Minimum quantity blended bio-lubricants for sustainable machining of superalloy: An MCDM model-based study

The imperative shift toward sustainability has driven contemporary scholars to explore the lubricating and cooling properties of vegetable oils in traditional metal-cutting processes. Palm oil, as an environmentally conscious derivative, emerges as a preferable option for the base fluid in Minimum Quantity Lubrication (MQL). However, its high viscosity impedes fluidity, limiting industrial applicability. In contrast, sunflower oil offers superior lubricating qualities and flowability. Consequently, efforts have been directed toward enhancing the lubricating efficacy of palm oil. Six blends of palm and sunflower oils (ranging from 1:0.5 to 1:3) were utilized as MQL fluids, followed by evaluations of machining outcomes, including average surface roughness, specific cutting energy, and tool wear. In addition, an integrated Shannon’s Entropy-based Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) framework was employed to determine the optimal volume ratio of the palm–sunflower oil blend. The TOPSIS analysis confirmed that the 1:2 ratio yielded the most favorable outcomes. Subsequent comparative analysis demonstrated that this optimal blend resulted in reductions of 16.79% and 14.92% in surface roughness, 11.82% and 10.98% in specific cutting energy, and 10.19% and 8.45% in tool wear compared to pure palm and sunflower oil media, respectively. Finally, sustainability assessments of various cooling media revealed that a minimal quantity of the blended bio-lubricant-based medium outperforms both compressed air and flooded media.