Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
1999-05-07
2001-03-13
Rosenbaum, I Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S888020
Reexamination Certificate
active
06199275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming crank shafts and a method for producing crank shafts, which make it possible to reduce the processing cost and shorten the processing time by decreasing the number of processing steps.
2. Description of the Related Art
Conventionally, the crank shaft to be used as an automobile part has been produced such that a steel material having a columnar configuration, which has been cut into a predetermined length, is subjected to the forging, followed by the cutting processing step.
The steps for producing the crank shaft concerning the conventional technique will be briefly explained below, taking notice of the processing performed for a shaft and a crank pin (referred to as “shaft section”) which constitute the crank shaft.
At first, a steel material, which has been heated to have a red-heated appearance, is subjected to the buster processing and the coarse (preliminary) processing, followed by performing the finishing processing. In the finishing processing, as shown in
FIG. 7
, a first intermediate formed product
7
a
is obtained by means of the forging processing based on the use of an upper die
1
a
and a lower die
1
b
. The upper die
1
a
and the lower die
1
b
comprise recesses
3
a
,
3
b
for forming a space having a substantially columnar configuration with a diameter &phgr;D therebetween when they make nearest approach to one another during the processing, and planar sections
5
a
,
5
b
disposed on both sides of the recesses
3
a
,
3
b
which are opposed to one another while leaving a spacing distance La therebetween.
The first intermediate formed product
7
a
, which is obtained by the finishing processing, has a columnar section
9
having the diameter &phgr;D corresponding to the recesses
3
a
,
3
b
and a burr
11
corresponding to the planar sections
5
a
,
5
b
. The thickness of the burr
11
is La. In this case, the diameter &phgr;D is a value obtained by adding a predetermined machining allowance “a” to a diameter &phgr;d of the shaft section of the crank shaft. That is, there is given &phgr;D=&phgr;d+2×a. The reason why the first intermediate formed product
7
a
is specially formed is that it is intended not to allow the inside of the formed product to be sparse by applying the processing to the steel material which is sufficient to obtain the fluidity of the lump during the forming process.
Subsequently, the trimming processing is performed. In the trimming processing, as shown in
FIG. 8
, the columnar section
9
is stamped out from the first intermediate formed product
7
a
placed on a die
13
a
by using a punch
13
b
to obtain a second intermediate formed product
7
b
. In this case, the width dimension of a hole
15
provided for the die
13
a
has a value obtained by adding a predetermined machining allowance “b” to the diameter &phgr;D, i.e., D+2×b. As shown in
FIG. 9
, the second intermediate formed product
7
b
, which is obtained by the trimming processing, has a shape including a burr
11
having a burr height (with the value “b” as well) which remains on the columnar section
9
corresponding to the machining allowance “b”.
Subsequently, the second intermediate formed product
7
b
is subjected to the restriking to correct the bending of the shaft generated when the respective processing steps are performed as described above.
Subsequently, the cutting processing (lace processing) is performed to obtain a third intermediate formed product (not shown) from which a part of the machining allowance “a” and the burr height “b” have been removed. Subsequently, the soft nitriding treatment (tufftride treatment) or the local high frequency heat treatment is applied thereto, and then the finishing polishing processing is performed. Thus, the remaining portion of the machining allowance “a” is removed to obtain the crank shaft including the shaft section which has the diameter &phgr;d.
In the finishing processing described above, the upper die
1
a
and the lower die
1
b
do not make abutment with each other. That is, the gap of the spacing distance La exists between the upper die
1
a
and the lower die
1
b
. For this reason, it is feared that the thickness of the first intermediate formed product
7
a
may involve any dispersion. Further, it is feared that any deviation may occur between the portion (upper portion) of the first intermediate formed product
7
a
corresponding to the upper die
1
a
and the portion (lower portion) of the first intermediate formed product
7
a
corresponding to the lower die
1
b
, on the basis of the positional deviation between the upper die
1
a
and the lower die
1
b.
When the finishing processing is performed, the steel material is heated to have a red-heated appearance. Further, the processing often brings about an amount of deformation of the steel material. Furthermore, the steel material has a heavy weight, and it has a columnar configuration which is long in the axial direction. Therefore, the steel material undesirably bites into the upper die
1
a
and the lower die
1
b
during the finishing processing. A large force is required to perform the operation (ejecting operation) for removing the steel material (first intermediate formed product
7
a
) from the upper die
1
a
and the lower die
1
b
. As a result, any deformation including, for example, bending of the axis occurs due to the force which is applied to the first intermediate formed product
7
a
during the ejecting operation. That is, there is a possibility that the axis may be bent at the columnar section
9
of the first intermediate formed product
7
a
. Further, a large shearing force is applied to the columnar section
9
when the trimming processing is performed. Therefore, it is feared that the axis of the columnar section
9
may be also bent by the shearing force.
Even when the restriking is effected for the second intermediate formed product
7
b
in which the deformation has occurred as described above, for example, any springback takes place. For this reason, it is impossible to completely correct the deformation. Therefore, in order to obtain the third intermediate formed product having the columnar section
9
in which the cross section is a perfect circle and no bending occurs in the axis, the following procedure is required. That is, it is necessary that the machining allowance “a”, which is provided for the columnar section
9
, is previously set to have a large value while considering the deviation and the bending of the axis generated in the columnar section
9
, and the machining allowance “a” is removed by means of the cutting processing.
Further, the burr
11
having the predetermined burr height “b” remains in the second intermediate formed product
7
b
. Therefore, it is necessary that the cutting processing is performed to remove the burr
11
as well.
As described above, in the process for producing the crank shaft concerning the conventional technique, it is necessary that the machining allowance “a” and the burr
11
, which have been provided to be large, are removed by means of the cutting processing. Therefore, inconveniences arise in that the production cost and the processing time for the crank shaft are increased.
SUMMARY OF THE INVENTION
The present invention relates to a method for forming crank shafts and a method for producing crank shafts in order to dissolve the inconveniences as described above, an object of which is to provide a method for forming crank shafts and a method for producing crank shafts, which make it possible to decrease the number of processing steps so that the production cost is reduced and the production time is shortened for the crank shaft.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.
REFERENCES:
pat
Goitsuka Takashi
Nemoto Kouji
Nozawa Yoshikatsu
Ryu Masahiko
Birch & Stewart Kolasch & Birch, LLP
Cuda Rosenbaum I
Honda Giken Kogyo Kabushiki Kaisha
LandOfFree
Method for forming crank shaft and method for producing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for forming crank shaft and method for producing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for forming crank shaft and method for producing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2436189