Laser beam welding

Laser beam welding, which a few years ago was still a rather exotic, special joining process reserved for very special applications is now increasingly considered to be a high-quality and often economic alternative to other, more established welding processes. Currently, there is a trend not only to apply the laser beam as a welding energy source in such more or less classical field of application such as in the production of car bodies but also in the aerospace industry for welding airplane structures. Morover, most recent research activities have led to the application of lasers in such industries as e.g. shipbuilding or pipe production which previously have been a rather classical domain of arc welding. On the basis of decades of experience in the field of laser materials processing especially of aluminium, steel and titanium, on the one hand a special emphasis is laid on basic research to lay the ground for furture technical developments. On the other hand, the BIAS faces the challenge of industrial application and conducts application studies for a variety of industries in order to optimize existing as well as to develop new systems and processes. In this context, three main fields of activity can be identified: " new beam sources: New developments in laser physics have led to the availability of new beams sources such as e.g. fibre lasers or thin disc lasers. In special, the thin disc laser has undergone a rapid development and is nowadays available with very high beam power. Due to its various advantages, among which there are high beam power at low energy input and an expected life expectancy significantly increased as compared to other diode-pumped beam sources, in the long run it can be seen an economic investment especially in such fields which have not yet been open for laser application. To investigate the potentials oft this new beam source, welding trials on aluminium and steel have been performed at the BIAS with an IPG Potonics fibre laser (Wavelength: 1070 nm, Figure. 1) with a maximum beam power of 6.9 kW and a beam quality of 17 mm*mrad.

Figure 1: 6.9 kW fibre laser at the BIAS

On the one hand, the high output power can be utilized th weld thicker sheets which previousliy could only have been welded by CO2-Lasers. On the other hand, it can be used to invrese the process window towards higher welding speeds for thin sheets. Especially in wagon building or in the aircraft industries, aluminium alloys up to sheet thicknesses of 6 mm and more are used for large structures. For these structures, the effort for CO2-Laser welding systems (especially considering beam guiding) is extremely high. With the fibre laser installed at BIAS, these sheet thicknesses could be welded with speeds up to 3 m/min at good weld quality. Figure 1 shows a cross section of a butt joint for the aluminium alloy AA60056 with a sheet thickness of 6 mm. Most remarkable was the observed stability of the processes, which enables the user to use a wide process window. For butt joints with different sheet thicknesses for Tailored Blanks godd results could be achieved, too. For welding thick sheets e.g. for offshore applications, in shipbuiliding and in pipe production, which have previously been a domain of CO2-Lasers, fibre lasers might be applied in future, too. The studies performed at the BIAS showed for all steel grades and aluminium alloys tested very promising results. The process limitations previously valid for solid state lasers colud be significantly expanded with these new power sources combining high power and good beam quality, thus resulting in economic as well as technological advantages for a wide variety of applications.

Figure 2: Aluminium butt joint, AA6056, t= 6 mm, P = 6.9 kW, v = 3,0 m/min, vD = 8 m/min, shielding gas Argon