It is a known fact that melted glass, such as SiO 2 , shows viscoelastic behavior. But in the range of processing temperatures the mechanical properties of SiO 2 vary strongly. While below 800°C the material behaves like an elastic solid, at temperatures above 1000°C it shows nearly pure viscous properties. In this paper the governing equation, the so called constitutive equation, describing viscoelastic behavior, and its discretization are presented. Especially the truncation error of the time discretization is investigated. The oxide viscosity depends on the local amount of shear stresses which leads to inhomogeneous material behavior and a non-linear theory. This new mechanical model was implemented into the process simulator DIOS- ISE . Some obtained simulation results are shown and discussed.