Experimental study on micro hole drilling using ultrashort pulse laser radiation

This paper discusses latest results obtained in micro hole percussion drilling in stainless steel. In the investigations a femtosecond laser source was used emitting 220 fs pulses at 1.03 mu m wavelength, whereas the spot size amounted to 31 mu m. Thereby, important process parameters like pulse energy, pulse repetition frequency, and pulse number were varied over a wide range in order to evaluate their influence both on the micro hole geometry like hole diameter, roundness, taper angle, and on the drilling quality such as thermal modification and melting residues. First, the required number of pulses for through hole drilling was estimated for material thicknesses ranging between 25 mu m and 1 mm. It was found, that the polarization state of the laser beam has a considerable impact on micro hole formation. Therefore, linear and circular polarized laser radiation was applied. Finally, optimum parameters for highest available drilling quality and speed were identified. (C) 2016 The Authors. Published by Elsevier B.V.