Shape imperfection in cylindrical cups formed by processes of deep- and stretch-drawing with ironing - (Three-dimensional radius distribution of cup wall)

In order to pave the way for development of a new field of cup-forming (i.e . 'precision cup-forming'), shape quality of formed cups is investigated in detail, for no such data have been reported thus far. Cups are formed by t he processes of deep-drawing and stretch-drawing with or without ironing ac tion. The shape quality is evaluated by the radius distribution of the cup wall, which is displayed as three-dimensional colored maps, representing cl early the distortion pattern of the cup. The materials tested are four kind s of metal, including pure titanium. Spring-back occurs very irregularly in three dimensions, whose magnitude differs from material to material depend ing on the process type. Initial planar anisotropy cannot explain the disto rtion pattern, which suggests that its strain-history dependency plays a si gnificant role. The cup wall radius becomes larger than the die cavity radi us over some region around the cup lip and smaller over other regions. Gene rally, the cup shape is better for greater ratio of ironing, but notable ex ceptions may exist for some materials.