Previous investigations on laser welding at reduced ambient pressure have shown an influence on the penetration depth, a change of the seam cross sections and a reduction of the amount of spatters [1 – 3]. These effects assume a change of the process behavior due to a lower ambient pressure. The shape and the dynamics of the keyhole during deep penetration laser welding is a main factor for the resulting weld seam properties and the process behavior. The present investigations show the influence of the ambient pressure on the keyhole shape and dynamic behavior for welding steel and aluminum.
Bead-on-plate welding experiments at reduced ambient pressure down to 5 mbar of 16MnCr5 steel and AlMg3 aluminum were carried out for the present paper. A 5 kW Yb:YAG thin-disk laser at a wavelength of 1.03 µm with focal spot sizes of 150 µm and 300 µm has been used. A vacuum chamber was set-up that enabled time-resolved observation of the keyhole and the melt pool using the IFSW-X-Ray system. The influence of the ambient pressure and different feed rates up to 6 m/min on keyhole behavior was investigated.
It was seen for both materials that pressure reduction results in a significant change of the keyhole shape. An influence on the capillary front angle as well as bending at the capillary bottom could be observed for steel welds. The impact on the resulting seam shapes will be discussed. Furthermore, a correlation between keyhole behavior and an increased process stability that results in pore reduction of aluminum laser welds under vacuum conditions will be shown.