A study of the effects of process parameters for injection molding on surface quality of optical lenses

The purpose of this study is to determine the effects of process parameters on optical quality of lenses during injection molding. The quality characteristics chosen are light transmission, surface waviness and surface finish. The Taguchi method is used to perform screening experiments to identify the important significant process parameters affecting quality of lenses. Through empirical and theoretical analysis, the most significant process parameters affecting surface waviness is the melt temperature, followed by mold temperature, injection pressure and packing pressure. On the other hand, injection molding process parameters are found to have little effect on light transmission and surface finish of lenses. Regression approach is then implemented based on surface waviness data from full factorial experiments to formulate the regression models. Three different regression methods are used, namely, linear, exponential and nonlinear regression. Verification experiments are executed to examine the accuracy of the regression model for predicting quality characteristics of lenses. The result showed the highest accuracy prediction of surface waviness was from a nonlinear regression model. An error of only 4.24% suggested the existence of a correlation among injection molding process parameters.