Study on Injection Molding of Shell Mold for Aspheric Contact Lens Fabrication

This study aims to propose a method to reduce the shrinkage error of shell molds in the injection molding process. The shell molds are used for casting bi-aspheric soft contact lens with HEMA material. Moldex3D R13.0 is used to simulate and analyze the shrinkage of the front contact lens curve on the front shell mold in Z-axis direction. First, the design of experiment (DOE) method is applied to obtain the optimal setting parameters (melt temperature, injection velocity, and packing pressure). Amount of the shrinkage error is used to compensate the original design curve to improve the shrinkage error in the next simulations. The simulation result after compensation shows that the shrinkage error is reduced as 80.8%. The adding value to compensate the original design curve should be optimized to minimize shrinkage error. Result of this study can effectively improve the shrinkage error before fabricating the shell molds of the soft aspheric contact lens.