Publications Details

VAR pool depth measurement and simulation for a large diameter Ti-6Al-4V ingot

Minisandram, Ramesh S.; Arnold, Matthew J.; Williamson, Rodney L.

During VAR of a 5377 kg, 0.76 m diameter Ti-6Al-4V alloy electrode into 0.86 m diameter ingot, tantalum balls were dropped into the ingot pool to measure the centerline pool depth. The first was introduced at full power after 1134 kg of electrode had been melted. A second marker was dropped after 4288 kg of electrode had been consumed, also at full power but just prior to power cutback. The third, and final, ball was released at the end of the cutback with 286 kg of electrode remaining. An external solenoidal stirring field was applied to the ingot throughout the melting process, as is typical in such practices. The ingot was sectioned, the marker ball positions recorded, and the pool depths subsequently calculated. The first market was located only 4.5 cm from the bottom of the ingot, but was off-center by nearly 22 cm, indicating a relatively flat pool bottom. The other two balls were located 36.2 cm and 105.4 cm from the bottom, both approximately centered. Pool depths for the three conditions were calculated to be ∼41 cm, ∼131 cm and ∼99 cm. BAR, a 21/2 D, axisymmetric ingot code developed at Sandia National Laboratories, was used to generate pool shapes corresponding to these conditions. The code, which solves heat transfer, fluid flow and electromagnetic effects in a coupled fashion, was able to match the pool depths by adjusting the strength of the stirring field as a parameter, and predicted relatively thin sidewalls under full power melting, a prediction supported by crucible temperature and current distribution data also collected during the test. The applied stirring field was 60 gauss for this test. The effective field strength setting in BAR required to match the pool depths was 30 gauss. All other parameters in BAR were set identical to those required to match low stirring field (4 gauss), full power ingot pool depths measured and reported in an earlier study, except those requiring consistency with observed arc behavior in the two cases. Thus, it is concluded that the 21/2 D code can accurately match pool depths under high field strength stirring conditions once properly benchmarked.