This paper presents a 3D finite element (FE) model of a thread forming screw assembly process based on the ABAQUS 6.5.4 Explicit software program. The model consists of two principal elements: an thread forming screw and a lower 4 mm plate into which the screw taps its threads. The aim was to develop a robust industrial dimensioning tool; the model can be extended to establish the preload and investigate other types of assemblies. A 45 deg sector, which represents 1/8 of the joint, was modeled to maintain a good compromise between calculation time and an accurate representation of the thread forming process. The intent of the study was to analyze the material flow throughout the thread forming process; a parametrical study was also conducted to identify the most influential process parameters. To validate the model, FE numerical simulation results are compared with published experimental results. The study shows that the lead hole diameter has an important influence on the screwing torque.