Modelling and simulation of forming processes of metallic suspensions under non-isothermal conditions

The processing of semisolid metal alloys in the innovative Thixoforming process induces several problems in the design of new dies and process strategies. This is mainly caused by the fact that segregation occurs in flows of suspensions and that semisolid metal alloys show shear thinning thixotropic behaviour and exhibit a yield stress. Beyond this the flow behaviour is influenced by the solid fraction, which depends on the slurry temperature. One way to reduce the development costs for new Thixoforming processes is to apply computational fluid dynamics. To this end a non-isothermal two-phase model has been developed and implemented into a proprietary developed FEM software. The model is based on a modified Herschel–Bulkley approach and comprises the entire non-Newtonian behaviour of semisolid alloys. The model has been validated with the experimental results of a specially designed die filling experiment. This experiment allows the observation of the flow front during the filling process for different filling velocities and die temperatures. The die geometries used represent two characteristic flow conditions of industrial casting processes, like sudden changes in flow direction and abrupt changes of the free cross-section. The reference values for the numerical simulation are the contour of the flow front, the spatial solid fraction distribution and the filling pressure.