Surface quality evaluation of AISI 4340 steel having varying hardness during machining with TiN-coated CBN inserts

Trends of turning hardened steel are increasing in manufacturing industries because it offers many significant benefits over grinding. One of the main advantages is attaining better surface quality along with high dimensional accuracy. However, during hard turning the friction between tool and workpiece is very high, which results in early tool wear that leads to decrease in surface quality and dimensional accuracy of the finished products. The coating on cutting tool plays a vital role in enhancing wear resistance. Therefore, the aim of this research work is to investigate the surface quality during machining hardened AISI 4340 steel with TiN-coated CBN tools. The process variables selected during experimentation are tool nose radius, workpiece hardness, cutting speed and feed rate. The machining is carried out in dry conditions. The second-order mathematical model of surface roughness has been developed using regression analysis. The significance of the model and influence of the process parameters have been carried out using analysis of variance technique. Results indicate that performance of TiN-coated CBN tools is superior when compared to uncoated CBN tools during machining of hardened AISI 4340 steel.