The effect of laser peak power and pulse width on the hole geometry repeatability in laser percussion drilling

In this work, the two main factors that influence the repeatability of the laser percussion drilling process are identified. Experimental parametric analysis was carried out to correlate the laser parameters with the repeatability of a laser percussion drilling process. The experiment was conducted using a flash lamp pumped Nd:YAG laser to drill 2 mm thick mild steel sheets. The relationship between the percentage standard deviation (PSD) of entrance hole diameter, hole circularity and the operating parameters is established. Thirty-five holes were drilled and analysed for each set of identical laser parameters. The PSD of entrance hole diameter ranges between 1.47% and 4.78% for an operating window of 3.5–7 kW peak power, and 1–3 ms pulse width. The circularity of the entrance hole (defined as the ratio between the minimum and maximum diameters of the hole) ranges from 0.94 to 0.87, and is found to correlate with repeatability. The work shows that higher peak power, and shorter pulse width gives better hole geometry repeatability. The effect of melt ejection on hole geometry repeatability is also investigated. Melt ejection and spatter formation have been found to contribute to the poor repeatability of the process.