E-bikes vary significantly in terms of drive train concepts. Design engineers are free to choose from a variety of joining techniques for their electric motors. Fazua has opted for bonding and uses metal adhesives from DELO for its compact and lightweight drive system.
The e-bike market is booming. In many markets, one in three is now an e-bike. Producing a very light and compact drive system, the start-up Fazua has carved its own path in this market.
Thanks to the integrated freewheel, e-bikes driven by a Fazua motor offer a natural riding experience without mechanical resistance, even above the legal speed limit. If this speed is exceeded, the engine shuts off imperceptibly. At the same time, the drive unit's mass of 4 kg to be moved is almost negligible – a big difference to most e-bikes where just the drive system weighs up to 9 kg, which can give them a total weight of 20 kg and more.
Another feature is that motor and battery form a closed unit. Not only are they designed to visually disappear in the frame, they can also be removed in a few simple steps. So the comparatively low total weight can even be reduced by another 3 kg, whereas on most commercially available e-bikes, the motor is always firmly installed in the frame. This young company based near Munich, Germany thus closes the gap between classic bikes powered by muscle and heavy e-bikes with plenty of torque and battery capacity, which demand little effort from the cyclist, but are hard to move when the battery is empty.
Two years after entering the market, more than 45 European bike manufacturers are already relying on this solution, especially providers of e-road and e-gravel bikes with all-terrain versatility. Fazua is already leader of this young market. Therefore, it is not only quality that counts for the drive system consisting of bottom bracket bearing, motor, and battery. With five-digit quantities per year, production efficiency also plays an important role.
The Right Joining Technique is Needed
The motor concept is crucial in order to obtain a compact, yet powerful motor. Fazua uses motors with rare earth magnets, since they have the highest efficiency. Traditional methods of fastening the high-quality magnets to the rotor are mechanical clamping or, in the case of surface-mounted magnets, also bandaging. Both methods are increasingly reaching their limits. The manufacturing tolerances required for clamping can quickly drive up costs. Above all, however, the magnetic coating and the magnet itself may be damaged, which can cause corrosion. Bandaging of the magnets is complex and requires precious space.
Adhesive bonding, in contrast, provides for better protection of the magnets' passivation, nickel, or epoxy coating during assembly than most other methods. Bonding ensures an optimal embedding of the magnets into the lamination stack, leaving the smallest gap possible between magnet and coil. And this technology offers even more advantages: adhesives are impact-resistant, which is essential given the high dynamic forces of electric motors. Their vibration-damping characteristics reduce noise and provide acoustic improvement. And thanks to a large bonding area, tensions arising, for example, from different coefficients of thermal expansion are distributed homogeneously.
Adhesives for High-Performance Motors
All these benefits persuaded Fazua to choose adhesives for embedding neodymium magnets in their e-bike motors. Pockets hold the passivated block magnet while the adhesive fixes it and prevents axial migration.
In order for the start-up to secure rapid market entry and maintain agile structures, it has its motors designed and manufactured by the Swiss drive specialist SmartDrives. In search of the right adhesive, the choice fell to DELO-ML DB135 after testing and after consultation with Credimex, a Swiss expert for adhesive solutions.
This methacrylate-based adhesive for metal is suitable for small gaps of up to 100 µm and is therefore often used in electric motors. The product features impact resistance and a service temperature range from -60 °C to +180 °C.
Fazua's compact e-bike motors use adhesives for securing the magnets
During motor manufacturing, Fazua and SmartDrives rely on the classic option of anaerobic adhesive curing – at room temperature with the exclusion of oxygen. No heat curing step is required here. After just two minutes, the product reaches its initial strength and the component can be passed on to the next process step.
This time span could be reduced to about 60 seconds if an activator is applied additionally, either by spraying the component or submerging it in an immersion bath. In addition, an activator significantly improves adhesion to coated materials and increases the maximum layer thickness to 300 µm, which could compensate for higher tolerances of the components to be joined.
If rapidly increasing production volumes demand shorter cycle times in the future, Fazua can benefit from the light fixation option of the DELO-ML DB135 adhesive it already uses. With this option, the adhesive cures within less than ten seconds when exposed to high-intensity UV light, thus allowing the components to be fixed and further processed immediately. Final strength will then be reached as usual under the exclusion of oxygen. With such solutions, Fazua is optimally equipped for further growth in the dynamic e-bike market.