A Method to set process parameters of local squeeze in HPDC

Abstract

In HPDC processes, pressurization of the mushy regions via local squeeze pins and plunger during the intensification stage is very important to decrease porosity defects. In order to better understand the process and to be able to set the process parameters more properly, we developed a simulation code to solve the flow field of mushy regions and porosity formation based on the following main assumptions: 1) Local squeeze pins and plunger tip can be treated as pressure boundaries, while the squeeze pins are treated as moving boundaries. 2)The intensification and local squeeze pressure can propagate inside regions where the solid fraction is less than critical values. 3) In the pressurized regions, the cast metal is treated as a Newtonian fluid and both the solid and liquid flow together when the solid fraction is low, and the D'Arcy flow only exists when the solid fraction goes higher. 3) Only the liquid flows in the unpressurized regions, following the D'Arcy's law. 4) Porosities grow in elements when the pressure decreases below critical values depending on the element condition. The simulation was applied to HPDC castings and showed that the pressure-duration was similar to the measured one though the simulated pressure drop in the pressurized region was much smaller than the measured one. The pressure drop, pressure-duration and pin-penetration depth were discussed and the simulation seems to be helpful to determine local squeeze parameters. Future challenges are also discussed.