Ultrafast Laser System for Drilling and Inspecting Straight and Shaped Cooling Holes

Machining cooling holes in turbine fan blades is non-trivial.  Blades and vanes are made from superalloys and coated with thermal barrier coatings (TBC) to survive extreme temperatures after the combustion section of a jet engine.  Classical methods such as EDM or nanosecond laser micromachining have serious drawbacks in the size of hole and the amount of collateral damage to the surrounding material, such as spatter, cracking and delamination of the TBC.  Femtosecond lasers on the other hand have been shown to greatly reduce this collateral damage and can make very small holes and/or shaped holes. With this in mind it is important be able to monitor the hole formation during the machining process.  In this work we propose to investigate coupling a 100kHz, 40fs (20-400uJ) laser system with a real time OCT measurement to produce clean shaped holes in superalloys and TBCs.  We will also experiment with pulses ranging from 150fs to 30fs, as we believe shorter pulses lead to cleaner machining. BENEFIT: If successful, this project will open up a new method for micromachining cooling holes in jet engine fan blades, with the ability to reliably monitor the machining process. This Phase I is important for laying the foundation of experiment and theory in order to demonstrate the full capability of the micromachining apparatus as well as the laser system, and OCT detection scheme that is necessary for a commercial tool, which would not only benefit the DOD, but the research community .