DK201670444A1 - Improvements relating to the manufacture of composite components - Google Patents

Abstract

A method of making a composite component for a wind turbine blade is described. One or more layers of prepreg material comprising reinforcing fibres impregnated with resin are provided. The reinforcing fibres of the prepreg material are cut using an ultrasonic cutting device along an edge of part line to create a line of weakness between a main portion and a peripheral portion of the one or more layers of prepreg material. The resin of the prepreg material is cured. The peripheral portion is detached from the main portion by snapping the cured resin along the edge of part line.

Description

IMPROVEMENTS RELATING TO THE MANUFACTURE OF COMPOSITE COMPONENTS

Field of the invention

The invention relates to methods of manufacturing composite components. The invention has particular application to composite components used in the manufacture of wind turbine blades, although the invention is not limited to such applications.

Background to the invention

Modern wind turbines generally include a number of components of composite construction. These components are often formed by moulding processes.

One method of manufacture involves using ‘prepreg’ materials; that is, fibre fabric layers that are pre-impregnated with semi-cured resin. The process generally involves arranging a number of prepreg layers on the surface of a mould, together with various other constituent materials if necessary, to form a ‘layup’. The layup is then covered using a vacuum bag which is sealed against the mould to form a sealed region encapsulating the layup. Thereafter, a vacuum is applied to the sealed region and the mould is then heated to cure the resin. Once the resin is cured, the resulting component is removed from the mould.

Other suitable methods of moulding composite components include vacuum assisted resin transfer moulding (VARTM), in which dry fibre fabric layers are arranged on the surface of the mould and liquid resin is admitted into the sealed region after the vacuum bag is sealed against the mould.

The edges of a moulded composite component are defined by the edges of the fibre fabric layers and the cured resin in the region of those edges. The edges of a composite component tend to be uneven as it is difficult to align the edges of the fibre fabric layers accurately as they are arranged on the mould. Furthermore, uneven amounts of excess resin tend to be present at the edge of a component, which may form serrations in the cured component. Therefore, the edge may present a safety hazard, making the component difficult and potentially unsafe to handle.

In order to produce a neater edge, the component is typically subjected to a finishing process in which excess material is trimmed from the edge of the component after the resin has been cured. However, the cured composite material is very hard, and a diamond cutting saw is often required to trim the edge, resulting in an expensive and time-consuming finishing process. It may also be necessary to sand the edge of the component after trimming. This adds further stages to the manufacturing process therefore increasing the time and cost of manufacture.

The present invention has been devised to mitigate or overcome at least some of the above-mentioned problems.

Summary of the invention

According to an aspect of the invention, there is a provided a method of making a composite component for a wind turbine blade. The method comprises: providing one or more layers of prepreg material comprising reinforcing fibres impregnated with resin; cutting the reinforcing fibres of the prepreg material using an ultrasonic cutting device along an edge of part line to create a line of weakness between a main portion and a peripheral portion of the one or more layers of prepreg material; curing the resin of the prepreg material; and detaching the peripheral portion from the main portion by snapping the cured resin along the edge of part line.

The peripheral portion may be detached from the main portion by snapping the cured resin by hand along the edge of part line. In other embodiments, a suitable tool such as a saw or laser may be used to detach the peripheral portion from the main portion.

The method may comprise providing a plurality of layers of prepreg material and arranging the plurality of layers in a stack.

The method may comprise arranging the one or more layers of prepreg material on a surface of a mould. In this case, the reinforcing fibres of the prepreg material may be cut in the mould.

The method may comprise consolidating the one or more layers of prepreg material. A pre-consolidation process may be performed prior to cutting the reinforcing fibres of the prepreg material.

Material that does not absorb ultrasonic vibrations may be provided beneath the edge of part line prior to cutting the prepreg material. The material may be polytetrafluoroethylene (PTFE). If the reinforcing fibres of the prepreg material are cut in the mould then the material may be an integral part of the mould surface. In other examples, the material may be arranged on the surface of the mould. The material may be arranged on the surface of the mould before or after the one or more layers of prepreg material are arranged on the surface of the mould. If the method comprises consolidating the one or more layers of prepreg material, the backer may be arranged in the mould either before or after consolidation. The one or more layers of prepreg material may be lifted up to allow the material to be arranged on the surface of the mould.

The reinforcing fibres may comprise glass fibres and the resin may comprise epoxy resin.

The composite component may be a shear web or part of a shear web for a wind turbine blade.

According to another aspect of the invention, there is provided a composite component made according to the method of the previously-described aspect.

According to a further aspect of the invention, there is provided a wind turbine blade comprising the composite component of the previous aspect.

The inventive concept extends to embrace the use of an ultrasonic cutting device to cut through fibres in prepreg material prior to curing the prepreg material to create a line of weakness in a cured component.

Brief description of the drawings

In order that the invention may be more readily understood, an embodiment of the invention will now be described by way of non-limiting example only with reference to the accompanying figures, in which:

Figure 1 shows a wind turbine blade in transverse cross-section, comprising two longitudinally extending shear webs;

Figure 1a shows a perspective view of an end region of one of the shear webs of Figure 1, the shear web generally comprises an elongate C-shaped panel and two L-shaped return flanges;

Figure 2 shows a cross-sectional view of a mould used in the manufacture of a return flange;

Figure 3 shows a plurality of prepreg layers arranged on the surface of the mould of Figure 2;

Figure 4 shows an ultrasonic cutting device cutting through the prepreg layers along a predefined ‘edge of part’ line;

Figure 4a shows an enlarged view of a portion of Figure 4;

Figure 5 illustrates a vacuum-bagging and curing process;

Figure 6 shows the resulting return flange removed from the mould after the curing process;

Figure 7 shows a sacrificial peripheral portion being removed from the return flange to define an edge of the return flange;

Figure 8 shows an enlarged view of an edge region of the return flange;

Figure 9 is a flowchart showing the steps of the process illustrated by Figures 3 to 8; and

Figure 10 is a flowchart showing the steps of a further example of a process for making a return flange.

Detailed description

Referring initially to Figure 1, a wind turbine blade 10 is shown in transverse cross-section. The blade 10 comprises a hollow shell 12 made up of two half-shells 12a, 12b bonded together along leading and trailing edges 14, 16 of the blade 10. Two longitudinally-extending shear webs 18 of composite construction are provided within the internal cavity 20 of the blade 10.

As shown in the figure, each shear web 18 comprises a web element 22 and two mounting flanges 24a, 24b, respectively provided at first and second ends of the web element 22 as viewed in cross-section. As such, each shear web 18 is substantially I-shaped in cross-section. The mounting flanges 24a, 24b of each shear web 18 are bonded to the inner surfaces 26a, 26b of the half-shells 12a, 12b.

Referring now to Figure 1a, this shows a schematic perspective view of an end region of one of the shear webs 18 shown in Figure 1. It can be seen in Figure 1a that the shear web 18 extends longitudinally in the direction of the arrow 28. In this example, the shear web 18 is formed of three component sections: an elongate moulded panel 30, which is substantially C-shaped in cross-section, and first and second elongate return flanges 32, which are substantially L-shaped in cross-section. The C-shaped panel 30 forms the web element 22 of the shear web 18 and half of each mounting flange 24a, 24b. The other half of each mounting flange 24a, 24b is formed from the respective L-shaped return flanges 32.

Each section 30, 32 of the shear web 18 is of composite construction. To manufacture the shear web 18, each component section 30, 32 is moulded separately and the return flanges 32 are then bonded to the C-shaped panel 30. The shear web 18 is constructed in this way as it is difficult to form an I-shaped structure using traditional moulding techniques. A process for manufacturing a return flange 32 for a shear web 18 in accordance with an example of the present invention will now be described with reference to Figures 2 to 9.

Referring initially to Figure 2, a mould 34 used in the manufacture of a return flange is shown in transverse cross-section. The mould 34 is substantially L-shaped in cross-section with a mould surface 36 corresponding in shape to the outer contour of the return flange to be formed in the mould 34. The mould 34 is elongate, extending longitudinally in a direction transverse to the plane of the page.

As shown in Figure 3, a number of ‘prepreg’ layers 38 are arranged on the surface 36 of the mould 34 to form a ‘layup’ 39. In this example, four prepreg layers 38 are arranged in a stack in the mould 34 but more or fewer layers may be provided as required. Each of the prepreg layers 38 includes one or more fibre fabric layers 40 pre-impregnated with semi-cured resin 42 such as epoxy. The skilled person will be familiar with prepreg materials and the present invention is applicable to all types of fibrous prepreg. In this example, the fibre fabric is glass fibre fabric but the skilled person will be aware of suitable alternative materials such as carbon fibre fabric. The layup 39 may also include a release film and a peel ply layer (not shown) arranged on the mould surface 36 before the prepreg layers 38 are arranged in the mould 34.

Furthermore, whilst only prepreg fibre fabric layers 38 are illustrated in the layup 39 in this example, it will be appreciated that additional elements may be arranged in the mould 34 as required based on the design specification of the composite component being manufactured. For example, if the component is of sandwich-panel construction, then core material such as foam or balsa wood may be provided between fibre fabric layers.

Once the layup 39 has been arranged in the mould 34, but whilst the resin 42 in the prepreg layers 38 remains in a semi-cured state (i.e. before a subsequent curing process), a preliminary cutting process is performed on the layup 39. As shown in Figures 4 and 4a, the preliminary cutting process involves using an ultrasonic cutting device 50 to sever the reinforcing fibres within the fibre fabric layers 40. In particular, the fibres are cut along a predefined cutting line 51 extending along the longitudinal extent of the layup 39. In the representations of Figures 4 and 4a, the predefined line 51 extends transversely to the plane of the page.

Cutting the fibres along the predefined line 51 defines two portions of the layup 39: a main portion 52 on one side of the cutting line 51 and a sacrificial peripheral portion 54 on the opposite side. The peripheral portion 54 is ultimately detached from the main portion 52 to form the finished return flange. As such, the cutting line 51 defines the position of an edge of the finished return flange. The predefined line 51 is therefore referred to hereafter as an ‘edge of part’ line 51.

Cutting the fibres along the edge of part line 51 at this stage (i.e. before the resin 42 is cured) results in a line of weakness along the edge of part line 51. As will be described in further detail below, this advantageously facilitates detachment of the peripheral portion, resulting in a neat edge on the finished return flange without requiring a time-consuming or expensive post-moulding finishing process.

In this example, the ultrasonic cutting device 50 comprises a transducer 56, including a blade 58, driven by an oscillator (not shown). Any suitable ultrasonic cutting device may be used, for example the SH-3510 oscillator in combination with the SF-8500RR transducer, both produced by Sonotec TM. This cutting device operates at a frequency of 22kHz. The present invention is not intended to be limited to any particular type, configuration or frequency of the ultrasonic cutting device 50, and the skilled person will be capable of selecting suitable parameters to ensure that the cutting device 50 is able to cut through the fibres of the prepreg. A cutting surface may advantageously be provided beneath the layup 39 to facilitate the ultrasonic cutting process. The cutting surface preferably does not absorb the ultrasonic vibrations produced by the ultrasonic cutting device 50. In this example, a backer (not shown) may be provided in the form of a layer of Polytetrafluoroethylene (PTFE) or other appropriate material situated beneath the layup 39. The backer may extend across substantially the entire surface 36 of the mould 34 or across only a portion of the mould 34. For example, the backer may be provided directly beneath the edge of part line 51 where the layup 39 is to be cut. In some examples, the backer may be integrated within the surface 36 of the mould 34, or it may be provided as a separate layer arranged on the surface 36 of the mould 34. In this case, the backer may be arranged on the surface 36 of the mould 34 either before or after the layup materials 38 have been arranged in the mould. An edge region of the layup 39 may be lifted up to allow the backer to be arranged beneath the edge of part line 51.

In the example shown in the figures, the adhesive qualities of the semi-cured resin 42 within the prepreg layers 38 hold the main portion 52 and the sacrificial peripheral portion 54 of the layup 39 together even after the fibres have been cut. In other cases, the cutting of the fibres may cause the peripheral portion 54 to detach from the main portion 52. However, as will be described and explained later, in order to produce a neat edge on the finished return flange, it is preferable to remove the peripheral portion 54 from the main portion 52 after the resin 42 has been cured. Therefore, if the peripheral portion 54 detaches from the main portion 52 during the preliminary cutting process, the peripheral portion 54 may be re-arranged on the surface 36 of the mould 34, butted up against the edge of the main portion 52 of the layup 39.

After the preliminary cutting process has been performed, the moulding process continues as usual. As shown in Figure 5, the whole layup 39 is covered by a vacuum bag 60 which is sealed to the mould 34 using sealing tape 62 to create a sealed region 63 around the layup 39. Although not shown, additional elements may be arranged in the mould 34 before the vacuum bag 60 is sealed in place if necessary. For example, a second peel ply layer and a layer of release film may be provided.

Using a vacuum pump (not shown), air is then evacuated from the sealed region 63 via a vacuum port 64 provided in the vacuum bag 60. As air is evacuated, negative pressure is created in the sealed region 63 and the pressure differential between the inside and the outside of the vacuum bag 60 causes the vacuum bag 60 to bear against the layup 39. The resin 42 is then cured by heating.

As the resin 42 is heated, it migrates throughout the layup 39. Therefore, the two portions 52, 54 are re-integrated by means of resin 42 during the curing process, even if the sacrificial peripheral portion 54 is detached from the main portion 52 during the preliminary cutting process.

Once the resin 42 has been cured, the vacuum bag 60 is removed and the resulting return flange 32 is removed from the mould 34, i.e. it is ‘de-moulded’. As shown in Figure 6, the cured return flange 32 comprises a main portion 52 and a sacrificial peripheral portion 54 respectively located either side of the edge of part line 51. The main portion 52 and the sacrificial peripheral portion 54 are integrated by means of the cured resin 42 along the edge of part line 51. Since the fibres of the prepreg layers 38 were severed along the edge of part line 51 during the preliminary cutting process, the edge of part line 51 is characterised by a gap in the fibres of the fibre fabric layers 40. That is to say, there is a discontinuity in the reinforcing fibres of the return flange 32 at the edge of part line 51. Therefore, there is an absence of reinforcing fibres along the edge of part line 51; only cured resin is present along the edge of part line 51. Since the role of the fibres is to reinforce and strengthen the return flange 32, the absence of fibres along the edge of part line 51 means that the edge of part line 51 constitutes a line of weakness in the cured return flange 32.

Referring now to Figure 7, this illustrates the finishing stage of the process. In the finishing stage, the sacrificial peripheral portion 54 is detached from the main portion 52 of the return flange 32 by snapping the cured resin 42 along the edge of part line 51 to form an edge 72 of the finished return flange 32. As discussed above, the main portion 52 and peripheral portion 54 are separated by a line of weakness in the return flange 32. Splitting the cured return flange 32 along the edge of part line 51 only requires splitting the cured resin along the edge of part line 51 and does not require the severing of any reinforcing fibres. It is therefore relatively easy to cleave the return flange 32 along the edge of part line 51 in order to detach the peripheral portion 54 from the main portion 52. In this example, the peripheral portion 54 is removed by snapping it off from the main portion 52 by hand. This is a convenient and time-efficient method of removing the excess material 54 but in other embodiments an appropriate tool may be used to detach the peripheral portion 54 from the main portion 52, for example a saw or laser if required.

This simple finishing process produces an edge 72 with a number of advantageous features as can be seen most clearly in Figure 8 which shows an enlarged view of an edge region of the return flange 32.

The finished return flange 32 comprises a laminate formed by a plurality of fibre fabric layers 40, which are integrated together by cured resin 42. As shown in the figure, the edges of the fibre fabric layers 40 are encased in cured resin 42. The cured resin 42 encasing the edges of the fibre fabric layers 40 acts as a buffer that shields the edges of the fibre fabric from the environment. This reduces the risk of external contamination and delamination of the fibre fabric layers 40 which can result in loss of mechanical performance of the composite.

The resin buffer also prevents the edges of the fibre fabric layers 40 from forming a sharp, serrated edge of the return flange 32. Instead, the return flange 32 presents a cured resin edge 72.

Furthermore, because the sacrificial peripheral portion 54 is removed after the curing process, the edge 72 of the finished return flange 32 is not defined by the edge of the layup 39 arranged in the mould 34. Therefore, uneven amounts of excess resin are not present at the edge 72 of the finished return flange 32. Instead, any undesirable accumulation of excess resin is limited to the edge 74 of the peripheral portion 54 which is formed at the edge of the layup 39. Since the peripheral portion 54 does not form part of the finished return flange 32, the uneven excess resin at this edge 74 does not affect the finished return flange 32. The finished return flange 32 advantageously presents a neat edge 72. As such, the return flange 32 may be safely handled in use; i.e. the edge 72 is ‘hand-safe’.

There is no need to process the edge 72 of the return flange 32 any further following removal of the sacrificial peripheral portion 54 as described above. However, further machining and finishing stages may nonetheless be employed if desired.

After the finishing process is complete, adhesive can then be applied to surface 76 of the return flange 32 in order to bond the return flange 32 to the C-shaped panel of the shear web 18 as shown in Figure 1a.

The manufacturing process described above produces a composite component 32 with a neat, hand-safe edge 72 without requiring the time-consuming, labour-intensive machining processes that must be employed to finish the edges of composite components made by conventional methods. The main steps of the process will now be summarised with reference to Figure 9, which shows the steps of the process in a flowchart.

At step 100, the layup materials, including one or more prepreg layers 38, are arranged on the surface 36 of a mould 34 as described above with reference to Figure 3.

At step 102, the preliminary cutting process is performed. As described above with reference to Figures 4 and 4a, the fibres of the prepreg layer(s) 38 are severed along the edge of part line 51 to define a sacrificial peripheral portion 54 of the layup 39. After the resin 42 is cured, the peripheral portion 54 is separated from the main portion 52 by a line of weakness in the return flange 32.

It is advantageous to sever the fibres along the edge of part line 51 at this stage (i.e. before the resin 42 is cured) rather than after the curing process. This is because it is relatively easy to cut through the prepreg layers 38 when the resin 42 is in a semi-cured state as the strength of a composite material is only fully realised when the resin matrix 42 is cured. This reduces the overall time required to produce the finished return flange 32.

Part of the present invention resides in the realisation of the inventor that the semi-cured resin 42 in the prepreg layers 38 acts as a stabilising matrix during the preliminary cutting process. This allows the fibres to be severed using an ultrasonic cutting device 50 to produce a neat cut that results in a neat edge 72 on the finished return flange 32. Using an ultrasonic cutting device 50 is a time-efficient and relatively inexpensive process. Furthermore, cutting through prepreg layers 38 is a clean and safe process that does not produce excessive dust and particles.

At step 104, the resin 42 in the prepreg layers 38 is cured by applying a vacuum and heat to the layup 39 as described above with reference to Figure 5.

At step 106, the cured return flange 32 is removed from the mould 34 as described above with reference to Figure 6.

At step 108, the cured return flange 32 is subject to a finishing process. As described above with reference to Figure 7, the cured return flange 32 is snapped along the edge of part line 51 to detach the sacrificial peripheral portion 54 from the main portion 52 of the return flange 32.

Since the preliminary cutting process creates a line of weakness in the cured return flange 32 at the edge of part line 51, it is relatively easy to remove the peripheral portion 54 by cleaving the cured return flange 32 along the edge of part line 51. The preliminary cutting process simplifies the finishing stage of the process by preparing the layup 39 for the removal of the peripheral portion 54.

As described above, the simple finishing stage produces a neat, hand-safe edge 72 on the finished return flange 32 and no further machining is required.

At step 110, the finished return flange 32 is then ready to be assembled into a shear web 18 as shown in Figure 1a.

In a further preferred example of the invention, which will now be described with reference to Figure 10, the layup 39 may be consolidated prior to performing the preliminary cutting process.

For example, at step 200, the layup materials 38 may be arranged on the surface of the mould as described above with reference to Figure 3. The layup 39 may then be subjected, at step 202, to a pre-consolidation process. The pre-consolidation process may comprise covering the layup 39 with a vacuum bag which is sealed to the mould 34 to create a sealed region around the layup 39. Air may then be evacuated from the sealed region, causing the vacuum bag to bear against the layup 39 and compress the prepreg layers 38. The pre-consolidation process draws trapped air out of the layup 39 and stabilises the relative arrangement of the prepreg layers 38.

At step 204, the vacuum bag may then be removed. The tackiness of the resin 42 within the prepreg layers 38 ensures that the layup 39 remains consolidated after the vacuum bag is removed.

At step 206, a cutting surface in the form of a backer may be arranged in the mould 34 beneath the edge of part line 51. An edge region of the pre-consolidated layup 39 may be lifted up to allow the backer to be arranged beneath the edge of part line 51.

After the pre-consolidation process, the preliminary cutting process may be performed at step 208. As described above with reference to Figures 4 and 4a, the fibres of the prepreg layers 38 are severed along the edge of part line 51 to define a sacrificial peripheral portion 54 of the layup 39. Since the layup 39 is pre-consolidated (and the prepreg layers 38 are therefore stabilised in their relative positions in the layup 39), there is little or no movement between the prepreg layers 38 during the preliminary cutting process. This enhances the accuracy and neatness of the cut, ensuring a neat edge on the finished return flange 32.

After the preliminary cutting process has been performed, the resin in the prepreg layers may be cured by applying a vacuum and heat to the pre-consolidated layup 39 at step 210. Similarly to the example described previously, the layup 39 may be covered with a vacuum bag to create a sealed region around the layup from which air is then evacuated. The resin 42 in the prepreg layers 38 may then be cured by heating. At step 212, the cured return flange 32 may be removed from the mould 34, following which, at step 214, the return flange 32 may be snapped along the edge of part line 51 to detach the sacrificial peripheral portion 54 from the main portion 52 of the return flange 32.

At step 216, the finished return flange 32 is then ready to be assembled into a shear web 18.

The present invention is not limited to the examples described above and many other variations or modifications will be apparent to the skilled person without departing from the scope of the present invention as defined in the following claims.

For example, in the examples described above, the cured return flange 32 is de-moulded before the sacrificial peripheral portion 54 is removed. In other examples, the peripheral portion 54 may be removed after the curing process whilst the cured return flange 32 remains arranged on the surface 36 of the mould 34. The finished return flange 32 is then removed from the mould 34.

In the examples described above, only one edge 72 of the return flange 32 is subjected to a preliminary cutting process and finishing stage. In other examples of the invention, both edges of the finished return flange 32 may be formed according to the method described above.

In addition, the examples described above relates to manufacturing a return flange 32. However, the skilled person will appreciate that a similar process may be employed to form the edges of a C-shaped elongate panel.

Furthermore, the above-described manufacturing processes are equally applicable to other composite components formed from prepreg that may require a neat and defined edge.

Claims (15)

1. A method of making a composite component for a wind turbine blade, the method comprising: (a) providing one or more layers of prepreg material comprising reinforcing fibres impregnated with resin; (b) cutting the reinforcing fibres of the prepreg material using an ultrasonic cutting device along an edge of part line to create a line of weakness between a main portion and a peripheral portion of the one or more layers of prepreg material (c) curing the resin of the prepreg material; and (d) detaching the peripheral portion from the main portion by snapping the cured resin along the edge of part line.

2. The method of Claim 1, wherein step (d) comprises snapping the cured resin by hand along the edge of part line.

3. The method of Claim 1 or Claim 2, wherein step (a) further comprises providing a plurality of layers of prepreg material and arranging the plurality of layers in a stack.

4. The method of any preceding claim, wherein step (a) further comprises arranging the one or more layers of prepreg material on a surface of a mould, and step (b) further comprises cutting the prepreg material in the mould.

5. The method of any preceding claim, wherein the method further comprises consolidating the one or more layers of prepreg material prior to cutting the reinforcing fibres of the prepreg material.

6. The method of any preceding claim, further comprising providing material beneath the edge of part line that does not absorb ultrasonic vibrations prior to cutting the prepreg material.

7. The method of Claim 6, wherein the material is polytetrafluoroethylene (PTFE).

8. The method of Claim 6 or Claim 7 when dependent upon Claim 4, wherein the material is an integral part of the mould surface.

9. The method of Claim 6 or Claim 7 when dependent on Claim 4, wherein the material is arranged on the surface of the mould.

10. The method of any preceding claim, wherein the reinforcing fibres comprise glass fibres.

11. The method of any preceding claim, wherein the resin comprises epoxy resin.

12. A composite component made according to the method of any preceding claim.

13. The method of any of Claims 1 to 11, or the composite component of Claim 12, wherein the component is a shear web or part of a shear web for a wind turbine blade.

14. A wind turbine blade comprising the composite component of Claim 13.

15. Use of an ultrasonic cutting device to cut through fibres in prepreg material prior to curing the prepreg material to create a line of weakness in a cured component.