Determination of convective heat transfer from rotating workpieces in dry and laser-assisted turning processes

Abstract

The heat transfer from rotating workpieces in dry and laser-assisted machining turning operations has significant effect on the part temperature field and consequently the cutting forces, microstructure evolution and the thermoelastic behaviour of the workpiece. Process modelling and simulation require knowing the convective coefficient of heat transfer ‘h’. The determination of ‘h’ is, however, difficult because the need for measuring the position-and time-dependent temperature field in a rotating part. In this study, a method for determining h is presented, where the measurement of the temperature gradient at the surface is replaced by contactless measurement of the surface temperature. This avoids the insertion of thermocouples into the rotating workpiece and the need for a slip ring. In this approach, ‘h’ is also related to a physically meaningful parameter, which is characterised by its universality, as it can be calculated or measured for parts of various geometric forms, and its insensitivity to the initial conditions. Using the FE method, the design of the experiment, in terms of the part aspect ratio (length-to-diameter) and the thermal end effect, was established. The effect of the temperature dependence of the material thermal properties and surface radiation on the accuracy of determining ‘h’ has been assessed. The accuracy of the method has been validated using reliable experimental data.