Process development and control of laser drilled and shaped holes in turbine components

Abstract

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 simulta-neous 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 de-termine the break through and prevent back wall damages by drilling hollow structures, e.g. turbine blades.