Feasibility of supercritical CO2-based minimum quantity lubrication to improve the surface integrity of 50% Sip/Al composites

Abstract

Although a lot of researches have been done to improve surface integrity of metal matrix composites under different cooling/lubrication conditions, the comprehensive analysis of the milling performance of 50% Sip/Al composites employing supercritical CO2-based minimum quantity lubrication with oil-on-water droplets cutting fluid (scCO2-OoWMQL) technologies has not been reported. The paper aims to study the surface integrity of 50% Sip/Al composites under dry cutting and scCO2-OoWMQL environments. Milling experiments were carried out under different speeds, feed rates, depths of cut and cutting environments. The experimental results show that lower cutting temperature, surface roughness and depth of sub-surface damage were obtained under scCO2-OoWMQL environments due to excellent cooling and lubricating properties when compared with dry conditions. Among them, the depth of subsurface damage is reduced from 15.8 μm to 10 μm employing scCO2-OoWMQL technology. Broken particles, cavities and large pits were found on the machined surface under dry and scCO2-OoWMQL conditions. Comparing with the dry cutting environment, the scCO2-OoWMQL environment can significantly reduce defects of pits on the machined surface. When fz = 0.04 mm/z, n = 6000 mm/min and ap = 1 mm, the thickness of the bonding layer on the tool surface decreased from 22.7 μm to 16.7 μm when using scCO2-OoWMQL technology, an improvement of 36%.