Dimensional stability of thin extruded sheets is analyzed as a function of draw ratio. It is assumed that the sheet keeps its rectangular cross section between the flat die and the chill roll and the flow is Newtonian. Through the analysis of linearized equations it is shown that the system is linearly unstable beyond a critical draw ratio similar to the one observed in experimental studies. The nonlinear model is then analyzed using singular perturbation analysis and simulations to confirm the existence of a stable limit cycle.

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