Extrusion of axi-symmetric bi-metallic tubes from solid circular billets: application of a generalised upper bound analysis and some experiments

The generalised upper bound technique previously applied to the determination of working pressures in extrusion–piercing of solid billets (Chitkara NR, Aleem A. Int J Mech Sci 2001;43:1685–709.) to form hollow monometallic tubes is extended to analyse the problem of bi-metallic tube extrusions through profile shaped dies and mandrel combinations. Theoretical results of mean extrusion pressures obtained from the generalised upper bound analysis are compared with those obtained earlier by the generalised slab method of analysis (Chitkara NR, Aleem A. Int J Mech Sci 2001;43:2857–82.) and some experiments. A few salient observations made during the experimental investigations carried out into forward extrusion of bi-metallic tubes made of h.c. copper and c.p. aluminium are also given and the results commented upon.