Increasingly heavy demands for weight and cost reduction have established self-tapping screw connections in multi-material design. In particular screws made of high-strength aluminium and magnesium base materials are prevalent in lightweight constructions. These lightweight materials show a tendency to creep at high temperature operational conditions. Thereby the screw connection suffers a loss of pretension. Because this can inhibit the functionability of the entire assemblage, a finite element model was set up to represent the fastening process and to predict the loss of pretension. This thesis shows that it is possible to describe the process of grooving and tensioning as well as to predict in principle the loss of pretension. The impact of different frictional conditions and model geometries on the momentum curve was studied. The forming process shows strong frictional dependency and the frictional moment takes up the biggest part of the forming moment. The forming moment strongly increases with ascending frictional coefficients. The deformation moment took only a small fraction of the total moment needed. To describe properly the tensioning and creep behaviour of the screw connection, a full model is needed. Only a quarter model is needed to ascertain the moment needed for forming the thread. This thesis developed a primary basis to describe the fastening and relaxation of lightweight, self-tapping screw connections. In future the number of real experiments can be reduced by using improved models. The required experiment time of virtual experiments depends only on the computational power.