Method for the production on a three-dimensional product

There is disclosed a method for the production of a three-dimensional product (2) via an additive layer manufacturing process such as an electron beam manufacturing process to selectively fuse parts (17) of a powder bed (16), said parts (17) corresponding to successive cross-sections of the product (2). The method involves the use of said additive layer manufacturing process to form a tool (12) by selectively fusing additional parts (18) of the powder bed (16), said additional parts (18) corresponding to successive cross-sections of the tool (12). The method also comprises a subsequent step of manipulating the tool (12) perform a processing function on the product (2).

The present invention relates to a method for the production of a three-dimensional product, and more particularly relates to such a method involving an additive layer manufacturing (ALM) process to selectively fuse parts of a powder bed.

Additive layer manufacturing has become more widely used over recent years in order to produce three-dimensional products. Electron Beam Melting (EBM) is a particular type of ALM technique which is used to form fully dense metal products (such as component parts for gas turbine engines in the aerospace industry). The technique involves using an electron beam in a high vacuum to melt metal powder in successive layers within a powder bed. Metal products manufactured by EBM are fully dense, void-free, and extremely strong.

FIG. 1illustrates a known and conventional configuration of apparatus1which is used in are EBM method to produce a three-dimensional metal product2from metal powder3. The apparatus comprises an adjustable height work platform4upon which the product2is to be built, a powder dispenser5such as a hopper, a rake6or other arrangement operable to lay down a thin layer of the powder3on the work platform4to form the powder bed7, and an electron beam column8for directing and focussing an electron beam9downwardly on the powder bed7in order to melt parts of uppermost layer of the powder bed7. The entire apparatus is housed within a vacuum housing and the operative parts are computer controlled.

During operation, the electron beam column8is energised under the control of the computer to focus the electron beam9onto the powder bed7and to scan the beam across the powder bed to melt a predetermined area of the top layer of the powder bed7and thereby form a cross-section of the three-dimensional product2.

The three-dimensional product2is built up by the successive laying down of powder layers on the powder bed7and melting of the powder in predetermined areas of the layers to form successive cross-sections of the product2. During a work cycle the work platform4is lowered successively relative to the electron beam column8after each added layer of powder has been melted, ready for the next layer to be laid down on top by operation of the rake6. This means that the work platform4starts in an initial position which is higher than the position illustrated inFIG. 1, and in which position a first layer of powder of necessary thickness is laid down on the work platform4by the rake6. In order to prevent damage to the work platform4by the electron beam9, the first layer of powder is typically made thicker than the other applied layers, thereby preventing melt-through by the electron beam9. This is why the product2appears spaced above the work platform4within the powder bed7inFIG. 1. The work platform4is then successively lowered for the laying down of a new powder layer for the formation of a new cross-section of the product2.

When the electron beam9in on the top layer of powder within the powder bed7, the kinetic energy of the electrons is transformed into heat which melts the powder to form the respective cross-section of the product2. The layer previously scanned usually serves as a rigid support for the next layer above. The exemplary product2depicted inFIG. 1(in vertical cross-section) is formed so as to have a cavity in the form of a narrow through-passage10extending from one side of the product to the other side of the product.

As will be appreciated, the above-described EBM process operates at very high temperatures (typically in the region of 600° C. in the case of manufacturing in titanium). The electron beam is used to sinter the loose powder in each layer before carrying out the actual step of melting the powder. A consequence of this process is therefore the creation of a “cake” of sintered powder which encases the component formed by the EBM process, which must then be removed from the component. Given the significant expense of some metal powders such as titanium it is also important to recycle the sintered powder after it has been removed from the component.

The “cake” of sintered powder is typically removed from the product2by placing the caked component in an air-operated blasting cabinet wherein loose metallic powder is used to break sinter bonds and re-atomise the sintered powder back to individual powder particles which can then be recycled and used again in subsequent EBM process.

However, it has been found that this technique for removing the sintered powder from components is only effective on external surfaces of components or in large enclosed cavities formed in the component where a spray nozzle can provide sufficient access to impinge on the sintered powder therein. In tortuous passages, through holes or narrow openings and deep cavities formed in the component, such as the narrow through-passage depicted inFIG. 1, it has been found that this conventional technique is not capable of removing sufficient sintered powder. This therefore increases the amount of powder which is lost in the sense that it cannot be recovered and recycled. Also, if powder is left trapped inside such cavities in the component then it can adversely affect the subsequent function of the component. For example, in the case of engine components, the powder could subsequently be ingested into the engine oil if it is not properly removed at the manufacturing stage.

Whilst the problems associated with the prior art are discussed above with specific reference to EBM processes, it is to be noted that the same or similar problems could also arise in other additive layer manufacturing processes such as Laser Melting and Laser Sintering processes. Therefore, whilst aspects of the present invention are described herein with particular reference to EBM processes, it should be noted that embodiments of the invention may involve the use of other additive layer manufacturing processes, such as Laser Melting processes or Laser Sintering processes.

It is therefore an object of the present invention to provide an improved method for the production of a three-dimensional product via an additive layer manufacturing process.

According to an aspect of the present invention, there is provided a method for the production of a three-dimensional product via an additive layer manufacturing process to selectively fuse parts of a powder bed, said parts corresponding to successive cross-sections of the product, the method involving the use of said additive layer manufacturing process to form a tool by selectively fusing additional parts of the powder bed, said additional parts corresponding to successive cross-sections of the tool, and wherein the method comprises a subsequent step of manipulating the tool to perform a processing function on the product.

The additive layer manufacturing process may be used to form said tool simultaneously with at least part of said product.

The additive layer manufacturing process may comprise the steps of a) laying down a powder layer on said powder bed, and b) focussing energy on a predetermined area of said powder layer to fuse said area of the powder layer and thereby form a cross-section of the product; wherein steps a) and b) are repeated to form successive cross-sections of the product, and wherein at least some of said successive steps b) involve focussing energy on a designated tool area of the respective powder layer, to fuse the tool area and thereby form successive cross-sections of said tool within the powder bed.

The method may be used to manufacture a metal component, in which said powder is metal powder, and in which said steps of focussing energy on said areas of the powder layers involves the use of an electron beam to melt said areas of the powder layers.

In preferred embodiments, the additive layer manufacturing process is an electron beam melting process.

Optionally, said tool is formed in spaced relation to at least one surface of the product.

Conveniently, said tool is shaped such that at least part of the tool substantially conforms to the shape of the or each said surface.

The tool can, optionally, be provided with surface protrusions, for example ribs or spikes which aid in the disruption of the powder when the tool is agitated.

Said processing function performed on the product may involve using the tool to remove sintered powder, arising from the additive layer manufacturing process, from the product.

Conveniently, said step of manipulating the tool involves vibrating the tool and/or the product in which the tool is contained. Vibration can be provided by a vibrating jig into which the product is introduced. Vibration can be in a single or multiple planes.

The tool and/or product may be subjected to ultrasonic vibrations.

In some embodiments, said product is formed so as to have a cavity, and said tool is formed in a position in which it is at least partially located within said cavity. In such embodiments, said processing function may involve using the tool to remove said sintered powder from within the cavity.

Said tool is optionally formed in a position in which part of the tool projects from the cavity, said projecting part of the tool being used for manipulation of the tool.

Said cavity may be provided in the form of a passage extending through at least part of the product.

Said tool may extend substantially completely through said passage in spaced relation to the or each internal surface of the passage.

Optionally, said passage follows a non-linear path, and said tool may be shaped to follow said path.

The cavity may comprise a simple passage with exit and entry through holes in a single plane. In more complex products, the cavity may comprise multiple holes and/or passages interconnecting along multiple planes. In the latter case, multi-plane vibration is particularly appropriate. In the latter case, the tool may be provided with multiple branches extending into multiple passages.

As an optional final step, the tool may be removed from the cleared cavity. To aid in the removal, the tool may be constructed to include one or more strategically placed frangible points at which, under an appropriately applied force, break, allowing the resulting pieces to clear bends in the cavity and pass through the cavity to an exit hole provided in the surface of the product. Alternative removal methods might involve a local chemical or heat treatment of the tool independent of the product to encourage its disintegration and removal from the product.

The method optionally further includes the step of chemically treating the material of the tool, after its formation and before said manipulation, to harden the material of the tool relative to the material of the product.

Said processing function performed on the product may, in some embodiments, involve using the tool to polish the product.

According to another aspect of the present invention, the above-defined method may be used to manufacture a component of a gas turbine engine.

Turning now to consider the drawings in more detail,FIG. 2shows a pair of discrete products2a,2bwhich have been produced by an EBM process along the lines explained above. Each product2a,2bis shown in the form of a simple hollow tube having a respective cavity10a,10bin the form of a through-passage, although it is to be appreciated that these configurations are illustrated merely for simplicity and convenience; it being envisaged that the method of the present invention will be useful in producing much more intricately shaped components. As will be noted, the left-hand product2ashown inFIG. 2is significantly shorter than the right-hand product2b,which means that the passage10athrough the left-hand product is relatively wide in the x-direction compared to its length in the y-direction, whilst the passage10bthrough the right-hand product2bis relatively narrow in the x-direction compared to its length in the y-direction.

FIG. 2also shows a “cake” of sintered powder11encasing the two products2a,2b.The sintered powder is formed during the EBM method used to form the two components in the manner described above, and must be removed from the products following their formation via the EBM process. It is of course preferable to remove the sintered powder in a manner which allows into be recycled for use in a subsequent EBM processes. As will be noted, the sintered powder11is shown entirely encapsulating the two products, and most notably substantially filling the passages10a,10bformed through the products. As explained above, it has been found to be particularly troublesome to remove all of the sintered powder11from within such internal passages10a,10bor other cavities, particularly those which are small, narrow or tortuous in configuration and hence difficult to penetrate with a jet of cleaning air.

FIG. 3shows the two products2a,2bfollowing an initial step to remove the sintered powder11, and in particular following a generally conventional prior art step in which the products are air-blasted as described generally above. As will be noted, whilst the prior art air-blasting process has been effective to remove substantially all of the sintered powder from the external surfaces of both products2a,2b,and also from within the relatively short passage10aof the left-hand product2a,it has not been effective to remove all of the sintered powder11from within the longer passage10bof the right-hand product2b.This is because the conventional air-blasting apparatus used in prior art methods cannot direct a jet of blasting air with sufficient energy sufficiently far in to the relatively long and narrow passage10bto break sinter bonds and re-atomise the sintered powder back to individual powder particles.

The method of the present invention proposes the production of a tool, from the same powder bed from which the product2is formed, in order to assist in removal of sintered powder from within hitherto difficult to access cavities and spaces such as the relatively long and narrow passage10billustrated inFIGS. 2 and 3. The manner in which the tool can be formed will be described in more detail hereinafter, butFIG. 4illustrates schematically the use of such a tool12to assist in removal of the sintered powder11from within the cavity10of a product which, as explained above, often cannot be completely removed via the prior art air-blasting process.

FIG. 4shows an exemplary tool12having a generally elongate configuration in which it extends into and passes through the central region of a cavity10formed within the product2. As will be noted, the cavity10illustrated inFIG. 4has a similar configuration to the cavity10bshown in the right-hand product2bofFIG. 2, and thus can be considered to be a somewhat long and narrow through-passage of a type which is thus particularly susceptible to the retention of sintered powder11following a prior art air-blasting process. It is proposed that the tool12will be formed in the position illustrated inFIG. 4, simultaneously with at least a region of the product2itself, from the same powder stock and via the same ALM method. However, it is to be appreciated that this is not an essential requirement. Embodiments of the present invention are envisaged in which the tool might be produced after the product itself has been formed; for example to remove sintered powder from an external surface of the product.

As shown inFIG. 4, the tool12is quite significantly narrower in the width direction than the internal width of the passage10, and is shown located generally along the longitudinal axis of the passage10. The tool12is thus provided in spaced relation to the internal surface of the passage10. Whilst in some embodiments a tool can be formed which has a width substantially equal to, or slightly narrower than, the internal width of the passage10, it has been found that often acceptable results can be achieved from a narrower tool12such as the type illustrated inFIG. 4.

FIG. 4shows the tool remaining in the position within the cavity10in which it was formed, after an initial prior art air blasting step to remove sintered powder from the product. As will be noted, however, a central plug of sintered powder11still remains within the passage, as described above with reference toFIG. 3. The tool12extends through the remaining plug of sintered powder11, and of course will itself be encased in the sintered powder arising from the EBM process used to form the tool. A short length of the tool12projects outwardly from one end of the passage10and can thus be used to manipulate the tool12, for example by being gripped or otherwise engaged by a suitable apparatus or robot.

The tool12can then be manipulated to assist in the removal of the remaining plug of sintered powder11in the passage10. The particular way in which the tool12might be manipulated can vary and will depend on the nature of the sintered powder11and the form and path of the passage10. However it has been found that particularly good results can be achieved by vibrating the tool12, for example in a longitudinal direction as denoted by arrow13inFIG. 4, at high frequency and low amplitude. The tool12may therefore be subjected to ultrasonic vibrations, which can be achieved by clamping the end of the tool in an ultrasonic vibrator.

By vibrating the tool12in this manner, the tool12abrades the sintered powder in contact with the tool and thereby rapidly disintegrates the sintered powder11, breaking the sinter bonds and re-atomising the sintered powder back to individual powder particles which can then be collected for recycling and re-use in a subsequent EBM process.

Whilst the vibrating tool12can be further manipulated to move it from side to side within the passage10, to thereby bring the tool into contact with more of the sintered powder plug11remaining in the passage, it has been found that in many cases this might not be required. For example,FIG. 5shows the sintered powder11remaining after the above-described step of axially vibrating the tool12with minimal side to side movement across the width of the passage10, and after subsequent removal of the tool12from the passage10. As will be noted, this manipulation of the tool12is effective to form a narrow central channel14through the plug of sintered powder11. It has been found that once this channel14has been formed in the plug of remaining sintered powder, a conventional prior art air-blasting process is then often sufficient to disintegrate and remove the remaining parts of the plug. This is because the channel14formed through the plug by the tool12allows a narrow flow of air from the air-blasting process to pass through the plug at increased speed, due to a throttling effect caused by the channel14, thereby allowing a sufficiently high-energy flow of air to impinge on the remaining parts of the plug to disintegrate them. The resulting product2is shown inFIG. 6, and can be seen to be completely free from sintered powder both outside and inside the central passage10.

Turning now to considerFIG. 7, an alternative configuration of product2is shown, which again has an internal cavity in the form of an elongate passage10. However, it will be noted that in this arrangement the passage10has a more intricately shaped configuration than those illustrated previously inFIGS. 2 to 6. In particular it will be noted that the passage10illustrated inFIG. 7has a somewhat tortuous or so-called serpentine configuration, having a number of bends or curves along its length. Furthermore, it will be noted that the passage10has a configuration in which there is only a very narrow line of sight completely through the passage10from one end to the other. This type of passage configuration has been found to be particularly difficult to remove sintered powder from via a conventional prior art air-blasting technique because it significantly limits the access to the inside of the passage by a high pressure air jet.

As will thus be noted, the internal passage10shown inFIG. 7is therefore provided with a tool12in a generally similar manner and for the same reasons as proposed above with respect toFIGS. 4 to 6. However, it will be noted that the tool12is shaped to follow the non-linear serpentine path of the passage, and again is provided in a form which is narrower than the passage such that the tool is spaced from the internal surface of the passage. The tool12will be used in a similar manner to that described above and may thus be subjected to ultrasonic vibrations as denoted by the arrows inFIG. 7, to disintegrate any remaining sintered powder in contact with the tool.

FIG. 8illustrates schematically a larger product2having a similar through-passage12to that illustrated inFIG. 7.FIG. 9shows a cross-sectional view through the product ofFIG. 8, taken along line IX-IX shown inFIG. 8, to more clearly show the cross-sectional profile of the passage10, which it is to be appreciated is merely exemplary and not limiting. The tool12is shown within the passage10, in the position in which it can be formed via the method of the present invention. An embodiment of a method to form the product2and the tool12will now be described in detail below with particular reference toFIGS. 10 to 15.

FIG. 10illustrates an initial step in the method of manufacturing the product2, and shows the work platform4of an EBM apparatus in an initial raised position. An initial layer15of metal powder feedstock is laid on the work table4to start a powder bed16. The powder may be spread into the layer15via the rake6of the apparatus shown inFIG. 1. In a similar manner to prior art methods, the initial layer15of the powder bed16can be laid thicker than subsequent layers.

FIG. 11shows a subsequent step in which an electron beam is focussed on and scanned across a predetermined area17of the initial powder layer15. The beam9thus melts the powder in the predetermined area17, thereby fusing the area17and forming an initial cross-section section of the product2. The shape of the cross-section is effectively defined by the shape of the predetermined area27.

The table4is then lowered and another layer of powder is laid on top of the first layer15, thereby adding to the powder bed16, whereupon the electron beam9is again focussed on and scanned across a corresponding predetermined area of the top layer, thereby forming the next cross-section of the product, on to of the first cross-section.

The steps of laying down a layer of powder and then focussing/scanning the electron beam over a predetermined area of the layer are repeated to form successive cross-sections of the product2, thereby gradually building the product from the bottom up. During the initial stages of the method to form the particular exemplary product shown inFIGS. 8 and 9, these steps are repeated to form identical and vertically aligned cross-sections of the product, thereby building up the lower part of the product2, below the passage10. It is to be noted that during this stage of the method, the respective predetermined areas17of each successive layer of powder are thus all aligned with one another.

FIG. 12illustrates a stage during the formation of the product2at which the lower part of the product2with uniform cross-section below the passage10is complete. This drawing therefore shows the final cross-section of the lower part of the product having just been formed by melting a predetermined area17of the top layer of powder on the powder bed16. Before the table4is subsequently lowered ready for the next powder layer to be laid on the powder bed16, the electron beam9is refocused on a relatively small designated tool area18of the top layer of the powder bed. The tool area18is spaced from the predetermined17area of the same layer of powder which is fused to form the cross-section of the lower part of the product2.

As will be appreciated, focussing the electron beam9on each of the tool area18melts the powder in that areas, thereby fusing the powder. The fused tool area18of the top layer of powder thus forms an initial cross-section of the tool12, and effectively the first end of the tool12.

It is to be noted that the first end of the tool12is thus formed in the top layer of the powder bed16(at the stage illustrated inFIG. 12), and is spaced from the product2. As will be appreciated hereinafter, this means that the end of the tool12will project outwardly of the passage10(still to be formed at the stage illustrated inFIG. 12).

A series of further successive layers of powder then continue to be laid on the powder bed16. When each layer has been laid, the electron beam9is focussed on a correspondingly shaped but slightly offset tool area18to melt the powder material in the support area and thereby steadily build up successive cross-sections of the tool12, as shown schematically inFIG. 13. Because the successive tool area18of each powder layer which is melted to form the tool12are slightly offset from one another, the tool is gradually built up to follow the serpentine path of the passage10.

As will also be evident fromFIG. 13, the electron beam9also continues to be focussed on respective predetermined areas17of the layers to melt the powder material in the predetermined areas17and thereby define respective cross-sections of the product. However, the predetermined areas17of each layer which are melted during this stage of the procedure differ from one another in the sense that each successive predetermined area17is slightly smaller than the preceding one. The serpentine lower region of the passage'2internal surface is thus built up gradually in this way, layer by layer.

FIG. 14shows a subsequent stage in the simultaneous production of the product2, with the tool located in position within the gradually forming passage10. As will be appreciated by the skilled person, in light of the foregoing, the size and position of each successive predetermined area17and tool area18is determined in dependence on the desired profile of the passage10and its associated tool12.

FIG. 15illustrates the product2at a stage in the production process in which its passage10is completed, and in which the tool12within the passage is also substantially completed, with the final tool area18being fused by the electron beam9to form the second end of the tool, which it will be noted also projects outwardly from the now complete passage10. The upper region of the product2can then be formed by continuance of the process to fuse successive predetermined areas17of the powder layers and thereby define the remaining cross-sections of the product.

Once the simultaneous EBM production of the product2, with its associated tool12in position within the passage10, the product and tool can be removed from the EBM apparatus for post-production processing, and of course most notably removal of the cake of sintered powder which will be present around the product and within the passage in the manner described above. This can be achieved by a combination of a conventional air-blasting technique and via vibration of the tool12within the passage10in the manner described above to disintegrate at least a proportion of any sintered powder remaining within the passage after the air-blasting step. Alternatively, the tool12can be manipulated in a vibratory manner to disintegrate a proposition of the sintered powder within the passage before subsequent air-blasting. The tool12can be removed from the passage and discarded after use.

Whilst the tool12has been described above with reference to a particular method of production in which the tool is formed in spaced relation to the internal surfaces of the passage10, and thus effectively in a central position within the passage supported by the sintered powder therein arising from the EBM process, it is to be appreciated that the tool could be formed so as to be initially connected to the structure of the product, for example by a plurality of breakable connecting tabs co-formed via the same EBM process. After completion of the product2and the tool12, the tool12could then be snapped free from the product by breaking the connecting tabs to facilitate its subsequent manipulation to remove sintered powder.

Optional methods for effecting the manipulation of the tool are further described inFIGS. 16 and 17.

Passages (channels)10are formed in the component2and are shown partly filled with powder16. A tool12is contained within the channels by a containment grid19. Vibration of the tool12(or optionally the product2) in the direction indicated by the arrows causes the tool12to oscillate within the channel and repeatedly impact on the exposed face of the powder16. Powder which is loosened by the impact of the tool12exits the channel10through the grid19and can be recycled.

In a method according to an embodiment of the present invention, the tool12and grid19are manufactured using the EBM method as part of the manufacture of product2so as to contain the tool12within the channel10. This method is illustrated schematically inFIG. 16.

The grid/bar contains the tool12within the channel10allowing loosened powder to fall out of the channel by gravity. The powder16is loosened by vibrating the tool12(or optionally the component2), causing the tool12to repeatedly impact on the powder as described in more detail below. This process may require a degree of manual set up to clear the first portion of the channel10, to enable free movement of tool12.

To improve the automation of the clearing process, in another embodiment, as illustrated inFIG. 17, the tool12and a containment feature20,21are sintered in during the manufacture of the hollow component2. The tool12is loosened prior to, or as part of, starting a vibrating step to enable the tool to gather momentum within the channel10and start the clearing process. For example a dropout21may be provided in the containment feature wall20which is formed of looser powder (e.g. similar to the powder formed in the cavity or channel10). This dropout21may be shaken free at the start of the cleaning process. Alternatively, if sufficient energy is imparted to the component by the vibrating step, the tool12may, by virtue of being more solidly formed than the surrounding material, shake itself free to start its motion. The containment feature20,21can be removed along with the manufacturing support structures following the clearing process.

In the described cleaning methods, once the tools12are contained in the channels10, the component2will be attached onto a vibration rig or other machine that is a source of vibration. The product2or tool12will be vibrated in the orientation of the axis of the channel. This will cause the tool12to travel back and forth along this path. Transfer of momentum to the tool12propels it through the powder16with high kinetic energy. The tool will impact the powder16on its exposed edge causing high local pressure on the powder causing it to break up and fall out of the product2under gravity (bottom aperture) or by the motion of vibration (top aperture). This continuous removal of the powder out of the channel10prevents dampening of the motion of the tool12as the cleaning progresses.

The tool12will continue to scavenge out the remaining powder16as time progresses as long as there is sufficient amplitude and energy input into the system. Optimisation of this process can be achieved by the use of a closed loop feedback system. This system controls the input frequency and amplitude by matching it to the depth of the powder cleared.

Upon completion of the clearing process, the containment feature20,21and the tool12can be removed from the product2.

FIGS. 16 and 17illustrate an embodiment of the tool which incorporates ribs or spikes extending radially from its longitudinal axis. As mentioned above, these can further assist an agitation and dislodgement of powder when the tool is caused to vibrate.

Furthermore, whilst the present invention has been described above with specific reference to manipulation of the tool12to remove sintered powder from the product2, in its broadest sense the invention can cover manipulation of the tool to perform other alternative processing functions on the product. For example, it envisaged that in some embodiments the material forming the tool12could be chemically treated or reacted to make it harder than the material forming the product. Chemically treating could include carburising or nitriding for example. This would then permit the tool to be used to polish adjacent surfaces of the product, such as the internal surfaces of a small and/or narrow cavity which would otherwise be unreachable by conventional polishing methods.

The invention may be used to manufacture components for a gas turbine engine100as shown inFIG. 18. The components may include any suitable components such as, for example, aerofoils, vanes, brackets, cowlings, air inlet scoops and combustor tiles. The skilled person may be aware of other components having one or more cavities or hollow portions which may benefit from the invention.

ThusFIG. 18shows a ducted fan gas turbine engine100comprising in axial flow series: an air intake112, a propulsive fan114having a plurality of fan blades116, an intermediate pressure compressor118, a high-pressure compressor120, a combustor122, a high-pressure turbine124, an intermediate pressure turbine126, a low-pressure turbine28and a core exhaust nozzle130. A nacelle132generally surrounds the engine100and defines the intake112, a bypass duct134and a bypass exhaust nozzle136. The engine has a principal axis of rotation131.

Air entering the intake112is accelerated by the fan114to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct134and exits the bypass exhaust nozzle136to provide the majority of the propulsive thrust produced by the engine100. The core flow enters in axial flow series the intermediate pressure compressor118, high pressure compressor120and the combustor122, where fuel is added to the compressed air and the mixture burnt. The hot combustion products expand through and drive the high, intermediate and low-pressure turbines124,126,128before being exhausted through the nozzle130to provide additional propulsive thrust. The high, intermediate and low-pressure turbines124,126,128respectively drive the high and intermediate pressure compressors120,118and the fan114by concentric interconnecting shafts138,140,142.