U.S. patent application number 09/895313 was filed with the patent office on 2001-11-15 for round die type form rolling apparatus.
This patent application is currently assigned to NISSEI CO., LTD.. Invention is credited to Amano, Shuichi, Nakata, Katsuyuki, Okino, Hiroshi, Shinbutsu, Toshinaka, Yoshikawa, Hiroshi, Yoshizawa, Minoru.
Application Number | 20010039820 09/895313 |
Document ID | / |
Family ID | 27467756 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010039820 |
Kind Code |
A1 |
Shinbutsu, Toshinaka ; et
al. |
November 15, 2001 |
Round die type form rolling apparatus
Abstract
A round die type form rolling apparatus comprises: a pair of die
moving blocks 15a, 15b rotatably supporting a pair of round dies
12a, 12b; four beam shafts 19 disposed around the rolling position
of a work 33 being rolled by the round dies 12a, 12b and extending
between the pair of die moving blocks 15a, 15b; and a push
mechanism 20 for moving the pair of die moving blocks 15a, 15b
toward each other. The die moving blocks 15a, 15b are moved, guided
by the beam shafts 19, toward each other and the reaction forces
generated between a pair of the round dies 12a, 12b by the rolling
pressure are shared by the beam shafts 19 to prevent the round dies
from escaping outwardly upwardly due to the reaction force from the
work that is generated when the rolling pressure is applied to the
work. This arrangement improves the machining precision of the
work.
Inventors: |
Shinbutsu, Toshinaka;
(Ohtsuki-shi, JP) ; Yoshizawa, Minoru;
(Ohtsuki-shi, JP) ; Amano, Shuichi; (Ohtsuki-shi,
JP) ; Nakata, Katsuyuki; (Tokyo, JP) ;
Yoshikawa, Hiroshi; (Tokyo, JP) ; Okino, Hiroshi;
(Tokyo, JP) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Assignee: |
NISSEI CO., LTD.
Ohtsuki-shi
JP
|
Family ID: |
27467756 |
Appl. No.: |
09/895313 |
Filed: |
July 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09895313 |
Jul 2, 2001 |
|
|
|
09280005 |
Mar 29, 1999 |
|
|
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Current U.S.
Class: |
72/108 |
Current CPC
Class: |
B21H 1/00 20130101 |
Class at
Publication: |
72/108 |
International
Class: |
B21D 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 1998 |
JP |
10-90288 |
Apr 2, 1998 |
JP |
10-90301 |
Apr 2, 1998 |
JP |
10-90305 |
Apr 2, 1998 |
JP |
10-90308 |
Claims
32. A round die type form rolling apparatus comprising: +P1 a base;
+P1 a first die moving block mounted an one end portion of the
base; +P1 a pressure plate mounted on the other end portion of the
base; +P1 two or more beam shafts disposed around a rolling
position of a work and having both ends thereof mounted to the
first die moving block and the pressure plate; +P1 a second die
moving block disposed between the first die moving block and the
pressure plate and guided by the beam shafts; +P1 a die push
mechanism disposed between the second die moving block and the
pressure plate; +P1 a first round die and a second round die
rotatably supported on the first die moving block and the second
die moving block, respectively; and +P1 a pinion mounted on the
base between the second die moving block and the pressure plate and
a pair of racks meshing with the pinion being secured to the
pressure plate; +P1 wherein at least one of the first die moving
block, the pressure plate and the second die moving block is
rigidly fixed on the base, with the others slidably disposed, and
the die push mechanism is operated to move the first die moving
block and the second die moving block toward each other to roll the
work between the first round die and the second round die.
33. A round die type form rolling apparatus comprising: a base; a
first die moving block mounted on one end portion of the base so
that it is slidable to left and right; a pressure plate mounted on
the other end portion of the base so that it is slidable to left
and right; two or more beam shafts disposed around a rolling
position of a work and having both ends thereof secured to the
first die moving block and the pressure plate; a second die moving
block disposed between the first die moving block and the pressure
plate and guided by the beam shafts to slide on the base to left
and right; a die push mechanism disposed between the second die
moving block and the pressure plate; a first round die and a second
round die rotatably supported on the first die moving block and the
second die moving block, respectively; a pair of slide rails are
fixedly mounted an the base; the first die moving block, the
pressure plate and the second die moving block am slidably mounted
on the slide rails; and a pinion mounted on the base between the
second die moving block and the pressure plate, and one of a pair
of racks meshing with the pinion being secured to the pressure
plate; wherein the die push mechanism is operated to slide the
second die moving block guided by the beam shafts toward the
rolling position, the pressure plate is slid the same distance in
the opposite direction to cause the first die moving block through
the beam shafts to slide the same distance toward the rolling
position to roll the work between the first round die and the
second round die that are disposed close to each other.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] 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 2a, 2b and pushes
the rotating round dies symmetrically toward the center of a work 4
by hydraulic mechanisms 3a, 3b 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 6a, 6b, on which are
laterally slidably mounted a pair of die moving blocks 7a, 7b that
rotatably support a pair of round dies 2a, 2b. Fixedly mounted on
the base 5 are a pair of pressure plates 8a, 8b to which the
hydraulic mechanisms 3a, 3b are secured. Front ends of cylinder
shafts 9a, 9b of the hydraulic mechanisms 3a, 3b are secured to the
pair of the die moving blocks 7a, 7b, respectively. Between the
round dies 2a, 2b is disposed a work support stand 10 that supports
the work 4. During the rolling operation, the hydraulic mechanisms
3a, 3b are operated to drive a pair of the die moving blocks 7a, 7b
toward each other, while rotating the round dies 2a, 2b, to form
gears and screws.
[0005] In the conventional round die type form rolling apparatus 1
described above, however, when the hydraulic mechanisms 3a, 3b
apply rolling pressures to the work 4, reaction forces P are
produced between a pair of the round dies 2a, 2b as shown in FIG.
2. The reaction forces P are transmitted to the pressure plates 8a,
8b, causing the pressure plates 8a, 8b cantilevered on the base 5
to deflect and open upwardly as shown by two-dotted chain lines in
the figure. When the pressure plates 8a, 8b are open, the cylinder
shafts 9a, 9b are tilted, causing the die moving blocks 7a, 7b to
pivot about their lower portions supported on the slide rails 6a,
6b and open upwardly as do the pressure plates 8a, 8b. Hence, the
round dies 2a, 2b escape outwardly upwardly from the work 4.
Therefore, the die moving blocks 7a, 7b, 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.
[0006] There is another drawback with the conventional round die
type form rolling apparatus. When performing a so-called continuous
rolling whereby an elongate work 4 longer than the widths of the
round dies 2a, 2b is rolled, the conventional rolling process
involves manually tilting main shafts 11a, 11b of the round dies
2a, 2b, fixing their tilt angles, with lead angles at contact
portions between the round dies 2a, 2b 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.
[0007] When forming threads in the work 4, as the round dies 2a, 2b
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 .delta.L from the circumferential length L
at the start of the threading to the circumferential length L1 at
the completion of the threading. With the conventional round die
type form rolling apparatus 1, however, because the main shafts
11a, 11b cannot be inclined vertically during rolling operation,
the lead angle .beta. is kept constant even when the thread's root
diameter of the work 4 changes. As a result, a deviation in pitch
.delta.P occurs between a pitch P of the work 4 at the start of the
threading and a pitch P1 at the completion of the threading, with
the result that the work 4 moves axially by a distance of the pitch
deviation .delta.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 2a, 2b 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 2a, 2b with a
reduced force, giving rise to a problem of degraded finish
precision of the rolled surfaces.
[0008] Further, when the work 4 is to be formed with serrations as
shown in FIG. 4, the process involves bringing the main shafts 11a
and 11b close to each other to slowly push the round dies 2a, 2b
from positions indicated by two-dotted chain line in the figure
toward the work 4. As a result, a root circle that connects roots
4a 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 2a, 2b 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 2a, 2b 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.
[0009] The conventional apparatus has still another problem, When
the rolling operation is started, the round dies 2a, 2b 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 11a, 11b 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 11a, 11b of the round dies 2a, 2b 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 2a,
2b, any increase in the peak value will lead to a reduced die
longevity.
SUMMARY OF THE INVENTION
[0010] 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.
[0011] 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.
[0012] A third object of the invention is to improve the finish
precision of tooth surfaces when the work is formed with axial
grooves such as serrations and splines.
[0013] A fourth object of the invention is to prevent a temporary
increase in the machining torques acting on the main shafts of the
round dies during the rolling operation to extend the longevity of
the dies and improve the efficiency of the rolling operation.
[0014] To achieve the above objectives, a round die type form
rolling apparatus according to the invention comprises: a set of
die moving blocks rotatably supporting a set of round dies; two or
more beam shafts disposed around a rolling position of a work being
rolled by the round dies and extending between the set of die
moving blocks; and a push mechanism for moving the set of die
moving blocks toward each other; wherein the die moving blocks are
moved, guided by the beam shafts, toward each other and reaction
forces generated between the set of round dies by a rolling
pressure are borne by the beam shafts.
[0015] A round die type form rolling apparatus according to another
aspect of the invention comprises: a base; a first die moving block
mounted on one end portion of the base; a pressure plate mounted on
the other end portion of the base; two or more beam shafts disposed
around a rolling position of a work and having both ends thereof
mounted to the first die moving block and the pressure plate; a
second die moving block disposed between the first die moving block
and the pressure plate and guided by the beam shafts; a die push
mechanism disposed between the second die moving block and the
pressure plate; and a first round die and a second round die
rotatably supported on the first die moving block and the second
die moving block, respectively; wherein at least one of the first
die moving block, the pressure plate and the second die moving
block is rigidly fixed on the base, with the others slidably
disposed, and the die push mechanism is operated to move the first
die moving block and the second die moving block toward each other
to roll the work between the first round die and the second round
die.
[0016] A round die type form rolling apparatus according to still
another aspect of the invention comprises: a base; a first die
moving block mounted on one end portion of the base so that it is
slidable to left and right; a pressure plate mounted on the other
end portion of the base so that it is slidable to left and right;
two or more beam shafts disposed around a rolling position of a
work and having both ends thereof secured to the first die moving
block and the pressure plate; a second die moving block disposed
between the first die moving block and the pressure plate and
guided by the beam shafts to slide on the base to left and right; a
die push mechanism disposed between the second die moving block and
the pressure plate; and a first round die and a second round die
rotatably supported on the first die moving block and the second
die moving block, respectively; wherein the die push mechanism is
operated to slide the second die moving block guided by the beam
shafts toward the rolling position, the pressure plate is slid the
same distance in the opposite direction to cause the first die
moving block through the beam shafts to slide the same distance
toward the rolling position to roll the work between the first
round die and the second round die that are disposed close to each
other.
[0017] A round die type form rolling apparatus according to still
another aspect of the invention is characterized in that three or
four of the beam shafts are arranged in good balance around the
rolling position of the work.
[0018] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that a pinion
is mounted on the base and that one of a pair of racks meshing with
the pinion is secured to either the first die moving block or the
pressure plate and the other of the pair of racks is secured to the
second die moving block.
[0019] A round die type form rolling apparatus according to a
further aspect of the invention is characterized by: distance
detection means mounted between the set of the die moving blocks to
measure a distance between the die moving blocks; and numerical
control means to drive the die push mechanism based on a measured
value of the distance detection means.
[0020] In a round die type form rolling apparatus which moves main
shafts of rotating round dies toward a work to roll the work; the
apparatus according to a further aspect of the invention is
characterized by: main shaft inclination mechanisms for inclining
the main shafts of the round dies in a plane perpendicular to a
direction of movement of the main shafts; and a drive source for
driving the main shaft inclination mechanisms.
[0021] A round die type form rolling apparatus according to a
further aspect of the invention is characterized by: inclination
angle detection means for detecting inclination angles of the main
shafts; and control means for feeding back the inclination angles
of the main shafts to control the inclination of the main
shafts
[0022] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that the main
shafts are inclined according to a change in a diameter of the work
during the rolling operation and that a lead angle is corrected
according to the change in the work diameter during the rolling
operation to control the movement of the work.
[0023] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that walking
detection means is provided for detecting a walking of the work
that occurs during the rolling of the work and that, based on a
detection signal obtained by the walking detection means, the
inclination angles of the main shafts are controlled to suppress
the walking of the work or to hold the walking of the work
constant.
[0024] In a round die type form rolling apparatus which clamps a
work between a set of round dies and moves main shafts of the
rotating round dies toward each other to roll the work; the round
die type form rolling apparatus according to a further aspect of
the invention is characterized by: servo motors for rotating the
set of round dies and rotation angle detection means for detecting
rotation angles of the set of round dies; and in that phases of the
rotation angles of the set of round dies are changed relative to
each other according to a change in a diameter of the work being
rolled.
[0025] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that the
rotation angle detection means are directly connected to the main
shafts of the round dies.
[0026] In a round die type form rolling apparatus which clamps a
work between a set of round dies to roll the work; the round die
type form rolling apparatus according to a further aspect of the
invention is characterized by torque detection means for detecting
rolling torques acting on the round dies and in that at least
either revolution speeds of the round dies or moving speeds of the
round dies are controlled to keep the rolling torques acting on the
round dies during the rolling operation in a predetermined
range.
[0027] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that torque
values detected by the torque detection means are compared with a
set torque value and that a control is performed in such a way that
when the detected torque values are higher than the set torque
value, revolution speeds of the round dies are raised and that when
the detected torque values are lower than the set torque value, the
revolution speeds of the round dies are lowered.
[0028] A round die type form rolling apparatus according to a
further aspect of the invention is characterized in that torque
values detected by the torque detection means are compared with a
set torque value and that a control is performed in such a way that
when the detected torque values are higher than the set torque
value, moving speeds of the round dies are lowered and that when
the detected torque values are lower than the set torque value, the
moving speeds of the round dies are raised.
[0029] With the construction described above, because the beam
shafts are disposed around the rolling position of the work to be
rolled by the round dies and extend between the left and right die
moving blocks so as to bear the reaction forces generated between a
set of the round dies by the rolling pressure, it is possible to
prevent the die moving blocks from opening due to the reaction
forces and the round dies from escaping outwardly upwardly as they
would in the conventional apparatus. This in turn can improve the
machining precision of the work.
[0030] Further, because at least one of the paired die moving
blocks and the pressure plate is rigidly fixed on the base with the
others slidably disposed, because the beam shafts are extended
between one of the die moving blocks and the pressure plate, with
the ends of the beam shafts secured to the die moving block and the
pressure plate, and because the die moving blocks are moved toward
each other by a single push mechanism, a simple construction using
a single push mechanism can have the beam shafts bear the reactions
generated between a set of the round dies.
[0031] Further, in the round die type form rolling apparatus
according to the invention, a pair of the die moving blocks that
are slidable to left and right and the pressure plate are mounted
on the base; the beam shafts are extended between one of the die
moving blocks and the pressure plate, with the ends of the beam
shafts secured to the die moving block and the pressure plate; and
a single push mechanism is used to push one of the die moving block
to cause both of the die moving blocks to slide simultaneously. In
this construction, because the left and right die moving blocks and
the pressure plate are not secured to the base, the reaction forces
generated between the round dies can be shared more uniformly among
the beam shafts.
[0032] Further, in the round die type form rolling apparatus
according to the invention, because three or four of the beam
shafts extending between a pair of the die moving blocks are
disposed around the rolling position of the work in good balance,
the reaction forces generated in the round dies by the rolling
pressure can be shared equally among the three or four beam
shafts.
[0033] Further, in the round die type form rolling apparatus
according to the invention, because the pinion is mounted on the
base and one of the paired racks meshing with the pinion is secured
to either the first die moving block or the pressure plate and the
other to the second die moving block, the center line of the work
being rolled can be held stationary at all times, thus improving
the machining precision of the work and facilitating the automation
of supply and discharge of the work.
[0034] Further, because the round die type form rolling apparatus
according to the invention includes the distance detection means
mounted between a pair of the die moving blocks and the numerical
control means for driving the push mechanism based on the
measurement from the distance detection means, the depth of
inscription formed by the round dies can be controlled with high
precision.
[0035] Further, because the round die type form rolling apparatus
according to the invention includes the main shaft inclination
mechanisms for inclining the main shafts of the round dies in a
plane perpendicular to the direction of movement of the main shafts
and the drive source for the main shaft inclination mechanism, it
is possible to suppress the walking of the work during the rolling
operation and thereby improve the finish precision of the work and
at the same time to diversify the mode of rolling by controlling
the walking of the work.
[0036] Further, because the round die type form rolling apparatus
according to the invention includes the inclination angle detection
device for detecting the inclination angles of the main shafts and
the control means for controlling the inclination of the main
shafts by feeding back the inclination angles of the main shafts,
the inclination angle of the main shafts can be controlled highly
precisely, which in turn improves the rolling precision.
[0037] Further, in the round die type form rolling apparatus
according to this invention, because the main shafts are inclined
according to a change in the diameter of the work being rolled to
correct the lead angle according to the change of the work
diameter, the walking of the work caused by the work diameter
change during the rolling operation can be prevented.
[0038] Further, in the round die type form rolling apparatus
according to the invention, because the walking detection means for
detecting the walking of the work is provided and because the main
shafts are inclined according to a detected signal from the walking
detection means to control the motion of the work, the walking of
the work can be reliably prevented or held constant and the pitch
kept constant, thereby improving the finish precision of the rolled
surfaces.
[0039] Further, in the round die type form rolling apparatus
according to the invention, the control is performed to change the
rotation angles of a set of the round dies relative to each other
as the diameter of the work being rolled changes, so that when the
work is to be formed with axial grooves, a change in the
circumferential length of the work can be distributed and absorbed
among each of the pitches from the start of inscription toward the
end of inscription, thereby producing smooth tooth surfaces of the
work.
[0040] Further, in the round die type form rolling apparatus
according to the invention, because the rotation angle detection
means are directly connected to the main shafts of the round dies,
the rotation angles of the round dies can be known precisely even
when errors occur due to backlash and distortion in the die
rotation transmission system.
[0041] Further, in the round die type form rolling apparatus
according to the invention, because the machining torques acting on
the round dies during the rolling operation are detected and at
least one of the revolution speed and the moving speed of the round
dies is controlled to bring the detected torques close to the
preset torque value, it is possible to prevent the die torques from
becoming large temporarily as observed in the conventional
apparatus, thus extending the service life of the rolling dies and
enhancing the efficiency of the rolling. Also by controlling the
machining torques acting on the round dies, the depth of
inscription in the work can be controlled with high precision,
further improving the rolling precision.
[0042] Further, in the round die type form rolling apparatus
according to the invention, the torque values detected by the
torque detection means are compared with the set torque value, and
when the detected torque values are higher than the set torque
value, the revolution speeds of the round dies are raised and when
the detected torque values are lower than the set torque value, the
revolution speeds are lowered to control the detected torques to
come close to the preset torque value. This makes it possible to
keep the torque constant from the start of the rolling to the end
and also keep the rolling time constant, which in turn makes the
apparatus suitable for mass production of works.
[0043] Furthermore, in the round die type form rolling apparatus
according to the invention, the torque values detected by the
torque detection means are compared with the set torque value, and
when the detected torque values are higher than the set torque
value, the moving speeds of the round dies are lowered and when the
detected torque values are lower than the set torque value, the
moving speeds are raised to control the detected torques to come
close to the preset torque value. This makes it possible to keep
the torque constant from the start of the rolling to the end and
also to know an ideal rolling time for each work.
[0044] These features and advantages of the present invention will
be described in more detail by referring to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a front view showing one example of a conventional
round die type form rolling apparatus.
[0046] FIG. 2 is a front view showing a state of the conventional
round die type form rolling apparatus during a rolling
operation.
[0047] FIG. 3 is a graph showing the relation between a
circumferential length of a work and a pitch in the conventional
round die type form rolling apparatus.
[0048] FIG. 4 is a schematic view showing the relation between
round dies of the conventional round die type form rolling
apparatus and the work.
[0049] FIG. 5 is a conceptual diagram showing how a rolling torque
acts on the round dies of the conventional round die type form
rolling apparatus.
[0050] FIG. 6 is a plan view showing one embodiment of a round die
type form rolling apparatus according to the invention.
[0051] FIG. 7 is a front view of the embodiment of the round die
type form rolling apparatus when it is operated.
[0052] FIG. 8 is a plan view of a round die type form rolling
apparatus according to the embodiment provided with main shaft
inclination mechanisms.
[0053] FIG. 9 is a cross section taken along the line A-A of FIG. 8
showing the main shaft inclination mechanisms in the embodiment of
a round die type form rolling apparatus.
[0054] FIG. 10 is a conceptual diagram showing the main shaft
inclination mechanisms in the embodiment of a round die type form
rolling apparatus.
[0055] FIG. 11 is a plan view showing a clamp mechanism for a work
in the embodiment of a round die type form rolling apparatus.
[0056] FIG. 12 is a side view showing the clamp mechanism for a
work in the embodiment of a round die type form rolling
apparatus.
[0057] FIG. 13 is a graph showing the relation between a
circumferential length of the work and a pitch when a round die
type form rolling apparatus according to the embodiment is
implemented.
[0058] FIG. 15 is a configuration diagram of a control system for a
round die type form rolling apparatus according to the
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0059] One embodiment of a round die type form rolling apparatus
according to the present invention will be described in detail by
referring to the accompanying drawings. FIGS. 6 through 15 show one
embodiment of the round die type form rolling apparatus according
to the invention. Of these figures, FIG. 6 represents a plan view
of the round die type form rolling apparatus according to the
invention; and FIG. 7 represents a front view of the round die type
form rolling apparatus of, the embodiment when it is operated. FIG.
8 is an overall plan view of the round die type form rolling
apparatus provided with main shaft inclination mechanisms; FIG. 9
is a cross section taken along the line A-A of FIG. 8; and FIG. 10
is a conceptual diagram of the main shaft inclination mechanisms.
FIG. 11 is a plan view showing a clamp mechanism for a work in the
round die type form rolling apparatus of the embodiment. FIG. 12 is
a side view of the clamp mechanism. Further, FIG. 13 is a graph
showing the relation between a circumferential length of the work
and a pitch when the embodiment of the round die type form rolling
apparatus is implemented. FIG. 14 is a graph showing the relation
between a rolling time and a generated torque. FIG. 15 is a control
system configuration for the round die type form rolling apparatus
of the embodiment.
[0060] Referring now to FIGS. 6 and 7, the round die type form
rolling apparatus rolls and forms a work 33 by clamping it between
a pair of rotating round dies 12a, 12b and pressing them against
the work 33. The apparatus has mounted on a base 17 a die moving
block drive mechanism 13 for driving a pair of round dies 12a, 12b
in a lateral direction, or in a radial direction of the work, to
bring the round dies 12a, 12b close to each other, and a round die
rotating mechanism 14 for rotating the round dies 12a, 12b.
[0061] The die moving block drive mechanism 13 includes a first die
moving block 15a, a second die moving block 15b and a pressure
plate 16, all arranged side by side on the base 17. The first die
moving block 15a rotatably supports one round die 12a on an inner
side surface of a die holder 28a. The second die moving block 15b
rotatably supports another round die 12b on an inner side surface
of a die holder 28b, which is opposite the die holder 28a. The
pressure plate 16 is disposed outside the second die moving block
15b. These die moving blocks 15a, 15b and the pressure plate 16 are
laterally slidably mounted on a pair of slide rails 18 fixedly
mounted on the base 17. Further, four beam shafts 19 extend between
the first die moving block 15a and the pressure plate 16 at four
corners of inner opposing sides of the block and the plate. Both
ends of the beam shafts 19 are secured to the first die moving
block 15a and the pressure plate 16, respectively. Hence, the first
die moving block 15a and the pressure plate 16 slide together on
the slide rails 18 without changing their relative positions. The
four beam shafts 19 have equal stiffness and are disposed at
circumferentially quartered positions around, and equidistant from,
a rolling center of the work 33 rolled by the round dies 12a, 12b.
It is also possible to use three beam shafts 19 with equal
stiffness and dispose them at circumferentially trisected positions
equidistant from a rolling center of the work 33 rolled by the
round dies 12a, 12b. With three or four beam shafts 19 disposed at
well-balanced positions, when a pressure is applied between the
first die moving block 15a and the pressure plate 16, the beam
shafts 19 can be elongated in a stable condition while maintaining
a parallel relationship between the first die moving block 15a and
the pressure plate 16.
[0062] As long as the beam shafts 19 can be elongated while keeping
the first die moving block 15a and the pressure plate 16 in a
parallel relationship, the beam shafts 19 may have different
stiffnesses or may be located at differing distances from the
rolling center. While the above embodiment concerns a case where
each of the die moving blocks 15a, 15b is provided with one round
die 12a, 12b, they may each have two or more round dies 12a, 12b
that can hold the work 33 between them.
[0063] The second die moving block 15b is slidably mounted on the
slide rails 18 between the first die moving block 15a and the
pressure plate 16 and has through-holes at four corners of side
surfaces thereof through which to pass the four beam shafts 19 that
guide the second die moving block 15b. The pressure plate 16 is
fixedly provided with a push mechanism 20 such as hydraulic
cylinder. The push mechanism 20 has a cylinder shaft 21 that
extends or contracts in the same direction as the die moving block,
and the front end of the cylinder shaft 21 is secured to an outer
side surface of the second die moving block 15b. The push mechanism
20 is not limited to a hydraulic cylinder but may use a pneumatic
device, a motor and a ball screw.
[0064] The round die rotating mechanism 14 rotates the first round
die 12a and the second round die 12b at the same speed with high
precision, The rotation control of the round dies is performed by
transmitting rotating forces of servo motors 23a, 23b to main
shafts 27a, 27b of the round dies 12a, 12b. Ends of the main shafts
27a, 27b projecting from the die holders 28a, 28b are mounted with
rotary angle detection means 52a, 52b, such as rotary encoders, for
controlling the revolution speeds of the round dies 12a, 12b in a
closed loop.
[0065] Between the second die moving block 15b and the pressure
plate 16 are installed a pair of racks 31a, 31b and a pinion 32,
with the pinion 32 secured to the upper surface of the base 17. A
pair of racks 31a, 31b each mesh with the pinion 32 from the front
and back, with one rack 31a secured to a lower end of the pressure
plate 16 and another rack 31b secured to a lower end of the second
die moving block 15b. Although in this embodiment the pair of racks
31a, 31b and the pinion 32 are installed between the second die
moving block 15b and the pressure plate 16, they may be disposed
between the first die moving block 15a and the second die moving
block 15b.
[0066] FIG. 7 shows the action of the first die moving block 15a,
the second die moving block 15b and the pressure plate 16 when the
die moving block drive mechanism 13 is operated. The condition
after the cylinder shaft 21 is extended by activating the push
mechanism 20 is shown by two-dotted chain line. When the cylinder
shaft 21 is extended, the second die moving block 15b is pushed to
slide on the slide rails 18 toward a center line 34 of the work 33
(in the direction of arrow A in the figure). In the mean timer
because the racks 31a, 31b and the pinion 32 are installed between
the second die moving block 15b and the pressure plate 16 as shown
in FIG. 6, the pressure plate 16 is made to slide the same distance
that the second die moving block 15b travels but in a direction
opposite the direction in which the second die moving block 15b
slides, i.e., toward the right in FIG. 7 (in the direction of arrow
B). At this time, the first die moving block 15a connected to the
pressure plate 16 by the four beam shafts 19 also moves the same
distance in the same direction as the pressure plate 16 (in the
direction of arrow B in the figure). Thus, the first die moving
block 15a and the second die moving block 15b slide the same
distances toward the center line 34 of the work 33, approaching
each other. In this way, with the die moving block drive mechanism
13 according to the invention, the left and right die moving blocks
15a, 15b can be driven toward each other by the single push
mechanism 20 to press the round dies 12a, 12b against the work 33
from both sides for rolling operation. The provision of the racks
31a, 31b and the pinion 32 enables the center line 34 of the work
33 to be held stationary, which in turn improves the machining
precision of the work 33 and facilitates the automated supply and
discharge of the work 33.
[0067] As the round dies 12a, 12b while being rotated are driven
toward each other to press radially against the work 33 and apply a
rolling pressure to it, the work 33 is rotated by the rolling
pressure and repetitively undergoes localized plastic deformations,
forming threads in the work 33. When the work 33 is applied with a
rolling pressure, reaction forces P from the work 33 act on a pair
of the round dies 12a, 12b, as shown in FIG. 7. The reaction force
P acting on the first round die 12a is transmitted to the first die
moving block 15a. The reaction force P acting on the second round
die 12b is transmitted to the second die moving block 15b. Because
the second die moving block 15b is secured to the cylinder shaft
21, the reaction force P transmitted to the second die moving block
15b is further transferred to the pressure plate 16 through the
cylinder shaft 21.
[0068] That is, the reaction forces P produced by the rolling
pressure ultimately act between the first die moving block 15a and
the pressure plate 16. Because the first die moving block 15a and
the pressure plate 16 are connected by the four beam shafts 19 and
because the first die moving block 15a and the pressure plate 16
are not secured to the base 17, the reaction forces P are shared by
the four beam shafts 19. Because the four beam shafts 19 are
arranged at positions above and below the work 33 and have equal
stiffness, the reaction forces P are divided into four equal
portions and equally shared by the four beam shafts 19. In other
words, the tensile force acting on each beam shaft is P/4. Although
the four beam shafts 19 are axially elongated slightly by the
reaction forces P, because they are elongated equally, the die
moving blocks 15a, 15b can be prevented from opening and the round
dies 12a, 12b from escaping outwardly upwardly as they would in the
conventional apparatus. Further, because four beam shafts 19 are
provided, the reaction forces generated in the round dies 12a, 12b
can be stably shared equally among the four beam shafts 19.
[0069] Further, as shown in FIGS. 6 and 7, this embodiment has a
linear scale 35 as distance detection means installed between a
pair of the die moving blocks 15a, 15b so that the distance between
the die moving blocks 15a, 15b can be directly measured. Because
the die moving blocks 15a, 15b do not escape outwardly upwardly,
the dimensional expansion that occurs between the round dies 12a,
12b during the rolling operation can be known precisely by
measuring the distance between the die moving blocks 15a, 15b and
the driving of the push mechanism 20 can be controlled based on the
dimensional expansion. That is, because the round dies 12a, 12b
open equally to the left and right when subjected to the reaction
forces during the rolling operation, the distance between the main
shafts 27a, 27b, i.e., the depth of inscription by the round dies
12a, 12b, can be controlled with high precision by measuring the
distance between the die moving blocks 15a, 15b with the linear
scale 35 during the rolling operation and feeding back a measured
signal in a control loop to numerically control the driving of the
push mechanism 20. The distance detection means may use a
magnetostrictive sensor and a laser sensor rather than the linear
scale 35.
[0070] In the round die type form rolling apparatus according to
the embodiment, as shown in FIG. 8, the die holders 28a, 28b that
rotatably support the main shafts 27a, 27b of the round dies 12a,
12b are pivotally mounted to the die moving blocks 15a, 15b so that
the die holders 28a, 28b can be inclined in a plane (vertical
plane) perpendicular to the direction of movement of the die moving
blocks 15a, 15b. Pivotal centers 29a, 29b of the main shafts 27a,
27b are set so that the rolling position of the work 33 lies on a
line S connecting the pivotal centers 29a, 29b.
[0071] The pivoting of the die holders 28a, 28b is performed by
main shaft inclination mechanisms 50a, 50b. The main shaft
inclination mechanisms 50a, 50b include die holder gears provided
in the die holders 28a, 28b and motor gears that mesh with the die
holder gears. Main shaft inclination servo motors 51a, 51b having
the motor gears attached at the front ends thereof are arranged by
the side of the die moving blocks 15a, 15b. The main shaft
inclination mechanisms 50a, 50b may use link mechanisms rather than
the gears, and the servo motors as a drive source may be replaced
with hydraulic cylinders and pneumatic cylinders.
[0072] When the pivoting motion of the die holder 28a is to be
controlled, the main shaft inclination servo motor 51a is operated
to rotate the motor gear to transmit the rotating force to the die
holder 28a through the die holder gear, as shown in FIG. 9. The die
holder 28a then pivots about a pivotal center 29a by an amount
corresponding to the rotation of the main shaft inclination servo
motor 51a. Thus, the main shaft 27a parallel to the other main
shaft can be inclined +.alpha..degree. upward (shown by a
two-dotted chain line in the figure) and -.alpha..degree. downward
(shown by a two-dotted chain line in the figure) in the vertical
plane. The similar control is also performed on the other die
holder 28b.
[0073] FIG. 10 shows control means for the main shaft inclination
mechanisms 50a, 50b. Encoders 25a, 25b for measuring inclination
angles of the main shafts 27a, 27b are attached to the ends of the
main shafts 27a, 27b, and the inclination angles measured by the
encoders 25a, 25b are fed back for numerical control of the number
of revolutions of the main shaft inclination servo motors 51a, 51b.
This makes it possible to precisely control the upward or downward
inclination (in + or - direction in the figure) of the parallel
main shafts 27a, 27b about the pivotal centers 29a, 29b. The
encoders 25a, 25b may be incorporated into the main shaft
inclination servo motors 51a, 51b. The control of the inclination
angles of the main shafts 27a, 27b varies depending on various
factors, such as the diameter and material of the work 33 to be
rolled, the kind of thread to be formed, and the pitch.
[0074] FIGS. 11 and 12 show a clamp mechanism for the work 33. The
work 33 is clamped axially between a support center 36a and a tail
center 36b. The support center 36a is rigidly secured to one center
stock 37a and the tail center 36b is slidably mounted to another
center stock 37b. The center stock 37b has a pneumatic or hydraulic
cylinder device 38 secured thereto, which drives the tail center
36b axially of the work 33 (in the direction of X in the figure).
At the bottom of the center stocks 37a, 37b are provided a center
stock adjustment rack 39 and a center stock adjustment pinion 40,
both used to adjust a span between the center stocks 37a, 37b. The
center stocks 37a, 37b are slidably mounted on a center stock slide
rail 41 extending in the axial direction of the work 33. Provided
by the side of the center stock 37b is walking detection means 42,
such as a linear scale, that detects an axial movement of the
center stock 37b axially clamping the work 33 to measure the amount
of walking of the work 33.
[0075] FIG. 13 shows the relation between the lead angle, the
circumferential length and the pitch of thread when the work 33 is
thread-rolled by the round die type form rolling apparatus of the
above construction. As shown in the figure, as the round dies 12a,
12b are progressively pressed against the work 33 and the threading
proceeds, the root diameter of the thread of the work 33 decreases
progressively. Hence, the circumferential length of the work 33 at
the root of the thread decreases by .delta.D from D at the start of
threading to D1 at the completion of threading. If the main shafts
27a, 27b are kept parallel, the lead angle .beta. of the work 33
does not change, which produces a pitch deviation .delta.P between
the pitch P of the work 33 at the start of threading and the pitch
P1 of the work 33 at the completion of threading. Hence, during the
rolling operation the work 33 axially moves a distance equal to the
pitch deviation .delta.P. By progressively inclining a pair of the
main shafts 27a, 27b in opposite directions during the rolling
operation, however, the lead angle .beta. of the work 33 can be
corrected according to a change in the circumferential length of
the work during the rolling operation, Correcting the lead angle in
this way can keep the pitch P of the work 33 constant and suppress
the walking of the work 33. That is, the walking of the work 33 can
be suppressed by slowly inclining the main shafts 27a, 27b to
correct the lead angle .beta. of the work 33 as the diameter of the
work 33 changes. At the end of the rolling operation, the lead
angle .beta. of the work 33 becomes a corrected lead angle .beta.1.
Suppression of the walking of the work 33 in turn prevents a
delamination of a flank of the thread which would occur in the
conventional apparatus when the flank of the thread on the same
side as the direction of movement of the work 33 engages the round
dies 12a, 12b with a great force. It can also improve the finish
precision of the worked surface. Further, it can prevent an
insufficient rise or depth of the thread and a tapering of the
thread due to rolling operation. In the case of a flanged work, the
prevention of the walking allows the work to be rolled close to the
flange. The change to the corrected lead angle .beta.1 is
sufficiently small that it falls well within the tolerance of the
finished screw.
[0076] The inclination angles of the main shafts 27a, 27b are
controlled by calculating in advance a lead angle value to which
the lead angle should be corrected according to the diameter of the
work 33 and the depth of inscription and using the calculated lead
angle value as a target value for the servo mechanism. When the
walking of the work 33 is detected by the walking detection means
42, both or one of the main shafts 27a, 27b are given a
predetermined inclination angle and their inclination angles are
controlled so that the reading of the walking detection means 42
remains constant.
[0077] In the round die type form rolling apparatus of the
embodiment, because the inclination angles of the main shafts 27a,
27b can be controlled with high precision, it is also possible to
make the work 33 move or walk, contrary to what was described
above, by inclining the main shafts 27a, 27b at a predetermined
angle. For example, fixing the dies shaped like abacus beads to the
main shafts followed by inclining these main shafts can give the
work an axial thrust force, and changing the distance between the
main shafts enables the work to be rolled into desired shapes, thus
permitting such machining as an external diameter drawing and an
inner diameter working of solid and hollow materials and a forming
of stepped shafts and pipes, all of which have only been achievable
with swaging and ironing spinning. In addition, the setting of the
shaft inclination angle for continuous rolling can be automated
and, by controlling the distance between the main shafts, the shaft
inclination angles and the die rotation angles with high precision,
a wide range of machining becomes possible.
[0078] In the round die type form rolling apparatus of the
embodiment, as shown in FIG. 6, the rotation anales of the main
shafts 27a, 27b can be directly measured with the rotary angle
detection means 52a, 52b such as rotary encoders directly attached
to the ends of the main shafts 27a, 27b. The measurements of
rotation angles are fed back to round die rotation control means
(not shown) to control the rotation of the servo motors 23a, 23b
for the main shafts. By controlling the rotation of the main shafts
27a, 27b in a full-closed loop, the rotation angles of the main
shafts 27a, 27b can be numerically controlled to a target value
with high precision even when errors are produced by gear backlash
or torsion.
[0079] Next, the operation of rolling the work 33 by controlling
the rotation angles of the main shafts 27a, 27b will be described.
First, let us explain about a case where axial grooves such as
splines and serrations are formed in the work 33 by rolling. A pair
of round dies 12a, 12b are controlled in their rotation angles
according to a change in the diameter of the work 33 during the
rolling. That is, at the start of the rolling operation both of the
round dies 12a, 12b rotate at the same speed in the same direction.
As the groove in the work 33 deepens progressively during the
course of rolling, however, a control is made to gradually change
the rotation angle of a second round die 12b with respect to the
rotation angle of a first round die 12a. For example, the
circumferential length of the work 33 being rolled is divided by
the number of teeth to be inscribed to determine a corrected pitch
and then the rotation angle control is performed in such a way as
to produce the corrected pitch. By controlling the rotation angle
in this way, a change in pitch, which is produced when the groove
diameter of the work 33 gradually changes from the start of
inscription toward the completion of inscription, can be
distributed and absorbed among a plurality of teeth. This prevents
a large, local pitch deviation, providing smooth tooth surfaces of
the work 33 and improving the finish precision. Such a control can
also be applied for the rolling of gears with a large module. A
rate of change of rotation angles of the main shafts 27a, 27b
varies depending on various factors including the diameter and
material of the work 33 to be rolled and the kind and pitch of the
threads to be formed by rolling.
[0080] Next, a case will be explained in which a spiral thread is
rolled on the outer circumference of the work 33 by controlling the
rotation angles of the main shafts 27a, 27b. In a manner similar to
that of the previous case, the rotation angles of a pair of the
round dies 12a, 12b are controlled according to a change in the
diameter of the work 33 being rolled. That is, at the start of
rolling, both of the round dies 12a, 12b rotate at the same speed
in the same direction. However, as the thread in the work 33
progressively deepens during the course of rolling, a control is
performed to gradually change the rotation angle of a second round
die 12b with respect to the rotation angle of a first round die
12a. This rotation angle control, as shown in FIG. 13, allows the
lead angle of the work 33 to be gradually changed from .beta. to a
corrected lead angle .beta.1 and therefore allows the pitch P to
remain constant even when the circumferential length of the work 33
should change from D at the inception of inscription to D1 at the
completion of inscription. Therefore, this control can eliminate a
problem experienced with the conventional apparatus that the pitch
may change during rolling operation causing the work 33 to walk in
the axial direction, and thus can ensure a uniform contact between
the flanks of the threads in the work 33 and the round dies 12a,
12b, resulting in an improved finish precision of the rolled
surfaces.
[0081] Further, in the round die type form rolling apparatus of the
embodiment, as show in FIG. 6, the main shafts 27a, 27b of the
round dies 12a, 12b are each provided with torque detection means
53a, 53b, and the first die moving block 15a has load detection
means 54 attached to the end thereof which measures the load of a
die in the rolling process. The torque detection means 53a, 53b
include, for example, a torque meter for directly measuring the
torque value and means for detecting the load of a servo motor in
the form of current or voltage and calculating a torque value from
the detected value.
[0082] FIG. 14 shows a change in torque when a torque control
method according to the invention is implemented. The abscissa
represents a rolling time and the ordinate a torque value as
detected by the torque detection means 53a, 53b. A chain-dotted
line represents a set torque value. The set torque value is
determined considering the detected values of die loads and die
torques that are generated when the rolling operation is performed
with the revolution speeds and the moving speeds of the main shafts
27a, 27b kept constant.
[0083] First, we will explain about a method of controlling the
rolling torques within a predetermined range by controlling the
revolution speeds of the main shafts 27a, 27b. Generally, as the
revolution speeds of the main shafts 27a, 27b are increased, the
number of rotations of the work 33 being rolled increases, thus
reducing the depth of inscription and the torque produced. On the
other hand, reducing the revolution speed reduces the number of
rotations of the work 33, thus increasing the torque. The present
invention takes advantage of this relation to control the generated
torque at a predetermined value. The revolution speeds of the main
shafts 27a, 27b are limited by upper and lower limits set by a
limiter and are allowed to vary automatically in the range of the
limiter. At point (1) in the figure immediately after the start of
the rolling operation, the main shafts 27a, 27b rotate at a preset
initial revolution speed. The torques produced gradually increase
and come close to a set torque value, at which time ((2) in the
figure) the torque control is started. The torque control involves,
as a first step, comparing the torque values detected by the torque
detection means 53a, 53b with the set torque value. When the
detected torque values are lower than the set torque value, the
main shafts 27a, 27b are given a rotation angle deceleration to
lower the revolution speeds and thereby increase the torque values.
When the torques further increase exceeding the set torque value
(point (3) in the figure), the main shafts 27a, 27b are given a
rotation angle acceleration to increase the revolution speeds and
thereby lower the torque values. If, even with this control, the
torques continue rising further (point (4) in the figure), the
upper limit revolution speed of the limiter is set. As the rolling
operation, while performing the torque control as described above,
nears its end, the torques decrease and the torque control is
terminated (point (5) in the figure). Then, the revolution speeds
of the main shafts 27a, 27b are set with the lower limit value of
the limiter. A plurality of rotation angle
accelerations/decelerations with stepwise differing values may be
set so that the rotation angle acceleration/deceleration
progressively increases as the deviation of the generated torques
from the set torque value increases. With this arrangement, when
the detected torques deviate away from the set torque value, it is
possible to quickly bring the generated torques close to the set
torque value. When the generated torques come near the set torque
value, this method can reduce a range of torque variations.
[0084] By controlling the machining torque produced during the
rolling operation to come close to a preset torque value, the main
shaft torque can be prevented from temporarily becoming excessively
high during a peak, thus significantly extending the rolling die
longevity compared with the conventional ones. Further, this torque
control enables even a thin-walled hollow member to be rolled. The
torque control method for the main shafts 27a, 27b described above
can also be applied to a differential speed type rolling machine
which pushes the work 33 by a feeder without moving the main shafts
of the round dies 12a, 12b.
[0085] Next, an explanation will be given concerning a method of
controlling the main shaft moving speeds so that the machining
torques acting on the main shafts 27a, 27b will come close to a
preset torque value. In this case, when the main shaft moving
speeds are lowered, the number of rotations of the work 33 being
rolled increases, reducing the depth of inscription and therefore
the generated torque. On the other hand, increasing the main shaft
moving speeds reduces the number of rotations of the work and
increases the torque. The present invention utilizes this relation
in performing the control to maintain the generated torque at a
constant value. As in the case of the revolution speeds of the main
shafts, the main shaft moving speeds are limited by upper and lower
limits of a limiter and are allowed to vary automatically within
the range of the limiter.
[0086] FIG. 15 shows an example configuration of a control system
for the embodiment. The control system processes programs and data
stored in a memory 46 by a CPU 45 and sends the processed result to
actuators such as servo motors 23a, 23b and push mechanism 20 via a
communication control unit 48 connected a bus line 43. These
actuators each have a driver circuit, and a plurality of these
drivers and I/O ports 47 are connected to the communication control
unit 48. The drivers, the I/O ports 47 and the communication
control unit 48 are interconnected by a serial communication line
44.
[0087] Although the above embodiment has been shown to slide the
left and right die moving blocks 15a, 15b together, it should be
noted that the present invention can also be applied to a case
where one of the die moving blocks 15a, 15b or the pressure plate
16 is rigidly fixed and the others are slidably movable. The round
die type form rolling apparatus of the invention can also be
applied to a case where the main shafts 27a, 27b are kept
stationary and the work 33 is pushed between the round dies 12a,
12b and driven to rotate to be rolled. Further, a numerical control
may be performed to rotate the main shafts 27a, 27b in opposite
directions and move the work 33 upward or downward which is
disposed perpendicular to the main shafts 27a, 27b, thus forming
axial grooves in the work 33.
* * * * *