WIND TURBINE BLADE BODY MANUFACTURING METHOD

Abstract

The invention provides a wind turbine blade body manufacturing method, the method comprising the steps of: providing a mould (40) having an elongated mould surface (43), placing a movable insert (50) on the mould surface, in a first position, forming, with the insert in the first position, a first blade body having a first length (L1), placing the insert (50) on the mould surface, in a second position, and forming, with the insert in the second position, a second blade body having a second length (L2) which is different from the first length.

Claims

1. A wind turbine blade body manufacturing method, the method comprising the steps of: providing a mould having an elongated mould surface, placing a movable insert on the mould surface, in a first position, forming, with the insert in the first position, a first blade body having a first length, placing the insert on the mould surface, in a second position, and forming, with the insert in the second position, a second blade body having a second length which is different from the first length.

2. The method according to claim 1, wherein the mould surface extends from a mould root end to a mould tip end, and comprises a portion presenting a constant cross-section, wherein the steps of placing the insert, in the first and second positions, comprises placing the insert with a proximal end thereof facing toward the mould root end, and placing the proximal end within the constant cross-section portion.

3. The method according to claim 2, wherein the proximal end has a shape which is substantially the same as the cross-sectional shape of the constant cross-section portion.

4. The method according to claim 1, wherein a difference, at the first position and at the second position, of the orientation of the insert around a longitudinal axis of the mould surface, is linearly dependent on the distance between the first position and the second position.

5. The method according to claim 1, wherein a difference, at the first position and at the second position, of the orientation of the insert around a lateral axis of the mould surface, is linearly dependent on the distance between the first position and the second position.

6. The method according to claim 1, wherein the steps of placing the insert, in the first and second positions, comprises fixing the insert in a lateral direction of the mould surface, by means of a mechanical locking arrangement extending along at least one of opposite longitudinal edges of the mould surface.

7. The method according to claim 6, wherein fixing the insert comprises placing the insert so as to partly cover the locking arrangement, wherein a cover device is placed to cover a part of the locking arrangement not covered by the insert.

8. The method according to claim 1, wherein the insert presents an insert tip end for forming a tip of the first and second blade bodies.

9. The method according to claim 1, further comprising: selecting the lengths of the first and second blade bodies based on required lengths of respective blades for a first wind turbine and a second wind turbine, and selecting the first and second positions to form the first and second blade bodies with the selected lengths.

10. A wind turbine blade installation method, comprising mounting on a first wind turbine in a wind farm, a first blade comprising the first blade body formed in the method according to claim 1, and mounting on a second wind turbine in the wind farm, a second blade comprising the second blade body formed in the method.

11. A wind farm comprising a first wind turbine comprising a first blade comprising the first blade body formed in the method according to claim 1, the wind farm further comprising a second wind turbine comprising a second blade comprising the second blade body formed in the method.

12. A wind turbine blade body manufacturing apparatus comprising: a mould, having an elongated mould surface extending from a mould root end to a mould tip end, and a movable insert, the apparatus being arranged to allow the insert to be placed on the mould surface, in a plurality of positions along the longitudinal direction of the mould surface, for forming blade bodies having respective lengths which are dependent on the insert position along the longitudinal direction of the mould surface.

13. The apparatus according to claim 12, wherein the mould surface comprises a portion presenting a constant cross-section.

14. The apparatus according to claim 13, wherein the insert comprises a proximal end arranged to face toward the mould root end and a distal end arranged to face away from the mould root end, the proximal end having a shape which is substantially the same as the cross-sectional shape of the constant cross-section portion.

15. The apparatus according to claim 13, wherein, in the constant cross-section portion, a twist of the mould surface changes linearly in the longitudinal direction of the mould surface.

16. The apparatus according to claim 13, wherein at least a part of the mould surface is curved in the longitudinal direction so as to provide a longitudinal bend on the blade bodies, the curvature of the mould surface being constant in the constant cross-section portion.

17. The apparatus according to claim 13, wherein the mould presents, at the constant cross-section portion, a mechanical locking arrangement along at least one of opposite longitudinal edges of the mould surface, for fixing the insert in a lateral direction of the mould surface.

18. The apparatus according to claim 17, wherein the insert is arranged to partly cover the locking arrangement, the apparatus further comprising a cover device arranged to cover a part of the locking arrangement not covered by the insert.

19. A wind turbine blade body manufacturing method, comprising forming a blade body with an apparatus according to claim 12, and with the insert in one of the plurality of positions.

20. The method according to claim 19, wherein the blade body has a length within 90-100%, of the length of the longest blade body that can be formed in the apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Examples of the invention will now be described in detail with reference to the following figures, in which:

[0032] FIG. 1 is a view of a wind turbine;

[0033] FIG. 2 is a perspective view of a wind turbine rotor blade;

[0034] FIG. 3 is a perspective view of a wind turbine rotor blade mould used to produce a part of the blade in FIG. 2;

[0035] FIG. 4 is a block diagram showing steps in a method according to an embodiment of the invention;

[0036] FIG. 5 shows the mould in FIG. 3 with an insert in a first position;

[0037] FIG. 6 is a perspective view of the insert in FIG. 5;

[0038] FIG. 7 is a perspective view of a blade partly produced by the mould in FIG. 5;

[0039] FIG. 8 shows the mould in FIG. 3 with an insert in a second position;

[0040] FIG. 9 is a perspective view of a blade partly produced by the mould in FIG. 8;

[0041] FIG. 10 is a graph showing the twist of the blade in FIG. 2;

[0042] FIG. 11 is a diagram showing a curvature of the primary mould surface in a further embodiment of the invention;

[0043] FIG. 12 is a perspective view of a mould in another embodiment of the invention;

[0044] FIG. 13 is a perspective view of a part of a mould with an insert;

[0045] FIG. 14 is a perspective view of the mould, part of which is shown in FIG. 13;

[0046] FIG. 15 is a cross section of a wind turbine rotor blade mould with an insert in the mould;

[0047] FIG. 16 is a plan view of a part of the mould in FIG. 15 with the insert in the mould;

[0048] FIG. 17a to FIG. 17d are cross section views of the mould in FIG. 15, along the line XVII-XVII of FIG. 16, with the insert in the mould, showing how the blade is fabricated;

[0049] FIG. 18a and FIG. 18b are cross section views of the mould in FIG. 15 showing how the insert is positioned on the mould;

[0050] FIG. 19 is a further cross section of a wind turbine rotor blade mould with an insert in the mould.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0051] FIG. 1 shows a horizontal axis wind turbine 10. The wind turbine 10 comprises a tower 12 supporting a nacelle 14 to which a rotor 16 is mounted. The rotor 16 comprises a plurality of wind turbine blades 18 that extend radially from a central hub 19. In this example, the rotor 16 comprises three blades 18.

[0052] FIG. 2 is a view of one of the blades 18 of the wind turbine 10. The blade 18 extends from a generally circular root end 20 to a tip end 22 in a longitudinal ‘spanwise’ direction, and between a leading edge 24 and a trailing edge 26 in a transverse ‘chordwise’ direction. The blade 18 comprises a shell 27 formed primarily of fibre-reinforced plastic (FRP). The shell 27 comprises a pressure surface 29 on a pressure side of the blade 18 and a suction surface 30 on a suction side of the blade 18. The blade has a length L0 in the spanwise direction extending from the root end 20 to the tip end 22. Spanwise positions on the blade can also be expressed in terms of a radius as measured from the rotational axis of the hub 19. In FIG. 2, the tip 22 is expressed as radius R1. The blade 18 transitions from a circular profile to an airfoil profile moving from the root end 20 of the blade 18 towards a shoulder 23 of the blade 18, which is the widest part of the blade 18 where the blade 18 has its maximum chord.

[0053] As explained closer below, a longitudinal portion 21 of the blade presents a constant cross-section. The constant cross-section portion 21 is located between the shoulder 23 and the tip end 22. The constant cross-section portion 21 extends from a radius R2 to a radius R3. From the shoulder 23 to the constant cross-section portion 21, the blade 18 has an airfoil profile of progressively decreasing thickness. From the constant cross-section portion 21 to the tip end 22, the blade 18 has an airfoil profile of progressively decreasing thickness.

[0054] It should be noted that the proportions of the blade, in particular the constant cross-section portion 21 thereof, are provided for ease of understanding, and not necessarily representative of the shape of a blade produced in practice. Below, are some examples of blade dimensions which are practically interesting in the context of embodiments the invention.

[0055] The shell 27 of the blade is fabricated from first and second half shells 32, 34, herein also referred to as blade bodies. The first and second half shells 32, 34 are adhesively joined together along the leading edge 24 and the trailing edge 26. The half shells 32, 34 are laminated structures that are moulded from fibre reinforced plastic (FRP) including glass fibres and possibly carbon fibres.

[0056] The half shells 32, 34 are moulded in separate mould halves, herein also referred to as first and second moulds, of a blade body manufacturing apparatus. Once each half shell 32, 34 has been moulded, the two half shells 32, 34 are brought together by bringing the two mould halves together, and the half shells 32, 34 are bonded together to form the complete blade 18. Structural elements, such as webs or spars, may be provided between the half shells.

[0057] FIG. 3 shows a mould half 40 for forming one of the half shells 32, 34. The mould half will be referred to hereafter for convenience as the mould. The mould 40 comprises a mould root end 41 and a mould distal end 45. The half shell is formed on a mould surface 43, herein also referred to as a primary mould surface, having a shape corresponding to the shape of the half shell 44 to be formed. The primary mould surface extends from the mould root end 41 to a mould tip end 42.

[0058] The mould 40 has a leading flange 46 and a trailing edge flange 47 which extend from the mould root end 41 to the mould distal end 45. The primary mould surface 43 forms a recess 48 between the mould flanges 46, 47.

[0059] To form a half shell, one or more layers of glass-fibre fabric are placed on the primary mould surface 43 of the mould 40. These layers will later form an outer skin of the blade 18. Structural elements, including spar caps and sandwich core panels are then arranged on top of the outer fabric layers. One or more further layers of dry glass-fibre fabric are then placed over the structural elements, and will later form an inner skin of the blade. The glass-fibre layers are then impregnated with a resin, which is subsequently hardened to form a solid plastic material. Such an impregnation can be done with a vacuum assisted resin transfer moulding (VARTM) process, which is known per se, and not described closed here.

[0060] It is understood that alternatives for forming the half shell are possible. For example, layers of pre-preg glass fibres, i.e. glass fabric sheets impregnated with polymer resin, may be used.

[0061] The primary mould surface 43 has a length L0, i.e. the same as that of the blade in FIG. 2. Thus, the mould shown in FIG. 3 may be used to form a blade body, in the form of a half shell, for the blade in FIG. 2. It should be noted that the primary mould surface 43 comprises a portion 49 presenting a constant cross-section. The mould surface constant cross-section portion 49 forms part of the blade constant cross-section 21 shown in FIG. 2.

[0062] Reference is made to FIG. 4, showing a block diagram depicting steps in a method according to an example. The method comprises placing S1 a movable insert 50 on the primary mould surface 43, in a first position.

[0063] Reference is also made to FIG. 5, showing the insert 50 placed in the first position. The insert 50 is located in the mould recess 48. The insert 50 is placed within the constant cross-section portion 49. The insert 50 shortens the effective mould surface, i.e. the combined mould surface provided by the primary mould surface 43 and an insert mould surface. In FIG. 5, the length of the combined mould surface is L1 defined between the mould root end and an insert tip end 142.

[0064] FIG. 6 shows the insert 50 in more detail, with the insert mould surface 143. The insert 50 extends between a proximal end 51 facing toward the mould root end 41 and a distal end 52 facing away from the mould root end 41. The insert 50 presents an insert tip end 142 which forms an end of the insert mould surface 143.

[0065] An underside 144 of the insert 50 has in this embodiment a constant cross-section. The shape of the cross-section of the underside 144 is substantially the same as the shape of the cross-section in the primary mould surface constant cross-section portion 49. At the proximal end 51, the insert mould surface 142 has a cross-sectional shape which is substantially the same as the shape of the cross-section in the constant cross-section portion 49. Thus, the proximal end 51 has a shape which is substantially the same as the cross-sectional shape of the constant cross-section portion 49. The thickness of the insert 50 at the proximal end 51 may be no larger than 10 mm, preferably no larger than 5 mm. To avoid a step in the combined mould surface, a filler material can be applied onto the primary mould surface 43, and adjacent to the insert proximal end 51.

[0066] The method comprises forming S2, with the insert 50 in the first position, a first blade body having a first length L1. The first blade body is a shell half, which is joined with another shell half, to form a first blade B1, depicted in FIG. 7. As indicated in FIG. 7, the length L1 of the first blade B1 is the same as the length L1 of the combined mould surface in FIG. 5. Between the blade root end 20 and a portion formed by the insert, the first blade B1 has a geometry which is identical with the geometry of the blade 18 shown in FIG. 2, produced by the mould without the insert 50.

[0067] Following removal of the first blade body from the mould 40, the insert 50 can be left in the mould 40 in order to manufacture further first blade bodies having the same length L1.

[0068] As depicted in FIG. 8, the method comprises placing S3 the insert 50 on the primary mould surface 43, in a second position. The insert 50 is placed within the constant cross-section portion 49. The second position is in this example, compared to the first position, closer to the mould root end 41. Thereby, the insert 50 further shortens the combined mould surface provided by the primary mould surface 43 and the insert mould surface 143. In FIG. 8, the length of the combined mould surface is L2 defined between the mould root end and the insert tip end 142.

[0069] The method comprises forming S4, with the insert 50 in the second position, a second blade body having a second length L2. The second blade body is a shell half, which is joined with another shell half, to form a second blade B2, depicted in FIG. 9. As indicated in FIG. 9, the length L2 of the second blade B2 is the same as the length L2 of the combined mould surface in FIG. 8.

[0070] The second blade B2 has a shorter spanwise length that the first blade B1 due to the different position of the insert 50 in the mould 40. Between the blade root end 20 and the respective portions formed by the insert, the first blade B1, (FIG. 7), and the second blade B2 have geometries which are identical. Although the first and second blades B1, B2 have an identical aerodynamic surface between the root end 20 and the respective portions formed by the insert, the internal structure can vary therein. For example, as the second blade B2 has a shorter length it may be subjected to less loads in use (compared to the first blade B1) such that it does not require the same amount of structural material.

[0071] Following removal of the second blade body from the mould 40, the insert 50 can be left in the mould 40 in order to manufacture further second blade bodies having the same length L2.

[0072] With this method, a number of blade variants having different blade lengths can be formed in the same mould. For example, if L0 (FIG. 2) is 60 metres, a movable insert 50 can be used to produce a plurality of blade variants having shorter lengths, e.g. 56 metres, 55 metres and 54 metres etc. For example, variations in blade length of from anywhere between about 0.1% to about 20% can be provided, although preferably the variation in length is in the region of from about 1% to about 10%, more preferably from about 3% to about 7%. As further examples, the blade bodies formed with the mould may have a length within 90-100%, preferably 95-100%, of the length of the longest blade body that can be formed in the mould.

[0073] In yet further examples, blade bodies may be produced with lengths differing in a stepwise manner, e.g. by 100-2000 mm, or 200-1000 mm, from one blade body to another. Thereby, blade lengths may be varied within a wind farm, from some wind turbines to others, in a manner which increases the energy output of the windfarm, as described above.

[0074] FIG. 10 shows the twist of the blade in FIG. 2 along its span, moving from the root of the blade (at the left hand side of the abscissa) to the tip end of the blade (at the right hand side of the abscissa). As background, blade twist is necessary as the effective flow at the blade in use comprises the rotor rotational speed and the oncoming wind speed. As the peripheral speed of the blades increases along the blade span, the angle of attack of a blade section also varies along the blade span. To maintain the angle of attack and the lift force along the blade, the blade has a twist distribution from the root to the tip. The tip of the blade is also “de-twisted” in order to reduce the induced drag from the tip of the blades.

[0075] As stated, the constant cross-section portion 21 extends from a radius R2 to a radius R3. As illustrated in FIG. 10, the twist of the blade changes, in the constant cross-section portion, linearly in the spanwise direction. For this, a twist of the primary mould surface 43 (FIG. 3) changes, in the constant cross-section portion 49, linearly in the longitudinal direction of the primary mould surface 43. Thereby, a difference, at the first position (FIG. 7) and at the second position (FIG. 9), of the orientation of the insert 50 around a longitudinal axis of the primary mould surface 43, is linearly dependent on the distance between the first position and the second position. The lower side of the insert 50 preferably has a form which is complementary to the linearly changing twist of the primary mould surface 43. Thereby, the combined mould surface, formed by the insert mould surface 143 and a part of the primary mould surface 43, may be altered by moving the insert 50 from the first position to the second position, without any special provisions needed in view of the changing primary mould surface 43 twist.

[0076] Reference is made to FIG. 11. As is known per se, to avoid tower strikes, wind turbine blades may be bent in the flapwise direction, i.e. bent in a plane which is parallel to the longitudinal blade direction, and perpendicular to the chordwise direction. Such a bend may be referred to as a pre-bend.

[0077] FIG. 11 is a diagram with a side elevation of the primary mould surface in a further example. The diagram shows the primary mould surface 43 along a vertical plane in the longitudinal direction of the mould, and along the lowest part of the recess formed by the primary mould surface 43. To provide pre-bent blades, an outer part of the primary mould surface 43 is curved in the longitudinal direction so as to provide a longitudinal bend on the blade bodies.

[0078] As can be seen in FIG. 11, the curvature of the primary mould surface 43 has a constant radius RB in the constant cross-section portion, between the spanwise radii R2 and R3.

[0079] In some embodiments, a difference, at the first position and at the second position, of the orientation of the insert 50 around a lateral axis of the primary mould surface 43, is linearly dependent on the distance between the first position and the second position. The underside 144 of the insert 50 has a form which is complementary to the constant curvature primary mould surface 43. More specifically, the underside 144 of the insert 50 has a longitudinal curvature with a radius which is the same as the radius RB of the constant curvature primary mould surface 43. Thereby, the combined mould surface, formed by the insert mould surface 143 and a part of the primary mould surface 43, may the altered by moving the insert 50 between any positions within the constant cross-section portion, without any special provisions needed in view of the curved primary mould surface 43.

[0080] Reference is made to FIG. 12 showing a mould in a further example. The mould 40 is not provided with a part for forming the tip of the blade bodies. Instead, the constant cross-section portion extends to the mould tip end 42. The mould tip end 42 coincides with the mould distal end 45. In addition, Thereby, the insert 50 may be placed on the primary mould surface 43, at the mould tip end 42. The insert 50 may even extend past the mould tip end 42.

[0081] Reference is made to FIG. 13. Fixing the insert in the mould may be done in a variety of manners. In one example, as suggested in FIG. 13, placing the insert 50, in the first and second positions, or in any position along the constant cross-section portion 49, comprises fixing the insert 50 in a lateral direction of the primary mould surface 43, by means of a mechanical locking arrangement 53. The mechanical locking arrangement comprises in this example a track 53 extending along both opposite longitudinal edges of the primary mould surface 43. The tracks are in this example provided as elongated grooves 53. It is understood that in alternative embodiments, the tracks 53 could be provided as elongated ridges.

[0082] The mechanical locking arrangement extends along the entire constant cross-section portion 49 of the primary mould surface 43, (FIG. 3). It is understood that the opposite longitudinal edges of the primary mould surface 43 are parallel. The insert 50 may be provided with engagement means for engagement with the locking arrangement. In this example the insert 50 is provided with ridges 54 arranged to engage the tracks 53. As can be seen in FIG. 13, the insert 50 partly covers the locking arrangement 53.

[0083] As exemplified in FIG. 14, in some embodiments, cover devices 55 are placed to cover parts of the locking arrangement 53 not covered by the insert 50. The covering devices 55 are in this example provided as elongated elements arranged to engage the respective tracks 53 of the locking arrangement. They may, in addition to covering the part of the locking arrangement not covered by the insert 50, provide a portion of the primary mould surface 43. As exemplified below, such a primary mould surface 43 portion may form at least one of opposite longitudinal edges of the primary mould surface 43.

[0084] Alternatives are possible for the locking arrangement. For example, it may comprise rows of separated protrusions or recesses. Complementary recesses or protrusions, may be provided on the insert 50. This would allow the insert to be placed at a limited number of discrete locations along primary mould surface 43.

[0085] Below, further measures for fitting and securing the insert 50 to the mould, disclosed in said WO2017088883A1, incorporated herein by reference, are described with reference to FIG. 15 to FIG. 19.

[0086] FIG. 15 and FIG. 16 show how the insert 50 may be held to the mould 40 via a vacuum. FIG. 15 is a cross-sectional view through the mould 40 and the insert 50, and FIG. 16 is a plan view. The insert 50 is placed in the mould 40 such that the insert leading edge flange 146 is aligned with the mould leading edge flange 46, and the insert trailing edge flange 147 is aligned with the mould trailing edge flange 47. As can be seen in FIG. 15, there is a gap 60 between the primary mould surface 43 and the underside 144 of the insert 50. This gap has a height of the order of 0.1 mm. The gap 60 allows an under pressure to be created between the insert 50 and the mould 40 so that the insert is retained in a fixed position against the mould. It will be appreciated that the gap 60 is shown enlarged in the figures for clarity.

[0087] A seal is provided between the mould 40 and the insert 50. Referring to FIG. 16, the following seals are provided:

[0088] (i) a seal 61a over the joint between the insert leading edge flange 146 and the mould leading edge flange 46. This seal can be a Polytetrafluoroethylene (PTFE) tape.

[0089] (ii) a seal 61b over the joint between the insert trailing edge flange 147 and the mould leading edge flange 47. This seal can be a PTFE tape.

[0090] (iii) a seal 62 over the joint between the primary mould surface 43 and the insert mould surface 143 at the proximal end 51 of the insert 50. This seal can be a PTFE tape.

[0091] (iv) a seal 63 over the joint between the insert 50 and the primary mould surface 43 at the distal end 52 of the insert 50. This seal 63 can be formed from a vacuum film with sealant tape around its periphery.

[0092] After the seals have been provided around the insert 50, a vacuum line 64 is attached and passes through the vacuum film of seal 63. A vacuum pump 65 then evacuates the air under the seal 63 which will also evacuate the air from the gap 60. Compared to the ambient air pressure, the pressure in the gap 60 will be at a relatively lower pressure such that the insert 50 is ‘sucked’ down onto the mould 40.

[0093] FIG. 17a to FIG. 17d are schematic cross-section views along the line XVII-XVII of FIG. 16. FIG. 17a to FIG. 17d illustrate the steps taken to manufacture the wind turbine blade shell in the mould 40 with the insert 50.

[0094] FIG. 17a shows the insert 50 placed in the mould 40. As can be seen there is the gap 60 between the primary mould surface 43 and the underside of the insert 50.

[0095] Next, as shown in FIG. 17b, the insert 50 is sealed against the mould 40 so that it is retained firmly in position. A seal 62 is provided between the proximal end 51 of the insert and the primary mould surface 43 as discussed above. The seal 63 at the distal end of the insert comprises strips of sealing tape 63a (for example butyl rubber) and a vacuum film 63b which provides an effective seal. Also shown in FIG. 17b is the vacuum line 64. The cavity under the vacuum film 63b is evacuated which as discussed above will force the insert 50 against the mould 40 and hold it tightly in position.

[0096] FIG. 17c shows the blade materials being laid into the mould, onto the primary mould surface 43 and the insert mould surface 143. In this example, the blade materials 70 comprise layers of pre-preg glass fibres and optionally sandwich core panels.

[0097] In FIG. 17d the blade materials 70 are covered with a vacuum film 75 and the cavity under the vacuum film 75 is evacuated in order to consolidate the blade materials as is conventional in a composite fabrication operation. The vacuum film 75 is sealed around the periphery of the mould with sealant tape 76. Then the mould is heated in order to cure the blade materials 70. The insert 50 may be heated by absorbing heat from the mould. Alternatively, or in addition, the insert 50 can have inbuilt electrical elements so that the insert can have its own heating system for curing the modified tip end of the blade.

[0098] The vacuum line 64 which is used to retain the insert 50 in position on the mould 40 can pass between the vacuum film 75 and the periphery of the mould 40. When air is evacuated from under the vacuum film 75 the vacuum film 75 will hold the insert 50 against the mould and it is not necessary to keep the vacuum pump 65 running.

[0099] Reference is made to FIG. 18a and FIG. 18b. As stated, the insert may have a shape which is complementary to the constant cross-section portion. FIG. 16a and FIG. 16b show schematically how the insert 50 can be manufactured such that it has an accurate fit with the primary mould surface 43 of the mould 40. In this example, the insert mould surface 143 is formed from glass fibre reinforced plastic (GFRP). Extending from an underside of the insert mould surface are a plurality of ribs 80 formed from core material. In this example, the ribs are formed from PET foam, but other structural core materials could be used. In other words, the ribs extend from the insert mould surface 143 toward the primary mould surface 43. The ribs 80 are fabricated such that they do not extend all the way to the primary mould surface 43. At the end of each rib 80, opposite the insert mould surface 143 there is a bead of uncured adhesive 81, e.g. epoxy or PUR adhesive. The primary mould surface 43 of the mould 40 has been treated with a release agent. As shown in FIG. 18a, the insert 50 is first held above the primary mould surface 43 of the mould 40 and then it is lowered such that the adhesive beads 81 make contact with the primary mould surface 43 shown in FIG. 18b. This compresses and deforms the adhesive beads 81 to the shape of the primary mould surface 43.

[0100] The insert 50 is held in the correct place on the mould 40 via clamps or the use of a jig. While the insert 50 is being held, the adhesive beads 81 will cure and thus this will provide an accurate matching shape between the insert 50 and the primary mould surface 43. Thus, the bottom of the adhesive beads 81 become the underside 144 of the insert. As the primary mould surface 43 has been treated with a release agent, once the adhesive beads 81 have cured, the insert can be lifted from the mould 40 ready for use in a blade manufacturing process. As all moulds 40 can be slightly different due to manufacturing tolerances, it is desirable to produce a bespoke insert 50 for each mould, and the use of the adhesive beads 81 provides a quick and simple solution to create an accurate alignment between the mould and the insert 50. To provide the gap 60 which allows the insert 50 to be held to the mould 40 by vacuum, grooves can simply be scored in the cured adhesive beads 81.

[0101] FIG. 19 shows a more detailed example of how the insert 50 can be secured to the mould 40. The mould 40 comprises a leading flange 46 and a trailing edge flange 47 as described above. Located below these flanges are a leading edge process flange 246 and a trailing edge process flange 247. These process flanges 246, 247 are connected to the mould flanges 46, 47 via side surfaces of the mould 90 and 91. The mould side surfaces extend in a substantially vertical plane. In this example, the side surfaces of the mould are inclined relative to the vertical plane. The inclined surface 90 is formed such that there is an acute angle between the inclined surface 90 and the process flange 246. Similarly, the inclined surface 91 is formed such that there is an acute angle between the inclined surface 91 and the process flange 247. The insert 50 is fabricated with a strip 150 of GFRP which extends out from the insert leading edge flange 146, over the mould leading edge flange 46, inclined surface 90 and leading edge process flange 246. The strip 150 is held against the inclined surface 90 with a clamp 92 which is connected to the leading edge process flange 246.

[0102] On the trailing edge side, the insert 50 is fabricated with a strip 151 of GFRP which extends out from the insert trailing edge flange 147, over the mould trailing edge flange 47, inclined surface 91 and trailing edge process flange 247. The strip 151 is held against the inclined surface 91 with a clamp 92 which is connected to the trailing edge process flange 247. By connecting the insert 50 at the process flanges 246, 247 the insert 50 is held more securely on the mould 40 than if it was just connected at the leading edge mould flange 46 and the trailing edge mould flange 47. This is because the insert 50, through the strips 150 and 151 can be clamped securely at these places. In addition, the inclined surfaces 90 and 91 provide a negative draft angle and therefore help to prevent the insert 50 from moving relative to the mould 40.

[0103] A vacuum seal (not shown) is provided between the strip 150 and the leading edge process flange 246 and between the strip 151 and the leading edge process flange 247. Vacuum seals are also provided at the proximal end and the distal end of the insert as described with reference to FIG. 16. Therefore, the insert 50 is held in place against the mould by a vacuum force and by the clamps 92.

[0104] The strips 150 and 151 are formed from GFRP and are typically just 0.5 millimetres thick. Thus they can be elastically deformed to fit around the negative draft angles of the inclined surfaces 90 and 91.

[0105] By “negative draft angle” is meant that the surfaces 90 and 91 are inclined relative to the mould flanges such that the insert 50 cannot be directly lifted off the mould 40 as the strips 150 and 151 will clash with the inclined surfaces. Instead, some force has to be applied to the strips 150, 151 in order to deform them and lift the insert from the mould.

[0106] The clamps 92 may also be in the form of bolts which connect the insert 50 to the process flanges 246, 247 of the mould 40. Using bolts is advantageous because holes in the insert 50 can be aligned with corresponding holes on the mould 40, so that the insert 50 is always located at the correct position when placed on the primary mould surface 43.

[0107] In the example shown in FIG. 19 the side surfaces of the mould 90, 91 both have a negative draft angle. However, in another example, only one of the side surfaces has a negative draft angle, and the other side surface has a zero draft or a positive draft angle. This arrangement will accommodate more variations in fit between the mould 40 and the insert 50. In a further example (not shown) there may be no draft angles and the insert 50 is primarily held to the mould via the vacuum, but there are also clamps (such as bolts) to hold the insert 50 in the event of a vacuum failure. These bolts may connect the insert 50 to the process flanges 246, 247 of the mould 40.

[0108] Many alternatives to the examples described are possible and will occur to those skilled in the art without departing from the scope of the invention which is defined by the following claims.

[0109] For example, although the moulds are described above as forming one half of a wind turbine blade, the principle of providing a movable insert is applicable to any suitable method of blade manufacture in a mould. For example, it is applicable to blades formed as a single piece within a single mould cavity, or to blades formed from any number of sub-components which are subsequently assembled.