GB2382539A

GB2382539A - Improved method of manufacture for hollow components

Info

Publication number: GB2382539A
Application number: GB0227650A
Authority: GB
Inventors: Stewart Roy Evison
Original assignee: Alstom SA
Current assignee: Alstom SA
Priority date: 2001-11-28
Filing date: 2002-11-27
Publication date: 2003-06-04
Anticipated expiration: 2022-11-27
Also published as: GB0227650D0; GB0128442D0; GB2382539B

Abstract

A method of manufacture involving the precision finish-machining of a hollow drum-shaped component (1), e.g., a turbine rotor drum, that has been previously roughly formed. The component has internal grooves (3) or similar annular features extending around an internal cavity. During finish-machining, swarf (5) can build up in the grooves and disrupt the machining process. To prevent build-up of the swarf (5), the grooves are provided with a filler material (6), thereby removing the need for periodic cleaning of the grooves during the machining process. The filler material is substantially softer than the material from which the component is made and thus is easily cut away as and when the groove is machined.

Description

Improved Method of Manufacture for Hollow Components Field of the Invention The present invention relates to the machining of work pieces. More specifically, it relates to the precision machining of hollow, generally drum-shaped components, which are provided with internal annular grooves or similar features that extend circumferentially around the cavity.

Background of the Invention The precision machining of hollow components such as turbomachine rotor drums can involve the use of two stages of machine shaping. The first stage involves the rough machining of the metal structure with a strong but relatively imprecise cutting tool, whereas the second stage involves the more precise shaping of the metal structure with a less robust cutting tool.

During the process of machining metal, heat is generated and to limit the build-up of heat it is standard practice to use a liquid coolant mix that is continually and forcefully supplied to the cutting region to help disperse the heat and carry away the swarf from the tool.

Figure 1 diagrammatically shows an axial cross-section of a turbine rotor drum 1 whose rough-machined interior surfaces are being finish-machined by a computercontrolled tool 4. The rotor drum 1 is held with its major axis X-X horizontal and is rotated relative to the tool 4. Tool 4 is not rotated but is moved radially inwards and outwards and axially fore-and-aft as necessary to finish-machine the surfaces of the annular recesses or grooves 6. Liquid coolant is supplied in the direction D to the cutting area of the tool 4 from a nozzle or nozzles (not shown) which may conveniently be mounted on the tool support S. During the machining operation, the coolant washes swarf away from the tool. At least some swarf is washed out of the groove being machined and into adjacent grooves, which are yet to be finish-machined. Due to the centrifugal effect of the drum's rotation, the swarf is thrown to the circumference of the grooves and becomes compacted. Computer-controlled machining operations assume free access for cutting tools to the surface to be machined and when that

access is impeded, the machining operation is disrupted, with possible breakage of the tool or even scrapping of the rotor drum. Before the present invention, the only way to prevent this from happening was to periodically clean out the grooves during the machining process, which slows down production.

If build-up of compacted swarf in those grooves that have yet to be finish-machined can be prevented, manufacturing time can be reduced and efficiency improved.

Summary of the Invention In response to the problems mentioned above, the invention provides a method of manufacturing a hollow, generally drum-shaped component, comprising the steps of (a) forming the component with a plurality of internal annular grooves, the grooves extending circumferentially around an internal cavity that extends axially of the component ; (b) providing a filler material that is substantially softer than the component material and at least partially filling the grooves around their circumferential extent with the filler material; (c) introducing a finish-machining tool into the cavity, rotating the component and the tool relative to each other, and moving the tool radially and axially to finishmachine a selected groove by removing the filler material and some component material therefrom ; (d) similarly finish-machining another groove which has yet to be finishmachined; and (e) repeating step (d) until all the grooves have been finish-machined.

The component may be a turbomachine rotor drum.

Conveniently, the component is held with its longitudinal axis horizontal and rotated with respect to the tool. The component may have a blind end and an open end and in this case the finish-machining process is preferably begun at the blind end of the cavity and progressed towards the open end.

At least in cases where the component is being rotated instead of the cutting tool, it will be important to fill the grooves completely around their circumferential extent so that swarf may not lodge in any of the radially outer parts of the grooves; however, it

may not be necessary to fill the grooves up to their full radial depths; rather, the grooves may be partially filled in their radial extents, to a discretionary radius.

During the machining process, a coolant is applied to the area being machined to reduce the build up of heat. Preferably, the coolant will be applied in such a way as to direct the flow of used coolant, which contains the swarf, towards the grooves provided with the filling material and on to a drainage point.

It should be understood that the turbomachine rotor drum, or other component with a plurality of internal grooves, may initially be formed by rough machining of an original work piece; alternatively, the component may initially be formed by a casting process.

The filling material should be plastically deformable or mouldable so that it can be provided into a wide variety of groove configurations. For example, a plastic foam that can be injected into the grooves to self-cure in situe would be suitable. Applicant prefers to use expanding polyurethane foam, which can be extruded into the grooves from a hand-held can through a nozzle by means of a propellant gas. Such expanding plastic foam is readily available from a number of suppliers.

The type of finish machining used in the method may be a precision turning or endmilling process. Alternatively, other types of machining may be used, such as routing. However, it will be appreciated that this invention may be used in conjunction with any machining tool that generates swarf.

It will be appreciated that the invention may be most suitably used in the machining of work pieces where the waste flow of the coolant/swarf mix is restricted. It will therefore be understood that this method may be applied to the manufacture of products other than turbine rotor drums.

Brief Description of the Drawings By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic representation of a machining process as in the prior art; and

Figure 2 shows a diagrammatic representation of a machining process according to the invention.

Detailed Description of the Preferred Embodiment.

A turbine rotor drum 1, as shown in both Figures, is formed from high-grade stainless steel with a plurality of dovetail-section, circumferentially extending slots 2 on its outer surface for receiving complementary-shaped roots of rotor blades (not shown). The rotor drum is formed hollow and is provided with a plurality of deep recesses or grooves 3 on its inner surface. The grooves 3 are defined between adjacent annular structural members 7, which strengthen the rotor drum against centrifugal forces exerted by the blades when the whole assembly is rotating at high speed during service.

Hence, the grooves 3 are located in the intervals between the rotor blade slots 2, thus allowing the rotor drum 1 to retain its structural strength.

Once the turbine rotor drum 1 is formed in to its general shape, it is necessary to machine it to achieve a more precise finished shape. The precision machining is carried out by a cutting tool 4 carried on a support S.

As the tool 4 machines the inside of the rotor drum 1, a build-up of heat occurs, which can, amongst other things, reduce the accuracy of the machining and overheat the drum material. To control this heat build-up, coolant is forcibly introduced to the area being machined, e. g., from the direction D. The flow of coolant also serves to remove the swarf that has been machined from the rotor drum. However, this swarf 5 can become deposited in the internal grooves 3 of the rotor drum 1 where it can become compacted due to rotation of the drum during the machining operation, as is shown in Figure 1.

As previously explained, the compacted swarf 5 can create a hazard to the machining tool 4. Hence, the manufacturing process must be stopped periodically so that the grooves 3 can be cleaned out. Failure to remove compacted swarf can cause the machining tool 4 to cut inaccurately or even break.

The preferred embodiment, as shown in Figure 2, provides an improvement in the manufacturing method, which eliminates the need to carry out periodic cleaning of the

grooves 3. The grooves 3 are filled with a relatively soft filler material 6, thus preventing the swarf from building up and becoming compacted therein.

The skilled person will understand that, at least in cases where the component is being rotated rather than the cutting tool, it will be necessary to ensure that the grooves are filled all around their circumference with the filler material. However, it will be appreciated that, although Figure 2 shows the grooves 3 as being completely filled to their maximum radial extent with the filler material 6, the grooves 3 do not need to be completely filled in the radial sense for a positive benefit to be achieved.

Because the filler material 6 is softer than the drum material being machined, it does not provide any deleterious resistance to the machine tool 4 as it works. A typical type of material that can be used as filler is a foamed thermoplastic, such as expanded polystyrene, although other suitable materials, such as foam rubber, may be of equal use. Besides being substantially softer than the drum material, the filler material must be plastically deformable or mouldable so that it can be placed into a variety of different shaped grooves.

The filler material may be manually placed into the grooves. For example, foamed plastic can be sprayed into the grooves from the nozzle of a hand-held spray-can. However, the filler material could alternatively be extruded into the grooves in an automated process.

Although the above description has focussed on turbine rotor drums, the skilled person will appreciate that the invention is equally applicable to compressor rotor drums, or indeed any hollow drum-shaped component with similar internal features requiring finish-machining.

Claims

1. A method of manufacturing a hollow, generally drum-shaped component, comprising the steps of : (a) forming the component with a plurality of internal annular grooves, the grooves extending circumferentially around an internal cavity that extends axially of the component; (b) providing a filler material that is substantially softer than the component material and at least partially filling the grooves around their circumferential extent with the filler material; (c) introducing a finish-machining tool into the cavity, rotating the component and the tool relative to each other, and moving the tool radially and axially to finishmachine a selected groove by removing the filler material and some component material therefrom, (d) similarly finish-machining a groove which has yet to be finish-machined, and (e) repeating step (d) until all the grooves have been finish-machined.

2. A method according to claim 1, wherein the component is a turbomachine rotor drum.

3. A method according to claim 1 or claim 2, in which the component is held with its longitudinal axis horizontal and rotated with respect to the tool.

4. A method according to claim 3, in which the grooves are filled completely around their circumferential extent.

5. A method according to any preceding claim, in which the grooves are partially filled in their radial extents.

6. A method according to any preceding claim, in which the component has a blind end and an open end and the finish-machining process is begun at the blind end of the cavity and progressed towards the open end.

7. A method according to any preceding claim, in which a coolant is applied to the area being machined such that used coolant containing waste material flows towards the grooves provided with the filling material

8. A method according to any preceding claim, in which the component with a plurality of internal grooves is initially formed by rough machining of an original work piece.

9. A method according to any preceding claim, in which the component with a plurality of internal grooves is initially formed by a casting process.

10. A method according to any preceding claim, in which the filling material is plastically deformable or mouldable.

11. A method according to any preceding claim, in which the filling material is a self-curing plastic foam.

12. A method according to claim 11, in which the plastic foam comprises expanded polystyrene.

13. A method of manufacturing a turbine rotor drum, substantially as described with reference to, or as shown in, Figure 2 of the accompanying drawings.