High-Precision Surface Profiling Using Multi-Hundred Watts Ultrashort Pulse Lasers and Ultrafast Polygon-Mirror Based Scanner

Abstract

High-precision surface profiling is studied by using ultrashort pulse lasers up to 450 W laser powers and 40 MHz maximum pulse repetition frequency. A polygon-mirror based scan system is applied for ultrafast and flexible laser beam raster scanning providing up to 560 m/s laser beam moving speeds. By investigating the high-average power picosecond and femtosecond laser systems in large-area processing, optimum parameter settings are derived with regard to machining quality, efficiency and throughput. In addition, the influence of the focus spot size on top width and tip angle of trapezoidal micro structures (Riblets) is evaluated. Inspired by bionic surface functionalities, the laser made Riblets are tested in a Goettingen-type wind tunnel to identify their effectiveness for aerodynamic drag reduction in turbulent flows. For the optimum Riblet geometries, a maximum total pressure loss reduction of 1.76% is achieved that is remarkable when comparing with literature data. The drag reducing effect of the Riblets is further confirmed by empirical-analytical and CFD analyses showing up to 6.4% skin friction reduction. By taking into account the effective processing time of 6.0 cm2/min with potential to be further scaled-up with higher laser powers, ultrafast laser-based Riblet profiling could be a key enabling technology to enhance the operational performance in the energy machinery sector.