Characterization of process and machine dynamics on the precision replication of microlens arrays using microinjection moulding

Injection moulding has shown its advantages and prevalence in the production of plastic optical components, the performance and functionality of which rely on the precision replication of surface forms and on minimizing residual stress. The present work constitutes a systematic and comprehensive analysis of practical microlens arrays that are designed for light-field applications. Process parameters are screened and optimized using a two-stage design of experiments approach. Based on in-line process monitoring and a quantitative and qualitative evaluation being carried out in terms of geometric accuracy, surface quality and stress birefringence, the replication is shown to relate directly to machine settings and dynamic machine responses. The geometric accuracy and stress birefringence are both largely associated with screw displacement and peak cavity pressure during the packing stage, while surface quality is closely related to cavity temperature. This study provides important insights and recommendations regarding the overall replication quality of microlens arrays, while advanced injection moulding solutions may be necessary to further improve the general replication quality.