Heat input analysis of variable polarity arc welding of aluminum

Abstract

Influence of direct current electrode positive (DCEP) duty ratio in variable polarity (VP) arc welding of aluminum has been investigated in the current work. VP arc adopts alternate current (AC) of DCEP and direct current electrode negative (DCEN) as power source, and the duty ratio indicates the polarity's durational portion in the current pulse. Experimental results showed proportional relationship between heat input and DCEP duty ratio although there was a fluctuation due to the arc instability increase caused by wearing of the tungsten electrode tip. This observation violates the conventional arc theory of anode heating, and therefore, a new theoretical approach combining the tunneling effect and random walk of cathode spot has been proposed. During DCEP duration, arc is concentrated on thinner oxide cathode spot, which further melts and breaks the oxide layer of the spot. This process is repeated at another cathode spot at a high frequency. Therefore, the higher the DECP duty ratio, the more cathode spots are generated and the longer was the arc concentration time. This in turn resulted in a higher heat input for longer DCEP polarity duration. The proposed mechanism combining the tunneling effect and random walk of cathode spot can not only explain the anomalous results of the current research but also could address the ambiguous result of deeper penetration in thicker oxide in the past research.

Assessing the effect of TIG alternating current time cycle on aluminium wire + arc additive manufacture

“…This was apparent since increasing the % EP increased the wear of the electrode tip correspondingly. From initial studies conducted by Cho et al [13], it is believed that the melting of the electrode tip affects the absorption of electrons on its surface which in turn makes the arc unstable.…”

“…In aluminium welding, the alternating current TIG (ACTIG) process has been used because of its ability to allow setting of the proportions of electrode positive (% EP) to negative (% EN) time cycle to enhance oxide removal and fusion effect [8,12,13]. This is possible because the % EP part of the AC cycle can effectively remove aluminium oxides through the mechanism known as the cleaning effect [6,14].…”

Reverse voltage generating circuit for rapid commutation of output current polarity in variable polarity arc welding power supply

“…The adjustment of welding process parameters in VP‐GTAW or VP‐PAW is flexible, including independent adjustable parameters of current amplitudes of DCEP polarity, I p , and DCEN polarity, I n , current VP frequency, f = 1/ T , and the ratio of the duration of DCEN polarity, t n , to the period of current VP, T , EN = t n / T [19, 20] and so on.…”

Effect of Arc Pressure on the Digging Process in Variable Polarity Plasma Arc Welding of A5052P Aluminum Alloy

“…There are two polarities in one current cycle: an EN (Electrode Negative) phase and an EP (Electrode Positive) phase. The cycle can achieve both deep penetration and remove the oxide layer on the surface of the base metal [2,3]. The keyhole digging process is very important, because the welding easily fails without proper keyhole generation [4].…”