GB2428396A

GB2428396A - A method of manufacturing an article with a reference datum feature

Info

Publication number: GB2428396A
Application number: GB0514949A
Authority: GB
Inventors: Matthew James Hibbs
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2005-07-21
Filing date: 2005-07-21
Publication date: 2007-01-31
Also published as: GB0514949D0

Abstract

A method of manufacturing an axi-symmetric article 14 such as a rotor blisk (figure 1, 10) for a gas turbine engine is described, where at least one reference feature 20 is formed on the article 14 prior to the step of final machining the article 14. The reference feature 20 provides a permanent position reference datum for use in subsequent stages of manufacture including final machining of the article 14 and additionally or alternatively subsequent repair or re-working of the article 14. The reference feature 20 may be an oversize diameter bolt hole in a pitch circle of similar but normal size diameter reference holes.

Description

METHOD OF MANUFACTURING AN ARTICLE HAVING A

REFERENCE DATUM FEATURE AND AN ARTICLE MANUFACTURED

THEREBY

The present invention relates to a method of manufacturing an axisymmetric article such as a gas turbine engine rotor wherein one or more reference features is/are formed on the article to provide a reference datum for precision manufacturing of the article.

The manufacture of complex articles such as gas turbine rotors usually involves the article being marked with one or more reference marks to establish a datum position on the article for use during the various manufacturing stages. The use of reference marks is well established in the manufacture of complex parts, particularly in the manufacture of gas turbine engine rotors such as integral bladed disc rotors, also referred to as bliscs, or blisks where the rotor blades and disc rotor are integrally formed, either by machining the blisc from solid or by friction welding blade stubs to the radially outer circumferential rim of the disc. Bliscs have a number of advantages when compared with more traditional bladed rotor assemblies. In particular buses are generally lighter than equivalent bladed disc assemblies because the blade to disc mounting features present in a conventional bladed disc, such as dovetail rim slots and blade roots, are no longer required.

Bliscs are increasingly found in axial flow compressors of modem gas turbine engines and are. also particularly suitable for use in lift-fan or lift-engine applications, the Rolls-Royce lift-fan being one such example.

Reference marks are used extensively in the manufacture of blisc type rotors, particularly where the bliscs are formed by friction welding. The reference marks enable the correct angular position for each blade to be friction welded to the disc circumference so that the resultant component conforms to precise predetermined dimensions. Following welding of the blades to the disc the reference marks are used to determine reference positions on the welded blisc for subsequent mhining operations. Prior to making the final or finishing cut for a particular surface containing a reference mark, the various dimensions of the article are chked, for example using an automatic probe, beibre the surface is machined with the reference mark being removed during this final machining step. This enares that all the reference marks on the blisc are removed during final n;1ining so that those surfaces are free of any discontinuities that would orwise be present due to the existence of the reference marks. This method of manufacturing rotor bliscs therefore has the advantage that the finished rotor is free of surface reference marks which could give rise to imprecise assembly of the firnshed rotor andlor stress concentration in the region of on the machined surfaces.

According to an aspect of the present invention there is provided a method of manufacturing an axi-symmetric article in which at least one reference feature is formed on the article at least prior to the step of final (or finish) machining the article such that the reference feature provides a permanent reference datum position for use in subsequent stages of manufacture including final (or finish) machining of the article, and additionally or alternati ely subsequent repair or re- The present invention therefore provides a method of manufacturing an axi- symmetric article wherein a permanent reference mark may be formed at an early stage of manufacture and which is used as a datum for the position of subsequent machining operations including final machining of the article and additionally or alternatively subsequent repair or re-working of the finished article. The method of the present invention has paricular advantages in the manufacture of complex axi-symmetric articles such as gas turbine engine rotor bliscs where repair may involve the removal of a damaged blade from the rim of the disc and friction welding a replacement blade in its place. The permanent reference datum provided by the reference feature readily enables friction welded bladed discs to be repaired within the tolerance limits of the blisc design. The use of a permanent reference datum also provides for improved accuracy when checking the final dimensions of the finished article and also any reworking if required, subsequent to the final machining if the final check shows that the dimensions of the article fall outside acceptable tolerance limits.

In preferred embodiments, the reference feature comprises at least one machined surface of the article. This has the advantage that a reference datum is provided by an accurately machined surface on the article which provides a reference datum for subsequent machining of the article. Alternatively, the reference feature may be formed during casting or forging of the article prior to machining.

The reference feature may comprise a permanent structural feature having a distinguishing structural characteristic. The permanent structural feature is preferably a structural feature of the article that is present on the article from an early manufacturing stage and that has a primary function unrelated to its secondary function as a permanent reference datum on the finished article, that is to say the reference feature may be provided by any permanent identifiable feature that is pre;eni at an early or initial stage of manufacture and is preserved in the finished arlicle.

In preferred embodiments the reference feature is structurally similar but not identical to other structural features of the article, for example other substantially identical structural features. The reference feature may, for example, have a similar but not identical shape and/or size to the ether structural features. This has the a1vantage that the reference feature nuv be readil-; identified by its distinguishing structural characteristic(s) when present in a group of similar features on the article both during manufacture and subsequent thereto.

In a preferred embodiment the reference feature comprises a bolt hole or the like formed in the article. The bolt hole may be in the form of a blind or through bore and may be one of a group of bolt holes formed in the article in which the reference bolt hole has at least one distinguishing geometric dimension that is different to the other bolt holes of that group. For example, the reference bolt hole may have either an under or over size diameter relative to the other bolt holes of the group. In embodiments of this type it is possible to form one or more reference bolt holes in the article in a group of bolt holes, for example in a group of bolt holes arranged circumferentiafly in a pitch circle around a part or region of the axi- symmetrical item such that the reference bolt hole or holes provide a permanent reference datum on the article at a specific circumferential position. The reference bolt hole or holes then provide a reference datum on the article analogous to timing marks that are often found on rotating components in rotating machines, for example internal combustion engines and the like. In this respect non-permanent reference datum features are frequently referred to as timing marks' by those skilled in the art.

In the method of the present invention it is preferred that the at least one reference feature is formed on the article during an initial or early stage of manufacturing the article. For example, if the article is manufactured from a casting or forging it is preferred that the reference feature or features, for example a bolt hole. is/are formed during an initial machining operation or at an early stage of machining before any precision machining steps take place. In this way the precise dimensions of the article being manufactured can be correctly determined using the pre-machined reference feature or features as a reference datum for the subsequent precision machining of the article including the final (or finish) machining of the article. This also has the advantage that if the finished article requires any re-work, for example to correct incorrectly machined dimensions the reference datum can be used for this purpose and also in the same way if the finished article is damaged and repair is required, for example during the service life of the article.

Preferab1 the article is a rotor. The method of the present invention is applicable to the manufacture of any axi-symmetric article but finds particular application in the manufacture of rotors having a series of blades extending radially from a radially outer circumferential rim of the rotor, for example in the manufacture of integrally bladed discs for a gas turbine engine or a similar turbo-machine such as an axial flow compressor or fan, including, for example, an aircraft lift-fan of the type founJ in certain aircraft types.

The method of the present invention is equally applicable to the manufacture of bladed rotors where the blades are welded to the rim, for example, by friction welding, or where the blades are machined from solid.

The method of the present invention finds particular application in the manufacture of integralv bladed discs for gas turbine engines, lift-fans and the like because the reference feature or features, which is/are a permanent feature of the finished article, can be used as a reference datum for repair purposes during the service life of the rotor, for example to replace a damaged blade by removing the blade and friction welding a replacement to the rim of the rotor in order to effect a precision repair.

A further advantage of using an oversize diameter bolt hole as the reference bolt hole occurs when the reference bolt hole or holes is/are part of a group of circumferentially spaced bolt holes provided for mounting the rotor to a rotor shaft since the final position of the normal size holes is often determined to some extent by the requirement to balance the rotor after final machining. Rotating components are often balanced by the removal of material from specific balancing lands provided on the component or by the method of mass centreing where location features, for example bolt holes or the like, are offset machined to compensate for unbalance. In the method of mass centreing the location features of the component are machined to their final dimensions such that the position of the axis of rotation of the rotor, as determined by the location features, is coincident with the centre of mass of the rotor. Mass centreing is a preferred balancing method for rotors such as bliscs arid therefore the present invention readily enables a blisc to be manufactured with one or more oversize bolt holes to provide a reference datum with the final position of the remaining holes being determined during balancing of the rotor by offset machining.

According to another aspect of the invention there is provided an integrally bladed disc for a gas turbine engine of the like manufactured directly of indirectly by a method according to the above mentioned method of the present invention.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a three dimensional view of part of a rotor blisc for a gas turbine engine or the like; Figure 2 is a rear view of a circumferential sector of the rotor blisc of Figure 1; Referring to Figure 1, a rotor stage of a gas turbine engine or lift-fan comprises a blisc 10 which includes a disc part 12 and a plurality of circumferentially spaced aerofoil blades 14 which extend radially around the disc rim 16. The disc 12 and aerofoil blades 14 may be of the same metal alloy material. Alternatively, different metal alloy ttaterials may be used for the disc and the blade. The disc and blades may be maclJned from a single forging by machining methods well known in the art. Altematvely the aerofoil blades may be friction welded to the disc rim 16 as is well know- in the art of blisc manufacture.

In the drawiiz Figure 1 only part of the blisc circumference is shown, however it is to be undersood that the blisc has axial symmetry about its nominal axis of rotation, tha: is to say the blisc is axi-symmetric and therefore the remaining part of the disc r1:: shown in the drawing of Figure 1 is identical to that which is shown.

In the drawir of Figure 1 the blisc is viewed from the rear, that is to say looking from the downstream side of the blisc. The blisc is provided with at least a rearward mounting flange 18 in the region of the disc hub. The mounting flange 18 is provided with a plurality of circumferentially spaced holes 20 which are drilled in a pitch circle about the disc axis of rotation and are used to bolt the blisc to an adjacent shaft section or another disc or blisc in the rotor sub-assembly. In the blisc of Figure 1 one or more of the holes 20 has an oversize internal bore diameter so that it may be readily identified as a reference feature for providing a reference datum for use during the manufacture of the blisc and subsequent re- The oversize hole is formed in the blisc during an early stage of ma=facture before the aerofoil blades 14 are machined from a solid rim of the blisc forging or joined to the disc periphery by welding or other means. In this way the Jxsition of each blade machining operation or blade joining operation is referenced back to the original oversize reference hole to ensure that the blades are correctly positioned in the blisc during manufacture.

The bolt hole having the oversize internal bore diameter s present in th finished article and therefore this reference feature is present in the finished article and hence is available for use as a reference datum feature in subsequent repair and/or inspection processes. The unique dimensions of the oversize bore ensurei that the reference feature is readily identifiable in the finished machined blisc by:s unique dimensions.

Referring now to Figure 2, which shows a sector of the blisc of Figure 1 with a single aerofoil blade 14 extending radially outwards from the disc rim 16. In this view the aerofoil blade 14 is fully shown while only that part of the disc to which the aerofoil is attached is shown. In this view the mounting flange I S is shown with the reference bolt hole 20 comprising the oversize internal bore for providing the reference datum of the blisc. As can be seen in the view of Figure 2 the oversize internal bore 20 is positioned approximately midway between the outer rim 16 and the radially inner hub 19 of the disc.

Although aspects of the present invention have been described with reference to the blisc shown in the accompanying drawings, it is to be understood that the invention is not limited to the illustrated embodiment and that various changes and modifications may be effected without exercise of further inventive skill and effort.

For example, in the manufacturing method of the present invention any feature that is normally present in the article being manufactured both during manufacture and in the finished article may be used as a reference datum if it is possible to be identified as such by a unique property or characteristic, for example a structural characteristic including but not limited to an oversize internal diameter bore as disclosed hereinbefore. In particular the selected reference datum is preferably one of a number of similar features present in the finished article so the reference datum is subsumed into the whole article during manufacture but remains identifiable by its unique characteristic or characteristics.

Claims

1. A method of manufacturing an axi-symmetric article wherein a least one reference feature is formed on the article at least prior to the step of final machining the article such that the said reference feature provides a permanent position reference datum for use in subsequent stages of manufacture including final machining of the article and additionally or alternatively subsequent repair or re-working of the finished article.

2. A method as claimed in Claim I wherein the said at least one reference feature comprises at least one machined surface.

3. A method as claimed in Claim 1 or Claim 2 wherein the said at least one reference feature comprises a permanent structural feature having a distinguishing structural characteristic.

4. A method as claimed in Claim 3 wherein the said at least one reference feature is similar but not identical to other substantially identical structural features of the article.

5. A method as claimed in Claim 4 wherein the said at least one reference feature has a similar but not identical shape and/or size to the said other structural features.

6. A method as claimed in any preceding claim wherein the said at least one reference feature comprises a bolt hole or the like formed in the said article.

7. A method as claimed in Claim 6 wherein the said reference bolt hole comprises one of a group of bolt holes formed in the said article and wherein the said reference bolt hole has at least one distinguishing geometric dimension relative to the other bolt holes of the said group.

8. A method as claimed in Claim 7 wherein the said reference bolt hole has either an under or over size diameter relative to the other bolt holes of the said group.

9. A method as claimed in any preceding claim wherein the said at least one reference feature is formed on the article during an initial or early stage of manufacturing the article.

10. A method as claimed in any preceding claim wherein the said article is a rotor.

11. A method as claimed in any preceding claim wherein the said article comprises a rotor having a series of blades extending radially form a radially outer circumferential rim thereof.

12. A method as claimed in Claim II wherein the said blades are welded to the said rim, preferably by friction welding.

13. A method as claimed in Claim 11 wherein the said blades are machined from solid material in the radial outer region of the said rotor.

14. A method as claimed in any of Claims 10 to 13 wherein the said rotor is an integrally bladed disc.

15. A method as claimed in Claim 14 wherein the rotor comprises an integrally bladed disc or disc for a gas turbine engine or the like.

16. A rotor manufactured directly or indirectl:. by a method according to an one of Claims ito 13.

17. An integrally bladed disc for a gas turbine engine or the like manufactured directly or indirectly by a method according to any one of Claims I to 15.

18. A method substantially as hereinbefore described with reference to the accompanying drawings.

19. An integrally bladed disc for a gas turbine engine or the like substantially as hereinbe fore described with reference to the accompanying drawings.