TITLE OF INVENTION
METHOD FOR PRODUCING FORGED CRANKSHAFT
TECHNICAL FIELD
[0001]
The present invention relates to a method for producing a crankshaft
by hot forging.
BACKGROUND ART
[0002]
A reciprocating engine to be employed in a motor vehicle, a motorcycle,
an agricultural machine, a marine vessel or the like requires a crankshaft to
extract power by converting reciprocating motions of pistons to rotational
motion. There are two types of crankshafts: the type manufactured by die
forging and the type manufactured by casting. Especially when high
strength and high stiffness are required, die forged crankshafts (which will
hereinafter be referred to as "forged crankshafts") are often employed.
[0003]
FIGS. lA to lC are schematic diagrams showing an example of a
shape of a commonly used crankshaft. FIG. lA is an overall view, FIG. lB is
a sectional view along the line IB-IB, and FIG. lC shows the phases of pins.
In order to facilitate understanding of the shape of the crankshaft, FIG. lB
shows only a crank arm Al, a counterweight Wl integrated with the crank
arm Al, a pin Pl and a journal Jl connected to the crank arm Al, which are
extracted from the crankshaft.
[0004]
The crankshaft 11 shown in FIGS. lA to lC is a four-counterweight
crankshaft to be mounted in a three-cylinder engine. The crankshaft 11
includes four journals Jl to J4, three pins Pl to P3, a front part Fr, a flange Fl,
and six crank arms (hereinafter referred to simply as "arms") Al to A6. The
six arms Alto A6 connect the journals Jl to J4 respectively to the pins Pl to
·I
P3. Some of the six arms A1 to A6 have counterweights (hereinafter referred
to simply as "weights") W1 to W 4, respectively, which are integrated therewith.
Specifically, the first arm A1, the second arm A2, the fifth arm A5 and the
sixth arm A6 incorporate the weight W1, W2, W3 and W 4, respectively. The
third armA3 and the fourth armA4 do not have weights.
[0005]
The front part Fr is located at a front edge of the crankshaft 11, and
the flange Fl is located at a rear edge of the crank shaft 11, the front edge and
the rear edge being edges in a direction along the axis of the crankshaft 11.
The front part Fr is connected to the front first journal J1, and the flange Fl is
connected to the rearmost fourth journal J4.
[0006]
In the following paragraphs, when the journals J1 to J4, the pins P1 to
P3, the arms A1 to A6, arid the weights W1 to W 4 are each collectively
referred to, a reference character "J" is used for the journals, a reference
character "P" for the pins, a reference character "A" for the arms, and a
reference character "W" for the weights. An arm A and a weight W
integrated therewith are referred to collectively as a "web".
[0007]
As shown in FIG. 1C, the pins P1 to P3 are arranged at intervals of
120 degrees around the journals. In other words, each of the pins P1 to P3 is
located at a first position L1, a second position L2 or a third position L3, and
the phase differences among the first to the third positions L1 to L3 are 120
degrees.
[0008]
As shown in FIG. 1B, the width Bw of the weights W is greater than
the width Ba of the arms A. Accordingly, each of the weights W bulges
greatly from an arm center plane (a plane including the axis of the pin P and
the axis of the journal J).
[0009]
A forged crankshaft having such a shape is generally produced by
using a billet as a starting material. A section of the billet in a direction
perpendicular to the longitudinal direction thereof, that is, a cross section of
3
jthe
billet is circular or square, and the cross-sectional area is constant
throughout the length. In the following paragraphs, a section of a crankshaft
in a direction perpendicular to the axis of the crankshaft is referred to as a
"cross section", and a section of the crankshaft in a direction parallel to the
axis of the crankshaft is referred to as a "longitudinal section". The area of
the cross section is referred to simply as a "sectional area". A method for
producing a forged crankshaft includes a preforming step, a die forging step,
and a trimming step that are to be executed in this order. After the trimming
step, a coining step may be executed if needed. Typically, the preforming step
includes a rolling step and a bending step, and the die forging step includes a
rough forging step and a finish forging step.
[0010]
FIGS. 2A to 2F are schematic diagrams showing a conventional
method for producing a common forged crankshaft. FIG. 2A shows a billet,
FIG. 2B shows a rolled blank, FIG. 2C shows a bent blank, FIG. 2D shows a
rough forged blank, FIG. 2E shows a finish forged blank, and FIG. 2F shows a
forged crankshaft. FIGS. 2A to 2F show a method for producing a crankshaft
having the configuration shown in FIGS. 1A to 1C.
[0011]
In the production method shown m FIGS. 2A to 2F, a forged
crankshaft 11 is produced as follows. First, a billet 12 with a specified length
as shown in FIG. 2Ais heated in a heating furnace, and in a preforming step,
the heated billet is rolled and subsequently bent. In the rolling, the billet 12
is rolled and reduced, for example, by grooved rolls. This is to distribute the
volume of the billet 12 in the axial direction, and thereby, a rolled blank 13,
which is an in-process material, is obtained (see FIG. 2B). Next, in the
bending, the rolled blank 13 is partly pressed and reduced from a direction
perpendicular to the axial direction. This is to distribute the volume of the
rolled blank 13, and thereby, a bent blank 14, which is a next in-process
material, is obtained (see FIG. 2C).
[0012]
Next, in a rough forging step, the bent blank 14 is forged by a pair of
an upper die and a lower die, and thereby, a rough forged blank 15 is obtained
j-
(see FIG. 2D). The rough forged blank 15 is roughly in the shape of the
crankshaft (final product). In the finish forging step, the rough forged blank
15 is forged by a pair of an upper die and a lower die, and thereby, a finish
forged blank 16 is obtained (see FIG. 2E). The finish forged blank 16 has a
shape in agreement with the shape of the finished crankshaft. During the
rough forging and the finish forging, excess material flows out through a space
between the mutually facing parting faces of the dies, which results in
formation of flash B. Accordingly, the rough forged blank 15 and the finish
forged blank 16 have great flash Bon the periphery.
[0013]
In a trimming step, for example, while the finish forged blank 16 is
nipped and held by a pair of dies, the finish forged blank 16 is punched by a
cutting die. Thereby, the flash B is removed from the finish forged blank 16,
and a forged blank with no flash is obtained. The forged blank with no flash
has substantially the same shape as the forged crankshaft 11 shown in FIG.
2F.
[0014]
In a coining step, main parts of the forged blank with no flash are
slightly pressed by dies from above and below so that the forged blank with no
flash can have the exact size and shape of the final product. The main parts
of the forged blank with no flash are, for example, shaft parts such as the
journals J, the pins P, the front part Fr, the flange Fl and the like, and further,
the arms A and the weights W. In this way, the forged crankshaft 11 is
produced. It is noted that, when the crankshaft to be produced is a
three-cylinder four-counterweight crankshaft or the like wherein the pins are
arranged around the journals at intervals of 120 degrees, after the trimming
step, a twisting step may be additionally executed for adjustment of the
placement angles of the pins.
[0015]
The production method shown in FIGS. 2A to 2F are applicable not
only to production of a three-cylinder four-counterweight crankshaft as shown
in FIGS. lA to 1C but also to production of any other crankshaft. For
example, crankshafts to be mounted in four-cylinder engines, in-line
·!
1-
six-cylinder engines, V·type six·cylinde:r:: engines, eight-cylinder engines and
others can be produced by the same production method.
[0016]
The main purpose of the preforming step is distributing the volume of
the billet, and therefore, the blank obtained thereby is hardly in the form of
the forged crankshaft. By distributing the volume of the billet in the
preforming step, it is possible to decrease the outflow of material and
accordingly to decrease the formation of flash in the next die forging step,
thereby improving the material yield rate. The material yield rate means
the rate (percentage) of the volume of the forged crankshaft (final product) to
the volume of the billet.
[0017]
For example, Japanese Patent Application Publication No.
2001-105087 (Patent Literature 1), Japanese Patent Application Publication
No. H2-255240 (Patent Literature 2) and Japanese Patent Application
Publication No. 862-244545 (Patent Literature 3) disclose techniques relating
to production of a forged crankshaft. Patent Literature 1 teaches a
preforming step using a pair of an upper die and a lower die. During
pressing of a rod-like workpiece by use of an upper die and a lower die in the
preforming step, while a part of the workpiece is elongated, another part
connecting thereto is offset from the axis. In the preforming step disclosed in
Patent Literature 1, rolling and bending are performed at the same time,
which allows a decrease in investment for facilities.
[0018]
According to Patent Literature 2, in a preforming step, a four-pass
high-speed rolling, rather than a conventional two-pass rolling, is performed.
A rolled blank obtained by the preforming step has sectional areas that are
congruent with the sectional area distribution among weights, arms and
journals of the forged crankshaft (final product). According to Patent
Literature 2, this improves the material yield rate.
[0019]
According to Patent Literature 3, in a preforming step, a billet is
pressed while being nipped by at least two dies that are movable relative to
each other. By rolling operation of the dies, the material of the billet is
distributed in the axial direction and the radial direction. Thereby, a blank
having a shape that is asymmetric about the axis and is congruent with the
general shape of the crankshaft to be produced can be obtained. In the
production method disclosed in Patent Literature 3, a blank having a shape
that is asymmetric about the axis can be obtained only by the preforming step,
which allows direct advancement to a die forging step.
CITATION LIST
PATENT LITERATURE
[0020]
Patent Literature 1: Japanese Patent Application Publication No.
2001-105087
Patent Literature 2~ Japanese Patent Application Publication No.
H2-255240
Patent Literature 3: Japanese Patent Application Publication No.
862-244545
Patent Literature 4: W02014/091730
SUJ\IIMARY OF INVETION
TECHNICAL PROBLEMS
[0021]
Regarding production of a forged crankshaft, as mentioned above, it is
demanded to decrease the outflow of material and accordingly to decrease the
formation of flash, thereby improving the material yield rate. In the
preforming step disclosed in Patent Literature 1, volume distribution of the
billet and offset of portions to be formed into pins (which will hereinafter be
referred to as "pin equivalent portions") can be performed to some extent.
However, the offset of pin equivalent portions and the volume distribution are
inadequate, and in the next die forging step, great flash is formed along with
formation of pins.
[0022]
The preforming step taught in Patent Literature 2 is to apply rolling,
I
and therefore, it is not possible to decenter pin equivalent portions in the
preforming step. Accordingly, in the next die forging step, great flash is
formed along with formation of pins.
[0023]
In the production method disclosed in Patent Literature 3, it is
possible to achieve offset of pin equivalent portions and volume distribution of
a billet to some extent without forming flash by the preforming step.
However, a special facility for rolling is required, and implementation of the
production method is not easy. Also, the offset of pin equivalent portions and
the volume distribution are inadequate, and in the next die forging step, great
flash is formed along with formation of pins.
[0024]
An object of the present invention is to provide a forged crankshaft
production method that achieves an improved material yield rate by
decentering and pressing portions of a blank to be formed into pins.
SOLUTIONS TO PROBLEM
[0025]
A forged crankshaft production method according to an embodiment of
the present invention is a method for producing a forged crankshaft including
journals serving as a center of rotation, pins decentered from the journals and
located at a first position, a second position and a third position, respectively,
having phase differences of 120 degrees thereamong, crank arms connecting
the journals and the pins, and counterweights integrated with some or all of
the crank arms.
[0026]
The production method includes a first preforming step, a second
preforming step, and a final preforming step. In the first preforming step, a
workpiece is pressed by a first pair of dies. Thereby, sectional areas of
portions of the workpiece to be formed into the pins and sectional areas of
portions of the workpiece to be formed into the journals are decreased,
whereby the portions to be formed into the pins and the portions to be formed
into the journals are formed into flat portions, and one of the flat portions to
I
be formed into the pin located at the second position is decentered. In the
second preforming step, an initial blank obtained by the first preforming step
is pressed by a second pair of dies with a direction perpendicular to the
decentering direction of the portion to be formed into the pin located at the
second position set as a pressing direction. Thereby, the portion to be formed
into the pin located at the first position is decentered, and the portion to be
formed into the pin located at the third position is decentered to a side
opposite to the portion to be formed into the pin located at the first position.
In the final preforming step, an intermediate blank obtained by the second
preforming step is pressed by a third pair of dies. Thereby, the portion to be
formed into the pin located at the first position is further decentered, and the
portion to be formed into the pin located at the third position is further
decentered.
[0027]
The workpiece is a billet or a stepped blank. The stepped blank has
small sectional areas in the portions to be formed into the pins and in the
portions to be formed into the journals, and the small sectional areas are
smaller than a total of a sectional area of a portion to be formed into a crank
arm incorporating a counterweight and a sectional area of a portion to be
formed into the counterweight integrated with the crank arm.
[0028]
The first pair of dies includes pin processing portions to come into
contact with the portions to be formed into the pins and journal processing
portions to come into contact with the portions to be formed into the journals.
In the first preforming step, the workpiece is pressed by the pin processing
portions and the journal processing portions, whereby the flat portions are
formed.
[0029]
In the final preforming step, the direction of the pressing by the third
pair of dies may be perpendicular to the decentering direction of the portion to
be formed into the pin located at the second position.
[0030]
The forged crankshaft may further include a front part at a front end
9
-I
in an axial direction. In this case, it is preferred that the first pair of dies
further includes a front processing portion to come into contact with a portion
of the workpiece to be formed into the front part. In the first preforming step,
it is preferred that the front processing portion elongates the portion to be
formed into the front part in the axial direction while decreasing a sectional
area of the portion to be formed into the front part to form the portion to be
formed into the front part into a flat portion.
[0031]
When the first pair of dies includes the front processing portion, in the
first preforming step, the front processing portion presses the portion to be
formed into the front part preferably such that, in the initial blank, a sectional
area of the portion to be formed into the front part decreases with decreasing
distance from an end surface of the front part.
[0032]
The forged crankshaft may further include a flange at a rear end in
the axial direction. In this case, it is preferred that the first pair of dies
further includes a flange processing portion to come into contact with a
portion of the workpiece to be formed into the flange. In the first preforming
step, while the flat portions are being formed, an end surface of the portion to
be formed into the flange is preferably brought into contact with the flange
processing portion, whereby a sectional area of the portion to be formed into
the flange is increased.
[0033]
In the second preforming step, the portions to be formed into the crank
arms incorporating the counterweights are processed preferably to be thicker
than a finished size, and the portions to be formed into the counterweights
integrated with the crank arms are processed preferably to be thicker than a
finished size. In this case, in the final preforming step, during the pressing
by the third pair of dies, the portions of the intermediate blank to be formed
into the crank arms incorporating the counterweights and the portions to be
formed into the counterweights integrated with the crank arms are pressed
from the axial direction of the intermediate blank.
[0034]
IO
In the second parr of dies used in the second preforming step
preferably includes web processing portions to come into contact with the
portions to be formed into the crank arms incorporating the counterweights
and the portions to be formed into the counterweights integrated with the
crank arms. In this case, each of the web processing portions includes an
arm processing part to come into contact with a portion to be formed into a
crank arm and a weight processing part to come into contact with a portion to
be formed into a counterweight integrated with the crank arm, and both of the
arm processing part and the weight processing part are provided in one of the
second pair of dies. The arm processing part and the weight processing part
form a recessed portion, where the arm processing part is located in a bottom
side of the recessed portion and the weight processing part is located in an
open side of the recessed portion. The width of an open side of the weight
processing part becomes greater with increasing distance from the bottom of
the recessed portion. In the second preforming step, as the portions to be
formed into the pins located at the first position and at the third position are
being decentered, the portions to be formed into the crank arms incorporating
the counterweights and the portions to be formed into the counterweights
integrated with the crank arms are pushed into the bottom sides of the web
processing portions and are deformed.
[0035]
In the second preforming step, when the portions to be formed into the
crank arms incorporating the counterweights and the portions to be formed
into the counterweights integrated with the crank arms are pushed into the
bottom sides of the web processing portions and are deformed, the portions to
be formed into the crank arms incorporating the counterweights and the
portions to be formed into the counterweights integrated with the crank arms
are pressed preferably from the open sides of the web processing portions for
volume distribution.
ADVATAGEOUS EFFECTS OF INVENTION
[0036]
In the forged crankshaft production method according to the present
II
}-
invention, the portion to be formed into the pin located at the second position
is decentered in the first preforming step, and is decreased in cross-section in
the first preforming step and the second preforming step. The portion to be
formed into the pin located at the first position and the portion to be formed
into the pin located at the third position are decentered in the second
preforming step and the final preforming step, and are decreased in
cross-section in the first preforming step and the second preforming step.
This decreases formation of flash caused by formation of pins in the next die
forging step (finish forging step), and accordingly improves the material yield
rate.
BRIEF DESCRIPTION OF DRAWINGS
[0037]
[FIG. lA] FIG. lA 'is an overall v1ew of a common crankshaft
schematically showing an example of a shape thereof.
[FIG. lB] FIG. lB is a sectional view along the line IB-IB in FIG. lA.
[FIG. lC] FIG. lC is a diagram showing the phases of pins of the
crankshaft shown in FIG. lA.
[FIG. 2A] FIG. 2A is a schematic diagram of a billet during a
conventional process of producing a common forged crankshaft.
[FIG. 2B] FIG. 2B is a schematic diagram of a rolled blank during the
conventional process of producing a common forged crankshaft.
[FIG. 2C] FIG. 2C is a schematic diagram of a bent blank during the
conventional process of producing a common forged crankshaft.
[FIG. 2D] FIG. 2D is a schematic diagram of a rough forged blank
during the conventional process of producing a common forged crankshaft.
[FIG. 2E] FIG. 2E is a schematic diagram of a finish forged blank
during the conventional process of producing a common forged crankshaft.
[FIG. 2F] FIG. 2F is a schematic diagram of a crankshaft during the
conventional process of producing a common forged crankshaft.
[FIG. 3A] FIG. 3A is a schematic diagram of a billet during an
exemplary forged crankshaft production process according to the present
invention.
IL
[FIG. 3B] FIG. 3B includes a front view of an initial blank during the
exemplary forged crankshaft production process according to the present
invention, and a side view of the initial blank showing the positions of pin
equivalent portions.
[FIG. 3C] FIG. 3C includes a front view of an intermediate blank
during the exemplary forged crankshaft production process according to the
present invention, and a side view of the intermediate blank showing the
positions of pin equivalent portions.
[FIG. 3D] FIG. 3D includes a front view of a final blank during the
exemplary forged crankshaft production process according to the present
invention, and a side view of the final blank showing the positions of pin
equivalent portions.
[FIG. 3E] FIG. 3E includes a front view of a forged blank during the
exemplary forged crankshaft production process according to the present
invention, and a side view of the forged blank showing the positions of pins.
[FIG. 3F] FIG. 3F includes a front view of a crankshaft during the
exemplary forged crankshaft production process according to the present
invention, and a side view of the crankshaft showing the positions of pins.
[FIG. 4A] FIG. 4A is a longitudinal sectional view showing a state at
the start of pressing in an exemplary process flow of a first preforming step.
[FIG. 4B] FIG. 4B is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process flow of the first
preforming step.
[FIG. 5A] FIG. 5A is a cross-sectional view of a portion to be formed
into a pin located at a second position at the start of pressing in the exemplary
process flow of the first preforming step.
[FIG. 5B] FIG. 5B is a cross-sectional view of the portion to be formed
into the pin located at the second position at the completion of pressing in the
exemplary process flow of the first preforming step.
[FIG. 6A] FIG. 6A is a cross-sectional view of a portion to be formed
into a journal at the start of pressing in the exemplary process flow of the first
preforming step.
[FIG. 6B] FIG. 6B is a cross-sectional view of the portion to be formed
13
·f·
into a journal at the completion of pressing in the exemplary process flow of
the first preforming step.
[FIG. 7A] FIG. 7Ais a cross-sectional view ofthe portion to be formed
into an arm incorporating a weight at the start of pressing in the exemplary
process flow of the first preforming step.
[FIG. 7B] FIG. 7B is a cross-sectional view of the portion to be formed
into an arm incorporating a weight at the completion of pressing in the
exemplary process flow of the first preforming step.
[FIG. 8A] FIG. 8A is a longitudinal sectional view showing a state at
the start of pressing in an exemplary process flow of the second preforming
step.
[FIG. 8B] FIG. 8B is a longitudinal sectional view showing a state at
the completion of pressmg in the exemplary -process flow of a second
preforming step.
[FIG. 9A] FIG. 9A is a cross-sectional view of a portion to be formed
into a pin located at a third position at the start of pressing in the exemplary
process flow of the second preforming step.
[FIG. 9B] FIG. 9B is a cross-sectional view of the portion to be formed
into the pin located at the third position at the completion of pressing in the
exemplary process flow of the second preforming step.
[FIG. lOA] FIG. lOA is a cross-sectional view of the portion to be
formed into the pin located at the second position at the start of pressing in
the exemplary process flow of the second preforming step.
[FIG. lOB] FIG. lOB is a cross-sectional view of the portion to be
formed into the pin located at the second position at the completion of pressing
in the exemplary process flow of the second preforming step.
[FIG. llA] FIG. llA is a cross-sectional view of a portion to be formed
into a journal at the start of pressing in the exemplary process flow of the
second preforming step.
[FIG. llB] FIG. llB is a cross-sectional view of the portion to be
formed into a journal at the completion of pressing in the exemplary process
flow of the second preforming step.
[FIG. 12A] FIG. 12A is a cross-sectional view of a portion to be formed
14-
·f·
into an arm incorporating a weight at the start of pressing in the exemplary
process flow of the second preforming step.
[FIG. 12B] FIG. 12B is a cross-sectional view of the portion to be
formed into an arm incorporating a weight at the completion of pressing in the
exemplary process flow of the second preforming step.
[FIG. 13A] FIG. 13Ais a cross-sectional view of a portion to be formed
into an arm without a weight at the start of pressing in the exemplary process
flow of the second preforming step.
[FIG. 13B] FIG. 13B is a cross-sectional view of the portion to be
formed into an arm without a weight at the completion of pressing in the
exemplary process flow of the second preforming step.
[FIG. 14A] FIG. 14A is a longitudinal sectional view showing a state
before pressing in an exemplary process flow of a final preforming step.
[FIG. 14B] FIG. 14B'is a longitudinal sectional view showing a state
where an upper die has reached the bottom dead point in the exemplary
process flow of the final preforming step.
[FIG. 14C] FIG. 14C is a longitudinal view showing a state at the
completion of an axial movement in the exemplary process flow of the final
preforming step.
[FIG. 15A] FIG. 15Ais a cross-sectional view of a portion to be formed
into an arm incorporating a weight showing a state before pressing in the
second preforming step in a case where each portion to be formed into an arm
incorporating a weight is pressed from the open side of a recessed web
processing portion in the second preforming step.
[FIG. 15B] FIG. 15B is a cross-sectional view of the portion to be
formed into an arm incorporating a weight showing a state at the completion
of pressing in the second preforming step in a case where each portion to be
formed into an arm incorporating a weight is pressed from the open side of a
recessed web processing portion in the second preforming step.
[FIG. 16A] FIG. 16A is a cross-sectional view of a pin equivalent
portion showing a state at the start of pressing in the second preforming step
in a case where each pin equivalent portion is partly pressed without a closed
cross-section formed by a pin processing portion in the second preforming
Is-
r
step.
[FIG. 16B] FIG. 16B is a cross-sectional view of the pin equivalent
portion showing a state at the completion of pressing in the second preforming
step in which each pin equivalent portion is partly pressed without a closed
cross ·section formed by a pin processing portion in the second preforming
step.
[FIG. 17A] FIG. 17Ais a cross-sectional view of a portion to be formed
into a journal showing a state at the start of pressing in the second preforming
step in a case where each portion to be formed into a journal is partly pressed
without a closed cross-section formed by a journal processing portion in the
second preforming step.
[FIG. 17B] FIG. 17B is a cross-sectional view of the portion to be
formed into a journal showing a state at the completion of pressing in the
second preforming step in which each portion to be formed into a journal is
partly pressed without a closed cross-section formed by a journal processing
portion.
[FIG. 18A] FIG. 18A is a cross-sectional view of a portion to be formed
into a journal showing a state before pressing in an exemplary flow to partly
press each portion to be formed into a journal by a journal processing portion
in the first preforming step.
[FIG. 18B] FIG. 18B is a cross-sectional view of the portion to be
formed into a journal showing a state at the completion of pressing in the
exemplary flow to perform partial pressing by the journal processing portion
in the first preforming step.
[FIG. 19] FIG. 19 is a diagram showing an example of a shape of a
stepped blank.
[FIG. 20A] FIG. 20A is a longitudinal sectional view showing a state
before pressing in an exemplary process flow to process a portion to be formed
into a front part and a portion to be formed into a flange in the first
preforming step.
[FIG. 20B] FIG. 20B is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process flow to process the portion
to be formed into the front part and the portion to be formed into the flange in
j·
the first preforming step.
[FIG. 21A] FIG. 21A is a cross-sectional view of the portion to be
formed into the front part before undergoing pressing in the exemplary
process flow of the first preforming step.
[FIG. 21B] FIG. 21B is a cross-sectional view of the portion to be
formed into the front part at the completion of pressing in the exemplary
process flow of the first preforming step.
[FIG. 22A] FIG. 22A is a cross-sectional view of the portion to be
formed into the flange before undergoing pressing in the exemplary process
flow of the first preforming step.
[FIG. 22B] FIG. 22B is a cross-sectional view of the portion to be
formed into the flange at the completion of pressing in the exemplary process
flow of the first preforming step.
[FIG. 23A] FIG. 23A'is a longitudinal sectional view showing a state
before pressing in an exemplary process flow to process the portion to be
formed into the front part and the portion to be formed into the flange in the
second preforming step.
[FIG. 23B] FIG. 23B is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process flow to process the portion
to be formed into the front part and the portion to be formed into the flange in
the second preforming step.
[FIG. 24A] FIG. 24A is a cross-sectional view of the portion to be
formed into the front part before undergoing pressing in the exemplary
process flow of the second preforming step.
[FIG. 24B] FIG. 24B is a cross-sectional view of the portion to be
formed into the front part at the completion of pressing in the exemplary
process flow of the second preforming step.
[FIG. 25A] FIG. 25A is a cross-sectional view of the portion to be
formed into the flange before undergoing pressing in the exemplary process
flow of the second preforming step.
[FIG. 25B] FIG. 25B is a cross-sectional view of the portion to be
formed into the flange at the completion of pressing in the exemplary process
flow of the second preforming step.
DESCRIPTION OF EMBODIMENTS
[0038]
A forged crankshaft production method according to an embodiment of
the present invention will hereinafter be described with reference to the
drawings.
[0039]
1. Exemplary Production Process
The method according to the present embodiment is intended to
produce a forged crankshaft including journals J serving as a center of
rotation, pins P decentered from the journals J, arms A connecting the
journals J and the pins P, and weights W integrated with some or all of the
arms A (see FIGS. 1A to 1C). The pins (P1 to P3) are located at a first
position L1, a second positio~ L2 and a third position L3, respectively. The
phase differences among the first position L1, the second position L2 and the
third position L3 are 120 degrees. The method is applicable to production of
a three-cylinder four-counterweight crankshaft as shown in FIGS. 1A to 1C.
[0040]
The forged crankshaft production method according to the present
embodiment includes a first preforming step, a second preforming step, and a
final preforming step to be executed in this order. After the final preforming
step, a finish forging step and a trimming step may be additionally executed.
If necessary, a coining step may be executed after the trimming step.
Adjustment of the placement angles of the pins can be performed after the
finish forging step. Alternatively, after the trimming step, a twisting step
may be executed for adjustment of the placement angles of the pins. These
steps are hot working and executed sequentially.
[0041]
FIGS. 3A to 3F are diagrams showing an exemplary forged crankshaft
production process according to the present invention. FIG. 3Ashows a billet.
FIG. 3B shows an initial blank in a front view and in a side view, FIG. 3C
shows an intermediate blank in a front view and in a side view, and FIG. 3D
shows a final blank in a front view and in a side view. FIG. 3E shows a
forged blank in a plan view and in a side view, and FIG. 3F shows a forged
crankshaft in a plan view and in a side view. FIGS. 3A to 3F show an
exemplary production process of a crankshaft having the shape shown in
FIGS. lA to lC. The side views in the right side of FIGS. 3B to 3D show the
positions of pin equivalent portions PAl to PA3 relative to the center of
portions to be formed into journals (which will hereinafter be referred to as
"journal equivalent portions"). The side views in the right side of FIGS. 3E
and 3F show the positions of the pins Pl to P3 relative to the center of the
journals. In the side views in the right side of FIGS. 3B to 3D, additionally,
the first to the third positions Ll to L3 of the pins of the finished forged
crankshaft are indicated by imaginary lines.
[0042]
In the first preforming step, a workpiece is pressed by a first pair of
dies. In the preforming step of this exemplary production process, a billet 22
is pressed by a first pair of dies. Thereby, the pin equivalent portions and the
journal equivalent portions of the billet 22 are crushed, and flat portions 23a
are formed in the billet 22.
[0043]
During the formation of flat portions 23a in the billet 22, the flat
portion 23a corresponding to the pin equivalent portion to be located at the
second position L2 (which will hereinafter be referred to as a "second position
pin equivalent portion" and denoted by "PA2") is decentered along the
pressing direction. In this way, an initial blank 23 is obtained, and in the
initial blank 23, volume has been distributed by the pressings of the pin
equivalent portions and the journal equivalent portions. In the initial blank
23, also, the second position pin equivalent portion has been decentered. For
example, the first preforming step can be executed following a process flow as
will be descried later.
[0044]
In the second preforming step, for further volume distribution, the
initial blank 23 is pressed by a second pair of dies. The pressing direction in
this step is a direction perpendicular to the decentering direction of the second
position pin equivalent portion PA2. Thereby, an intermediate blank 24 is
I~
·f
obtained. In the intermediate blank 24, the pin equivalent portion PAl to be
located at the first position Ll (which will hereinafter be referred to as a "first
position pin equivalent portion") is decentered along the pressing direction.
The pin equivalent portion PA3 to be located at the third position L3 (which
will hereinafter be referred to as a "third position pin equivalent portion") is
decentered along the pressing direction to a side opposite to the first position
pin equivalent portion PAL In the intermediate blank 24, the phase
difference between the first position pin equivalent portion PAl and the
second position pin equivalent portion PA2 is 90 degrees. The phase
difference between the first position pin equivalent portion PAl and the third
position pin equivalent portion PA3 is 180 degrees. The details of the second
preforming step will be described later.
[0045]
In the final preforming step, the intermediate blank 24 is pressed by a
third pair of dies. The direction of the pressing by the third pair of dies may
be a direction perpendicular to the decentering direction of the second position
pin equivalent portion PA2. Thereby, the first position pin equivalent portion
PAl and the third position pin equivalent portion PA3 are further decentered,
and a final blank 25 is obtained. During the pressing, the phase differences
among the first position to the third position pin equivalent portions PAl to
PA3 are kept the same. The final blank 25 is roughly in the form of a
crankshaft shape. In the final preforming step, for example, the forming
apparatus disclosed by W02014/091730 (which will hereinafter be referred to
as Patent Literature 4) may be used. An exemplary process flow of the final
preforming step will be described later.
[0046]
In the finish forging step, pressing is performed by a pair of dies with
the decentering direction of the second position pin equivalent portion P A2 set
as the pressing direction, and thereby, a finish forged blank 26 is obtained
from the final blank 25. In this step, excess material flows out, and flash B is
formed. The finish forged blank 26 has a shape in agreement with the shape
of the finished crankshaft. As mentioned above, the final blank 25 is roughly
in the form of a crankshaft shape, and in the final blank 25, the first position
-1-
to the third position pin equivalent portions PAl to PA3 have been decentered.
This decreases the outflow of material in the finish forging step, which
minimizes the flash B formed in the finish forging step.
[0047]
In the finish forging step of this exemplary production process, for
adjustment of the placement angles of the pins, the first position pin
equivalent portion PAl is offset along the pressing direction to the side
opposite to the second position pin equivalent portion PA2 and thereby placed
in the first pin position L 1 of the finished crankshaft. Also, the third position
pin equivalent portion PA3 is offset along the pressing direction to the side
opposite to the second position pin equivalent portion PA2 and thereby placed
in the third pin position L3 of the finished crankshaft. In this way, the pins
Pl to P3 are placed in positions having phase differences of 120 degrees.
[0048]
In the trimming step, for example, while the finish forged blank 26
with flash is held in a pair of dies, the flash B is cut out by a cutting die.
Thus, the flash B is removed from the finish forged blank 26. Then, a forged
crankshaft 21 (final product) is obtained.
[0049]
Patent Literature 4 suggests a forming apparatus that forms a rough
blank that is roughly in the form of a crankshaft shape into a blank for finish
forging. The rough blank is obtained by applying reduction rolling and
bending to a round billet repeatedly. Then, after the blank for finish forging
is formed, finish forging and trimming are applied sequentially to the blank
for finish forging.
[0050]
The production method according to the present embodiment differs
from the production process disclosed in Patent Literature 4 in the step of
obtaining a rough blank from a billet. Specifically, the production method
according to the present embodiment does not include a step of applying
reduction rolling and bending repeatedly to the billet, and instead includes
the first preforming step and the second preforming step. The final
preforming step in the production method according to the present
-yembodiment
corresponds to the processmg performed by the forming
apparatus disclosed in Patent Literature 4, that is, corresponds to the
formation of a blank for finish forging from a rough blank. In the method
according to the present embodiment, moreover, finish forging and trimming
are sequentially applied to the final blank (corresponding to the blank for
finish forging in Patent Literature 4).
[0051]
The finish forging step in the production method according to the
present embodiment and the finish forging step in the production method
disclosed in Patent Literature 4 correspond to the die forging step in the
conventional production process described with reference to FIGS. 2A to 2F.
In the conventional production process, the die forging step includes rough
forging and finish forging. On the other hand, in the production method
according to the present embodiment and in the production method disclosed
in Patent Literature 4, the die forging step includes only finish forging.
[0052]
2. Exemplary Process Flow of First Preforming Step
FIGS. 4A to 7B are diagrams showing an exemplary process flow of
the first preforming step. FIG. 4A is a longitudinal sectional view showing a
state at the start of pressing, and FIG. 4B is a longitudinal sectional view
showing a state at the completion of pressing.
[0053]
FIGS. 5A and 5B are cross-sectional views of a portion to be formed
into a pin located at the second position (second position pin equivalent
portion). FIG. 5A shows a state at the start of pressing, and FIG. 5B shows a
state at the completion of pressing. FIG. 5A is a sectional view along the line
VA-VA in FIG. 4A, and FIG. 5B is a sectional view along the line VB-VB in
FIG. 4B.
[0054]
FIGS. 6A and 6B are cross-sectional views of a portion to be formed
into a journal Gournal equivalent portion). FIG. 6A shows a state at the start
of pressing, and FIG. 6B shows a state at the completion of pressing. FIG. 6A
is a sectional view along the line VIA -VIA in FIG. 4A, and FIG. 6B is a
-jsectional
view along the line VIB-VIB in FIG. 4B.
[0055]
FIGS. 7A and 7B are cross-sectional views of a portion to be formed
into an arm incorporating a weight. FIG. 7A shows a state at the start of
pressing, and FIG. 7B shows a state at the completion of pressing. FIG. 7Ais
a sectional view along the line VIIA-VIIA in FIG. 4A, and FIG. 7B is a
sectional view along the line VIIB-VIIB in FIG. 4B. The "portion to be
formed into an arm incorporating a weight" includes a portion to be formed
into the weight integrated with the arm. A portion to be formed into an arm
and a portion to be formed into a weight integrated with the arm will
hereinafter be referred to as a "web equivalent portion".
[0056]
In FIGS. 4A to 7B, a billet 22 that is circular in cross section, and a
first pair of dies 30 are shown. The first pair of dies 30 includes a first upper
die 31 and a first lower die 32. For easy understanding of the drawings, in
FIGS. 5A to 7B, the axis position of the journal equivalent portion is indicated
by a black circle (see reference symbol C). In FIGS. 5B, 6B and 7B, the first
upper die 31, the first lower die 32 and the billet 22 at the start of pressing are
indicated by two-dot chain lines. The first pair of dies 30 includes pin
processing portions to come into contact with pin equivalent portions, and
journal processing portions to come into contact with journal equivalent
portions.
[0057]
In this exemplary process flow, as indicated by the heavy lines in FIG.
5A, each of the pin processing portions includes a first pin processing part 31 b
provided in one of the first pair of dies, and a second pin processing part 32b
provided in the other of the third pair of dies. The first pin processing part
31b is recessed and is capable of housing a billet 22. In this process flow, the
pin processing part provided in the upper die 31 is recessed and is capable of
housing a billet 22, that is, the first pin processing part 31 b. The pin
processing part provided in the lower die 32 is the second pin processing part
32b, and the second pin processing part 32b is located on the edge surface of a
raised portion. There is no limit as to which of the upper die and the lower
;l
die includes such recessed processing parts that are capable of housing a billet
(first pin processing parts). Accordingly, the lower die may include recessed
processing parts that are capable of housing a billet (first pin processing
parts).
[0058]
The pin processing portions to come into contact with the first position
pm equivalent portion and the third position pin equivalent portion,
respectively, have the same structure as that of the pin processing portion to
come into contact with the second position pin equivalent portion shown in
FIGS. 5A and 5B, though no cross-sectional views of these pin processing
portions are not given. However, the pin processing portions to come into
contact with the first position pin equivalent portion and the third position pin
equivalent portion, respectively, differ from the pin processing portion to come
into contact with the second 'position pin equivalent portion in the position in
the pressing direction (see FIGS. 4Aand 4B).
[0059]
In this exemplary process flow, as indicated by the heavy lines in FIG.
6A, each of the journal processing portions includes a first journal processing
part 31a provided in one of the first pair of dies, and a second journal
processing part 32a provided in the other of the first pair of dies. The first
journal processing part 31a is recessed and is capable of housing a billet 22.
In this process flow, the journal processing part provided in the upper die 31 is
recessed and is capable of housing a billet 22, that is, the first journal
processing part 31a. The journal processing part provided in the lower die 32
is the second journal processing part 32a, and the second journal portions 32a
is located on the edge surface of a raised portion. There is no limit as to
which of the upper die and the lower die includes such recessed processing
parts that are capable of housing a billet (first journal processing parts).
Accordingly, the lower die may include recessed processing parts that are
capable of housing a billet (first journal processing parts).
[0060]
In the exemplary process flow of the first preforming step, the upper
die 31 is moved up and is separated from the lower die 32, and the billet 22 is
-1-
placed between the upper die 31 and the lower die 32. Then, when the upper
die 31 is moved down, the pin equivalent portions of the billet 22 are housed in
the respective recessed first pin processing parts 31b as shown in FIG. 5A,
and the journal equivalent portions of the billet 22 are housed in the
respective recessed first journal processing parts 31a as shown in FIG. 6A.
When the upper die 31 is moved further down, the billet 22 is pressed by the
pin processing parts 31b and 32b and by the journal processing parts 31a and
32a, and the sectional areas of the pin equivalent portions and the journal
equivalent portions are decreased. Then, flat portions as shown in FIGS. 5B
and 6B are formed.
[0061]
As shown in FIG. 4A, the pm processmg portion for the second
position pin equivalent portion differs from the pin processing portions for the
first position and the third position pin equivalent portions in the position in
the pressing direction. Accordingly, the second position pin equivalent
portion is deformed and decentered in the pressing direction. After
completion of the pressing by the first pair of dies 30, the upper die 31 is
moved up, and the processed billet 22 (initial blank 23) is taken out.
[0062]
In such a process flow, while the pin equivalent portions and the
journal equivalent portions are pressed, the material of the pin equivalent
portions and the journal equivalent portions flows in the axial direction of the
billet 22 and flows into portions to be formed into arms without a weight
(which will hereinafter be referred to as "non-weight arm equivalent
portions") and the web equivalent portions. Then, in the obtained initial
blank 23, the volume has been distributed in the axial direction. Additionally,
the second position pin equivalent portion has been decentered.
[0063]
In the process flow of the first preforming step, as the upper die is
being moved down, the holes of the recessed first pin processing parts 31b are
closed by the second pin processing parts 32b, and the first and the second pin
processing parts form closed cross-sections (see FIGS. 5A and 5B). Also, the
holes of the recessed first journal processing parts 31a are closed by the
-ysecond
journal processing parts 32a, and the first and the second journal
processing parts form closed cross-sections (see FIGS. 6A and 6B). This
prevents the material from flowing in between the upper die 31 and the lower
die 32 and accordingly prevents formation of flash. This improves the
material yield rate and facilitates volume distribution in the axial direction.
[0064]
In the forged crankshaft production method according to the present
embodiment, the outflow of material and the formation of flash may be
prevented by partial pressing of the journal equivalent portions by the journal
processing portions as will be described later. Also, the outflow of material
and the formation of flash may be prevented by partial pressing of the pin
equivalent portions by the pin processing portions.
[0065]
In the preforming step, with a view to facilitating the volume
distribution in the axial direction, the web equivalent portions are not
required to be pressed by the first pair of dies. With a view to adjusting the
shapes (dimensions) of the web equivalent portions, the web equivalent
portions may be partly pressed by the first pair of dies (see FIGS. 7 A and 7B).
[0066]
Also, the non-weight arm equivalent portions may be partly pressed
by the first pair of dies for adjustment of the shapes (dimensions) thereof.
[0067]
The cross-sectional shape of each of the flat portions only needs to
have a width (dimension in a direction perpendicular to the pressing
direction) Ba greater than a thickness ta (dimension in the pressing direction),
and may be elliptic or oval, for example (see FIGS. 5B and 6B).
[0068]
3. Exemplary Process Flow of Second Preforming Step
FIGS. SA to 13B are diagrams showing an exemplary process flow of
the second preforming step. FIG. 8Ais a longitudinal sectional view showing
a state at the start of pressing, and FIG. 8B is a longitudinal sectional view
showing a state at the completion of pressing.
[0069]
-~-
FIGS. 9A and 9B are sectional views of the portion to be formed into
the pin located at the third position (third position pin equivalent portion).
FIG. 9A shows a state at the start of pressing, and FIG. 9B shows a state at
the completion of pressing. FIG. 9A is a sectional view along the line
IXA-IXAin FIG. 8A, and FIG. 9B is a sectional view along the line IXB-IXB in
FIG. 8B.
[0070]
FIGS. lOA and lOB are cross-sectional views of the portion to be
formed into the pin located at the second position (second position pin
equivalent portion). FIG. lOA shows a state at the start of pressing, and FIG.
lOB shows a state at the completion of pressing. FIG. lOA is a sectional view
along the line XA-XA in FIG. 8A, and FIG. lOB is a sectional view along the
line XB-XB in FIG. 8B.
[0071]
FIGS. llA and llB are cross-sectional views of a portion to be formed
into a journal Gournal equivalent portion). FIG. llA shows a state at the
start of pressing, and FIG. llB shows a state at the completion of pressing.
FIG. llA is a sectional view along the line XIA-XIA in FIG. 8A, and FIG. llB
is a sectional view along the line XIB-XIB in FIG. 8B.
[0072]
FIGS. 12A and 12B are sectional views of a portion to be formed into
an arm incorporating a weight (web equivalent portion). FIG. 12A shows a
state at the start of pressing, and FIG. 12B shows a state at the completion of
pressing. FIG. 12A is a sectional view along the line XIIA-XIIA in FIG. 8A,
and FIG. 12B is a sectional view along the line XIIB-XIIB in FIG. 8B.
[0073]
FIGS. 13A and 13B are sectional views of a portion to be formed into
an arm without a weight (non-weight arm equivalent portion). FIG. 13A
shows a state at the start of pressing, and FIG. 13B shows a state at the
completion of pressing. FIG. 13A is a sectional view along the line
XIIIA-XIIIA in FIG. 8A, and FIG. 13B is a sectional view along the line
XIIIB-XIIIB in FIG. 8B.
[0074]
-y-
In FIGS. SA to 13B, the initial blank 23 obtained by the first
preforming step, and a second pair of dies 40 are shown. The second pair of
dies 40 includes a second upper die 41 and a second lower die 42. For easy
understanding of the drawings, in FIGS. 9A to 13B, the axis position of the
journal equivalent portion is indicated by a black circle (see reference symbol
C). In FIGS. 9B, lOB, llB, 12B and 13B, the second upper die 41, the second
lower die 42 and the initial blank 23 at the start of pressing are indicated by
two-dot chain lines. The second pair of dies 40 includes pin processing
portions including parts 4lb, 42b, 41f and 42f to come into contact with the
pin equivalent portions of the initial blank 23, and journal processing portions
including parts 4la and 42a to come into contact with the journal equivalent
portions, and web processing portions including parts 4lc and 42c to come into
contact with the web equivalent portions.
[0075]
In this exemplary process flow, each of the pin processing portions
includes a first pin processing part 41b or 42f provided in one of the first dies
41 and 42, and a second pin processing part 42b or 4lf provided in the other of
the first dies (see the heavy lines in FIGS. 9A and lOA). The first pin
processing parts 4lb and 42f are each recessed and capable of entirely housing
a flat portion of the initial blank 23. There is no limit as to, in each of the pin
processing portions, which of the pin processing part provided in the upper die
and the pin processing part provided in the lower die is a recessed part
capable of entirely housing a flat portion of the initial blank (first pin
processing part).
[0076]
In the exemplary process flow, for the third position pin equivalent
portion, as indicated by the heavy line in FIG. 9A, the pin processing part
provided in the upper die 41 is a recessed and is capable of housing a flat
portion of the initial blank 23, that is, the first pin processing part 4lb. Also,
the pin processing part provided in the lower die 42 is the second pin
processing part 42b, and the second pin processing part 42b is located on the
edge surface of a raised portion. On the other hand, for the second position
pin equivalent portion, as indicated by the heavy lines in FIG. lOA, the pin
processing part provided in the lower die 42 is the recessed first pin processing
part 42f, and the pin processing part provided in the upper die 41 is the
second pin processing part 41f.
[0077]
The pin processing portion for the second position pin equivalent
portion shown in FIGS. lOA and lOB differs from the pin processing portion
for the third position pin equivalent portion in the position in the pressing
direction and in the position in a direction perpendicular thereto (decentering
direction of the second position pin equivalent portion). The pin processing
portion for the first position pin equivalent portion (of which cross-sectional
view is not presented) differs from the pin processing portion for the third
position pin equivalent portion in the position in the pressing direction.
[0078]
In this exemplary process flow, as indicated by the heavy lines in FIG.
llA, each of the journal processing portions includes a first journal processing
part 4la provided in one of the second dies 41 and 42, and a second journal
processing part 42a provided in the other of the second dies. The first journal
processing part 4la is recessed and is capable of entirely housing a flat portion
of the initial blank 23. In this exemplary process flow, the journal processing
part provided in the upper die 41 is a recessed portion that is capable of
entirely housing a flat portion of the initial blank 23, that is, the first journal
processing part 4la. The journal processing part provided in the lower die 42
is the second journal processing part 42a, and the second journal processing
part 42a is located on the edge surface of a raised portion. There is no limit
as to which of the upper die and the lower die includes such recessed journal
processing parts each of which is capable of entirely housing a flat portion of
the initial blank (first journal processing parts). Accordingly, the lower die
may include recessed parts each of which is capable of entirely housing a flat
portion of the initial blank (first journal processing parts).
[0079]
In each of the web processing portions, as indicated by the heavy lines
in FIG. 12A, one of the upper die 41 and the lower die 42 has a generally
concave cross-sectional shape. In this exemplary process flow, in each of the
-yweb
processing portions, the lower web processing part 42c is wholly recessed,
and the other (upper) web processing part 41c is flat. Which of the upper die
and the lower die includes recessed web processing parts can be determined
according to the shape of the forged crankshaft to be produced.
[0080]
The recessed web processing part 42c (provided in the lower die in the
case of FIG. 12A) includes an arm processing part 42d to come into contact
with a portion to be formed into an arm (which will hereinafter be referred to
as an "arm equivalent portion"), and a weight processing part 42e to come into
contact with a portion to be formed into a weight (which will hereinafter be
referred to as a "weight equivalent portion"). The arm processing part 42d
occupies the bottom side of the recessed web processing part 42c, and the
weight processing part 42e occupies the open side of the recessed web
processing part 42c. The w!dth Bw of the open side of the weight processing
part 42e becomes greater with increasing distance from the bottom of the
recessed web processing part. In this process flow, as shown in FIG. 12A,
both sides of the weight processing part 42e are inclined surfaces. Both sides
of the arm processing part 42d are parallel surfaces, and accordingly, the
width Bw of the open side of the arm processing part 42d is constant.
[0081]
In this exemplary process flow of the second preforming step, each of
the web equivalent portions is processed to have a thickness t1 greater than a
finished size tO (see FIGS. 3C and 3F). For this purpose, the web processing
parts 41c and 42c are designed to have a length (dimension in the axial
direction) greater than that of a finished arm incorporating a weight. The
finished size tO means the thickness of the arms and weights of the forged
crankshaft (final product).
[0082]
In the process flow of the second preforming step using the second pair
of dies 40, the upper die 41 is moved up and separated from the lower die 42,
and the initial blank 23 is placed between the upper die 41 and the lower die
42. In this regard, the initial blank 23 is rotated 90 degrees around the axis
from the state at the completion of the first preforming step (the billet) around
jo
-t'-
the aXIs, and then placed between the dies 41 and 42. Accordingly, the
direction of the pressing by the second pair of dies 40 is a direction
perpendicular to the decentering direction of the second position pin
equivalent portion.
[0083]
Then, the upper die 41 is moved down, and as shown in FIGS. 9A, lOA
and llA, the flat portions of the initial blank 23 are housed in the recessed
first journal processing parts 41a and the recessed first pin processing parts
41b and 42f. At this time, as shown FIG. 12A, each of the web equivalent
portions is mostly placed in the weight processing part 42e without contacting
the bottom of the web processing part.
[0084]
When the upper die 41 is moved further down, the first pin processing
parts 41 b and 42f, and the second pin processing parts 42b and 41f form closed
cross-sections. Also, the first journal processing parts 41a and the second
journal processing parts 42a form closed cross-sections. Then, when the
upper die 41 is moved further down to the bottom dead point, the flat portions
in the spaces enclosed by the first pin processing parts 41 b and 42f and the
second pin processing parts 42b and 41f are pressed thereby. Also, the flat
portions in the spaces enclosed by the first journal processing parts 41a and
the second journal processing parts 42a are pressed thereby. In this way, the
flat portions of the initial blank 23 are pressed by the second pair of dies, and
the sectional areas of the journal equivalent portions and the pin equivalent
portions are decreased. At the same time, excess material flows in the axial
direction into the web equivalent portions, and thus, volume distribution is
progressed.
[0085]
Also, the first position pin equivalent portion is decentered along the
pressing direction, and the third position pin equivalent portion is decentered
along the pressing direction to the side opposite to the first position pin
equivalent portion.
[0086]
Each of the web equivalent portions is pushed into the bottom side of
the recessed web processing part 42c without being pressed by the other web
processing part 41c (web processing part provided in the upper die in the case
ofFIGS. 12Aand 12B). The pushing arises along with the decentering ofthe
first position pin equivalent portion and the third position pin equivalent
portion located in the front side and the rear side, respectively, of the web
equivalent portion. At the time of pushing, the web equivalent portion
deforms along the arm processing part 42d and the weight processing part 42e.
Thereby, the width of the web equivalent portion becomes smaller in the
portion located in the bottom side of the recessed processing part (arm
equivalent portion) and becomes greater in the portion located in the open
side of the recessed processing part (weight equivalent portion). Also, the
open-side surface 23b of the web equivalent portion becomes arc-shaped in
cross section.
[0087]
After the completion of pressing by the second pair of dies 40, the
upper die 41 is moved up, and a processed initial blank 23 (intermediate blank
24) is taken out.
[0088]
In the second preforming step, as described above, the first position
pin equivalent portion and the third position pin equivalent portion can be
decentered with no flash formed. Also, since the material flows from the pin
equivalent portions to the web equivalent portions, the volume can be
distributed in the axial direction. Further, by causing the material to flow
from the journal equivalent portions to the web equivalent portions as needed,
the volume distribution in the axial direction can be further progressed.
[0089]
The non -weight arm equivalent portions may be partly pressed by the
second pair of dies 40 for adjustment of the shapes and the dimensions thereof
(see FIGS. 13Aand 13B). Alternatively, when the material should be caused
to flow to the non-weight arm equivalent portions, the non-weight arm
equivalent portions shall not be pressed by the second pair of dies 40.
[0090]
4. Exemplary Process Flow of Final Preforming Step
FIGS. 14A to 14C are longitudinal sectional VIews schematically
showing an exemplary process flow of the final preforming step. FIG. 14A
shows a state before pressing, FIG. 14B shows a state where the upper die has
reached the bottom dead point, and FIG. 14C shows a state at the completion
of an axial movement. The second position pin equivalent portion is actually
located in front of or behind the first position pin equivalent portion and the
third position pin equivalent portion. In FIGS. 14A to 14C, however, the first
to the third position pin equivalent portions are drawn in the same plane.
[0091]
In FIGS. 14A to 14C, the intermediate blank 24 obtained by the
second preforming step, a third pair of dies 51, an upper plate 52 and a lower
plate 53 are shown. The third pair of dies 51 includes a third upper die 60
and a third lower die 70. The third upper die 60 is held by the upper plate 52,
and the upper plate 52 moves up and down along with operation of a pressing
machine (not shown). The third lower die 70 is held by the lower plate 53,
and the lower plate 53 is fixed to the pressing machine (not shown).
[0092]
In order to press the web equivalent portions (portions to be formed
into arms and portions to be formed into weights integrated with the arms) in
the axial direction of the intermediate blank 24, the third upper die 60 and the
third lower die 70 are each composed of some components. The components
of the third upper die 60 are arranged in the axial direction of the
intermediate blank 24, and the components of the third lower die 70 are
arranged in the axial direction of the intermediate blank 24. The third upper
die 60 includes a fixed pin die component 64, fixed journal die components 61,
movable journal die components 62 and movable pin die components 63. The
third lower die 70 includes a fixed pin die component 7 4, fixed journal die
components 71, movable journal die components 72 and movable pin die
components 73.
[0093]
The fixed pin die components 64 and 7 4 are to press the central pin
equivalent portion (second position pin equivalent portion) of the intermediate
blank 24, and are not movable in the axial direction. The fixed journal die
33
-fcomponents
61 and 71 are located in front of and in back of the fixed pin die
components 64 and 7 4 with respect to the axial direction, and are not movable
in the axial direction. The fixed journal die components 61 and 71 are to
press the non-weight arm equivalent portions connected to the central pin
equivalent portion, the journal equivalent portions connected to the
non-weight arm equivalent portions and the web equivalent portions
connected to the journal equivalent portions.
[0094]
The movable journal die components 62 and 72 form some pairs of die
components and are movable in the axial direction. The third upper die 60
and the third lower die 70 shown in FIGS. 14A to 14C include two pairs of
movable journal die components 62 and 72. One of the pairs is to press the
front equivalent portion, the first journal equivalent portion and the first web
equivalent portion (first arm equivalent portion). The other is to press the
sixth web equivalent portion (sixth arm equivalent portion), the fourth journal
equivalent portion and the flange equivalent portion.
[0095]
The movable pin die components 63 and 73 form some pairs of die
components and are movable in the axial direction. The movable pin die
components 63 and 73 form two pairs of die components that are to press the
first position pin equivalent portion and the third position pin equivalent
portion (the pin equivalent portions other than the central pin equivalent
portion), respectively. Moreover, in order to decenter the first position pin
equivalent portion and the third position pin equivalent portion, either the
movable pin die components 63 of the upper die 60 or the movable pin die
components 73 of the lower die 70 are movable in a direction perpendicular to
the axial direction relative to the plate 52 or 53 holding the die components.
The direction of the relative movement is along the pressing direction. The
relative movement can be made by a hydraulic cylinder 54, for example. It is
determined according to the shape of the forged crankshaft to be produced,
which are relatively movable, the movable pin die components 63 of the upper
die 60 or the movable pin die components 73 of the lower die 70.
[0096]
34-
f·
The third upper die 60 and the third lower die 70 formed by such
components each have impressions (see reference symbols 61a, 62a, 63a, 71a,
72a, 73a and 74a in FIG. 14A). The impressions reflect the approximate
shape of the crankshaft (final product).
[0097]
In the final preforming step, the upper die 60 is moved up, and the
intermediate blank 24 is placed between the upper die 60 and the lower die 70
(see FIG. 14A). In this regard, the posture of the intermediate blank 24 is
adjusted such that the pressing direction will be perpendicular to the
decentering direction of the second position pin equivalent portion. Next, the
upper die 60 is moved down, and the intermediate blank 24 is pressed by the
upper die 60 and the lower die 70 (see FIG. 14B). Thereby, the journal
equivalent portions, the second position pin equivalent portion and the
non-weight arm equivalent portion of the intermediate blank 24 are pressed
and formed into approximate shapes of those of the crankshaft.
[0098]
While the journal equivalent portions of the intermediate blank 24 are
kept pressed, the movable journal die components 62 and 72 and the movable
pin die components 63 and 73 are moved in the axial direction toward the
central fixed journal die components 64 and 7 4. The movements can be made
by a wedge mechanism or a hydraulic cylinder, for example.
[0099]
Along with the axial movements of the movable journal die
components 62 and 72 and the movable pin die components 63 and 73, the
web equivalent portions are pressed in the axial direction of the intermediate
blank 24. Thereby, the web equivalent portions are formed into approximate
shapes of the arms and the weights. At this time, the thickness of the web
equivalent portions becomes equal to the finished size.
[0100]
According to the axial movements of the movable journal die
components 62 and 72 and the movable pin die components 63 and 73, either
the pin die components 63 of the upper die 60 or the pin die components 73 of
the lower die 70 are moved in a direction perpendicular to the axial direction.
-,t-
At the same time, also, the first position pin equivalent portion and the third
position pin equivalent portion are further decentered along the pressing
direction. At the same time, also, the first position pin equivalent portion
and the third position pin equivalent portion are pressed by the movable pin
die components 63 and 73, and the pin equivalent portions are formed into
approximate shapes of the pins (see FIG. 14C).
[0101]
After the completion of pressing by the third pair of dies 51, the upper
die 60 is moved up, and a processed intermediate blank 24 (final blank) is
taken out.
[0102]
In the final preforming step, the first position pin equivalent portion
and the third position pin equivalent portion can be decentered with no or
almost no flash formed, and the intermediate blank can be formed into an
approximate shape of the forged crankshaft.
[0103]
In the forged crankshaft production method according to the
embodiment, the second position pin equivalent portion is decentered in the
first preforming step and is pressed in the first and the second preforming
steps to have a decreased cross-sectional area. The first position pm
equivalent portion and the third position pin equivalent portion are
decentered in the second and the final preforming steps and are pressed in the
first and the second preforming steps to have a decreased cross-sectional area.
Consequently, in the final blank obtained through the first, the second and the
final preforming steps, all of the pin equivalent portions have been decentered
and have been pressed to have decreased cross-sectional areas. Accordingly,
during formation of the pins in the die forging step (finish forging step) after
the final preforming step, almost no flash is formed, and therefore, the
material yield rate can be improved.
[0104]
No flash is formed in the first and the second preforming steps, and
additionally, formation of flash is inhibited in the final preforming step. For
this reason also, the forged crankshaft production method according to the
present invention allows facilitation ()f the volume distribution and an
improvement of the material yield rate. All of the preforming steps can be
implemented by pressing by use of a pressing machine. Thus, no special
facility is required, which leads to a decrease in facility cost.
[0105]
5. Thickness of Web Equivalent Portions and Volume Distribution
In the above-described process flow of the second preforming step, the
web equivalent portions are processed to have a thickness greater than the
finished size. Then, in the final preforming step, the web equivalent portions
are p.ressed in the axial direction. In the forged crankshaft production
method according to the present embodiment, however, the processing applied
to the web equivalent portions in the second and the final preforming steps is
not limited to this processing. The web equivalent portions may be processed
I to have a thickness equal to the finished size in the second preforming step,
and the web equivalent portions of the intermediate blank shall not be
pressed in the axial direction in the final preforming step.
[0106]
As mentioned above, in the forged crankshaft, each of the weights
greatly bulges from the arm. Therefore, in the finish die forging step, the
filling of material in the weights is likely to be insufficient, thereby causing
deficiency in the weights. In order to prevent the deficiency in the weights, a
blank with an increased volume shall be used. However, this inevitably
decreases the material yield rate. In order to avoid this, it is preferred that
the web equivalent portions are processed to have a thickness greater than
the finished size in the second preforming step and are pressed in the axial
direction of the intermediate blank in the final preforming step. In this case,
the non-weight arm equivalent portions also may be processed to have a
thickness greater than the finished size in the second preforming step and
may be pressed in the axial direction of the intermediate blank in the final
preforming step. In this case, the fixed journal die components 61 and 71
shall be replaced with movable journal die components.
[0107]
In the above-described process flow of the second preforming step, the
-rsecond
pair of dies having the web processing portions is used. In the forged
crankshaft production method according to the present invention, however,
the second preforming step is not limited to a step with this configuration. In
other words, the second preforming step may be the same as the first
preforming step in that the web equivalent portions are not pressed and that
the material is caused to flow from the pin equivalent portions and the journal
equivalent portions to the web equivalent portions.
[0108]
As in the above-described process flow of the second preforming step,
it is preferred that the second pair of dies having the web processing portions
is used. This allows each of the web equivalent portions to be processed to
have a smaller width in the arm equivalent portion and a greater width in the
weight equivalent portion while facilitating the flow of material from the pin
equivalent portions and the j~urnal equivalent portions to the web equivalent
portions. In short, volume distribution inside each web equivalent portion
can be performed. This leads to an improvement of the degree of filling of
material in the weight equivalent portions in the next final preforming step.
Further, this leads to an improvement of the degree of filling of material in the
weight equivalent portions in the finish forging step and minimization of flash
formed in the finish forging step.
[0109]
When the second pair of dies having the web processing portions is
used, the volume distribution inside each of the web equivalent portions can
be adjusted by changing the shape of the arm equivalent part as appropriate
according to the shape of the forged crankshaft (final product)_ For example,
by changing the width of the open side of the arm processing part or designing
the arm processing part to have inclined surfaces, it is possible to change the
volume of the arm equivalent portion, whereby the volume distribution inside
the web equivalent portion can be adjusted. In order to permit the processed
initial blank (intermediate blank) to be taken out from the second pair of dies
smoothly after the completion of pressing, the arm processing part may
include inclined surfaces to form a draft.
[0110]
-IThe
weights of the forged crankshaft (final product) may be any of
various shapes. For example, there is a case of forming each of the weights
to bulge greatly in the width direction and to have a small dimension in the
pin decentering direction. In order to comply with such a case, in the second
preforming step, the shape of the weight processing part may be changed as
appropriate such that the volume can be distributed inside the web equivalent
portion 'appropriately in the width direction and in the pin decentering
direction. The change to the shape of the weight processing part may be
adjusting the angle of inclination of the inclined surfaces or designing the
weight processing part to have curved surfaces, for example. Further, each of
the web equivalent portions may be pressed from the open side of the recessed
web processing portion for volume distribution inside the weight equivalent
portion.
[0111]
FIGS. 15A and 15B are cross-sectional views of a portion to be formed
into an arm incorporating a weight showing a case where each of the portions
to be formed into arms incorporating a weight (the web equivalent portions)
from the open side of the recessed web processing portion. FIG. 15A shows a
state before pressing, and FIG. 15B shows a state at the completion of
pressing. In the case shown m FIGS. 15A and 15B, the recessed web
processing portion 42c shown m FIGS. 12A and 12B is modified to be
shallower.
[0112]
In the process flow shown in FIGS. 15A and 15B, as in the process flow
shown in FIGS. 12A and 12B, each of the web equivalent portions is pushed
into the bottom side of the recessed web processing part 42c and is deformed
along the recessed web processing part 42c. Since the recessed web
processing part 42c is shallower, at the last stage of the pressing by the second
pair of dies, the flat web processing part 41c is pressed against the open side
surface of the web equivalent portion. Accordingly, the web equivalent
portion is pressed from the open side of the recessed web processing part 42c
and is deformed to have a greater width and a smaller length. Thus, the
volume is distributed inside the weight equivalent portion.
-f-
[0113]
The pressing to press the web equivalent portion from the open side is
preferably a light pressing so that the material can flow into the web
equivalent portion without blockage_ The light pressing can be performed by
pressing a part of the open side surface 23b (see FIG. 12B) of the web
equivalent portion. In this case, the material flows to a portion that is out of
contact with the dies, thereby resulting in a light pressing.
[0114]
6. Another Example of Second Preforming Step
In the above-described process flow of the second preforming step, the
pin equivalent portions are pressed while closed cross-sections are formed by
the first and the second pin processing parts. In the forged crankshaft
production method according to the present embodiment, however, it is not
necessary to form closed cross-sections by the first and the second pin
processing parts in pressing the pin equivalent portions as long as it does not
cause outflow of material and formation of flash.
[0115]
FIGS. 16A and 16B are cross-sectional views of a pm equivalent
portion showing a case where each of the pin equivalent portions is pressed
without a closed cross-section formed by the pin processing parts. FIG. 16A
shows a state at the time of pressing, and FIG. 16B shows a state at the
completion of pressing. The case shown in FIGS. 16A and 16B differs from·
the case shown in FIGS. 9A and 9B in the shapes of the pin processing parts
41b and 42b. In the case shown in FIGS. 16A and 16B, the pin processing
part 41b provided in the upper die 41 and the pin processing part 42b
provided in the lower die 42 are recessed. The depth of the pin processing
part 41b provided in the upper die 41 is greater than the depth of the pin
processing part 42b provided in the lower die 42.
[0116]
By the pair of dies having such pin processing parts 41b and 42b,
along with a downward movement of the upper die 41, the third position pin
equivalent portion (flat portion) is mostly housed in the pin processing part
41 b provided in the upper die 41. Then, the third position pin equivalent
-y)-
portion (flat portion) is decentered along the pressing direction. At this time,
the upper pin processing part 41b and the lower pin processing part 42b are
partly contact the pin equivalent portion of the initial blank 23. In other
words, the portions of the pin processing parts 41b and 42b near the parting
faces do not contact the pin equivalent portion. Also, along with the
decentering of the pin equivalent portion, the material flows out in the axial
direction, and the pin equivalent portion is pressed, whereby the
cross-sectional area thereof is decreased. Thus, it is possible to decenter and
press the pin equivalent portion without forming flash.
[0117]
When the volume distribution is to be facilitated in the second
preforming step, it is preferred that each of the pin equivalent portions is
pressed while a closed cross-section is formed by the first and the second pin
processing parts. With a 'view to preventing outflow of material, it is
preferred that each of the pin equivalent portions is partly pressed by the pin
processing parts. When outflow of material and formation of flash are to be
prevented by the partial pressing by the pin processing parts, the pin
processing parts may have the same structures as the journal equivalent
portions which will be described later with reference to FIG. 17.
[0118]
In the above-described process flow of the second preforming step, the
journal equivalent portions are pressed while closed cross-sections are formed
by the first and the second journal processing parts. In the forged crankshaft
production method according to the present embodiment, however, it is not
necessary to form closed cross-sections by the first and the second journal
processing parts in pressing the journal equivalent portions as long as it does
not cause outflow of material and formation of flash. For example, the
journal processing parts may have the same structures of the pin processing
parts shown in FIGS. 16Aand 16B.
[0119]
FIGS. 17 A and 17B are cross-sectional views of a journal equivalent
portion showing a case where each of the journal equivalent portions is
pressed without a closed cross-section formed by the journal processing parts.
4--f
-r-
FIG. 17A shows a state at the start of pressing, and FIG. 17B shows a state at
the completion of pressing. The case shown in FIGS. 17A and 17B differs
from the case shown in FIGS. llA and llB in the shapes of the journal
processing parts 41a and 42a. In the case shown in FIGS. 17A and 17B, as
indicated by the heavy lines in FIG. 17A, the journal processing part provided
in the upper die 41 is recessed and is capable of entirely housing a flat portion
of the initial blank 23, that is, the first journal processing part 41a. The
journal processing part provided in the lower die 42 is arc-shaped, that is, the
second journal processing part 42a, and the second processing part 42a is
located on the edge surface of a raised portion as indicated by the heavy line in
FIG. 17A. The journal processing parts 41a and 42a have clearances 41g and
42g at both sides in the width direction, and the clearances 41g and 42g
project outward in the width direction.
[0120]
By the pair of dies having such journal processing parts 41a and 42a,
along with a downward movement of the upper die 41, each of the flat portions
of the initial blank 23 is entirely housed in the first journal part 41a. When
the upper die 41 is moved further down, the first journal processing part 41a
contacts the flat portion, and subsequently, the second journal processing part
42a contacts the flat portions. By the contacts, the flat portion is pressed,
and the sectional area thereof is decreased. At the time, the material flows
in the axial direction, whereby the volume is distributed. In this regard, the
material partly flows in the clearances 41g and 42g, but the clearances 41g
and 42g are partly kept out of contact with the flat portion. Thus, the flat
portion is partly pressed, and the material does not flow out, thereby resulting
in formation of no flash.
[0121]
When the volume distribution in the second preforming step is to be
facilitated, it is preferred that each of the flat portions is entirely pressed
while a closed cross-section is formed by the first journal processing part 41a
and the second journal processing part 42a. With a view to preventing
outflow of material, it is preferred that each ofthe journal equivalent portions
is partly pressed by the journal processing parts.
[0122]
7. Another Example of First Preforming Step
In the above-described process flow of the first preforming step, the
first pair of dies 30 is used, and closed cross-sections are formed by the first
journal processing parts 31a and the second journal processing parts 32a.
Also, closed cross-sections are formed by the first pin processing parts 31b and
the second pin processing parts 32b. In this state, the entire circumferences
of the journal equivalent portions and the pin equivalent portion of the billet
are pressed, and this prevents outflow of material and formation of flash. In
the forged crankshaft production method according to the present
embodiment, however, outflow of material and formation of flash may be
prevented by partial pressing of the journal equivalent portions by the journal
processing parts of the first pair of dies.
[0123]
FIGS. 18A and 18B are cross-sectional views of a journal equivalent
portion showing a process flow to partly press the journal equivalent portion
by the journal processing parts in the first preforming step. FIG. 18A shows
a state before pressing, and FIG. 18B shows a state at the completion of
pressing. The journal processing parts 31a and 32a shown in FIGS. 18A and
18B differ from those shown in FIGS. 6A and 6B in shape. As indicated by
the heavy lines in FIG. 18A, the journal processing part 31a provided in the
upper die 31 and the journal processing part 32a provided in the lower die 32
are recessed and have the same depth.
[0124]
By the pair of dies having such journal processing portions, along with
a downward movement of the upper die 31, the bottoms of the journal
processing parts 31a provided in the upper die 31 and the journal processing
parts 32a provided in the lower die 32 come into contact with the billet 22.
When the upper die 31 is moved further down, the journal processing parts
31a provided in the upper die 31 and the journal processing parts 32a
provided in the lower die 32 partly come into contact with the billet 22. In
other words, the portions of the journal processing parts 31a and 32a around
the parting faces do not contact the billet 22. Accordingly, it is possible to
-rform
flat portions having decreased sectional areas without forming flash.
[0125]
With a view to facilitating volume distribution, it is preferred that the
billet is entirely pressed while the journal processing parts of each of the
journal processing portions form a closed cross-section as shown in FIGS. 6A
and 6B. With a view to preventing outflow of material, it is preferred that
partial pressing of the billet is performed by each of the journal processing
portions as shown in FIGS. 18A and 18B.
[0126]
The pin processing portions provided in the first pair of dies may have
a structure similar to the structure of the journal processing portions shown
in FIGS. 18A and 18B though it is not shown in the drawings, and the pin
processing portions may perform partial pressing of a billet. With a view to
facilitating volume distribution, it is preferred that the billet is entirely
pressed while the pin processing parts of each of the pin processing portions
form a closed cross-section as shown in FIGS. 5A and 5B. With a view to
preventing outflow of material, it is preferred that the billet is partly pressed
by each of the journal processing portions.
[0127]
8. Preferred Examples
The ratio (Sp2/Sp0) of the sectional area Sp2 (mm2) of each of the pin
equivalent portions of the intermediate blank to the sectional area SpO (mm2)
of each of the pins of the forged crankshaft (final product) is desirably 0. 7 to
1.9 with a view to diminishing flash formed in the after steps. For the same
purpose, the ratio (Sp 1/SpO) of the sectional area Sp 1 (mm 2) of each of the pin
equivalent portions of the initial blank to the sectional area SpO (mm 2) of each
of the pins of the forged crankshaft (final product) is desirably 0.9 to 1.9.
[0128]
The amount of decentering (mm) of the second position pin equivalent
portion in the first preforming step, that is, the amount of decentering (mm) of
the second pin equivalent portion of the initial blank 23 is desirably not less
than 20 %, more desirably not less than 50 %, and ideally 100 % of the amount
of decentering (mm) of the pin of the forged crankshaft (final product). If the
-;Jamount
of decentering of the pin equivalent portion in the first preforming
step is too small, the pin equivalent portion will need to be decentered greatly
in the finish forging step after the final preforming step, and with the increase
of the amount of decentering in the finish forging step, outflow of material and
formation of flash will be increased.
[0129]
The amounts of decentering (mm) of the first position pin equivalent
portion and the third position pin equivalent portion in the final preforming
step, that is, the amounts of decentering (mm) of the first pin equivalent
portion and the third pin equivalent portion of the final blank 25 are adjusted
as appropriate according to the method of adjusting the placement angles of
the pin equivalent portions in the after steps. When the amounts of
decentering of the pins located at the first and the third positions of the forged
crankshaft (final product) are denoted by E (mm), the amounts of decentering
(mm) of the first position pin equivalent portion and the third pin equivalent
portion shall be Ex3112/2 in a case where the placement angles are adjusted in
the finish forging step as shown in FIGS. 3D and 3E. In a case where the
placement angles of the pin equivalent portions are adjusted in the twisting
step, the amounts of decentering (mm) of the first position pin equivalent
portion and the third pin equivalent portion in the final preforming step shall
beE.
[0130]
In a case where the placement angles of the pin equivalent portions
are adjusted in the finish forging step, the amounts of decentering (mm) of the
first position pin equivalent portion and the third position pin equivalent
portion in the second preforming step, that is, the amounts of decentering
(mm) of the first position pin equivalent portion and the third position pin
equivalent portion of the initial blank 24 are desirably 20 to 70 % and more
desirably 40 to 50 % of the amounts of decentering (mm) of the pins of the
forged crankshaft (final product), with a view to facilitating volume
distribution inside each of the web equivalent portions. In a case where the
placement angles of the pin equivalent portions are adjusted in the second
preforming step, the amounts of decentering (mm) of the first position pin
-Iequivalent
portion and the third position pin equivalent portion in the second
preforming step, that is, the amounts of decentering (mm) of the first position
pin equivalent portion and the third position pin equivalent portion of the
initial blank 24 is desirably 20 to 70 % and more desirably 40 to 50 % of the
amounts of decentering (mm) of the pins of the forged crankshaft (final
product), with a view to facilitating volume distribution inside each of the web
equivalent portions.
[0131]
In the second preforming step, the ratio (tlltO) of the thickness t1
(mm) of each of the web equivalent portions (portions to be formed into arms
and portions to be formed into weights integrated with the arms) of the
intermediate blank to the finished size tO (mm) is desirably not less than 1.1,
and more desirably not less than 1.5 with a view to improving the degree of
filling of material in the weights in the after steps. If the ratio (tlltO) is
greater than 3.5, the bulging/deforming areas of the material surface will be
too great, whereby the form accuracy ofthe outer peripherals of the arms may
be decreased. Therefore, the ratio (tl/tO) is desirably not more than 3.5.
[0132]
The ratio (Sw2/Sw0) of the sectional area Sw2 (mm 2) of each of the
web equivalent portions of the intermediate blank to the sectional area SwO
(mm2) of each of the webs of the forged crankshaft (final product) is desirably
0.3 to· 0.9 with a view to preventing deficiency in the weights while
maintaining the degree of filling of material in the weights sufficiently high in
the after steps. For the same purpose, the ratio (Swl/SwO) of the sectional
area Sw1 (mm2) of each of the web equivalent portions of the initial blank to
the sectional area SwO (mm2) of each of the webs of the forged crankshaft
(final product) is desirably 0.2 to 0.8. The sectional area of a web equivalent
portion means the total of the sectional area of a portion to be formed into an
arm and the sectional area of a portion to be formed into a weight integrated
with the arm. The sectional area of a web means the total of the sectional
area of an arm and the sectional area of a weight integrated with the arm.
[0133]
The ratio (Sj2/Sj0) of the sectional area Sj2 (mm2) of each of the
. -:1-
journal equivalent portions of the intermediate blank to the sectional area SjO
(mm2) of each of the journals of the forged crankshaft (final product) is
desirably LO to L9 with a view to diminishing flash formed in the after steps.
For the same purpose, the ratio (Sj 1/SjO) of the sectional area Sj 1 (mm2) of
each of the journal equivalent portions of the initial blank to the sectional
area SjO (mm2) of each of the journals of the forged crankshaft (final product)
is desirably L2 to 1.9.
[0134]
In the above-described process flow of the final preforming step shown
in FIGS. 14A to 14C, either the movable pin die components 63 or the movable
pin die components 73 are movable in a direction perpendicular to the axial
direction relative to the plate 52 or 53 holding the components 63 or 73. In
this case, after the intermediate blank 24 is pressed by the upper die 60 and
the lower die 70, the movable journal die components 62 and 72 and the
movable pin die components 63 and 73 are moved in the axial direction.
Along with the axial movements, either the pin die components 63 of the
upper die 60 or the pin die components 73 of the lower die 70 are relatively
moved in the direction perpendicular to the axial direction to decenter the pin
equivalent portions and more specifically to decrease the amounts of
decentering of the first position pin equivalent portions and the third position
pin equivalent portion. In the forged crankshaft production method
according to the present embodiment, the final preforming step is not limited
to a step with this configuration.
[0135]
Specifically, both of the pm die components 63 and 73 may be
immovable relative to the plates 52 and 53 holding the pin die components 63
and 73. In this case, the movable pin die components 63 and 73 connected to
the hydraulic cylinder 54 are replaced with movable pin die components 63
and 73 that are relatively immovable in the direction perpendicular to the
axial direction. When the intermediate blank 24 is pressed by the upper die
60 and the lower die 70, the first position pin equivalent portion and the third
position pin equivalent portion are pressed. Thereby, the first position pin
equivalent portion and the third position pin equivalent portion are
-Idecentered
and are formed into approximate shapes of the pins.
[0136]
With a view to improving the processing accuracy of the first position
pin equivalent portion and the third position pin equivalent portion, it is
preferred that either the pin die components 63 or the pin die components 73
are moved in the direction perpendicular to the axial direction for pressing of
the pin equivalent portions along with the pressing in the axial direction as in
the process flow of the final preforming step shown in FIGS. 14 A to 14C.
Thereby, the pin equivalent portions are decentered, and at the same time, the
pin equivalent portions are formed into approximate shapes of the pins.
[0137]
In the exemplary production process shown in FIGS. 3A to 3F, a billet
22 is used as the workpiece. However, a stepped blank may be used as the
workpiece.
[0138]
FIG. 19 is a diagram showing an example of a shape of a stepped
blank. In the stepped blank 26 shown in FIG. 19, the pin equivalent portions
and the journal equivalent portions are pressed compared with the web
equivalent portions as in the initial blank 23 shown in FIG. 3B. In other
words, the sectional area of each of the pin equivalent portions and the journal
equivalent portions is smaller than the sectional area of each of the web
equivalent portions (the total sectional area of a portion to be formed into an
arm and a portion to be formed into a weight integrated with the arm).
Unlike in the initial blank 23 shown in FIG. 3B, none of the pin equivalent
portions of the stepped blank 26 is decentered. The stepped blank 26 is
obtained by pressing some parts of a billet by use of press rolls or cross rolls.
[0139]
When such a stepped blank is used as the workpiece, in the first
preforming step, the stepped blank is pressed by the above-described first pair
of dies. Specifically, the pin equivalent portions are pressed by the pin
processing portions, whereby the cross-sectional areas of the pin equivalent
portions are decreased, which results in formation of flat portions. Also, the
journal equivalent portions are pressed by the journal processing portions,
-Jiwhereby
the cross-sectional areas of the journal equivalent portions are
decreased, which results in formation of flat portions. Further, the second
position pin equivalent portion is decentered.
[0140]
As mentioned above, the placement angles of the pins can be adjusted
in the finish forging step or in the twisting step. With a view to consolidating
processing, it is preferred that the first position pin equivalent portion is
pressed and offset in the pressing direction to be placed in the first position in
the finish die forging step.
[0141]
In the exemplary process flow of the final preforming step shown in
FIGS. 14A to 14C, the fixed pin die component 64 is a separate component
from the fixed journal die component 61, and the fixed die component 7 4 is a
separate component from the fixed journal die component 71. However, the
die components 64 and 61 may be one component, and the die components 74
and 71 may be one component. In the exemplary process flow of the final
preforming step shown in FIGS. 14A to 14C, the non-weight arm equivalent
portions are pressed by the fixed journal die components 61 and 71. However,
it is not always necessary to press the non-weight arm equivalent portions in
the final preforming step.
[0142]
In the above-described process flow of the final preforming step, as
shown in FIGS. 14A to 14C, the direction of the pressing by the third pair of
dies 51 is perpendicular to the decentering direction of the second position pin
equivalent portion. However, the direction of the pressing may be along the
decentering direction of the second position pin equivalent portion. When
the direction of the pressing by the third pair of dies 51 is along the
decentering direction of the second position pin equivalent portion, for
decentering of the first position pin equivalent portion and the third position
pin equivalent portion, the movable pin die components 63 and 73 shall be
movable not in the direction of the pressing by the third pair of dies 51 but in a
direction perpendicular to the direction of the pressing by the third pair of dies
51. In this case, both of the movable pin die components 63 and 73 shall be
movable in the direction perpendicular to the direction of the pressing by the
third pair of dies 5 L
[0143]
In a crankshaft, the positions of the respective far ends of the pins
vary depending on various factors. Specifically, the far end of a pin may be in
the same position as the tip of the arm or may be in an inner position than the
tip of the arm along the decentering direction. In either case, the forged
crankshaft production method according to the present embodiment is
applicable. As shown in FIG. lB, the far end PT of the pin P1 is the point of
the pin P1 that is the farthest from the center ofthe journal JL As shown in
FIG. 1B, the tip AT of the armA1 is the point of the armA1 (portion excluding
the weight W1) that is the farthest from the center of the journal J1.
[0144]
9. Front Part and Flange
Next, an exemplary process flow to process a portion to be formed into
the front part (which will hereinafter be referred to as a "front equivalent
portion") and a portion to be formed into the flange (which will hereinafter be
referred to as a "flange equivalent portion") is described.
[0145]
FIGS. 20A to 22B are diagrams showing the exemplary process flow
to process the front equivalent portion and the flange equivalent portion in
the first preforming step. FIG. 20A is a longitudinal sectional view showing
a state before pressing, and FIG. 20B is a longitudinal sectional view showing
a state at the completion of pressing.
[0146]
FIGS. 21A and 21B are cross-sectional views of the front equivalent
portion. FIG. 21A shows a state before pressing, and FIG. 21B shows a state
at the completion of pressing. FIG. 21A is a sectional view along the line
XXIA-XXIA in FIG. 20A, and FIG. 21B is a sectional view along the line
XXIB-XXIB in FIG. 20B.
[0147]
FIGS. 22A and 22B are cross·sectional views of the flange equivalent
portion. FIG. 22A shows a state before pressing, and FIG. 22B shows a state
-rat
the completion of pressing. FIG. 22A is a sectional view along the line
XXIIA-XXIIA in FIG. 20A, and FIG. 22B is a sectional view along the line
XXIIB-XXIIB in FIG. 20B.
[0148]
In FIGS. 20A to 22B, a billet 22 having a round cross-sectional shape,
and a first pair of dies 30 composed of an upper die and a lower die are shown.
For easy understanding of the drawings, in FIGS. 21B and 22B, the first
upper die 31 and the first lower die 32 before pressing are indicated by two-dot
chain lines, and the axis position C of the journal equivalent portion is
indicated by a black circle. In FIG. 22B, the billet 22 is further indicated by a
two-dot chain line. The first pair of dies 30 shown in FIGS. 20A to 22B
includes pin processing portions and journal processing portions as the first
pair of dies 30 shown in FIGS. 4A to 7B. The first pair of dies 30 further
includes a front processing 'portion to come into contact with the front
equivalent portion.
[0149]
In this exemplary process flow, the front processing portion includes
inner surfaces 31c and 32c as indicated by the heavy lines in FIGS. 20A and
21A, and an edge surface 32d as shown in FIG. 20A. The inner surfaces 31c
and 32c of the front processing portion face the periphery of the front
equivalent portion. The edge surface 32d of the front processing portion
faces the end surface of the front equivalent portion. The cross-sectional
shapes of the front processing part provided in the upper die 31 and the front
processing part provided in the lower die 32 are both recessed, and the
recessed parts have the same depth.
[0150]
-
By the pair of dies including the front processing portion, along with a
downward movement of the upper die 31, the bottoms of the front prdcessing
parts provided in the upper die 31 and the lower die 32 (in this exemplary
process flow, the inner surfaces 31c and 32c) come into contact with the
periphery of the front equivalent portion of the billet 22. When the upper die
31 is moved further down, both of the front processing parts (inner surfaces
31c and 32c) provided in the upper die 31 and the lower die 32 partly contact
-sjthe
periphery of the billet. In other words, the portions of the front
processing parts (inner surfaces 31c and 32c) near the parting faces do not
contact the periphery of the billet 22. Accordingly, it is possible to decrease
the sectional area, thereby resulting in formation of a flat portion, without
forming flash. Moreover, by elongating the front equivalent portion in the
axial direction along with the formation of a flat portion, it is possible to
distribute the volume in the axial direction. Thus, the material yield rate
can be further improved.
[0151]
The front processing portion of the third pair of dies 30 is not limited
to the structure shown in FIGS. 21A and 21B for partial pressing of the
periphery of the billet, and the front processing portion may have a structure
similar to the structure of the journal processing portions shown in FIGS. 6A
and 6B. In short, the front processing portion may include a first front
processing part provided in one of the first dies and a second front processing
part provided in the other of the first dies, and the first front processing part
may be recessed and capable of housing the front equivalent portion of a billet.
In this case, the front processing parts form a closed cross-section, and in the
state, the entire front equivalent portion (the entire periphery of the front
equivalent portion) of the billet is pressed. This makes it possible to decrease
the sectional area, thereby resulting in formation of a flat portion, without
forming flash. Moreover, by elongating the front equivalent portion in the
axial direction along with the formation of a flat portion, it is possible to
distribute the volume in the axial direction. Thus, the material yield rate
can be further improved.
[0152]
During the pressing in the first preforming step, when the end surface
of the front equivalent portion entirely contacts the front processing part, the
elongation of the front equivalent portion is stopped, and the material may
partly flow out into the space. In order to prevent this outflow, it is preferred
that the end surface of the front equivalent portion is prevented from
contacting the front processing part Gn this process flow, the edge surface 32d)
during the pressing in the first preforming step. In other words, it is
preferred that a space is made between the end surface of the front equivalent
portion and the front processing part (edge surface 32d). Alternatively, the
end surface of the front equivalent portion may partly contact the front
processing part (edge surface 32d).
[0153]
If the rate of decrease of the sectional area of the front equivalent
portion during the first preforming step is set too high, fishtail will occur in
the end portion, which may cause a defect in the after steps. The fishtail
means that a recess is formed in the end portion of the front equivalent
portion, whereby the end portion is formed into a fish tail shape. In order to
prevent the fishtail, it is preferred that the pressing is carried out in the first
preforming step such that the sectional area of the front equivalent portion of
the initial blank 23 to be obtained thereby will decrease with decreasing
distance from the end surface of the front equivalent portion. The decrease of
the sectional area of the front equivalent portion can be achieved by
decreasing the thickness ta linearly, in a curve or in a staircase pattern, for
example. In the case of FIG. 20B and 21B, the thickness ta of the front
equivalent portion decreases linearly in a part of the whole dimension in the
axial direction and is constant in the other part. It is possible to adjust the
thickness ta of the front equivalent portion by adjusting the shapes of the
front processing parts provided in the first dies 30 (in this process flow, the
inner surfaces 31c and 32c of the front processing portion) as appropriate.
[0154]
When the front equivalent portion of the initial blank 23 is made such
that the thickness ta thereof decreases with decreasing distance from the end
surface of the front equivalent portion, the sectional area of the journal-facing
side of the front equivalent portion is slightly greater than the sectional area
of the end-surface side of the front equivalent portion. In this case, the
pressing in the next second preforming step permits the end-surface side of
the front equivalent portion and the journal-facing side of the front equivalent
portion to have substantially the same sectional area without forming flash.
Thus, even when the front equivalent portion of the initial blank 23 is made
such that the thickness ta thereof decreases with decreasing distance from the
-fend
surface of the front equivalent portion, the material yield rate can be
maintained high.
[0155]
In this exemplary process flow, the flange processing portion includes
inner surfaces 31e and 32e as indicated by the heavy lines in FIGS. 20A and
22A, and an edge surface 32f as shown in FIG. 20A. The inner surfaces 31e
and 32e of the flange processing portion face the periphery of the flange
equivalent portion. The edge surface 32f of the flange processing portion
faces the end surface of the flange equivalent portion.
[0156]
With a view to further improving the material yield rate, it is desired
that the sectional area ofthe flange equivalent portion is increased in the first
preforming step. For this purpose, it is preferred that the end surface of the
flange equivalent portion is 'brought into contact with the flange processing
part (in this exemplary flow, the edge surface 32f) along with the pressing by
the first pair of dies. In this case, while the sectional area of the journal
equivalent portion connected to the flange equivalent portion is being
decreased, whereby the journal equivalent portion is formed into a flat portion,
the material flows into the flange equivalent portion. At this time, since the
end surface of the flange equivalent portion is held by the flange processing
part (edge surface 32fJ, the sectional area of the flange equivalent portion
increases. Thus, the volume is distributed in the axial direction, and the
material yield rate can be further improved.
[0157]
In order to facilitate the increase of the sectional area of the flange
equivalent portion, it is preferred that the periphery of the flange equivalent
portion is prevented from contacting the first dies (in this process flow, the
inner surfaces 31e and 32e) in the first preforming step. Alternatively, for
adjustment of the shape (dimensions) of the flange equivalent portion, the
periphery of the flange equivalent portion may partly contact the first dies (in
this process flow, the inner surfaces 31e and 32e) (see FIGS. 22Aand 22B).
[0158]
At the start of pressing in the first preforming step, the end surface of
-1-
the flange equivalent portion may be brought into contact with the flange
processing part (in this process flow, the edge surface 32f). Alternatively,
there may be a space between the end surface of the flange equivalent portion
and the flange processing part (edge surface 32f) at the start of pressing, and
the end surface of the flange equivalent portion may be brought into contact
with the flange processing part (edge surface 32f) during the pressing.
Either the former or the latter shall be selected depending on the outer
diameter (sectional area) of the flange of the crankshaft (final product).
[0159]
Next, an exemplary process flow to process the front equivalent
portion and the flange equivalent portion in the second preforming step is
described.
[0160]
FIGS. 23A to 25B are' diagrams showing the exemplary process flow to
process the front equivalent portion and the flange equivalent portion in the
second preforming step. FIG. 23A is a cross-sectional view showing a state
before pressing, and FIG. 23B is a cross-sectional view showing a state at the
completion of pressing.
[0161]
FIGS. 24A and 24B are cross-sectional views of the front equivalent
portion in the second preforming step. FIG. 24A shows a state before
pressing, and FIG. 24B shows a state at the completion of pressing. FIG. 24A
is a cross-sectional view along the line XXIVA-XXIVA in FIG. 23A, and FIG.
24B is a cross-sectional view along the line XXIVB-XXIVB in FIG. 23B.
[0162]
FIGS. 25A and 25B are cross-sectional views of the flange equivalent
portion in the second preforming step. FIG. 25A shows a state before
pressing, and FIG. 25B shows a state at the completion of pressing. FIG. 25A
is a cross-sectional view along the line XXVA-XXVAin FIG. 23A, and FIG. 25B
is a cross-sectional view along the line XXVB-XXVB in FIG. 23B.
[0163]
In FIGS. 23A to 25B, the initial blank 23 and a second pair of dies 40
are shown. For easy understanding of the drawings, in FIGS. 24B and 25B,
the second upper die 41, the second lower die 42 before pressing and the initial
blank 23 are indicated by two-dot chain lines, and the axis position C of the
journal equivalent portion is indicated by a black circle. The second pair of
dies 40 shown in FIGS. 23A to 25B includes web processing portions, pin
processing portions and journal processing portions as the second pair of dies
40 shown in FIGS. SA to 13B. The second pair of dies 40 further includes a
front processing portion to come into contact with the front equivalent portion.
[0164]
In this exemplary process flow, the front processing portion includes
inner surfaces 41h and 42h as indicated by the heavy lines in FIGS. 23A and
24A, and an edge surface 42i as shown in FIG. 23A. The inner surfaces 41h
and 42h of the front processing portion face the periphery of the front
equivalent portion. The edge surface 42i of the front processing portion faces
the end surface of the front' equivalent portion. As indicated by the heavy
lines in FIG. 24A, the cross-sectional shape of the front processing part
provided in the upper die 41 and the cross-sectional shape of the front
processing part provided in the lower die 42 are both recessed, and the
recessed portions have the same depth.
[0165]
By the pair of dies including the front processing portion, along with a
downward movement of the upper die 41, the bottoms of the front processing
parts provided in the upper die 41 and the lower die 42 (in this exemplary
process flow, the inner surfaces 41h and 42h) come into contact with the
periphery of the flat portion (front equivalent portion) of the initial blank 23.
When the upper die 41 is moved further down, both of the front processing
parts (inner surfaces 41h and 42h) provided in the upper die 41 and the lower
die 42 partly contact the periphery of the front equivalent portion. In other
words, the portions of the front processing parts (inner surfaces 41h and 42hl
near the parting faces do not contact the periphery of the front equivalent
portion. Accordingly, it is possible to decrease the sectional area of the front
equivalent portion by the pressing without forming flash. Moreover, by
elongating the front equivalent portion in the axial direction along with the
decrease of the sectional area of the front equivalent portion, it is possible to
distribute the volume in the axial direction. Thus, the material yield rate
can be further improved.
[0166]
The front processing portion of the second pair of dies 40 are not
limited to the structure shown in FIGS. 24A and 24B for partial pressing of
the periphery of the front equivalent portion, and the front processing portion
may have a structure similar to the structure of the journal processing
portions shown in FIGS. llA and llB. In short, the front processing portion
may include a first front processing part provided in one of the first dies and a
second front processing part provided in the other of the first dies, and the
first front processing part may be recessed and capable of housing the front
equivalent portion. In this case, during the pressing by the second pair of
dies, the front processing parts form a closed cross-section, and in the state,
the entire front equivalent portion (the entire periphery of the front
equivalent portion) is pressed. This permits a decrease of the sectional area
of the front equivalent portion without causing formation of flash. Moreover,
by elongating the front equivalent portion in the axial direction along with the
decrease of the sectional area of the front equivalent portion, it is possible to
distribute the volume in the axial direction. Thus, the material yield rate
can be further improved.
[0167]
During the pressing in the second preforming step, when the end
surface of the front equivalent portion entirely contacts the front processing
portion, the elongation of the front equivalent portion is stopped, and the
material may partly flow out. In order to prevent this outflow, it is preferred
that the end surface of the front equivalent portion is prevented from
contacting the front processing part (in this process flow, the edge surface 42i)
during the pressing in the second preforming step. In other words, it is
preferred that a space is made between the end surface of the front equivalent
portion and the front processing part (edge surface 42i). Alternatively, the
end surface of the front equivalent portion may partly contact the front
processing part (edge surface 42i).
[0168]
-v-
In this exemplary process flow, the flange processing portion includes
inner surfaces 41j and 42j as indicated by the heavy lines in FIGS. 23A and
25A, and an edge surface 42k as shown in FIG. 23A. The inner surfaces 41j
and 42j of the flange processing portion face the periphery of the flange
equivalent portion. The edge surface 42k of the flange processing portion
faces the end surface of the flange equivalent portion.
[0169]
With a view to further improving the material yield rate, it is desired
that the sectional area of the flange equivalent portion is increased in the
second preforming step. For this purpose, it is preferred that the end surface
of the flange equivalent portion is brought into contact with the flange
processing part (in this exemplary flow, the edge surface 42k) along with the
pressing of the flat portions. In this case, while the sectional area of the
journal equivalent portion 'is being decreased by pressing of the journal
equivalent portion connected to the flange equivalent portion, the material
flows into the flange equivalent portion. At this time, since the end surface of
the flange equivalent portion is held by the flange processing part (edge
surface 42k), the sectional area of the flange equivalent portion increases.
Thus, the volume is distributed in the axial direction, and the material yield
rate can be further improved.
[0170]
In order to facilitate the increase of the sectional area of the flange
equivalent portion, it is preferred that the periphery of the flange equivalent
portion is prevented from contacting the flange processing parts (in this
process flow, the inner surfaces 41j and 42j) in the second preforming step.
Alternatively, for adjustment of the shape (dimensions) of the flange
equivalent portion, it is preferred that the periphery of the flange equivalent
portion partly contacts the flange processing parts (in this process flow, the
inner surfaces 41j and 42j) (see FIGS. 25Aand 25B).
[0171]
At the start of pressing in the second preforming step, the end surface
of the flange equivalent portion may be brought into contact with the flange
processing part (in this process flow, the edge surface 42k). Alternatively,
jsthere
may be a space between the end surface of the flange equivalent portion
and the flange processing part (edge surface 42k) at the start of pressing, and
the end surface of the flange equivalent portion may be brought into contact
with the flange processing part (edge surface 42k) during the pressing.
Either the former or the latter shall be selected depending on the outer
diameter (cross-sectional area) of the flange of the crankshaft (final product).
INDUSTRIAL APPLICABILITY
[0172]
The present invention is efficiently utilized in production of a forged
crankshaft to be mounted in a reciprocating engine.
LIST OF REFERENCE SYMBOLS
[0173]
11, 21: forged crankshaft
12, 22: billet
13: rolled blank
14: bent blank
15: rough forged blank
16, 26: finish forged blank
23: initial blank
23a: flat portion
23b: open-side surface of web equivalent portion
24: intermediate blank
25: final blank
26: stepped blank
30: first pair of dies
31: first upper die
31a: first journal processing part
31b: first pin processing part
31c: inner surface of front processing portion
31e: inner surface of flange processing portion
32: first lower die
32a: second journal processing part
32b: second pin processing part
32c: inner surface of front processing portion
32d: edge surface of front processing portion
31e: inner surface of flange processing portion
32f edge surface of flange processing portion
40: second pair of dies
41: second upper die
41a: first journal processing part
41b: first pin processing part
41c: flat web equivalent portion
41f second pin processing part
41g: clearance
41h: inner surface of front processing portion
41j: inner surface of flange processing portion
42: second lower die
42a: second journal processing part
42b: second pin processing part
42c: recessed web processing part
42d: arm processing part
42e: weight processing part
42f first pin processing part
42g: clearance
42h: inner surface of front processing portion
42i: edge surface of front processing portion
42j: inner surface of flange processing portion
42k: edge surface of flange processing portion
51: third pair of dies
52: upper plate
53: lower plate
54: hydraulic cylinder
60: third upper die
61: fixed journal die component
f
62: movable journal die component
63: movable pin die component
64: fixed pin die component
70: third lower die
71: fixed journal die component
72: movable journal die component
73: movable pin die component
7 4: fixed pin die component
A, Al to AS: crank arm
B: flash
J, Jl to J4: journal
P, Pl to P3: pin
Fr: front part
Fl: flange
W, Wl to W 4: counterweight
PA, PAl to PAS: pin equivalent portion

We claim:
1. A method for producing a forged crankshaft including journals serving
as a center of rotation, pins decentered from the journals and located at a first
position, a second position and a third position, respectively, having phase
differences of 120 degrees thereamong, crank arms connecting the journals
and the pins, and counterweights integrated with some or all of the crank
arms, the method comprising:
a first preforming step of pressing a workpiece by a first pair of dies to
decrease sectional areas of portions of the workpiece to be formed into the pins
and sectional areas of portions of the workpiece to be formed into the journals,
thereby forming the portions to be formed into the pins and the portions to be
formed into the journals into flat portions, and to decenter one of the flat
I
portions to be formed into the pin located at the second position;
a second preforming step of pressing an initial blank obtained by the
first preforming step by a second pair of dies with a direction perpendicular to
the decentering direction of the portion to be formed into the pin located at the
second position set as a pressing direction to decenter the portion to be formed
into the pin located at the first position and to decenter the portion to be
formed into the pin located at the third position to a side opposite to the
portion to be formed into the pin located at the first position;
a final preforming step of pressing an intermedia_t~ blank obtained by
the second preforming step by a third pair of dies to further decenter the
portion to be formed into the pin located at the first position and to further
decenter the portion to be formed into the pin located at the third position,
wherein:
the workpiece is a billet or a stepped blank;
the stepped blank has small sectional areas in the portions to be
formed into the pins and in the portions to be formed into the journals, the
small sectional areas being smaller than a total of a sectional area of a portion
to be formed into a crank arm incorporating a counterweight and a sectional
area of a portion to be formed into the counterweight integrated with the
crank arm;
-fthe
first pair of dies includes pin processing portions to come into
contact with the portions to be formed into the pins and journal processing
portions to come into contact with the portions to be formed into the journals;
and
m the first preforming step, the workpiece is pressed by the pm
processing portions and the journal processing portions, whereby the flat
portions are formed.
2. The method for producing a forged crankshaft according to claim 1,
wherein
in the final preforming step, the direction of the pressing by the third
pair of dies is perpendicular to the decentering direction of the portion to be
formed into the pin located at the second position.
3. The method for producing a forged crankshaft according to claim 1 or
2, wherein:
the forged crankshaft further includes a front part located at a front
end in an axial direction;
the first pair of dies further includes a front processing portion to come
into contact with a portion of the workpiece to be formed into the front part;
and
in the first preforming step, the front processing part elongates the
portion to be formed into the front part in the axial direction while decreasing
a sectional area of the portion to be formed into the front part to form the
portion to be formed into the front part into a flat portion.
4. The method for producing a forged crankshaft according to claim 3,
wherein:
in the first preforming step, the portion to be formed into the front
part is pressed by the front processing portion such that, in the initial blank, a
sectional area of the portion to be formed into the front part decreases with
decreasing distance from an end surface of the front part.
5. The method for producing a forged crankshaft according to any one of
claims 1 to 4, wherein:
the forged crankshaft further includes a flange located at a rear end in
the axial direction;
the first pair of dies further includes a flange processing portion to
come into contact with a portion of the workpiece to be formed into the flange;
and
in the first preforming step, while the flat portions are formed, an end
surface of the portion to be formed into the flange is brought into contact with
the flange processing portion, whereby a sectional area of the portion to be
formed into the flange is increased.
6. The method for producing a forged crankshaft according to any one of
claims 1 to 5, wherein:
in the second preforming step, the portions to be formed into the crank
arms incorporating the counterweights are processed to be thicker than a
finished size, and the portions to be formed into the counterweights integrated
with the crank arms are processed to be thicker than a finished size;
in the final preforming step, during the pressing by the third pair of
dies, the portions of the intermediate blank to be formed into the crank arms
incorporating the counterweights and the portions to be formed into the
counterweights integrated with the crank arms are pressed from the axial
direction of the intermediate blank.
7. The method for producing a forged crankshaft according to any one of
claims 1 to 6, wherein:
the second pair of dies used in the second preforming step includes
web processing portions to come into contact with the portions to be formed
into the crank arms incorporating the counterweights and the portions to be
formed into the counterweights integrated with the crank arms;
each of the web processing portions includes an arm processing part to
come into contact with a portion to be formed into a crank arm and a weight
processing part to come into contact with a portion to be formed into a
-r
counterweight integrated with the crank arm, the arm processing part and
the weight processing part being provided in one of the second pair of dies;
the arm processing part and the weight processing part form a
recessed portion, where the arm processing part is located in a bottom side of
the rec~ssed portion and the weight proc._~.ssing part is located in an open side -
of the recessed portion;
a width of an open side of the weight processing part becomes greater
with increasing distance from the bottoin_ ofthe recessed portion;
in the second preforming step, as the portions to be formed into the
pins located at the first position and at the third position are being decentered,
the portions to be formed into the crank arms incorporating the
counterweights and the portions to be formed into the counterweights
integrated with the crank arms are pushed into the bottom sides of the web
processing portions and are deformed.
8_ The method for producing a forged crankshaft according to claim 7,
wherein
in the second preforming step, when the portions to be formed into the
crank arms incorporating the counterweights and the portions to be formed
into the counterweights integrated with the cr~nk arms are pushed into the
bottom sides of the web processing portions and are deformed, the portions to
be formed into the crank arms incorporating the cou1;1terweights and the
portions to be formed into the counterweights integrated with the crank arms
are pressed from the open sides of the web processing portions for volume
distribution.