Analysis Of Gate Freeze-Off Time In Injection Molding

Abstract

Gate solidification time is an important topic in injection molding technology, as it determines cycle time, which itself is an important issue in the economics of the production process. In this work, a study of the effect of both gate and cavity geometries on gate solidification time was conducted, using a commercial polymer, injection molded with constant holding pressure into a rectangular cavity. Three cavity lengths were used, and for each, two cavity thicknesses were adopted. Spe- cial dies containing different gates were assembled in the mold. Gate thickness was found to be the most important factor determining gate sealing time. However, the cavity geometry is also quite important. A clear indication on gate solidification could be drawn by analyzing time evolution of pressure distribution inside the mold. The solidification phenomenon leading to gate sealing was analyzed by a sim- ple model, which also takes into account the effect of cavity geometry, by compar- ing the heat flow through the gate walls and the energy required to solidify the packing flow rate. Model results satisfactorily describe the main features of the ex- perimental data.