CROSS-REFERENCE TO RELATED APPLICATIONS

This specification is based upon and claims the benefit of priority from UK Patent Application Number 1803802.6 filed on 9 Mar. 2018, the entire contents of which are incorporated herein by reference.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a method of manufacturing a composite fan blade and a composite fan blade manufactured by the method.

Description of the Related Art

A fan blade may be manufactured for gas turbine engines. A gas turbine engine generally comprises, in axial flow series, an air intake, a fan, one or more compressors, a combustor, one or more turbines, and an exhaust nozzle. Air entering the air intake is accelerated by the fan to produce two air flows: a first air flow (core engine flow) into compressor and a second air flow (bypass flow) which passes through a bypass duct to provide propulsive thrust. Air entering the compressor is compressed, mixed with fuel and then fed into the combustor, where combustion of the air/fuel mixture occurs. The high temperature and high energy exhaust fluids are then fed to the turbine, where the energy of the fluids is converted to mechanical energy to drive the compressor in rotation by suitable interconnecting shaft. Downstream of the turbine, the core engine flow passes through a tail bearing housing provided with vanes.

The fan comprises a rotor hub and an array of fan blades radially extending therefrom. The fan blades generally comprises an aerofoil portion having a leading edge, a trailing edge, a pressure surface wall extending from the leading edge to the trailing edge and a suction surface wall extending from the leading edge to the trailing edge. The fan blades have a root via which the blade can be connected to the rotor hub and, at an opposing end to the root, a tip. The fan blades may be metallic fan blades or composite fan blades. Composite fan blades generally include a composite body made from a fibre reinforced resin matrix, e.g. carbon fibres in a resin matrix. The leading edge and the trailing edge of the fan blade may be shielded and/or reinforced, for example a metallic member may be provided on the trailing and/or leading edge of the composite body.

Composite fan blades are generally lighter than metallic fan blades with comparable mechanical properties, so, although more expensive to manufacture, composite fan blades are increasingly used in the aerospace industry and for gas turbine engines in particular.

The composite body of the fan blade is generally a laminate having a plurality of plies laid up into a stack. The laminate can be formed using a number of different methods, for example lay-up by hand or automated fibre placement (AFP). In known methods, the plies are laid-up manually or automatically on a preform tool shaped to the finished blade suction surface to produce a fan blade preform. Once all of the plies have been laid up, the preform is transferred into a tool and cured in an autoclave to the final shape. Briefly, in AFP, the fibre reinforcement material is applied in form of a single “tow”, or multiple “tows”. A “tow” may be a narrow width of tape slit from a wider tape. A lay-up head is typically used to dispense, apply and cut tows of fibre reinforcement material on the preform tool. Generally, as the lay-up head stops each time a tow (or tape) is cut, the more plies are cut, or, in other words, the shorter the applied tows, the more time is required to complete the lay-up process. Short plies are particularly ineffective at being deposited using AFP since there is less time spent placing material and more time spent in secondary operations such as cutting, positioning, accelerating and decelerating. As the lay-up head may be required to supply tows (or tapes) with different mutual orientation and therefore different length, the lay-up process may be quite time consuming.

Reducing the number of plies may speed up the process, but, as the lay-up head cannot apply tows (or tapes) longer than a longitudinal dimension of the preform tool, which substantially corresponds to the length of the fan blade along a spanwise direction, there is a minimum number of cuts required to build up the preform and therefore a minimum lay-up time. The same considerations apply to a manual lay-up process, namely the higher the number of plies, the slower the process.

Accordingly, it is desirable to overcome the above mentioned problems and reduce the lay-up time of a composite fan blade manufacturing method.

SUMMARY

According to a first aspect, there is provided a method of manufacturing a composite fan blade extending spanwise from a root to a tip, chordwise from a leading edge to a trailing edge, the composite fan blade comprising an outer part and a core, the outer part defining a pressure surface wall extending from the leading edge to the trailing edge and a suction surface wall extending from the leading edge to the trailing edge, the method comprising:laying up a plurality of continuous plies extending along a longitudinal direction from a first end to a second end to achieve a stack of continuous plies, the stack comprising a first portion corresponding to the pressure surface wall, a second portion corresponding to the suction surface wall, and a central portion corresponding to the root, wherein the first end corresponds to a pressure surface tip region of the composite fan blade and the second end corresponds to a suction surface tip region of the composite fan blade;placing the core on the central portion of the stack of continuous plies to achieve an unfolded preform;folding the continuous plies about the core, such that the central portion of the stack folds about the core and the first portion is superimposed to the second portion, to achieve a folded preform;applying pressure to the folded preform to achieve a consolidated curved folded preform;curing the consolidated curved folded preform to achieve the composite fan blade.

The laying-up of the plurality of continuous plies may be carried out manually or automatically using automatic fibre placement. The continuous plies may be unidirectional (UD) plies. All of the continuous plies in the stack may have a same orientation. Alternatively, the continuous plies in the stack may have different mutual orientations.

The continuous plies may be made of dry fibres. Alternatively, the continuous fibres may be made of pre-impregnated fibres. Where the continuous plies are made of dry fibres, the method may further comprise, after the laying up of each continuous ply, depositing on an internal surface of said continuous ply a layer of thermoplastic or epoxy resin.

The composite fan blade may further comprise filler plies and the method may further comprise laying up the filler plies on the continuous plies both on the first portion and on the second portion. Alternatively, the method may comprise laying up the filler plies either on the first portion or on the second portion. The filler plies may not extend from the first portion to the second portion through the central portion. In other words, the filler ply may be interrupted at the central portion. The laying up of the filler plies on the continuous plies may be carried out before the placing of the core on the central portion. Alternatively, the laying up of the filler plies on the continuous plies may be carried out after the placing of the core on the central portion. Further alternatively, the method may comprise, in sequence, laying up filler plies on either the first or the second portion of the stack, placing the core on the central portion of the stack, and then laying up filler plies on either the second or the first portion of the stack, respectively.

Folding of the continuous plies may comprise folding all of the continuous plies at one time. Alternatively, folding of the continuous plies may comprise folding each continuous ply individually. Moreover, folding of the continuous plies may comprise folding the continuous plies in groups of two of more continuous plies.

Folding of the continuous plies may comprise rotating either the first portion or the second portion towards the second portion or the first portion, respectively, or both the first and the second portion towards each other.

The folding of the continuous plies may comprise rotating either the first or the second end by substantially 180° about the core towards the second or the first end, respectively, or both the first and the second end towards each other. In other words, the folding of the continuous plies may comprise rotating at least one of the first and the second portion about a chordwise direction, i.e. a direction perpendicular to a spanwise direction.

During the folding of the continuous plies, the method may further comprise keeping the core in position by means of a frame. Alternatively, during the folding of the continuous plies, the method may further comprise keeping the core in position manually or by means of an automated robotic arm.

During the folding of the continuous plies, the method may comprise applying pressure either manually or by means of a roller to the continuous ply being folded from the root to the tip. In addition, during the folding of the continuous plies, the method may comprise applying tension to the continuous ply being folded. For example, applying tension to the continuous ply being folded may comprise clamping opposite ends of the ply being folded to suppress the formation of wrinkles in the central portion.

The method may further comprise, after the folding of the continuous plies, transferring the folded preform to a resin transfer moulding operation in which a resin is injected and cured.

The method may further comprise, after the folding of the continuous plies, applying heat and/or pressure to the folded preform to promote adhesion of the core to the outer part. The method may further comprise, after the folding of the continuous plies, applying vacuum to the folded preform to promote debulk. For example, heat and/or pressure and/or vacuum may be applied concurrently to achieve the consolidated curved folded preform and promote debulk.

The method may further comprise applying through thickness reinforcement to reinforce the core to the outer part. The method may further comprise mutually reinforcing the continuous plies. For example, the method may comprise applying through thickness reinforcement to the first portion and the second portion of the stack to enhance their mutual adhesion.

Through thickness reinforcement may comprise any one of tufting, stitching, felting, z-pinning, or intra-layer toughening using veils and nanoforests or thermoplastic toughening particles.

The placing of the core in the central portion may comprise depositing a plurality of chopped fibres on the central portion of the continuous plies. Alternatively, the placing of the core in the central portion may comprise depositing a pre-moulded core on the central portion of the continuous plies.

In a further alternative solution, the placing of the core in the central portion may comprise depositing a preformed core made of a metallic insert that allows for the blade to be mounted in a holding fixture. For example, the holding fixture may be a pin hinged root and the metallic insert may be a hollow metallic tube.

Where the continuous plies are made of dry fibres, after a consolidated curved folded preform is achieved and before curing, the method may comprise incorporating a matrix resin to the consolidated curved folded preform in an infiltration step.

According to a second aspect, there is provided an unfolded preform for manufacturing a composite fan blade comprising a plurality of continuous plies extending along a longitudinal direction from a first end to a second end to achieve a stack of continuous plies. The stack comprises a first portion corresponding to a pressure surface wall of the composite fan blade, a second portion corresponding to a suction surface wall of the composite fan blade, and a central portion corresponding to a root of the composite fan blade, wherein the first end corresponds to a pressure surface tip region of the composite fan blade and the second end corresponds to a suction surface tip region of the composite fan blade. The unfolded preform further comprises a core arranged at the central portion of the stack.

The first portion, the central portion, and the second portion may be arranged along the longitudinal direction. In other words, the central portion may be arranged midway between the first and the second portion along the longitudinal direction.

The unfolded preform may extend longitudinally at least twice a spanwise length of the fan blade.

The unfolded preform may further comprise filler plies arranged on the first portion and/or the second portion of the stack, the filler plies not extending from the first portion to the second portion through the central portion.

According to a third aspect, there is provided a composite fan blade extending spanwise from a root to a tip, chordwise from a leading edge to a trailing edge, the composite fan blade comprising an outer part and a core, the outer part defining a pressure surface wall extending from the leading edge to the trailing edge and a suction surface wall extending from the leading edge to the trailing edge, the composite fan blade being obtained by a method comprising:laying up a plurality of continuous plies extending along a longitudinal direction from a first end to a second end to achieve a stack of continuous plies, the stack comprising a first portion corresponding to the pressure surface wall, a second portion corresponding to the suction surface wall, and a central portion corresponding to the root, wherein the first end corresponds to a pressure surface tip region of the composite fan blade and the second end corresponds to a suction surface tip region of the composite fan blade;placing the core on the central portion of the stack of continuous plies to achieve an unfolded preform;folding the continuous plies about the core, such that the central portion of the stack folds about the core and the first portion is superimposed to the second portion, to achieve a folded preform;applying pressure to the folded preform to achieve a consolidated curved folded preform;curing the consolidated curved folded preform to achieve the composite fan blade.

According to a forth aspect there is provided a gas turbine engine for an aircraft comprising a turbine, a compressor, and a shaft connecting the turbine to the compressor; a fan located upstream of the compressor, the fan comprising a plurality of composite fan blades according to the third aspect.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

