Machinability of Inconel 718 in MQL turning using hybrid microwaved silicon nitride inserts

Machining Inconel 718 requires high strength inserts with high hot hardness and is challenging due to its high strength and thermal stability. Nonetheless, high wear rates, frequent tool change, extra time and increased tool cost are anticipated despite using large amounts of ecologically unfriendly synthetic cutting fluids. Several options on using vegetable oils and Minimum Quantity Lubrication (MQL) were explored but not with microwave treated inserts. This study intends to investigate using eco-friendly options such as dry and MQL turning on Inconel 718 with untreated and hybrid microwaved (HMW) treated Si3N4 inserts at 200C for 15 minutes. The cutting speed (145 m/min), feed rate (0.08mm/rev) and depth-of-cut (0.1 mm) remained constant. The tool wear and surface roughness were measured and the efficacy of the HMW treatment was analyzed. In dry turning, Si3N4 (HMW) performs better with reduced flank wear by 13.85% than the Si3N4 (untreated) insert. Meanwhile, in MQL turning, the Si3N4 (HMW) had decreased flank wear by 30.53% when compared to the Si3N4 (untreated) insert. The surface roughness from MQL turning using the Si3N4 (HMW) was much lower (0.53m) than the Si3N4 (untreated) (0.85m). The Si3N4 (HMW) insert was found to be appropriate for MQL turning, but unsuitable for dry turning of Inconel 718 due to excessive tool wear.