U.S. patent application number 10/617552 was filed with the patent office on 2005-01-13 for investment casting method and cores and dies used therein.
This patent application is currently assigned to General Electric Company. Invention is credited to Lee, Ching-Pang, Wang, Hsin-Pang.
Application Number | 20050006047 10/617552 |
Document ID | / |
Family ID | 33452696 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050006047 |
Kind Code |
A1 |
Wang, Hsin-Pang ; et
al. |
January 13, 2005 |
Investment casting method and cores and dies used therein
Abstract
A method for making an article by an investment casting process
is presented, along with a method for making casting cores, the
casting cores made by this method, and dies for making such cores.
The method for making a component comprises providing a
single-piece sacrificial die, the die comprising at least one
internal cavity; introducing a ceramic slurry into the at least one
cavity of the die, the slurry comprising a ceramic and a carrier
fluid; curing the slurry to form a ceramic casting core; removing
the sacrificial die by exposing the die to an environment adapted
to destroy the die while leaving the ceramic casting core intact;
and performing an investment casting process using the ceramic
casting core as part of a mold-core assembly to form the
component.
Inventors: |
Wang, Hsin-Pang; (Rexford,
NY) ; Lee, Ching-Pang; (Cincinnati, OH) |
Correspondence
Address: |
General Electric Company
CRD Patent Docket Rm 4A59
Bldg. K-1
P.O. Box 8
Schenectady
NY
12301
US
|
Assignee: |
General Electric Company
|
Family ID: |
33452696 |
Appl. No.: |
10/617552 |
Filed: |
July 10, 2003 |
Current U.S.
Class: |
164/516 ; 164/34;
164/35; 164/361; 164/369; 164/46; 249/134; 249/135; 264/401;
264/651 |
Current CPC
Class: |
B22C 9/10 20130101; Y02P
10/25 20151101; B33Y 80/00 20141201 |
Class at
Publication: |
164/516 ;
264/401; 264/651; 164/034; 164/035; 164/046; 164/361; 164/369;
249/134; 249/135 |
International
Class: |
B29C 035/04 |
Claims
1. A method for making a component, said method comprising:
providing a single-piece sacrificial die, said die comprising at
least one internal cavity; introducing a ceramic slurry into said
at least one cavity of said die, said slurry comprising a ceramic
and a carrier fluid; curing said slurry to form a ceramic casting
core; removing said sacrificial die by exposing said die to an
environment adapted to destroy said die while leaving said ceramic
casting core intact; and performing an investment casting process
using said ceramic casting core as part of a mold-core assembly to
form said component.
2. The method of claim 1, wherein providing said single-piece
sacrificial die comprises producing said die by at least one
additive layer manufacturing process.
3. The method of claim 2, wherein said additive layer manufacturing
process comprises stereolithography.
4. The method of claim 2, wherein said additive layer manufacturing
process comprises at least one of micro-pen deposition, selective
laser sintering, and laser wire deposition.
5. The method of claim 1, wherein said die comprises at least one
sacrificial material selected from the group consisting of an
epoxy, a silicone, and a metal.
6. The method of claim 1, wherein said ceramic slurry comprises at
least one of alumina, yttria, ceria, zirconia, magnesia, and
calcia.
7. The method of claim 1, wherein said component comprises an
external wall and at least one internal wall disposed in a
spaced-apart relationship with said external wall.
8. The method of claim 1, wherein introducing said slurry comprises
operating an injection molding apparatus to introduce said slurry
into said cavity of said die.
9. The method of claim 1, wherein curing comprises heating said
slurry to evaporate said carrier fluid.
10. The method of claim 1, wherein removing said die comprises
heating said die.
11. The method of claim 1, wherein removing said die comprises
dissolving said die in a solvent.
12. The method of claim 1, wherein removing said die comprises
chemically removing said die.
13. The method of claim 1, wherein said component is a component of
a turbine assembly.
14. The method of claim 13, wherein said component comprises one of
a vane and a blade.
15. The method of claim 14, wherein said component comprises an
external wall and at least one internal wall disposed in a
spaced-apart relationship with said external wall.
16. The method of claim 14, wherein said component comprises at
least one internal cooling passage.
17. The method of claim 16, wherein said at least one passage
further comprises turbulators.
18. A method for making a component for a turbine assembly, said
method comprising: using a stereolithography process to provide a
single-piece sacrificial die, said die comprising at least one
internal cavity; introducing a ceramic slurry into said at least
one cavity of said die, said slurry comprising a ceramic and a
carrier fluid; curing said slurry to form a ceramic casting core;
removing said sacrificial die by exposing said die to an
environment adapted to destroy said die while leaving said ceramic
casting core intact; and performing an investment casting process
using said ceramic casting core as part of a mold-core assembly to
form said component; wherein said component comprises an external
wall and at least one internal wall disposed in a spaced-apart
relationship with said external wall, and further comprises at
least one cooling passage disposed between said external wall and
said internal wall.
19. A method for making a casting core, comprising: manufacturing a
single-piece sacrificial die using an additive layer manufacturing
method, said die comprising at least one internal cavity;
introducing a ceramic slurry into said cavity of said die, said
slurry comprising a ceramic and a carrier fluid; curing said slurry
to form a ceramic casting core; and removing said sacrificial die
by exposing said die to an environment adapted to destroy said die
while leaving said ceramic casting core intact.
20. The method of claim 19, wherein said additive layer
manufacturing process comprises stereolithography.
21. The method of claim 19, wherein said additive layer
manufacturing process comprises at least one of micro-pen
deposition, selective laser sintering, and laser wire
deposition.
22. The method of claim 19, wherein said die comprises at least one
sacrificial material selected from the group consisting of an
epoxy, a silicone, and a metal.
23. The method of claim 19, wherein introducing said slurry
comprises operating an injection molding apparatus to introduce
said slurry into said cavity of said die.
24. The method of claim 19, wherein removing said die comprises at
least one of heating said die, dissolving said die in a solvent,
and chemically removing said die.
25. The method of claim 19, wherein said core is configured to form
internal passages in an investment cast article.
26. The method of claim 25, wherein said article comprises an
external wall and at least one internal wall disposed in a
spaced-apart relationship with said external wall, and further
comprises at least one cooling passage disposed between said
external wall and said internal wall.
27. The method of claim 25, wherein said article is a component of
a turbine assembly.
28. A casting core manufactured by the method of claim 19.
29. A die for making a casting core, comprising: a single piece
structure comprising at least one cavity, said cavity configured to
correspond to a desired configuration of at least one internal
cooling circuit of a gas turbine component; wherein said structure
comprises a material capable of being selectively removed from a
ceramic casting core when said ceramic casting core is disposed in
said at least one cavity.
30. The die of claim 29, wherein said structure comprises a
structure assembled in an additive layer manufacturing process.
31. The die of claim 30, wherein said additive layer manufacturing
process comprises stereolithography.
32. The die of claim 30, wherein said material comprises at least
one sacrificial material selected from the group consisting of an
epoxy, a silicone, and a metal.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to investment casting of complex
articles. More particularly, this invention relates to the
manufacture and use of integral, sacrificial cores for investment
casting complex articles.
[0002] In a gas turbine engine, compressed air is mixed with fuel
in a combustor and ignited, generating a flow of hot combustion
gases through one or more turbine stages that extract energy from
the gas, producing output power. Each turbine stage includes a
stator nozzle having vanes that direct the combustion gases against
a corresponding row of turbine blades extending radially outwardly
from a supporting rotor disk. The vanes and blades include airfoils
having a generally concave "pressure" side and a generally convex
"suction" side, both sides extending axially between leading and
trailing edges over which the combustion gases flow during
operation. The vanes and blades are subject to substantial heat
load, and, because the efficiency of a gas turbine engine is a
function of gas temperature, the continuous demand for efficiency
translates to a demand for airfoils that are capable of
withstanding higher temperatures for longer service times.
[0003] Gas turbine airfoils on such components as vanes and blades
are usually made of superalloys and are often cooled by means of
internal cooling chambers. The internal air-cooling of turbine
airfoils is often accomplished via a complex cooling scheme in
which cooling air flows through channels within the airfoil
("internal air-cooling channels") and is then discharged through a
configuration of cooling holes at the airfoil surface. Convection
cooling occurs within the airfoil from heat transfer to the cooling
air as it flows through the cooling channels.
[0004] Turbine components such as blades and vanes are often
fabricated by investment casting, a technique used to manufacture
complex, high-precision parts. Investment casting is performed by
first forming a wax pattern of the part to be cast, then
encapsulating the wax pattern with a ceramic shell. The
encapsulated shell is then heated to cure the ceramic and melt the
wax, leaving a ceramic mold having a cavity in the precise shape of
the part to be cast. Molten metal is then poured into the ceramic
shell and solidified, and the ceramic is removed by a combination
of mechanical and chemical means to produce a final metal casting
suitable for various finishing operations. Using this method to
produce parts with internal channels is complicated by the need for
the ceramic shell to include internal mold cores that define the
channels. These ceramic mold cores are often formed by injection
molding, and as the desired cooling channel configuration for an
airfoil component becomes more complicated, the ability to form the
required mold cores becomes more difficult due to the demands
placed upon the injection molding process to completely fill
convoluted, narrow passageways in the injection molding die.
[0005] Recently, turbine components having multiple airfoil walls
have been designed to achieve still further enhanced cooling
efficiency. Examples of these designs include those set forth in
U.S. Pat. Nos. 5,484,258; 5,660,524; 6,126,396; and 6,174,133. One
drawback to such complicated designs is the difficulty and expense
involved in investment casting airfoils with multiple walls,
because the complexity of the cooling circuits is such that the
required mold cores cannot be formed in a single injection into a
conventional die. Instead, multiple cores are generally formed by
separate injections, followed by assembling the multiple cores into
a composite core. This assembly step is time-consuming and
introduces a source for variation in the final dimensions of the
cast part, particularly in the thickness dimension of the various
walls. Therefore, an alternative method for forming casting cores
that allows the formation of an integral core would be
advantageous, especially in the fabrication of components having
multiple walls. Furthermore, alternative methods for forming
articles having multiple walls, where the method is less
time-consuming and repeatable than current methods, would also be
advantageous.
BRIEF DESCRIPTION
[0006] These and other needs are addressed by embodiments of the
present invention.
[0007] One embodiment is a method for making a component. The
method comprises providing a single-piece sacrificial die, the die
comprising at least one internal cavity; introducing a ceramic
slurry into the at least one cavity of the die, the slurry
comprising a ceramic and a carrier fluid; curing the slurry to form
a ceramic casting core; removing the sacrificial die by exposing
the die to an environment adapted to destroy the die while leaving
the ceramic casting core intact; and performing an investment
casting process using the ceramic casting core as part of a
mold-core assembly to form the component.
[0008] A second embodiment is a method for making a casting core.
The method comprises manufacturing a single-piece sacrificial die
using an additive layer manufacturing method, the die comprising an
internal cavity; introducing a ceramic slurry into the cavity of
the die, the slurry comprising a ceramic and a carrier fluid;
curing the slurry to form a ceramic casting core; and removing the
sacrificial die by exposing the die to an environment adapted to
destroy the die while leaving the ceramic casting core intact.
Embodiments of the present invention further include the casting
core made by the above method.
[0009] A further embodiment is a die for making a casting core. The
die comprises a single-piece structure comprising at least one
cavity, and this structure comprises a material capable of being
selectively removed from a ceramic casting core when the ceramic
casting core is disposed in the at least one cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0011] FIG. 1 is a cross sectional view of an exemplary component
which is capable of being manufactured by embodiments of the
present invention.
DETAILED DESCRIPTION
[0012] Referring to FIG. 1, a component 10 is made according to
method embodiments of the present invention. In particular
embodiments, component 10 comprises an external wall 20 and at
least one internal wall 30 disposed in a spaced-apart relationship
with external wall 20. Such components are referred to herein as
"multi-wall components." In the method of the present invention, a
single-piece sacrificial die is provided. Conventional dies are
generally constructed to be used multiple times and are usually
two-piece designs, but the complicated geometry of the cooling
circuits used in multi-wall components 10 makes the use of dies
having two pieces very difficult and often impossible, requiring in
conventional methods additional time and effort for multiple
injected cores to be formed and assembled into a composite core.
The single-piece sacrificial die comprises at least one internal
cavity. As used hereinafter, the singular term "cavity" will be
used to refer to the at least one cavity within the die, but it
should be understood that the use of the singular term "cavity"
also refers to the case where more than one cavity is contained
within the die. The shape of the cavity corresponds to the shape
desired for the complex mold core to be used in casting the
component 10.
[0013] According to certain embodiments of the present invention,
the single-piece sacrificial die is provided through the use of one
or more additive layer manufacturing processes. The die, in
particular embodiments, comprises at least one sacrificial material
selected from the group consisting of an epoxy, a silicone, and a
metal. In an additive layer process, a product is "assembled" by
producing and sequentially stacking thin cross-sectional layers one
on top of the other, generally starting at one end of the product
and working towards the opposite end. Such methods often use a
three-dimensional computer-aided drafting ("CAD") file of the
product to guide an automated assembly process, where the CAD model
file is digitally partitioned into "slices" corresponding to the
actual layers being generated and stacked, and these "slices" guide
automated assembling equipment such as, for example, robotic arms.
The nature of the additive layer process allows single-piece
articles of high internal complexity, such as, for example, closed
internal chambers and tortuous internal channels, to be easily
assembled in one continuous operation. Therefore, additive layer
manufacturing processes are well suited to the creation of a
complicated single-piece die as used in embodiments of the present
invention, because such a die will often be designed to have a
complicated internal structure that corresponds to the complex
internal cooling circuits of the component desired to be cast.
[0014] Stereolithography (SLA) is an example of an additive layer
process that is suitable for use in embodiments of the present
invention. During SLA, a robotic arm holds a laser, and the arm
precisely guides the motion of the laser along a motion path
described by the "sliced" CAD file. The laser directs highly
focused radiation upon a curable material medium, often a liquid
resin, which is instantly solidified ("cured") upon exposure to the
laser, thereby creating a single, precisely rendered
cross-sectional layer of the product that corresponds with the
"slice" of the partitioned CAD file. This procedure is repeated for
all subsequent layers, with each layer being bonded to the previous
one by the action of the solidifying material medium. The finished
product is a three-dimensional product rendered in cured material
with all dimensions in accordance with the CAD file.
[0015] A long list of other additive layer manufacturing processes
are available in the art and are suitable for providing the
single-piece sacrificial die in embodiments of the present
invention, including, but not limited to, micro-pen deposition,
where liquid media is dispensed with high precision at the pen tip
and then cured; selective laser sintering, where a laser is used to
sinter a powder media in precisely controlled locations; and laser
wire deposition, where a wire feedstock is melted by a laser and
then deposited and solidified in precise locations to build the
product. Those skilled in the art will appreciate that a variety of
curable material media may be applied, including liquid resins, as
described above, and solid media in various forms such as powders,
wires, and sheets. Silicone-based and organic-based resins are the
most common examples of curable material media used in these
methods, although in some methods the media comprises at least one
metal, often mixed with some type of resin.
[0016] A ceramic slurry is introduced into the cavity (or cavities)
of the sacrificial die. The slurry comprises a ceramic powder and a
liquid phase, or "carrier fluid." The slurry contains sufficient
liquid phase to provide a viscosity that is usually less than about
10,000 Pascal-seconds, that is, a viscosity that renders the slurry
suitable for introduction into, and proper filling of, the die
cavity. Suitable ceramics for use in the slurry include, but are
not limited to, alumina, yttria, ceria, zirconia, magnesia, and
calcia. In many cases the introduction of the ceramic slurry into
the cavity of the die is done with the slurry under pressure to
ensure the slurry completely fills the cavity. Injection molding is
an example of a suitable method for introducing the slurry into the
die cavity, because the quantity and pressure of the slurry may be
precisely controlled as the slurry fills the die cavity.
[0017] After the slurry has completely filled the die cavity, the
slurry is cured to form a ceramic casting core. Curing the slurry
is done by removing the liquid phase, and in certain embodiments
this is done by heating the slurry to evaporate the carrier fluid,
leaving only the ceramic phase contained within the die cavity.
[0018] The die is then removed from around the ceramic casting core
contained in the die cavity. Because the die is one piece, it
cannot be removed without being destroyed, hence the die is
sacrificial in the method of the present invention. The die is
exposed to an environment, such as, for example, mechanical stress,
temperature, chemicals, and combinations thereof, that is adapted
to destroy the die while leaving the ceramic casting core intact.
In certain embodiments, removing the die comprises heating the die.
In these embodiments, the die is heated to a temperature that
causes the die to decompose or burn away, while the ceramic core
remains unaffected. In some embodiments, the die is removed by
dissolving it in a solvent. Those skilled in the art will
appreciate that the choice of solvent depends upon the composition
of the die. In some embodiments, the die is chemically removed,
such as, for example, by reacting the die material with an acid,
base, or other compound or mixture that chemically reacts with and
removes the die material. Regardless of how the die is removed, the
environment is chosen to selectively remove the die material while
leaving the ceramic material intact.
[0019] After removing the die, a freestanding, one-piece ceramic
core remains, suitable for use in investment casting multi-wall
component 10. The ceramic core may be of a much higher complexity
than is possible to achieve in a one-piece core made by
conventional techniques, due to the use of the single-piece
sacrificial die and, in certain embodiments, the use of the
additive layer manufacturing process in making the die. The core is
often fired at a temperature in the range from about 870.degree. C.
to about 1100.degree. C. to provide the core with sufficient
strength to survive subsequent operations. An investment casting
process is performed in accordance with industry practice, using
the ceramic core made above as part of a mold-core assembly to form
component 10. In general, the core and appropriate ancillary
material known to those skilled in the art (such as positioning and
support pins, sprues, gates, etc.) are disposed in a mold
appropriately shaped in accordance with the design of the component
to be cast. Wax is injected into the mold and solidified to form a
wax model, and this wax model with embedded core is repeatedly
dipped in ceramic slurry to form a ceramic shell mold around the
wax pattern. After removing the wax, all that remains is the
ceramic core disposed in and attached to the ceramic shell mold,
thereby forming the mold-core assembly referred to above. After
casting the component by solidifying molten metal in the mold-core
assembly, the ceramic mold is removed by chemical or mechanical
means and the core is "leached" out of the component by a chemical
removal agent.
[0020] The use of the single-piece sacrificial die to make a
one-piece ceramic core, particularly in embodiments employing SLA
or other additive layer manufacturing process to make the
sacrificial die, allows for repeatable production of high quality
castings without the time-consuming steps of forming multiple core
components and joining them together into a composite core prior to
wax injection.
[0021] The method described above is suitable for forming any
investment cast article. In some embodiments, the component 10
being made is a component of a turbine assembly, such as, for
example, a turbine blade or a vane, including multi-wall blades or
vanes. In particular embodiments, component 10 comprises at least
one internal air-cooling passage 40. Because the complexity of
internal passage geometry is easily accommodated by the additive
layer manufacturing process used to fashion the core die, adding
additional features to the component is readily accomplished with
little added expense. For instance, in certain embodiments, the at
least one cooling passage 40 of component 10 comprises turbulators
(not shown) to enhance heat transfer within cooling passage 40.
[0022] The advantages offered by the method of the present
invention are most apparent when the method is employed to make
such complicated, multi-wall components, due to the savings in both
time and cost attributable to the use of the single-piece
sacrificial die as described above. For example, one embodiment of
the present invention is a method for making a component for a
turbine assembly. The component is a multi-wall component, and
therefore it comprises an external wall and at least one internal
wall disposed in a spaced-apart relationship with the external
wall, and further comprises at least one cooling passage disposed
between the external wall and the internal wall. The method
comprises using a stereolithography process to provide a
single-piece sacrificial die having at least one internal cavity;
introducing a ceramic slurry as described previously into the at
least one cavity of the die; curing the slurry to form a ceramic
casting core; removing the sacrificial die by exposing the die to
an environment adapted to destroy the die while leaving the ceramic
casting core intact; and performing an investment casting process
using the ceramic casting core as part of a mold-core assembly to
form the component.
[0023] Other embodiments of the present invention include a method
for making a casting core, and the casting core made by the method.
In this method a single-piece sacrificial die is manufactured using
an additive layer manufacturing method as described above. The die
comprises at least one internal cavity, into which a ceramic slurry
is introduced and then cured. After curing, the die is removed as
previously described. The various alternatives for materials and
processes described for previous embodiments are equally applicable
in this embodiment.
[0024] In particular embodiments the core is configured to form
internal passages, such as, for example, air-cooling passages, in
an investment cast article. That is, the core is designed to
correspond with the geometry of these passages, so that when the
investment casting process is carried out, the ceramic core will be
leached away from the internal surfaces of the component, leaving
behind the desired configuration of internal passages. In certain
embodiments, the investment cast article for which the core is
configured is a component of a turbine assembly, such as, for
instance, a multi-wall component.
[0025] A further embodiment of the present invention is a die for
making a casting core. The die comprises a single piece structure
having at least one cavity, and is made of a material capable of
being selectively removed from a ceramic casting core when such a
core is disposed in the cavity of the die. That is, the die
material can be destroyed by an environment while a ceramic casting
core disposed within the cavity of the die remains intact, as
described previously. In certain embodiments the structure of the
die comprises a structure assembled in an additive layer
manufacturing process, such as the SLA process described
previously.
[0026] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations, equivalents, or improvements therein may be
made by those skilled in the art, and are still within the scope of
the invention as defined in the appended claims.
* * * * *