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J Weld Join > Volume 33(2); 2015 > Article
Journal of Welding and Joining 2015;33(2):14-17.
DOI: https://doi.org/10.5781/JWJ.2015.33.2.14    Published online April 30, 2015.
Theoretical background discussion on variable polarity arc welding of aluminum
Jungho Cho*, Jungjae Lee*, Seunghwan Bae*, Yongki Lee*, Kyungbae Park*, Yongjun Kim*, Junkyung Lee**
Correspondence:  Jungho Cho,
Email: junghocho@chungbuk.ac.kr
Cleaning effect is well known mechanism of oxide layer removal in DCEP polarity. It is also known that DCEN has higher heat input efficiency than DCEP in GTAW process. Based on these two renowned arc theories, conventional variable polarity arc for aluminum welding was set up to have minimum DCEP and maximum DCEN duty ratio to achieve the highest heat input efficiency and weldability increase. However, recent several variable polarity GTA research papers reported unexpected result of proportional relationship between DCEP duty ratio and heat input. The authors also observed the same result then suggested combination of tunneling effect and random walk of cathode spot to fill up the gap between experiment and conventional arc theory. In this research, suggested combinational work of tunneling effect and rapid cathode spot changing is applied to another unexpected phenomena of variable polarity aluminum arc welding. From previous research, it is reported that wider oxide removal range, narrower bead width and shallower penetration depth are observed in thin oxide layered aluminum compared to the case of thick oxide. This result was reported for the first time and it was hard to explain the reason at that time therefore the inference by the authors was hardly acceptable. However, the suggested combinational theory successfully explains the result of the previous report in logical way.
Key Words: Variable polarity, Aluminum, GTAW, Cleaning effect, Tunneling effect, Cathode spot
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