Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PRODUCTION OF A CAST COMPONENT
This application is a divisional application of Canadian Patent No. 2,714,871
which is a
divisional of Canadian Patent No. 2,628,350 filed in Canada on November 19,
1999.
BACKGROUND OF THE INVENTION
The present invention relates generally to a method and apparatus for the
production
of a cast component. More particularly, in one embodiment of the present
invention, a single cast single crystal structure is formed by the directional
solidification
of a superalloy within a precision casting mold containing a starter seed.
Although the
invention was developed for casting gas turbine engine components, certain
applications
may be outside of this field.
The performance of a gas turbine engine generally increases with an increase
in the
operating temperature of a high temperature working fluid flowing from a
combustion
chamber. One factor recognized by gas turbine engine designers as limiting the
allowable temperature of the working fluid is the capability of the engine
components to
not degrade when exposed to the high temperature working fluid. The airfoils,
such as
blades and vanes, within the engine are among the components exposed to
significant
thermal and kinetic loading during engine operation.
One cooling technique often utilized in a gas turbine engine component is an
internal network of apertures and passageways. A flow of cooling media is
passed
through the internal passageways of the component, and exhausted onto the
exterior
surface of the component The passage of the cooling media through the internal
passageways provides for heat transfer from the component to the cooling
media.
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A process and apparatus are disclosed in U.S. Patent No. 5,295,530, by which
the production of a high temperature thin wall cast structure is described.
The '530
patent describes a process of pouring a molten metal into a ceramic casting
mold which
is carried on a water-cooled chill plate within a vacuum furnace. The
injection pressure
of the molten metal can be varied over time so that the walls of the casting
mold do not
substantially distort during the process. Thereafter, the molten metal within
the casting
mold is directionally solidified.
Although the prior techniques can produce thin walled cast components with
internal passageways and apertures, there remains a need for an improved
method and
apparatus for casting a component. The present invention satisfies this and
other needs
in a novel and unobvious way.
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SUMMARY OF THE INVENTION
One form of the present invention contemplates an apparatus, comprising: a
metallic seed applicable to grow at least one crystal by directional
solidification of
a molten metal, the starter seed has a portion for receiving the molten metal
thereon
and at least one internal passageway adapted for the passage of a heat
transfer
media.
Another form of the present invention contemplates a metallic seed crystal for
the
use in solidification of a molten metal to an article. The seed crystal,
comprising: a
metallic member having a melt end and a base end with a melt portioh and a non-
melt
portion therebetween, the base end defines a first surface adapted to contact
a heat sink
to transfer heat from the member; and, the melt portion formed at the melt end
and
adapted for receiving molten metal thereagainst, the melt portion has an
unmelted state
with a cross sectional area less than the area of the first surface and a
melted state
wherein the melt portion has a cross sectional area substantially equal to the
first surface
so as not to restrict heat transfer to the base end.
Another form of the present invention contemplates an apparatus for exchanging
heat with a metallic starter seed during the directional solidification of a
molten metal.
The apparatus, comprising: at least one member for mechanically gripping the
metallic
starter seed and maintaining a heat transfer path with the starter seed as the
metal
material solidifies; and a heat transfer sink connected with the at least one
member for
removing heat therefrom.
Yet another form of the present invention contemplates an apparatus,
comprising: a crucible having a discharge; a vacuum furnace having the
crucible
positioned therein for melting metal material within the crucible; a metallic
starter
seed; a casting mold having an opening adapted to receive the starter seed and
an
internal cavity for receiving the molten metal material discharged from the
t discharge, the starter seed is positioned within the opening and
contactable by the
molten metal material received in the internal cavity; and, a heater coupled
with
the starter seed to selectively add energy to the starter seed during a first
period,
and wherein the starter seed is joined to the metal poured in the cavity and
heat is
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withdrawn through the starter seed during the directional solidification of
the metal
material within the cavity.
Yet another form of the present invention contemplates an apparatus for
pouring a molten metal. The apparatus, comprising: a crucible having a bottom
wall member with an aperture formed therethrough; an upstanding first tube
positioned within the crucible and having a first end located around the
aperture
and coupled to the bottom wall member and another second end that is closed,
the
first tube having at least one entrance for allowing the passage of molten
metal
from the crucible to the first tube; an upstanding second tube located within
the
first tube and having one end coupled to the bottom wall member and in fluid
communication with the aperture and another end defining an inlet from the
tube,
the second tube has a first cavity adapted for receiving a volume of molten
metal
therein; and a passageway extending along the second tube for the passage of
the
molten metal from the at least one entrance to the inlet.
Yet another form of the present invention contemplates, a method for
pouring molten metal into a casting mold within a furnace. The method,
comprising: providing a crucible with a discharge aperture and a pour assembly
located within the crucible, the pour assembly including an upstanding outer
tube
positioned around an upstanding inner tube, the inner tube is in fluid
communication with the discharge aperture; melting a metal material within the
crucible to a liquid state; flowing the liquid state metal from the crucible
into a
cavity defined between the outer tube and the inner tube; overfilling the
cavity so
that liquid state metal flows into and fills the inner tube; stopping the
filling of the
inner tube; and discharging the liquid state metal from the inner tube.
Yet another form of the present invention contemplates an apparatus for
pouring a molten metal. The apparatus, comprising: a mechanical housing with a
bottom wall member and an interior volume adapted to hold a molten metal; and
a
molten metal delivery member having a first molten metal inlet end adapted to
receive molten metal from below the surface of the molten metal within the
interior
volume and a second molten metal outlet end with a passageway therebetween, at
least a portion of the delivery member positioned within the mechanical
housing,
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the passageway has a first passageway portion and a second passageway portion
and an
inflection portion wherein the direction of molten metal flow changes, in a
first discharge mode a
first direction of molten metal flow within the first passageway portion is
from the molten metal
inlet to the inflection portion and from the inflection portion through the
second passageway
5 portion in a second direction to said outlet.
Yet another form of the present invention contemplates a casting mold,
comprising: a free
form fabricated ceramic shell, the ceramic shell having a thin first outer
wall defining a cavity
therein that is adapted for receiving a molten metal; a container having a
second outer wall with
an inner surface, wherein the shell is positioned within the container and
spaced from the inner
surface; and at least one support member substantially filling the space
between the first outer
wall and the inner surface and reinforcing said shell.
Yet another form of the present invention contemplates a method, comprising:
providing
a mold having an internal cavity adapted for the receipt of molten metal
therein, the cavity has a
top portion, bottom portion and side portion; insulating the ceramic shell to
minimize heat
transfer through said side portion; placing the mold within an environmental
control chamber;
filling the cavity with molten metal to form a casting defined by the cavity;
and directionally
solidifying the molten metal within the mold by withdrawing energy from one
end of the casting.
Yet another form of the present invention contemplates a method, comprising:
providing
a casting mold having a plurality of layers of a material bonded together to
define a cavity for
receiving a molten metal material therein and an exit in communication with
the cavity; orienting
the casting mold at an inclination; rotating the casting mold to free any
material located within
the cavity and not bonded to one of the plurality of layers of material;
passing the material
located within the cavity out of the cavity and through the exit; and moving
the casting mold
along a pathway; wherein the providing a casting mold includes providing at
least two casting
molds, and which further includes conveying a spacer between the at least two
of the casting
molds.
Yet another form of the present invention contemplates a method, comprising:
forming
an integral ceramic shell by three dimensional printing, the ceramic shell
includes a plurality of
layers of a ceramic material bonded together to define a cavity therein for
receiving a molten
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metal material and at least one exit in fluid communication with the cavity;
orienting the ceramic
shell at an inclination; rotating the ceramic shell about a first axis to free
ceramic material
located within the cavity that is not bonded to one of the plurality of layers
of material; passing
the material located within the cavity out of the cavity and through the at
least one exit; and
moving the ceramic shell along a predetermined pathway; wherein the rotating
includes engaging
a toothed member formed in the casting mold with a member that engages the
toothed member to
rotate the casting mold.
Yet another form of the present invention contemplates a green ceramic casting
mold
system, comprising: a shell having a thin outer wall member with a
substantially smooth as
formed inner surface defining a complex shaped volume adapted for receiving a
molten metallic
material, the thin outer wall member is a layered structure of ceramic
particles bound together by
a polymer binder; and a core positioned within the volume and adapted to
create at least one
passage within the component formed from the molten metallic material received
in the volume,
the core is a layered structure of ceramic particles bound together by an
organic polymer binder.
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One object of the present invention is to provide a unique system for
production of a cast component.
Related objects and advantages of the present invention will be apparent
from the following description.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustrative view of a gas turbine engine.
FIG. 2 is a perspective view of a gas turbine engine blade within the FIG. 1
gas
turbine engine.
FIG. 3 is a plan view of one embodiment of an internal cooling passageway
comprising a portion of the FIG. 2 gas turbine engine blade.
FIG. 4 is a cross section of one embodiment of a cast airfoil having a thin
outer
wall.
FIG. 5 is an illustration of one embodiment of a cast multi-wall structure.
FIG. 6 is an illustration of one embodiment of an atmospheric air/spacecraft
having
a leading edge made with a process according to one aspect of the present
invention.
FIG. 7 is an illustration of one embodiment of a cast valve body.
FIG. 8 is an illustration of the growth of dendrites from a starter seed.
FIG. 9 is an illustrative view of a portion of a casting mold according to one
embodiment of the present invention.
FIG. 10 is an illustrative view of a portion of a casting mold according to
another
embodiment of the present invention.
FIG. 11 is an illustrative view of the casting mold of FIG. 10 upon the
substantial
completion of the build cycle.
FIG. 12 is a flow chart of one embodiment of a method for creating a build
file for
a casting mold system.
FIG. 13 is an illustrative view of the casting mold of FIG. 10 being
fabricated by a
stereolithography process.
FIG. 14 is an illustrative view of the casting mold of FIG. 10 with the
boundaries
defining the layers of the layered build structure amplified.
FIG. 15 is an enlarged illustrative view of a portion of the layered build
structure of
FIG. 14.
FIG. 16 is an illustrative view of an alternate embodiment of a wall structure
comprising a portion of the FIG. 10 casting mold.
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FIG. 17 is an illustrative view of an alternate embodiment of a wall structure
comprising a portion of the FIG. 10 casting mold.
FIG. 18 is an illustrative view of an alternative embodiment of a core
comprising a
portion of the FIG. 10 casting mold.
FIG. 19 is an illustrative view of an alternative embodiment of a core
comprising a
portion of the FIG. 10 casting mold.
FIG. 20 is an illustrative sectional view of an alternative embodiment of a
casting
mold of the present invention.
FIG. 21 is a perspective view of the casting mold of FIG. 20.
FIG. 22 is a sectional view taken along line 22-22 of the casting mold of FIG.
20
FIG. 23 is an illustrative sectional view of another embodiment of a casting
mold
of the present invention.
FIG. 24 is a diagrammatic representation of a casting mold within a furnace
for
sintering the green ceramic mold.
FIG. 25 is an illustration of a free form fabricated integral casting mold
according
to one embodiment of the present invention which further comprises a top
member.
FIG. 26 is a partially fragmented view of a mold container with the integral
casting
mold of FIG. 25 positioned therein.
FIG. 27 is a partially fragmented view of an alternate embodiment of the mold
container of FIG. 26 that further comprises a heating ring.
FIG. 28 is a cross sectional view of FIG. 27 taken along line 28-28.
FIG. 29 is a cross sectional view of an alternate embodiment of the mold
container
of FIG. 27, which further includes a heater.
FIG. 30 is an illustration of a system for removing unbonded material from a
casting mold.
FIG. 31. is an illustrative view of one embodiment of the system of FIG. 30
for
removing the unbonded material from the casting mold.
FIG. 32 is an illustrative view of one embodiment of a casting system of the
present invention.
FIG. 33 is an illustrative sectional view of one embodiment of the casting
apparatus
for casting a component of the present invention.
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FIG. 34 is an illustrative plan view of the FIG. 33 casting apparatus.
FIG. 35 is an illustrative sectional view of an alternate embodiment of the
casting
apparatus for casting a component of the present invention.
FIG. 36 is an illustrative sectional view of an alternate embodiment of the
casting
5 apparatus for casting a component of the present invention.
FIG. 37 is an illustrative sectional view of an alternate embodiment of the
casting
apparatus for casting a component of the present invention.
FIG. 38 is an illustrative perspective view of one embodiment of the heat
transfer
apparatus for transferring energy with a starter seed.
10 FIG. 39 is an illustrative perspective view of the heat transfer
apparatus of FIG. 38,
which further comprises an electrical means for heating the starter seed.
FIG. 40 is an illustrative sectional view of an alternate embodiment of a heat
transfer apparatus for transferring energy with a starter seed located within
a mold
container and the apparatus is in an open position.
FIG. 41 is an illustrative sectional view of the heat transfer device of FIG.
40 in a
closed position.
FIG. 42 is an illustrative sectional view of an alternate embodiment of a heat
transfer apparatus for transferring energy with a starter seed within a
casting mold.
FIG. 43 is an illustrative sectional view of an alternate embodiment of the
heat
transfer apparatus for transferring energy with a starter seed located within
a casting.
FIG. 44 is an illustrative sectional view of an alternate embodiment of a heat
transfer apparatus for removing heat from a casting mold.
FIG. 45 is a perspective view of the heat transfer apparatus of FIG. 44.
FIG. 46A is an illustrative view of a portion of a casting mold having a
metallic
starter seed therein.
FIG. 46B is an illustrative sectional view taken along lines 46-46 of FIG.
46A.
FIG. 47A is an illustrative perspective view of one embodiment of a metallic
starter
seed.
FIG. 47B is an illustrative perspective view of the metallic starter seed of
FIG. 47A
after a quantity of molten metal has passed thereover.
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FIG. 47C is an illustrative perspective view of the metallic starter seed of
FIG. 471B
after an additional quantity of molten metal has passed thereover.
FIG. 48 is an illustrative view of an alternate embodiment of a starter seed
of the
present invention.
FIG. 49 is an illustrative view of a starter seed of the present invention
including a
passage therethrough.
FIG. 50 is an illustrative sectional view of an alternative embodiment of the
molten
metal delivery system located within a casting apparatus.
FIG. 51 is an illustrative sectional view of an alternate embodiment of the
molten
metal delivery system located within a casting apparatus.
FIG. 52 is an enlarged view of the molten metal delivery system of FIG. 33.
FIG. 52a is an illustrative view of an alternate embodiment of a molten metal
delivery system. =
FIG. 53A is an illustration of the molten metal delivery system of FIG. 52 in
a first
stage.
FIG. 53B is an illustration of the molten metal delivery system of FIG. 52 in
a
second stage.
FIG. 53C is an illustration of the molten metal delivery system of FIG. 52 in
a third
stage.
FIG. 53D is an illustration of the molten metal delivery system of FIG. 52 in
a
fourth stage.
FIG. 53E is an illustration of the molten metal delivery system of FIG. 52 in
a fifth
stage.
FIG. 54 is a graphic illustration of the process of varying charge pressure
with time.
FIG. 55 is an illustrative view of the gas turbine engine blade of FIG. 2
within a
pressure and temperature environment.
FIG. 56 is an illustrative view of a directionally solidified starter crystal
with a
molten metal solidifying thereon to form a directional solidified multi-
crystal product.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the principles of the
invention,
reference will now be made to the embodiment illustrated in the drawings and
specific
language will be used to describe the same. It will nevertheless be understood
that no
limitation of the scope of the invention is thereby intended, such alterations
and further
modifications in the illustrated device, and such further applications of the
principles of
the invention as illustrated therein being contemplated as would normally
occur to one
skilled in the art to which the invention relates.
Referring to FIG. 1, there is illustrated a gas turbine engine 20 which
includes a fan section 21, a compressor section 22, a combustor section 23,
and a
turbine section 24 that are integrated together to produce an aircraft flight
propulsion engine. This type of gas turbine engine is generally referred to as
a
turbo-fan. One alternate form of a gas turbine engine includes a compressor, a
combustor, and a turbine that have been integrated together to produce an
aircraft
flight propulsion engine without the fan section. The term aircraft is generic
and
includes helicopters, airplanes, missiles, unmanned space devices and any
other
substantially similar devices. It is important to realize that there are a
multitude of
ways in which the gas turbine engine components can be linked together.
Additional compressors and turbines could be added with intercoolers
connecting
between the compressors and reheat combustion chambers could be added between
the turbines.
A gas turbine engine is equally suited to be used for an industrial
application. Historically, there has been widespread application of industrial
gas
turbine engines, such as pumping sets for gas and oil transmission lines,
electricity
generation, and naval propulsion.
The compressor section 22 includes a rotor 25 having a plurality of
compressor blades 26 coupled thereto. The rotor 25 is affixed to a shaft 27
that is
rotatable within the gas turbine engine 20. A plurality of compressor vanes 28
are
positioned within the compressor section 22 to direct the fluid flow relative
to
blades 26. Turbine section 24 includes a plurality of turbine blades 30 that
are
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coupled to a rotor disk 31. The rotor disk 31 is affixed to the shaft 27,
which is
rotatable within the gas turbine engine 20. Energy extracted in the turbine
section
24 from the hot gas exiting the combustor section 23 is transmitted through
shaft
27 to drive the compressor section 22. Further, a plurality of turbine vanes
32 are
positioned within the turbine section 24 to direct the hot gaseous flow stream
exiting the combustor section 23.
The turbine section 24 provides power to a fan shaft 33, which drives the
fan section 21. The fan section 21 includes a fan 34 having a plurality of fan
blades 35. Air enters the gas turbine engine 20 in the direction of arrows A
and
passes through the fan section 21 into the compressor section 22 and a bypass
duct
36. The term airfoil will be utilized herein to refer to fan blades, fan
vanes,
compressor blades, turbine blades, compressor vanes, and turbine vanes unless
specifically stated otherwise in the text. Further details related to the
principles and
components of a conventional gas turbine engine will not be described herein
as
they are believed known to one of ordinary skill in the art.
With reference to FIGS. 2-7, there are illustrated examples of cast
components that could be produced from a casting mold system of the present
system. The present disclosure is not intended to be limited to the examples
set
forth in FIGS. 2-7, unless specifically set forth herein. More specifically,
with
reference to FIG. 2, there is illustrated a gas turbine engine blade 30. In
one
embodiment, the gas turbine engine blade 30 defines a single cast article
having an
internal flow path for the passage of cooling media. The internal cooling path
includes a passageway with a plurality of heat transfer pedestals 37. In one
embodiment, the plurality of pedestals 37 are integrally formed between a pair
of
spaced walls. The pedestals are representative of the types of details that
can be
produced with the casting mold systems of the present invention. It is
understood
herein that the shape, size, and distribution of the cooling pedestals are a
function
of heat transfer parameters and design specific parameters. The FIG. 3
illustration
is utilized herein merely to represent that pedestals having the following
dimensions are more particularly contemplated, and the dimensional sizes of
one
embodiment of the channels and pedestals are set forth in Table I. However, it
is
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understood that other pedestal and channel sizes and geometry's are
contemplated
herein.
PEDESTAL
Length Width Height
0.020-.050" 0.020-.050" 0.012-.020"
CHANNEL
Length Width Height
N/A 0.012-.020" 0.012-.020"
TABLE 1
Referring to FIGS. 4 and 5, there is illustrated a sectional view of one
embodiment of a single piece multi-wall gas turbine engine component
producible
by the present system. Further, FIG. 6 illustrates the leading edge 43 of a
spacecraft 42, which is producible with the system of the present invention.
While
in FIG. 7 there is illustrated a hydraulic valve body 44 with internal fluid
flow
circuitry that depicts another example of the types of cast products that
could be
produced with the present system. The products illustrated herein are not
intended
to be limiting and other cast products are contemplated for production by the
present system including, but not limited to art, jewelry, dental prosthesis,
general
=
prosthesis, custom hardware, golf club heads, propellers, electronic
packaging,
tubes, valves and other items that have been traditionally investment cast for
precision tolerance and/or detail.
The methods and apparatuses of the present invention may be utilized to
produce single piece single cast components or multi piece cast components
having
microstructures that are commonly categorized as equiaxed, directionally
solidified
or single crystal. The preferred casting mold system of the present invention
is
suitable for producing virtually any type of cast metallic product, however in
a
more preferred embodiment it is particularly useful for producing thin walled
single crystal structures. The cast structures may have many different shapes,
sizes,
configurations, and can be formed of a variety of metallic materials. For
example,
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the system of the present invention allows the casting of multi-wall
structures with
at least one wall having a thickness less than about 0.03 inches. Further, in
a
preferred embodiment there can be formed very thin passageways within the cast
structure/component and in a more preferred embodiment the very thin
5 passageways having a width of about 0.005 inches to about 0.015 inches.
However, casting having passageways and wall thickness of other widths and/or
sizes and/or thickness are contemplated herein.
Gas turbine engine components are preferably formed of a superalloy
composition material. There are various types of superalloy compositions, such
as
10 but not limited to nickel based or cobalt based compositions, and the
manufacture
of such compositions are generally known to those skilled in the art. Most
superalloy compositions of interest are complicated mixtures of nickel,
chromium,
aluminum and other select elements.
With reference to FIG. 8, there is illustrated the controlled solidification
of
15 molten metal from a starter seed 300. The controlled solidification of
the molten
metal is preferably used to produce products having a columnar grain or a
single
crystal microstructure. More specifically, the controlled solidification of
the
molten metal is accomplished by the directional solidification of the molten
metal.
Directional solidification involves moving a solidification interface
progressively
through a casting mold 301 filled with molten metal. In many circumstances,
the
metallic starter seed 300 is used to impart strictly oriented crystallographic
structure to the crystal being grown. The metallic starter seed 300 is placed
within
the casting mold 301 and the introduction of the molten metal 302 into the
mold
301 causes the starter seed to melt back from an original surface 303 to a
surface
defined as the liquidus interface 304. In one form of the present invention,
the melt
back of the starter seed forms a puddle of liquid molten metal from the
starter seed.
In one embodiment the depth of the puddle is about 0.050 inches, however other
puddle depths are contemplated herein. A solidification zone 305 is positioned
between the liquidus interface 304 and a solidus interface 306. As the thermal
gradient moves vertically through the molten metal 302 in the mold 301, the
material solidifies through the growth of dendrites 307 and the solidification
of the
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matrix material. In a single crystal process the molten material solidifies
epitaxially from the unmelted portion of the seed 302.
With reference to FIG. 9, there is illustrated an integral mold 45a for
receiving molten metal therein. In one embodiment the mold 45a is formed by a
free form fabrication technique generally known as three-dimensional printing.
In
three-dimension printing systems a ceramic material is deposited in layers to
form
a direct ceramic casting mold. The density of the layers can be varied by the
number of dots per inch of material deposited. Information related to three-
dimensional printing techniques is disclosed in U.S. Patent Nos. 5,340,650,
5,387,380, and 5,204,055. A commercially available system for three-
dimensional
printing is available from Soligen Technologies, Inc. of North Ridge,
California.
Integral mold 45a is formed by the layerwise printing and binding of
ceramic material, with each layer being bonded to an adjacent layer to form a
ceramic shell for receiving molten metal therein. An apparatus 46a deposits
the
layers of material and binder to form the integral mold 45a based upon a
design
file. It is preferred that the design file be generated from a computer aided
design
of the component. Preferably, mold 45a is a thin walled shell having a main
body
47a with an internal cavity for receiving molten metal to define a component
upon
solidification. A portion of the internal metal receiving cavity is depicted
at 48a.
The integral mold 45a includes a plurality of thin walls 48a, internal mold
cores
50a, and the internal metal receiving cavity. In one embodiment, the thin wall
49a
has a thickness in the range of about 0.005 inches to about 1.50 inches, and
more
preferably the thin wall has a thickness of less than about 0.040 inches, and
most
preferably is about 0.020 inches. Integrally formed with the main body 47a are
a
bottom support member 51a, a fill tube 52a, a support member 53a, and a wall
member 54a. In a preferred embodiment, the wall member 54a is defined by a web
structure. Other integral mold styles are contemplated herein and the present
invention is not intended to be limited to the specific mold configuration and
or
material of FIG. 9.
With reference to FIGS. 10 and 11, there is illustrated one embodiment of a
casting mold system 45 for receiving molten metal therein. The casting mold
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system 45 has a shell mold and cores produced integrally from a photocurable
ceramic resin, however the present invention is not limited to integral
casting
molds. More particularly, in another embodiment a non-integral casting mold
system has a separable core(s) and shell mold formed from the photocurable
ceramic resin; the components are subsequently mechanically coupled to form a
casting mold system. The mold 45 is formed by a free form fabrication
technique
generally known as selective laser activation (SLA). Selective laser
activation is
based upon a stereolithography process that utilizes liquid resins that
solidify when
exposed to an energy dose. In the present invention a photocurable ceramic
filled
resin has at least one monomer that is polymerized by the energy dose to form
a
polymer binder holding the ceramic particles together. The energy dose can be
delivered by any of a plurality of energy sources known to those skilled in
the art.
Preferably, the energy dose is defined by electromagnetic radiation, and more
preferably the energy dose is an ultraviolet light emitted from a laser source
having
a wavelength of about 260 to 380 nanometers, and most preferably is about 350
nanometers. However, light of other wavelengths is contemplated herein.
Commercially available machines for selective laser activation are available
from
3D systems of Valencia, California. Further information related to selective
laser
activation and stereolithography is disclosed in U.S. Patent Nos. 5,256,340,
5,556,590, 5,571,471, 5,609,812 and 5,610,824,
Integral mold 45 is formed by photopolymerization of the ceramic filled
resin into layers of ceramic particles that are held together by a polymer
binder.
However, the present invention is not limited to a ceramic filled resin and
one
alternate embodiment includes a metallic filled resin. Further, the
utilization of
other fillers are contemplated herein. In one embodiment a wall member layer
is
defined by a plurality of adjoining portions of ceramic material that are
indicated
schematically as lines 49a, 49b, 49c, and 49d. It is understood herein that
the
number of adjoining lines in a layer and the number of layers in the figure is
purely
representative and is not intended to be limiting herein. Preferably, an
individual
layer of the wall member is formed of between one and about five lines drawn
by
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the energy beam in the ceramic resin. More preferably, an individual layer of
the
wall member is formed of two lines drawn by the energy beam in the ceramic
resin.
However, the present invention contemplates individual layers having other
numbers of individual lines in a layer.
While the wall member layers have been illustrated as being formed of lines
it is understood that in alternate embodiment the wall member is formed of
layers
of spaced dots, and/or linked dots. The lines as defined above for 49a, 49b,
49c
and 49d could also be formed by a series of dots. The series of dots are
spaced
relative to one another to define a layer, and a plurality of layers is
arranged to
define a wall member. In one embodiment the wall member has a grid structure
of
spaced dots that can contain the molten metal poured into a casting mold.
Further,
in another embodiment the grid structure can contain the molten metal poured
into
the casting mold while allowing the venting of gases from the internal cavity
in the
mold through the wall member.
The width of the individual line(s) forming the layers is determined by the
width of the energy beam, and more preferably a laser defines the energy beam.
In
one embodiment the width of energy beam is preferably in the range of about
0.005
inches to about 0.025 inches and more preferably is about 0.008 inches.
However,
an energy beams having a width of about .001 inches is contemplated herein for
producing very fine detail in the casting mold system. Further, the ability to
vary
the width/size of the energy beam on command is also contemplated herein. More
specifically, in one embodiment the size of the energy beam is variable within
a
specific layer and/or between layers within the component. In one commercially
available stereolothography apparatus (SLA 250 from 3D Systems) the laser
source
is a He/Cd laser with 30rn watts of power at the surface of the ceramic resin.
However, other stereolithography devices having different laser sources are
contemplated herein.
The generation of the casting mold system 45 is controlled by a data file
that defines the three dimensional shape of the casting mold system. With
reference to FIG. 12, there is illustrated one embodiment of a system for
creating
the build file 1005 that determines how the casting mold system is created. In
act
CA 02824923 2013-08-28
19
1000 data defining parameters of the component (example a gas turbine blade)
is
collected and processed to define a specification for the component design.
The
data from act 1000 is utilized in act 1001 to construct a component model
using a
computer modeling system, and in one embodiment the computer modeling system
. _
is defined by a ComputerVision (CV) product. However, other modeling systems
are contemplated herein. The computer aided design model from act 1001 is
processed in a mold modeling act 1002 to create a model of the casting mold
system. In one preferred embodiment the model of the casting mold system is
created by a Unigraphics system in act 1002. A conversion act 1003 is utilized
to
convert the mold model, produced in act 1002, of the casting mold system to a
specific file format, such as STL or SLC. Next the file from act 1003 is
processed
in act 1004 to create discrete two dimensional slices appropriate for drawing
the
layers of the casting mold system and any required supports. In act 1005 the
build
file is completed which will drive the energy source in the stereolithography
apparatus and produce the casting mold system.
In a preferred embodiment a scanning laser beam 46b is directed by a
computer reading the data file and giving instructions to draw cross-sections
of the
three-dimensional shape on the quantity of ceramic filled resin to so as
locally
polymerize the monomer within the ceramic filled mixture. The irradiation of
the
monomer mixture with the laser forms a solid polymer gel. The integral mold 45
is
preferably a thin shell having a main body 47 with an internal cavity for
receiving
molten metal therein for solidification to a product. A portion of the
internal metal
receiving cavity is depicted at 48. The integral mold 45 includes thin walls
49,
internal mold cores 50, and an internal metal receiving cavity. In one
preferred
form the thin wall 49 has a thickness less than about 0.060 inches, and more
preferably has a thickness in the range of about 0.015 inches to about 0.060
inches,
and most preferably has a thickness of about 0.020 inches. However, casting
molds having other wall thickness are contemplated herein. In one preferred
casting mold there is formed with the main body 47, a bottom support member
51,
a fill tube 52, a support member 53, and a wall member 54. In the one
preferred
embodiment, the wall member 54 is defined by a web structure. The illustrated
CA 02824923 2013-08-28
casting mold of FIG. 10, is purely representative of the types of casting
molds that
can be fabricated with the present invention. More particularly, other casting
mold
configurations are contemplated herein and the present invention is not
intended to
be limited to the specific mold shown in FIGS. 10 and 11.
5 With reference to FIG.13, there is illustrated the casting mold system
45
being fabricated within a stereolithography apparatus 500. The
stereolithography
apparatus 500 is believed generally known by one of ordinary skill in the art
and
has been shown greatly simplified to facilitate explanation of the method of
making
the casting mold system. A fluid containment reservoir 501, elevation-changing
10 member 502, and the laser 46c comprise a portion of the
stereolithography
apparatus 500. The reservoir 501 is filled with a quantity of the photocurable
ceramic filled resin from which the mold system 45 is fabricated.
- In a preferred form of the present invention the elevation-changing member
502 defines an elevator moveable to immerse the previously cured layers of the
15 casting mold system 45 in the ceramic filled resin to a predetermined
depth. The
ceramic filled resin recoating the uppermost cured layer with a layer of
uncured
ceramic filled resin. In a more preferred embodiment the elevator is a
computer
controlled device that incrementally lowers the fabricated casting mold in the
bath
of ceramic filled resin in coordination with the rest of the process. In one
20 embodiment, the nominal thickness of the uncured resin coating is about
0.004
inches to about 0.010 inches, and more preferably is about 0.004 inches.
However,
other layer thickness are contemplated herein. Further, the thickness of the
individual layer can be made to vary between layers, or held to a
substantially
similar thickness between layers. It is preferred that the system have
provisions to
insure a substantially uniform recoat thickness for those resins with a rather
low
viscosity. The utilization of the following techniques are contemplated to
level the
resin: a time delay to allow the resin to self level; and/or ultrasonic
processing to
assist the resin in leveling; and/or a mechanically assisted process to assist
the resin
in leveling. The laser beam 46b is driven by the data in the three-dimensional
data
file to draw cross-sections of the casting mold on the photocurable ceramic
filled
CA 02824923 2013-08-28
21
resin. The drawing and recoating acts are continued until the green ceramic
part
has been completed.
With reference to FIG. 14, there is illustrated a casting mold system 45
. being fabricated in the stereolithography apparatus 500 at a build
orientation angle
0. The build orientation angle 0 is selected so that the tangent of the angle
for a
given planar or near planar surface (or the collection of solid surfaces) to
be built is
maximized. The build orientation angle 0 is measured from an axis Z extending
substantially perpendicular to the surface 503 of the ceramic resin filled
reservoir.
One form of the present invention orients the cross sections to minimize the
drawing of relatively large uninterrupted planar surfaces on the ceramic
filled resin.
The cross sections are defined and drawn substantially perpendicular to the
axis Z
and substantially parallel with the surface 503 of the resin. A build platform
505 is
constructed within the reservoir 501 at the angle 0 to orient the fabrication
of the
casting mold system 45 at the build orientation angle 0. In the preferred
embodiment the build orientation angle 0 is an acute angle, and more
preferably is
an acute angle within a range of about 10 degrees to about 45 degrees, and
most
preferably is about 45 degrees.
In simple two dimensional shapes the build orientation is relatively easy to
define; for example a hollow cylinder would be preferably built by fabricating
a
plurality of rings on each other. A hollow rectangular tube would be
preferably
built by fabricating a plurality of rectangular sections on each other to
avoid having
to build a relatively large unsupported ceiling. A complex shape, like a cored
casting mold system for a gas turbine engine blade, requires an analysis of
all the
ceramic surfaces to calculate an optimum build orientation.
With reference to FIG. 15, there is illustrated an enlarged view of a
plurality
of cured layers 506, 507, 508 and 509 defining a portion of the casting mold
system
45. The cured layers in a preferred alumina filled resin have a thickness
Within a
range of about 0.002 inches to about 0.008 inches, and more preferably have a
thickness of about 0.004 inches. The cured layers in a preferred silica filled
resin
have a thickness within a range of about 0.002 inches to about 0.020 inches,
and
CA 02824923 2013-08-28
22
more preferably have a thickness of about 0.006 inches. However, other cured
thickness are contemplated herein. Further, the individual cured layers can be
of
the same or different thickness. However, it is preferred that each of the
individual
curved layer have a substantially uniform thickness.
The particle size for the individual ceramic particles 510 are preferably less
than about 20 microns, and more preferably are within a range of about
0.1microns
to about 3.0 microns. The control of the particle size allows for the
fabrication of
finer detail and substantially smooth surfaces in comparison to other known
techniques for making ceramic casting mold systems.
The casting mold system is a layered built structure and FIGS. 14 and 15
have been exaggerated to emphasize the individual cured layers. The individual
layers are formed of a plurality of ceramic particles 510 and a polymer binder
511
that holds the particles within an individual layer. together. In one
embodiment the
polymer binder 511 extends between the adjacent layers to couple the cured
layers
together. Each of a pair of adjacent cured layers, such as layers 506 and 507
have a
respective cross-sectional area abutting at a layer line 600. In a preferred
embodiment there is joining between the complimentary surfaces of the adjacent
layers in the range of about 10% to about 100% of each of the respective
surfaces.
More preferably, in one embodiment of the silica filled resin there is joining
between the complimentary surfaces of the adjacent layers at about 10 percent
of
the respective surfaces; and in one embodiment of the alumina filled resin
there is
joining between the complimentary surfaces of the adjacent layers at about 50
percent of the respective surfaces. However, in some alternate embodiments,
the
adjacent cured layers are not joined together by the polymer binder. The
layers are
held one against the other by mechanical and/or secondary chemical reactions.
The thickness of the layers depends upon the thickness of the recoated
uncured layer and the depth of penetration of the laser beam. More
specifically the
cure depth is indicated as the cured layer thickness plus an overcure depth.
In one
embodiment the overcure depth is about 50 % of the cured thickness layer
directly
beneath the layer being cured. In one embodiment a substantial overcure is
required in the alumina filled resin to minimize the subsequent green
delamination
CA 02824923 2013-08-28
23
or layer separation. However, embodiments of the present invention utilize an
overcure cure depth within a range of about 10 % to about 150% of the cured
layer.
However, the present invention is not limited to the above cure depths and
other
, cure depths are contemplated herein.
The ceramic filled resin includes a sinterable ceramic material, a
photocurable monomer, a photoinitiator and a dispersant. The ceramic filled
resin
is particularly adapted for use in stereolithography to produce a green
ceramic mold
that resists cracking when sintered. The filled resin is prepared by admixing
the
components to provide a filled resin having viscosity of less than about 4,000
cPs,
more preferable between about 90 cPs and about 3,000 cPs and most preferably
between about 100 to about 1000 cPs. The resulting filled resin has a solids
loading of about 40 % to about 60 % volume solids in the resin. Further, in
one
embodiment the filled resin has a density of between about 1.0 to about 4.0
g/ml,
more preferable between about 1_5 and 2.5 g/ml.
The sinterable ceramic material for use in this invention can be selected
from a wide variety of ceramic materials. Specific examples include alumina,
yttria, magnesia, silicon nitride, silica and mixtures thereof. The sinterable
ceramic
material is included in the filled resin at about 50 volume percent (vol. %)
based
upon the total volume of the filled resin. Expressed in other terms, the
filled resin
includes about 50 to about 85 weight percent (wt %) of the sinterable ceramic
material, most preferably about 65 to about 80 wt % based upon the total
weight of
the filled resin.
In one example silica is selected as the sinterable ceramic material. Silica
can be provided as a dry powder having an average particle size suitable for
sintering to provide a cured mold in accordance with this invention.
Preferably the
powdered silica is selected to have an average particle size of about 0.5
microns to
about 20.0 microns and, more preferably about 1.0 micron to 20.0 microns, and
most preferably about 1.0 micron to about 5.0 microns. Preferably, the amount
of
silica is between about 50.0 wt % and about 72.0 wt % based upon the total
weight
of the filled resin.
CA 02824923 2013-08-28
24
The monomer is selected from any suitable monomer that can be induced to
polymerize when irradiated in the presence of a photoinitiator. Examples of
monomers include acrylate esters and substituted acrylate esters. A
combination of
two or more monomers may be used. Preferably at least one of the monomers is a
multifunctional monomer. By multifunctional monomer it is understood that the
monomer includes more than two functional moieties capable of forming bonds
with a growing polymer chain. Specific examples of monomers that can be used
with this invention include 1,6-hexanediol diacrylate (HDDA) and 2-
phenoxyethyl
acrylate (POEA). The photocurable monomers are present in an amount between
about 10 to about 40 wt %, more preferably about 10 to about 35 wt % , and
most
preferably about 20-35 wt % based upon the total weight of the filled resin.
The dispersant is provided in an amount suitable to maintain a uniform
colloidal suspension of the silica in the filled resin. The dispersant can be
selected
from a wide variety of known surfactants. Preferred dispersants include
ammonium salts, more preferably tetraalkyl ammonium salts. The tetraalkyl
groups can include a variety of substituents. Specific examples of dispersants
for
use in this invention include, but are not limited to: polyoxypropylene
diethy1-2-
hydroxyethyl ammonium acetate, and ammonium chloride. Preferably, the amount
of dispersant is between about 1.0 wt % and about 10 wt % based upon the total
weight of the ceramic within the filled resin.
The initiator can be selected from a number of photoinitiators known to
those skilled in the art. The photoinitiator is selected to be suitable to
induce
polymerization of the desired monomer when irradiated. Typically the selection
of
a photoinitiator will be dictated by the wavelength of radiation used to
induce
polymerization. Preferred photoinitiators include benzophenone, trimethyl
benzophenone, 1-hydroxycyclohexyl phenyl ketone, isopropylthioxanthone, 2-
methyl-144 (methylthio)pheny1]-2-morpholinoprophanone and mixtures thereof.
The photoinitiator is added in an amount sufficient to rapidly polymerize the
monomers when the filled resin is irradiated with radiation of appropriate
wavelength. Preferably the amount of photoinitiator is between about 0.05 and
about 5 wt % based upon the total weight of the monomer within the filled
resin.
CA 02824923 2013-08-28
?5
In an alternate form of the ceramic filled resin a quantity of a nonreactive
diluent is substituted for a quantity of the monomer. Preferably, the amount
of
substituted nonreactive diluent is equal to between about 5% and about 20% (by
weight or volume) of the monomer in the resin. An illustration of a given
ceramic
resin composition requires 100 grams of a monomer that in the alternate form
will
replace about 5 ¨20 wt % of the monomer with a nonreactive diluent (i.e. 95 ¨
80
grams of monomer + 5-20 grams of nonreactive diluent). The nonreactive diluent
includes but is not limited to a dibasic ester or a decallydronaphthalene.
Examples
of dibasic esters include dimethyl succinate, dimethyl glutarate, and dimethyl
adipate, which are available in a pure form or a mixture.
The filled resin is prepared by first combining the monomer, the dispersant
and the sinterable ceramic to form a homogeneous mixture. Although the order
of
addition is not critical to this invention typically, the monomer and the
dispersant
are combined first and then the sinterable ceramic is added. Preferably the
sinterable ceramic material is added to the monomer/dispersant combination in
increments of about 5 to about 20 vol. %. Between each incremental addition of
the ceramic material, the resulting mixture is thoroughly mixed by any
suitable
method, for example, ball milling for about 5 to about 120 minutes. When all
of
the sinterable ceramic material has been added, the resulting mixture is mixed
for
an additional amount of time up to 10 hours or more. The photoinitiator is
added
and blended into the mixture just prior to irradiation of the resin,
preferably not
more than about 2 hour prior to irradiation.
A preferred silica filled resin comprises about 67.1 wt % silica, about 31 wt
To monomer, about 1.37 wt % dispersant, and about 0.619 wt % photoinitiator.
The wt % are based upon the total weight of the silica filled resin. A
preferred
alumina filled resin comprises about 78.2 % alumina, about 20.1 wt % monomer,
about 1.56 wt % dispersant, and about 0.101 wt % photoinitiator.
With reference to Table 11 there is set forth a preferred silica filled resin
and
a preferred alumina filled resin.
CA 02824923 2013-08-28
26
wt/g vol wt % vol %
cc
Alumina 1980 500 78.2 48.0
Monomer 510 500 20.1 48.0
Dispersant 39.6 38.8 1.56 3.73
Photoinitiator 2.55 2.32 0.101 0.223
Total 2532 1041 100% 100%
Silica 2210 1000 67.1 48.5
Monomer 1020 1000 31.0 48.5
Dispersant 44.2 43.33 1.37 2.14
Photoinitiator 5.10 4.636 0.619 0.899
Total 3279 2048 100% 100%
TABLE II
In an alternate embodiment, the ceramic filled resin is defined as a duplex
curing resin. The duplex curing resin utilizes two types of initiators to
cause the
polymerization of the monomer. In a preferred form there is one photoinitiator
for
UV light curing, and another initiator for thermal curing. One example of an
initiator for thermal curing is benzoyl peroxide or A1BN. AIM comprises 2-2'-
azo-bis-isobutyrylnitrile. However, the initiator for thermal curing can be
selected
from a number of other initiators known to those skilled in the art.
With reference to FIG. 16, there is illustrated an alternate embodiment 55 of
the thin wall structure 49. The composite wall structure 55 comprises a pair
of
spaced thin outer walls 56 and 57 with a plurality of internal wall members 58
connecting therebetween. A plurality of cavities 63 is formed in the wall
structure
55 and in one embodiment includes an internal core structure 59. In a
preferred
embodiment, the internal core structures 59 are hollow and integrally
connected to
the walls that define the cavity 63.
With reference to FIG. 17, there is illustrated a third embodiment 60 of the
thin wall structure 49 of the integral mold 45. Wall structure 60 includes a
pair of
CA 02824923 2013-08-28
27
spaced thin outer walls 61 formed with and coupled to a porous inner member
62.
The density of the inner member 62 is preferably less than the density of the
outer
_
walls 61. Wall structure 60, 55, and 49 can be used together or separately as
required by the design. It is understood herein that wall structures 49, 55,
and 60
are purely illustrative of wall structures of the present invention and are
not
intended to be limiting in regards to other designs for composite wall
structures.
Referring to FIGS. 18 and 19, there are illustrated alternate forms 65 and 70
respectively of a portion of the mold core 50. Mold core 65 has an integral
thin
wall structure 66 with an internal hollow core structure 67 formed therewith.
Formed between the outer wall structure 66 and the internal hollow core
structure
67 is a porous structure 69. Mold core 70 includes a thin wall 71 with an
internal
hollow core 72 formed therewith. A plurality of reinforcing ribs 74 are formed
between the outer wall 71 and the internal hollowcore 72. The configurations
of
the mold cores 50, 65, and 70 are not intended to be limiting herein and other
designs of mold cores are contemplated herein.
Referring to FIGS. 20 and 21, there is illustrated another embodiment of a
green casting mold system. The casting mold 525 is substantially similar to
the
previously described casting mold system 45. More specifically, the casting
mold
system 525 has an integral ceramic shell 526 and ceramic core 527. The volume
528 between the core ceramic shell 526 and the core 527 defines the component
to
be formed from a molten metallic material. Preferably, the volume 528 includes
no
supporting structure extending therein to interfere with the receipt of molten
metal.
More specifically, in a more preferred embodiment the drawing of the cross-
sections does not draw any structure within the volume 528. However, in
another
embodiment of the present invention the fabrication process produces
supporting
structure within the volume 528 that can be removed without damaging the
ceramic shell 526 and/or the core 527. In a preferred form the inner wall
surface
529 of the ceramic shell 526 and the outer surface 530 of the ceramic core 527
as
formed are substantially smooth. The wall surface will be defined as either a
stepped surface which is defined by a portion of a plurality of abutting
layers, or a
flat surface which is defined by a surface of a single layer. More
specifically, the
CA 02824923 2013-08-28
28
green state components have an as formed surface finish for a stepped surface
within a range of about ten microns to about 30 microns, and an as formed
surface
finish for a flat surface within a range of about 0.5 microns to about 10
microns.
In one embodiment of the casting mold system 525 the core 527 is
substantially hollow. A thin outer wall shell 540 has a plurality of spaced
inner
wall members 541 integrally formed therewith. It is contemplated herein that
cores
having a solid configuration and a substantially hollow configuration are
within the
contemplation of the present invention.
Referring to FIG. 22, there is illustrated a partial sectional view taken
along
line 22-22 of FIG. 20. The ceramic core 527 has a passageway 532 formed
therein
that is adapted for the receipt of molten metal. More specifically, there is a
plurality of spaced passageways 532 formed in the ceramic core 527 for the
receipt
of molten metal. The passageways 532 allow the casting of details in the
component. In a preferred embodiment each of the passageways 532 has an as
formed width/diameter in the range of about 0.005 inches to about 0.030
inches,
and more preferably defines a width/diameter less than about 0.020 inches, and
most preferably defines a width/diameter of about 0.010. FIG. 23 is an
illustration
of another embodiment of an integral multi-wall ceramic casing mold system.
With reference to FIG. 24, there is schematically shown a casting mold
system 45 positioned within a furnace 550. The furnace provides the heat
required
for substantially burning out the polymer binder from a green ceramic casting
mold
system and sintering the ceramic particles. In a preferred form the casting
mold
system is oriented within the furnace so as to minimize the number of
individual
layers resting on the surface 551 of the furnace. A firing schedule for a
green
ceramic mold system includes heating the mold within the furnace from a normal
room temperature at a rate of about 0.1 degrees centigrade per minute to about
5.0
degrees centigrade per minute to a first temperature of about three hundred
degrees
centigrade to about five hundred degrees centigrade. Thereafter holding the
maximum temperature for a time range of about zero hours to about four hours
to
burn out the polymer binder. After the heating portion the densified casting
mold
system is subjected to a sintering schedule. The sintering schedule increasing
the
CA 02824923 2013-08-28
29
temperature within the furnace from the first temperature at a rate of about
5.0
degrees per minute centigrade to about 10.0 degrees per minute centigrade to a
second temperature within a range of about 1300 degrees centigrade to about
1600
degrees centigrade. The casting mold system is held at the second temperature
for
a time range of about zero hours to about four hours. The casting mold system
is
then cooled to room temperature at a rate of about 5.0 degrees centigrade per
minute to about 10.0 degrees centigrade per minute. The casting mold system is
preferably sintered to a density greater than about 70%, and more preferably
the
casting mold system is sintered to a density within a range of about 90-98 %.
Most
preferably, the casting mold system is sintered to a substantially full
density. In
one embodiment the sintered ceramic casting mold system is about 99 wt %
ceramic particles, and more preferably about 99 wt % alumina
A preferred firing schedule for an alumina based green ceramic mold
system includes heating the mold within the furnace from a normal room
temperature at a rate of about one degree centigrade per minute to a first
temperature of about 300 degrees centigrade and holding at the first
temperature
for about four hours. Thereafter increasing the temperature from the first
temperature to a second temperature of about 500 degrees centigrade at a rate
of
about one degree centigrade per minute. Holding at the second temperature for
about zero hours. Increasing the temperature at a rate of about ten degrees
centigrade per minute from the second temperature to a third temperature of
about
1550 degrees centigrade. Holding at the third temperature for about two hours.
The casting mold system is then cooled from the third temperature to room
temperature at a rate of about five degrees centigrade per minute.
A preferred firing schedule for a silica based green ceramic mold system
includes heating the mold within the furnace from a normal room temperature at
a
rate of about one degree centigrade per minute to a first temperature of about
300
degrees centigrade and holding at the first temperature for about four hours.
Thereafter increasing the temperature from the first temperature to a second
temperature of about 500 degrees centigrade at a rate of about one degree
centigrade per minute. Holding at the second temperature for about zero hours.
CA 02824923 2013-08-28
Increasing the temperature at a rate of about ten degrees centigrade per
minute
from the second temperature to a third temperature of about 1500 degrees
centigrade. Holding at the third temperature for about two hours. The casting
mold system is then cooled from the third temperature to room temperature at a
5 rate of about five degrees centigrade per minute.
The integral casting molds 45 and 45a are produced by different processes
and while they do have different properties, they both form a ceramic shell
for
receiving molten metal therein. However, it is understood that in another form
of
the present invention the ceramics shell can receive other material for
solidification
10 besides molten material. While the forming of a ceramic mold by three-
dimensional printing and selective laser activation have been discussed
herein, the
present casting inventions are not intended to be limited to these types of
molds,
unless specifically stated. For example, a mold produced with conventional
techniques of cores and patterns which are shelled by dipping in a ceramic
slurry,
15 resin shell molds, or sand molds are also contemplated herein.
Hereinafter, the
term casting mold will be referred to generically as casting mold 45 and is
intended
to include all types of ceramic casting molds, unless specifically stated to
the
contrary.
With reference to FIG. 25, there is illustrated one embodiment of the
20 integral casting mold 45. The completed integral mold 45 has a base
member 51, a
top member 77, and a main body 47 extending therebetween. Support member 53
extends between the bottom member 51 and the top member 77, while the fill
tube
52 extends from the fill inlet 78 to a bottom portion 47a of the main body 47
and is
in fluid communication with the internal metal receiving cavity of the mold.
25 Preferably the base member 51 is defined by a ring structure. A vent 79
is formed
in the integral mold 45 and opens into the internal metal receiving cavity to
allow
gaseous material to enter and leave the mold, aid in material removal, and aid
in
casting fill. It is understood herein that in alternate embodiments the
integral
casting mold 45 may be of a different configuration and may not include
features
30 such as the base member and/or the top member.
CA 02824923 2013-08-28
31
In one embodiment, the top member 77 defines a toothed ring or disk
structure disk contactable with the container 80. Preferably, the integral
mold 45
has been designed to minimize the quantity of material needed to produce it,
and
therefore its thin shell causes it to resemble the contour of the product
being cast
therein: In the present example, the mold 45 resembles a gas turbine blade,
however, other shapes are contemplated. Further, the integral mold could be
formed such that its outer surface does not conform to the shape of the
product/component being cast within the internal cavity.
In the designing and forming of the integral mold 45 there are many
parameters to consider including: (1) the desired strength and stiffness of
the
mold; (2) the speed at which the mold can be created; (3) the ability for the
cores
within the mold to crush as the metal solidifies; (4) the rate of the
heating/cooling
during the casting; (5) the removal/leach speed of the cores; and, (6)
restraint of the
casting during cooling after solidification. The crushability of portions of
the mold
as the molten metal solidifies around it can be addressed by the variation in
densities, structures and the porosity of the components. For example with
reference to FIGS. 18 and 19 there is illustrated core structures 65 and 70
that have
a porous structure 68 and a reinforcing web structure 74 that will partially
collapse/give as molten metal solidifies therein.
With reference to FIG. 26, there is illustrated a mold container 80 and
integral mold 45 positioned in a furnace 81. While the mold container 80 has
been
illustrated with the integral mold 45 positioned therein, it is understood
that other
types of molds may also be positioned within the mold container 80. The mold
container 80 is designed and constructed to contain the integral mold 45,
during the
casting process. An outer wall member 82 of the container 80 has an opening
therethrough that is sized to provide an interference fit between an inner
surface of
the mold container and the outer surface 51a of the base member 51 and a
portion
of the outer surface 77b of the top member 77. In one embodiment, the mold
container 80 is defined by a thick walled fibrous ceramic tube that is shrink
fitted
over the bottom member 51 and the top member 77. The term tube, as used
herein,
defines a hollow member and is not intended to be limited to a hollow
cylindrical
CA 02824923 2013-08-28
32
structure, unless specifically stated. The container in an alternate
embodiment
includes an integral bottom wall member that generally, defines a cup shaped
container. However, other shapes for the container are contemplated herein.
Further, in an alternate embodiment the container and the mold are not in an
interference fit.
In a preferred embodiment the mold container 80 is defined by an elongated
cylindrical shaped tube. In one form the wall thickness for the outer wall
member
82 is within a range of about 0.010 to about 1 inch, and more preferably is
about
0.5 inches. However, other wall thickness are contemplated herein. The outer
wall
member 82 being formed of a ceramic material that has been selected for
specific
heat transfer requirements. In one embodiment, the member transfers the heat
from
its outer surface 82a quickly so as to facilitate handling, while in another
embodiment the member has been designed to insulate the integral mold 45.
Materials such as, but not limited to, porous ceramics, ceramic fiberrnatts ,
metals,
and metals with thermal barrier coatings are contemplated herein for the outer
wall
member 82.
At least one supporting members 83 is positioned within the space between
the inner surface 84 of the outer wall 82 and the outer surface 45a of the
integral
mold 45. The supporting member provides support for the thin walled integral
mold 45 during the casting process. The reinforced mold container 80 allows
the
delivery of the molten metal at high pressures to a thin shell mold. In one
embodiment molten metal pressures within the range of about three inches to
about
twenty-four inches of nickel are contemplated herein for use with the
reinforced
thin walled integral mold. However, other molten metal pressures are
contemplated herein.
In a preferred embodiment, the supporting member 83 is defined by a
plurality of supporting members, and more preferably is defined by a plurality
of
ceramic media members. In one embodiment, the plurality of supporting members
having a size within the range of about 0.010 inches to about 0.100 inches and
are
defined as a spherical/ball. However, other sizes are contemplated herein. The
plurality of supporting members fill the space within the mold container 80
and
CA 02824923 2013-08-28
33
abut the outer surface 45d of the integral mold. It is understood that the
shape of
the plurality of supporting members includes, but is not limited to, tablet,
spherical,
or fibrous. Moreover, in an alternate embodiment of the present invention, the
supporting member within the mold container can be defined by: a continuous
-
ceramic material formed between the inner surface 84 of the outer wall 82 and
the
outer surface 45d of integral mold 45; a ceramic foam such as alumina,
mullite,
silica, zirconica, or zircon. The web structure 54 is designed and constructed
to
minimize the amount of material utilized to create a bottom wall member for
preventing the passage of the plurality of support members 83 from the
container
80. However, other structures such as but not limited to a solid wall are
contemplated herein. The plurality of ceramic supporting media 83 are readily
removable from the containers for reuse and/or recycling.
With reference to FIG. 27, there is illustrated the mold container 80 which
further includes a supplemental mold heater 91. Supplemental mold heater 91 is
controlled to add energy as needed during the solidification of the molten
metal
and growth of the crystal within the integral mold cavity. In one form the
supplemental mold heater 91 is coupled to the inner surface 84 of the outer
wall 82
of the mold container 80 and is positioned at the top portion of the mold
container
80. However, other locations along the mold container are contemplated herein.
With reference to FIG. 28, there is illustrated a cross sectional view of the
mold container 80 with the integral mold 45 located therein. The cross section
has
been taken through line 28-28 of FIG. 27, which corresponds, to an airfoil-
forming
portion of the internal cavity for receiving a molten metal therein. The
plurality of
supporting members 83 abut the outer surface 45d in order to support the thin
wall
49 during the pouring of molten metal within the cavity 48. The plurality of
supporting members 83 have spaces 94 therebetween which serve as an insulator
to
- - prevent the transfer of heat from the integral mold 45 to the outer
wall 82. Further,
the plurality of supporting members 83 define a discontinuous heat transfer
path to
the outer wall 82 of the container. The plurality of members 83 function to
retain
the heat radiating from the integral mold 45 so as to help maintain a desired
temperature for the integral mold 45.
CA 02824923 2013-08-28
34
With reference to FIG. 29, there is illustrated the mold container 80 with
the integral casting mold located therein. A localized mold heater 93 is
positioned
within the space defined between the outer wall 82 of the container 80 and the
outer surface 45a of the mold 45 so as to heat a portion of the integral mold
45.
The utilization of a localized mold heater 93 within the mold container can be
adjacent or proximate any portion of the outer surface 45a of the mold 45. It
is
contemplated that the localized mold heater 93 can be continuous along a
surface,
or discontinuous along a surface or spaced from a surface as required by
parameters related to the mold design. The depiction of the supplemental mold
heater in FIG. 29 is not intended to be limiting therein.
With reference to FIGS. 30 and 31, there is illustrated a method and
apparatus for removing unbonded material 400 from within the internal cavity
of
the integral mold 45. While the process is illustrated with a free form
fabricated
mold having a plurality of layers of a material bonded together, it is also
contemplated as being useful for other mold structures having unbonded
particles
located within a metal receiving cavity. The unbonded material relates to
powders,
particulate, and other material that is not bonded to the walls of the
integral mold
45 within the cavity 48. In one form, the process for removing unbonded
material
from within a casting metal receiving cavity relates to a mold produced by the
printing and binding of layers of powder to form a direct ceramic casting
mold. In
another embodiment the integral mold 45 has been heated to dry the unbonded
materials within the cavity. In another form, the process for removing
unbonded
material from within a casting metal receiving cavity is related to a mold
produced
by a selective laser activation technique to form a ceramic shell. The
unjelled
slurry may be dried and removed or removed in an undried state.
The mold container 80 with integral mold 45 is positioned at an inclination
angle 9 and rotated about an axis Z. In the preferred embodiment, the angle 0
is an
acute angle within the range of about 5 to about 90 degrees, and more
preferably,
the angle 0 is about 15 degrees. However, in the alternate embodiment the
angle 0
is variable. Rotation and movement of the integral mold 45 causes the unbonded
material 400 to be dislodged from the walls defining the internal cavity and
passed
CA 02824923 2013-08-28
through an exit aperture 101 that is in communication with the internal
cavity, and
into a bin 104. In an alternate embodiment the integral mold has a plug (not
illustrated) put into the exit aperture 101 after the unbonded material 400
has been
removed from the internal cavity. In a preferred embodiment, the exit aperture
101
5 is sized to receive a metallic starter seed utilized during the casting
operation to
facilitate a specific crystallographic structure and/or speed solidification.
In one form, the sprocket 77 of the integral mold 45 is engaged with a drive
102. The drive 102 is driven such that the container is revolved at speeds in
the
range of about 0.1 to 2 revolutions per minute, and more preferably rotates at
a
10 speed of about 1/3 revolutions per minute, however, other speeds are
contemplated
herein. The dwell time for which the integral mold is subjected to rotation is
in the
range of about 15 minutes to about 2 days and more preferably is about 2
hours.
However, other dwell times are contemplated herein. The containers 80 pass
along
a container support 103 in the direction of arrow P as they are rotated about
axis Z.
15 A container spacer 105 is positioned between pairs of mold containers 80
so as to
prevent contact between the containers. Further, the containers 80 may be
inverted
as necessary to facilitate removal of the material 400 from the internal
cavity, and a
fluid scrubbing can be introduced into the internal cavity to facilitate
material
removal. The introduction of fluids within the internal cavity can occur in
the
20 normal or inverted state.
The integral mold 45 is subjected to a thermal processing operation prior to
the receipt of molten metal within its internal cavity. The integral mold 45
whether
formed by the three-dimensional printing or the selective laser activation
process,
has a green state strength that is not sufficient for the casting process and
therefore
25 to increase it's strength it has been fired as previously discussed. In
some mold
constructions it is necessary to burn out polymers and other materials present
in the
_
green state mold. More specifically, in the case of the integral mold which is
formed by the selective laser activation process, it is necessary to burn out
the
polymers within the green phase mold. The mold produced by the three-
30 dimensional printing techniques generally do not require the burn out
process as
there are not significant materials to be removed from the green state
integral mold
CA 02824923 2013-08-28
36
45. Lastly, the mold must be preheated to the appropriate temperature, which
is
chosen to facilitate the growth of the microstructure desired. In the case of
a
columnar grain structure the temperature desired to preheat the mold is about
2700
degrees Fahrenheit and in the case of a single crystal casting the temperature
desired for the mold preheat is about 2800 degrees Fahrenheit.
In one form of the present invention, it is preferred to have an integrated
thermal processing operation for the integral mold 45. The integrated thermal
processing will include firing the green state mold 45, burning out the
unwanted
materials in the green state mold, and preheating the mold to the desired
temperature necessary for casting the desired microstructure. The molds after
the
firing and sintering operation are then cooled, inspected, repaired as
necessary and
prepared for casting. Thereafter, the mold is elevated to the temperature
desired
for preheating the mold. In a more preferred form, each of these steps occur
in the
same furnace in a substantially continuous fashion. Elimination of thermal
cycling
of the mold will enhance the ability to cast hollow structures with
intricate/delicate
passages.
With reference to FIG. 32, there is depicted a functional representation of a
casting apparatus 420 for delivering a charge of molten metal 108 to a casting
mold, such as the mold container 80 with integral mold 45 therein. The present
invention contemplates a casting apparatus that functions in a substantially
continuous or a batch processing fashion. The casting mold utilized with the
casting apparatus is not intended to be limited herein to a specific mold
style or
construction. The casting apparatus includes a precision molten metal delivery
system 106 that is located within a furnace 107. In a preferred form of the
present
invention, the furnace 107 is defined by a dual chambered vacuum furnace.
However, it is understood that other types of furnaces such as air melt or
pressurized casting furnaces are contemplated herein. The precision molten
metal
delivery system for discharging a quantity of molten metal to the mold 80 is
located
within an environmentally controlled chamber 109. The molten metal delivery
system 106 is fed molten metal from beneath the surface of the molten metal
within a crucible 111. A supply of metal material 110 passes into the chamber
109
CA 02824923 2013-08-28
37
and is melted within the crucible Ill. The supply of metal material within the
crucible is heated to a super heated state, and for the alloys associated with
casting
turbine engine components the super heat is in the range of 350-400
Fahrenheit.
However, it is understood that other super heat temperatures for these alloys
and
_
other types of metals is contemplated herein.
In one embodiment, the control chamber 109 is supplied with an inert gas
112 that forms a shield and/or membrane to slow surface vaporization of the
molten metal within the crucible 111. Dispensing of the molten metal is
controlled
by a pressure differential between the molten metal delivery system 106 and
the
mold 80. In one embodiment, the discharge of molten metal is controlled by the
application of a positive pressure to the surface of the molten metal, which
in turn
drives a quantity of molten metal from the crucible 111 into the mold 80. The
mold 80 is positioned within a second chamber of the vacuum furnace and is at
a
lower pressure than the molten metal delivery system 106.
With reference to FIGS. 33 and 34, there is illustrated one embodiment 115
of the casting apparatus of the present invention. The casting apparatus 115
includes a dual chambered vacuum furnace 116 with an upper chamber 117 and a
lower chamber 118 separated by a wall 114. The creation of a pressure
difference
between the chambers is utilized to deliver the charge of molten metal to the
mold.
A mold entry port 119 allows for the introduction and removal of casting mold
containers, such as 80, from the lower chamber 118. In one form of the present
invention, the mold entry port 119 defines a fluid tight interlock that
enables the
maintenance of a vacuum environment within the lower chamber 118 as the mold
container 80 is removed or inserted into the lower chamber. Positioned within
the
lower chamber is a rotatable fixture 121 for holding the molds 80 during the
pouring and solidification of the molten metal. A starter seed 421 is
positioned
with the mold container 80 and coupled with the fixture 121. In a preferred
form
of the present invention, the fixture 121 includes a heat transfer apparatus
in heat
transfer communication with the starter seed 421 to withdraw energy from the
starter seed so as to directionally solidify the molten metal within the mold
45.
CA 02824923 2013-08-28
38
A metal material feeder 120 allows for the introduction of unmelted metal
material 137 into the melting crucible 122 located within upper chamber 117.
In
one form of the present invention, the unmelted metal material 137 is in bar
form
and is passed into the crucible without interrupting the operation of the
casting
apparatus 115. In the preferred embodiment, the melting crucible 122 defines a
refractory crucible in which the metal material is inductively heated by an
induction heater 123. It is understood that other forms of heaters, such as
but not
limited to levitation and resistant, are contemplated herein for melting and
elevating the temperature of the metal material within the crucible .122. The
crucible 122 is designed and constructed to hold a quantity of molten metal
from,
which is removed smaller charges of molten metal to fill the individual molds.
The
quantity of molten metal that the crucible can hold is preferably in the range
of
about 5-200 pounds, and more preferably is about 50 pounds. However, as
discussed previously the crucible can have sufficient capacity for a
continuous
process or be sized for an individual single pour. In one embodiment, the
crucible
holding a reservoir of molten metal reduces temperature fluctuations related
to the
delivery of charges of molten metal and the introduction of unmelted metal
material into the crucible for melting. The molten metal 124 within the
melting
crucible 122 passes into a molten metal dispensing system. In one embodiment,
the molten metal dispensing system defines an apparatus for the precision
pouring
of molten metal through a nozzle 253 to a precision located input 78 of the
fill tube
52. A more detailed description of the molten metal dispensing system 125 and
alternate embodiments for dispensing molten metal from the crucible 122 will
be
discussed below.
In one embodiment of the present invention, the rotatable fixture 121 is
liquid cooled and located within the lower chamber 118 of the vacuum furnace.
The heat transfer system is coupled with each of the casting molds 45 and '
maintains a heat transfer pathway during the solidification of the molten
metal.
The rotatable fixture includes a plurality of mold container holders 129. In
the
embodiment of FIG. 34, the mold container holders 129 are spoke members,
however, other structures are contemplated for holding the molds as they are
filled
CA 02824923 2013-08-28
39
with molten metal and solidified into the particular microstructure desired.
The
mold container 80 is rotated to a position 131 wherein the filler tubes inlet
78 is in
alignment with the pouring nozzle 253.
With reference to FIG. 35, there is illustrated an alternate embodiment 135
of the casting apparatus. The casting apparatus 135 is substantially similar
to
casting apparatus 115 and like features will be indicated by like feature
numbers.
The major distinction between the casting apparatus 135 and the casting
apparatus
115 is the inclusion of a seal 136 for forming a fluid tight seal with the
unmelted
metal stock 137 as it moves into the upper chamber 117. In a preferred form,
the
seal 136 abuts an outer surface 137a of the unmelted metal stock 137. The
advancement of the metal stock 137 into the upper chamber 117 in the direction
of
arrow S will cause an increased pressure acting on the molten alloy 124 in the
crucible 122. The increasing of pressure and/or force on the molten metal 124
can
be attributed to the advancement of the metal stock 137 into the molten metal
124
and/or by increasing the pressure of an inert gas 127 supplied through the
valve
126. In a preferred form the inert gas is argon or helium and the pressure
difference associated with the inert gas is 60 milli-torr.
Referring to FIG. 36, there is illustrated another embodiment 140 of the
casting apparatus of the present invention. The casting apparatus 140 is
substantially identical to the casting apparatus 135 with like feature numbers
indicating like features. The casting apparatus 140 provides for the
positioning of
nozzle 253 into the inlet 78 of the metal fill tube 52. The coupling of the
nozzle to
the fill tube enables increased head pressure to improve fill. Further, in one
form
the system is applicable to control molten metal pressure over time.
Therefore,
upon discharge of the molten metal from the nozzle there is a confined
passageway
that the molten alloy passes through to the fill tube 52. In order to
effectuate the
- mating of the nozzle 253 with the inlet 78 of the mold container 80,
the rotatable
fixture 121 is moveable vertically. The fixture 121 is lowered to receive the
mold
container 80 from the mold changer 130 and then raised to position the mold
container in a seating relationship when it is desired to pour the charge of
molten
metal into the mold.
CA 02824923 2013-08-28
Referring to FIG. 37, there is illustrated a casting apparatus 145 that is
substantially similar to the prior casting apparatuses of FIGS. 33-36, with
the
notable difference being the capability of casting apparatus 145 to handle
larger
casting molds. Casting apparatus 145 allows for the introduction of a larger
casting
5 mold 525 through a 'doorway 146 adjoining the lower chamber 528. In one
embodiment, the molten metal 124 is delivered from a molten metal dispensing
system into the inlet 523 of the mold cavity 525. Thereafter, the mold 522 is
withdrawn from the pour position with chamber 528 by an elevator 548.
With reference to FIG. 38, there is illustrated one embodiment of a heat
10 transfer apparatus 150 for causing heat transfer with a metallic starter
seed 151. In
a preferred form the thermal gradient across the seed is varied over time.
More
particularly, in one embodiment the thermal gradient is low during nucleation
and
substantially higher during the growth of the crystal. The thermal gradient in
one
form is greater than about 550 F/inch at the liquid to solid interface. In
one
15 embodiment the starter seed 151 has a length 'B' within a range of about
0.25
inches to about 3.00 inches, however, other starter seeds lengths are
contemplated
herein. Heat transfer apparatus 150 has a pair of jaws 152 that are normally
mechanically biased to place a surface 154 of the jaws in an abutting
thermally
conductive arrangement with the body of the starter seed 151. The jaws 152
20 maintain a heat transfer path with the starter seed 151 as the molten
metal
solidifies. A mechanical actuation structure 153 has a pair of moveable arms
155
that are normally spring biased towards a closed position so that the surfaces
154
are maintained in contact with the starter seed 151. The starter seed 151 is
readily
decoupled from the heat transfer apparatus 150 by applying a mechanical force
F
25 to the ends of the arms 154 and 155.
Each of the pair of jaws 152 has an internal cooling passageway 530 therein
for receiving a quantity of heat transfer media 161 therethrough to change the
temperature of the starter seed 151. While the heat transfer apparatus 150
utilizes
an active cooling system the present disclosure also contemplates a passive
cooling
30 system. Preferably, the heat transfer media 161 is a coolant/sink for
withdrawing
energy/heat from the metallic starter seed 151. The heat is passed by
conduction
CA 02824923 2013-08-28
,
41
from the molten metal solidifying within the mold cavity to the starter seed.
Thereafter the passage of cooling media through the jaws 152 causes heat
transfer
_
through the starter seed to cause a thermal gradient and directional
solidification of
= the molten metal within the mold cavity. Further, many types of cooling
media
may be used. The simplest type being solids whose heat capacity and/or phase
changes make them attractive, such as but not limited to copper. A fluid, such
as
water and/or argon may also define the cooling media. Further, heat transfer
cooling media with higher heat transfer capacity or heat transfer include
liquid
metals like aluminum, tin, or mercury.
Referring to FIG. 39, there is illustrated an alternate embodiment 165 of the
heat transfer apparatus of the present invention. In a preferred form the
thermal
gradient across the seed is varied over time. More particularly, in one
embodiment
the thermal gradient is low during nucleation and substantially higher during
growth of the crystal. The thermal gradient in one form is greater than about
5500
F/inch at the liquid to solid interface. The heat transfer apparatus 165 is
substantially similar to heat transfer apparatus 150 with a distinction being
the
capability to locally heat the metallic starter seed 151 through the pair of
jaws 166.
Further, in one embodiment the starter seed can be locally heated and cooled
at the
same time. The ability to heat is utilized to adjust the heat flux at the seed
and
molten metal interface. Since the heat transfer apparatus 150 and the heat
transfer
apparatus 165 are substantially similar like features will be given the same
feature
number. In a preferred embodiment of the heat transfer apparatus 165, the jaws
166 are connected to a source of electrical power by leads 531 and the passage
of
current through the jaws 166 causes the resistant heating of the metallic
starter seed
151. The ability to locally heat the metallic starter seed 151 is desirable to
control
the crystal structure growth from the starter seed 151.
With reference to FIGS. 40 and 41, there is illustrated another embodiment
170 of a heat transfer apparatus for transferring heat with a metallic starter
seed
171. In a preferred form the thermal gradient across the seed is varied over
time.
More particularly, in one embodiment the thermal gradient is low during
nucleation
and substantially higher gradient during growth of the crystal. The thermal
CA 02824923 2013-08-28
42
gradient in one form is greater than about 550 F/inch. Starter seed 171 is
substantially similar to the metallic starter seed 151 and additionally
includes a pair
of precision locating features 172. The metallic starter seed 171 is located
within
an opening in the mold container 80 and is placed in communication with the
metal
receiving cavity such that upon pouring molten metal therein a portion of the
metallic starter seed 171 receives molten metal thereagainst and is partially
melted.
The precision locating features 172 are designed and constructed to receive a
contacting end 174 of each of a pair of jaws 173. A heat removal end 175 of
each
of the jaws 173 is positioned within a housing 180. The housing 180 has a
passageway 176 therein for the passage of a cooling media. The passage of the
cooling media through the housing 180 and across the heat removal ends 175 of
the
jaws is depicted diagrammatically by arrows. In one embodiment, a local heater
178 is coupled to the mechanical housing 180. Heater 178 is in a thermally
conductive heat transfer relationship with the pair of jaws 173 so as to
impart
energy to the starter seed 171 through the contacting ends 174 of the jaws.
The
local heater 178 is controlled to adjust the heat flux at the interface
between the
molten metal and the metallic starter seed. A mechanical actuator 177 is
utilized to
open the heat transfer apparatus jaws 173 from the position shown in FIG. 40
and
then close the pair of jaws 173 to the position shown in FIG. 41. The actuator
177
is preferably a hydraulic actuator, however, other actuators having the
properties
necessary to function in a casting environment are contemplated herein.
With reference to FIG. 42, there is illustrated a mold 185 having an internal
cavity 186 for the receipt of molten metal. The mold 186 has a vent end 187
for
the passage of gaseous material to and from the internal cavity 186 and
starter seed
receiving inlet 189 for receiving and snugly engaging a metallic starter seed
188.
The metallic starter seed 188 is positioned to receive molten metal on a
surface
188a. The metallic starter seed is not intended to be limited to the seed
shape
shown in FIG. 42 as other seed shapes are contemplated herein. Located within
the
mold 185 is a starter seed auxiliary heater 195 and a supplemental mold heater
196.
An insulator 190 is positioned between a lower surface 185a of the mold 185
and a
heat transfer apparatus 191 to minimize heat transfer from the casting mold
185. In
CA 02824923 2013-08-28
43
a preferred form the thermal gradient across the seed is varied over time.
More
particularly, in one embodiment the thermal gradient is low during nucleation
and
substantially higher during growth of the crystal. The thermal gradient in one
form
is greater than about 550 F/inch at the liquid to solid interface.
The heat transfer apparatus 191 includes a pair of arms 193 and 194 that are
moveable into a position to abut and maintain contact with a surface 198 of
the
starter seed 188. The abutting relationship of the heat transfer apparatus 191
and
the starter seed 199 is maintainable until the arms 193 and 194 are positively
released from the starter seed 188. A precision locating member 192 contacts a
bottom surface 188b of the starter seed 188 so as to precisely locate the
vertical
height of the melt surfaces 188a within the molten metal receiving cavity 186.
A
cooling media passageway 197 is formed in each of the pair of arms 193 and 194
for the passage of cooling media therethrough. The molten metal within the
cavity =
185 transfers heat to the starter seed 188 which in turn transfers the heat
through
the surfaces 198 to the chilled pair of arms 193 and 194. The cooling media
flowing through the passageways 197 removes the heat from the arms 193 and
194.
Thus a temperature gradient is created through the starter seed 188 to cause
directional solidification of the molten metal within the cavity 186.
With reference to FIG. 43, there is illustrated a mold container 200 coupled
with the heat transfer apparatus 191. The mold container 200 is substantially
similar to mold container 80 and substantially identical features will be
indicated
by like feature numbers. The thin wall integral mold 45 has an internal cavity
186
with a top portion 186a, a bottom portion 186b, and a side portion 186c.
Positioned proximate the top portion 186a is a vent 79 for allowing the
passage of
hot gaseous material to and from the cavity 186. The starter seed receiving
inlet
189 is formed in the bottom portion 186b, and the side portion 186c is
insulated to
minimize heat transfer from the side wall 49 of the mold. In a preferred form
the
thermal gradient across the seed is varied over time. More particularly, in
one
embodiment the thermal gradient is low during nucleation and substantially
higher
during growth of the crystal. The thermal gradient in one form is greater than
about 550 F/inch at the liquid to solid interface. The shape of the molten
metal
CA 02824923 2013-08-28
44
receiving cavity 186 is purely illustrative and is not intended to be limiting
to the
present invention.
Referring to FIG. 44, there is illustrated an alternate embodiment 201 of a
heat transfer apparatus for withdrawing heat through a starter seed positioned
within a casting mold. In a preferred form the thermal gradient across the
seed is
varied over time. More particularly, in one embodiment the thermal gradient is
low during nucleation and substantially higher during growth of the crystal.
The
thermal gradient in one form is greater than about 550 F/inch. In one
embodiment, the integral heat transfer apparatus 201 has a starter seed
portion 202,
a precision locating surface 203, and a passageway 204 therethrough. The
starter
seed portion 202 is received within and abuts a surface 550 of the thin
ceramic
shell of the mold. The vertical position of the starter seed portion 202 is
fixed by
the precision locating member 192 which abuts the precision locating surface
203.
The passageway 204 is formed through the heat transfer apparatus 201 and is
designed for the passage of a heat transfer media. More particularly, the
passageway is designed to be coupled with a pair of couplers 205 (only one
illustrated) that are firmly engagable and alignable with a bearing surface
206
formed on the heat transfer apparatus. With the pair of couplers 205 connected
with the heat transfer apparatus 201 and aligned with the passageway 204, a
flow
of heat transfer media can pass through a passageway 551 within the coupler
205
and into the passageway 204 of the heat transfer apparatus 201.
The bearing surface 206 and a corresponding surface on each of the
couplers 205 creates a substantially fluid tight seal to prevent the leakage
of the
cooling media around the joint. Further, in one embodiment, the bearing
surface
206 defines an electrical contact such that upon the pair of couplers 205
being
mated with the heat transfer apparatus 201 a circuit is completed and current
can be
passed through the heat transfer apparatus 201 to create a heater for heating
the
seed portion 202. The heat transfer apparatus 201 allows for the localized
heating
of the starter seed portion 202 and the withdrawal of energy from the molten
metal
solidifying in the mold on the starter seed portion 202.
CA 02824923 2013-08-28
With reference to FIG. 45, there is illustrated a perspective view of one
embodiment of the energy transfer apparatus 201 removed from its abutting
- =
relationship with the thin ceramic shell of the mold. In one form, the energy
transfer apparatus 201 has an integral main body 207, which includes the
starter
= =
5 seed portion 202. The starter seed portion is position able within the
seed receiving
portion of a casting mold such that molten metal can flow across the melt
surface
208 in the direction of arrow F. However, the present invention is not limited
to an
integral system and including an assembled system having a variety of
geometry's
and flow paths.
10 With reference to FIG. 46A and 468, there is illustrated a portion
of a
casting mold 210. In a preferred form, the casting mold 210 is formed by
selective
laser activation or three dimensional printing, however, the mold is not
intended to
be limited herein to a mold made by these processes and can be produced by
other
processes known to one of ordinary skill in the art. The casting mold 210
includes
15 a pour tube 211 that provides a passageway for the delivery of molten
metal to the
cavity 212 within the integral casting mold 210. In one embodiment, a starter
seed
213 is positioned within the casting mold 210 and is located by a locating
member
214 so as to place the initial melting surface 215a of the starter seed 213 at
a
predetermined position relative to the discharge portion 216 of a diffuser
211a.
20 The diffuser 21 la provides for the full coverage with molten metal of
the initial
melting surface 215a of the starter seed. The walls of the diffuser portion
211a
open at an angle (1), which is preferably within the range of 15 ¨45 degrees.
The
diffuser portion 211a slowing the movement of the molten metal across the
starter
seed to increase the energy transferred to the starter seed 213 during an
initial melt
25 of a portion of the starter seed body. In one embodiment, the elevation
of the
initial melting surface 215 and configuration of the diffuser portion 211a are
selected to maximize the amount of heat removed from the molten metal and
transferred to the starter seed 213 in order to melt a portion of the seed.
In one embodiment of the present invention a meltable member 220 is
30 positionable within the casting mold 210 such that the flow of molten
metal melts
the member 220 and delivers the material comprising the meltable member along
CA 02824923 2013-08-28
46
with the molten metal into the mold cavity 212. The meltable member 220 is
positioned within a portion of the pour tube 211. However, the placement of
the
meltable member 220 may be in other places such as the diffuser 211a. In a
preferred form, the member 220 is a wire or mesh that does not substantially
impede the flow of molten metal through the fill tube 211 and is readily
melted by
the heat of the molten metal. The meltable member 220 is melted and mixes with
the molten alloy and imparts properties to the cast component such as, but not
limited to improved ductility ancUor oxidation resistance. In one form the
meltable
member 220 is formed of a reactive metal such as, but not limited to a rare
earth
elements.
With references to FIGS. 47A-47C, there is illustrated the melt back of a
portion of a starter seed 188 as molten metal flows in the direction of arrow
G
across the melt surface 188a. The starter seed 188 is a metallic member having
a
melt end and a base end that is contactable with a heat transfer device to
transfer
heat to and/or from the member. A melt acceleration portion 225 is formed at
the
melt end and has an initial height of material indicated by P. With reference
to
FIG. 47A, there is shown the melt portion in an unmelted state and it has a
cross
sectional area less than the cross sectional area of the base end. After a
period of
time in which the molten metal has flowed across surface 188a, the melt
portion
225 has been partially melted back. Surface 188b (FIG. 47B) indicates the
profile
of the melt portion 225 after having molten metal passed thereon for a period
of
time, and its height is indicated by Q. Moving to FIG. 47C, the process of
melting
continues as additional molten metal flows across the melt portion 225 and the
profile is represented by 188C, and has a height indicated by R. As the
melting of
the melt portion 225 continues, the surface area of the melt portion from
which
heat transfer from the solidifying metal occurs begins to approach the same
size as
the surface area of the base 226 of the starter seed 188. When the melt back
of the
seed is completed in one embodiment the melt portion has a cross sectional
area
substantially equal to the base end so as not to restrict heat transfer from
the molten
metal to the starter seed.
CA 02824923 2013-08-28
47
With reference to FIGS. 48 and 49, there are illustrated other embodiments
of starter seeds contemplated herein. Starter seed 230 has a melt acceleration
portion 231 that is semi-circular in cross section, however, other geometric
shapes
such as but not limited to a grooved surface and/or a knurled surface are
contemplated herein. The starter seed 235 has a melt portion 235a and a
passageway 236 formed therein for the passage of a heat transfer media. It is
understood herein that the starter seed can have other geometric shapes and
may
not have a melt acceleration portion 235a, while still having a passageway for
the
flow of a heat transfer material. In an alternate embodiment there is
contemplated
a plurality of internal passageways to form a more intricate cooling
passageway.
With reference to FIG. 50, there is illustrated another embodiment 230 of
the apparatus for dispensing molten metal from a casting apparatus, such as
casting
apparatus 115. The melting crucible 231 is substantially identical to=the
melting
crucible 122 except that the molten metal does not pass through an aperture in
the
bottom wall member. A molten metal delivery passageway 232 has an input end
233 and a discharge end 234. Input end 233 is fed molten metal from beneath
the
surface of the molten metal and the passageway 232 is filled to the height of
the
column of molten metal within the crucible 231. The discharge of the molten
metal from the delivery passageway 232 into the mold container 80 is
controlled by
the difference in pressure between the chamber 117 and chamber 118.
The molten metal delivery passageway 232 includes a positive molten
metal flow control feature. In one embodiment the portion 232a of the
passageway
232 functions as a flow control means. Upon the application of sufficient
pressure
to the molten metal within the crucible the passageway 232 is filled with
molten
metal. Upon releasing the applied pressure molten metal will return to the
crucible
and be maintained at a height within the passageway substantially equal to the
height of the molten metal within the crucible. In one form, the delivery of
molten
metal from portion 232a and out nozzle 600 will have a predetermined pressure
and velocity controlled by the height "C" plus the pressure difference between
chamber 117 and chamber 118. The activation energy necessary to fill the
passageway 232 is indicated by "D".
CA 02824923 2013-08-28
48
In a preferred form of the apparatus the discharge of molten metal is
controlled by the application of pressure to the molten metal within the
crucible
231. As discussed previously, the pressure applied to the molten metal can be
created by advancing the metal stock 137 into the molten metal and/or by
applying
pressure to the surface of the molten metal with an inert gas. Upon the
increase in
pressure on the surface of the molten metal, additional molten metal is forced
through the input end 233 and up through the delivery passageway 232 to the
output end 234. At the output end 234 the molten metal passes through a nozzle
600 to the mold container inlet. Upon release of the pressure on the molten
metal,
the molten metal beyond point 235 is delivered, and the remaining molten metal
within the passageway remains there and/or is returned to the crucible 231.
Therefore, the delivery of molten metal to the mold container 80 is controlled
by
the difference in pressure between chamber -117 and 118. In an alternate
embodiment, the passage of molten metal to the mold container 80 could be
effectuated by lowering the pressure around the container instead of raising
the
pressure on the molten metal.
With reference to FIG. 51, there is illustrated an alternate embodiment 240
of the molten metal dispensing system for dispensing molten metal from a
casting
apparatus, such as casting apparatus 115. More particularly, the molten metal
dispensing system 240 is located within the upper chamber 117 and the mold 80
is
located within the lower chamber 118. Crucible 241 is substantially similar to
the
crucible 122 and is heated by the heater 123 to melt the metal material stock.
A
crucible discharge aperture 242 is formed in the crucible and aligned with a
passageway 243 through the wall member 114. A stopper rod 244 is disposed
within the upper chamber 117 and moveable between a position wherein a sealing
surface 245 engages the wall of the crucible around aperture 242 to prevent
the
passage of molten metal therethrough, and another position wherein the sealing
surface 245 is removed from the abutting relationship with the walls around
the
aperture 242. Gravitational forces will allow the passage of the molten metal
into
the mold 80 upon the removal of the stopper rod sealing surface 245 from it's
sealing position.
CA 02824923 2013-08-28
=
49
With reference to FIG. 52, there is illustrated an enlarged view of the
crucible 122 with the molten metal dispensing system 125 located therein. The
crucible 122 having an aperture 700. The molten metal dispensing system 125
includes an outer passageway 250 and an inner passageway 251 that are in fluid
communication with each other and the crucible 122. A plurality of filling
apertures 252 allow the molten metal within the crucible 122 to flow into the
outer
passageway 250 of the system 125. Upon the outer passageway 250 being filled
with molten metal, the molten metal can overflow into an inlet end 251a of the
inner passageway 251. The inner passageway 251 has an outlet end 251b through
which the molten metal flows to a nozzle 253. A portion 255 of the inner
passageway 251 around the nozzle 253 allows the accumulation of molten metal -
which is used to maintain the temperature of the nozzle 253 close to that of
the
crucible of molten metal.
In one embodiment, a heat shield and/or heater 254 is spaced from and
positioned around the nozzle 253 to mechanically guard the nozzle and reduce
heat
loss therefrom. The nozzle 253 passes through the aperture 700 in the crucible
and
has a discharge aperture designed to provide a concentrated stream of molten
metal. In one form the stream of molten metal is discharged substantially
vertical,
however in alternate embodiments the stream is discharged in other relative
directions. In one embodiment the discharge aperture has a diameter of about
0.125 inches, however, other sizes are contemplated herein. Further, the
nozzle is
self cleaning in that it purges itself every time the discharge of molten
metal is
completed. More specifically, in one embodiment the nozzle 253 has a pointed
end
253a.
The structure of the molten metal dispensing system 125 preferably
includes an outer member 257 having the plurality of inlet fill holes 252
formed
= therethrough with an inner member 256 spaced therefrom. The inner member
256
and the outer member 257 are preferably formed of alumina or other suitable
ceramics, and the outer member includes four equally spaced inlet fill holes
252,
however other numbers and spacing of inlet holes is contemplated herein. The
inner and outer members being coupled to the base of the crucible 122. More
CA 02824923 2013-08-28
preferably, the dispensing system 125 defines a first upstanding outer tube
257 that
is closed at one end and a second upstanding inner tube 256 spaced inwardly
therefrom. The inner tube 256 and outer tube 257 are coupled to the bottom
wall
member 701 of the crucible 122 and positioned around the aperture 700. In a
5 preferred embodiment the inner tube 256 defines a metering cavity for
holding a
predetermined volume of molten metal therein.
With reference to FIG. 52a, there is illustrated an alternate embodiment of
the molten metal dispensing system. The molten metal dispensing system 650 is
positioned within a mechanical housing/crucible 651. The mechanical housing
has
10 an interior volume 652 adapted to receive molten metal therein. The
molten metal
dispensing system includes a member 653 having a passageway 654 formed
therein. At one end of the passageway 654 is a molten metal inlet 655 and at
the
other end is a molten metal outlet In an alternate embodiment only a portion
of
the molten metal dispensing system is located within the interior volume where
15 molten metal is located. An inflection portion 655 is defined within the
passageway 654. The molten metal enters the passageway 654 and flows through
the passageway to the height of the molten metal within the housing 651. Upon
the
application of a pressure to the molten metal within the mechanical housing
the
molten metal is driven to the inflection portion 655, and continues through
the
20 passageway 654 to the molten metal outlet and is discharged. In one form
the
molten metal flows in a first direction indicated by arrow A to the inflection
portion 655 and from the inflection portion 655 in a second direction as
indicated
by arrow B. The molten metal inlet 655 is located beneath the surface 670 of
the
molten metal within the interior volume. In one embodiment the molten metal
25 dispensing system is integrally formed.
In a preferred form of the molten metal dispensing system 650 the
passageways have substantially upstanding portions that meet with the
inflection
portion to form a substantially U shape passageway. Further, it is preferred
that
the inflection portion is above the molten metal height within the mechanical
30 housing/crucible 651. In one form a portion of the passageway varies in
cross-
sectional area between the molten metal inlet and the molten metal outlet. In
a
CA 02824923 2013-08-28
51
more preferred form at least a portion of the passageway tapers prior to the
inflection portion, and more preferably defines a passageway having a frustum-
conical shape. In one embodiment the passageway 654 has a vent 700 disposed in
fluid communication therewith. However in an alternate embodiment the
passageway does not have the vent 700 connected therewith. The vent has
utilization for venting the passageway and allowing the purging of the
passageway
with a pressurized fluid. The present invention contemplates other geometric
shapes and sizes for the components of the molten metal dispensing system.
With reference to FIGS. 53A-53E, there is illustrated the process of
dispensing molten metal from one embodiment of the molten metal dispensing
system 125. As the unmelted metal material 137 is advanced into the crucible
122
the material is melted and forms a quantity of molten metal 124. The molten
metal
124 flows through the plurality of filling apertures 252 into the outer
passageway
250 of the system 125. The continued advancement of the unmelted metal stock
137 into the crucible and the subsequent melting thereof raises the height H
of the
molten metal within the crucible 122 to the height of the inlet end 25Ia of
the inner
passageway 251. In order to fill the inner passageway/metering chamber 251
with
molten metal it is necessary to apply an additional force to the molten metal
124
within the chamber.
The additional force can be applied by the continued advancement of the
unmelted metal material 137 into the quantity of melted metal within the
crucible.
A second method for increasing the pressure on the molten metal 124 within the
crucible is to introduce a pressurized inert gas against the surface of the
molten
alloy. The additional pressure on the molten metal will cause the continued
flow of
molten metal through the filling apertures 252. Subsequent overflowing of the
molten metal from the outer passageway 250 to the inlet end 251a of the inner
passageway. The filling of the inner passageway is a relatively quick process
as the
filling apertures 252 have been sized to allow an inflow of material that is
significantly greater than the nozzle 253 can discharge from the inner
passageway.
Upon the inner passageway 251 being substantially filled with molten metal,
the
pressure applied to the surface 124a is removed such that the inner passageway
251
CA 02824923 2013-08-28
52
no longer receives molten metal from the outer passageway 250 and the inner
passageway discharges its charge of molten metal through the nozzle 253 in a
concentrated stream.
In one embodiment of the molten metal dispensing system, a sensor 800
(FIG. 53D) is positioned proximate the nozzle 253 to detect the initial flow
of
molten metal from the nozzle. Upon the detection of the initial flow of molten
metal from the nozzle 253, the sensor will send a signal to have the
additional
pressure removed from the surface 124a of the molten metal. In one embodiment
the signal is sent to a controller that controls the application of pressure
to the
molten metal. The early indication of a slight molten metal discharge from the
nozzle 253 is substantially contemporaneous with the completion of filling of
the
inner passageway 251 due to the difference in the total size of the filling
apertures
252 and the nozzle aperture. In one embodiment, the material inflow through
filing
apertures 252 is significantly greater than the material outflow through the
nozzle
aperture.
With reference to FIG. 54, there is an illustration of the pressure of the
molten metal as a function of time. In one embodiment illustrated in FIG. 36
the
nozzle 253 is coupled in fluid communication to the inlet 78 of the fill tube
52.
Flow of molten metal can then be initiated by either increasing the pressure
in
chamber 117 or reducing the pressure in chamber 118. The reduction in pressure
in 118 can function to: vacuum the internal mold cavity and thereby remove
loose
material like residual powder; and/or reduce the mold gases level to protect
reactive elements like aluminum, titanium, and halfnium. Further, the increase
in
pressure in chamber 117 would aid in the fill of details in the mold cavity.
The
higher pressures within chamber 117 can be used to suppress reactions among
many materials as well as reduce shrinkage from solidification.
With reference to FIG. 55, there is illustrated a gas turbine engine blade 30
positioned within furnace 801 for having post casting operations performed
thereon. The post casting processing operations for a single crystal and/or
columnar grain casting include: a hot isostatic pressing operation; a
homogenizing
operation; and, a quench operation. The hot isostatic pressing operation
involves
CA 02824923 2013-08-28
53
placing the component 30 within the furnace 801 and subjecting the component
to
high temperature and pressure so as to remove porosity from the cast
structure. In
_
one embodiment, the hot isostatic processing taking place at a temperature of
about
2375 to 2400 degrees Fahrenheit and at a pressure of about 30,000 lbs. per
square
inch. The pressure is preferably supplied by an inert gas, such as argon. With
reference to FIG. 55, the pressure is indicated by arrows 802 and the
temperature is
indicated by arrows 803.
Subsequent to the hot isostatic pressing operation, the component is
subjected to a homogenizing operation that causes diffusion between the
elements
that may have separated during the solidification process and is designed to
raise
the incipient melting point of the cast structure. The homogenizing cycle is
concluded by subjecting the component to a quenching step and subsequent
tempering operations.
In one embodiment of the present invention, the three post casting
operations are combined into a sequential process within the furnace 801. The
hot
isostatic pressing operation is performed within the furnace 801 by raising
the
temperature and pressure within the furnace 801 for a period of time so as to
reduce the porosity in the casting. Thereafter, the temperature within the
furnace
801 is raised to a value within about 25 degrees Fahrenheit of the incipient
melting
point of the material forming the component 30. Preferably the temperature
within
the furnace 801 is raised to within 5 Fahrenheit of the melting point of the
material for a period of time. After the completion of the homogenizing
operation,
the quenching operation is undertaken by the high pressure transfer of a cold
inert
gas into the furnace 801. The aging of the cast component can continue under
vacuum or pressure as desired.
A preferred form of the casting operation allows the growth of a single
crystal at a rate up to about 100 inches per hour and more preferably at a
rate of
about 60 inches per hour. However, other growth rates are contemplated herein.
The ability to grow the crystal at these rates minimizes the segregation of
elements
in the alloy that occur during slower solidification processes. Due to the
decrease
in segregation of the elements in the alloy, the homogenizing cycle of the
post
CA 02824923 2013-08-28
54
casting operation can be accomplished in about 24 hours, and more preferably
is
accomplished in about 2 hours. The utilization of a high thermal gradient and
a
relatively short starter seed lead to faster processing; lower shrinkage,
which gives
improved fatigue properties; and lower segregation, which facilitates higher
stress
rupture strength.
With reference to FIG. 56, there is illustrated a metallic columnar grain
starter seed 900. The starter seed 900 is designed to grow a directionally
solidified
columnar grain component 901. The starter seed 900 has very fine grains 902
that
are desired to be replicated in the cast component. This strictly oriented
crystallographic structure of the metallic starter seed 900 is used to impart
this
structure to the cast component.
While the invention has been illustrated and described in detail in the
drawings and foregoing description, the same is to be considered as
illustrative and
not restrictive in character, it being understood that only the preferred
embodiment
has been shown and described and that all changes and modifications that come
within the spirit of the invention are desired to be protected.
