P W French (A), D P Hand (B), C Peters (C), G J Shannon (A), P Byrd (D), W M Steen (A)
(A) Laser Group, Department of Mechanical Engineering, The University of Liverpool, PO Box 147, Liverpool L69 3BX UK
(B) Department of Physics, Heriot Watt University, Riccarton, Edinburgh EH14 4AS UK
(C) Lumonics Ltd, Cosford Lane, Swift Valley, Rugby CV21 1QN UK
(D) Aerospace Group, Bristol UK

Abstract:
Modern aerospace gas turbines require large numbers of small diameter holes (<1 mm) to provide cooling in the turbine blades, nozzle guide vanes, combustion chambers and afterburner. A typical modern engine will have ~ 100,000 such holes. Such holes can be successfully produced by laser trepanning, but this is a relatively slow process compared with laser percussion drilling. With percussion drilling however the control of hole parameters are of the utmost importance for such applications. There are a large number of factors which can potentially affect this process, so it is important to know which ones are critical, and therefore need to be well-controlled. We have therefore used experimental design techniques to determine which factors are dominant. In order to understand how changes in these dominant factors affect the process, we used a speed camera operaating at up to 40,000 frames per second, which gives 40 frames within the 1 ms second drilling laser pulse. The results are presented in this paper.

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