Role of strong focusability on the welding process

Thin disk lasers as well as fiber lasers are distinguished by their strong focusability and high efficiency. With the availability of such laser sources in a high power region, keyhole welding with very small focus diameters down to 50 μm became possible. Typical focus diameter regimes of such laser sources can now be compared with regard to their effect on welding depth and process efficiency. Based on results of thin disk laser experiments it has been shown in earlier publications that the influence of the divergence angle on the achievable welding depth increases dramatically for lower spot diameters. This effect stands in contrast to the behavior at higher spot diameters, but was now confirmed by additional experiments with a fiber laser which made available smaller divergence values. No influence of focus diameter and divergence angle on the reachable cross sectional area for both laser systems has been observed, on the other hand. That means that in the investigated parameter range the process efficiency of keyhole welding is in fact independent of the focusability of the laser source.