A fully-coupled thermal-stress model to predict the behavior of the casting-chill interface in an engine block sand casting process

摘要

The sole use of light alloys in the production of automotive parts might not be the best strategy to reduce the emission of CO_2, as for this purpose, one should consider the life-cycle of the final part. One way to address this issue is to increase the in-service life of the components by modifying the manufacturing process. In the first phase of this study, we used a different chill format in the bonded sand casting process for the production of engine blocks, and it was concluded that this method might increase the fatigue life of the component by refining the microstructure. However, to better understand the dynamics of the casting-chill interface, the development of a thermal-stress model was necessary. This paper summarizes the methodology used to develop a thermal-stress model that predicts the evolution of temperature within the casting and the chill and the evolution of gap and/or pressure at the casting-chill interface. The work identified that the gap size between the H13 chill and the casting at the bottom of the chill in the main bearing bulkhead could reach a maximum of 0.17 mm. Additionally, it was found that the heat transfer coefficient decreased from a peak value of 2500 W m~(-2) K~(-1) to 500 W m~(-2) K~(-1) at a gap size of 0.2 mm. The numerical analysis uncovered a couple of important factors that play a major role in the development of the gap at the interface including the thermal contraction/deformation of the casting; the thermal expansion/deformation of the chill; the constitutive behavior of the casting; the constitutive behavior of the bonded sand mold cap; and, the geometry of the casting-chill interface. Overall, the modeling results show that the interface gap/pressure dynamics are complicated and play a critical role in governing heat transport across the casting-chill interface.