For the extrusion of hard aluminum alloys like AA 2024 a special indirect extrusion method is mentioned in the literature. For getting practical data about this process additional hydraulic equipment was build in the 8 MN extrusion press at the R&D-center of extrusion at the Technical University of Berlin. With the help of a high pressure, cylinder and the control of the speed of the dummy block indirect extrusion with active friction could be realized. Generally, by this process an additional frictional force, acting in the direction of the material flow, is used for changing the stress behavior in the billet and also in the extrudate. The 8 MN extrusion press unit, capable of producing extrudates of hollow and solid shapes, running in both extrusion procedures direct and indirect, is equipped with load cells to record the total force F-T, friction force F-F, and die force F-D, whereby friction force only occurs during direct extrusiom By means of computer aided measuring system forces can be determined in relation to the ram displacement. Investigations were done in the field of the initial stage with a view to establishing the optimum conditions for the beginning of extrusion with active friction, since the flow behavior of the material when long billets are upset in the container depends on the extrusion process. The initial stage of direct and indirect extrusion are simulated with the computer FEM - programs 2D and QForm. Extrusion trials were carried out under a wide range of extrusion conditions. The tests confirmed the calculated data as: an upsetting force of about 38% of the maximum deformation force leads at the beginning of the process to indirect extrusion of the usual kind. In this, a significant part of the process is effected by the static friction force between the billet and the container, so no additional active force is acting. Reduction of the upsetting force to 18% of the total load leads to ISA from the very beginning. With this upsetting force and an extrusion ratio of about 30:1 AA 2024 could be extruded at about 380degreesC in a stable way. Comparisons were made with the regular indirect extrusion concerning the maximum speed and temperature development of the extrudate. Additional investigations were carried out in the field of microscopy and measuring of the residual stresses on the surface of the product. The ISA process leads in generally to lower tension stresses on the surface and due to this cracking of the surface could be avoided. By optimization of the extrusion conditions a gain in about 8 - 10% of productivity, compared to indirect extrusion, is possible.
