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Laser transmission welding is known for high flexibility, extraordinary potential for process automation and outstanding weld seam properties. Problems may occur due to the poor gap-bridging capability of contour welding. Gaps of a few tens of microns can lead to processing issues such as welding failures, poor achievable process speed or low weld seam strengths. To overcome this, laser transmission welding with part-adapted temperature fields was developed, and is experimentally investigated here. Results concerning the process behavior, dependent on several oscillation types of the laser beam, as well as achieved tensile shear strengths and the monitored gap-bridging capability are presented.

Within this work the ablation behaviour of both carbon and glass fibre reinforced epoxy resin was assessed when ablated by a nanosecond-pulsed laser source emitting radiation in the ultra-violet spectrum. The investigation focussed on the influences of pulse overlap, focus spot diameter and resulting fluence on process quality and machining time. Results showed that ns-pulsed UV-lasers are capable of machining both types of fibre reinforced composites, while achieving good quality surfaces without burn marks or otherwise heat-damaged areas.

Laser ablation of silicon is investigated with a large set of laser parameters to determine the ablation rate over five laser fluence decades. A thermodynamic model approach for the ablation of silicon has been derived. This simplified model determines the achievable ablation depth per pulse as a function of the applied laser fluence ranging from femtosecond to microsecond laser pulse duration. Furthermore different laser wavelengths from near-infrared to ultra-violet are investigated to determine the dependence on the optical penetration depth and on the ablation efficiency. The measured ablation depth per pulse is in agreement to the models predictions with the restrictions made.

We demonstrate a technique, which significantly enhances the stability of copper welding with laser radiation. After modelling spot welding stability we conclude that oxide layer morphology typical for native oxide layers has to be avoided. We locally normalize the surface oxidation degree using laser pulses in the nanosecond pulse duration regime (short prepulsing). Thereby, the absorptivity is reliably increased, setting uniform starting conditions for laser welding. A process window is identified, where all experimental repetitions lead to successful welds. With prepulsing, the spot weld diameter variation is decreased to 2% and the necessary welding energy is decreased up to 40%.