The aim of this thesis is to find some essential rules for preform design in die forging. Based on an H-shaped finish product a convenient preform shall be found. Thereby a special attention is turned to the material flow with respect to die filling and flash formation. Various parameters like web thickness, draft angle, fillet radii, corner radii or height of the ribs are investigated. Furthermore, different initial temperatures and heat transfer coefficients between the dies and the forging material are regarded. Since friction plays an outstanding role with respect to material flow the friction coefficient is varied in a suitable range and the influence on the die filling is determined. In a parameter study different preforms are designed. The hot forging process from the preform to the finished form is analysed by means of the finite element code DEFORM 2D. In all computations plain strain is assumed. As different materials show different forming properties a comparison between aluminium and steel is performed. So one can easily see that each material needs its own specially designed preform and that one optimal preform does not exist for the same forging part. In a practical test the forging process of an H-shaped aluminium part is examined. Resulting folds and overlaps due to a non convenient preform are highlighted. Therefore, polished and etched microsections are prepared.