U.S. patent application number 11/224269 was filed with the patent office on 2007-10-11 for piston formed by powder metallurgical methods.
Invention is credited to John L. Cagney, Valeri B. Petrov.
Application Number | 20070235003 11/224269 |
Document ID | / |
Family ID | 32681465 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070235003 |
Kind Code |
A1 |
Cagney; John L. ; et
al. |
October 11, 2007 |
Piston formed by powder metallurgical methods
Abstract
A piston includes a piston structure being unitarily formed in a
powder metallurgy process, the piston structure having a crown
assembly and a skirt assembly, at least a partial combustion
chamber being formed intersecting a piston crown surface during the
powder metallurgy process, the skirt assembly depending from the
crown assembly and having two spaced apart pin bosses, each pin
boss having a pin bore defined therein, a pair of opposed
semi-circular skirt members, each skirt member extending outwardly
from and being integrally joined to both of the pin bosses. The
piston may be formed by executing a powder metallurgy process on at
least two different metallic constituents to define a
non-homogenous piston structure. A method of forming a piston is
further included.
Inventors: |
Cagney; John L.; (Downers
Grove, IL) ; Petrov; Valeri B.; (Elmhurst,
IL) |
Correspondence
Address: |
INTERNATIONAL ENGINE INTELLECTUAL PROPERTY COMPANY
4201 WINFIELD ROAD
P.O. BOX 1488
WARRENVILLE
IL
60555
US
|
Family ID: |
32681465 |
Appl. No.: |
11/224269 |
Filed: |
September 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10338500 |
Jan 8, 2003 |
6973723 |
|
|
11224269 |
Sep 12, 2005 |
|
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|
Current U.S.
Class: |
123/279 ;
123/193.6; 29/888.047; 92/208 |
Current CPC
Class: |
Y10T 29/49249 20150115;
F02F 3/26 20130101; F02F 3/0084 20130101; B22F 7/06 20130101; Y10T
29/49252 20150115; Y10T 29/49261 20150115; Y10T 29/49256 20150115;
Y10T 29/49266 20150115; B22F 5/008 20130101; B22F 2998/00 20130101;
B22F 2998/00 20130101; B22F 5/008 20130101 |
Class at
Publication: |
123/279 ;
029/888.047; 123/193.6; 092/208 |
International
Class: |
F02F 3/26 20060101
F02F003/26; F02F 3/00 20060101 F02F003/00; F16J 1/04 20060101
F16J001/04; B22D 19/00 20060101 B22D019/00 |
Claims
1. A piston, comprising: a piston structure being unitarily formed
in a powder metallurgy process, the piston structure having a crown
assembly and a skirt assembly, at least a partial combustion
chamber being formed intersecting a piston crown surface during the
powder metallurgy process, the skirt assembly depending from the
crown assembly and having two spaced apart pin bosses, each pin
boss having a pin bore defined therein, a pair of opposed
semi-circular skirt members, each skirt member extending outwardly
from and being integrally joined to both of the pin bosses.
2. The piston of claim 1, a void being defined between the crown
assembly and the skirt assembly.
3. The piston of claim 2, the void being defined between a skirt
member upper margin and an undercrown of the crown assembly.
4. The piston of claim 1 being formed of a homogenous material.
5. The piston of claim 4, the homogenous material forming a bearing
surface of each pin bore for rotatably supporting a wrist pin.
6. The piston of claim 4, a bearing formed separately of a material
distinct from the homogenous material being disposed in each pin
bore in a secondary operation for supporting a wrist pin.
7. The piston of claim 1, the piston structure being unitarily
formed in a powder metallurgy process with at least two different
metallic constituents providing dissimilar characteristics at
discrete locations of the piston structure.
8. The piston of claim 7, a one of the at least two different
metallic constituents presenting a bearing surface defining an
inner margin of each pin bore.
9. A piston, comprising: non-homogenous piston structure being
unitarily formed in a powder metallurgy process with at least two
different metallic constituents providing dissimilar
characteristics at discrete locations of the structure.
10. The piston of claim 9, a one of the at least two different
metallic constituents presenting a bearing surface defining an
inner margin of each of two pin bores.
11. The piston of claim 9, including, the piston structure having a
crown assembly and a skirt assembly, at least a partial combustion
chamber being formed intersecting a piston crown surface during the
powder metallurgy process, the skirt assembly depending from the
crown assembly and having two spaced apart pin bosses, each pin
boss having a pin bore defined therein, and having a pair of
opposed semi-circular skirt members, each skirt member extending
outwardly from and being integrally joined to both of the pin
bosses.
12. The piston of claim 11, a void being defined between the crown
assembly and the skirt assembly.
13. The piston of claim 12, the void being defined between a skirt
member upper margin and an undercrown of the crown assembly.
14-20. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to components formed by powder
metallurgy and, more specifically, to a method and apparatus for
forming a piston by powder metallurgy.
BACKGROUND OF THE INVENTION
[0002] Powder metallurgy is a common manufacturing process used to
produce components of high quality for applications, including
vehicular engines. Powder metallurgy is often employed in the
manufacture of engine components because it is economical, flexible
and can produce a finished part that requires much less machining
or secondary processing than other methods of forming components.
Powder metallurgy allows for a component to be formed of a wide
variety of alloys, composites, and other materials to provide the
finished component with desirable characteristics. Moreover, powder
metallurgy allows the porosity of a part to be controlled for
lubricant impregnation. Powder metallurgy is well suited to
manufacture parts of a wide range of sizes and shapes. Also, powder
metallurgy can reliably produce parts with consistent dimensions
and advantageous physical properties.
[0003] The powder metallurgy manufacturing process is often
employed to form engine components. However, no examples of a
piston, formed homogeneously or non-homogeneously, by a powder
metallurgy forging process are known. Such a piston would provide
substantial benefits in the industry over the present forged steel
and cast aluminum pistons.
[0004] The art of making pistons is old and crowded. Nonetheless,
considerable inventive effort continues to the present in order to
form pistons having advantageous characteristics. A recent example
is U.S. Pat. No. 6,435,077, issued Aug. 20, 2002, to Damour et al.
The Damour reference discloses an integral, unitary piston wherein
the pin bosses are carefully formed in order to permit a working
tool to be inserted between the two bosses in order to form a
relatively large cavity beneath the center post of the combustion
chamber formed in the crown of the piston. It would be advantageous
to form a piston that minimized the amount of machining that was
necessary subsequent to initial formation of the piston in order to
achieve the desired shape.
[0005] A second recent example of piston technology found in U.S.
Pat. No. 6,279,455, issued Aug. 28, 2001, to Kruse. The Kruse
reference discloses a piston in which the crown has an upper
portion and a lower portion formed separately and then joined along
specific faces to form a two piece crown of the piston. It would be
advantageous to form a suitable piston in a single operation to
minimize the complexity of suitably joining two portions of the
crown and yet achieve a satisfactory piston structure.
SUMMARY OF THE INVENTION
[0006] The present invention substantially meets the aforementioned
needs of the industry. A piston formed by the process of the
present invention is unitary and integral, formed of a single
operation. Particular attention has been paid to certain bends and
radii in the undercrown region that make the piston more forgeable.
Additionally, significantly less material is utilized in the
process compared with a traditional forging. It should be noted
that a bowl forming at least a partial combustion chamber in the
crown of the piston may be formed during the powder metallurgy
forging process of the piston. The combustion chamber bowl may
include valve pockets in the forging.
[0007] The present invention is a piston including a piston
structure being unitarily formed in a powder metallurgy process,
the piston structure having a crown assembly and a skirt assembly,
at least a partial combustion chamber being formed intersecting a
piston crown surface during the powder metallurgy process, the
skirt assembly depending from the crown assembly and having two
spaced apart pin bosses, each pin boss having a pin bore defined
therein, a pair of opposed semi-circular skirt members, each skirt
member extending outwardly from and being integrally joined to both
of the pin bosses. The piston may be formed by executing a powder
metallurgy process on at least two different metallic constituents
to define a non-homogenous piston structure. A method of forming a
piston is a further aspect of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective side view of a piston made in
accordance with the present invention;
[0009] FIG. 2 is a perspective undercrown view of the piston of
FIG. 1;
[0010] FIG. 3 is a partial cutaway perspective view of a vehicular
engine including an exemplary embodiment of a piston made in
accordance with the present invention;
[0011] FIG. 4 is a process flowchart for a powder metallurgy
manufacturing process for forming the piston of FIG. 1;
[0012] FIG. 5 is a process flowchart for fabricating a
non-homogenous component using the powder metallurgy manufacturing
process according to an embodiment of the present invention;
[0013] FIG. 6 is a side cutaway view of the green part forming
apparatus according to an embodiment of the present invention;
[0014] FIG. 7 is a front view of a green part forming apparatus
according to an embodiment of the present invention;
[0015] FIG. 8 is a top view of a green part forming apparatus
according to an embodiment of the present invention;
[0016] FIG. 9 is a partial top cutaway detailed view of a feed
valve for a green part forming apparatus according to an embodiment
of the present invention;
[0017] FIG. 10 is a partial cutaway side detailed view of a powder
egress in the open position according to an embodiment of the
present invention;
[0018] FIG. 11 is a partial cutaway side detailed view of a powder
egress in the closed position according to an embodiment of the
present invention;
[0019] FIG. 12 is a process flowchart for fabricating a
non-homogenous component using the powder metallurgy manufacturing
process according to an embodiment of the present invention;
[0020] FIG. 13 is a side cutaway view of the green part forming
apparatus according to an embodiment of the present invention;
and
[0021] FIG. 14 is a side cutaway view of the green part forming
apparatus according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0022] The piston of the present invention is shown generally at 10
in FIGS. 1 and 2. The piston 10 of the present invention has two
major subcomponents: crown assembly 250 and skirt assembly 252.
[0023] The crown assembly 250 of the piston 10 presents a top
margin 254. At least a partial combustion chamber (bowl) 256 is
defined in the top margin (crown surface) 254. The combustion
chamber 256 is preferably centrally defined in the piston 10 such
that a central axis of the combustion chamber 256 is coincident
with a central axis of the piston 10. Valve clearance (pockets not
shown) may be forged into the combustion chamber 256, as desired.
Additionally, secondary machining may be employed after the forging
of the piston 10 in order to define the desired combustion chamber
256.
[0024] An exemplary combustion chamber 256 preferably has an
annular reentrant surface 258. The annular reentrant surface 258
preferably smoothly transitions to an annular or spherical side
margin 260. The side margin 260 in turn preferably smoothly
transitions to an annular or spherical bottom margin 262. A center
post 264, which is preferably spherical, is smoothly joined to the
bottom margin 262.
[0025] The crown assembly 250 includes a side margin 268. As
forged, the side margin 268 may be smooth. A plurality of grooves
including compression ring grooves 270 and wiper ring groove 272
are depicted formed in the side margin 268. It is understood that
secondary machining after forging of the piston 10 may be necessary
to form the compression ring grooves 270 and wiper ring groove 272.
A plurality of oil passages 274 are formed in the bottom margin of
the wiper ring groove 272 to return lubricating oil to the engine
oil sump.
[0026] A web 276 is formed on the undercrown of the piston 10. The
web 276 is preferably a depending structure that couples the crown
assembly 250 to the skirt assembly 252.
[0027] The skirt assembly 252 includes a pair of pin bosses 278a,
b, each pin boss 278 depending from the web 276. Each of the pin
bosses 278a, b has a substantially planar outer margin 280 and an
inclined inner margin 282. The inclined inner margin 282 is thicker
at the point of juncture with the web 276 than at the lower margin
of the respective pin bosses 278a, b.
[0028] A pair of pin bores 284a, b are in registry and are defined
through the respective pin bosses 278a, b. The inner margin of the
respective pin bores 284a, b may be formed of as bearing 286a, b.
It is understood that the bearing 286a, b may simply be a surface
formed of the same material as the rest of the piston 10.
Alternatively, the bearing 286a, b could be separately formed of a
different material and affixed in the respective pin bores 284a, b
as by pressing or the like. Such a process is described in greater
detail below. Alternatively, a different material may be injected
during the powder forging process in the vicinity of the bearings
286a, b and forged therein at the same time as the forging of the
remainder of the piston 10. Such a process is also described in
greater detail below.
[0029] Planar lateral extensions 290a, b extend outward from the
respective pin bosses 278a, b on both sides of the respective pin
bosses 278a, b. Accordingly, there are four planar lateral
extensions 290. Two semicircular skirts 292a, b are formed integral
with the outer margin of a respective parallel pair of the planar
lateral extensions 290.
[0030] Each of the semicircular skirts 292a, b presents a skirt
outer margin 294 that has a radius that is generally equal to the
radius of the crown assembly 250 of the piston 10. As such, the
skirt outer margin 294 presents a bearing surface riding on the
inner margin of the cylinder in which the piston 10 is
translationally disposed.
[0031] Each of the skirt outer margins 294 has a depending skirt
lip 296.
[0032] Each of the skirt outer margins 294 presents a skirt upper
margin 298. The upper skirt margin 298 defines in part a lightening
void 300 that is defined between the undercrown portion of the
crown assembly 250 and the skirt assembly 252.
[0033] FIG. 3 illustrates the internal detail of a conventional
internal combustion engine to illustrate the use of the piston 10.
Connecting rod 64 is pivotally connected to the piston 10 and to
the crankshaft 74. The connecting rod 64 is connected to the
crankshaft 74 at a large or crank end 76. The large end 76 of the
rod 64 receives a shaft portion ("crank pin") 78 of the crankshaft
74. The connecting rod 64 is further connected to the piston 10 at
a small or piston end 70 of the rod 64. A pin ("wristpin") 68 is
used to rotatably secure the small end 70 of the connecting rod 64
within the skirt portion of the piston 66.
[0034] Referring to FIG. 4, a process chart for a powder
metallurgical component forming process 30 is shown that is
suitable to form a homogeneous embodiment of the piston 10. First,
the metal powders 32 that will comprise the component (piston 10 of
the present invention) are provided. Often, lubricants are added to
the metal powders to decrease the wear of pressing machinery. Next,
the base powders are mixed 34 to form a homogenous mixture. The
finished piston 10 will ultimately be a homogeneous alloy of the
constituent metal powders.
[0035] A mold or die is then filled 36 with the mixed powders. The
die, when closed, has an internal cavity in the same shape as the
final part, piston 10. The powder is compressed 38 within the die
to form a so-called "green part", which has the substantially the
shape of the finished piston 10. The compaction 38 is usually
performed at room temperature and at pressures in the range of
30-50 tons per square inch. The green part, also referred to as a
"green compact," has the desired size and shape of the finished
piston 10 when ejected from the die. After compaction 38, the green
part has sufficient strength for further processing.
[0036] Next, the green part is subjected to a sintering process 40.
Generally, sintering 40 involves subjecting the green part to a
temperature of 70-90% of the melting point of the metal or alloy
comprising the green part. The variables of temperature, time and
atmosphere are controlled in the furnace to produce a sintered part
having improved strength due to bonding or alloying of the metal
particles. The sintering process 40 most generally comprises three
basic steps conducted in a sintering furnace: (a) burnoff 46; (b)
sinter 48; and (c) cooling 50. Continuous-type sintering furnaces
are commonly used to perform these steps. Burnoff 46 is performed
in a burnoff chamber and is used to volatize the lubricants used in
forming green part 10. A high-temperature chamber performs the
actual sintering 48. The cooling chamber performs the cooling 50
and cools the sintered part 10 prior to handling.
[0037] The pistons 10 that exit the sintering furnace 40 after
cooling 50 may be considered complete. Alternatively, they may
undergo one or more secondary operations 42. Exemplary secondary
operations include re-pressing the component 52, machining 54,
tumbling 56 and joining the component with additional components 58
as part of an overall assembly. The secondary operations 42 may
also include the impregnation of oils or lubricants 60 into the
part for conveying self-lubricating properties. The sintered
component may also undergo heat treatment 62 to provide certain
characteristics and properties to the component, such as strength.
Those skilled in the art will recognize that other secondary
operations may be performed. The secondary operations 42 may be
performed individually or in combination with other secondary
operations.
[0038] After sintering 40, a variety of secondary operations 42 may
be performed on the part depending its intended use. It is
understood that the bearings 286a, b may be formed of the
homogenous material forming the remainder of the piston 10,
However, a separate component defining a bearing 286a, b may be
disposed in the wrist pin aperture bore 284a, b of FIGS. 1 and 2 by
pressing into the pin bore 284a, b. The bearing 286a, b may be
formed of bronze or other material suitable to provide the rotating
contact with the wrist pin 68. In certain uses, the material
forming the bearing may advantageously be a different material than
that forming the remainder of the piston 10. Finally, the finished
piston 10 is ready for employment.
[0039] FIG. 5 illustrates the process for manufacturing a
non-homogenous powder metallurgical manufactured piston 10. A first
metal powder 100 is provided to a mold 102. Then, a second metal
powder 104 is provided to the mold 106. The powder in the mold 106
is next pressed 108 to form a green part comprising the piston 10.
The green part 10 is then sintered 110 before performing one or
more secondary operations 112. After the green part 10 is sintered
110 and all secondary operations 112 performed, the part is then
finished 114. This process may be modified as shown in step 107 by
providing a first metal powder to the mold following the provision
of the second metal powder 104 to the mold 106. Those skilled in
the art will recognize that additional layering of powdered metals
may be performed without deviating from the spirit and scope of the
present invention.
[0040] The above procedure is performed to provide a piston 10 with
dissimilar characteristics at discrete locations in the piston 10.
For example, the piston 10 may be provided with a unitary layer of
material forming the bearings 286a, b by way of the forming
operation. The method of manufacturing the piston 10 by the present
method allows the secondary step of separately forming and
providing wrist pin bearings 286a, b to be eliminated, thereby
saving cost, time, and complexity. The bearing 286a, b is instead
formed integrally during the powder forging process, as described
in greater detail below.
[0041] Referring to FIG. 7, a green component forming apparatus 120
according to an embodiment of the present invention is shown. The
green part forming apparatus 120 may be referred to generally as a
feedshoe apparatus 120. The feedshoe apparatus 126 most generally
comprises a powder filling vessel 122 actuatable by an actuator
cylinder 134, an upper punch 140, a lower punch 142, and a powder
hopper 148. More particularly, a first vessel 122 is rigidly
connected to a second vessel 126 by one or more connection members
138. The second vessel 126 is connected to an actuator cylinder 134
via a piston 136. The actuator cylinder 134 may be a hydraulic or
pneumatic cylinder for urging the piston 136 in or out, thereby
guiding first 124 and second 125 vessels in a linearly controlled
movement. Each vessel 124, 126 comprises side walls 125 defining an
interior cavity 124, 128 therein. The side walls 125 have sloped
portions 129 for directing powder towards a powder outlet valve
146. A top opening 127 in the vessel 122, 126 is sized to receive a
chute 152, 154 connected to hopper 148, 150. The hoppers 148, 150
are for receiving a respective first and second powdered metal that
will be provided to a respective first interior cavity 124 and
second interior cavity 128. The first chute 152 and second chute
154 comprise a flexible tube configured to allow for the linear
movement of the first vessel 122 and second vessel 126. Both first
and second vessels 122, 126 move linearly by sliding on bridge
member 132. Each of the bridge member 132 and actuator cylinder 134
are mounted on a die table 130.
[0042] Referring to FIG. 7, a side view of the feedshoe apparatus
120 is depicted. One or more locking mechanisms 160 are provided to
the die table 130. The locking mechanisms 160 allow for
registration of the vessels 122, 126 during a die cavity 144
filling operation. The locking mechanism 160 may be a magnet or
other locking means such as a male-female socket or equivalent
thereto.
[0043] The bridge member 132 is slidably disposed on the guides
166. Each guide 166 is further disposed upon a rail 168. An
elevation cylinder 162 is disposed on each bridge member 132 and
configured to elevate the bridge member 132 above the guides 166 by
extension of an elevation piston 154. The separation shown in FIG.
2 between the first vessel 122 and the die cavity 144 allows the
actuator cylinder 162 to move the vessel 122 transverse to the
cavity 144. The vessels 122, 126 must be moved away from the
punches 140, 142 to a distance that will not interfere with the
pressing process.
[0044] Referring to FIG. 8, a top view of the feed shoe apparatus
120 is shown. Each vessel 122, 126 is depicted in a partial cutaway
to illustrate interior detail. A dashed outline of the die cavity
perimeter 172 is shown for reference purposes. One or more powder
egresses 170 are disposed in the bottom surface of each vessel 122,
126. The powder egresses 170 include the valves 148 for controlling
the passing of the powder metal into the die cavity 144. The
egresses 170 may be sized to control the relative amount of flow
through a particular egress 170 during a filling operation. The
first vessel 122 is shown with a single egress 170. The second
vessel 126 is shown as having three egresses 170 with differing
sizes. Various polygonal or eccentric shapes or varying size may be
employed in place of the circular-shaped egresses without departing
from the scope of the present invention.
[0045] The size and placement of the powder egresses 170 are
carefully chosen to correspond with the provision of predetermined
characteristics for the finished part. For example, the piston 10
in an internal combustion engine needs to include a bearing race
286a, b as part of the pin bores 284a, b. As noted above, the
method for manufacturing the piston 10 is to provide separately
formed bearings 286a, b to the preformed piston 10 as part of a
secondary operation. The apparatus and method disclosed herein
provides for a powder egress positioned at the precise location for
the bearing race 286a, b portion of the piston 10.
[0046] The feedshoe apparatus shown in FIG. 8 additionally includes
a liquid injection apparatus 174. The liquid injection apparatus
174 injects liquids to the first interior cavity 124 during a
forming process. An inlet to the injection apparatus 176 is
connected to a liquid conduit 178, which supplies a liquid
solution. The apparatus may comprise a solenoid valve, such as a
zero dead leg volume solenoid valve. However, a variety of suitable
dripless valves may be used without departing from the scope of the
present invention. Those of skill in the art will recognize that
the present invention may also be practiced with a second liquid
injection apparatus provided to the second vessel, or
alternatively, one liquid injection apparatus in communication with
both of the first and second vessels.
[0047] The liquid solution may include aqueous solutions,
lubricants, surfactants, or activation solutions for cleaning metal
particulates for cold welding. The liquid solution may also include
any solution that is intended to be incorporated into the material,
such as a hardener, or solvent. The injection of lubricants may be
employed to reduce wear to the die cavity of the apparatus.
[0048] FIG. 9 illustrates a valve assembly 148 that comprises the
powder egress 170 of the vessel 122, 126. A housing surface 182 in
conjunction with slide hole 124 define an open position P.sub.1 and
a closed position P.sub.2 for the powder egress 170. The slide hole
184 moves between positions P.sub.1 and P.sub.2 as the actuator 134
linearly translates the vessel 122, 126. The open condition permits
metal powder to freely exit the vessel and enter the die cavity.
The closed position blocks the transfer of powder to the cavity.
Other methods or devices for cutting off the flow of powder from
the feedshoe to the die cavity may utilized without departing from
the scope of the present invention.
[0049] Referring to FIGS. 10 and 11, depict an alternative
embodiment of an apparatus and method for controlling the flow of
metal powder into the die cavity 144. A feedtube 186 communicates
between the interior cavity 124, 128 of the vessel 122, 126 and the
die cavity 144. The feedtube 186 is comprised of a flexible
material, such as rubber. The bottom sidewall of the vessel 122,
126 defines a channel 188 therein as shown in the figures. A
pincher or crimper device 190 is disposed within the channel 188.
The feedtube 186 is in the open position, as shown in FIG. 10, when
the crimping devices 190 are withdrawn or not pressing on the tube
186. FIG. 11 shows the tube 186 in a closed position wherein the
crimping devices 190 press on the tube sidewalls until the
sidewalls contact, thereby blocking powder flow. The crimpers 190
are urged towards the feedtube 186 by way of pneumatic control.
High pressure is presented to the channel 188, which urges the
crimpers 190 towards the tube 186. The removal of this high
pressure condition causes the natural resiliency of the tube 186 to
re-open, thereby permitting powder flow. Mechanical means, such as
a linkage, may be used instead of the pneumatic drive means without
departing from the intended scope of the present invention.
[0050] Referring to FIGS. 6-8, the method and apparatus for
manufacturing a non-homogeneous article with powder metallurgy will
be described in operation. The following description is more
particularly directed towards manufacturing a piston 10 for an
internal combustion engine wherein the piston 10 has unitary
bearing material formed as bearing 296a, b as part of a single
forming procedure. A first metal powder, such as steel, is placed
in the first hopper 148 and a second metal powder, such as bronze,
is placed in a second hopper 150. The first vessel 122 is also
centered over the die cavity 144 by either expanding or retracting
the piston 136 of the actuator cylinder 134 as necessary.
[0051] Then the first metal powder is introduced to the first
interior cavity 124. The first powder then fills the mold or die
cavity 144 through the powder egress 170 with a predetermined
amount of powder. The flow of first powder is stopped by the valve
148 at the powder egress 170. The piston 136 is next extended until
the second vessel 126 centers over the die cavity 144. Note that
the powder egress 170 is not centered over the die cavity 144. This
allows the second powder to deposit at the discreet location needed
to form the bearings 286a, b of the finished piston 10. A
predetermined amount of the second powder is then filled into the
die cavity 144. The first and second powder fill operations are
then repeated until the cavity 144 is filled with a sufficient
amount of metal powder to form a finished part.
[0052] The piston 136 is next retracted until the first vessel 122
is clear of the upper 140 and lower 142 punches. Then the powder in
the die cavity 144 is pressed to form a green part (piston 10) once
the clearance has been established. The green part is next placed
in a sintering oven and cooled. Once cool, the sintered piston 10
is machined to final tolerances. Other secondary operations, such
as carburizing nitriding, or machining, may be performed without
departing from the scope of the present invention. It is not
necessary to provide the piston 10 with a separately formed bearing
as part of a secondary operation due to the bearing 286a, b being
provided as part of the forming operation. A finished connecting
piston 10 results from the completion of any other required
secondary operations.
[0053] Referring to FIG. 12, an alternative method of manufacturing
a non-homogenous piston 10 with an integral bearing 286a, b is
shown. Each of the first metal powder 200 and second metal powder
202 is filled in the mold or cavity simultaneously 204. Then the
part is pressed 206, sintered 208 and subjected to secondary
operations 210 before it is finished 212.
[0054] FIG. 13 depicts an alternative apparatus for forming a green
part (piston 10) according to either the method described in FIG. 5
or FIG. 12. The feedshoe apparatus according to this embodiment
comprises a single vessel 222. The vessel 222 comprises sidewalls
223 and a center divider 224. The sidewalls 223 and center divider
224 define a first section or chamber 226, and a second section or
chamber 228. The first section 226 receives a first metal powder
from a first hopper 230 and the second section 228 receives a
second metal powder from a second hopper 232. A first powder egress
234 is provided to the first chamber 226 and a second powder egress
226 is provided to the second chamber 228.
[0055] In operation, the first and second powders may be provided
to the die cavity at the same time. The respective powder egresses
234, 236 are located and sized to promote the filling of the cavity
238 with the first and second powders in their desired locations
before pressing. Alternatively, the piston 240 may move the vessel
222 in a linear direction to place a respective first 234 or second
236 egress over a portion of the die cavity 238 prior to filling
with a metal powder. As a further alternative, the powder egresses
234, 236 may be selectively opened and closed to create density
gradients in the part or to further place a second material within
the first. Additionally, a combination of the above alternatives
may be employed as part of the same forming operation.
[0056] FIG. 14 depicts another alternative embodiment of the green
part forming (feedshoe) apparatus 250. This embodiment again
comprises a single vessel 252. The vessel comprises first 256 and
second 254 dividers for defining a first chamber or section 258, a
second chamber 260 and a third chamber 262. Each chamber 258, 260
and 262 receives a respective first 264, second 266 or third 268
powder egress and is in communication with a respective first 270,
second 272 or third 274 hopper. Those having skill in the art will
appreciate that the present invention may be practiced with more
than three chambers without departing from the scope of the present
invention. Moreover, a single hopper may be in communication with
two or more chambers.
[0057] The use of three chambers 258, 260 and 262 allows a first of
two different powders to be presented to the die cavity 276 in two
places simultaneously. Alternatively the three chambers 258, 260
and 262 allow three powders to be introduced to the die cavity 276
as part of a single forming operation. The embodiment of FIG. 14 is
operated in substantially the same manner as set forth above for
the two-chamber embodiment.
[0058] Although the present invention has been described with
reference to the preferred embodiments, workers skilled in the art
will recognize changes may be made in form and detail without
departing from the spirit and scope of the invention.
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