1998 Volume 16 Issue 1 Pages 45-50
With respect to the blowholes to be formed by the vaporized zinc gas coming into a molten pool through the gap of seams in the consumable electrode type pulsed arc welding of galvanized carbon steel sheets, the means to decrease the number of them by inducing the flow of molten metal along the bottom face of the molten pool has been examined and studied. As the result of the vibration of mother metals by 1 mm while welding so as to produce the back and forth flow of molten metal at the bottom face by the longitudinal vibration of molten pool, the significant reduction of blowholes has been achieved. The optimum frequency of vibration seems to be about scores of frequency (Hz) which can be supposed to be the self vibration frequency to be determined depending on the size of molten pool, physical properties of type of molten metal, etc. In order to obtain the same effect as the above by the control of electric current, by minimizing the variation of arc length, the process to alternately repeat the pulse electric current wave groups of both high peak in a short time and low peak in a long time to periodically change arc force at the same time has been studied. It has been found that the molten pool can be vibrated in a longitudinal direction also by the control of arc force and it has also been found that the generation of blowholes can significantly be reduced by this vibration. The vibration of molten pool is effective for the promotion of removal of not only the blowholes to be caused by generation of zinc gas but also those of supersaturation type by the nitrogen to be formed on the metal surface in the progress of their solidification.
