Heart of glass

A lightweight commuter bicycle with a difference has been developed in the UK using injection moulded, glass-fibre-reinforced plastic parts.

The GoCycle can be pedalled like a traditional bicycle until the rider hits a button that revs up a high-powered electric motor in the front hub. It can travel at full legal urban driving speed for about 12 miles before needing a re-charge.

It is based on a magnesium frame, but vital mechanical components, such as the rear suspension unit, are made from nylon filled with long, glass fibres. The strong, lightweight material, which is 60 per cent glass, was injection moulded by Protomold of Shropshire.

Managing director John Tumelty said it was the first time Protomold's senior engineers worked with a material that was as much as 60 per cent glass.

The engineers were unsure how the material would flow into the cavity of the injection-moulding tool. 'Glass-filled resins are generally more prone to warp problems,' said Tumelty. 'The higher the glass content, the worse it can be.'

Protomold worked with Karbon Kinetics, the UK designer of the bike, and studied the CAD geometry of the parts that needed moulding. Protomold used this information to create a visual prediction of the injection moulding process with its in-house flow analysis software Protoflow.

The engineers experimented with different locations for the gates, the points where the plastic enters the cavity, and they studied the various temperature and pressure conditions needed to mould the parts. Eventually the company was able to develop 47 different injection-moulding tools to create all the parts.

The bike was designed to be durable, which meant the Protomold engineers designed tools that would distribute the flow of material evenly without creating weak spots.

It was also designed to be sleek and stylish — something that would attract the urban commuter.

The majority of the bike's components are a shiny black, and Protomold's engineers had to discover the exact speed to inject the material into the cavity to maintain colour consistency.

'On aesthetically critical components you could end up with literally changes in colour or changes in texture as a result of sudden acceleration,' said Tumelty.

'If you get the moulding process wrong with very high glass content, glass fibres will rise to the top of the part so you're actually looking at black plastic through glass fibre. It's an odd silvering effect that's not very attractive.'

While the UK teams were working on the mechanical parts of GoCycle, the magnesium frame was being manufactured by a Canadian firm using a process previously unknown to bicycle production. Called thixomolding, a type of injection moulding for metal, the technique is typically used for automotive parts, creating magnesium pieces that are thin walled and very strong.

GoCycle is being assembled by Ideal Bicycle Co of Taiwan which plans to launch it commercially in Europe this year.

Tumelty said the bike, which is lightweight and folds up easily, could be a big hit with town and city commuters.

'It's not only fun, but it's also hugely practical,' he said. 'It's got a range of several miles and if you've got a five-mile commute to work and you don't want to get too hot in your best suit, it's perfect.'