To increase corrosion protection, the thickness of zinc on the steel parts of a Japanese automotive electric window winder was increased from 6 to 24µm but this increase in zinc thickness caused a severe reduction in quality of the spot welds holding the assembly together.
Despite dressing the spot welder electrodes every 50 welds, serious structural failure of the assembly was commonplace, both during production of the window winder at the sub-contractor, and after the completed winder had been fitted in the vehicle. These failures resulted in high costs of production, scrap and liability for the sub-contractor producing the window winders, together with a loss of confidence by the vehicle manufacturer.
To overcome the problem of poor spot weld quality, alternative fastening techniques were evaluated, with self-piercing riveting proving to be the most appropriate.
Riveted assemblies were stringently tested for strength, resistance to vibration and corrosion, and ability to cope with process variations such as incorrectly set rivets. They passed all the required tests and were adopted for one model in the manufacturer's range of vehicles.
After a year of trouble free production, self-piercing riveted window winder assemblies were adopted across the manufacturer's range of vehicles, and the spot welding equipment at the sub-contractor's factory was replaced with automated self-piecing riveting production cells.
There were additional benefits to the sub-contractor from adopting self-piercing riveting as follows:
~ The appearance and working environment of the factory were improved
~ Worker fatigue was reduced
~ The skill level required to produce the assemblies was reduced, resulting in a lower assembly cost
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