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A process to join metals directly to composites, creating an extremely strong bond, could significantly reduce the weight of aircraft and cars.

Composite materials, although used with increasing confidence by aerospace and automotive designers, are typically difficult to join to metals. Engineers wishing to create metal to composite joints often have no choice but to settle on relatively conservative designs based on the use of fasteners, which increase weight and negate many of the benefits of composite materials.

TWI’s Comeld process, unveiled this week at the Farnborough Airshow, could allow designers to make the most of composite materials by ending a reliance on fasteners and even enabling the production of weldable composite sheets.

Early indications are that the process, which allows joints to be made between fibre reinforced plastic (FRP) composites and either titanium, aluminium or stainless steel, could enable the creation of joints that can absorb more than twice as much energy as conventional joints.

Dr. Faye Smith, senior project leader, said Comeld is currently the most advanced application of Surfisculpt, an innovative surface treatment process announced recently by TWI.

Surfisculpt draws on modern improvements in electron beam welding, and uses high-intensity electron beams to reshape metal surfaces precisely by creating protrusions and corresponding holes in a material. These protrusions can be created in controlled arrays and with physical parameters that can be modified with extreme precision.

Following the treatment of a metal, conventional composite production methods such as vacuum infusion processing can then be used to lay a composite on to the treated metal surface, where the protrusions help form an extremely strong joint.

Dr. Smith added the process could also make it possible to give sheets of composite material a metal edge, thereby creating weldable composite materials.

Comeld is currently at its earliest stages of development, and while early tests indicate that it is likely the method will enable the creation of metal-composite joints of great strength, Dr. Smith said that she would prefer to wait for the results of further tests before making too many claims for its potential.

This September will see the start of a 24-month project in which the method will be put through a series of tests to judge the performance of comeld joints against the requirements of a number of industries, including aerospace, marine, motor sport, military and specialist construction.

Smith added that a number of prominent companies from the aerospace and automotive industries are expected to participate. She declined to reveal these companies but claimed that they are very excited about what they have seen so far.

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