Statistical approach to fiber laser Microcutting of NIMONIC® C263 Superalloy sheet used in effusion cooling system of aero engines

In order to reduce thermal stress and avoid premature failure of turbine blades in the hot section of aero-engines, a diffusion cooling system is often adopted. This system is a thin sheet, with a closely spaced holes array allowing a uniform cooling of the turbine blade thanks to the evenly distributing of the cooling fluid within its wall. The holes diameters vary in the range of 0.3-1.0 mm. Furthermore, tight tolerances, perpendicular surfaces, no burr, no recast layer, are required. In order to satisfy the hole requirements, typically EDM technique is adopted. However, EDM micro-drilling needs long process time (about 20 s for hole). A promising alternative is laser trepanning. In this technique, a laser beam, with a very small focused spot, is used to make a hole by circular cutting. The hole is obtained in few seconds (<3 s). In this work a preliminary study on laser microcutting of NIMONIC® C263 sheet is presented in order to verify the possibility to adopt a low-power Yb:YAG fiber laser for the microdrilling. Linear cutting tests were carried out on NIMONIC® C263 superalloy sheet, 0.38 mm thick, using a 100 W Yb:YAG fiber laser working in modulated regime. A systematic approach based on Design of Experiment (DoE) has been successfully adopted with the aim to detect which and how the process parameters affect the kerf geometry in term of kerf width, taper angle and tolerances. The examined process parameters were scan speed, on-Time, pulse duration and gas pressure. A full factorial design and ANalysis Of VAriance (ANOVA) were applied. Experimental results show the possibility to obtain kerf characterized by narrow width (<100 μm), low taper angle values (<1.8°) and small tolerance (<0.22 μm). Then, the possibility to produce in-Tolerance holes was proved.