IDEAL-VISCOPLASTIC EXTRUSION MODEL

An approximate one-dimensional analysis is presented for the extrusion of incompressible ideal-viscoplastic material through converging axisymmetric dies. The extrusion model incorporates the fundamental effects of inertia, plastic deformation, strain-rate behaviour, and surface friction by employing the constitutive relations for a Bingham-type body to describe the stress-strain-rate behaviour of the extrudite, an appropriate quasi-steady locally-spherical kinematically-admissible velocity field to represent the actual flow field, and a combination Coulomb and constant-shear-factor laws to estimate the frictional forces along the die surface. Comparisons of the predictions of the theory to experimental data and finite-element computations demonstrate that it is a useful and economical tool for predicting many extrusion processes.