  The analysis and the simulation of fluid extruded out of a die opening are of
great importance in different industrial applications. Mathematical modeling
and experimental studies of extrusion out of a constant die gap has been the
subject of numerous publications in the literature. Extrusion Blow Molding is a
polymer forming technique used to manufacture a wide range of large hollow
parts such as fuel tanks used in the automotive industry. The die gap is varied
during extrusion to adjust the manufactured product's final thickness and to
compensate for uneven stretching during molding. In this work, mathematical
modeling of varying die gap extrusion is introduced. Two models using different
approaches are presented to model the time dependent effects of varying the die
gap on the extrudate. In the first approach, physics based partial differential
equations are used to simulate extrusion. The Navier Stokes equations are used
as governing equations to simulate molten polymers. The governing equations are
solved using Arbitrary Lagrangian Eulerian based Finite Element Method. A novel
numerical method for defining the free surface of the extrudate is proposed. In
addition, the effects of varying the die gap on the material velocity, pressure
and extrudate shape are reported. In the second approach, a parameter
identification scheme is used to obtain the parameters of a novel model with a
predefined structure. The purpose of the proposed model is to replicate time
dependent extrudate thickness of the physics based model.
