The present invention relates to a method for producing a crankshaft
by hot forging.
BACKGROUNDART
looozl
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 t¡le manufactured by die
forging and the type manufactured by casting. Especially when high
strength and high stiffness are required, die forged crankshafts (which wiII
hereinafter be referred to as "forged crankshafts") are often employed.
[ooos]
FIGS. 1A and 18 are schematic diagrams showing an example of a
shape of a commonly used crankshaft. FIG. 1A is an overall view, and FIG.
18 is à sectional view along the line IB-IB. In order to facilitate
understanding of the shape of the crankshaft, FIG. 1B shows only a crank arm
A7, a counterweight W7 integrated with the crank arm A7, a pin P4 and a
journal J4 connected to the crank arm 47, which are extracted from the
crankshaft.
looo¿l
The crankshaft 11 shown in FIGS. 1A and 18 is a four-cylinder
eight-counterweight crankshaft to be mounted in a four-cylinder engine. The
crankshaft 11 includes five journals Jl to J5, four pins Pl to P4, a front part
Fr, a flange Fl, and eight crank arms (hereinafter referred to simply as
"arms") A1 to 48. The eight arms A1 to A8 connect the journals Jl to J5
L
respectively to the pins Pl to P4. The eight arms (¿t of the arms) Al to A8
have counterweights (hereinafter referred to simply as "weights") Wl to W8,
which are integrally formed with the arms A1 to 48, respectively. The front
part Fr is located at a front end of the crankshaft 11, and the flange FI is
located at a rear end of the crank shaft 11, the front end and the rear end
being ends in a direction along the axis of the crankshaft 11. The front part
Fr is connected to the front first journal Jl, and the fl.ange FI is connected to
the rearmost fifth journal J5.
looorl
In the following paragraphs, when the journals J1 to J5, the pins Pl to
P4, the arms A1 to 48, and the weights Wl to W'8 are each collectively
referred to, a reference character "J" is used for the journals, a reference
character "P" for the pins, a reference character rrA' 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 "\ry'eb".
loooel
As shown in FIG. 18, 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).
looozl
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
the 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. Tþpically, the preforming step
3
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includes a rolling step and a bending step, and the die forging step includes a
rough forging step and a finish forging step.
looosl
FIGS. 2A to 2F arc schematic diagrams showing a conventional
method for producing a common forged crankshaft. FIG. 2A shows a billet,
FIG. 28 shows a rolled blank, FIG. 2C shows a bent blank, FIG. 2D shows a
rough forged blank, FIG. 2E shows a fi.nish forged blank, and FIG. 2F shows a
forged crankshaft. FIGS. Zy'.to 2F show a method for producing a crankshaft
having the confi.guration shown in FIGS. 1A and 18.
looogl
In the production method shown in FIGS. 2A to 2F, a forged
crankshaft 11 is produced as follows. First, a billet 12 with a specifi.ed 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 12tr' the axial direction, and thereby, a rolledblank 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).
loorol
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
(see FIG. 2D). The rough forged blank 15 is roughly in the shape of the
crankshaft (¡nat 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 fihish
forged blank 16 is obtained (see FIG. 2E). The finish forged blank 16 has a
shape in agreement with the shape of the final product, that is, the 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 fl.ash B on the periphery.
+
loorrl
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.
loorzl
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 fi.nal product. The main parts
of the forged blank with no fl.ash are, for example, shaft parts such as the
journals J, the pins P, the front part Fr, the flange Fl and the like, and frrrther,
the arms A and the weights W. In this way, the forged crankshaft 11 is
produced.
loors]
The production method shown in FIGS. 2[to 2F is applicable not only
to production of a four-cylinder eight-counterweight crankshaft as shown in
FIGS. lAand 1B but also to production of any other crankshaft. For example,
the production method is applicable to a four-cylinder four-counterweight
crankshaft.
loor¿I
In a four-cylinder four-counterweight crankshaft, only some of the
eight armsAl toAS incorporate a weight W. For example, the front first arm
41, the rearmost eighth arm A8 and the central two arms (the fourth arm A4
and the fifth arm A5) incoqporate a weight W. The other aïms, namely the
second, the third, the sixth and the seventh arms (A2, .L3, A6 and A7) do not
have a weight, and these arms are like oval-shaped.
loorrl
Other crankshafts, for example, crankshafts to be mounted in
three-cylinder engines, in-line six-cylinder engines, V-type six-cylinder
engines, eight-cylinder engines and others can be produced by the same
production method. It is noted that, when adjustment of the placement
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angles of the pins is necessary, a twisting step is added after the trimming
step.
loorol
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 (nnd product) to
the volume of the billet.
loorz]
For example, Japanese Patent Application Publication No.
2001-105087 (Patent Literature 1), Japanese Patent Application Publication
No. }J2-255240 (Patent Literature 2) and Japanese Patent Application
Publication No. H10-029032 (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 worþiece 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.
looral
According to Patent Literature 2, in apreforming step, a four-pass
high;speed rolling, rather than a conventional two-pass rolling, is performed.
A rolled blank obtained by the preforming step have sectional areas that are
congruent with the sectional area distribution among weights, arms and
journals of the forged crankshaft (nn¿ product). According to Patent
Literature 2, this improves the material yield rate.
loorgl
Patent Literature 3 suggests that pressing direction (pressing
direction) in a die'forgrng step should be perpendicular to a bulging direction
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of weights. Thereby, in the die-forging step, the degree of filling of material
in the weights greatly bulging from the arm center plane can be improved.
In the method disclosed in Patent Literature 3, the parting faces of the upper
die and the lower die are located at the vertexes of the bulging weights, and
accordingly, excess material fl.ows out through the space between the upper
die and the lower die and forms into flash.
CITATION LIST
PATENT LITERATIIRE
loozol
Patent Literature 1: Japanese Patent Application Publication No.
2001-105087
Patent Literature 2: Japanese Patent Application Publication
H2-255240
Patent Literature 3: Japanese Patent Application Publication
H10-029032
Patent Literature 4: WO20I4/038 183
SUMMARY OF INVETION
TECHMCAL PROBLEMS
loozrl
Regarding production of a forged crankshaft, as mentioned above, it is
demanded to decrease the outfl.ow 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 can be performed to some extent.
Íoozzl
Patent Literature 1, however, does not discuss the volume distribution
performed in the preforming step in each portion to be formed into an arm
incorporating a weight. More specif.cally, Patent Literature 1 does not
discuss distributing the volume of each portion to be formed into an arm
incorporating a weight between the weight and the arm. Therefore, the
fillipg of material in the weight, which greatly bulges from the arm center
No.
No.
/
plane, is likely to be insufficient, and defi.ciency of material is likely to occur rn
the weight. In order to avoid the deficiency in the weight, a blank with an
increased volume shall be used. However, this inevitably decreases the
material yield rate. The "portion to be formed into an arm incorporating a
weight" includes a portion to be formed into a weight integrated with the arm.
In the following paragraphs, a portion to be formed into an arm and a portion
to be formed into a weight integrated with the arm are referred to collectively
as a "\¡reb equivalent portion".
loozel
The preforming step taught in Patent Literature 2 is to apply rolling,
and therefore, volume distribution in each web equivalent portion between
the weight and the arm cannot be performed in the preforming step.
Accordingly, in the subsequent die forging step, the fr[ing of material in the
weight becomes insufficient, thereby causing problems that defi.ciency is likely
to occur and that the material yield rate becomes lower.
looz+l
In the method disclosed in Patent Literature 3, the degree of frlling of
material in a weight in the die forging step can be improved to some extent.
In the method disclosed in Patent Literature 3, however, the material yield
rate becomes lower as flash is formed. Moreover, in conventional methods for
forming a forged crankshaft, the material yield rate is not satisfactorily high.
Therefore, a further improvement of material yield rate is demanded.
loozrl
An object of the present invention is to provide a forged crankshaft
production method that achieves an improved material yreld rate by
distributing the volume of a blank and specifi.cally distributing the volume of
each portion to be formed into an arm incorporating a weight between a
portion to be formed into the weight and a portion to be formed into the arm.
SOLUTIONS TO PROBLEMS
loozol
Aforged crankshaft production method according to an embodiment of
the present invention is a method for producing a forged crankshaft including
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journals serving as a center of rotation, pins decentered from the journals,
crank ârms connecting the journals and the pins, and counterweights
integrated with some or all of the crank arms.
looztl
The forged crankshaft production method includes a first preforming
step, a second preforming step, and a final preforming step. In the first
preforming step, the sectional areas of portions of a billet to be formed into the
pins and the sectional areas of portions of the billet to be formed into the
journals are decreased, whereby flat portions are formed. In the second
preforming step, an initial blank obtained by the first preforming step is
pressed by a first pair of dies with a width direction of the flat portions set as a
pressing direction, whereby an intermediate blank is obtained. In the
intermediate blank, portions to be formed into the crank arms incoryorating
the counterweights are thicker than a finished size, and portions to be formed
into the counterweights integrated with the crank arms are thicker than a
finished size. In the final preforming step, the portions of the intermediate
blank to be formed into the crank arms incoryorating the counterweights and
the portions of the intermediate blank to be formed into the counterweights
integrated with the crank arms are pressed from an axial direction of the
intermediate blank, and the intermediate blank is pressed from a direction
perpendicular to the axial direction of the intermediate blank, whereby the
intermediate blank is formed into a crankshaft shape.
loozsl
The first pair of dies 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, 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. Each of
the web processing portions provided in one of the first pair of dies 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. The arm processing part and the weight
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processing part form a recessed portion, where the arm processing part is
Iocated in a bottom side of the recessed portion and the weight processing
portion is located in an open side of the recessed portion, and the width of the
open side of the weight processing part becomes greater with increasing
distance from the bottom of the recessed portion.
loozgl
In the second preforming step, the pin processing portions and the
journal processing portions press the fl.at portions, and while the fl.at portions
are pressed, 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.
loosol
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 preferably pressed from
the open sides of the web processing portions, whereby volume is distributed.
loosrl
The forged crankshaft may further include a front part located at a
front end in the axial direction. In this case, it is preferred that in the first
preforming step, further, a seciional area of a portion of the billet to be formed
into the front part is decreased, whereby the portion to be formed into the
front part is formed into a flat portion. It is preferred that the first pair of
dies further includes a front processing portion to come into contact with the
portion to be formed into the front part, and in the second preforming step, the
portion to be formed into the front part is pressed and elongated by the front
processing portion.
looszl
The forged crankshaft may further include a flange located at a rear
end in the axial direction. In this case, it is preferred that the first pair of
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further includes a fLange processing portion to come into contact with the
portion to be formed into the flange, and in the second preforming step, while
the flat portions are pressed, an end surface of the portion to be formed into
the fl.ange 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.
ADVANTAGEOUS EFFECTS OF INVENTION
[ooss]
In a forged crankshaft production method according to the present
invention, it is possible to obtain an intermediate blank, in which volume
distribution in the axial direction is facilitated with no fl.ash formed, through a
first preforming step and a second preforming step. In each web equivalent
portion (a portion to be formed into an arm and a portion to be formed into a
weight integral with the arm) of the intermediate blank, the volume is
distributed appropriately between the portion to be formed into an arm and
the portion to be formed into a weight integral with the arm. Accordingly, in
a final preforming step, it is possible to form a crankshaft shape with forming
almost no fLash. This leads to an improvement of the material yield rate.
BRIEF DESCRIPTION OF DRAWINGS
loos¿l
[f'tC. ß] FIG.IA is a schematic diagram of a common forged
crankshaft showing an example of the overall shape thereof.
[f'tG. 18] FIG. 1B is a sectional view along the line IB-IB in FIG. 14.
[f'lC. 2A] FIG. 2A is a schematic diagram of a billet during a
conventional process of prod.ucing a common forged crankshaft.
[f'lC. 2B] FIG. 28 is a schematic diagram of a rolled blank during the
conventional process of producing a common forged crankshaft.
[f'tC. 2C] FIG. 2C is a schematic diagram of a bent blank during the
conventional process of producing a common forged crankshaft
[f'lC. 2D] FIG. 2D is a schematic diagram of a rough forged blank
during the conventional process of producing a common forged crankshaft.
tt
[f'tG. Zp] fIC. 2E is a schematic diagram of a finish forged btank
during the conventional process of producing a common forged crankshaft.
[f'IC. 2F] FIG. 2F is a schematic diagram of a crankshaft during the
conventional process of producing a common forged crankshaft.
[f'lC. 3A] FIG. 3A is a schematic diagram of a billet during an
exemplary forged crankshaft production process according to the present
invention.
[f'tC. 3B] FIG. 3B is a schematic diagram of an initial blank during
the exemplary forged crankshaft production process according to the present
invention.
[f'lC. 3C] FIG. 3C is a schematic diagram of an intermediate blank
during the exemplary forged crankshaft production process according to the
present invention.
[f'IC. 3D] FIG. 3D is a schematic diagram of a final blank during the
exemplary forged crankshaft production process according to the present
invention.
[f'IC. 3E] FIG. 3E is a schematic diagram of a finish forged blank
during the exemplary forged crankshaft production process according to the
present invention.
[f'tC. 3F] FIG. 3F is a schematic diagram of a forged crankshaft
during the exempì.ary forged crankshaft production process according to the
present invention.
[f'tC. ¿e] f'lC. 4A is a longitudinal sectional view showing a state
before pressing in an exemplary process fl.ow of a first preforming step.
[f'lC. 48] FIG. 48 is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process flow of the first
preforming step.
[f'IC. 5A] FIG. 5A is a cross-sectional view of a portion to be formed
into a journal before undergoing pressing in the exemplary process fl.ow of the
first preforming step.
[f'fC. 5B] FIG. 5B is a cross-sectional view of the portion to be formed
into a journal at the completion of pressing in the exemplary process fl.ow of
the first preforming step.
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[¡'tC. Ae] f'lC. 6A is a cross-sectional view of a portion to be formed
into a pin before undergoing pressing in the exemplary process fl.ow of the first
preforming step.
[f'tC. 68] FIG. 68 is a cross-sectional view of the portion to be formed
into a pin at the completion of pressing in the exemplary process flow of the
first preforming step.
[f'tC. 7A] FIG. 7A is a cross-sectional view of a portion to be formed
into an arm incorporating a weight before undergoing pressing in the
exemplary process flow of the first preforming step.
[f'tC. 78] 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 fl.ow of the first preforming step.
[f'IG. 8A] FIG. 8A is a longitudinal sectional view showing a state at
the start of pressing in an exemplary process flow of a second preforming step.
[f'tC. 8B] FIG. 8B is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process fl.ow of the second
preforming step.
[f'IC. 9A] FIG. 9A is a cross-sectional view of a portion to be formed
into an arm incorporating a weight at the start of pressing in the exemplary
process fl.ow of the second preforming step.
[f'IC. 98] FIG. 9B is a cross'sectional view of the portion to be formed
into an arm incorlporating a weight at the completion of pressing in the
exemplary process flow of the second preforming step.
[f'fG. 104] FIG. 104 is a cross-sectional view of a portion to be formed
into a journal at the start of pressing in the exemplary process fl.ow of the
second preforming step.
[f'tC. 108] FIG. 108 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.
[f'tG. 1ß] FIG. 114 is a cross-sectional view of a portion to be formed
into a pin at the start of pressing in the exemplary process fl.ow of the second
preforming step.
[f'fC. 1ß] FIG. 118 is a cross'sectional view of the poriion to be
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formed into a pin at the completion of pressing in the exemplary process fLow
of the second preforming step.
[f'IC. 12AJ FIG. 124 is a longitudinal sectional view showing a state
before pressing in an exemplary process fLow of a final preforming step.
[f'lC. 128] FIG. 128 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.
[f'IC. 12C] FIG. 12C is a longitudinal view showing a state at the
completion of an axial movement in the exemplary process fl.ow of the final
preforming step.
[f'lC. 134] FIG. 13Ais a cross-sectional view of a portion to be formed
into an arm incorporating a weight before undergoing pressing to press the
portion to be formed into an arm incorporating a weight from the open side of
a recessed web processing portion.
[f'IC. 138] FIG. 138 is a cross-sectional view of the portion to be
formed into an arm incorporating a weight at the completion of pressing to
press the portion to be formed into an arm incorporating a weight is pressed
from the open side of the recessed web processing portion.
[f'tC. 144] FIG. 14A is a cross-sectional view of a portion to be formed
into a journal at the start of pressing in an exemplary process flow of the
second preforming step to partly press the portion to be formed into a journal
by a journal processing portion.
[f'tG. 148] FIG. 148 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 to partly press the portion to be formed into
a journal by the journal processing portion.
tf'lG. 154] FIG. 15Ais a cross-sectional view of a portion to be formed
into a pin at the start of pressing in an s¡smplary process flow of the second
preforming step to partly press the portion to be formed into a pin by a pin
processing portion.
[f'tC. 158] FIG. 158 is a cross-sectional view of the portion to be
formed into a pin at the completion of pressing in the exemplary process fl.ow
of the second preforming step to partly press the portion to be formed into a
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pin by the pin processing portion.
[f'tC. 164] FIG. 16Ais a cross-sectional view of a portion to be formed
into a journal before undergoing pressing in an exemplary process flow of the
first preforming step to partly press the portion to be formed into a journal by
a journal processing portion.
[f'lC. 168] FIG. 168 is a cïoss-sectional view of the portion to be
formed into a journal at the completion of pressing in the exemplary process
fl.ow of the first preforming step to partty press the portion to be formed into a
journal by the journal processing portion.
[f'tC. 17A,] FIG. 174 is a longitudinal sectional view showing a state
before pressing in an exemplary process flow of the first preforming step to
process a portion to be formed into a front part and a portion to be formed into
a fl.ange.
[f'lC. 178] FIG. 178 is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process flow of the first
preforming step to process the portion to be formed into the front part and the
portion to be formed into the flange.
[f'lC. 184] FIG. 184 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.
[f'lC. 188] FIG. 188 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 preforr¡ing s¿"n.
[f'IC. 19,A,] FIG. 19.A. is a cross-sectional view of the portion to be
formed into the fl.ange before undergoing pressing in the exemplary process
flow of the first preforming step.
[f'tC. 198] FIG. 198 is a cross'sectional view of the portion to be
formed into the fl.ange at the completion of pressing in the exemplary process
fl.ow of the first preforming step.
[f'tG. 204] FIG. 204 is a longitudinal sectional view showing a state
before pressing in an exemplary process fl.ow of the second preforming step to
process the portion to be formed into the front part and the portion to be
formed into the fl.ange.
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[nC. ZOg] FlC. 208 is a longitudinal sectional view showing a state at
the completion of pressing in the exemplary process fLow of the second
preforming step to process the portion to be formed into the front part and the
portion to be formed into the flange.
[n'lC. 2ß] FIG.zLA is a cross-sectional view of the poriion to be
formed into the front part before undergoing pressing in the exemplary
process flow of the second preforming step.
[f'tC. 218] FIG. zLB is a cross-sectional view of the portion to be
formed into the front part at the completion of pressing in the exemplary
process fl.ow of the second preforming step.
[f'lC. 22N FIG.22A is a cross-sectional view of the portion to be
formed into the flange before undergoing pressing in the exemplary process
fl.ow of the second preforming step.
[f'lC. 228] FIG. 228 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
loossl
Aforged crankshafb production method according to an embodiment of
the present invention wilI hereinafter be described with reference to the
drawings.
loosol
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. For example, the method according to the embodiment is intended
to produce a four-cylinder eight-counterweight crankshaft as shown in FIGS.
1A and 18. The method is applicable to production of a four-cylinder
four-counterweight crankshaft as described above.
looszl
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The forged crankshaft production method according to the present
embodiment includes a first preforming step, a second preforming step, and a
fi.nal preforming step to be executed in this order. After the fi.nal 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. When
adjustment of the placement angles of the pins is necessary a twisting step
may be executed after the trimming step. These steps are hot working and
executed sequentially.
loossl
FIGS. SAto 3F are diagrams showing an exemplary forged crankshaft
production process according to the present invention. FIG. SAsho\¡¡s a billet,
FIG. 3B shows an initial blank, FIG. 3C shows an intermediate blank, FIG.
3D shows a final blank, FIG. 3E shows a forged blank, and FIG. 3F shows a'
forged crankshaft. FIGS. 3A to 3F show an exemplary production process of
a crankshaft having the shape shown in FIG. 1.
loosgl
In the first preforming step, the sectional areas of the portions of a
workpiece, that is, a billet 22, to be formed into pins (the portions hereinafter
being referred to as 'lpin equivalent portions") and to be formed into journals
(the portions hereinafter being referred to as ;'journal equivalent portions")
are decreased. Thereby, flat portions 23a are formed in the billet, and each of
the flat portions 23a has a width (dimension in a direction per?endicular to a
pressing direction) Ba greater than a thickness (dimension in the pressing
direction) ta as shown in FIGS. 5B and 68, which will be described later.
Thus, an initial blank 23, írL which the volume has been distributed, is
obtained. In the first preforming step, for example, reduce rolls or cross rolls
may be used. Alternatively, the first preforming step may be executed.
following a process fl.ow using a third pair of dies as will be described later.
loo¿ol
In the second preforming step, for further volume distribution, the
initial blank 23 is pressed by a first pair of dies. The pressing direction in
this step is the width direction of the flat portions 23a. Thereby, an
intermediate blank 24 without flash is obtained. In the intermediate blank
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24, tlne web equivalent portions (portions to be formed into arms and portions
to be formed into weights integrated with the arms) have a thickness
(dimension in the axial direction) tl greater than the finished size t0. The
finished size t0 means the thickness (dimension in the axial direction) of the
arms and weights of a forged crankshaft (finat product). The details of the
second preforming step will be described later.
loo¿rl
In the fi.nal preforming step, the web equivalent portions of the
intermediate blank 24 âre pressed along the axial direction of the
intermediate blank 24 and in a direction perpendicular to the axial direction
of the intermediate blariJ< 24- In this way, the intermediate blank 24 is
roughly formed into a forged crankshaft shape, and thereby, a final blank 25 is
obtained. In the fi.nal preforming step, for example, a forming apparatus
disclosed in Patent Literature 4 may be used. An exemplary process flow of
the final preforming step will be described later.
[oo+z]
In the finish forging step, die forging is carried out in the same
manner as in the above-described conventional finish forging step.
Specifically, the final blank 25 is forged by a pair of an upper die and a lower
die. During this step, excess material flows out and forms into flash B, and
then, a finish forged blank 26 is obtained. The finish forged blank 26 has a
shape in agreement with the shape of a crankshafb that is a final product.
Since the final blank 25, which is an in-process material, is roughly formed
into a crankshaft shape, it is possible to decrease the outflow of excess
material, thereby minimizing the fl.ash B formed in the finish forging step.
loo¿sl
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 fl.ash B is removed from the finish forged blank 26. Then, a forged
crankshaft 21 (final product) is obtained.
loo¿¿l
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
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forging. The rough blank is obtained by applying reduction rolling and
bending to a round billet repeatedly. Then, after the blank for fi.nish forging
is formed, finish forging and trimming are applied sequentially to the blank
for finish forging.
loo¿sl
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 the step of appþing
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 embodiment
corresponds to the processing 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 finat blank (corresponding to the blank for finish forging in Patent
Literature 4).
loo¿ol
2. Exemplary Process Flow of First Preforming Step
FIGS. 4[to 7B are diagrams showing an exemplary process flow of
the first preforming step. FIG. 4A is a longitudinal sectional view showing a
state before pressing, and FIG. 4B is a longitudinal sectional view showing a
state at the completion of pressing.
loo¿zl
FIGS. 5A and 5B are cross-sectional views of a portion to be formed
into a journal (ournal equivalent portiod. FIG. 5A shows a state before
pressing, and FIG. 58 shows a state at the completion of pressing. FIG. SAis
a sectipnal view along the line VA-VA in FIG. 4.A', and FIG. 58 is a sectional
view along the line VB'VB in FIG. 48.
loo¿sl
FIGS. 6A and 68 are cross-sectional views of a portion to be formed
into a pin (pin equivalent portion). FIG. 6A shows a state before pressing,
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FIG. 68 shows a state at the completion of pressing. FIG. 6A is a
sectional view along the line VIA-VIA in FIG. 44, and FIG. 68 is a sectional
view along the line VIB-VIB in F'IG. 48.
loo¿gl
FIGS. 7A and 78 are cross-sectional views of a portion to be formed
into an arm incorlporating a weight (web equivalent portion). FIG. 7A shows
a state before pressing, and FIG. 7B shows a state at the completion of
pressing. FIG. 7A is a sectional view along the line VIIA-VIIA in FIG. 44,
and FIG. 7B is a sectional view along the line VIIB-VIIB in FIG. 48.
loosol
In FIGS. 4A to 7B, a billet 22 t}rat is circular in cross section, and a
third pair of dies 30 are shown. The thfud pair of dies 30 includes a third
upper die 31 and a third lower die 32. For easy understanding of the
drawings, in FIGS. 5B, 68 and 78, the third upper die 31, the third lower die
32 and the billet 22 rn a state 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. The third 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.
loo¡rl
In this exemplary process fl.ow, as indicated by the heavy lines in FIG.
54, each of the journal processing portions includes a first journal processing
part 31a provided in one of the third pair of dies, and a second journal
processing paú 32a provided in the other of the third pair of dies. The first
journal processing part 3la is recessed and is capable of housing a billet. In
this process fl.ow, the journal processing part provided in the upper die 31 is
recessed and is capable of housing a billet, that is, the first journal processing
part 31a. The journal processing part provid.ed in the lower die 32 is the
second journal processing part 32a, and the second journal part 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 journal processing parts
that are capable of housing a billet (nrst journal processing parts).
Accordingly, the lower die may include recessed journal processing parts that
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capable of housing a billet (first journal processing parts).
looszl
In this exemplary process fl.ow, as indicated in the heavy lines in FIG.
6,4,, each of the pin processing portions includes a first pin processing parb 3lb
provided in one of the third pair of dies, and a second pin processing pari 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. In this process flow, the pin
processing part provided in the upper die 31 is recessed and is capable of
housing a billet, that is, the fi.rst pin processing part 31b. 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 die
includes such recessed pin processing parts that are capable of housing a billet
(first pin processing parts). Accordingty, the lower die may include recessed
pin processing parts that are capable of housing a billet (first pin processing
parts).
loossl
In the exemplary process flow of the first preforming step, as shown in
FIG. 44, the upper die 31 is moved up and is separated from the lower die 32,
and the billet 22 ís 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 arc housed in the respective recessed first pin processing parts 31b,
and the journal equivalent portions of the billet 22 are housed in the
respective recessed first journal processing parts 31a. When the upper die 31
is moved further down, the billet 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, fl.at portions as shown in FIGS. 5B and 68 are formed.
Each of the flat portions has a width Ba greater than a thickness ta (see FIGS.
5B and 68). After the completion of pressing by the thiïd pair of dies 30, the
upper die 31 is moved up, and a processed billet 22 (irrlrtíalblank 23) is taken
out.
loos¿l
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In such a process flow, while the pin equivalent portions and the
journal equivalent portions are pressed, the material flows in the axial
direction of the billet and fLows into the web equivalent portions between the
pin equivalent portions and the journal equivalent portions. This results in
obtair¡ment of an initial blank with its volume distributed in the axial
direction.
loosrl
In the process fl.ow shown in FIGS. 4Ato 78, 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. Also, the holes of the recessed
first journal processing parts 31a are closed by the second journal processing
parts 32a, and the first and the second journal processing parts form closed
cross-sections. 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.
loo¡al
When the third pair of dies is used in the first preforming step, with a
view to facilitating the volume distribution in the axial direction, the web
equivalent portions shall not be pressed by the thfud 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 thiïd pair of dies (see FIGS.
TAand 7B). For example, in order to make the web equivalent portions have
a width Bb equal to the width Ba of the fl.at portions, the web equivalent
portions may be parily pressed by the third pair of dies.
looszl
3. Exemplary Process Flow of Second Preforming Step
FIGS. 8A to 118 are diagrams showing an exemplaly process fl.ow of
the second preforming step. FIG. SAis 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.
loossl
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FIGS. 9A and 98 are sectional views of a portion to be formed into an
arm incorlporating a weight (web equivalent portion). FIG. 9A shows a state
at the start of pressing, and FIG. 98 shows a state at the completion of
pressing. FIG. 9A is a sectional view along the line IXA-IXA in FIG. 84, and
FIG. 9B is a sectional view along the line DG-IXB in FIG. 88.
loosgl
FIGS. 104 and 10B are cross-sectional views of a portion to be formed
into a journal (ournal equivalent portion). FIG. 104 shows a state at the
start of pressing, and FIG. 108 shows a state at the completion of pressing.
FIG. 10Ais a sectional view along the line XA-XAin FIG. 84, and FIG. 108 is
a sectional view along the line XB-)G in FIG. 88.
looool
FIGS. 11A' and 118 are cross-sectional views of a portion to be formed
into a pin 6in equivalent portion). FIG. 11.A' shows a state at the start of
pressing, and FIG. 118 shows a state at the completion of pressing. FIG. 114
is a sectional view along the line XIA-)OA in FIG. 84, and FIG. 118 is a
sectional view along the line )trB-XIB in FIG. 88.
looarl
In FIGS. 8A to 118, the initial blank 23 obtained by the first
preforming step, and a first pair of dies 40 arc shown. The first pair of dies
40 includes a first upper die 41 and a first lower dte 42. For easy
understanding of the drawings, in FIGS. 98, 108 and 118, the first upper die
4L, the first lower dte 42 and the initial blank 23 aI the start of pressing are
indicated by two-dot chain lines, and the axis position C of the journal
equivalent portion is indicated by a black circle. The first pair of dies 40
includes web processing portions including parts 41c and 42c to come into
contact with the web equivalent portions, pin processing portions including
parts 41b and 42b to come into contact with the pin equivalent portions, and
journal processing portions including parts 41a and 42a to come into contact
with the journal equivalent portions.
looazl
In each of the web processing portions, as indicated by the heavy lines
in FIG. 9.A', one of the upper die 41 and the lower dte 42 has a generally
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concave cross-sectional shape. In this exemplary process flow, in each of the
web processing portions, the lower web processing part 42c is wholly recessed,
and the other (upper) web processing part Atc is flat. Which of the upper die
and the lower die includes recessed web processing parts can be determined
according to the shape ofthe forged crankshaft to be produced.
looo¡l
The recessed web processing part 42c (provided in the lower die in the
case of FIG. 9Ð includes an arm processing paú 42dto come into contact with
a portion to be formed into an ârm (which will hereinafter be refemed to as an
"arm equivalent portion"), and a weight processing paú 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 paú 42e occupies the open side of the recessed web
processing paú 42c. The width Bw of the open side of the weight processing
paú 42e becomes greater with increasing distance from the bottom of the
recessed web processing part. In this process flow, as shown in FIG. 94, 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 paú 42dis constant.
looo¿l
In the second preforming step, as mentioned above, each of the web
equivalent portions is formed into a shape having a greater thickness than the
finished size. Accordingly, the web processing parts 41c and 42c arc designed
to have a dimension in the axial direction greater than that of a finished web
(arm incorporating a weight).
tooasl
In this exemplary process fl.ow, as indicated by the heavy lines in FIG.
104, each of the journal processing portions includes a first journal processing
part 4La provided in one of the first dies 41 and 42, and a second jor.tnal
processing paú 42a provided in the other of the first dies. The first journal
processing part 4lais recessed and is capable of entirely housing aflat portion
of the initial blank 23. More specifically, the journal processing part provided
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in the upper die 41 is a recessed part that is capable of entirely housing a flaI
portion of the initial blank 23, lhat is, the first journal processing part 41a.
The journal processing part provided in the lower dte 42 is the second journal
processing paú 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 journal processing parts each of which is capable of entirely housing
a fl.at portion of the initial blank (first journal processing parts).
looael
In this exemplary process fl.ow; as indicated by the heavy lines in FIG.
114, each of the pin processing portions includes a first pin processing part
41b provided in one of the first dies 41 and 42, and a second pin processing
paú 42b provided in the other of the first dies. The first pin processing part
41b is recessed and is capable of entirely housing aflat portion of the initial
blank 23. More specifically, the pin processing part provided in the upper die
41 is a recessed part that is capable of entirely housing a flat portion of the
initial blank 23,t}lrat is, the first pin processing part 41b. The pin processing
part provided in the lower dte 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. There is no limit as to which of the upper die and the lower die
includes such recessed pin processing parts each of which is capable of
entirely housing a flat portion of the initial blank (first pin processing paris).
Accordingly, the lower die may include recessed pin processing parts each of
which is capable of entirely housing a flat portion of the initial blank (first pin
processing parts).
[oooz]
In the process flow of the second preforming step using the first 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 dte 42.
In this regard, in order to set the width direction of the flat portions (major
radial direction when the fl.at portions are ellipses) of the initiat blank 23 as
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the pressing direction, the initial blank 23 is rotated 90 degrees around the
axis from the state at the completion of the first preforming step (the billet),
and then placed between the dies 4l and 42.
[ooes]
Then, the upper die 41 is moved down, and as shown in FIGS. 104 and
114, the flat portions of the initial blank 23 arc housed in the recessed first
journal processing parts 41a and the recessed first pin processing parts 41b.
At this time, as shown FIG. 9.A., each of the web equivalent portions is mostly
placed in the weight processing part 42e without contacting the bottom of the
web processing part.
looagl
lVhen the upper die 41 is moved further down, the first pin processing
parts 41b and the second pin processing parts 42b form closed cross-sections.
Also, the first journal processing parts 41a and the second journal processing
parts 42aform 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 41b and the second pin processing parts 42b
are entirely pressed. Also, the flat portions in the spaces enclosed by the first
journal processing parts 41b and the secondjournal processing parts 42b are
entirely pressed. In this way, the flat portions of the initial blank 23 arc
pressed by the first 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 fl.ows in the axial direction into the arm equivalent
portions, and thus, volume distribution is progressed. Also, the center of
mass of each of the pin equivalent portions moves in the decentering direction
of the pin (see the hatched arrow in FIG. ß).
loozol
Each of the web equivalent portions is not pressed by the other web
processing part (web processing part provided in the upper die in the case of
FIGS. 9A and 9B). However, each of the web equivalent portions is pushed
into the bottom side of the recessed web processing paú 42c as the pressing by
the first pair of dies 40 is advancing. The pushing arises along with the
pressings (deformations) of the journal equivalent portion and the pin
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equivalent portion located adjacent to the web equivalent portion. At the
time of pushing, the web equivalent portion deforms along the arm processing
part and the weight processing part. 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.
loozrl
Thus, when each of the web equivalent portions deforms, especially
when the weight equivalent portion is shaped by the weight processing part,
the pin processing parts 4Lb, 42b and the journal processing parts 41a and
42a are present on the front side and the rear side of the weight equivalent
portion along the axial direction. In this case, the upper portion of the first
pin processing part 41b (portion enclosed by the circle D2 in FIG. 88) and the
upper portion of the first journal processing part 41a (portion enclosed by the
ellipse Dl in FIG. 88) serve as partitions that control the flow of material in
the axial direction. This prevents the material from fl.owing in the axial
direction from each of the weight equivalent portions. As mentioned above,
the web processing parts 41c (web processing parts provided in the upper die
in the case of FIGS. 9A and 98) do not press the web equivalent portions, and
this facilitates the material to fl.ow into the web equivalent portions from the
pin equivalent portions and the journal equivalent portions. Moreover, this
prevents outfl.ow of excess material and makes it possible to form weight
equivalent portions without forming flash.
lootzl
A-fter the completion of pressing by the first pair of dies 40, tlne upper
die 41 is moved up, and. a processed initial btank 23 (intermediate blank 24) is
taken out. The web equivalent portions of the obtained intermediate blank
24have a thickness greater than the finished size.
loozsl
In the second preforming step, the material is caused to flow from the
pin equivalent portions and the journal equivalent portions to the web
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equivalent portions, which results in volume distribution in the axial direction.
Also, in each of the web equivalent portions, the material fl.ows inside kept
back by the arm processing part and the weight processing part, and the web
equivalent portion is formed into a shape having a smaller width in the
portion in the bottom side of the recessed processing part and a greater width
in the portion in the open side of the recessed processing part. Thus, volume
distribution inside each of the web equivalent portions can be done, and
thereby, the risk of deficiency in the weights possibly caused in the subsequent
fi.nal preforming and finish forging steps can be pressed. Also, the amount of
excess material for the weight equivalent portions can be pressed, and the
material yield rate can be increased.
looz+l
In the exemplary process flow, the flat portions are housed in the
recessed first pin processing parts 4Lb and the recessed first journal
processing parts 41a. Thereafter, closed cross-sections are formed by the first
pin processing parts 41b and the second pin processing parts 42b, and closed
cross-sections are formed by the first journal processing parts 41a and the
second journal processing paús 42a. The flat portions are pressed in this
state, and therefore, the material never flows to between the upper die 41 and
the lower dte 42. This improves the material yreld rate and facilitates the
fl.ow of material from the pin equivalent portions and the journal equivalent
portions to the web equivalent portions.
looz¡l
As will be described later, in the second preforming step, the outfl.ow of
material and the formation of flash may be prevented by partial pressing by
the first pin processing parts 41b and the second pin processing parts 42b.
Also, the outfLow of material and the formation of fl.ash may be prevented
partial pressing by the first journal processing parts 41a and the second
journal processing paús 42a.
loozol
4. Exemplary Process Flow of Final Preforming Step
FIGS. I2A to t2C arc longitudinal sectional views schematically
showing an exemplary process fl.ow of the final preforming step. FIG. 124
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shows a state before pressing, FIG. 128 shows a state where the upper die has
reached the bottom dead point, and FIG. 12C shows a state at the completion
of an axial movement. In FIGS. L2A to L2C, t}re intermediate blank 24
obtained by the second preforming step, a second pair of dies 51, an upper
plate 52 and a lower plate 53 are shown. The second pair of dies 51 includes
a second upper die 60 and a second lower die 70. The second 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 second lower die 70 is
held by the lower plate 53, and the lower plate 53 is fixed to the pressing
machine (not shown).
Íooztl
For pressing of the web equivalent portions (portions to be formed into
arms and portions to be formed into weights integrated with the arms) from
the axial direction of the intermediate blank 24, each of the second upper die
60 and the second lower die 70 is divided into some parts. The parts
composing the second upper die 60 are arranged in the axial direction of the
intermediate blank 24, and the parts composing the second lower die 70 are
arranged in the axial direction of the intermediate blank 24. The second
upper die 60 includes a fixed journal die component 61, movable journal die
components 62 and pin die components 63. The second lower die 70 includes
a fixed journal die component 71, movable journal die components 72 and pin
die components 73.
loozsl
The fixed journal die components 61 and 'll arc to press the central
journal equivalent portion of the intermediate blank 24 and the web
e_quivalent portions adjacent thereto, and the fixed journal die components 61
and 71 are not movable in the axial direction. The movable journal die
components 62 and T2formsome pairs of die components that are to press the
journal equivalent portions other than the central journal equivalent portion.
The movable journal die components 62 and 72 arc also to press the web
equivalent portions, a portion to be formed into the front part and a portion to
be formed into the fl.ange that are connected to the journal equivalent portions.
The movable journal die components 62 and 72 are movable in the axial
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loozgl
The pin die components 63 and 73 ate to press the pin equivalent
portions of the intermediate blank 24, and are movable in the axial direction.
Moreover, either the pin die components 63 of the upper die 60 or the pin die
components 73 of the lower die 70 are movable relative to the plate 52 or 53
holding the die components 63 or 73. The direction of the relative movement
is along the pin decentering direction. Thereby, the pin equivalent portions
of the intermediate blank 24 canbe decentered. 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 pin die components 63 of the upper die 60 or the pin die
components 73 of the lower die 70.
loosol
The third upper die 60 and the thfud lower die 70 formed by such
components have impressions (see reference symbols 6La, 62a, 63a,71a,72a
and 73a in FIG. 12Ð. The impressions reflect the approximate shape of the
crankshaft (final product).
loosrl
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
with the pin decentering direction set as the pressing direction. 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. Thereby, the journal equivalent portions
of the intermediate blank 24 arc pressed and formed into approximate shapes
of the journals.
looszl
While the journal equivalent portions of the intermediate blank 24 are
kept pressed, the movable journal die components 62 and 72 and the pin die
components 63 and 73 are moved in the axial direction toward the central
fixed journal die components 61 and 71. The movements can be made by a
wedge mechanism or a hydraulic cylinder, for example.
loossl
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Aì.ong with the axial movements of the movable journal die
components 62 and 72 and the 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.
loos¿l
According to the axial movements of the movable journal die
components 62 and 72 and the pin die components 63 and 73, the pin die
components 63 of the upper die 60 or the pin die components 73 of the lower
die 70 arc moved in the pin decentering direction. Thereby, the pin
equivalent portions are decentered. The pin equivalent portions are also
pressed by the pin die components 63 and 73, and the pin equivalent portions
are formed into approximate shapes of the pins.
loossl
After the completion of pressing by the second pair of dies 51, the
upper die 60 is moved up, and a processed intermediate blank 24 (frnalblank)
is taken out.
loosol
In the final preforming step, the web equivalent portions are pressed
in the axial direction, and this improves the degree ef filling of material in the
weights, thereby preventing deficiency of material in the weights. Since the
filling of material in the weights is good, a fi.nal blank with no or almost no
flash can be obtained.
looszl
In the forged crankshaft production method according to the
embodiment, an intermediate blank without flash can be obtained by the first
preforming step and the second preforming step. Accordingly, the material
yield rate can be improved.
loossl
In the forged crankshaft production method according to the
embodiment, additionally, volume d.istribution in the axial direction can be
facilitated in the first preforming step and the second preforming step. Thus,
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the sectional areas of the pin equivalent portions and the journal equivalent
portions are decreased, and the sectional areas of the web equivalent portions
are increased. In the second preforming step, each of the web equivalent
portions is formed to have a smaller width in the arm equivalent portion and a
greater width in the weight equivalent portion, and thus, the volume is
distributed inside each of the web equivalent portions. This permits
formation of an approximate crankshaft shape without flash in the next final
preforming step. By using the final blank having an approximate crankshaft
shape in the finish forging step, it is possible to minimize outfl.ow of excess
material, thereby minimizing formation of fl.ash, in the finish forging step.
Also for this reason, the material yield rate can be improved.
loosgl
5. Volume Distribution inside Web Equivalent Portion
The volume distribution inside each of the web equivalent portions
performed in the second preforming step can be adjusted by changing the
shape ofthe arm processing part as appropriate according to the shape ofthe
forged crankshaft (final product). For example, by changing the width of the
open side ofthe 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.
loogol
The weights of the forged crankshaft (final product) may be any of
various shapes. For example, there is a case where each of the weights
bulges greatly in the width direction and has a small dimension in the pin
decentering direction. In order to comply with such a case, the shape of the
weight processing part may be changed such that the volume can be
distributed inside the web equivalent portion appropriately in the width
direction and in the pin decentering direction in the second preforming step.
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
3/,
processing part for volume distribution inside the weight equivalent portion.
loogrl
FIGS. 134 and 138 are cross-sectional views of a portion to be formed
into an arm incorporating a weight (web equivalent portion) in a case where
the web equivalent portion is pressed from the open side of the recessed web
processing part. FIG. l3Ashows a state before pressing, and FIG. 13B shows
a state at the completion of pressing. In the case shown in FIGS. 134 and
138, the recessed web processing part shown in FIGS. 9A and 98 is modified
to be shallower.
loogzl
In the process fl.ow shown in FIGS. l3Aand 138, as inthe process fl.ow
shown in FIGS. 9A and 98, each of the web equivalent portions is pushed to
the bottom side of the recessed web processing part 42c and is deformed along
the recessed web processing paú 42c. Since the recessed web processing part
42c is shallower, at the last stage of the pressing by the first pair of dies, the
fl.at 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 paú 42c and is deformed to
have a greater width and a smaller length (dimension in the decentering
direction). Thus, the volume is distributed inside the weight equivalent
portion.
looggl
The pressing of 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,
for example, by pressing a part of the open side surface 23b (see FIG. 98) of
the web equivalent portion. In this case, the material fl.ows to a portion that
is out of contact with the dies, thereby resulting in a light pressing.
loog¿l
6. Preferred Examples
In the intermediate blank obtained by the second preforming step, the
ratio (tUtO) of the thickness tl (mm) of each of the web equivalent portions
(portions to be formed into arms and portions to be formed into weights
Z3
integrated with the arms) to the fi.nished size t0 (md is desirably equal to or
greater than 1.1, and more desirably equal to or greater than 1.5, with a view
to improving the degree of filling of material in the weights in the after steps.
If the ratio (t1lt0) is greater than 3.5, the bulging/deforming areas of the
material surface will be too great, whereby the form accuracy of the outer
peripheries of the arms may be decreased. Therefore, the ratio (ttlt0) is
desirably not more than 3.5.
loogsl
The ratio (Sw2/SwO) of the sectional area Sw2 (mm2) of each of the
web equivalent portions of the intermediate blank to the sectional area SwO
(mmz) of each of the webs of the forged crankshaft (final product) is desirably
0.3 to 0.9, with a view to preventing defi.ciency in the weights while
maintaining the degree of frlling of material in the weights sufficiently high in
the after steps. For the same purpose, the ratio (SwUSw0) of the sectional
area Swl (mmz) 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.
loogal
The ratio (Sj2/SjO) of the sectional area Sj2 (mmz) of each of the
journal equivalent portions of the intermediate blank to the sectional area SjO
(mmz) of each of the journals of the forged crankshaft (final product) is
desirably 1.0 to 1.9, with a view to diminishing flash formed in the after steps.
For the same purpose, the ratio (Sjl/SjO) of the sectional area Sjl (mmz) 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 (finat product)
is desirably L.2to I.9.
loogzl
The ratio (SpzlSpO) of the sectional area Sp2 (mmz) of each of the pin
equivalent portions of the intermediate blank to the sectional area SpO (mm2)
3 tt-
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of each of the pins of the forged crankshaft (finat product) is desirably 0.7 to
1.9, with a view to diminishing flash formed in the after steps. For the same
pu{pose, the ratio (Sp 1/Sp0) of the sectional area Sp 1 (mm2) of each of the pin
equivalent portions of the initial blank to the sectional area.SpO (mm2) of each
of the pins of the forged crankshaft (final product) is desirably 0.9 to 1.9.
loogel
In the second preforming step, as described above, the upper portions
of the fi.rst pin processing parts 41b and the upper portions of the first journal
processing parts 41a serve as partitions that controls the flow of material in
the axial direction. In order to strengthen this effect, it is important to
decrease the widths of the open sides of the recessed first pin processing parts
41b and the widths of the open sides of the recessed first journal processing
parts 41a (see Bp inFIG. llAand Bj in FIG. 10Ð. However, ifthe widths Bp
of the open sides of the recessed first pin processing parts and the widths Bj of
the open sides ofthe recessed first journal processing parts are too narrow, the
load in the after steps will be g¡eat.
looggl
For these reasons, in a case of employing a process fl.ow as shown in
FIGS. 8Ato 118, the ratio of the width Bp (mm) of the open side of each of the
recessed first pin processing parts to the diameter Dp (mm) of each of the pins
of the forged crankshaft (final product) is desirably 0.5 to 1.5. Also, the ratio
of the width Bj (mm) of the open side of each of the recessed first journal
processing parts to the diameter Dj (mm) of each of the journals of the forged
crankshaft (final product) is desirably 0.5 to 1.5.
lorool
In the above-described process fl.ow of the second preforming step, the
initial blank 23 (the fl.at portions thereoÐ is pressed.. During the pressing,
the first journal processing parts 41a and the second journal processing parts
42a form closed cross-sections, and the first pin processing paris 41b and the
second pin forming sections 42b form closed cross-sections. This prevents
outflow of material and accordingly prevents formation of flash. In the
forged crankshaft production method according to the present embodiment,
partial pressing may be performed by the first journal processing parts 4La
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and the second journal processing parts 42a to prevent outflow of material
and formation of flash. Also, partial pressing may be performed by the first
pin processing parts 41b and the second pin processing parts 42b to prevent
outfLow of material and formation of flash.
lororl
FIGS. 14A. and I4B arc cross-sectional views of a portion to be formed
into a journal showing an exemplaly process flow to perform partial pressing
by the journal processing parts in the second preforming step. FIG. 144
shows a state at the start of pressing, and FIG. 148 shows a state at the
completion of pressing. FIGS. 144 and 14B show a modification of the
journal processing parts 41a and 42a shown in FIGS. 10.A' and 108. As
indicated by the heavy lines in FIG. 144, each of the journal processing parts
provided in the upper die 41 is a recessed portion capable of entirely housing á
flat portion of the initial blank, that is, the first journal processing paft 4La.
Each of the journal processing parts provided in the lower dte 42 is arc-shaped,
that is, the second journal processing part 42a, and the second journal
processing pafi 42a is located on the edge surface of a raised poriion. The
journal processing parts 41a and AZahave clearances 41f and 42f at both sides
in the width direction, and the clearances 41f and 42f project outward in the
width direction.
lorozl
By the pair of dies having these journal processing parts 4La and 42a,
along with a downward movement of the upper die 41, the flat portions of the
initial blank 23 arc entirely housed in the first journal portions 41a. When
the upper die 41 is moved further down, the first journal processing parts 41a
contact the flat portions, and subsequently, the second journal processing
parts 42a contact the fl.at portions. By the contacts, the flat portions are
pressed, and the sectional areas thereof are decreased. At the time, the
material fl.ows in the axial direction, whereby the volume is distributed. In
this regard, the material partly fLows in the clearances 41f and 42f, but t}re
clearances 41f and 42f. are partly kept out of contact with the fl.at portions.
Thus, the flat portions are partly pressed, and the material does not fl.ow out,
thereby resulting in formation of no flash.
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lorosl
It is possible to apply the structure to be described below with
reference to FIG. 154 and 158 to the journal processing portions, and the
journal equivalent portions may be partly pressed by the journal processing
portions having the structure for prevention of outflow of material and
formation of flash. With a view to facilitating volume distribution, it is
preferred that the flat portions are entirely pressed while the first journal
processing parts 41a and the second journal processing parts 42a form closed
cross-sections. With a view to preventing the material from fl.owing into the
spaces between the upper die and the lower die, it is preferred that partial
pressing is carried out by the first journal processing parts 4la andthe second
journal processing parts 42a.
loro¿l
FIGS. 154 and 158 are cross'sectional views of a portion to be formed
into a pin showing an exemplary process fl.ow to perform partial pressing by
the pin processing portions in the secondary preforming step. FIG. 154
shows a state at the start of pressing, and FIG. 15B is a state at the
completion of pressing. FIGS. 154 and 15B show a modification of the pin
processing parts 41b and 42b shown in FIGS. 114 and 118. As indicated by
the heavy lines in FIG. 154, each of the pin processing parts provided in the
upper die 41 is a recessed portion capable of housing the most part of a fl.at
portion of the initial blank 23, t}rat is, the first pin procesding part 41b. Each
of the pin processing parts provided in the lower dte 42 is arc-shaped, that is,
the second pin processing part 42b, and the second pin processing part 42b is
recessed. The depth ofthe first pin processing part 4Lb is greater than the
depth ofthe second pin processing part 42b.
lororl
By the pair of dies having such pin processing parts 4lb and 42b,
along with a downward movement of the upper die 41, the fl.at portions of the
initial blank 23 arc mostly housed in the first pin processing parts 41b.
When the upper die 41 is moved further down, the first pin processing parts
41b contact the flat portions, and subsequently, the second pin processing
parts 42b contact the fl.at portions. At this time, regarding the first pin ,'
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processing parts 41b and the second pin processing part 42b in each pair, both
ofthe first and the second pin processing parts 41b and 42b contact part ofa
flat portion. In other words, the flat portion does not contact the pin
equivalent portion near the parting faces. This allows the material to fl.ow
from the pin equivalent portions to the web equivalent portions without
causing formation of flash. This also allows the pin equivalent portions to be
decentered.
lorool
It is possible to apply the structure described above with reference to
FIG. 144 and 148 to the pin processing portions, and the pin equivalent
portions may be partly pressed by the pin processing portions having the
structure for prevention of outflow of material and formation of flash. With a
view to facilitating volume distribution, it is preferred that the flat portions
are entirely pressed while the first pin processing parts 41b and the second
pin processing parts 42b form closed cross-sections. With a view to
preventing the material from fl.owing into the spaces between the upper die
and the lower die, it is preferred that partial pressing is carried out by the
first pin processing parts 41b and the second pin processing parts 42b.
lorozl
In the above-described process fl.ow of the first preforming step, the
entire circumference of a billet is pressed by the thfud pair of dies 30. During
the pressing, the first journal processing parts 31a and the second journal
processing parts 32a form closed cross-sections, and the first pin processing
parts 3lb and the second pin processing parts 32b form closed cross-sections.
This prevents outfl.ow of material and formation of flash. In the forged
crankshaft production method according to the present embodiment, it is
possible to prevent outflow of material and formation of fl.ash by carrying out
partial pressing of the journal equivalent portions by the journal processing
portions. It is also possible to prevent outfLow of material and formation of
flash by carrying out partial pressing of the pin equivalent portions by the pin
processing portions.
lorosl
FIGS. 16 A and 168 are cross-sectional views of a portion to be formed
3V
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into a journal showing an exemplar1y process fl.ow to perform partial pressing
by the journal processing portions in the first preforming step. FIG. 16A'
shows a state before pressing, and FIG. 168 shows a state at the completion of
pressing. FIGS. 16.4' and 16B show u modification of the journal processing
parts 31a and 32a shown in FIGS. 5A and 58. As indicated by the heavy
lines in FIG. 164, the journal processing parts provided in the upper die 31
and the journal processing parts provided in the lower die 32 are recessed, and
the journal processing parts have the same depth.
lorogl
By the pair of dies having these journal processing portions, along
with a downward movement of the upper die 31, the bottoms of the journal
processing parts 3la 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. In other
words, the portions of the journal processing parts 31a and 32a around the
parting faces do not contact the blllet 22. Accordingly, it is possible to
decrease the sectional areas, thereby forming flat portions, without forming
flash. With a view to facilitating volume distribution, it is preferred that the
billet is entirely pressed while the journal processing parts form closed
cross-sections as shown in FIGS. SAand 58.
lorrol
The pin processing portions provided in the thiïd pair of dies may
have a structure similar to the structure of the journal processing portions
shown in FIGS. 164 and 168 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 portions form closed cross-sections as shown
in FIGS. 6Aand 68.
lorrrl
In the above-described process flow of the final preforming step shown
in FIGS. 124 and 128, either the pin die ssmponents 63 or the pin die
i-e
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components 73 are movable in the decentering direction relative to the plate
õ2 or 53 holding the components 63 or 73. In this case, the intermediate
blank 24 is pressed by the upper die 60 and the lower die 70. Thereafter,
along with the axial movements of the movable journal die components 62 and
72 andthe 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 relatively
moved in the decentering direction. Thereby, the pin equivalent portions are
decentered. In the forged crankshaft production method according to the
present embodiment, the final preforming step is not limited to a step with
this configuration.
lorrzl
Specifi.cally, both of the pin die components 63 and 73 may be
immovable relative to the plates 52 and 53. In this case, when the.
intermediate blank 24 is pressed by the upper die 60 and the lower die 70, the
pin equivalent portions are pressed by the pin die components 63 of the upper
die and the pin die components 73 of the lower die. Thereby, the pin
equivalent portions are decentered and are formed into approximate shapes of
the pins. With a view to improving the processing accuracy of the pins, it is
preferred that, along with the pressing in the axial direction, either the pin die
components 63 or the pin die components 73 arc moved in the decentering
direction for pressing of the pin equivalent portions to decenter the pin
equivalent portions and to form the pin equivalent portions into approximate
shapes of the pins.
lorrel
In a crankshaft, the positions of the respective far ends of the pins
vary depending on various factors. As shown in FIG. 18, the far end PT of
the pin P4 is the point of the pin P4 that is the farthest from the center of the
journal J4. Specifi.cally, 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.
18, the tip AT of the arm A7 is the point of the arm A7 (portion excluding the
weight W7) that is the farthest from the center of the journal J4.
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7. Front Part and Flange
Next, an exemplary process flow to process the portion to be formed
into the front part (which will hereinafter be referred to as a "front equivalent
portion") and the poriion to be formed into the fl.ange (which will hereinafter
be referred to as a "f1.ange equivalent portion") in the fi.rst preforming step
employing the third pair of dies is described.
lorrsl
FIGS. 174 to 198 are diagrams showing the exemplary process fLow
to process the front equivalent portion and the flange equivalent portion in
the first preforming step. FIG. 174 is a longitudinal sectional view showing
a state before pressing, and FIG. 17B is a longitudinal sectional view showing
a state at the completion of pressing.
lorrol
FIGS. 18.A. and 188 are cross-sectional views of the front equivalent
pârt. FIG. 184 shows a state before pressing, and FIG. 188 shows a state at
the completion of pressing. FIG. 18A' is a sectional view along the line
XVIIIA-XWIIA in FIG. 174, and FIG. 188 is a sectional view along the line
XVIIIB-XUIIB in FIG. 178.
lorrzl
FIGS. 194 and 198 are cross-sectional views of the fl.ange equivalent
portion. FIG. l9Ashows a state before pressing, and FIG. 198 shows a state
at the completion of pressing. FIG. 194 is a sectional view along the line
XIXA')OXA in FIG. 174, and. FIG. 198 is a sectional view along the line
XIXB-)0XB in FIG. 178.
lorrsl
In FIGS. 17Ato 198, a billet Z2lnavtng a round cross-sectional shape,
and a thfud pair of dies 30 composed of an upper die and a lower die are shown.
For easy understanding of the drawings, in FIGS. 18B and 198, the thfud
upper die 31 and the third 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. 198, the billet 22 is further indicated by a
two'dot chain line. The third pair of dies 30 shown in FIGS. 174 to 198 il
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includes pin processing portions and journal processing portions as the third
pair of dies 30 shown in FIGS. 4Ato 78. The third pair of dies 30 further
includes a front processing portion to come into contact with the front
equivalent portion.
lorrgl
In this exemplary process flow, the front processing portion includes
inner surfaces 31c and 32c as indicated by the heavy lines in FIGS. 17,A. and
184, and an edge surface 32d as shown in FIG. 17.A.. 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 thé
recessed parts have the same depth.
lorzol
By the pair of dies including the front processing portion, along with a
downward movement of the upper ùie 31, the bottoms of the front processing
parts provided in the upper die 31 and the lower die 32 (in this exemplary
process fl.ow, the inner surfaces 31c and 32c) come into contact with the
periphery of the front equivalent portion of the bilTet 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
the periphery of the billet 22. 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 t}re biTlet 22. Accordingly, it is possible to decrease
the sectional area, thereby resulting in formation of a fl.at portion, without
forming flash. Moreover, by elongating the front equivalent portion in the
axial direction along with the formation of a fl.at portion, it is possible to
distribute the volume in the axial direction. Thus, the material yield rate
can be further improved.
lorzrl
The front processing portion of the third pair of dies 30 is not limited
to the structure shown in FIGS. 18A' and 18B for partial pressing of the
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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. 5A
and 58. In short, the front processing portion may include a first front
processing part provided in one of the third dies and a second front processing
part provided in the other of the thfud 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. Thereby the sectional area is
decreased, and a flat portion can be formed with no flash formed. 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 materiat yield rate can be further improvedlotzzl
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 (in this process fl.ow, 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).
lorzsl
If the rate of decrease of the sectional area of the front equivalent
portion during the fi.rst 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 pressing is carried out in the first
preforming step such that the thickness ta (dimension in the pressing
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direction) 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 thickness ta of the front equivalent portion can
be decreased linearly, in a curve or in a staircase pattern, for example. In the
case of FIG. 178, the thickness ta of the front equivalent portion becomes
thinner linearly in the part facing the journaL (the opposite side from the end
surface) and is constant in the side near the end surface. 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 third dies 30 (in this process fl.ow,
the inner surfaces 3lc and 32c of the front processing poriion) as appropriate.
lotz+l
'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, in the
next second preforming step, the end-surface side of the front equivalent
portion and the journal-facing side of the front equivalent portion can be
pressed to have substantially the same sectional area with no flash formed.
Thus, even when the front equivalent portion of the initial blank 23 is made
such that the thickness ta thereof decreases with increasing distance from the
end surface of the front equivalent portion, the material yield rate can be
maintained high.
lorzsl
In this exemplary process flow, the flange processing portion includes
inner surfaces 31e and 32e as indicated by the heavy lines in FIGS. 17.A' and
194, and an edge surface 32f as shown in FIG. 174. The inner surfaces 31e
and 32e of the fl.ange processing portion face the periphery of the flange
equivalent portion. The edge surface 32f of the fl.ange processing portion
faces the end surface of the flange equivalent portion.
lorzol
With a view to firrther improving the material yield rate, it is desired
that the sectional area of the fLange equivalent portion is increased in the first
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preforming step. For this purpose, it is preferred that the end surface of the
fl.ange equivalent portion is brought into contact with the fl.ange processing
part (in this exemplary flow, the edge surface 32f) along with the pressing by
the third pair of dies. In this case, while the sectional area of the journal
equivalent portion connected to the fl.ange equivalent portion is being
decreased, whereby the journal equivalent portion is formed into a flat portion,
the material fl.ows into the fl.ange equivalent portion. At this time, since the
end surface of the fl.ange equivalent portion is held by the flange processing
part (edge surface 32Ð, 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.
lotztl
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 third 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 fl.ange equivalent portion may partly contact the third dies (in
this process fl.ow, the inner surfaces 3le and 32e) (see FIGS. 194 and 198).
lorzsl
At the start of pressing in the first preforming step, the end surface of
the flange equivalent portion may be brought into contact with the flange
processing part (in this process fl.ow; the edge surface 32f). Alternatively,
there may be a space between the end surface of the flange equivalent portion
and the fl.ange 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 32Ð 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.
lorzgl
Next, an exemplary process fl.ow to process the front equivalent
portion and the fl.ange equivalent portion in the second preforming step is
described.
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lorsol
FIGS. 20Ato 22F^ are diagrams showing the exemplary process fLow to
process the front equivalent portion and the fLange equivalent portion in the
second preforming step. FIG. 204 is a cross-sectional view showing a state
before pressing, and FIG. 20B is a cross-sectional view showing a state at the
completion of pressing.
lorsrl
FIGS. 21.A. and 2lF- arc cross-sectional views showing the front
equivalent portion in the second preforming step. FIG. 214 shows a state
before pressing, and FIG. 218 shows a state at the ¿empletion of pressing.
FIG. 21Ais a cross-sectional view along the line )OilA-)OilAin FIG. 204, and
FIG. 218 is a cross-sectional view along the line )OilB-)OilB in FIG. 208.
lorszl
FIGS. 22A and 22r- arc cross-sectional views of the flange equivalent
portion in the second preforming step. FIG. 224 shows a state before
pressing, and FIG. 228 shows a state at the completion of pressing. FIG. 224
is a cross-sectional view along the line )OtrIA-)OilIA in FIG. 20Ao and FIG.
22r- is a cross-sectional view along the line >CtrIB')OilIB in FIG. 208.
lorssl
In FIGS. 204 to 228, t}lLe initial blank 23 and a first pair of dies 40 are
shown. For easy understanding of the drawings, in FIGS. 218 and 228, t}re
first upper die 41 and the first lower dte 42 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. The first pair of dies 40 shown in FIGS. 204 to
228 includes web processing portions, pin processing portions and journal
processing portions as the first pair of dies 40 shown in FIGS. SAto 118. The
first pair of dies 40 further includes a front processing portion to come into
contact with the front equivalent portion.
lors¿l
In this exemplary process fl.ow, the front processing portion includes
inner surfaces 41g and 429 as indicated by the heavy lines in FIGS. 20.A. and
214, and an edge surface 42}n as shown in FIG. 204. The inner surfaces 419
and 42g of the front processing portion face the periphery of the front
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equivalent portion. The edge surface 42};' of the front processing portion
faces the end surface of the front equivalent portion. As indicated by the
heavy lines in FIG. 214, 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 dte 42 are both recessed, and the
recessed portions have the same depth.
lorssl
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 dte 42 (in this exemplary
process flow; the inner surfaces 41g and 42g) come into contact with the
periphery of the fl.at portion (front equivalent portiorù of the initial blank 23.
When the upper die 41 is moved further down, both of the front processingj
parts (inner surfaces 41g and 42g) provided in the upper die 41 and the lower
dte 42 partly contact the periphery of the front equivalent portion. In other
words, the portions of the front processing parts (inner surfaces 4lg and, 425)
near the parting faces do not contact the periphery of the front equivalent
portion. Accordingly, the sectional area of the front equivalent portion can be
decreased by the pressing with no flash formed. 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.
lorgal
The front processing portion of the first pair of dies 40 arc not limited
to the structure shown in FIGS. 21.A. and 218 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. 104 and 108. 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, the foont processing parts form a closed
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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.
lorszl
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 outfl.ow, it is preferred
that the end surface of the front equivalent portion is prevented from
contacting the front processing part (in this process fl.ow, the edge surface 42h)
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 42h). Alternatively, the
end surface of the front equivalent portion may partly contact the front
processing part (edge surface 42h).
lorsal
In this exemplary process flow, the fl.ange processing portion includes
inner surfaces 41i and 42i as indicated by the heavy lines in FIGS. 204 and
22A, and.an edge surface 42j as shown in FIG. 204. The inner surfaces 41i
and. 42i of the fLange processing portion face the periphery of the flange
equivalent portion. The edge surface 42j of the flange processing portion
faces the end surface of the fLange equivalent portion.
lorsgl
With a view to further improving the material yield rate, it is desired
that the sectional area of the fl.ange equivalent portion is increased in the
second preforming step. For this purpose, it is preferred that the end surface
of the fl.ange equivalent portion is brought into contact with the flange
processing part (in this exemplary flow, the edge surface 42j) alons with the
pressing of the fl.at portions. In this case, while the sectional area of the
\s
-4/ljournal
equivalent portion connected to the fl.ange equivalent portion is being
decreased by pressing of the journal equivalent portion, the material flows
into the flange equivalent portion. At this time, since the end surface of the
flange equivalent portion is hetd by the fLange processing part (edge surface
42j), tlne 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.
lor¿ol
In order to faci-litate the increase of the sectional area of the fl.ange
equivalent portion, it is preferred that the periphery of the fl.ange equivalent
portion is prevented from contacting the flange processing parts (in this
process flow, the inner surfaces 41i and 421) in the second preforming step.
Alternatively, for adjustment of the shape (dimensions) of the fl.ange
equivalent portion, it is preferred that the periphery of the flange equivalent
portion partly contacts the fl.ange processing parts (in ttris process flow, the
inner surfaces 41i and 42Ð (see FIGS. 22Land22B).
lor¿rl
At the start of pressing in the second preforming step, the end surface
of the fl.ange equivalent portion may be brought into contact with the flange
processing part (in this process fl.ow, the edge surface 42j). Alternatively,
there may be a space between the end surface of the flange equivalent portion
and the fLange processing part (edge surface aàj) at the start of pressing, and
the end surface of the fl.ange equivalent portion may be brought into contact
with the fLange processing part (edge surface 42) during the pressing.
Either the former or the latter shall be selected depending on the outer
diameter (cross-sectional area) of the fl.ange of the crankshaft.
INDUSTRIAL APPLI CABILITY
lot+zl
The present invention is effrciently utilized in production of a forged
crankshaft to be mounted in a reciprocating engine.
LIST OF REFERENCE SYMBOLS
+1
[or+s]
LI, 2L: forged crankshaft
12,22: billet
13: rolled blank
14: bent blank
15: rough forged blank
L6,26: finish forged blank
23: initial blank
23a: flat portion
23b: open-side surface of web equivalent portion
24:. intermediate blank
25: final blank
30: thtud pair of dies
31: third upper die
3la: first journal processing part
3lb: first pin processing part
3lc: inner surface of front processing portion
31e: inner surface of fl.ange processing portion
32: thfud 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
32e: inner surface of flange processing portion
32f edge surface offlange processing portion
40: first pair of dies
41: first upper die
41a: first journal processing part
41b: first pin processing part
4Lc: flat web processing part
41f clearance
41g: i¡tr"" surface of front processing portion
41i: inner surface of fl.ange processing portion
ii
Ço
42: frrst 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
42fr clearance
42g: i¡tru" surface of front processing portion
42h: edge surface of front processing portion
42i: inner surface of fl.ange processing portion
42j: s¿*. surface of flange processing portion
51: second pair of dies
52: upper plate
53: lower plate
54: hydraulic cylinder
60: second upper die
61: fixed journal die component
62: movable journal die component
6$: pin die component
70: second lower die
71: fixed journal die component
72: movable journal die component
73: pin die component
A, A1 toAS: crank arm
B: flash
J, Jl to Jb: journal
P, Pl ¡o P{: pin
Fr: front part
FI: flange
W Wl to W8: counterweight

We claim:
1. A method for producing a forged crankshaft including journals serving
as a center of rotation, pins decentered from the journals, 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 decreasing sectional areas of portions of a
billet to be formed into the pins and cross-sectional areas of portions of the
billet to be formed into the journals, thereby forming flat portionsi
a second preforming step of pressing an initial blank obtained by the
fi.rst preforming step by a fi.rst pair of dies with a width dirlction of the flat
portions set as a pressing direction to obtain an intermediat