COMPOSITE BLADE AND METHOD OF MANUFACTURE

Abstract

A method is disclosed for manufacture of a composite blade with an airfoil and a root, wherein the blade comprises a core of chopped fibre composite material and a textile composite material encasing the chopped fibre core. The method comprises: forming a blade insert using chopped fibre composite; surrounding the blade insert with a plurality of layers of a textile in a textile composite material; and thermoforming the blade insert and the surrounding textile composite material in a thermoforming mould in order to consolidate the part.

Claims

1. A method for manufacture of a composite blade with an airfoil and a root, the blade comprising a core of chopped fibre composite material and a textile composite material encasing the chopped fibre core, the method comprising: forming a blade insert using chopped fibre composite; surrounding the blade insert with a plurality of layers of a textile in a textile composite material; and thermoforming the blade insert and the surrounding textile composite material in a thermoforming mould in order to consolidate the part.

2. A method as claimed in claim 1, wherein the blade insert is formed by at least one of moulding and machining in order to provide it with a required shape reflecting a required final contoured shape of the part of the blade where the blade insert is located.

3. A method as claimed in claim 1, wherein the blade insert is shaped such that the final shape of the blade can be formed by the use of multiple continuous textile layers extending from the root to the airfoil tip.

4. A method as claimed in claim 1, wherein the blade insert is situated at a location where the cross-sectional area of the blade changes significantly.

5. A method as claimed in claim 4, wherein the blade insert is located at the root of the blade where the cross-section increases compared to the cross-section of the airfoil.

6. A method as claimed in claim 5, wherein the blade insert has a taper at the airfoil end of the insert with decreasing cross-section toward the airfoil end.

7. A method as claimed in claim 5, wherein the shape of the blade insert extends further toward the airfoil tip at its centre in a dorsal fin shape with the upper tip of the dorsal fin shape extending into the airfoil from the root along the centre line of the airfoil.

8. A method as claimed in claim 1, where the surrounding step comprises: placing a number of the textile layers into a bottom mould, placing the blade insert into the mould on top of the textile layers, and then placing further layers on top of the blade insert.

9. A method as claimed in claim 8, wherein a top mould is used to ensure that the textile layers form the required shape both above and below the blade insert, wherein the top mould and bottom mould together form the thermoforming mould.

10. A method as claimed in claim 1, wherein the textile composite material includes a fabric structure comprising: yarns including both reinforcing material filaments and a matrix material combined with yarns of reinforcing material filaments and/or yarns including at least one filament of matrix material; or yarns of reinforcing material filaments combined with yarns including at least one filament of matrix material; or yarns comprising both reinforcing material filaments and a matrix material combined with other yarns comprising both reinforcing material filaments and a matrix material.

11. A method as claimed in claim 1, wherein the same material is used for the matrix of the blade insert and for the matrix of the surrounding textile composite.

12. A method as claimed in claim 1, wherein the textile composite material uses a thermoplastic matrix and the method includes over-moulding the blade with the same thermoplastic after the thermoforming step.

13. A composite blade with an airfoil and a root, the blade comprising: a textile composite outer casing that surrounds a chopped fibre blade insert.

14. A composite blade as claimed in claim 13, the blade being formed by a method comprising: forming a blade insert using chopped fibre composite; surrounding the blade insert with a plurality of layers of a textile in a textile composite material; and thermoforming the blade insert and the surrounding textile composite material in a thermoforming mould in order to consolidate the part.

15. A composite blade as claimed in claim 13, wherein the blade insert is an insert for location in the root of the blade at a point where the cross-sectional area of the blade increases compared to the airfoil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0032] FIG. 1 shows a fan blade with a blade insert in the root;

[0033] FIG. 2 shows a close up view of the root in FIG. 1;

[0034] FIG. 3 is a schematic drawing of a prior art blade root formed with textile composite layers;

[0035] FIG. 4 shows the use of an insert in the blade root to replace stepped layers of textile composite;

[0036] FIG. 5 shows the use of a two-part blade insert in the root; and

[0037] FIG. 6 shows a thermoforming temperature and pressure profile.

DETAILED DESCRIPTION

[0038] The invention is described by way of example in the context of a fan blade 12 having a blade insert 18 in the root 16. It will be appreciated that a similar construction could also be used with a propeller blade. As shown in FIGS. 1 and 2 a composite fan blade 12 has an airfoil 14 and a root 16. The fan blade comprises a textile composite outer casing 20 that forms the airfoil 14 and that surrounds a chopped fibre blade insert 18 in the root 16. The example fan blade 12 is a fan blade for a gas turbine engine such as an aircraft jet engine. The fan blade 12 may be manufactured by forming a blade insert 18 using chopped fibre composite; surrounding the blade insert 18 with a plurality of layers of a textile in a textile composite material 20; and thermoforming the blade insert 18 and the surrounding textile composite material 20 in a thermoforming mould in order to consolidate the part.

[0039] The blade insert 18 may be formed by moulding in order to provide it with a required shape, which may for example be a contoured shape reflecting the required final contoured shape of the blade root 16. Forming the blade insert 18 may include machining steps. In some examples the blade insert 18 is manufactured in multiple parts and then assembled together before it is surrounded by the textile layers 20.

[0040] The blade insert 18 in this example sits within the blade root 16 where the cross-section of the blade increases compared to the airfoil 14. The insert 18 is arranged to span the majority of the width of the blade root 16 and it has a cross-section with a tapering part 22 extending toward the airfoil 14. This taper 22 can be seen in the perspective views of FIGS. 1 and 2, as well as being shown in cross-section in FIGS. 4 and 5. The extent of the taper 22 varies across the width if the insert since the airfoil 14 has a thicker cross-section along its centre-line. As a consequence of this the tapered part 22 includes a dorsal fin shape 24 at the mid-point of the insert.

[0041] FIG. 3 shows a prior art arrangement where there is no chopped fibre insert 18. It will be seen that in order to allow for the difference in cross-section at the root 16 there is a need for numerous stepped layers 26 with drop-off plies. As explained above, there are disadvantages to this arrangement. FIG. 4 shows a similar cross-section to FIG. 3 where the proposed chopped fibre insert 18 is used at the blade root 14. The chopped fibre insert 18 can be accurately shaped using a curved and tapered section 22 without any steps, and this can fit tightly with the textile layers 20 to form the required root cross-section. FIG. 4 shows a single piece insert 18. An alternative arrangement uses a multi-part insert 18, such as an arrangement as shown in FIG. 5.

[0042] A mould is used to form the shape of the fan blade 12. In one example the method of manufacturing the fan blade 12 includes placing a number of the textile layers 20 into a bottom mould, placing the blade insert 18 into the mould on top of the textile layers 20 at the root portion 16 of the blade 12, and then placing further layers 20 to complete the airfoil section 14 and to encase blade insert 18 by placing them on top of the blade insert 18. A top mould is used to ensure that the textile layers 20 form the required shape both above and below the blade insert 18 at the root 16 as well as at the airfoil section 14. The further textile layers 20 may first be placed onto the blade insert 18 on top of the bottom mould, with the top mould being applied after the further textile layers 20 are placed onto the blade insert 18, or alternatively some or all of the further textile layers 20 may be placed into the top mould and applied to the other parts in the bottom mould by joining the top and bottom mould together. After the textile layers 20 and blade insert 18 are assembled together, with addition of a matrix for the textile composite 20 as appropriate, then the thermoforming step can be carried out. The thermoforming mould used in the thermoforming step is formed by the combination of the top mould and the bottom mould.

[0043] The textile composite material can be a three dimensional woven textile including carbon fibres as well as thermoplastic fibres. In one example the textile composite material includes a fabric structure comprising: yarns including both reinforcing material filaments and a matrix material combined with yarns of reinforcing material filaments and/or yarns including at least one filament of matrix material; or yarns of reinforcing material filaments combined with yarns including at least one filament of matrix material; or yarns comprising both reinforcing material filaments and a matrix material combined with other yarns comprising both reinforcing material filaments and a matrix material.

[0044] The fan blade insert in this example uses chopped fibre carbon fibres along with a PEEK matrix. Using the same material for the matrix as is used for the textile composite allows for better consolidation of the fan blade during thermoforming. It will be appreciated that other thermoplastic materials that PEEK could alternatively be used for the matrix of the insert and the textile composite.

[0045] The thermoforming cycle can be as shown in FIG. 6. Thus, the thermoforming may include gradually raising the temperature to a forming temperature whilst the pressure remains unchanged, holding the temperature at the forming temperature whilst the pressure is increased in step changes through to a forming pressure, and then gradually reducing the temperature to ambient temperature. The forming temperature may be a temperature at which the thermoplastic softens sufficiently, or melts.

[0046] After thermoforming the fan blade 12 is removed from the mould and subsequently it is machined to obtain a final shape. A leading edge and a tip cap added and are joined to the remainder of the fan blade 12 by means of a surface matrix film with a lower fusion temperature than the matrix material. Additional layers such as over-moulded layers, coatings or films may be added after thermoforming. In one example the fan blade 12 is over-moulded with a PEEK layer of similar composition to the matrix of the textile composite 20 in order to obtain superior erosion resistance and resistance to bird impact whilst also avoiding the need for adhesives.