Study on One-side Narrow-gap MAG Welding (Rept. III)

Developing of control system for "Uranami Welding"

Abstract

The authors have been carrying out practical studies on one-side narrow-gap MAG welding with DCEN polarity. In the previous paper, observation of "Uranami bead" shapes and determination of suitable range of welding condition for "Uranami Welding" were carried out and it was made clear that "Uranami beads" without defect could be achieved over a wide range of welding conditions with this welding method. However, in case of long weld line and changing groove width, it became clear too that fine adjustment of welding conditions (mainly adjustment of welding speed) would be necessary in order to achieve constant shapes of "Uranami bead" all along the weld line.
Consequently, the relationships between arc phenomena in "Uranami welding" and shapes of "Uranami bead" were observed, and it was found that the shape of the "Uranami bead" was dependent on the welding speed and the wave pattern of the welding current. Based on these results, a new "Uranami welding" control method was developed. In this method, a control signal which was obtained by monitoring the welding current with a micro-computer, was used to adjust the welding speed continuously in order to achieve a good "Uranami bead".
Application of this control system to one-side narrow-gap MAG welding with DCEN polarity confirmed that uniform "Uranami beads" could be obtained even if the root gap varies from 9 to 12 mm.