How edgewinding can optimise e-bike design

2 mins read

Simon Ward, technical manager at TFC, explains why electric bike manufacturers are turning to components manufactured via edgewinding to solve design challenges.

AdobeStock: By diy13

To provide some context, data from the Bicycle Association shows that 165,000 e-bikes were purchased in the UK in 2022. The results show that the UK remains a less mature market than Germany, where two million are sold a year. However, representatives at the 2023 Cycle Show in London agree that the market is gaining momentum after a bumpy few years. Growing the e-bike market requires manufacturers to effectively design appealing products, manufacture them efficiently and scale up e-bike production profitably.

Cycling industry experts are calling for increased investment in infrastructure, but e-bike manufacturers have a role to play too, in manufacturing economic, lightweight and reliable e-bikes.

In e-bikes, springs and retaining rings can be used in drive technology, wheel hubs, braking systems as well as throughout the structural framework. Wave springs provide solutions to design and manufacturing problems by compensating for tolerances, and preloading bearings for optimal performance. Spirolox retaining rings provide 360° retention across multiple internal and external applications, while Hoopsters are well suited to tubular frames due to the shallow groove requirements.

In recent years, design engineers have moved away from stamped springs and retaining rings, and towards ones made via edgewinding. This method involves coiling wire on edge to create springs or retaining rings to precise specifications. The process gives more flexibility to manufacturers in terms of bespoke sizing and allows wider material choices to be considered.

In addition, the circular grain metallurgy increases the strength and stability of the material — cold rolling causes metal grains to elongate and lock together, which improves mechanical properties. Since the grain follows the direction of the coil, it provides better mechanical properties than if it were to be stamped from sheet material where grain flow is in just one direction.

One example of a component made by edgewinding is a Crest to Crest wave spring, an alternative to the traditional coil spring. Crest to Crest Wave springs are flat-wire compression springs offering the same spring force as a traditional wire round spring, but at 50 percent of the operating height.

Single turn wave springs are suitable for preloading bearings, while for applications with higher forces, designers may prefer nested wave springs composed of multiple layers nested together to provide a compact high force solution.

The potential for a 50 percent saving in space benefits the work of design engineers working on electric drive designs for e-bikes, which must be compact so that they can be integrated into different bicycle frames. The space-saving opens up new design possibilities, in particular reducing material usage and making bikes lighter — a significant efficiency advantage.

In e-bike drivetrain technology, retaining rings are used for securing bearings on shafts, as retaining elements in gear assemblies. Here too, designers are opting of flat-wire spirals due to their improved performance. Compared with traditional stamped circlips (DIN 471/472), they have no protruding lugs and, depending on the variant, no gap in the circumference.

Even in situations with limited radial space or where rotating components require minimal imbalance, flat wire retaining rings are the preferred choice of many e-bike designers.

The edgewinding process creates components with many technical benefits. From space saving to easy installation, wave springs and retaining rings can help UK e-bike manufacturers produce appealing products to support this growing industry.