Metal deforming – By use of closed-die and coacting work-forcer – Forcing work into or within closed die; e.g. – forging
Reexamination Certificate
1999-09-08
2001-05-22
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Forcing work into or within closed die; e.g., forging
C072S348000, C072S358000
Reexamination Certificate
active
06233999
ABSTRACT:
FIELD OF THE ART
The present invention concerns a method of forming spline teeth by ironing by engagement of a punch and die in the axial direction on the respective peripheral walls of a stepped, press-formed sheet-metal article, having peripheral walls of different diameter disposed in a continuous manner via a step portion, and particularly concerns a method of forming spline teeth by ironing on a press-formed sheet-metal article by which the spline teeth can be formed on a plurality of peripheral wall steps in a single forming operation. The formed article with spline teeth that is to be obtained by the method of the present invention is, for example, a clutch drum (formed article), in which, as shown in
FIG. 1
, spline teeth
2
and
3
are formed by ironing on each of the peripheral walls of a solid, press-formed sheet-metal drum
1
with which a bottomed small-diameter drum part
1
b
is disposed in continuation to a large-diameter drum part
1
c
via a step portion
1
a.
BACKGROUND ART
Priorly, such a formed article
1
was obtained through two forming processes, that is, a process in which spline teeth are formed on large-diameter drum part
1
c
and a process in which spline teeth are formed on small-diameter drum part
1
b.
However, since this procedure causes man-hours to increase and since deviations may occur in the concentricity of the upper and lower teeth
2
and
3
, methods of simultaneously forming teeth
2
and
3
by a single forming process have been proposed.
FIG. 10
shows the structure of a die assembly for this type of simultaneous forming in which the inner periphery of die
4
is comprised of two steps in the vertical direction, that is, a small-diameter part
5
and a large-diameter part
6
disposed above small-diameter part
5
and wherein forming teeth
5
a
and
6
a
are formed on the inner periphery of each part.
On the other hand, punch
7
has a small-diameter punch part
8
and a continuing large-diameter punch part
9
formed integrally, and forming teeth
8
a
and
9
a
are formed on the outer periphery of the respective punch parts.
With the above arrangement, a to-be-processed article
10
, which is a cup-shaped, press-formed sheet-metal article, having two step portions of a large and small diameter, respectively, prior to forming, is fitted onto punch
7
and then pressed into die
4
as shown in FIGS.
11
(
a
) and (
b
) so that the forming teeth
5
a,
8
a,
6
a,
and
9
a
engage in the axial direction respectively. The peripheral walls of the to-be-processed article
10
is thereby ironed in the axial direction and a stepped, cup-shaped formed article
1
, having spline teeth
2
and
3
of a protruded and indented form formed on the inner and outer peripheries, is thus obtained in one shot.
However, with the above-described simultaneous forming method, punch
7
is lowered at a constant pressurizing force to iron large-diameter drum part
1
c
and small-diameter drum part
1
b
of formed article
1
simultaneously. Thus in the forming process, the ironed material on the peripheral wall of small-diameter drum part
1
b
is pushed outwards (made to flow outwards) at step portion
1
a
of formed article
1
as shown by the arrow in FIG.
11
(
a
) and bulges in the form of excess thickness A at the upper side of step
1
a.
Furthermore, as shown in on enlarged manner in FIG.
11
(
b
), the excess thickness A is pressed by the step
7
a
of punch
7
, causing a defect B, which may be a gouge, shrinkage cavity, or entrainment, to occur and cause a portion of the article to become thin and weak in strength.
The bulge due to the excess thickness that forms at step
1
a
is especially significant when step
1
a
is to be formed to be perpendicular to the peripheral walls, and such a bulge must be cut off if the formed article is to be used in a clutch drum. Thus if the formed article is to be used as it is in a clutch drum and without performing a cutting process, the step
1
a
between small-diameter drum part
1
b
and large-diameter drum part
1
c
must be inclined as shown in FIG.
11
(
b
) so that the bulge due to excess thickness A will not protrude towards the inner side of large-diameter drum part
1
c.
It was therefore difficult to form step
1
a
to be perpendicular to the peripheral walls.
Thus with the prior art, it was difficult to make the diameter difference D between the upper and lower parts at step
1
a
large since this lead to the increasing of the axial length of step
1
a,
and thus to the increasing of the axial length of the clutch drum, which in turn lead to the increasing of the size of the entire clutch device.
Upon examining the causes by which excess thickness A and defect B occur, the present inventor found that since a gap C is formed between formed article
1
and punch step
7
a
in consideration of the elongation of small-diameter drum part
1
b,
the material that flows upward in the axial direction by the iron-forming of small-diameter drum part
1
b
bulges at step
1
a
and is then pressed by punch step
7
a
to give rise to excess thickness A and defect B.
Thus in order to prevent a gap from being formed between the step portions of the processed article and the punch, the present inventor provided the punch with an arrangement in which it was split into a first punch for forming small-diameter part
1
b
and an outer peripheral punch for forming large-diameter drum part
1
c,
and by maintaining the ironing pressure of the first punch after forming large-diameter drum part
1
c
and controlling the ironing pressure of the outer peripheral punch to be lower than the normal ironing pressure in ironing the small-diameter drum part
1
b
so that the ironing pressure of the outer peripheral punch will not act on the step of the processed article or the small-diameter drum part, was able to obtain a processed item with which neither excess thickness A nor defect B occurred at the step portion.
The present invention was made based on the above-described problems of the prior art and on the findings of the inventor, and the objects thereof include the provision of a method for forming spline teeth by ironing on a stepped, press-formed sheet-metal article and a provision for a sheet metal clutch drum formed by ironing by said method, with which excess thickness does not occur at the step portions in the process of iron-forming the spline teeth on a plurality of step portions in one shot and with which forming can be performed without geometrical restrictions such as in the differences in diameter between upper and lower parts, inclination of the step portion, etc.
DISCLOSURE OF THE INVENTION
To achieve the above object, the invention provides a method for forming spline teeth by ironing on a stepped, press-formed sheet-metal article, wherein a forming die, having a plurality of steps of ironing surfaces corresponding to the outer peripheral shape of a to-be-processed article, which is a press-formed article, and a forming punch, having a plurality of steps of ironing surfaces corresponding to the inner peripheral shape of the to-be-processed article, are engaged in the axial direction to form spline teeth by ironing on at least one of either the inner or outer surfaces of the respective peripheral walls of a solid, stepped, cup-shaped, press-formed sheet-metal article with which a plurality of peripheral walls of different diameters are disposed in a continuous manner via step portions, said method being characterized in that the abovementioned punch has an arrangement in which it is split into a first punch, which coacts with the corresponding ironing surface at the die side to form spline teeth by ironing on the peripheral wall of the deepest part of the to-be-processed article, and one or a plurality of outer peripheral punches, each of which is disposed coaxially at the outer periphery of the first punch, coacts with the corresponding ironing surface at the die side to form spline teeth by ironing on the peripheral wall of the corresponding step portion of the to-be-processed article, and is lowere
Nitou Satoru
Yabutani Mitsumasa
Cole Thomas W.
Larson Lowell A.
Nixon & Peabody LLP
Unipres Corporation
LandOfFree
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