Apparatus and method for molding an article

An apparatus and method for use in casting a metal article includes a mold structure having wall sections with pins extending between the wall sections. The pins have opposite end portions which are embedded in the wall sections of the mold structure to interlock the pins and the wall sections of the mold structure. When molten metal is poured into the mold structure, the molten metal urges the wall sections away from each other. The wall sections are retained against movement relative to each other by the pins. Although the apparatus and method of the present invention can be utilized to cast many different types of articles, the invention is advantageously utilized in the casting of thin metal articles and specifically a thin metal article which is formed as a single crystal.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved method and apparatus 
for use in casting a metal article and more specifically to a method and 
apparatus which may be used in casting of a thin metal article. 
When a thin metal article is to be cast, a thin mold cavity is formed to 
shape molten metal to the desired configuration of the article. When 
molten metal is poured into the mold cavity, opposite side walls of the 
mold tend to bulge or creep under the influence of the force applied 
against the inner side surfaces of the mold by the molten metal. Various 
attempts to solve this problem have been made but with only marginal 
improvement. The attempts to solve the problem have included extra ceramic 
dips for a shell forming the mold, ceramic reinforcement rods on the mold, 
wrapping the mold with ceramic fiber, and running what has been referred 
to as a hot process only near the growth interface in the mold. 
SUMMARY OF THE INVENTION 
The present invention provides a new improved method and apparatus for use 
in casting a metal article. The apparatus includes a mold structure having 
one or more pins which extend between wall sections of the mold structure. 
A first end portion of a pin is disposed in the first wall section of the 
mold structure and a second end portion of the pin is disposed in a second 
wall section of the mold structure. A third or connector portion of the 
pin is disposed in the mold cavity. The end portions of the pin and the 
wall sections of the mold structure are interlocked to prevent relative 
movement between the wall sections. 
To interlock the end portions of a pin and a wall section of the mold 
structure, in some embodiments of the invention the pin has a surface 
which faces toward the mold cavity and transmits force to the wall section 
of the mold structure. The end portion of the pin may have an outwardly 
flaring head end section, a circular groove, and/or a roughened portion 
which provides an interlock with the ceramic material of the wall section 
of the mold. 
In another embodiment of the invention, the pins have central axes which 
are disposed in different orientations relative to a wall section of the 
mold. These pins apply forces in different directions relative to the mold 
structure. 
Although the method and apparatus of the present invention may be utilized 
to cast may different types of objects, it is believed that the method and 
apparatus will be particularly advantageous in casting relatively long, 
and/or wide metal objects which are very thin. Thus, the method and 
apparatus may be used to cast a metal object having a thickness of 0.050 
or less and a length and width of four inches or more. Although the thin 
metal article could be formed of many different metals having any one of 
many different crystallographic structures, the method and apparatus may 
advantageously be used to form a single crystal metal article, such as a 
plate or airfoil.

DESCRIPTION OF SPECIFIC PREFERRED EMBODIMENTS OF THE INVENTION 
Cast Metal Article 
A thin metal panel 12 (FIG. 1) is formed as a single crystal of metal using 
the method and apparatus of the present invention. The thin metal panel 12 
includes a thin flat main section 14. The thin main section 14 has flat 
parallel side surfaces 16 and 18 (FIG. 2). A rectangular array of linear 
ribs 22 extend from the side surface 16 of the main section 14 of the 
panel 12. The ribs 22 reinforce the main section 14 of the metal panel. If 
desired, the ribs 22 could be omitted. 
A plurality of relatively small holes or openings 24 (FIGS. 1 and 2) are 
formed in the main section 14 of the panel 12. Although there are nine 
openings 24 in each rectangular cell or section of the array of ribs 22, a 
greater or lesser number of openings could be provided if desired. 
The main section 14 of the panel 12 is relatively thin. Thus, the main 
section 14 of the panel 12 has a thickness, that is, the distance between 
the side surfaces 16 and 18 of FIG. 2, of 0.050 inches or less. In one 
specific embodiment of the panel 12, the main section 14 of the panel had 
a thickness of 0.015 inches. In this specific embodiment of the panel 12, 
the ribs 22 had a thickness of 0.020 inches and a height, that is, the 
distance from the side surface 16 (FIG. 2) of the rib to the outer edge of 
the rib, of 0.060 inches. 
In this specific embodiment of the panel 12, the thin metal panel was 
formed as a single crystal of metal. Specifically, the thin metal panel 12 
was cast as a single crystal of a nickel-chrome superalloy metal. However, 
it should be understood that the thin metal panel 12 could be formed with 
a different crystallographic structure and/or of a different material if 
desired. For example, it is contemplated that the thin metal panel 12 
could have a columnar grained or equiaxed crystallographic structure. The 
metal panel 12 could be formed of a metal other than a nickel-chrome 
superalloy, for instance, the metal could be titanium or a titanium alloy. 
The thin metal panel 12 is relatively long and wide. Thus, the main section 
14 of the panel has a length of more than four inches and a width of more 
than four inches. In the illustrated embodiment of the panel 12, the thin 
metal panel has a width of approximately five inches and a height of 
approximately seven inches. However, it is contemplated that the thin 
metal panel 12 could be formed with many different dimensions. For 
example, the thin metal panel 12 could have a square configuration with a 
height and width of approximately four inches. Although the thin metal 
panel 12 has been illustrated in FIG. 1 as being the entire metal article, 
the thin metal panel could form a portion of a larger cast article. 
It should be understood that the method and apparatus of the present 
invention may be used in the formation of articles other than thin metal 
panels. For example, the cast metal article could be a thin metal airfoil 
having the same general construction disclosed in U.S. Pat. No. 4,905,752 
issued Mar. 6, 1990 and entitled "Method of Casting a Metal Article". 
Alternatively, the metal article could be a turbine engine component 
having a construction similar to the construction illustrated in U.S. Pat. 
No. 4,724,891 issued Feb. 16, 1988 and entitled "Thin Wall Casting". It is 
contemplated that the thin metal panel 12 could be an interior wall of an 
airfoil which is cast as one piece. 
The method and/or apparatus of the present invention are advantageously 
utilized to cast large thin metal articles. As used herein, a large thin 
metal article is a metal article having a height and a width of more than 
four inches and a thickness of 0.050 inches or less. However, the method 
and/or apparatus of the present invention may be used to cast articles of 
any desired size, including large thick articles or hollow articles. 
Mold Structure 
A mold structure 32 (FIG. 3), constructed in accordance with the present 
invention, is used to cast the thin metal panel 12 as a single crystal. 
The mold structure 32 includes an article mold 34 having an article mold 
cavity 36 in which the thin metal panel 12 is cast as a single crystal of 
metal. The article mold cavity 36 has a configuration which corresponds to 
the configuration of the thin metal panel 12. Of course, if a different 
article was to be cast, such as an airfoil, the article mold cavity 36 
would have a configuration corresponding to the configuration of the 
article to be cast. 
A pour cup 40 is connected with the upper portion of the article mold 34 
and is connected in fluid communication with the article mold cavity 36. A 
single crystal selector 42 extends downward from the article mold 34 to a 
starter 44. The starter 44 is disposed on a chill plate 46. The 
construction of the single crystal selector 42 and starter 44 is the same 
as disclosed in U.S. Pat. No. 4,940,073 issued Jul. 10, 1990 and entitled 
"Mold For Casting a Single Crystal Metal Article". However, single crystal 
selectors and starters having a different construction could be used if 
desired. 
When the thin metal panel 12 is to be cast in the article mold cavity 36 of 
the mold structure 32, molten metal is poured into the pour cup 40. The 
molten metal flows from the pour cup 40 through the article mold cavity 36 
and single crystal selector 42 into the starter 44. The molten metal 
solidifies in the starter 44 as a plurality of elongated grains or 
crystals which extend upward from the chill plate 46 to the upper end of 
the starter. A few of the grains of metal grow from the starter 44 into 
the single crystal selector 42. 
As the few grains which enter the single crystal selector 42 continue to 
grow, the most favorably oriented grain or crystal grows at a greater rate 
than the other grains or crystals. Therefore, the most favorably oriented 
grain or crystal crowds out the less favorably oriented grains. This 
results in the single grain or crystal which is most favorably oriented 
growing from the crystal selector 42 into the article mold cavity 36. 
The single grain or crystal which emerges from the crystal selector 42 into 
the article mold cavity 36 solidifies to completely fill the article mold 
cavity. The single crystal of metal which solidifies in the article mold 
cavity 36 has a configuration which corresponds to the desired 
configuration of the article to be cast. Thus, in the illustrated 
embodiment of the invention, the single crystal of metal solidifies with 
the desired configuration for the thin metal panel 12. The molten metal in 
the pour cup 40 then solidifies. During solidification of the molten metal 
in the pour cup 40, additional crystals may nucleate. 
It should be understood that mold structures constructed in accordance with 
the present invention may be used to cast articles having many different 
crystallographic structures. When the article to be cast does not have a 
single crystal type crystallographic structure, the crystal selector 42 
and starter 44 would not be included in the mold structure. 
The mold structure 32 illustrated schematically in FIG. 3, has a relatively 
simple construction. It is contemplated that the mold structure 32 could, 
and probably will, have a more complex construction than the construction 
illustrated in FIG. 3. For example, the mold structure 32 could include a 
plurality of core sections enclosed by outer wall sections. If desired, 
the mold structure 32 could include gating which interconnects a plurality 
of article mold cavities. 
Retainer Pins 
The article mold portion 34 of the mold structure 32 includes a pair of 
parallel wall sections 50 and 52 (FIG. 4). The article mold cavity 36 in 
which the thin metal panel 12 is cast, is disposed between the wall 
sections 50 and 52. When the molten metal flows from the pour cup 40 into 
the article mold cavity 36, fluid pressure is applied against opposite 
side surfaces 54 and 56 of the wall sections 50 and 52. 
The fluid pressure applied against the wall sections 50 and 52 by the 
molten metal tends to cause the wall sections to creep or bulge. Thus, the 
wall sections 50 and 52 tend to move away from each other thereby 
increasing the distance between the side surfaces 54 and 56 and the 
thickness of the main section 14 of the thin metal panel 12. Since the 
main section 14 of the thin metal panel 12 is relatively thin, that is, 
0.050 inches or less, even a small amount of deflection of the wall 
sections 50 and 52 can result in a substantial percentage increase in the 
thickness of the main section of the thin metal panel. 
In accordance with one of the features of the present invention, retainer 
pins 60 are provided to retain the mold wall sections 50 and 52 against 
movement relative to each other. Although only a single retainer pin 60 is 
illustrated in FIG. 4, it should be understood that a substantial number 
of retainer pins may be used. Thus, each of the openings 24 (FIGS. 1 and 
2) in the thin metal panel 12 is formed by a retainer pin 60. In the 
specific embodiment of the thin metal panel 12 illustrated in FIGS. 1 and 
2, more than three hundred retainer pins 60 were used. 
To retain the mold wall sections 50 and 52 (FIG. 4) against movement 
relative to each other, each of the retainer pins 60 has end portions 62 
and 64 which are mechanically interlocked with the wall sections. This 
enables each retainer pin 60 to transmit force between the wall sections 
50 and 52 to hold the wall sections against movement relative to each 
other. By retaining the wall sections 50 and 52 against movement relative 
to each other, the thin main section 14 of the metal panel 12 is 
accurately formed with the desired thickness. Although the retainer pins 
60 have been illustrated in FIG. 4 as extending between outer mold wall 
sections 50 and 52 of the mold structure 32, the retainer pins could 
extend between inner mold wall sections or between an inner mold wall 
section and an outer mold wall section of a more complicated mold 
structure. 
In the embodiment of the retainer pin 60 illustrated in FIG. 4, the 
retainer pin has end portions 62 and 64 which project outward from a 
cylindrical connector portion 70 of the retainer pin. The end portions 62 
and 64 of the retainer pin 60 have a circular cross sectional 
configuration, as viewed in a plane perpendicular to a central axis of the 
retainer pin. The centers of the end portions 62 and 64 of the retainer 
pin 60 are disposed on a longitudinal central axis of the connector 
portion 70. 
In this embodiment of the invention, a plurality of evenly spaced retainer 
pins 60 have connector portions 70 with parallel central axes are used to 
retain the wall sections 50 and 52 against movement relative to each 
other. However, if desired, the connector portions 70 of at least some of 
the retainer pins 60 could have central axes which extend transverse to 
central axes of other retainer pins. It is contemplated that the number of 
retainer pins 60 which are used and/or the spacing between retainer pins 
may vary depending upon the article to be cast. 
The end portion 62 of the retainer pin 60 (FIG. 5) has a flat annular side 
surface 74 which faces toward the article mold cavity 36. The flat annular 
side surface 74 has a center which is disposed on a longitudinal central 
axis of the connector portion 70. The flat annular side surface 74 engages 
the ceramic mold material forming the wall section 50 of the article mold 
34. 
In addition to the flat annular side surface 74, the end portion 62 of the 
retainer pin 60 has a flat circular end surface 78 which extends parallel 
to the flat annular side surface 74 and faces away from the article mold 
cavity 36. The parallel surfaces 74 and 78 on the end portion 62 of the 
retainer pin 60 are interconnected by an arcuate side surface 80 having a 
semicircular cross sectional configuration. 
The end portion 64 (FIG. 4) of the retainer pin 60 has the same 
construction as the end portion 62 of the retainer pin. Thus, the end 
portion 64 of the retainer pin 60 has a flat annular side surface 84 which 
faces toward the mold cavity 36 and is parallel to the flat annular side 
surface 74 on the end portion 62. The flat annular side surface 84 on the 
end portion 64 of the retainer pin 60 is disposed in engagement with the 
ceramic mold material forming the wall section 52. 
In the embodiment of the invention illustrated in FIG. 4, the retainer pins 
60 have parallel central axes. Therefore, the flat side surfaces 74 and 84 
on the end portions 62 and 64 of the retainer pins 60 extend parallel to 
each other. However, it is contemplated that the orientations of at least 
some of the retainer pins 60 could be different than other retainer pins 
so that some side surfaces 74 and 84 are skewed relative to other side 
surfaces. 
When the molten metal which is to form the thin metal panel 12 is poured 
into the mold cavity 36, the fluid pressure against the side surfaces 54 
and 56 of the wall sections 50 and 52 urge the wall sections away from 
each other. The end portions 62 and 64 (FIG. 4) of the retainer pin 60 
transmit equal and oppositely directed reaction forces to the connector 
portion 70 of the retainer pin 60. The connector portion 70 is capable of 
withstanding these reaction forces to hold the wall sections 50 and 52 of 
the article mold 34 against movement relative to each other. 
Since the end portions 62 and 64 of the retainer pin 60 bulge or project 
outward from the connector portion 70 of the retainer pin, there is a 
mechanical interlock between the end portions 62 and 64 of the retainer 
pin and the wall sections 50 and 52 of the article mold 34. This 
mechanical interlock prevents the end portion 62 of the retainer pin 60 
from moving relative to the wall section 50. Similarly, the mechanical 
interlock prevents the end portion 64 of the retainer pin 60 from moving 
relative to the wall section 52. 
In the embodiment of the invention illustrated in FIGS. 4 and 5, the 
mechanical interlock between the end portions 62 and 64 of the retainer 
pin 60 and the wall sections 50 and 52 is provided by the flat annular 
side surfaces 74 and 84 which engage the ceramic mold material of the wall 
sections. Thus, when molten metal is poured into the article mold cavity 
36, the fluid pressure force exerted by the molten metal against the side 
surface 54 of the mold wall section 50 presses the ceramic mold material 
of the mold wall section against the flat annular side surface 74 on the 
end portion 62 of the retainer pin 60. The force of the molten metal 
against the side surface 54 of the wall section 50 of the mold structure 
32 urges the flat annular side surface 74 of the retainer pin 60 downward 
(as viewed in FIGS. 4 and 5), that is, away from the mold wall section 52. 
This results in a reaction force, indicated by the arrow 88 in FIG. 5, 
being transmitted to the connector portion 70 of the retainer pin 60. 
When molten metal is poured into the article mold cavity 36, the fluid 
pressure force against the side surface 56 (FIG. 4) on the mold wall 
section 52 urges the mold wall section 52 away from the mold wall section 
50. The ceramic mold material of the mold wall section 52 is pressed 
against the flat annular side surface 84 on the end portion 64 of the 
retainer pin 60. This results in a downward (as viewed in FIG. 4) reaction 
force being transmitted to the connector portion 70 of the retainer pin 
60. 
The downward (as viewed in FIG. 4) reaction force transmitted from the end 
portion 64 of the retainer pin 60 to the connector portion 70 of the 
retainer pin is equal to and oppositely directed from the reaction force 
88 transmitted from the end portion 62 of the retainer pin to the 
connector portion 70 of the retainer pin. The connector portion 70 of the 
retainer pin 60 is more than strong enough to withstand the reaction 
forces. Therefore, the end portions 62 and 64 of the retainer pin 60 do 
not move relative to each other and the wall sections 50 and 52 are held 
against movement relative to each other. 
In one specific embodiment of the retainer pin 60, the retainer pin was 
formed of alumina (Al.sub.2 O.sub.3). However, the retainer pin 60 could 
be formed of quartz or a similar material if desired. The end portions 62 
and 64 and connector portion 70 of the retainer pin 60 are sized to have 
sufficient strength at high temperatures to withstand the forces applied 
to the wall sections 50 and 52 by the molten metal in the article mold 
cavity 36. 
The specific retainer pins 60 used in the mold structure 32 to cast the 
thin metal plate 12 each had a cylindrical connector portion 70 of with a 
diameter of approximately 0.020 inches and a length of approximately 0.14 
inches. The end portions 62 and 64 of this specific retainer pin 60 had a 
diameter which was approximately 1.5 times the diameter of the connector 
portion 70 of the retainer pin. The foregoing specific embodiment of the 
retainer pin 60 was utilized with a mold structure 32 having a mold cavity 
36 with a thickness of 0.016 to 0.017 inches. 
It should be understood that the foregoing specific dimensions for an 
alumina (Al.sub.2 O.sub.3) retainer pin 60 have been set forth herein for 
purposes of clarity of description and not for purposes of limitation of 
the invention. It should be understood that the retainer pin 60 may be 
formed of different materials and with different dimensions if desired. 
For example, the end portions 60 and 62 of the retainer pin 60 may have a 
diameter of 2.0 or more times the diameter of the connector portion 70. 
The retainer pin 60 illustrated in FIG. 4 has end portions 62 and 64 with 
one particular configuration. It is contemplated that it may be preferred 
to form the end portions 62 and 64 with a different configuration. For 
example, the end portions 62 and 64 could be formed by upsetting opposite 
ends of a heated pin to form bulges having freely formed outer side 
surfaces corresponding to the surfaces 74 and 84. If this was done, at 
least portions of the surfaces corresponding to the surfaces 74 and 84 
would slope at an acute angle to a central axis of the connector portion 
70. 
The retainer pin 60 illustrated in FIG. 4 is integrally formed as 
one-piece. However, it is contemplated that the retainer pin 60 could be 
formed as two or more pieces which are subsequently interconnected. For 
example, the end portion 62 of the retainer pin 60 could be formed 
separately from the connector portion 70 and connected with the connector 
portion after the connector portion has been inserted through a wax 
pattern. 
The retainer pin 60 has a longitudinal central axis which extends through 
opposite end portions 62 and 64 of the pin and extends perpendicular to 
the side surfaces 54 and 56 of the wall sections 50 and 52. The central 
axis of the pin 60 could be skewed at an acute angle to the side surfaces 
54 and 56 of the wall sections 50 and 52. Adjacent retainer pins 60 could 
be positioned in different orientations relative to the side surfaces 54 
and 56 of the wall sections 50 and 52 if desired. 
Mold To Cast Metal Article 
When the mold structure 32 is to be fabricated, a wax pattern (not shown) 
is formed. The wax pattern of the mold structure includes an article 
pattern section having a configuration corresponding to the configuration 
of the article to be cast, that is, the thin metal panel 12. The wax 
pattern of the article to be cast may be injection molded of either a 
natural wax or an artificial substance having characteristics which are 
generally similar to natural waxes. If desired, the pattern could be a 
thermoformed or machined polymeric material. It is also contemplated that 
the pattern may be reaction injection molded. 
Since the main section 14 (FIGS. 1 and 2) of the thin metal panel 12 has a 
thickness of less than 0.050 inches, the wax pattern of the main section 
14 of the panel 12 will have a thickness of less than 0.050 inches. In the 
specific embodiment of the thin metal panel 12 previously referred to, the 
main section 14 had a thickness of 0.015 inches, a width of approximately 
5 inches and a height of approximately 7 inches. The ribs 22 had a 
thickness of approximately 0.020 inches, a height as measured upward, as 
viewed in FIG. 2, from the side surface 16 of approximately 0.060 inches. 
The array of ribs formed rectangles having an area of approximately one 
square inch. The wax pattern for the thin metal panel 12 was formed to 
correspond to these dimensions. 
The retainer pins 60 are inserted through the wax pattern of the thin metal 
panel 12. In the previously mentioned specific embodiment of the pattern 
for the thin metal panel 12, there were nine pins for each of the one inch 
square areas formed by the ribs 22. Since the head end portions 62 and 64 
of the retainer pins 60 have a cross sectional area which is greater than 
the cross sectional area of the connector portion 70 of the retainer pins, 
holes were formed in the main section of the panel pattern having a 
diameter corresponding to the diameter of the end portions 62 and 64 of 
the retainer pins. The holes were located at equally spaced intervals in 
each of the rectangles formed by the ribs of the pattern of the thin metal 
panel 12. 
The retainer pins 60 were inserted through the holes or openings in the 
main section of the wax pattern. The holes were then sealed around the 
connector portions 70 of the retainer pins. This resulted in the 
fabrication of a wax pattern of the thin metal panel 12 with retainer pins 
extending through the pattern. The end portions 62 of the retainer pins 
project from one side of the wax pattern and the end portions 64 of the 
retainer pins 60 project from the other side of the pattern. 
In the illustrated embodiment of the invention, the retainer pins 60 are 
all positioned with their central axes extending perpendicular to flat 
outer side surfaces of the wax pattern. However, the retainer pins could 
be oriented with their central axes skewed at acute angles to flat outer 
side surfaces of the pattern. The retainer pins 60 could be positioned 
with their central axes in different orientations relative to the flat 
outer side surfaces of the wax pattern. 
Once the pattern of the article to be cast, that is, the thin metal panel 
12, has been formed with the retainer pins 60 projecting from opposite 
sides of the pattern, a wax pattern of the pour cup 40 is connected to the 
article pattern. In addition, a wax pattern of the single crystal selector 
62 and starter 44 is connected to the wax pattern of the article. The 
resulting pattern assembly has a configuration which corresponds to and is 
smaller than the configuration of the mold structure 32. 
Once the pattern assembly has been fabricated, it is covered with a 
suitable mold material. Thus, the entire pattern assembly, including the 
exposed end portions of the retainer pins 60, is completely covered with a 
liquid ceramic mold material. The entire pattern assembly may be covered 
with the liquid ceramic mold material by repetitively dipping the pattern 
assembly in a slurry of liquid ceramic mold material. 
Although many different types of the slurries of the ceramic mold material 
could be utilized, one illustrative slurry contains fused silica, zircon, 
and other refractory materials in combination with binders. Chemical 
binders such as ethylsilicate, sodium silicate and colloidal silica can be 
utilized. In addition, the slurry may contain suitable film formers such 
as alginates, to control viscosity and wetting agents to control flow 
characteristics and pattern wettability. 
Alternatively, the ceramic slurry which forms the mold material could have 
the composition disclosed in U.S. Pat. No. 4,947,927 issued Aug. 14, 1990 
and entitled "Method of Casting a Reactive Metal Against a Surface Formed 
From an Improved Slurry Containing Yttria". It is believed that the 
ceramic slurry disclosed in the aforementioned U.S. Pat. No. 4,947,927 may 
be particularly advantageous when the article to be cast is formed of a 
reactive metal, such as titanium or a nickel-chrome superalloy. Of course, 
other known ceramic slurries could be used if desired. 
The wax pattern assembly is repetitively dipped in the ceramic slurry until 
a coating of wet ceramic mold material has been formed over the pattern 
assembly having a desired thickness. The wet coating of ceramic mold 
material completely encloses the portions of the retainer pins 60 which 
projected from the article pattern. After the wet ceramic mold material 
has at least partially dried, the mold structure 32 is heated to melt the 
wax material of the pattern assembly. The melted wax is poured out of the 
mold structure 32 through the open end of the pour cup 40. Although the 
mold structure 32 has been shown as having only a single article mold 34 
connected with a single pour cup 40, it is contemplated that the mold 
structure 32 could be constructed in such a manner as to have a plurality 
of article molds and single crystal selectors 42 connected with a single 
pour cup 40 by a suitable gating constructed in a known manner. 
After the wax pattern material has been removed from the mold structure 32, 
the mold structure is fired at a temperature of approximately 
1,900.degree. F. for a time sufficient to cure the mold structure. During 
firing of the mold structure 32, the end portions 62 and 64 of the 
retainer pins 60 are fixedly embedded in the ceramic material of the wall 
sections 50 and 52 of the mold structure. Thus, the end portions 62 and 64 
of the retainer pins 60 were completely enclosed by the wet ceramic slurry 
of the mold materials during dipping of the pattern assembly. Upon 
subsequent drying and firing of the ceramic mold material, the end 
portions 62 and 64 of the retainer pins 60 are embedded in the hardened 
ceramic mold material of the wall sections 50 and 52 to interlock the 
retainer pins 60 and the mold structure 32. 
The connector portions 70 of the retainer pins 60 extend across the space 
corresponding to the mold cavity 36 (FIG. 4). Thus, the connector portion 
70 of each retainer pin 60 spans a distance corresponding to the thickness 
of the thin main section 14 of the metal panel 12. For the previously 
mentioned embodiment of the thin metal panel 12, this distance is 
approximately 0.015 inches. 
The retainer pins 60 retain the mold wall sections 50 and 52 against 
movement relative to each other during firing of the mold structure 32. 
During firing of the mold structure 32 the end portions 62 and 64 of the 
retainer pins transmit force to the connector portions 70 of the retainer 
pins to prevent relative movement between the mold wall sections. This 
prevents deformation of the mold wall sections from the pressures 
developed during firing and removal of the pattern. 
Once the mold structure 32 has been formed in the manner previously 
described, molten metal is poured into the mold structure through the pour 
cup 40. Although many different metals could be utilized, the molten metal 
was a nickel-chrome superalloy. The molten metal flows from the pour cup 
40 through the article mold cavity 36 into the single crystal selector 42 
and starter 44. Molten metal is poured into the pour cup 40 until the 
starter 44, single crystal selector 42, article mold cavity 36 are 
completely filled with molten metal and the pour cup is at least partially 
filled with molten metal. The pouring of the molten metal into the mold 
structure 32 may advantageously be preformed in an evacuated environment 
in order to avoid contamination of the molten metal. 
As the molten metal enters the article mold cavity 36, the molten metal 
applies force against the side surfaces 54 and 56 of the wall sections 50 
and 52. The pressure applied against the side surfaces 54 and 56 of the 
wall sections 50 and 52 urges the wall sections away from each other. 
However, the retainer pins 60 are effective to retain the wall sections 50 
and 52 against movement relative to each other under the influence of the 
force applied against the wall sections by the molten metal. 
The force applied against the wall section 50 by the molten metal in the 
mold cavity 36 presses the ceramic mold material of the wall section 
against the flat side surface 74 on the end portion 62 of the retainer pin 
60. The connector portion 70 of the retainer pin 60 holds the end portions 
62 of the retainer pin against movement under the influence of the force 
applied against the side surface 74 of the end portion 62 by the ceramic 
mold material of the wall section 50. Therefore, the wall section 50 does 
not move relative to the wall section 52. 
Similarly, the force applied against the wall section 52 by the molten 
metal in the mold cavity 36 presses the ceramic mold material of the wall 
section 52 against the flat annular side surface 84 on the end portion 64 
of the retainer pin 60. The force applied against the end portion 60 of 
the retainer pin by the ceramic mold material of the wall section 52 is 
transmitted to the connector portion 70. The connector portion 70 retains 
the end portion 64 of the retainer pin 60 and the mold wall section 52 
against movement relative to the mold wall section 50. 
During pouring of molten metal into the mold cavity 36 and the subsequent 
solidification of the molten metal in the mold cavity, the end portions 62 
and 64 of the retainer pins 60 hold the wall sections 50 and 52 of the 
mold structure 32 against movement relative to each other. This results in 
the cast metal panel 12 being accurately formed with the desired 
dimensions. It should be understood that although the foregoing 
description has been in conjunction with the casting of a thin metal panel 
12 formed of a reactive metal, specifically a nickel-chrome superalloy, 
retainer pins having a construction similar to the retainer pins 60 could 
be utilized in many different types of mold structures during the casting 
of many different types of articles from many different metals. For 
example, relatively large retainer pins 60 could be spaced relatively 
large distances apart and used to hold mold wall sections of a mold 
structure in which a relatively thick article is cast. The relatively 
thick article could be cast from any desired metal. Of course, the 
retainer pins would be formed of a material which would not react with the 
metal from which the article is to be cast and would be capable of 
withstanding the relatively high temperatures of the molten metal poured 
into the mold cavity. 
In FIG. 4, the end portions 62 and 64 of the retainer pin 60 are 
illustrated as being embedded in outer wall sections 50 and 52 of a 
relatively simple mold structure. However, in a more complicated mold 
structure, the head end portion 62 of the retainer pin 60 could be 
embedded in a core section and the head end portion 64 embedded in either 
another core section or a wall section of the mold structure. 
Retainer Pin--Second Embodiment 
In the embodiment of the invention illustrated in FIGS. 1-5, the retainer 
pins 60 have relatively large end portions 62 and 64. The use of the 
relatively large end portions 62 and 64 facilitates forming a mechanical 
interlock between the retainer pins and the wall sections 50 and 52. 
However, the use of the relatively large end portions 62 and 64 requires 
the formation of a relatively large opening or hole in the wax pattern of 
the article to be cast so that a retainer pin 60 can be inserted through 
the wax pattern with the end portions projecting from opposite sides of 
the pattern. The relatively large holes in the wax pattern are sealed 
against the relatively small diameter connector portions 70 of the 
retainer pins 60. 
In the embodiment of the invention illustrated in FIGS. 6 and 7, the end 
portions of the retainer pins are of the same size as the connector 
portion of the retainer pins. The surfaces which face toward the mold 
cavity to interlock the retainer pins and the mold sections are located in 
recesses in the retainer pins. Therefore, it is not necessary to seal 
openings around the central portions of the retainer pins. Since the 
embodiment of the invention illustrated in FIGS. 6 and 7 is generally 
similar to the embodiment of the invention illustrated in FIGS. 1-5, 
similar numerals will be used to designate similar components, the suffix 
letter "a" being associated with the numerals of FIGS. 6 and 7 to avoid 
confusion. 
A mold structure 32a (FIG. 6) has the same construction as the mold 
structure 32 of FIG. 3. Thus, the mold structure 32a (FIG. 6) includes an 
article mold 34a. The article mold 34a has an article mold cavity 36a 
disposed between wall sections 50a and 52a of the article mold. The wall 
sections 50a and 52a have flat parallel inner side surfaces 54a and 56a 
which cooperate to at least partially define the article mold cavity 36a. 
Although the article mold cavity 36a could have a configuration 
corresponding to the configuration of many different articles, in the 
specific embodiment of the invention illustrated in FIGS. 6 and 7, the 
article mold cavity 36a has a configuration corresponding to the 
configuration of a thin metal panel 12a. The thin metal panel 12a has a 
main section 14a with flat parallel opposite side surfaces 16a and 18a. 
The main section 14a of the thin metal panel 12a has a thickness of less 
than 0.050 inches. In one specific embodiment of the invention, the main 
section 14a of the thin metal panel 12a had a thickness of 0.015 inches, 
as measured perpendicular to and between the side surfaces 16a and 18a of 
the main section 14a of the thin metal panel 12a. 
A plurality of retainer pins 60a extend between and interconnects the wall 
sections 50a and 52a. Each of the retainer pins 60a has opposite end 
portions 62a and 64a. The end portions 62a and 64a of the retainer pin 60a 
are interconnected by a connector portion 70a. The connector portion 70a 
extends across or spans the mold cavity 36a. 
The retainer pin 60a has a longitudinal central axis which extends through 
opposite end portions 62a and 64a of the pin and extends perpendicular to 
the side surfaces 54a and 56a of the wall sections 50a and 52a. The 
central axis of the pin 60a could be skewed at an acute angle to the side 
surfaces 54a and 56a of the wall sections 50a and 52a. Adjacent retainer 
pins 60a could be positioned in different orientations relative to the 
side surfaces 54a and 56a of the wall sections 50a and 52a if desired. 
In accordance with a feature of this embodiment of the invention, the 
retainer pin end portion 62a has a plurality of annular grooves or 
recesses 100 and 102. The groove 100 has a flat annular side surface 106 
(FIG. 7) which faces toward the article mold cavity 36a and which is 
engaged by the ceramic mold material of the wall section 50a. Similarly, 
the groove 102 has a flat annular side surface 108 which faces toward the 
article mold cavity 36a and engages the ceramic mold material of the wall 
section 50a. The annular grooves 100 and 102 in the end portion 62a of the 
retainer pin 60a are completely filled with the ceramic mold material of 
the wall section 50a. The ceramic mold material received in the annular 
grooves 100 and 102 interlocks the end portion 62a of the retainer pin 60a 
and the wall section 50a to hold the retainer pin against movement 
relative to the wall section. 
The opposite end portion 64a (FIG. 6) of the retainer pin 60a also has a 
pair of annular grooves or recesses 112 and 114. The grooves 112 and 114 
in the end portion 64a of the retainer pin 60a have the same configuration 
as the grooves or recesses 100 and 102 in the end portion 62a. The grooves 
112 and 114 in the end portion 64a of the retainer pin 60a are completely 
filled with the ceramic mold material of the wall section 52a. Therefore, 
the end portion 64a and the wall section 52a are mechanically interlocked 
to prevent relative movement between the retainer pin 60a and the wall 
section. 
The grooves 100, 102, 112 and 114 (FIG. 6) in the retainer pin 60a extend 
inwardly from a cylindrical outer side surface 118 on the retainer pin 
60a. Therefore, the end portions 62a and 64a of the retainer pin 60a have 
the same maximum size as the connector portion 70a of the retainer pin. 
This enables the retainer pin 60a to be inserted through a relatively 
small opening in a wax pattern. The small opening in the wax pattern would 
have the same diameter as the cylindrical outer side surface 118 of the 
retainer pin 60a. 
In the illustrated embodiment of the invention, the retainer pins 60a are 
all positioned with their central axes extending perpendicular to flat 
outer side surfaces of the wax pattern. However, the retainer pins 60a 
could be oriented with their central axes skewed at acute angles to flat 
outer side surfaces of the pattern. The retainer pins 60a could be 
positioned with their central axes in different orientations relative to 
the flat outer side surfaces of the wax pattern. 
When molten metal is conducted into the mold cavity 36a, the molten metal 
applies force against the side surfaces 54a and 56a of the wall sections 
50a and 52a. This force urges the wall sections 50a and 52a away from each 
other. The retainer pins 60a have end portions 62a and 64a which are 
mechanically interlocked with the ceramic mold material of the wall 
sections 50a and 52a to transmit force between the wall sections and 
retain them against movement relative to each other. 
The annular side surface 106 of the groove 100 in the end portion 62a (FIG. 
7) of the retainer pin 60a is pressed against the ceramic mold material 
filling the groove 100a. Similarly, the annular side surface 108 of the 
groove or recess 102 is pressed against the ceramic mold material filling 
the groove 102. This results in a reaction force being transmitted to the 
connector portion 70a of the retainer pin 60a. This reaction force is 
offset by the equal and opposite reaction force from the end portion 64a 
of the retainer pin. 
Although only a single retainer pin 60a is illustrated in FIGS. 6 and 7, a 
plurality of retainer pins are utilized with the mold structure 32a. 
Although the grooves 100, 102, 112 and 114 have a V-shaped radial cross 
sectional configuration, the grooves could be provided with a different 
configuration if desired. For example, a single spiral groove having a 
rectangular radial cross sectional configuration could be utilized if 
desired. 
Retainer Pin--Third Embodiment 
In the embodiments of the retainer pins 60 and 60a illustrated in FIGS. 
4-7, outwardly extending or inwardly extending side surfaces on the end 
portions of the retainer pins engage the ceramic mold material of the wall 
sections to hold the wall sections against movement relative to each 
other. In the embodiment of the invention illustrated in FIGS. 8 and 9, 
the end portions of the retainer pins are roughened to have an irregular 
surface which is mechanically interlocked with the ceramic material of the 
wall sections of the mold. Since the embodiment of the invention 
illustrated in FIGS. 8 and 9 is generally similar to the embodiment of the 
invention illustrated in FIGS. 1-7, similar numerals will be utilized to 
designate similar components, the suffix letter "b" being associated with 
the numerals of FIGS. 8 and 9 to avoid confusion. 
A mold structure 32b (FIG. 8) includes an article mold 34b. The article 
mold 34b has tan article mold cavity 36b which is disposed between wall 
sections 50b and 50b of the mold structure 32b. The wall sections 50b and 
50b have inner side surfaces 54b and 56b which at least partially define 
the article mold cavity 36b. A thin metal panel 12b is cast in the article 
mold cavity 36b. The thin panel 12b includes a main section 14b having 
side surfaces 16b and 18b which engage the side surfaces 54b and 56b of 
the article mold cavity 36b. 
A plurality of retainer pins 60b interconnect the wall sections 50b and 50b 
and hold the wall sections against movement relative to each other. The 
retainer pin 60b includes an end portion 62b which is mechanically 
interlocked with the wall section 50b and an end portion 64b which is 
mechanically interlocked with the wall section 52b. A connector portion 
70b extends between the end portions 62b and 64b of the connector pin 60b. 
The end portions 62b and 64b have a generally cylindrical configuration 
with a diameter which is slightly smaller than the diameter of the 
connector portion 70b. Therefore, the retainer pin 60b can be inserted 
through a circular opening in a wax pattern if the opening is large enough 
to receive the connector portion 70b of the retainer pin. 
The retainer pin 60b has a longitudinal central axis which extends through 
opposite end portions 62b and 64b of the pin and extends perpendicular to 
the side surfaces 54b and 56b the wall sections 50b and 50b. The central 
axis of the pin 60b could be skewed at an acute angle to the side surfaces 
54b and 56b of the wall sections 50b and 50b. Adjacent retainer pins 60b 
could be positioned in different orientations relative to the side 
surfaces 54b and 56b of the wall sections 50b and 50b if desired. 
In accordance with a feature of this embodiment of the invention, the end 
portions 62b of the retainer pin 60b is formed with an irregular outer 
side surface. As originally formed, the retainer pin 60b had a smooth 
cylindrical outer side surface 118b which extended between opposite ends 
of the retainer pin 60b. The end portion 62b (FIG. 9) was formed with an 
irregular surface by roughening the smooth outer side surface 118b the end 
portion 62b of the retainer pin 60b. 
The end portion 62b of the retainer pin 60b was sand blasted to form 
irregular recesses 124 and irregular projections 126 on the end portion 
62b of the retainer pin 60b. Since the smooth outer side surface 118b as 
sand blasted to form the recesses 124 and projections 126, the projections 
do not extend outward of the smooth outer side surfaces 118b the retainer 
pin 60b. Therefore, the retainer pin can be inserted through an opening in 
a wax pattern having a diameter which is only slightly greater than the 
diameter of the cylindrical outer side surface 118b the retainer pins 60b. 
The projections 126 on the axially extending side of the retainer pins 60b 
have surfaces which face toward the article mold cavity 36b. Although the 
projections 126 are irregular about the end portion 62b, each of the 
projections has an outer side surface which faces toward the article mold 
cavity 36b. Since the ceramic mold material of the wall section 50b fills 
recesses 124 and completely encloses the projections 126, there is a 
mechanical interlock between the end portion 62b of the retainer pin 60b 
and the wall section 50b. 
Although only the end portion 62b of the retainer pin 60b is illustrated in 
FIG. 9, it should be understood that the end portion 64b (FIG. 8) of the 
retainer pin 60b has been roughened in the same manner as in which the end 
portion 62b of the retainer pin has been roughened. Therefore, there are 
irregular recesses and projections on the end portion 64b of the retainer 
pin 60b. The recesses are completely filled with the ceramic mold material 
of the wall sections 50b. The projections have side surfaces which face 
toward the article mold cavity 36b. 
In the illustrated embodiment of the invention, the retainer pins 60b are 
all positioned with their central axes extending perpendicular to flat 
outer side surfaces of the wax pattern. However, the retainer pins 60b 
could be oriented with their central axes skewed at acute angles to flat 
outer side surfaces of the pattern. The retainer pins 60b could be 
positioned with their central axes in different orientations to the flat 
outer side surfaces of the wax pattern. 
When molten metal is conducted into the article mold chamber 36b, the 
molten metal applies force against the side surfaces 54b and 56b of the 
article mold 34b. This force tends to separate the wall sections 50b and 
50b. However, the mechanical interlock between the end portions 62b and 
64b of the retainer pin 60b resists relative movement between the wall 
sections 50b and 50b so that the wall sections do not move relative to 
each other. Thus, when molten metal is poured into the article mold cavity 
36b, the ceramic mold material of the wall sections 50b and 52b is pressed 
against the side surfaces of the projections 126 on the end portions 62b 
and 64b of the retainer pin 60b to hold the wall sections 50b and 50b 
against movement relative to each other. 
Retainer Pin--Fourth Embodiment 
In the embodiments of the retainer pins 60, 60a and 60b illustrated in 
FIGS. 4-9, side surfaces on the end portions of the retainer pins engage 
the ceramic mold material of the wall sections to hold the wall sections 
against movement relative to each other. In the embodiment of the 
invention illustrated in FIG. 10, the end portions of the retainer pins 
have a smooth cylindrical configuration which is a continuation of the 
smooth cylindrical configuration of the central portions of the retainer 
pins. The retainer pins of the embodiment of the invention illustrated in 
FIG. 10 are mechanically interlocked with the ceramic material of the wall 
sections of the mold by having the retainer pins skewed at acute angles 
relative to flat side surfaces on the wall sections. Since the embodiment 
of the invention illustrated in FIG. 10 is generally similar to the 
embodiment of the invention illustrated in FIGS. 1-9, similar numerals 
will be utilized to designate similar components, the suffix letter "c" 
being associated with the numerals of FIG. 10 to avoid confusion. 
A mold structure 32c (FIG. 10) includes an article mold 34c. The article 
mold 34c has an article mold cavity 36c which is disposed between wall 
sections 50c and 52c of the mold structure 32c. The wall sections 50c and 
52c have inner side surfaces 54c and 56c which at least partially define 
the article mold cavity 36c. A thin metal panel 12c is cast in the article 
mold cavity 36c. The thin metal panel 12c includes a main section 14c 
having side surfaces 16c and 18c which engage side surfaces 54c and 56c of 
the article mold cavity 36c. 
A plurality of identical retainer pins 60c interconnect the wall sections 
50c and 52c to hold the wall sections against movement relative to each 
other. The retainer pins 60c cooperate with each other to form a 
mechanical interlock with the wall sections 50c and 52c. A connector 
portion 70c extends between end portions 62c and 64c of each of the 
connector pins 60c. The end portions 62c and 64c of the connector pins 60c 
have a cylindrical configuration with a smooth outer side surface. 
Therefore, the retainer pins 60c can be inserted through a circular 
opening in a wax pattern if the opening is large enough to receive the 
connector portion 70c of the retainer pin. 
In accordance with a feature of this embodiment of the invention, the 
retainer pins 60c have longitudinal central axes which extend through 
opposite end portions 62c and 64c of the retainer pins and are skewed at 
an acute angle relative to the side surfaces 54c and 56c of the wall 
sections 50c and 52c. The adjacent retainer pins 60c are positioned in 
different orientations relative to the side surfaces 54c and 56c of the 
wall sections 50c and 52c. 
In the embodiment of the invention illustrated in FIG. 10, the relationship 
between three adjacent connector pins 60c and the mold structure 32c is 
illustrated. The central connector pin 60c has a longitudinal central axis 
which extends transverse to the longitudinal central axes of the pins 60c 
disposed at the left and right end portions of FIG. 10. In the illustrated 
embodiment of the invention, the retainer pins 60c all have central axes 
which are skewed at an acute angle of approximately 45.degree. relative to 
the side surfaces 54c and 56c of the Wall sections 50c and 52c of the mold 
structure 32c. However, the retainer pins 60c could, if desired, have 
longitudinal central axes which are skewed at different angles relative to 
the side surfaces 54c and 56c of the mold structure 32c. For example, the 
left (as viewed in FIG. 10) pin 60c could have a central axis which is 
skewed at an angle of 60.degree. to the side surfaces 54c and 56c of the 
mold wall sections 50c and 52c while the right pin 60c could have a 
central axis which is skewed at angle of 30.degree. to the side surfaces 
54c and 56c of the mold wall sections 50c and 52c. 
The adjacent connector pins 60c are disposed in different orientations 
relative to each other. It is contemplated that the connector pins will be 
randomly oriented in different orientations relative to each other so that 
the adjacent connector pins do not have the same orientation relative to 
the side surfaces 54c and 56c of the mold wall sections 50c and 52c. By 
randomly orienting the retainer pins 60c relative to each other and to the 
side surfaces 54c and 56c of the mold wall sections 50c and 52c, the pins 
interlock with the mold wall sections with a wedging-type action so that 
force is transmitted between the smooth cylindrical outer side surfaces of 
the retainer pin 60c and the mold wall sections 50c and 52c have different 
lines of action. The resulting meshing engagement of the plurality of 
retainer pins 60c with the wall sections 50c and 52c holds the wall 
sections against movement relative to each other. 
When molten metal is conducted into the article mold chamber 36c, the 
molten metal applies force against the side surfaces 54c and 56c of the 
article mold 34c. This force tends to separate the mold wall sections 50c 
and 52c. However, the mechanical interlock provided by having the retainer 
pins 60c in different orientations relative to the mold wall sections 50c 
and 52c resists relative movement between the mold wall sections. Thus, 
when molten metal is poured into the article mold cavity 36c, the ceramic 
mold material of the wall sections 50c and 52c is pressed in different 
directions against the smooth cylindrical outer side surfaces of the 
retainer pins 60c. This results in the mold wall sections 50c and 52c 
being held against movement relative to each other. 
Although the retainer pins 60c have been illustrated in FIG. 10 as having a 
smooth cylindrical outer side surface, it is contemplated that the 
retainer pins could be constructed in the manner illustrated in FIGS. 4-9. 
Thus, the retainer pins could be provided with end portions 62c and 64c 
which project outward from the cylindrical connector portion 70c of the 
retainer pin in the same manner as is illustrated in FIG. 4. 
Alternatively, the end portions 62c and 64c could be provided with a 
plurality of annular grooves or recesses in the same manner as disclosed 
in FIG. 7. Another alternative embodiment of the retainer pins 60c could 
have roughened end portions 62c and 64c and was described in connection 
with the embodiment of the invention illustrated in FIG. 8. By positioning 
the retainer pins having any one of these alternative constructions in 
different orientations relative to the mold structure, in the manner 
illustrated in FIG. 10 for the retainer pin 60c, the orientation of the 
longitudinal central axes of the retainer pins results in an intermeshing 
type interlock between the retainer pins and the mold wall sections. 
CONCLUSION 
The present invention provides a new improved method and apparatus for use 
in casting a metal article. The apparatus includes a mold structure 32 
having one or more pins 60 which extend between wall sections 50 and 52 of 
the mold structure. A first end portion 62 of a pin 60 is disposed in the 
first wall section 50 of the mold structure 32 and a second end portion 64 
of the pin is disposed in a second wall section 52 of the mold structure. 
A third or connector portion 70 of the pin 60 is disposed in the mold 
cavity 36. The end portions 62 and 64 of the pin 60 and the wall sections 
50 and 52 of the mold structure 32 are interlocked to prevent relative 
movement between the wall sections. 
To interlock the end portions of a pin 60 and a wall section 50 of the mold 
structure, in the embodiment of the invention illustrated in FIGS. 4-9, 
the pin has a surface 74 which faces toward the mold cavity 30 and 
transmits force to the wall section of the mold structure. The end portion 
62 of the pin 60 may have an outwardly flaring head end section (FIG. 4), 
a circular groove (FIG. 6), and/or a roughened portion (FIG. 8) which 
provides an interlock with the ceramic material of the wall section of the 
mold. 
In the embodiment of the invention illustrated in FIG. 10, the pins 60c 
have central axes which are disposed in different orientations relative to 
wall sections 50c and 52c of the mold. These pins 60c are effective to 
apply forces in different directions relative to the mold structure. 
Although the method and apparatus of the present invention may be utilized 
to cast many different types of objects, it is believed that the method 
and apparatus will be particularly advantageous in casting relatively 
long, and/or wide metal objects which are very thin. Thus, the method and 
apparatus may be used to cast a metal object 12 having a thickness of 
0.050 or less and a length and width of four inches or more. Although the 
thin metal article 12 could be formed of many different metals having any 
one of many different crystallographic structures, the method and 
apparatus may advantageously be used to form a single crystal metal 
article, such as a plate or airfoil.