Abstract
In order to obtain high quality welded joints, the ultra-narrow gap GMA welding (UNGW) process has been developed in which the arc moves up-to-downwards along the groove wall. In this process, the arc up-to-down oscillation pattern depends on the wire melting tip behavior that is controlled by low frequency pulse current waveform below 10 Hz. In the low frequency pulse arc welding condition, it can be suggested that the wire-melting behavior is in the non-steady state. Firstly, the one-dimensional heat coduction FDM analysis is proposed for the non-steady wire-melting behavior in GMA welding. For the numerical analysis, both values of the equivalent anode melting potential (Φ) and superheat temperature of droplet(ΔT) must be given, however there are significant experimental uncertainties in these values reported by many researchers. Therefore, in constant welding current, some pairs of these values are searched so that the wire extension calculated by the FDM analysis agrees with the measured one. As the results, the correlation between Φ and ΔT for each welding current can be found out in MIG and MAG arc welding. Secondly, unsteady wire melting behavior in low frequency pulse arc welding is simulated by the numerical analysis using the Φ-ΔT correlation. As the remarkable behavior in the simulation results, it can be found that the wire extension almost does not change for a few times under the transition period from the peak current to the base current. The wire melting rate by Joul’s heat energy stored in the wire extension during peak current period produced the delayed time. Finally, the high-speed camera and current data sampling system are used to measure the unsteady wire melting behavior, and the simulated results are compared with the measured results in UNGW. The measured locus of melting wire tip shows good agreement with the calculated one. From the results, the proposed one-dimensional heat conduction FDM analysis is effective for the prediction of the suitable arc up-to-down oscillation pattern in UNGW.
