GB2271737A - Manufacture of annular articles - Google Patents

Abstract

Ring-like articles are made by depositing a coating 4 of metal upon the surface of a rotatable mandrel 1 by means of a rapidly rotating bar 3 of consumable material and continuing the rotation of the mandrel and bar until a coating of the required thickness has been deposited. The mandrel and coating are then separated. A grinding wheel may be used to skim the surface of the coating to prepare that surface for the addition of further coating material. <IMAGE>

Description

MANUFACTURE OF ANNULAR ARTICLES This invention relates to a method and apparatus for manufacturing ring-like articles such as annular combustion rings and discs for the bladed disc assemblies of the turbines and compressor of gas turbine engines.

A gas turbine power plant such as an aircraft propulsion unit includes a wide variety of ring-like objects ranging from bearing rings only a few inches in diameter to rotor discs which may be many times that size.

A conventional technique employed for the manufacture of such ring-like objects is forging whereby a billet of metal such as nickel-base alloy or titanium is forged to as near optimum shape as practicable. Such forging calls for a very close control of the temperature during the various operations and an exceptionally high standard of furnace control equipment, careful maintenance and cleanliness of the forging hammers, presses and dies is essential.

Annular combustion rings can be cold forged from nickel base alloys to exacting tolerances and surface finishes which alleviates the need for further machining before welding them together to produce the combustion casing.

High pressure compressor casings are often forged as rings or half rings which, when assembled together form the rigid structure of the engine. They are produced in various materials, eg stainless steel titanium and nickel alloys.

However carefully are the various forging operations carried out the finished product is always liable to contain defects.

In an alternative to forging the ring-like objects can be cast but, again, it is always possible for the finished product to include occlusions and other defects.

An object of the present invention is to provide a method and apparatus for producing ring-like objects having a fine wrought microstructure substantially free of defects.

According to one aspect of the invention a method of making a ring-like object comprises the steps of preparing the surface of a cylindrical mandrel having a longitudinal axis, mounting said mandrel for rotation about said axis, rotatably mounting a bar of consumable material with a free end directed towards said surface, rotating said bar, pressing said free end of said bar against said surface to induce frictional heat at the interface between said free end and said surface thereby bringing the engaging surfaces to a plastic state and causing coalescence, rotating said mandrel whilst building up a coating of said consumable material on said surface, continuing to apply said pressure whilst rotating said bar and said mandrel until a ring of the required thickness is built up, removing said bar from contact with said ring, arresting rotation of said mandrel, and separating said ring and said mandrel.

Preferably a grinding wheel is put into contact with the surface for further coating.

The mandrel may comprise a tubular bar so as to facilitate the separation of the mandrel from the ring may be facilitated as by machining.

Various materials may be employed for the consumable bar, eg stellite, nickel based alloys, titanium and stainless steel.

In one particular arrangement the consumable bar and the grinding wheel are diametrically opposed relative to the mandrel, and the bar is rotatable about an axis normal to the longitudinal axis of the mandrel.

It will be realised that the method of the present invention has certain characteristics of the known friction surfacing and friction welding. It is well-known to add metal to a part to restore that part to a required dimension after damage and it is also well known that when thick coatings of hard materials are required upon an article some form of welding is used.

In this case the overlay materials include such as high carbon steel, ferrous alloys of chromium and manganese and numerous non-ferrous alloys containing principally cobalt, manganese and tungsten. The hardness of these materials varies very considerably. High carbon welding rod with a carbon content ranging from 0.9 to 1.1% is the most economical hard-facing material to apply from the standpoint of initial cost. Such rods form a tough surface of moderate hardness ranging from Rockwell C30 to C45. Increased hardness and wear resistance an be obtained by alloying steel with such elements as nickel, manganese, molybdenum and chromium. The above mentioned materials may all be employed for the material of the consumable bar as convenient.

In friction welding coalescence is produced by the heat of friction generated by rotating one piece against another under controlled axial pressure or controlled rate of feed, the two surfaces in contact being heated until the adjacent material becomes plastic. The relative motion between the two is then stopped and a forging pressure applied which upsets the joint slightly. This pressure may be equal or in excess of the pressure prevailing during the heating.

In friction surfacing the surface of an article is then engaged by the end of a rapidly rotating bar which is pressed against the surface as it is traversed over the surface.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 illustrates the positioning of a mandrel and a consumable bar as the application of a coating on the mandrel commences, Figure 2 is a plan view of the equipment shown in Figure 1, Figure 3 illustrates the apparatus of Figure 1 with the addition of a grinding wheel and a flash shearing device, and Figure 4 is a perspective view of a ring made by the method and apparatus of the invention.

Referring to the drawing Figures 1 and 2 show a hollow cylindrical mandrel 1 of mild steel mounted for rotation about its longitudinal axis 2. A bar 3 of consumable material such as stellite is mounted with its longitudinal axis 4 normal to the axis 2 of the mandrel.

The bar 3 is rotated at high speed as its free end is pressed into engagement with the mandrel 1. The friction created at the unction of the bar 3 and mandrel 1 generates sufficient heat as to increase the temperature of the bar so that the engaging surfaces of bar and mandrel are brought to plasticising temperatures. As this occurs the mandrel is slowly rotated and some of the material of the bar remains coalesced with the mandrel surface and forms a coating 4 on that surface. The high speed rotation of the bar, the pressure of the bar against the mandrel and the low speed rotation of the mandrel are continued as the thickness of the coating is gradually built up until a ring of the desired thickness is achieved whereupon the bar 3 is removed from engagement with the ring and its rotation is stopped as is the rotation of the mandrel.

The side faces 5,6 of the ring coating 4 are then trimmed as required and the mandrel and ring coating are separated. Separation may be by means of a machining operation.

In an alternative arrangement shown in Figure 3 a grinding wheel 7 is brought into contact with the surface of the coating 8 so as to skim the surface thus preparing it for the deposition of the next to be applied layer.

To prevent the build-up of flash at the free end of the bar 3 a cutter 9 is provided which shears off the flash as it occurs.

When the coating has been built up to the required thickness the bar is disengaged from the mandrel and its rotation is stopped as is the rotation of the mandrel.

The ring 10, after removal of the mandrel is finish-machined to remove any defects at the edge of the ring and the resulting product is found to have a fine, wrought microstructure with no internal occlusions or other defects.

In a further embodiment of the invention the surface of the mandrel is pre-heated to a temperature a little below its plasticising temperature and is then engaged by the end of a rapidly rotating bar which is pressed against the mandrel surface. By pre-heating the surface, the plasticising of the material requires less time in contact with the consumable bar the end of which can be moved relatively rapidly over the surface, depositing a coating of the material of the consumable bar uon the surface as it does so.

In a further alternative embodiment the grinding wheel may be replaced by other forms of machinery to skim the surface, or may be replaced by chemical pickling.

Yet again, the entire process may be carried out in a controlled inert atmosphere, such as argon, so as to avoid oxidation or other corrosion of the surfaces.

It can thus be seen that ring-like objects of any diameter can be produced by the method and apparatus described.

Claims (15)

1 A method of making a ring-like object comprises the steps of preparing the surface of a cylindrical mandrel having a longitudinal axis, mounting said mandrel for rotation about said axis, rotatably mounting a bar of consumable material with a free end directed towards said surface, rotating said bar, pressing said free end of said bar against said surface to induce frictional heat at the interface between said free end and said surface thereby bringing the engaging surfaces to a plasticising temperature and causing coalescence, rotating said mandrel whilst building up a coating of said consumable material on said surface, continuing to apply said pressure whilst rotating said bar and said mandrel until a ring of the required thickness is built up, removing said bar from contact with said ring, arresting rotation of said mandrel, and separating said ring and said mandrel.

2 A method as claimed in claim 1 and including the step of engaging the surface of said coating by a grinding wheel whereby the surface of said coating may be prepared for the addition of further coating material.

3 A method as claimed in claim 1 wherein the mandrel is pre-heated to below its melting temperature prior to the engagement of the rotating bar.

4 A method as claimed in any preceding claim wherein the mandrel comprises a tube.

5 A method as claimed in any one of claims 1-3 wherein the bar of consumable material comprises a bar of stellite.

6 A method as claimed in any one of claims 1-4 wherein the bar of consumable material comprises a bar of nickel base alloy.

7 A method as claimed in any one of claims 1-4 wherein the bar of consumable material comprises a bar of titanium.

8 A method as claimed in any one of claims 1-4 wherein the bar of consumable material comprises a bar of stainless steel.

9 A method as claimed in any preceding claim, when carried out in an inert atmosphere.

10 An apparatus for making a ring-like object comprising a cylindrical mandrel having a longitudinal axis of rotation, rotatable mounting means for mounting and rotating said mandrel, a bar of consumable material, rotatable mounting means for mounting and rotating said bar, and extension means whereby the bar may be brought into and out of engagement with said mandrel to provide a coating on said mandrel.

11 An apparatus as claimed in claim 10 and including means for skimming said coating whereby said coating may be prepared for the addition of further coating material.

12 An apparatus as claimed in claim 11 wherein the skimming means is a grinding wheel.

13 A ring-like object made by the method and apparatus claimed in any preceding claim.

14 A method of making a ring-like object, substantially as described hereinbefore with reference to the accompanying drawings.

15 An apparatus for making a ring-like object, substantially as hereinbefore described with reference to the accompanying drawings.