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Highlights • A numerical study of the influence of pulsing parameters in GMAW-P is presented. • Waveforms using different pulsing parameters but an identical average current are considered and compared. • Pulse with higher peak current but shorter duration leads to significantly higher detaching speed. • Average temperature of the transferring drop increases slightly with the peak current. Abstract The effect of pulsing parameters on the metal and heat transfer behaviors in pulsed gas metal arc welding is investigated by a numerical model based on the solution of the magnetohydrodynamic equations within the framework of phase field method. Five sets of current waveforms using different peak current and duration (i.e. 300 A-2.30 ms, 350 A-1.80 ms, 400 A-1.45 ms, 450 A-1.20 ms and 500 A-1.00 ms) but maintaining an identical average current (i.e. 170 A) are considered and compared. The pulses using higher current but shorter duration result in more elongated shape of the pendent drop, earlier detachment, and significantly higher velocity of the detached drop. Unlike the drop velocity, higher peak current merely leads to a slight increase in the average temperature of the detached drop. The reason for this slight increase is that only the joule heating increases with the peak current, while the sheath heating and arc heating is governed by the average current and keeps almost constant using different pulsing parameters. The simulation results are compared with the high speed photos and exhibit good agreements. [ABSTRACT FROM AUTHOR]

A numerical model has been constructed based on the solution of the magnetohydrodynamic equations within the framework of phase field algorithm to simulate the metal transfer process and to investigate the effect of power source dynamics on metal transfer and heat transfer behaviors in pulsed gas metal arc welding. Three typical kinds of power source dynamics (i.e. exponential, ideal square and trapezoidal waveform) using identical nominal pulsing parameters are considered and compared. The ideal square waveform with infinitely steep-sided pulse would lead to a higher detaching speed and an earlier detachment than other waveforms. Decrease in the response rate of the power source shows a retarding effect on the dynamic characteristics of the metal transfer, leading to a delay of detachment and a lower detaching speed. Moreover, this retarding effect is more and more significant as the response rate decreased and may even alter the transfer mode from one-drop-per-pulse to an undesired irregular pattern. Besides, a quantitative analysis of the heat fluxes into the electrode is further conducted, and the result shows that power source dynamics only has a quite slight influence on the heat transfer behavior. [ABSTRACT FROM AUTHOR]

Gas metal arc welding (GMAW) using an alternating current waveform is usually termed as variable polarity GMAW (VP-GMAW), during which the electrode polarity switches between positive and negative periodically. The arc properties and the droplet transfer in VP-GMAW would be different from traditional direct current GMAW. In order to clarify the droplet transfer phenomena during a VP-GMAW process, a unified numerical model including the interaction between the arc plasma and the moving droplet is developed. The simulation results indicate that the arc plasma generated at electrode negative polarity shows a less constricted shape, a lower plasma temperature and velocity, compared to positive polarity. The resultant droplet is found to have a bigger size and a lower temperature than that of direct current gas metal arc welding with the same average welding current. Moreover, a quantitative analysis of the heat fluxes into the electrode is further conducted to explain the thermal mechanism for the differences in droplet properties between variable polarity and direct current gas metal arc welding. Finally, the simulated results are compared with the high-speed images, and the simulated and experiment results show good agreements. [ABSTRACT FROM AUTHOR]

Resistance spot welding (RSW) with inserted strips, a recent variant of traditional RSW, was usually adopted in joining thin gage steels to lower the temperature developed at the electrode surface and to extend electrode life. In order to understand the influencing mechanism how the inserted strips affect the heat transfer behavior and to optimize the selection of suitable strips, an approach integrated with FEM and response surface methodology (RSM) was employed. FEM results showed that the inserted strips would not only lead to earlier initiation of weld and bigger weld size in both diameter and thickness but also lower the electrode surface temperature. Based on FEM, uniform design and RSM were further employed to build a regression model between the strip properties (i.e., electrical/thermal conductivity, thickness) and the responses (i.e., electrode tip temperature, weld diameter, and temperature at strip/sheet interface). A graphical optimization was conducted to identify a preferable strip, and a Cu55Ni45 strip with a thickness of 0.12 mm was recommended for a 0.4 mm steel sheet. [ABSTRACT FROM AUTHOR]