Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    A novel leaf sequencing optimization algorithm which considers previous underdose and overdose events for MLC tracking radiotherapy. Technical Note
    ( 2016)
    Wisotzky, E.
    ;
    O'Brien, R.
    ;
    Keall, P.J.
    Purpose: Multileaf collimator (MLC) tracking radiotherapy is complex as the beam pattern needs to be modified due to the planned intensity modulation as well as the real-time target motion. The target motion cannot be planned; therefore, the modified beam pattern differs from the original plan and the MLC sequence needs to be recomputed online. Current MLC tracking algorithms use a greedy heuristic in that they optimize for a given time, but ignore past errors. To overcome this problem, the authors have developed and improved an algorithm that minimizes large underdose and overdose regions. Additionally, previous underdose and overdose events are taken into account to avoid regions with high quantity of dose events. Methods: The authors improved the existing MLC motion control algorithm by introducing a cumulative underdose/overdose map. This map represents the actual projection of the planned tumor shape and logs occurring dose events at each specific regions. These events have an impact on the dose cost calculation and reduce recurrence of dose events at each region. The authors studied the improvement of the new temporal optimization algorithm in terms of the L1-norm minimization of the sum of overdose and underdose compared to not accounting for previous dose events. For evaluation, the authors simulated the delivery of 5 conformal and 14 intensity-modulated radiotherapy (IMRT)-plans with 7 3D patient measured tumor motion traces. Results: Simulations with conformal shapes showed an improvement of L1-norm up to 8.5% after 100 MLC modification steps. Experiments showed comparable improvements with the same type of treatment plans. Conclusions: A novel leaf sequencing optimization algorithm which considers previous dose events for MLC tracking radiotherapy has been developed and investigated. Reductions in underdose/overdose are observed for conformal and IMRT delivery.
  • Publication
    Laser metal deposition as repair technology for a gas turbine burner made of Inconel 718
    ( 2016)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Maintenance, repair and overhaul of components are of increasing interest for parts of high complexity and expensive manufacturing costs. In this paper a production process for laser metal deposition is presented, and used to repair a gas turbine burner of Inconel 718. Different parameters for defined track geometries were determined to attain a near net shape deposition with consistent build-up rate for changing wall thicknesses over the manufacturing process. Spot diameter, powder feed rate, welding velocity and laser power were changed as main parameters for a different track size. An optimal overlap rate for a constant layer height was used to calculate the best track size for a fitting layer width similar to the part dimension. Deviations in width and height over the whole build-up process were detected and customized build-up strategies for the 3D sequences were designed. The results show the possibility of a near net shape repair by using different track geometries with laser metal deposition.
  • Publication
    Welding with high-power lasers: Trends and developments
    ( 2016)
    Bachmann, M.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    High-power laser beam welding became new stimuli within the last 10 years due to the availability of a new generation of high brightness multi kilowatt solid state lasers. In the welding research new approaches have been developed to establish reliable and praxis oriented welding processes meeting the demands of modern industrial applications during this time. The paper focuses on some of the current scientific and technological aspects in this research field like hybrid laser arc welding, simulation techniques, utilization of electromagnetic fields or reduced pressure environment for laser beam welding processes, which contributed to the further development of this technology or will play a crucial role in its further industrial implementation.
  • Publication
    Technical applications
    ( 2009)
    Bayat, N.
    ;
    Nethe, A.
    ;
    Guldbakke, J.M.
    ;
    Hesselbach, J.
    ;
    Naletova, V.A.
    ;
    Stahlmann, H.-D.
    ;
    Uhlmann, E.
    ;
    Zimmermann, K.
    New controllable, active and adaptive materials like ferrofluids enable scientific engineering disciplines to carry out fundamental research investigations and to develop innovative technical applications. Thereby, the properties of ferrofluids, their modeling as well as relevant requirements to ferrofluids with regard to their different technical applications represent the main focus of investigations, which were carried out simultaneously within the scope of a priority research program. The wide spectra of reported investigations and applications include the use of ferrofluids in actuators and in rotating or linear electrical drives, in biologically inspired locomotion systems, in fine positioning systems, in lubricated systems as well as in adaptive bearings and dampers. The specific requirements to ferrofluids deviated from corresponding technical applications can differ completely, so that general requirements to ferrofluids are concretised in a higher degree. Results of fundamental investigations as well as results of experimental investigations based on developed prototypes will be described and discussed in this chapter.
  • Publication
    Mikrostrukturen im Visier. Laser-Meßtechnik für die Dünnglasprüfung
    ( 1996)
    Körner, K.
    ;
    Nyarsik, L.
    ;
    Fritz, H.
    ;
    Fuchs, H.