1 Introduction
Drawing of conical parts is considerably more difficult than
the deep drawing of cylindrical cups. Conical shape
forming through conventional deep drawing is shown in
Fig. 1. As it is shown in the figure, due to small contact
area of the punch tip with the blank at initial stages of
deformation, high stresses are applied to this area of the
sheet. This may cause bursting in the sheet. In addition,
when forming conical cups through conventional deep
drawing, wrinkling occurs on the sheet wall because the
blank is free between the punch and the die [1, 2]. Thus,
conical parts are normally formed by multi-stage deep
drawing [1], spinning [3], or explosive forming [4].
Because of the large radial tensile stresses, small
drawing ratios must be used in each stage when making
conical components in multi-stage deep drawing. In
addition, the ratio of the sheet thickness to the initial blank
diameter influences the limiting drawing ratio to a greater
extent than when drawing cylindrical parts. The limiting
drawing ratio also depends on the cone angle and the ratio
of the largest to the smallest cone diameter [1].
Thiruvarudchelvan and Tan [5] developed the conventional
deep drawing process for drawing conical cups using
an annular urethane pad. In this technique, the tip of the
punch does not touch the sheet metal at any stage of
drawing. This prevents early bursting of the sheet. These
researchers formed a conical copper cup from a sheet with
an initial thickness of 1 mm. But, their method has the same
drawbacks; not only the punch and die should be
manufactured according to the shape of the cup, but also
some wrinkles appear on the cup wall as stated in reference
[5]. No further research work has been reported about
forming conical cups through this technique.