Cavity Pressure and Cell Formation Characteristics in FIM of PP Using a Chemical Blowing Agent

This paper describes the foam injection molding (FIM) of polypropylene containing a chemical blowing agent (CBA). Cavity pressures were measured according to the injection temperature, injection speed, plasticization speed, and back pressure in the heating cylinder. We then observed the cell formations and weight reductions in the specimens. When there was tail pressure near the gate it was hard to form a cell near the gate. We found that there was a suitable temperature and injection speed for cell formation and weight reduction ratio. As the back pressure in the heating cylinder of injection molding machine increased, the density and size of the cell and weight reduction ratio decreased proportionally. The cavity pressure in the FIM was much lower than that of the conventional injection molding (CIM). This study demonstrates that FIM with a CBA can lower the manufacturing cost as well as product weight compared to the CIM.