Effect of tool edge geometry and cutting conditions on experimental and simulated chip morphology in orthogonal hard turning of 100Cr6 steel

Understanding chip formation mechanisms in hard turning is an important area of research. In this study, experiments with varying cutting conditions and tool edge geometry were performed concurrently with finite element simulations. The aim was to investigate how the two mechanisms reported in literature namely—surface shear-cracking (SCH) and catastrophic thermoplastic instability (CTI) contribute to overall chip geometry and machining forces. By varying tool edge geometry and cutting conditions predominance of one over another is discussed. The calculation prescribed by Recht [Recht, R., 1964. Catastrophic thermoplastic shear. J. Appl. Mech. 31, 189–193] for representative cutting conditions resulted in a small critical cutting speed of 0.034 m/min indicating CTI was operative in the range of cutting conditions tested. FEM simulations were conducted on a subset of experimental conditions. Chip geometry and forces were compared between experiments and simulations. The experimental results indicated that SCH predominated in a majority of conditions. However, formation of saw-tooth chips in the FEM simulations established the occurrence of CTI also. Specifically, the edge radius did not alter chip geometry parameters. However, machining forces decreased with cutting speed and chip formation frequency increased linearly with cutting speed. A more negative rake angle also increased the chip pitch. The findings also indicate that only an intrinsic length scale governs saw-tooth chip formation in hard turning.