PERFORMANCE ANALYSIS OF AISI 4340 HARDENED STEEL IN DUAL JET MQL TURNING SYSTEM: A COMPARISON STUDY BETWEEN CVD AND PVD-COATED CARBIDE TOOLS

The hard part turning process used to finish the cylindrical surfaces has some critical machining responses like tool wear with the lower quality of the machined surfaces. Minimum quantity lubrication (MQL)-based machining environment is currently considered an advanced cooling and lubrication technique. Cutting speed, feed rate, and cutting depth are considered input parameters, and the TaguchiL27 orthogonal array (OA) has been adopted as the design of the experiment. In this context, average surface roughness (Ra), tool flank wear (VBc), cutting temperature (T degrees C), and chip morphology have been selected as measured outputs. To improve the machining performance of hardened steel, a sustainable MQL (flank+rake directions) cooling system has been employed at the cutting zone. Iron-aluminum LRT 30 was considered as the base fluid for the hard turning of AISI 4340 steel by PVD (AlTiN) and CVD (TiN/TiCN/Al2O3) coating cutting inserts. The primary effects of process parameters and their influences on the measured outputs have been discussed. The dual jet MQL-based hard turning was performed at three levels of cutting speeds (80, 170, and 260m/min), feed rate (0.5, 0.1, and 0.15mm/rev), and cutting depth (0.2, 0.3, and 0.4mm) with an air pressure of 5bar and mist flow rate 50ml/h. The findings showed that PVD-coated carbide tools outperformed CVD-coated tools. The model of the measured outputs of both tools has been developed using second-order regression analysis. Utilizing ANOVA analysis, all the predictive models were observed to be significant and acceptable with larger than 90% of R2 value.