Different concepts of thixoforging and experiments for rheological data

The Institute for Metal Forming (IBF) works on the held of thixoforming in the framework of a Collaborative Research Centre. One forming process to be examined is thixoforging. This process is similar to closed die forging. During thixoforging the available initial material is formed completely to the component. As possible drip off losses may occur during the inductive heating to the semi-solid state and the following billet-transport to the die, an exact volume of the initial material cannot always be ensured. Different tool- and forming-concepts may solve this problem of varying initial material volume. One possibility is to work with excess-material, on the one hand in order to strip off an existing oxide skin before the forming process and on the other hand to direct the excess-material into defined areas in or outside of the component. Another different forming process is the so-called thixo transverse impact extrusion. During the process the material is squeezed sideways from a gating section into a closed die. Therefore the component volume is exactly adjusted and the excess-material remains in the gating section. Simulating the forming process saves time and costs. The simulation of metal forming in the semi-solid state can be difficult. as rheological models and suitable data are required. These data are being obtained by different experiments, such as the classical concentric cylinder and capillary rheometers. But these are only conditionally inserted in the temperature range of semi-solid aluminium. In order to obtain suitable data for this material as well, different experiments have to be used. Upsetting tests. known from the forming technology to investigate flow stresses, can only be used as long as the definiteness of the stress-conditions is guaranteed. Therefore the IBF examines different experiments in order to determine suitable data. (C) 2001 Elsevier Science B.V. All rights reserved.