An approach to modelling of laser polishing of metals

Based on heat transfer analysis and the consideration of the evaporation of surface asperities, a simplified model for laser surface polishing was established. As the dimension of asperities is usually in the scale of sub-micron, the model thus assumed uniform temperature over and in an asperity entity and the heat transfer could thus be treated as a point unit problem. The model aimed at preliminary prediction of the adequate setting of the processing parameters (typically the laser irradiation time) for laser polishing of a metal with known geometric surface consisting of micro-asperities and material properties. Prediction for polishing metallic materials of Fe, Al, Ti, and the 304 stainless steel showed the temperature rise in asperity varying significantly with the original surface topography of the substrates. Results indicate that, for the polishing of most metals with pulsed laser, laser with short pulse duration normally in the range of nano-second or less is required. Laser polishing of steel using a KF excimer laser with the pulse duration of 30 ns was subsequently performed. Characterizing the irradiated surface morphology by scanning electron microscope (SEM) and atomic force microscope (AFM) showed evident improvement in surface finish of the tested specimens.