Abstract: The displacement and circumferential strain of particles on the sidewall which does not lean against die wall during tapered part drawing are analyzed. The result indicates that materials located in the orifice of the concave die at the beginning have the largest displacement and circumferential strain. The compression buckling deformation takes place first at here during tapered part drawing. To overcome the mechanical difficulty in calculating tapered part drawing and seize its essence, a material ring is cut at the orifice and defined as key ring during drawing. The key ring has two possible deformation modes, i.e. circumferential compression and circumferential compression buckling during drawing. The choice of deformation mode is restricted by tapered part size, sheet thickness and physical properties of material. The part only having circumferential compression deformation is called thick-wall tapered part, otherwise called thin-wall tapered part. By comparing the load of compression deformation and that of compression buckling deformation, the critical relative thickness is derived. It can be seen from the analysis of the expression that the instantaneous yield stress and plastic modulus are the main factors of influencing the critical relative thickness. The condition for distinguishing thick-wall tapered part from thin-wall one is obtained by means of the critical relative thickness. Experiment shows that the difference between theoretical calculation and experimental result is not great.

Key words: Drawing, Material processing, Plastic deformation, Punching, Tapered part