Microsurface texturing for a minimum coefficient of friction

In recent years, micro surface texturing for friction and adhesion control has gained momentum in a wide range of applications, such as MEMS devices, punches, and tools used metal forming processes, and injection molding machines. In this study, air hardened tool steel, A2, with micro hexagonal dimples of different sizes and densities but constant depth, have been modeled and tested under dry sliding contact. Three-dimensional finite element models depict sliding dry contact between a rigid indenter and elastic-plastic textured surfaces are simulated. Coefficients of friction have been determined and compared for different texturing sizes and densities. In addition, these hexagonal patterns were fabricated on tool steel (A2) samples using photolithography. Coefficients of friction were experimentally measured using micro scratch tribometer. Both simulation and experimental results show there is a strong correlation between micro-texturing parameters and coefficient of friction. The results demonstrate that under dry sliding contact, coefficient of friction can be controlled through optimization of micro texturing parameters, specifically the spatial texture density (D/L) which is equal to the ratio of the size of the dimple (D) to the distance between the centers of two consecutive dimples (L). A minimum coefficient of friction exits at values of spatial texture densities (D/L) that range between 0.25 and 0.5 for this specific material.