Experimental evaluation of the lubrication performance of mixtures of castor oil with other vegetable oils in MQL grinding of nickel-based alloy

Vegetable oil is employed as base fluid in precision grinding because of its biodegradability and non pollutant properties. Castor oil exhibits superior lubrication performance to other vegetable oils, but its high viscosity and poor flow limit its application in industrial production. In this study, castor oil was used as base oil and individually mixed with six other kinds of vegetable oils (i.e., soybean, maize, peanut, sunflower, palm, and rapeseed oils) at a ratio of 1:1 to change the rheological properties of the former. Each mixture was obtained as base oil for minimum quantity lubrication grinding. The high-temperature nickel-based alloy GH4169 was used as workpiece to evaluate the lubrication performance at the grinding wheel/workpiece interface. The mechanism of lubrication was also studied based on the molecular structure of vegetable oil. Specific grinding force, specific grinding energy, surface roughness, surface microtopography, and grinding debris were compared among the experimental and comparison groups (castor oil). The workpiece surface profile was analyzed using the correlation function and cross correlation coefficient. Results indicated that the comprehensive lubricating performance of mixed oil was superior to that of castor oil, and soybean/castor oil exhibited the optimal performance. The specific tangential grinding force and specific normal grinding force were 0.664 and 1.886 N/mm, respectively, with 27.03% and 23.15% reduction, respectively, with respect to those of castor oil. The surface profile curves of the workpiece obtained from four kinds of working conditions (castor oil, castor/soybean oil, castor/maize oil, and castor/palm oil) were also analyzed. The amplitude of the surface profile curve in castor/soybean oil is larger and the correlation coefficient is higher (0.51) than those under other mixed oils; hence, the workpiece showed the optimal surface quality. (C) 2016 Elsevier Ltd. All rights reserved.