Component casting

Abstract

A method includes forming a mold, the mold having at least one mold portion defining the shape of an element to be removed from the component in a subsequent manufacturing step and having a reduced cross-sectional area. The at least one mold portion includes at least one recess which further reduces the cross sectional area of the cavity and increases the surface area of the at least one mold portion or the at least one mold portion includes a plurality of projections which increase the surface area of the least one mold portion thereby increasing radiative heat loss from the at least one mold portion during the process. A mold for use in this method and a turbine blade formed using this method, are also provided.

Claims

1. A mould for casting a component using a directional solidification process, said mould comprising a mould portion which defines a shape of an element to be removed from the component in a subsequent manufacturing step, the mould portion being positioned at an end of the mould and defining a cavity with a reduced cross-sectional area reduced relative to a cross-sectional area of at least one other cavity of the mould, wherein the mould portion comprises at least one recess which further reduces the reduced cross sectional area of the cavity of the mould portion and increases a surface area of the mould portion or a plurality of projections which increase the surface area of the mould portion, such that, in use, a radiative heat loss from said mould portion during said directional solidification process is increased.

2. A mould according to claim 1 wherein the mould portion comprises a plurality of recesses.

3. A mould according to claim 2 wherein the plurality of recesses are elongated recesses and are separated by one or more interspaced elongated projecting ribs.

4. A mould according to claim 1 wherein the mould portion comprises a plurality of projections and the projections are elongated projecting ribs.

5. A mould according to claim 1 wherein the plurality of projections have a semi-circular-, square-, triangular-, trapezoidal-, or dovetail-shaped cross section (at 90 degrees to a direction of elongation of the projection).

6. A mould according to claim 1 wherein the recesses and/or projections have a major axis, and this axis is arranged parallel to a major axis of the mould portion.

7. A mould according to claim 1 wherein the recesses and/or projections have a major axis, and this axis is transversely aligned with a major axis of the mould portion.

8. A mould according to claim 1 wherein the recesses and/or projections are arranged in zig-zag pattern.

9. A mould according to claim 1 wherein the recesses and/or projections are branched.

10. A mould according to claim 1 wherein the or each recess or at least one of said plurality of projections is circular-, ovular-, diamond- or dog-bone-shaped.

11. A mould according to claim 1 wherein the mould portion has a posterior and anterior surface and the recess or series of recesses or plurality of projections/elongated projecting ribs is provided on one or both of said surfaces.

12. A mould according to claim 1 wherein the element defined by the mould portion is positioned to support the component during the subsequent manufacturing step.

13. A mould for casting a turbine blade using a directional solidification process, said mould comprising a mould portion which defines a shape of an element to be removed from the turbine blade in a subsequent manufacturing step, the mould portion being positioned at an end of the mould and defining a cavity with a reduced cross-sectional area reduced relative to a cross-sectional area of at least one other cavity of the mould, wherein the mould portion comprises at least one recess which further reduces the reduced cross sectional area of the cavity of the mould portion and increases a surface area of the mould portion or a plurality of projections which increase the surface area of the mould portion, such that, in use, a radiative heat loss from said mould portion during said directional solidification process is increased, wherein the mould comprises a main body defining a cavity for forming a blade body and the mould portion defining the cavity with a reduced cross-sectional area is for forming a tang portion of the turbine blade to be removed during subsequent manufacturing steps.

14. A method of casting a component using a directional solidification process comprising: forming a mould portion of a mould, the mould portion defining a cavity with a reduced cross-sectional area reduced relative to a cross-sectional area of at least one other cavity of the mould, the mould portion being positioned at an end of the mould and defining a shape of an element to be removed from the component in a subsequent manufacturing step; and forming at least one recess in the mould portion which further reduces the reduced cross sectional area of the cavity of the mould portion and increases a surface area of the at least one mould portion or a plurality of projections in the mould portion which increase the surface area of the mould portion thereby increasing radiative heat loss from said mould portion during said process.

15. A method according to claim 14 wherein forming at least one recess includes forming a plurality of recesses.

16. A method according to claim 15 wherein the recesses are a series of elongated recesses separated by one or more interspaced elongated ribs on the mould portion.

17. A method according to claim 14 wherein the plurality of projections comprises a plurality of elongated projecting ribs.

18. A method according to claim 17 wherein the plurality of elongated projecting ribs each has a semi-circular-, square-, triangular-, trapezoidal-, or dovetail-shaped cross section (at 90 degrees to the direction of elongation).

19. A method according to claim 14 further comprising forming the at least one recess or the plurality of projections parallel to a major axis of the mould portion.

20. A method according to claim 14 further comprising forming the at least one recess or the plurality of projections to be transversely aligned with a major axis of the mould portion.

21. A method according to claim 14 wherein the at least one recess or at least one of plurality of projections is zig-zagged.

22. A method according to claim 14 wherein the at least one recess is branched with the branches at least partly surrounding a protrusion on the mould portion or wherein at least one of the plurality of projections is branched.

23. A method according to claim 14 wherein the at least one recess or at least one of the plurality of projections is a circular-, ovular-, diamond- or dog-bone-shaped recess or projection.

24. A method according to claim 14 wherein there is a series of recesses which are parallel to and/or transversely aligned with a major axis of the at least one mould portion or the plurality of projections/elongated projecting ribs are parallel to and/or transversely aligned with the major axis of the mould portion.

25. A method according to claim 14 wherein the mould portion has a posterior and an anterior surface and the at least one recess or plurality of projections is provided on one or both of said surfaces.

26. A method according to claim 14 for casting a turbine blade wherein the mould comprises a main body defining a cavity for forming a blade body and the mould portion defining the cavity with a reduced cross-sectional area is for forming a tang portion of the turbine blade.

27. A method according to claim 14 wherein the element defined by the mould portion is positioned to support the component during the subsequent manufacturing step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 shows a ducted fan gas turbine engine incorporating a series of turbines each having a plurality of aerofoil blades formed using a method according to an embodiment of the present invention.

(3) FIG. 2a shows a tang portion of a turbine blade cast using a method according to an embodiment of the present invention.

(4) FIG. 2b shows a cross-sectional view of the tang portion of FIG. 2a.

(5) FIGS. 3a-e show possible cross-sectional shapes for the elongated ribs shown in FIGS. 2a and 2b.

(6) FIGS. 4a and 4b show second and third embodiments of a tang portion with alternative arrangements for the series of elongated recesses.

(7) FIG. 5 shows a fourth embodiment of a tang portion with a recess extending into a side surface.

(8) FIGS. 6a-6i show further embodiments of a tang portion with shaped recesses.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES OF THE INVENTION

(9) With reference to FIG. 1, a ducted fan gas turbine engine incorporating a series of turbines each having a plurality of aerofoil blades formed using a method according to an embodiment of the present invention is generally indicated at 10 and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, the propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, an intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

(10) During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

(11) The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

(12) The turbines 16, 17 and 18 each comprise a plurality of turbine blades 24 formed according to a first embodiment of the present invention.

(13) Each turbine blade is cast from molten metal (e.g. a nickel-based super-alloy) using a directional solidification process. As seen in FIGS. 2a and 2b, the resulting cast component has a blade body 25 and two opposing tang portions 26 (only one shown).

(14) The anterior surface 29 of the tang portion 26 comprises a series of elongated recesses 27 inter-spaced by a series of elongated ribs 28. The elongated recesses 27 and ribs 28 are axially aligned with the major axis (A-A) of the cast component. The posterior surface 30 of the tang portion 26 also comprises a series of elongated recesses 27 and ribs 28.

(15) The cross-sectional shape and/or cross-sectional area of the interspaced elongated ribs 28 may vary along the length of each rib. Examples of possible cross-sectional shapes (at 90 degrees to the direction of elongation/major axis (A-A) of the cast component) for the interspaced elongated ribs 28 are shown in FIGS. 3a-e.

(16) FIG. 3a, shows an elongated rib 28 with a semi-circular-shaped cross-section. FIG. 3b, shows an elongated rib 28 with a square-shaped cross-section. FIG. 3c, shows an elongated rib 28 with a triangular-shaped cross-section. FIG. 3d, shows an elongated rib 28 with a trapezoidal-shaped cross-section. FIG. 3e, shows an elongated rib 28 with a dovetail cross-section. The apices of the cross-sectional shapes shown in FIGS. 3b, 3c, 3d and 3e may optionally be rounded.

(17) Alternative arrangements for the series of elongated recesses 27 inter-spaced by a series of elongated ribs 28 are shown in FIGS. 4a and 4b. In FIG. 4a, the elongated recesses 27 and ribs 28 are aligned transverse to the major axis (A-A) of the cast component, i.e. at 90 degrees to the major axis. In FIG. 4b, the elongated recesses 27 and ribs 28 are aligned at substantially 45 degrees to the major axis (A-A) of the cast component.

(18) In the embodiments, shown in FIGS. 4a and 4b, the elongated recesses 27 are entirely contained within the anterior surface 29 of the tang portion 26.

(19) As shown in FIG. 5, one or more of the elongated recesses 27 may extend into a side surface 35 of the tang portion 26, the side surface 35 separating the anterior and posterior surfaces 29, 30.

(20) FIGS. 6a-i show alternative arrangements for the series of recesses. In FIG. 6a, the recesses are spaced circular recesses 27a, axially and transversely aligned with the major axis of the component. In FIG. 6b, the recesses are elongated zig-zagged, axially aligned recesses 27b interspaced by elongated zig-zagged, axially aligned ribs 28b. In FIG. 6c, the recesses are a series of rows of axially aligned, staggered rectangles 27c. In FIG. 6d, the recesses are a series of axially aligned ovular recesses 27d. In FIG. 6e, the recesses are a series of transversely aligned ovular recesses, 27e. In FIG. 6f, the recesses are a series of transversely aligned dog-bone recesses, 27f. In FIG. 6g, the recesses are spaced diamond-shaped recesses 27g, axially and transversely aligned with the major axis of the component. In FIGS. 6h and 6i, the recesses are elongated, axially aligned branched recesses 27h with the branch portions at least partly surrounding projections 32 on the anterior surface 29.

(21) The tip 33 of the anterior and posterior surfaces 29, 30 of the tang portion 26 is trapezoid-shaped. The angle of the two sloped edges 34, 34 is between 50 and 70 degrees to the vertical (where the vertical is at 90 degrees to the parallel edges).

(22) The tang portion is used to support the cast component during finishing and the tang portion is subsequently clipped from the cast component to form the turbine blade 24 for incorporation into the turbines 16, 17, 18 of the engine.

(23) The directional solidification process used for forming the cast component comprises forming a mould comprising a main body defining a cavity corresponding in shape to the blade body 25 and at least one mould portion defining a cavity with a reduced cross-sectional area corresponding in shape to the tang portion 26.

(24) The mould portion defining the tang cavity comprises the recess or series of recesses and ribs corresponding to those shown in FIGS. 2a-b, 3a-e, 4a-b, 5 and 6a-i since these recesses and ribs will define the recesses/ribs on the tang portion 26 of the cast component.

(25) The mould portion defining the tang cavity will be interposed between the main body of the mould and a selector portion, the selector portion defining a cavity corresponding to the shape of the pig-tail selector.

(26) During the directional solidification process, molten metal will be poured into the mould and the mould slowly withdrawn (selector portion first) from a heating zone of a vacuum furnace into a cooling zone of the furnace towards an end chill plate. As the mould portion defining the tang cavity enters the cooling zone, the increased surface area of the mould portion and the reduced thermal mass of the portion of the cast component within the mould portion results in increased radiative heat loss from the mould portion. This, in turn, results in a high thermal gradient across the solid/liquid metal interface which minimises defects in the single crystal structure of the component.

(27) In the embodiments shown in FIGS. 2a-b, 6b-d and 6g-i, the radiation of heat from the increased surface area is predominantly towards the walls of the cooling zone rather than the chill plate. This is because the increased surface area of the mould portion faces the walls of the cooling zone rather than the chill plate i.e. there is an increased view factor towards the walls of the cooling zone rather than towards the chill plate.

(28) While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.