U.S. patent application number 10/181041 was filed with the patent office on 2003-01-02 for forming large titanium parts.
Invention is credited to Carolan, John Thomas, O'Sullivan, Maurice.
Application Number | 20030000270 10/181041 |
Document ID | / |
Family ID | 9883479 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030000270 |
Kind Code |
A1 |
Carolan, John Thomas ; et
al. |
January 2, 2003 |
Forming large titanium parts
Abstract
Apparatus for superplastically forming large parts from titanium
comprising: a furnace (10) having an interior, the inside surface
of the furnace (10) being contoured and finished so as to form a
mold for the part to be superplastically formed; means (70) for
heating the interior of the furnace (10); and a supply (60) of an
inert gas. The surface of the mold is adapted to receive a
substantially unformed titanium blank (80). The heating means (70)
is adapted to heat the titanium blank (80) to the required
temperature for superplastic forming. The supply (60) of the inert
gas is operable to exert a pressure onto the surface of the
titanium blank (80) furthermost from the surface of the mold such
that the inert gas causes the titanium blank (80) to deform and
take up the shape of the mold, thereby forming the required part.
The heating means (70) includes one or more electrical induction
coils positioned in the furnace (10) so as to be on the side of the
titanium blank (80) furthermost from the mold when that titanium
blank (80) is positioned in the furnace (10) for superplastic
forming in the mold, such that the or each induction coil induces a
current in the titanium blank (80) which is heated thereby.
Inventors: |
Carolan, John Thomas; (West
Midlands, GB) ; O'Sullivan, Maurice; (Stoke-On-Trent,
GB) |
Correspondence
Address: |
Clifford W Browning
Woodard Emhardt Naughton Moriarty & McNett
Bank One Center Tower
111 Monument Circle Suite 3700
Indianapolis
IN
46204-5137
US
|
Family ID: |
9883479 |
Appl. No.: |
10/181041 |
Filed: |
July 11, 2002 |
PCT Filed: |
January 11, 2001 |
PCT NO: |
PCT/GB01/00109 |
Current U.S.
Class: |
72/62 |
Current CPC
Class: |
B21D 26/031 20130101;
B21D 26/045 20130101; B21D 26/047 20130101; B21D 37/16 20130101;
B21D 26/055 20130101 |
Class at
Publication: |
72/62 |
International
Class: |
B21D 028/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2000 |
GB |
0000529.8 |
Claims
1. A method of superplastically forming large parts from titanium,
comprising the steps of: a) constructing a furnace (10) with an
inside surface which is contoured and finished so as to form a
mould for the part to be superplastically formed; b) introducing a
substantially unformed titanium blank (80) into the furnace (10);
c) heating the titanium blank (80) to the required temperature for
superplastic forming; d) applying inert gas to the surface of the
titanium blank (80) furthermost from the mould, wherein the gas
pressure is such that it causes the titanium blank (80) to deform
and take up the shape of the mould, thereby forming the required
part, characterised in that the heating is by one or more
electrical induction coils positioned on the side of the titanium
blank (80) furthermost from the mould such that the or each
induction coil induces a current in the titanium blank (80) which
is heated thereby.
2. A method according to claim 1, wherein the or each induction
coil extends the full height of the mould.
3. A method according to claim 1 or claim 2, wherein the
substantially unformed blank (80) is substantially cylindrical and
the or each induction coil is positioned inside said substantially
cylindrical blank (80).
4. A method according to claim 3, wherein the or each induction
coil is orientated such that its axis is substantially parallel to
the axis of said substantially cylindrical blank (80).
5. A method according to claim 3 or claim 4, wherein there is a
plurality of such induction coils, the induction coils being
distributed so that collectively they define an annulus that is
substantially coaxial with the substantially cylindrical blank
(80).
6. A method according to any one of the preceding claims, wherein
the furnace (10) is constructed from a plurality of furnace walls
or furnace wall sections (30) which collectively form the inside
surface of the furnace (10).
7. A method according to claim 6, wherein the or each furnace wall
or furnace wall section (30) is formed of a ceramic material.
8. A method according to any one of the preceding claims, wherein
the inert gas is argon.
9. Apparatus for superplastically forming large parts from titanium
comprising: a furnace (10) having an interior, the inside surface
of the furnace (10) being contoured and finished so as to form a
mould for the part to be superplastically formed; means (70) for
heating the interior of the furnace (10); and a supply (60) of an
inert gas, wherein the surface of the mould is adapted to receive a
substantially unformed titanium blank (80), the heating means (70)
is adapted to heat the titanium blank (80) to the required
temperature for superplastic forming when that titanium blank (80)
is positioned in the furnace (10) for superplastic forming in the
mould, and the supply (60) of the inert gas is operable to exert a
pressure onto the surface of the titanium blank (80) furthermost
from the surface of the mould when that titanium blank (80) is
positioned in the furnace (10) for superplastic forming in the
mould such that the inert gas causes the titanium blank (80) to
deform and take up the shape of the mould, thereby forming the
required part, characterised in that the heating means (70) include
one or more electrical induction coils positioned in the furnace
(10) so as to be on the side of the titanium blank (80) furthermost
from the mould when that titanium blank (80) is positioned in the
furnace (10) for superplastic forming in the mould, such that the
or each induction coil induces a current in the titanium blank (80)
which is heated thereby.
10. Apparatus according to claim 9, wherein the or each induction
coil extends the full height of the mould.
11. Apparatus according to claim 9 or claim 10, wherein the
substantially unformed blank (80) is substantially cylindrical and
the or each induction coil is positioned in the furnace (10) so as
to be inside said substantially cylindrical blank (80) when that
titanium blank (80) is positioned in the furnace (10) for
superplastic forming in the mould.
12. Apparatus according to claim 11 wherein the or each induction
coil is orientated such that its axis is substantially parallel to
the axis of said substantially cylindrical blank (80) when that
titanium blank (80) is positioned in the furnace (10) for
superplastic forming in the mould.
13. Apparatus according to claim 11 or claim 12, wherein there is a
plurality of such induction coils, the induction coils being
distributed so that collectively they define an annulus that is
substantially coaxial with the substantially cylindrical blank (80)
when that titanium blank (80) is positioned in the furnace (10) for
superplastic forming in the mould.
14. Apparatus according to any one of claims 9 to 13, wherein the
furnace (10) is constructed of a plurality of furnace walls or
furnace wall sections (30), which collectively form the inside
surface of the furnace (10).
15. Apparatus according to claim 14, wherein the or each furnace
wall or furnace wall section (30) is formed of a ceramic
material.
16. Apparatus according to any one of claims 9 to 15, wherein the
inert gas is argon.
Description
[0001] This invention relates to the forming of large parts from
titanium. More particularly, it relates to the forming of such
parts with external dimensions of the order of meters.
[0002] Superplastic forming of titanium involves heating titanium
sheet to a specified temperature (usually in the region of 950
degrees centigrade) and blow forming the heated titanium by using
an inert gas, such as argon. This process is usually performed in
either an industrial press or a furnace. However, the finite
dimensions of these two items impose restrictions on the size of
the parts that can be superplastically formed within them.
Consequently, parts too large to be accommodated in existing
presses or furnaces have to be fabricated from two or more smaller
sections that have been superplastically formed individually. This
increases both the time and cost associated with the forming of
large parts from titanium. Furthermore, it may lead to dimensional
inaccuracies in the finished part owing to its fabrication from a
number of smaller constituent sections: unacceptably large
dimensional variations resulting from the aggregate of the normal
individual dimensional variations.
[0003] U.S. Pat. No. 5,209,093 discloses apparatus for
superplastically forming large cylindrical structures,
comprising:
[0004] (i) a generally cylindrical ceramic die having a radially
inwardly facing surface defining the contours of a structure to be
formed from a cylindrically rolled metal sheet positioned radially
inwardly therefrom;
[0005] (ii) radiant heating means positioned radially inwardly of
the rolled metal sheet for heating a medial portion thereof to a
predetermined temperature at which it achieves a superplastic
condition; and
[0006] (iii) means for introducing a pressurised gas to force the
medial portion of the rolled metal sheet radially outwardly against
the ceramic die when the medial portion of the rolled metal sheet
has been heated to a superplastic condition.
[0007] The ceramic die may be formed of segments that mate along
radial planes, for example 120 degree segments. This allows the die
to be disassembled to enable removal of titanium structures formed
therein which cannot be removed in any other way.
[0008] Radiant heating means tend to heat indiscriminately any
object that lies in the path of radiation emitted from the heating
means. Although this will result in the desired heating of the
rolled metal sheet if the sheet is in the path of the emitted
radiation, it may also result in objects being unnecessarily
heated, such as the die or end portions of the apparatus. As a
consequence, a greater amount of energy will be needed to operate
the radiant heating means than would be the case if only the rolled
metal sheet were heated. A corollary of this is that, for any given
operating power of the heating means, the rolled metal sheet will
take longer to reach the required temperature under the action of
radiant heating means than would be the case if only the rolled
metal sheet were heated.
[0009] It is an object of this invention to address these
disadvantages.
[0010] According to a first aspect of this invention there is
provided a method of superplastically forming large parts from
titanium, comprising the steps of:
[0011] a) constructing a furnace, the inside surface of the furnace
being contoured and finished so as to form a mould for the part to
be superplastically formed;
[0012] b) introducing a substantially unformed titanium blank into
the furnace;
[0013] c) heating the titanium blank to the required temperature
for superplastic forming;
[0014] d) applying inert gas to the surface of the titanium blank
furthermost from the surface of the mould, wherein the gas pressure
is such that it causes the titanium blank to deform and take up the
shape of the mould, thereby forming the required part,
characterised in that the heating is by one or more electrical
induction coils positioned on the side of the titanium blank
furthermost from the mould such that the or each induction coil
induces a current in the titanium blank which is heated
thereby.
[0015] The substantially unformed blank may be substantially
cylindrical and the or each induction coil may be positioned inside
said substantially cylindrical blank.
[0016] The or each induction coil may be orientated such that its
axis is substantially parallel to the axis of said substantially
cylindrical blank.
[0017] There may be a plurality of such induction coils, the
induction coils being distributed so that collectively they define
an annulus that is substantially coaxial with the substantially
cylindrical blank.
[0018] According to another aspect of this invention there is
provided apparatus for superplastically forming large parts from
titanium comprising: a furnace having an interior, the inside
surface of the furnace being contoured and finished so as to form a
mould for the part to be superplastically formed; means for heating
the interior of the furnace; and a supply of an inert gas, wherein
the surface of the mould is adapted to receive a substantially
unformed titanium blank, the heating means is adapted to heat the
titanium blank to the required temperature for superplastic forming
when that titanium blank is positioned in the furnace for
superplastic forming in the mould, and the supply of the inert gas
is operable to exert a pressure onto the surface of the titanium
blank furthermost from the surface of the mould when that titanium
blank is positioned in the furnace for superplastic forming in the
mould such that the inert gas causes the titanium blank to deform
and take up the shape of the mould, thereby forming the required
part, characterised in that the heating means include one or more
electrical induction coils positioned in the furnace so as to be on
the side of the titanium blank furthermost from the mould when that
titanium blank is positioned in the furnace for superplastic
forming in the mould, such that the or each induction coil induces
a current in the titanium blank which is heated thereby.
[0019] The or each induction coil may extend the full height of the
surface of the mould.
[0020] The substantially unformed blank may be substantially
cylindrical and the or each induction coil may be positioned inside
said substantially cylindrical blank when that titanium blank is
positioned in the furnace for superplastic forming in the
mould.
[0021] The or each induction coil may be orientated such that its
axis is substantially parallel to the axis of said substantially
cylindrical blank when that titanium blank is positioned in the
furnace for superplastic forming in the mould.
[0022] There may be a plurality of such induction coils, the
induction coils being distributed so that collectively they define
an annulus that is substantially coaxial with the substantially
cylindrical blank when that titanium blank is positioned in the
furnace for superplastic forming in the mould.
[0023] The contoured inside of the furnace surface may be formed of
a ceramic material. The contoured inside of the furnace surface may
be formed of a metallic or nonmetallic material that may be
magnetiseable or non-magnetiseable.
[0024] The furnace may be constructed of a plurality of furnace
walls or furnace wall sections.
[0025] The inert gas may be argon.
[0026] To assist the deformation of the titanium blank under the
action of the inert gas, a vacuum may be applied to the side of the
blank that is adjacent the mould.
[0027] The titanium blank may be partially formed, before it is
introduced into the furnace.
[0028] Specific embodiments of the present invention are now
described by way of example and with reference to the accompanying
drawings, of which:
[0029] FIG. 1 is a transverse cross-section of a furnace for
forming a large diameter titanium tube by superplastic forming;
[0030] FIG. 2 is an enlarged view of the detail within the circle
labelled A of FIG. 1;
[0031] FIG. 3 is a plan view of the apparatus of FIG. 1;
[0032] FIG. 4 is a plan view of another furnace, wall sections of
the furnace being in mutual abutment; and
[0033] FIG. 5 is another plan view of the other furnace, the wall
sections being spaced apart.
[0034] FIGS. 1 and 3 show a cylindrical furnace 10 which 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.
[0035] 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.
[0036] The furnace 10 rests on a base plate 40, which in turn is
situated on legs 50. The centre of the base plate 40 includes a
lower argon gas inlet aperture 60 which is connected to a
controllable supply of argon gas.
[0037] FIG. 1 also shows a heating assembly 70. This assembly
consists of a circular top plate 71 with a central top aperture 72
and several induction coils. The induction coils are attached to
the underside of the top plate 71 and are orientated so as to lie
vertically and are circumferentially spaced from one another so as
to form a circular array that is coaxial with the circular top
plate 71. The induction coils themselves are not shown, but each of
them has a support member 73, of which two are shown in FIG. 1. An
annular bottom plate 74 is attached to the lower end of the support
members 73 and is also coaxial with the top plate 71.
[0038] The heating assembly 70 may be inserted into and withdrawn
from the cylindrical furnace 10. FIG. 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 30. The
induction coils extend the full height of the inside surface of the
sections 30.
[0039] The method of operation is described now with reference to
FIG. 1. A substantially unformed titanium blank 80 (in the form of
a cylinder fabricated from a length of titanium sheet) is placed
around the annulus defined by the induction coils. The positioning
of the blank 80 relative to the heating assembly 70 is such that
the top edge of the blank 80 contacts an O-ring seal situated in
the top plate 71 of the heating assembly 70 and the bottom edge of
the blank 80 contacts an O-ring seal situated in the bottom plate
74 of the heating assembly 70. FIG. 2 shows the O-ring seal 90
included in the top plate 71. This provides airtight contact
between this plate 71 and the blank 80. A similar arrangement is
included in the bottom plate 74. Although FIG. 2 shows the top edge
of the blank 80 in contact with the top plate 71, it is envisaged
that, when the blank is at ambient temperature, a gap should exist
between the top edge of the blank 80 and the top plate 71 to allow
for thermal expansion of the blank 80.
[0040] The heating assembly 70 and the blank 80 are then inserted
into the centre of the furnace 10. To facilitate this insertion,
two of the ceramic wall sections 30 are pivotably mounted, thereby
serving as doors to the furnace 10. This arrangement is shown in
FIG. 3, the pivotably mounted sections being labelled 30a, 30b.
[0041] 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 titanium blank
80. The inclusion of seals 90 in the top and bottom edge of the
inside surfaces of the sections 30 provides for an airtight contact
against the blank 80. This completes the arrangement shown in FIG.
1. The titanium blank 80 is firmly held in position by the airtight
abutment of the three circular sections 30 on its outside surface
and the airtight abutment of the top plate 71 and bottom plate 74
on its inside surface.
[0042] Argon gas is introduced into the furnace 10 through the
lower 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 top aperture 72. The top 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.
[0043] The electrical induction coils are then operated. A current
flows in each coil and this results in a respective associated
magnetic field being set up around the coil. The current in each
coil is in the same direction, thus causing each respective field
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 titanium blank 80 that is adjacent and
surrounds the annular arrangement of the coils, thereby causing a
current to be induced in the titanium blank 80. This induced
current results in the titanium blank 80 being heated. Positioning
the annular arrangement of coils inside the titanium blank 80 does
not optimise the induction heating effect of the coils as far as
heating the titanium blank 80 is concerned. This is because the
flux density outside the annular arrangement of coils is less than
the flux density inside the annular arrangement of coils.
Positioning the annular arrangement of coils inside the titanium
blank 80 therefore puts the titanium blank 80 in a weaker part of
the field. However, by positioning the annular arrangement of coils
inside the titanium blank 80, it is possible to more accurately
predict how the titanium blank will be heated, as each of the coils
is at a known and easily verifiable distance from the surface of
the blank 80. 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 titanium blank 80.
[0044] 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 blank 80 buckling.
[0045] Once the titanium blank 80 has been heated to the required
temperature for superplastic forming, more argon gas is introduced
into the furnace via the aperture 60. This is continued such that
the pressure of the argon on the inside surface of the titanium
blank 80 is greater than the pressure against the outside surface
of the blank 80, the two spaces being sealed from one another in an
airtight fashion as previously described. This pressure difference
causes the titanium blank 80 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 titanium blank 80, it is envisaged
that a vacuum may be applied to the outside surface of the titanium
blank 80. Techniques for achieving this are known to the skilled
addressee.
[0046] The heating is then stopped, allowing the superplastically
formed part to cool prior to removal from the furnace 10 and the
heating apparatus 70.
[0047] In an alternative embodiment, shown in FIG. 4, 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.
[0048] Each pair of actuators 120 are positioned so that their
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. FIG. 4
shows the wall sections 30 in mutual abutment. It will be
appreciated that the heating and forming operations would be
performed in this position. FIG. 5 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.
* * * * *