A composite simulation model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder has been developed. The model is based on combining new melt conveying models with melting and solids conveying models, and the die is included into considerations. A general approach is applied using fully three-dimensional non-Newtonian FEM modeling for melt conveying to develop screw pumping characteristics which are implemented into the composite model. Several screw configurations are considered including non-classical elements. Computations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. (C) 2015 Society of Plastics Engineers