Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
DEVICE FOR FORGING A HELICAL GEAR
BACKGROUND OF THE INVENTION
Fleld of the Invention
The present invention relates to a device for forging a
helical gear by plastic working means.
Description of the Related Art
Development of plastic working means allows helical gears
to be manufactured by forging in place of conventional
machining. A typical example of forged helical gears is
disclosed in Japanese Patent Laying-Open Gazette No. 64-
22442, wherein helical teeth are formed on a circumference of
a work while the work is pressed by a punch into a die.
In such a conventional system, since helical teeth are
formed inclining to a central axis of a gear body, the die or
the work is to be rotated relative to each other. The
relative rotation causes insufficient precision or accuracy
in formation of helical teeth as well as undesirably limits
an angle of torsion or a module of the forged helical gear.
In another conventional method, a plurality of helical-
tooth punches for forming helical teeth are arranged to be
movable in radial direction in the same manner as straight
teeth formation means as shown in Fig. 10. A plurality of
straight-tooth punches 7a,7a (shown by the solid lines in
Fig. 10) form straight teeth which are disposed in parallel
with a central axis of a gear body. Flat sliding faces of
the plurality of straight-tooth punches 7a,7a respectively
correspond to and engage with flat cam faces of a plurality
of extrusion cams 8a,8a (shown by the one-dot broken lines in
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Fig. 10) which are movable along the central axis. A
plurality of helical-tooth punches 7,7 (shown by the doted
lines in Fig. 10) form helical teeth which are inclined to
the central axis of the gear body. Each flat sliding face of
the helical-tooth punches 7,7 does not preferably correspond
to or engage with each flat cam face of the extrusion cams
8a,8a due to interference of an ad~acent extrusion cam 8a.
Of course, the sliding faces of the helical-tooth punche~ can
theoretically be arranged in parallel with the central axis
of the gear by distorting the helical-tooth punches by
respective required angles. This method is, however, not
practical because of insufficient pressure resistance of the
forged helical teeth. Namely, there is no practical method
of mass producing hellcal gears with high precision by
plastic working means.
SUMMARY OF THE INVENTION
- One ob~ect of the invention is to provide a novel device
for forging a helical gear by plastic working means.
Another ob~ect of the invention is to provide a helical
gear forglng devlce including a die which is free from a
rotation relative to a work.
The above and other related ob~ects are realized by a
device for forging a helical gear. The device includes: a
die having a cylindrical cavity formed on the center thereof
for receiving a work; a punch assembly disposed above the
cavity and movable in a vertical direction; and a plurality
of helical~tooth punches for forming rough profiles of
helical teeth around the work set in the cavity. The
plurality of helical-tooth punches are mounted on a
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circumference of the cylindrical cavity and movable in a
radial direction towards a center of the cavity. The device
further lncludes an extrusion cam disposed above the
plurality of helical-tooth punches and mo~able in the
vertical direction.
The extrusion cam has a bottom inner surface formed as a
cam face constituting a side face of a first truncated cone
having predetermined first dimensions and a slope. The
plurality of helical-tooth punches respectively have sliding
faces which are arranged to integrally form a side face of a
second truncated cone and engage with the cam face of the
extrusion cam. The second truncated cone has predetermine
second dimensions and a slope identical with or corresponding
to those of the first truncated cone, and thereby perfectly
fits in the first truncated cone.
When the extrusion cam goes down in the vertical
direction, the cam face of the extrusion cam fittingly
engages with and presses against the sliding faces of the
hellcal-tooth punches to move the helical-tooth punches in
the radial direction towards the center of the cavity to form
rough profiles of helical teeth around a side wall of a work
set in the cavity. The punch assembly is then pressed down
to finish the helical teeth roughly formed on the side wall
of the work.
The above structure of the invention allows the truncated
cone-shaped cam face of the e~trusion cam to effectively
press the sliding faces of the helical-tooth punches in the
radial direction towards the center of the cavity. Each
helical-tooth punch is partly overlapped ~ith ad~acent
helical-tooth punches. Since the second truncated cone
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formed by integrating the sliding faces of the helical-tooth
punches perfectly fits in the first truncated cone of the cam
face of the extrusion cam, the cam face sufficiently presses
all the partly overlapped helical-tooth punches in the radial
direction to form rough profiles of helical teeth around a
work.
These and other ob~ects, features, aspects, and advantages
of the present invention will become more apparent from the
following detailed description of the preferred embodiment
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a device for forging a helical gear embodying
the invention;
Fig. 2 shows a relationship between a cam face of an
extrusion cam and sliding faces of a plurality of helical-
tooth punches;
Fig. 3 shows a process for forging a helical gear with the
helical gear forging device of Fig. 1;
Fig. 4 shows a process for forging a helical gear with the
helical gear forging device of Fig. 1;
Fig. 5 shows a first step for forming helical teeth on a
gear;
Fig. 6 shows a second step for forming helical teeth on a
gear;
Fig. 7 shows a third step for forming helical teeth on a
gear;
Fig. 8 shows a process for forging a helical gear with the
helical gear forging device of Fig. 1;
Fig. 9 shows a process for forging a helical gear with the
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helical gear forging device of Fig. 1; and
Fig. 10 shows a relationship between cam faces of a
plurality of extrusion cams and sliding faces of a plurality
of helical-tooth punches in a prior art structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A device for forging a helical gear embodying the
invention is described in detail according to the drawings.
As shown in Fig. 1, a helical gear forming device of the
embodiment includes a die 1, a punch assembly 3, and an
e~ector 5. The die 1 includes a disk-shaped cavity 2 formed
on its center. The punch assembly 3 is located immediately
above the die 1 to be movable in a vertical direction between
an upper position and a lower position for pressing a work 4
down into the cavity 2. The work 4 has a larger-diametral
element and a smaller-diametral element. The ejector 5,
which is also movable in the vertical direction between an
upper position and a lower position, goes through a central
portion of the cavity 2 to press the work 4 up.
The cavity 2 includes a smaller-diametral portion having a
straight teeth forging element 6 arranged on a circumference
thereof for forming straight teeth on the smaller-diametral
element of the work 4, and a larger-diametral portion having
a plurality of helical-tooth punches 7,7 mounted on a
circumference thereof for forming rough profiles of helical
teeth on the larger-diametral element of the work 4. The
helical-tooth punches 7,7 are supported on the larger-
diametral portion of the cavity 2 to be freely movable in a
radial direction between a first radial position and a second
radial position. The larger-diametral portion of the cavity
2 also has a helical teeth forging element consisting of a
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plurallty of grooves 9,9 for forming helical teeth around the
larger-diametral element of the work 4, in combination with
the plurality of helical-tooth punches 7,7.
A cylindrical extrusion cam 8, which is movable in the
vertical direction between a first vertical position and a
second vertical position, is further disposed above the
plurality of helical-tooth punches 7,7. The extrusion cam 8
goes down to the second vertical position to press the
helical-tooth punches 7,7 towards the center of the cavity 2
to the second radial position. Each helical-tooth punch 7 is
provided with a spring 12 for returning the helical-tooth
punch 7, which is pressed to the second radial position by
the extrusion cam 8, to the first radial position.
~ ach helical-tooth punch 7, in combination with an
ad~acent helical-tooth groove 9 of the ca~ity 2, roughly
forms a helical-tooth profile on the larger-diametral element
of the work 4 when being pressed in the radial direction by
the extrusion cam 8. The cylindrical extrusion cam 8
concentrically arranged with the punch assembly 3 has an
inner bottom surface formed as a cam face constituting a side
face of a first truncated cone having predetermined first
dimensions and slope. The helical-tooth punches 7,7
respectively have sliding faces which are arranged to
integrally form a side face of a second truncated cone and
engage with the cam face of the extrusion cam R as clearly
seen in Fig. 2. That is, the sliding face of each helical-
tooth punch 7 is a curved surface constituting part of the
second truncated cone. The second truncated cone has
predetermine second dimensions and a slope identical with or
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corresponding to those of the first truncated cone, and
thereby perfectly fits in the first truncated cone. This
structure allows any part of the circular cam face of the
cylindrical extrusion cam 8 to sufficiently press the
helical-tooth punches 7,7 towards the center of the cavity 2.
A process for manufacturing a helical gear with the
helical gear forging device thus constructed is described
according to the drawings.
The work 4 is placed on an upper surface of the e~ector 5
lifted up to its upper position, and then set into the cavity
2 by lifting down the e~ector 5 to its lo~er position ~see
Fig. 3). In a subsequent step, the extrusion cam 8 is
lowered to the second vertical position to press the
plurality of helical-tooth punches 7,7 to~ards the center of
the cavity to the second radial position as clearly seen in
Fig. 4. While the plurality of helical-tooth punches 7,7 are
pressed in the radial direction by the extrusion cam 8, each
helical-tooth punch 7, in combination with an ad~acent
helical-tooth groove 9, roughly forms a helical-tooth profile
on the larger-diametral element of the work 4 set in the
cavity 2 (see Figs. 5 and 6).
The punch assembly 3 is then lifted do~n to its lower
position to press the work 4 down as sho~n in Fig. 8. The
work 4 is radially expanded by the pressing force of the
punch asse~bly 3 to fill the straight teeth forging element 6
and the plurality of helical-tooth grooves 9,9. This results
in forming straight teeth 10 around the s~aller-diametral
portion of the work 4 and finishing helical teeth 11 around
the larger-diametral portion of the wor~ $ (see Fig. 7).
After formation of the straight teeth 10 and the helical
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teeth 11 is completed, the plurality of helical-tooth punches
7,7 are returned to the first radial position by means of the
' plurality of springs 12,12 while the punch assembly 3 is
lifted up to its upper position. At a last step, the ejector
5 is lifted up to its upper position to press the work 4
having the straight teeth 10 and the helical teeth 11 out of
the cavity 2 as shown in Fig. 9. A through hole for a shaft
may be formed in the work 4 after completion of the above
forging process, or alternatively formed simultaneously with
formation of gear teeth on a ring-shaped ~ork using a
mandrel.
As described above in detail, the helical gear forging
device of the invention allows formation of helical teeth
with high precision without rotating a work or a die relative
to each other. The integrally formed extrusion cam of the
device has sufficient strength and preferable durability and
is applicable to any teeth number, module, and tooth profile.
Since there may be many modifications, alterations, and
changes without departing from the scope or spirit of
essential characteristics of the invention, it is clearly
understood that the above embodiment is only illustrative and
not restrictive in any sense. For example, the plurality of
helical-tooth punches and the vertically movable punch
assembly may be operated simultaneously to form helical teeth
on a side wall of a work. Although the smaller-diametral
portion of the cavity has the straight teeth forging element
in the above embodiment, it may be omitted to form a flat
boss on the smaller-diametral element of the work. In
another example, the d~e may have a one-step cavity insteaA
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of the two-step cavity of the embodiment.
