Nichtlinear dynamisches Modell zum Laserstrahlschweißen von Aluminiumlegierungen

Abstract

Laser beam welding is an established production technique to join metals like steel or aluminum alloys. In the case of deep penetration welding a focused high power laser beam evaporates the metal and creates a so-called keyhole in the workpiece. The keyhole is filled with metal vapor and surrounded by molten material. This molten pool resolidifies and forms the weld seam. Neither keyhole nor weld pool are stable but perform dynamic movements.:p:In the case of aluminum alloys these movements are strong enough to lead to unwanted geometric imperfections of the weld seam. The dynamic process causing these imperfections is not well understood. Some experimental results indicate further that the laser beam welding process exhibits chaotic behavior.:p:In this thesis a nonlinear model for the laser beam welding of aluminum alloys is developed. It combines the dynamic of keyhole and weld pool with the absorption of laser light in the keyhole. Thus the response of the system to temporal variations of the laser beam power can be calculated.:p:The model is verified with experimental results, e.g.: a) The power spectrum of the temporal variation of the light intensity emitted by the hot vaporized metal during the welding process shows good agreement with the power spectrum of the model dynamic driven by the measured output power of the laser. b) Seam imperfections can be induced artificially by laser power modulations. Consistently the modeled kinetic energy of the weld pool only for these modulations is high enough to eject droplets of molten material leading to seam imperfections.:p:The presented nonlinear model exhibits chaotic behavior and resembles some of the experimentally observed characteristics of the laser beam welding process. It is thus a step towards the understanding and modeling of laser beam welding as a nonlinear dynamical system.:p:Für weitere Informationen siehe:http://www.uni-bremen.de/~skupin/diss/diss.html