Investigation of the temperature field developed by a spinning beam in laser processing

Various laser treatments have been developed for metallic surface modification. In these processes, rapid heating of a specific area on the surface by a laser is the critical feature employed to produce a different phase or layer on the surface. The laser beam mode, such as a Gaussian, rectangular, or annular beam in a stationary or spinning state, has been found to have a very important effect in the laser processing. Many significant models have been established to estimate the temperature field developed by a laser and therefore to predict the optimum conditions in the process, but these models are mainly applicable to a stationary beam. Previous work has shown the advantages in some applications of using a spinning beam. Therefore, modeling work for a spinning beam is necessary. The present article reworked our previous model on a spinning beam mode for a continuous CO2 laser, to calculate a two-dimensional temperature profile by using a line source and superposition of a number of Gaussian sources. An excellent agreement with experimental work for a nitrided Ti-6Al-4V alloy (IMI 318) for a situation of a small (50-mu m) melt pool was achieved. A relationship was derived between the normalized laser power and specimen speed to produce a uniformly thick surface layer.