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HOW IT'S MADE - Electric bike wheel hub using recycled composites

News International-French

28 Aug 2020

To reduce the footprint of daily mobility, Cogit Composites conducted a project that focused on the use of composite production waste to develop a new electric bike wheel hub with a specific design.

Integrated electric bike Wheel Hub valued by reused composite

Integrated electric bike Wheel Hub valued by reused composite

Thermoplastic polymers are increasingly used as matrix materials in long-fibre composite materials. This implies dealing with more production scrap in the short term and more end-of-life parts in the long term.

There is currently no easy way to separate carbon fibre from the matrix in unused composite materials, so that composite waste is buried or burnt, generating toxic fumes, greenhouse gases or water and soil pollution. To comply with the latest EU regulations, such as the Waste Framework Directive and the Directive on End of Life Vehicles, recycling and re-use have to be integrated into development plans.

Christophe ROUA, Owner and CEO, Cogit Composites:

Christophe ROUA, Owner and CEO, Cogit Composites
"Twelve years ago, whereas I intended to JEC Show in Paris, I became aware of the potential of thermoplastic composite materials in advanced applications and also in medium and large market. I firstly take into account the ability of short cycle process (such as plastic injection) and the opportunities of functionalizing (overmolding and welding). Although it wasn’t developed enough by this time, the recycling was also an advantage. In 2012, a French collaboration between Plasticompo platform, Orleans University and COGIT Composites was engaged to better understand how to recycle and/or reuse thermoplastic composite. Here, you could read a few results of our previews works. Since, COGIT has fully integrated engineering, prototyping and manufacturing of thermoplastic composites including eco-design and life cycle."


How it's made? Recycling method
The recycling method commonly used in the plastics industry involves a shredding step followed by a grinding step, resulting in a finer material that can be used as a reinforcement in thermoplastic injection processes. Unfortunately, this leads to low reinforcement levels compared to the initial part. An alternative solution is to chop the composite parts or production scrap (Figure 1) into not-so-small compounds (Figure 2), usually 25-50 mm long and 2-6 mm wide, and to use them as a primary material in compression moulding processes.

An alternative solution is to chop the composite parts or production scrap (Left) into not-so-small compounds (Right)

An alternative solution is to chop the composite parts or production scrap (Left) into not-so-small compounds: 25-50 mm long and 2-6 mm wide (Right)

For 15 years, thermoplastic composite materials and processes have been at the core of Cogit Composites’ strategy. Working on compression moulding, stamping and over-injection/moulding, especially for aeronautic applications, the company rapidly thought it could use its advanced skills to produce parts requiring the same level of quality but in totally different fields such as medical, luxury or sports products. The aim was not to manufacture just simple products but to be eco-friendly. So the decision was taken to use production waste to reduce the footprint of daily mobility. This is how a new electric bike wheel hub was developed.

Technical feasibility
A specific design was created to replace the existing aluminium part with a lighter wheel hub while ensuring complex shape forming, structural and kinematic functions and a high-end perception by the final customer.

Existing aluminium part

Existing aluminium part

 

Main body of reused composites Wheel Hub

Main body of reused composites Wheel Hub which include a specific design

The team first applied compression moulding design rules to evaluate the technical feasibility and properly integrate original functions. Parallel to this engineering stage, a collaborative R&T project called RTL3 (2012-2015) was conducted with the University of Orleans and the Plasticompo platform in the centre of France. The goal was specifically to define the best compound size comparing mechanical strength and processability. The investigated parameters included grain or pellet sizes and their distribution in the mould at the beginning and the end of the compression process. The experiment design, mechanical characterization and tomography inspections followed a scientific approach to gain a better knowledge of random material properties in a complex part.

Typical fracture between aggregated grains

R&T project called RTL3 defined the best compound size comparing mechanical strength and processability. Parameters like best grain or pellet sizes and their distribution in the mould at the beginning and the end of the compression process was studied. In picture a typical fracture between aggregated grains

 

Tensile properties relative to quasi isotropic reference

Mechanical characterization hereupper described the tensile properties relative to quasi isotropic reference

Following this experience, Cogit Composites kept on studying other raw materials such as carbon/PA and carbon/PEEK. This research provided a more detailed overview of processing parameters and mechanical properties depending on the matrix.

A promising way forward was also identified by looking at other sources of recycled material such as production waste of AFP UD tapes used for airplane wings and airframe layouts. Conditioned as 10mm to 25mm long chopped tapes, this waste showed a good ability to be re-used by compression moulding, especially into complex shapes. A study was conducted at the coupon scale to define mechanical engineering allowable values. The results matched those of commercial chopped UD tapes.

The key benefits of this wheel hub are the re-use of production waste, the valuable perception of high-performance materials and the short-cycle recycling required by green mobility. The eco-design shouldered by scientific and experimental support becomes a real advantage to customers. Indeed, the finish provided by forged carbon adds value to the final electric bike.

Repairing fglass-fibre components is easily done at the depot. All this contributes to reduce the operational-maintenance and life-cycle costs.

The final part made by compression moulding processes:

Finished recycled composite Wheel Hub