UBA analysis of the process of pipe extrusion through a porthole die

Abstract

The deformation behavior in the extrusion of pipes through a porthole die has been analyzed by means of the upper-bound approach (UBA) and the results compared with experimental ones. The proposed model has a smooth boundary to the plastic region and a continuous velocity field. The predicted extrusion loads were found to be less than 10% greater than the experimentally recorded loads. The results of the analysis show that there exists an optimum depth of the welding chamber with regard to the extrusion pressure. The analysis suggests also that the pressure is greater with a larger ratio of the diameter of the welding chamber to that of the container, and that the variation tendency of the pressure with the number of portholes is effected by whether the circumcircle of portholes is fixed or not. When the length of the billet remaining in the container is smaller than the radius of the container, the plastic region extends over the whole of the billet. For the distribution of the flow velocity and the shape and volume of the dead-metal zone, there exist some differences between the predicted and the experimental results.