Process Development and Control of Laser Drilled and Shaped Holes in Turbine Components

Cooling holes (100 holes/cm2, diameter 0.2 0.6 mm, inclination angle up to 60°) are drilled by pulsed laser radiation (Nd:YAG, 1064 nm, 0.1 1 ms) in X5CrNi18 10 and CMSX-4 multi layer systems with BC (MCrAlY bond coating) and TBC (ZrO2 thermal barrier coating). There are two different options to drill and shape the holes: The first layout is a one-step procedure with a simultaneous five-axis trepanning movement of the laser beam. The second layout is a two-step procedure with percussion drilling or trepanning a through hole and structuring a fan by short pulse ablation in the second step. The thermal radiation from the drilling process is detected by an in-situ CPC (coaxial process control) during percussion drilling using high speed photography (50 kHz frame rate) in order to determine the break through and prevent back wall damages by drilling hollow structures, e.g. turbine blades.