The study is concerned with the analysis of the axisymmetric combined extrusion using a generalized upper bound method.
For the steady state, three kinds of model are assumed and upper bound solutions for extrusion pressures is obtained for each model. Computations are carried out for the following three models :
(1) velocity field with straight plastic boundary
(2) velocity field with curved plastic boundary
(3) central flow model using adequate velocity transformation.
Experiments are carried out with commercially pure aluminum billets for various reduction of area.
There is generally good agreement between the theoretical prediction and the experimental observation for the forming load. Especially, the third model renders the best result for the prediction of extrusion load and the second model shows the acceptable flow pattern similar to the actual one.
