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Process Requirements


After the development of the fundamental physical possibilities to simulate the pouring and solidification process of castings, the focus quickly switched to the specific requirements of dif- ferent casting processes, including the evaluation of multiple cycles in permanent mold applications to consider the heat-up sequence of permanent molds and dies, as well as process in- terruptions. Even small process steps, such as the die opening sequence and spraying processes, are considered in detail by simulation tools. Heating and cooling channels cannot only be considered, but can be controlled by virtual thermocouples. The simulation of the low pressure die casting process allows for the input of the exact pressure curve to determine the filling process, as well as the air cooling of die parts (Fig. 13).


Vertically parted sand molds are simulated under differen- tiation between the “hot side” and the “cold side”. It is also possible to consider the shakeout and cooling conditions in cooling drums.


One focus of further development is the utilization of simula- tion results for the optimization of process steps and for the determination of control parameters for diecasting machines


and molding lines. The consideration of a known cooling con- veyor length and a desired shakeout temperature can be used for the prediction of the molding line’s productivity. The final goal is to couple this data directly with the machines.


The Multitude of Materials


Even if the physical fundamentals for filling, solidification, stresses, and cooling process are the same for all alloys, the specific material behavior makes a difference, as displayed in Fig. 14 for aluminum alloys. Beside the process condi- tions, the nominal composition and metallurgical parameters (grain refinement) are defined. Based on this information, the program calculates the potential equilibrium phases, which are impacted by the accelerated cooling condition they experience (phase kinetics). The inhomogeneous solu- bility of alloying elements in the solid and the liquid phase leads to segregations and thereby to the potential creation of new, and sometimes undesired, phases. Only in the final step, based on this information, the solidification progress and the resulting temperature distribution are calculated in a time step. These steps are repeated for every location and every point in time before microstructures and mechanical properties are predicted.


Figure 13. Permanent molds and dies provide a stable process only after they reach a quasi-steady-state condition. Simulation considers all predominant parameters with impact on the heat balance of a die, i.e. cooling and heating channels or coatings. The influence of process interruptions on the temperature distribution in the die, as well as the number of cycles necessary to get back to the steady-state condition can be calculated easily.


International Journal of Metalcasting/Spring 10 13


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