Joined-up thinking

The principle behind Velcro inspired development of an injection moulding tool to create a surface allowing plastic car parts to bond. Siobhan Wagner reports


Plastic car parts could one day be joined like Velcro with a new injection moulding process under development at Warwick University.

Gordon Smith, the lead researcher of the project at Warwick Manufacturing Group, said the technique could create external components such as bumpers and wing mirrors coated with a surface of nano metre-sized hooks and eyes that could be bonded.

The process requires a new kind of micro-machined injection moulding tool that would emboss microscopic indentations on to a plastic surface. To determine whether the idea could work on a high volume production scale Smith was recently awarded more than £60,000 by the Warwick Innovative Manufacturing Research Centre.

The project follows up on Smith and his colleagues’ previous work, which demonstrated how to create holograms on the surface of polymer parts by moulding plastic on to a specially engineered nickel shell. The group is currently seeking a patent for a more robust steel version of the mould.

‘We were able to show that microscale and even nanoscale indentations were picked up and reproduced by the plastic surface,’ he said. ‘The idea was then born that if you could somehow engineer those surfaces to have the same sort of hooks and eyes as Velcro, it would be an ideal way of bonding surfaces together or peeling them apart at the point of recycling or disposal.’

Detailed surfaces would be created through a technique Smith’s team developed for painting plastic car parts inside the injection moulding machine.

The process would begin by injecting an initial plastic into the mould using an explosive blast of gas. The plastic would rapidly coat the surface and take on the desired form. A following plastic would then be injected using traditional injection moulding equipment, tooling and processes.

Cycle time will depend on how the materials — whether thermoplastics or thermosetting plastics or one of each —cure. The focus of Smith’s research is deciding what materials to use. His main concern will be on the plastic used for the Velcro-like surface. ‘We would need a plastic that had a more flexible characteristic so that it would unzip as well as zip. It would also have to work with our surface coating technique of gas explosion,’ Smith said.

While the technology sounds highly ambitious, Smith is confident he will be able to demonstrate a working model in six months.

He said Velcro speaks for itself as a technology that has produced a stunning amount of applications. ‘This is just another joining technique using the principle that you can bond materials together just through the surface defects.’

The main application for this new joining technology would be the automotive industry. While he currently does not have any industry partners, Smith has received initial interest from Jaguar Land Rover.

‘It could well be an easier method for bonding parts that could be removed easily for disposal,’ he said. ‘Of course you have to be a bit careful because you don’t want it to be so easily removed that a vandal could take it off.’