Product Code: ICAL07_108

Acoustic Phenomena during Laser Drilling
Paul Jacobs, LFI Inc.; Smithfield RI USA
Matthew Hayman, LFI Inc.; Smithfield RI USA
Terri Marsico, Connecticut Center for Advanced Technology; East Hartford CT USA
Abby Ilumoka, University of Hartford; West Hartford CT USA
Paul Denney, Conneticut Center for Advance Technology; East Hartford CT USA
Robin Bright, Univeristy of Connecticut; Storrs CT USA
Presented at ICALEO 2007

Precision laser drilled holes are critical to enable film cooling of numerous jet engine components. A single modern jet engine can require nearly one million film cooling holes! At present, laser drilling is not sufficiently precise to eliminate costly air flow testing. Since flow through tiny holes is proportional to the fourth power of the effective hole-diameter, even small errors in diameter will lead to substantial changes in air flow. Reduced coolant flow from an undersized hole can produce a local hot spot, excessive thermal stress, and hence overly conservative engine operation. Laser percussion drilling currently yields a standard deviation in effective hole-diameter 20 m, for diameters from 0.2 to1 mm. Laser trepanned holes can achieve 10 m for the same range of diameters, but with an increase in drilling time and unit cost. We are currently studying the acoustic phenomena that occur during laser drilling. Our goal is 5 m, achieved through acoustic feedback and control. Precedence in laser welding, and the ability of laser system operators to hear the difference between good and bad laser drilled holes suggests potential benefits. This paper will discuss our initial acoustic test results.

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