DESCRIPTION
TITLE OF MVENTION
METHOD OF MANUFACTURING DIE FORGED CRANKSHAFT
TECHNICAL FIELD
[000l]
The present invention relates to a method of manufacturing a crankshaft product
by hot die forging (hereinafter referred to as a "die forged crankshaft"). In particular,
the present invention relates to a method of manufacturing a die forged crankshaft to be
mounted in a two or more cylinder reciprocating apparatus (e.g., an automotive
reciprocating engine, a reciprocating compressor, and a reciprocating pump).
BACKGROUND ART
[0002]
A crankshaft is a principal component of a reciprocating engine, which produces
power by converting reciprocating motion of pistons to rotary motion. Generally, there
are two types of crankshafts: one that is manufactured by die forging and one that is
manufactured by casting. For engines of automobiles such as passenger cars, freight
cars, and specialized work vehicles, particularly multiple cylinder engines having two or
more cylinders, it is necessary that their crankshafts have high strength and stiffness,
and therefore die forged crankshafts are widely used. For engines of motorcycles,
agricultural machines, and marine vessels, die forged crankshafts are also used.
Further, for reciprocating compressors and reciprocating pumps, in which power
transmission occurs in a reverse direction to that of a reciprocating engine, i.e., rotary
motion is converted to reciprocating motion, die forged crankshafts are also used.
[0003]
In general, as described in Patent Literatures 1 and 2, for example, die forged
crankshafts for use in such reciprocating apparatus are manufactured in the following
manner: a billet having a circular or square cross section and having a constant
cross-sectional area along the entire length is prepared as a starting material, and the
billet is subjected to the steps of preforming, die forging, trimming and coining in order.
The preforming step includes roll forming and bend forging, and the die forging step
includes block forging and finish forging.
[0004]
FIG. 1 is a diagram schematically showing a typical conventional process for
manufacturing a die forged crankshaft. A crankshaft 1 illustrated in FIG. 1 is intended
to be mounted in a 4-cylinder engine. It is a 4-cylinder 8-counterweight crankshaft
that includes: five journals J1 to J5; four crank pins P1 to P4; a front part Fr, a flange F1,
and eight crank arms (hereinafter referred to as "crank arms") A1 to A8 that connect the
journals J1 to J5 and the crank pins PI to P4 to each other, wherein each of the eight
crank arms A1 to A8 has a balance weight. Hereinafter, when the journals J1 to J5, the
crank pins P1 to P4, and the crank arms A1 to A8 are each collectively referred to, a
reference character "J" is used for the journals, a reference character "P" for the crank
pins, and a reference character "A" for the crank arms.
[0005]
In the manufacturing method shown in FIG. 1, a billet 2 shown in FIG. l(a),
which has been previously cut to a predetermined length, is heated by an induction
heater or a gas atmosphere furnace and then is subjected to roll forming. In the roll
forming step, the billet 2 is rolled and reduced in cross-section by grooved rolls, for
example, to distribute its volume in the longitudinal direction, whereby a rolled blank
103, which is an intermediate material, is formed (see FIG. 1 (b)). In the bend forging
step, the rolled blank 103 obtained by roll forming is partially pressed in a press in a
direction perpendicular to the longitudinal direction to distribute its volume, whereby a
bent blank 104, which is a secondary intermediate material, is formed (see FIG. 1 (c)).
[0006]
In the block forging step, the bent blank 104 obtained by bend forging is press
forged with a pair of upper and lower dies, whereby a forged blank 6 having a general
shape of a crankshaft (forged product) is formed (see FIG. l(d)). Furthermore, in the
finish forging step, the block forged blank 6 obtained by block forging is press forged
with a pair of upper and lower dies, whereby a forged blank 7 having a shape that
corresponds to the shape of the crankshaft is formed (see FIG. 1 (e)). In the block
forging and the finish forging, excess material flows out as a flash from between the
parting surfaces of the dies that oppose each other. Thus, the block forged blank 6 and
the finish forged blank 7 include flashes 6% 7a, respectively, around the formed shape of
the crankshaft.
[0007]
In the trimming step, the finish forged blank 7 with the flash 7a, obtained by
finish forging, is held by dies from above and below and the flash 7a is trimmed by a
cutting die. In this manner, a die forged crankshaft 1 is obtained as shown in FIG. I (f).
In the coining step, principal parts of the die forged crankshaft 1, from which the flash
has been removed, e.g., shaft parts such as the journals J, the crank pins P, the front part
Fr, and the flange F1, and in some cases the crank arms A, are slightly pressed with dies
from above and below and formed into a desired size and shape. In this manner, the
die forged crankshaft is manufactured.
[0008]
The manufacturing process shown in FIG. 1 is applicable not only to a 4-cylinder
8-counterweight crankshaft as exemplified, but also to a 4-cylinder 4-counterweight
crankshaft in which, among 8 crank arms A, the leading crank arm Al, the trailing crank
arm A8, and the two central crank arms A4, A5 have balance weights. Also, the same
manufacturing process can be applied to crankshafts that are to be mounted in a
3-cylinder engine, an inline 6-cylinder engine, a V-type 6-cylinder engine, an 8-cylinder
engine, and the like. It is noted that, when adjustment of the placement angle of the
crank pins is necessary, a step of twisting is added after the trimming step.
CITATION LIST
PATENT LITERATURE
[0009]
Patent Literature 1: Japanese Patent Application Publication No. H05-228574
Patent Literature 2: Japanese Patent Application Publication No. H08-24988
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[OO 1 01
Typically, a manufacturing process for a die forged crankshaft includes the steps
of preforming (roll forming and bend forging), die forging (block forging and finish
forging), trimming and coining as described above, and these steps are continuously
performed in an online process. However, in some cases, the preforming step is
eliminated. This is because rolling equipment that is used in the roll forming in the
preforming step is dedicated equipment and has a complex structure on a large scale,
and therefore an enormous cost will be required for the installation and management
thereof. For comparison, the bend forging in the preforming step can be carried out in
pressing equipment in which die forging (block forging and finish forging) is to be
performed.
[OO 1 11
FIG. 2 is a diagram schematically showing a process for manufacturing a die
forged crankshaft in which the preforming step is eliminated. When the preforming
step is eliminated, die forging is carried out by directly block forging the billet 2 having
a constant cross-sectional area along the entire length as shown in FIGS. 2(a) and 2(b).
[OO 121
Typically, the cross-sectional size of a billet to be used (in the case of a round
billet, its diameter, and in the case of a square billet, the length of its side) is determined
based on the maximum cross sectional area of the crankshaft to be manufactured as
defined in a direction perpendicular to the longitudinal direction, i.e., the cross-sectional
area of crank arms having a balance weight (counterweight). Thus, if the preforming
step is eliminated in manufacturing a crankshaft, the material utilization is extremely
reduced at portions to be formed into opposite end portions having small cross-sectional
areas in the crankshaft, i.e., the front part, the flange, and the journals located adjacent
thereto.
[00 131
Furthermore, actual billets come in cross-sectional sizes that have been grouped
into several classes. Thus, in the case of manufacturing a crankshaft without the
preforming step, if an ideal billet cross-sectional size, which is determined based on the
maximum cross-sectional area of the crankshaft to be manufactured, falls in between
classes, it becomes necessary to use a billet of a class of a cross-sectional size greater
than the ideal cross-sectional size. For example, assuming that a round billet is used, if
an available size class that is next larger than a size class of 90 mm diameter is a size
class of 95 mm diameter while the ideal cross-sectional size is 93 mm in diameter,
which is in between the available size classes, it becomes necessary to employ a billet of
the size class of 95 mm diameter, which is greater than the ideal cross-sectional size.
This will result in further reducing the material utilization.
[OO 1 41
Furthermore, crankshafts are provided in different sizes and shapes depending on
the type of engine. Thus, the billet cross-sectional size is varied in accordance with the
size and shape of each crankshaft to be manufactured, and thus is in a wide variety from
a small one to a large one. Moreover, when an induction heater is used to heat the
billet, it is necessary to prepare and install, each time, an electromagnetic coil of a
suitable size in accordance with the cross-sectional size of the billet to be used.
[00 151
The present invention has been made in view of the foregoing problems.
Accordingly, it is an object of the present invention to provide a method of
manufacturing a die forged crankshaft for use in a multiple cylinder reciprocating
apparatus whereby it is possible to improve the material utilization and to use a billet
having a cross-sectional size as small as possible.
SOLUTION TO PROBLEM
[00 161
In order to achieve the above object, the present inventors turned their attention
to the step of forming a blank, which affects the material utilization, among the steps for
manufacturing a die forged crankshaft, and they conducted intensive studies thereon.
Consequently, they have found that it is advantageous to perform an upsetting operation,
prior to die forging (block forging and finish forging), to upset a billet in the
longitudinal direction to prepare a blank having the following configuration (hereinafter
also referred to as an "upset blank"): at opposite end portions, i.e. portions to be formed
into a front part, a flange and journals located adjacent thereto of a crankshaft, the
cross-sectional size of the billet is maintained, while, at the remaining intermediate
region, i.e., at the region between a portion to be formed into a leading crank arm of the
crankshaft and a portion to be formed into a trailing crank arm thereof, the
cross-sectional area is enlarged, and to die forge such an upset blank.
[OO 171
The present invention has been accomplished based on this finding, and the
summaries thereof are set forth below as to a method of manufacturing a die forged
crankshaft. That is, there is provided a method of manufacturing a die forged
crankshaft to be mounted in a multiple cylinder reciprocating apparatus, the method
comprising: an upsetting step that includes upsetting a billet having a constant
cross-sectional area along an entire length thereof to form a blank having an enlarged
cross-sectional area at a region between a portion to be formed into a leading crank arm
of the crankshaft and a portion to be formed into a trailing crank arm of the crankshaft;
a die forging step that includes die forging the blank formed in the upsetting step to
form a forged blank having a shape of the crankshaft with a flash; and a trimming step
that includes trimming the flash from the forged blank formed in the die forging step.
[00 181
This method of manufacturing a die forged crankshaft is useful when the
crankshaft is intended for use in a multiple cylinder engine having two or more
cylinders. When the crankshaft includes a disc-shaped crank arm that is coaxial with
the central axis of itself, the upsetting step may be performed in such a manner that the
blank has a portion to be formed into the disc-shaped crank arm, the portion having a
further enlarged cross sectional area.
[OO 191
These methods of manufacturing a die forged crankshaft may include a
preforming step prior to the die forging step, the preforming step including: partially
pressing the blank in accordance with the shape of the crankshaft and distributing the
volume of the blank at least in a longitudinal direction thereof, of the longitudinal
direction and a direction perpendicular to the longitudinal direction.
ADVANTAGEOUS EFFECTS OF INVENTION
[0020]
According to a method of manufacturing a die forged crankshaft of the present
invention, an upsetting operation is applied to a billet having a cross-sectional size
smaller than an ideal cross-sectional size that is determined based on the maximum
cross-sectional area of a crankshaft to be manufactured, and with this, it is possible to
form an upset blank having an ideally enlarged cross-sectional area at an intermediate
region including portions which will become portions of the maximum cross-sectional
area in the crankshaft to be manufactured, while having cross-sectional areas maintained
to be small at the opposite end portions, which will become portions of small
cross-sectional areas in the crankshaft to be manufactured. Since die forging is applied
to such an upset blank, it is possible to improve the material utilization along the entire
length of the crankshaft and also to use a billet having a cross-sectional size as small as
possible.
BRIEF DESCRIPTION OF DRAWINGS
[002 11
[FIG. 11 FIG. 1 is a diagram schematically showing a typical conventional
process for manufacturing a die forged crankshaft.
[FIG. 21 FIG. 2 is a diagram schematically showing a process for manufacturing a
die forged crankshaft in which the preforming step is eliminated.
[FIG. 31 FIG. 3 is a diagram schematically showing an exemplary process for
manufacturing a die forged crankshaft according to a method of the present invention.
[FIG. 41 FIG. 4 is a diagram schematically showing the shapes of an upset blank
and a crankshaft in the case of manufacturing a die forged crankshaft having a
disc-shaped crank arm.
[FIG. 51 FIG. 5 is a diagram schematically showing a variation of the process for
manufacturing a die forged crankshaft according to a method of the present invention.
[FIG. 61 FIG. 6 is a diagram schematically showing an exemplary upsetting
operation in a method of manufacturing a die forged crankshaft according to the present
invention.
[FIG. 71 FIG. 7 is a diagram schematically showing another example of an
upsetting operation in a method of manufacturing a die forged crankshaft according to
the present invention.
DESCRIPTION OF EMBODIMENTS
[0022]
Hereinafter, embodiments of the method of manufacturing a die forged crankshaft
of the present invention are described in detail.
[0023]
FIG. 3 is a diagram schematically showing an exemplary process for
manufacturing a die forged crankshaft according to a method of the present invention.
The crankshaft illustrated in FIG. 3 is a 4-cylinder 8-counterweight crankshaft. The
manufacturing process therefor includes the steps of upsetting, die forging (block
forging and finish forging), trimming and coining, using as a starting material a billet 2
having a circular or square cross section and having a constant cross-sectional area
along the entire length.
[0024]
In the method of manufacturing a die forged crankshaft of the present invention, a
billet 2 shown in FIG. 3(a), which has been previously cut to a predetermined length, is
heated by an induction heater or a gas atmosphere furnace, and then an upsetting
operation is performed on the billet. In the upsetting step, as detailed later, an
upsetting operation is performed to upset the billet 2 in the longitudinal direction,
whereby a blank 3, which is an intermediate material, is formed (see FIG. 3(b)). This
upset blank 3 has such a configuration that: at opposite end portions, i.e. portions to be
formed into a front part Fr, a flange F1 and journals J1, J5 located adjacent thereto of the
crankshaft 1, the cross-sectional size of the billet 2 is maintained to the extent possible,
while, at the remaining intermediate region, i.e., at the region between a portion to be
formed into a leading crank arm A1 of the crankshaft 1 and a portion to be formed into a
trailing crank arm A8 thereof, the cross-sectional area is enlarged.
[0025]
The enlargement of the cross-sectional area of the intermediate region in the
upset blank 3 is carried out by the upsetting operation in such a manner that the
cross-sectional area necessary for the crank arms A is ensured in the crankshaft 1 to be
manufactured.
[0026]
In the block forging step, the upset blank 3 obtained by the upsetting operation is
press forged with a pair of upper and lower dies, whereby a forged blank 6 with a flash
6a having a general shape of the crankshaft (forged product) is formed (see FIG. 3(c)).
Furthermore, in the finish forging step, the block forged blank 6 obtained by block
forging is press forged with a pair of upper and lower dies, whereby a forged blank 7
with a flash 7a having a shape that corresponds to the shape of the crankshaft is formed
(see FIG. 3(d)).
[0027]
In the trimming step, the finish forged blank 7 with the flash 7% obtained by
finish forging, is held by dies from above and below and the flash 7a is trimmed by a
cutting die. In this manner, a die forged crankshaft 1 as shown in FIG. 3(e) is obtained.
In the coining step, principal parts of the die forged crankshaft 1 from which the flash
has been removed are slightly pressed with dies from above and below, so that it is
formed into a desired size and shape. In this manner, the die forged crankshaft is
manufactured.
[0028]
Such a method of manufacturing a die forged crankshaft of the present invention
is capable of achieving the following. For example, assuming that a round billet is
used and an available size class that is next larger than a size class of 90 mm diameter is
a size class of 95 mm diameter, even if an ideal cross-sectional size that is determined
based on the maximum cross-sectional area of a crankshaft to be manufactured is 93
mm in diameter, which falls in between the available size classes, a billet of the smaller
size class of 90 mm diameter can be employed or a billet of an even smaller size class of
85 mm diameter can be employed because an upsetting operation is applied to such a
billet having a smaller cross-sectional size, which makes it possible to form an upset
blank having an ideally enlarged cross-sectional area at an intermediate region including
portions which will become portions of the maximum cross-sectional area in the
crankshaft to be manufactured, while having cross-sectional areas maintained to be
small at the opposite end portions, which will become portions of small cross-sectional
areas in the crankshaft to be manufactured. Since die forging is applied to such an
upset blank, it is possible to improve the material utilization along the entire length of
the crankshaft.
[0029]
Also, the cross-sectional size of the billet to be used is not restricted by the
maximum cross-sectional area of the crankshaft to be manufactured, and therefore it is
possible to use a billet having a size as small as possible. Thus, when an induction
heater is used to heat the billet, the electromagnetic coil to be installed can also be as
small as possible.
[0030]
The manufacturing process shown in FIG. 3 is applicable not only to a 4-cylinder
8-counterweight crankshaft as exemplified, but also to a 4-cylinder 4-counterweight
crankshaft and moreover crankshafts that are to be mounted in a 3-cylinder engine, an
inline 6-cylinder engine, a V-type 6-cylinder engine, an 8-cylinder engine, and the like.
Further, the manufacturing process is applicable to manufacturing of crankshafts not
only for automotive engines but also of those to be mounted in a variety of reciprocating
apparatus such as engines of motorcycles, agricultural machines, and marine vessels,
and also reciprocating compressors and reciprocating pumps. It is noted that, when
adjustment of the placement angle of the crank pins is necessary, a step of misting is
added after the trimming step.
[003 11
The method of manufacturing a die forged crankshaft of the present invention is
useful when the crankshaft is intended for use in a multiple cylinder engine having two
or more cylinders. Also, the method of manufacturing a die forged crankshaft of the
present invention is suitable when a round billet is used. This is because, with a round
billet, enlargement of the cross-sectional area can be achieved more steadily during the
upsetting operation than with a square billet.
[0032]
It is to be noted that automotive engines sometimes include a balance shaft in
order to prevent vibration and noise. A balance shaft is driven by a ring gear mounted
on one of crank arms of a crankshaft. In such a case, the crankshaft includes a
disc-shaped crank arm that is coaxial with the central axis of itself for attachment of a
ring gear. This disc-shaped crank arm is much larger than the other crank arms, and
has the largest cross-sectional area among the components of the crankshaft.
[0033]
In the case of manufacturing such a die forged crankshaft having a disc-shaped
crank arm, the manufacturing process shown in FIG. 3 is again applicable. In this case,
however, the upsetting step of the manufacturing process may be performed in such a
manner that the cross-sectional area of the intermediate region of the upset blank is
further enlarged at a portion to be formed into the disc-shaped crank arm.
[0034]
FIG. 4 is a diagram schematically showing the shapes of an upset blank and a
crankshaft in the case of manufacturing a die forged crankshaft having a disc-shaped
crank arm. In the crankshaft 1 illustrated in FIG. 4, the crank arm A2, which is the
second from the leading crank arm, is disc-shaped. The upset blank 3 which is to be
used in die forging of this crankshaft 1 has such a configuration, obtained by upsetting a
billet, that: at opposite end portions, the cross-sectional size of the billet is maintained,
while, at the intermediate region between a portion to be formed into a leading crank
arm A1 of the crankshaft 1 and a portion to be formed into a trailing crank arm A8
thereof, the cross-sectional area is enlarged, and moreover, at a portion, in the
intermediate region, to be formed into the disc-shaped crank arm A2, the cross-sectional
area is further enlarged. That is, the upset blank 3 in this case has two stages of
enlarged cross sectional areas.
[0035]
In the upset blank 3, the cross-sectional area of the portion to be formed into the
disc-shaped crank arm A2 is configured so that the cross-sectional area necessary for the
disc-shaped crank arm A2 is ensured in the crankshaft 1 to be manufactured. The
cross-sectional area of the remaining intermediate region of the upset blank 3 is
configured so that the cross-sectional area necessary for the crank arms A other than the
disc-shaped crank arm A2 is ensured.
[0036]
When die forging is applied to such an upset blank 3, it is possible to manufacture
a crankshaft with an improved material utilization along the entire length even if it is a
crankshaft having a disc-shaped crank arm A2.
[0037]
As described above, the manufacturing process shown in FIG. 3 is applicable to
manufacturing of die forged crankshafts to be mounted in a variety of automotive
engines. However, in the case of crankshafts including oval-shaped crank arms
without a balance weight, e.g., a 4-cylinder 4-counterweight crankshaft, a crankshaft
that is to be mounted in a V-type 6-cylinder engine, and the like, since such oval-shaped
crank arms have a small cross-sectional area, the manufacturing process shown in FIG.
3 is not sufficient to improve the material utilization at portions to be formed into the
oval-shaped crank arms. To address this, in the manufacturing process shown in FIG.
3, preforming for further deforming the upset blank may be carried out prior to die
forging depending on the shape of the crankshaft to be manufactured.
[003 81
FIG. 5 is a diagram schematically showing a variation of the process for
manufacturing a die forged crankshaft according to a method of the present invention.
The crankshaft 1 illustrated in FIG. 5 is a 4-cylinder 4-counterweight crankshaft in
which the second, third, sixth, and seventh crank arms A from the leading crank arm are
oval-shaped (see FIG. 5(g)). The manufacturing process for this crankshaft 1 includes
the steps of upsetting, preforming, die forging (block forging and finish forging),
trimming and coining. That is, a preforming step is incorporated between the upsetting
step and the die forging step in the manufacturing process shown in FIG. 3. The
preforming step includes a first preforming step and a second preforming step.
[0039]
In the first preforming step, using the pressing equipment in which the die
forging is to be performed, the upset blank 3 shown in FIG. 5(b) obtained by the
upsetting operation is partially pressed in the press in a direction perpendicular to the
longitudinal direction, so that its volume is distributed in the longitudinal direction (see
FIG. 5(c)). This pressing is applied to portions to be formed into oval-shaped crank
arms A of the crankshaft.
[0040]
In the subsequent second preforming step, using again the pressing equipment in
which the die forging is to be performed, the upset blank 4 shown in FIG. 5(c) obtained
by the first preforming step is partially pressed in the press in a direction perpendicular
to the longitudinal direction in a state where it has been rotated by 90" about its central
axis, so that its volume is distributed in the longitudinal direction and in the direction
perpendicular to the longitudinal direction (see FIG. 5(d)). This pressing corresponds
to the bend forging shown in FIG. l(c).
[0041]
Then, the upset blank 5 shown in FIG. 5(d) obtained by the second preforming
step is subjected to die forging.
[0042]
According to such a manufacturing method that is implemented by the
manufacturing process shown in FIG. 5, the cross-sectional area of the upset blank 5
can be reduced, in accordance with the shape of the crankshaft 1 to be manufactured, at
portions which will become portions of small cross-sectional areas in the crankshaft 1,
e.g., at portions to be formed into oval-shaped crank arms A, and therefore it is possible
to sufficiently improve the material utilization at such portions too.
[0043]
FIG. 6 is a diagram schematically showing an exemplary upsetting operation in a
method of manufacturing a die forged crankshaft according to the present invention.
The upsetting operation illustrated in FIG. 6 is intended to form the upset blank 3 shown
in FIG. 3 having a region at which the cross-sectional area is uniformly enlarged.
[0044]
When dedicated pressing equipment is used for the upsetting operation, examples
of pressing equipment that is employable include a screw press, a hydraulic press, and a
crank press. It is to be noted, though, that the upsetting operation is an operation for
compressing a long billet in the longitudinal direction and it is performed in series with
other steps in an online process, and therefore that the pressing equipment must be
operable at high speed and have a longer stroke.
[0045]
As shown in FIG. 6, the pressing equipment that is used for the upsetting
operation includes a lower die 12 supported by a stationary pressure pad 11 which
serves as a base and an upper die 22 supported by a pressure pad 21 which is movable
in the vertical direction. The lower die 12 and the upper die 22 have die cavities 13, 23,
respectively, which oppose each other.
[0046]
The die cavity 13 of the lower die 12 is a stepped cavity having a bottom-side
cavity portion and an opening-side cavity portion. The cross section of the
bottom-side cavity portion of the die cavity 13 in the lower die 12 corresponds to the
cross-sectional shape of the billet 2, and the cross section of the opening-side cavity
portion corresponds to the cross-sectional shape of the intermediate region of a desired
upset blank 3. On the other hand, the die cavity 23 of the upper die 22 is a simple
opening having a cross section that corresponds to the cross-sectional shape of the billet
2. Strictly speaking, both the die cavities 13,23 are configured such that their
diameters slightly increase toward the opening sides. This is intended to avoid
difficulties in inserting the billet 2 and removing the upset blank 3.
[0047]
As shown in FIG. 6(a), in the upsetting operation, the billet 2 is inserted into the
die cavity 13 of the lower die 12, and one end portion 2a of the billet 2 is restrained by
the bottom-side cavity portion of the die cavity 13. Then, as shown in FIG. 6(b), when
the upper die 22 is lowered, the other end portion 2b of the billet 2 is received by the die
cavity 23 of the upper die 22, and the other end portion 2b of the billet 2 is restrained by
the die cavity 23. As the upper die 22 is further lowered, the region of the billet 2
excluding both end portions 2% 2b, which are restrained, is compressed in the
longitudinal direction, and accordingly enlarged in a direction perpendicular to the
longitudinal direction.
[0048]
In this operation, with the adjustment of the bottom dead center of the upper die
22, the finished amount of enlargement of the billet 2 and the final length of the
enlarged portion are determined. It is noted, however, that the amount of enlargement
of the billet 2 is also restricted by contact with the opening-side cavity portion of the die
cavity 13 of the lower die 12. In this manner, it is possible to form the upset blank 3 in
which, at opposite end portions, the cross-sectional size of the billet 2 is maintained, and,
at the intermediate region excluding the opposite end portions, the cross-sectional area
is uniformly enlarged, as shown in FIG. 6(c).
[0049]
FIG. 7 is a diagram schematically showing another example of an upsetting
operation in a method of manufacturing a die forged crankshaft according to the present
invention. The upsetting operation illustrated in FIG. 7 is intended to form the upset
blank 3 shown in FIG. 4 having two stages of enlarged cross sectional areas.
[OOSO]
The upsetting operation shown in FIG. 7 differs from the upsetting operation
shown in FIG. 6 in that the die cavity 23 of the upper die 22 is also a stepped cavity
having a bottom-side cavity portion and an opening-side cavity portion similarly to the
die cavity 13 of the lower die 12. In this case, as shown in FIG. 7(b), one end portion
2a of the billet 2 is restrained by the bottom-side cavity portion of the die cavity 13 of
the lower die 12 and the other end portion 2b of the billet 2 is restrained by the
bottom-side cavity portion of the die cavity 23 of the upper die 22, and in this state, as
the upper die 22 is hrther lowered, the region of the billet 2 excluding both the end
portions 2% 2b, which are restrained, is compressed in the longitudinal direction and
accordingly enlarged.
[OOS 11
In this operation, the amount of enlargement of the billet 2 is restricted, first by
contact with the opening-side cavity portion of the die cavity 13 of the lower die 12 and
contact with the opening-side cavity portion of the die cavity 23 of the upper die 22.
Then, with the adjustment of the bottom dead center of the upper die 22, the billet 2
expands fiom between the parting surfaces of the lower die 12 and the upper die 22 that
oppose each other, and the finished amount of enlargement of the portion and the final
length of the enlarged portion are determined while, at the same time, the final length of
the enlarged portion as a whole is determined. In this manner, it is possible to form the
upset blank 3 in which, at opposite end portions, the cross-sectional size of the billet 2 is
maintained, and, at the intermediate region excluding the opposite end portions, the
cross-sectional area is enlarged in two stages, as shown in FIG. 7(c).
[0052]
An issue to be addressed regarding the upsetting operation described in the above
is buckling of the billet. This is because, in the method of manufacturing a die forged
crankshaft of the present invention, a long billet is subjected to an enlargement
operation over a wide range in the longitudinal direction, and therefore there is a
concern that buckling thereof might occur. If buckling occurs, it is impossible to
obtain an upset blank having a desired shape and size. Therefore, it is preferred that
experiments are conducted under various conditions in advance, and that, for example,
when a round billet is used, threshold conditions for the occurrence of buckling are
ascertained from the relationship between the diameter expansion ratio "DO/D1"
represented by the ratio of the diameter Do of the billet to the diameter Dl of the
enlarged portion after the upsetting operation and the slenderness ratio "LdDoM
represented by the ratio of the free length Lf of the billet to the diameter Do of the billet,
as shown in FIG. 6, and that the conditions for the upsetting operation are specified
based on the relationship.
[0053]
The present invention is not limited to the embodiments described above, and
various modifications may be made without departing from the spirit and scope of the
present invention. For example, the configuration of the upset blank is not limited to
one having an intermediate region that is uniformly enlarged in cross-sectional area, but
may be one having an intermediate region that is gradually enlarged in cross-sectional
area.
INDUSTRIAL APPLICABILITY
[0054]
The present invention is capable of being effectively utilized in manufacturing a
die forged crankshaft to be mounted in a two or more cylinder reciprocating apparatus,
particularly in manufacturing a die forged crankshaft to be mounted in a multiple
cylinder engine for automobiles.
REFERENCE SIGNS LIST
[0055]
1: die forged crankshaft, J1 to J5: journals
P1 to P4: crank pins, Fr: front part, F1: flange
A1 to AS: crank arms, 2: billet,
2a: one end portion, 2b: the other end portion, 3,4, 5: upset blank,
6: block forged blank, 6a: flash,
7: finish forged blank, 7a: flash,
11 : pressure pad, 12: lower die, 13: die cavity,
21: pressure pad, 22: upper die, 23: die cavity
We claim:
1. A method of manufacturing a die forged crankshaft to be mounted in an at least
two cylinder reciprocating apparatus, characterized in that the method comprises:
an upsetting step that includes upsetting a billet having a constant cross-sectional
area along an entire length thereof to fonn a blank having an enlarged cross-sectional
area at a region between a portion to be fonned into a leading crank arm of the
crankshaft and a portion to be formed into a trailing crank arm of the crankshaft;
a die forging step that includes die forging the blank fonned in the upsetting step
to form a forged blank having a shape of the crankshaft with a flash; and
a trimming step that includes trimming the flash fiom the forged blank fonned in
the die forging step.
The method of manufacturing a die forged crankshaft according to claim 1,
characterized in that the crankshaft includes a disc-shaped crank arm that is
coaxial with the central axis of the crankshaft, and,
the upsetting step is performed in such a manner that the blank has a portion to be
formed into the disc-shaped crank arm, the portion having a further enlarged cross
sectional area.
3. The method of manufacturing a die forged crankshaft according to claiin 1 or 2,
characterized in that the method further comprises:
a preforming step prior to the die forging step, the preforming step including:
partially pressing the blank in accordance with the shape of the crankshaft and
distributing a volume of the blank at least in a longitudinal direction thereof, of the
longitudinal direction and a direction perpendicular to the longitudinal direction.