The efficiency of gas turbines can be improved by raising the temperature of combustion. This necessitates stronger cooling which is achieved by blowing additional air through numerous very small holes, having typical diameters between 0.3 and 2.5 mm. To enable higher temperatures the NiCo-alloys are additionally coated with zirconia oxide.
A 350 W cw-pumped Nd:YAG-laser with a beam parameter product of 10 mm*mrad which was acousto-optically Q-switched is used for trepan drilling. With argon as an assisted gas with a pressure of abt. 10 bar, clean cuts were obtained. Any diameter between 0.3 and several mm can be chosen. Perpendicular as well as 17°, 33°, 45° and 57° inclined trepan drillings were made. A 0.6 mm hole into a 2 mm alloy was made in 1 s. This is four to ten times faster as with a free-running pulsed laser. Thus, process time and heat load of the work piece are substantially reduced: The recast layer is narrower. The smooth process in the absence of oxygen yields crack-free and purely metallic surfaces. With zirconia coated sheets, no case of chipping was observed.
Another drilling application for the aircraft industry is the perforation of the wings with millions of small holes. Numerical simulations have shown that these holes with diameters between 40 and 70 μm drilled into the so called laminar wing can improve the aerodynamic conditions. This could effectivly reduce the fuel consumption. 400 holes per cm2drilled in an acceptable time through 0.8 mm thick titanium are required.
A two rod Nd:YAG-laser including birefringence compensation, delivers an output power up to 200 W with a beam parameter product less than 3 mm*mrad. Using argon as assisted gas 185 holes per second with 80 μm diameter were drilled in a 1 mm thick titanium alloy. The single shot technique enables the treatment at a moving workpiece.