2021 Volume 93 Issue 7 Pages 387-393
In diecasting, the J factor is an index defined by the gate speed and gate shape. In this work, the J factor was increased using a diecast piston mold (high J factor method) to determine whether this method can reduce porosities in products. In the experiments, the J factor was adjusted by varying the gate shape and injection speed. Porosity was quantified as the volume fraction of porosity in a specific region measured by micro CT. In all cases, the porosity in thick parts of pistons was reduced. Next, the high J factor method was used to examine the transmission of molten metal pressure to the overflow part. At higher J factors, the surge pressure increased linearly and pressure was transmitted more efficiently. Additionally, the gas content in the product increased at high J factors obtained by increasing the gate speed. However, the gas content in each part of the product was almost constant regardless of porosity amounts. Secondary ion mass spectroscopy (SIMS) was also used to measure amounts of gas microscopically. Hydrogen and nitrogen were observed in the base material in parts where no porosity was observed. Although increasing the J factor changed the shape of porosity from a shrinkage shape to spherical, dendrites were observed for both porosity shapes. The above results suggest that the shrinkage shaped porosity and spherical porosity were formed by the same process. The experimental results were quantitatively reproduced using casting CAE software with a nucleation model for porosity formation.
