Papers by Author: Ortwin Hahn

Abstract: In this paper a method for simulating hybrid joining processes will be described. The simulation of joining processes with adhesives is necessary because mechanical joining processes are mostly applied in combination with adhesives. However, the simulation of hybrid joining processes is not state of the art. The reason is the Fluid-Structure-Interaction between the adhesive and the plates, which occurs due to the highly uneven stiffness of the materials. This problem is minimized by the use of an elastic‑plastic material model and a Lagrange formulation for the adhesives. The parameters for the material formulation and the friction have been evaluated by conducting a design of experiment. The correlation between simulation and experiment is ensured by an evaluation of the geometrical distribution of the adhesives within the clinch‑bonding point and the force-displacement diagram. Considering the very low computing time of approximately thirty minutes, the obtained result is very satisfying.

Abstract: The aspect of lightweight constructions becomes more and more important. This particularly applies to the automotive industry which wants to lower the fuel consumption by a smaller vehicle weight. Under this point of view in recent years steel has often been replaced by aluminum alloys. In comparison with this the application of lightweight magnesium alloys, whose specific density is appropriate within the range of plastics, opens further prospects for weight reduction. The pre-condition for this purpose is the supply of suitable joining processes for magnesium alloys, which are universally applicable and offer the maximum utilization of the materials of the joined parts under operating loads. Mechanical joining techniques provide the opportunity of connecting magnesium components homogeneously as well as in material mix. However, the anisotropic deformation characteristics of the hexagonal crystal structure of magnesium at room temperature contain the application for mechanical joining techniques. Only starting from temperatures of approx. 225°C a sufficient plastic deformation and thus a crack-free shaping of the magnesium material is given. Therefore preheating of magnesium substrates leads to a broad extension of deformability and offers the chance to realize a high quality mechanical joint. This article describes a process-safe realization of the mechanical joining operations clinching, self piercing riveting and clinch riveting of magnesium sheets by means of an inductive heating of the substrates in laboratory scale. In this context, feasibilities and limits of the considered joining techniques are shown.

Abstract: In modern car concepts the aspect of lightweight constructions becomes more and more important. Lightweight materials, as aluminum and magnesium, get in the spotlight, thereby. Particularly because of the enormous potential for lightweight constructions industrial interests in magnesium wrought- and casting materials have increased in recent years. Against this background new alternative methods in the range of joining techniques are necessary which consider the specific mechanical-technological properties, such as limited deformability at room temperature and high corrosion-affinity of magnesium. The present article discusses the integration of heating principles in a mechanical joining process of magnesium components without an additional pre-punch operation. In this connection, feasibilities and limits of the considered joining techniques are shown and a concept for thermal support is presented.

Abstract: In order to achieve further reductions in the weight of the body-in-white, efforts are being made in the field of car design to replace structural elements by magnesium components. In addition to the use of extrusion and sheet metal processes, die casting in particular is an especially important method of producing thin-walled, highly integrative components, because of the very good casting properties of magnesium. Integrating of die casted components into a vehicle structure calls for joining techniques which offer the maximum utilization of the materials of the joined parts under operating loads. This article discusses the necessity for material-specific joining techniques for future magnesium body structures. Using the example of aluminium/magnesium joints, the article describes the benefits of different joining techniques with regard to their efficient use of material in the case of both quasi-static and dynamic loads.