Extensive Micro-Structuring of Metals using Picosecond Pulses – Ablation Behavior and Industrial Relevance

The micro-structuring of technical metallic surfaces is an effective technique to change their mechanical, chemical or fluidic characteristics. Based on increasing demands on the capability of technical surfaces, for example, higher process resolution for texture geometries in the m-range as well as excellent process stability and reproducibility, an increased level of surface technologies is developing. Laser-based generation of defined micro structures on extensive metallic surfaces is under development. Micro-machining of metals using a diode-pumped, regenerative-amplified ps-Nd:YVO 4 -laser source has been investigated. Eight different metals and a metallic alloy (Al, Cu, Fe, Mg, Ni, Pb, Ti, W and X20Cr13) have been investigated concerning the ablation rate per pulse, ablation geometry, formation of melt phase, influence of pulse overlap and number of loops. The ablation characteristics are correlated with thermal conductivity, specific heat capacity and the melting temperature regarding processing window and machining throughput. Based on the presented results, the generation of rib-structures, so-called riblets, are fabricated on compressor blades and tested in a cascade wind tunnel. The achieved improvement of skin friction reduction as well as an efficiency-consideration regarding industrial applications and their demands will be discussed.