This paper presents a method for a NC-Simulation based prediction of shape errors caused by thermal expansions in machining of complex workpieces. In the first part of the paper the basic approach of modeling a thermomechanical NC-Simulation for a faster and more precise process simulation is shown. Therefore, a fast dexel based material removal simulation including process models for calculation of localized heat flux and forces is linked to a FE model for simulation of thermal conduction in the workpiece. Interdependencies of thermal process and workpiece conditions are considered by a closed simulation loop. In the second part of the paper the modeling of each component is explained. To consider thermomechanical effects in material removal simulation the dexel based workpiece model is extended by additional information like temperature and deformation in every dexel. An inverse projection of the workpiece deformation on a triangulated tool model allows consideration this effect by deformation of the tool model. Thereby, a realistic shape of the workpiece can be simulated. In addition, the current cutting conditions like area of undeformed chip-thickness or contact length are changed. This results in diversified cutting forces and heat fluxes. For a realistic simulation of the thermal conduction the dimensions of the FE model have to be adapted by a time dependent virtual domain method. In the last part of the paper, results of the simulation are compared to measured data. The comparison shows that process temperatures in different workpiece areas are predicted accurately.