Methodology for Parameter Calculation of VP-GMAW : A straightforward procedure is presented for the calculation of welding parameters to reach both arc and metal transfer stability

The development of electronic power sources has allowed the study of innovative processes, generally with the objective to improve productivity allied to low levels of heat input. The existing processes are based on metal transfer evaluation and the development of different waveforms for improving the process control. The variable polarity gas metal arc welding (VP-GMAW) process is a derivative process of conventional GMAW that joins the advantages of the use of positive polarity, as the good stability of arc and cathodic cleaning, with the supplied ones for the negative polarity, which is the high melting rate of the electrode and low heat input to the base metal. However, this process still has a limited use due to shortage of technical and scientific literature devoted to parameter calculation, as the one observed for DC pulsed GMAW (Refs. 1,2). Also, most of literature is dedicated to aluminum welding (Refs. 3-7). Thus, in this work, a methodology for determination of the process parameters is proposed and evaluated for different waveforms and variable electrode negative ratio (percentage of time at negative polarity). Both arc and metal transfer stabilities are observed as indicators. The experimental procedure was carried out with bead-on-plate welding of mild steel and employing high-speed filming and analysis of bead geometrical features. It is concluded that the proposed methodology is suitable for parameters calculation during VP-GMAW, where a positive base time after the negative one is more effective in reducing abrupt polarity changes and therefore provides more stable arcs and avoids spattering. Finally, it is possible to select the best combination of waveform and electrode-negative time for the application, using the equations presented to predict the weld bead geometry.