VFA welding process, a new process variant in the field of collision welding technique basically to weld dissimilar materials. Researchers from The Ohio State University have discovered this technique.

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.

In this technique a high-voltage capacitor bank generates a short electrical pulse, which is passed through a piece of thin aluminum foil. The foil vaporizes within microseconds, and a burst of hot gas pushes both the pieces of metal together at speed of thousands of miles per hour. The metals don’t melt, so there’s no weakening of metal; instead the impact directly makes a bond of atoms of one metal to atoms of the other metal.

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

The technique uses a lesser amount of energy because the electrical pulse is so short, and because the energy essential to vaporize the foil is less than what would be used to melt the metal parts. Thus far, the team have used this method to join different combinations of copper, magnesium, aluminum, nickel, iron, and titanium.

 

Reference:

• Collision Welding of Dissimilar Materials by Vaporizing Foil Actuator: A Breakthrough Technology for Dissimilar Materials Joining, Glenn Daehn, Anupam Vivek
• Vaporizing foil actuator: A tool for collision welding, A. Vivek, S.R. Hansen, B.C. Liu, Glenn S. Daehn

Keep reading, Happy welding

KP Bhatt