Extrusion machines like single or twin screw extruders are important for product quality and line speed of the whole extrusion line. The responsibility of good quality and high output is the task of the polymer processing company, but at the beginning it is the task of the machine manufacturer. So everyone is interested in knowing the quality and quantity before the real process takes place. The processes in the screw (pellet conveying, melting, melt conveying and mixing) are quite difficult, so that engineering these systems requires modeling and simulation. We will show current results in calculating the pellet feeding situation in single screw extruders for high speed extrusion machines. Furthermore, we will show results of our new 3D FVM Solver for twin screw extrusion, which was developed with university of Dortmund. Looking to commercial applications, the major challenge is the modeling approach due to the calculation time. First of all we have the analytical approaches which describe the processes with a lot of neglections and simplifications, but require a short calculation time which fits in the industrial engineering timeframe. Software systems have been developed at some institutes, for example the ExtrudPC and REX. A second approach are numerical FDM-solutions which makes possible to have nonlinear and stepwise modeling. But still the geometrical accuracy is limited. Software systems have been developed in some institutes like IKV and University of Stuttgart. The best possible process description will be achieved with fully 3D FEM or FVM with nonlinear viscoelastic flow behavior, but in these techniques we still have two weak points: First, we have to accept long calculation times, which does not fit to industrial engineering. Second, the coupling of melt and pellet conveying and the modeling of the phase transition is not solved well enough. The future work in the institutes will focus on this point to give better solution to the community.