AbstractCapacitor discharge welding (CDW) is a rapid solidification joining process where high cooling rates (106 K/s) are obtained as a result of the large weld surface area to small weld volume. The objective of this study, directed by the U.S. Bureau of Mines and the Oregon Graduate Institute of Science and Technology, was to use ultra-high speed photography to quantify transient arc behavior during the CDW cycle. The simple cylindrical geometries of the CD welds have been used to formulate analytical models which are compared to the high speed photographs of the welding process. The high speed photographs were analyzed with respect to welding time and process weld variables and compared to predicted values from the analytical model. The detailed photographic analyses revealed that material is continuously ejected as a plasma from the weld area due to induced magnetic forces, rather than having the liquid metal squeezed out of the weld upon contact. It was found that welding time was controlled by tip length and drop height. Results from high speed photographs found the arc travel speed around tube welds to be 109m/s. Finally, the high speed photographs revealed that the velocity of arc propagation during ignition was fast enough to allow the CDW process to be modelled as onedimensional heat flow.
Flash! Seeing the Unseen by Ultra-High Speed Photography
