An investigation of the geometry and transmission error of injection molded gears

The use of plastic gears is expanding into many different markets. Their application is cost-effective when produced on a large scale using a net-shape process such as injection molding. Variables in the molding process, however, have a direct impact on the final gear geometry. In this research Polyketone gears were molded using three different gating configurations. The effect of gating scheme and packing pressure on the gear's runout, lead variation, and transmission error has been studied. Lastly, a commercially available flow simulation package is used to model molding shrinkage, melt front advancement and temperature. The results of these simulations are compared to experimental data. Gating was shown to have a strong influence on the periodicity of both runout and long term transmission error. However, the gating scheme had minimal influence on the total magnitude of the errors. Packing pressure was shown to decrease all forms of geometric and transmission error for the pressure levels investigated in this study.