METHOD AND APPARATUS FOR SIMULTANEOUS HOT FORMATION OF HOLLOW COMPONENT

Abstract

A method of hot forming a pair of hollow components. The method involves heating a die stack comprising a first die, an intermediate die and a second die, in which the first die and the intermediate die form a first die set, and the intermediate die and the second die form a second die set. The die stack is opened and loaded with a first component preform in the first space and a second component preform in the second space. Once loaded, the die stack is closed and a pressurised fluid is then provided via a first conduit to an internal cavity of the first component preform, while a pressurised fluid is also provided via a second conduit to an internal cavity of the second component preform. The die stack is opened and the first component and the second component removed from the respective first space and the second space.

Claims

1. A method of hot forming a pair of hollow components, the method comprising: heating a die stack comprising a first die, an intermediate die and a second die, wherein the first die and the intermediate die form a first die set, and the intermediate die and the second die form a second die set; opening the die stack, creating a first space between the first die and the intermediate die of the first die set, and a second space between the intermediate die and the second die of the second die set; loading a first component preform into the first space and a second component preform into the second space; closing the die stack to hold the first component preform in the first die set, and the second component preform in the second die set; providing a pressurised fluid from a first finite reservoir via a first conduit to an internal cavity of the first component preform, and a pressurised fluid from a second finite reservoir via a second conduit to an internal cavity of the second component preform, thereby deforming the first component preform and the second component preform; determining that both a first pressure in the internal cavity of the first component preform and a second pressure in the internal cavity of the second component preform have fallen below a first threshold; re-pressurising the internal cavity of the first component preform and the internal cavity of the second component preform based at least in part on a common pressure: time schedule, thereby respectively forming the first component and second component of the pair of components; opening the die stack; and removing the first component from the first space and the second component from the second space.

2. The method of claim 1, wherein the first component preform and the second component preform are heated in the die stack to a conditioning temperature for a conditioning period before their respective internal cavities are provided with the pressurised fluid.

3. The method of claim 2, wherein the conditioning period has a variable duration.

4. The method of claim 3, wherein completion of the conditioning period is determined by a temperature of both the first component preform and a temperature of the second component preform exceeding a temperature threshold.

5. The method of claim 1, wherein the internal cavity of the first component preform and the internal cavity of the second preform component are purged of air prior to loading into the first space and second space respectively.

6. The method of claim 1, wherein an orientation of the first component preform in the first die set is equal to the orientation of the second component preform.

7. The method of claim 1, wherein formation of the first component preform and formation of the second component preform comprises a diffusion bonding process.

8. The method of claim 1, wherein the pressurised fluid is an inert gas.

9. The method of claim 1, wherein re-pressurisation of the first component preform is controlled independently from re-pressurisation of the second component preform.

10. The method of claim 1, wherein re-pressurisation of one of the first component preform and the second component preform is controlled based upon re-pressurisation of the other of the first component preform and the second component preform.

11. The method of claim 1, wherein the hot forming process is a super-plastic forming process.

12. The method of claim 1, wherein the component is a gas turbine engine fan blade.

13. A hot forming machine for hollow components, the hot forming machine comprising: a first platen; a second platen; an actuation mechanism for a die stack in which the die stack has a first die set which comprises a first die and an intermediate die, and a second die set which comprises the intermediate die and a second die, and the die stack is holdable between the first platen and the second platen; a heat source for heating the first die set and the second die set; and a pressurisation device comprising a first conduit connectable to a first component preform held in the first die set, a second conduit connectable to a second component preform held in the second die set, and at least one pressure sensor for sensing an internal cavity pressure of the first component preform and an internal cavity pressure of the second component preform; wherein the pressurisation device is switchable between a pressurisation mode and a re-pressurisation mode; and: in the pressurisation mode, the pressurisation device couples the first component preform to a first finite pressure reservoir and the second component preform to a second finite pressure reservoir; in the re-pressurisation mode, the first component preform and the second component preform are re-pressurised based upon a common pressure: time schedule; and switching from the pressurisation mode to the re-pressurisation mode occurs in dependence upon the sensed pressure in the first hollow component and sensed pressure in the second hollow component both falling below a first threshold.

14. The hot forming machine of claim 13, further comprising at least one temperature sensor, and the pressurisation device additionally comprising an isolation mode, wherein the pressurisation device is switchable from the isolation mode to the pressurisation mode in dependence upon both a sensed temperature of the first hollow component preform and a sensed temperature of the second hollow component preform exceeding a temperature threshold.

15. The hot forming machine of claim 13, wherein the pressurisation device further comprises a third conduit and a fourth conduit, wherein the third conduit is connectable to a third component preform and the fourth conduit is connectable to a fourth component preform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments will now be described by way of example only with reference to the accompanying drawings, in which:

[0020] FIG. 1 shows a schematic representation of a gas turbine engine;

[0021] FIG. 2 shows a method for simultaneous hot-forming of hollow components;

[0022] FIG. 3 shows a hot-forming apparatus comprising a die stack, in a closed configuration;

[0023] FIG. 4 shows the hot-forming apparatus of FIG. 3 in an open configuration;

[0024] FIG. 5 shows a first example actuation mechanism for a die stack in a closed configuration;

[0025] FIG. 6 shows a first example actuation mechanism for a die stack in an open configuration;

[0026] FIG. 7 shows a second example actuation mechanism for a die stack in a closed configuration; and

[0027] FIG. 8 shows a second example actuation mechanism for a die stack in an open configuration.

DETAILED DESCRIPTION

[0028] With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, an intermediate pressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20.

[0029] The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.

[0030] 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 combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, each by suitable interconnecting shaft.

[0031] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

[0032] The fan 13 of gas turbine engine 10 comprises a plurality of fan blades. The fan blades may be metallic fan blades, comprising, for example, titanium. The metallic fan blades may be hollow for engine weight reduction purposes.

[0033] Known methods of producing hollow metallic fan blades involve manufacturing individual blades, by for example a hot forming process such as super-plastic forming. However, the individual formation of blades is both time consuming and energy intensive.

[0034] Simultaneously forming multiple fan blades in a common apparatus would be beneficial in reducing both manufacturing time and energy consumed.

[0035] FIG. 2 illustrates a method 100 of forming a pair of hollow components in a common hot forming apparatus, for example a pair of metallic fan blades, in a hot forming apparatus. It will be explained later how this method of forming a pair of hollow components may be modified (for example, via a change of die stack design) to simultaneously form three hollow components etc.

[0036] Further details of the hot forming apparatus and the component preforms etc are shown in FIG. 3 onwards.

[0037] The method 100 takes as input a pair of component preforms (i.e., a first component preform 300 and a second component preform 300). Each component preform 300 comprises a first sheet 300a, and a second sheet 300b, the first sheet 300a and second sheet 300b being joined together by a joining method at a joining region proximal to their edges, to form a pocket 300c. The periphery of pocket 300c is therefore bounded by the joining region.

[0038] Diffusion bonding is a suitable joining method to join the first sheet 300a and the second sheet 300b proximal to their edges at a joining region.

[0039] When joined by the joining method, facing surfaces of first sheet 300a and second sheet 300b may have substantially the same shape, and hence, may be contacting each other. When sheets 300a 300 b are joined, a volume of pocket 300c may therefore be minimal.

[0040] Each pocket 300c, i.e., the pocket of the first component preform 300, and the pocket of the second component preform 300 comprises an opening (i.e., a hole in either the first sheet 300a or the second sheet 300b) such that the pocket 300c is fluidically communicable with a pressure source.

[0041] Sheets 300a, 300b may be formed from a metallic, ductile material such as titanium or a titanium alloy.

[0042] As is disclosed in further detail below, application of a pressurised fluid from a pressure source to pocket 300c via the opening expands the pocket 300c, increasing its volume.

[0043] By controlling the shape adopted by the pocket 300c as it expands, it is therefore possible to form a hollow component to a required shape. The required shape may be produced by inflating pocket 300c whilst the component preform is held within a pair of dies.

[0044] In this case, inflation of pocket 300c caused the exterior surface of the component preform to adopt the surface profile of the pair of dies, and in so doing, the component preform is formed to become a hollow component.

[0045] Forming the hollow component may be improved by increasing the ductility of the component preform material before inflation. This may be achieved by heating the component preform material before inflation of pocket 300c. The forming method may therefore also be described as a hot forming method.

[0046] If the component preform is heated to a sufficient temperature such that there is a significant increase in ductility, and the application of the pressure to pocket 300c is controlled such that inflation of pocket occurs slowly (for example, over 10's of minutes), then significant strain may occur within the inflating component preform without damaging (for example, tearing) the material. In this case, the hot forming method may also be described as a super-plastic forming method.

[0047] Sufficient heating of the component preform is therefore important. Heating may be by any suitable means.

[0048] Typical times, temperature profiles and/or minimum temperature thresholds for hot forming and in particular, super plastic forming are known in the art and are therefore not discussed further within this document.

[0049] In method 100, in step 110 a die stack is heated, with heat transferred to the component preforms 300.

[0050] As shown in FIGS. 3 to 8, the die stack 200 comprises a first die 210, an intermediate die 220 and a second die 230, stacked one above the other. The first die 210 and the intermediate die 220 form a first die set. The intermediate die 220 and the second die 230 form a second die set. The first die set forms a first hollow component, while the second dies set forms a second hollow component simultaneously with the first hollow component.

[0051] Whereas the first die 210 and the second die 230 each form a single surface of the respective first hollow component and the second hollow component, the intermediate die comprises opposing surfaces, each surface of which forms a single surface of the first hollow component and the second hollow component.

[0052] The die stack is located between a pair of opposing platens 240, 250 of a hot forming apparatus. Each platen (first platen 240 and second platen 250) may be heated.

[0053] The first platen may also be referred to as an upper platen, whereas the second platen may also be referred to as a lower platen.

[0054] In the example shown in FIG. 3, the first die 210 is mechanically connected to the first platen 240 and the second die 230 is mechanically connected to the second platen 250. As is subsequently disclosed, an actuation mechanism connects the intermediate die 220 to at least one of the first die 210 and/or the second die 230.

[0055] Thus, moving the second platen away 250 from the first platen 240 opens the die stack 200, while moving the second platen 250 towards the first platen 240 closes the die stack 200.

[0056] Once heated, in step 120 the die stack 200 is opened by moving the intermediate die 220 from the first die 210, and the second die 230 from the intermediate die 220. This creates a first space 215 between the first die 210 and the intermediate die 220 of the first die set, and a second space 225 between the intermediate die 220 and the second die 230 of the second die set.

[0057] With the die stack open, in step 130 the first component preform 300 is loaded into the first space 215, while the second component preform 300 is loaded into the second space 225 (see FIG. 4).

[0058] Loading may be by any suitable means. As the die stack has been heated prior to opening, mechanised loading may be desirable, to protect a human operator of the hot forming machine.

[0059] The first and second component preform may be loaded simultaneously or sequentially by the mechanised loader.

[0060] Once the first component preform and the second component preform have been loaded into their respective spaces, in step 140 the die stack is closed. Closing the die stack holds the first component preform in the first die set and the second component preform in the second die set.

[0061] When the die stack is closed, such that the first component preform is held in the first die and the second component preform is held in the second die, a compressive force is applied between the first platen and the second platen to hold the component preforms in place. Increasing compressive loading between the first platen 240 and the second platen 250 increases the respective compressive forces which hold the first component preform 300 in the first die set and hold the second component preform in the second die set.

[0062] The degree of compressive loading between the first platen 240 and the second platen 250 may vary over the duration of the method 100. For example, the degree of compressive loading may vary in dependence upon a degree of internal pressurisation of pocket 300c of the first component preform 300 and the second component preform 300.

[0063] Once the preforms are held in the die stack, a hot separation operation is performed in step 150.

[0064] The purpose of the hot separation operation is to create an initial inflation of the pockets 300c of the first component preform 300 and the second component preform 300, such that a further subsequent and more prolonged inflation of the pockets may be performed. The separation operation is performed hot in the sense that the first component preform 300 and the second component preform are heated to a temperature above atmospheric temperature such that the material of the first component preform 300 and the second component preform 300 has increased ductility and does not tear or rip during the initial inflation process.

[0065] As the first component preform and the second component preform are within the heated die stack 200, the first component preform 300 and the second component preform 300 are also heated and become ductile.

[0066] To ensure that the component preforms 300 are sufficiently ductile prior to hot separation the first component preform and the second component preform may be heated in the die stack to a conditioning temperature for a conditioning period before their respective pockets 300 cavities are provided with the pressurised fluid from the first reservoir and the second reservoir.

[0067] A temperature measurement means, such as at least one thermocouple, may be attached to each of the component preforms to determine when the conditioning temperature is reached.

[0068] This may be desirable because the risk of material ripping is minimised during inflation.

[0069] The duration of the (temperature) conditioning period may be fixed.

[0070] However, for both economic and environmental grounds, it is desirable to reduce the duration of this conditioning period, if possible. Hence, a variable conditioning period may be implemented, with the cessation of the variable conditioning period determined based upon at least one material temperature measurement of each of the first component preform and the second component preform. For example, completion of the conditioning period may be determined by a temperature of both the first component preform and a temperature of the second component preform exceeding a pre-determined conditioning temperature.

[0071] Furthermore, depending upon the material from which the first component preform and the second component preform and the required mechanical properties of the resulting hollow component, prior to hot separation the pockets 300c of component preforms 300, it may be preferable to purge the pockets 300c of air, to avoid formation of oxidation products which cannot be subsequently easily removed from the inflated pockets. Purging may be performed by volumetrically displacing air within the internal cavities with an inert gas such as argon.

[0072] During hot separation it is desirable to have a knowledge of the degree of the inflation of pockets 300c that occur. However, estimating this deformation, by for example, measurement of strain gauges fitted to a surface of the preform may be problematic.

[0073] An alternative solution is therefore provided in which the pressurised fluid provided to the pocket 300c of the first component preform and a pressurised fluid is also provided to the pocket (internal cavity) of the second component preform from respective first and second fluid reservoirs.

[0074] Each of the first and second fluid reservoir has a finite, and known, volume.

[0075] Each of the first and second fluid reservoirs is pressurised to a known pressure.

[0076] Preferably, the first fluid reservoir and second fluid reservoir have the same volume and are pressurised to the same pressure. Thus, when pressurised, the first and second fluid reservoirs contain substantially the same mass of pressurised fluid.

[0077] During hot separation the contents of the first fluid reservoir and second fluid reservoir are simultaneously but independently discharged into the internal cavities of the first component preform and the second component preform respectively. In the above context, independently discharged means that the pressurised fluid supply, conduit and internal cavity of the first component preform is not fluidically coupled to the pressurised fluid supply, conduit and internal cavity of the second component preform.

[0078] The provision of pressurised fluid to pockets 300 causes an initial inflation of each pocket. For each of the first component preform 300 and the second component preform 300, this inflation increases the total volume of a system comprising the pocket 300c, fluid reservoir and conduit fluidically connecting the fluid reservoir to the pocket 300c, causing a corresponding decrease in pressure within the system.

[0079] Thus, by measuring a pressure in this system, it is possible to assess the degree of inflation of the internal cavity that has occurred. Furthermore, as the system of the first component preform is separate from and independent of the system of the second component preform, by comparing the pressure in the pocket 300c of the first component preform 300 and the pressure in the pocket 300c of the second component preform, it is possible to estimate the relative degrees of inflation that have taken place in the pockets of the first component preform and the second component preform.

[0080] Once it is determined in step 160 that sufficient inflation has taken place (for example, determining from pressure measurements that both a first pressure in the internal cavity of the first component preform and a second pressure in the internal cavity of the second component preform have fallen below a first threshold), a re-pressurisation of the internal cavity of the first component preform and a re-pressurisation of the internal cavity the 2.sup.nd component preform may be made in step 170. Re pressurisation of the two cavities of the respective preforms may be made independently of each other, in that a common pressurisation component such as a pressure regulating valve may not be used to regulate re-pressurisation of the two cavities. However, the internal cavities are pressurised based at least in part on a common pressure: time schedule. In some embodiments, the internal cavities may be pressurised simultaneously, albeit independently.

[0081] The initial ramping rate off the pressure: time schedule may be set such that an inflation rate an inflation strain rate of the respective components does not result in a tearing off the material from which they are made.

[0082] Once the re-pressurisation schedule has completed and the first and second components have been formed, the die stack may be opened in step 180 and the first and 2.sup.nd component removed from the respective first space and 2.sup.nd space in step 190.

[0083] As is disclosed below in relation to a hot forming apparatus, the inflation and/or re-inflation method steps impose a mechanical loading upon the dies of the die stack, such that relative movement is promoted between adjacent dies. Examples of relative movement include a lateral movement and/or a rotational movement of adjacent dies. This may be undesirable as it may adversely affect the resulting shape of the formed component.

[0084] In the case that the gas formed component is a gas turbine engine fan blade, malformation of the shape of the fan blade could have a detrimental effect on the aerodynamic behaviour of the fan blade, and consequently, the aerodynamic behaviour of the fan comprising the fan blade.

[0085] Preventing undesired relative movement between adjacent dies (for example lateral movement, rotational movement) is therefore desirable.

[0086] This may be achieved by a temporal synchronisation of the inflation process between the first component preform and the second component preform and/or by orientation of the first component preform and the second component preform within the die stack such that the mechanical loading acting on the dies at any one time is reduced.

[0087] This may be particularly beneficial for the intermediate die, which may be more susceptible to undesired movement as it is not directly connected to a platen of the hot forming machine and may therefore be more prone to movement than either the first die or the second die.

[0088] As the intermediate die forms a surface of each of the first component and the second component, undesired movement of the intermediate die may have a detrimental effect on both of the formed components.

[0089] Undesired movement may be mitigated against by suitable mechanical design of the hot forming machine, but may also be mitigated by orientating the first component preform relative to the second component preform such that forces generated on the intermediate die due to the pressurisation and/or re-pressurisation method steps of the first component preform are at least partially offset by forces generated on the intermediate die due to the pressurisation and/or re-pressurisation method steps of the second component. For this to occur, it is desirable that the pressurisation and re-pressurisation method steps are simultaneously applied to the first component preform and the second component preform (i.e., pressurisation of the first component preform and the second component preform is synchronised; re-pressurisation of the first component preform and the second component preform is synchronised).

[0090] In the case of manufacturing a pair of identical components (for example, gas turbine engine fan blade) undesired movement of the intermediate die may be mitigated by orientating the first component preform and the second component preform such that an orientation of the first component preform in the first die set is equal to the orientation of the second component preform.

[0091] From the above disclosure, it will be understood that in the above method, when forming a pair of components from a pair of component preforms, temporal synchronisation of the re-pressurisation step for the first and second component preforms is desirable.

[0092] This temporal synchronisation of pressurisation and/or re-pressurisation of component preforms may be either independent or coupled.

[0093] In independent re-pressurisation, inflation of the first component preform is controlled independently from inflation of the second component preform. In other words, even though re-pressurisation of the first component preform and the second component preform may take place simultaneously and use the same (i.e., common) pressure: time schedule, the supply of pressurised fluid to each internal cavity is done in isolation from the other component preform, using separate pressure transducers for control, each measuring a pressure in the internal cavity of one of the first component preform and the second component preform.

[0094] Alternatively, coupled re-pressurisation may be used. Like independent re-pressurisation, a pair of pressure transducers are used to determine and control the pressure of pressurised fluid provided in both the pockets during re-pressurisation.

[0095] Like in independent re-pressurisation, one of the pair of pressure transducers also measures the pressure in one of the pockets of one of the component preforms.

[0096] However, unlike independent re-pressurisation, the second pressure transducer of the pair is a differential pressure transducer, measuring the pressure difference between the internal cavities (pockets) of the component preforms.

[0097] Thus, the rate of re-pressurisation of one of the internal cavities is controlled based upon the measured pressure within that cavity, whereas the rate of re-pressurisation of the other internal cavity is controlled based on minimisation of the pressure differential measured by the differential pressure transducer.

[0098] A potential advantage of coupled re-pressurisation over independent re-pressurisation is that the differential pressure transducer may be more sensitive (have a lower full scale deflection). This may reduce the pressure difference between the two internal cavities of during re-pressurisation and in so doing, reduce the forces acting on the intermediate die, in turn reducing the likelihood of distortion due to undesired movement (lateral and/or rotational) of the intermediate die.

[0099] Further details of the die stack are shown in FIGS. 5 to 8, in which FIGS. 5 and 6 show a first example of a die stack actuation mechanism, while FIGS. 7 and 8 show a second example of a die stack actuation mechanism.

[0100] As previous disclosed, the first die and the second die may each be connected (for example, rigidly mechanically connected) to a respective platen of a hot forming machine.

[0101] As previously disclosed, an advantage of this is that lateral loads (i.e., mechanical loads that are substantially parallel to the interfacing surfaces between the platen and its respective die) generated during either holding, pressurising and/or re-pressurising of the preforms if the preforms have a surface that has a component that it not normal to the platen. Thus, slippage between the first die and its platen, and the second die and its platen may be minimised. This is beneficial in ensuring that that the resulting surface of the finished component has the required profile.

[0102] However, the intermediate die, between the first die and the second die may also be prone to lateral slippage during holding, pressurising and/or re-pressurising, whilst accurate alignment between the first die, intermediate die and the second die is required if the resulting component is to have the desired surface profile.

[0103] A first example actuation mechanism is shown in FIGS. 5 (die stack closed) and 6 (die stack open).

[0104] In the example of FIGS. 5 and 6, the intermediate die 220 comprises a plurality of through holes 222, through each of which a related connection member 211 that is connected to one of the first platen or second die passes. Connection member 211 and through holes 222 may form a sliding fit.

[0105] It will be appreciated that FIGS. 5 and 6 show the connection members 211 being connected to first die 210, but other alternatives are also possible, for example, connection member 211 could be connected to second die 230 etc.

[0106] The arrangement of through holes 222 and connection members 211 is such that separating the first platen from the second platen also separates the intermediate die from both the first die and the second die. This is because connection member 211 comprises a stop 211a that is configured to interface with a seat 223, 233 in at least one of the other dies to that which it is connected. For example, in FIGS. 5 and 6, connection member 211 is connected to first die 210, with seats provided in the second die 230 and intermediate die 220. Hence, as the first and second dies are moved apart, for example, be separating platens to which they are connected, when contact is made between a stop and its respective seat, the first die is separated from the intermediate die and the intermediate die is separated from the second die.

[0107] Although actuation could be achieved with a single through hole through which a single connection member passes, an advantage of a plurality of through holes and related connection members around a periphery of the die stack is that rotation of the intermediate die relative to at least one of the first die or the second die is mitigated. For example, a plurality of connection members and seats may be provided to control actuation of the first die relative to the intermediate die; similarly, a plurality of connection members and seats may be provided to control actuation of the intermediate die relative to the second die, etc.

[0108] FIGS. 7 and 8 show an alternative actuation mechanism which may be used in place, or in combination with the actuation mechanism of FIGS. 5 and 6. Like the first example of FIGS. 5 and 6, an arrangement of stops and seats are used to separate adjacent dies. For example, in FIGS. 7 and 8, connection member 211 comprises stop 211a (in the form of a hook) that may make contact with seat 223 of intermediate die 220 to separate intermediate die 220 from second die 230.

[0109] Alternatively or additionally, adjacent dies of the die stack may comprise a plurality of anti-rotation and/or anti-translation features to prevent lateral movement and/or rotation of adjacent dies. For example, facing surfaces of adjacent dies may compromise projections and corresponding recesses, the projections and recessed configured to form an interlock between adjacent dies when held together. The projections and recesses may have any suitable shape. For example, the projections and recesses may be pyramidal, trapezoidal etc.

[0110] From the above disclosure, it will therefore be understood that according to this disclosure, a hot forming machine, suitable for forming hollow components such as a metallic gas turbine engine fan blade comprises a first (upper) platen, a second (lower) platen and an actuation mechanism for a die stack in which the die stack has a first die set and a second die set, and the die stack is holdable between the first platen and the second platen. A heat source is provided for heating the first die set and the second die set and as a consequence, component preforms held by the die stack. A pressurisation device is also provided, the pressurisation device comprising a first conduit that is connectable to a first component preform held in the first die set and a second conduit that is connectable to a second component preform held in the second die set.

[0111] Pressure measurement means (for example, a pair of pressure transducers) is also provided for sensing an internal cavity pressure of the first component preform and an internal cavity pressure of the second component preform.

[0112] Optionally, temperature measurement means for measuring a temperature of the component preforms during the manufacture is also provided.

[0113] Alternatively, a series of trial tests (i.e., pre-production trials) may be conducted to determine typical operating conditions and time periods which result in the component preforms reaching a suitable temperature. In this way it is not necessary to fit instrumentation to each component preform during production.

[0114] The pressurisation device is switchable between a pressurisation mode and a re-pressurisation mode. In the pressurisation mode, the pressurisation device couples the first component preform to the first finite pressure reservoir and the second component preform to the second finite pressure reservoir. Conversely, in the re-pressurisation mode, the first component preform and the second component preform are re-pressurised based upon a common pressure: time schedule. In this mode, the pressurisation device regulates the pressure of fluid provided to the first and second component preform such that it follows the common pressure: time schedule. The common pressure: time schedule is common in that the same pressure: time schedule is used for re-pressurisation of the internal cavity of the first component preform and the internal cavity of the second component preform. This means that during re-pressurisation, the pressure within the internal cavity of the first component preform is nominally identical to the pressure within the internal cavity of the second preform. Thus, mechanical loading on the hot-forming machine caused by inflation of the first component preform and second component preform during re-pressurisation may be reduced as by intent there is no significant difference in pressure between the pressure in the internal cavity of the first component preform and the pressure in the internal cavity of the second component preform.

[0115] Switching from the pressurisation mode to the re-pressurisation mode occurs in dependence upon the sensed pressure in the first hollow component and sensed pressure in the second hollow component both falling below a first threshold.

[0116] Optionally, the pressurisation device additionally comprises an isolation mode, the pressurisation device being switchable from the isolation mode to the pressurisation mode in dependence upon both a sensed temperature of the first hollow component preform and a sensed temperature of the second hollow component preform exceeding a temperature threshold sensed by the temperature measurement means.

[0117] Optionally, in the isolation mode, the first conduit that is connectable to the first component preform held in the first die set and the second conduit that is connectable to the second component preform held in the second die set may be independently isolatable from an upstream pressure source. This may be desirable such that at least one of the first conduit and second conduit, may at any one time be isolated from an upstream pressure source.

[0118] Optionally, the pressurisation device may be switched from the pressurisation mode to the isolation mode during the performance of method 100.

[0119] For example, it may be desirable to isolate both the first component preform and the second component preform from a source of pressurised fluid as a safety precaution if a fault is detected during execution of method 100.

[0120] For example, it may be desirable to isolate one of the first conduit and the second conduit (and hence one of the first component preform and the second component preform) from a source of pressurised fluid if it determined as part of step 160 that a pressure in the internal cavity of one of the first component preform and the second component preform has reached its first threshold pressure before the other.

[0121] This is because the mechanical loading on the hot-forming machine may be reduced by reducing the difference in pressure between the pressure in the internal cavity of the first component preform and the pressure in the internal cavity of the second component preform.

[0122] Thus, the component preform whose internal cavity pressure first falls below the first pressure threshold of step 160 may be isolated from its pressure source while the cavity pressure of the lagging component preform continues to fall until it also reaches the first pressure threshold of step 160.

[0123] It will be appreciated that although ideally there should be little difference in the time taken for the pressures in the respective internal cavities of the first and second component preforms to reach the first pressure threshold, in practice, differences may arise due to tolerancing issues. For example, the component preforms may be heated to slightly different temperatures (and hence have different ductilities during the performance of step 160), portions of the component preforms may have different geometric dimensions due to geometric tolerancing, different component preforms may be manufactured from a different batch of material etc.

[0124] Once the internal cavity pressures of both the first component preform and the second component preform have reached the first pressure threshold, the isolated component preform may be switched from the isolation mode to the pressurisation mode, and the subsequent method step simultaneously performed for both the first component preform and the second component preform. For example, method step 170 may be performed simultaneously for both the first and second component preforms. Performing method step 170 simultaneously for both the first and second component preforms may be desirable because it may reduce the mechanical loading acting on the dies in the die stack.

[0125] The pressurisation device, and optionally, actuation of the actuation mechanism by movement of the first die and/or second die, are controlled by a controller.

[0126] To control the pressurisation device, the controller has as input, the output from the pressure measurement means, and the output from the optional temperature measurement means. The controller may also control power supplied to the heat source (for example, an electrical supply, a supply of combustible gas) in dependence upon the temperatures measured by the temperature measurement means).

[0127] To control the actuation mechanism, the controller may control movement of at least one platen (first platen, second platen).

[0128] From the above disclosure, it will be understood that an advantage of the hot forming machine is that it improves the production rate of hollow components via a hot forming method, as a pair of components may be formed substantially simultaneously by a single machine.

[0129] To this end, further modifications are envisaged.

[0130] For example, rather than forming component preforms in pairs via a 3 piece die stack, the number of dies in the die stack may be increased. For example, three components may be formed simultaneously via a hot forming machine that utilises a 4 die stack (comprising in order a first die, a first intermediate die, a second intermediate die and a second die) etc.

[0131] It will be appreciated that in this example, the hot forming machine would require an additional conduit, additional pressure sensing means and optionally, additional temperature sensing means etc to enable simultaneous formation of the additional component with the first and second component etc.

[0132] Alternatively or additionally, the pressurisation device may comprise a third conduit and a fourth conduit. Like the first conduit and the second conduit, the third and fourth conduits are connectable to a pocket of a third component preform and a fourth component preform and can provide a pressurised fluid (e.g., an inert gas such as argon) to the pockets of the component preforms for pressurisation and re-pressurisation purposes.

[0133] The third conduit may be connected to the third component preform and the fourth conduit may be connected to the fourth component preform whilst the third and fourth component preforms are external to the hot forming apparatus and the first and second components are being formed from the first and second component preforms.

[0134] Thus, the third conduit and fourth conduit permit the connection of the third and fourth component preforms to the pressurisation device of the hot forming apparatus prior to the third component preform and the fourth component preform being placed within the die stack of the hot forming machine. This permits a more rapid throughput of component preforms through the hot forming machine and is desirable for operator safety as pressure-connections (third conduit, fourth conduit) can be made to the respective component preforms away from the heated components (e.g., die stack, first platen, second platen etc) of the hot forming machine.

[0135] Various examples have been described, each of which comprise one or more combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein.