Metal deforming – By use of tool acting during relative rotation between tool... – During rotation of work
Reexamination Certificate
1999-12-21
2001-05-01
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
During rotation of work
C072S111000
Reexamination Certificate
active
06223576
ABSTRACT:
This application is based on Japanese Patent Application No. 10-369859 filed Dec. 25, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of forming a peripheral portion of a blank in the form of a circular plate so as to increase the thickness of the peripheral portion, and more particularly to such a method which permits desired thickening of the peripheral portion with comparatively easy control of a swaging force acting between the peripheral portion and a roller die, while avoiding buckling or folding of the peripheral portion.
2. Discussion of the Related Art
Automotive vehicles use a drive plate such as a flywheel connected to a crankshaft of an engine. Conventionally, such a drive plate consists of a circular plate and a ring gear fixedly mounted on the circumferential surface of the circular plate. To meet a recent need for further reduction of the cost of manufacture of the drive plate, there has been proposed an integral or one-piece type drive plate consisting of a circular plate whose outer peripheral portion is formed into an integral toothed portion. For increased shock or impact resistance and mechanical strength, it is desired that the drive plate be formed to have a larger thickness at its peripheral portion than at its radially inner portion. An example of a method to thicken the peripheral portion of a blank in the form of a circular plate uses a rotary swaging apparatus which includes (a) a rotatably supported roller die having an annular forming groove which is open in its outer circumferential surface and substantially V-shaped in cross section in a plane including an axis Si of rotation of the roller die such that an axial dimension of the forming groove as measured in an axial direction of the roller die increases in a radially outward direction of the roller die, (b) a blank holder jig which is rotated about an axis S
2
of rotation thereof and which holds the blank such that the blank is coaxial with the blank holder jig and has a peripheral portion which extends radially outwardly from the blank holder jig over a predetermined radial distance, and (c) a drive device for rotating the roller die and the blank holder jig about their respective axes S
1
and S
2
, such that the blank is held pressed at its outer circumferential surface, in rolling contact with a bottom surface of the forming groove of the roller die, so that the peripheral portion of the blank is thickened following the cross sectional shape of the forming groove.
JP-A-9-10885 shows such a method, wherein the axes S
1
, S
2
of rotation of the roller die and the blank holder jig are parallel with each other, and the blank is held by the blank holder jig such that the blank is subsonically aligned with the forming groove in the roller die, in the axial direction of the roller die and the blank holder jig, and the roller die and the blank holder jig are moved toward each other in the radial direction so that the peripheral portion of the blank
104
is swaged into a thickened portion
100
as shown in FIG.
6
A. The thickened portion
100
is thickened substantially symmetrically on both of its upper and lower sides, to have an arrow shape in cross section in a plane parallel to a direction of thickness of the blank. The peripheral portion of the blank is swaged in two steps into the thickened portion
100
, which is then bent or folded almost at right angles, by a roller die
102
, so that the blank has a cylindrical peripheral portion
108
which extends from one of the opposite surfaces of a radially inner flat portion
106
of the blank
104
in the axial direction, as shown in
FIGS. 6A-6C
.
In the conventional method of swaging the peripheral portion of the blank, the peripheral portion of the blank must be forced against the bottom surface of the forming groove of the roller die so that the peripheral portion is thickened substantially symmetrically on the opposite sides of the blank while the blank is held substantially flat, except the radially outermost part being thickened. However, the peripheral portion of the blank tends to buckle soon after the force acting between the blank and the roller die in the radial direction of the roller die exceeds a given critical value. It is considerably difficult to control this radial force so as to thicken the peripheral portion without buckling. Further, the thickened peripheral portion
100
which has been formed by the swaging described above is subsequently bent or folded about 90° by the roller die
102
to form the cylindrical peripheral portion
108
, as described above. Accordingly, the cylindrical portion
108
suffers from undesirable folds (hairpin bend) as indicated at A in FIG.
6
C. These folds A adversely influence a subsequent forging or machining operation on the cylindrical peripheral portion
108
to form a toothed portion. Namely, the formed toothed portion may not have sufficiently high degrees of durability and mechanical strength, during use of a drive plate having the toothed portion at its periphery.
JP-A-9-66330 shows another method of thickening the peripheral portion of a circular plate blank, wherein the peripheral portion of the blank is brought into sliding contact with one of opposed side surfaces which partially define a forming groove formed in a roller die, so that the outer circumferential surface of the peripheral portion is brought into abutting contact with the other side surface of the forming groove, so as to bend the peripheral portion into a substantially L-shaped thickened peripheral portion. This method also suffers from buckling of the peripheral portion of the blank toward the above-indicated other side surface of the forming groove when the force acting between the blank and the roller die exceeds a critical value. In this method, too, the force is difficult to control for intended thickening of the peripheral portion of the blank without buckling. If the thickening operation is continued after the buckling, the peripheral portion of the blank has a meandering or alternating flow of the material, as indicated at fM in
FIG. 7
during the thickening operation, causing a fold between alternate curves of the material flow. It is noted that
FIG. 7
corresponds to the cross sectional view of FIG.
6
C. The alternating flow of the material is generated by initial buckling of the peripheral portion of the blank from the above-indicated one side surface of the forming groove toward the other side surface, and subsequent buckling of the peripheral portion in the reverse direction toward the above-indicated one side surface, as a reaction of the initial buckling. If an angle &bgr; one side surface
110
of a forming groove with respect to the radial direction of the roller die is larger than 15°, as indicated in
FIG. 8
, a blank
112
in the form of a circular plate is buckled at its peripheral portion, as indicated at B in
FIG. 8
, toward the other side surface
114
of the forming groove, without thickening of the peripheral portion. In this case, the thickening operation is restricted.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of forming a peripheral portion of a blank in the form of a circular plate, so as to thicken the peripheral portion, which method reduces or eliminates at least one of the problems encountered in the prior art described above.
The above object may be achieved according to the principle of this invention, which provides a method of forming a peripheral portion of a blank in the form of a circular plate, so as to thicken the peripheral portion, comprising the steps of: providing a roller die supported rotatably about an axis thereof and having an outer circumferential surface and an annular forming groove which is open in the outer circumferential surface, the forming groove having a first side surface, a second side surface spaced from the first side surface in an axial direction of the roller die, and
Aisin Kiko Co., Ltd.
Larson Lowell A.
Oliff & Berridge PLC.
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