Forging die apparatus

Details Forging die apparatus Forging die apparatus

2000-01-20

2001-02-20

Larson, Lowell A. (Department: 3725)

Metal deforming

By use of closed-die and coacting work-forcer

With stripping or ejecting from tool

Reexamination Certificate

active

06189362

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a forging die apparatus for processing a forging material arranged in a cavity formed by a die member so that the forging material is subjected to forging in accordance with a pressurizing action of a punch.
2. Description of the Related Art
A die apparatus has been hitherto known, in which a forging material is inserted into a cavity formed by an upper die and a lower die which are joined to one another, and a pressurizing force is applied to the forging material by the aid of a punch so that the forging material is forged to have a predetermined shape.
A cold forging die suggested by the present applicant is shown in
FIG. 39
(see Japanese Laid-Open Patent Publication No. 7-178493).
The cold forging die
1
comprises a lower die
3
and an upper die
4
which are joined to one another by the aid of a clamping means
2
and which are installed on a die holder
5
. A cavity
7
, which is charged with a forging material
6
, is formed by the lower die
3
and the upper die
4
. A punch
8
is provided to pressurize the forging material
6
charged in the cavity
7
.
A general forging die apparatus including the cold forging die
1
is usually designed, as shown in
FIG. 40
, such that a predetermined clearance A (about 0.1 mm) is provided between the punch
8
for applying the pressurizing force to the forging material
6
and a hole
9
of the upper die
4
into which the punch
8
is inserted. In other words, the hole
9
of the upper die
4
, into which the punch
8
is inserted, has a diameter which is formed to be slightly larger than a diameter of the punch
8
at its portion which is inserted into the hole
9
of the upper die
4
.
In this case, if the clearance A is small, the following inconvenience arises. That is, the punch
8
generates heat as the number of shots is increased. As a result, scuffing occurs on an outer circumferential surface of the punch
8
and on an inner wall surface of the hole
9
of the upper die
4
respectively.
Since the clearance A is provided, the upper die
4
and the lower die
3
are assembled in a state of involving any centering deviation within a range of the clearance A. Further, if any unbalanced load is applied in the lateral direction to the punch
8
during the forging, the pressurizing force is applied to the forging material
6
in a state in which the punch
8
is deviated in the lateral direction within the range of the clearance A.
As described above, the clearance A causes the centering deviation between the punch
8
and the cavity
7
which is formed by the upper and lower dies
4
,
3
. For example, when an outer cup for constructing a constant velocity universal joint is formed by forging, an inconvenience arises in that the axis of a cup of the outer cup is not coincident with the axis of a shaft thereof, i.e., the centering deviation occurs.
In the case of the cold forging die
1
described above, a clearance (not shown) is formed during the forming process at a joining surface (dividing surface)
10
(see
FIG. 40
) between the upper die
4
and the lower die
3
. It is feared that any burr is formed by the plastically deformed forging material
6
which has entered the clearance (not shown).
An unillustrated clearance for assembling is provided at a joined section
11
based on a step section between the upper die
4
and the lower die
3
(see FIG.
39
). As a result, the upper die
4
and the lower die
3
are assembled in a state in which they involve centering deviation within a range of the clearance. Therefore, there is a fear that it is possible to highly accurately maintain the coaxial degree of a product obtained by the forging, for example, the coaxial degree between the shaft and the cup of the outer cup for constructing the constant velocity universal joint.
The present applicant has already suggested a method for cooling a die which makes it possible to greatly enhance the cooling effect and improve the service life of the die (life of the die) (see Japanese Laid-Open Patent Publication No. 61-255737).
That is, as shown in
FIGS. 41 and 42
, the following method has been adopted. A predetermined amount of a lubricant is allowed to flow into a cavity
21
from the top. The lubricant is discharged from the cavity
21
via an outflow groove
23
formed on a knockout pin
22
. After that, air is introduced into the cavity
21
via a passage
24
which communicates with the outflow groove
23
. Thus, the die, which is composed of an upper die
25
and a lower die
26
, is cooled. Reference numeral
27
indicates a billet after being subjected to the forging applied with a pressurizing force by the aid of a punch
28
.
A mechanical press
31
as shown in
FIG. 43
is generally known as a processing machine for allowing the punch to perform reciprocating motion. The mechanical press
31
is composed of a crank press having a crank mechanism, and it comprises frames
33
a
,
33
b
provided vertically on a bolster
32
, a crank shaft
34
rotatably supported by the frames
33
a
,
33
b
, and a ram
36
for performing reciprocating motion in the vertical direction in accordance with the guiding action of the frames
33
a
,
33
b
by the aid of a connecting rod
35
connected to the crank shaft
34
.
A material
38
is arranged on a die member
37
on the upper surface of the bolster
32
. A punch
39
, which is fixed to the ram
36
, performs reciprocating motion in the vertical direction integrally with the ram
36
to apply a pressurizing force to the material
38
. Thus, the material
38
is forged to have a predetermined shape.
In the crank press, the rotary driving force of the motor is transmitted to the crank shaft
34
, and the force is converted into the reciprocating motion of the ram
36
and the punch
39
by the aid of the connecting rod
35
connected to the crank shaft
34
to generate the forming load to be applied to the material
38
.
When the forging is performed by using the well known mechanical press
31
as described above, any elongation occurs, for example, in the frames
33
a
,
33
b
, the connecting rod
35
, and the ram
36
for constructing the mechanical press
31
. For this reason, the bottom dead center of the punch
39
which makes the vertical reciprocating motion is varied. As a result, an inconvenience arises in that any dispersion occurs in the dimension of an obtained forged product in the thickness direction.
For example, when an outer cup for constructing a constant velocity universal joint is formed by forging by using the mechanical press
31
, dispersion occurs in the bottom thickness dimension of a cup of the outer cup due to the influence of the elongation.
Therefore, the conventional technique involves an inconvenience that cutting processing should be applied after the forging in order to obtain a constant bottom thickness dimension of the cup of the outer cup.
If the forming load, which is applied to the material, hugely exceeds a preset value due to the influence of the elongation (if a overloaded forming load is applied), the mechanical press
31
is stopped In a locked state, resulting in an inconvenience that it is impossible to perform continuous forming.
Further, the conventional die apparatus generally adopts a method in which a forged product is taken out by the aid of a knockout pin
43
provided movably back and forth in a hole
42
of a lower die
41
. As shown in
FIG. 44
, a predetermined clearance C is provided between the columnar knockout pin
43
formed to have a substantially identical diameter over its outer circumferential surface and the hole
42
of the lower die
41
for inserting the knockout pin
43
thereinto.
When an outer cup for constructing a constant velocity universal joint is produced by using such a die apparatus, it is necessary to form an unillustrated centering hole at a center of one end of a shaft of the outer cup in order to apply finishing processing such as polishing. In this procedure, the centering hole is formed by mechanical proces

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