Millisecond Pulsed Laser Micro-drilling of Stainless Steel - Optimizing Hole Quality Using Response Surface Methodology

Quasi-continuous wave (QCW) fiber lasers have revolutionized micro-hole drilling in various industries by generating highenergy pulses lasting milliseconds. A single pulse of this laser can drill micro-holes with aspect ratios exceeding 10 on metal sheets ranging from 1-5 mm thick. However, challenges like hole taper and burr formation have limited their widespread adoption. Despite being introduced in 2011, there is limited research on drilling with QCW fiber lasers. To overcome the challenges, understanding hole quality and optimizing process parameters are required. Therefore, experiments have been conducted when pulse energy is greater than the threshold pulse energy of 3 mm thickness of the SS304 sample to identify an optimal range. A 2-factor, 3-level face-centered central composite design is employed to design experiments in the optimal power and pulse duration range. Optimal conditions were determined: a 308 mu m minimum hole entry diameter at 3000 W power and 1 ms pulse width (yielding an aspect ratio of 10), a 0.38 degrees minimum taper angle at 5902 W power and 8 ms pulse width, and a 39 mu m minimum mean burr height at 4779 W power and 2 ms pulse width. These findings pave the path for enhanced methods to create superior quality micro-holes.