GB2440345A

GB2440345A - Integrally bladed rotor having blades made of metallic and non-metallic materials

Info

Publication number: GB2440345A
Application number: GB0614894A
Authority: GB
Inventors: Nigel James David Chivers
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2006-07-26
Filing date: 2006-07-26
Publication date: 2008-01-30
Also published as: GB0614894D0

Abstract

An integrally bladed rotor (IBR) suitable for turbo-machinery comprises a metallic disc and a plurality of blades of metallic and non-metallic material extending radially outwards from the disc. The blades may comprise a metallic root 20 and a non-metallic aerofoil section 21. The metallic root 20 preferably comprises a radially extending portion 24 extending into the aerofoil section 21. The radially extending portion 24 comprises apertures 40 through which reinforcement fibres 60 can be laid up prior to the aerofoil section 21 being moulded onto the extending portion 24. The non-metallic aerofoil material preferably comprises a fibre reinforced composite material. The blades are preferably joined to the disc / hub by friction welding. Once joined, machining can be done to finish the integrally bladed rotor / blisk (i.e. bladed disk). An independent claim entails a method for manufacturing a composite blade suitable for an IBR.

Description

INTEGRALLY BLADED ROTOR

The present invention relates to a method of manufacturing an integrally bladed rotor and manufacturing a blade member for use in the manufacture thereof. The invention also concerns an integrally bladed rotor, a method of manufacturing a composite blade for an integrally bladed rotor and a method of manufacturing, re-working or repairing an integrally bladed rotor.

Integrally bladed disc rotors, in which the blades and disc are either formed integrally or the blades are joined permanently to the periphery of the disc, comprise a plurality of aerofoil blades which extend generally, radially outwards from the circumference of the disc. Metal alloy integrally bladed rotors may be machined from solid, but more usually the blades are friction welded to the rim of the disc. It is known to join metallic blades to the rim of a metallic disc by linear friction welding, whereby one part is held stationery while the other part is oscillated against it under load. In the manufacture of integrally bladed rotors, a blade member, that is subsequently machined to form the finished blade, is oscillated relative to a stationery disc while a forging load is applied in the radial direction of the blade towards the disc. The blades are friction welded to stubs of material upstanding from the periphery of the disc.

Integrally bladed rotor assemblies can be fabricated, re-worked or repaired by joining separately formed blades to a disc or ring using linear friction welding methods. For the purpose of the following description the word "disc" refers to both conventional disc arrangements and also integrally bladed ring type structures. Integrally bladed rotors provide a number of advantages over more traditional bladed disc rotor assemblies.

For example, integrally bladed rotors are generally lighter than bladed disc assemblies which incorporate blade to disc mounting features such as dove-tail rim slots and blade roots. Integrally bladed rotor s also overcome many of the problems associated with such mounting arrangements including frethng of the blade root and disc slot due to compression of the blade root in contact with the rim slot. Design limitations on maximum pitch/chord ratio of the blade are also avoided.

Linear friction welding of metallic hollow blades to metallic disc/rings is nearing its limit as far as weight reduction is concerned, and although whole composite integrally bladed rotors have been proposed for certain applications, traditional bladed disc assemblies comprising organic composite blades having conventional dove-tail root attachment arrangements are often preferred. However, drawbacks exist in conventional arrangements in which composite blades are mounted in disc rim slots.

As previously mentioned, the blade root is held in compression when the disc rotates.

The rotational load generated by the blade is therefore supported by compression of the composite matrix material rather than tensioning of the reinforcement fibre of the composite material.

There is a requirement therefore for an improved integrally bladed rotor arrangement which combines the benefits of both metallic integrally bladed rotors and composite aerofoil blades.

According to an aspect of the invention there is provided an integrally bladed rotor for turbo-machinery comprising a metallic disc and a plurality of blades of metallic and non-metallic material extending radially outwards from the disc.

This aspect of the present invention provides an integrally bladed rotor in which blades comprising non-metallic material extend from the circumference of a metallic disc. This enables different materials to be used for the disc and aerofoil blade parts of the blisk to optimise the design of the integrally bladed rotor.

In preferred embodiments the blades each comprise a metallic root section and a non-metallic aerofoil section. This readily enables blades of mainly non-metallic material to be joined to the rim of the integrally bladed rotor, for example by linear friction welding.

Each metallic root section may comprise a radially extending element at one end that extends at least partially into the interior of the non-metallic aerofoil section for joining the non-metallic aerofoil to the root section. In this way the radially extending element * provides a metallic core that extends into the non-metallic aerofoil material at the root of the blade. The metallic core not only strengthens the structure of the aerofoil towards the root section of the blade but also provides a means for joining the non-metallic material of the aerofoil section to the metallic root section. For example, in preferred embodiments the non-metallic aerofoil material comprises a fibre-reinforced material and the reinforcement fibres of the non-metallic material are arranged so that they pass through one or more apertures in the radially extending metallic core element.

The reinforcement fibres may be looped through the aperture or apertures so that they extend on both sides of the metallic element towards the tip of the blade. Strands of fibres may be threaded through the aperture or apertures and folded back on themselves so that the fibres extend in a substantially uni-directional radial orientation from the tip of the blade through the aperture in the metallic element positioned towards the root of the blade and back towards the tip so that the fibres are orientated in the direction of the principal stress field of the blade when the blisk rotates. In this way the rotational load generated by the blade material is supported by tensioning of the radially aligned fibres and transferred to the metallic root structure and hence the metallic disc as a direct consequence of the fibres being looped through one or more apertures in the metallic core element.

In preferred embodiments the radially outermost surface of the aperture or apertures in the radially extending metallic core element is rounded so that no sharp edges or surface discontinuities are presented to the reinforcement fibres threaded there through. In this respect the radially outermost surface of each slot may have a convex curvature.

In preferred embodiments, the apertures comprise a plurality of aligned slots that may be arranged in a plurality of radially spaced rows. In preferred embodiments the adjacent rows may be staggered in the longitudinal direction of the slots. This enables a plurality of different strands of reinforcement fibres to be passed through the metallic radially extending core element so that strands of fibres may be positioned at different locations along the chord of the blade for reinforcing the blade along its chord between the leading and trailing edges of the blade.

The radially extending metallic core element may extend half-way or less along the radial length of the blade. Preferably the metallic core element extends a third of the way or less along the radial (span-wise) length of the blade.

In preferred embodiments the radially extending core element comprises a substantially planar element. This is particularly suitable for aerofoil sections having a high aspect ratio.

The planar element may extend substantially from the leading edge to the trailing edge of the aerofoil. Alternatively the planar element may extend along a smaller part of the chord of the aerofoil.

The non-metallic material of the blades preferably comprises a fibre reinforced cothposite material. This readily enables the aerofoil section to be moulded using pre-impregnated composite sheets comprising strands of reinforcement fibres to provide an organic composite aerofoil attached to the metallic disc. Preferably the blades are joined to the circumference of the disc by friction welding, preferably linear friction welding, of the metallic root section of the blade to respective stubs formed on the disc.

In preferred embodiments the integrally bladed rotor comprises a gas turbine engine rotor or a rotor for a lift fan or the like. The integrally bladed rotor may comprise part of the fan or compressor section of an axial flow turbo machine. In this respect it is to be understood that the term "disc" used herein refers not only to conventional discs but also bladed ring-type structures as are often found in gas turbine engine rotors, particularly in the fan or low pressure compressor stages of an engine or axial flow turbo machine.

According to another aspect of the invention there is provided a method of manufacturing a composite blade for an integrally bladed rotor, the said method comprising the step of providing a metallic blade root section having a stub portion for friction welding the blade to the rim of a metallic disc and an upstanding portion, and moulding a non-metallic aerofoil section on said upstanding portion such that said upstanding portion extends at least partially into the interior of the moulded aerofoil section.

The manufacture of a composite blade for an integrally bladed rotor according to the above method readily enables non-metallic aerofoils to be constructed in a way that readily provides for joining the non-metallic aerofoil to the circumference of a metallic disc by friction welding using established friction welding methods, that is to say method established for joining metallic blades to metallic discs in the manufacture of an integrally bladed rotor. This can minimise the number of changes in the manufacture of integrally bladed rotors since the same methods for joining metal blades to metal discs can be employed in the manufacture of integrally bladed rotors having composite blades.

The method according to this aspect of the invention therefore readily enables the manufacture of integrally bladed rotors having composite blades extending from the rim of a metallic disc. It is possible therefore using the method according to this aspect of the invention to manufacture integrally bladed rotors in which the disc portion is constructed of a metallic material such that the disc part is capable of carrying high rotational loads while relatively lighter composite aerofoils can be provided having sufficient strength to support the rotational and aerodynamic loads acting on the blade in use.

Preferably the aerofoil moulding step includes the step of providing additional layers of fibre on the fibres arranged in the radial direction of the blade to provide sufficient strength in other directions, for example, to resist untwisting of the aerofoil due to aerodynamic loads acting on the aerofoil in use.

The present invention also contemplates a method of manufacturing, re-working or repairing a integrally bladed rotor for a turbo machine comprising the steps of friction S. welding one or more composite blades manufactured in accordance with the aforesaid method to the circumference of a metallic disc.

Various embodiments of the invention will now be more particularly described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a part of an integrally bladed rotor; Figure 2 illustrates friction welding of a blade to the circumference of a disc to form an integrally bladed rotor assembly of the type shown in Figure 1; Figure 3 is a perspective view from the side of a metallic blade root section of an aerofoil blade prior to the aerofoil section being moulded thereon; Figure 4 is a perspective view of the metallic root section of Figure 3 from below; Figure 4a is a cross section through a metallic root section of the type shown in Figures 3 and 4, according to an embodiment of the present invention; Figure 4b is a cross section view similar to that of 4a showing a metallic blade root section according to another embodiment of the invention; Figure 4c is a cross section view similar to Figures 4a and 4b showing a root section according to a further embodiment of the invention; Figure 4d is a cross section view similar to that of Figures 4a to 4c showing the metallic root section of Figure 4c welded to the rim of a disc rotor with a composite aerofoil section moulded to the metallic root section of the blade; and Figure 4e is a cross section view of the blade of Figure 4d friction welded to the circumference of a metallic disc.

An integrally bladed rotor 10 suitable for use in the fan or compressor section of a gas turbine engine is shown in Figure 1. In the drawing of Figure 1 only part of the circumference of the integrally bladed rotor is shown, as the rotor is essentially axi-symmetric the remaining part of the rotor is substantially identical to the section shown.

The integrally bladed rotor 10 comprises a plurality of blades 14 attached to the outer periphery cia disc 12 so that they extend radially outward therefrom.

The blades 14 are formed separately from the disc 12 and are attached thereto by friction welding. During the friction welding process the blades 14 are oscillated relative to the disc as shown in Figure 2. Each blade 14 is oscillated tangentially, shown by arrow 15, against a stub 13 on the outer periphery of the disc 12 whilst a radial load 16 is applied. The heat generated by the oscillation 15 together with the load 16 results in a weld between the stub 13 and the blade 14. The integrally bladed rotor 10 is then machined to remove any material extruded during the welding process and to give the stub 13 and the blade 12 their final form.

In one embodiment of the present invention each blade comprises a metallic root section 18 (Figures 3 and 4) and a non-metallic aerofoil section 21 joined to the metallic root section as described in more detail below.

The radially inner base region of the root section 18 that contacts the disc 12, for joining thereto by linear friction welding, is referred to as a stub. In the embodiment of Figures 3 and 4 the metallic root section comprises a stub or foot portion 20, in the form of a curvilinear block, an understub portion 22 on one side of the foot portion and a substantially planar upstanding element 24 on the other side thereof. The foot portion includes a leading edge end 26 and a trailing edge end 28, a suction side 30 and a pressure side 32. Each of the sides 30 and 32 curve smoothly between the leading and trailing edge ends 26 and 28, on their respective side of the foot portion.

The understub 22 has a similar curvilinear shape as the foot portion and although slightly narrower extends from the leading edge end 26 to the trailing edge end 28 substantially along the length of the foot portion 20. The understub 22 has a substantially constant width but tapers slightly towards the leading and trailing edge ends from a mid-chordal position on the underside of the foot portion where it is widest.

The planar element 24 extends in the radial direction of the root section, i.e. in the spanwise direction of the blade, from the radially outer surface 34 of the foot portion 20.

As can best be seen in the drawings of Figures 4a to 4d the element 24 is arranged substantially perpendicular to the plane of the foot portion 20. The element 24 extends substantially between the leading edge and trailing edge ends 26 and 28 of the foot portion having curvilinear pressure and suction side surfaces 36 and 38 on respective sides thereof. The element 24 is disposed substantially along the chord of the aerofoil section joined to the root section as will be described.

A plurality of apertures in the form of elongate slots 40 are provided in the planar element so that fibres of the composite aerofoil can pass through the slots 40 prior to moulding of the composite aerofoil section. The slots 40 are arranged in an end to end configuration in one or more row. In the illustrated embodiment three rows 40a, 40b and 40c are provided with the slots of adjacent rows staggered in the chordal direction of the element 24 in an overlapping manner so that reinforcement fibres may be threaded through the slots 40 along the chordal length of the aerofoil.

Referring now to the drawings of Figures 4a to 4c, in each of the illustrated embodiments it can be seen that a transition portion 42 is located between the radially outer surface 34 of the foot portion 20 and the planar element 24. The transition portion 42 has a width dimension approximately twice that of the planar element and is blended at one end to the root foot portion 20 by fillets 44 on both the suction and pressure sides of the root section and blended to the planar element 24 by fillets 46 also on both sides of the element. As can be seen in the drawings of Figures 4a to 4c the under-stub portion 22 has a depth dimension 48 that is substantially between one quarter and one half the depth dimension 50 of the foot portion. The cross section of the under-stub portion 22 tapers in the direction towards its surface 52 which contacts the disc stub.

In the embodiment of Figure 4 the planar element 24 has a substantially constant cross section and comprises a first row of slots 40a that are formed at the base of the planar element 24 such that the slots 40a extend into the transition region 42 between the element 24 and the foot 20. A second row of slots 40b and a third row of slots 40c are located at different radial positions along the element with the rows 40a, 40b and 40c being equally spaced in that direction. The upper and lower surfaces 54 and 56 of the slots are rounded such that the upper surface 54 has a convex profile and the lower surface 56 has a concave profile. The convex profile of the upper surface 54 provides a smooth transition between the slot and the suction and pressure surfaces 36 and 38 of the element so that reinforcement fibres of the composite aerofoil material extending in the radial direction of the blade may pass through the respective slots without encountering any sharp edges or other surface discontinuities which could damage the fibres during manufacture and/or operation.

In the embodiment of Figure 4b the cross section shape of the first row of slots has been modified such that the lower concave surface 56 of the slot 48 has a V-shape profile which extends between the respective ends of the filets 46 on the pressure and suction sides of the element. In this embodiment the slot 48 extends deep into the transition region 42 to a position close to the foot region 20.

In the embodiment of Figure 4c the cross section of the slots in the first row 40a is similar, but not identical, to the slots 40a in the embodiment of Figure 4a. The embodiment of Figure 4c is different from the embodiments of Figures 4a and 4b in that the element 24 tapers from the transition region 42 to its radially outermost end 58.

The drawing of Figure 4d illustrates a composite blade having a metallic root section identical to that shown in Figure 4c. The blade has been linear friction welded to the outer periphery of the disc 12. In this illustrated embodiment only part of the composite aerofoil section of the blade is shown, that is to say the aerofoil section below, or radially inwards of, line 60. The dashed lines 62 represent the material that is subsequently removed from the welded formation to give the disc stub and the blade its final form. -10-

In preferred embodiments the element 24 extends approximately one third the radial (spanwise) length of the blade, however this may vary depending on the particular design considerations for each integrally bladed rotor rotor design.

For the purpose of illustration only, Figure 4e shows a plurality of strands of reinforcement fibres 60 of the composite aerofoil material passing through a slot in the row 40c. The drawing of Figure 4e is identical to that of figure 4d except that it shows reinforcement fibres passing through one of the slots. It will be understood that all of the slots provided in the element 24 will accommodate, if necessary, strands of reinforcement fibres as illustrated in the drawing of Figure 4e. As shown the fibres are arranged in a substantially uni-directional direction extending from the tip of the blade (not shown) radially towards the slot 40, through which they pass, and return to the tip of the blade in the same uni-directional radial direction. The fibres may be considered to be folded back upon themselves after passing through the respective slot. This is an important consideration when the reinforcement fibres are laid up during the moulding process by which the aerofoil section is formed. During manufacture strands of fibres preferably in the form of a pre-impregnated sheet are fed through the respective slots and arranged in the radial direction so that they extend uni-directionally in the principal stress field of the blade during operation. Other layers of fibres are laid on top of the radial strands to provide the respective blades with strength in other directions, notably to resist untwisting of the blades due to aerodynamic loads and on the blades in use.

The aerofoil sections are then moulded by methods well known in the art to form the composite aerofoil section on the metallic root section 18.

As is well known in the art the blades of a metallic integrally bladed rotor are typically of titanium, nickel or steel and these materials and other suitable metals and metal alloys may be used for the root section 18 in the embodiments of the present invention previously described.

The present invention therefore provides, in one aspect, a method of joining an organic composite aerofoil assembly to a metallic disc by linear friction welding. The stub of the -11 -disc and understub of the blade are subsequently milled, or finished machined in other ways, to provide the finished aerofoil and root fillet. The composite blade is joined to a metallic root section by means of a radially extending planar element in the form of a paddle or fin type structure 24 machined on the metallic root section. Uni-directional composite fibre strands 60 are located through slots on the planar element and then folded back on themselves to give a continuous fibre from tip to blade root and back to the tip. Additional fibre weaves required for providing torsional strength to the blade are optionally layered on the outside of the uni-directional strands and then the whole metallic/composite blade assembly is baked to form the aerofoil section using methods well known in the art of composite blade manufacture. As is well known in the art, FOD protection shields, for example metallic strips along the leading edge of the blades, may be inserted into the aerofoil section moulds before moulding the blades.

Claims

CLAIMS

1 An integrally bladed rotor for turbo-machinery, the integrally bladed rotor comprising a metallic disc and a plurality of blades of metallic and non-metallic material extending radially outwards from the disc.

2 An integrally bladed rotor as claimed in any Claim I wherein the said blades each comprise a metallic root section and a non-metallic aerofoil section.

3 An integrally bladed rotor as claimed in Claim 2 wherein the said metallic root comprises a radially extending element at one end thereof which extends at least partially into the interior of the said aerofoil section joining the non-metallic aerofoil material to the said root section.

4 An integrally bladed rotor as claimed in Claim 3 wherein said non-metallic aerofoil comprises a fibre reinforced material and wherein fibres of said non-metallic material pass through at least one aperture in said radially extending.

element.

An integrally bladed rotor as claimed in Claim 4 wherein the said fibres are looped through the said at least one aperture so that they extend on both sides of the said element towards the tip of the blade.

6 An integrally bladed rotor as claimed in Claim 5 wherein at least the radially outermost surface of said aperture is rounded.

7 An integrally bladed rotor as claimed in Claim 6 wherein the said fibres extend in a substantially uni-directional radial orientation from tip to root to tip of the respective blade.

8 An integrally bladed rotor as claimed in any of Claims 4 to 7 wherein the said at least one aperture comprises a plurality of aligned slots.

9 An integrally bladed rotor as claimed in Claim 8 wherein said slots are arranged in a plurality of radially spaced rows.

An integrally bladed rotor as claimed in Claim 9 wherein the slots in adjacent rows are staggered in the longitudinal direction of the slots.

11 An integrally bladed rotor as claimed in any of Claims 3 to 10 wherein the said radially extending element extends half way or less along the radial length of the blade 12 An integrally bladed rotor as claimed in Claim 11 wherein the said radially extending element extends a third of the way, or less, along the radial length blade 13 An integrally bladed rotor as claimed in any of Claims 3 to 12 wherein the said radially extending element comprises a substantially planar element.

14 An integrally bladed rotor as claimed in Claim 13 wherein said planar element extends substantially from the leading edge to the trailing edge of the said aerofoil.

An integrally bladed rotor as claimed in any preceding claim wherein said non-metallic material comprises a fibre reinforced composite material.

16. 16 An integrally bladed rotor as claimed in any preceding claim wherein the said blades are joined to the disc circumference by friction welding.

17 An integrally bladed rotor as claimed in any preceding claim wherein said blisk comprises a gas turbine engine rotor.

18 A method of manufacturing a composite blade for an integrally bladed rotor rotor, the said method comprising the step of providing a metallic blade root section having a stub portion for friction welding the blade to the rim of a metallic disc and an upstanding portion, and moulding a non-metallic aerofoil section on said upstanding portion such that said upstanding portion extends at least partially into the interior of the moulded aerofoil section.

19 A method as claimed in Claim 18 wherein said non metallic aerofoil comprises a fibre reinforced material and said method includes the step of threading fibres of said non-metallic material through at least one aperture in said upstanding portion prior to moulding said aerofoil section.

A method as claimed in Claim 19 wherein the said fibres are looped through the said at east one aperture so that they extend on both sides of the said upstanding portion towards the tip of the blade.

21 A method as claimed in Claim 20 wherein the said fibres extend in a substantially uni-directional orientation from tip to root to tip of the respective blade.

22 A method as claimed in Claim 21 wherein said moulding step includes the step of providing additional layers of fibre on said fibres threaded through said aperture.

23 A method as claimed in any of Claims 19 to 22 wherein the said at least one aperture comprises a plurality of aligned slots through which said fibres are fed.

* 24 A method as claimed in Claim 23 wherein said slots are arranged in a plurality of radially spaced rows.

A method as claimed in Claim 24 wherein the slots in adjacent rows are staggered in the longitudinal direction of the slots.

26 A method as claimed in any of Claims 18 to 25 wherein the said upstanding portion extends half way or less along the spanwise length of the moulded aerofoil section.

27 A method as claimed in Claim 26 wherein the said upstanding portion extends a third of the way, or less, along the spanwise length of the moulded aerofoil section.

28 A method as claimed in any of Claims 18 to 27 wherein the said upstanding portion comprises a substantially planar element.

29 A method as claimed in Claim 28 wherein said planar element extends substantially from the leading edge to the trailing edge of the said aerofoil.

A method as claimed in Claim 18 to Claim 29 wherein said non-metallic material comprises a fibre reinforced composite material.

31 A method as claimed in any one of Claims 18 to 30 wherein said moulding step includes the step of providing additional layers of fibre on said fibres threaded through said aperture.

32 A method of manufacturing, re-working or repairing an integrally bladed rotor for a turbo-machine, said method comprising the steps of friction welding at least one composite blade, manufactured in accordance with the method of any of Claims 18 to 31, to the circumference of a metallic disc.

33 A method of manufacturing a composite blade for an integrally bladed rotor substantially as hereinbefore described with reference to the accompanying drawings.

34 A method of manufacturing, re-working or repairing an integrally bladed rotor substantially as hereinbefore described with reference to the accompanying drawings.

An integrally bladed rotor substantially as hereinbefore described with reference to the accompanying drawings.