Research on Extrusion Process with Effective Stick Friction : 1st Report, Theoretical Analysis on Forming of Thin-Wall Cup

Abstract

A new concept of "tribo-forming" for producing a thin-wall cup is proposed in the present work. The process proposed is similar to a backward extrusion. The solid workpiece is compressed between the punch and the anvil punch in the container cavity, but the anvil punch is retarded by pushing the punch under constant pressure. The cup wall is formed by stick friction between the internal face of the container cavity and the side face of the workpiece. The process combines extrusion with effective stick friction : hence the name "tribo-extrusion". A relative punch pressure p_m/Y in the tribo-extrusion was predicted at a relatively low value of 2∼2.5 within the 60∼97.5% in reduction of area by the upper bound approach when the stick friction drag was employed effectively. On the other hand, the value of p_m/Y predicted in the backward extrusion was higher than about 4 and increased as the reduction of area increased.