Physical processes during pulsed Nd:YAG laser and CW-CO{sub}2 laser welding of zinc coated steel

摘要

Using Nd:YAG and CO{sub}2-laser, the weldability of zinc coated metal sheets in overlap configuration without gap between the sheets has been investigated. The use of a high speed camera and a CCD camera has allowed to study the characteristics of a pulsed and CW process by visualizing the phenomenon of melt pool ejection. We have observed that the Zn vapor is ejected inside the keyhole through tunnels mainly located in front of the keyhole. The effect of these tunnels leading to different types of melt pool ejection, is analyzed for each welding condition and the resulting gas jet has been modeled. New results about keyhole and melt pool movements as well as zinc vapor behavior are discussed. Finally, we show that the use of elongated focal spots allows us to correctly weld these sheets in overlap position without a gap.