04-12-2012, 04:58 PM
Laser beam machining (LBM), state ofthe art and new opportunities
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Abstract
An overview is given of the state of the art of laser beam machining in general with special emphasis on applications of short and
ultrashort lasers. In laser welding the trend is to apply optical sensors for process control. Laser surface treatment is mostly used to apply
corrosion and wear resistant layers, but also for repair of engine and machine parts. In micro-machining, shorter pulses reduce heat-affected
damage of the material and opens new ways for nanometer accuracy. Even 40 years after the development of the laser there is a lot of
effort in developing new and better performing lasers. The driving force is higher accuracy at reasonable cost, which is realised by compact
systems delivering short laser pulses of high beam quality. Another trend is the shift towards shorter wavelengths, which are better absorbed
by the material and which allows smaller feature sizes to be produced. Examples of new products, which became possible by this technique,
are given. The trends in miniaturisation as predicted by Moore and Taniguchi are expected to continue over the next decade too thanks to
short and ultrashort laser machining techniques.
Introduction
Photons are in this century. They are replacing electrons
as the favourite tool in modern industry. Light is used for
everything from eye surgery to telephone technology and
materials processing. Photons are applied in an increasing
number of topics addressed by this ISEM 14. An important
property of light is that it has no volume, photons have no
charge, so when concentrated into a very small space, they
do not repulse each other like negative charged electrons do.
This is an important property especial for ultrashort machining.
Light moves through space as a wave, but when it encounters
matter it behaves like a particle of energy, a photon.
Not all photons have the same amount of energy. The visible
part of the spectrum contains wavelengths from 400 to
750 nm. Radiation below 400 nm includes the harmful frequencies
of UV and X-rays, while above 750 nm the invisible
infrared, microwave and radio frequencies are included.
The energy of photons is E = hν. For the visible 500 nm
wavelength this is 4 × 10−19 J or 2.5 eV per photon, which
is not enough to break the chemical bonds in the material,
which requires 3–10 eV. In the laser materials processing
this can be overcome in different ways.
Laser welding
After the maturation of laser cutting also welding is becoming
everyday technology. For 10 years people said ‘we
can weld any material, as long as it is stainless steel’. Now
indeed almost all materials can be laser welded. Challenges
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. Laser welded parts for a TV electron gun (Philips CFT).
are found in the area of beam and product handling. In the
high volume market, e.g. in the electronics industry special
machines are built around one product for just a few welds
(Fig. 1). In such applications, the required accuracy for laser
welding is built-in in the machine.
Laser cladding and alloying
Lasercladden is used to improve the surface quality by
applying a hard or a corrosion resistant layer on a product of
cheap or better to machine material. The common technique
is to create a shallow melt pool by a defocussed laserbeam
and supply metal powder in that pool using an inert gas flow.
Examples are shown in Fig. 5, left the cladding of a roller
wheel for sheet metal forming, centre cross section of the
wheel and right a diesel engine crankshaft.