Sweating the small stuff Home

Micro-Sculptures Give Metal The Velcro Touch

Minuscule shapes sculpted on metal surfaces could have a profound impact in many fields of engineering.

By training intense electron beams on the surface of metals, Bruce Dance and his team have found a way to fashion delicate metal projections that will act like ultra-strong Velcro to form much tougher joints between metals and lightweight composite materials in aircraft and cars.

The projections could be used to encourage bone to grow onto artificial hips. They could also be used in electronics to produce heat sinks of just about any shape.

Developed at the Welding Institute (TWI) in Great Abington, near Cambridge in the UK, the technology - dubbed Surfi-Sculpt - can grow structures up to 2 millimetres high and 0.2 millimetres in diameter.

To make a projection, researchers focus a beam of electrons in a vacuum chamber at the point on a metal surface where they want it to grow. The metal melts at the centre of the beam. When the beam is moved sideways, surface tension pulls the molten metal into a droplet.

And the metal vaporised next to the droplet adds even more metal to the droplet, which then solidifies to start the projection. "When we first realised we could do this we were absolutely gobsmacked," Dance says.

Surface eruption

The projection is grown by repeating the process and sluicing molten metal over it from different directions. "It's a bit like sweeping up leaves, except you start at the point where you want them to accumulate," says Dance's colleague, Colin Ribton.

Electromagnetic fields controlled by software choreograph the electron beam's movements around the metal, teasing out many projections at once.

The process is fast. It takes less than 10 seconds to create thousands of projections on a plate 10 centimetres square. "The whole surface erupts seemingly simultaneously," Ribton says.

Dance hopes an early application will be in improving the joints between metals and composites. The sculpted surface area is between two and 10 times larger than smooth metal, and composite fibres will easily become entangled with it.

Glass and plastics

Like joining two pieces of Velcro, TWI says it can bond a metal to a composite simply by pressing them together. The carbon fibres in the composite wrap tightly around the protrusions, creating a firm bond without any kind of glue.

Dance says his early tests show that these joints will last far longer than current composite-metal joints, which are held together by adhesives.

Surfi-Sculpt has so far been successfully tested on stainless steel, aluminium and titanium, but TWI expects that it will work on any material that melts, such as glass and plastics.

TWI says 20 aerospace and automotive companies are now examining its sculpting technology, for which it has recently filed world patent applications. It expects products using the technique to be on the market within a couple of years.

"This technology is a world first," says John Cumberland of Cambridge Vacuum Engineering, a firm that makes electron beam welders. "It solves a major jointing problem."

Mick Hamer