For variable polarity plasma are welding (VPPAW) of 1100 Al, it was fo
und that the net heat input to the aluminum workpiece did not decrease
as independent changes in polarity balance enabled the tungsten elect
rode to be come the predominant anode in the alternating current are.
For the thin sheet edge welds made in this study, the independent para
meters used to var); the are current polarity balance were very effect
ive in delivering a wide range of actual are power polarity balance. T
he ratio of electrode positive polarity are energy to the total are en
ergy ranged from as little as 0.03 to as high as 0.99. Despite this pr
onounced difference in are polarity, no significant variation in the a
verage are efficiency (net heat input/arc energy) of 0.51 was found. S
ubstantial heating of the workpiece during electrode positive polarity
was attributed to field type emission of electrons from the low boili
ng point aluminum cathode. Unlike thermionic emission at the tungsten,
field emission electrons do not cool the cathode. While the actual ar
e efficiencies were relatively constant, there were significant differ
ences in the measured heat input, the weld size, and the effectiveness
of the cathodic cleaning. Increases in the are voltage resulted in a
gradual increase in are power as the aluminum workpiece became the pri
mary cathode. This resulted in an increase in the measured heat input
to the part and an increase in the melted volume. Despite variations i
n melted volume, no correlation between are polarity and weld dimensio
ns was observed. The effectiveness of positive polarity are power in r
emoving the surface oxide was clearly apparent when examining the resu
lting welds. Cleaning (i.e., removal of the oxide) can be effectively
controlled and optimized through proper selection of the independent p
arameters used to create the test weld matrix.