Computational Modeling of Hole Distortion in Extruded Microstructured Optical Fiber Glass Preforms

Extrusion of glass preforms that are used to draw microstructured optical fibers was simulated using computational mechanics. The study focused on a preform with a cross-section geometry that contains 36 holes arranged in three hexagonal rings. Symmetry allowed for the modeling of a 30° portion of the cross section, which included five holes within this reduced computational domain. The simulations took into account flow through an array of 13 feed holes, flow along five circular pins to create the holes, exit from the die, and the development of a constant profile for the cross section of the preform. The primary concern in the study was exploring the capacity of the model to reproduce the observed distortion of the extruded holes, i.e., the difference between the holes that develop and the negative of the pin arrangement, by taking into account the complexity of the flow. The key features that describe the model are viscous flow, uniform temperature, interface slip using the Navier friction model, and the assumption of a steady-state solution. Validation of the procedure was based on a comparison between the predicted cross section and an actual preform. The results show that distortion of the holes is rather sensitive to the level of friction, which provides insight into reducing the magnitude of distortion in future experimental work.