Papers by Author: Marco Schikorra

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Authors: Daniel Pietzka, Marco Schikorra, A. Erman Tekkaya
Abstract: Extruded aluminum profiles are essential for lightweight constructions in contemporary transport and automotive applications. The reinforcement of such aluminum-based profiles with high-strength materials offers a high potential for weight reduction and an improvement of functional and mechanical properties. In comparison to conventional composite extrusion using fiber or particle reinforced billets, the alternatively developed process for the embedding of endless reinforcing elements provides enormous advantages regarding extrusion forces, load-adapted reinforcement, and tool abrasion. In this extrusion process with conventional billets, modified tools with portholes are used to position reinforcing elements from outside the pressing tool and to embed them into the material flow during the pressing operation. This composite extrusion process is part of the research work started in 2003 and carried out within the scope of the Collaborative Research Center SFB/TR10. To increase the potential of composite extrusion with endless reinforcing elements, the manufacture of composite extrusion profiles with high-strength non-metallic alumina wires is planned. Due to the wires’ specific properties, e.g. high stiffness, their deflection behavior must be analyzed to guarantee a stable feeding-in process. In this paper the specific behavior of alumina reinforcing elements regarding the feeding-in process is analyzed by experimental investigations. The main influencing factors are determined and a process window is deduced.
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Authors: Marco Schikorra, Lorenzo Donati, Luca Tomesani, A. Erman Tekkaya
Abstract: The experimental conditions chosen as a reference for the 2007 edition of the extrusion benchmark and the corresponding main results are summarized in this work. The die design stage is first explained in order to address the main features of the experiment and its objectives. The die is a flat one with multiple holes; four angular profiles were produced with different pocket geometries, the experimental plan being entirely described. The initial temperatures for the billet and the die set, together with the temperature development during the process strokes are also reported. The results are shown, for each profile, in terms of final profile length, mean exit speed, global process load, profile exit temperature.
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Authors: Dirk Becker, Marco Schikorra, A. Erman Tekkaya
Abstract: Curved Profile Extrusion (CPE) is an extension of the common extrusion process and offers the possibility to manufacture three-dimensionally curved profiles. Due to the flexibility of the process different curvatures can be produced with the same setup, which makes this technique efficient especially for low volume production. The process is characterized by a controlled lateral deflection of the strand which influences the material flow in the die and causes the profile curvature. In this paper, a direct comparison of the power rating between warm bending and CPE is presented. Furthermore, the investigations concerning the choice of support strategy of the surmounting profile by a robot to increase the curvature accuracy are continued. Finally, some extensions of the equipment are explained to increase the level of process integration.
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Authors: Thomas Kloppenborg, Marco Schikorra, Michael Schomäcker, A. Erman Tekkaya
Abstract: The decrease of the bearing length in extrusion processes results in increasing of the material flow and offers, through this, the possibility for manipulation and optimization. This paper presents a simulation based optimization technique which uses this effect for optimizing the material flow in direct extrusion processes. Firstly, the method is used in a multi-extrusion process with equal pitch circle profiles, then in an extrusion process of an asymmetric profile. Furthermore, a composite extrusion process is analyzed where endless wires of high strength steel are embedded in a base material of aluminum. The insertion of reinforcement elements into the base material flow, especially within the small ratio between profile thickness and the reinforcement diameter, can lead to significant local disturbances inside the die, which result in undesirable profile defects. Hence, the simulation-based optimization method is especially used to optimize inhomogeneous wall thicknesses in composite profiles.
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Authors: Thomas Kloppenborg, Marco Schikorra, Jan P. Rottberg, A. Erman Tekkaya
Abstract: This paper presents the results of investigations on topology optimizations in extrusion dies. The change of material viscosity of finite elements in the numerical model is utilized to allow or to block the material flow through the finite elements in simplified two-dimensional extrusion models. Two different optimization procedures are presented. In the first part of the paper dead zones in a flat and in a porthole die were improved by enhance the streamlining of the extrusion die. In the second part an evolutionary optimization algorithm has been used to optimize the extrusion die topology in order to reduce the difference between the strand exit velocities in a multi extrusion process. Finally, both methods were sequentially combined.
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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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Authors: Nooman Ben Khalifa, Dirk Becker, Marco Schikorra, A. Erman Tekkaya
Abstract: New innovative direct extrusion process variants, curved profile extrusion (CPE), twisted profile extrusion (TPE), and hollow profile extrusion (HPE), which increase the flexibility of aluminum profile manufacturing processes, are presented in this paper. These processes are characterized by influencing the material flow inside the die so that the forming process is completed when exiting the die. On the one hand, three-dimensionally curved profiles are produced and analyzed by CPE regarding the accuracy, the influencing parameters, and the compensation strategies. On the other hand, TPE and HPE make it possible to manufacture helical profiles usable, for example, as screw rotors in fluid machinery.
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Authors: Marco Schikorra, Matthias Kleiner
Abstract: The production of continuously reinforced profiles by use of aluminium as base material and a reinforcement made of steel or carbon offers a great potential for modern lightweight constructions. Within this scope, they present the potential for an increase in usage of space frame constructions in automotive or aerospace engineering. But with the insertion of reinforcement in the material flow of the extrusion process some problems can occur that are negligible in thee conventional extrusion processes: in the composite development area a significant local perturbation of the material flow is induced that can lead to the induction of high tensile stresses into the reinforcement. Due to this, failures like cracking of the reinforcement elements during the extrusion process has been detected in experimental investigations. A second problem occurring is the necessity of prediction of the seam weld position and prediction of the seam weld quality. The reinforcement can only be induced by bridge dies between two strands and due to this it is always positioned in a seam weld. While in conventional extrusion the seam weld positions is often only an aesthetical problem, now this position mainly influences the extruded profiles properties like moment of inertia. This paper deals with the problem of determination of seam weld position on the example of a double-t-profile extrusion. By use of a coupled thermo-mechanical finite element simulation with the commercial FE code HyperXtrude from Altair the velocity fields of an extrusion process with and without reinforcement were calculated and the resulting material flow was analysed. The numerical results went along with experimental investigations to verify the calculated results.
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Authors: Marco Schikorra, R. Govindarajan, Alexander Brosius, Matthias Kleiner
Abstract: The phenomenon of springback of thin-walled sheet metal parts after forming is a well known problem of forming technology in general, but particularly since the finite element simulation offers the opportunity to predict geometrical and material properties after forming. Irrespective of the intensive efforts in the previous years, a reliable and accurate prediction of springback deviations by use of the finite element simulation is still not possible. This paper deals with the numerical and experimental analysis of the springback effect itself, which dependents on the final stress states of a part after the forming process. Experimental investigations have been carried out to analyze geometrical accuracy in loaded and unloaded conditions to isolate the springback effect. Additional finite element simulations have been conducted in order to compare the experimental and numerical results and to determine the geometrical differences and their reasons. Two experimental set-ups are being discussed: Air bending on the one hand, which offers good access to the specimen in the testing equipment, and draw bending on the other hand, which is characterized by a simple strain state, but also by strain reversal within the tests. Both experiments were carried out using DP600 and X5CrNi18.10 with three different sheet thicknesses and bend radii and were compared with according FE-models. An additional shear test experiment has been developed to characterize the material behavior of the tested sheet metals for strain reversal. Furthermore, the importance of the Bauschinger effect and usable hardening models were analyzed. This study intended to investigate reasons for insufficient form and dimensional accuracy between simulations and experiments after springback and to propose modeling methods to improve the accuracy.
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Authors: Sami Chatti, Uwe Dirksen, Marco Schikorra, Matthias Kleiner
Abstract: The process chain for the production of lightweight profile structures consists of the design and computation phases, the manufacturing of straight profiles, the manufacturing and further processing of bent profiles, and the joining of single profiles to lightweight structures. A sophisticated lightweight construction design of profile structures is characterised by the use of the correct material at the correct place with the correct dimensions. To design in this way means to purposefully find the technically and economically best solution. This requires a holistic technological approach covering the whole system “design-material-manufacturing”. Furthermore, appropriate experiences in design and the use of calculation software for the determination of several mechanical component properties as well as the simulation of manufacturing processes are necessary. A satisfactory component optimisation and a manufacturing specific design of the components presupposes, however, the integration of design, computation, and manufacturing knowledge into a single system using modern CA technologies to realise simultaneous engineering.
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