Simulation on the Thixocasting Process of the Turbocharger Impellers and Selection of the Viscosity Models

Abstract

The thixocasting technology is chosen to produce the turbocharger impellers as it is capable of producing castings with high precision dimension, free of oxide and shrinkage porosity defects and therefore long service life. The thixocasting turbocharger impellers have the similar mechanical property to those produced by forging and machine processes, but much less costs. In the thixocasting process, the semisolid slurry with certain solid fraction is injected into mould at a high speed. Since high viscosity and thixotropic characteristics, the semisolid slurry reveals unique flow condition and characteristics in the filling process. So, its very desirable for the die design, process optimization, and defect control to visualize the high-speed filling process of semisolid slurry by numerical simulation. In this paper, several commonly used viscosity models for semisolid slurry are analysed. The Power law cut-off model (PLCO) model is selected to simulate the filling process in the thixocasting process of the impellers of 319s alloy, compared with actual results by partial filling testing. The causes of the casting defects are also analysed, indicating that the simulation results can accurately reproduce the filling process of semisolid slurry, and PLCO model is a successful choice for simulating the filling process of semisolid slurry with high solid fraction.

Numerical simulation of mechanical deformation of semi-solid material using a level-set based finite element method

“…In the case of semi-solid material, the velocity field is highly heterogeneous, as the deformation can also be accommodated by the flow of liquid which is much easier than the deformation of solid phase. Note that both the solid and the liquid phases are considered as incompressible, and an incompressibility equation v 0,  ⋅ =  as shown in equation (9), is also resolved through the whole domain.…”

“…Numerical methods therefore provide a good alternative to experimentation to examine the mechanical behavior of materials in a semi-solid state, which allows us, in turn, to optimize the semi-solid processing. One-phase modeling was widely used as an optimization and design tool for semisolid processing [8,9]. In this approach, the semi-solid state is generally taken as a homogeneous material and the flow behavior is represented by using the rheological properties of the mixture [10].…”

Application of Multiphase Modelling in Semi-Solid Die Casting: Blister Prediction

“…In the fluid approach, the majority of researchers [e.g. [6][7][8][9] have considered the semi-solid slurry as a homogeneous single fluid with properties of the mixture and single set of governing equations is solved to simulate the cavity filling process. This one-phase simulation enables the prediction of die filling behaviour in terms of flow pattern in a reasonable range.…”