New nanolubricants formulation as cutting fluids for machinability performance of the Inconel 718 alloy

Bio-based nanolubricants are a sustainable alternative to improve machining output since the tribological enhancement yield at the tool-chip interface leads to less friction; thus, results in superior surface quality and longer tool life. Furthermore, supplying this fluid with the minimum quantity lubricant (MQL) in machining minimises the consumption of lubrication oil; consequently, less pollution will be caused. However, the existing vegetable-based nanolubricants lacked in term of oxidation degradation and have low heat or temperature properties. Therefore, this demands for further exploration on the new formulation of bio-based nanolubricants that can solve the aforementioned limitation. This work features extensive experimental investigations on machining of Inconel 718 using novel formulations of coconut bio-based oil with enhanced aluminium oxide (Al₂O₃) nanoparticles and coco-amido-propyl-betaine (CAPB). Three-stage of experiment was planned and carried out. The first stage experiment was mainly focused on the production of bio-based nanolubricants. Following that, the performance of bio-based nanolubricants with MQL in terms of machining responses was compared through different coolant approaches (SolCut, coconut oil, bio-based, bio-based nanolubricants with three different nanoparticles concentration (0.2%, 0.5%, and 0.8%). Lastly, an optimum mixture Design of Experiment (DOE) methodology was used to determine the optimum bio-based nanolubricants formulation for enhanced machinability performance of Inconel 718 under a cutting speed of 60 and 80 m/min. The results from the first stage experiment showed that the bio-based nanolubricants possess a good lubrication property, higher thermal conductivity, high corrosion resistance, biodegradable, and moderately toxic. The second stage experiment revealed that bio-based nanolubricants 0.8 wt% of Al₂O₃ managed to minimise the rapid growth of tool wear and prolong the tool life by 40.17%. Conversely, bio-based with 0.5 wt% of Al2O3 yielded lower values of cutting force (64.32 N), spindle power (2070 kW), specific cutting energy (6.55 W/mm3), and surface roughness (0.29 μm). The final experiment stage exposes that a combination of 128.9 g of coconut oil (CO), 8.8 g of sodiumdodecylbenzenesulfonate, and 7.3 g of CAPB was an ideal formulation for attaining excellent tribological and machining efficiency of tool wear (TW), surface roughness (Ra), cutting power (CP) and spindle power (SP) in the turning of Inconel 718 under a cutting speed of 60 and 80 m/min. The outstanding performance of bio-based nanolubricants contributed to superior machinability efficiency and eco-friendly machining environments.