Ultra-short pulse laser processing of ultra-hard materials requires an
accurate and agile experimental and analytical investigation to
determine an efficient choice of parameters and settings to optimize
ablation. Therefore, this work presents a quality-oriented experimental
approach and an analytical approach for the modeling and validation of
multi-pulse picosecond laser beam ablation on cemented tungsten carbide.
This work starts with a review of literature and state-of-the-art
theories of four relevant areas for this research: picosecond lasers,
laser beam ablation process, cemented tungsten carbide (WC) and
quality-oriented tools. Subsequently, a concept for an efficient
material laser beam ablation with a picosecond laser was introduced.
Furthermore, two approaches for the investigation are presented from an
experimental and analytical perspective, respectively. The first
approach introduced a methodology for the identification of influential
parameters. It executes a quality-oriented methodology based on the SWOT
analysis, cause-and-effect diagram and the variable search methodology.
The conclusion of the methodology gave the interaction of pulse
repetition rate and scanner speed in the form of pulse overlap and track
overlap PO/TO as the most influential parameter in the maximization of
the ablation rate. The second most influential factors resulted laser
beam power and burst-mode. The second approach, description of the
model, executes a theoretical analysis of the picosecond laser beam
ablation of cemented WC by the application of the Beer-Lambert law and
multi-pulse ablation modeling. The unavailable material properties were
obtained by experimental investigations, like in the cases of the
incubation factor and the reflectivity factor. Threshold fluence for
cemented WC was determined by the application of the heat transfer
theory and input power intensity was adapted to a Gaussian beam profile.
At the end of the approach, power density visualizations of a picosecond
laser pulse under the five available pulse repetition rates were modeled
and validated. The findings from the adaptation of the Beer-Lambert law
acted as basis for development of the multi-pulse laser ablation model
for both single-pulse mode and burst-mode, respectively. Based on the
definition of the number of pulses N irradiating the same area, the
corresponding threshold fluence for N, the input fluence and
incubation factor, ablation depth was modeled and experimentally
validated. Finally, results and conclusions of both approaches were
discussed and a framework for an efficient laser beam ablation was
presented. Recommendations for further actions on research and industry
were introduced at the end of the work.
