FAN OUTLET GUIDE VANE MANUFACTURE

Abstract

A method of forming an article for finish fabrication into a fan outlet guide vane of a turbofan engine is provided. The method includes steps of: providing first and second sides of a metallic workpiece, each side having a relatively thin central region and a relatively thick peripheral region, and each side being formed from a plurality of separate pieces which are assembled in position relative to each other to provide the respective side, the pieces of each side including a plate which at least partially forms the central region, and one or more thicker blocks which at least partially form the peripheral region; stacking the first and second sides so that a contact interface is formed between the sides; diffusion bonding the first and second sides together across the interface over regions of the interface other than a preselected region thereof corresponding with the thin central regions of the first and second sides; and hot creep forming the bonded first and second sides and inflating the workpiece at the preselected region to produce the article such that the first and second sides form opposite aerofoil surfaces of the fan outlet guide vane.

Claims

1. A method of forming an article for finish fabrication into a fan outlet guide vane of a turbofan engine, the method including steps of: providing first and second sides of a metallic workpiece, each side having a central region and a peripheral region, a thickness of the central region being smaller than a thickness of the peripheral region, and each side being formed from a plurality of separate pieces which are assembled in position relative to each other to provide the respective side, the pieces of each side including a plate which at least partially forms the central region, and one or more thicker blocks which at least partially form the peripheral region; stacking the first and second sides so that a contact interface is formed between the sides; diffusion bonding the first and second sides together across the interface over regions of the interface other than a preselected region thereof corresponding with the thin central regions of the first and second sides; and hot creep forming the bonded first and second sides and inflating the workpiece at the preselected region to produce the article such that the first and second sides form opposite aerofoil surfaces of the fan outlet guide vane.

2. The method of claim 1, further including a step before the stacking step of diffusion bonding the assembled pieces of each side in their assembled relative positions.

3. The method of claim 1, wherein the step of diffusion bonding the first and second sides together also includes diffusion bonding the assembled pieces of each side in their assembled relative positions.

4. The method of claim 1, further including a step before the hot creep forming and inflating step of machining each side to refine the shape of its central region.

5. The method of claim 1, wherein the pieces of each side include at least four thick blocks which at least partially form the peripheral region.

6. The method of claim 1, wherein the thin plate of each side forms the entire central region.

7. The method of claim 1, wherein the thin plate of each side extends across to partially form the peripheral region, the one or more thick blocks of that side being stacked on the thin plate in their assembled relative positions to complete the peripheral region.

8. The method of any claim 1, wherein the thin plate of each side has a perimeter edge, the thick blocks of that side abutting the perimeter edge in their assembled relative positions.

9. The method of claim 1, wherein each side has a boundary between its thin central region and its thick peripheral region, the boundary substantially coinciding with leading, trailing, outer end wall and inner end wall edges of the respective aerofoil surface of the fan outlet guide vane.

10. A process for manufacturing a fan outlet guide vane of a turbofan engine, the process including: performing the method of claim 1; and finish fabrication of the article into the fan outlet guide vane.

11. A fan outlet guide vane manufactured by the process as claimed in claim 10.

12. A turbofan engine having a circumferential row of fan outlet guide vanes as claimed in claim 11.

Description

DESCRIPTION OF THE DRAWINGS

[0056] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0057] FIG. 1 shows schematically a plan view of a metallic plate for use in forming an OGV of a large civil turbofan;

[0058] FIG. 2 shows a schematic cross-section through the plate of FIG. 1 on line A-A;

[0059] FIG. 3 shows schematically two such plates assembled together and diffusion bonded to form a joined workpiece ready for hot creep forming and inflation;

[0060] FIG. 4 is a sectional side view of a gas turbine engine;

[0061] FIG. 5 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0062] FIG. 6 is a partially cut-away view of a gearbox for a gas turbine engine;

[0063] FIG. 7 shows a plan view of one side of a workpiece for use in a method of forming a precursor article of an OGV of the engine of FIG. 4;

[0064] FIG. 8 shows a schematic cross-section through the side of FIG. 7 on line A-A;

[0065] FIG. 9 shows a schematic cross-section through the side of FIG. 7 on line B-B;

[0066] FIG. 10 shows a schematic cross-section through two diffusion bonded sides of the workpiece in a first variant of the method;

[0067] FIG. 11 shows a plan view of one side of the workpiece for use in a second variant of the method;

[0068] FIG. 12 shows a schematic cross-section through a side of the workpiece for use in a third variant of the method; and

[0069] FIG. 13 shows a schematic cross-section through two diffusion bonded sides of the workpiece in an approach combining the first and third variants of the method.

DETAILED DESCRIPTION

[0070] FIG. 4 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30. Behind the fan 23, a row of OGVs 41 straighten the bypass airflow B and form a load path between a fan case 42 and the engine core 11. The OGVs also protect downstream components.

[0071] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0072] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 5. The low pressure turbine 19 (see FIG. 4) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0073] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0074] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 6. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 6. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the present disclosure. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0075] The epicyclic gearbox 30 illustrated by way of example in FIGS. 5 and 6 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0076] It will be appreciated that the arrangement shown in FIGS. 5 and 6 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 5 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 5. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 5.

[0077] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0078] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0079] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 4 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0080] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 4), and a circumferential direction (perpendicular to the page in the FIG. 4 view). The axial, radial and circumferential directions are mutually perpendicular.

[0081] The OGVs 41 are formed by hot creep and inflation of a precursor article, followed by final fabrication operations, such as finish machining. This precursor article in turn is formed from a metallic (e.g. titanium 6-4 alloy) workpiece.

[0082] The hot creep forming and inflation, and subsequent final fabrication operations can be performed conventionally, e.g. as described in US 2002/174540. The workpiece, by contrast, is unconventional and differs in important respects from that described above in relation to FIGS. 1 to 3.

[0083] More particularly, the workpiece has first and second sides, which are both rectangular in outline, each side ultimately forming opposite aerofoil surfaces of the OGV. FIG. 7 shows a plan view of one of the sides, FIG. 8 shows a schematic cross-section through the side on line A-A, and FIG. 9 shows a schematic cross-section through the side on line B-B. The approximate position of the outline of the respective aerofoil surface of the OGV is indicated with a dashed line on FIG. 7. The OGV has a leading edge 52, a trailing edge 53, an outer end wall edge 54 and an inner end wall edge 55.

[0084] Each side is formed from separate pieces of metal which are assembled in position relative to each. In the example of FIGS. 7 to 9, these include a thin rectangular plate 61 which covers the whole area of the side, and four thicker blocks 62 which are assembled on top of and around the edges of the plate. In this way, the plate forms a thin central region of the side, while the combination of the plate and the blocks forms a thicker peripheral region of the side. In FIG. 7 the edges of the blocks are indicated with thicker lines.

[0085] The assembled pieces 61, 62 of each side can then be diffusion bonded together and thereafter machined to refine the shape of the central region so that a profiled cavity like that shown in FIG. 2 is produced. Subsequently, the two sides are stacked together to form a contact interface (as per FIG. 3), diffusion bonded across the interface over regions of the interface other than a preselected region thereof corresponding with the thin central regions of the first and second sides, and subjected to hot creep forming and inflating at the preselected region to produce the precursor article, before undergoing final fabrication operations.

[0086] The thickness and dimensions of each piece 61, 62 can be selected to provide just enough material to allow machining to the desired profile. This method of forming the workpiece significantly reduces the amount of input material that needs to be machined to achieve a desired geometry before the hot creep forming and inflation.

[0087] In a first variant of the method, and as an alternative to diffusion bonding the assembled pieces 61, 62 of each side before machining to refine the shape of the central region, this diffusion bonding step can be combined with diffusion bonding across the interface of the stacked sides, to produce a workpiece as shown schematically in FIG. 10. Machining to refine the shapes of the central regions of both sides can then be performed on this workpiece. Overall, this approach reduces the number of separate diffusion bonding steps, but can complicate the assembling of the pieces and the machining to form the profiled cavities.

[0088] In a second variant of the method, the thick blocks 62 can be shaped to better conform with the desired profile of the cavity of each side of the workpiece. For example, as shown in FIG. 11, the blocks can be shaped so that the boundary between the thin central region and the thick peripheral region of each side substantially coincides with the leading 52, trailing 53, outer end wall 54 and inner end wall 55 edges of the respective aerofoil surface of the OGV. This then helps to further reduce the amount of machining needed to achieve a desired geometry before the hot creep forming and inflation.

[0089] In a third variant of the method, illustrated in FIG. 12, the thick blocks 62 of each side can be assembled so that they abut the edges of the thin plate 61, rather than being located on top of the plate. The diffusion bonds between the plate and blocks of each side are then formed across these abutting edges. FIG. 13 shows schematically the workpiece formed by combining the approaches of the first and third variants of the method before machining to refine the shapes of the central regions of both its sides.

[0090] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.