to a further embodiment, the at least two mandrel portions comprise at least two upper mandrel portions and at least two lower mandrel portions. Further, the method includes, during step a), the step of arranging a web element between the at least two upper mandrel portions and between the at least two lower mandrel portions. The web element includes a first portion, a second portion and a middle portion arranged between the first and second portions. Furthermore, the method includes, before step b), the step of removing the middle portion. The method also includes, after step d), the step of re-arranging the middle portion between the first and second portions of the web element.

The steps of removing and re-arranging a middle portion of a web element allow to more easily reduce a height of the mandrel tool even when using a pre-casted web element.

The mandrel tool may comprise one or more clamps to fix the first and/or second portions of the web element during the absence of the middle portion.

According to a further embodiment, the method includes, after step b) and before step c), the step of strapping the fibre-lay up to the mandrel tool.

By strapping the fibre-lay up to the mandrel tool, the fibre lay-up can be secured to the mandrel tool during arranging the mandrel tool inside the adjacent blade sections.

For example, several straps distributed along the longitudinal direction of the mandrel tool may be fixed to the mandrel tool. Furthermore, the mandrel tool with the fibre lay-up may also be wrapped in a foil, after step b) and before step c) and before applying the one or more straps.

According to a further embodiment, the fibre lay-up comprises a fibre lay-up forming, once infused and cured, a shell joint joining a shell of a first one of the adjacent blade sections with a shell of a second one of the adjacent blade sections. Additionally or alternatively, the fibre lay-up comprises a fibre lay-up forming, once infused and cured, one or more beam joints joining one or more beams of a first one of the adjacent blade sections with one or more corresponding beams of a second one of the adjacent blade sections. Additionally or alternatively, the fibre lay-up comprises a fibre lay-up forming, once infused and cured, a web joint joining a web of a first one of the adjacent blade sections with a web of a second one of the adjacent blade sections.

Arranging one, several or all of said fibre lay-ups on the mandrel tool allows to provide a light-weight and strong blade section joint including a shell joint, one or more beam joints and/or a web joint in a more efficient manufacturing process. In particular, several or all of the shell, beam(s) and/or web may be joined in a single process step by infusing and curing the resin.

The one or more beams comprise, for example, a pressure-side beam, a suction-side beam, a leading edge beam and/or a trailing edge beam.

The fibre lay-up, e.g., for the shell joint, comprises, for example, circumferentially arranged plies.

The (shear) web connects, in particular, the blade shells of the pressure side and the suction side in the interior cavity of the manufactured blade. The web provides shear strength to the blade.

A web element arranged in step a) in the mandrel tool may comprise a pre-casted web element and in addition a fibre lay-up (dry fibre lay-up and/or prepreg) at a connection region between the web element and the fibre lay-up for an upper and lower shell.

Alternatively, a web element arranged in step a) in the mandrel tool may comprise only a fibre lay-up (dry fibre lay-up and/or prepreg) and no pre-casted web element.

According to a further embodiment, the mandrel tool is arranged partially inside a first one of the blade sections such that a portion of the mandrel tool protrudes from the first one of the blade sections, and a second one of the blade sections is arranged adjacent to the first one of the blade sections such that the second one of the blade sections receives the portion of the mandrel tool protruding from the first one of the blade sections.

Inserting the mandrel tool partially into the first one of the blade sections and arranging the second one of the blade sections on the protruding portion of the mandrel tool allows to more easily arrange the mandrel tool. Further, it allows to better position the second one of the blade sections adjacent to the first one of the blade sections.

According to embodiments, the mandrel tool comprises an inner cavity between the mandrel portions. Having the inner cavity provides access for a worker. A worker may, for example, access an outboard blade section through the inner cavity when the mandrel tool is inserted into the adjacent blade sections. Further, a worker can, for example, seal a vacuum bag and/or connect vacuum and resin inlet hoses from within cavity.

According to embodiments, the mandrel tool comprises one or more resin inlets and/or one or more vacuum hoses. The resin inlets and/or vacuum hoses are, for example, connectable to a space covered by a vacuum bag, the vacuum bag covering the fibre lay-up and the adjacent blade sections at least partially.

According to embodiments, the mandrel tool comprises a heating system. The heating system allows to heat the resin up to, for example, <NUM> degrees Celsius to cure the resin. According to embodiments, the mandrel tool is configured for removing it through a root end of the blade after joining the blade sections. For example, the mandrel tool can be removed in parts through the root end.

According to embodiments, the mandrel tool comprises one or more terminals for electrical grounding. For example, the mandrel tool comprises one terminal for electrical grounding on each of two end portions of the mandrel tool.

According to embodiments, the mandrel tool comprises inspection gates to visually inspect the fibre lay-up after arranging it.

According to a further aspect, a mandrel tool according to claim <NUM> for joining two blade sections of a wind turbine blade is provided. The mandrel tool is configured for arranging it inside adjacent blade sections. The mandrel tool comprises a frame, and, as seen in cross-section, at least two mandrel portions connected to the frame. At least one of the mandrel portions is connected to the frame by actuator means configured for retracting and/or extending the mandrel portion towards/away from the frame- Furthermore, an outer surface of the at least two mandrel portions is configured for at least partially supporting a fibre lay-up for a joining portion, wherein the at least two mandrel portions include at least one leading edge mandrel portion and/or at least one trailing edge mandrel portion.

According to an embodiment of the further aspect, the actuator means comprise one or more lifting jacks and/or one or more retractable rods.

According to a further embodiment of the further aspect, the mandrel includes:.

According to a further embodiment of the further aspect, the mandrel tool includes guiding rods connected to the frame and configured for guiding the mandrel tool during arranging it into the adjacent blade sections.

According to a further embodiment of the further aspect, the at least two mandrel portions include at least one upper mandrel portion and/or at least one lower mandrel portion.

The embodiments and features described with reference to the method of the present invention apply mutatis mutandis to the mandrel tool of the present invention.

<FIG> shows a wind turbine <NUM> according to an embodiment. The wind turbine <NUM> comprises a rotor <NUM> having one or more blades <NUM> connected to a hub <NUM>. The hub <NUM> is connected to a generator (not shown) arranged inside a nacelle <NUM>. During operation of the wind turbine <NUM>, the blades <NUM> are driven by wind to rotate and the wind's kinetic energy is converted into electrical energy by the generator in the nacelle <NUM>. The nacelle <NUM> is arranged at the upper end of a tower <NUM> of the wind turbine <NUM>. The tower <NUM> is erected on a foundation <NUM> such as a monopile driven into the ground or seabed.

As shown in <FIG>, the blades <NUM> of the wind turbine <NUM> are manufactured from two or more lengthwise blade sections <NUM>, <NUM>. The lengthwise blade sections <NUM>, <NUM> are joined by using a fibre lay-up <NUM> arranged on a mandrel tool <NUM>, as described in the following.

<FIG> shows a perspective view of the mandrel tool <NUM> viewed from a trailing edge side TE of the mandrel tool <NUM>. <FIG> shows a perspective view of the mandrel tool <NUM> viewed from a leading edge side LE of the mandrel tool <NUM>. <FIG> and <FIG> show cross-section views of the mandrel tool <NUM> along lines V, VI and VII in <FIG> and <FIG>, respectively.

As shown in <FIG>, the mandrel tool <NUM> comprises a frame <NUM>. Further, the mandrel tool <NUM> comprises at least two mandrel portions <NUM>, <NUM>, <NUM>, <NUM> connected to the frame <NUM>. In the shown example, the mandrel tool <NUM> comprises two upper mandrel portions <NUM>, two lower mandrel portions <NUM>, two leading edge mandrel portions <NUM> and one trailing edge mandrel portion <NUM> (<FIG>).

It is noted that in the view of <FIG>, the two leading edge mandrel portions <NUM> are not visible. In the view of <FIG>, the trailing edge mandrel portion <NUM> is not visible.

As visible in <FIG>, <FIG> and <FIG>, the two upper mandrel portions <NUM> are connected to a lower portion of the frame <NUM> and to the lower mandrel portions <NUM> by actuator means <NUM>. The actuator means <NUM> are, for example, lifting jacks <NUM>. Using the lifting jacks <NUM>, the upper mandrel portions <NUM> can be lowered towards the lower mandrel portions <NUM>. In this way, a height H of the mandrel tool <NUM> (<FIG>) can be reduced.

In addition, the trailing edge mandrel portion <NUM> is connected to the frame <NUM> by actuator means <NUM>, as shown in <FIG> and <FIG>. The actuator means <NUM> are, for example, retracting rods <NUM>. Using the retracting rods <NUM>, the trailing edge mandrel portion <NUM> can be retracted in a direction R towards the frame <NUM>. In this way, a width W of the mandrel tool <NUM> (<FIG>) can be reduced.

Outer surfaces <NUM> of the mandrel portions <NUM>, <NUM>, <NUM>, <NUM> (<FIG>) define an enveloping surface <NUM> of the mandrel tool <NUM> (<FIG>). The enveloping surface <NUM> has an airfoil section at least when the mandrel tool <NUM> is in its original extended state.

The outer surfaces <NUM> of the mandrel portions <NUM>, <NUM>, <NUM>, <NUM> are configured to at least partially support the fibre lay-up <NUM> (<FIG>, <FIG>).

The mandrel tool <NUM> comprises an inner cavity <NUM> between the mandrel portions <NUM>, <NUM>, <NUM>, <NUM>, as shown in <FIG>. When the mandrel tool <NUM> is inserted into the adjacent blade sections <NUM>, <NUM>, an operator can access, for example, the outboard blade section <NUM> through the inner cavity <NUM>. Further, a worker can, for example, seal a vacuum bag and/or connect vacuum and resin inlet hoses from the cavity <NUM>.

The mandrel tool <NUM> further comprises at least one moveable longitudinal member <NUM> arranged along a longitudinal direction L of the mandrel tool <NUM>. In the shown example, the mandrel tool <NUM> comprises one longitudinal member <NUM> at the leading edge LE (<FIG>) and two longitudinal members <NUM> at the trailing edge TE (<FIG>). The longitudinal members <NUM> in the shown example are bars. The bars <NUM> are configured for actively folding the fibre lay-up <NUM> inwards into/towards an inside <NUM> of the mandrel tool <NUM> (<FIG>) when reducing the cross-section size S (for example the width W and the height H) of the mandrel tool <NUM>. The bars <NUM> are releasably attached to the mandrel tool <NUM>, for example to the frame <NUM> and/or to one or more of the mandrel portions <NUM>, <NUM>, <NUM>.

<FIG> shows a portion VIII of <FIG> displaying the two bars <NUM> attached to the frame <NUM> at the trailing edge TE. Each of the bars <NUM> is connected to an arm <NUM>. Each arm <NUM> is pivotably connected to the frame <NUM> such that it can pivot about an axis A to move the respective bar <NUM>. There may be further longitudinal members (bars) <NUM> arranged next to each bar <NUM>, as visible in <FIG>.

Furthermore, the mandrel tool <NUM> comprises at least one gap <NUM>, <NUM> extending along the longitudinal direction L of the mandrel tool <NUM>. In the shown example, the mandrel tool <NUM> comprises the gap <NUM> (<FIG> and <FIG>) arranged between the two adjacent mandrel portions <NUM>. Further, the mandrel tool <NUM> comprises two gaps <NUM> (<FIG> and <FIG>) arranged between the two adjacent mandrel portions <NUM> and <NUM> and <NUM> and <NUM>, respectively. The gaps <NUM>, <NUM> are configured for receiving a fold <NUM> (<FIG>) of the fibre lay-up <NUM> when the fibre lay-up <NUM> is folded inwards by means of the bars <NUM> moving into the gaps <NUM>, <NUM>.

In particular, the bar <NUM> at the leading edge LE (<FIG>) is arranged outside of the gap <NUM> and is configured to move into the gap <NUM> to fold the fibre lay-up <NUM> into the gap <NUM>. Further, the two bars <NUM> at the trailing edge TE (<FIG> and <FIG>) are arranged outside of the two gaps <NUM> and are configured to move into the gaps <NUM> to fold the fibre lay-up <NUM> into the gaps <NUM>, respectively.

The mandrel tool <NUM> may further comprise a clamp <NUM> connected in a gap <NUM> between the two upper mandrel portions <NUM>, as shown in <FIG>. The clamp <NUM> is configured to temporarily fix a (portion of a) web element <NUM> (<FIG>) during and after reducing the height H of the mandrel tool <NUM>. The (portion of the) web element <NUM> may be a pre-casted element and/or may comprise a (dry or prepreg) fibre lay-up. Any suitable clamp or clamping mechanism can be used for the clamp <NUM>.

As shown in <FIG>, the mandrel tool <NUM> may also include guiding rods <NUM> connected to the frame <NUM>. The guiding rods <NUM> are configured for guiding the mandrel tool <NUM> during arranging it into the adjacent blade sections <NUM>, <NUM>. In the shown example, the mandrel tool <NUM> comprises four guiding rods <NUM>. However, the mandrel tool may also include a different number of guiding rods <NUM>.

As shown in <FIG> and <FIG>, the mandrel tool <NUM> may also include wheels <NUM> (releasably) connected to the frame <NUM> for moving the mandrel tool <NUM>.

In the following, a method for joining the two blade sections <NUM>,<NUM> (<FIG>) by means of the mandrel tool <NUM> is described.

In a first step S1 of the method, the fibre lay-up <NUM> is arranged on the mandrel tool <NUM>.

<FIG> shows the fibre lay-up <NUM> without the mandrel tool <NUM> for clarity. The fibre lay-up <NUM> comprises a fibre lay-up <NUM> for a pressure-side beam joint and a fibre lay-up <NUM> for a suction-side beam joint. Further, the fibre lay-up <NUM> comprises a fibre lay-up <NUM> for a leading edge beam joint and a fibre lay-up <NUM> for a trailing edge beam joint. Furthermore, the fibre lay-up <NUM> comprises a fibre lay-up <NUM> for a shell joint.

Also shown in <FIG> is a web element <NUM>, <NUM>'. The web element <NUM> is, for example, a pre-casted web element <NUM>. In another embodiment, the fibre lay-up <NUM> may also comprise a fibre lay-up <NUM>' for a web joint.

<FIG> shows a detailed view of the web element <NUM> which is in this example a pre-casted web element. The web element <NUM> comprises a first portion <NUM> and a second portion <NUM>. Further, the web element <NUM> comprises a middle portion <NUM> arranged between the first and second portions <NUM>, <NUM>. The middle portion <NUM> can be removed from the web element <NUM>, as indicated by the arrows M and N. In the shown example, the middle portion <NUM> comprises two parts which can be removed to the left (direction M) and right side (direction N). In another example, the middle portion may be a single element which can be removed in direction M and/or in direction N.

For pre-packing the fibre lay-up <NUM> on the mandrel tool <NUM>, firstly a mould or packing table (not shown) is provided. On the mould or packing table, the fibre lay-up <NUM> (<FIG>) for the suction-side beam joint and a part of the fibre lay-up <NUM> for the shell joint are provided. Then, vacuum bags (only shown in <FIG>, reference sign <NUM>) are provided on the fibre lay-up <NUM> and the lower portion of the fibre lay-up <NUM>. Next, for example, the web element <NUM> comprising all portions <NUM>, <NUM>, <NUM> (<FIG>) is arranged.

In the next step, the mandrel tool <NUM> is arranged. In particular, the mandrel tool <NUM> can be divided into a leading edge mandrel tool part <NUM> and a trailing edge mandrel tool part <NUM>, as shown in <FIG>. Both the leading edge mandrel tool part <NUM> and the trailing edge mandrel part <NUM> are arranged on the fibre lay-ups <NUM>, <NUM> such that the web element <NUM> is arranged in between them. The web element <NUM> (e. , its second portion <NUM>) may be clamped to the upper mandrel portions <NUM> by means of the clamp <NUM> (<FIG>).

Further, the vacuum bags (<NUM>, <FIG>) are wrapped around the leading edge mandrel tool part <NUM> and the trailing edge mandrel part <NUM> of the mandrel tool <NUM>.

Next, the fibre lay-up <NUM> for the pressure-side beam joint, the fibre lay-up <NUM> for the leading edge beam joint, the fibre lay-up <NUM> for the trailing edge beam joint, and the remaining of the fibre lay-up <NUM> for the shell joint are provided. Finally, the vacuum bags (<NUM>, <FIG>) are arranged such that all fibre lay-ups <NUM>, <NUM>, <NUM>, <NUM> and <NUM> and the web element <NUM> are covered on one side thereof by a vacuum bag (<NUM>, <FIG>).

In step S2 of the method, the bars <NUM> are fixed to the frame <NUM> of the mandrel tool <NUM>, as shown in <FIG>, <FIG> and <FIG>. The bars <NUM> are fixed to the mandrel tool <NUM> such that the bars <NUM> are arranged outside of the gap <NUM> at the leading edge LE (<FIG>) and outside of the two gaps <NUM> at the trailing edge (<FIG> and <FIG>).

When fixing the bars <NUM> to the mandrel tool <NUM> (step S2), the fibre lay-up <NUM> is already arranged on the mandrel tool <NUM> (step s1). Thus, the bars <NUM> are arranged outside of the fibre lay-up <NUM>, in particular outside of the fibre lay-up <NUM> for the shell joint (<FIG>).

In step S3 of the method, the cross-section size S of the mandrel tool <NUM> is reduced. In particular, the height H of the mandrel tool <NUM> is reduced by retracting the lifting jacks <NUM> such that the upper mandrel portions <NUM> are lowered (<FIG>).

Furthermore, also the width W of the mandrel tool <NUM> is reduced by retracting the retracting rods <NUM> in the direction R such that the leading edge mandrel portion <NUM> is retracted towards the frame <NUM> and the inside <NUM> of the mandrel tool <NUM> (<FIG>).

At the beginning of step S3 and before reducing the height H of the mandrel tool, the middle portion <NUM> of the web element <NUM> may be removed from the web element <NUM>, as shown in <FIG>.

In step S4 of the method, the fibre lay-up <NUM> is folded inwards and tensioned. Preferentially, step S4 is carried out simultaneously with step S3. When folding the fibre lay-up <NUM> inwards, in particular, the fibre lay-up <NUM> for the shell joint and the fibre lay-up <NUM> for the pressure-side beam joint are folded inwards (<FIG>).

<FIG> shows schematically the process of retracting the trailing edge mandrel portion <NUM> inwards and simultaneously folding the fibre lay-up <NUM> (in particular, the fibre lay-up <NUM> for the shell joint) inwards by means of the bars <NUM>. The left panel in <FIG> illustrates the initial state in which the mandrel tool <NUM> is in its original extended state, the fibre lay-up <NUM>, <NUM> is already arranged on the mandrel tool <NUM> and the bars <NUM> were already fixed to the mandrel tool <NUM>. In the right panel of <FIG>, the two bars <NUM> were pivoted around the axis A and moved into the two gaps <NUM>, respectively. When the bars <NUM> move into the gaps <NUM>, they apply a pushing force onto an outer surface <NUM> of the fibre lay-up <NUM>, <NUM>. Further, each bar <NUM> folds the fibre lay-up <NUM>, <NUM> into a respective fold <NUM>. Thereby, the fibre lay-up <NUM>, <NUM> is tensioned.

Furthermore, the fibre lay-up <NUM>, <NUM> (<FIG>) can be folded into the gap <NUM> between the two upper mandrel portions <NUM> (<FIG>) when reducing the height H of the mandrel tool <NUM> by means of the lifting jacks <NUM>. In particular, the lifting jacks <NUM> are used to slowly lower the upper mandrel portions <NUM>. Thereby, the fibre lay-up <NUM> arranged on the upper mandrel portions <NUM> is slowly lowered in form of a fold (not shown) into the gap <NUM> due to gravity. Further, the gravity force acting on the fibre lay-up <NUM> lowered in form of the fold (not shown) into the gap <NUM> will also tension it.

By the described folding and tensioning processes, it can be avoided that the fibre lay-up <NUM> is arranged and/or folded in an undesired way during the reduction of the size of the mandrel tool <NUM>.

In step S5 of the method, the fibre-lay up <NUM> is strapped to the mandrel tool <NUM> by using several straps (not shown) distributed along the longitudinal direction L of the mandrel tool <NUM>. Before applying the straps (not shown), the fibre lay-up <NUM> may also be wrapped in a foil (not shown). By step S5, the fibre lay-up <NUM> can be secured to the mandrel tool <NUM> during the following arrangement of the mandrel tool <NUM> inside the adjacent blade sections <NUM>,<NUM>.

In step S6 of the method, the mandrel tool <NUM> having the reduced cross-section size S (i.e. the reduced height H and width W) and comprising the fibre lay-up <NUM> is inserted partially into a first blade section such as the outboard blade section <NUM> (<FIG>).

It is noted that in <FIG> - which also shows the process of inserting the mandrel tool <NUM> into the blade section <NUM> - the leading edge and trailing edge mandrel portions <NUM>, <NUM> and the bars <NUM> are omitted for illustration purposes. Further, in <FIG> also the fibre lay-up <NUM> and web element <NUM> is omitted for illustration purposes.

The first blade section <NUM> has, in particular, been manufactured using fibre-reinforced resin. The first blade section <NUM> has, for example, been manufactured simultaneously to the step S1 of pre-packing the fibre lay-up <NUM> on the mandrel tool <NUM>.

In this example, the first blade section <NUM> is an inboard section of the blade <NUM> comprising a root end <NUM> (<FIG>). However, the mandrel tool <NUM> could also be firstly inserted into an outboard section of the blade <NUM>. Further, in the shown example, the blade <NUM> is manufactured from two lengthwise sections <NUM>, <NUM>. However, in another example, the blade <NUM> could also be manufactured from more than two lengthwise blade sections. In such a case, the described process may be applied for joining any of two adjacent blade sections of the blade.

In <FIG>, the first blade section <NUM> is fixed in position by alignment jigs <NUM>. The mandrel tool <NUM> is inserted into the first blade section <NUM> by means of a lifting tool <NUM>. The lifting tool <NUM> in this example is a lifting truck. However, the lifting tool may also be, for example, a crane. The mandrel tool <NUM> is, in particular, inserted partially into the first blade section <NUM> such that a portion <NUM> of the mandrel tool <NUM> is protruding from the first blade section <NUM>, as shown in <FIG>.

In step S7 of the method, a second blade section <NUM> of the blade <NUM> is arranged adjacent to the first blade section <NUM>. In particular, the second blade section <NUM> is arranged adjacent to the first blade section <NUM> such that it accommodates the portion <NUM> of the mandrel tool <NUM> protruding from the first blade section <NUM>, as shown in <FIG>. The second blade section <NUM> is arranged adjacent to the first blade section <NUM> by means of alignment jigs <NUM>. The alignment jigs <NUM> are, for example, mounted such that the second blade section <NUM> can be moved, e.g., on rails <NUM>.

The second blade section <NUM> has, in particular, been manufactured using fibre-reinforced resin. The second blade section <NUM> has, for example, been manufactured simultaneously to the step S1 of pre-packing the fibre lay-up <NUM> on the mandrel tool <NUM>.

The second blade section <NUM> in this example is an outboard blade section. Further, in this example, the second blade section <NUM> comprises a blade tip <NUM>. However, the second blade section <NUM> could also be an inboard blade section.

Arranging the second blade section <NUM> adjacent to the first blade section <NUM> includes, for example, aligning the second blade section <NUM> to the first blade section <NUM> using the guiding rods <NUM> (<FIG>).

In step S8 of the method, the cross-section size S of the mandrel tool <NUM> (i.e. its height H and width W) is increased to its initial size. In particular, the lifting jacks <NUM> and the retracting rod <NUM> are extended such that the upper mandrel portions <NUM> and the trailing edge mandrel portion <NUM> are moved to their original positions.

Using the bars <NUM>, the fibre lay-up <NUM> folded into the gaps <NUM>, <NUM> is tensioned during increasing the size of the mandrel tool <NUM> and, thus, during unfolding the fibre lay-up <NUM> out of the gaps <NUM>, <NUM>. Further, due to gravity also the fibre lay-up <NUM> folded into the upper gap <NUM> is tensioned during increasing the size of the mandrel tool <NUM> and, thus, during unfolding the fibre lay-up <NUM> out of the gap <NUM>.

At the end of step S8, the middle portion <NUM> of the web element <NUM> is re-arranged between its first end second portions <NUM>, <NUM> (<FIG>).

Inserting the mandrel tool <NUM> into the first blade section <NUM> (step S6), arranging the second blade section <NUM> adjacent to the first blade section <NUM> (step S7) and/or increasing the size S of the mandrel tool <NUM> (step S8) includes matching the fibre lay-ups <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the web element <NUM>, <NUM>' (<FIG>) arranged on the mandrel tool <NUM> with corresponding layers of the first blade section <NUM> and second blade section <NUM>.

<FIG> shows a cross-section view of a part of the blade <NUM> taken along plane position B in <FIG>. Shown in <FIG> are the first and second blade sections <NUM> and <NUM> arranged adjacent to each other as well as the fibre lay-up <NUM> arranged inside the first and second blade sections <NUM> and <NUM>. The cross-section is taken through a pressure-side beam and a suction-side beam of the blade <NUM>. In the upper part of <FIG> are shown the pressure-side beam <NUM> of the first blade section <NUM>, the pressure-side beam joint <NUM> of the fibre lay-up <NUM>, and the pressure-side beam <NUM> of the second blade section <NUM> in cross-section. In the lower part of <FIG> are shown the suction-side beam <NUM> of the first blade section <NUM>, the suction-side beam joint <NUM> of the fibre lay-up <NUM>, and the suction-side beam <NUM> of the second blade section <NUM>.

Each of the pressure-side beams <NUM> and <NUM> and of the suction-side beams <NUM> and <NUM> comprises an outwardly tapered portion <NUM>, <NUM>, <NUM>, <NUM>. The outwardly tapered portions <NUM> and <NUM> of the pressure-side beams <NUM> and <NUM> of the first and second blade sections <NUM>, <NUM> form a common recess <NUM>. The fibre lay-up <NUM> for the pressure-side beam joint of the fibre lay-up <NUM> is arranged in the common recess <NUM>. Likewise, the outwardly tapered portions <NUM> and <NUM> of the suction-side beams <NUM> and <NUM> of the first and second blade sections <NUM>, <NUM> form a common recess <NUM>. The fibre lay-up <NUM> for the suction-side beam joint of the fibre lay-up <NUM> is arranged in the common recess <NUM>.

In step S9 of the method, the fibre lay-up <NUM> and the adjacent first and second blade sections <NUM>, <NUM> are at least partially covered with a vacuum bag <NUM>, <NUM>. In this example, vacuum bags <NUM> have already been provided in step S1 during prepacking the mandrel tool <NUM>. In step S9, a second vacuum bag <NUM> is provided at the outside surfaces <NUM>, <NUM> of the first and second blade sections <NUM>, <NUM>. In step S9, the vacuum bags <NUM>, <NUM> are sealed around the inner surfaces <NUM>, <NUM> and the outer surfaces <NUM>, <NUM> of the first and second blade sections <NUM>, <NUM>. <FIG> shows the sealing of the vacuum bags <NUM>, <NUM> covering the fibre lay-up <NUM> for the pressure-side beam joint and the fibre lay-up <NUM> for the suction-side beam joint. The sealing is schematically and exemplarily indicated by sealing points <NUM> in <FIG>. The sealing of the vacuum bags <NUM>, <NUM> might be done by applying a sealing tape or any other suitable method. Although not shown in <FIG>, the vacuum bags <NUM> and <NUM> are also sealed around the fibre lay-ups <NUM>, <NUM>, <NUM> for the leading and trailing edge beam joints and the shell joint and around the web element <NUM>, <NUM>'.

Then, a vacuum is generated within a cavity <NUM> defined by the sealed vacuum bags <NUM>, <NUM>. Further, a resin <NUM> is infused into the cavity <NUM>. <FIG> shows the resin <NUM> starting to fill the cavity <NUM> and to embed the fibre lay-up <NUM> for the pressure-side beam joint. After completion of the infusion process, the infused resin <NUM> is fully embedding the complete fibre lay-up <NUM> arranged on the mandrel tool <NUM>. The resin <NUM> is then cured to obtain a cured joining portion. In <FIG> the reference sign <NUM> indicates the cured joining portion which is formed when the fibre lay-up <NUM> (shown in <FIG> is <NUM> and <NUM> of <NUM>) are fully embedded in the infused and cured resin <NUM>.

The cured joining portion <NUM> joins the two blade sections <NUM>, <NUM> from inside providing a light-weight and at the same time strong blade section joint.

In step S10 of the method, the mandrel tool <NUM>, i.e. its leading edge part <NUM> and its trailing edge part <NUM>, are removed through the root end <NUM> of the blade <NUM> (<FIG>).

Claim 1:
A method for manufacturing a wind turbine blade, comprising the steps of:
a) arranging (S1) a fibre lay-up (<NUM>) on a mandrel tool (<NUM>), the mandrel tool (<NUM>) comprising a frame (<NUM>) and, as seen in cross-section, at least two mandrel portions (<NUM>, <NUM>, <NUM>, <NUM>) connected to the frame (<NUM>), and wherein at least a portion of the fibre lay-up (<NUM>) is supported by an outer surface (<NUM>) of the at least two mandrel portions (<NUM>, <NUM>, <NUM>, <NUM>),
b) reducing (S3) a cross-section size (S) of the mandrel tool (<NUM>) by retracting at least one of the mandrel portions (<NUM>, <NUM>, <NUM>, <NUM>) towards the frame (<NUM>),
c) arranging (S6, S7) the mandrel tool (<NUM>) inside adjacent blade sections (<NUM>, <NUM>),
d) increasing (S8) the cross-section size (S) of the mandrel tool (<NUM>) by extending at least one of the mandrel portions (<NUM>, <NUM>, <NUM>, <NUM>) away from the frame (<NUM>), and
e) infusing (S9) at least a portion of the fibre lay-up (<NUM>) with a resin (<NUM>) and curing the resin (<NUM>) to obtain a cured joining portion (<NUM>) joining the blade sections (<NUM>, <NUM>) inside.