Robert Bielak

Vienna University of Technology, Wien, Vienna, Austria

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Publications (8)0 Total impact

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    ABSTRACT: A combined cutting and joining process of technical textiles should help to reduce the number of production steps. Additionally, resources needed and waste should be minimized by a combined process. Process development is supported by Finite Element (FE)‐simulations keep the number of experiments as low as possible. Ansys software has been chosen for process simulation and examples of polypropylene fibres cutting are presented. Depending on process characteristics one or two laser sources will be used for experiments. First experiments have been performed on polyamide, polyester and polypropylene woven and knitted fabrics. It is intended that energy consumption as well as resource‐ efficiency of the combined laser cutting and joining process will be optimized and compared to conventional processes. Increased efficiency simplified and reduced requirements on storage and logistics could be beneficial especially for small‐ and medium‐sized enterprises (SME´s) in Europe.
    ACTA TECHNICA CORVINIENSIS - Bulletin of Engineering. 01/2012; 1:117-121.
  • Robert Bielak, Gerhard Liedl
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    ABSTRACT: Zinc-coated steel sheets have been joined with aluminum samples in an overlapping as well as in a butt-joint configuration. A bi-metal-wire composed from aluminum and steel was used as a filling metal in a series of welding experiment. An advantage of the laser-assisted bi-metal-wire welding is that the welding process is simplified since the primary joint between aluminium and steel exists already and laser welding occurs only between similar materials. FEM-simulations of the process were chosen to determine the proper dimensions with respect to the formability and thus possible debonding of the bi-metal-wire.
    Material Science and Technology. 01/2011;
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    ABSTRACT: Zinc-coated steel sheets have been joined with aluminum samples in an overlapping as well as in a butt-joint configuration. A bi-metal-wire composed from aluminum and steel was used for additional welding experiments. An advantage of the laser-assisted bi-metal-wire welding is that the welding process is simplified since the primary joint between aluminium and steel exists already and laser welding occurs only between similar materials. FEM-simulations of the process were chosen to determine the ideal dimensions with respect to the formability of the bi-metal-wire. A prototype demonstrated the feasibility of the process. 2011 Published by Elsevier Ltd.
    01/2011
  • Technology 2011; 01/2011
  • Proceedings of the 3rd International Scientific Conference Management of Technology Step to Sustainable Production; 01/2011
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    ABSTRACT: In the current work, cup drawing experiments with laser assistance are presented where only selected areas of the work piece have been heated up. Since the strongest deformations occur at the outer circumference of the blank, only that area has been heated up by a defocused laser beam. Selective laser heating of the work pieces was performed by diode as well as Nd:YAG laser radiation. The forming load for the experiments was established by a small hydraulic press with a maximum drawing force of 630kN and a hydraulic die cushion. During the experiments, the drawing path and all relevant forces have been recorded. Experimental results clearly demonstrate that this combined laser forming process is enlarging the possibilities of conventional deep drawing.
    LANE 2004; 09/2004
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    ABSTRACT: In conventional wire drawing the diameter of a wire or rod-like workpiece is reduced by drawing it through a conical die. Dieless drawing of a wire or a rod is realized by a localized heating of the work piece. As heat source for example an induction coil can be used. Immediately after having passed the heating zone the work piece is cooled to restrict the heat input on very small region. By applying a drawing force to the workpiece, deformation and thus the required diameter reduction appears in the heated zone. The diameter of the wire can be chosen in a flexible way by adjusting the velocities of the rod or wire in front of and behind the forming zone. Since temperature represents a sensible process parameter, even very small changes can lead to fracture. In the present work, a laser was chosen as a heat source of the dieless wire drawing process, together with closed-loop control of forces and temperatures. Laser heating allows an excellent control of temporal as well as spatial heat input. A wire drawing apparatus has been constructed which used a speed controlled electric motor together with a controllable brake for applying the drawing forces. Heat input was realized by a 1 kW diode laser system. Wires have been cooled by compressed air immediately after the laser heated zone. FEM analysis of the process showed that for relatively low drawing speeds one single laser is sufficient since heat spreads fast enough through the wire. Different wire types and diameters have been used during the experiments. Results of the theoretical and experimental work showed that it is possible to draw wires with this new process. For example, with copper- or steel wires it was possible to reduce the cross section of the wires by more than 20 % in one step.
    LANE 2004; 09/2004
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    Robert Bielak, Gerhard Liedl, Maria Behulova
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    ABSTRACT: Lightweight materials like aluminium and magnesium alloys promise a high potential for weight reduction of automotive constructions. Unfortunately, the structure of these materials leads to the relatively low formability which can be enhanced by realization of the forming operation at elevated temperatures. This approach is commonly used in rolling and forming but still not widely used in a tube hydroforming.