A novel approach to accelerate attainment of thermal steady state in coupled thermomechanical analysis of machining

Abstract

A novel approach for obtaining the steady state temperature distribution of cutting tools involves reducing the specific heat capacity of the cutting tool by a scale factor and carrying out a short duration single step thermomechanical analysis. Reduction of the specific heat causes the thermal time constant of the tool to be reduced by the same scale factor, making it closer to the mechanical time constant required for stabilization of the chip geometry, and enables rapid attainment of mechanical and thermal steady state conditions. As expected, FEA results show that the steady state temperature distribution achieved by the reduced specific heat approach is exact. Results obtained from a single step simulation of the first 1200μs of cutting, using this approach, are found to be more accurate than those obtained using the time consuming multistep analysis approach used to date. Rapid attainment of an accurate steady state temperature distribution permits tool wear rate to be calculated accurately using tool wear models. This enables tracking of changes in tool geometry due to wear over time, and resulting changes in the machining process and quality of parts produced. It is also shown that this approach is essential for accurate simulation of processes such as saw-tooth chip formation, where the ‘steady state’ involves local periodic thermomechanical changes, and leads to accurate thermomechanical results so long as the specific heat of the local region experiencing significant thermal oscillations is not scaled. An estimate for the size of this boundary layer, related to the wavelength of the thermal waves, is also given. The reduced specific heat approach can be used in many other applications involving a range of phenomena coupled with temperature, where the thermal changes are the most sluggish and take the most time to reach steady state.