Tool Life, Wear Rates, and Surface Quality in Hard Turning

An on-going comparative study of wear rates and tool lives under varying cutting parameters is presented in this paper, along with results indicating the abilities and limitations of the hard turning process to produce finished surfaces with acceptable roughness and integrity. To date, the study has consisted of thirteen combinations of machining conditions. The tests were performed with four different cutting tool materials supplied by two manufacturers. Tool life results agree with previous research in this area, indicating that low content CBN tools have improved lives resulting from the increased bonding strength of the ceramic binders compared to the cobalt binder typically used for higher CBN content tools. More interesting is a resulting trend in flank wear patterns that could help to predict tool life under certain cutting conditions. Further work is being done to understand the wear process in an attempt to model this relationship for a larger range of conditions. Surface quality limitations are also presented, in terms of limited achievable surface roughness due to increased plowing action at low feeds. Microstructural changes on machined surfaces are then discussed, with an explanation given for the ability to produce surfaces free of white layer, even when cutting with worn cutting tools.