Advanced Welding Processes: Technologies and Process Control

Reflecting
mirror
Laser
cavity
Power
supply
Gas cooling and
recirculating
system
8.7 Principles of the CO 2 laser.
High-energy density processes 145
Partially
reflecting
mirror
Beam
focus
system
workpiece by a series of mirrors and lenses. Since glass lenses are unsuitable
at the operating wavelength, lenses for CO 2 systems are usually made from
ZnSe whilst mirrors are normally made from copper coated with a gold
reflecting surface. A beam with low divergence is essential if long-delivery
systems and flexibility of layout are required. Even with these constraints
beam delivery systems have been incorporated into robot welding and cutting
installations where flexible positioning of the welding head is required.
Whilst CO 2 is the gas which is responsible for the emission of radiation,
industrial lasers use gas mixtures which may contain up to 80% helium and
15% nitrogen. In the process of stimulating emission, heat is generated in the
cavity and, to avoid overheating and instability, the gas is continuously
circulated through a cooling system.
The beam power delivered by CO 2 laser systems is commonly between
0.1 and 45 kW and the output may be pulsed or continuous. The overall
efficiency is normally less than 10% and large chillers are required to remove
excess heat from the system.