| Abstract Scope |
Introduction: During welding, there are several voltage losses associated with the electrode. By performing an energy balance on the electrode stickout and the molten droplet, based on the experimental measures of the droplet temperature, it was possible to ascertain an effective anode fall voltage and likely effect of vaporization. Results suggest that the lower currents observed under the same wire feed speed for ER 5183 compared to ER1100 are more likely due to the lower droplet temperature than to the different resistivity of the alloys in the electrode extension. Also, it is likely that the metal vapors increase the anode fall voltage.
Experimental Procedures: In this experiment, two alloys ER1100 and ER5183 are subjected through GMAW, and their AWS A5 notation droplet temperature, current, total voltage, and wire feed speed were measured. Droplet temperatures were measured using a solid-state calorimeter. A copper tube with a hole functioned as a cathode, allowing the molten droplet to fall through and onto the calorimeter. The contact tip to workpiece distance (CTWD) and the arc length was maintained constant while the total voltage and wire feed speed were controlled manually. The shielding gas composition was pure argon and remained unchanged under direct current and electrode positive (EP) conditions. High speed videography was used to confirm the required droplet transfer mode. Thermophysical properties for both ER1100 and ER5183 were obtained through JMatPro and all the other data was analysed using excel.
Results and Discussion: A higher wire feed speed was found for ER5183 in comparison to ER1100. This phenomenon was initially attributed to the higher resistivity of ER5183, which would increase the Joule heating, thus requiring lower energy to maintain a similar wire feed speed. Verifying the resistivity of both the wires at varied currents revealed that their difference was very small and that this could not be the main reason contributing to the difference in droplet temperature by Joule heating. Even though the Joule heating of ER5183 provides more heat when compared to ER1100 for the same current, the droplet temperature of ER5183 was lower.
Evaporation of the molten droplet in the electrode could not be decoupled at this stage from the anode fall voltage analysis. The anode fall voltage was based on three components, work function being the major contributor along with evaporation and pre-sheath. The shielding gas and metal vapors of Al and Mg could have an impact on the pre-sheath voltage. With an increase in current, the amount of evaporated mass seemed to increase, alongside temperature. A small dip and rise were found with the droplet temperature data, and this trend was followed for both the fall voltages and the evaporation behaviour. Different percentages were calculated for the melting process of the wire, according to the total energy of the process. The measured droplet temperature for ER1100 was higher than ER5183 for the same current, and this trend line was followed for all the current values measured.
Conclusion:The higher deposition rate in Mg containing alloys is more likely due to the lower droplet temperature than to the increased resistivity of the alloys. The effective fall voltage inferred (which accounts for plasma effects and energy lost by vaporization) seems to indicate that the anode fall voltage increases with the presence of metal vapors. |