This paper presents the results of comparative evaluation of soybean oil based MQL oil flow rates at 10, 30, 50, 70, and 90 ml/h with emulsion flood coolant (EC) at 1200 l/h as a benchmark in face milling of Inconel 718 using coated carbide inserts. Resultant cutting force, tool wear/ mechanism, and surface roughness are the machining performance parameters analyzed. The results show that MQL oil flow rate at 70 ml/h gave the least tool wear comparable to that of EC, while 10 ml/h gave the highest tool wear. Also, 70 ml/h gave the lowest resultant cutting force among all MQL flow rates. Increasing soybean oil-based MQL flow rate improves surface roughness and reduces tool wear by providing enough thin lubrication film but also leads to an increase in chip affinity and formation of large built-up-edges (BUEs) as the MQL flow rate reaches 90 ml/h. At lower soybean oil-based MQL flow rate, tool wear mechanism is predominantly abrasion due to large surface friction, while at higher soybean oil-based MQL flow rate, tool wear mechanism is adhesion leading to excessive BUEs. Soybean oil-based MQL flow rate at 70 ml/h is recommended when face milling Inconel 718 and is demonstrated to be a potential replacement of EC for machining difficult-to-cut metal.

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