Laser heating including the phase change process and thermal stress generation in relation to drilling

Abstract

Laser heating including phase change processes finds wide application in industry such as in laser machining. The large temperature gradient in the solid region of the substrate material generates considerable stress levels in the region affected by a laser beam. Modelling of the laser heating process enhances understanding of physical processes involved and reduces experimental cost. Moreover, the commercially available lasers, used as a machine tool, have pulse lengths of several nanoseconds. Consequently, when modelling a laser pulse heating process, a heating period needs to be limited to the nanosecond range. In the present study, laser heating of steel is considered. The heating process is modelled employing the Fourier heating model and allowing the phase change processes. The governing equation of energy transport is solved numerically using a control volume approach. The thermal stresses generated in the solid region of the substrate material heated by a laser beam is modelled. The grid independence tests are carried out in order to ensure grid independent results. An experiment is carried out to validate the cavity profile predicted from the present simulations. It is found that the predicted cavity profile agrees well with the experimental findings. The temperature profile decays sharply in the liquid region close to the cavity wall. The equivalent stress reaches its maxima at two locations in the radial direction. As the heating progresses, the magnitude of the second peak of equivalent stress reduces.