Diffusion Theory Applied to Tool Life Stochastic Modeling Under a Progressive Wear Process

Abstract

In this paper, a novel approach to the derivation of the toollife distribution, when the tool useful life ends after a progressive wear process, is presented. It is based on the diffusion theory and exploits the Fokker–Planck equation. The Fokker–Planck coefficients are derived on the basis of the injury theory assumptions. That is, toolwear occurs by detachment of small particles from the tool working surfaces, which are assumed to be identical and timeindependent. In addition, they are supposed to be small enough to consider the detachment process as continuous. The tool useful life ends when a specified total volume of material is thus removed. Toollife distributions are derived in two situations: (i) both Fokker–Planck coefficients are timedependent only and (ii) the diffusion coefficient is neglected and the drift is weardependent. Theoretical results are finally compared to experimental data concerning flank wear land in continuous turning of a C40 carbon steel bar adopting a P10 type sintered carbide insert. The adherence to the experimental data of the toollife distributions derived exploiting the Fokker–Planck equation is satisfactory. Moreover, the toollife distribution obtained, when the diffusion coefficient is neglected and the drift is weardependent, is able to wellrepresent the wear behavior at intermediate and later times.