GB2373749A

GB2373749A - Apparatus and method for forming a body

Info

Publication number: GB2373749A
Application number: GB0107561A
Authority: GB
Inventors: Steven Alan Jones
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2001-03-27
Filing date: 2001-03-27
Publication date: 2002-10-02
Also published as: GB0107561D0

Abstract

An apparatus 10 is disclosed for forming a body by deposition of weld material. The apparatus 10 comprises a welding head 12, support means 34 for supporting the body, and a supply 22 of a welding material to be deposited on the support means 34 by the welding head 12 to form a body. A chamber 52 is also provided which surrounds the support means 34 and the welding head 12, and the apparatus further includes means 54 for supplying to the chamber 52 a gas to provide an atmosphere in the chamber 52 which is substantially unreactive to the weld material. The gas may enter the chamber through a porous bed (64, figure 2).

Description

Apparatus and Method for Forming a Body This invention relates to apparatus for forming bodies. More particularly, the invention relates to apparatus and methods for forming bodies by deposition of a weld material.

The formation of components for aerospace engines can be carried out by any of several techniques of deposition of a weld material. These techniques involve the striking of an arc between two electrodes, the first electrode being held in a welding head to which is fed a supply of a weld material, the supply being in the form of a wire of the material wound upon a reel. The second electrode is in the form of a substrate or foundation upon which the weld material is to be deposited to form the component. The foundation may be in the form of a metal plate. A supply of an inert gas is fed to the welding head during its operation.

When the welding head and the foundation are connected to a supply of electricity, the inert gas is ionised to form a plasma and an arc is created in the plasma which melts the metal wire and the substrate. The metal is then

deposited onto the foundation in a controlled manner. The welding head is mounted on a robotic arm and the foundation is mounted on a movable turntable. By controlling the movement of the arm and the turntable, the metal can be deposited on the foundation in order to form components of any design shape.

One such method of forming components is to provide he welding head with a permanent electrode and to provide a separate metal wire to the welding head. This method is generally known in the art as tungsten inert gas welding which is generally shortened to TIG welding. The use of he word tungsten is intended as a synecdoche, and it will he appreciated by those skilled in the art that other suitable materials could be used as the electrode.

Another such method involves the use of a sacrificial electrode in the welding head. With this arrangement, the metal wire which provides the weld material also constitutes the electrode and is fed through the welding head. This method is generally known in the art as metal inert gas welding, which is generally shortened to MIG welding. The presence of oxygen and nitrogen during the formation of bodies from titanium alloy using either MIG or TIG welding deposition processes causes the formation of oxides and nitrides and the body being brittle and susceptible to cracking.

Attempts have been made to overcome this problem by providing a trailing shield of the argon gas from the welding head. However, components manufactured using this technique were still prone to cracking.

According to one aspect of this invention there is provided apparatus for forming a body by deposition of a weld material, the apparatus comprising a welding head, support means for supporting the body, a supply of a welding material to be deposited on the support means by the welding head to form the body, means defining a chamber in which the support means and the welding head are arranged, and means for supplying to the chamber a gaseous medium to provide an atmosphere in the chamber which is substantially unreactive to the weld material.

Preferably, the welding head is mounted on manipulating means, for example a robot arm, and the manipulating means is also arranged in the chamber.

The atmosphere may contain less than substantially 500ppm oxygen, desirably less than substantially 200ppm oxygen, preferably less than substantially 100ppm oxygen, and more preferably less than substantially 40ppm oxygen.

The atmosphere may also contain less than substantially 1700ppm nitrogen, suitably less than substantially lOOOppm nitrogen, desirably less than substantially 700ppm nitrogen, preferably less than substantially 350ppm nitrogen and more preferably less than substantially 140ppm nitrogen.

The gaseous medium supplied to the chamber to provide the unreactive atmosphere may be substantially wholly inert, comprising at least one inert gas, for example argon.

The apparatus may further include monitoring means for monitoring the composition of the atmosphere in the chamber and control means for controlling the supply of the gaseous medium to ensure that the atmosphere remains substantially unreactive to the weld material.

The weld material may be a titanium alloy, for example titanium 6/4 which includes 6% aluminium and 4% vanadium, or the weld material may be any other suitable alloy.

The apparatus may further include means for controlling the temperature and moisture content of the atmosphere.

In a first embodiment, the supply means for supplying the substantially unreactive atmosphere includes feed means for feeding the gaseous medium to the chamber to form the atmosphere, the feed means being arranged to feed the gaseous medium to the chamber generally at the level of the floor of the chamber. Preferably, the gaseous medium is so fed at a rate of flow to create turbulent flow therein.

The gaseous medium may be fed at a rate of up to substantially 1000 litres/min, desirably in the range of substantially 150 litres/min to substantially 500 litres/min, preferably in the range of substantially 300 litres/min to substantially 400 litres/min.

In a second embodiment, the apparatus includes a gas diffusion bed and a plenum adjacent the gas diffusion bed. The supply means for supplying the substantially gaseous medium may include feed means for feeding the gaseous medium to the plenum, whereby the gaseous medium diffuses through the diffusion bed to the chamber. Preferably, the

gas diffusion bed and the plenum constitute the floor of the apparatus.

The gaseous medium is preferably fed to the plenum at a rate to provide laminar flow of the gaseous medium into the chamber. The gaseous medium may be fed to the chamber at a rate of up to substantially 100 litres/min, desirably in the range of substantially 10 litres/min to substantially 50 litres/min, preferably at a rate of substantially 40 litres/min.

According to another aspect of this invention, there is provided a method for forming a body by deposition of a weld material, the method comprising providing a welding head, providing support means for supporting the body, supplying a weld material to the welding head, surrounding the welding head and the support means with an atmosphere which is substantially unreactive to the weld material, and connecting the welding head and the support means to a supply of electricity to form an arc between the welding head and the support means or the body to melt the weld material and deposit the material on the support means to form the body in said substantially unreactive atmosphere.

The substantially unreactive atmosphere may be provided in a chamber.

Preferably, the step of surrounding the welding head and the support means with said substantially unreactive atmosphere comprises providing means to supply a gaseous medium to provide said unreactive atmosphere.

The amount of nitrogen in the chamber may be reduced to less than substantially 1700ppm, desirably less than substantially 700ppm, preferably less than substantially 350ppm and, more preferably, less than substantially 140ppm.

The step of surrounding the welding head and the support means with said substantially unreactive gaseous atmosphere may include initially purging the chamber with said inert gas.

Preferably, the method further includes providing a further supply of an unreactive gas to the welding head to provide the plasma in which the arc is created for melting the weld material. The gas may be the same gas as used for providing the atmosphere.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic section side view of one embodiment of apparatus for forming a body; and Fig. 2 is a diagrammatic sectional side view of another embodiment of apparatus for forming a body.

Referring to the Fig. 1, there is shown apparatus 10 for forming a body by deposition of a weld material. The apparatus 10 comprises an arc welding head 12, mounted on the free end of a support mechanism in the form of a robot arm 14. The robot arm 14 comprises a base member 16 on which is pivotally mounted a plurality of sections 18 which are movable about a plurality of axes 20 so that the welding head 12 can be manipulated to any desired position.

The welding head 12 includes a first electrode 19.

A supply 22 of a metal wire 24 is provided, in the form of a reel around which the wire 24 is wound. The metal is in the form of a titanium alloy, for example titanium 6/4 which includes 6% aluminium and 4% vanadium.

The wire 24 is fed from the reel 22 to the welding head 12 such that the end of the wire 24 is arranged just below the tip of the welding head 12. The wire 24 is held in place by suitable holding means 26.

The apparatus 10 also includes a supply of an inert gas, in the form of a cylinder 28, having a pipe 30 leading from the cylinder 28 to the welding head 12 through a pipe extending adjacent the robot arm 14. The gas is any suitable inert gas or gases, or combination of inert and active gases, for example argon or argon/carbon dioxide and provides the medium in which an arc is created, as will

be explained below.

Support means 34 is provided beneath the welding head 12 and comprises a turntable 36 mounted upon a platform 38.

The platform 38 is pivotally mounted, as indicated by the arrow A, by pivot 40 to a pedestal 42 which, in turn, is rotatably mounted, as indicated by the arrow B, upon a base member 44.

A support arrangement 48 is mounted onto the turntable 36. The support arrangement supports the body formed from the deposition of the material of the wire 24 to form the body. The support arrangement 48 constitutes a second electrode, with the arc being created between the first electrode in the welding head and the second electrode which is in the form of the support arrangement 48.

Control means in the form of a computer 46 controls the movement of the support means 34 and the robot arm 14, as well as controlling the supply of argon from the cylinder 28, and the supply of the metal wire 24.

An enclosure 50 defining a chamber 52 surrounds the arm 14 and the support means 34, thereby also surrounding the support arrangement 48 and the body formed thereon. In the embodiment shown, the cylinder 28 of the inert gas and the computer 46 are contained within the enclosure 50. The enclosure 50 can be formed by a suitable rigid material, for example aluminium or a plastics material. The enclosure may also comprise windows to view the body being formed therein and at a door to allow access inside the enclosure 50.

A second supply of an inert gas in the form of a second cylinder 54 is provided to supply the inert gas, for example argon, to the chamber 52 via a pipe 56 so that the atmosphere within the chamber 52 is substantially devoid of oxygen, or at least having less than 40ppm oxygen therein, and is substantially devoid of nitrogen, or at least having less than 140 ppm nitrogen therein. In the embodiment shown in Fig. 1, the argon is fed to the chamber 52 just

above the floor 60.

The argon is supplied at a rate of 300-400 litres/min.

This rate of supply of argon is required to create turbulence and thereby dislodge any trapped pockets of air in the chamber 50.

The air, and the argon fed to the chamber 52 are evacuated therefrom via one or more valves 62 arranged at the too of the enclosure 50.

The embodiment shown in Fig. 2 is generally the same as the embodiment shown in Fig. 1 and the same features have been designated with the same reference numeral. In this embodiment, the floor 60 is replaced by a gas diffusion bed 64 under which is defined a plenum 66. The argon from the cylinder 54 is supplied to the plenum 66 at a rate of about 40 litres/min. The argon fed to the plenum 66 permeates through the diffusion bed 64 under laminar flow and pushes up all the air in the chamber 52, so that it is evacuated from the chamber from the valve (or valves) 62 at the top.

Before the welding operation begins, the chamber 52 of both embodiments is initially purged with the argon from the second cylinder 54 to remove from the chamber 52 as much air as possible. When the purging is completed the amount of oxygen in the chamber is less than 40ppm, and the amount of nitrogen less than 140 ppm After this has been done, the supply of argon is maintained to ensure that the level of oxygen, nitrogen and other residual gases in the chamber remains below a predetermined level. The argon continuously exhausts from the chamber 52 via the valve 62.

Monitoring means 58 may be provided to monitor the composition of the atmosphere in the chamber 52. The monitoring means 58 may include further control means to control the supply from the second cylinder 54 to ensure that the atmosphere within the chamber remains inert.

After the chamber 52 has been purged with argon, the welding process can begin under the argon atmosphere then

formed in me chamber 52. The turntable 36 and the welding head 12 are both connected to a supply of electricity, and argon is fed via the pipe 30 from a cylinder 28 to the welding head 12 to form an argon shroud round the electrode 19 of the welding head 12. The shroud extends from the welding head 12 to the support arrangement 48 or to the part of the body thereon which is currently being worked.

This argon shroud is ionised to form a plasma and to create an arc between the first electrode 19 in the welding head 12 and the foundation 48, or the part of the body being worked upon. The arc produces a high temperature, which is sufficient to melt the material of the foundation 48 or the body in the vicinity of the arc and also to melt the end of the wire 24 which is also in the vicinity of the arc in the plasma. This melted material from the wire 24 and from the support arrangement 48 forms a molten weld pool.

The position of the welding head 12 relative to the turntable 36 is controlled by the computer 46 by manipulating both the position of the welding head 12 and the position of the turntable 36. The computer 46 also controls the rate of feeding the wire 24. Thus by appropriate manipulation of the welding head 12 relative to the turntable 36, a component, for example for use in a gas turbine engine, can be built up layer by layer by the deposition of the weld material from the wire 24.

The provision of a chamber 52 to receive an inert gas provides the advantage in the preferred embodiment that the body produced from the welding material is not contaminated by oxygen and nitrogen forming unwanted formation of oxides and nitrides and other reactive products on the deposited material. This provides for improved longevity of the body so formed. Also, the absence of oxides and nitrides improves the surface appearance of the body.

A further advantage in connection with TIG welding is an improvement in the longevity of the electrode in the welding head, because of the absence of oxidised surfaces

and, thereby, the absence of ionic metal vapour transferred to the electrode, thereby minimising erosion of the electrode. A further advantage is that the surface finish of the body is improved, because of the absence of oxides and nitrides.

Various modifications can be made without departing from the scope of the invention. For example, the enclosure 50 can be of any suitable configuration and may be formed of a rigid or non-rigid material. Also, the amount of oxygen and nitrogen remaining in the chamber 52 can be varied depending upon the nature of the weld material. In addition, while the above described embodiment uses tungsten inert gas (TIG) welding in which the metal wire is separate from the electrode 19, the method and apparatus could also be used with a metal inert gas (MIG) welding process in which the wire 24 is fed through the centre of the welding head 12. The wire 24 constitutes the first electrode 19 and is consumed during the deposition process.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS 1. Apparatus for forming a body by deposition of a weld material, the apparatus comprising a welding head, support means for supporting the body, a supply of a welding material to be deposited on the support means by the welding head to form the body, means defining a chamber in which the support means and the welding head are arranged, and means for supplying to the chamber a gaseous medium to provide an atmosphere in the chamber which is substantially unreactive to the weld material.
2. Apparatus according to claim 1 wherein the welding head is mounted on manipulating means and also surrounds the manipulating means.
3. Apparatus according to claim 1 or 2 wherein the gaseous medium supplied to the chamber to provide the unreactive atmosphere is substantially wholly inert, comprising at least one inert gas.
4. Apparatus according to claim 3 wherein the inert gas is argon.
5. Apparatus according to any preceding claim wherein the atmosphere contains less than substantially 500ppm oxygen and less than substantially 1700ppm nitrogen.
6. Apparatus according to claim 5 wherein the atmosphere contains less than substantially 200ppm oxygen and less than substantially 700ppm nitrogen.
7. Apparatus according to claim 5 or 6 wherein the atmosphere contains less than substantially 100ppm oxygen and less than substantially 350ppm nitrogen.
8. Apparatus according to any of claims 5 to 7 wherein the atmosphere contains less than substantially 40ppm oxygen and less than substantially 140ppm nitrogen.
9. Apparatus according to any preceding claim further including monitoring means for monitoring the composition of the atmosphere in the chamber and control means for controlling the supply of the gaseous medium to ensure that

the atmosphere remains substantially unreactive to the weld material.
10. Apparatus according to any preceding claim further including means for controlling the temperature and moisture content of the atmosphere.
11. Apparatus according to any preceding claim wherein the supply means for supplying the substantially unreactive gaseous atmosphere includes feed means for feeding the gaseous medium to the chamber to form the atmosphere, and the feed means is arranged to deliver the gaseous medium to the chamber at the level of the floor of the chamber at a rate of flow of the gas to create turbulent flow therein.
12. Apparatus according to claim 11 wherein the gaseous medium is fed to the chamber at a rate of up to substantially 1000 litres/min.
13. Apparatus according to claim 12 wherein the gaseous medium is fed to the chamber at a rate of substantially 150 litres/min to substantially 500 litres/min.
14. Apparatus according to claim 12 or 13 wherein the gaseous medium is fed to the chamber at a rate of between substantially 300 litres/min to substantially 400 litres/min.
15. Apparatus according to any of claims 1 to 10 including a floor comprising a gas diffusion bed and a plenum beneath the gas diffusion bed, wherein the supply means for supplying the gaseous medium includes feed means for feeding the gaseous medium to the plenum whereby the gaseous medium diffuses through the gas diffusion bed to the chamber.
16. Apparatus according to claim 15 wherein the gaseous medium is delivered to the plenum at a rate to provide laminar floor of the gas into the chamber.
17. Apparatus according to claim 15 or 16 wherein the gaseous medium is fed to the plenum at a rate of up to substantially 100 litres/min.
18. Apparatus according to claim 17 wherein the gaseous

I medium is fed to the plenum at a rate of between substantially 10 litres/min and substantially 50 litres/min.
19. Apparatus according to claim 17 or 18 wherein the gaseous medium is fed to the plenum at a rate of substantially 40 litres/min.
20. A method for forming a body by deposition of a weld material, the method comprising providing a welding head, providing support means for supporting the body, supplying a welding material to the welding head, surrounding the welding head and the support means with a gaseous atmosphere which is substantially unreactive to the weld material, and connecting the welding head and the support means to a supply of electricity to form an arc between the welding head and the support means to melt the weld material and deposit material on the support means to form the body in said substantially unreactive atmosphere.
21. A method according to claim 20 wherein the step of surrounding the welding head and the support means with said substantially unreactive atmosphere comprises providing means to supply a gaseous medium to provide said unreactive atmosphere.
22. Apparatus according to claim 21 wherein the step of supplying the gaseous medium comprises initially purging the chamber with said gas to reduce the amount of oxygen and nitrogen therein to less than substantially 500ppm oxygen, and less than substantially 1700ppm nitrogen.
23. A method according to claim 22 wherein the amount of oxygen and nitrogen in the chamber is reduced to less than substantially 200ppm oxygen and less than substantially 700ppm nitrogen.
24. A method according to claim 22 or 23 wherein the

amount of oxygen and nitrogen in the chamber is reduced to less than substantially 100ppm oxygen and less than 350ppm nitrogen.
25. Apparatus according to any of claims 22 to 24 wherein the amount of oxygen is reduced to less than substantially less than 40ppm oxygen, and less than substantially 140ppm nitrogen.
26. A method according to any of claims 20 to 25 further including providing a further supply of an unreactive gas to the welding head in which the arc for melting the weld material can be formed.
27. A method according to claim 20 wherein the gas provided by the further supply of unreactive gas is the same as the gas for providing the unreactive atmosphere.
28. A method according to any of claims 20 to 27 including feeding the gaseous medium to provide the substantially unreactive gaseous atmosphere at the level of the floor of the chamber at a rate of flow of the gas to create turbulent flow therein.
29. A method according to claim 28 including feeding the gaseous medium to the chamber at a rate of up to 1000 litres/min.
30. A method according to claim 28 including feeding the gaseous medium to the chamber at a rate of substantially 150 litres/min to substantially 500 litres/min.
31. A method according to claim 28 including feeding the gaseous medium to the chamber at a rate of substantially 300 litres/min to substantially 400 litres/min.
32. A method according to any of claims 20 to 27 including providing a floor in the form of a gas diffusion bed and a plenum beneath the gas diffusion bed, and feeding the gaseous medium to provide the substantially unreactive gaseous atmosphere to the plenum whereby the gas diffuses through the gas diffusion bed to the chamber.
33. A method according to claim 32 including feeding the gaseous medium to the plenum at a rate to provide laminar flow of the gas into the chamber.
34. A method according to claim 33 including feeding the gaseous medium to the chamber at a rate of up to substantially 100 litres/min.
35. A method according to claim 33 including feeding the gaseous medium to the chamber at a rate of between substantially 10 litres/min and substantially 50 litres/min.
36. A method according to claim 33 including feeding the gaseous medium to the chamber at a rate of substantially 40 litres/min.
37. Apparatus substantially as herein described with reference to the accompanying drawing.
38. A method substantially as herein described with reference to the accompanying drawing.
39. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.