Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
∑ excimer lasers;
∑ RF- and microwave-excited CO 2 lasers;
∑ diode-pumped lasers;
∑ carbon monoxide (CO) lasers;
∑ high-power diode lasers;
∑ fibre lasers.
Excimer lasers. The active component of the laser medium used for excimer
lasers is a rare gas such as xenon, krypton or argon containing a halogen
such as fluorine, bromine or chlorine. The pulsed output is in the ultraviolet
wavelength range usually from 193 to 350 nm. The average output power of
commercial excimer lasers is currently quite limited, but peak powers as
high as 100 kW are possible. The photo-ablation process which allows
molecular bonds to be broken without introducing excess thermal damage is
used for accurate drilling, cutting, marking and cleaning applications in the
electronics, semiconductor and medical component industries.
RF- and microwave-excited CO 2 lasers. The DC-excited CO 2 lasers are
capable of producing high beam quality at reasonably high power levels. The
use of high-frequency excitation has been shown to offer improved beam
quality and RF excitation systems for welding are now available. It is expected,
however, that microwave systems will offer improved quality, high efficiency
and lower overall cost.
Diode-pumped lasers. In general, the pumping of solid state lasers by
flashlamps is inefficient [173] because of the fairly broad spectrum of
wavelengths produced by the lamps and the fairly narrow band of useful
pump bands. Greater efficiency can be achieved by pumping with
semiconductor lasers such as gallium–aluminium–arsenide (GaAlAs) lasers
which emit wavelengths in the range 750–900 nm. Development of highpower
semi-conductor pumped lasers has been limited. Commercial devices
with powers of around 1 W are available, but the low power limits the
applications to areas such as microsoldering.
Carbon monoxide (CO) lasers. Work on the development of CO gas lasers
has taken place in Japan. [174] The wavelength of 5 mm falls between that
of CO 2 and Nd:YAG and may offer potential benefits in the ability to use
fibre optic beam delivery. The use of these devices for cutting has been
demonstrated, but welding applications have yet to be developed.
High-power diode lasers. High-power direct diode lasers have recently
been developed and are being investigated for welding and surfacing
applications. Current systems offer power levels up to 4 kW and operate in
the 800 to 940 nm wavelength range. The rectangular beam profile is suitable
for hardening and surface treatment applications, but can be coupled to an
optical fibre to facilitate welding operations. The main advantage of these
devices is the increased electrical efficiency (typically 25%) and compact
size when compared with CO 2 and Nd:YAG systems. Fibre delivered diode