AerospAce ApplicAtions
involves a localised molten spot of metal, which much material they’re able to remove. The hole surface means that this technique is limited in
would lead to significant heat damage to the looks great, but it takes five minutes to drill one the range of shapes it can produce. ‘You can’t put
expensive component. Instead, pulsed lasers are hole, where I need to be drilling one a second. a negative contour on the electrode, because you
used to vaporise the material quickly so it has This is the trade-off that we’re facing, but if can’t push it into the material,’ he says. EDM
only a minimal effect on the surrounding area. someone could give me a picosecond laser with does, however, offer higher processing speeds
Denney has investigated using fibre lasers, 1kW of average power, that would be a winner.’ than laser machining or drilling, and so it is
known for their reliability and efficiency, to drill So the practical necessities of a factory mean employed as an alternative for some applications.
cooling holes. Microsecond pulses are possible that the precision offered by picosecond regimes When the alloys used are expensive,
with fibre lasers, rather than the usual is sacrificed for process speed. There are, machining can involve significant extra costs in
millisecond pulses used, and high repetition however, some applications for which no other terms of material wastage. ‘In the case of one
rates can also be employed to produce high techniques will suffice. For high-performance particular engine component,’ says Denney, ‘the
quality holes quickly. Denney states that, engines, such as those under development for manufacturer would normally take it out of a
although the fibre lasers produce good results in military jets, designers would like to use angled forging before machining away 75 per cent of
some thinner materials, there are significant and fan-shaped holes to spread the cooling air that component.’ This wouldn’t be a problem
differences in beam profile when compared to over the widest possible area. ‘It’s the holy grail of when using inexpensive steels or aluminium
the established technologies. A fibre laser turbine cooling,’ says Boor. ‘Fan-shaped holes alloys, but when nickel superalloys or titanium
produces several modes of light, and it is as yet alloys are used, the associated cost becomes
unclear how to optimise these for drilling.
By the time the last
prohibitively high. Where an application calls for
Micro-machining equipment firm Swisstec a component with some sort of projection, CCAT
takes a different approach to drilling. The
B-52 is retired, many of
uses laser additive techniques to deposit new
company avoids the problems of heat affected
its components will have
material where it is needed. This technique can’t
zones by using an ultrafast regime in a system it be used where high material strength is required,
calls Precision Power Percussion Ablation
been made by lasers
but offers an alternative route in some cases.
(PPPA). Picosecond pulses are one billion times
shorter than the millisecond pulses used in older mean that the air sticks to the surface of the Maintaining an ageing fleet
systems, and several hundred thousand pulses blade, leading to better insulation. This kind of Laser manufacturing techniques can be used to
arrive at the metal surface every second. The angled hole is a difficult engineering challenge.’ produce a component that would otherwise be
pulses are short enough to prevent thermal The precision offered by precision percussion unavailable, or prohibitively expensive. The
diffusion through the bulk material, but they ablation allows engineers to drill a hole, and then American Air Force’s B52 bombers, for example,
contain enough energy to break atomic bonds trepan (widen) the fan. Boor describes it as have been in service for more than 50 years, and
and vaporise small amounts of the material. ‘If ‘changing the direction of the chisel’. there are plans to use the bomber for another 40
you think of using a hammer and chisel, you can years. High-brightness lasers, coupled with the
drill quite a big hole in a piece of concrete by Fixing faults latest advancements in drivers and motion
chipping a little bit off at a time,’ explains Alan Lasers have been used in blade repair control systems mean that replacement parts can
Boor, application manager at Swisstec. ‘That’s applications for the past 20 years. As mentioned be produced easily from sheets of aluminium.
exactly what picosecond laser ablation is; it’s only above, the turbine blades are expected to ‘Better linear drives and higher speed computer
a small amount of material that’s removed each elongate during use, because of the high control may one day reduce HAZ to the point at
time, but it’s done very fast.’ temperatures and huge centrifugal forces which it’s no longer a factor,’ says Denney, but for
The amount of energy can be controlled to a involved. The tips of the blade are therefore now these techniques are able to produce
high degree of sensitivity too. ‘We need to think expected to wear out, as they rub against an non-critical components that would otherwise
about how much energy we need to vaporise a abradable seal on the inside of the engine require custom tooling to be produced.
given amount of material. Excess energy would cowling. The tips of the blades can be When an aircraft has an expected service life
go into the bulk material and that’s not good, but restructured by blowing powdered metal onto of 90 years, any advancement in manufacturing
not enough energy means that you can’t remove the surface and melting it with a high power processes are going to be popular. ‘It’s like
material at a high enough rate,’ says Boor. The laser. This technique can only be applied to some owning a very old car,’ says Denney: ‘After a
average power of a pulsed laser is low compared parts of the blade, so as to avoid damaging its while you’re replacing everything. You’ve
to CW lasers, usually in the region of 5-10W, surface, but it is routinely used in the aerospace replaced the transmission, you’ve pulled the
rather than the kilowatt systems usually used. industry to repair these expensive components. rings and replaced the pistons, you’ve done the
This accuracy and minimal HAZ therefore comes Denney from CCAT is a proponent of laser muffler, and tyres and breaks, and at some point
with an associated cost in terms of process speed. additive manufacturing for aerospace, in which a you’ve almost got a whole new car. Planes aren’t
Denney from CCAT believes that to be similar technique is used to create metal so different – you pull all the avionics out; you
competitive, a drilling system needs to be components from metal powder, fusing the replace the engines, wing components, skins etc.
powerful: ‘The primary success value is average powder using a laser, before machining away How much of that plane that is sitting there on
power,’ he says. ‘The average power really excess material. ‘If you have a concept for a the tarmac after 50 years is actually the same
determines how much material you can remove. shape, you can basically machine it,’ he says. plane? Is any part of it original?’
I can do some really impressive things with Electron discharge machining (EDM) is the Whether it’s the same plane or not, by the time
femtosecond or picosecond lasers, but their competing technique, but Denney says that the the last B52 is retired, many of its components
average power is 5-10W, and that tells me how necessity for a comb-like electrode to skim the will have been made by lasers.
www.lasersystemseurope.com issue 5 • lAser sYsteMs eUrope 15
LSEwin09 pp14-15 aero.indd 15 2/12/09 15:43:05
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