Method of manufacturing a composite aircraft blade

Abstract

A method of manufacturing a fabric structure for use in manufacturing a composite aircraft blade. The method comprises: combining yarns including both reinforcing material filaments and a matrix material with yarns of reinforcing material filaments and/or yarns including at least one filament of matrix material; or by combining yarns of reinforcing material filaments with yarns including at least one filament of matrix material; or by combining yarns each comprising both reinforcing material filaments and matrix material. Combining may comprise weaving, knitting or braiding. The matrix material may be a thermoplastic.

Claims

1. A method of manufacturing a fabric structure for use in manufacturing a composite aircraft blade, the method comprising: combining yarns comprising both reinforcing material filaments and filaments of matrix material with other yarns comprising reinforcing material filaments and filaments of matrix material by three-dimensional weaving, knitting or braiding techniques to form a three-dimensional fabric structure.

2. A method as claimed in claim 1, wherein the matrix material comprises a thermoplastic material.

3. A method as claimed in claim 1, wherein the reinforcing material filaments comprise carbon, glass, a thermoplastic, an aramid or mixtures thereof.

4. A method as claimed in claim 1, wherein the yarns including both reinforcing material filaments and a matrix material each comprise: a mixture of reinforcing material filaments and matrix material filaments combined to form a single comingled yarn; and/or one or more yarns of reinforcing material filaments twisted with one or more yarns including at least one filament of matrix material; and/or a yarn of reinforcing material filaments coated with matrix material; and/or a yarn of reinforcing material filaments powdered with matrix material.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Certain preferred embodiments on the present disclosure will now be described in greater detail, by way of example only and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a flow diagram illustrating the steps required to manufacture a composite aircraft blade according to an embodiment of the disclosure;

(3) FIG. 2 illustrates a cross section of an exemplary comingled yarn;

(4) FIGS. 3 and 4 illustrate examples of three-dimensional woven preforms;

(5) FIGS. 5 and 6 illustrate exemplary temperature and pressure cycles applied to consolidate the composite material; and

(6) FIG. 7 illustrates perspective views of a composite aircraft blade formed using a method according to an embodiment of the disclosure.

DETAILED DESCRIPTION

(7) By way of example, the present disclosure is described in the context of a method of manufacturing a composite aircraft blade comprising a polyether ether ketone (PEEK) thermoplastic matrix material reinforced with carbon filaments. Whilst a composite comprising PEEK matrix and carbon filaments is considered advantageous, such materials are not essential, and other matrix materials and reinforcing material filaments may alternatively be used. For example, the matrix material may alternatively be polyetherketoneketone (PEKK), polyetherimide (PEI), polyphenylene sulfide (PPS) or polyaryletherketone (PAEK). Similarly, the reinforcing material may alternatively be glass filaments or aramid filaments.

(8) A method of manufacturing a composite aircraft blade, in particular a fan blade, according to an embodiment of the disclosure will now be described in relation to the method steps illustrated in FIG. 1. At step 12, a three-dimensional fabric structure is formed by weaving together comingled yarns that contain both carbon filaments and PEEK filaments. It will be appreciated that such a three-dimensional fabric structure may also be termed a three-dimensional woven preform.

(9) Other fabric manufacturing processes may alternatively be used to form the three-dimensional fabric structure. For example, the three-dimensional fabric structure may alternatively be formed by knitting or braiding yarns together. Such structures may be known as knitted preforms or braided preforms.

(10) An example of a comingled yarn 20 is shown in cross section in FIG. 2. In this example, the comingled yarn comprises a mixture of both carbon filaments 22 and PEEK filaments 24, combined to form a single yarn.

(11) In other embodiments, other types of yarns including both reinforcing material filaments and a matrix material may be used. For example, one or more yarns containing reinforcing material filaments may be twisted with one or more yarns containing at least one matrix material filament. Or, a yarn comprising reinforcing material filaments may be coated with matrix material. Or, a yarn comprising reinforcing material filaments may be powdered with matrix material.

(12) Such yarns including both reinforcing material filaments and a matrix material are known to those skilled in the art.

(13) Mixtures of any two or more of the above types of yarn may also be used.

(14) Instead of (or in addition to) using yarns including both reinforcing material filaments and a matrix material, yarns comprising only reinforcing material filaments and yarns comprising only matrix material filaments may be woven together to form the three-dimensional fabric structure. For example, the three-dimensional fabric structure may be formed by weaving yarns containing only reinforcing material filaments with yarns containing only matrix material filament(s).

(15) The yarns may be formed of stretch broken filaments, comprising discontinuous filaments. Yarns of stretch broken filaments are more pliable and can be more easily formed into complex shapes than yarns containing continuous filaments. Alternatively, the yarns may comprise continuous filaments.

(16) Thus, as described above, the matrix material is combined with the reinforcing material in the three-dimensional structure. In the presently described embodiment, the matrix material is woven within the preform.

(17) The provision of a three-dimensional fabric structure removes the need to layer individual laminae to form a three-dimensional composite component, and also provides three-dimensional reinforcement to the composite component. This removes the need to stitch or weld numerous laminae together in order to form a laminate product, thus enabling the product to be produced more quickly and easily. This process also obviates the problem of delamination of the composite product by providing full three-dimensional reinforcement. The resulting composite component therefore has a superior strength and impact resistance compared to a laminated component.

(18) Example 3D woven preforms 30 are illustrated in FIGS. 3 and 4. These Figures each schematically illustrate a small segment of a 3D woven preform 30 according to embodiments of the invention. In these embodiments, comingled yarns 20 comprising both carbon filaments 22 and PEEK 24 filaments are woven together in a three-dimensional shape.

(19) Returning now to the process illustrated in FIG. 1, at step 14, the three-dimensional woven preform undergoes a thermoforming process to form and consolidate the composite fan blade.

(20) The woven preform is placed into a mold cavity (the mold cavity having the shape of the desired fan blade). A thermoforming temperature/pressure cycle is then carried out to consolidate the fan blade. Firstly, the mold is heated above the melting temperature of the PEEK so that the matrix material becomes liquid. In order to ensure that all of the PEEK woven within the woven preform is melted, the woven preform should generally be heated to at least 343° C. A small pressure is applied to the materials within the mold during the heating process in order to maintain contact between the PEEK and the carbon filaments. This ensures that the liquid PEEK fills any gaps between the carbon filaments. By melting the PEEK, the woven preform becomes impregnated with liquid PEEK and is immersed within the liquid PEEK matrix material. The liquid PEEK takes the shape of the mold, thus the matrix material takes the shape of a fan blade. The pressure is then increased to a “forming pressure”, to form the part. The skilled person would readily be able to determine suitable temperatures and pressures to apply according to the particular situation.

(21) An example thermoforming cycle for such a carbon filament—PEEK composite is schematically shown in FIG. 5. In this example, the temperature cycle comprises heating the three-dimensional woven preform to a temperature above the melting point of the PEEK matrix material, followed by cooling it gradually to below the glass transition temperature of the PEEK matrix material (143° C.), ready for demoulding. In conjunction with this temperature cycle, a pressure cycle comprises applying a small pressure (i.e. a first low pressure, just to keep the materials in contact) to the woven preform. The pressure is then raised as the matrix begins to melt. Then, once the matrix is melted a higher pressure is applied to form the part, and this higher pressure is maintained for the remainder of the pressure cycle.

(22) Another example thermoforming cycle for a carbon filament—PEEK composite is schematically illustrated in FIG. 6. The temperature cycle comprises gradually heating the woven preform to above the melting point of the PEEK matrix material. The temperature is then maintained at this value before being gradually reduced to below the glass transition temperature of the PEEK matrix material. Simultaneously, a pressure cycle comprises applying a small pressure to the woven preform. The pressure is then raised, and then raised once more and maintained at this pressure for the remainder of the pressure cycle. In other words, this thermoforming includes gradually raising the temperature whilst the pressure remains unchanged, holding the temperature constant whilst the pressure is increased in step changes to a forming pressure, and then gradually reducing the temperature to ambient temperature.

(23) While the composite part cools within the mold, the PEEK matrix material impregnated within the woven preform cools and solidifies in the required shape. Once the PEEK has cooled to below its glass transition temperature the composite part can be removed from the mold (step 16). For example, when the matrix material comprises PEEK, the composite part must be cooled to below 143° C. before it can be removed from the mold. By removing the composite part from the mold at a temperature below the glass transition temperature of the matrix material, it is ensured that the matrix material has hardened sufficiently so that it does not deform once it is removed from the mold.

(24) The composite part removed from the mold is the composite aircraft blade. This may be formed net shaped so that no additional machining is required to obtain the desired blade geometry. However, optionally, a further step 18 may be carried out in which the composite blade is machined into the desired finished shape. Alternatively, or in addition, an overmolding process may be applied to the composite blade to provide a thermoplastic matrix coating to the blade.

(25) A fan blade 40 produced according to the above described method is illustrated in FIG. 7.

(26) Since the PEEK matrix material is within the yarns which are woven together, there is no need to impregnate the woven preform with liquid PEEK after it has been formed. This is advantageous because it is difficult to inject thermoplastics into conventional woven preforms due to the high viscosity of liquid thermoplastics. Consequently it is difficult to fully impregnate conventional woven preforms with thermoplastic matrix material, and also to inject thermoplastics into woven preforms containing a high density of reinforcing material filaments. When the matrix material is part of the yarns that are woven together into the woven preform and this is heated in accordance with the present disclosure, the matrix material melts and the liquid matrix material impregnates the reinforcing material filaments. This allows for quicker and easier manufacturing, avoiding the need for complex prior art manufacturing steps. It will be appreciated that these advantages are equally applicable for all different types of reinforcing material, and for structures manufactured by techniques other than weaving, e.g. knitting or braiding. The important feature is that the matrix is combined within the initial fabric structure, so that subsequent injection of matrix material is not required.

(27) One difficult manufacturing step avoided by the present disclosure is the polymerisation of the thermoplastic matrix material once it has impregnated the woven preform, which is required in the prior art. Thermoplastics comprising smaller polymer chains are less viscous than those with longer polymer chains. However, thermoplastics with small polymer chains do not possess the necessary properties for use in the manufacture of aircraft blades. Often, thermoplastics comprising small polymer chains are injected into a woven preform and polymerised in order to produce longer polymer chains. In the presently disclosed method this process is not required so there is no need to perform any chemical polymerisation reactions once the thermoplastic has impregnated the woven preform. Since such steps are obviated by the present disclosure, the process of the present disclosure is simpler and quicker than prior art processes for manufacturing aircraft blades.

(28) Thus, it will be appreciated that the method of this disclosure enables reinforced thermoplastic composite aircraft blades to be manufactured more quickly and more easily than other previously disclosed methods. Typically, thermosetting matrix materials have been utilised in composite aircraft blades because of their relative ease of production. Thermosetting plastics have lower viscosity than thermoplastics, and therefore do not suffer from many of the issues caused when injecting the matrix material into the woven preform. However, thermoplastic materials are known to have superior mechanical resistance properties when compared with thermosetting plastics. Thermoplastics can also be remolded or reshaped allowing for simple and cost effective repair of thermoplastic components. Thus, the method of the present disclosure which provides a process in which a three-dimensional preform is used with a thermoplastic, but in which the thermoplastic does not need to be injected, allows for the improved production of aircraft blades with better resistance to high speed impacts with birds and other foreign objects.

(29) Aircraft blades produced by the method of the disclosure benefit from increased impact resistance due to the combination of a 3D fabric structure and a thermoplastic matrix. Another advantage is the failure propagation, the PEEK has a G1c of 2000 J/m.sup.2 compared to the thermoset solution (G1c for RTM6: 200 J/m.sup.2 and 203ST: 1000 J/m.sup.2). Following the recommendations made in US005672417A, a G1c of minimum 2000 J/m.sup.2 is desirable to avoid damage from bird impact.

(30) Furthermore, thermoplastic is more easily stored than thermoset, which avoids issues due to expiration date. Moreover, there is no chemical reaction during the manufacturing process, and thus no hazardous chemicals are produced.

(31) Although the present disclosure has been described in the context of a method of manufacturing a composite fan blade, the disclosed method is equally applicable for the manufacture of other aircraft blades, such as composite propeller blades.