Vaporizing foil actuator: A tool for collision welding

A method for implementing collision welding at moderate to small length scales has been developed. The flyer, instead of being driven by chemical explosives (explosive welding) or magnetic forces (magnetic pulse welding), is launched toward the target by the pressure created from the electrically driven rapid vaporization of a thin metallic conductor. Mechanical impulse is developed from 0.0762 mm thick aluminum foils, which are vaporized using capacitor bank discharge with nominal charging voltage of 5.5 kV and peak current on the order of 100 kA delivered with rise times of about 12 μs. Welding couples of copper-titanium, copper-steel, aluminum-copper, aluminum-magnesium and titanium-steel have been successfully created with the same input parameters such as foil geometry, input energy and standoff distance. Instrumented peel tests, lap shear tests and optical and scanning electron microscopy reveal a wide spectrum of both strengths and interface structures. Copper-titanium and copper-steel welds are strong and have characteristic wavy interfaces with little intermetallics or void formation. The other combinations are seen to have brittle interfaces with intermetallics and defects, with the collision welding parameters used presently. For the titanium-steel system, a thin nickel interlayer is introduced and all the layers are welded in a single experiment. Peel strength of the weld was observed to be quadrupled. Peak velocities of up to 560 m/s were obtained for titanium flyer sheets.