Fiber lasers combine the advantages of solid-state lasers and diode lasers, such as high beam quality and high efficiency. Examinations concerning the micro-welding process were carried out with a 9 Watt CW fiber laser. The wavelength of 1100 nanometers is similar to Nd:YAG radiation, which is established in material processing. Due to the core diameter of only 8 microns and a numerical aperture of 0.08 of the collimated beam, focussing to less than 8 microns is possible. Therefore, power densities of more than 107 W/cm2 are obtainable, which make processes like marking, cutting, welding or soldering of metals possible [2, 3],
Investigations concentrated on the welding process of metal foils with a thickness of 25 to 50 microns. Stainless steel and mild steel were overlap-welded with argon and nitrogen as shielding gas. Foils with a thickness of 25μm, for example, were successfully welded at a speed of about 250 millimeters per minute. The stability of the process is extremely influenced by the welding speed and the shielding gas flow which affects the thermal conditions in the welding zone. In particular, slight alterations of the gas flow have much higher effects on the process than it is known from high power welding.