WO2001054842A1

WO2001054842A1 - Forming tubular titanium components

Info

Publication number: WO2001054842A1
Application number: PCT/GB2001/000328
Authority: WO
Inventors: John Thomas Carolan; Maurice O'sullivan
Original assignee: Loades Plc
Priority date: 2000-01-28
Filing date: 2001-01-26
Publication date: 2001-08-02
Also published as: AU2001230351A1; GB0002044D0

Abstract

A method of forming a plurality of large diameter tubular titanium components each suitable for use as a portion of a jet engine exhaust tube, the method includes the step of forming a large diameter titanium tube (1), and then subjecting the tube to a superplastic forming process. The superplastically formed titanium tube is then cut at at least one selected location (14, 15) along its length to sever it into at least two large diameter tubular titanium components (11, 12, 13). The titanium components (11, 12, 13) are particularly suitable for assembly to form an adjustable exhaust jet pipe for a VTOL aircraft.

Description

FORMING TUBULAR TITANIUM COMPONENTS

This invention relates to a method of forming a plurality of large diameter tubular titanium components, each suitable for use as a portion of a jet engine exhaust tube. A large diameter tubular component has a diameter of the order of 1 metre or more.

An object of this invention is to provide an economical method of forming a plurality of large diameter tubular titanium components.

According to this invention there is provided a method of forming a plurality of large diameter tubular titanium components each suitable for use as a portion of a jet engine exhaust tube, including the steps of forming a large diameter titanium tube, subjecting the tube so formed to a superplastic forming

process and then cutting the superplastically formed titanium tube at at least one selected location along its length whereby to sever it into at least two large diameter tubular titanium components.

The superplastically formed large diameter titanium tube may be cut in a transverse plane which is oblique to its axis so the ends of the two large diameter tubular titanium components so formed lie in such an oblique transverse plane. The superplastically formed titanium tube may be cut so that one of the severed large diameter tubular titanium components has both its ends cut in respective transverse planes which are oblique to its axis and which converge to one side of the respective large diameter tubular titanium component.

The superplastic forming process may include the step of inserting said large diameter tube into a furnace having an interior surface which defines a

mould, heating the large diameter tube to a temperature at which superplastic forming can occur and applying a pressurised gas to an inner surface of the

large diameter tube such that the large diameter tube is deformed against said mould.

Advantageously, a heating source for heating the large diameter tube is disposed internally of the large diameter tube.

Advantageously, the heating step comprises heating by at least one electrical induction coil.

Advantageously, there is a plurality of said induction coils disposed internally of the large diameter tube, each said coil having a plurality of coil turns having a turn spacing and the method comprise the step of modifying the turn spacing of at least one said coil to provide a desired heating profile.

Such a method is particularly suitable for forming three tubular titanium components which are to be assembled together to form an adjustable exhaust jet pipe for a VTOL aircraft. In order that the invention may be well understood, an embodiment thereof will now be described with reference to the drawings, in which: Figure 1 shows a one piece titanium component which is divided into three tubular components;

Figure 2 is a transverse cross-section of a furnace for use in forming the

one piece component shown in Figure 1 ; Figure 3 is an enlarged view of the detail within the circle labelled A of

Figure 2;

Figure 4 is a plan view of the furnace of Figure 2;

Figure 5 is a plan view showing one condition of an alternative furnace

wall arrangement; and Figure 6 shows a second condition of the alternative furnace.

A large diameter tube 1 is fabricated by first cutting segments of sheet titanium and then rolling them so that when presented one to another side by side and welding them along their abutting edges they form the tube 1. The tube is then mounted in a furnace 10 where it is superplastically formed into the desired shape by blow moulding.

As shown in Figures 2 to 4, the furnace 10 is constructed predominantly from three furnace wall sections 30, each moulded from the same ceramic material. Collectively, the three sections 30 form the curved surfaces of a cylinder whose longitudinal axis lies vertically. The inside surface of the cylinder formed by the three ceramic wall sections 30 is shaped and finished so as to form a mould suitable for forming titanium.

The furnace 10 rests on a base plate 40, which in turn is situated on legs 50. The centre of the base plate includes a gas inlet aperture 60 which is connected to a controllable supply of argon gas.

Figure 2 also shows a heating assembly 70. This assembly consists of a circular top plate 71 with a central aperture 72 and several induction coils 73a.

The induction coils are attached to the underside of the top plate 71 and are orientated so as to lie vertically and are distributed so as to define a circular array that is coaxial with the circular top plate 71. The induction coils 73a are shown schematically in Figure 2 and are each provided with a support member

73. An annular bottom plate 74 is attached to the lower end of the induction coils 73a and is also coaxial with the top plate 71.

The heating assembly 70 can be inserted into and withdrawn from the cylindrical furnace 10. Figure 1 shows the heating assembly 70 inserted into the furnace 10. In this position, the top plate 71 of the heating assembly 70 rests on and is coaxial with the cylinder formed by the three ceramic wall sections 20. The induction coils 73 extend the full height of the inside surface of the sections.

In use of the furnace 10, the unformed tube 1 is placed around the annulus defined by the induction coils 73a. The positioning of the tube 1 relative to the heating assembly 70 is such that the top edge and bottom edge of the blank contact the top plate 71 and the bottom plate 74 respectively of the heating assembly 70. Figure 3 shows a seal 90 included in the top plate 71 to provide airtight contact between this plate 71 and the tube 1. Although not shown in detail, a similar arrangement is included in the bottom plate 74.

Although Figure 3 shows the top edge of the tube 1 in contact with the top plate 71, it is envisaged that, when the tube is at ambient temperature, a gap

should exist between the top edge of the tube and the top plate, to allow for thermal expansion of the blank.

The heating assembly 70 and the tube 1 are then inserted into the centre of the furnace 10. To facilitate this insertion, two of the ceramic wall sections are pivotably mounted, thereby serving as doors to the furnace 10. This arrangement is shown in Figure 4, the pivotably mounted sections being labelled 30a, 30b.

Closing the two doors 30a, 30b causes the top and bottom edges of the inside surface of all three ceramic sections 30 to abut the top and bottom edges respectively of the tube 1. The inclusion of seals 90 in the top (as shown in Figure 3) and bottom edge of the inside surfaces of the sections 30 provides for an airtight contact against the tube 1. This completes the arrangement shown in Figure 2. The tube 1 is firmly held in position by the airtight abutment of the three circular sections on its outside surface and the airtight abutment of the top plate 71 and bottom plate 74 on its inside surface. Argon gas is introduced into the furnace 10 through the gas inlet aperture 60 in the base plate 40. The argon gas replaces air that was previously inside the furnace by forcing that air out of the aperture 72 in the top plate 71.

The aperture 72 is then closed by any known means, such as a bung or a

cut-off valve, and the introduction of argon gas is ceased.

The electrical induction coils are then operated. A current flows in each

coil and this results in respective associated magnetic fields being set up around the coils 73a. The current in each coil is in the same direction, thus causing the respective fields to be orientated in the same direction. As a result, a substantially toroidal magnetic field is set up around the annular arrangement of the coils. Magnetic flux of this field passes, in an axial direction, through the tube 1 that is adjacent and surrounds the annular arrangement of the coils, thereby causing a current to be induced in the tube. This induced current results in heating of the tube. Positioning the annular arrangement of coils inside the tube does not optimise the induction heating effect of the coils as far as heating the tube is concerned. This is because the flux density outside the coils is less than the flux density inside the coils. Positioning the coils inside the tube therefore puts the tube in a weaker part of the field. However, by positioning the annular arrangement of coils inside the tube, it is possible to more accurately predict how the tube will be heated, as each of the coils is at a known and easily verifiable distance from the surface of the tube. Furthermore, the coils may be more easily replaced in the event of failure, or altered in order to achieve different heating characteristics. One such alteration may be to move some of the turns of one or more coils apart and others of the turns of the or each coil together, in order to achieve a different heating profile

of the tube.

Using induction is advantageous as compared with using radiant heating

means. Induction coils may be used to avoid heating parts of the apparatus that need not be heated, for example the circular top plate 71 or the base plate 40,

if such parts are fabricated from non-magnetiseable material. The use of induction coils therefore results in improved efficiency and a shorter heating time for any given operating power of the induction coils. A shorter heating time is advantageous in reducing the thermal stress to which components of the apparatus are subjected. This may result in prolonging the useful life of the components, or in the use of cheaper components. For example conventional O-ring seals may be used to provide a gas-tight seal whilst permitting movement of the blank due to thermal expansion. It will be appreciated that high temperature, mechanical-type seals may hinder such expansion and increase the likelihood of the tube buckling.

Once the tube 1 has been heated to the required temperature for supeφlastic forming, more argon gas is introduced into the furnace via the gas inlet aperture 60. This is continued such that the pressure of the argon on the inside surface of the tube is greater than the pressure against its outside surface, the two spaces being sealed from one another in an airtight fashion as previously described. This pressure difference causes the tube to deform

outwards and take up the shape of the mould comprised of the inside surface of the three ceramic sections 30. To further increase the pressure difference across

the two surfaces of the tube, it is envisaged that a vacuum may be applied to

its outside surface. Techniques for achieving this are known to the skilled addressee and thus a vacuum source 90 which communicates with the outside

surface of the tube 1 through, for example, one or more apertures in the furnace wall, is merely indicated schematically in Figure 2.

The heating is then stopped, allowing the supeφlastically formed part to cool prior to removal from the furnace 10 and the heating apparatus 70.

When superplastically formed into the desired shape, the tube 1 is removed from the furnace 10 and divided into three tubular components 11,12,13 by severing along two joint lines 14,15 which are oblique to the axis 16 of the tube 1 and which converge to one side of the tube .

In an alternative embodiment of the furnace, shown in Figure 5, the furnace wall sections 30 are not pivotably mounted. Instead, the furnace wall sections 30 are surrounded by a cylindrical outer wall 100. The cylindrical outer wall 100 is coaxial with the wall sections 30 and has an internal diameter that is greater than the external diameter of the wall sections 30. Thus, when the wall sections 30 are in mutual abutment, there is an annular space 110 between the wall sections 30 and the cylindrical outer wall 100. Six actuators

120, only three of which are shown, are mounted on the outer surface of the outer cylindrical wall 100. A pair of actuators 120 are provided for each wall

section 30: an upper actuator 120 and a lower actuator 120. Each pair of

actuators 120 is positioned so that its lines of action pass radially through a respective one of the wall sections. Each actuator includes an actuator rod 125.

The actuator rods 125 of each pair of actuators 120 pass through the cylindrical outer wall 100 and mechanically engage the respective wall section 30. Operation of the actuators 120 causes the wall sections 30 to be moved radially between a position in which they are in mutual abutment and a position in which they are spaced apart. Figure 5 shows the wall sections 30 in mutual abutment. It will be appreciated that the heating and forming operations would be performed in this position. Figure 6 shows the wall sections 30 spaced apart. It will be appreciated that it is in this position that the titanium blank would be inserted into the furnace 10, the heating assembly 70 (not shown) would be inserted into and withdrawn from the furnace 10, and the formed titanium part (not shown) would be withdrawn from the furnace 10.

It will be understood that whilst the induction coils are advantageously positioned inwardly of the tube 1, the invention is not so limited and the induction coils may be positioned externally of the tube. It will also be understood that other heating means, for example radiant heating means, may be used to heat the tube.

Claims

1. A method of forming a plurality of large diameter tubular titanium components each suitable for use as a portion of a jet engine exhaust tube, the method including the steps of forming a large diameter titanium tube,

subjecting the tube so formed to a supeφlastic forming process and then cutting the supeφlastically formed titanium tube at least one selected location

along its length whereby to sever it into at least two large diameter tubular titanium components.

2. A method as claimed in claim 1, wherein the superplastically formed large diameter titanium tube is cut in a transverse plane which is oblique to its axis so the respective ends of the two large diameter tubular titanium components so formed lie in such an oblique transverse plane.

3. A method as claimed in claim 2, wherein the superplastically formed large diameter titanium tube is cut so that one of the severed large diameter tubular titanium components has both its ends cut in respective transverse planes which are oblique to its axis and which converge to one side of the respective large diameter tubular titanium component.

4. A method as claimed in claim 1, 2 or 3, wherein said supeφlastic forming process includes the step of inserting said large diameter tube into a furnace having an interior surface which defines a mould, heating the large diameter tube to a temperature at which superplastic forming can occur and

applying a pressurised gas to an inner surface of the large diameter tube such that the large diameter tube is deformed against said mould.

5. A method as claimed in claim 4, wherein a heat source for heating the large diameter tube is disposed internally of the large diameter tube.

6. A method as claimed in claim 4 or 5, wherein said heating step comprises heating by at least one electrical induction coil.

7. A method as claimed in claim 6, wherein there is a plurality of said induction coils disposed internally of the large diameter tube, each said coil having a plurality of coil turns having a turn spacing, further comprising the step of modifying the turn spacing of at least one said coil to provide a desired heating profile.

8. A method of forming a jet engine exhaust tube comprising forming a plurality of large diameter tubular components from a large diameter titanium tube as claimed in any one of the preceding claims.