Product Code: ICAL09_1802

Influence of Oxygen on Weld Geometry in Fibre Laser Welding
Authors:
Lin Zhao, National Institute for Materials Science; Tsukuba Japan
Susumu Tsukamoto, National Institute for Materials Science; Tsukuba Japan
Goro Arakane, National Institute for Materials Science; Tsukuba Japan
Tomohiro Sugino, Ihi Corp.; Yokohama Japan
Presented at ICALEO 2009

Oxygen can significantly increase the penetration depth in arc welding. It is caused by change in the Marangoni flow direction from outward to inward with increasing the oxygen content. Increase in the penetration depth by oxygen was also reported in laser welding by some researchers, but the mechanism is still unclear. In the present paper, the effect of oxygen on the keyhole and fluid flow behaviour has been investigated to understand the mechanism of different weld geometries for various oxygen contents in fibre laser welding. The results indicate that the penetration depth increases with increasing the oxygen content. In high oxygen content, the fluid flow is inward. This means the inward Marangoni flow is promoted by oxygen. However, the keyhole depth observed from the X-ray transmission image increases with increasing the oxygen content, coinciding well with the penetration depth in the transverse section both in high and low oxygen contents. This indicates that increase in the penetration depth by oxygen is not caused by the fluid flow. Deeper keyhole formed in high oxygen shielding increases the penetration depth. Reduction in surface tension of the molten metal must be the main reason to increase the keyhole depth by adding oxygen.
Keywords: fibre laser welding, penetration depth, oxygen content, surface tension