Flexible Manufacture of Lightweight Frame Structures, 2008

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Authors: Eduard Ungemach, Tobias Surmann, Andreas Zabel
Abstract: Lightweight extrusion profiles with reinforcement elements are promising news in the domain of lightweight construction. The machining of them suffers from several problems: Aside from the question of choosing a suitable tool, feed rate, and milling strategy, an excessive rise in temperature could lead to stress and even a distortion due to the differing thermal expansion of the reinforcement material and the surrounding matrix material. A simulation of the milling process could, in addition to force and collision calculations, recognize this case before manufacturing. For certain milling applications like seal surfaces, a certain roughness of the manufactured surface is necessary. In many other cases, a smooth surface of very high quality is desirable. Available simulation systems usually completely lack the simulation of dynamic effects, which have a great effect on the final surface quality, and therefore are not able to predict the resulting surface quality. In this paper simulation methods are presented that are capable of simulating the dynamic behavior of the tool in the milling process and the resulting flank and ground surface structures. Additionally, a fast temperature simulation for heterogeneous workpieces with reinforcement elements, which is based on the finite difference method and cellular automata, is introduced.
Authors: Klaus Weinert, Dirk Biermann, Michael Kersting, Sven Grünert
Abstract: Different possible reasons for defects have to be considered in machining light-weight aluminum structures. In the machining process, the cutting power affecting the workpiece leads to a thermo-mechanical load that can cause undesirable workpiece deformations and thus shape deviations. Moreover, the microstructure and the machined surface can be influenced, which is detrimental to the later application of the structures. Previously conducted experimental and simulative investigations, estimated the circular milling process to be the most suitable machining operation that provides the best compromise between mechanical and thermal loads compared to drilling operations [1,2]. In this paper the results of machining end-cross-sections of an aluminum profile are presented. The machining was obtained by a milling process, which is demanding, because of the low profile stiffness. For this process it is important to know the effects of machining in view of the shape deviations. By means of a Finite-Element-Analysis the deformations of the profile web can be calculated as well as validated by experiments. Based on these results, the appropriate process parameter values for end machining can be defined.
Authors: Michael F. Zaeh, Alexander Schober
Abstract: In the field of light weight frame structures the assurance of dimensional accuracy and the prediction of structural properties especially during and after welding processes are of great importance. The problem in this regard mostly arises from the used welding technique which is characterised by complex interactions of various parameters. A simulative approach is useful in order to predict the structural behaviour and to improve the geometrical quality of joined light weight components after welding. As such, it contributes to reduce process adjustments in the early stage of the product life cycle, and therefore helps to save time and costs. In this paper an approach for modelling the innovative joining process of composite extruded profiles by friction stir welding is presented.
Authors: Martin Huber, Ö. Petersson, H. Baier
Abstract: In this paper we present a method for the multidisciplinary optimization of structures including qualitative expert knowledge. In addition to multi objective and discrete tasks, which are solved with a genetic algorithm, mainly expert knowledge and experience is available for certain influences in early design stages. Fuzzy Rule Based Systems (FRBS) provide a powerful tool to model such influences via qualitative human knowledge. Based on this idea, a method for building qualitative, knowledge based models has been developed at the institute and enhanced. As an example, structural components constructed from composite aluminum profiles with embedded continuous reinforcing elements have been optimized.
Authors: G. Lanza, Jürgen Fleischer, Daniel Ruch
Abstract: This article describes a clamping concept for the flexible machining of spatially curved profiles developed at the wbk Institute of Production Science of the Universität Karlsruhe (TH). Simple geometrical considerations form the basis of the prototypically implemented clamping system design. The approach presented in this article allows for accuracy improvements regarding the positioning of the profile in the clamping system on the basis of markings applied onto the surface of the profile. Besides, the preliminary test rig set up and first results on the detection of the markings by means of digital image processing are presented.
Authors: Jürgen Fleischer, Jan Philipp Schmidt-Ewig
Abstract: Within traffic engineering, the importance of lightweight space frame structures continuously grows. The space frame design offers many advantages for light weight construction but also brings challenges for the production technology. For example, the important requests concerning product flexibility and reconfiguration can only be achieved with a high technical effort, if current machine technology is used. For this reason, the collaborative research center SFB/TR10 investigates the scientific fundamentals of a process chain for the product flexible and automated production of space frame structures. An important component in space frame structures are curved extrusion profiles. Within the investigated process chain, the extrusions must be machined mechanically in order to apply holes and to prepare the extrusion ends for the following welding operation.The machining is currently done by clamping the profile into a fixture and processing it within a machining center. This procedure has two disadvantages due to the complex geometry and the partially high length of the extrusion profiles: On the one hand, a complex fixture is needed for clamping the work piece [1]. On the other hand, a machining center with a large workspace and five machine axes is required [2]. Due to this, the product flexible machining with current technology is only possible with high technical and economical effort. For this reason, a new machine concept for the product flexible machining of three dimensionally curved extrusion profiles was developed at the University of Karlsruhe. In this paper, the function of the machine is explained and a prototype is presented. In addition, investigation results of the machining accuracy are shown and possibilities for improving the precision are discussed.
Authors: M. Wedekind, H. Baier
Abstract: Compound extruded unidirectionally reinforced profiles are heterogeneously reinforced metal matrix composites. Profiles made from this material show a different mechanical behaviour than classical composite components. Homogenized material properties are required for an efficient design process. Within this paper an approach is shown to provide homogenized data for stiffness and strength for compound-extruded components. The usability of the Tsai-Hill failure criterion is investigated, and shown for cases with negligible residual stresses. Load cases including thermal stresses cannot be investigated by the Tsai- Hill failure criterion. Within the failure investigation a procedure is shown to include residual and thermal stresses.
Authors: Michael F. Zaeh, Mirko Langhorst
Abstract: In order to support production tasks in the automotive industry, to reduce costs due to a trial and error procedure during process design and plant construction and to secure the accuracy of frame component assemblies, modern simulation methods are applied. In production chains a row of different manufacturing techniques are established. To accompany the number of manufacturing steps with the aid of calculation methods, an interacting of each simulation with the preliminary one is necessary. Such process chains help to determine the structural properties and geometrical accuracy of components and assemblies during manufacturing of composite lightweight structures and ensure their final quality. The basic difficulty of handling aluminium composites with steel reinforcements is the high residual stress level in the reinforcing elements and the adjoining matrix. This stress state can have a significant effect on the desired machining results and the related process itself. Contemplating this reveals the importance of defining a process chain by simulation.
Authors: Thomas Kloppenborg, Thilo Hammers, Marco Schikorra, Eberhard Kerscher, A. Erman Tekkaya, Detlef Löhe
Abstract: For an increase in safety against crack initiation and growth in metallic structures of airplanes different concepts were developed in the past. In the focus of this work are profiles made of continuously reinforced extruded aluminum. The production and the used die set of these profiles is presented as well as problems occurring in terms of geometrical inaccuracies of the embedded high strength wires. In addition, this paper attends to the problem of lateral seam weld formation. The interface between the AA-2099 as well as AA-6056 aluminum alloy and the high strength wires Nivaflex and Nanoflex were characterized by metallurgic investigations and push-out tests. As a result it can be stated that a sufficient geometrical accuracy could be achieved and a high interface strength can be accomplished even if a slight gap is still present in the interface layer between matrix and reinforcing element.

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