Parametric design optimization of hard turning of AISI 4340 steel (69 HRC)

Abstract

Continuous research endeavors on hard turning (HT), both on machine tools and cutting tools, have made the previously reported daunting limits easily attainable in the modern scenario. This presents an opportunity for a sys- tematic investigationonfinding the current attainablelimitsof hard turning using a CNC turret lathe. Accordingly, this study aims to contribute to the existing literature by providing the latest experimental results of hard turning of AISI 4340 steel (69 HRC) using a CBN cutting tool. An orthogonal array was implemented using a set of judiciously chosen cutting param- eters. Subsequently, the longitudinal turning trials were car- ried out in accordance with a well-designed full factorial- based Taguchi matrix. The speculation indeed proved correct as a mirror finished optical quality machined surface (an av- erage surface roughness value of 45 nm) was achieved by the conventional cutting method using a CBN cutting tool. Fur- thermore, signal to noise (S/N) ratio analysis, analysis of var- iance (ANOVA), and multiple regression analysis were car- ried out on the experimental datasets to assert the dominance of each machining variable in dictating the machined surface roughness and to optimize the machining parameters. One of the key findings was that when feed rate during hard turning approaches very low (about 0.02 mm/rev), it could alone be most significant (99.16 %) parameter in influencing the ma- chined surface roughness (Ra). This has, however, also been shown that low feed rate results in high tool wear; so, the selection of machining parameters for carrying out hard turn- ing must be governed by a trade-off between the cost and quality considerations.