Laser applications, such as cutting of medical devices (e.g. stents) and watch components (e.g. gear wheels, hands), demand highest cutting accuracy in combination with extremely high cutting edge quality and minimum cutting kerf. For single pass laser cutting of small components with high precision the application of fiber lasers is the common industrial practice [1]. In this fusion cutting process, molten material in the cutting kerf is ejected by the process gas. Besides the formation of a heat affected zone (HAZ), the weakness of the fusion cutting process is the formation of striations on the cutting surface, which increases the surface roughness of laser cut components [2].
Ultra-short pulse lasers provide the possibility of material processing with minimum thermal impact on the remaining material structure [3,4]. Thus laser cutting with very small feature sizes (several microns) and negligible HAZ can be realized. This laser vaporization process using ultra-short laser pulses can replace the common fusion cutting process, if an optimization of the cutting quality and cutting precision is developed. Specifically, the influence of pulse duration on the cutting characteristics must be characterized.
In this study, the laser cutting process of different materials is examined by reducing the pulse duration from 6 ps to 900 fs, then down to 400 fs. The results of the micro-cutting process of thin metal sheets with regard to pulse duration, pulse energy, laser repetition rate and cutting velocity have been determined. Quality criteria were identified for evaluating the influence of cutting parameters on the cutting results. The HAZ and micro-structural changes, the striation formation and surface roughness and the taper lead angle of the cutting kerf and surface deposition of material were chosen as criteria and have been analyzed in detail.
The results show that ultra-short laser pulses enable high quality cutting with improved roughness and minimized HAZ. The highest quality and cutting speed are reached with sub-ps pulses. Furthermore the processing window for laser vaporization cutting is enlarged by using femtosecond pulses. Finally, with shorter pulses under optimal cutting conditions, an improvement of cutting efficiency and cutting quality is possible.