The Effect of Equivalent Strain on Punch Load for Cold Backward Extrusion of Copper Cans

Abstract

The paper presents experimental and computer modelling (FEM) results of investigations into cold backward extrusion of copper cans. The simulations were performed using QFORM software based the finite element method (FEM). The samples used in investigations were pieces of copper rods having the diameter d0 = 24,5 mm and height h0 = 16 mm (h0/d0=0,65). The billets were heat treated (annealed). Heat treatment is used to increase the plasticity of the material before cold backward extrusion. The material was annealed at 550°C for a period of 1 h, and then subjected to solution treatment in water. The flat and conical punch-face shapes with different diameter of punch used for cold extrusion (ds=15mm; 16mm; 17mm; 19mm and 20mm, respectively). The deformation ratios of material in paper was defined as relative: strain of can bottom thickness εh =Δh/h0 (where Δh – the punch displacement, h0 – billet height), reduction in area εA= (A0-A1)/A0 and equivalent strain ε= ln (A0/A1) (where A0 – cross sectional area of the billet, A1 - cross sectional area of the die stamping). In investigations, computer calculated and experimental force waveforms as the function of displacement and εh were obtained. Comparing changes in forces in cold backward extrusion for different diameter of punch, it is stated that the load Pw increases with an increase in εh. The effect of equivalent strain ε on punch load Pw for cold backward extrusion of copper cans is presented. Both in experimental and modeling investigations, the axial force increased together with an increase in the equivalent strain.