Abstract
A numerical model based on the upper bound elemental technique for prediction of extrusion pressure in threedimensional direct extrusion process is presented. Using square billets, the study of the effect of die land length has been extended to the evaluations of the extrusion pressures to extrude complex sections such as square, rectangular, I, and T shaped sections with power of deformation due to ironing effect at the die land taken into account. The extrusion pressure contributions due to the die land evaluated theoretically for shaped sections considered are found to increase with die land lengths for any given percentage reduction and also increase with increasing percentage die reductions at any given die land length. The effect of die land lengths on the extrusion pressures increase with increasing complexity of die openings geometry with I-shaped section giving the highest extrusion pressure followed by T-shaped section, rectangular, circular shaped die openings with square section die opening, giving the least extrusion pressure for any given die reduction at any given die land length. The proper choice of die land length is, therefore, imperative if excessive pressure buildup at the emergent section is to be avoided so as to maintain the quality and metallurgical structure of the product. Comparison of the least upper bounds extrusion pressures computed with the experimental results and SERR analysis shows that the upper bound method predicts reasonable extrusion loads well within engineering accuracy.