Snap fit and vibration-free for BMW

Justin Cunningham reports on how demountable, vibration-free fasteners ensure that the mirrors on BMW motorcycles give drivers the steadiest view ever.

Specialist fastener manufacturer Bollhoff has recently completed a project with BMW to reduce the vibration experienced on its wing mirrors. With many of the BMW motorbikes able to travel up to 140mph, and accelerate from 0 to 60 in less than 3 seconds, it is vital that the driver has a steady and clear prospective when glancing in the mirror. A shaky rear view mirror is definitely unwelcome and a potential danger.

BMW wanted to increase the on-road safety and optimise the manufacturing procedures of its motorcycles and found a solution for both of these problems with Bollhoff. Its Snaploc fastening system minimises the vibration of the mirror assembly while allowing a quick and easy 'snap-fit' installation that needs no special tools.

The customised fastening solution comprises three Snaploc ball pins which are fitted to the metal frame of the motorcycle. These connect with three mating couplings which are press fitted into the engineering plastic mirror housing and held in place by an undercut.

The ball pins, or studs, are then injection over-moulded in glass filled nylon engineering plastics around steel fasteners whose M6 threads are finished in a black Zn/Ni coating to enhance corrosion resistance. The receiving couplings are precision injection moulded in black EPDM – X: a grade of material that provides resistance to UV exposure as well as positive snap fit and essential vibration absorption properties critical for the application.

Three basic designs of Snaploc couplings have been developed for plate fastenings, for mounting domes and for fixing with adhesive. Different ball diameters accommodate a range of stress conditions while stud sizes and other physical dimensions can be varied to suit application requirements. Ball studs, like this project, are injection over-moulded in engineering plastics around steel fasteners.

When initially designing the fastening system, the major challenge was developing a connection that consisted of a maximum of two elements to almost completely isolate against vibration and noise, while reducing the assembly time compared to traditional fasteners.

Justin Cunningham

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