Flow restrictor design for extrusion slit dies for a range of materials: Simulation and comparison of optimization techniques

Based on a finite element simulation of slit die performance that takes into account the coupling of melt flow and die body deflection due to melt pressure, a genetic algorithm, a multipoint approximation optimization technique, and a gradient-based optimization technique are applied to determine choker bar profiles to give optimum melt flow distribution. The performances of the optimization methods are compared with respect to efficiency and ability to obtain a global optimum. This work involves three materials of varying degrees of shear thinning, each at a high and a low flow rate. The developed software makes it possible to predict whether restrictor adjustment can produce acceptably uniform flow distribution in a given application, using a given die, and shows what restrictor profile should be set up, thereby eliminating or reducing the need for on-line trial and adjustment, and establishing if the same die can be used for a range of materials to reduce costs.