Mathematical and computational modeling of die filling in semisolid metal processing

Semisolid metal processing is gaining interest very rapidly in the casting industry. It offers distinct advantages over other near-net-shape technolog ies, such as a more homogeneous microstructure, less porosity and thus impr oved mechanical properties. A perfect control of die filling during process ing is however necessary, especially in the case of semisolid forming of al uminum, where a non-controlled die filling can lead to oxide inclusions. Numerical simulation can be used to predict die filling, and hence to optim ize the die design. However, the constitutive behavior of semisolid metals is quite complex. Their non-Newtonian behavior depends not only on the volu me fraction of liquid, but also on the metal's history prior to processing, and the processing conditions. In this study, a "Bingham type", or Herschel-Bulkley constitutive relation is introduced, capable of describing correctly the bulk behavior of the sem isolid slurry. This constitutive equation is implemented in a modified vers ion of the casting simulation package PAM CAST SIMULOR. Simulations for the filling of 2-D and 3-D cavities using different injection speeds and mater ial parameters are presented. The results are in good agreement with experi mental evidences featuring similar geometric characteristics. Optimization of die design using numerical simulation is also introduced. (C) 1999 Publi shed by Elsevier Science S.A. All rights reserved.