U.S. patent application number 13/747653 was filed with the patent office on 2014-07-24 for quasi self-destructive core for investment casting.
This patent application is currently assigned to SIKORSKY AIRCRAFT CORPORATION. The applicant listed for this patent is SIKORSKY AIRCRAFT CORPORATION. Invention is credited to James S. Giampapa, John H. Meeson, JR., Shihong G. Song.
Application Number | 20140202650 13/747653 |
Document ID | / |
Family ID | 49709475 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140202650 |
Kind Code |
A1 |
Song; Shihong G. ; et
al. |
July 24, 2014 |
QUASI SELF-DESTRUCTIVE CORE FOR INVESTMENT CASTING
Abstract
A composite core for forming a passage in an investment casting
mold is provided including a generally hollow structural element.
The structural element is configured to deform when a force is
applied to an end thereof. A rigid shell element is formed about
the structural element. The shell element extends beyond both an
interior surface and an exterior surface of the structural element.
The shell element is configured to shatter when the structural
element deforms.
Inventors: |
Song; Shihong G.; (Cheshire,
CT) ; Giampapa; James S.; (Oxford, CT) ;
Meeson, JR.; John H.; (Trumbull, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIKORSKY AIRCRAFT CORPORATION |
Stratford |
CT |
US |
|
|
Assignee: |
SIKORSKY AIRCRAFT
CORPORATION
Stratford
CT
|
Family ID: |
49709475 |
Appl. No.: |
13/747653 |
Filed: |
January 23, 2013 |
Current U.S.
Class: |
164/23 ; 164/137;
164/228; 164/369 |
Current CPC
Class: |
B22C 9/10 20130101 |
Class at
Publication: |
164/23 ; 164/369;
164/228; 164/137 |
International
Class: |
B22C 9/10 20060101
B22C009/10 |
Goverment Interests
This invention was made with Government support under
N00019-06-C-0081 awarded by the Department of the Navy. The
Government has certain rights in this invention.
Claims
1. A composite core positioned within an investment casting mold to
form a passage, comprising: a hollow structural element configured
to deform when a force is applied to an end thereof; and a rigid
shell element including a plurality of layers of slurry having
particles of varying sizes formed about the structural element, the
shell element extending beyond from an interior surface and to an
exterior surface of the structural element such that the composite
core has a hollow interior extending to adjacent the interior
surface of the structural element, the shell element being
configured to shatter when the structural element deforms.
2. The composite core according to claim 1, wherein the rigid shell
element is integrally formed with the structural element.
3. The composite core according to claim 1, wherein the structural
element comprises a coiled wire.
4. The composite core according to claim 1, wherein a material of
the structural element is substantially identical to a material of
a component to be formed from the investment casting mold.
5. The composite core according to claim 1, wherein the structural
element is generally the same size as the passage being formed.
6. The composite core according to claim 1, wherein the shell
element is formed by curing the layers of slurry to form the rigid
shell element.
7. The composite core according to claim 6, wherein a material of
the slurry is substantially identical to a material of the
investment casting mold.
8. The composite core according to claim 6, wherein the material of
the slurry is ceramic.
9. The composite core according to claim 6, further comprising: a
core element positioned adjacent an interior surface of the
structural element, the core element being configured to melt when
heat is applied during formation of the rigid shell element such
that the structural element retains the general shape of the core
element.
10. (canceled)
11. The composite core according to claim 9, wherein the core
element is a wax element.
12. The composite core according to claim 9, wherein the core
element is a metallic mesh or foil.
13. The composite core according to claim 12, wherein the core
element is coupled to the interior surface of the structural
element.
14. (canceled)
15. (canceled)
16. (canceled)
17. A method for manufacturing a composite core for forming a
passage in an investment casting mold, comprising: forming a
generally hollow structural element configured to deform when a
force is applied to an end thereof; and forming a rigid shell
element about the structural element, the shell element extending
beyond an interior surface and an exterior surface of the
structural element and being configured to shatter when the
structural element deforms.
18. The method according to claim 17, wherein the hollow structural
element is formed about a core element.
19. The method according to claim 18, wherein the rigid shell is
formed by layering slurry particles of various sizes about the
structural element.
20. The method according to claim 18, wherein heat is applied to
the composite core to harden the slurry particles and to melt the
core element.
21. A method for forming a passage in a cast component, comprising:
arranging a composite core into an interior of a mold, the
composite core including: a generally hollow structural element
configured to deform when a force is applied to an end thereof; and
a rigid shell formed about the structural element, the shell
element extending beyond an interior surface and an exterior
surface of the structural element, wherein the shell element is
configured to shatter when the structural element deforms; pouring
material of the component into the mold; curing the material to
form the component; and applying a force to an exposed portion of
the composite core such that the composite core deforms inside the
component.
22. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] Exemplary embodiments of the invention generally relate to
investment casting, and more particularly, to a core for forming a
passage in an investment casting mold.
[0002] Investment casting is a commonly used technique for forming
metallic components having complex shapes and geometries,
especially hollow components such as those used in aerospace
applications for example. The production of an investment cast part
generally involves producing a ceramic casting mold having an outer
ceramic shell with an inside surface corresponding to the shape of
the part, and one or more ceramic cores positioned within the outer
ceramic shell, corresponding to interior passages to he formed
within the part, Molten alloy is introduced into the ceramic
casting mold and is then allowed to cool and to harden. The outer
ceramic shell and ceramic core(s) are then removed to reveal a cast
part having a desired external shape and hollow interior passages
in the shape of the ceramic core(s).
[0003] In comparison to other processes, for example sand casting
or permanent mold casting, investment casting provides flexibility
while maintaining tight tolerances. In particular, controlled
solidification investment casting (CSIC) uses rapid directional
cooling to enhance microstructure and mechanical properties. CSIC,
therefore, may be useful for an expanded range of applications,
particularly in the aerospace industry. However, investment casting
is limited by the design of passages within the mold. Unlike a sand
core used in a sand casting process, the ceramic cores used in CSIC
are difficult to remove or destroy without affecting the molded
part. As a result, the process of designing passages severely
restricts the use of CSIC for applications requiring complex cored
passages.
BRIEF DESCRIPTION OF THE INVENTION
[0004] According to one embodiment of the invention, a composite
core for forming a passage in an investment casting mold is
provided including a generally hollow structural element. The
structural element is configured to deform when a force is applied
to an end thereof. A rigid shell element is formed about the
structural element. The shell element extends beyond both an
interior surface and an exterior surface of the structural element.
The shell element is configured to shatter when the structural
element deforms.
[0005] According to one embodiment of the invention, a preform for
making a composite core configured for use in an investment casting
mold is provided including a generally hollow structural element.
The structural element is configured to deform when a force is
applied to an end thereof. A core element having a shape is
positioned adjacent an interior of the structural element. The core
element is configured to melt when heat is applied to the preform
such that the structural element retains the shape of the core
element.
[0006] According to yet another embodiment of the invention, a
method for manufacturing a composite core for forming a passage in
an investment casting mold is provided including arranging a core
element adjacent an interior surface of a generally hollow
structural element to form a preform. Slurry having particles of
varying sizes is layered about the structural element. Heat is then
applied to the preform.
[0007] According to another embodiment, a method of forming a
passage in a cast component is provided including arranging a
composite core into an interior of a mold. Material of the
component is then poured into the mold. The material is cured to
form the component. A force is then applied to an exposed portion
of the composite core such that the composite core deforms inside
the component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The subject matter, which is regarded as the invention, is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0009] FIG. 1 is a cross-sectional view of a composite core
according to an embodiment of the invention;
[0010] FIG. 2 is a cross-sectional view of a preform according to
an embodiment of the invention;
[0011] FIG. 3 is side view of a structural element of the preform
according to an embodiment of the invention;
[0012] FIG. 4 is a perspective view of a preform including layers
of slurry according to an embodiment of the invention; and
[0013] FIG. 5 is a cross-sectional view of a component formed from
an investment casting mold having a passage formed by a composite
core according to an embodiment of the invention.
[0014] The detailed description explains embodiments of the
invention, together with advantages and features, by way of example
with reference to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0015] With reference now to FIG. 1, a cross-section of a composite
core 20 for forming a passage in an investment casting mold is
illustrated. When inserted into a mold (not shown), the composite
core 20 includes a generally hollow structural element 40 and a
shell element 60 arranged about the exterior 46 of the structural
element 40. The structural element 40 is configured to deform, and
therefore break the shell element 60 coupled thereto, when a force
is applied to an end 42 (FIG. 2) of the structural element 40.
[0016] The composite core 20 is formed using a preform 30,
illustrated in more detail in FIG. 2. The preform 30 includes the
generally hollow structural element 40 as well as a core element 50
positioned adjacent the interior surface 44 of the structural
element. The structural element 40 may be pre-formed and the core
element 50 inserted into the hollow center 47 of the structural
element 40, or alternatively, the structural element 40 may be
formed around the exterior of the core element 50.
[0017] An example of the structural element 40, shown in FIG. 3, is
the general size of a passage being formed within an investment
casting mold. The material used to form the structural element 40
is selected based on the material of the component being cast. For
example, the material of the structural element 40 may be the same
alloy as the component being cast. Exemplary metallic materials
include, but are not limited to, steel, copper, and nickel for
example. In the illustrated embodiment, the structural element 40
is fabricated from a coiled wire 48 such that the structural
element 40 behaves in a manner similar to a tensile or compression
spring. The specifications of the wire 48 are selected to
facilitate contact between the structural element 40 and the core
element 50, as well as the ultimate breakdown of the composite core
20. As a result, the cross-section of the wire 48 may be any of a
variety of shapes, such as circular, square, triangular, or
trapezoidal for example, and the coils of the wire 48 need not be
evenly spaced as shown. Considerations for the strength and
ductility of the structural element 40 include the ability of the
structural element 40 to support itself once coupled to the core
element 50, the ability of the structural element 40 to support the
composite core 20 once the shell element 60 is formed, and the
ability of the structural element 40 to deform when a force is
applied thereto.
[0018] The core element 50 acts as a base to support the outer
shell element 60 as it is formed about the structural element 40.
The core element 50 is made from a material configured to melt
during the formation of the composite core 20, prior to the casting
process, or during the casting process. In one embodiment, the core
element 50 is a wax core, the contour of which is substantially
similar to a passage being formed in a mold. In another embodiment,
the core element 50 is a metallic mesh or foil, for example made
from the same material as the working metal to be poured into the
investment casting mold. The metallic mesh or foil 50 is bonded to
the interior surface 44 of the structural element 40, such as
through a brazing process for example. The gauge of the foil or
mesh 50 is selected to support the shell element 60 as it is formed
about the structural element 40. Once the metallic mesh or foil 50
and the structural element 40 are coupled, the contour of the
preform 30 may be altered to a desired shape.
[0019] After the preform 30 is assembled, the outer shell element
60 is formed, for example through a shelling process. As
illustrated in FIG. 4, the preform 30 is coated with a slurry 62
having particles of varying sizes. In one embodiment, the material
of the slurry 62 used to form the outer shell 60 is substantially
identical to the material used to form the investment casting mold,
such as ceramic for example. Alternatively, the material of the
slurry 62 may be modified to facilitate breakdown of the outer
shell 60 when a force is applied to the structural element 40. The
slurry 62 is arranged in a plurality of layers extending outwardly
from the surface 52 of the core element 50 to at least the outer
surface 46 of the structural element 40 such that the structural
element 40 and the shell element 60 are integrally formed. In one
embodiment, for example where the core element 50 is a wax core,
the surface 52 of the core element 50 may be dipped in the slurry
62 before being inserted into the structural element 40, to aid in
the formation of an inner surface of the shell element 60. As a
result, slurry 62 is positioned about the structural element 40
such that when the composite core 20 is formed, the shell element
60 extends beyond both the inner diameter 44 and the outer diameter
46 of the structural element 40 (see FIG. 1).
[0020] After layering the slurry 62 about the structural element
40, the slurry 62 is hardened, such as by firing the preform 30 in
an oven or kiln for example. Heat causes the slurry 62 to
strengthen and solidify into a cured, rigid, shell element 60. The
core element 50 is designed to melt, or otherwise degrade during
the making of the composite core 20, or during the formation of the
finished component. Therefore, application of heat transforms the
preform 30 to a composite core 20, having a generally hollow cross
section that allows the structural element 40 and the shell element
60 to be easily removed. When the composite core 20 is formed, the
outer surface 64 of the shell element 60 may be substantially
uniform, or alternatively, may include slight variations, such as
waves or grooves for example.
[0021] Referring now to FIG. 5, a component 80 formed using an
investment casting mold and at least one composite core 20 is
illustrated. To remove the composite core 20 from a passage 82 of
the component 80, a portion of the shell element 60 is broken to
reveal an end 42 of the structural element 40. A force is then
applied to the exposed end 42, causing the structural element to
deform 40. Because the shell element 60 is formed about the
structural element 40, deformation thereof causes the brittle shell
element 60 to shatter and break away from coiled wire 48 of the
structural element 40. The pieces of the shell element 60 and the
structural element 40 may then be easily removed from the passage
82 of the component 80.
[0022] The composite core 20 may be constructed to create a complex
cored passage within an investment casting mold, thereby expanding
the range of applications to which controlled solidification
investment casting (CSIC) may be applied. Further, by incorporating
waves or grooves into the outer surface 64 of the shell element 60,
the passage 82 can have specific patterns such as rifling. The
rapid and directional solidification of the investment casting
process will result in high quality castings having enhanced
microstructures. Because a significant portion of the CSIC process
is automated, more stringent quality control measures may be
implemented to improve and stabilize the casting process. Forming
parts that were previously too complex using a CSIC process will
reduce both scrap rates and production cycle time.
[0023] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
* * * * *