Note: Descriptions are shown in the official language in which they were submitted.
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INJECTION MOLDING METHODS FOR MANUFACTURING COMPONENTS
CAPABLE OF TRANSPORTING LIQUIDS
TECHNICAL FIELD
Embodiments described herein generally relate to methods of manufacturing
components capable of transporting liquids. More specifically, embodiments
described herein relate generally to metal injection molded components capable
of
transporting jet fuel.
BACKGROUND OF THE INVENTION
In gas turbine engines, such as aircraft engines, air is drawn into the front
of
the engine and then compressed by a shaft-mounted compressor. The compressed
air
is then transported to the combustor while fuel is concurrently transported
from a fuel
supply by a fuel distribution system to the combustor. More specifically, the
fuel is
introduced at the front end of a burner in a highly atomized spray from a fuel
nozzle.
Compressed air flows in around the fuel nozzle and mixes with the fuel to form
a fuel-
air mixture, which is ignited by the burner. The temperature of the ignited
fuel-air
mixture can reach an excess of 3500 F (1920 C). It is therefore important that
the
fuel supply and distribution systems are substantially leak free, as a leak in
the fuel
supply or distribution systems could be catastrophic.
Currently available fuel nozzles may be made using macro-laminate
technology, which generally involves shaping and coupling plies of material
together
using a series of bonded joints. Surrounding the macro-laminate may be a
variety of
components that require numerous braze joints. Due largely to the number of
braze
joints required to construct fuel nozzles in this manner, the use of macro-
laminate
technology is not ideal.
More specifically, the use of braze joints can increase the time needed to
fabricate such components and can also complicate the fabrication process for
any of
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several reasons, including: the need for an adequate region to allow for braze
alloy
placement; the need for minimizing unwanted braze alloy flow; the need for an
acceptable inspection technique to verify braze quality; and, the necessity of
having
several braze alloys available in order to prevent the re-melting of previous
braze
joints. Moreover, numerous braze joints can result in several braze runs,
which can
weaken the parent material of the component. In a related aspect, the presence
of
numerous braze joints can undesirably increase the weight and manufacturing
cost of
the component.
Therefore, there remains a need for improved processes for manufacturing
fuel supply and distribution systems that can reduce the risk of fuel leakage
by
providing integrated parts and dense structures through the use of metal
injection
molding techniques.
BRIEF DESCRIPTION OF THE INVENTION
Embodiments herein generally relate to methods for manufacturing
components capable of transporting a liquid involving providing a mold,
placing at
least one core made from a core material into the mold, injecting a component
material into the mold about the core to produce a green component, heating
the green
component to burn out the core and produce a brown component, and sintering
the
brown component to produce a finished component capable of transporting a
liquid
wherein the finished component is from about 95% to about 99% dense.
Embodiments herein also generally relate to methods for manufacturing
components capable of transporting a liquid involving providing a mold,
placing at least
one core made from a core material into the mold, injecting a component
material into
the mold about the core to produce a green component, heating the green
component
to burn out the core and produce a brown component, sintering the brown
component
to produce a finished component capable of transporting a liquid, and hipping
the
finished component to produce a densified component that is about 99.9% dense.
Embodiments herein also generally relate to methods for manufacturing
components capable of transporting a liquid involving providing a mold,
placing
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multiple non-linear cores made from a core material selected from the group
consisting of stereolithography (SLA)-type resins, polycarbonates,
polypropylene, and
combinations thereof, into the mold, injecting a component material selected
from the
group consisting of nickel based alloys, cobalt based alloys, and combinations
thereof,
into the mold about the cores to produce a green component, heating the green
component over a temperature range of from about 150 F (about 65 C) to about
500 F (about 260 C) to burn out the cores and produce a brown component, and
sintering the brown component over a temperature range of from about 700 F
(about
370 C) to about 2300 F (about 1260 C) to produce a finished component capable
of
transporting jet fuel wherein the finished component is a fuel nozzle
comprising a fuel
conduit and a fuel distributor ring and wherein the finished component is from
about
95% to about 99% dense.
These and other features, aspects and advantages will become evident to
those skilled in the art from the following disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and
distinctly claiming the invention, it is believed that the embodiments set
forth herein
will be better understood from the following description in conjunction with
the
accompanying figures, in which like reference numerals identify like elements.
FIG. 1 is a schematic representation of one embodiment of a fuel
nozzle in accordance with the description herein;
FIG. 2 is a schematic representation of one embodiment of a fuel
nozzle having a branched main cavity and a plurality of injection posts in
accordance
with the description herein;
FIG. 3 is a schematic cross-sectional representation of one embodiment
of a fuel nozzle enclosed by heat shields and having an insulation gap in
accordance
with the description herein;
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FIG. 4 is a schematic representation of one embodiment of a fuel
nozzle having a pilot injector in accordance with the description herein;
FIG. 5 is a schematic partial cut-away view of one embodiment of a
gas turbine engine having an axially oriented fuel nozzle in accordance with
the
description herein; and
FIG. 6 is a schematic partial cut-away view of one embodiment of a
gas turbine engine having a circumferentially oriented fuel nozzle in
accordance with
the description herein.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments described herein generally relate to metal injection molding
methods for fabricating components capable of transporting liquids. While
embodiments herein may generally focus on methods for making components useful
in the transport of jet fuel through the fuel systems of gas turbine engines,
it will be
understood by those skilled in the art that the description should not be
limited to
such. Indeed, as the following description explains, the methods described
herein
may be utilized to produce any component capable of being used to transport a
liquid.
Generally, embodiments set forth herein relate to providing a mold, injecting
a component material into the mold to produce a green component, heating the
green
component to produce a brown component, and sintering the brown component to
produce a finished component capable of transporting a liquid.
Initially, a mold may be provided having the form of the desired finished
component. The mold may be any mold suitable for use with metal injection
molding
processes as set forth in greater detail herein below. Generally, the mold may
be
constructed of steel or other comparable material. As is typical of metal
injection
molding, the mold can have an internal space corresponding to the external
shape of
the component being fabricated.
At least one core may be placed inside the mold to form a cavity within the
finished component. As used herein, the term "core" means at least one. It
will be
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understood that the embodiments described herein may include more than one
core.
The core may be fabricated from any core material having a lower melting point
than
the component material as described herein below to facilitate removal of the
core. In
one embodiment, the core may be fabricated from a core material selected from
the
group consisting of SLA-type resins, polycarbonates, polypropylene, and
combinations thereof. The core may be either linear or non-linear. Depending
on the
type of component being fabricated, it may be desirable to suspend the core in
the
mold using known techniques in the art. Suspending the core can help ensure
that the
core is completely surrounded by the component material. This can further
reduce the
likelihood of leaks in the finished component.
A component material may then be injected into the mold about the core
using conventional injection molding practices, which can typically involve
injecting
the component material into the mold at a pressure of from about 200 psi to
about 400
psi. If desired, the mold into which the component material is injected may be
heated
to a temperature of about 90 C (about 200 F) to facilitate injection and
dispersal of
the component material in the mold. While the component material may comprise
any material capable of being injection molded, in one embodiment the
component
material may be selected from the group consisting of nickel based alloys,
cobalt
based alloys, and combinations thereof. More specifically, the component
material
may comprise a metallic powder mixed with from about 3% to about 20% of a
binder
material, by weight. For example, the component material may comprise about
93%
by weight Inconel 718 powder combined with about 7% by weight of a binder
material. Any common binder material known to those skilled in the art is
acceptable
for use herein. The component material can have a consistency that is capable
of
being injected under pressure into the mold without leaking out of the mold.
Once injected, the component material may be allowed to firm up inside the
mold to produce a green component. The time necessary for this set up to occur
will
vary depending on the particular component material selected. After the
component
material has set up, the mold may be pulled and the green component removed.
If
desired, the green component may be dried and/or cooled to make handling
easier.
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The green component may then be heated to produce a brown component, as
well as to burn out any cores present. The resulting brown component will be
hardened and will have an internal cavity located where each core had been. As
previously discussed, it is desirable that the cores are made from a material
having a
melting point that is lower than the melting point of the component material
in order
to facilitate burning-out of the cores. The temperature to which the green
component
can be heated to produce the brown component, and to burn out any cores
present,
may vary depending on the particular component material and core material
used.
However, in one embodiment, the green component can be heated to a temperature
ranging from about 150 F to about 500 F (about 65 C to about 260 C). Core
burnout
can occur by transporting out several heating steps over the previously set
forth
temperature range wherein the temperature of the furnace containing the
component
can be increased by about twenty-five degrees over about five minutes,
followed by
holding the temperature constant for a defined length of time.
More specifically, core burnout can include the following steps: the furnace
can be heated to a temperature of about 300 F (about 148 C) and held constant
for
about one hour; the temperature can then be raised to about 325 F (about 162
C) over
a period of about a five minutes and held constant for about two hours; the
temperature can then be raised to about 350 F (about 176 C) over a period of
about
five minutes and held constant for about two additional hours; the temperature
can
then be raised to about 375 F (about 190 C) over a period of about five
minutes and
held constant for about two hours; the temperature can then be raised to about
400 F
(about 204 C) over a period of about five minutes and held constant for about
two
hours during which time the core will start to liquefy and burn out of the
component.
The temperature can then be raised to about 425 F (about 218 C) over a period
of
about five minutes and held constant for about six to seven hours. After about
six to
seven hours, the resulting brown component can be inspected to ensure the core
has
been substantially removed.
In addition to burning out the core, this heating process can be used to
remove any ash remaining in the resulting brown component and/or the air
furnace in
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which the core burnout occurs. More particularly, after completion of the core
burnout and while the brown component is still present inside, the furnace can
be
heated to about 625 F (about 329 C), to burn any residual ash content from
within the
brown component and the furnace. When satisfied that the core burnout is
complete,
the furnace can be turned off and the brown component allowed to cool.
Concurrent with burning out the core, partial debinding of the component
material may occur. During partial debinding, at least a portion of the binder
material
used in the component material is burned out of the green component. Partial
debinding provides ease of handling and transport of the resulting brown
component
from the air furnace to a vacuum furnace, where sintering occurs. It should be
noted
that complete debinding of the component material generally does not occur
until
completion of the sintering cycle as explained herein below.
Sintering involves heating the brown component to volatilize any remaining
binder and densifying the remaining metal particles of the component material
together to produce a finished component. In particular, sintering can densify
the
brown component by eliminating the voids created during debinding. Generally,
sintering can shrink the finished component by about 3% to about 20% when
compared to the size of the brown component. Those skilled in the art will
understand that it may be desirable to control the amount of shrinkage to
provide
dimensional reproducibility and help minimize variation between components
made
using the methods set forth herein.
While the heating and cooling cycles used for sintering can vary, in one
embodiment, sintering may be carried out in a series of cycles over a
temperature
range of from about 700 F to about 2300 F (about 370 C to about 1260 C).
Sintering
may be carried out in a vacuum furnace having partial pressure capability. In
one
embodiment, the furnace may be evacuated and then backfilled with argon or
hydrogen gas to a pressure of about 600 microns of Hg. The gas may be
intermittently or continuously flowed through the furnace to purge the
volatized
binder generated throughout the sintering process.
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The sintering process may be initiated while the furnace is at ambient
temperature. The brown component may be placed into the furnace and the
furnace
heated at a temperature increase of about 5 F (about 2.7 C)/minute until the
temperature reaches about 1200 F (about 648 C). Once a temperature of about
1200 F (about 648 C) is reached, it may be held constant for about one hour.
The
furnace may then be cooled at a rate of about 5 F (about 2.7 C)/minute until a
temperature of about 300 F (148 C) is reached. Cooling may be accomplished by,
for
example, controlled power reduction to the heating elements of the furnace.
The
furnace may then be heated again at a rate of about 5 F (about 2.7 C)/minute
to a
temperature of about 1200 F (about 648 C) where it may be held constant for
about
two hours. The furnace may then be cooled at a rate of about 5 F (about
2.7 C)/minute until a temperature of about 300 F (148 C) is reached. The
furnace
may then be heated at a rate of about 5 F (about 2.7 C)/minute to a
temperature of
about 1200 F (about 648 C) where it may be held constant for about two hours.
Next, the furnace may be cooled at a rate of about 5 F (about 2.7 C)/minute to
a
temperature of about 300 F (about 148 C), followed by heating one additional
time at
a rate of about 10 F (about 5 C)/minute to a temperature of about 1200 F
(about
648 C). The furnace may then be allowed to cool to ambient temperature.
The chamber of the vacuum furnace may then be evacuated to a pressure of
less than about 1 micron of mercury. Heating may then be reinitiated by
increasing
the temperature at a rate of about 5 F (about 2.7 C)/minute to a temperature
of about
1500 F (about 815 C) where it may be held constant for about two hours. The
temperature may then be increased to about 2000 F (about 1093 C) at a rate of
about
F (about 2.7 C)/minute. After holding the temperature constant for about two
hours, it may again be increased, this time at a rate of about 35 F (about 19
C)/minute
until it reaches a temperature of about 2300 F (about 1260 C). The temperature
may
be held at this temperature for an additional two hours before being vacuum
cooled at
a rate of about 10 F (about 5 C)/minute until a temperature of about 2000 F
(about
1093 C) is reached. Vacuum cooling may then be continued at an uncontrolled
rate
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until the temperature reaches below about 1200 F (about 648 C), and in one
embodiment, until the temperature reaches about 250 F (about 121 C).
The resulting finished component is capable of transporting a liquid, which
in one embodiment, may be a flammable liquid such as liquid jet fuel. More
specifically, sintering densifies the cavities resulting from the burned-out
cores and
reduces the porosity of the cavity walls to enable the transport of liquids.
This
reduction of porosity results in a finished component that can be from about
95% to
about 99% dense. As used herein, the term "dense" refers to the percent of the
finished component that is non-porous and can be measured using conventional
image
analysis techniques. For example, the fuiished component can be cut up and a
piece
of the finished component can be placed under a microscope. A microscopic
photograph of the piece of the finished component can be taken and the area of
any
voids, or porous areas, present can be calculated with respect to the total
area of the
piece of the finished component shown in the photograph.
Optionally, pressure may be applied to the finished product using a technique
known in the art as Hot Isostatic Pressing, or HIP/"hipping." More
specifically,
during hipping, any remaining voids within the finished component resulting
from
debinding can be removed by heating the finished component to a temperature of
from about 2100 F (about 1149 C) to about 2200 F (about 1204 C), and in one
embodiment about 2125 F (about 1163 C), under from about lOksi to about 20ksi
argon pressure, and in one embodiment about 15 ksi (about 1055 kgf/cm2) argon
pressure, and holding these parameters constant for about four hours. The end
result
of the hipping process is a densified component that is at least about 99.9%
dense.
While the previously described injection molding methods may be used to
fabricate any component capable of trariLsporting a fluid, in one embodiment,
the
methods may be used to fabricate a fuel nozzle 10, as shown generally in FIG.
1. Fuel
nozzle 10 may include a fuel conduit supply 12 and a distributor ring 14.
Turning to FIG. 2, fuel conduit supply 12 may comprise at least one pilot
cavity 16 and at least one main cavity 18, each fabricated using the
previously
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described cores during the injection molding process. As used herein
throughout, the
term "at least one" includes both one and more than one. Pilot cavity 16 and
main
cavity 18 may each be generally linear, non-linear, or some combination
thereof. In
one embodiment, as shown in FIG. 2, main cavity 18 may branch into a main
cavity
right side 20 and a main cavity left side 22. Regardless of the number or
orientation
of pilot cavity 16 and main cavity 18, it may be desirable that all cavities
present in
fuel conduit supply 12 are separated from each other by a distance D of at
least about
0.02cm. Spacing the cavities by at least about 0.02cm can help ensure that the
cores
that form the cavities are adequately surrounded by the component material
during
fabrication, which can help to prevent leakage in the fmished coniponent.
Distributor ring 14, which may be operably coupled to at least one pilot
cavity 16 and at least one main cavity 18, may have at least one injection
post 24
extending outwardly therefrom. In the embodiment shown in FIG. 2, distributor
ring
14 includes a plurality of injection posts 24, which can help maintain the
fuel velocity
until the fuel is injected into a mixer cavity where the fuel mixes with air
causing
combustion. Because the metal injection molding process set forth herein
includes the
use of cores, injection post 24 can be integral with distributor ring 14. More
specifically, prior to injection molding distributor ring 14 having injection
post 24,
one or more cores can be suspended within the mold as described previously to
account for channels (not shown) within distributor ring 14 and injection post
24.
This arrangement allows distributor ring 14 to be molded with integral
injection posts
24 rather than the current practice of fabricating the distributor ring and
then
subsequently attaching one or more injection posts manually.
In one embodiment, the previously detailed metal injection molding process
may be used to separately fabricate fuel conduit supply 12 and distributor
ring 14 up
through the brown component portion of the process. The brown fuel conduit and
the
brown distributor ring may then be coupled together by inserting the brown
fuel
conduit into at least one corresponding inlet 13, shown in FIG. 3, of the
distributor
ring prior to carrying out the sintering and optional hipping processes such
that the
fuel conduit supply 12 and distributor ring 14 are fixed together during
fabrication to
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form fuel nozzle 10. This permanent coupling of fuel conduit supply 12 and
distributor ring 14 can eliminate the use of braze joints and reduce the
likelihood of
leakage that may result therefrom.
Distributor ring 14 may also be enclosed by a forward heat shield 26 coupled
to an aft heat shield 28 that together can form an insulation gap 30 about
distributor
ring 14, as shown in FIG. 3. Forward heat shield 26 and aft heat shield 28 may
be
constructed from, for example, Inconel 718, and can be fabricated using any of
a
variety of methods known to those skilled in the art, such as, for example,
casting,
metal injection molding or other machining method. Heat shields 26, 28 can be
brazed together around fuel distributor ring 14. Gap 30 insulates the fuel
from the hot
air that flows through cavities in fuel nozzle 10, which helps prevent the
fuel from
getting too hot and coking.
Fuel nozzle 10 may additionally comprise at least one pilot injector 32 as
shown in FIG. 4. In general, pilot injector 32 can be operably coupled to the
pilot
cavity where it can serve as the main fuel supply for ignition of the engine.
Pilot
injector 32 may generally be a machined part that can be brazed to fuel
conduit supply
12. In one embodiment, pilot injector 32 can be made from the same material as
fuel
conduit supply 12.
Regardless of the exact configuration, the fuel nozzle may be oriented either
axially, as shown in FIG. 5, or circumferentially as shown in FIG. 6, in
relation to the
engine 34 in which it is placed. Axial orientation may be desired to help
reduce the
weight and size of nozzle 10, however, those skilled in the art will
understand that
nozzle 10 must have low enough thermal stresses to meet part life
requirements.
Circumferential orientation may be desired to reduce thermal stresses on
nozzle 10.
Either orientation is acceptable for use in conjunction with the embodiments
set forth
herein.
This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the. art to make and
use the
invention. The patentable scope of the invention is defined by the claims, and
may
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include other examples that occur to those skilled in the art. Such other
examples are
intended to be within the scope of the claims if they have structural elements
that do
not differ from the literal language of the claims, or if they include
equivalent
structural elements with insubstantial differences from the literal language
of the
claims.
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