Laserdurchstrahlschweißen transparenter Thermoplaste ohne Strahlungsabsorber

  • Laser transmission welding of transparent thermoplastics without radiation absorbers

Mamuschkin, Viktor; Poprawe, Reinhart (Thesis advisor); Hopmann, Christian (Thesis advisor)

1. Auflage. - Aachen : Apprimus Verlag (2021)
Book, Dissertation / PhD Thesis

In: Ergebnisse aus der Lasertechnik
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

In many applications it is not possible to adjust the absorption properties of a joining part in a way that is normally required for laser transmission welding of plastics. The additives used to enhance absorption not only change the color of the plastic, they also cause additional costs and can impair the functionality or even biocompatibility of the component. In this thesis a variant of laser transmission welding is investigated that exploits the intrinsic absorption of the plastics by an appropriate laser wavelength to bypass the use of those additives. At first, the range is derived in which the Rayleigh length of the laser beam should be in order to not heat up the volume of two optically identical parts over a large area, but selectively in the contact area. Then, simulations are carried out showing the influence of Rayleigh length and other process parameters on the temperature field. In addition to the Rayleigh length and the absorption coefficient, the diffraction index and the feed rate of the laser beam are identified as significant factors influencing the selectivity of the energy input inside the volume. The knowledge gained from this leads to the approach of quasisimultaneous irradiation, with which selective heating can be achieved without the Rayleigh length of the beam being in the previously derived range. Instead of an instantaneous input as in contour welding, the energy is introduced gradually in fast successive cycles and thus accumulated in the contact area of the joined parts. With regard to the use in series production, a comparison of both irradiation variants is made followed by an examination of pyrometry, the most common method of quality assurance in laser transmission welding. Due to the longer-wave laser radiation in absorber-free welding, there is a superposition with the less intensive thermal radiation, which can therefore no longer be measured by the pyrometer. Since the extraction of the laser wavelength by optical filters would further reduce the already narrow band of thermal radiation, a pulsed operation of the laser beam source is being tested in which the thermal radiation can be measured without interference in the intervals between the pulses.

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