Comparison of injection molding processability of polylactic acid and high density polyethylene via computational approach

The purpose of this paper is to compare the injection molding processability of polylactic acid (PLA) and high density polyethylene (HDPE) via a computational method. This study was conducted using injection molding simulation software Moldflow ® using an iPhone 4 case (I4C) to evaluate the filling and packing stages of PLA and HDPE. The fill time, velocity/pressure switch over (VPSO), frozen layer fraction, time to freeze, volumetric shrinkages and clamp force were analyzed. The results showed that PLA requires a slightly longer time to fill the cavity compared to HDPE. At the mean time, the VPSO of PLA was larger than HDPE, as a result of the higher viscosity characteristic of PLA. From the packing analysis, it was found that the extent of shrinkage for PLA and HDPE was 4.11% and 4.78%, respectively. This result shows that an I4C produced by either PLA or HDPE have very close dimensions. In other words, the redesign of mold to fulfill the different shrinkage extent for PLA and HDPE is unnecessary, which indicates a cost of production saving. Finally, the manufacturing of PLA required a higher tonnage injection molding machine compared to HDPE where the clamp tonnage of PLA is 2.5 times higher than HDPE.