Laser drilling of cooling holes in aeroengines: state of the art and future challenges

Advances in the efficiency of the aeroengine have led to an increase in combustion and exhaust gas temperatures. Although superalloys have been developed to withstand these high temperatures, additional cooling of the components is often necessary. This is achieved through thousands of closely spaced cooling holes drilled into the components. Laser drilling offers economical advantages over other non-conventional drilling techniques (e.g. electrical discharge machining). The key limitations and the areas requiring further investigation to develop the laser drilling process to meet future aeroengine requirements have been identified. Principal areas include the development and investigation of laser barrier methods when drilling through increasingly complicated and smaller cavities, the successful drilling of lower angled effusion holes and the increased use of laser drilling to produce the cooling holes in rotating components. More recent designs of the aeroengine have incorporated thermal barrier coatings, sprayed onto the components to further protect against high temperatures. Successful laser drilling through these coatings, with particular attention to preventing spalling of the coatings also requires more research. Each of these areas will need to be addressed while, at the same time, decreasing the overall drilling times.