The effect of packing phase and mold temperature on the directional warpage of spherical lenses using the injection molding process

Abstract

This study investigated the directional warpage on bi-convex and bi-concave spherical lenses by experimentally monitoring the changes in the pressure and temperature of mold cavity and comparing them with the simulation results. Warpage was investigated in the direction of the introduction of molten materials into the cavity of the mold, and when it was perpendicular to the direction of the fluid wave front. Packing conditions, including packing time and packing pressure, and mold temperatures are among the important factors influencing lens warpage and their geometric quality. In this research, these factors were investigated in a full factorial design of experiment. Also, simulation results are in good agreement with the experimental results obtained by the vision measuring machine apparatus. According to the results of this study, the least warpage values in bi-convex and bi-concave lenses in the direction of the fluid wave front were 180 and 200 microns, respectively; while these values were 172 and 198 microns when the lenses were perpendicular to the fluid wave front. The experimental values of these in the direction of the melt in the entrance of the mold for bi-convex and bi-concave lenses were 149 and 186 microns, respectively, while these values were 143 and 180 microns when the lenses were perpendicular to the flow front direction. In addition, the results of the pressure diagram inside the mold cavities indicated the correlation with the warpage, such that when the slope of the pressure graph was lower, the lens warpage was less too.