The presented apparatus enables laser beam welding of thick materials under local reduced pressure conditions, thus improving the quality of welds and reducing the laser beam power necessary for complete penetration welding. The vacuum cap presented in this article uses a local reduced ambient pressure environment in a tight zone around the welding area and, in contrast to a conventional vacuum chamber, it is movable in the welding direction. The mobile installation is very compact and reaches pressure values of around 200 mbar. The reduced pressure in the vacuum cap is sufficient to generate 50 % higher penetration depth in comparison to welding under ambient pressure conditions. The low pressure around the keyhole reduces the vapour-plasma plume and therefore prevents a defocusing and scattering of the laser radiation. This allows to raise the amount of laser beam power entering the keyhole as well as the effective power density.
The ever larger requirements of the material selection in the range of maritime industry necessitate the application of high-tech materials. Titanium because of its excellent mechanical properties at low weight is an attractive alternative for the construction of ships. The goal of this investigation was to design a welding method for joining samples of 16 mm thick Ti3Al2.5 V. The welding experiments with a 20 kW Yb-fiber laser source and varying combinations of parameters were intended to qualify the laser beam welding process. The welding results were analyzed by non-destructive and destructive testing. In addition, the welding tests were recorded with two high-speed cameras to observe the weld pool and the vapor plume. The evaluation of the high-speed images in correlation with the results of non-destructive testing shows, that a significant improvement of process stability and weld quality can be achieved by the suppression of the vapor plume.