Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02365335 2001-08-30
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METHOD FOR MANUFACTURING INTERNAL
COMBUSTION ENGINE PISTONS
BACKGROUND OF THE INVENTION
This invention is relates to the manufacture of internal combustion
engine pistons, such as, but not limited to, internal combustion engine
pistons used in
automobiles engines, treaded or crawler-type machinery, aeronautical engines,
and
marine based motors.
A piston is typically a highly-stressed engine component. While a
piston is in motion, the top or crown of the piston may be subjected to high
temperatures. Any grooves formed in the piston, for example grooves for
compression rings, may be subjected to high impact stresses. Additionally, if
the
piston comprises a wrist pin port, the port may be subjected to adverse
cyclical loads.
These piston features undergo varying operational stresses, loads,
temperatures, and
other operation characteristics (hereinafter "operational characteristics")
and may lead
to different piston areas needing different mechanical attributes and
qualities (also
known as "piston characteristics") to endure these operational
characteristics.
A piston's mechanical attributes may be determined by its properties.
Pistons, such as, but not limited to, engine internal combustion pistons,
often
comprise aluminum alloys. These aluminum alloys include, but are not limited
to,
silumins, which can possess a silicon content in a range from about 11 % to
about
35%. Additionally, if the piston comprises silumin alloy-based compounds, the
piston
may also comprise hardening agents, such as silicon carbides (SiC) and
aluminum
oxides (A1203), The silicon and intermetallic particles in the alloys, in
combination
with the above agents, may enhance a material's heat resistance and wear
properties.
However, a material's resistance to metal fatigue and plasticity may decrease
with the
enhancement of its heat resistance and wear properties.
If a piston's base materials do not provide it with desired properties,
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piston areas that may undergo stress can be formed from a material that can be
hardened. The hardening may be conducted by incorporating at least one of
ferrous-
based alloy and ceramic materials. For example, a piston portion may include
an iron-
holder, which is generally recognized as heat resistant that can reduce a
compression
ring groove wear. This piston portion can be reinforced by plasma-arc welding
and
injecting alloying constituents, such as nickel, iron, and other such
reinforcing
constituents, into the piston. The heat resistant nature of these materials
protects the
piston.
Piston design and production may depend on the desired application of
the piston. For example, pistons can be formed by casting, as set forth Yu, et
al.,
"Aluminum Alloys in Tractor Building", Machine Building, 1971. This casting
method provides a relatively efficient and low cost production method, which
permits
casting of pistons with reinforcements thereon. These reinforcements include,
but not
limited to, piston ring holders and brackets. However, these aluminum-cast
pistons
are generally used in low dynamic loads (pressures) applications because the
aluminum-cast pistons can only be subjected to low mechanical stress levels.
Another known piston production process comprises hot-deformation
forging from an aluminum alloy billet, as disclosed in Yu et al., "Isothermal
Forging
of Pistons from an Alloy", Forging Production, 1979. This forging method may
be
more expensive than a casting method, however, forging silumin-alloy pistons
can
provide enhanced mechanical properties. Thus, these silumin-alloy pistons can
be
used in applications that undergo powerful loads. The forging method typically
is
conducted for small and relatively simple pistons because of silumin's low
plasticity
under hot-deformation forging conditions. Therefore, reinforcements are added
to
overcome this plasticity deficiency, for example brackets can be added by
being
mounted on a piston. This reinforcement can complicate a piston's design and
increase its production costs. Further, the forging method may be limited by
forging
temperatures that do not provide a desired quantity and size of the silicon
and other
hardening particles in the silumin-alloy. Therefore, known forging processes
muy
prevent an silumin-alloy piston from achieving desired plasticity and
mechanical
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properties. Therefore, a need exists for a piston production method that can
produce
pistons with desired plasticity and mechanical properties. Further, a need
exists for a
piston production method that overcomes the above-noted deficiencies. Also, a
need
exists for a piston production method for producing silumin-alloy pistons.
SUMMARY OF THE INVENTION
A piston production method produces an internal combustion engine
piston. The method comprises forging a billet from an initial billet
comprising an
aluminum alloy that comprises silicon, intermetallic particles, and injected
hardening
particles, the forging is conducted under at least one of super-plasticity and
hot
deformation conditions; and heat treating the forged billet. The forging
comprises
forging at a temperature in a range from about 0.8 Tmei, to about 0.98 Tmei~.
The
forging also comprises forging at a strain rate in a range from about SxlO-2 s-
~ to about
SxlO-5 s~'. The piston being formed with a configuration that enables other
parts to be
connected to the piston. The initial billet comprises at least one of: coarse
grain
silicon, intermetallic particles, and injected hardening particles having at
least one of a
lamellar, comprehensive shape, and fine grain silicon, intermetallic
particles, and
injected hardening particles being globular in shape. The silicon,
intermetallic and
injected hardening panicle volume content is in a range from about 25% to
about
60%, and an average grain size of the silicon, intermetallic, and injected
hardening
particles is less than about 15 ~m2.
These and other aspects, advantages and salient features of the
invention will become apparent from the following detailed description, which,
when
taken in conjunction with the annexed drawings, where like parts are
designated by
like reference characters throughout the drawings, disclose embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of piston production system, and
method in which the left side of the axis is before deformation occurs, and
the right
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side of the axis is after deformation has occurred;
Figure 2 is a schematic illustration of piston in a ring holder production
system with a billet and ring holder in a piston die;
Figure 3 is a schematic illustration of piston in a ring holder production
system with the forging of the piston crown on left side of the axis, and with
the
forging of the piston inner part on the right side of the axis;
Figure 4 is a schematic illustration of fused piston production system,
in which the left side of the axis illustrates before deformation, and the
right side of
the axis illustrates after deformation;
Figure 5 is an exploded schematic illustration of pressing a ring holder;
Figure 6 is a schematic illustration of band-shaped piston with a ring
holder;
Figures 7-12 are schematic illustrations of composite piston being
forged by a process, as embodied by the invention, in which Fig. 7 illustrates
n ~up-
~5 shaped inner case; Fig. 8 illustrates a cup-shaped outer piston case; Fig.
8 illustrates
fitting an inner case into an outer case; Fig. 9 illustrates a compound piston
after
forging; Fig. 10 illustrates a washer-shaped outer case and a cup-shaped inner
case;
and Fig. 12 illustrates washer-shaped inner and outer cases;
Figure 13 is a schematic illustration of a billet being fit into a piston
die, as embodied by the invention;
Figure 14 is a photograph of various sized billets as produced by the
piston production method, as embodied by the invention;
Figure 15 is a photograph of cross-sectional pistons with brackets, as
embodied by the invention;
Figure 16 is a photograph of a silumins microstructure with silicon and
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intermetallic particles having a size less than about 6 ~tmz; and
Figure 17 is a photograph of a silumins microstructure with silicon and
intermetallic particles sized less particles having a size greater than about
15 ~tm-.
DESCRIPTION OF THE INVENTION
A piston production method and its associated system, as embodied by
the invention, enables pistons comprising silumin alloy to be produced. The
piston
production method can form pistons by forging. The silumin-alloy pistons that
are
produced by forging, as embodied by the invention, comprise varying mechanical
properties and characteristics combined in one piston. These mechanical
properties
and characteristics may be further dependent upon a silumin-alloy piston's
initial
configuration and microstructure. Also, mechanical properties and
characteristics
may be dependent upon a silumin-alloy piston's configuration and
microstructure
produced by deformation treatments in the piston production method, as
embodied by
the invention.
The piston production method, as embodied by the invention, is
schematically illustrated with the piston die system of Fig. 1. In Fig. 1, the
piston die
system comprises a piston die matrix 1, a piston die 2, a pusher 3, a heater
element 4,
at least one liner plate 5, a billet 6, and forged piston 7. Figure 2 also
illustrates
features of the piston die system and related structures for the piston
production
method, as embodied by the invention. Figure 2 illustrates a ring holder 8, a
spring 9,
a piston die matrix guide 10, a piston billet with ring groove 11, a piston
blank, ring
holder, and crown 12, and a piston comprising a ring holder 13. Figure 3
illustrates
fused material 14 that has been formed by a piston production method, as
embodied
by the invention.
Further features of the piston die system and related structures are
illustrated in the remainder of the figures. These features include an
aligning tlange
15, a partially formed billet inner part 16, a ring 17, a band-shaped ring
holder 18, a
cup-shaped billet outer case 19, a cup-shaped billet inner case 20, a washer-
shaped
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outer billet case 21, and a washer-shaped inner billet case 22.
The silumin-alloy piston production method, as embodied by the
invention, can produce silumin-alloy pistons by forging fully formed pistons
including
structural reinforcements features (hereinafter "reinforcements"). The
reinforcements
comprise, but are not limited to, ring holders and piston brackets. The piston
production method, as embodied by the invention, can be used to form pistons
of
varying sizes, for internal combustion engines, such as pistons used in
automobiles,
aeronautical and marine applications, and large treaded machinery. The piston
production method, can increase piston production efficiency by providing
pistons
with mechanical properties and characteristics that meet those desired
mechanical
properties and characteristics for an intended application.
The piston production method, as embodied by the invention,
comprises forging a billet, which can comprise an aluminum alloy composition.
The
aluminum alloy composition comprises at least one of silicon, intermetallic
particles,
and injected hardening particles. The following description of the invention
will
describe an aluminum alloy composition as set forth above, however other
compositions are within the scope of the invention. The particles can be
provided in a
lamellar configuration. The composition for the initial billet, for example an
aluminum alloy composition, may also comprise at least one of fine silicon,
intermetallic particles, and injected hardening particles. The injected
hardening
particles can be generally globular in configuration.
The forging step of the piston production method can be followed by a
heat treatment step. In the piston production method, as embodied by the
invention,
the forging can produce large-sized pistons and pistons that comprise
reinforcements.
The piston production method also permits pistons to be formed with a
configuration
that enables piston components to be readily connected with the piston. The
forging is
typically conducted in a temperature range from about 0.8 Tn,er~ to about 0.98
Tmer, of
the piston material. The forging of the piston production method is generally
conducted with a strain rate of in a range from about 5x10-' s-r to about
SxIO~' s-'.
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The piston production method may also comprise forging steps that are
conducted under super-plasticity or common hot deformation conditions. These
conditions are generally provided if at least one of silicon, intermetallic
particles, and
injected hardening panicles have a volume content in a range from about ?>~lo
to
about 60% of the aluminum alloy composition, with an average Grain size of
silicon.
intermetallic particles, and injected hardening particles less than about 15
~tm'. If the
billet material composition includes a particle content and size that is
outside of the
above ranges, forging may be conducted under hot deformation conditions. Thus,
a
larger a silicon or panicle size can provide forging steps with a lower strain
rate. For
example, forging with a strain rate in a range from about 10-' s-' to about
SxlO-' s-'.
and a lower forging temperature range, for example a temperature range from
about
0.83 Tmeic to about 0.89 Tme,c can be conducted.
Billet material composition and configuration characteristics can be
considered in determining piston production method parameters. For example, if
a
billet material composition comprises a particle weight content that is
greater than
about 20% and an average grain size that is greater than about 15 ~tm~, the
initial billet
configuration and the disposing of a billet into a forging device can be
considered for
piston production. These billet material composition and configuration
characteristics
may decrease deformation that occurs during a piston production method, as
embodied by the invention. The piston production method, which can include
forging, as described above, may comprise a one-step process. The piston
production
method that includes a one-step process can be conducted under hot deformation
and
super-plasticity conditions.
Alternatively, the piston production method can be conducted in a
temperature range from about 0.90 Tme,c to about 0.98 Tmetc and at strain rate
in a range
from about Sx 10-2 s-' to about 10-3 s~' . These temperature and strain rate
ranges are
employed with a piston production method that uses billet material composition
comprising at least one of silicon, intermetallic particles, and injected
hardening
particles with an average grain size that is less than 6 ~tm2. In the piston
production
method of a billet with such a billet material composition, the billet can
undergo
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primary deformation before forging steps. The primary deformation can occur m
a
temperature range from about 0.79 Tme,, to about 0.86 Tme,c and in a strain
rate range
from about SxIO-~s-~ to about SxlO-' s-~.
Alternatively, the piston production method, as embodied by the
invention, can form pistons from a billet that comprises a billet material
composition
with at least one of average grain sized silicon, or intermetallic particles,
and injected
hardening particles with a size that is in a range from about 6~m'' to about
15 pm~.
The parts per million (ppm) for this billet material composition can comprise
hot
deformation forging that is conducted in a temperature range from about 0.84
Tme,, to
about 0.96 Tme,c and in strain rate range from about 103 s-~ to about Sx 10 -
'' s'~.
Further another alternative of the piston production method, as
embodied by the invention can form pistons a billet that comprises at least
one of
silicon, intermetallic particles, and injected hardening panicles with an
average grain
size less than about 15 ~mz, and where the injected hardening particles have a
generally globular configuration. In this aspect of the piston production
method, a5
embodied by the invention, a volume percent of silicon particles,
intermetallic
particles, and the injected hardening particles is in a range from about 25%
to about
60%. With such a billet material composition, the piston production method
comprises forging conducted under super-plasticity conditions in a temperature
range
from about 0.88 Tme,c to about 0.98 Tme,c and in strain rate range from about
Sx 10 ~5 s-~
to about 1 x 10 -'s~' .
Furthermore, the piston production method can form pistons from a
billet that has a billet material composition comprising at least one of
silicon,
intermetallic particles, and injected hardening particles with volume less
than about
15% of the total billet mass. This piston production method, as embodied by
the
invention, can use the billet material that can be provided with a generally
tapered-
cone configuration. The billet, which can be a casting, comprises a billet
material
composition with a configuration that contact of the billet and the piston die
matrix is
achieved only by side surface, that is more than about 30% of its area.
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A gap distance that can occur in the piston production method between
a billet's lower butt end a:;d a piston die matrix base. The gap distance can
be
determined by the billet material configuration. For example, the gap distance
can be
determined with respect to the size and content of at least one of the silicon
particle,
intermetallic particles, and hardening particles. This gap distance is
generally is equal
to:
h=dK/C~F
where d is an internal diameter of the bottom of the piston die matrix, (mm);
C is a
content of at least one of silicon, intermetallic particles, and hardening
particles
injected, (% for mass); F is an average area of at least one of silicon
particles, and
intermetallic particles, and injected hardening particles (pm2); and K is a
coefficient
that is reflective of the shape and size of a forging piston die-bit and is
typically
provided in a range from about 0.5 to about 10. Therefore, with a billet that
comprises an average grain size of silicon, intermetallic particles, and
injected
hardening particles that is less than about 15 pmt, any deformation is
generally at a
certain temperature essentially equal to a quenching temperature. Any
quenching
cooling that is immediately after the deformation process can complete the
piston
production method.
If a billet comprises average grain size of silicon, intermetallic
particles, and injected hardening particles less than 15 ~m2, and contains
less than
15% silicon particles, intermetallic, and injected hardening panicles, a ring
holder can
be made from alloys containing about 20% to about 45% by volume silicon,
intermetallic particles, and injected hardening particles, with a size of 20
~m~. In
addition, a ring holder for the piston production method, as embodied by the
invention, can be mounted with an interference fit on a piston side and
against a butt
end of a piston die matrix surface. Thus, any hot deformation forging can be
conducted and may result in a piston crown being shaped first followed by an
inner
part.
The piston production method, as embodied by the invention, can be
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used with a billet material composition that comprise silicon, intermetallic
particles,
and injected hardening particles with an average grain size are less than
about 151.tm-
and a volume in a range from about 25% to about 6070. In this combination. a
rinU
holder comprising an alloy having silicon, intermetallic, and injected
hardening
particles with an average size less than 20pm2 and in a volume range from
about 20~7~
to about 45% can be used. If the ring holder is mounted with an interference
fit on a
piston side and disposed against a butt end of the piston, the forging steps
can be
conducted under super plasticity conditions. Therefore, the piston crown can
be
shaped followed by shaping of an inner part of the piston.
A billet that comprises silicon, intermetallic particles, and injected
hardening particles with an average grain size are less than about 15 ftm' and
that
contains less than about 15% silicon, intermetallic, and injected hardening
particles,
can use a ring holder made from pig-iron or steel. Additionally, a ring holder
can be
mounted with an interference fit on a side and against a butt end of the
piston die
matrix in the piston for such billet. Any forging of the piston in the piston
production
method, as embodied by the invention, can be conducted under super plasticity
conditions. Therefore, the piston crown can be shaped first and then followed
by
shaping of the inner part of a piston.
A billet that comprises silicon, intermetallic particles, and injected
hardening particles with an average grain size less than about 15pm2 and that
contains
silicon, intermetallic, and injected hardening particles in a range from about
25% to
about 60%, can use a ring holder made from pig-iron or steel. Additionally, a
ring
holder can be mounted with an interference fit on a side and against a butt
end of the
piston die matrix in the piston for this type of billet. Any forging of the
piston in the
piston production method, as embodied by the invention, can be conducted under
super plasticity conditions. Therefore, the piston crown can be shaped first
and then
followed by shaping of the inner part of a piston.
Another aspect of the invention can provide aligned surfaces of a ring
holder and piston's body billet that comprise a conical shape. The conical
shape may
CA 02365335 2001-08-30
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comprise an angle in a range from about 1° to about 10°. The
body's billet can be
made with a ring shoulder having a negative angle in a range from about 1 to
about 3°.
The ring hula~r gun b~ plated intu a ring ~huulder with an interference i~it
sire in a
range from about O.lmm to about 0.2mm in diameter. The positioning of the ring
holder is generally conducted at room temperature in the piston production
method, as
embodied by the invention.
The piston production method that comprises forging can be conducted
in two steps. First, the forging can comprise placing a ring holder in a
piston die
matrix. The placing step can be followed by providing an interference fit
between the
ring holder's outer surface and an inner surface of the piston die matrix. The
interference fit can be calculated as follows:
1.0017<_ d/D _< 1.0035
where d is a ring holder outer diameter at a forging temperature, and D is a
piston die
matrix inner diameter at the forging temperature. The forging can be conducted
by
physically moving the piston die matrix in the forging direction with the ring
holder
being fixed during any subsequent piston crown forging.
The ring holder in the piston production method, as embodied by the
invention, can be coated with a layer of an aluminum-containing alloy. The
coating
and piston case can be made from essentially the same composition.
Two billets can be used to forge a piston with an inner and outer case
by the piston production method, as embodied by the invention. For example,
and in
no way limiting of the invention, a billet for the piston production method
can
comprise about 15% (total) silicon, intermetallic particles, and injected
hardening
particles. This billet can be used to make a piston outer case. Another
exemplary
billet material composition comprises about 15% (total) silicon, ~
intermetallic
particles, and injected hardening particles. This billet material composition
can be
used to make a piston inner case, in which the outer case can be mounted by an
interference fit to a side surface of the piston.
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The piston production method, which comprises forging of two billets.
can use a billet having an exemplary billet material composition with about
4~% to
about 60% (total) silicon, intermetallic particles, and injected hardening
particles by
volume. This billet material composition can be used to make the piston outer
case.
An exemplary billet material composition comprises a range of about 25% to
about
40% (total) silicon, intermetallic particles, and injected hardening particles
by volume
can be used to make the piston inner body. While forging such a piston, the
piston die
can be heated to a temperature that enhances deformation of an inner billet.
such as
under super plasticity conditions. The piston die matrix can be heated to a
temperature that enhances deformation of the outer billet under super
plasticity
conditions. Further, this piston production method can use billets that are
generally
washer shaped. Alternatively, piston production method, which comprises
forging of
two billets, can use billets that are cup-shaped with an outer cup-shaped
billet
comprising a taper to a butt end of the billet. In the piston production
method. which
comprises forging of two billets, pressing an inner cup into an outer cup can
complete
an assembly of a compound billet, as embodied by the invention.
The billet for the piston production method, as embodied by the
invention, can include a protuberance, shoulder, or other extension. The
shoulder's
surface can comprise a wave-shaped surface, with a wave period L (Fig. 6). A
billet
material composition with an increase of silicon, intermetallic, particle
size. and
injected hardening particles may result in an increase in wave period L. For
example,
the piston production method, as embodied by the invention, can further employ
a
steel washer, spacer, or other separating device. The spacer can be placed on
the
shoulder's surface. The washer's thickness generally satisfies the following
condition:
IJl=4-42.
Additionally, a relationship between the billet's height and shoulder can be
determined so that a wave-shaped washer can be on a same general ,level at the
piston's compression ring groove when forging is complete.
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A billet with silicon, intermetallic particles, and injected hardening
particles having an average grain size less than about l5~tm~ can be placed in
a piston
die matrix against a bracket, in which the bracket mirrors a billet's surface.
This
orientation results in a lock joint being formed after the piston has been
forged. for
example forged using hot deformation. The bracket surface area S that is
created in
the formed lock joint can be determined by the formula:
S=KP/SinccF,
where P is a separation force required to overcome a dynamic force created
during
motor performance; K is a reliability coefficient; F is a aluminum alloy flow
resistance at a working temperature; and a is an angle between a shoulder and
a piston
movement direction.
Alternatively, a billet with silicon, intermetallic particles, and injected
hardening particles having an average grain size less than about 15~m2 and
that
comprises a total volume content of silicon, intermetallic, and injected
hardening
particles in a range between about 25% and about 60% can be placed in a piston
die
matrix during a piston production method, as embodied by the invention. The
placement can include placement against a bracket that mirrors a billet's
surface. This
placement can result in a lock joint being formed after the piston has been
forged
under super-plasticity conditions. The bracket surface area S may be
determined by
the formula:
S=KP/SinccF,
as above.
As another alternative, a billet with silicon, intermetallic particles, and
injected hardening particles having an average grain size less than about
l5~tm'', and
comprising a total volume silicon, intermetallic, and injected hardening
particles in a
range from about 25% to about 60%, can be placed in a piston die matrix
against a
bracket. The bracket can be formed from a porous ceramic material, such as a
porous
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ceramic material that is infiltrated with an aluminum alloy. The porosity of
the porous
ceramic material is in a range from about 35% to about 50%. Thus. forging in
the
piston production method, as embodied by the invention, can be conducted under
super-plasticity conditions. The same aluminum alloy composition can used for
infiltration of the porous ceramic material as is used in production of a
piston case.
After forging steps, a piston that is formed by the piston production
method, as embodied by the invention, can be subjected to further deformation.
For
example, the further deformation comprises deformation in a close-end piston
die at a
strain rate in a range from about 10-5 s-' to about 10 -4 s-' for at time in a
range from
about 0.5 minutes to about 5 minutes. For billet material compositions
comprising
silicon, intermetallic particles, and injected hardening particles having an
average
grain size less than about 15~m2, a hardened layer can be deposited on a
piston
surface. In this scenario, hot deformation forging can be conducted at a
temperature
of in a range from about 0.9 Tmen to about 0.96 Tmeu and at a strain rate in a
range from
about 5 x 10-'' s~' to about lO-3 S~'.
The piston production method, as embodied by the invention, can
enhance forging conditions in the production of pistons. This enhancing can be
conducted by considering a billet's initial microstructure and chemical
composition.
Experiments reveal that desired forging temperature intervals may be provided
to
develop desirable mechanical properties. Forging of complex-shaped and large-
sized
billets can be achieved in the above-described temperature and strain rate
intervals,
while conducting techniques of disposition of the billet in the piston die, as
embodied
by the invention.
Pistons, such as simple shaped pistons that are unhardened or without
reinforcing elements added thereto, can be employed in low-rated motors. These
pistons can be produced from billets by mold casting, in a further piston
production
method, as embodied by the invention. This piston production method can
produce
pistons with relatively low manufacturing costs. Casting is the most
inexpensive
method of billet production. The raw material for mold casting can comprise a
coarse
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microstructure comprising silicon, intermetallic particles with an average
gram size
greater than about 15pm2.
For example, silumins comprising this microstructure typically exhibit
low levels of plasticity under hot deformation conditions. These silumms also
muy
exhibit high plasticity at temperatures in a range from about 0.86 Tm~ic to
about 0.91 of
Tme,~ and at a strain rate in a range from about 10-'s~' to about SxIO~' s-~.
Fine-grained
structured silumins, with particles comprising an average grain size less than
about 6
p,mz, may exhibit higher plasticity and may be is acceptable for use in
production of
complex- shaped pistons and large pistons. If the piston production method
comprises
pre-forged billets with this microstructure, continuous casting and hot
deformation
forging can be provided, for example, by a pressing step. A decrease in alloy
particle
size can permit an increase in a deformation temperature range. The
temperature and
strain rate at which deformation forging in the piston production method is
conducted
can influence a silumin material's mechanical properties. These influenced
properties
can be recognized after the forging step of the piston production method
following
any subsequent heat treatment.
The piston production method, as embodied by the invention, can
produce pistons from fine grain microstructure alloys. The fine grain
microstructure
alloys can develop desirable mechanical properties after deformation in a
temperature
range from about 0.9Tmeu to about 0.96 Tme,~ and strain rate in a range from
about 5 x
10-Z s-I to about 1 x 10-3 s-~. These properties, which are formed in the
above-
described ranges, can be attributable to a formation of micropores in the
billet material
near silicon, intermetallic, and injected hardening particles. The micropores
can form
under high temperature deformation conditions of the piston production method.
The
micropore size can increase with a decrease in an applied strain rate during
the piston
production method. This decrease can be attributable to the mechanical
properties
that are attained at high strain rates, as embodied by the invention.
Conversely, the piston production method can also produce pistons
from coarse grain microstructure alloys. It has been determined that coarse
grain
CA 02365335 2001-08-30
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microstructure alloys can develop desired mechanical properties after
deformation at a
strain rate in a range from about 10-' s ~~ to about 5 x 10~' s -~. Further,
detormation
conditions for an billet material composition comprising silicon,
intermetallic
panicles. and injected hardening particles with an average grain size in a
range from
about 6~tmz to about 15 pmz have also been determined. These deformation
conditions comprise deformation at a temperature in a range from about 0.84
T",~,, to
about 0.96 Tme,c and at a strain rate in a range from about 10 -3 s-~ - 5 x 10
-' s-~ .
A fine grain alloy for the piston production method that comprises
silicon, intermetallic particles, and injected hardening particles with an
average gram
size less than about 6 ~tmz in the billet can be produced by hot deformation
of cast
billets, in which the cast billets comprise a coarse lamellar grain
microstructure. The
piston production method conditions for deformation forging of such silicon
and
intermetallic particles are at a temperature in a range from about 0.79 Tmeu
to about
0.96 Tme~c and at a strain rate in a range from about 5x10-4s-' to about SxlO-
3 s -1.
The piston production method, as embodied by the invention, can be
used to produce pistons, which comprise various compositions, microstructures,
and
grain sizes, under super-plasticity conditions. For example, and in no way
limiting of
the invention, pistons comprising brittle materials. for example. eutectic
silumins
reinforced with hardened particles can be produced by the piston production
method,
as embodied by the invention. Alternatively, pistons comprising a complex
shape and
being hardened with low stress-flow materials, which are materials that
deciease ring
holder deformation and displacement relative to the piston itself, can be
formed by the
piston production method, as embodied by the invention. As a further
alternative.
pistons comprising a large size that are stamped by low force presses can be
formed
by the piston production method.
Super-plastic deformation conditions for the piston production method,
as embodied by the invention, may be used with silicon, intermetallic, and
injected
hardening particles comprising an average grain size that is less than about I
S ~tm-.
Further, super-plastic deformation conditions comprise a volume of silicon,
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intermetallic, and injected hardening particles in a range between about ?~r~
to about
60%. A strain rate in a range from about SxlO-5 s-~ to about SxlO-' s-', and a
deformation temperature in a range from about of 0.88 Tmen to about 0.98 Tmen
can be
used as super-plastic deformation conditions for the above-noted grain size.
The piston production method, as embodied by the invention. can tore
billets that comprise greater than about 15% by weight of silicon,
intermetallic, and
injected hardening particles, all of which have an average grain size of more
than
about 15 wm2. Such a billet material composition typically exhibits low levels
of
plasticity. During the piston production method, contact between the piston
billet and
piston die matrix's surfaces should occur within about 30% to about 100% of a
side
surface area, until a piston die-bit contacts a butt end. This contact should
prevent at
least one of billet cleaving and formation of cracks.
Further, the piston production method should provide a maximum
distance between a billet base and piston die matrix base. The distance
generally is
dependent on a plasticity of the billet material composition, for example, but
not
limited to at least one of: a quantity and size of silicon, intermetallic, and
injected
hardening particles; a billet diameter; and a size and shape of the piston
die. A shorter
distance between the base of a piston billet and base of a piston die matrix
can be
provided if the billet material composition is brittle. This distance is
desired to
prevent distortion of the billet as a piston die bit is disposed in the piston
die matrix.
The piston production method, as embodied by the invention, can
comprise quench-cooling after forging is complete, if a piston has been forged
at an
essentially same temperature for quenching. This procedure reduces piston
production method time since a heating for quenching step will be redundant,
and thus
can be skipped. Further, an absence of "heating for quenching" can prevent
crystal
growth in solidifying aluminum of the billet material composition. This
procedure
may also provide a finer grain microstructure in a final piston.
Ring grooves in the piston can be reinforced in the piston production
method for limiting disintegration of piston ring grooves while a motor
operates. The
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ring grooves can be reinforced with metal ring holder, which provide strength
at
working temperature that is generally is greater than that of the billet
material. For
example, if a piston is formed as a casting, a ring holder can usually
comprise pig-iron
that is reinforced by coating formed by molten metal. Alternatively, if a
piston is
forged, a ring holder can comprise a microstructure including coarse gain
silumin
with silicon, intermetallic, and injected hardening particles, since silumin
typically
possesses higher strength characteristics than the piston billet material.
For example, fine grain silimins or intermediate materials with silicon,
intermetallic, and injected hardening panicles that have an average grain size
less than
about 15 ~tm2, and that comprise silicon, intermetallic, and injected
hardening
panicles less than about 15% volume can be used in a piston production method,
as
embodied by the invention. These materials can exhibit plasticity that can
enable
forging with a ring holder formed from silumins. The silumin can comprise
about
20% to about 45% silicon, intermetallic, and injected hardening particles,
with silicon,
intermetallic, and injected hardening particles having an average grain size
greater
than about 20 p.m2.
The ring holder can be placed on the billet, and placed with billet into
the piston die matrix. An interference fit can be established between a piston
billet
surface and butt end sides of the piston die matrix to prevent the blank from
cracking.
A piston crown can be formed first and enable a ring holder to be located on a
billet
and avoid deformation. Stress on the billet material is typically lower than
that
applied to reinforcing ring holder material during any hot deformation
treatments.
Thus, the reinforcing material will fill a space around the ring holder, in
which the
ring holder normally undergoes minimal deformation, such as less than about
20%. A
piston billet with a "microduplex structure", which means that the billet
comprises a
billet material composition having a volume content of particles in a range
from about
25% to about 60%, can undergo piston production method, as embodied by the
invention, under super-plasticity conditions. In this piston production
method, forging
is conducted with a press and a ring holder experiences less deformation.
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A ring holder, which comprises at least one of pig iron and steel, with
an average grain size of the silicon, intermetallic, and injected hardening
particles less
than about l5~tm'', an be used with the piston production method to prevent
ring
holder relocation and avoid ring holder deformation or destruction. To
accomplish
this prevention, a ring holder can be inserted into a piston die matrix with
an
interference-fit on the side surface and against butt end surface. The piston
crown is
forged first followed by the piston inner part under super-plasticity
conditions, which
simplifies forging.
A reliable joint should be formed between a ring holder and piston in
piston production method, as embodied by the invention. Such a joint can be
created
by piston material filling a ring holder cavity followed by joint deformation.
If an
oxide film is provided on the ring holder, such as by previous treatments,
removal of
film occurs when the ring holder is placed on the piston blank. Mating
surfaces of the
ring holder and piston blank can be cone shaped with a conical angle in a
range from
about 1° to about 10°. The piston and billet ring shoulder can
comprise a negative
angle in a range from about 1 ° to about 3°. Further, the ring
holder can be pressed
with a temperature in a range from about 15°C to about 540°C
with an interference fit
in a range from about O.lmm to about 0.2mm at the diameter. The forging
conditions,
as embodied by the invention, can produce reliable diffusion joint between the
ring
holder and piston. The negative angle prevents mating surfaces of the butt end
of the
ring holder and piston billet from oxidizing during heating and forging. A
closed
cavity can then form because of different shapes between a lower end of the
ring
holder and ring shoulder. Additionally, contact of these surfaces with furnace
atmosphere is prevented, which can lower piston billet and ring holder
oxidation rates
during forging.
Further, deformation at the ring holder base and shoulder can occur
during forging because of shape differences. The deformation can reduce the
oxide
film, and in turn, promotes formation of a diffusion joint between the ring
holder base
and shoulder surface.
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Forging a piston with ring holder can be conducted in a two-stage
piston production method. First, the billet can be placed butt end against the
piston
die with its ring groove zone disposed upwardly. A piston die stamps the
piston
crown that is followed by the ring holder being pressed. The piston blank can
then be
inverted so the crown now faces downwardly, and a second piston pruductiun
stage
commences with the formation of the piston inner.
The ring holder can be located in the piston die matrix where by an
interference fit forms between the ring holder outer surface and piston die
matrix inner
surface. This disposition can prevent a ring holder from cracking, while the
piston is
undergoing hot deformation treatment. The disposition can also prevent
distorting
caused by variations in metal flow rates during formation of the piston inner.
The
interference fit characteristics can be calculated as follows:
1.0017<_ d/D <_ 1.0035
where d is the ring groove outer diameter at forging temperature and D is the
piston
die matrix inner diameter at forge temperature.
If an interference fit is less than desired, cracking and distortion of the
ring holder may occur. A close interference fit may complicate insertion of
the piston
billet with ring holder within the piston die matrix. If the piston production
method
comprises placing a ring holder on a cylindrically shaped billet with very
little or no
gap therebetween, the piston die matrix can provide enhanced ring holder
stability
during the piston production method, as embodied by the invention. This
orientation
can also prevent uneven metal distribution above and below a ring holder. This
orientation, in combination with a ring holder position during forging, can
provide a
stable platform for the ring holder.
Aluminum may be diffusion coated on the ring holder. The diffusion
coating at high temperatures can provide the aluminum, for example man
aluminum
alloy for penetrating the steel ring holder. This procedure may remove oxide
films
from the aluminum alloy piston and ring holder surfaces. To enhance piston
case and
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ring holder joint reliability, any alloys for example for coatings, used in
the piston
production method, as embodied by the invention, should possess a similar if
not the
same coefficient of linear extension.
A two-layer piston configuration, and the piston production method
used to form such a two-layer piston configuration, can provide reliable
piston
performance during initial motor startup. The two-layer piston configuration
can also
provide enhanced reliability when a motor is hot and under stress. A two-layer
piston
configuration with high silicon, intermefallic, and injected hardening
particle content
can provide desired strength characteristics at operating temperatures.
However, at
low temperatures, such as when a motor is initially started, materials used
for the two-
layer piston configuration may offer low levels of plasticity. However, a two-
layer
piston configuration comprising an alloy with low silicon, intermetallic, and
injected
hardening particle content that has a high plasticity level can offer fatigue
resistance.
During motor startup and warming, the two-layer piston configuration
can transmit wrist pin forces to a piston inner portion. The piston inner
portion can be
formed from an alloy comprising low silicon, intermetallic, and injected
hardening
particles. A motor with pistons formed by the piston production method, as
embodied
by the invention, during operating can achieve a temperature in the ring
groove zone
in a range from about 250°C to about 350°C, and higher if fully
stressed. The piston
outer case alloy comprises a composition with high content silicon,
intermetallic, and
injected hardening particles that can prevent at least one of the piston rings
from
destroying a piston ring groove and piston base from burning out at high
operating
temperatures.
Variations in a piston thickness can be determined to enhance piston
production method characteristics, piston wear resistance, and plasticity. For
example, a working temperature while the motor operates around a piston lower
edge
can be lower than the temperature at a ring groove zone. During cold startup
of an
engine, a piston skirt lower edge can be subjected to impact stress as the
piston moves
from top deadcenter through to bottom deadcenter. This stress may cause a
piston
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skirt lower edge to comprise a material with a high plasticity and sufficient
resistance
to wear. These characteristics can be provided by minimizing a piston outer
body
thickness. If the plasticity is sufficient for forging, piston billets can be
washer shaped
(as discussed above) since the shape is conductive to forging. Conversely. if
alloy
plasticity is insufficient for either forging or pressing, the piston billets
can be cup
shaped.
Assembling a compound piston billet before forging can facilitate
removal of oxide films that coat inner and outer case contact points. The
removal
may comprise pressing an inner case into an outer case. The exemplary forging
steps
for producing a diffusion joint may comprise providing a wave-shaped piston
billet.
The billet shape can be provided by a low weight piston and reinforced ring
holder.
The ring holder reinforcement blank can also comprise a thin washer placed on
the
wave-shaped piston billet butt end. After initial forging, this washer also
assumes the
wave shape. During forging of the piston crown, molten metal from the piston
billet
can pour between the washers. The molten metal can fill any space between the
washers. Moreover, during forging of a blank comprising silicon,
intermetallic. and
injected hardening particles with an average grain size about 15 ~tm~, a gap
tree joint I
around the ring holder with an interval of: 1/1 = 4 - 14 may result. Forging a
blank
with average grain sized silicon, intermetallic particles, and injected
hardening
particles with an average grain size greater than about 15 ~mz can create a
gap free
joint with ring holder. The gap free joint 1 comprises an interval that is
determined by
1/1= 15 - 42.
A piston production method that utilizes a washer, as discussed above,
can comprise steps of cutting a groove in the washer, for accepting a
compression
ring. A compression ring is in physical contact with a ring groove and can
decrease a
ring groove wear rate. A ring holder weight and groove ware rate can be
enhanced by
a reinforcement washer.
A piston production method, can also comprise attaching a bracket,
which is formed of heat resistant material, to a piston case. The attachment
can
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comprise any appropriate means, such as but not limited to attaching by bolts.
This
bolt attachment step can be time consuming and costly, therefore the piston
production method, as embodied by the invention, can comprise attaching
brackets to
the piston. The brackets can be formed as integral flanges, so the bracket can
be
attached to a piston without bolts. The formed mechanical joint can be created
by a
flange surface area, and its orientation relative to a dynamic force generated
during
motor operation. The joint can overcome inertia within a motor, and thus
should he
sufficient to hold a bracket and piston case together. Pouring of molten
piston
material into the bracket cavity during forging in the piston production
method, as
embodied by the invention, can provide for super-plastic deformation
conditions,
including those discussed above.
Brackets can comprise porous ceramic materials, which can be infused
with aluminum alloy in order to reduce its weight. The ceramic material can
comprise
an open porosity with a porosity value in a range from about 35% to about 50%
to
provide frame strength. The infusing of the ceramic material frame with
aluminum
alloy can be followed by bonding an aluminum layer to a surface, which can
mate
with the piston case. This bonding step can result in a diffusion joint formed
between
the bracket and piston case after deformation. If both the infusion material
and piston
case comprise the same composition, then the formed joint reliability can be
enhanced
because differences in coefficients of the linear extension have been
eliminated.
Additional deformation in a close end piston die, for example those exposed to
compression from all sides, can be applied under a strain rate in a range from
about 10
-5 s I to about 10 -4 s -1 for time period in a range from about O.Smin to
about Smin.
This time period can result in elimination of micropores, which may result in
enhanced mechanical properties in the piston.
Wear in the ring groove can be attributed to a decrease in piston alloy
strength. The decrease results from exposure to high temperatures during the
piston
production method. An increase in material strength at the ring groove zone
can be
provided by plasma welding. The plasma welding comprises melting of material
in a
ring groove zone often relying on a plasma arc. This plasma welding can be
followed
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by alloying element injection into the melt. However, these steps of material
melting
and resultant properties are essentially the same for hot deformation and cast
pistons.
Any differences therebetween may result when fusing steps are used on a piston
billet
and not used on the piston case.
A fused material may be characterized by large ferrous or nickel-based
intermetallic plates, and shrinkage holes. Deformation of the fused material
can be
conducted while the piston is being forged. The deformed fused material may
possess
levels of hardness and ultimate strength that often remain the same even after
heating
to up to temperatures of about 250°C. Any enhanced characteristics in
the material
can be attributed to a dispersed microstructure as intermetallic particle
fragmentation
can occur during hot deformation treatments. Further, enhanced characteristics
can
also be attributed lack of stress points, such as but not limited to shrinkage
holes. The
absence of shrinkage holes can contribute to an increase in a material's
ultimate
strength, since the absence can increase the materials' plasticity.
A set of examples of piston production methods within the scope of the
invention will now be described. The following operative steps for the piston
production method, as embodied by the invention, should not be construed as
limiting,
but merely provide guidance to steps within the scope of the invention. The
values set
forth below are approximate, unless specified as exact.
A piston blank and piston die can undergo primary heating. Any
deformation is conducted under isothermal conditions. The forging temperature
is
selected dependent on a piston blank initial microstructure and configuration.
The
billet shape can depend on billet material composition and average grain size
of the
silicon, intermetallic particles, and injected hardening particles therein.
The
subsequent heat treatment steps for the piston production method comprises
quenching and artificial aging.
Example 1. A cylindrical piston billet comprising an approximate
alloy composition of 12% Si, 2.2 % Cu,. 1.1 % Mg, 0.1 % Ti, 1.1 % Ni, 0.4% Mn,
0.8%
Fe, with Al as a balance. The billet was cut from a bar of stock. This bar was
made
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by hot pressing an ingot at 440°C or 0.86 Tmen with a strain rate of
90%s-~. Tmep for
the above alloy is equal to 552°C and was chosen from a phase diagram
for AI- and
Mg-based systems. The resulting billet's microstructure comprises globular
silicon
and intermetallic panicles with an average grain size of about 5 p.m''. The
billet was
deformed in a piston die system, as in Fig. 1, at 520°C (0.96 Tn,ei,)
with a strain rate of
1x102 s-'. Quench cooling occurred in water at 20°C was conducted after
the
deformation process. Aging was conducted at 210°C for 10 hours.
Microstructural
analysis of the material indicated an absence of defects, such as microcracks
and
micropores. The material had the following mechanical property: ab = 390MPa.
Example 2. A piston billet of alloy composition comprising 21%Si,
1.6%Cu, 1.1%Mg, 0.1%Ti, 1.1%Ni, 0.5%Mn, 0.7%Fe with A1 as the balance was
made by block mold casting. An average grain size of silicon and intermetallic
particles is about 120 ~tm2 with lamellar shapes. The billet was tampered to a
cone
shape with a 4° angle. The billet size was such that when fit into a
piston die matrix,
which has an inner diameter of 150mm and a cone angle of 4°, 50% of the
surface area
made contact with the piston die matrix. A distance from the billet's lower
butt end to
that of the piston die matrix lower butt end may be determined as:
H = dK/C~IF,
where d = 150, K = 5, C = 21, F = 120. The distance was calculated at
3.2 mm. The billet was deformed in a piston die system (Fig.l ) at
480°C (0.91
Tmei~) at an average strain rate of 1x10-4 s ~'. The heat treatment sequence
included quenching at 510°C and aging at 210°C for 10 hours. The
resultant
piston was determined to be essentially defect free. Further testing showed
that 6b = 250MPa.
Example 3. A billet with comprising an part was forged at a
temperature of 520°C (0.96 Tme~c) and strain rate of 1x10-2 s-1 from a
cylindrical blank
in the piston die system of Fig 1. The blank was cut from a pressed ingot. The
pressing temperature was in a range from about 440 to about 450°C (0.86
T~,ei~ to
about 0.88 Tmeu) with a strain of 90%. The ingot composition comprised 12%Si,
CA 02365335 2001-08-30
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2.2%Cu, 1.1 %Mg, 0.1 %Ti, 0.4%Mn, 0.8%Fe with AI as a balance, and comprised
an
average grain size of silicon and intermetallic particles about 6 ~tm~.
Mechanical
treatment to the head of the billet's conical surface with ring shoulder was
conducted
to form a cone angle about 6°, and negative shoulder angle of about
3°. .A rind holder
with a flat lower butt end was formed from aluminum alloy with about a 18%
silicon
content. The ring holder was pressed into the billet's head using a ring
against the
shoulder at 20°C.
In this series of above-described steps, a closed cavity was formed
between the flat butt end of the ring holder and billet's ring shoulder. The
billet with
pressed ring holder and can be heated in a furnace to a temperature of
510°C. The
billet was fit in a piston die system with simultaneous pressing of the ring
holder and
forming a piston fire chamber. Forging was conducted under isothermal
conditions at
510°C (0.95 Tmen) using a hydraulic press with strain rate of 10-3 s-'.
After forging the
ring holder, the piston was quenched in water and aged at 210°C for 10
hours.
Strength testing revealed the joint between the piston body and ring holder to
be
140MPa.
Example 4. A piston blank comprising aluminum alloy with a
composition comprising 12%Si, 2.2%Cu, 1.1%Mg, 0.1%Ti, 1.1%Ni, 0.4%Mn,
0.8%Fe, with Al as a balance is used in a piston production method. The alloy
comprised an average grain size of silicon and intermetallic particles at
Sp,m2 and the
grains were globular in shape. An aligning protuberance was formed on the
piston,
and a pig-iron ring holder was installed against the protuberance. The pig-
iron ring
holder was installed by pressing the ring holder into the protuberance. Prior
to its
installation on the billet, the ring holder was coated with a layer of
aluminum alloy
melt, which comprises essentially the same composition as the billet. The
billet with
ring holder was fit into the piston die matrix with an interference fit
therebetween.
Forging was conducted under hot deformation conditions at 490°C (0.93
Tme,~) with a
average strain rate of 10-3 s-'. The piston crown was formed first (left side
of Fig. 2),
and then its inner part (right side of the figure). Subsequently, steps of
forging,
quenching, and artificial aging were conducted.
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WO 00/53914 PCT/US00/06238
An aluminum alloy can be coated on the holder in this example. After
cooling, the aluminum alloy coating was fusion joined to the ring Groove
surface. .As
the ring holder was pressed into the piston billet, the oxide film coatings
from both the
piston billet and ring holder surfaces were removed. High temperature and
deformation that occur during forging provide conditions for creation of a
permanent
fusion joint. The strength of this joint is typically sufficient to. prevent a
Gap from
developing between the piston body and ring holder during subsequent heat
treatment
and use.
Example 5. An aluminum alloy billet that compt~ised 12%Si, 2.2%Cu,
1.1%Mg, 0.1%Ti, 0.4%Mn, 8%Fe and A1 as a balance, further comprised an average
grain size of silicon and intermetallic particles at l2pmz. This billet was
formed with
an integral shoulder. A butt end surrounding the shoulder was wave-shaped, as
described above. The ring holder was made from wave-shaped sheet steel with a
thickness of 3mm. The billet and ring holder wave period was calculated using
the
formula:
L =1(4-14)
where 1 is a thickness of the sheet from which a ring holder was made, for
example 3
mm. Using the above-formula above, L is in a range from about l2mm to about
42mm. For the experiment, L was about 30mm. The ring holder was fixed to the
blank and placed into the piston die matrix. The piston was then forged. The
subsequent heat treatment included quenching and artificial aging.
Example 6. A compound piston comprised two cases, an inner and
outer case. The billet for the outer case comprised an aluminum alloy with 21
%Si,
1.6%Cu, 1.1%Mg, 0.1%Ni, 0.5%Mn, 0.7%Fe, with Al as the balance. It also
comprised silicon and intermetallic particles with an average grain size of
301.tm2.
The inner case billet was formed from an alloy comprising 12%Si, 2.2%Cu, 1.1
%M~.
0.1%Ti, 1.1%Ni, 0.4%Mn, 0.8%Fe and a balance Al, with silicon and
intermetallic
particles having an average grain size of S~tm2, and being globular in shape.
The outer
and inner case billets were washer shaped. The piston was forged by
simultaneously
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forging both billets at 490°C (0.93 T,ne,,) with a deformation rate of
10-~ 5-~.
Subsequent heat treatment sequence included quenching and artificial aging.
Example 7. A piston billet body was made from the aluminum alloy
with a composition of 12%Si, 2.2%Cu, 1.1%Mg, O1.%Ti, 1.1%Ni, 0.4%Mn, 0.8%Fe
and a balance aluminum. An aluminum alloy piston blank comprised an alloy with
a
composition of 21%Si, 1.6%Cu, 1.1%Mg, 0.1%Ti, 0.5%Mn. 0.7%Fe and a balance
of Al. The alloy included an average grain sized of silicon and intermetallic
particle
of 120~m2. A bracket made from silica mullite with 40% porosity was infused
with an
aluminum alloy having a same composition as the piston billet. The inner
bracket
surface was coated with an aluminum alloy layer and had a thickness of 2 mm.
The
bracket and billet were fit into the piston die piston die matrix and heated
to 480°C
(0.91 Tme,~). The deformation was conducted a strain rate of 104 s -~. After
foraina.
quench cooling was conducted in open air. Aging was conducted at 350°C
for 8
hours. The joint between piston and bracket was determined to be reliable and
~ 5 permanent.
Example 8. A blank cut from hot pressed aluminum alloy rod was
formed with a composition of 12%Si, 2.2%Cu, 1.1%Mg, 0.1%Ti, 1.1%Ni, 0.4%Mn>
0.8%Fe, with Al as a balance. The alloy comprised an average grain size of
silicon
and intermetallic particles of 6p.mz with a globular shape. At a distance of
20mm
from an end, a piston ring section was melted, and injected with a nickel-
chrome flux.
for example nickel-chrome wire. Melting was conducted using a solid electrode
in an
argon atmosphere in a three step or 3 turns operation. The first step involved
a nickel-
chrome flux injection rate of 65m/hour and a welding speed of 41m/hour,. In
second
and third steps, welding was conducted without injecting alloying elements,
and a
welding rate was 25 m/hour. Electric current during the steps was in a range
from
about 680 A to about 700 A, and the voltage was 220 V. The melt depth was 7
mm.
A billet with a melt layer with a nickel content of 7% and chrome
content of 2 % was heated in a furnace to 470°C (0.9 Tmeit). The billet
was then
placed in a piston die matrix piston die mounted under a hydraulic press.
28
CA 02365335 2001-08-30
WO 00/53914 PCT/US00/06238
Billet, joint, and melted layer deformation was conducted with a strain
rate of 10-' s-~. Forging was conducted under isothermal conditions with the
blank
and piston die temperature at about 470°C with an average strain rate
of 10-'s-~. The
piston was removed from the piston die with the help of a pusher. Quenching
was
conducted at a temperature of 510~10°C in water. Aging was conducted at
a
temperature of 210°C for 10 hours. During final mechanical processing
of the piston
the ring groove was formed. No microcracks or micropores were found.
While various embodiments are described herein, it will be appreciated
from the specification that various combinations of elements, variations or
improvements therein may be made by those skilled in the art, and are within
the
scope of the invention.
29
