U.S. patent application number 11/124512 was filed with the patent office on 2006-11-02 for soluble casting core for metal matrix composite components and method of producing thereof.
This patent application is currently assigned to United States of America, represented by Secretary of the U.S. Army, United States of America, represented by Secretary of the U.S. Army. Invention is credited to James A. Cornie, Stephen S. Cornie, Shiyu Zhang.
Application Number | 20060243421 11/124512 |
Document ID | / |
Family ID | 37233306 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243421 |
Kind Code |
A1 |
Zhang; Shiyu ; et
al. |
November 2, 2006 |
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: |
Jack K. Greer, JR.;U.S. Army Aviation & Missile Command, Legal Office
AMSAM-L-G-I, Bldg. 5300
5300 Martin Road, 4th Floor
Redstone Arsenal
AL
35898-5000
US
|
Assignee: |
United States of America,
represented by Secretary of the U.S. Army
|
Family ID: |
37233306 |
Appl. No.: |
11/124512 |
Filed: |
April 29, 2005 |
Current U.S.
Class: |
164/522 ;
164/132; 164/369 |
Current CPC
Class: |
B22C 9/105 20130101;
B22C 9/106 20130101; B22D 29/002 20130101 |
Class at
Publication: |
164/522 ;
164/132; 164/369 |
International
Class: |
B22C 1/00 20060101
B22C001/00; B22C 9/10 20060101 B22C009/10; B22D 29/00 20060101
B22D029/00 |
Claims
1. A method of producing a soluble casting core for casting a
complex shaped metal composite component, comprising the steps of:
(a) heating a slurry composed of a water soluble metal salt to form
a molten slurry; (b) mixing a plurality of ceramic particulates
selected from a singular continuous size range of less than 150
microns, with sad molten slurry to form a molten slurry mixture;
(c) providing a mold pattern having a cavity therein and having a
designed core shape substantially matching the complex shaped metal
composite component, said step of providing including preheating
said mold pattern to a selected temperature; (d) pouring said
molten slurry mixture Into said mold pattern; (e) cooling said
molten slurry mixture within said mold pattern, said step of
cooling forming a solidified casting core having a plurality of
casting surfaces configured in duplication of said designed core
shape; (f) removing sad solidified casting core from said mold
pattern; (g) pressure infiltrating molten metal into said
solidified casting core, said step of pressure infiltrating
including said molten metal being retained by said solidified
casting core for a sufficient time for solidification of said
molten metal forming a cast metal composite component; (h) exposing
said solidified casting core to heated liquid by immersing said
casting core in said heated liquid; and (i) dissolving said
solidified casting core by continued exposure to heated liquid
thereby releasing the metal composite component having said
designed core shape.
2. The method of claim 1, further comprising: (ii) machining said
solidified casting core following said step of removing, said step
of machining providing substantially exact duplication of said
plurality of casting surfaces in relation to said selected core
shape; and (iii) coating said plurality of casting surfaces of said
solidified casting core with coating materials forming
substantially impervious casting surfaces.
3. The method of claim 2 wherein said step of heating said slurry
including a sodium carbonate compound maintained as said molten
slurry.
4. The method of claim 3 wherein said step of mixing said plurality
of ceramic particulates includes adding a plurality of magnesium
oxide particulates having a powder size selected from said singular
continuous size range of between about 5 microns to about 150
microns.
5. The method of claim 4 wherein said step of mixing further
including said molten slurry mixture composed of sodium carbonate
by weight percentage of between about 50% to about 97%, and mixing
in said magnesium oxide particulates by weight percentage of
between about 3% to about 50%.
6. The method of claim 1 wherein said step of providing said
preheated mold pattern including said preheated mold pattern being
composed of stainless steel or graphite and having at least one
configuration having an internal void therein.
7. The method of claim 1 wherein said step of providing said mold
pattern preheated to said selected temperature further including a
step of preheating said mold pattern to a temperature selected from
a range of between about 400.degree. C. to about 650.degree. C.
before said step of pouring said molten slurry mixture into sad
mold pattern.
8. The method of claim 1 wherein said step of providing said mold
pattern preheated to said selected temperature further including a
step of superheating said mold pattern to a temperature selected
from a range of between about 850.degree. C. to about 950.degree.
C. before said step of pouring said molten slurry mixture into said
mold pattern.
9. A process for manufacturing a casting core for casting a complex
shaped metal composite component, comprising the steps of: (a)
heating a slurry composed of a water soluble metal salt to form a
molten slurry; (b) mixing a plurality of ceramic particulates
selected from a continuous size range of less than about 140
microns with said molten slurry to form a molten slurry mixture;
(c) providing a mold pattern having a cavity therein and having a
designed core shape substantially matching the complex shaped metal
composite component, said step of providing including preheating
said mold pattern to a selected temperature; (d) pouring said
molten slurry mixture into said mold pattern; (e) cooling said
molten slurry mixture within said mold pattern, said step of
cooling forming a solidified water soluble casting core having a
plurality of casting surfaces configured to match said designed
core shape; and (f) removing said solidified casting core from said
mold pattern, whereby said solidified casting core is water soluble
and configured for pressure casting the complex shaped metal
composite component.
10. The process of claim 9, further comprising: (i) machining said
solidified casting core following said step of removing, said step
of machining providing exact duplication of said plurality of
casting surfaces with said selected core shape; (ii) coating said
plurality of casting surfaces of said solidified casting core with
coating materials forming substantially impermeable casting
surfaces; (iii) infiltrating molten metal into said solidified
casting core, said step of infiltrating including said molten metal
being retained by said solidified casting core until said molten
metal is solidified in the cast metal composite component; (iv)
exposing said solidified casting core to superheated liquid; and
(v) dissolving said solidified casting core by continued exposing
to superheated liquid thereby providing the metal composite
component having said designed core shape.
11. The process of claim 9 wherein said step of heating said slurry
composed of said water soluble metal salt including a sodium
carbonate compound maintained in said molten slurry.
12. The process of claim 11 wherein said step of mixing said
plurality of ceramic particulates includes selecting magnesium
oxide particulates having a powder size selected from said
continuous size range of between about 5 microns to about 140
microns.
13. The process of claim 12 wherein said step of mixing her
including said molten slurry mixture composing said sodium
carbonate compound by weight percentage of between about 50% to
about 97%, and composing said magnesium oxide particulates by
weight percentage of between about 3% to about 50%.
14. The process of claim 9 wherein said step of providing said mold
pattern including said mold pattern being composed of stainless
steel or graphite and having a complex shaped configuration having
an internal void therein.
15. The process of claim 14 wherein said step of providing said
mold pattern preheated to said selected temperature further
including preheating said mold pattern to a temperature selected
from a range of between about 400.degree. C. to about 650.degree.
C. before said step of pouring said molten slurry mixture into said
mold pattern.
16. The process of claim 14 wherein said step of providing said
mold pattern preheated to said selected temperature further
including a step of superheating said mold pattern to a temperature
selected from a range of between about 850.degree. C. to about
950.degree. C. before said step of pouring said molten slurry
mixture into said mold pattern.
17. A casting core composed of soluble material for use in casting
a complex shaped metal component, comprising: a mold pattern
composed of a water soluble metal salt having a plurality of
ceramic particulates in a selected continuous size range dispersed
throughout, said mold pattern being solidified in 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 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 a 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 about 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. The process of claim 9, wherein said solidified casting core
includes: water soluble metal salt composed of 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 said selected
continuous size range of between about 5 microns to about 140
microns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] 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.
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 CAE 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 when 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.
* * * * *