Experimental Investigation of Micro-Dimples for Improving Lubrication and Friction in Piston-Liner Contacts of Internal Combustion Engines

Surface texture shapes and texturing methods were created to improve the tribological performance of mechanical systems. High-speed conventional micromachining in general and semi-hemispherical micro-dimples prepared through ball nose end milling in particular have recently gained recognition as an effective method for improving tribological performance. The tribological behavior of semi-hemispherical micro-dimples created through ball nose end milling was investigated in this research at constant and accelerated sliding speeds. Experiments were conducted using an oscillating pin-on-disc arrangement with varying load (2 and 4N), lubrication (0.2, 2 and 20 μl), and temperature (50, 100 and 150 °C) to replicate the characteristics of the piston-liner contact in an internal combustion engine. The coefficient of friction decreases with an increase in lubrication and a drop in load, sliding speed, and temperature across all evaluated surfaces. D40 surfaces exhibited better efficiency throughout most tribological test settings, with a mean texture efficiency of 26.86% for the evaluated conditions. Analysis of texture efficacy for the variation of linear speed similar to the piston-ring-liner interface at higher load and temperature suggests a novel approach to study the variation of friction for the variation of lubrication regimes in reciprocating motion. Overall, it was found that the textured surfaces with semi-hemispherical micro-dimples of 240 μm in diameter, 40 μm in depth, and 10% area density, created by conventional micromachining, are suitable for piston applications.