The study is concerned with the axisymmetric thermo-viscoplastic finite element analysis of axisymmetric forward hot extrusion of round billets through square dies. In the extrusion through square dies, temperature distribution is changing continuously with the punch travel. Accordingly, the distribution of material property and eventually deformation change. In the present analysis, the problem is thus treated as a nonsteady state.
In square-die extrusion, difficulties arise from the severe distortion and die interference of elements at the aperture rim of the die even with a small punch travel and finite element computation is impossible without intermittent remeshing. An automatic remeshing technique is proposed by employing specially designed mesh structure near the aperture rim. The analysis of temperature distribution includes heat conduction through material interfaces, heat convection and radiation to the atmosphere and is carried out by decoupling the heat analysis from the analysis of deformation. A method of treatment for heat transfer through the contact interface between the die and the workpiece is need in order to avoid the remeshing of die elements.
Experiments are carried out for hot extrusion of lead billets through square dies at the room temperature. The experiment results are compared with the computation for lead extrusion. The computed distortions are found to be in good agreement with the experimental obsrevations. Computations are also carried out for hot aluminum extrusion through square dies for two initial die temperature. The extrusion load in case of lead billets shows some discrepancy between computation and experiment. This discrepancy is explained from the analysis of aluminum extrusion. The distributions of stress, strain rate and temperature are computed for two cases of extrusion ratios in hot aluminum extrusion. It has been thus showm that the proposed method of analysis can be effectively applied to the axisymmetric hot extrusion through square dies.