Niklas Malmberg and Joakim Hedegård

Abstract

High power lasers known as CO2,YAG, diode, disk and fiber lasers are suitable for material processing such as welding and cutting. Recently, the highpower solid state lasers have been receiving attention due to their advantages with high power, high beam quality and high efficiency. Fiber lasers as well as thin disk lasers are distinguished by their high beam quality and strong focusability, enabling deep penetration welding at high welding speeds. Keyhole welding with focus diameters down to 50 μm is possible using high laser power. However, to utilize small focus diameters for deep penetration welding the divergence angle has to be sufficiently small to achieve a large depth of focus.

Laser welding in keyhole mode requires a laser power above 1 kW with a spotsize of 0.8 mm or smaller. Laser cutting requires a laser power above 0.5 kW with a spot size of 0.6 mm or smaller. Cutting edge quality is still an issue for thicknesses above 5 mm, when using solid state lasers. Laser brazing can be performed with many commercial laser sources above 1 kW with a spot size of 3 mm or smaller.

The market for laser materials processing is rapidly increasing due to a fast development in laser processes and a decreasing cost. Recent developments are increased power and better beam quality. The high brightness lasers available today opens up new possibilities. These high power lasers  also make the process hard to control. The high energy density results in a high thermal load on the optical components and it will cause focal-shift problems. Different activities are ongoing to solve these optical issues. Finally, direct diode lasers are now beginning to replace the lamp pumped Nd:YAG lasers.