Fixing the composite question

Written by: Paul Fanning | Published:

Strong as many engineering composites are, they can be easily damaged by a fastener that would give excellent service when joining metals. A second limitation on the use of metal fasteners with advanced composites is the fact that certain metals commonly used for high-strength fasteners can experience galvanic corrosion in composites containing graphite or carbon fibres.

The advantage of composites, of course, is that the fibres can be placed in the ideal direction to carry the loads. This, combined with their inherent light weight, results in dramatic weight saving possibilities. Another benefit of using composite materials in design is that complex parts can often be made in a single moulding, reducing the need for assembly and mechanical fastening operations.

Composites, particularly high-performance composites such as those containing carbon fibres, are generally perceived to be expensive, time-consuming to make and difficult to joint. Overcoming these problems is therefore a major challenge to their more widespread acceptance. Even the aerospace industry, like automotive, is facing the challenge of rapid processing of composite parts and structures, and there is a clear demand for rapid manufacturing processes.

For these reasons, there is a requirement for composites specifically for use with composite materials. One company that specialises in this is the UK's own bighead. which has made automotive fasteners, marine fasteners, construction fasteners, panel fasteners, composite fasteners and special fasteners for over 40 years. These fasteners all share the original bigHead design: a flat perforated head which locks the product securely into position and spreads the load, is welded to a wide choice of studs, nuts, collars, pins and other fixings to offer versatility.

Critically, this design can support a huge range of design solutions. Consequently, bigHead has made over 5,000 designs for customers – in addition to the 400 standard products supplied on a day-to-day basis.

A recent example where this fastening solution came into its own was as a specialist fastening solution to Proseat for a high-end ventilated seat module. Embedded directly in the polyurethane seat cushion, the bigHead fastener provides a very secure anchor point for a fan unit to be attached under the seat cover. The threaded stud connection allows the fan unit to be easily assembled and later removed for repair. The bighead makes the whole construction simple and quick to install.

The design of the fasteners allows the product to be embedded in foam, rubber, plastic or composite material. Alternatively bigHead fasteners can be surface bonded with adhesive. An instance of this is seen in the carbon fibre diffusers on Aston Martins, which are attached using bigHead fasteners and bigBond adhesive. Discrete and very strong, the bigHead fasteners provide a unique solution. Surface mounted on the inside of the diffuser the bigHeads are completely invisible, with no rivets or drill holes necessary. Due to the unique design of the perforated head, the glue flows through the holes and hooks the fastener into position, achieving high stability and strength.

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