(The) wire melting rate of alternating current gas metal arc welding for mild steel

Abstract

Since the development of gas metal arc welding (GMAW) in the early 1940s, several types of GMAW processes have been commonly used such as direct current GMAW (DC-GMAW), pulsed GMAW (P-GMAW) and alternating current GMAW (AC-GMAW). Among them, AC-GMAW which is relatively new process can take advantage of both positive and negative electrode polarity. Despite its advantages, the research into the understanding of AC-GMAW principles is quite limited. Wire melting rate which quantitatively describes the productivity of the welding process is one of the most important representative characteristics of GMAW process and thus should be well investigated. In this regard, the wire melting phenomenon in AC-GMAW process should be carefully observed and analyzed. Therefore, in this study, a new form of wire melting rate equation for AC-GMAW process is proposed based on energy conservation theory and arc physics. Welding experiments and high speed photography were conducted to investigate the effect of welding parameters on arc behavior and wire melting rate. By making use of these experimental data, the wire melting rate coefficients of AC-GMAW are obtained through nonlinear regression analysis. The wire melting rate is influ-enced by not only the current waveform, electrode polarity and droplet size but also the shape of the wire tip. That is, if the wire tip becomes more slender, arc heating has more influence on the wire melting. Using the wire melting rate proposed in this research, the uncertainty of calculating wire melting rate coefficients of AC-GMAW can be excluded comparing to existing method. Also, even if the wire melting rate of certain period which has complex arc behavior cannot be obtained, the wire melting rate coefficients of AC-GMAW can be calculated using average wire feeding speed.