A study on barrelling behaviour of aluminium billets during cold upsetting with an extrusion die constraint at one end

During the cold upsetting process, barrelling occurs due to the friction between the work piece and the die surfaces. The existence of this frictional constraint directly affects the plastic deformation of the work piece. When a solid cylinder is compressed axially between an extrusion die and a bottom platen, the work piece in contact with the die surfaces undergoes heterogeneous deformation resulting in three geometries, i.e., barreled cylinder, truncated cone part, and extruded part. This work has been taken up to study experimentally the bulging effect of aluminium solid cylinders by introducing an extrusion die at one end. Introducing different lubricants also varies the frictional condition at the die surfaces. Experiments are conducted for three aspect ratios by using different lubricants. The calculations are made on the assumption that the curvature of the bulge follows the form of a circular arc. A relationship is established between various bulge parameters like new hoop strain, geometrical shape factor (1), geometrical shape factor (2), and stress ratio factor.