This invention relates to a method and an apparatus for manufacturing a ring with which it is possible to form a ring plate of any thickness, width, and internal and external diameter from the same starting rod material and which is suitable for high variety, low volume production.
Ring plates such as separating plates of wet multiplate clutches in automatic transmissions have generally been manufactured by being punched from a flat plate. However, with this method, the yield is poor. Also, while the realization of high performance and high quality in automobiles and the like has been progressing in recent years, a limit to reductions in cost has been reached.
To overcome this, a ring forming method has been proposed wherein a specially shaped plate material whose cross-section is tapered so that its thickness increases in the width direction from one side to the other is prepared and this specially shaped plate material is formed into the shape of a ring so that the thinner side thereof becomes the inner side and a ring having a uniform thickness is thereby obtained (Automobile Technology Society, Science Lecture Meeting Advance Notes 921 1992-5).
In this ring manufacturing method, deformation occurring in the formation of the ring is calculated, and the cross-sectional shape of the specially shaped plate material before it is formed into a ring is set so that the thickness, the width, and the internal and external diameters and so on of the ring plate being manufactured are obtained to a predetermined accuracy.
However, in the related art, this specially shaped plate material has been manufactured by drawing using a die. Consequently, when ring plates of various types having different thicknesses, widths, and internal and external diameters are to be manufactured, it has been necessary for different specially shaped plate material s to be selected and correspondingly different dies become necessary, and consequently high-variety, low-volume production has been expensive.
There have also been problems such as that:
(1) With a specially shaped plate material manufactured by drawing, because the working accuracy of an ordinary drawing die is about 0.05 mm and even with a drawing die worked using shape measurement about 0.02 mm as the limit, it is extremely difficult to obtain a highly accurate specially shaped plate material;
(2) Because the surface roughness of a drawn material is Rz=about 4.5, to obtain the surface roughness required of a ring plate, it is necessary for polishing or barreling to be carried out in a later step;
(3) With drawing, it is difficult to manufacture a thin plate and therefore drawing is not suitable for application to thin ring plates;
(4) With drawing, it is difficult to obtain a wide rod material; and
(5) The cost of the starting material constitutes a large proportion of the production cost.