Round die type form rolling apparatus

Details Round die type form rolling apparatus Round die type form rolling apparatus

2001-07-02

2002-07-16

Larson, Lowell A. (Department: 3725)

Metal deforming

With use of control means energized in response to activator...

Metal deforming by use of roller or roller-like tool element

C072S014400, C072S108000

Reexamination Certificate

active

06418767

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a form rolling apparatus for manufacturing screws, gears, shafts, pipes and the like by rolling operations, and more specifically to a round die type form rolling apparatus which clamps a work between a pair of round dies and rolls the work in circumferential and axial directions by rotating the round dies.
2. Description of the Related Art
A conventionally known round die type form rolling apparatus of this kind is shown in FIG.
1
and FIG.
2
. The round die type form rolling apparatus
1
rotates a pair of round dies
2
a
,
2
b
and pushes the rotating round dies symmetrically toward the center of a work
4
by hydraulic mechanisms
3
a
,
3
b
to apply a rolling pressure in the radial direction of the work
4
and thereby roll the work
4
. On a base
5
are installed a pair of slide rails
6
a
,
6
b
, on which are laterally slidably mounted a pair of die moving blocks
7
a
,
7
b
that rotatably support a pair of round dies
2
a
,
2
b
. Fixedly mounted on the base
5
are a pair of pressure plates
8
a
,
8
b
to which the hydraulic mechanisms
3
a
,
3
b
are secured. Front ends of cylinder shafts
9
a
,
9
b
of the hydraulic mechanisms
3
a
,
3
b
are secured to the pair of the die moving blocks
7
a
,
7
b
, respectively. Between the round dies
2
a
,
2
b
is disposed a work support stand
10
that supports the work
4
. During the rolling operation, the hydraulic mechanisms
3
a
,
3
b
are operated to drive a pair of the die moving blocks
7
a
,
7
b
toward each other, while rotating the round dies
2
a
,
2
b
, to form gears and screws.
In the conventional round die type form rolling apparatus
1
described above, however, when the hydraulic mechanisms
3
a
,
3
b
apply rolling pressures to the work
4
, reaction forces P are produced between a pair of the round dies
2
a
,
2
b
as shown in FIG.
2
. The reaction forces P are transmitted to the pressure plates
8
a
,
8
b
, causing the pressure plates
8
a
,
8
b
cantilevered on the base
5
to deflect and open upwardly as shown by two-dotted chain lines in the figure. When the pressure plates
8
a
,
8
b
are open, the cylinder shafts
9
a
,
9
b
are tilted, causing the die moving blocks
7
a
,
7
b
to pivot about their lower portions supported on the slide rails
6
a
,
6
b
and open upwardly as do the pressure plates
8
a
,
8
b
. Hence, the round dies
2
a
,
2
b
escape outwardly upwardly from the work
4
. Therefore, the die moving blocks
7
a
,
7
b
, even when positioned correctly, move away from the work, making it impossible to form threads in the work
4
with high precision or, in the case of a gear, producing errors in a tooth shape of the work.
There is another drawback with the conventional round die type form rolling apparatus. When performing a so-called continuous rolling whereby an elongate work A longer than the widths of the round dies
2
a
,
2
b
is rolled, the conventional rolling process involves manually tilting main shafts
11
a
,
11
b
of the round dies
2
a
,
2
b
, fixing their tilt angles, with lead angles at contact portions between the round dies
2
a
,
2
b
and the work
4
kept aligned with each other, and moving the work
4
in the axial direction. With this method the tilt or inclination angle cannot be changed during the rolling operation, rendering versatile rolling operations on a work impossible.
When forming threads in the work
4
, as the round dies
2
a
,
2
b
are progressively pressed against the work
4
, the diameter of the root of a thread decreases. As a result, the circumferential length of the work.
4
at the root of the thread is shorter at the completion of threading or inscription than at the start of the threading.
FIG. 3
shows the relation between the circumferential length of the work
4
and the pitch. The circumferential length of the work
4
decreases by &dgr;L from the circumferential length L at the start of the threading to the circumferential length L
1
at the completion of the threading. With the conventional round die type form rolling apparatus
1
, however, because the main shafts
11
a
,
11
b
cannot be inclined vertically during rolling operation, the lead angle &bgr; is kept constant even when the thread's root diameter of the work
4
changes. As a result, a deviation in pitch &dgr;P occurs between a pitch P of the work
4
at the start of the threading and a pitch P
1
at the completion of the threading, with the result that the work
4
moves axially by a distance of the pitch deviation &dgr;P during the rolling operation. The phenomenon that the work
4
moves in the axial direction during the rolling operation is called a stepping or walking of the work
4
and this becomes most conspicuous when threads to be formed have a large difference between an external diameter and a root diameter. When the walking occurs, a flank of a screw thread on the same side as the direction of the walking-induced movement of the work
4
contacts the round dies
2
a
,
2
b
with an increased force, whereas a flank on the side opposite the direction of the walking-induced movement of the work
4
contacts the round dies
2
a
,
2
b
with a reduced force, giving rise to a problem of degraded finish precision of the rolled surfaces.
Further, when the work
4
is to be formed with serrations as shown in
FIG. 4
, the process involves bringing the main shafts
11
a
and
11
b
close to each other to slowly push the round dies
2
a
,
2
b
from positions indicated by two-dotted chain line in the figure toward the work
4
. As a result, a root circle that connects roots
4
a
of the work
4
becomes small from a size indicated by two-dotted chain line in the figure to a size indicated by solid line. Because the modules of the round dies
2
a
,
2
b
are constant, as the root circle decreases in size, a large deviation occurs locally between a pitch formed in the work
4
at the start of inscription and a pitch formed in the work
4
at the completion of inscription. In the conventional round die type form rolling apparatus
1
, because a pair of round dies
2
a
,
2
b
are rotated at the same speed by a combination of gears, this local pitch deviation cannot be absorbed, with the result that some tooth surfaces of the work
4
contact the dies with an increased force and other tooth surfaces with a reduced force. This in turn deteriorates the finish precision of the rolled tooth surfaces.
The conventional apparatus has still another problem. When the rolling operation is started, the round dies
2
a
,
2
b
are applied at the work contact surfaces with a force Fp, or a die load, in a direction normal to the dies and a force Ft in a tangential direction Ft. In the conventional round die type form rolling apparatus
1
, because the main shafts
11
a
,
11
b
are controlled to rotate at a constant speed and move under a constant pressure or at a constant speed, both of the die load Fp and a rolling torque T acting on the main shafts
11
a
,
11
b
of the round dies
2
a
,
2
b
change between the start and completion of the rolling operation. The main shaft torque T, in particular, exhibits a temporary sharp increase or peak during the rolling operation. Because the peak of the main shaft torque T has a grave effect on the life of the round dies
2
a
,
2
b
, any increase in the peak value will lead to a reduced die longevity.
SUMMARY OF THE INVENTION
A first object of the present invention is to prevent the round dies from escaping outwardly upwardly due to the reaction force from the work when the work is applied with a rolling pressure.
A second object of the invention is to diversify the rolling operation on the work and to improve the finish precision of rolled surfaces by suppressing the walking of the work during the rolling operation.
A third object of the intention is to improve the finish precision of tooth surfaces when the work is formed with axial grooves such as serrations and splines.
A fourth object of the invention is to prevent a temporary

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