ANALYSIS OF METAL TRANSFER IN SHIELDED METAL ARC-WELDING

In this work, a conventional rectifier-type power source was used with an automatic covered electrode feeder to investigate metal transfer in shielded metal arc (SMA) welding with commercial AWS E6011,E6013 and E7018 grade electrodes. The arc was established between the electrode and a rotating copper disk. The individual metal droplets transferred across the arc were collected in water and then processed using standard mineral dressing techniques to remove the slag coverings and to determine the droplet size and size distribution. The tips of the electrodes used in the experiments were examined metallographically for internal defects such as gas bubbles and evidence of liquid metal flow. Experiments were conducted following a 2(4) factorial matrix and Yate's analysis was carried out to determine the effects of electrode coating, electrode diameter, welding current, welding position, and polarity on metal transfer. The three major types of transfer identified were explosive transfer, short-circuiting transfer, and slag-guided transfer. In all three electrodes, the size distributions of the metal droplets collected were found to be nonuniform, with unusually high spatter-size droplets, supporting the explosive transfer conclusion. However, E6013 grade electrodes produced droplets with comparably more uniform size distribution (than the other electrodes) with intermediate characteristic diameter. The droplets from E7018 grade electrodes showed more slag covering than those collected from the other electrodes, which can be related to the higher volume of slag and the thicker coating on the electrodes. This is also the reason why the core wire diameter showed the strongest influence on metal transfer in E7018 grade electrodes. Finally, polarity has the strongest effect on droplet diameter in E6011 electrode, while welding current affected E6013 electrode the most.