Evolution of cutting forces and tool failure mechanisms in intermittent turning of hardened steel with ceramic tool

Compared with traditional grinding, hard turning with ceramic tools has lots of advantages such as lower cost, higher productivity, better machining accuracy, and elimination of cutting fluids. However, the catastrophic fracture of ceramic tool frequently occurs in turning of hardened steel. Hence, there is a need to recognize the evolution of machinability aspects (cutting forces and tool wear) in the whole turning process. An orthogonal experiment was designed to investigate the evolution of cutting forces and tool failure mechanisms in intermittent turning of hardened 20CrMnTi steel with Al2O3-TiC ceramic tool. The effects of cutting parameters on cutting forces were analyzed by Taguchi method and analysis of variance (ANOVA) during different tool wear stages. The results revealed that the influence of cutting parameters on cutting forces gradually declined with the increased tool wear, and the contribution of depth of cut on cutting forces gradually increased. The optimal cutting parameters of cutting forces were calculated for different wear stages. In addition, the fracture modes and mechanisms of tool under different cutting conditions were investigated. The fatigue striations and fatigue beaches were observed at the fracture surface. The propagation paths and mechanisms of fatigue cracks were analyzed under different cutting speeds. The results indicated that the fracture area of tool was mainly affected by mechanical stress, while the depth of crack propagation was determined by thermal stress.