Computer Simulation


A finite element model was created using commercial soft- ware to simulate the solidification process of the casting. The model setup is as shown in the figure below. The ini- tial melt temperature was maintained at 660C (1220F). Pure copper was chosen as the chill material and was initially set at 190C (374F) as was measured during the experiments. The mold and chill surfaces were assigned adiabatic bound- ary conditions to simulate one dimensional heat flow. The cooling water effect was simulated by assigning a constant film coefficient at the cooling channels.


Heat transfer coefficients were calculated by an inverse analysis approach using an in-house optimization pack- age7


(OPTCASTTM ). An initial heat transfer coefficient was


guessed at the interface to calculate the temperature profile at nodes 1502 and 3954 (representing thermocouples Td1 and Td2 respectively). These calculated temperature profiles were then compared with experimentally measured tempera- ture profiles. The initial heat transfer coefficient was chosen from preliminary modeling and by using a trial and error approach. Although solidification between the casting and the chill depends on several parameters, heat transfer coef- ficients (effectively air gaps) were considered as the domi-


(a)


(b)


Figure 7. (a) Model setup using casting simulation software; (b) Increased mesh intensity at casting-chill interface.


70 International Journal of Metalcasting/Spring 11


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