U.S. patent application number 12/589801 was filed with the patent office on 2011-04-28 for fugitive core tooling and method.
This patent application is currently assigned to Howmet Corporation. Invention is credited to Robert E. Grunstra.
Application Number | 20110094698 12/589801 |
Document ID | / |
Family ID | 43598122 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094698 |
Kind Code |
A1 |
Grunstra; Robert E. |
April 28, 2011 |
Fugitive core tooling and method
Abstract
A ceramic core is produced by introducing a fluid ceramic core
material, such as a ceramic slurry, into a core-shaped cavity
formed at least in part by one or more fugitive core tooling liners
residing in a back-up body, removing the ceramic core from the
cavity, and removing the one or more fugitive tooling liners from
the back-up die body and discarding them. The fugitive tooling
liners and optional tooling inserts are used in one or more
production cycles (e.g. ceramic slurry injection cycle) to make a
single or multiple ceramic cores and then replaced with fresh
(un-used) tooling liners and optional inserts to make other ceramic
cores.
Inventors: |
Grunstra; Robert E.; (Spring
Lake, MI) |
Assignee: |
Howmet Corporation
|
Family ID: |
43598122 |
Appl. No.: |
12/589801 |
Filed: |
October 28, 2009 |
Current U.S.
Class: |
164/33 ;
164/228 |
Current CPC
Class: |
B22C 7/02 20130101; B22C
9/04 20130101 |
Class at
Publication: |
164/33 ;
164/228 |
International
Class: |
B22C 9/10 20060101
B22C009/10; B22C 7/06 20060101 B22C007/06; B22C 13/12 20060101
B22C013/12 |
Claims
1. Tooling for making a ceramic core, comprising a back-up body and
one or more fugitive tooling liners disposed in the back-up body to
form at least a portion of a core-shaped cavity.
2. The tooling of claim 1 wherein the back-up body comprises
multiple parts positionable to form a tooling cavity to receive the
tooling liners.
3. The tooling of claim 2 wherein first and second fugitive tooling
liners are placed in the tooling cavity and each first and second
tooling liner includes an outer surface having a simple geometry to
match that of an adjacent inner support surface of an adjacent part
of the back-up body and an inner surface that is configured to form
at least a portion of the desired core surface features when the
tooling liners are placed in the back-up body.
4. The tooling of claim 3 wherein the inner surfaces of the first
and second fugitive tooling liners form all of the core
surface.
5. The tooling of claim 3 wherein the inner surfaces of the first
and second fugitive tooling liners form a portion of the core
surface and surfaces of the back-up body form remaining core
surface.
6. The tooling of claim 1 wherein the back-up body includes easily
machined interior surfaces.
7. The tooling of claim 6 wherein the tooling liners include
surfaces that mate with respective easily machined surfaces of the
back-up body.
8. The tooling of claim 1 wherein the tooling liners comprise a
polymer.
9. The tooling of claim 1 including one or more fugitive inserts
between the tooling liners.
10. The tooling of claim 1 including one or more fugitive inserts
on the tooling liners.
11. The tooling of claim 1 wherein the tooling liners form an
airfoil-shaped cavity.
12. A method of making a ceramic core, comprising introducing a
fluid ceramic core material into a core-shaped cavity formed at
least in part by one or more fugitive tooling liners in a back-up
body, removing the ceramic core from the cavity, and removing the
one or more fugitive tooling liners from the back-up body.
13. The method of claim 12 wherein the steps thereof are repeated
using fresh, un-used tooling liners to make another ceramic
core.
14. The method of claim 12 wherein the steps thereof are repeated
using the same tooling liners to make another ceramic core.
15. The method of claim 12 wherein the fluid ceramic material is
introduced under pressure into the cavity.
16. The method of claim 12 including placing the tool liners in the
back-up body so that surfaces of the tooling liners conform to
easily machined surfaces of the back-up body.
17. The method of claim 12 including injection molding the tooling
liners before placing them in the back-up body.
18. The method of claim 12 including discarding the used tooling
liners.
19. The method of claim 12 wherein the core-shaped cavity is formed
to have an airfoil shape.
20. The method of claim 12 including placing one or more fugitive
inserts between the tooling liners.
21. The method of claim 12 including placing one or more fugitive
inserts on the tooling liners.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to manufacture of a ceramic
core for use in casting a hollow metallic article, such as a hollow
turbine components, and more particularly, to tooling and a method
for making a ceramic core.
BACKGROUND OF THE INVENTION
[0002] Most manufacturers of gas turbine engines are evaluating
advanced multi-walled, thin-walled superalloy gas turbine airfoils
(i.e. turbine blade or vane) which include intricate air cooling
channels to improve efficiency of airfoil internal cooling to
permit greater engine thrust and provide satisfactory airfoil
service life. U.S. Pat. Nos. 5,295,530 and 5,545,003 describe
advanced multi-walled, thin-walled turbine blade or vane designs
which include intricate air cooling channels to this end.
[0003] In casting hollow gas turbine engine blades and vanes
(airfoils) and also shrouds having internal cooling passageways, a
fired ceramic core is positioned in a ceramic investment shell mold
to form internal cooling passageways in the cast airfoil. The fired
ceramic core used in investment casting of hollow airfoils
typically has an airfoil-shaped region with a thin cross-section
leading edge region and trailing edge region. Between the leading
and trailing edge regions, the core may include elongated and other
shaped openings so as to form multiple internal walls, pedestals,
turbulators, ribs, chambers, plenums, and similar features
separating and/or residing in cooling passageways in the cast
airfoil or cast shroud.
[0004] The ceramic core typically is formed to desired core
configuration by injection molding, transfer molding or pouring of
an appropriate fluid ceramic core material that includes one or
more ceramic powders, a binder, and optional additives into a
suitably shaped core molding die. After the green molded core is
removed from the die, it is subjected to firing at elevated
(superambient) temperature in one or more steps to remove the
fugitive binder and sinter and strengthen the core for use in
casting metallic material, such as a nickel or cobalt base
superalloy typically used to cast gas turbine engine blades and
vanes (airfoils).
[0005] Conventional core tooling requires expensive EDM machining
for hardened tool steel permanent tooling and sophisticated
machining techniques for tooling dies and tooling inserts, ribs,
inserts, and other cooling features to be imparted to the core
formed using the tooling. Unfortunately, the ceramic core materials
are abrasive to tooling and result in wear of the tooling over
time. Such tooling wear produces undesirable changes and
inconsistencies in core geometry and performance of castings made
with the cores over time.
[0006] The fired ceramic core then is used in manufacture of the
shell mold by the well known lost wax process wherein the ceramic
core is placed in a pattern molding die and a fugitive pattern is
formed about the core by injecting under pressure pattern material,
such as wax, thermoplastic and the like, into the die in the space
between the core the inner die walls. The pattern typically has an
airfoil-shaped region with a thin cross-section trailing edge
region corresponding in location to trailing edge features of the
core. The pattern also can include other features such as
including, but not limited to, one or more platforms, shrouds and
the like.
[0007] The fugitive pattern with the ceramic core therein is
subjected to repeated steps to build up the shell mold thereon. For
example, the pattern/core assembly is repeatedly dipped in ceramic
slurry, drained of excess slurry, stuccoed with coarse ceramic
stucco or sand, and then air dried to build up multiple ceramic
layers that form the shell mold on the assembly. The resulting
invested pattern/core assembly then is subjected to a pattern
removal operation, such as steam autoclaving, to selectively remove
the fugitive pattern, leaving the shell mold with the ceramic core
located therein. The shell mold then is fired at elevated
temperature to develop adequate shell mold strength for metal
casting.
[0008] Molten metallic material, such as a nickel or cobalt base
superalloy, is cast into a preheated shell mold and solidified to
produce an equiaxed grain, columnar grain or single crystal
airfoil. The resulting cast airfoil includes the ceramic core
therein so as to form internal cooling passageways upon removal of
the core. The core can be removed by leaching or other conventional
techniques, leaving a hollow cast metallic airfoil.
SUMMARY OF THE INVENTION
[0009] The present invention provides tooling for making a ceramic
core wherein the core tooling employs one or more fugitive tooling
liners and optional fugitive tooling inserts that are placed in a
simple-geometry back-up or support body in a manner to form at
least a portion of a core-shaped cavity and that eliminate the need
for costly hardened/machined permanent steel tooling.
[0010] In an illustrative embodiment of the invention, each
fugitive tooling liner includes an outer surface having a simple
geometry to conform to that of an adjacent inner support surface of
the back-up body and an inner surface that is configured to form
desired core surface features when the tooling liners are placed in
the back-up body with the tooling liners forming the core-shaped
cavity. Optional fugitive inserts can be placed between the tooling
liners to form ribs, holes, passages and other features on and/or
in the ceramic core. The core-shaped cavity may have one or more
airfoil-shaped surfaces in the production of a ceramic core for use
in casting of a hollow airfoil, such as a hollow gas turbine blade
or vane, or other hollow article.
[0011] A ceramic core is produced pursuant to a method embodiment
of the invention by introducing a fluid ceramic core mixture
typically under pressure into the core-shaped cavity formed at
least in part by the fugitive tooling liners in the back-up body,
removing the molded ceramic core from the cavity, and removing the
fugitive tooling liners with the core or from the back-up die body
(separately from the core) for discarding. The next ceramic core is
produced using fresh (un-used) tooling liners and optional tooling
inserts. Alternately, the fugitive tooling liners may be left in
the back-up body and reused if the liners are in acceptable
condition to this end. That is, the fugitive tooling liners and
inserts are used in one or more production cycles (e.g. ceramic
slurry injection cycles) to make a single ceramic core and then
replaced with fresh (un-used) tooling liners and optional
inserts.
[0012] Other advantages of the present invention will become more
readily apparent from the following detailed description taken with
following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is a cross-sectional view of tooling in accordance
with an illustrative embodiment of the invention where facing
tooling liners are employed.
[0014] FIG. 1B is a cross-sectional view of tooling in accordance
with another illustrative embodiment of the invention where facing
tooling liners are employed to form only portions of the core
molding surfaces and the back-up body surfaces form the remaining
portions of the core molding surface.
[0015] FIG. 2 is a cross-sectional view of still another embodiment
of the invention wherein various types of fugitive inserts are
placed between facing tooling liners.
[0016] FIG. 3 is a perspective view of a core with fugitive
liners/inserts wherein the core resides between facing fugitive
tooling liners after removal from the back-up body.
[0017] FIG. 4 is a perspective view of a core with the fugitive
liners/inserts removed.
[0018] FIG. 5 is an exploded view of the back-up bodies with the
fugitive tooling liners and inserts between the liners showing
where the inserts are pre-located into the liners.
DESCRIPTION OF THE INVENTION
[0019] The present invention provides tooling for making a ceramic
core wherein the tooling employs one or more fugitive tooling
liners and optional fugitive tooling inserts that are placed in a
simple-geometry back-up or support body in a manner to form at
least a portion of a core-shaped cavity and that eliminate the need
for costly hardened/machined permanent steel tooling. Although the
invention is described in detail below with respect to making a
ceramic core having an airfoil shape for use in casting metallic
airfoils, such as gas turbine engine blades and vanes, it is not so
limited and can be used to make a ceramic core having any desired
shape.
[0020] Referring to FIGS. 1-5, an illustrative embodiment of the
invention provides tooling including a back-up or support body 10
and multiple fugitive tooling liners 20a, 20b disposed in the
back-up body 10 to form at least a portion of a core-shaped cavity
C.
[0021] The back-up body 10 comprises multiple parts (first and
second parts 10a, 10b shown) positionable to form a tooling cavity
TC to receive the tooling liners 20a, 20b. The multiple parts of
the back-up body can be incorporated and positioned as an injection
die of a conventional core injection machine.
[0022] Referring to FIGS. 1A, 1B and 5, the parts 10a, 10b of the
back-up body 10 include interior flat and curved geometry surfaces
10s so as to provide a simple geometry that is not costly to
machine. Although particular simple flat and curved surfaces 10s
are shown, surfaces 10s of other simple geometry can be used
including, but not limited to, easily-machined surfaces which are
all curved or all flat, or a combination thereof, as well as other
easy-to-machine surface profiles. The back-up body can be made of
hardened steel or other material that can withstand the pressure of
the liquid ceramic material introduced typically under pressure to
form the ceramic core.
[0023] In FIG. 1A, all core surfaces will be formed by the inner
surfaces of the tooling liners 20a, 20b. However, the invention is
not limited to this embodiment since simple surfaces of the
core-shaped cavity and thus the core may be formed by surfaces of
the permanent tooling; i.e. by surfaces BS on the back-up parts
10a, 10b, as shown in FIG. 1B. Also, a single tooling liner 20a or
20b may be employed for simple core surfaces.
[0024] The core tooling includes one or more fugitive tooling
liners 20. For purposes of illustration, the core tooling is shown
including first and second fugitive tooling liners 20a 20b that are
placed in the tooling cavity TC. Each first and second tooling
liner includes an outer surface 20s having a simple flat and/or
curved or other simple geometry to conform to or match that of an
adjacent inner support surface 10s of an adjacent part of the
back-up body 10 and an inner surface 10c that is configured to form
desired core surface features when the tooling liners 20a, 20b are
placed in the back-up body 10 in facing relation to form the
core-shaped cavity C. Although the tooling liners are shown
including flat and curved outer surfaces 20s that mate with an
adjacent flat and curved surface 10s of the back-up body, other
simple surfaces 20s can be used that match or mate with those of
the adjacent parts of the back-up body 10. The tooling liners 20a,
20b can be designed to snap-fit into place in the parts 10a, 10b of
the back-up body 10, or they can be held by releasable adhesive or
releasable fasteners or clamps.
[0025] The inner surfaces 20c of the tooling liners form an
air-foil core-shaped cavity C therebetween, FIG. 1A, or at least a
portion of the air-foil core-shaped cavity C, FIG. 1B, when the
tooling liners 20a, 20b are placed in the back-up body 10. As
mentioned above, simple surfaces of the core-shaped cavity C and
thus the core may be formed by surfaces BS of the back-up parts
10a, 10b, as shown in FIG. 1B. The inner surfaces 20c are
configured to form desired core surface features when the tooling
liners 20a, 20b are placed in the back-up body 10 in facing or
other relation to form at least a portion of the airfoil
core-shaped cavity C.
[0026] The fugitive tooling liners typically are injection molded
to shape using a suitable polymer, although other fugitive liner
materials can be used including, but not limited to, polylactone,
polyvinyl, and starch-modified polymers.
[0027] The core tooling can include one or more optional fugitive
inserts 30a-30h placed between the tooling liners 20a, 20b and/or
on the inner surfaces 20c of the tooling liners 20a, 20b, FIGS. 2
and 5. The inserts 30a-30h extending between the tooling liners can
be used to form holes, passages and other through-openings in the
ceramic core. The inserts 30a-30h disposed on the surface 20c of
the tooling liners can be used to form core surface features such
as ribs, channels, shrouds, chambers, back-locked features (e.g. a
dovetail joint) not easily formed in a complicated end product
core.
[0028] The fugitive inserts alternately can be provided as fugitive
subassemblies where different inserts are provided in one
subassembly to form through-passages and core surface features as
shown for inserts 30a and 30b in FIG. 2. The fugitive inserts can
be injection molded on the liner surface 20c as shown for insert
30h in FIG. 2, or as part of the liner surface as shown for insert
30g in FIG. 2. The inserts 30a, 30b can be assembled from
separately injection molded insert elements and located on the
liner surface 20c. The fugitive inserts can comprise or be
incorporated as a part of the final molded core to produce a
composite core having certain fugitive features such as spacers,
layers, through-extending fastener, and the like for use in
subsequent investment mold forming processing.
[0029] The fugitive inserts can include connection features to the
liner surface 20c that may be normal (perpendicular) to the liner
surface 20c as shown for insert 30d in FIG. 2. The fugitive inserts
can also include connection features to the liner surface 20c that
may be normal (perpendicular) to the parting plane PP of the cavity
C as shown for inserts 30e, 30f in FIG. 2.
[0030] A ceramic core is produced pursuant to a method embodiment
of the invention by introducing a fluid ceramic core material, such
as a ceramic slurry, typically under pressure into the core-shaped
cavity C formed by the fugitive tooling liners 20a, 20b in the
back-up body 10. The fluid ceramic material is introduced via a
passage CP (FIG. 1B) in the back-up body 10. After the ceramic core
is molded and set, the molded green (unfired) core is removed by
opening the parts 10a, 10b of the back-up body 10 and removing the
molded green ceramic core. The fugitive tooling liners 20a, 20b are
removed from the back-up die body with the molded green ceramic
core, FIG. 3, or separately from the molded green core and then
discarded (not re-used). The optional fugitive inserts 30a-30h can
be removed from the molded green ceramic core by thermal treatment
to melt and/or vaporize them, solvent treatment to dissolve them,
or other process that selectively removes the inserts from the
molded core. A final core 100 remains as shown in FIG. 4 with core
interior and exterior features 100a-100h formed by the respective
inserts 30a-30h that have been selectively removed.
[0031] The next ceramic core is produced using fresh (un-used)
tooling liners 20a, 20b and optional fresh tooling inserts 30. That
is, the fugitive tooling liners and inserts can be used in one
production cycle (e.g. ceramic injection cycle) to make a single
ceramic core and then replaced with fresh (un-used) tooling liners
and optional inserts. Alternately, the fugitive tooling liners may
be left in the back-up body 10 and reused if the tooling liners are
in acceptable condition to this end. That is, the fugitive tooling
liners and inserts can be used in multiple production cycles (e.g.
ceramic slurry injection cycles) to make multiple ceramic cores and
then replaced with fresh (un-used) tooling liners and optional
inserts when the tooling liners are not longer in acceptable
condition to this end. However, when back-locked core features are
produced, the tooling liners are used only in one production cycle
since they are destroyed to separate them from the core.
[0032] It will be apparent to those skilled in the art that various
modifications and variations can be made in the embodiments of the
present invention described above without departing from the spirit
and scope of the invention as set forth in the appended claims.
* * * * *