U.S. patent application number 12/712632 was filed with the patent office on 2011-08-25 for casting core for turbine engine components and method of making the same.
Invention is credited to Michael P. Appleby, Daniel Ellgass, Iain Alasdair Fraser, Dhafer Jouini, Ahmed Kamel, Jill Klinger, Gary B. Merrill, Gabriel Victor Orsinger, John R. Paulus.
Application Number | 20110204205 12/712632 |
Document ID | / |
Family ID | 43896861 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110204205 |
Kind Code |
A1 |
Kamel; Ahmed ; et
al. |
August 25, 2011 |
CASTING CORE FOR TURBINE ENGINE COMPONENTS AND METHOD OF MAKING THE
SAME
Abstract
A turbine engine component, such as a turbine blade or vane,
with complex internal features can be cast using a core having a
first region with normal resolution features and a second region
with high resolution features. The core can be formed from a single
structure. Alternatively, the first region can be defined by a
first ceramic core piece, which can be formed by any conventional
process, such as by injection molding or transfer molding. The
second region can be defined by a second ceramic core piece formed
separately by a method effective to produce high resolution
features, such as tomo lithographic molding. The first core piece
and the second core piece can be joined by interlocking engagement,
such as by male and female dovetails. The high resolution features
can be effective to produce high efficiency internal cooling
features in the cast component.
Inventors: |
Kamel; Ahmed; (Orlando,
FL) ; Jouini; Dhafer; (Orlando, FL) ; Merrill;
Gary B.; (Orlando, FL) ; Paulus; John R.;
(Afton, VA) ; Appleby; Michael P.; (Crozet,
VA) ; Fraser; Iain Alasdair; (Ruckersville, VA)
; Klinger; Jill; (Charlottesville, VA) ; Orsinger;
Gabriel Victor; (Tucson, AZ) ; Ellgass; Daniel;
(Big Island, VA) |
Family ID: |
43896861 |
Appl. No.: |
12/712632 |
Filed: |
February 25, 2010 |
Current U.S.
Class: |
249/184 ;
164/6 |
Current CPC
Class: |
B22C 9/103 20130101 |
Class at
Publication: |
249/184 ;
164/6 |
International
Class: |
B22C 9/10 20060101
B22C009/10 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT
[0001] Development for this invention was supported in part by
Contract No. DE-FC26-05NT42644 awarded by the United States
Department of Energy. Accordingly, the United States Government may
have certain rights in this invention.
Claims
1. A method of forming a core for use in casting a turbine engine
component comprising: forming a normal resolution region of the
core; and forming a high resolution region of the core using a
method effective to produce high resolution features.
2. The method of claim 1 wherein the normal resolution region is
defined by a first core piece and the high resolution region is
defined by a second core piece, and further including the step of
joining the first and second core pieces.
3. The method of claim 2 wherein the first core piece includes a
passage therein, wherein the second core piece includes a
protrusion, wherein the protrusion includes a first portion and a
second portion, wherein the first portion is configured to be
received in the passage and the second portion is configured to
prevent receipt into the passage, wherein the joining step results
in only the first portion of the protrusion being received in the
passage, whereby a spacing between the first and second core pieces
is maintained, and further including the steps of: heating the
first portion of the protrusion; and forming the first portion of
the protrusion such that the first and second core pieces are in
interlocking engagement.
4. The method of claim 2 wherein the first core piece includes a
plurality of recesses and the second core piece includes a
plurality of protrusions, wherein the recesses and the protrusions
are configured for interlocking engagement, wherein the joining
step results in each protrusion being received in a respective one
of the recesses.
5. The method of claim 2 wherein during in joining step, both the
first core piece and the second core piece are fully fired.
6. The method of claim 2 wherein during in joining step, both the
first core piece and the second core piece are in a green
state.
7. The method of claim 2 wherein the joining step is performed
outside of a mold.
8. The method of claim 2 wherein the first core piece includes a
recess and further including the steps of: forming the second core
piece with a foil member, wherein a portion of the foil member is
embedded in the second core piece and a portion of the foil member
protrudes beyond the second core piece; wherein the joining step
comprises inserting the protruding portion of the foil member into
the recess of the first core piece.
9. The method of claim 1 wherein the core is a multi-wall core.
10. The method of claim 1 further including the steps of: forming a
core print separately from the core; and joining the core print to
the core.
11. A method of joining a multi-piece core for a cast airfoil
comprising: forming a first ceramic core piece, the first core
piece being shaped as an airfoil body portion and having one of a
plurality of recesses and a plurality of protrusions, the first
core piece including an engaging surface; separately forming a
second ceramic core piece having a high resolution region, the
second core piece having an engaging surface, the second core piece
having an opposite one of a plurality of protrusions and a
plurality of recess, the recesses and the protrusions of the first
and second core pieces being configured for substantially
interlocking engagement, the second core piece shaped as a trailing
edge portion of an airfoil; and joining the first core piece and
the second core piece such that each protrusion is received in a
respective recess and such that the engaging surfaces abut, whereby
a core assembly is formed.
12. The method of claim 11 wherein during joining step, both the
first core piece and the second core piece are in a green
state.
13. The method of claim 11 wherein the joining step is performed
outside of a mold.
14. The method of claim 11 wherein the first core piece includes a
recess and further including the step of forming the second core
piece with a foil member, wherein a portion of the foil member is
embedded in the second core piece and a portion of the foil member
protrudes beyond the engaging surface of the second core piece; and
wherein the joining step comprises inserting the protruding portion
of the foil member into the recess of the first core piece.
15. The method of claim 11 wherein at least one of the first core
piece and the second core piece is a multi-wall core.
16. The method of claim 11 further including the steps of: forming
a core print separately from the first and second core pieces; and
joining the core print to at least one of the first core piece and
the second core piece.
17. The method of claim 11 wherein at least a portion of the first
ceramic core piece is made using a method effective to produce high
resolution features.
18. The method of claim 11 wherein the step of separately forming
the second ceramic core piece is performed using a method effective
to produce high resolution features.
19. A casting core for a turbine engine component comprising: a
ceramic core body having a first region of normal resolution detail
and a second region of high resolution detail.
20. The casting core of claim 19 wherein the first region is an
airfoil body portion and the second region is an airfoil trailing
edge portion.
21. The casting core of claim 19 wherein the first region is
defined by a first core piece and the second region is defined by a
separate second core piece.
22. The casting core of claim 19 wherein the core body is a
multi-wall core.
23. The casting core of claim 19 further including a core print
formed separately from but attached to the ceramic core body.
Description
FIELD OF THE INVENTION
[0002] Aspects of the invention relate in general to turbine engine
components and, more particularly, to cast turbine engine
components.
BACKGROUND OF THE INVENTION
[0003] In a turbine engine, many components, such as turbine blades
or vanes, are exposed to hot gases during engine operation. In
order to withstand the operational environment, these components
are typically cooled during engine operation. To promote cooling,
these components can include a number of internal features, such as
cooling channels and passages. The inclusion of such features can
dramatically increase the difficulty of manufacturing the
component. Thus, the ability to manufacture a cooled turbine
component economically is essential to the viability of any
design.
[0004] Turbine blades are typically made by investment casting
using a core to form the internal features of the blade. As a
result, the core is critical to achieving the features needed to
obtain the desired cooling performance of the blade.
Conventionally, the core is manufactured by injection molding (low
pressure or high pressure) or transfer molding. In either process,
precision dies are required. The directions in which the segments
of the dies are pulled apart to remove the core are important
factors in the design of the core and impose limitations on the
core design, as it must be ensured that the various die segments
can be withdrawn without interference. As the required number of
separation planes increases, it becomes increasingly challenging to
separate the dies and, at some point, it becomes impossible. Thus,
the design of the core can ultimately affect the design of the
blade.
[0005] With the drive toward advanced cooling schemes, including
near wall cooling, conventional core production methods alone will
not be able to meet the requirements of the advanced designs. Thus,
there is a need for a system and method the can facilitate the
inclusion of advanced internal cooling features in turbine engine
components.
SUMMARY OF THE INVENTION
[0006] Aspects of the invention are directed to a method of forming
a core for use in casting a turbine engine component. The method
includes the steps of forming a normal resolution region of the
core, and forming a high resolution region of the core using a
method effective to produce high resolution features. The core may
be a multi-wall core.
[0007] In one embodiment, the normal resolution region can be
defined by a first core piece, and the high resolution region can
be defined by a second core piece. In such case, the method can
include the step of joining the first and second core pieces. In
some instances, the step of joining the first and second core
pieces can be performed outside of a mold. The high resolution
region can be formed by tomo lithographic molding. At least a
portion of the first core piece can be made using a method
effective to produce high resolution features, which can be, for
example, tomo lithographic molding.
[0008] The first core piece can include a passage within the first
core piece that extends from a inner side to an outer side. The
second core piece can include a protrusion. In such case, the
joining step can result in the protrusion being received in the
passage. At least a portion of the protrusion can be heated. The
heated protrusion can be formed such that the first and second core
pieces are in interlocking engagement. In one embodiment, the
forming step can include folding the protrusion over onto the outer
side of the first core piece. A recess can be formed in the first
core piece such that the recess receives at least a part of the
folded over portion of the protrusion. Thus, the protrusion can be
substantially flush with the outer side of the first core piece. In
another embodiment, the forming step can include shaping at least a
portion of the protrusion to substantially correspond to at least a
portion of the passage.
[0009] The first core piece can include a passage therein, and the
second core piece can include a protrusion. The protrusion can
include a first portion and a second portion. The first portion can
be configured to be received in the passage, and the second portion
can be configured to prevent receipt into the passage. In such
case, the joining step can result in only the first portion of the
protrusion being received in the passage. As a result, a desired
spacing between the first and second core pieces can be maintained.
The first portion of the protrusion can be heated and formed such
that the first and second core pieces are in interlocking
engagement
[0010] The first core piece can include a plurality of recesses,
and the second core piece can include a plurality of protrusions.
The recesses and the protrusions can be configured for interlocking
engagement. The joining step can result in each protrusion being
received in a respective one of the recesses. Any suitable type of
interlock can be employed. In one embodiment, the recesses can be
female dovetails, and the protrusions can be male dovetails. In
some instances, a gap can be formed between each recess and
protrusion received therein. In such case, the method can further
include the steps of: applying a ceramic material in at least a
portion of the gap and firing the joined first and second core
pieces.
[0011] In one embodiment, both the first core piece and the second
core piece can be fully fired during the joining step. In another
embodiment, at least one of the first core piece and the second
core piece can be in a green state. The first core piece and/or the
second core piece can be formed with a binder comprising a solvent,
a plasticizer, and at least one of a urethane or an epoxy resin. In
such case, the method can further include the step of selecting the
solvent, the plasticizer, and the at least one of a urethane or an
epoxy resin to achieve a target property of the first core piece
and/or the second core piece in the green state. The first core
piece and/or the second core piece can be heated in the green state
to a cure temperature. The first core piece and/or the second core
piece can be thermally formed to a target configuration.
[0012] In one embodiment, the first core piece can include a
recess. In such case, the method can further include forming the
second core piece with a foil member. A portion of the foil member
can be embedded in the second core piece, and a portion of the foil
member can protrude beyond the second core piece. In such case, the
joining step includes inserting the protruding portion of the foil
member into the recess of the first core piece.
[0013] The method can further include the steps of: forming a core
print separately from the core, and joining the core print to the
core. The core can include either a plurality of recesses or a
plurality of protrusions; the core print can include the opposite
one of a plurality of protrusions and a plurality of protrusions.
The recesses and the protrusions are configured for interlocking
engagement, wherein the joining step results in each protrusion
being received in a respective one of the recesses. In some
instances, the method can include the additional step of forming a
core lock in the core print.
[0014] Other embodiments according to aspects of the invention are
directed to a method of joining a multi-piece core for a cast
airfoil. In such a method, a first ceramic core piece is formed.
The first core piece is generally shaped as an airfoil body portion
and has either a plurality of recesses or a plurality of
protrusions. The first core piece includes an engaging surface. At
least a portion of the first ceramic core piece can be made using a
method effective to produce high resolution features, such as, for
example, tomo lithographic molding.
[0015] A second ceramic core piece is formed separately from the
first core piece. The second core piece has a high resolution
region. The second core piece has an engaging surface. The second
core piece has an opposite one of a plurality of protrusions and a
plurality of recess. The recesses and the protrusions of the first
and second core pieces are configured for substantially
interlocking engagement. The second core piece is generally shaped
as a trailing edge portion of an airfoil. The step of separately
forming the second ceramic core piece can be performed using a
method effective to produce high resolution features. One example
of a method effective to produce high resolution features is tomo
lithographic molding
[0016] The first core piece and the second core piece can be joined
such that each protrusion is received in a respective recess and
such that the engaging surfaces abut. As a result, a core assembly
is formed. The joining step can be performed outside of a mold.
[0017] In one embodiment, both the first core piece and the second
core piece can be in a green state during the joining step. In such
case, at least the second core piece can be formed with a binder
comprising a solvent, a plasticizer, and at least one of a urethane
or an epoxy resin. The method can further include the step of
selecting the solvent, the plasticizer, and the at least one of a
urethane or an epoxy resin to achieve a target property of the
second core piece in the green state. While in the green state, the
second core piece can be heated to a cure temperature. At that
point, the second core piece can be thermally formed to a target
configuration.
[0018] The first core piece can include a recess and further
including the step of forming the second core piece with a foil
member, wherein a portion of the foil member is embedded in the
second core piece and a portion of the foil member protrudes beyond
the engaging surface of the second core piece; and wherein the
joining step comprises inserting the protruding portion of the foil
member into the recess of the first core piece. The first core
piece and/or the second core piece can be a multi-wall core.
[0019] The method can further include the steps of: forming a core
print separately from the first and second core pieces, and joining
the core print to at least one of the first core piece and the
second core piece. The first core piece and/or the second core
piece can include either a plurality of recesses or a plurality of
protrusions. The core print can include the opposite one of a
plurality of protrusions and a plurality of protrusions. The
recesses and the protrusions can be configured for interlocking
engagement. The step of joining the core print to the first core
piece and/or the second core piece results in each protrusion being
received in a respective one of the recesses. In one embodiment, a
core lock can be formed in the core print.
[0020] In another respect, aspects of the invention are directed to
a casting core for a turbine engine component. The casting core
includes a ceramic core body having a first region of normal
resolution detail and a second region of high resolution detail. In
one embodiment, the first region can be an airfoil body portion,
and the second region can be an airfoil trailing edge portion. The
core body may be a multi-wall core.
[0021] In some instances, the first region can be defined by a
first core piece, and the second region can be defined by a
separate second core piece. The second core piece can be a
monolithic structure. A foil member can extend between and into
engagement with the first and second core pieces. A portion of the
foil member can be embedded in the second core piece, and another
portion of the foil member can be received in a recess in the first
core piece.
[0022] The first ceramic core piece can have a plurality of
recesses, and the second ceramic core piece can have a plurality of
protrusions. Each protrusion can be adapted for interlocking
engagement with a respective one of the recesses. Each protrusion
can be received in a respective one of the recesses so as to join
the first ceramic core piece to the second ceramic core piece. A
gap may be formed between each recess and respective protrusion
received in the recess. The gap can be filled with a ceramic
material.
[0023] The recesses can be female dovetails, and the protrusions
can be male dovetails. One or more of the male dovetails can
include a thickness surface. The thickness surface can be angled at
less than 90 degrees relative to the engaging surface of the second
ceramic core piece. Each dovetail can include a first side face and
a second side face and at least one thickness surface. The
thickness surface can include a plurality of protruding
undercuts.
[0024] The casting core can further include a core print formed
separately from but attached to the ceramic core body. A core lock
can be formed in the core print. The core body can include either a
plurality of recesses or a plurality of protrusions; the core print
can include the opposite one of a plurality of protrusions and a
plurality of protrusions. The recesses and the protrusions can be
configured for interlocking engagement. Each protrusion can be
received in a respective one of the recesses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a perspective view of a casting core having a
first region and a second region according to aspects of the
invention.
[0026] FIG. 2 is a perspective exploded view of a casting core
assembly according to aspects of the invention, showing a first
casting core piece and a second casting core piece.
[0027] FIG. 3 is a close-up view of the interface between a female
dovetail slot on a first casting core piece and a male dovetail
protrusion on the second casting core piece according to aspects of
the invention.
[0028] FIG. 4 is a perspective view of a male dovetail protrusion
on a casting core piece formed in accordance with aspects of the
invention, showing a plurality of protruding undercuts on various
surfaces of the second casting core piece.
[0029] FIG. 5 is a top plan view of a casting core piece formed
according to aspects of the invention, showing a male dovetail
protrusion with a thickness surface that is angled relative to an
engaging surface of the second casting core piece.
[0030] FIG. 6 is a close up view of a casting core according to
aspects of the invention, showing a first region with normal
resolution features and a second region with high resolution
features.
[0031] FIG. 7 is a perspective view of a casting core with core
prints and a core lock according to aspects of the invention.
[0032] FIG. 8 is a perspective view of a portion of a multi-wall
casting core formed in accordance with aspects of the
invention.
[0033] FIG. 9A is a perspective cross-sectional view of an
alternative manner of joining a first core piece and a second core
piece, showing a protrusion of the second core piece being received
in a passage in the first core piece and extending beyond an outer
side of the first core piece.
[0034] FIG. 9B is a perspective cross-sectional view of the
alternative manner of joining the first core piece and the second
core piece, showing the protrusion of the second core piece being
folded over on the first core piece to thereby bring the first and
second core pieces into interlocking engagement according to
aspects of the invention.
[0035] FIG. 10A is a side elevation cross-sectional view of an
alternative manner of joining a first core piece and a second core
piece, showing a protrusion of the second core piece with a first
region that is received in a passage in the first core piece and
with a second region that is larger than the passage so as to fix
the distance between the first and second core pieces.
[0036] FIG. 10B is a side elevation cross-sectional view of the
alternative manner of joining the first core piece and the second
core piece, showing the protrusion of the second core piece being
locally formed within the passage to thereby bring the first and
second core pieces into interlocking engagement according to
aspects of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0037] Embodiments of the invention are directed to a casting core
system with one or more high resolution regions for use in casting
a turbine engine component. Aspects of the invention will be
described in connection with a casting core for a turbine airfoil,
but the detailed description is intended only as exemplary. Indeed,
aspects of the invention can be used in connection with any hollow
cast turbine engine component, especially those with complex
internal features. Embodiments of the invention are shown in FIGS.
1-8, but the present invention is not limited to the illustrated
structure or application.
[0038] Referring to FIG. 1, a casting core 10 according to aspects
of the invention is shown. The casting core 10 can include a first
region 11 and a second region 13. In one embodiment, the core 10
can be used in connection with the casting of a turbine blade or
vane. In such case, the second region 13 can define an airfoil
trailing edge portion 16 of the core 10, and the first region 11
can define an airfoil body portion 18 of the core 10.
[0039] The first region 11 can include one or more features,
including, for example, recesses, passages, openings, protrusions,
channels, grooves, slots, and/or depressions. These features can be
of a normal resolution; that is, these features can be produced by
conventional casting techniques, including, for example, injection
molding (low pressure or high pressure) or transfer molding. The
first region 11 can be sized and shaped as necessary, depending on
the ultimate part being made.
[0040] The second region 13 can be a high resolution region having
one or more high resolution features or details, which can be, for
example, recesses, passages, openings, protrusions, channels,
grooves, slots, and/or depressions, depending on the desired
internal features in the part ultimately being made. The high
resolution region of the core can be used to form internal features
or details in the ultimate part being made. Such features or
details can be effective to optimize cooling in the ultimate part
being cast.
[0041] A high resolution region is beyond the natural capacity or
scope of conventional core formation methods. For example, a high
resolution region is one that would require more than three planes
of die separation using conventional core formation techniques.
Thus, according to aspects of the invention, the second region 13
can include one or more high resolution features that were not
previously attainable using conventional core formation techniques.
It should be noted that, while the following description will be
directed to a casting core 10 with one high resolution region 13,
it will be understood that a casting core in accordance with
aspects of the invention can have a plurality of high resolution
regions. Further, while the high resolution region is shown as
being associated with the trailing edge portion 16 of the casting
core 10, it will be understood that embodiments of the invention
are not limited to such a location. Indeed, in some instances, the
trailing edge portion 16 may not have a high resolution region. The
high resolution region can be applied in any suitable location,
including in the airfoil body portion 18.
[0042] The casting core 10 can be made of any suitable material. In
one embodiment, the casting core 10 can be made of ceramic,
including, for example, silica-based ceramic compositions. The
first and second regions 11, 13 of the casting core 10 can be made
of the same material. Alternatively, the first and second regions
11, 13 of the casting core 10 can be made of different
materials.
[0043] The first region 11 and the second region 13 can be sized
and/or shaped as necessary, depending on the ultimate part being
made and the desired internal features therein. According to
aspects of the invention, the second region 13 can generally have
more complex, higher resolution, critical and/or intricate features
than, the first region 11. FIG. 6 shows an example of the relative
complexity of the first and second regions 11, 13. As can be seen,
the first region 11 can include a plurality of elongated channels
21 extending at a depth in the first region 11 and/or an elongated
passage 23 extending through the core in the first region 11. In
contrast, the second region 13 can include one or more high
resolution features. Such high resolution features can include
short, thin-walled members or cross-overs 34 in a highly intricate
arrangement. The cross-overs 34 can be formed by passages 35 that
extend though the thickness of the core 10 in the second region 13.
As a result, the cross-overs 34 are not surrounded by other
material along their length. In some instances, there can be a
greater quantity of features in the high resolution region than in
the normal resolution region.
[0044] A casting core 10 according to aspects of the invention can
be formed in any suitable manner. In one embodiment, the first and
second regions 11, 13 can be formed in a single monolithic core.
Alternatively, the first and second regions 11, 13 can be formed as
separate pieces joined together to form a core assembly, as is
shown in FIGS. 2-5. In such case, the first region 11 can be
defined by a first core piece 12, and the second region 13 can be
defined by a second core piece 14. The second core piece 14 can be
formed separately from the first core piece 12.
[0045] A normal resolution region, such as the first region 11
and/or the first core piece 12, can be made using any suitable core
formation techniques, including, for example, conventional
techniques like injection molding (low pressure or high pressure)
or transfer molding. A high resolution region, such as the second
region 13 and/or the second core piece 14, can be formed by a
method effective to produce the high resolution features and/or
details. That is, a high resolution region can be formed by a
process that can yield high resolution features or detail that
cannot be achieved using conventional core formation processes.
[0046] One example of a process that can yield high resolution
features or detail is tomo lithographic molding, a process which is
available from Mikro Systems Inc., Charlottesville, Va. Tomo
lithographic molding is described in U.S. Pat. Nos. 7,411,204;
7,410,606; and 7,141,812 and U.S. Patent Application Publication
Nos. 2004/0156478, 2008/0053638 and 2009/0084933, each of which is
incorporated herein by reference. Tomo lithographic molding can
provide greater geometric and dimensional control with respect to
high resolution features compared to conventional core formation
processes.
[0047] Generally, tomo lithographic molding can include a number of
constituent processes, such as lithographic micromachining,
precision stack lamination, molding, and casting processes.
Initially, a three dimensional digital model can be transformed
into a series of lithographic masks. Each mask can represent a
cross-sectional slice of the desired three dimensional solid (in
this case, the second core piece 14). Each mask can then be used to
lithographically machine an exact replica from metal foil or
polymeric film. The foils and/or films ("toma") can be
stack-laminated to form a durable, ultra-high precision master
mold. Finally, material can be poured into the mold to cast a
high-fidelity, monolithic part.
[0048] While processes that can yield high resolution features or
detail are effective in producing a high quality casting core, it
may not be necessary to make the entire core using such processes.
One or more criteria can be used to determine whether to employ a
process effective to produce high resolution features and/or
details to form one or more regions of the core 10, as opposed to
using conventional casting techniques. For instance, one criterion
can be the complexity of the region. A method effective to produce
high resolution features and/or details can be used in connection
with those regions of the core that have complex, critical and/or
intricate features, especially compared to other portions of the
core. For instance, in a casting core for a turbine blade, a large
number of cooling passages and/or a complicated trailing edge
region can make conventional tooling overly complex, if not
impossible, thereby weighing in favor of using a method effective
to produce high resolution features and/or details, such as tomo
lithographic molding.
[0049] Alternatively or in addition, another criterion can be the
complexity of the core injection die that would be needed using
conventional core formation techniques. In conventional core
formation methods, the maximum number of planes in which a die can
be pulled apart is typically three. If a core design would require
more than three planes for pulling the die apart, then it may
become cost prohibitive under conventional techniques, if not
impossible due to the lack of technology or physical interferences.
Thus, it may be more cost effective to use an alternative method
effective to produce the high resolution features and/or detail,
such as tomo lithographic molding, to produce at least a portion of
the core.
[0050] An additional criterion, which can be in addition or as an
alternative to one or more of the above criteria, can be time
and/or cost. In some instances, the time involved and/or cost
associated with forming at least a portion of the casting core
using conventional techniques can exceed the time and/or cost
associated with forming at least a portion of the casting core by
methods effective to produce high resolution features and/or
detail, such as those described herein. In such cases, it may be
more desirable to form at least a portion of the core by methods
effective to produce high resolution features and/or detail.
[0051] When the first and second regions 11, 13 are formed by
separate core pieces 12, 14, as described above, the core pieces
12, 14 can be joined in any suitable manner to form a core
assembly. One manner of joining the core pieces 12, 14 is described
herein, but aspects of the invention are not limited to any
particular manner of joining. As an example, the first and/or
second core pieces 12, 14 can have one or more features to
facilitate such joining. For instance, the first and second core
pieces 12, 14 can be joined by way of a plurality of interlocking
features. For example, one of the core pieces 12, 14 can have at
least one protrusion and the other one of the core pieces 12, 14
can have at least one recess. At least a portion of each protrusion
and each recess can be adapted for substantially interlocking
engagement with each other. For instance, the protrusions and the
recesses can be configured as male and female dovetails, generally
spherical protrusions and recesses, or generally T-shaped
protrusions and recesses, just to name a few possibilities.
Additional examples of suitable interlocking engagements are
described herein as well as in U.S. Patent Application Publication
No. 2009/0084933, which is incorporated herein by reference. Each
protrusion can be received in a respective one of the recesses.
[0052] In one embodiment, the first core piece 12 can include a
plurality of female dovetails 20, such as in the form of slots, and
the second core piece 14 can include a plurality of male dovetails
22, as shown in FIG. 2. While the drawing figures and the following
description will be directed to this arrangement, it will be
understood that, alternatively or in addition, the first core piece
12 can include a plurality of male dovetails (not shown), and the
second core piece 14 can include a plurality of female dovetails
(not shown). Further, as noted above, there are several other
manners in which core pieces can be joined in accordance with
aspects of the invention.
[0053] It will be appreciated that the male dovetails 22 would
ordinarily be difficult to make using conventional core formation
techniques, particularly when the second core piece 14 is made of
ceramic. However, because the second core piece 14 is made by using
a process effective to produce high resolution features, such as
tomo lithographic molding, the male dovetails 22 can be provided on
the second core piece 14 with a high degree of reliability as well
as control over the features of the male dovetails 22.
[0054] There can be any number of male dovetails 22 and female
dovetails 20. In one embodiment, there can be four male dovetails
20 and four female dovetails 20. The male dovetails 22 can all be
substantially the same size and shape, or at least one of the male
dovetails 22 can be a different size and/or shape. Naturally, the
female dovetails 20 are sized and shaped to receive the male
dovetails 22.
[0055] The male dovetails 22 can have a first side face 36 and a
second side face 38 (see FIGS. 2 and 4). The first side face 36 and
the second side face 38 can be generally planar. The first side
face 36 and the second side face 38 can be substantially parallel
to each other. The male dovetails 22 can also have one or more
thickness surfaces, including, for example, a first thickness
surface 40, a second thickness surface 42 and a third thickness
surface 44. Each male dovetail 22 can have an associated axis
46.
[0056] It should be noted that one or more of the surfaces of the
male dovetails 22, such as thickness surfaces 40, 42 and/or 44
(FIGS. 2 and 4), can have one or more "protruding undercuts," as
that term is described in U.S. Pat. Nos. 7,411,204; 7,410,606; and
7,141,812 and U.S. Patent Application Publication Nos. 2004/0156478
and 2008/0053638, each of which is incorporated in its entirety
herein by reference. A protruding undercut can be a resultant
feature of casting in the multi-layer mold used in the tomo
lithographic molding process. An example of a male dovetail 22
having protruding undercuts 50 is shown in FIG. 4. The protruding
undercuts 50 can appear on other surfaces of the second core piece
14, including, for example, an upper end surface 52 and/or an
engaging surface 24. The protruding undercuts 50 can provide
numerous benefits, which will be described in greater detail below.
It should be noted that, while formed by casting in a multi-layer
mold, the second core piece 14 is itself a monolithic
structure.
[0057] The male dovetails 22 can project from the engaging surface
24 on the second core piece 14. Apart from the male dovetails 22
and the protruding undercuts 50, the engaging surface 24 can
otherwise be generally planar. When the second core piece 14 is a
trailing edge core 18, the engaging surface 24 can be elongated in
generally the radial direction R. The term radial direction is
intended to mean generally radial to the turbine axis if such an
airfoil were installed in its operational position in a turbine
engine.
[0058] The male dovetails 22 can be oriented in any suitable
manner. In one embodiment, the dovetails can be oriented so that
the first and second core pieces 12, 14 can be brought together by
bringing the first core piece 12 and/or the second core piece 14
together laterally, as is generally shown in FIG. 2.
[0059] A Cartesian coordinate system with X-Y-Z axes can be applied
to the second core piece 14 (see FIGS. 2 and 4-5). The engaging
surface 24 of the second core piece 14 can be in a plane that is
defined substantially by the Y-Z axes. The radial direction R can
extend in a direction that is substantially parallel to the Y axis.
The male dovetails 22 can project from the engaging surface 24
generally along the X axis. The first side surface 36 and the
second side surface 38 can be in planes that can be defined
substantially by the X-Y axes. In such case, the axis 46 of the
male dovetail 22 can extend substantially in the direction of the X
axis, as is shown in FIG. 4.
[0060] It should be noted that use of tomo lithographic molding can
permit a high degree of dimensional control and reliability. Thus,
the male dovetails 22 can be provided so that each dovetail axis 46
extends at any suitable angle relative to the engagement surface 24
or to a plane substantially defined by the Y-Z axes. As shown in
FIG. 4, the dovetail axis 46 can be at about 90 degrees relative to
the engagement surface 24 or to a plane substantially defined by
the Y-Z axes. However, the male dovetails 22 can be oriented so
that the dovetail axis 46 is less than 90 degrees relative to the
engagement surface 24 or to a plane substantially defined by the
Y-Z axes.
[0061] Further, referring to FIG. 5, one or more of the thickness
surfaces 40, 42, 44 can extend at almost any angle relative to the
engaging surface 24 or to a plane substantially defined by the Y-Z
axes. For instance, the second thickness surface 42 can extend at
an angle .alpha. relative to the engaging surface 24 or to a plane
substantially defined by the Y-Z axes. In one embodiment, the
second thickness surface 42 can be angled at about 28 degrees
relative to the engaging surface 24 or to a plane substantially
defined by the Y-Z axes.
[0062] In the case of multiple male dovetails 22, the second
thickness surface 42 of each dovetail 22 can all be at the same
angle .alpha. relative to the engaging surface 24 or to a plane
substantially defined by the Y-Z axes, or at least one of the
dovetails 22 can have a second thickness surface 42 that extends at
a different angle to the engaging surface 24 or to a plane
substantially defined by the Y-Z axes.
[0063] The male dovetails 22 can be substantially aligned on the
engaging surface 24 in the radial direction R or in the direction
of the Y-axis. However, in one embodiment, at least one of the
dovetails 22 can be offset from the other male dovetails 22, such
as in the Z-direction (not shown).
[0064] The first core piece 12 can include an engaging surface 26.
The engaging surface 26 can be substantially planar, and it can
include an opening 28 for each female dovetail 20. The engaging
surfaces 24, 26 can be configured for substantially mating
engagement. The engaging surfaces 24, 26 can defined an interface
27 between the first and second core pieces 12, 14. The interface
27 can be located in any suitable location. In one embodiment, the
interface 27 can be located in a region of normal resolution in the
casting core 10.
[0065] The dovetails (referring to both the male dovetails 22 and
female dovetails 20) can be spaced in any suitable manner. For
instance, the dovetails can be equally spaced to spread load
equally across entire part. However, the dovetails do not have to
be equally spaced. The dovetails can be spaced as needed to provide
support where needed and to avoid interference with any intricate
detail. It will be appreciated that the male dovetails 22 can be
placed on the second component 14 with a high degree of accuracy
using a method effective to produce high resolution features and/or
detail, such as tomo lithographic molding. The male dovetails can
be placed in substantially direct alignment with cross-overs 34
(FIG. 3) in the second core part 14 to provide strength to the male
dovetail 22 and prevent distortion of the thin wall between the
male dovetails 22. The cross-overs 34 can provide structural
strength and can form cooling passages in the ultimate part being
cast.
[0066] The first core part 12 and the second core part 14 can be
brought together so that each male dovetail 22 is received in a
respective female dovetail 20. The male dovetail 22 can
interlockingly engage the female dovetail 20 so as to generally to
restrain movement in at least two dimensions, such as in the X and
Y directions. However, it should be noted that, when the second
core piece 14 is made using tomo lithographic molding or other
process effective to produce high resolution features and/or
detail, the second core piece 14 can be configured to provide
additional engagement with the female dovetail 20. For instance,
the protruding undercuts 50 can provide additional engagement with
the female dovetail 20. Alternatively or in addition, male
dovetails 22 with second thickness surfaces 42 that are angled
relative to the engaging surface 24 or to a plane substantially
defined by the Y-Z axes can provide a third directional component
of engagement (including, for example, at least partially in the Z
direction).
[0067] Thus, a system according to aspects of the invention can
provide three dimensional interlocking engagement between the male
and female dovetails 20, 22. Thus, it will be appreciated that the
tomo lithographic molding process can enhance the engageability and
alignability of the first and second core pieces 12, 14. When
assembled, the engaging surface 26 of the first core piece 12 can
abut the engaging surface 24 of the second core piece 14.
[0068] The joining of the first and second core pieces 12, 14 can
be done outside of a mold. That is, the first and second core
pieces 12, 14 can be formed separately in their own dies or molds.
The first and second core pieces 12, 14 can then be brought
together and joined out of their respective dies/molds or any other
die/mold. Because the joining process is not confined to a mold or
die, it will be appreciated that greater flexibility in making the
first and second core pieces 12, 14 and the core assembly 10
overall can be realized. The handling of the first and second core
pieces 12, 14 outside of a die/mold can be facilitated by the use
of a binder system in forming the first and second core pieces 12,
14. The details of such a binder system will be described
later.
[0069] When the male dovetail 22 is received in the female dovetail
20, there may be a slight gap 30 between them, as shown in FIG. 3.
The gap 30 can extend about at least a portion of the interface
between the male dovetail 22 and the female dovetail 20. In one
embodiment, the gap 30 can extend entirely about the interface
between the male dovetail 22 and the female dovetail 20. The gap 30
can be about 0.005 inch. The gap 30 can be filled with an adhesive
material.
[0070] When the first and second core pieces 12, 14 are made of a
ceramic material, the adhesive material can be a fireable, ceramic
material 32. The material 32 can be in the form of a slurry. This
ceramic material 32 can be identical or substantially similar to
the material of the first and/or second core pieces 12, 14. The
ceramic material 32 can be selected so that its properties are
identical or otherwise well-matched to the properties of the
material of the first and second core pieces 12, 14 so that, when
the joined core pieces 14, 16 are subsequently fired, the material
properties of the core assembly 10 remain substantially constant
throughout. In one embodiment, the ceramic material 32 can be
substantially the same as the material of the second core piece 14.
The joined first and second core pieces 12, 14 can then be fired
together in a kiln or furnace to form the core assembly 10.
[0071] It will be appreciated that if one or more surfaces of the
male dovetail 22 (such as thickness surfaces 40, 42, 44) have one
or more protruding undercuts 50, then the ceramic material 32 will
have additional surface area to adhere to, thereby potentially
increasing the integrity and/or strength of the interface. Such
additional surface area can lead to better green state binding and
better high temperature sintering. Further, use of tomo
lithographic molding to form the second core piece 14 allows the
male dovetails 22 to be selectively sized, shaped and oriented to
minimize distortions due to core twist or core shift that may be
experienced when the first and second core pieces are fired
together.
[0072] The interface 27 between the engaging surfaces 24, 26 of the
first and second core pieces 12, 14 can be strengthened in
additional ways. For instance, a strengthening member can extend
across the interface 27 and into each of the core pieces 12, 14.
The strengthening member can be any suitable structure. In one
embodiment, the strengthening member can be a foil 60. The foil 60
can be a very thin, often flexible sheet. The foil 60 can be
composed of a single foil or a plurality of foils precisely aligned
and/or bonded into a laminated, monolithic solid object. The
individual foils 60 can be formed in any suitable manner, such as
by chemical-machining or etching. The foil 60 can be formed of any
suitable metal, such as, for example, Molybdenum, or any suitable
alloy. The foil 60 can be made to give the desired strength and/or
functionality in joining the core pieces 12, 14. The foil 60 can
have any suitable size, shape and/or features to provide the
desired properties at the interface 27. In one embodiment, the foil
60 can extend across the entire engaging surface 24 of the second
core piece 14 generally in the Z-direction (FIG. 2).
[0073] The foil 60 can be provided in the core 10 in any suitable
way. In one embodiment, a portion of the foil 60 can be embedded in
the second core piece 14, as is shown in FIG. 3. To that end, the
foil 60 can be inserted into the core mold/die, which can be a
Tomolithographic mold/die. A ceramic slurry can be poured into the
mold/die and around a portion of the foil 60. The slurry can be
subsequently cured to form the second core piece 14. As a result, a
portion 60a of the foil 60 can be embedded in the second core piece
14, and a portion 60b of the foil 60 can protrude from an exterior
of the second core piece 14, such as the engaging surface 24. The
protruding portion 60b of the foil 60 can be received in a recess
62 in the first core piece 12. The recess 62 can be formed in the
first core piece 12 in any suitable manner. For instance, the
recess 62 can be formed during the casting process or during a
subsequent machining operation. In one embodiment, the recess 62
can be open on one of its ends to receive the foil 60
laterally.
[0074] When two core pieces (such as the first and second core
pieces 12, 14) are brought together as described herein, the foil
60 can extend across an interface 27 defined therebetween (such as
between engaging surfaces 24, 26). The protruding portion 60b of
the foil 60 can help to accurately align the first and second core
pieces 12, 14 during their assembly. When the first and second core
pieces 12, 14 are joined, the foil 60 can extend into each of the
core pieces 12, 14. As a result, the joint between the two core
pieces 12, 14 can be fortified, which can improve the quality of
the casting core 10. The foil 60 can be chemically leached out of
or otherwise removed from the core 10 at a later point, if
necessary.
[0075] The first and second core pieces 12, 14 can be brought
together at different stages in their processing. For instance, the
first core piece 12 and the second core piece 14 can be brought
together when they are both fully fired or sintered. Alternatively,
the first and second core pieces 12, 14 can be brought together
when both are in a green state, that is, in a pre-fired or
pre-sintered condition. In the green state, both the first and
second core pieces 12, 14 have been cast and have hardened enough
to enable each core piece 12, 14 to be removed from its respective
mold, but they are not fully fired or sintered. Thus, it will be
appreciated that the system and method according to aspects of the
invention can allow increased flexibility in the mold design.
[0076] Typically, the strength of a conventionally-formed casting
core in a green state is weak. As a result, it is difficult to
transfer such core bodies out of a mold. Such transfer can be
particularly difficult when such core bodies include one or more
high resolution features or regions, as described herein. Core
yields are low because cores can break when removed from a mold/die
due to their fragile green body strength and or because their
features are so small and complex. The addition of a binder can
improve the strength of the green bodies to allow for handling
and/or other beneficial properties.
[0077] Additional details of the binder system and the molding
composition will now be provided. To prepare and/or provide a
molding composition for at least partially filling the mold, a
powder material can be combined with a binder system to form a
molding composition, such as a slurry. The powder can comprise any
of ceramic, silica, alumina, zirconia, silicon carbide, boron
nitride, and/or yttria, etc. The powder, molding composition,
and/or casting method can be any of those described herein,
including any of those described in the following set of US patent
documents, each of which is incorporated by reference herein in its
entirety: U.S. Pat. No. 2,961,751 (titled "Ceramic Metal Casting
Process"); U.S. Pat. No. 3,957,715 (titled "Casting of High Melting
Point Metals and Cores Therefore"); U.S. Pat. No. 4,190,450 (titled
"Ceramic Cores for Manufacturing Hollow Metal Castings"); U.S. Pat.
No. 4,284,121 (titled "Process and Materials for Making Refractory
Cores"); U.S. Pat. No. 4,837,187 (titled "Alumina-Based Core
Containing Yttria"); U.S. Pat. No. 5,394,932 (titled "Multiple Part
Cores for Investment Casting"); U.S. Pat. No. 6,588,484 (titled
"Ceramic Casting Cores with Controlled Surface Textures"); U.S.
Pat. No. 7,413,001 (titled "Synthetic Model Casting"); and US
Patent Application Publication 2008/0169081 (titled "Method and
Apparatus for Production of a Cast Component").
[0078] What follows are several examples of potential molding
composition for parts, whose approximate composition can range as
follows: Silica 10%-99%; alumina 1%-90%; cristobalite 1%-20%;
zircon 1%-20%; magnesium oxide 0.01%-1.0%; silicone resin 1%-30%;
organic binder 1%-30%.
[0079] Ceramic materials, such as those of the type described in
U.S. Pat. No. 4,837,187, which is incorporated by reference herein
in its entirety, can be used for the molding composition and/or in
forming core parts of gas turbine engine blade cores by low
pressure injection molding. Specifically, a molding composition
with a composition of: approximately 1 wt % to approximately 90 wt
% alumina, such as 84.5 wt % alumina; approximately 1 wt % yttria
to approximately 20 wt % yttria, such as approximately 7.0 wt %
yttria; approximately 0.05 wt % magnesia to approximately 10 wt %
magnesia, such as 1.9 wt % magnesia; and/or approximately 1 wt %
graphite (flour) to approximately 15 wt % graphite (flour), such as
approximately 6.6 wt % graphite (flour) was found to perform
acceptably in a two piece core construction. For example, an
illustrative molding composition can comprise approximately 94 wt %
of 200 mesh fused silica, approximately 6 wt % of 400 mesh
Cristobalite, approximately 6 wt % of 325 mesh tabular alumina,
and/or approximately 0.2% superfine MgO.
[0080] The alumina component of a produced exemplary embodiment of
this molding composition included approximately 70.2% of
approximately 37 micrometer sized grains, approximately 11.3% of
approximately 5 micrometer grains, and approximately 3% of
approximately 0.7 micrometer grains. The grain sizes of the other
components were: graphite--approximately 17.5 micrometer;
yttria--approximately 4 micrometer; and magnesia--approximately 4
micrometer. The thermoplastic binder used included the following
components (wt % of mixture): Okerin 1865Q (Astor Chemical);
paraffin based wax approximately 14.41 wt %; DuPont Elvax 310
FINNECAN, approximately 0.49 wt %; oleic acid--approximately 0.59
wt %. Other ceramic material components and thermoplastic binders
could be used, including those set forth in U.S. Pat. No.
4,837,187.
[0081] In certain exemplary embodiments of the molding composition,
any of a wide variety of silicone resins can be used. For example,
siloxanes of the type described in U.S. Pat. Nos. 3,090,691 and
3,108,985, each of which is incorporated by reference herein in its
entirety, can be utilized, including any organic siloxane in which
the substituent groups are hydrogen atoms or organic radicals
attached directly to the silicone atoms. In general, siloxanes
containing 1 to 3 hydrogen and/or organic substituents per silicon
atom, and the organic group contains 1-12 carbon atoms, optionally
substituted by a group containing an oxygen atom and/or a nitrogen
atom can be utilized. As used herein, the term "siloxane" is
intended to refer to and include a material which contains at least
one linkage per molecule. In an exemplary embodiment, approximately
11 g to 19 g (including all values and subranges therebetween) of
Momentive 355 silicone resin can be used with each 100 g of ceramic
powder.
[0082] Certain exemplary embodiments of the molding composition can
employ siloxane resins such as dimethyl siloxane, monomethyl
siloxane, phenylmethyl siloxane, monophenyl siloxane, diphenyl
siloxane, monethyl siloxane, ethylmethyl siloxane, diethyl
siloxane, phenylethyl siloxane, monopropyl siloxane, ethylpropyl
siloxane, divinyl siloxane, monovinyl siloxane, ethyl vinyl
siloxane, phenyl vinyl siloxane, diallyl siloxane, monoallyl
siloxane, allylethyl siloxane, allylvinyl siloxane, monocyclohexyl
siloxane, gamma-hydroxypropylmethyl siloxane,
beta-methoxyethylmethyl siloxane, gamma-carboxypropyl siloxane,
gamma-aminopropyl siloxane, and/or gamma-cyanopropylmethyl
siloxane, etc.
[0083] Certain exemplary embodiments of the molding composition can
utilize any of a variety of filler materials of the type typically
used in the preparation of molds and cast parts, such as the Group
IVB metals, including refractory and/or ceramic materials, such as
silica, alumina, and/or zircon, etc. As indicated above, the filler
particles can be bonded together by a siliceous bond on firing of
the preformed part as a result of partial decomposition of the
siloxane resin. The bulk density, apparent density, apparent
porosity, and/or other properties of the baked or fired part can be
controlled by varying the relative proportions of the filler and/or
siloxane resin, by varying the size distribution of the ceramic
particles employed in the molding composition, and/or by adding to
the molding composition graphite and/or wood flour which can
burn-out on firing to increase the porosity of the part.
[0084] When silica is the primary filler, the baked and/or fired
part can have a bulk density within the range of approximately 1 to
approximately 3 g/ml, such as, for example, from approximately 1.4
to approximately 2.0 g/ml. This range can correspond to an apparent
solid density of approximately 1.80 to approximately 2.50 g/ml and
an apparent porosity of approximately 15 to approximately 35
percent. For this purpose, use can be made of filler material
having particle sizes within the range of approximately 100 to
approximately 400 mesh.
[0085] Graphite can be used as the filler material in combination
with a silicone resin as described above for molding a pre-formed
part configuration. On baking and firing, a carbon and/or graphite
bond can be formed in addition to the siliceous bond to form the
desired part having a minimum bulk density of approximately 1.2
g/ml, and a maximum of approximately 5 g/ml. Such graphite parts
can be particularly useful in the production of intricately cored,
precision cast titanium components.
[0086] In addition to the filler, silicone resin, and/or catalyst
components, the molding composition can be formulated to include,
if desired, a plasticizer for the silicone resin to improve its
working characteristics during molding of the composition in the
preparation of a pre-formed part. Any suitable plasticizer for
silicone resins can be used, including, for example, paraffin
waxes, styrene, phenol or low molecular weight phenolic resins,
and/or fatty amines such as N,N'-distearyl ethylenediamine, etc.
The amount of plasticizer in the molding composition can be varied
from approximately 0 to approximately 7% by weight of the resin
content of the molding composition.
[0087] Any of a number of additives, such as parting agents or
lubricants can be added to the molding composition to improve the
processing characteristics of the molding composition during
molding in the preparation of the pre-formed core configuration.
Representative materials include, for example, calcium stearate as
well as other metal salts of fatty acids.
[0088] The molding composition can be formulated in accordance with
well known mixing techniques, including dry blending, wet mixing,
hot mixing, etc., and then molded in a conventional manner using
conventional molding techniques, such as transfer molding,
injection molding, and/or compression molding, etc. Molding
parameters including pressures, die temperatures, compound
temperatures, and/or cure times can vary depending somewhat on the
configuration of the part being molded and/or the particular
composition of the molding composition. Typical pressure ranges
normally used for transfer or injection molding can be from
approximately 100 psi to approximately 10,000 psig, and
approximately 100 psig to approximately 5,000 psig for compression
molding. Compound and/or die temperatures usually can range from
approximately room temperature up to approximately 400.degree. F.
and/or can be timed from approximately 1 to approximately 10
minutes.
[0089] The distribution of the particles of the powder comprised by
the molding composition can be controlled over the entire cast part
and/or any portion thereof, such as, in the case of a core, the
core body, trailing edge of the core, and/or leading edge of the
core, etc.
[0090] The binder system can comprise one or more urethane and/or
epoxy resins, one or more solvents and/or wetting agents, and/or
one or more plasticizers, etc. Any of a variety of plasticizers can
be used, including paraffin waxes, styrene, phenol or low molecular
weight phenolic resins, and/or fatty amines such as N,N'-distearyl
ethylenediamine, etc. Binder systems can be produced using acrylics
such as, for example, PMMA acrylic powder, resins, 2 part epoxy
systems and/or composites, and/or methacrylates such as butyl,
lauryl, stearyl, isobutyl, hydroxethyl, hydroxpropyl, glycidyl
and/or ethyl, etc.; thermoplastics, such as, for example, ABS,
acetyl, acrylic, alkyd, flourothermoplastic, liquid crystal
polymer, styrene acrylonitrile, polybutylene terephthalate,
thermoplastic elastomer, polyketone, polypropylene, polyethylene,
polystyrene, PVC, polyester, polyurethane, thermoplastic rubber,
and/or polyamide, etc., thermo-sets, such as, for example,
phenolic, vinyl ester, urea, and/or amelamine, etc.; and/or
rubbers: such as, for example, elastomer, natural rubber, nitrile
rubber, silicone rubber, acrylic rubber, neoprene, butyl rubber,
flurosilicone, TFE, SBR, and/or styrene butadiene, etc. Certain
exemplary embodiments can employ a cycloaliphatic thermal cure
epoxy. For example, approximately 10 g to 20 g of WO32701-8 epoxy
from Resinlab of Germantown, Wis. can be used per 100 g of total
ceramic powder weight, blended according to the manufacturer's
directions of A:B approximately equals 0.94:1.
[0091] Binder materials and/or components can be liquids that can
be fully soluable in, and/or diluted using, various solvents such
as MEK, acetone, heptane, and/or isopropyl alcohol, etc. In the
case of MEK, solvent additions can range between 10-22 grams per
100 grams of total ceramic powder weight. In the case of acetone,
solvent additions can range between 14 grams and 27 grams per 100
grams of total ceramic powder weight. In the case of isopropyl
alcohol, solvent additions can range between 11-21 grams per 100
grams of total ceramic powder weight. The binder system can
comprise any of those appropriate materials described herein,
including any of those described in any of the patents incorporated
herein.
[0092] It has been found that ceramic cores having the desired
thermal stability at temperatures as high as approximately
2700.degree. F. and above can be produced when the molding
composition is formulated to replace all or at least part of the
silica component with a crystalline phase of silica which can be
identified as Cristobalite. When Cristobalite is present as a
constituent of the molding composition in an amount greater than
approximately 2.5%, but not greater than approximately 10% by
weight, the high temperature stability of the ceramic core can be
superior to that of a core in which the silica component is formed
of amorphous fused silica or fused silica combinations with zircon
and/or alumina as the ceramic component of the core.
[0093] The amount of Cristobalite in the core body, at the time
that the molten metal is cast into the mold cavity, can be
important. The quantity can be sufficient to achieve the desired
improvement in high temperature stability without adversely
affecting the strength of the core or the thermal shock properties.
While beneficial use can be obtained when all of the silica is
replaced with Cristobalite, it can be desirable to limit the
maximum concentration in the fired core to approximately 35% by
weight and/or approximately 5 to approximately 20% by weight
Cristobalite in the fired core. The remainder of the core can be
formulated with fused silica and/or fused silica and zircon, and/or
fused silica, zircon and/or alumina, with binders such as organo
silicone resins, such as described in the aforementioned U.S. Pat.
No. 3,957,715. The presence of Cristobalite can be achieved by the
direct addition of Cristobalite to the components making up the
molding composition. For this purpose, Cristobalite can be used in
finely divided form such as in the range of approximately 70 to
approximately -325 mesh. The core can be formed by transfer molding
technique using silicone resins as the binder.
[0094] The following example identifies the approximate ingredient
ranges for the molding composition by weight: silica 10%-99%;
alumina 1%-90%; cristobalite 1%-20%; zircon 1%-20%; magnesium oxide
0.01%-1.0%; silicone resin 1%-30%; organic binder 1%-30%. For
example, a composition of fused silica (60%) and alumina (40%) can
be used.
[0095] The above compositions can include additional ingredients
such as calcium stearate as a lubricant, and/or a catalyst that can
be in the form of finely divided magnesium oxide and/or benzoic
acid in equal parts by weight, with the lubricant being present in
an amount within the range of approximately 0.2 to approximately 2%
by weight and the catalyst being present in an amount within the
range of approximately 0.2 to approximately 2% by weight.
[0096] The binder can be partially and/or fully mixed using
standard mixing techniques. For example, a kitchen mixer such as a
food blender and/or a ceramic slurry mixer such as an approximately
1 horsepower Ross Dispersion Mixer, model 100 LC, can be used.
Mixing times to disperse the binder and/or mix it into the powder
can range from approximately 1 minute to approximately 24 hours.
The binder can be partially and/or fully mixed with the powder
prior to filling mold with the molding composition or directly in
the mold. The mixing can occur via any known technique, including
shear, vibration, centrifugal force, resonant mixing, static
mixing, and/or rotational ball-milling, etc.
[0097] The slurry composition can comprise any desired wetting
agent and/or alternate binder system, which can comprise poly-vinyl
alcohol and poly-ethylene glycol.
[0098] Generally, the viscosities ranging from approximately 500 to
approximately 10,000 cps of the powder, binder, and/or molding
composition can be appropriate to allow them to flow into and/or
fill the mold. The binder concentration (ranging from approximately
10 percent to approximately 20 percent binder to ceramic powder by
weight) of the molding composition can be sufficiently low to
facilitate burnout of the binder and/or allow for the sintering of
the powder.
[0099] Adequate time can be allowed to vent and/or de-gas the
filled mold and/or to cure and/or set the cast part in the mold.
For example, the time for venting, de-gasing, and/or mold filling
can range from approximately 1 minute to approximately 60 minutes.
The cast part can be released from the mold after the binder has at
least partially cross-linked and/or cured. The cure temperature of
the binder can be compatible with the mold material. The cure
temperature can range from approximately 90.degree. F. to
approximately 350.degree. F. The cure time can range from
approximately 15 minutes to approximately 24 hours. The binder can
have compatible reversion properties that can allow the cured
"green" state ceramic part to be heated and thermo-formed prior to
binder burn-out and sintering. The thermo-forming temperature is
dependent on the initial cure temperature used to produce the green
state ceramic core and the specific glass transition temperature
(Tg) of the polymer binder. Manufacturers of resins, epoxies,
urethanes and other organic polymers (binders) specify the Tg of
their products on the materials properties data sheet. During
sintering, the binder can burnout clean, leaving substantially no
carbon to react with the investment casting material.
[0100] The mold can be configured to be closed before, during,
and/or after filling. In certain exemplary embodiments, the mold
can be configured as two or more mold portions that remain open
during and/or after filling, which can potentially more easily vent
air from the mold, de-gas solvent in the molding composition,
de-mold the cast part, etc.
[0101] The mold can be filled via any known technique, such as
gravity pouring, injection pressure, vacuum, and/or dispersion,
etc. The mold can be overfilled to insure a proper fill. A vacuum
can be used to assist with air venting and/or de-gassing.
[0102] During and/or after filling of the mold with the molding
composition, its particles can be compacted, densified, and/or
packed in a maximum density configuration to substantially
eliminate gaps between ceramic particles, thereby helping the
particles to sinter to each other during ceramic firing. That is,
the location, size distribution, count, and/or packing density of
the particles can be adjusted and/or controlled via applying
energy, such as vibrational energy, to the mold during and/or after
filling. As desired, adjustments can be made to the pre-vibration
settling time (approximately 2 minutes to approximately 2 hours),
vibration time (approximately 2 minutes to approximately 2 hours),
the vibration frequency range and/or amplitude, post-vibration
settling time (approximately 2 minutes to approximately 2 hours),
and/or solvent separation time (approximately 2 minutes to
approximately 2 hours), etc. A linear action Jogger table can be
used at a power setting range of approximately 10% to approximately
90% to adjust the amplitude and at a frequency of approximately
250-5000, approximately 250-3600, and/or approximately 3600-5000
pulses per minute. While the mold is being vibrated, the mold can
stay open to allow the solvent to more easily evaporate out of the
molding composition. While the mold is being vibrated and/or while
open, the mold can be heated (temperature range from approximately
100.degree. F. to approximately 350.degree. F. for approximately 15
minutes to approximately 24 hours) and/or cooled (temperature range
from approximately 60.degree. F. to approximately 80.degree. F. for
approximately 1 minute to approximately 3 hours) to affect molding
composition flow, densification, and/or curing, etc.
[0103] In short, a binder system according to aspects of the
invention can include three main ingredients--a resin, a solvent
and a plasticizer. These three main ingredients can be selectively
used in the binder to provide the desired properties in the green
body core. For instance, a suitable epoxy resin can be selected to
provide a desired work time.
[0104] The binder system according to aspects of the invention can
provide significant benefits. For instance, it can produce cores
with relatively high green body strength, improved yields, fine
feature control and the ability to thermally form the green bodies.
A strong green body is advantageous because it enables one to pull
the core from a die/mold with substantially minimized risk of
breakage. Further, a strong green body can allow the inclusion of
fine and complex features that cannot otherwise be included with
conventional core molds/dies. Such fine and complex features can be
in provided in any plane and have non-traditional draft angles.
[0105] The binder system can also allow the green body to be
thermally formed. If the green body is heated to a temperature
above a certain curing temperature, then the green body goes into a
state in which it becomes formable. In this state, the green body
can be manipulated to correct defects or to provide corrections
that may be necessary to compensate for warping that has occurred.
Once the desired features are achieve, the final firing can occur
in which the binder is burnt off and the particles are sintered
together, thereby hardening the body into the final configuration.
It should be noted that over or under compensations can be made in
the green body to account for movements in the green body that may
occur during firing or sintering. It will be recognized that the
ability to thermally form a green body can have significant
advantages over past practices.
[0106] Once it is completed, the core 10 can be used in casting the
ultimate component. In the case of a turbine vane or blade, such
casting can be done by investment casting. In such case, wax is
injected onto the core 10 so that the core 10 is covered by wax. A
ceramic shell can be formed over the wax. The wax can be melted out
and molten metal can be poured in the space between the core 10 and
the ceramic shell. Once the metal solidifies, the core 10 can be
chemically leached out of the casting, leaving the desired internal
features in the vane or blade. In the investment casting process,
the core 10 formed in accordance with aspects of the invention is
used only one time.
[0107] As noted above, additional forms of interlocking engagement
are possible. FIGS. 9A and 9B show another example of a way in
which interlocking engagement between the first and second core
pieces 12, 14 can be achieved. The first core piece 12 can have an
inner side 90 and an outer side 92. While the first core 12 piece
is shown as being generally rectangular in FIGS. 9A and 9B,
embodiments of the invention are not limited to any particular
shape or configuration. A passage 94 can extend through the first
core piece 12 from the inner side 90 to the outer side 92. The
passage 94 can have any suitable size, shape and orientation. In
one embodiment, the passage 94 can be generally rectangular, as is
shown in FIGS. 9A and 9B.
[0108] The second core piece 14 can have an inner side 96 and an
outer side 98. While the second core piece 14 is shown as being
generally rectangular in FIGS. 9A and 9B, embodiments of the
invention are not limited to any particular shape or configuration.
The second core piece 14 can include a protrusion 99. The
protrusion 99 is shown in FIG. 9A as being generally rectangular,
but it can have any suitable configuration. At least a portion of
the protrusion 99 can be configured to be received within the
passage 94.
[0109] The protrusion 99 can be sufficiently long such that a
portion of the protrusion 99 extends beyond the outer side of the
first core piece 12, as is shown in FIG. 9A. Heat can be applied to
at least a portion of the protrusion 99 and/or the second core
piece 14 to achieve the preferred flow, formability or other
properties of the binder when the second core piece 14 is in the
green state. In some instances, localized portions of the
protrusion 99 and/or the second core piece 14 can be heated to
achieve the preferred flow, formability or other properties of the
binder without affecting the rest of the second core piece 14. The
second core piece 14 can then be manipulated or formed such that
the protrusion 99 is folded over onto the first core piece 12, such
as onto the outer side 92. In this way, the first and second core
pieces 12, 14 can be maintained in interlocking engagement. The
joined first and second core pieces 12, 14 can be fired together in
a kiln or furnace to form a core assembly.
[0110] In some instances, a recess 100 can be formed in the first
core piece 12. The recess 100 can open to the outer side 92 of the
first core piece 12. The recess 100 can be sized and shaped to
receive the folded over portion of the protrusion 99. As a result,
the protrusion 99 can be substantially flush with the outer side 92
of the first core piece 12, as is shown in FIG. 9B.
[0111] FIGS. 10A and 10B show yet another possible manner of
forming an interlocking engagement between the first and second
core pieces 12, 14. The first core piece 12 can have an inner side
102 and an outer side 104. The first core piece 12 is shown as
being generally rectangular in FIGS. 10A and 10B, but embodiments
of the invention are not limited to any particular shape or
configuration for the first core piece 12. A passage 106 can extend
through the first core piece 12 from the inner side 102 to the
outer side 104. The passage 106 can have any suitable size, shape
and orientation. In one embodiment, the passage 106 can be
generally conical, expanding in diameter when moving from the inner
side 102 to the outer side 104, as is shown in FIGS. 10A and
10B.
[0112] The second core piece 14 can have an inner side 108 and an
outer side 110. The second core piece 14 is shown as being
generally rectangular in FIGS. 10A and 10B; however, embodiments of
the invention are not limited to any particular shape or
configuration of the second core piece 14. The second core piece 14
can include a protrusion 112. At least a portion of the protrusion
112 can be configured to be received within the passage 106.
[0113] Once at least a portion of the protrusion 112 is received in
the passage 106, at least a portion of the protrusion 112 and/or
the second core piece 14 can be heated to achieve the preferred
flow, formability or other properties of the binder when the second
core piece 14 is in the green state. In some instance, localized
portions of the protrusion 112 and/or the second core piece 14 can
be heated to achieve the preferred flow, formability or other
properties of the binder without affecting the rest of the second
core piece 14. In such condition, the second core piece 14 can be
formed to bring the first and second core pieces 12, 14 into
interlocking engagement. For example, the protrusion 112 can be
formed to correspond to at least a portion of the passage 106, as
is shown in FIG. 10B. In one embodiment, the protrusion 112 can be
formed to fill the entire passage 106. One the protrusion 112 is
formed into the desired configuration, the first and second pieces
12, 14 can be interlockingly engaged. The joined first and second
core pieces 12, 14 can fired together in a kiln or furnace to form
a core assembly.
[0114] In some instances, the protrusion 112 and/or the passage 106
can be configured to maintain a desired spacing S between the inner
surface 102 of the first core piece 12 and the inner surface 108 of
the second core piece 14. For example, the protrusion 112 can
include a first portion 114 and a second portion 116. The first
portion 114 can be sized and shaped to be received in the passage
106. The second portion 116 can be sized, shaped and/or otherwise
configured to ensure that the second portion 116 is not received in
the passage 106. For example, when the passage 106 and the
protrusion 112 are generally circular in cross-sectional shape, the
diameter of the second portion 116 of the protrusion 112 can be
greater than the diameter of the passage 106. In this way, the
distance between the first and second core pieces 14, 16 can be
fixed and maintained during assembly as well as during firing.
[0115] It should be noted that systems and methods according to
aspects of the invention can be applied to provide benefits in
connection with other portions of the molding and/or investment
casting side casting process. For example, systems and methods
according to aspects of the invention can be applied in connection
with core prints and/or core locks associated with the core 10.
Generally, core prints can hold and align the core in the mold/die
during wax injection, and core locks can locate and hold a core
and/or ceramic shell during casting of the component. Core prints
and core locks typically extend beyond the footprint of the part
being cast and do not form a part of the final cast component. An
example of a casting core 10 having core prints and core locks in
accordance with aspects of the invention in shown in FIG. 7. The
core 10 shown includes two core prints 70, one at each end of the
core 10. A core lock 72 can be formed on one of the core prints 70.
The core prints 70 and the core locks 72 can be provided in any
suitable location. The core locks 72 can be any suitable size and
shape. The casting core is shown in phantom because it can have any
suitable configuration.
[0116] Aspects of the invention can allow greater flexibility in
making core prints and core locks. For instance, the core prints
can be formed together with the core pieces. Alternatively, the
core prints can be formed separately from the core pieces. When the
core prints are formed separately, they can be subsequently joined
to one or more of the core pieces using any of the joining
techniques for two core pieces, as described herein. Thus, the core
pieces and the core prints can include one or more features to
align the pieces in a precision way, thereby enhancing the
manufacturability of the core.
[0117] In one embodiment, the core prints can include recesses and
the core pieces can include protrusions adapted for interlocking
engagement with the recesses. Any suitable type of interlocking
engagement can be used, including any of those described herein in
connection with the joining to two core pieces. These features
allow for better alignment between the separately formed core
prints and the core pieces, which, in turn, will lead to better
alignment and functionality in subsequent stages in the casting
process. It will be appreciated that the opposite arrangement can
be provided in which the core prints include protrusions adapted
for interlocking engagement with recesses in the core pieces. Still
alternatively, the core prints can include both protrusions and
recesses adapted for interlocking engagement with corresponding
recesses and protrusions on the core pieces.
[0118] The core prints are relatively large structures that are of
normal resolution; that it, they typically do not include any
special features or geometries. Thus, the methods of forming high
resolution regions in the core may not be suitable for the
formation of the core prints. By forming the core prints separately
from the core pieces, it will be appreciated that forming holding
structures can provide a previously unavailable degree of freedom.
For instance, greater flexibility is allowed in the manipulation of
the core pieces and the core prints. In addition, because the
separately formed parts can be later aligned and joined in a high
precision way, a greater range of options becomes available for the
shape and the location of the core prints. Likewise, there are more
options available for the shape and location of the core locks.
[0119] In light of the above, it will be appreciated that aspects
of invention can provide a robust system and method for forming a
casting core. The system and method according to aspects of the
invention can reduce the core development process, which, in turn,
can reduce the time to market for new product developments.
Further, because the core pieces with the most complex, critical
and/or intricate features can be made using a process that offers a
high degree of geometric and dimensional control, the amount of
scrap castings can be reduced.
[0120] It should be noted that, while a portion of the above
description has been directed to a core made of two core pieces, it
will be understood that aspects of the invention can readily be
applied to cores that are made of more than two pieces. For
instance, a third core piece (not shown) that is made using
conventional casting techniques can be joined to the first core
piece 12 in any conventional manner, or it can be joined to the
second core piece 14 in any of the manners described above, such as
by interlocking engagement. If the third core piece is made using a
method effective to produce high resolution features and/or detail,
then it can be joined to the first core piece 12 by interlocking
engagement or in any of the manners described above, or it can be
joined to the second core piece 14 in any suitable manner. Again,
there can be any number of core pieces.
[0121] In addition to forming multi-piece structures, systems and
methods according to aspects of the invention can be used to
produce multi-wall cores. The term "multi-wall" means a core with a
plurality of closely-positioned walls. One example of a multi-wall
core 100 according to aspects of the invention is shown in FIG. 8.
The multi-wall core 100 includes a first core piece 80 and a second
core piece 82. The first core piece can include a first wall 84,
and the second core piece 82 can include a second wall 86. Each
wall can comprise a single wall, as in the case of the first wall
84, or a plurality of walls, as in the case of the second wall 86.
The first and second walls 84, 86 can include high resolution
features or regions. In some instances, one or both walls 84, 86
may be of normal resolution.
[0122] The spacing between two neighboring walls may or may not be
substantially constant. Neighboring walls in a multi-wall core may
be generally complimentary to each other. It should be noted that,
while the term "wall" may connote a planar structure, embodiments
of the invention are not so limited, as the walls can have any of a
number of non-planar features, including curves, bends, compound
surfaces, protrusions and recesses, just to name a few
possibilities. The walls can be relatively thin.
[0123] While the example multi-wall core 100 in FIG. 8 shows has
two walls 84, 86, it will be understood that there can be more than
two walls. Further, while the multi-wall core 100 includes a first
core piece 80 and a second core piece 82, the multi-wall core 100
can be formed together as a single piece structure. Alternatively,
each wall can be defined by separately formed core pieces 80, 82,
and the core pieces 80, 82 can be brought together in any suitable
manner. The separate core pieces 80, 82 can be joined together in
any suitable location. For instance, the core pieces 80, 82 can be
joined at one or more of their ends regions. The core pieces 80, 82
can be directly connected together in any of the manners described
herein, or they can be indirectly connected, such as by a core
print. Alternatively or in addition, there can be interconnections
between neighboring walls in or more locations along their length.
Any suitable form of interconnection can be made, including, for
example, any of those described above in connection with joining
two or more separate core pieces.
[0124] It will be appreciated that, if the core includes a
plurality of walls, the overall surface area of the core can be
increased, thereby allowing more features that can affect the heat
transfer properties of the ultimate part. Further, by providing
more internal features in the component being cast, an overall
decrease in weight can be realized over conventional component
designs. Moreover, the internal features can collectively increase
the strength of the component.
[0125] It will be readily appreciated that a multi-wall core as
described herein is not attainable using conventional core
formation techniques. In some instances, a multi-wall core can be
formed using a method effective to produce high resolution
features, such as tomo lithographic molding and including any of
the techniques and systems described herein. Multi-walled cores
according to aspects of the invention may or may not have high
resolution features. A multi-wall structure can be effective to
produce high efficiency cooling features in the component being
cast.
[0126] It should also be noted that, in some instances, glass or
quartz rods are used as connecting members to join multiple casting
core pieces when the assembly is fired or sintered. It will be
readily appreciated that such practice can be eliminated by systems
and methods for joining casting core pieces as described herein.
Alternatively, systems and methods for joining casting core pieces
according to aspects of the invention can be used to optimize the
use of glass and quartz rods in joining casting core pieces.
[0127] The foregoing description is provided in the context of one
possible application for the system and method according to aspects
of the invention. While the above description is made in the
context of casting a turbine blade or vane, it will be understood
that the system according to aspects of the invention can be
readily applied to any hollow cast turbine engine component,
especially those with complex internal features. Thus, it will of
course be understood that the invention is not limited to the
specific details described herein, which are given by way of
example only, and that various modifications and alterations are
possible within the scope of the invention as defined in the
following claims.
* * * * *