Note: Descriptions are shown in the official language in which they were submitted.
P-342 11'7'~ 5
BACKGROUND OF THE INVENTION
This invention relates to a method of forming
an article to a final form in a cavity which surrounds the
article to define the final desired form of the article.
Such forming is accomplished in forging and like processes.
Although applicable to forging and like processes, the
subject invention has particular utility and will be
described in connection with forming an article by the hot
consolidation of powder material.
Hot consolidation can be accomplished by filling
a container with a powder to be consolidated. The con-
tainer is usually evacuated prior to filling and then
hermetically sealed. Heat and pressure are applied to the
filled and sealed container. At elevated temperatures,
the container functions as a pressure-transmitting medium
to subject the powder to the pressure applied to the
container. Simultaneously, the heat causes the powder to
fuse by sintering. In short, the combination of heat
and pressure causes consolidation of the powder into a
substantially fully densified and fused mass in which the
individual powder particles change shape as they are
forced together and are united into a substantially
homogeneous mass.
After consolidation, the container is removed
from the densified powder compact or preform and the
preform is then further processed through one or more
steps, such as forging, machining, grinding and/or heat
treating.
Because the volume of the cavity in the
P-342 ~ 15
container for hot consolidation may vary from container to
container, the final configuration may vary from compacted
part to compacted part. Another variable is that the
density of the powder may vary from one fill to the next.
In addition, the particle size may differ from one fill to
the next. All of these factors can contribute to parts
being below or above tolerances when it is, of course,
desirable to consistently produce part after part with the
same shape or form with the same amount of material or
mass in each part. ~nother problem which occurs is ~hat
when the part is compacted between two dies, flash may
occur on the part at the parting line of the two dies.
This flash, of course, must be removed in a subsequent
operation.
5UM~RY OF THE I~IVENTION
These problems may be overcome by the subject
invention which provides a method of forming an article
to a final form in a final cavity completely surrounding
and having the final form of the article. The method in-
cludes the steps of forming a preform having the generalshape of the final form of the article, measuring the
amount of material contained in the preform, removing any
material from the preform in excess of the amount of
material required to completely fill the volume of the
final cavity and enclosing the preform in the final
cavity to completely surround the preform and conform the
preform to the shape of the cavity to produce the final
form of the article.
P-342 11'7Z~S
BRIEF DESCRIPTION OF THE DRAWING
Other advantages o the present invention will be
readily appreciated as the same becomes better understood by
reference to the following detailed description when
considered in connection with the accompanying drawing which
is a flow diagram illustrating the major steps involved in
the method of the subject invention.
DESCRIPTION OF THE INVENTION
It will be appreciated that the subject invention
may be utilized for shaping parts by forging or in any other
process where a part is to be conformed to the shape of a
cavity. However, the invention has particular utility and
will be described in connection with the hot consolidation
of various metallic powders and nonmetallic powders, as well
as combinations thereof, to form a densified powder article.
The invention may be utilized to consolidate metallic powder
into complex shapes by utilizing a "fluid die~' or "thick-
walled" container of the type described in United States
Patent 4,142,888 granted March 6, 1979 in the name of Walter
J. Rozmus. By way of definition, a thick-walled container
is of sufficient thickness so that the exterior surface of
the walls do not closely follow the contour or shape of the
cavity. This insures that sufficient container material is
provided so that, upon the application of heat and pressure,
the container material will act like a fluid to apply
hydrostatic pressure to the powder in the cavity. The use
of a thick-walled
1 ~'7;~t~15
P-342
container produces a near-net shape having close dimen-
sional tolerances with a minimum of distortion.
The drawing illustrates the steps of the method
of forming an article to a final form in a final cavity
completely surrounding and having the final form of the
article. Step 1 is the forming of a preform having the
general shape and mass of the final form of the article.
Step 2 includes measuring the amount of material or mass
of the material contained in the preform resulting from
Step 1. Step 3 includes removing any material or mass
from the preform in excess of the amount of material or
mass required to completely fill the volume of the final
cavity. Step 5 is tne enclosing of the preform in the
final cavity to completely surround the preform and con-
form the preform to the shape of the final cavity toproduce the final form of the article.
Step 1 shows a thick-walled container formed
by at least two mating container parts 12 and 14. The
container parts 12 and 14 define a cavity 16 in which
powder 18 is disposed for consolidation. As illustrated,
the container parts 12 and 14 define the cavity 16 when
they are mated together at the mating surfaces 20, as
by welding.
The densified or compacted preform 18 may be of
various complex shapes. As illustrated in Step 1, there
is shown a cross section through the container and the
compacted preform illustrating a cross section of the
preform which is elongated or oval. The final shape or
form of the article, by way of illustration, will be
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11'72~115
P-342
circular as illustrated in Step 5. Although it will be
appreciated that various shapes may be produced in
accordance with the subject invention and that the shapes
along the longitudinal axis of a given part may change
significantly.
In Step 1 a quantity of powder 18 is encapsu-
lated in a cavity 16 in a thick walled container defined
by the parts 12 and 14 with the container having walls
entirely surrounding the cavity 16 and of sufficient
thickness so as not to closely follow the contour of the
cavity 16 and of a material which is substantially fully
dense and incompressible and capable of plastic flow at
elevated temperatures. The container defined by the parts
12 and 14 is generally rectangular in cross section and
does not follow the contour of the cavity 16 as there are
different thicknesses of the container about the cavity
16.
The container parts 12 and 14 and the powder
are heated to a temperature at which the powder 18 will
densify. External pressure is applied to the entire
exterior surface of the container parts 12 and 14 thereby
causing plastic flow of the container parts 12 and 14
to subject the powder to hydrostatic pressure which
causes the powder to densify into a preform. The pressure
is applied to the container parts 12 and 14 by placing
the container parts within a constraining cavity in a
press die 22 and applying downward pressure to the con-
tainer parts 12 and 14 by a ram 24 of a press. This is
accomplished in accordance with the teachings of the
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P-342 1~7Z(~15
aforemen-tioned United States Patent 4,142,888.
The preform 18 is then removed from the container
parts 12 and 14. This may be accomplished by various means
such as etching, pickling, machining, etc. One very
satisfactory method of removing the preform 18 from the
container parts 12 and 14 is by melting the container
material from about the preform 18. The container parts 12
and 14 may be formed from a material which melts at a
combination of temperature and time at that temperature
which combination would not undesirably or adversely affect
the properties of the powder preform 18, i.e., after having
been consolidated to define the densified powder compacted
preform 18. For example, the container may be made from a
metal such as a copper.
After compaction of the preform 18 and the removal
of the preform 18 from the container parts 12 and 14, the
amount of material or mass contained in the preform is
measured. This may be accomplished by weighing the preform
in Step 2. Thereafter, the method includes the step of
removing any material about the exterior of the preform 18
which is in excess of the amount of material in the final
desired form of the article. The material may be removed in
Step 3 by passing the preform 18 through an etching bath.
The preform would be submerged in a solution in an etching
bath under
,
P-342 ~ 2~ 1 5
predetermined conditions to remove the proper amount of
material or mass from the preform. The predetermined con-
ditions would include the temperature of the solution, the
electrical current passing through the solution and the
time the preform is submerged within the solution~
Step 4 illustrates the enclosing of the preform
18 in the final cavity 26 to completely surround the
preform 18 and conform the preform 18 to the shape of the
final cavity 26 to produce the final form of the article
28. The preform 18 is enclosed in the final cavity 26
by placing the heated preform between dies 30 of a press.
The dies 30 define the final cavity 26 and the closing of
the dies 30 apply pressure to the preform 18 to form it
into th~ final form of the article 28. The dies 30 may
be placed in a variety of well-known presses.
As the drawing illustrates, the preform 18 is
formed so as to have a greater dimension in a first
direction therethrough ~vertical as shown~ than the final
desired dimension in the first (vertical~, direction
through the ~inal form 28. The preform 18 is also formed
to have a lesser dimension in a second direction (hori-
zontal) transverse to the first direction than the final
desired dimension in the second direction (horizontal)
through the final form 28. As illustrated, the cross-
sectional configuration of the preform 18 is oblong oroval whereas the cross-sectional configuration of the
final form is circular.
The preform 18 is enclosed in the dies 30 by
closing the dies 30 to initially apply pressure to the
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11'~2Vl~P-342
preform 18 in the first direction which is vertical
as illustrated. In other words, the dies 30 first contact
the ends of the oblong shape to initially apply pressure
to the preform 18 in the first or vertical direction to
decrease the dimension in the first or vertical direction
to the final desired dimension of the article 28. As this
occurs, there is also an increase in the dimension in the
second or horizontal direction of the preform 18 to the
final desired dimension of the article 28. In other
words, as the dies 30 move together, they initially engage
the praform at the intentionally oversize dimension in
the direction of the closing of the dies and, since the
other transverse dimension between the sides is smaller
than required, that dimension grows or increases. Since
the preform 18 has been measured and any mass or material
in excess of that required to precisely fill the cavity
26 has been removed, the sides of the preform 18, when
increasing in dimension horizontally, contact the walls
of the cavity 26 at the same time the dies 30 engage one
another at the parting line therebetween. As will be
appreciated, in this manner there is no resulting flash
in the final article 28, i.e., there is no material of
the article 28 squeezed outwardly between the dies 30
between the parting faces thereof and outside the cavity
26. Accordingly, not only is there a precise article in
terms of shape resulting from the method but the wear of
the dies 30 at the parting faces therebetween adjacent
the cavity 26 should be eliminated.
In many instances it will be desirable to
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P-342 11~7Z~ 5
initially form the preform 18 with a greater amount of
material or mass than the amount of material in the final
form of the article 28. This will prevent forming pre-
forms 18 which are unusable because of less material or
mass than desired in the final article 28.
It will be appreciated that the final cavity 26
is final only in that it provides the final shape of the
desired article but the term does not mean that the
article 28 may not be processed further to undergo fur-
ther processing. It should also be appreciated that inthe removal step, particularly when processing articles of
complex shapes, different portions of the articles may
have proportionally different amounts of material removed
therefrom than other portions of the article. The impor-
tance being to remove material from the preform 18 so
that the different portions of the preform are in pro-
portion to the final cavity 26 and that the total volume
in terms of material or mass of the preform is precisely
the same as the volume of the final cavity 26.
It should also be appreciated that the preform
may also be formed in an autoclave instead of a press.
The invention has been described in an illus-
trative manner, and it is to be understood that the
terminology which has been used is intended to be in the
nature of words of description rather than of limitation.
Obviously, many modifications and variations of
the present invention are possible in light of the above
teachings. It is, therefore, to be understood that with-
in the scope of the appended claims wherein reference
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P-342 li'7~0~S
numerals are merely for convenience and are not to be
in any way limiting, the invention may be practiced
otherwise than as specifically described.
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