The influence of the punch land in backward can extrusion

Backward can extrusion punches are commonly made with a cylindrical punch land as also recommended by the ICFG. The contact forces on the punch land have been determined using the slab analysis method and FEM. The results show that a slight tilt of the punch land changes the contact conditions between punch land and can wall causing on the punch a net force, which will deflect the punch off centre leading to variations in wall thickness. A new punch design is proposed in which the cylindrical punch land is replaced with a circular profiled punch land. Using a circular profiled punch land, a slight tilt of the punch gives only rise to minor changes in the contact conditions between punch land and can wall and thus only rise to minor variations in the wall thickness. The backward extrusion of a high thin walled aluminium can has been carried out experimentally and the results show that cans produced with the circular profiled punch land have a significant lower variation in wall thickness than the cans produced with the punch with the cylindrical punch land.