Photon06 Conference Manchester, Institute of Physics, OPD: P1.22, September 2006
P W French 1, M Naeem 2, M Sharp 1and K G Watkins 3
1 Lairdside Laser Engineering Centre, Campbeltown Rd, Birkenhead, CH41 9HP, ENGLAND
2 GSI GROUP, Cosford Lane, Swift Valley, Rugby, CV21 1QN, ENGLAND
3 Laser Group, Department of Engineering, University of Liverpool, Brownlow Street Liverpool, L69 3GH, ENGLAND
Abstract: Laser percussion drilling is now a well established material processing technique for producing holes in certain aerospace components for boundary layer cooling. Percussion drilling allows a components cycle time to be reduced compared with the other laser drilling technique, laser trepanning. This is a very important factor as some components can have up to 40,000 holes. One of the major factors that concern the aerospace industry is the quality of the holes. Hole geometry such as taper, roundness and variation between holes must be within certain limits if the component is going to be used in an aero engine. Other important factors with respect to hole quality are metallurgical issues concerning recast layer and micro cracking with in the hole. This paper investigates how temporal pulse shaping and other factors such as focal position; gas pressure and gas type can improve laser-drilled holes. The study uses laser percussion drilling technique and four different pulse shapes, the square shaped pulse, the ramping up pulse, the ramping down pulse and the pulse train. A sensor designed especially to measure the drilling velocity was used to determine the drilling efficiency of each laser drilling pulse. Interactions between the different pulse shapes and other important drilling parameters were also examined and best-drilling practices is discussed.