Evolution of geometric and quality features during ultrasonic vibration-assisted continuous wave laser surface drilling

Recently, the processes involving simultaneous application of ultrasonic vibrations during conventional materials processing are attracting significant interests for improving process efficiency and material quality. It has been previously shown that the simultaneous application of ultrasonic vibrations (frequency of 20 kHz and vibration displacement of 23 mu m) during continuous wave (CW) CO2 laser surface melting results in melt expulsion and formation of surface holes. In this paper, a systematic evolution of geometric features (hole depth, diameter, aspect ratio, and taper) and quality parameters(material buildup,spatter, recast layer thickness, and heat affected zone) of holes with laser irradiation time (0.05, 0.1, 0.2, 0.25, 0.35, 0.75, and 1.25 s) for the ultrasonic vibration-assisted CW CO2 laser surface drilling of AISI 316 stainless steel is investigated. Also, a multi-step finite element analysis, taking into account the observations of melt expulsion from high speed photography, is presented for the prediction of laser drilled hole volume. The results indicate that the laser melting regime of the continuous wave laser-material interactions can be extended for drilling of materials, expanding the applications of these widely used lasers for flexible manufacturing. (C) 2016 Elsevier B.V. All rights reserved.