New approach for the dimensional control of plastic gears manufactured by injection molding in the automotive industry

The injection molding process to produce a plastic gear for automotive application has been primarily empirical leading to poor manufacturing practices, a high level of energy waste, and product reprocessing resulting in a negative environmental impact. In this study, we used Taguchi method to solve these issues for improving dimension stability of the plastic gear, considering the five most critical control factors: three mold temperatures (core zone, injection side, and ejection side), packing pressure, and cooling cycle time. Also, an additional parameter was used to elucidate the effect of using recycled resin in the polyoxymethylene (POM) formulation. Melt flow index (MFI) was selected as the noise factor because of the variability in the used composition of virgin POM/recycled POM that could be correlated to the molecular structure and molecular weight of both virgin and recycled POM resins. Results showed that the packing pressure and the mold temperatures are the main parameters to well control the dimensions required in the analyzed plastic gear, it means, the external diameter, empty setDA, hub diameter or position where the gear shaft is fixed, empty setD, and the length, L, of the gear from one end to the other are in the required dimensions of the plastic gear when a blend of virgin and recycled POM resins is used with no effect on mechanical properties of the gear.