The preferred embodiment of the present invention relates
to gas turbine engines. More particularly, the preferred embodiment relates to the
casting of cooled airfoils for gas turbine engine blades and vanes.
Investment casting is a commonly used technique for forming
metallic components having complex geometries, especially hollow components, and
is used in the fabrication of superalloy gas turbine engine components. The preferred
embodiment is described in respect to the production of particular superalloy castings,
however it is understood that the invention is not so limited.
Gas turbine engines are widely used in aircraft propulsion,
electric power generation, and ship propulsion. In gas turbine engine applications,
efficiency is a prime objective. Improved gas turbine engine efficiency can be obtained
by operating at higher temperatures, however current operating temperatures in the
turbine section exceed the melting points of the superalloy materials used in turbine
components. Consequently, it is a general practice to provide air cooling. Cooling
is provided by flowing relatively cool air from the compressor section of the engine
through passages in the turbine components to be cooled. Such cooling comes with
an associated cost in engine efficiency. Consequently, there is a strong desire
to provide enhanced specific cooling, maximizing the amount of cooling benefit obtained
from a given amount of cooling air. This may be obtained by the use of fine, precisely
located, cooling passageway sections.
The cooling passageway sections may be cast over casting
cores. Ceramic casting cores may be formed by molding a mixture of ceramic powder
and binder material by injecting the mixture into hardened steel dies. After removal
from the dies, the green cores are thermally post-processed to remove the binder
and fired to sinter the ceramic powder together. The trend toward finer cooling
features has taxed core manufacturing techniques. The fine features may be difficult
to manufacture and/or, once manufactured, may prove fragile. Commonly-assigned
U.S. Patent Nos. 6,637,500 of Shah et al.
6,929,054 of Beals et al.
7,014,424 of Cunha et al.
7,134,475 of Snyder et al.
7,216,689 of Verner et al.
U.S. Patent Publication Nos. 20060239819 of Albert et al.
20070044934 of Santeler et al.
disclose use of ceramic and refractory metal core combinations.
One aspect of the invention comprises a method for inspecting
a part having an in-wall cooling passageway. The in-wall cooling passageway separates
an interior wall section from an exterior wall section. A reference location along
the in-wall cooling passageway is observed. A size of an aperture at the reference
location is determined. Based upon the determined size, a condition of the associated
wall section is determined.
The method may be performed sequentially on a plurality
of said parts. The parts may be a plurality of cooled airfoils, each having a pressure
side and a suction side. The method may be performed for both the wall sections
on each part. The method may be performed for a plurality of the in-wall passageways
on each part. The method may be performed for multiple walls on each part.
Another aspect of the invention comprises a method for
manufacturing a casting pattern. A pattern-forming die is assembled with a ceramic
feedcore and a refractory metal core (RMC). The assembling leaves an inlet portion
of the RMC engaged to the ceramic feedcore and leaves an outlet portion of the RMC
engaged to the die. A pattern-forming material is molded in the die at least partially
over the ceramic feedcore and RMC. The die is disengaged from the pattern-forming
material. The assembling engages a stepped projection of the RMC with a mating surface
of the die. The stepped projection may be intermediate the inlet and outlet portions.
Another aspect of the invention comprises a casting pattern.
The pattern includes a ceramic feedcore, a refractory metal core (RMC) mated to
the ceramic feedcore, and a sacrificial pattern material which is preferably molded
at least partially over the ceramic feedcore and RMC. The sacrificial pattern material
may define a pressure side and a suction side. The RMC has an inlet portion mated
to the ceramic feedcore, an outlet portion protruding from the sacrificial pattern
material, a main body portion extending between the inlet and outlet portions, and
a stepped portion that may protrude from the main body portion.
Another aspect of the invention comprises a casting core
assembly comprising a ceramic feedcore and a refractory metal core (RMC). The RMC
is mated to the ceramic feedcore and comprises means for providing a wall thickness
check feature in a casting cast over the core.
The details of one or more embodiments are set forth in
the accompanying drawings and the description below. Other features, objects, and
advantages will be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view of a gas turbine engine
FIG. 2 is a cross-sectional view of the
blade of FIG. 1, taken along line 2-2.
FIG. 3 is an enlarged view of the blade
of FIG. 2.
FIG. 4 is a view of a refractory metal
core for casting a passageway of the blade of FIG.
FIG. 5 is a sectional view of a pattern
in a pattern forming die.
FIG. 6 is a sectional view of a shell formed
from the pattern of FIG. 5.
FIG. 7 is a sectional view of a first worn
or defective airfoil.
FIG. 8 is a sectional view of a second
FIG. 9 is a view of a third defective.airfoil.
FIG. 10 is a sectional view of a fourth
FIG. 11 is a sectional view of an alternate
refractory metal core.
Like reference numbers and designations in the various
drawings indicate like elements.
FIG. 1 shows a gas turbine engine blade
20 having an airfoil 22, an attachment root 24, and a platform 26. The exemplary
airfoil, root, and platform may be formed as a unitary casting (e.g., of a nickel-
or cobalt- based superalloy). The exemplary root 24 extends from an inboard end
28 to an outboard end 30 at an underside 32 of the platform 26. The root 24 has
a convoluted so-called fir tree profile for attaching to a complementary slot (not
shown) in a disk.
The airfoil 22 extends from an inboard end 34 at an outboard
surface 36 of the platform to an outboard end 38. The exemplary outboard end 38
is a free distal tip. Alternative blades may have outboard shrouds. Alternative
airfoils may be implemented in fixed vanes.
The airfoil 22 has an exterior/external aerodynamic surface
extending from a leading edge 40 to a trailing edge 42. The airfoil has a pressure
side (surface) 44 and a suction side (surface) 46.
The airfoil 22 is cooled via a cooling passageway system
50. The passageway system 50 includes one or more trunks 52 extending from one or
more inlets 54 in the root 24. The exemplary network 50 includes a plurality of
span-wise passageway legs (e.g., feed passageways) 60A-G (FIG.
2). The exemplary passageway legs leave a pressure side wall 62 and a suction
side wall 64. The pressure side wall 62 and suction side wall 64 may be connected
by a number of dividing walls 66 which separate adjacent pairs of the feed passageway
legs. The feed passageway legs may be, in one or more combinations, separate passageways
or legs of one or more common passageways connected by turns or other means.
One or both of the pressure side wall 62 and the suction
side wall 64 may be cooled via one or more wall cooling passageways (in-wall passageways)
70. The exemplary wall cooling passageways include inlets (ports) 72 at one or more
of the feed passageway legs, a slot-like main section 74 extending in the span-wise
and stream-wise directions, and outlets (ports) 76 to the associated pressure side
44 or suction side 46. Respective inlet and outlet terminal portions 78 and 79 extend
between the inlets and outlets on the one hand and the main section 74 on the other
Such wall cooling passageways 70 may be cast using refractory
metal cores (RMCs) as are known or may be developed. Each of the wall cooling passageways
70 separates an interior section/portion 80 of its associated pressure side wall
62 or suction side wall 64 from an exterior section/portion 82 of that wall. With
the interior section 80 typically exposed directly to the cool cooling air flowing
through the passageway legs, the section 80 is typically designated the "cooled
wall". The exterior section 82 is typically exposed to hot gas of the engine core
flowpath and is typically designated the "hot wall". An overall wall thickness is
shown as TW. TW (FIG. 3)
is equal to the sum of the cooled wall thickness TC, the wall cooling
passageway thickness TP, and the hot wall thickness TH. TW,
TC, TP, and TH may vary in relative or absolute
terms with the particular location along the airfoil.
It is desired to visually determine wall condition (e.g.,
of the pressure side wall and/or suction side wall). More particularly it is desired
to verify that the wall thicknesses TC and TH are within specified
limits. For example, erosion during use may reduce the thickness TH below
an acceptable minimum value. Additionally, or alternatively, as-manufactured (e.g.,
as-cast) thickness may be verified for TC, TH, or both.
Exemplary means for providing the thickness check include
an extension (e.g., a branch or alcove) 90 of the wall cooling passageway into the
interior wall section and another extension 92 into the exterior wall section. Exemplary
extensions are from the main section 74 of the wall cooling passageway.
Some implementations may not include both extensions 90
Exemplary extensions 90 and 92 are nominally through-extensions,
penetrating through the associated wall section 62 or 64. The term "nominally" contemplates
the possibility that they may be through-extensions only in a normal situation (e.g.,
when the thickness is not excessive). In such a situation, the absence of penetration
would indicate an excessive wall thickness. The,exemplary extensions have stepped
cross-section (e.g., a proximal portion 94 of the extension has a larger cross-section
in at least one dimension than does a distal portion 96). Normally, the distal portion
96 will be open to the associated surface (i.e., exterior surface (pressure side
44 or suction side 46) or an interior surface 100). Thus, normally, observation
of that surface (at a reference location where the extension is) will yield a view
of an aperture characterized by the cross-section of the distal portion 96. If the
distal portion 96 is effectively worn away or if a manufacturing defect similarly
reduces the thickness of the wall section, the inspection will show in the cross-section
of the proximal portion and will, thereby, indicate an insufficient thickness thereby
causing part rejection (e.g., leading to disposal or restoration).
The extensions 90 and 92 may be cast by associated projections
120 and 122 (FIGS. 4 and 5)
from the refractory metal core (RMC) 124. An exemplary casting process is an investment
casting process wherein the RMCs are assembled to a feedcore (e.g., a ceramic feedcore)
in a pattern-forming die. A sacrificial pattern material (e.g., a wax) is molded
in the die at least partially over the feedcore and RMCs to define a pressure side
and a suction side of the pattern. The die elements are separated and the pattern
removed from the die. The pattern may be shelled (e.g., via a multi-stage stuccoing
process). The sacrificial pattern material may be removed (e.g., in a dewaxing)
to leave a void for casting the blade or vane. Molten metal is introduced to the
void and cooled to solidify. The shell may be removed (e.g., via mechanical means).
The core may be removed (e.g., via chemical means) to leave a raw casting. The casting
may be machined, treated, and/or coated.
An exemplary RMC 124 for forming the wall cooling passageways
has a main body portion 126 which may be flat or off-flat to conform to the shape
of the associated side wall. An inlet end portion 128 (FIG.
4) may project transverse to the main body portion 126. A distal end 130
of the inlet end portion may mate with an associated leg 132 of the feedcore 136.
A proximal portion 140 of the inlet end portion casts inlet apertures/ports 72 to
the wall cooling passageway. Similarly, an outlet end portion 144 may project transverse
to the main body portion opposite the inlet end portion (e.g., at a downstream end
of the main body portion). A distal end 146 of the outlet end portion may be positioned
to be received by a die element 150 of the pattern-forming die to project from the
sacrificial pattern material 152 and, in turn, become embedded in the shell 154
(FIG. 6). A proximal portion 156 (FIG.
6) of the outlet end portion casts outlet holes/ports 76 to the associated
pressure side or suction side.
Exemplary extensions 90 and 92 are formed as streamwise
intermediate portions of the RMC (i.e., intermediate the inlet and outlet ends of
the main section 74).
The exemplary RMC is formed from sheetstock (e.g., by cutting
and shaping followed by coating). A first face of the sheet forms an outboard face
of the main body portion 126 and the second face of the sheet forms the inboard
face of the main body portion 126.
An exemplary manufacturing process involves separately
forming the projections 120 and 122 and then attaching them to the remainder of
the RMC. This, for example, may allow greater choice of cross-sectional shape for
the projections. For example, the projections may be formed as stepped right circular
cylinders. A large diameter/cross-section base portion 200 of the projection could
be secured at the RMC main body portion such as by a mechanical interfit (e.g.,
a depending projection 202 of the cylinder interfitting with an aperture 204 of
the main body portion) and/or a metallurgical attachment (e.g., weld, braze, and
the like). After the attachment, the RMC may be coated (if at all).
In the exemplary stepped right circular cylindrical projections,
the base portion 200 casts the extension proximal portion 94. A projection intermediate
portion 210 casts the distal portion 96. A shoulder 212 separates the intermediate
portion 210 from the base portion 200. The intermediate portion 210 has a distal
end 214. The exemplary distal end 214 is a shoulder separating the intermediate
portion 210 from a distal portion 216. The distal portion 216 extends to an end
The projections mate with associated compartments 220 and
222 respectively in the feedcore 136 and die element 150. In the exemplary implementation,
these compartments 220 and 222 are stepped with a base portion capturing the projection
distal portion 216 and an outer portion capturing an end of the projection intermediate
portion 210. For the outer/exterior projection 122, the distal portion 216 and the
end of the intermediate portion 210 which were received in the die compartment 222
protrude from the sacrificial pattern material after molding and become embedded
in a corresponding compartment 228 formed in the shell 154.
FIG. 7 shows a first situation wherein
the hot wall 82 is excessively thin while the cooled wall 80 is of acceptable (e.g.,
nominal/normal) thickness. For example, the hot wall 82 may have been cast with
insufficient thickness. Alternatively, the hot wall may have eroded along the exterior
surface (e.g., the suction side 46 in FIG. 7)
sufficiently to get down below the distal portion 96. In such a situation, the larger
size of the proximal portion 94 will be visible from external inspection. Accordingly,
the proximal portion may be formed with a height Hp that represents the
minimum tolerable thickness (Tc or TH) of the corresponding
section 80 or 82. Although shown of equal size, Hp and other dimensions
may differ between the two projections.
FIG. 8 shows a situation in which the hot
wall 82 is excessively thick. An end portion 260 of the associated extension 92
has been cast by the projection distal portion 216, leaving a particularly small
cross-section opening/aperture which may be distinguished from the cross-section
of the normal extension distal portion 96. The projection intermediate portion 210
may have a thickness such that the overall projection height at the intermediate
portion distal end 214 corresponds to the maximum acceptable associated wall thickness
TH or TC.
FIG. 9 shows a situation where the cooled
wall 80 is excessively thin. This may be observed via use of an endoscope 300 (e.g.,
inserted through an inlet 54 and associated feed passageway).
FIG. 10 shows a situation wherein the cooled
wall 80 is excessively thick.
In situations where the extensions are provided along both
the interior wall section and the exterior wall section, the extensions may be distributed
so as to eliminate or limit the chances for leakage flow (e.g., a leakage flow from
a feed passageway through the interior wall extension and out the exterior wall
extension). In one example, there are multiple wall cooling passageways. One or
more of the wall cooling passageways have only the interior wall extension 90 while
one or more others of the wall cooling passageways have only the exterior wall extension
92. In situations where a given wall cooling passageway has both one or more interior
wall extensions 90 and one or more exterior wall extensions 92, the respective extensions
may be offset from each other in span-wise and/or stream-wise directions to limit
In an alternative method of manufacture, the projections
may be formed in the same process from the same sheet. For example, the projections
400 and 402 (FIG. 11) may be cut (e.g.,
laser cut) to have a stepped cross-section (stepped in only one direction) while
the sheet is flat. The projections may then be bent out of local coplanarity to
the main body portion. In the FIG. 11 example,
the projections 400 and 402 are formed along an aperture 404 with the RMC main body
portion. This allows the projections to be unitarily formed with the adjacent portions
of the RMC (e.g., unitarily formed with a by-mass majority portion of the RMC or
essentially a remainder of the RMC).
The foregoing principles may be applied in the reengineering
of an existing core/process/part configuration. For example, the projections could
be added to an existing core configuration for making a drop-in replacement for
an existing airfoil. However, the principles may be applied in a clean sheet engineering
or a more comprehensive reengineering.
One or more embodiments have been described. Nevertheless,
it will be understood that various modifications may be made. For example, when
implemented in a reengineering of a given part configuration, details of the existing
configuration and/or details of existing manufacturing equipment may influence details
of any particular implementation. Accordingly, other embodiments are within the
scope of the following claims.