GB2590400A

GB2590400A - Single crystal casting

Info

Publication number: GB2590400A
Application number: GB1918484.5A
Authority: GB
Inventors: Bing Graham; Solanki Riten; Mithal Abeer; Kapoor Sumant; Date Yash; Pelayo Andres Jaime
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2019-12-16
Filing date: 2019-12-16
Publication date: 2021-06-30
Also published as: GB201918484D0

Abstract

The method comprises measuring the crystal orientation of a metal seed 41, comparing the measured orientation 71-73 to a nominal crystal orientation for the seed 41 and calculating orientation data based on the comparison whereby the orientation of the seed 41 would align with its nominal orientation. This data can then be used to orientate a fugitive seed 41 relative to a fugitive component 42 when making a lost pattern, form a fugitive seed including a base, form a support for a seed holder or form a seed holder where the base, support and seed holder are configured to hold a seed in the target orientation relative to a component mould. Apparatus (Fig. 9) for holding one or both of a fugitive seed and a fugitive component relative to each other comprising actuators to adjust their relative orientation and a die for forming a fugitive seed comprising actuators for adjusting the shape of the die. The method and apparatus can be used to make single crystal gas turbine engine components.

Description

SINGLE CRYSTAL CASTING

Field of the disclosure

The present disclosure relates to single crystal casting for casting metallic components, in particular components for gas turbine engines.

Background

In gas turbine engines, turbine blades are frequently subjected to high temperatures and high mechanical loads resulting from their rotation speed. A turbine blade which is cast using a conventional casting method would typically have a polycrystalline microstructure. At high temperatures and high mechanical loads, the crystals in the polycrystalline microstructure can slide against each other, resulting in creep. In later development, casting methods were improved so that the crystalline structure of the turbine blade has grain boundaries that are parallel to the direction of the centrifugal loading on the turbine blade when the gas turbine engine is in operation.

In other words, turbine blades were cast so that elongate metal crystals that run from the root to the tip of the turbine blade are formed.

In more recent development, the elongate crystalline microstructure has been eliminated altogether, resulting in turbine blades which are formed of a single metal crystal with no grain boundaries at all. Due to the absence of grain boundaries, creep performance is improved. Furthermore, not only were turbine blades cast as a single metal crystal, the crystal orientation has also been subject to careful control because the single crystal is more resistant to creep in some crystal orientation than others. Another reason for controlling the crystal orientation is that the anisotropic physical properties may be exploited, e.g. by aligning the axis of maximum stiffness (Young's modulus) in a particular direction, thereby reducing engine vibrations. A further reason for controlling the crystal orientation is to improve joints between components made by e.g. diffusion bonding or brazing. Stronger joints may result due to good crystal orientation matching.

Therefore, it has been known to cast single crystal components with tighter control of the crystal orientation. In order to achieve the tight orientation control, a metal seed may be used. By carefully controlling the casting process, molten metal in a casting mould is allowed to come into contact with the metal seed, and a single metal crystal grows from the metal seed as the metal solidifies. The resulting component therefore has substantially the same crystal orientation as the metal seed and, by carefully controlling the crystal orientation of the metal seed, the crystal orientation of the cast component may also be controlled.

CN 109513881 A discloses a method of single crystal casting with crystal orientation control.

Metal seeds are manufactured in a similar way as components such as turbine blades. In order words, instead of providing a mould for a turbine blade, a mould for producing metal seeds may be used. For this purpose, special seed bar moulds may be used, and the metal bars or pieces produced by these seed bar moulds are subsequently machined into the required seed shape so as to form new seeds. Therefore, starting from an existing metal seed, multiple new seeds can be is manufactured.

Whether the cast component is a turbine blade or another turbine component or a seed bar, despite careful control, the crystal orientation of the metal seed may not be perfectly propagated into the case component due to various sources of error. For example, error may be introduced by misalignment of the input seed compared to the intended orientation direction. For example, error may be introduced in the initial alignment of the metal seed to the mould of the component to be cast. For example, in the production of a ceramic mould comprising a component cavity and a seed holder, further error may be introduced. Further error may be introduced as a result of grain distortion as the molten metal solidifies to form the solid cast component.

Finally, error may be introduced in the measurement of metallurgical orientation, which underpins the whole process. Therefore, new metal seeds, test bars or turbine components produced using this method may have a range of deviations from the nominal crystal orientation. Depending on the application, different degrees of deviation may be tolerable.

Due to the natural variation in crystal orientation of the metal seeds produced, the crystal orientation of the metal seeds must be measured and divided into different classes for use in different applications. If the crystal orientation of a metal seed deviates too far from the nominal orientation, the metal seed is scrapped. Therefore, depending on the level of orientation control required, a proportion of the new metal seeds produced are scrapped, and this results in higher costs and higher factory capacity in order to produce a sufficient volume of metal seeds that meet the crystal orientation requirements of particular applications.

Furthermore, even if the deviation of the crystal orientation of a metal seed is tolerable, and the seed is used then to cast a component (e.g. a turbine blade), the casting process may add further deviation due to sources of errors described above, leading to a high scrap level of cast components. In other words, any initial deviation in the metal seed may increase the probability that a cast component will be scrapped.

There is thus a desire to reduce the scrap level of metal seeds and/or cast components.

Summary of the disclosure

According to a first aspect there is provided a method for preparing for making a single crystal casting, the method comprising the steps of: measuring the crystal orientation of a metal seed for single crystal casting; comparing the measured crystal orientation to a nominal crystal orientation for the metal seed; and calculating orientation data based on the comparison indicative of a target seed orientation in which the crystal orientation of the metal seed would align with the nominal crystal orientation.

Optionally, the method comprises controlling a controllable fixture holding a fugitive material seed so as to orient the fugitive material seed in the target seed orientation based on the orientation data.

Optionally, the method comprises making a fugitive material assembly comprising a component shape and the fugitive material seed, wherein the orientation of the fugitive material seed relative to the component shape is controlled by the controllable fixture. Optionally, the method comprises coating the fugitive material assembly to form a component mould and a seed holder, such that the orientation of the seed holder relative to the component mould is determined by the controlling of the controllable fixture Optionally, the method comprises making a fugitive material seed based on the orientation data, wherein the fugitive material seed comprises a base configured to hold the fugitive material seed in the target orientation. Optionally, the method comprises 3D printing the fugitive material seed based on the orientation data. Alternatively, the method comprises adapting an adaptable die for the fugitive material seed based on the orientation data; and using the adapted die to form the fugitive material seed.

Optionally, the method comprises making a fugitive material assembly comprising a component shape and the fugitive material seed, wherein the orientation of the fugitive material seed relative to the component shape is at least partly controlled by the shape of the fugitive material seed. Optionally, the method comprises coating the fugitive material assembly to form a component mould and a seed holder, wherein the orientation of the seed holder relative to the component mould is at least partly determined by the shape of the fugitive material seed.

Optionally, the method comprises using the orientation data to provide a support to position a seed holder configured to hold the metal seed in the target orientation relative to the component mould. Optionally, the method comprises producing the support for the seed holder based on the orientation data to have location features so as to hold the seed holder in the target orientation. Optionally, the method comprises producing the support for the seed holder by 3D printing the location features.

Optionally, the method comprises 3D printing a seed holder configured to hold the metal seed in the target orientation based on the orientation data. Optionally, the method comprises 3D printing the seed holder fixedly together with the component mould based on the orientation data.

Optionally, the method comprises providing that the seed holder has an identifier for identifying the metal seed. Optionally, the identifier is a barcode, a QR code, an RFID tag or an alphanumeric code. Optionally, the method comprises providing the metal seed with an identifier corresponding to the identifier of the seed holder.

Optionally, the method comprises inserting the metal seed into the seed holder; inserting molten metal into the component mould; and allowing the inserted metal to solidify such that its crystal orientation matches that of the metal seed.

Optionally, the method comprises storing the measured crystal orientation of the metal seed and/or the calculated orientation data in a database in correspondence with information identifying the metal seed.

According to a second aspect there is provided a controllable fixture for holding one or both of a fugitive material seed and a component shape relative to each other, wherein the controllable fixture comprises: a plurality of actuators configured to adjust the orientation of one or both of a fugitive material seed and/or a component shape held by the controllable fixture; and a controller configured to control the actuators so as to orient the fugitive material seed in a target seed orientation relative to the component shape based on calculated orientation data.

Optionally, the controllable fixture is configured to hold and control the orientation of the fugitive material seed. Alternatively, the controllable fixture is configured to hold and control the orientation of the component shape.

Alternatively, the controllable fixture is configured to hold both the fugitive material seed and the component shape and to control the orientation of the fugitive material seed relative to the component shape. Optionally, the controllable fixture comprises a heater configured to heat a region where the fugitive material seed joins to the component shape.

According to a third aspect there is provided an adaptable die for a fugitive material seed, wherein the adaptable die comprises: a plurality of actuators configured to adjust the shape of a fugitive material seed formed by the adaptable die; and a controller configured to control the actuators so as to shape the fugitive material seed based on calculated orientation data.

As noted elsewhere herein, the present disclosure may relate to a gas turbine engine. Such a gas turbine engine may comprise an engine core comprising a turbine, a combustor, a compressor, and a core shaft connecting the turbine to the compressor. Such a gas turbine engine may comprise a fan (having fan blades) located upstream of the engine core.

Arrangements of the present disclosure may be particularly, although not exclusively, beneficial for fans that are driven via a gearbox. Accordingly, the gas turbine engine may comprise a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft. The input to the gearbox may be directly from the core shaft, or indirectly from the core shaft, for example via a spur shaft and/or gear. The core shaft may rigidly connect the turbine and the compressor, such that the turbine and compressor rotate at the same speed (with the fan rotating at a lower speed).

The gas turbine engine as described and/or claimed herein may have any suitable general architecture. For example, the gas turbine engine may have any desired number of shafts that connect turbines and compressors, for example one, two or three shafts. Purely by way of example, the turbine connected to the core shaft may be a first turbine, the compressor connected to the core shaft may be a first compressor, and the core shaft may be a first core shaft. The engine core may further comprise a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor. The second turbine, second compressor, and second core shaft may be arranged to rotate at a higher rotational speed than the first core shaft.

In such an arrangement, the second compressor may be positioned axially downstream of the first compressor. The second compressor may be arranged to receive (for example directly receive, for example via a generally annular duct) flow from the first compressor.

The gearbox may be arranged to be driven by the core shaft that is configured to rotate (for example in use) at the lowest rotational speed (for example the first core shaft in the example above). For example; the gearbox may be arranged to be driven only by the core shaft that is configured to rotate (for example in use) at the lowest rotational speed (for example only be the first core shaft, and not the second core shaft, in the example above). Alternatively, the gearbox may be arranged to be driven by any one or more shafts, for example the first and/or second shafts in the

example above.

The gearbox may be a reduction gearbox (in that the output to the fan is a lower rotational rate than the input from the core shaft). Any type of gearbox may be used.

For example, the gearbox may be a "planetary" or "star" gearbox, as described in more detail elsewhere herein. The gearbox may have any desired reduction ratio (defined as the rotational speed of the input shaft divided by the rotational speed of the output shaft), for example greater than 2.5, for example in the range of from 3 to 4.2, or 3.2 to 3.8, for example on the order of or at least 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1 or 4.2. The gear ratio may be, for example, between any two of the values in the previous sentence. Purely by way of example, the gearbox may be a "star" gearbox having a ratio in the range of from 3.1 or 3.2 to 3.8. . In some arrangements, the gear ratio may be outside these ranges.

In any gas turbine engine as described and/or claimed herein, a combustor may be provided axially downstream of the fan and compressor(s). For example, the combustor may be directly downstream of (for example at the exit of) the second compressor, where a second compressor is provided. By way of further example, the flow at the exit to the combustor may be provided to the inlet of the second turbine, where a second turbine is provided. The combustor may be provided upstream of the turbine(s).

The or each compressor (for example the first compressor and second compressor as described above) may comprise any number of stages, for example multiple stages. Each stage may comprise a row of rotor blades and a row of stator vanes, which may be variable stator vanes On that their angle of incidence may be variable). The row of rotor blades and the row of stator vanes may be axially offset from each other.

The or each turbine (for example the first turbine and second turbine as described above) may comprise any number of stages, for example multiple stages. Each 25 stage may comprise a row of rotor blades and a row of stator vanes. The row of rotor blades and the row of stator vanes may be axially offset from each other.

Each fan blade may be defined as having a radial span extending from a root (or hub) at a radially inner gas-washed location, or 0% span position, to a tip at a 100% span position. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be less than (or on the order of) any of: 0.4, 0.39, 0.38 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.3, 0.29, 0.28, 0.27, 0.26, or 0.25. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 0.28 to 0.32. These ratios may commonly be referred to as the hub-to-tip ratio. The radius at the hub and the radius at the tip may both be measured at the leading edge (or axially forwardmost) part of the blade. The hub-to-tip ratio refers, of course, to the gas-washed portion of the fan blade, i.e. the portion radially outside any plafform.

The radius of the fan may be measured between the engine centreline and the tip of a fan blade at its leading edge. The fan diameter (which may simply be twice the radius of the fan) may be greater than (or on the order of) any of: 220 cm, 230 cm, 240 cm, 250 cm (around 100 inches), 260 cm, 270 cm (around 105 inches), 280 cm (around 110 inches), 290 cm (around 115 inches), 300 cm (around 120 inches), 310 cm, 320 cm (around 125 inches), 330 cm (around 130 inches), 340 cm (around 135 inches), 350cm, 360cm (around 140 inches), 370 cm (around 145 inches), 380 (around 150 inches) cm, 390 cm (around 155 inches), 400 cm, 410 cm (around 160 inches) or 420 cm (around 165 inches). The fan diameter may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 240 cm to 280 cm or 330 cm to 380 cm.

The rotational speed of the fan may vary in use. Generally, the rotational speed is lower for fans with a higher diameter. Purely by way of non-limitative example, the rotational speed of the fan at cruise conditions may be less than 2500 rpm, for example less than 2300 rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from 220 cm to 300 cm (for example 240 cm to 280 cm or 250 cm to 270cm) may be in the range of from 1700 rpm to 2500 rpm, for example in the range of from 1800 rpm to 2300 rpm, for example in the range of from 1900 rpm to 2100 rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from 330 cm to 380 cm may be in the range of from 1200 rpm to 2000 rpm, for example in the range of from 1300 rpm to 1800 rpm, for example in the range of from 1400 rpm to 1800 rpm.

In use of the gas turbine engine, the fan (with associated fan blades) rotates about a rotational axis. This rotation results in the tip of the fan blade moving with a velocity U. The work done by the fan blades 13 on the flow results in an enthalpy rise dH of the flow. A fan tip loading may be defined as dH/Ut1p2, where dH is the enthalpy rise (for example the 1-D average enthalpy rise) across the fan and Utip is the (translational) velocity of the fan tip, for example at the leading edge of the tip (which may be defined as fan tip radius at leading edge multiplied by angular speed). The fan tip loading at cruise conditions may be greater than (or on the order of) any of: 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39 or 0.4 (all units in this paragraph being Jkg-1K-1/(ms-1)2). The fan tip loading may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 0.28 to 0.31, or 0.29 to 0.3 Gas turbine engines in accordance with the present disclosure may have any desired bypass ratio, where the bypass ratio is defined as the ratio of the mass flow rate of the flow through the bypass duct to the mass flow rate of the flow through the core at cruise conditions. In some arrangements the bypass ratio may be greater than (or on the order of) any of the following: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5 or 20. The bypass ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of form 12 to 16, 13 to 15, or 13 to 14. The bypass duct may be substantially annular. The bypass duct may be radially outside the engine core. The radially outer surface of the bypass duct may be defined by a nacelle and/or a fan case.

The overall pressure ratio of a gas turbine engine as described and/or claimed herein may be defined as the ratio of the stagnation pressure upstream of the fan to the stagnation pressure at the exit of the highest pressure compressor (before entry into the combustor). By way of non-limitative example, the overall pressure ratio of a gas turbine engine as described and/or claimed herein at cruise may be greater than (or on the order of) any of the following: 35, 40, 45, 50, 55, 60, 65, 70, 75. The overall pressure ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 50 to 70.

Specific thrust of an engine may be defined as the net thrust of the engine divided by the total mass flow through the engine. At cruise conditions, the specific thrust of an engine described and/or claimed herein may be less than (or on the order of) any of the following: 110 Nkg-ls, 105 Nkg-ls, 100 Nkg-ls, 95 Nkg-ls, 90 Nkg-ls, 85 Nkg-ls or 80 Nkg-ls. The specific thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 80 Nkg-ls to 100 Nkg-ls, or 85 Nkg-ls to 95 Nkg-ls. Such engines may be particularly efficient in comparison with conventional gas turbine engines.

A gas turbine engine as described and/or claimed herein may have any desired maximum thrust. Purely by way of non-limitative example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust of at least (or on the order of) any of the following: 160kN, 170kN, 180kN, 190kN, 200kN, 250kN, 300kN, 350kN, 400kN, 450kN, 500kN, or 550kN. The maximum thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). Purely by way of example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust in the range of from 330kN to 420 kN, for example 350kN to 400kN. The thrust referred to above may be the maximum net thrust at standard atmospheric conditions at sea level plus 15 degrees C (ambient pressure 101.3kPa, temperature 30 degrees C), with the engine static.

In use, the temperature of the flow at the entry to the high pressure turbine may be particularly high. This temperature, which may be referred to as TET, may be measured at the exit to the combustor, for example immediately upstream of the first turbine vane, which itself may be referred to as a nozzle guide vane. At cruise, the TET may be at least (or on the order of) any of the following: 1400K, 1450K, 1500K, 1550K, 1600K or 1650K. The TET at cruise may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET in use of the engine may be, for example, at least (or on the order of) any of the following: 1700K, 1750K, 1800K, 1850K, 1900K, 1950K or 2000K. The maximum TET may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 1800K to 1950K. The maximum TET may occur, for example, at a high thrust condition, for example at a maximum take-off (MTO) condition.

A fan blade and/or aerofoil portion of a fan blade described and/or claimed herein may be manufactured from any suitable material or combination of materials. For example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a composite, for example a metal matrix composite and/or an organic matrix composite, such as carbon fibre. By way of further example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a metal, such as a titanium based metal or an aluminium based material (such as an aluminium-lithium alloy) or a steel based material. The fan blade may comprise at least two regions manufactured using different materials. For example, the fan blade may have a protective leading edge, which may be manufactured using a material that is better able to resist impact (for example from birds, ice or other material) than the rest of the blade. Such a leading edge may, for example, be manufactured using titanium or a titanium-based alloy. Thus, purely by way of example, the fan blade may have a carbon-fibre or aluminium based body (such as an aluminium lithium alloy) with a titanium leading edge.

A fan as described and/or claimed herein may comprise a central portion, from which the fan blades may extend, for example in a radial direction. The fan blades may be attached to the central portion in any desired manner. For example, each fan blade may comprise a fixture which may engage a corresponding slot in the hub (or disc).

Purely by way of example, such a fixture may be in the form of a dovetail that may slot into and/or engage a corresponding slot in the hub/disc in order to fix the fan blade to the hub/disc. By way of further example, the fan blades maybe formed integrally with a central portion. Such an arrangement may be referred to as a bladed disc or a bladed ring. Any suitable method may be used to manufacture such a bladed disc or bladed ring. For example, at least a part of the fan blades may be machined from a block and/or at least part of the fan blades may be attached to the hub/disc by welding, such as linear friction welding.

The gas turbine engines described and/or claimed herein may or may not be provided with a variable area nozzle (VAN). Such a variable area nozzle may allow the exit area of the bypass duct to be varied in use. The general principles of the present disclosure may apply to engines with or without a VAN.

The fan of a gas turbine as described and/or claimed herein may have any desired number of fan blades, for example 14, 16, 18, 20, 22, 24 or 26 fan blades.

As used herein, cruise conditions have the conventional meaning and would be readily understood by the skilled person. Thus, for a given gas turbine engine for an aircraft, the skilled person would immediately recognise cruise conditions to mean the operating point of the engine at mid-cruise of a given mission (which may be referred to in the industry as the "economic mission") of an aircraft to which the gas turbine engine is designed to be attached. In this regard, mid-cruise is the point in an aircraft flight cycle at which 50% of the total fuel that is burned between top of climb and start of descent has been burned (which may be approximated by the midpoint -in terms of time and/or distance-between top of climb and start of descent. Cruise conditions thus define an operating point of, the gas turbine engine that provides a thrust that would ensure steady state operation (i.e. maintaining a constant altitude and constant Mach Number) at mid-cruise of an aircraft to which it is designed to be attached, taking into account the number of engines provided to that aircraft. For example where an engine is designed to be attached to an aircraft that has two engines of the same type, at cruise conditions the engine provides half of the total thrust that would be required for steady state operation of that aircraft at mid-cruise.

In other words, for a given gas turbine engine for an aircraft, cruise conditions are defined as the operating point of the engine that provides a specified thrust (required to provide -in combination with any other engines on the aircraft -steady state operation of the aircraft to which it is designed to be attached at a given mid-cruise Mach Number) at the mid-cruise atmospheric conditions (defined by the International Standard Atmosphere according to ISO 2533 at the mid-cruise altitude). For any given gas turbine engine for an aircraft, the mid-cruise thrust, atmospheric conditions and Mach Number are known, and thus the operating point of the engine at cruise conditions is clearly defined.

Purely by way of example, the forward speed at the cruise condition may be any point in the range of from Mach 0.7 to 0.9, for example 0.75 to 0.85, for example 0.76 to 0.84, for example 0.77 to 0.83, for example 0.78 to 0.82, for example 0.79 to 0.81, for example on the order of Mach 0.8, on the order of Mach 0.85 or in the range of from 0.8 to 0.85. Any single speed within these ranges may be part of the cruise condition. For some aircraft, the cruise conditions may be outside these ranges, for example below Mach 0.7 or above Mach 0.9.

Purely by way of example, the cruise conditions may correspond to standard atmospheric conditions (according to the International Standard Atmosphere, ISA) at an altitude that is in the range of from 10000 m to 15000 m, for example in the range of from 10000 m to 12000 m, for example in the range of from 10400 m to 11600 m (around 38000 ft), for example in the range of from 10500 m to 11500 m, for example in the range of from 10600 m to 11400 m, for example in the range of from 10700 m (around 35000 ft) to 11300 m, for example in the range of from 10800 m to 11200 m, for example in the range of from 10900 m to 11100 m, for example on the order of 11000 m. The cruise conditions may correspond to standard atmospheric conditions at any given altitude in these ranges.

Purely by way of example, the cruise conditions may correspond to an operating point of the engine that provides a known required thrust level (for example a value in the range of from 30kN to 35kN) at a forward Mach number of 0.8 and standard atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 38000ft (11582m). Purely by way of further example, the cruise conditions may correspond to an operating point of the engine that provides a known required thrust level (for example a value in the range of from 50kN to 65kN) at a forward Mach number of 0.85 and standard atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 35000 ft (10668 m).

In use, a gas turbine engine described and/or claimed herein may operate at the cruise conditions defined elsewhere herein. Such cruise conditions may be determined by the cruise conditions (for example the mid-cruise conditions) of an aircraft to which at least one (for example 2 or 4) gas turbine engine may be mounted in order to provide propulsive thrust.

According to an aspect, there is provided an aircraft comprising a gas turbine engine as described and/or claimed herein. The aircraft according to this aspect is the aircraft for which the gas turbine engine has been designed to be attached. Accordingly, the cruise conditions according to this aspect correspond to the mid-cruise of the aircraft, as defined elsewhere herein.

According to an aspect, there is provided a method of operating a gas turbine engine as described and/or claimed herein. The operation may be at the cruise conditions as defined elsewhere herein (for example in terms of the thrust, atmospheric conditions and Mach Number).

According to an aspect, there is provided a method of operating an aircraft comprising a gas turbine engine as described and/or claimed herein. The operation according to this aspect may include (or may be) operation at the mid-cruise of the aircraft, as defined elsewhere herein.

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

Brief description of the drawings

Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a sectional side view of a gas turbine engine; Figure 2 is a close up sectional side view of an upstream portion of a gas turbine engine; Figure 3 is a partially cut-away view of a gearbox for a gas turbine engine; 20 Figure 4 shows known single crystal casting of a component; Figure 5 shows manufacturing new metal seeds; Figure 6 shows rotationally offsetting the metal seed in accordance with the method herein disclosed; Figure 7 shows rotationally offsetting the metal seed to compensate for off-nominal crystal orientation; Figure 8 is a schematic diagram of a fugitive material assembly in accordance with the method herein disclosed; Figure 9 is a schematic diagram of a controllable fixture for holding a fugitive material seed; Figure 10 is a close up view of part of the controllable fixture shown in Figure 9; Figure 11 is a close up view of part of the controllable fixture shown in Figure 9; Figure 12 is a close up view of part of the controllable fixture shown in Figure 9; Figure 13 is a schematic diagram of an alternative controllable fixture for holding a fugitive material seed; Figure 14 is a close up view of the controllable fixture shown in Figure 13; Figure 15 is a schematic diagram of a fugitive material seed made in accordance with the method herein disclosed; Figure 16 is a schematic diagram of a code scanning assembly for use in accordance with the method herein disclosed; Figure 17 is a flow chart of a method for preparing for making a single crystal casting; Figure 18 is a flow chart of an alternative method for preparing for making a single crystal casting; Figure 19 is a flow chart of a method for making a single crystal casting; Figure 20 is a schematic diagram of shims being used to control the angle of the seed; Figure 21 is a schematic diagram of an alternative controllable fixture.

Detailed description

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying Figures. Further aspects and embodiments will be apparent to those skilled in the art.

Figure 1 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.

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 core exhaust 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.

An exemplary arrangement for a geared fan gas turbine engine 10 is shown in Figure 2. The low pressure turbine 19 (see Figure 1) 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.

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.

The epicyclic gearbox 30 is shown by way of example in greater detail in Figure 3.

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 Figure 3. 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 claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

The epicyclic gearbox 30 illustrated by way of example in Figures 2 and 3 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.

It will be appreciated that the arrangement shown in Figures 2 and 3 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 Figure 2 example) between the gearbox 30 and other pads 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 pads 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 Figure 2. For example, where the gearbox 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 Figure 2.

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.

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

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 Figure 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core exhaust 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.

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 Figure 1), and a circumferential direction (perpendicular to the page in the Figure 1 view). The axial, radial and circumferential directions are mutually perpendicular.

As noted before, due to the high temperatures and the high mechanical loads to which turbine blades are subjected, in the latest development, single crystal casting with tight orientation control is used to produce turbine blades. It should be noted that single crystal casting with tight orientation control can also be used to produce other components that are subjected to high temperatures and high mechanical loads.

In single crystal casting, the crystal orientation of the resulting component is controlled by a metal seed, which has a crystal orientation close to a nominal orientation. Figure 4 depicts known single crystal casting. As shown in Figure 4, a is mould 43 may be provided. The mould 43 may be made of a ceramic material The mould 43 may comprise a component cavity 431 and a seed cavity 432.

The seed cavity 432 and the component cavity 431 may be connected via a corkscrew-shaped passage known in the art as "pigtail" 433. The passage of the pigtail 433 may be sized so as to allow a single metal grain to pass through.

Although the present disclosure refers to the passage as a pigtail 433, it should be understood that the passage may in practice have any suitable geometry other than a corkscrew shape.

As shown in Figure 4, a metal seed may be inserted into a seed cavity 432. Molten metal may be inserted into the mould 43 so as to fill the component cavity 431 and the pigtail 433. The molten metal may contact the metal seed 41. The molten metal inserted into the mould 43 may be allowed to solidify starting from where molten metal contacts the solid metal of the metal seed 41. By carefully controlling the cooling process, a crystalline structure may begin to propagate through the pigtail 433 and into the component cavity 431, forming a single crystal in the process. The solidification may continue until all the metal in the component cavity has solidified, thereby forming a component 42 which is a single metal crystal.

The mould 43 may be provided by an investment casting process. In the investment casting process, fugitive material models of the component 42, the metal seed 41 and the pigtail 433 may be provided. These fugitive material models are then joined together to produce a fugitive material assembly. The fugitive material assembly may be coated to form the mould 43. A ceramic slurry may be used to produce a ceramic mould 43. After the mould 43 is formed, the mould may be heated up so as to melt the fugitive material assembly within. Once the fugitive material is removed, the mould 43 may be produced. As such, the mould 43 may comprise the component cavity 431, the seed cavity 432 and the pigtail 433.

The term "fugitive material" is used in the present disclosure to refer to any material used to form the mould, which can then be removed (so that the casting can take place), such as by melting, combusting and/or dissolving. For example, the fugitive material may be a wax material which melts upon application of heat. The fugitive material may be a resin. The fugitive material may be a polymer. The fugitive material may be polystyrene, including expanded polystyrene. The fugitive material assembly may be made entirely of one fugitive material, or may be composed of parts made of different fugitive materials.

As shown in Figure 4, the component 42 may be a shape, such as a metal bar, suitable for producing new metal seeds. As shown in Figure 5, the metal bar may be cut off into one or more shorter section to produce one or more new metal seed 41'. A metal bar may produce any number of new metal seeds 41'. The new metal seed 41' may have the same shape and dimensions as the original metal seed 41. The new metal seeds 41' may be used for further single crystal castings to produce further new metal seeds, or to produce components 42 of a gas turbine engine such as turbine blades. Although a single metal bar is shown in Figure 4, the component 42 may comprise more than one metal bar at a time, so that more new metal seeds 41' may be produced in one casting.

As noted above, a number of errors in the above investment casting process may be present and may result in varying degrees of deviation of the crystal orientation of the resulting component 42 from the nominal crystal orientation. Depending on the application of the component 42, a degree of deviation may be tolerable. If the component 42 is a turbine blade, then turbine blades whose crystal orientation deviates too far from the nominal orientation will be scrapped. If the component 42 is a metal bar as described above, in which case one or more new metal seed 41' may be produced, then the new metal seeds 41 may be inspected for their crystal orientation. The metal seeds 41' thus produced may be divided into different classes depending on how closely their crystal orientation matches the nominal crystal orientation. In known methods, metal seeds 41' that do not meet the tolerance requirement in terms of crystal orientation will be scrapped, resulting in a level of scrapped metal seeds.

For the avoidance of doubt, it should be noted that the "nominal crystal orientation" is not necessarily one in which the primary crystal orientation is aligned with the axial 113 or lengthwise direction of the component 42 to be cast or, indeed, the lengthwise direction of the metal seed 41. The nominal crystal orientation may be any orientation as required by a particular casting. As noted above, any anisotropicity in single-crystal cast components may be exploited for technical advantages. For example, the axis of maximum stiffness in the single crystal may be controlled. For example, the single crystal orientation may be controlled to improve the strength of joints made by diffusion bonding, brazing, etc. Therefore, the nominal crystal orientation may be chosen accordingly.

In order to reduce the level of scrap, there is disclosed a method of preparation for single crystal casting. As shown in Figure 6, the core concept of the method is to rotationally offset the metal seed 41 so as to compensate for any difference between the actual crystal orientation of the metal seed 41 and the nominal crystal orientation. The nominal crystal orientation may depend on the specific requirements of the component 42 to be cast. Therefore, by choosing an appropriate amount of rotational offset, it may be possible to reduce or substantially eliminate the difference between the actual crystal orientation of the metal seed 41 and the required nominal crystal orientation.

Furthermore, as noted above, the crystal orientation of a cast component may differ somewhat from that of the metal seed 41 due to various sources of error. Therefore, any orientational difference in the metal seed 41 from the nominal crystal orientation may add to the crystal orientational difference between the cast component and the nominal crystal orientation, leading to a high scrap level of cast components. Therefore, by reducing or substantially eliminating the difference between the actual crystal orientation of the metal seed 41 and the required nominal crystal orientation, the scrap level of cast components may also be reduced.

With reference to Figures 7 and 17, the method 100 may comprise measuring 1001 the crystal orientation of the metal seed 41 to be used in the single crystal casting.

The crystal orientation of the metal seed 41 may be measured using any known means. For example X-ray diffractography may be used. The crystal orientation is represented by the crystal coordinate system 73 in Figure 7. As shown, by way of example, the crystal coordinate system 73 is not in alignment with the nominal crystal orientation 72. For the purpose of illustration, the nominal crystal orientation 72 is in alignment with the bulk geometry of the metal seed 41, though in practice, the nominal crystal orientation 72 may be in any arbitrary orientation as required by the component to be cast. For ease of explanation, Figure 7 also shows the world coordinate system 71, which will remain invariable throughout the method. After the crystal orientation 73 of the metal seed 41 has been measured, the measured crystal orientation 73 may be compared to the nominal crystal orientation 72 (1002).

The difference between the measured crystal orientation 73 and the nominal crystal orientation 72 may be calculated and described by any known means. For example, the difference may be represented by Euler angles. In other words, the difference may be represented by three angular measurements. Alternatively, the difference between the measured crystal orientation 73 and the nominal crystal orientation 72 may be more simply described in two dimensions so that only two angular measurements are used, although a loss of information may result. For further simplicity, the difference may even be measured using one angular measurement only. It is understood that the skilled person in the art would choose a suitable way of representing the orientational difference depending on the circumstances.

After comparing 1002 the measured crystal orientation 73 to the nominal crystal orientation 72, orientation data based on the comparison indicative of a target seed orientation 72' in which the crystal orientation of the metal seed would align with the nominal crystal orientation 72 may be calculated 1003. For example a rotation offset may calculated, i.e. a rotation required to re-orientate the metal seed 41 to a target seed orientation 72'. The target seed orientation 72' may be calculated such that the orientational difference is reduced. In other words, in the target seed orientation 72', the difference between the rotational offset crystal orientation 73' and the nominal crystal orientation 72 may be smaller than the difference between the original crystal orientation 73 and the nominal crystal orientation 72.

By applying the calculated orientation data, a better alignment of the crystal orientation of the metal seed 41 with the nominal crystal orientation 72 may be achieved. Therefore, whereas, in known methods, metal seeds 41 that do not meet the crystal orientation tolerance are scrapped, in the method herein disclosed, the deviation in crystal orientation may be compensated so as to reduce the deviation to meet tolerance requirements. As a result, the scrap level of metal seeds 41 may be reduced. As noted above, the scrap level of cast components may also be reduced.

One way of applying the calculated orientation data is taking it into account when making a fugitive material assembly 80. This allows the orientation of a bespoke seed holder 432 relative to the component mould 43 to be controlled to mitigate for any misalignment of the crystal orientation of the metal seed 41.

Figure 8 is a schematic view of a fugitive material assembly 80 that may be made in accordance with the present invention. As shown in Figure 8, optionally the fugitive material assembly 80 comprises a fugitive material component shape 81. The component shape 81 is made to be in the shape of the component 42 that is to be cast. The fugitive material assembly 80 may further comprise a spiral 83 corresponding to the pigtail 433 as shown in Figure 8. Optionally the fugitive material assembly 80 comprises a fugitive material seed 82. The fugitive material assembly 80 is made comprising the component shape 81 and the fugitive material seed 82.

Optionally, the orientation of the fugitive material seed 82 relative of the components shape 81 is controlled based on the calculated orientation data.

For example, in an embodiment the method for preparing for making a single crystal casting comprises controlling a controllable fixture 90 holding the fugitive material seed 82 so as to orientate the fugitive material seed 82 in the target seed orientation 72'. As shown in Figure 8 this may lead to the fugitive material seed 82 having an orientation offset relative to the nominal crystal orientation 72 (which may be straight up and down in the view shown in Figure 8). Optionally, the orientation of the fugitive material seed 82 relative to the component shape 81 is controlled by the controllable fixture 90. The step of controlling the controllable fixture 90 based on the orientation data is given the reference numeral 1004 in Figure 17.

Optionally, the method comprises coating the fugitive material assembly 80 to form a component mould 43 (defining the component cavity 431) and a seed holder (defining the seed cavity 432). The orientation of the seed holder relative to the component mould is determined by controlling of the controllable fixture 90.

Figure 9 is a schematic diagram of a fugitive material assembly 80 with the controllable fixture 90. Optionally, an assembly housing 70 is provided to house the fugitive material assembly 80. The assembly housing 70 is configured to support the fugitive material assembly 80. As shown in Figure 9 the controllable fixture 90 holds the fugitive material seed 82. The controllable fixture 90 is controlled so as to accurately control the orientation of the fugitive material seed 82 relative to the components shape 81.

Figure 10 is a schematic diagram of the controllable fixture 90 shown in Figure 9.

Optionally, the controllable fixture 90 is configured to control the orientation of the fugitive material seed 82 is three dimensions. The controllable fixture 90 may comprise a rotation mechanism 91 configured to rotate fugitive material seed 82 about is longitudinal axis. For example, the rotation mechanism 91 may comprise a seed gear 92 fixably attached to the fugitive material seed 82. The rotation mechanism 91 may further comprise a controller gear 93 that engages with the seed gear 92. The controller gear 93 may be situated so as to control the rotation of the fugitive material seed 82 about its longitudinal axis.

As shown in Figure 10, optionally the rotation mechanism 91 is mounted on a carriage 96. The carriage 96 is configured to support the fugitive material seed 82 and the rotation mechanism 91. The carriage 96 comprises wheel gears 95. The wheel gears 95 are configured to engage with and run along a first curved track 94. The movement of the carriage 96 along the first curved track 94 can be controlled so as to control the orientation of the fugitive material seed 82 in a second degree of freedom On addition to the rotation about its longitudinal axis).

Figure 11 is a close up view of part of the controllable fixture 90 shown in Figure 10.

As shown in Figure 11, optionally the carriage 96 comprises two wheel gears 95 either side of a connector gear 98. The connector gear 98 is provided so that the two wheel gears 95 rotate in the same rotational direction. The left hand side of Figure 11 shows a close up view of how the wheel gears 95 may be actuated. A controller gear 97 is mounted via a mounting 99 to the carriage 96. The controller gear 97 can be manipulated so as to rotate the wheel gears 95. The controller gear 97 may be fixably attached to the wheel gear 95.

Figure 12 shows another part of the controllable fixture 90. As shown in Figure 12 (and also in Figure 9), optionally the controllable fixture 90 comprises a second curved track 74. The second curved track 74 is for providing control of the orientation of the fugitive material seed 82 in a third degree of freedom. The second curved track 74 runs in a different orientation from the first curved track 94.

Optionally, the second curved track 74 is substantially orthogonal to the first curved track 94. As shown in Figure 12, optionally the first curved track 94 may be mounted on further wheel gears 75 (connected by a server connector gear 78) so as to run along the second curved track 74. The server connector gear 78 is the user input gear. The user may provide input by turning a dial connected to the server connector gear 78. Optionally, the user may provide input through a physical operation on a mechanical arrangement or through an electronic dial.

Figure 13 is a schematic diagram of an alternative to the arrangement shown in Figure 9. Figure 13 shows an alternative controllable fixture 60 to the one shown in Figures 9 to 12. As shown in Figure 13, optionally the assembly housing 70 may comprise a component support section for supporting the component shape 81 and a plurality of struts for holding the component support section relative to a base. The controllable fixture 60 is positioned below the component shape 81 and the spiral 83.

Figure 14 shows a close up view of the controllable fixture 60 shown in Figure 13.

As shown in Figure 14, optionally the controllable fixture 60 comprises a cavity 61 for holding the fugitive material seed. The controllable fixture 60 may be called a seed locator holder. Optionally, the controllable fixture 60 is configured to control positioning of the seed in three degrees of freedom.

As shown in Figure 14, optionally the controllable fixture 60 comprises an adjustable pin screw 62. The adjustable pin screw 62 is configured to move radially towards the centre of the cavity 61 or further away from the centre of the cavity 61. The pin screw 62 is configured to engage with the seed so as to control the positioning of the seed within the cavity 61.

As shown in Figure 14, optionally the controllable fixture 60 comprises one or more actuator elements 63. The actuator elements 63 are configured to engage with the seed so as to control the repositioning of the seed in the cavity 61. Optionally one or more piezoelectric (e.g. piezoceramic) actuators are configured to control the actuator elements 63. Alternatively, the actuator elements 63 may be replaced by fixed plugs. The orientation of the seed in the cavity 61 relative to the component shape 81 may be controlled by other actuators external to the cavity 61. For 113 example, as shown in Figure 13, optionally a plurality of actuators 131 (e.g. pistons) extend between a base platform 132 and the assembly housing 70. The actuators 131 control the orientation of the assembly housing 70, thereby controlling the orientation of the seed relative to the component shape 81.

In Figures 9 to 14, the controllable fixture 90, 60 holds the fugitive material seed 82.

Alternatively, the controllable fixture 90, 60 may be configured to hold, and control the orientation of, the component shape 81. This may be particularly appropriate for the production of smaller components.

According to a further alternative, the controllable fixture 90, 60 may hold both the fugitive material seed 82 and the component shape 81 relative to each other. This allows the fugitive material seed 82 and the component shape 81 to be initially formed with a standard orientation relative to each other. The controllable fixture 90, 60 may then adjust the orientation of the fugitive material seed 82 and the component shape 81 relative to each other.

Optionally, the controllable fixture 90, 60 comprises a heater. The heater is configured to heat a region where the fugitive material seed 82 and the component shape 81 join each other. This reduces the possibility of the joint breaking while the orientation is being adjusted.

A further alternative controllable fixture is described with reference to Figure 20. Figure 20 shows shims 201 being used to control the orientation of the fugitive material seed 82 relative to the component shape 81 and spiral 83. As shown in Figure 20, optionally the controllable fixture comprises a component plate 202. The component plate 202 is fixed relative to the component shape 81 and spiral 83. As shown in Figure 20, optionally the component plate 202 is part of the assembly housing 70. Optionally, an arrangement using shims can be applied to any form of fugitive material assembly built in the manufacturing process.

As shown in Figure 20, optionally the controllable fixture comprises a seed plate 203. The seed plate 203 has a fixed orientation relative to the fugitive material seed 82. The orientation of the fugitive material seed 82 relative to the component shape 81 depends on the angle 6 between the component plate 202 and the seed plate 203. The angle 8 between the component plate 202 and the seed plate 203 is adjustable.

As shown in Figure 20, optionally one or more shims 201 are positioned between the 10 component plate 202 and the seed plate 203. The thickness and/or number of shims 201 can be selected so as to control the angle 8 between the component plate 202 and the seed plate 203.

The arrangement shown in Figure 20 can be combined with the arrangements shown in Figures 9 or 13, for example. Different ways of controlling the orientation of the fugitive material seed 82 can be used for different degrees of freedom.

Optionally, the controllable fixture comprises a hybrid arrangement of using shims 201 to achieve an angle orientation on one axis and a gear/curved slide to achieve a different angle.

A further alternative controllable fixture 90 is described with reference to Figure 21.

As shown in Figure 21, optionally the controllable fixture 90 comprises a moving platform 212 configured to move relative to a base platform 211. The fugitive material seed 82 is fixed relative to the moving platform 212. For example, a mounting 214 may be provided for mounting the fugitive material seed 82 to the moving platform 212.

As shown in Figure 21, the moving platform is connected to the base platform 213 via a plurality of SMA (shape memory alloy) wires 213. Optionally, at least three SMA wires 213 are provided. The SMA wires are spaced around the circumference of the moving platform 212.

The SMA wires 213 form SMA actuators for controlling the orientation of the moving platform 212 relative to the base platform 211. The orientation of the fugitive material seed 82 relative to the component shape 81 depends on the orientation of the moving platform 212. The component shape 81 is not fixed to the moving platform 212. The SMA wires 213 can be independently controlled (e.g. contracted by heating) so as to control the force tensioning sides of the moving platform 212 towards the base platform 211. Optionally, the centre of the moving platform 212 is connected to a strut that keeps the centre of the moving platform 212 a fixed distance above the base platform 211.

As shown in Figure 21, optionally the controllable fixture 90 comprises a base servo 215. The base servo 215 is configured to control rotation of the base platform 211 about a vertical axis. Optionally, a shaft 216 connects the base servo 215 to the base platform 211. This provides a further degree of freedom for the controlled orientation of the fugitive material seed 82.

In an alternative arrangement, the SMA wires 213 can be replaced by pistons or other types of actuator that may be mechanically or electronically powered.

An alternative method for preparing for making a single crystal casting is described below, with particular reference to Figures 15 and 18. As can be seen from a comparison between Figures 17 and 18, the first 3 steps 1001 to 1003 of the alternative method 110 are the same as those for the method 100 described above and shown in Figure 17. That is, the steps of measuring 1001, comparing 1002 and calculating 1003 are the same as described above. As an alternative to controlling a controllable fixture 90, the method 110 may comprise the step of making 1005 a fugitive material seed 82 based on the calculated orientation data. As shown in Figure 15, optionally the fugitive material seed 82 comprises a base 55 configured to hold the fugitive material seed 82 in the target orientation. As shown in Figure 15, optionally the fugitive material seed 82 comprises a longitudinal part 66 that is joined to the based 65. The orientation of the longitudinal part 66 is controlled by the base being placed on a flat surface.

The calculated orientation data can be used to determine the appropriate shape of the fugitive material seed 82 so that the longitudinal part 66 is orientated correctly when base 65 is positioned on a flat surface.

Optionally, a fugitive material assembly 80 comprising a component shape 81 and the fugitive material seed 82 is made. The orientation of the fugitive material seed 82 (and in particular the longitudinal part 66) relative to the component shape 81 is controlled by the shape of the fugitive material seed 82.

The fugitive material assembly 80 may then be coated to form the component mould 43 and the seed holder 432. The orientation of the seed holder 432 relative to the component mould 43 is determined by the shape of the fugitive material seed 82.

The shape of the fugitive material seed 82 that is made can be used to compensate for misalignment between the measured crystal orientation of the metal seed 41 and the nominal crystal orientation for the metal seed 41. When the metal seed 41 is positioned into the seed holder 432, the crystal orientation of the metal seed 41 may more closely align with the nominal crystal orientation.

There are different ways for making the fugitive material seed 82. In an embodiment, the fugitive material seed 82 is 3-D printed based on the orientation data. Any method of additive layer manufacturing may be used to make the fugitive material seed 82. The material used for making the fugitive material seed 82 is not particularly limited.

As an alternative to 3-D printing, optionally the method comprises adapting an adaptable die for the fugitive material seed 82 based on the orientation data. The adapted die may be used to cast the fugitive material seed 82.

Optionally, the controllable fixture 60, 90 comprises a controller configured to control the actuators of the controllable fixture so as to orient the fugitive material seed 82 in a target seed orientation based on the calculated orientation data.

For example, the adaptable die may comprise a plurality of actuators configured to adjust the shape of a fugitive material seed 82 cast by the adaptable die. Optionally, the adaptable die comprises a controller configured to control the actuators so as to shape the fugitive material seed 82 based on the calculated orientation data.

As described above, a seed holder 432 can be formed to hold a metal seed 41 in a specific orientation by controlling the shape and/or orientation of a fugitive material seed 82. Alternative methods for forming the seed holder 432 are described below.

Optionally, the orientation data is used to provide a support for a seed holder 432 configured such that the metal seed is held in the target orientation. For example, optionally a support for a standard seed holder may be formed based on the orientation data to have location features so as to position the standard seed holder in a particular orientation relative to the mould for the component. The location features help to maintain the orientation of the seed holder 432. The location features may be, for example, beads or other protrusions that abut the seed holder 432. The location features may be made of a plastic or ceramic, for example.

Optionally, the support for the seed holder is produced by 3D printing the location features.

Alternatively, a specific seed holder 432 may be 3D printed based on the orientation data. In other words, the whole of the seed holder 432 may be 3D printed from scratch, rather than modifying an existing standard seed holder. Alternatively, the combination of the seed holder 432 and the component mould 43 (and optionally also the spiral) may be 3D printed together based on the orientation data.

The method of the present invention allows a seed holder 432 to have a specific orientation relative to the component mould 43. The orientation is based on measurements of a specific metal seed 41. Hence, a specific seed holder 432 can be made for each measured metal seed 41. It is desirable for the correct metal seed 41 to be inserted into the seed holder 432 that was made for that specific metal seed 41.

Optionally, the method comprises providing that the seed holder 432 has an identifier for identifying the metal seed. For example, the seed holder 432 may be provided with an identifying number, a barcode or a OR code. As a further alternative, the seed holder 432 may be provided with a RFID tag to identify the metal seed 41 that is to be placed in the seed holder 432. The identifier could be provided by printing it (or its negative) into, for example, the base 65 of the fugitive material seed 62.

Optionally, the method comprises providing the metal seed 41 with an identifier corresponding to the identifier of the seed holder 432. Optionally, the method comprises storing the measured crystal orientation of the metal seed 41 and/or the calculated orientation data in a database in correspondence identifying the metal seed 41. This allows the orientation data of the metal seed 41 to be known after the measurements have been performed.

It can be ensured that each metal seed 41 is positioned into the correct seed holder 432. This allows a plurality of casting operations to be performed at the same time, without the danger of mixing up the seeds 41. For example, a rotary dial table could be provided with a plurality of (e.g. eight) stations, each station for casting a component. Each station could perform the casting process simultaneously, or in a staggered fashion. For example, in one station, the metal seed 41 may be inserted into the seed holder 432. In another station in the same time, molten metal may be inserted into the component mould 43. In a further station at the same time the inserted metal may be allowed to solidify such that its crystal orientation makings that of the metal seed 41.

A casting process 120 according to the present invention will be described below with reference to Figure 19. In step 1201 the fugitive material assembly 80 is made.

As described before, this may involve controlling a controllable fixture 90, 60 so as to orient the fugitive material seed 82 in the target seed orientation. Alternatively, this may involve making a fugitive material seed 82 based on the orientation data, wherein the fugitive material seed 82 comprises a base 65 configured to hold the fugitive material seed 82 in the target orientation. It is expected that this process can be adopted in a wide range of foundries. An embodiment of the invention is expected to allow a wider range of input seed orientations.

In step 1202, the fugitive material assembly 80 is coated. The fugitive material assembly 80 is shelled, thereby creating the component mould 43.

In step 1203, each metal seed 41 is posted in the correct cavity i.e. the seed holder 432. By inserting the correct metal seed 41 in the correct cavity, the crystal structure is in (or nearer) the nominal direction with respect to the casting cavity. The cavity has been creating by shelling a bespoke particularly aligned fugitive material seed 82 as described above.

In step 1204, molten metal is inserted into the component mould 43, and the inserted metal is allowed to solidify such that its crystal orientation matches that of the metal seed 41. Optionally, the casting is performed with a tightly controlled process to transfer the crystal orientation from the seed 41 to the component 42. Optionally, grain distortion is minimized along the component 42 (e.g. a metal bar for producing new metal seeds 41'). It may be that the crystal orientation of the inserted metal does not exactly match that of the metal seed 41. It may be expected that there may be a transfer error of up to 3 degrees or more depending on the shape of the part.

The error produced from the imperfect crystal orientation is reduced or eliminated according to the present invention.

In step 1205, the crystal orientation of the component 42 is measured The orientation may be measured to within 1 to 2 degrees per angle.

In step 1206, acceptable seed bars (from the metal bar) are cut to form one or a plurality of individual seeds 41' as shown in Figure 5. Optionally, the individual seeds 41' maybe measured and sentenced (i.e. a decision made as to whether the seed is to be used or scrapped). However it may not be necessary to measure individual seeds 41'. If the seed is not measured individually, then the measurements for the seed bar may be used instead of measuring and sentencing individual seeds. This helps to reduce costs of the casting process 120.

In step 1207, alignment data unique to each seed 41' is recorded. This data may be recorded in a central database for use later in the process 120, or for use in another process. The alignment data may be recorded in, for example, a 2-D barcode, an RFID tag, a dot matrix, a QR code, an alphanumeric code or by any other means.

Optionally, each seed 41' is marked with the code or an RF ID tag so that the physical seed is linked to its alignment data.

In step 1208, the seeds 41' are sentenced. For example, the tightest (i.e. with the crystal orientation that most closely matches the nominal crystal orientation) may be used to derive the next generation of seed bars. The next tightest seeds 41' may be used to grow components of the seed bars, for example, plates or vanes. The remainder may be scrapped. For example, it may be decided that seeds 41' that have a misalignment of more than, for example, five degrees may be scrapped. The invention is expected to reduce the scrap levels. The tolerance for seeds to be misaligned from the nominal crystal orientation may be greater for the present invention because the casting process 120 adapts (i.e. compensates) for crystal variation.

In step 1209, a metal seed 41' is used to make a component of the van another seed bar. For example, the metal seed 41' may be used to make a blade for a blisk or a vane for a guide vane assembly. This process may involve the creation of a bespoke fugitive material assembly 80 as described above so as to compensate for any misalignment in crystal orientation of the seed 41' that is being used.

Figure 16 is a schematic diagram of a scanner assembly for automatically reading codes identifying the metal seed 41 and the seed holder 432. As shown in Figure 16, the scanner assembly may comprise a seed capsule 64. The seed capsule 64 is configured to house the metal seed 41. Optionally, the metal seed 41 is provided with a OR code (or a different type of code or tag identifying the metal seed 41).

Optionally, the QR code 68 may be laser etched onto the metal seed 41. As shown in Figure 16 the OR code may be later etched onto a longitudinal end of the metal seed 41.

As shown in Figure 16, optionally the scanner assembly comprises one or more code scanners 67. Figure 16 shows a metal seed QR code scanner 67 attached to the seed capsule 64. The metal OR scanner 67 is for scanning the OR code 68 of the metal seed 41. Optionally, a further OR code scanner is provided on top of the seed capsule 64 facing away from the metal seed 41. This OR code scanner 67 on top of the seed capsule 64 is configured to scan the OR code of the seed holder 432.

In particular, the OR code may be imprinted as a ceramic pattern in the seed holder 432.

Optionally, as shown in Figure 16 the seed capsule 64 comprises a seed release flap 69. The seed release flap 69 is configured to open so as to allow the metal seed 41 to move out from the seed capsule 64. Optionally, a controller is configured to control the seed release flap 69 to release the metal seed 41 when matching OR codes are scanned by the code scanners 67. Hence, it is possible to automatically match the metal seed 41 to the appropriate seed holder 432.

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. For example, instead of investment casting, die casting or sand casting may be used with the present disclosure. 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.

Claims

CLAIMS1 A method for preparing for making a single crystal casting, the method comprising the steps of: measuring the crystal orientation of a metal seed (41) for single crystal casting; comparing the measured crystal orientation to a nominal crystal orientation for the metal seed; and calculating orientation data based on the comparison indicative of a target seed orientation in which the crystal orientation of the metal seed would align with the nominal crystal orientation.
2 The method of claim 1, further comprising: controlling a controllable fixture (90; 60) holding a fugitive material seed (82) so as to orient the fugitive material seed in the target seed orientation based on the orientation data.
3 The method of claim 2, further comprising: making a fugitive material assembly (80) comprising a component shape (81) and the fugitive material seed, wherein the orientation of the fugitive material seed relative to the component shape is controlled by the controllable fixture.
4 The method of claim 3, further comprising: coating the fugitive material assembly to form a component mould (431) and a seed holder (432), such that the orientation of the seed holder relative to the component mould is determined by the controlling of the controllable fixture.
5. The method of claim 1, further comprising: making a fugitive material seed (82) based on the orientation data, wherein the fugitive material seed comprises a base (65) configured to hold the fugitive material seed in the target orientation.
6. The method of claim 5, further comprising: 3D printing the fugitive material seed based on the orientation data.
7 The method of claim 5, further comprising: adapting an adaptable die for the fugitive material seed based on the orientation data; and using the adapted die to form the fugitive material seed.
8 The method of any one of claims 5 to 7, further comprising: making a fugitive material assembly (80) comprising a component shape (82) and the fugitive material seed, wherein the orientation of the fugitive material seed relative to the component shape is at least partly controlled by the shape of the fugitive material seed.
9 The method of claim 8, further comprising: coating the fugitive material assembly to form a component mould (431) and a seed holder (432), wherein the orientation of the seed holder relative to the component mould is at least partly determined by the shape of the fugitive material seed.
10. The method of claim 1, further comprising: using the orientation data to provide a support to position a seed holder (432) configured to hold the metal seed in the target orientation relative to the component mould.
11.The method of claim 10, further comprising: producing the support for the seed holder based on the orientation data to have location features so as to hold the seed holder in the target orientation.
12.The method of claim 11, further comprising: producing the support for the seed holder by 3D printing the location features.
13. The method of claim 1, further comprising: 3D printing a seed holder (432) configured to hold the metal seed in the target orientation based on the orientation data.
14.The method of claim 13, further comprising: 3D printing the seed holder (432) fixedly together with the component mould based on the orientation data.
15. The method of claim 4 or any one of claims 9 to 14, further comprising: providing that the seed holder has an identifier for identifying the metal seed
16. The method of claim 15, wherein the identifier is a barcode, a QR code, an RFID tag or an alphanumeric code.
17.The method of claim 15 or 16, further comprising: providing the metal seed with an identifier corresponding to the identifier of the seed holder.
18. The method of claim 4 or any one of claims 9 to 17, further comprising: inserting the metal seed into the seed holder; inserting molten metal into the component mould; and allowing the inserted metal to solidify such that its crystal orientation matches that of the metal seed.
19. The method of any preceding claim, further comprising: storing the measured crystal orientation of the metal seed and/or the calculated orientation data in a database in correspondence with information identifying the metal seed.
20.A controllable fixture (90; 60) for holding one or both of a fugitive material seed (82) and a component shape (81) relative to each other, wherein the controllable fixture comprises: a plurality of actuators (63) configured to adjust the orientation of one or both of a fugitive material seed and/or a component shape held by the controllable fixture; and a controller configured to control the actuators so as to orient the fugitive material seed in a target seed orientation relative to the component shape based on calculated orientation data.
21. The controllable fixture of claim 20, configured to hold and control the orientation of the fugitive material seed.
22. The controllable fixture of claim 20, configured to hold and control the orientation of the component shape.
23. The controllable fixture of claim 20, configured to hold both the fugitive material seed and the component shape and to control the orientation of the fugitive material seed relative to the component shape.
24. The controllable fixture of claim 23, further comprising a heater configured to heat a region where the fugitive material seed joins to the component shape.
25. An adaptable die for a fugitive material seed (82), wherein the adaptable die comprises: a plurality of actuators configured to adjust the shape of a fugitive material seed formed by the adaptable die; and a controller configured to control the actuators so as to shape the fugitive material seed based on calculated orientation data.