U.S. patent application number 11/423992 was filed with the patent office on 2007-06-14 for soluble casting core for metal matrix composite components and method of producing thereof.
This patent application is currently assigned to U.S. GOVERNMENT, REPRESENTED BY SECRETARY OF THE ARMY. Invention is credited to James A. Cornie, Stephen S. Cornie, Shiyu Zhang.
Application Number | 20070131374 11/423992 |
Document ID | / |
Family ID | 37233306 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070131374 |
Kind Code |
A1 |
Zhang; Shiyu ; et
al. |
June 14, 2007 |
Soluble Casting Core For Metal Matrix Composite Components and
Method of Producing Thereof
Abstract
A process for manufacturing a soluble casting core for use in
casting complex shaped metal matrix composite components. The
soluble casting core is generated by a sequence of steps which
provide a molten slurry mixture composed of an alkali metal salt
such as sodium carbonate and a plurality of ceramic particulates
such as magnesium oxide dispersed therein. After heating and mixing
the slurry mixture is solidified in a mold pattern to form a
casting core configured to generate a complex shaped component
during a casting process. The soluble casting core is used for
casting molten metal alloys therein, without failure of the casting
surfaces and forming of a complex shaped metal matrix composite
component. The soluble casting core is readily dissolved and
separated from the soluble casting core by immersing the core mold
in heated water and/or exposing to steam, without damage to the
metal matrix composite component.
Inventors: |
Zhang; Shiyu; (Cambridge,
MA) ; Cornie; James A.; (Cambridge, MA) ;
Cornie; Stephen S.; (Watertown, MA) |
Correspondence
Address: |
DEPARTMENT OF THE ARMY;LEGAL OFFICE
AMSAM - L - G - I
U.S. ARMY AVIATION & MISSILE COMMAND
REDSTONE ARSENAL
AL
35898-5000
US
|
Assignee: |
U.S. GOVERNMENT, REPRESENTED BY
SECRETARY OF THE ARMY
US Army Aviation and Missile Command, Legal Office AMSAM-L-G-I,
5300 Martin Road
Redstone Arsenal
AL
|
Family ID: |
37233306 |
Appl. No.: |
11/423992 |
Filed: |
June 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11124512 |
Apr 29, 2005 |
|
|
|
11423992 |
Jun 14, 2006 |
|
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Current U.S.
Class: |
164/6 ; 523/139;
524/425 |
Current CPC
Class: |
B22D 29/002 20130101;
B22C 9/106 20130101; B22C 9/105 20130101 |
Class at
Publication: |
164/006 ;
523/139; 524/425 |
International
Class: |
B22D 7/10 20060101
B22D007/10; B22C 1/22 20060101 B22C001/22 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] The invention described herein may be manufactured, used and
licensed by or for the Government for governmental purposes without
the payment to the inventors and/or the assignee of any royalties
thereon.
Claims
1-16. (canceled)
17. A casting core composed of soluble material for use in casting
a complex shaped metal component, comprising: a solidified mold
pattern composed of a water soluble metal salt having a plurality
of ceramic particulates in a selected continuous size range
dispersed throughout, said solidified mold pattern formed to
include a designed core shape configured to substantially duplicate
a complex shaped metal component; whereby upon said solidified mold
pattern being used to cast the complex shaped metal component, said
solidified mold pattern is readily separated from the complex
shaped metal component by dissolution in heated water.
18. The casting core of claim 17 wherein said water soluble metal
salt includes a sodium carbonate compound composing between about
50% to about 97% by weight percentage of said solidified mold
pattern.
19. The casting core of claim 18 wherein said plurality of ceramic
particulates in said selected continuous size range includes a
plurality of magnesium oxide particulates having a powder size
selected from the range of between about 5 microns to less than 150
microns, said plurality of magnesium oxide particulates being
evenly disposed throughout said solidified mold pattern.
20. The casting core of claim 19 wherein said plurality of
magnesium oxide particulates composing between about 3% to about
50% by weight percentage of said solidified mold pattern.
21. A solidified casting core for casting a complex shaped metal
component, comprising: water soluble metal salt composed of molten
sodium carbonate in a weight percentage of about 50% to about 97%;
and ceramic particulates composed of magnesium oxide particulates
in a weight percentage of about 3% to about 50%, said magnesium
oxide particulates having a powder size selected in a selected
continuous size range of between about 5 microns to about 140
microns.
22. The solidified casting core of claim 21, wherein said water
soluble metal salt includes a proportion of about 95 parts of
molten sodium carbonate, and said ceramic particulates include a
proportion of about 5 parts of magnesium oxide particulates having
the powder size of between about 5 microns to about 140 microns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to methods and materials for
manufacture of casting cores utilized to form complex metal
components. More specifically, the present invention relates to
methods of manufacture of casting cores composed of soluble
materials mixed with ceramic materials for casting complex metal
components.
[0005] 2. Description of the Related Art
[0006] Conventional investment casting methods typically utilize
casting cores composed of machined graphite or steel for
manufacture of relatively non-complex shapes. Use of molds lacking
the need for expensive and time-consuming machining of metal
compounds is preferred to provide cost-effective production of a
wide range of complex metal matrix composite (MMC) components. A
multitude of technological advances in the automobile and aerospace
industries, and in the field of generating exotic composite
materials have led to the need for casting molds which are capable
of forming complex shaped and structurally rigid MMC components by
known pressure molding processes without the need for machining of
the casting mold.
[0007] Benefits have been identified in the use of a hardened salt
compound as a non-machined mold core utilized for pressure molding
of complex components, as explained in U.S. Pat. No. 4,904,423,
issued to Foreman et al. Methods for pressure infiltration casting
have been disclosed for generation of complex metal matrix
composite components, as explained in U.S. Pat. No. 6,360,809,
issued to J. A. Cornie, et al. As disclosed in U.S. Pat. No.
6,776,219, issued to J. A. Cornie, et al. (hereinafter, the '219
patent), use of graphite or steel molds are excessively expensive
when the molds must be machined into complex or intricate shapes.
The '219 patent discloses a method and materials for preparing
investment molds useful in pressure infiltration casting of near
net-shape metal or MMC components. The investment mold materials
disclosed in the '219 patent include commercially available
castable refractory cement materials modified by the addition of
magnesium oxide in order to maintain the stability of the
investment mold during pressure infiltration casting with molten
metal. The '219 patent discloses use of other refractory materials
including alumina, silica, magnesia, graphite, feldspar, and other
refractory materials which are closely packed to form a dense, low
porosity investment mold. The '219 patent does not disclose use of
a molten salt such as sodium carbonate mixed with ceramic
particulates, which, when solidified into a casting core, is
impermeable when subjected to molten metal and is readily dissolved
after casting when exposed to non-corrosive solvents such as water
for separating the casting core from a cast MMC component.
[0008] Accordingly, there is a need for a slurry mixture composed
of non-reactive soluble materials mixed with ceramic particulates,
with the slurry mixture being readily solidified into a complex
shaped mold which is resistant to thermal expansion during exposure
to molten metal in pressurized casting. Further, a need exists for
a process of producing a casting core composed of a mixture of a
metal salt and ceramic particulates which, when solidified,
provides casting surfaces impervious to molten metals during
pressurized casting. In addition, a need exists for a method of
manufacturing a casting core composed of selected materials which
are impermeable to molten metals during pressure casting to form a
complex composite component, while the casting core is rapidly
separated from the complex composite component at completion of the
casting process by exposure to a non-reactive solvent.
BRIEF SUMMARY OF THE INVENTION
[0009] A process of manufacturing a soluble casting core mold is
disclosed for the production of complex shaped MMC components which
may include hollow portions therein. The soluble casting core is
generated by a sequence of steps which provide a molten slurry
mixture composed of an alkali metal salt having ceramic particulate
materials dispersed therein. After sufficient mixing, the slurry
mixture is solidified in a mold pattern to form a casting core mold
configured to generate a complex shaped component during a casting
process. The casting core mold is utilized for casting molten metal
alloys to form a complex shaped metal matrix composite (MMC)
component which is readily separated from the casting core mold by
dissolving the core mold by immersion in heated water or exposure
to steam.
[0010] The process includes providing molten sodium carbonate to
form the basic component of the slurry mixture in which a ceramic
particulate material is dispersed evenly therein. One embodiment
includes magnesium oxide particulates mixed throughout the molten
sodium carbonate salt in a mixing ratio including about 1 part
magnesium oxide mixed with about 3 parts molten sodium carbonate.
Alternative ratios of magnesium oxide mixed with molten sodium
carbonate are utilized to adjust the density of the casting core
slurry and to adjust the coefficient of thermal expansion (CTE) of
the solidified casting core mold to approximate the CTE of the
molten metal composite material selected to form the MMC component.
The magnesium oxide particulates serve as heterogeneous nucleation
agents within the molten sodium carbonate, and further serve to
reduce the grain size of the sodium carbonate salt during
solidification of the molten slurry mixture thereby resulting in a
dense core mold when the molten sodium carbonate and magnesium
oxide mixture is solidified after being poured in a preheated mold
pattern formed of metal such as stainless steel or graphite. The
dense core mold formed is resistant to surface etching and mold
failure upon contact with molten metal during pressure infiltration
casting.
[0011] The process further includes the casting core slurry mixture
being solidified in a preheated mold pattern thereby attaining a
casting core mold having smooth surfaces impervious to molten metal
during high temperature and pressure casting. Upon removal of the
preheated mold pattern from the solidified casting core mold, the
non-metal casting core mold is easily machined as needed in order
to form exactly configured surfaces utilized as a complex shape
mold during pressure infiltration casting with molten metals.
[0012] The process of manufacturing water soluble casting cores
further includes applying surface coating materials lacking water
contamination onto the contact surfaces of the casting core mold. A
step of casting proceeds with the casting core mold filled with
liquid aluminum, magnesium, or other alloy matrix composites,
preferably utilizing a pressure infiltration casting process. After
cooling, the solidified complex shaped MMC component is separated
from the casting core mold by exposure of the core mold to a
non-reactive solvent such as steam and/or heated water, resulting
in dissolution of the casting core mold and separation from the MMC
component. Additional machining of the MMC component is not
typically required due to the ability of the casting core mold to
accurately duplicate each surface contour for generation of the
complex shaped MMC components. The complex shaped MMC components
generated by the process of manufacture are utilized in various
industries including production of automobiles, aircraft and
spacecraft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention is illustrated in the drawings in
which like element numbers represent like parts in each figure,
including:
[0014] FIG. 1 is a process flow diagram for manufacturing soluble
casting core molds of the present invention, for use in production
of complex shaped MMC components.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to FIG. 1, a process 10 of manufacturing a
soluble casting core mold 40 is disclosed, with the soluble casting
core mold 40 being composed of a salt material which is water
soluble and mixed with metal oxide particulates forming a slurry
mixture when molten which is readily poured for casting, and is
impervious to molten metal when the slurry mixture is solidified
into the core mold which is readily dissolved when exposed to
heated water in order to free a complex shaped cast MMC component
50 formed within the soluble casting core mold 40. The soluble
casting core mold 40 is utilizable in pressure casting processes
such as a pressure infiltration casting process. Benefits of
utilizing the soluble casting core mold 40 include the core mold is
impermeable when exposed to molten metal under typical pressure and
temperatures used for pressure infiltration casting. Further, the
core mold is readily dissolved in non-corrosive solutions such as
heated water for rapid removal of the casting core mold 40 from the
complex shaped cast MMC component 50 generated by the process 10 of
manufacturing the soluble casting core mold 40.
[0016] The selected materials and steps utilized in the process 10
of manufacturing the soluble casting core mold 40 include providing
and heating 12 a soluble salt such as sodium carbonate 32 to form a
molten sodium carbonate base solution referred hereinafter as a
molten slurry 36. Sodium carbonate is selected due to its low cost,
higher melting point, ease of flow when molten, and its dissolution
when exposed to heated water. A step of mixing 14 includes
selecting a ceramic particulate such as magnesium oxide
particulates 34, and mixing the magnesium oxide particulates with
the molten slurry 36. One embodiment for the process 10 includes
mixing magnesium oxide particulates having a powder size of between
5 microns to about 150 microns throughout the molten sodium
carbonate. One proportion for mixing 14 includes adding between
about 5 parts of magnesium oxide particulates to about 95 parts of
molten sodium carbonate. Alternate proportions for mixing include a
range of between 5 parts of magnesium oxide particulates up to
about 30 parts of magnesium oxide particulates, mixed with between
about 95 parts of molten sodium carbonate, or reduced to about 70
parts of molten sodium carbonate. An alternate proportion range for
the molten slurry mixture being composed of molten sodium carbonate
by weight percentage in a range of between about 50% to about 97%,
and mixing in magnesium oxide particulates by weight percentage in
a range of between about 50% to about 3%. The molten sodium
carbonate mixed with magnesium oxide particulates forms a casting
slurry mixture 36 readily pourable 18 after a step of providing 16
a mold pattern 38 composed of metal such as stainless steel and/or
graphite, or a similar high temperature resistant material such as
ceramic compounds utilized by those skilled in the art for molds
used in pressure infiltration casting processes.
[0017] During the manufacturing process 10, the step of providing
16 further includes a step of preheating the mold pattern 38 to a
temperature between about 400.degree. C. to about 650.degree. C.
before or simultaneously with the molten slurry mixture 36 being
poured therein. An alternative step of preheating the mold pattern
38 includes superheating the mold pattern 38 to a temperature
between about 850.degree. C. to about 950.degree. C. before the
molten slurry mixture 36 is poured therein. The mold pattern 38 is
configured to include at least one inlet for rapid receipt of the
poured molten slurry mixture 36 in sufficient volume to fill the
mold pattern 38 before solidification of the slurry mixture 36
occurs during a step of cooling 20 for the slurry mixture. Further,
the mold pattern 38 is configured of sufficient volume and in the
preferred design core shape configuration of which the molten
slurry mixture adopts upon cooling 20 of the molten slurry mixture
36 to form a solidified casting core mold 40 which can be readily
dissolved in heated water. Upon solidification, the casting contact
surfaces of the casting core mold 40 are preferably impermeable
during an upcoming step of infiltrating 24 with aluminum or similar
casting metals heated within typical casting temperature ranges
utilized for the pressure infiltration casting processes. In a step
of removing 22, the casting core mold 40 is removed from contact
with the mold pattern 38. The casting core mold 40 preferably
retains complex shaped surfaces 42 configured to include inwardly
extending channels or voids to provide the preferred mold pattern
38.
[0018] A step of infiltrating 24 includes pouring molten metal such
as aluminum and/or magnesium alloys in matrix composite solutions
into the solidified casting core mold 40. The step of infiltrating
24 further includes the poured molten metal being retained by the
casting core mold 40 without casting surface breakthrough, until
the molten metal solidifies to form a cast metal matrix component
50. Pressures utilized by pressure infiltration casting into the
casting core mold 40 include pressurization of molten metal for
infiltration casting at hydrostatic pressures up to about 75
atmospheres. One preferred pressure for the infiltration casting of
molten metals in the casting core mold 40 is about 68
atmospheres.
[0019] After removing 22 the casting core mold 40 from the mold
pattern 38, a step of machining 23 may be utilized for machining
and/or surface polishing of the casting surfaces 42 of the casting
core mold 40. The step of machining 23 provides for exact
duplication of the plurality of casting surfaces of the casting
core mold 40 with a preferred design for the MMC component 50
having outer and inner contours and/or interior void spaces 52,
when manufactured with the casting core mold 40. Due to the casting
surfaces 42 of the casting core mold 40 being composed of
solidified sodium carbonate providing a base solution having a
plurality of magnesium oxide particulates dispersed therein, the
casting surfaces 42 are readily machined at a lesser expense than
typical machining of molds composed of stainless steel or graphite
materials. An additional step of coating may be included following
the step of machining 23, in order to distribute substantially
impervious coating materials on the plurality of casting surfaces
of the casting core mold 40. The steps of machining 23 and/or
surface coating are completed before the step of infiltrating 24
the molten metal into the casting core mold 40, in order to
minimize leakage of molten metal through, or infiltration into the
coated casting surfaces 42, and to improve the efficiency for
separating the casting core mold 40 upon exposing 26 to heated
water 46 or steam 48, from the solidified cast metal component 50.
The finished complex shaped surface configuration of the solidified
cast metal matrix component 50 is intended to be an exact duplicate
of the designed mold pattern 38, without a requirement for
additional metal machining or surface finishing other than cleaning
the metal matrix component 50.
[0020] The benefits of producing a soluble casting core mold 40
having sodium carbonate as the main core content include sodium
carbonate is widely available and is inexpensive, and sodium
carbonate is readily mixed when in a molten state in any selected
ratio of sodium carbonate and magnesium oxide particulates.
Alternative ratios of magnesium oxide mixed with molten sodium
carbonate are utilized to adjust the density and the CTE of the
solidified casting core mold to approximate the CTE of the molten
metal composite material selected to form the complex shaped MMC
component 50. When dispersed within the molten sodium carbonate,
the magnesium oxide particulates provide: (a) heterogeneous
nucleation agents in the slurry mixture, (b) reduction of the grain
size of the sodium carbonate salt during solidification of the
molten slurry mixture thereby resulting in a dense solidified core
mold, and (c) acceleration for dissolution of the sodium carbonate
material during exposure of the solidified casting core mold 40 to
heated water, steam or a similarly non-corrosive heated liquid. The
dense casting core mold 40 formed is resistant to surface etching
and resistant to core mold failure upon contact with molten metal
during pressure infiltration casting. Further benefits of the
process 10 of manufacturing and utilizing the soluble casting core
mold 40 for generation of complex shaped MMC components 50 include
the core mold being impermeable when exposed to molten metal under
typical pressures and temperatures used for pressure infiltration
casting. Upon completion of the casting process for the complex
shaped MMC component 50 and solidification within the core mold 40,
dissolving 28 the core mold 40 is achieved by immersion in a heated
water solution 46 or another liquid which is not corrosive to the
MMC component 50. In the alternative, the core mold 40 is readily
dissolved 28 by exposure to steam 48 or another superheated liquid
which is not corrosive to the MMC component 50. The step of
dissolving provides for rapid release 30 of the complex shaped MMC
component 50 without damage to the cast metal matrix components of
the complex shaped MMC component 50 and with minimal expense.
[0021] While numerous embodiments and methods of use for this
invention are illustrated and disclosed herein, it will be
recognized that various modifications and embodiments of the
invention may be employed without departing from the spirit and
scope of the invention as set forth in the appended claims.
Further, the disclosed invention is intended to cover all
modifications and alternate methods falling within the spirit and
scope of the invention as set forth in the appended claims.
* * * * *