Study on the Prevention of Weld Defects in C02 Laser Welding

Laser welding is suitable to produce high-precision weldments, because of low heat input and deep penetrations as compared with bead widths. The partially penetrated weld of steels, in general, is susceptible to porosities. It is suspected that gases such as oxygen and nitrogen in the base metal, the metallic vapor generated from the molten pool or the shielding gas are trapped in the weld metal due to unstable flow of the molten metal. However, the definite causes of porosity formation in laser welding have not yet been clarified.

In the present report, the causes and the prevention of the porosity formation in partially penetrated welds of steels made by C0₂ laser welding were investigated. The results are summarized as follows:

(1) The porosities are caused by the metallic vapor and the gases trapped in the molten metal due to unstable metal flow in the molten pool with a key hole.

(2) The porosities can be prevented by using a mixed gas of 0₂ and N₂ as a shielding gas and stabilizing the flow of the molten metal.

(3) The porosities can be prevented if the shape of the molten pool is stabilized by a beam oscillation along the weld center line.