Processing characteristics and lubrication performance of castor oil-ethanol blended coolant-based minimal quantity lubrication.

• The lubrication performance studies on the blended coolant were carried out with difficult-to-process materials. • This study gives the optimum blended coolant concentration according to different processing conditions. • The effects of different lubricating conditions on surface quality and tool wear were discussed. • The improved TOPSIS algorithm was applied for determining the preferable blended coolant concentration. Minimal quantity lubrication (MQL) has often been adopted to improve the machinability of difficult-to-process materials such as Ti-6Al-4 V. High disposal costs, toxicity, and environmental pollution generally prevent the further application of traditional coolants. Hence, this study aimed to determine the best ratio of castor oil (CO) and ethanol (E) in a new eco-friendly vegetable oil-based coolant fluid, along with the best combination of cutting parameters. The performance of the coolant fluid was evaluated by measuring the surface roughness and flank wear under three different lubricating conditions (dry machining, flood machining, and CO-E blended coolant-based MQL conditions). Under the blended coolant-based MQL conditions, the surface roughness was reduced by 36% and 15% compared with that of dry machining and flood machining, respectively, and the tool wear was reduced by 38% and 53%, respectively. The best parameter combinations are a blended coolant ratio R CO/E = 31% / 69%, cutting velocity v c = 100 m/min, feed f = 0.075 mm, and depth of cut a p = 0.2 mm. This eco-friendly blended coolant fluid can boost the heat exchange capacity and lubrication performance, thereby improving the processing characteristics. [ABSTRACT FROM AUTHOR]