Modelling the pressure die casting process with the boundary element method: Steady state approximation

This paper describes a model which can predict the temperatures on the cavity surfaces of a die. The time varying boundary conditions are averaged so that the process can be modelled as a steady state problem. Since the model considers only thin components, it is reasonable to assume that the melt has totally solidified before ejection, and therefore the quantity of heat energy entering the die over the casting cycle can be estimated. This and other assumptions relating to the boundary conditions also enable the value of thermal resistance between the melt and the die to be estimated. Under certain conditions, subcooled nucleate boiling takes place in the cooling channels of the die. An iterative procedure is used to take account of this, which involves the repeated calculation of global heat transfer coefficients for the cooling channels, with the criteria that the total energy transferred through the channels is equal to that transferred due to boiling and convection. The boundary element method is used to predict the cavity temperatures. In die casting, only the temperatures on the cavity surfaces are of interest since the surface quality of a component is related significantly to the temperature distribution over the cavity. Since only thin components are considered herein, it is not necessary to model the solidifcation process and discretize the cast. These factors make the BEM ideally suited for the work described in this paper. To verify the model, the predicted temperatures for two components are compared with experimental values measured using thermocouples and a thermal imaging camera. It was found that there is fairly good agreement between the two sets of results.