DIE DESIGN FOR AXISYMMETRICAL HOT EXTRUSION

A comprehensive finite element model is presented to obtain the temper ature distribution in the workpiece as well as in the tooling in hot a nd warm extrusion processes. Thermo-mechanical analysis of hot extrusi on process is carried out by combining the comprehensive finite elemen t thermal model with the deformation models [upper bound and rigid-pla stic finite element models presented earlier (N. Venkata Reddy, P. M. Dixit and G. K. Lal, J. Mater. Process. Technol. 55, 331 (1995); N. Ve nkata Reddy, P. M. Dixit and G. K. Lal, ASME J. Engng Ind. 118 (1996)) [1, 2]. The predictions of the combined thermo-mechanical finite elem ent method (TMFEM) are first compared with experimental results to val idate the method. Then it is shown that the temperature distribution a nd the extrusion power obtained by the combined upper bound/finite ele ment method (UBFEM) are in good agreement with those of TMFEM. Since U BFEM takes significantly less computational time than TMFEM, it is use d to obtain the optimal die profile at various process conditions by m inimizing the extrusion power. A simple fracture criterion proposed by Venkata Reddy et al. [ASME J. Engng lnd. 118 (1996)] [2] based on the concept of the hydrostatic stress component in the deformation zone f alling to zero is used along with TMFEM to predict the die lengths at which the initiation of internal defects takes place. Finally, it is s hown that the optimal die profiles satisfy the conditions for preventi on of internal defects. (C) 1997 Elsevier Science Ltd.