FASTENINGS & ADHESIVES FEATURE M


any factors including government legislation and increasing concern


over carbon emissions are resulting in a huge growth in electric vehicle use – from cars to buses. But one e-vehicle which is seeing what could be described as a boom in sales is the e-bike, which is being used across the world both for commuting and for pleasure. In fact according to DELO Adhesives, in many markets one in three bikes now sold is electric. However, e-bikes vary significantly in


terms of drive train concepts, and there are a variety of joining techniques that designers can choose for their electric motors. Fazua, a young company based near Munich, has opted for bonding and uses metal adhesives from DELO for its compact and lightweight drive system.


In order for Fazua to secure rapid market entry and maintain agile structures, it has its motors designed and manufactured by the Swiss drive specialist SmartDrives. And, for the adhesives, the company specified DELO-ML DB135


A LIGHT DRIVE SYSTEM Fazua wanted to produce a very light and compact drive system. So, thanks to their 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 4kg to be moved is almost negligible – a big difference to most e-bikes where the drive system can weigh up to 9kg, which can give them a total weight of 20kg or more. Of additional benefit,


the motor and battery form a closed unit. Not only are they designed to visually disappear


Joining the growing e-bike market


Adhesives from DELO are being specified


for the light and compact drive system of e-bikes. Here we find out why…


manufacturers are already relying on this solution, especially providers of e-road and e-gravel bikes with all-terrain versatility. However, it is not only quality that counts for the drive system, which consists of a bottom bracket bearing, motor and battery. With five-digit quantities per year, production efficiency also plays an important role.


CHOOSING THE ADHESIVE The motor concept is crucial in order to obtain a compact yet powerful motor. So, 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.


Fazua uses


motors with rare earth magnets


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


in the frame, but they can also be removed in a few simple steps. So the comparatively low total weight can even be reduced by another 3kg. The company is therefore closing 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


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. In addition, 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


/ DESIGNSOLUTIONS


expansion are distributed homogeneously. 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. And, for the adhesives, the company specified 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 100μm, offers impact resistance, and has a service temperature range from -60˚C to +180˚C. During motor manufacturing, Fazua


and SmartDrives rely on 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 300µm, 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, 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.


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DESIGN SOLUTIONS | MAY 2021 23


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