Blowholes on Pulsed MAG Welding Yamada, Tadaaki; Kobayashi, Minoru
QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY,
1985, Volume:
3, Issue:
4
Journal Article
Open access
Blowholes and their formation of Pulsed MAG welding was investigated. Among welding parameters such as arc length, average current, wire extension, welding speed and shielding gases, arc length was ...the most important factor. The average size of blowholes was as small as 0.62 mm. As results of analysing gas components of the blowholes by means of gas chromatograph, Ar, H2, and CH4 were detected and CO2 and CO and O2 were not in the blowholes. H2 and CH4 were also detected in blank test pieces. From SEM observation, the shape of the blowhole was like a sphere, the bottom of which was flat and the upper side was uneven like a corn having a slag spot at the top. The slag composition in the blowhole was Al, Si, Mn, Ca, La and Ce etc., and differed from the slag on the weld bead. From these results, the mechanism of blowhole formation in Pulsed MAG welding was considered as follows. Disturbance of the weld pool accompanied with spattering forms gas bubbles of the shielding gas in the pool. Small bubbles tend to be dragged into the bottom of the pool by whirling action, and be confirmed there to form blowholes close to the fusion line. CO2 in the blowholes are deoxidized to form the slag at the top of the blowholes.
Compared to conventional MIG welding, the MIG welding with filler wire, where a filler wire is fed into MIG welding arc, improves efficiency by minimizing the heat input and increasing the deposition ...rate. However, discussion arises on controlling the convex bead which arises at increased deposition rate. In this study, it is attempted to control the uneven bead in the MIG welding with filler wire by applying magnetic control of the arc. Furthermore, possibility of controlling the weld metal content is investigated which is favourable for cladding by welding of dissimilar metal i.e. clad steel, corrosion and heat resistant alloys and so on. The diameter of the filler wire was 1.2 mm, the electric current for the welding was 180-350A, the magnetic field for oscillating the arc was 0.004-0.006T and 5Hz. Experimental results showed that the bead of excellent appearance was obtained and it could be flattened by applying magnetic field even at increased deposition rate of MIG welding with filler wire. The penetration was found to be approximately 50% of conventional MIG welding. It was also found possible to control the amount of Ni and Cr, which are important elements for corrosion and heat resistant alloys, and to deviate for them to the bead surface by varying composition and feed rate of the electrode wire and the filler wire. It is said from these findings that this welding method is suitable for cladding by welding to improve efficiency and quality.
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