Comparative study on machinability improvement in hard turning using coated and uncoated carbide inserts: part II modeling, multi-response optimization, tool life, and economic aspects

The present study focused on mathematical modeling, multi response optimization, tool life, and economical analysis in finish hard turning of AISI D2 steel ((55 +/- 1) HRC) using CVD-coated carbide (TiN/TiCN/Al2O3) and uncoated carbide inserts under dry environmental conditions. Regression methodology and the grey relational approach were implemented for modeling and multi-response optimization, respectively. Comparative economic statistics were carried out for both inserts, and the adequacy of the correlation model was verified. The experimental and predicted values for all responses were very close to each other, implying the significance of the model and indicating that the correlation coefficients were close to unity. The optimal parametric combinations for Al2O3 coated carbide were d1-f1-v2 (depth of cut = 0.1 mm, feed = 0.04 mm/r and cutting speed = 108 m/min), and those for the uncoated tool were d1-(0.1 mm)-f1 (0.04 mm/r)-v1 (63 m/min). The observed tool life for the coated carbide insert was 15 times higher than that for the uncoated carbide insert, considering flank wear criteria of 0.3 mm. The chip volume after machining for the coated carbide insert was 26.14 times higher than that of the uncoated carbide insert and could be better utilized for higher material removal rate. Abrasion, diffusion, notching, chipping, and built-up edge have been observed to be the principal wear mechanisms for tool life estimation. Use of the coated carbide tool reduced machining costs by about 3.55 times compared to the use of the uncoated carbide insert, and provided economic benefits in hard turning.