Tool Life Variation and Its Influence on the Development of Tool Life Models

An investigation into the nature of the inherent variation of tool life over a range of cutting conditions for a finish turning process is presented. In this study, tool life is based upon a fixed amount of wear on the clearance face of the tool. The nature of tool life variation as a function of the prespecified wear level is also examined. It was found that the inherent variation of tool life increased as the wear level increased, to the point where an optimum wear level should be definable through an economic optimization of the process. Statistical tests showed that the variance of logarithmically transformed tool life data is not homogeneous over the range of cutting conditions examined. To account for this behavior, the method of weighted least squares is employed in developing tool-life-predicting equations. A comparison between the weighted least-squares method and the ordinary (unweighted) least-squares method is presented. More realistic predicting capabilities resulted by using the weighted method given the inherent behavior of the tool life variation.