keywords: Finite element, solidification, shrinkage, Al-Si A1200, Al-Si A8011 castings
Solidification plays a critical role in the production of sound castings. Hence, an understanding of the casting solidification mechanism and how it can be controlled are important considerations in foundry work. Model flow charts were developed for the Gating, Mould Filling and Solidification processes. Finite Element method was used to discretize and solve the governing equations developed for the models using the commercial software, Comsol Multi-Physics. Models developed were validated from experimental data obtained from the Foundry using three different dimensions each for Aluminium alloys A1200 and A8011 by study the temperature profiles and nature of the solidification of the alloys. A comparison of the temperature profiles generated from the experiments and simulations show that in 64% of the processes, there were no significant differences between the experimental and simulated values. However, in comparing the Niyama values obtained from the experiments and those from the simulations, there were no significant differences in 46% of the processes. Threshold Niyama values of 0.103°C-s)1/2 /mm for A1200 and 0.143°C-s)1/2/mm for A8011 were also established. Below these threshold values, it is predicted that shrinkage will occur in castings from these metals. This research work showed that temperature gradients and cooling rates are important in predicting the occurrence of shrinkage in casting. Also, alloy composition affects the threshold Niyama values. This is because the Niyama value obtained for alloy A8011 (0.143°C-s)1/2/mm) was higher than that of alloy A1200 (0.103°C-s)1/2/mm) which had a lower silicon content.