Study of Flow and Heat Transfer in High Pressure Die Casting Cooling Channel

Abstract

High-pressure die casting (HPDC) is a widely used process with short cycle times to manufacture complex shapes of aluminium castings for the automotive industry. Most of the die casting companies use specialized commercial software to simulate molten metal filling and solidification. This approach works satisfactorily and is industrially accepted for defect prediction capability. Die cooling is an effective technique to reduce internal porosity in die cast components. But die cooling process is not completely captured in the approach used in the casting simulations. This often resulted in false positives in the defect predictions. One of the main reasons for the lack of precision in simulation is the uncertainty in assigning the boundary conditions such as heat transfer coefficients (HTC) for the die cooling channel. In this study, a coupled simulation strategy was developed to determine accurate HTC values of the die cooling channel. The computational domain was divided into two sub-domains, i.e., casting zone and die cooling zone. Two different industrially accepted simulation tools were used: (a) for casting simulation and (b) for turbulent fluid flow and heat transfer simulation in the cooling channel. A series of iterations were performed by exchanging information at the interface between the two sub-domains till the convergence was achieved. Experiments were also conducted with a thermocouple inserted in the die and the actual die temperature readings were measured. The converged simulation results agreed well with the experimental measurements. Also, the influence of flow rate on HTC was studied by conducting experiments with two different flow rates and the castings produced were analyzed with the help of CT scan analysis, micro-structure evaluation and thermal imaging. The obtained results demonstrated the efficacy of the method adopted in prescribing the values of heat transfer conditions in casting simulations. With the coupled simulation approach developed in this work, parametric studies were conducted to maximize the heat removal rate from a given die, for different flow velocities, nozzle diameters, cooling hole diameters and nozzle-to-surface spacings.