Effect of intergranular cohesion on the intermittency of automotive headlamp switch contacts

The effect of intergranular cohesion of silver-plating on the intermittent operation of a lubricated sliding automotive headlamp switch was investigated. Fretting types of testing were used to follow the evolution of the intermittent behavior of the switch. It was found that processing variations of the silver electroplate exerted pronounced effect on the quality and surface topography of silver-plated contacts. The intermittency was found to be a switch break-in phenomenon caused by the changes in surface topology resulting from a reduced intergranular cohesion of silver-plating. Subsequent burnishing eliminated the intermittency and it was not present later in the switch life. Plausible explanations to account for the observed intermittent effect were discussed. Fretting type testing proved to be a very useful technique in obtaining information on the plating quality that simple hardness measurements could not provide.