Abstract
The aim of the present work is to extend the applicability of Oxley’s analysis of machining to a broader class of materials beyond the hot rolled low-carbon steel used by Oxley and coworkers. The Johnson-Cook material model has been chosen to represent the mechanical properties of the material being machined as a function of strain, strain rate and temperature. Necessary changes have been made to Oxley’s analysis to make it self-consistent for this material model. A new approach has been introduced to calculate the pressure variation along the beta slip lines in the primary shear zone including the effects of both the strain gradient and the thermal gradient along the alpha lines. The shear force along the primary shear zone is calculated in a consistent manner using the energy dissipated in this zone. The thickness of the primary and secondary shear zones, the heat partition at the primary shear zone, the temperature distribution along the chip-tool interface and the shear plane angle are all calculated using Oxley’s original approach. Two constants are used to fine tune the model — the strain in the chip material at the chip tool interface (εint), and the ratio of the average temperature to the maximum temperature at the chip-tool interface (ψ).
The performance of the model has been studied by comparing its predictions with experimental data available in the literature for aluminum 2024-T4. It is found that the model accurately reproduces the dependence of cutting force as a function of depth of cut and cutting speed. The shear plane angle predicted is smaller than that observed in practice. It is also observed that the constant ψ needs to be very small, implying very little increase in the temperature along the chip-tool interface. The model is highly nonlinear in the constant C that relates the length of the primary shear zone to its thickness.