Simulation and Experimental Study of the Flow Mechanism of Injection-Molded Materials for Optical Non-Spherical Cylindrical Lens

The surface quality of polycarbonate optical lenses during injection molding is critical to their optical performance. This study investigates the formation mechanism of haze-like defects on aspherical lenses under different injection speeds through a combination of simulation and experimental methods. Inappropriate injection speed leads to the appearance of noticeable haze-like opaque regions on the surface of aspherical lenses. Microscopy observations indicate the presence of oriented fiber flow lines in these haze-like regions. The experimental findings suggest that the formation of these fiber flow lines is closely related to injection speed, gate position, and abrupt changes in the flow region. Through Moldflow numerical simulations, the filling and flow behavior under different injection speeds were analyzed. The study reveals that in abrupt flow cross-section transition regions, elevated injection velocities induce significant variations in melt flow velocity, shear rate, and shear stress. High shear conditions trigger flow instabilities, while localized flow resistance caused by abrupt cross-sectional changes further amplifies these instabilities. Furthermore, localized pressure fluctuations promote bubble nucleation and premature melt solidification, ultimately leading to fiber flow mark formation. These findings establish a crucial theoretical foundation for the surface quality enhancement of polycarbonate optical lenses.