Speaker
Description
High pressure die casting (HPDC) is an increasingly important production process for large components and thin-walled housings. When geometries combine large thin areas with volumetric areas, defects due to misrun, cold shut, air entrainment and porosity can be found in one part and influence each other. The simulation based process optimization must describe these defects in a fully coupled manner using a combined modelling approach.
A three phase fully coupled mold filling and solidification methodology is used to accomplish this task. Liquid melt and gas are treated as compressible fluids separated by a sharp interface. Reduced melt flow due to solidification is achieved by a mushy-zone model. At higher volume fractions of solidified melt, a flow stop model completely hinders the melt flow, even if high pressure is still present. The methodology enables a fully coupled simulation of reduced melt flow, air entrainments, misruns and cold shots.
The formation of porosity due to volume shrinkage is combined with this method using a gas evaporation model: If the pressure in areas enclosed by the solidified melt falls below a critical value due to the volume shrinkage of the melt, the model creates a gas phase to compensate for the volume deficit and keep the pressure at the critical level. In this way, the formation of the shrinkage porosity is modeled in a realistic way. Only after the velocities in the melt have fallen below a critical value, the flow simulation is stopped and a pure thermal macro-shrinkage model is used to calculate the formation of porosity up to complete solidification.
The model has been validated by casting trials using a specially developed test geometry for thin-walled aluminum HPDC applications.
| Speaker Country | Germany |
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