AerospAce ApplicAtions
lasers take flight
Stephen Mounsey looks
at ways in which laser
processing is enabling
innovation in the
aerospace industry
Image courtesy of Lockheed Martin
W
hen designing and manufacturing
components for aircraft, the
specifications are high, the tolerances
are tight, and the budgets are large – particularly
when the military is footing the bill. As with
many areas of engineering, however, energy
efficiency and cost-effectiveness have joined
safety at the forefront of design consideration.
Welding, additive manufacturing, drilling,
cutting, and machining can be carried out by a
The hot part of the engine in an
F-22 requires approximately 1.5m
range of techniques, but processes based on laser
holes to be precisely drilled.
systems are becoming the standard for many
aerospace applications. The turbine blades are operating at of cooling airflow over different parts of the
Advanced materials are the reason for laser temperatures that are technically above their component is controlled by fine adjustments to
processing’s dominance in the aerospace melting point, and so they must be actively this diameter. The rate of airflow scales with the
industry. Cheaper techniques, such as cooled by way of thousands of holes through area of the hole – not its diameter – and so, if the
mechanical machining, TIG welding or which cold air is blown, forming an insulating manufacturer specifies an airflow tolerance of
deformation processing, are inferior when layer of air between the hot gas and the surface of ±10 per cent, the diameter of the hole must be
working with high-tech metals, plastics or the metal. In addition, the blades are spun so accurate to five per cent, i.e. 25µm on a typical
composites. Even aluminium alloys, used as a rapidly that they actually elongate by way of a 0.5mm hole. Additionally, the holes need to be
structural material since the early days of jet process called creep. To minimise creep, and to drilled quickly.
aircraft, present unusual challenges when it make the blades as temperature resistant as Paul Denney is a senior research engineer at
comes to welding, as they are more sensitive to possible, they are cast from so-called ‘superalloys’ the Connecticut Center for Advanced
heat treatments than steels, and so great care has (nickel-based, with cobalt, titanium and Technology (CCAT), and he chairs the Laser
to be taken to control and minimise the extent of aluminium additions). These alloys are Institute of America’s Laser Materials Processing
the resulting heat-affected zone (HAZ). expensive, and they can be difficult to machine conference. He has been looking at ways of
Aside from structural aluminium alloys, some by normal processes. A single turbine blade may increasing the processing speed and quality
of the most advanced alloys yet developed are cost tens of thousands of pounds, and there may when drilling cooling holes. Older laser drilling
used in the hot parts of a jet engine. A modern jet be hundreds of the components in a single jet systems are based on lamp-pumped Nd:YAG
engine sucks cold air through the front, and engine, each requiring hundreds of cooling holes technology, which is inefficient and high-
compresses it using a sequence of compressor to be drilled. As an example, there are maintenance. Fibre and disk lasers are being
blades. The compression also heats the air. At the approximately 1.5 million holes in the hot part of investigated for their potential to create better
point within the engine where the air is most an F-22 Raptor fighter jet’s engine. quality holes while offering advantages in terms
compressed, fuel is injected and burned, and this of factory overheads.
heats the gases to temperatures as high as Drill to keep cool In order to drill such small holes, the lasers
1,100°C. This hot exhaust expands, and is forced Often, the addition of the holes for cooling must be pulsed by way of a process called
out through the back of the engine. Some of the airflow is the last task performed on the percussion drilling. ‘Continuous wave lasers are
energy of the rapidly moving gas is captured by a otherwise completed turbine blade – a OK for larger, trepanned holes,’ explains Denney,
series of high-temperature turbine blades as it component, which may cost up to £100,000, ‘but for most of the stuff we’re doing you have to
exits the engine. The turbine blades power a and must have up to 2,000 precisely sized and get an interaction with the material and get the
rotating shaft, which powers the compressors positioned holes added. These holes are material out. As soon as you use a [CW] beam,
and fan blades in turn. approximately 0.5mm in diameter, and the rate you start running into problems.’ A CW process
14 lAser sYsteMs eUrope • issue 5 www.lasersystemseurope.com
LSEwin09 pp14-15 aero.indd 14 2/12/09 15:43:05
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