Sequential laser and mechanical micro-drilling of nickel based superalloys at acute angles have been demonstrated for the first time. The process reduces the width of cut compared to mechanical drilling, relieves the load on the drill point and significantly increases drill life (2.5 times for through holes) compared to purely mechanical micro-drilling at high feed rate (28 mm/min). The performance of the hybrid technique is better at a higher feed rate and hence providing a potential for utilising the process at competitive drilling cycle times. Thus, the complimentary process can be used to extend the life of micro-drills and alleviate some of the size effect challenges and quality issues (e.g. burr size) that are driven by a rapid enlargement of drill edge radius. It can also alleviate the thermal and geometric defects associated with laser-drilled micro holes. The size of the drill chisel edge is a key factor in deciding the target diameter for the laser-drilled pilot hole and hence choice of drilling parameters. The size of the laser pre-drilled hole should ideally be smaller than the chisel edge length to promote tool balance and reduce drill wander. Current practise is to manufacture micro-drills with a smaller web thickness in order to improve cutting action. Sequential laser and mechanical micro-drilling alleviates the indentation and secondary cutting edge action and should enable manufacturers to grind drills to thicker web thickness increasing drill strength. The cycle time for laser drilling is 50% faster when micro-drilling is done using compressed air compared to oxygen assist gas. This can be attributed to formation of oxides which reduce the efficiency of the drilling process. Since the air assist gas process can be used to produce the recommended laser pre-drilled hole size, i.e. less than the chisel edge length, it is an alternative to using oxygen assist gas. This is an important economic and environmental advantage since air is cheaper and is also an abundant resource. Additionally, the present work has shown that sequential laser and mechanical drilling of laser-blind holes will be an effective technique for avoiding the back-wall problem in laser drilling of hollow parts especially when the exit surface of the components to be drilled have a closed cavity or is hard to access.
Sequential laser and mechanical micro-drilling of Ni superalloy for aerospace application
Sequentielles Laser- und mechanisches Mikrobohren von Ni-Superlegierung für Luft- und Raumfahrt
2010
4 Seiten, 3 Bilder, 2 Tabellen, 19 Quellen
Conference paper
English
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