Bimetallic case

Abstract

The invention concerns a compressor case for a gas turbine engine, the case comprising a generally cylindrical body formed of a plurality of adjacent cylindrical sub-sections being formed of Ti-6242 and Ti-64.

Description

[0001] Bimetallic Case

[0002] Background

[0003] The present invention is concerned with an alternative arrangement and associated manufacturing process for forming a compressor case particularly, but not exclusively, for use in an aircraft gas turbine engine.

[0004] Conventionally casings of turbine engines are formed using a forging or similar process. As part of the forging process a single material is used, the selection of which is determined by the maximum operating requirements of the casing. This may for example be defined by thermal and mechanical requirements. Conventional manufacturing techniques have allowed casings to be successfully manufactured to meet industry requirements.

[0005] However, the inventors have established an alternative approach that conveniently allows dissimilar materials to be used such that the specific thermal and mechanical characteristics can be met in a material specific way. Although this could be interpreted as increasing the complexity of manufacture it allows for tailored casing design and optimised material selection as will be described herein.

[0006] RECTIFIED SHEET (RULE 91) ISA / EP Summary of the Invention

[0007] Aspects of the invention are set out in the accompanying claims.

[0008] Viewed from a first aspect of an invention described herein there is provided a compressor case for a gas turbine engine, the case comprising a generally cylindrical body formed of a plurality of adjacent cylindrical sub-sections, wherein the cylindrical body has a first end and an opposing second end and wherein the second end is arranged in use at a position within the engine operating at a higher temperature than the first end, and wherein one or more of the cylindrical sub-sections at the second end of the body is formed of Ti-6242 and one or more of the cylindrical sub-section at the first end of the body is formed of Ti-64.

[0009] In effect a bi-metallic compressor case is used. Using multiple alloys to form the casing complicates the manufacturing process since two alloys need to be used and brought together. However, the material properties provided by the dissimilar alloys allows the specific requirements at different parts of the casing (corresponding to different temperatures in an operating engine) to be realised.

[0010] Any number of sub-components may be brought together to form the generally cylindrical casing body. In one example, the cylindrical body may be formed of 4 adjacent cylindrical subsections. This allows the internal geometries required within the casing to be conveniently formed on the inner surfaces.

[0011] Advantageously the 3 cylindrical sub-sections extending from the first end of the body towards the second end may be formed of Ti-64 and the last cylindrical sub-section may be formed of Ti-6242. In another arrangement a single sub-section of Ti-64 could be used and a single subsection of Ti-6242 with ratio of length as described herein.

[0012] As discussed above the temperature profile along the casing in use can be dramatically different. The second end of the body may be arranged in use towards an exhaust end of a gas turbine engine i.e. the hotter end of the casing.

[0013] The method and arrangements described herein may be used for a variety of compressors but in one example the compressor case is a high pressure compressor case of a gas turbine engine. The individual sub-sections may also advantageously have lengths measured along the elongate axis of the cylindrical body that are different to one or more of the other sub-sections forming the cylindrical body. This allows for flexibility in the internal geometries and also for efficiencies by making longer sub-sections where internal geometries allow.

[0014] Any suitable number of sub-sections may be used. Advantageously, approximately 70% of the length of the cylindrical body measured along the elongate axis of the body may be formed of Ti-64 and approximately 30% formed of Ti-6242. This allows the creep and other thermal characteristics to be achieved whilst minimising the material usage and ultimately costs of manufacture. In another arrangements at 50:50 division between alloys may be used or alternatively an 80:20 division depending on the specific application.

[0015] The individual sub-sections may be formed using a variety of additive manufacturing processes. For example, the sub-sections may be formed using a laser directed energy deposition with wire (L-DED-w) additive manufacturing process.

[0016] The individual sub-sections may also be coupled together using any suitable process. In one example one or more sub-sections may be coupled to an adjacent sub-section by a weld such as an electron-beam weld.

[0017] Viewed from another aspect there is provided a method of manufacturing a compressor case for a gas turbine engine, the compressor case comprising a generally cylindrical body formed of a plurality of adjacent cylindrical sub-sections, wherein the cylindrical body has a first end and an opposing second end and wherein the second end is arranged in use at a position within the engine operating at a higher temperature than the first end, the method comprising the steps of:

[0018] (A) forming one or more of the cylindrical sub-sections at the second end of the body with Ti-6242; and

[0019] (B) forming one or more of the cylindrical sub-section at the first end of the body with Ti- 64.

[0020] As described above, the one or more cylindrical sub-sections at the second end of the body may be coupled to the one or more cylindrical sub-sections at the first end by means of an electron beam weld. Each of the sub-sections may be formed using a variety of AM processes. One advantageous example is laser directed energy deposition with wire (L-DED-w) additive manufacturing process. Each sub-section may then be welded to an adjacent sub-section. For example, the sub-sections may be formed my means of a laser directed energy deposition with wire (L-DED-w) additive manufacturing process, and then transitioning from a Ti-64 wire input to the manufacturing process to a Ti-6242 wire input at the point along the body where the sub-section is to be formed of Ti-6242. In effect the feedstock material is changed at the appropriate position.

[0021] RECTIFIED SHEET (RULE 91) ISA / EP Drawings

[0022] Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

[0023] Figure 1 shows a schematic of a compressor case as described herein;

[0024] Figure 2 shows a cross-section through section A-A’ in figure 1 ;

[0025] Figure 3 shows an embodiment with a welded connection between adjacent sub-sections; and

[0026] Figure 4 show an embodiment where an additive manufacturing process has been used to form the body

[0027] While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that the drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention.

[0028] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[0029] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

[0030] It will be recognised that the features of the aspects of the invention(s) described herein can conveniently and interchangeably be used in any suitable combination.

[0031] RECTIFIED SHEET (RULE 91) ISA / EP Detailed Description

[0032] Figure 1 shows a schematic view of a compressor case (such as a high pressure compressor case) of a gas turbine engine. The function and location of a compressor case will be well understood by a person skilled in the art and will not be described herein.

[0033] As shown in figure 1 the compressor case 1 comprising an elongate cylindrical body which, in use surround the compressor of the gas turbine engine. As shown the case is in the form of a number of sub-sections. 4 sub-sections 2a to 2d are shown in figure 1 but it will be recognised that other numbers may be used and benefit from the teaching herein.

[0034] Sub-sections 2a to 2d are all located so as to be in abutment with one another to define the elongate cylindrical body 1. Each adjacent sub-section is coupled to the next sub-section by means of a connection 3a to 3c. This is discussed further below with reference to figures 3 and 4.

[0035] The ends of the compressor body operate in use at very different temperatures within the engine as will be described.

[0036] Figure 2 is a cross-section through the wall of the casing body shown by section A-A’ in figure 1. Figure 2 shows the left hand end of the body as the cooler end within the engine and an opposing hotter end at the right hand end.

[0037] The sub-components 2a to 2d are shown corresponding to those from figure 1. In effect the sub-sections allow the casing to be divided to allow for the internal machining of the features F1 , F2 and F3 which may be internal hooks, brackets or provision for mounting other parts within the casing. These internal features can be machined and the sub-section brought together to create an elongate cylindrical body with complex internal geometries. Each of the dividing lines (Split 1 , 2 and 3) correspond to the couplings 3a to 3c in figure 1.

[0038] As also illustrated in figure 2 the length of the casing body; that is measure along the elongate axis of the body (the axis of rotation), has different zones or regions formed of dissimilar materials. As shown the cooler end of the body is formed of Alloy 1 and the hotter end with Alloy 2.

[0039] The inventors have established that dissimilar alloys may be used for a casing of a gas turbine engine to meet the mechanical and thermal characteristics of an engine. Specifically, the highest creep capabilities are not required along the entire length of the body and consequently a two-regional casing can advantageously be used to meet 2 different creep requirements.

[0040] More specifically, the inventors have established that Alloy 1 may be a Titanium-64 material with a lower creep capability than a second Alloy, Alloy 2 which may be Titanium-6242. In doing so the creep requirements can be met but significant savings in costs can be realised.

[0041] Although 4 sub-sections are shown any suitable number may be used depending on the desired internal complexities and machining required. Furthermore, the length measured along the elongate axis of the body may be different for one or each of the sub-sections.

[0042] As shown split 3 represents the transition between Alloy 1 and Alloy 2 in this example. The inventors have established that advantageously Alloy 1 may be Titanium 64 and Alloy 2 may be Titanium 6242.

[0043] The sub-section may each be formed in a variety of ways and may then be joined together again using a variety of methods.

[0044] Figure 3 illustrates a first example in which the transition between Ti-64 and Ti-6242 in made at connection 3a (corresponding to split 3 in figure 2). In this example an electron beam weld has been used to connection the 2 alloy sections or regions together. Each of the individual sub-sections may be formed using a suitable additive manufacturing process for example such as a laser directed energy deposition with wire (L-DED-w) additive manufacturing process. Each sub-section may then be brought together and welded. It has been established that an electron-beam weld provides a sufficiently strong weld between Ti-64 and Ti-6242.

[0045] Figure 4 shows an alternative approach in which the entire cylindrical body is formed using an additive manufacturing process and the transition between Ti-64 to Ti6242 is made by simply changing the wire feed stock to the second alloy at the appropriate position (connection 3a) during the L-DED-w process.

[0046] It will be recognised that a variety of welding techniques and metal deposition AM processes to form each sub-section may be used. Other AM techniques include:

[0047] Powder bed fusion methods

[0048] Direct metal laser sintering (DMLS)

[0049] Electron beam melting (EBM) Selective laser melting (SLM) Selective laser sintering (SLS) Direct metal wire deposition Direct metal powder deposition

Claims

CLAIMS1. A compressor case for a gas turbine engine, the case comprising a generally cylindrical body formed of a plurality of adjacent cylindrical sub-sections, wherein the cylindrical body has a first end and an opposing second end and wherein the second end is arranged in use at a position within the engine operating at a higher temperature than the first end, and wherein one or more of the cylindrical sub-sections at the second end of the body is formed of Ti-6242 and one or more of the cylindrical sub-section at the first end of the body is formed of Ti-64.

2. A compressor case as claimed in claim 1 , wherein the cylindrical body is formed of 4 adjacent cylindrical sub-sections.

3. A compressor case as claimed in claim 2, wherein the 3 cylindrical sub-sections extending from the first end of the body towards the second end are formed of Ti-64 and the last cylindrical sub-section is formed of Ti-6242.

4. A compressor case as claimed in any preceding claim wherein the second end of the body is arranged in use towards an exhaust end of a gas turbine engine.

5. A compressor case as claimed in any preceding claim wherein the compressor case is a high pressure compressor case of a gas turbine engine.

6. A compressor case as claimed in any preceding claim wherein one or more of the cylindrical sub-sections has a length measured along the elongate axis of the cylindrical body that is different to one or more of the other sub-sections forming the cylindrical body.

7. A compressor case as claimed in any preceding claim wherein approximately 70% of the length of the cylindrical body measured along the elongate axis of the body is formed of Ti-64 and approximately 30% is formed of Ti-6242.

8. A compressor case as claimed in any preceding claim wherein the sub-sections have been formed using an additive manufacturing process.

9. A compressor case as claimed in claim 8, wherein the sub-sections have been formed using a laser directed energy deposition with wire (L-DED-w) additive manufacturing process.

10. A compressor case as claimed in any preceding claim wherein one or more sub-sections have been coupled to an adjacent sub-section by a weld.

11. A method of manufacturing a compressor case for a gas turbine engine, the compressor case comprising a generally cylindrical body formed of a plurality of adjacent cylindrical subsections, wherein the cylindrical body has a first end and an opposing second end and wherein the second end is arranged in use at a position within the engine operating at a higher temperature than the first end, the method comprising the steps of:(A) forming one or more of the cylindrical sub-sections at the second end of the body with Ti-6242; and(B) forming one or more of the cylindrical sub-section at the first end of the body with Ti- 64.

12. A method as claimed in claim 11 , wherein the one or more cylindrical sub-sections at the second end of the body are coupled to the one or more cylindrical sub-sections at the first end by means of an electron beam weld.

13. A method as claimed in claim 11 or 12, wherein the individual sub-sections are formed using a laser directed energy deposition with wire (L-DED-w) additive manufacturing process and each subsequently welded to an adjacent sub-section.

14. A method as claimed in claim 11 , wherein the sub-sections are formed by means of a laser directed energy deposition with wire (L-DED-w) additive manufacturing process, the method further comprising the step of transitioning from a Ti-64 wire input to the manufacturing process to a Ti-6242 wire input at the point along the body where the sub-section is to be formed of Ti-6242.

15. A method as claimed in any of claims 11 to 14, wherein the compressor case is a high pressure compressor case of a gas turbine engine.

16. A gas turbine engine for an aircraft comprising a compressor case as claimed in any of claims 1 to 10.

17. A method of manufacturing a compressor case of a gas turbine engine as claimed in any of claims 11 to 15

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