Surface dynamics of unipolar arcing
Downs, Richard Keith
Schwirzke, Fred R.
Olsen, Richard C.
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A 4.55 microsecond, 15 joule pulsed CO2 laser was used to illuminate a copper target. Bulk plasma was found to be emitted normally to the target surface independent of the laser angle of incidence over the range of 45 degrees +/- 15 degrees. Material ejected from a copper target was allowed to deposit onto polished type 304 stainless steel surfaces. The ejected material deposited in concentric 'rings' many places. The mechanism for this is unknown. Polished type 304 stainless steel surfaces were coated with one to ten micron copper films and shot with the laser. Damage to the films indicate that the damage mechanism may simply be Joule heating from the arc current. This lead to a procedure for calculating that arc current. The arc lifetime is necessary but still unknown. No correlation was found between unipolar are pit diameter and depth. Investigations into the role of surface tension on the dynamics of the molten surface lead to a comparison between unipolar arcing and arc welding. Much of the physics known about arc welding is qualitatively applied to describe the surface dynamics of molten metal produced by unipolar arcing.
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