Note: Descriptions are shown in the official language in which they were submitted.
CA 02588626 2007-05-15
86930-20
TITLE: A PROCESS FOR PRODUCING STATIC COMPONENTS FOR A GAS
TURBINE ENGINE
FIELD OF THE INVENTION
[001] The present invention relates generally to the field of gas turbine
engines, and
more particularly to static components of a gas turbine engine formed from a
metal
injection process that imparts certain material characteristics.
1 o BACKGROUND OF THE INVENTION
[002] In the aerospace industry, there is a constant effort to reduce
manufacturing
costs while maintaining the quality and safety standards associated with
building
commercial and military aircraft. Some of the most expensive and complicated
parts of
an aircraft are found in the gas turbine engines that provide the thrust
necessary for
flight.
[003] Gas turbine engines contain both static and rotating parts. In general,
many of
the parts that go into gas turbine engines are made from raw pieces of
material that are
machined into the desired shape. There are many deficiencies associated with
the
manner in which turbine components are manufactured. One deficiency is that
the
components are made from expensive raw materials, and machining these
expensive
raw materials results in significant waste of both costs and useful raw
material. In
addition, many of these expensive materials are very difficult to work with,
which
results in increased costs for manufacturing the components. For example,
Rhenium
metal, which is one of the materials that is used for gas turbine engine
components
cannot be worked at room temperature. Thus, production of components made out
of
this material is both difficult and expensive.
[004] A further deficiency is that many materials that could be desirable for
use in a
gas turbine engine cannot be processed using existing manufacturing and
production
techniques. For example, many metals, metal alloys, ceramics and composites
cannot
I
CA 02588626 2007-05-15
86930-20
be processed via machining. Likewise, many components having obscure shapes
and
configurations can also not be manufactured using traditional techniques.
[005] In light of the above, it can be seen that there is a need in aerospace
industry to
lower the effective cost of manufacturing quality, high density, fatigue
resistant parts,
including parts destined for the hot section of a gas turbine engine (GTE),
and for
reducing at least in part, the deficiencies associated with existing
manufacturing
techniques. There is also the need for a technique that provides increased
manufacturing
freedom for new materials, and shapes of components.
SUMMARY OF THE INVENTION
[006] In accordance with a first broad aspect, the present invention provides
a static
component for a gas turbine engine made from an alloy in the group consisting
of
Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt or nickel-iron
superalloy.
The component has a density less than 99% of a theoretical possible density
for the
alloy, and is made by a metal injection molding process.
[007] In accordance with a second broad aspect, the present invention provides
a static
component for a gas turbine engine. The precursor is made from an alloy in the
group
consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt or
nickel-iron
superalloy. The precursor has a density less than 99% of a theoretical
possible density
for the alloy, and is made by a metal injection molding process.
[008] In accordance with a third broad aspect, the present invention provides
a process
for making a static component for a gas turbine engine. The process comprises
preparing a fluid feedstock including metallic powder selected from the group
consisting Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt or nickel-
iron
superalloy and binder material, injecting the feedstock into a mold having
cavity
approximating the shape of the component to form a green part, debinding the
green
part to provide a debound part and sintering the debound part. The preparing,
injecting,
2
CA 02588626 2007-05-15
86930-20
debinding and sintering is performed at process conditions such that said
component
has a density less than 99% of a theoretical possible density for the alloy.
[009] In accordance with a fourth broad aspect, the present invention provides
a
process for making a static component for a gas turbine engine as described
above,
further comprising performing one or more process step on said precursor to
yield a
component that has a higher density than said precursor.
[010] In accordance with a fifth broad aspect, the present invention provides
a static
component for a gas turbine engine. The component being made from an alloy in
the
group consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt
or
nickel-iron superalloy from a metal injection molding process. The components
have
pores throughout, the pores having an average sphericity greater than 0.5.
[011] In accordance with a sixth broad aspect, the present invention provides
a static
component for a gas turbine engine. The precursor being made from an alloy in
the
group consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt
or
nickel-iron superalloy and having pores throughout. The pores having an
average
sphericity greater than 0.5. The precursor is made by a metal injection
molding process.
[012] In accordance with a seventh broad aspect, the present invention
provides a static
component for a gas turbine engine. The process comprises preparing a fluid
feedstock
including metallic powder selected from the group consisting of Inconel 625,
Inconel
718, MAR-M 247 or any nickel, cobalt or nickel-iron superalloy and binder
material,
injecting the feedstock into a mold having a cavity approximating the shape of
the
component to form a green part, debinding the green part to provide a debound
part and
sintering the debound part to yield the component. The preparing, injecting,
debinding
and sintering being performed at process conditions such that the component
has pores
throughout, the pores having an average sphericity greater than 0.5.
[013] In accordance with an eighth broad aspect, the present invention
provides a static
component for a gas turbine engine. The component being made from an alloy in
the
3
CA 02588626 2007-05-15
86930-20
group consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt
or
nickel-iron superalloy and having pores throughout. The pores have an average
pore
size diameter of less than 10 microns. The component being made by a metal
injection
molding process.
[0141 In accordance with a ninth broad aspect, the present invention provides
a static
component for a gas turbine engine. The precursor is made from an alloy in the
group
consisting of Incone1625, Inconel 718, MAR-M 247 or any nickel, cobalt or
nickel-iron
superalloy and has pores throughout. The pores have an average pore size
diameter of
less than 10 microns. The component being made by a metal injection molding
process.
[015] In accordance with a tenth broad aspect, the present invention provides
a static
component for a gas turbine engine. The process comprising preparing a fluid
feedstock
including metallic powder selected from the group consisting of Inconel 625,
Inconel
718, MAR-M 247 or any nickel, cobalt or nickel-iron superalloy and binder
material,
injecting the feedstock into a mold having a cavity approximating the shape of
the
component to form a green part, debinding the green part to provide a debound
part,
sintering the debound part to yield the component. The preparing, injecting,
debinding
and sintering being performed at process conditions such that the collar has
pores
throughout. The pores have an average pore size diameter of less than 10
microns.
[016] In accordance with an eleventh broad aspect, the present invention
provides a
static component for a gas turbine engine as described above, further
comprising
performing one or more process step on said precursor to yield a component
that has a
higher density than said precursor.
[017] In accordance with a twelfth broad aspect, the present invention
provides a set of
static components for a gas turbine engine. Each component in the set being
made from
an alloy in the group consisting of Inconel 625, Inconel 718, MAR-M 247 or any
nickel, cobalt or nickel-iron superalloy. The set of components being made by
a metal
injection molding process from a common mold having a component-shaped cavity,
each component in the set of components is produced during a different molding
cycle
4
CA 02588626 2007-05-15
86930-20
of the common mold. The set of components have dimensional tolerances
variation of
less than 0.5% between components in said set.
[018] In accordance with a thirteenth broad aspect, the present invention
provides a
process for making a set of static components for a gas turbine engine. The
process
comprising preparing a fluid feedstock including metallic powder selected from
the
group consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt
or
nickel-iron superalloy and binder material, injecting the feedstock into a
mold having
cavity approximating the shape of the compoent to form a green part, debinding
the
green part to provide a debound part, sintering the debound part to yield the
component.
The preparing, injecting, debinding and sintering being performed at process
conditions
such that the component has pores throughout. The pores having an average pore
size
diameter of less than 10 microns.
[019]In accordance with a fourteenth broad aspect, the present invention
provides a
process for making a set of static components for a gas turbine engine. The
process
comprises preparing a fluid feedstock including metallic powder selected from
the
group consisting of Inconel 625, Inconel 718, MAR-M 247 or any nickel, cobalt
or
nickel-iron superalloy and binder material, injecting the feedstock into a
mold having a
component-shaped cavity to form a green part, debinding the green part to
provide a
debound part, sintering the debound part to yield a component of the set and
repeating
the injecting, debinding and sintering a number of times sufficient to make
all the
components of the set of components, wherein the preparing, injecting,
debinding and
sintering are performed at process conditions such that the set of components
has a
dimensional tolerance variation of less than 0.5% between components in said
set.
[020] In accordance with a fourteenth broad aspect, the present invention
provides a gas
turbine engine including a hot section in which is mounted a rotating assembly
and a
plurality of static components about which the rotating assembly turns during
operation
of the gas turbine engine. At least one of the static components are made by
metal
injection molding from an alloy in the group consisting of Inconel 625,
Inconel 718,
MAR-M 247 or any nickel, cobalt or nickel-iron superalloy and have pores
throughout
5
CA 02588626 2007-05-15
86930-20
which donate to the at least one static component a density less than 100% of
a
theoretical possible density for the alloy.
[021] These and other aspects and features of the present invention will now
become
apparent to those of ordinary skill in the art upon review of the following
description of
specific embodiments of the invention and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[022] In the accompanying drawings:
[023] Figure 1 shows a cross-sectional diagram of a gas turbine engine in
accordance
with a non-limiting example of implementation of the present invention;
[024] Figure 2a shows a side view of a stator vane having a non-limiting shape
that can
be manufactured in accordance with the present invention;
[025] Figure 2b shows a cross sectional view of the stator vane of Figure 2;
[026] Figure 3 shows a perspective view of a fuel swirler having a non-
limiting shape
that can be manufactured in accordance with the present invention;
[027] Figure 4 shows a cross sectional view of a floating collar having a non-
limiting
shape that can be manufactured in accordance with the present invention;
[028] Figure 5 shows a front view of a heat shield having a non-limiting shape
that can
be manufactured in accordance with the present invention;
[029] Figure 6 shows a side view of a shroud segment having a non-limiting
shape that
can be manufactured in accordance with the present invention;
6
CA 02588626 2007-05-15
86930-20
[030] Figure 7 shows a flow diagram of a non-limiting process used for metal
injection
molding in accordance with the present invention;
[031] Figure 8 shows a non-limiting example of a machine for performing the
mixing
and injection molding steps of the metal injection molding process shown in
Figure 7;
and
[032] Figure 9 shows an optical micrograph of a sintered component
manufactured in
accordance with the present invention.
[033] Other aspects and features of the present invention will become apparent
to those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
7
CA 02588626 2007-05-15
86930-20
DETAILED DESCRIPTION
[034] As will be described in detail below, the present invention relates
generally to
static components for gas turbine engines that are produced using a metal
injection
molding process. For the sake of simplicity, the present invention will be
described in
the context of gas turbine engines used for powering aircraft. However, it
should be
understood that the components and processes described herein are equally
applicable
to gas turbine engines used for other applications, such as electrical power
generation,
among other possibilities.
Gas turbine engines
[035] Shown in Figure 1 is a non-limiting example of a gas turbine engine 10
suitable
for use in powering a subsonic aircraft. Gas turbine engines, such as the one
shown in
Figure 1, generally have three major operating sections; the compressors 12,
the
combustion chamber 14, and the turbines 16. The compressors 12 include a
plurality of
fan blades 22, and the turbines 16, which are located downstream from the
compressors
12, include a plurality of turbine blades 26. As shown, both the turbine
blades 26 and
the compressor fan blades 22 are connected to a common shaft 20. During
operation, air
enters the gas turbine engine 10 and is compressed by the compressors 12. This
compressed air is then mixed with fuel and ignited in the combustion chamber
14,
resulting in gasses that exit the combustion chamber 14 and flow over the
turbine blades
26, thus causing the shaft 20 to rotate. The rotation of the shaft 20, in
turn, powers the
compressor 12. Finally, the gasses that have flowed over the turbine blades 26
pass
through a nozzle 18, which generates additional thrust by accelerating the hot
exhaust
gasses as they expand back to atmospheric pressure. Energy can be extracted
from the
gas turbine engine in the form of shaft power, compressed air and thrust for
powering
the aircraft.
[036] Contained within the gas turbine engine 10 are a hot section, a
plurality of static
components and a rotating assembly that rotates in relation to the static
components
during operation of the gas turbine engine 10. For the purposes of the present
invention,
"the hot section" refers to the sections and components of a gas turbine
engine that are
8
CA 02588626 2007-05-15
86930-20
exposed to hot gases, such as the combustion chamber, the high pressure guide
vanes,
the high pressure turbine, the high pressure turbine shroud, the housing
assembly, the
low pressure turbine guide vanes, the low pressure turbines and the exhaust
case,
among other possibilities. In general hot sections of an engine are exposed to
temperatures of greater than 300 C. It should however, be appreciated that
this
temperature may vary depending on the size of the gas turbine engine. For
example,
typical gas turbine engines will have a hot section that is exposed to
temperatures of
between 800-1400 C.
[037] The rotating assembly generally comprises one or more rotating shafts 20
as well
as a plurality of rotating turbine blades 26 and compressor fan blades 22. In
the non-
limiting embodiment shown in Figure 1, the gas turbine engine 10 includes two
concentric rotating shafts; namely shaft 20a and shaft 20b. The outermost
turbine blades
26 and compressor fan blades 22 are connected to rotating shaft 20a, and the
innermost
turbine blades 26 and compressor fan blades 22 are connected to rotating shaft
20b.
[038] The gas turbine engine 10 further includes a plurality of static
components that
are either not designed to move during operation of the engine or that are
subject to
motion which induces forces in the part that may cause it to break (such as an
actuator
arm, for example). For the purposes of the present application, the static
components
located within the gas turbine engine 10 are the parts that do not rotate
above 100 RPM.
Such static components include stator vanes 28 located between the compressor
fan
blades 22 and the turbine blades 26, a fuel swirler 30, shown in Figure 3, for
introducing fuel into the combustion chamber 14, a floating collar 32, shown
in Figure
4, for coupling the fuel swirler to the combustion chamber 14, a heat shield
34, shown
in Figure 5, located at the head area of the combustion chamber 14 and a
shroud
segment 35 that surrounds the stator vanes.
[039] In accordance with the present invention, the above listed static
components,
namely the stator vanes 28, the fuel swirler 30, the floating collar 32, the
heat shield 34
and the shroud segment 35 are produced via a metal injection molding process
which
will be described in more detail below. The process conditions for the metal
injection
9
CA 02588626 2007-05-15
86930-20
molding procedure are controlled so as to impart to the static components
certain
material characteristics relating to density, pore sphericity and pore size
distribution.
Metal Injection Molding
[040] In accordance with the present invention, each of the static components
is
produced via a metal injection molding process (otherwise known as powder
injection
molding process), which gives the components certain material characteristics
relating
to density, pore size and pore sphericity. Metal injection molding is a
relatively low cost
manufacturing process that can produce complex net-shape components from
metals,
metal alloys, ceramics, cemented carbides and cermets (ceramic-metal
composites),
among other possibilities.
[041] Shown in Figure 7 is a non-limiting flow diagram of the four main steps
in a
metal injection molding process. The first step 100 is to form a feedstock
material by
mixing together a powder of the base material/alloy from which the component
is to be
manufactured, and a binder. The powder can be any fine metallic powder, alloy
powder,
ceramic powder or carbide powder, depending on the desired material for the
final part.
As indicated above, some non-limiting examples of alloys that can be used for
the stator
vanes, fuel swirlers, floating collars and heat shields of a gas turbine
include Inconel
625, Inconel 718, MAR-M 247 or any nickel, cobalt or nickel-iron superalloys.
In
general, it is preferable to use alloys that have at least 60% nickel, cobalt
or iron, or a
combination thereof. In addition, the powder is preferably made of spherical
particles
having a diameter of less than 25 m. It should, however, be appreciated that a
powder
having particles of any shape and size can be used without departing from the
spirit of
the invention.
[042] Although certain examples of alloys are identified above, it should be
appreciated
that any alloy having desired material characteristics (i.e. mechanical,
chemical and
physical characteristics) can be used without departing from the spirit of the
invention.
For example, the alloy from which the part is made may be selected on the
basis of
desired characteristics relating to oxidation resistance, corrosion resistance
and material
CA 02588626 2007-05-15
86930-20
strength. Corrosion resistance and oxidation resistance can be measured in
terms of
mm/yr under certain conditions.
[043] The binder that is mixed with the metal alloy powder may be any
polymeric
binder, and may include a mixture of polymers, such as waxes, dispersants and
surfactants. Typical polymers include polyethylene, polyethylene glycol,
polymethyl
methacrylate, polypropylene. A typical wax that is used is a paraffin wax. It
should be
appreciated that any type of binder suitable for the intended purpose can be
used
without departing from the spirit of the invention. The manner in which the
appropriate
powder and binder are chosen, as well as the percentage of each that is used
to form the
feedstock, are known to those of skill in the art, and as such will not be
described in
more detail herein.
[044] During the mixing step 100, pre-calculated proportions of the powder and
binder
are mixed together to obtain a homogeneous and predictable feedstock with
desirable
rheological behaviour. In accordance with a non-limiting example, the powder
and
binder are hot mixed together using a continuous or batch mixer, and are then
cooled
and granulated to form the feedstock material to be supplied to an injection
molding
machine. The powder and binder can be mixed together under isothermal
conditions to
form a homogenous suspension. In accordance with a non-limiting example, the
mixing
temperature is maintained below 90 C. However the process conditions used to
produce
the appropriate temperature and consistency of feedstock are known in the art,
and will
not be described in more detail herein.
[045] Once the feedstock has been mixed, the process proceeds to step 110, at
which
point the feedstock is injected into a suitable mold for being molded into the
shape of
the desired part. In accordance with a non-limiting embodiment, the feedstock
is
supplied to the mold using low-pressure injection conditions of less than
100psi. In
order to ensure proper filling of the mold under these conditions, the
rheological
parameters of the feedstock are adjusted in accordance with the molding
parameters
(i.e. the injection pressure, injection duration, mold material and
temperature of the
mixture). For example, the feedstock is generally prepared at step 100 such
that it has at
11
CA 02588626 2007-05-15
86930-20
least one of its rate of shear, elasticity, plasticity, viscosity and
behaviour in relation to
temperature and pressure adapted for use with the molding apparatus.
[046] Shown in Figure 8 is a non-limiting example of a machine 60 suitable for
use in
the mixing and molding steps of the metal injection molding process. The
machine 60
includes a feedstock cartridge 62 for holding the feedstock in a solid state
prior to use.
Located below the feedstock cartridge 62 is a feedstock supply screw 64 for
transferring
the feedstock in its solid state through the feedstock transfer chamber 68
into the mixing
chamber 66. The feedstock transfer chamber 68 transfers the feedstock into the
mixing
chamber 66 under vacuum. Once in the mixing chamber 66, the feedstock is
heated and
mixed so as to form the feedstock that is supplied to the injection chamber
70. The
volume of feedstock within the mixing chamber 66 is kept at a constant fill
level by
synchronising the addition of the feedstock from the cartridge 62 and the
volume
injected into the injection molds in the injection chamber 70.
[047] Located below the mixing chamber 66 is an injection chamber 70 into
which a
specific volume of the feedstock is injected into a mold. The mold includes a
cavity in
the shape of the component being formed, whether that is a stator vane, a fuel
swirler, a
floating collar, a heat shield, or a shroud segment among other possible
components. In
accordance with a non-limiting example, the injection chamber 70 is kept at
the same
temperature as the mixing chamber 66, and the injection pressure is typically
less than
700 KPa. This pressure is maintained while the part is cooling to prevent void
or crack
formation due to contraction. The molding time typically takes less than 30
seconds.
[048] The mold can be made from steel, aluminum, bronze, brass or any other
metallic
material or from polymeric resins such as epoxy, or other thermoplastics, for
example.
The mold may or may not include another material to facilitate the heat
transfer, the
shrinkage or any other molding-related aspect. The molds can be hand-made
using
techniques from the jewelry field or from stereolithography. These mold
manufacturing
techniques allow reducing development-related and production costs, especially
when
manufacturing small volumes of components.
12
CA 02588626 2007-05-15
86930-20
[049] The mold is operative for shaping the mixed feedstock into a defined
shape, so as
to form what is called a "green part". Once the green part has been formed,
meaning
that the feedstock has acquired the desired shape and has been removed from
the mold,
the process proceeds to step 120, which is the debinding step. The purpose of
the
debinding step 120 is to remove the binder from the powder material, without
distorting
the molded shape of the green part. Thermal debinding is the most common
technique
used to debind the part, but any debinding technique can be used without
departing
from the spirit of the invention. For example, the debinding can be done using
solvents,
or even water in the case where water soluble polymers, such as polyethylene
glycol are
used as binders.
[050] In the case of thermal debinding, the molded part is heated in an oven
under
controlled conditions, such that part of the binder is eliminated at a lower
temperature,
while the backbone polymer of the binder maintains the powder particles of the
molded
part in place. This first stage of the debinding process forms a porous
network, which
eventually helps in the evacuation of the degradation residues from the
backbone
polymer. It also reduces the internal pressure that could deform the part. The
backbone
polymer is then thermally removed. Even in the cases where a portion of the
binder is
removed via solvent, the backbone polymer is generally still thermally removed
in a
second stage procedure. In some cases, this second stage of the debinding
process is
performed during the sintering stage, which will be described below, in order
to avoid
any damage to the debound part.
[051] As shown in Figure 7, the final step in the metal injection molding
process is the
sintering step 130. During the sintering step 130 the debound part is heated
to a
temperature that is lower, but close to, the melting temperature of the powder
material
for bonding the powder particles together. The temperature, duration of heat
application
and furnace atmosphere are controlled to ensure that the sintered component
has the
required densification and material properties desired. The sintering step
densifies the
component by removing the voids left behind from the debinding step 120. In
many
cases the sintering step can result in the part shrinking slightly. As such,
the mold that is
used during the molding stage 110 is designed to compensate for the final
shrinkage
13
CA 02588626 2007-05-15
86930-20
that occurs during sintering. The typical shrinkage of a part is between 10%-
18%
depending on the solid loading of the feedstock and the level of densification
achieved
during sintering.
[052] Once the metal powder has been processed in the manner described above,
the
sintered component will have a certain grain size. In accordance with a non-
limiting
example, the grain size for the Inconel 625 alloy, once processed, is
typically under 75
microns. When using the ASTM E112 standard for grain size characterisation,
the grain
size for static components formed in connection with the present invention are
lo typically, ASTM #4 to ASTM #7. In general, the smaller the grain size, the
better the
mechanical properties of the end component.
[053] In some circumstances, the component formed after the sintering step 130
is a
precursor to the final component. Once the precursor has been produced, one or
more
additional process steps can be performed on the precursor to yield the final
component.
For example, the additional process steps may cause the final component to
have a
higher density than the precursor that was formed by the metal injection
molding
process. In accordance with a non-limiting example of implementation, the
additional
process step could be a hot isostatic pressing operation (HIP). HIP is a
process in which
the porosity level of the part can be reduced thus further densifying the
part, sometimes
up to 100%.
[054] In order to perform a hot isostatic pressing operation, the parts to be
treated are
placed in a sealed chamber, which is heated to between 800-1000 C. Once
heated, the
chamber is then pressurised to a pressure above 150 MPa. When performing the
pressurization operation on sintered parts, the pores within the parts should
be closed,
such that gas pressure does not build up in the pores, which could impede
deformation
to higher density levels. According to Powder Metallurgy and Particulate
Materials
Processing (German R.M., MPIF, 2005, p.366), for a sintered part having a
density of
96%, 100% of the pores are closed. For a sintered part having a density of
92%,
approximately 50% of the pores are closed. As such, for sintered parts that
have a
14
CA 02588626 2007-05-15
86930-20
density of at least 95%, 100% of the pores are closed and non-communicative,
meaning
that they do not overlap other pores.
[055] Other processes that can be performed on the precursor include finishing
machining, different types of surface treatments and/or heat treating.
[056] The metal injection molding process described above has many advantages.
For
example, forming components via metal injection molding can result in cost
savings
given that there is very little wastage of expensive raw materials. Further
advantages
include increased design and material flexibility, high-speed production and
good
mechanical properties. In general, the mechanical, physical and chemical
properties of
the static components formed using the metal injection molding technique
described
above are comparable to those of wrought material. In addition, components
formed
from the metal injection molding process require minimal secondary and
assembly
operations in order to complete the component being manufactured.
[057] The metal injection process is also able to produce components that are
consistently able to meet strict tolerance requirements. In the case of the
floating collar,
the stator vanes, the fuel swirler and the shroud segment, the tolerance for
each
dimension can be 0.5% or lower. As such, for a 1 inch dimension, there is a
variation
of 0.0025 of an inch. Likewise, for a dimension of 1/2 an inch, there is a
variation of
0.001 of an inch. In certain circumstances, the metal injection process is
able to
achieve tolerances lower than 0.3%. Although the heat shield is a bigger part,
in certain
circumstances, the tolerances can also be lower than 0.5%.
[058] A further advantage of the metal injection molding process is that it is
able to
produce a set of components from a common injection mold, such that there is a
relatively small variation in dimensional tolerance between each component in
a given
production lot. Each component in the set of components is produced during a
different
molding cycle using a common mold. As described above, the set of components
may
be a set of stator vanes, a set of fuel swirlers, a set of floating collars, a
set of heat
shields or a set of shroud segments among other possibilities. In accordance
with a non-
CA 02588626 2007-05-15
86930-20
limiting example of implementation, the process conditions used during the
mixing,
injecting, debinding and sintering steps are such that each component in the
set of
components has a relatively consistent variation in dimensional tolerance. In
addition, a
consistent variation in dimensional tolerances in components from production
lot to
production lot is also achieved. In accordance with a non-limiting example,
the
variation in dimensional tolerance is typically in the range of 0.5%. For
components
having dimensions in the range of from '/4" to 3", this process can achieve la
results,
meaning that approximately 68% of the components in the set of components
achieve a
dimensional tolerance in the range of 0.5%. These results are even better for
components having smaller dimensions. More specifically, for components having
dimensions of 1/8" or less, the metal injection molding process described
above can
achieve 6a results, meaning that 99.9997% of the components have a dimensional
tolerance in the range of 0.5%.
[059] In general, the set of components can include anywhere from 200-800
parts, while
still maintaining the variation in dimensional tolerances as described above.
For
example, a production lot of heat shields may include 225 parts, a production
lot of
stator vanes may include 500 parts and a production lot of floating collars,
fuel swirlers
and shroud components may include 800 components.
In order to measure the dimensional tolerances between components in a
production lot,
or between components from production lot to production lot, different
techniques can
be used. Some non-limiting examples of different techniques include CMM
testing, and
testing using micrometers, callipers and no/no-go gauges. In accordance with a
specific
non-limiting example, a calliper is used to measure each dimension specified
on an
engineering drawing. This measurement verification is performed on each part
in the
production lot.
[060] As previously mentioned, using the above described metal injection
molding
technique provides either the final components, or the precursors to the final
components with certain material characteristics in terms of density, pore
size and pore
sphericity. Each of these characteristics will now be described in more
detail.
16
CA 02588626 2007-05-15
86930-20
Sphericity
The debinding step that is performed during the metal injection molding
process
described above causes pores to be created in the material from which the
component is
formed. In this manner, the components produced from the metal injection
process are
porous components, having a density less than the theoretical density possible
in the
case where the material does not contain pores. Shown in Figure 9 is an
optical
micrograph of a sintered component having pores contained throughout. In the
Micrograph of Figure 9, a combination of pores and second phase particles are
shown
in black. Ideally, the pores and second phase particles are substantially
spherical in
shape. The more spherical the pores, the less likely they are to propagate
cracks or
weakness than if they had a more jagged shape.
[061] In accordance with the present invention, the sphericity of the pores is
calculated
according to the following formula:
S=(4=7r=A)/P2
Where: A area of the pore
P perimeter of the pore
[062] The following is a non-limiting example of a method for measuring the
sphericity
of the pores within a static component formed from the metal injection molding
process
described above. The method involves using a scanning electron microscope, or
optical
microscope, to capture micrograph images of the microstructure of the
component and
then analysing the images using a software program, such as Clemex Vision, to
isolate
details in the microstructure of the component.
[063] The following is a detailed process used for measuring the sphericity of
the pores
within a static component:
Step 1- A portion of the component is cut using a slow-cutting saw to expose a
cross-
sectional (thickness) of the component;
Step 2 - A sample of the cut component is prepared for metalographic
examination.
This preparation involves polishing the sample;
17
CA 02588626 2007-05-15
. t.
86930-20
Step 3 - Images of the polished sample are captured via a scanning electron
microscope. A back scattering technique is used to capture the images. The
images are
taken at a magnification, which gives a minimum of 150 contrasting features in
the
image to be analysed. These contrasting features can be pores or a combination
of pores
and second phase particles. More specifically, images are taken at
magnifications,
which enable the analysis of 102 - 103 contrasting features;
Step 4 - The images are imported into Clemex Vision software, and a threshold
is
created between the contrasting features and the matrix of material. The
software then
counts the pixels of the contrasting features and transforms the count into
dimensions
according to a predetermined scale;
Step 5 - The imaging software then obtains values in terms of the spherical
diameter,
sphericity and pore size distribution of the contrasting features. The imaging
software is
able to use the above formula for calculating the sphericity of the pores.
These analyses
are done on several images taken in the same conditions on the microscope for
a total
number of analyzed features greater than 3000;
[064] When processing the contrasting features, it is assumed that the pores
and the
second phase particles are of roughly the same size.
[065] In accordance with the present invention, the static components of the
gas turbine
engine that are formed from the metal injection molding process have pores
with an
average sphericity greater than 0.5. A sphericity of 1 is close to perfect
sphericity and a
sphericity of 0 is substantially flat. In accordance with a more specific non-
limiting
embodiment, the pores have an average sphericity greater than 0.7. And in
accordance
with an even more specific non-limiting embodiment, the pores have an average
sphericity of greater than 0.9.
[066] In the case of the micrograph shown in Figure 9, the software is
instructed to
provide values for the contrasting features that fall into the following three
categories:
a) contrasting features larger than 2gm2; b) contrasting features between 0.5
and 2 mz;
and c) contrasting features smaller than 0.5 m2 . The following table outlines
the results
for this micrograph:
18
CA 02588626 2007-05-15
86930-20
Microstructural feature based on size Mean Spherical Diameter Sphericity
( m2) ( m)
contrasting features larger than 2 m2 2.43 0.78
contrasting features between 0.5 and 1.35 0.90
2 m2
contrasting features smaller than 0.5 m2 0.50 0.99
Pore Size
[067] The pores contained within the static components produced from the metal
injection molding procedure preferably have a pore size diameter of less than
10microns. In accordance with a more specific non-limiting example of
implementation, the components have pores with an average pore size diameter
of less
than 5 microns. In accordance with a still more specific non-limiting example
of
implementation, at least 50% of the pores have a pore size diameter of less
than 3
microns.
[068] The above described process that uses a microscope for capturing images
of the
microstructure of the component and then a software program, such as Clemex
Vision,
to analyse the captured images can be used in order to obtain the values for
the pore size
of the pores within the components.
Density
[069] The static components of the gas turbine engine formed from the metal
injection
molding procedure described above have a density that is less than the
theoretical
density possible for the material from which the components are made. This is
due to
the fact that as the binder is removed from the green part, voids are created
between the
powder particles. These voids turn into substantially spherical pores as the
powder
particles are thermally bonded together during the sintering process.
[070] As a result, the component, whether it is a stator vane, a fuel swirler,
a floating
collar, a heat shield or a shroud segment, is less dense than the theoretical
possible
19
CA 02588626 2007-05-15
86930-20
density for the material from which it is made. In other words, the component
made
from the metal injection process is less dense than if it had been machined
from a solid
block of the given material. In accordance with a non-limiting example, the
static
components formed from the above described metal injection process have a
density of
between 96-99.5% of a theoretical possible density. In accordance with a
further non-
limiting example, the component has a density of between 97-98% of a
theoretical
possible density.
[071] The following is a non-limiting example of a method for measuring the
density of
the components formed from the metal injection molding process described
above. The
density of the parts can be evaluated using Archimedes technique, wherein a
part is
weighed dry and is then weighed again when suspended in water. The difference
in
weights is due to a buoyant force created by the porosities. This difference
in weights
enables the calculation of density according to the following equation:
SINTERED
DENSITY= (dry mass*density of water)/(dry mass - wet mass).
10721 The following is a specific manner in which density is calculated:
Step 1- A sample of the component is taken. The sample can be cut using a slow-
cutting saw;
Step 2 - The dry sample is weighed using a measuring scale;
Step 3 - The sample is then suspended within a body of liquid, and the weight
of the
suspended sample is taken;
Step 4- The density of the component is determined by entering the dry weight
and the
weight when suspended in water into the formula DENSITY= (dry mass*density of
water)/(dry mass - wet mass). The density can be calculated manually or using
a
computer program.
[073] Density measurements by the Archimedes technique are ASTM B328 (which is
a
standard test method for density, oil content and interconnected porosity of
sintered
metal structural parts) and ASTM B311 of MPIF std. 42.
CA 02588626 2007-05-15
86930-20
[074] The above described metal injection process described above can be used
to
manufacture the stator vanes 28, the fuel swirler 30, the floating collar 32,
the heat
shield 34 and the shroud segment 50 of the gas turbine engine, such that these
components have the density and pore characteristics described above. Some non-
limiting examples of each of these static components will now be described
briefly
below.
Stator vanes 28
[075] Shown in Figures 2a and 2b is a non-limiting example of a stator vane 28
suitable
for being produced in accordance with the metal injection process of the
present
invention. Stator vanes, such as the one shown in Figure 2a, are generally
mounted to
the inner walls 31 (shown in Figure 1) of the gas turbine engine 10, and are
positioned
before and after the fan blades 22 of the compressors 12 and the turbine
blades 26 of the
turbines 16. In operation, the stator vanes 28 are operative for directing
airflow towards
the fan blades 22 and the turbine blades 26.
[076] The stator vane 28 shown in Figure 2a includes an airfoil portion 36,
and has
leading and trailing edges that are not straight. The interior of the stator
vane 28 is
hollow, thus making it a more complicated component to manufacture. The
particular
configuration and shape of the stator vane 28 shown in Figure 2 was developed
by Rolls
Royce, and is described in more detail in U.S. patent 4,504,189. It should be
appreciated that stator vanes 28 having any size, shape and configuration
capable of
being produced via the metal injection molding process that will be described
in more
detail below, are included within the spirit of the present invention.
[077] In accordance with a non-limiting example of implementation, the stator
vane 28
is made from an alloy in the group of alloys consisting of Inconel 625,
Inconel 718,
MAR-M 247 or any nickel, cobalt or nickel-iron superalloys. The stator vane 28
has a
wall portion that has a thickness in the range from about 0.065 to 0.25 of an
inch. In
accordance with a more specific non-limiting example, the stator vane 28 has a
wall
portion that has a thickness in the range from 0.1-0.2 of an inch. In a still
more specific
21
CA 02588626 2007-05-15
86930-20
non-limiting embodiment, the stator vane 28 has a wall portion that has a
thickness in
the range of from 0.125-0.175 of an inch.
Fuel swirler
[078] Shown in Figure 3 is a non-limiting example of a fuel swirler 30 for a
gas turbine
engine that is suitable for being produced in accordance with the present
invention. The
fuel swirler 30 is operative for being mounted in proximity to an opening of
the
combustion chamber 14, so as to be able to provide an air/fuel mix to the
combustion
chamber 12.
[079] The fuel swirler 30 shown in Figure 3 includes a ferrule 38 for
supporting a fuel
injector, swirl vanes 40 and a radial flange 42. The particular configuration
and shape of
the fuel swirler 30 shown in Figure 3 was developed by General Electric
Company, and
is described in more detail in U.S. patent 7,131,273. It should be appreciated
that fuel
swirlers 30 having any size, shape and configuration capable of being produced
via the
metal injection molding process that will be described in more detail below,
are
included within the spirit of the present invention.
[080] In accordance with a non-limiting example of implementation, the fuel
swirler 30
is made from an alloy in the group of alloys consisting of Inconel 625,
Inconel 718,
MAR-M 247 or any nickel, cobalt or nickel-iron superalloys. The fuel swirler
30 has a
wall portion that has a thickness in the range from about 0.065 to 0.25 of an
inch. In
accordance with a more specific non-limiting example, the fuel swirler 30 has
a wall
portion that has a thickness in the range from 0.1-0.2 of an inch. In a still
more specific
non-limiting embodiment, the fuel swirler 30 has a wall portion that has a
thickness in
the range of from 0.125-0.175 of an inch.
Floating Collar
[081] Shown in Figure 4 is a non-limiting example of a floating collar 32 for
a gas
turbine engine, suitable for being produced in accordance with the present
invention. In
operation, the floating collar 32 is positioned between the fuel swirler 30,
or fuel
injection nozzles, and the combustion chamber 14 for damping vibration, and
22
CA 02588626 2007-05-15
86930-20
permitting minor relative movement between the fuel swirler or nozzles and the
combustion chamber 14.
[082] The floating collar 32 shown in Figure 4 is in the shape of an annular
ring. The
particular configuration and shape of the floating collar 32 shown in Figure 4
was
developed by Rolls Royce, and is described in more detail in U.S. patent
6,324,830. It
should be appreciated that floating collars 32 having any size, shape and
configuration
capable of being produced via the metal injection molding process that will be
described in more detail below, are included within the spirit of the present
invention.
[083] In accordance with a non-limiting example of implementation, the
floating collar
32 is made from an alloy in the group of alloys consisting of Inconel 625,
Inconel 718,
MAR-M 247 or any nickel, cobalt or nickel-iron superalloys. The floating
collar 32 has
a wall portion that has a thickness in the range from about 0.065 to 0.25 of
an inch. In
accordance with a more specific non-limiting example, the stator vane has a
wall
portion that has a thickness in the range from 0.1-0.2 of an inch. In a still
more specific
non-limiting embodiment, the stator vane 28 has a wall portion that has a
thickness in
the range of from 0.125-0.175 of an inch.
Heat shield
[084] Shown in Figure 5 is a non-limiting example of a heat shield 34 suitable
for being
produced in accordance with the present invention. In operation, the heat
shield 34 is
positioned at a head area of the combustion chamber 14 for protecting the head
area of
the combustion chamber 14 from the effects of the hot gasses and radiation
caused by
ignition reactions that take place in the combustion chamber 14.
[085] The heat shield 34 shown in Figure 5 includes a through hole 44 for the
burner
and a plurality of air passage holes 46. The particular configuration and
shape of the
heat shield 34 shown in Figure 5 was developed by BMW Rolls Royce, and is
described
in more detail in U.S. patent 5,956,955. It should be appreciated that heat
shields 34
having any size, shape and configuration capable of being produced via the
metal
23
CA 02588626 2007-05-15
86930-20
injection molding process that will be described in more detail below, are
included
within the spirit of the present invention.
[086] In accordance with a non-limiting example of implementation, the heat
shield 34
is made from an alloy in the group of alloys consisting of Inconel 625,
Inconel 718,
MAR-M 247 or any nickel, cobalt or nickel-iron superalloys. The heat shield 34
has a
wall portion that has a thickness in the range from about 0.065 to 0.25 of an
inch. In
accordance with a more specific non-limiting example, the heat shield 34 has a
wall
portion that has a thickness in the range from 0.1-0.2 of an inch. In a still
more specific
non-limiting embodiment, the heat shield 34 has a wall portion that has a
thickness in
the range of from 0.125-0.175 of an inch.
Shroud Segment
[087] Shown in Figure 6 is a non-limiting example of a shroud segment 50
suitable for
being produced in accordance with the present invention. A shroud assembly
that is
made up of a plurality of shroud segments 50 encircles the turbine blades 26.
[088] The shroud segment 50 shown in Figure 6 includes a shroud body 52 formed
with
a forward side mounting rail 54 and an aft side mounting rail 56 and a
concavely
arcuate inner face 58. The particular configuration and shape of the shroud
segment 50
shown in Figure 6 was developed by General Electric Company, and is described
in
more detail in U.S. patent 5,071,313. It should be appreciated that shroud
segments 50
having any size, shape and configuration capable of being produced via the
metal
injection molding process that will be described in more detail below, are
included
within the spirit of the present invention.
[089] In accordance with a non-limiting example of implementation, the shroud
segment 50 is made from an alloy in the group of alloys consisting of Inconel
625,
Inconel 718, MAR-M 247 or any nickel, cobalt or nickel-iron superalloys. The
shroud
segment 50 has a wall portion that has a thickness in the range from about
0.065 to 0.25
of an inch. In accordance with a more specific non-limiting example, the
shroud
segment 50 has a wall portion that has a thickness in the range from 0.1-0.2
of an inch.
24
CA 02588626 2007-05-15
86930-20
In a still more specific non-limiting embodiment, the shroud segment 50 has a
wall
portion that has a thickness in the range of from 0.125-0.175 of an inch.
Recipe for making Static Components
[090] The following describes suitable feedstock and operating parameters for
manufacturing a stator vane 28, a fuel swirler 30, a floating collar 32, a
heat shield 34
and a shroud segment 50 in accordance with the metal injection molding process
described above. In accordance with a specific embodiment, the feedstock
includes a
powder of gas atomised Inconel 625 with 80% of the particles having a diameter
of less
than 22 microns, and a binder that is made of 85% paraffin wax, 5% bees wax,
5%
stearic acid and 5% PE-EVA copolymer. The powder and binder are mixed together
in
proportions suitable for forming a feedstock having between 60-70% solid
loading.
The powder and binder feedstock is kept at a temperature of 90C.
[091] Once mixed, the feedstock is injected into a mold that is made out of
steel (P20).
The mold is kept at a temperature between 25-40C and preferably between 30-
35C. The
feedstock is injected into the mold such that the feedstock is pushed into the
mold at a
pressure below 60psi and preferably at a pressure of between 20-40 psi. More
specifically, the feedstock is injected into the mold with low pressure such
that there is
no shearing separation between the powder and the binder as it is being
injected. The
cycle time used to mold the part is less than 30 seconds.
[092] Once the shaped part is removed from the mold, the debinding process is
conducted in a wicking media of high purity alumina powders. More
specifically, the
parts are buried in the wicking media. The debinding treatment is then
conducted under
argon gas. The temperature profile applied to the part is as follows: 1) the
heat is
ramped to 200C at a rate of 0.5C/min, and then 2) the heat is ramped from 200C
to
900C at 0.85C/min. Once the heat has reached 900C, it is then held at 900C for
2 hours,
after which time the heat is ramped back down to an ambient temperature.
CA 02588626 2007-05-15
86930-20
[093] Once the debinding process is complete, the parts are sintered under a
hydrogen/argon atmosphere mixture at 1245C for 2 hours. The parts are placed
on low-
density alumina setters during this process.
Conclusion
[094] Due to the porous nature of the components formed by the metal injection
molding process described above, it is not necessarily advisable to form the
moving
components of the gas turbine engine using this process. The performance and
quality
standards that are applied to the dynamic, rotating components of the gas
turbine engine
are more stringent than those for the static components since it is possible
that pores
within moving components may cause cracks to propagate much more readily than
in
static components.
[095] Referring back to Figure 1, in accordance with a non-limiting example of
implementation, the gas turbine engine 10 includes a hot section, in which is
mounted
the rotating assembly and the plurality of static components. In accordance
with the
present invention, at least one of the static components is made by metal
injection
molding from an alloy in the group consisting of Inconel 625, Inconel 718, MAR-
M
247 or any nickel, cobalt or nickel-iron superalloys. Alternatively, any alloy
that has
desired material characteristics for the end part can also be used. As such,
the static
component that is formed from the metal injection molding process has a
density of less
than 100% of its theoretical possible density, while the components that form
the
rotating assembly have a density of 100% of their theoretical possible
density. This
difference in density is caused, at least in part by the fact that the static
components
formed from the metal injection molding process are more porous than the
components
that form the rotating assembly. In general, the components that form the
rotating
assembly are manufactured by techniques, such as machining, that cause these
components to be substantially free of pores.
[096] Although the present invention has been described in considerable detail
with
reference to certain preferred embodiments thereof, variations and refinements
are
26
CA 02588626 2007-05-15
86930-20
possible without departing from the spirit of the invention. Therefore, the
scope of the
invention should be limited only by the appended claims and their equivalents.
27
