New techniques for welding very different materials could enable better cars

Making vehicle structures out of a combination of metals and plastics could make them lighter, stronger, safer, and more environmentally friendly than all steel or aluminum. However, the traditional methods for joining metal and plastic—adhesives or mechanical fasteners—are slow and expensive.

The first viable method for welding plastic and metal directly together was recently developed at the University of Michigan under the leadership of Pingsha Dong, the Robert F. Beck Collegiate Professor of Engineering, and is now reported in Journal of Manufacturing Processes.

“Computer models show us we can make the structures of cars and light trucks as much as 40% lighter by building them with a combination of metals and plastics. Lighter weight brings a variety of advantages, chiefly better efficiency,” Dong explained.

“The conventional wisdom for decades has been that plastic and metal are fundamentally incompatible, and there's no reason to try welding them together. However, we discovered that the right combination of heat and pressure in the right areas can cause the carbon and oxygen in plastic to bond with metal.”

The process employs a machine similar to a drill press. The metal is placed on top of the plastic, and a cylindrical, spinning head is lowered onto the materials, creating heat and pressure to bond the materials in a spot or linear weld.

“We've patented the process and we're already working with equipment makers to develop commercial equipment that can be licensed to automakers and other manufacturers,” Dong said. “I'd say we'll see this technology in industry within the next two years.”

Dong has also researched joining steel and aluminum through inexpensive 3D printing of aluminum alloys onto steel.

“Previous attempts have led to the formation of brittle compounds at the interface between the two metals, reducing the strength of the alloy. Our process uses a precise combination of heat and pressure to prevent those compounds from forming, and it could offer new ways to combine the light weight of aluminum with the high strength of steel.”