Two-phase simulations as a development tool for thixoforming processes

Semi-solid metal alloys are employed in Thixoforming processes. In the mushy state alloys, consisting of spherical solid particles suspended in a liquid matrix, show shear thinning thixotropic behaviour and exhibit a yield stress. Beyond this the flow behaviour is influenced by the solid fraction, which is dependent on the slurry temperature. Due to the complex flow behaviour of metallic suspensions new concepts of die and process design are required to guarantee a reproducible high quality of the produced parts. To this end a non-isothermal two-phase model has been developed and implemented into a proprietary developed FEM software. The model bases on a modified Herschel-Bulkley approach and comprises the entire non-Newtonian behaviour of semi-solid alloys. A specially designed die filling experiment is used to validate the numerical simulation. The experimental set-up allows to observe the moving flow front during die filling and to measure the pressure. The filling experiments are carried out with various filling velocities and die temperatures.