Estimation of Work Material Flow Stress and Tool-chip Interfacial Friction by Inverse Computation of Modified Oxley’s Model of Machining

Finite Element Analysis (FEA) based techniques have become increasingly available to simulate metal cutting process and offer several advantages including prediction of tool forces, distribution of stresses and temperatures, estimation of tool wear, optimization of cutting conditions, tool edge geometry and coatings, and determination of residual stresses on machined surfaces. However, accuracy and reliability of the predictions heavily depend on the work material flow stress at cutting regimes i.e. high deformation rates and temperatures, and variable friction characteristics at tool-chip interface, which are not completely understood and need to be determined. This paper utilizes an extended metal cutting analysis originally developed by Oxley and coworkers [6] and presents an improved methodology to expand applicability of Johnson-Cook material model to the cutting regimes and simultaneously determine friction characteristics at tool-chip interface from the results of orthogonal cutting tests. A number of cutting temperature models are also assessed in characterizing the accuracy of the average temperatures at primary and secondary deformation zones. Predictions using cutting models are compared with the results of testing data obtained for AISI 1045 through assessment of machining models (AMM) activity. The methodology requires experimental data for cutting and thrust forces, chip thickness and tool-chip contact length. The methodology is practical and estimates both the parameters of work material Johnson-Cook constitutive flow stress model and the interfacial friction characteristics along tool rake face. The friction model is based on estimation of normal stress distribution over the rake face. Predicted friction characteristics include parameters of the stress distribution on the rake face σnmax and power exponent a, the average shear flow stress at tool-chip interface, kchip, plastic contact length, lp, at sticking region of the tool-chip interface, an average coefficient of friction, μe, in sliding region of the tool-chip interface. The extended Johnson-Cook work material flow stress parameters and tool-chip interfacial friction characteristics can directly be entered into most FEA software.