Analytical insights into SQL-assisted machining of Nitronic-50 using MT-CVD and MT-PVD inserts

Machining of Nitronic-50 involves high cutting forces, elevated temperatures, and rapid tool degradation. Although previous studies on difficult-to-machine materials have examined multilayer coatings and MQL separately, their combined influence, particularly considering cutting-fluid atomization behaviour remains insufficiently understood, and has not yet been explored for Nitronic-50. Current study integrates machining experiments and CFD-based droplet analysis to evaluate multi-layered MT-CVD and MT-PVD inserts under small quantity lubrication (SQL) using soapwater, propylene glycol–water, rice bran oil, and sunflower oil, analyzing major machinability indicators. Machining with MT-CVD tools showed greater requirement of cutting forces. However, SQL, particularly with soapwater, reversed this trend, reducing tangential cutting forces by up to 52.7%. MT-PVD inserts recorded higher tool-tip temperatures under dry cutting, while soapwater SQL reduced them by 68.44%. Lowest apparent coefficient of friction was observed under propylene glycol-water-SQL with MT-CVD. Tool wear was notably mitigated under SQL using soapwater, with MT-CVD at intermediate cutting velocity, yielding 58.09% lower flank wear. Chip reduction coefficient and saw-tooth spacing showed notable improvements, under same condition. Chip segmentation frequency with MT-PVD under propylene glycol-water-SQL at higher cutting velocity, showed 607.16% rise compared to lowest value obtained under dry cutting at lower cutting velocity. Surface roughness dropped by 66.27% under soapwater-SQL with MT-CVD at lower speed. Residual stresses were mostly compressive with MT-CVD under SQL, with soapwater application producing higher magnitude observed. Among tested conditions, MT-CVD inserts with soapwater or propylene glycol–water SQL yielded favourable machining performance, offering a viable pathway for sustainable machining of the alloy. • SQL-assisted turning of Nitronic-50 was done with MT-CVD and MT-PVD inserts. • Soapwater, PG–water, rice bran oil, and sunflower oil are used as cutting fluids. • Droplet dynamics of cutting fluids analyzed through ANSYS. • MT-CVD with soapwater or PG–water SQL achieved superior machining outcomes. • Study underscores potential of eco-friendly fluids in sustainable machining.