Analysis of the casting process by means of the Control Volume Method
The results of a sample analysis are briefly discussed in the following.
The filling of the mould and the temperature field can be evaluated at different times during the filling process, as shown above. The cooling of titanium and the resultant solidification process is observed. The cylinders at a lower temperature are shown. It is possible to identify the areas where the low temperature of titanium results in high viscosity. If the viscosity is too high to permit proper flow of titanium the presence of voids may occur. A better design of the process may require a different feeding rate or a different number and/or position of the feeders. These changes can be simulated by changing the boundary conditions and/or by changing the geometry of the model.
The velocity field at a given instant is shown above. The velocity field in the mould can be analysed in order to understand if the feeding system is appropriate for the mould.
The cooling rate shown above indicates how fast the temperature lowers in time: it is defined as the module of the temperature change divided by time. The cooling rate can be used as an index of the final micro-porosity and of the resultant mechanical characteristics of titanium. A higher cooling rate determines the formation of smaller mineral crystals, obtaining a material with better mechanical characteristics.
The cooling rate determines the solidification time shown in the above picture. The higher the cooling rate, the shorter it takes to titanium to solidify. Solidification time in the bar should be as homogeneous as possible. Micro-porosity tends to be higher in correspondence to longer solidification times. Shorter solidification times imply smaller mineral crystals and better mechanical characteristics. Hot spots may also be detected. These are the last areas to solidify due to the high solidification time. If hot spots are not properly fed shrinkage macro porosity may result.
