New welding technique to produce sturdier cars

Engineers have developed a new welding technique that consumes 80 percent less energy than the common welding pratice yet creates 50 percent stronger bonds.

They have already successfully created strong bonds between commercial steel and aluminium alloys -- a feat which is impossible normally.

The new technique could have a huge impact on the auto industry, which is poised to offer new cars which combine traditional heavy steel parts with lighter, alternative metals to reduce vehicle weight.

"Despite recent advances in materials design, alternative metals still pose a challenge to manufacturers in practice. Many are considered un-weldable by traditional means, in part because high heat and re-solidification weaken them," said professor Glenn Daehn from Ohio State University, who helped develop the new technique.

"With our method, materials are shaped and bonded together at the same time, and they actually get stronger," he added.

In a common technique called resistance spot welding, manufacturers pass a high electrical current through pieces of metal, so that the metals' natural electrical resistance generates heat that partially melts them together and forms a weld.

But generating high currents consumes a lot of energy, and the melted portions of metal are never as strong afterward as they were before.

Daehn and his team have developed a system called vaporized foil actuator (VFA) welding.

In VFA, a high-voltage capacitor bank creates a very short electrical pulse inside a thin piece of aluminium foil. Within microseconds, the foil vaporises, and a burst of hot gas pushes two pieces of metal together at speeds approaching thousands of kms per hour.

The pieces do not melt, so there is no seam of weakened metal between them. Instead, the impact directly bonds the atoms of one metal to atoms of the other.

Daehn explained the new process in a keynote address at the Materials Science and Technology 2015 meeting recently in Columbus.