Perspective on Double Pulsed Gas Metal Arc Welding

Abstract

Aluminum alloy welding suffers from problems such as solidification cracking and hydrogen-induced porosity, which are sufficiently severe to limit its potential applications. Because mitigated porosity incidence and solidification cracking are observed in aluminum welds using double pulsed gas metal arc welding (DP-GMAW), a comprehensive review of the mechanism is necessary, but absent from the literature. The oscillation of arc force and droplet pressure causes a weld pool stir effect. The expansion and shrinkage of the weld pool cause unusual remelting and resolidification of the previously solidified metal. DP-GMAW has an increased solidification growth rate and cooling rate, compared with conventional pulsed welding at same heat input. Both numerical and experimental results reveal the remarkable concept that refined microstructure in the fusion zone is obtained by using DP-GMAW. The mechanism of microstructural refinement is revealed as a weld pool stir effect and increased cooling rate. Hydrogen bubbles easily float out and then release from the weld pool originated from the weld pool stir effect. Reduced solidification cracking is achieved due to the refined solidification structure that originated from the increased cooling rate. The advantages, evolution process, and future trend of DP-GMAW are discussed.

Process and Parameter Optimization of the Double-Pulsed GMAW Process

“…where the meanings of i and j were the same as those in Equation (8). It can be seen that the robot welding speed is the most influential factor on the appearance; the corresponding range value was 21.667, and the following influential factors were twin pulse current change in percent, twin pulse frequency and twin pulse relation.…”

“…The bead width and bead height were also proper, and the forming was satisfactory, which was the same as that in former analyses. Where the range value D can be calculated based on Equation (9): where the meanings of i and j were the same as those in Equation (8). It can be seen that the robot welding speed is the most influential factor on the appearance; the corresponding range value was 21.667, and the following influential factors were twin pulse current change in percent, twin pulse frequency and twin pulse relation.…”

“…The difference between P-GMAW and DP-GMAW processes is the current waveform. During the DP-GMAW process, the current waveform is composed of a rhythmic thermal pulse phase (TPP) and a thermal base phase (TBP) [7], which have different frequencies and amplitudes, and the sum of durations of the two phases is equal to a thermal period (TP) [8]. Because of the existence of double pulses, it was also been named the twin-pulsed GMAW process in some published literature.…”

“…The original waveform was a usual types of square waveforms where strong current and weak current were alternately appeared during the process. Under the circumstance, arc quenching may appear when actual currents switch between TPP and TBP, because the wire feeding equipment may not be able to catch up with the variation of the current pulse with adequate speed due to the mechanical inertia [8]. To alleviate the sudden changes of the current amplitude differences in these two phases, corresponding improvements have been revealed, such as trapezoid waveform, or sinusoidal waveform [8,9].…”

“…Under the circumstance, arc quenching may appear when actual currents switch between TPP and TBP, because the wire feeding equipment may not be able to catch up with the variation of the current pulse with adequate speed due to the mechanical inertia [8]. To alleviate the sudden changes of the current amplitude differences in these two phases, corresponding improvements have been revealed, such as trapezoid waveform, or sinusoidal waveform [8,9]. By means of the changes, the changes of the currents were replaced by gradual switches, which can improve the stability of the arc to achieve a stable droplet transfer [10].…”