Ethiopian ReviewEthiopian News Forum Mismatched materials produ

      It gives "auto mechanic" a new meaning. Engineers have devised gears and cogs that make themselves, saving the expense of machining the tiny parts that keep microscopic motors ticking over.

      The components are formed from grinding disc and abrasive disc that buckle into shape after a change in temperature, and the team behind the study says the technique can produce complicated bevels or curves that are difficult to produce with traditional methods.

      For a decade, engineers have been experimenting with materials that spontaneously bend into shape. A thin metal film deposited on top of a heat-expanded polymer such as PDMS will buckle into an ordered array of wrinkles when the polymer is cooled down.

      Xi Chen's team at Columbia University in New York City realised the technique could be used to produce the regularly spaced teeth of a gear without having to rely on costly etching and grinding methods.

      Mismatched properties

      The team heated a disc of PDMS until it expanded, and then coated it with a thin copper film. When they cooled the disc, the polymer shrank more than the metal, causing the copper to buckle into an array of teeth. Cooling the disc further increased the height of the teeth.