Effect of repeated insertions into a mesoscale pinhole assembly: Case of interference fit

Abstract

The importance of micro-scale tolerance has increased due to the growing demands for micro component devices. However most existing standards and previous studies of tolerances have focused on milli-scale assemblies. In this study, a micro-scale pinhole assembly was analyzed, and the forces obtained under repeated insertions were measured. Tungsten carbide pins with different tip edges were fabricated and inserted into an aluminum hole element. From the force-measurement results, most of the plastic deformation occurred during the first insertion, as repeated insertions showed the same magnitude of force. For a given micro-scale tolerance, tools with sharpened tip edges had larger insertion forces because they had larger frictional areas. The shear stress values obtained during the insertions were calculated from the measured forces and compared with each other. The shear limit under elastic deformation was analyzed using a thick-walled cylinder model. During the repeated insertions, the calculated shear limit matched the experimental results well, and it was not affected by the interference or pin diameter. The contribution of this study is a shear stress model for repeated interference fits of a pinhole assembly with micro-scale tolerance, considering different pin-tip edges.