Thermal history analysis of surface heating of mild steel with different laser beam geometries

Lasers are in use in the material processing industry for well over 30 years now. The way in which the temperature is distributed inside the material is of prime importance in laser material processing, as it directly affects the heating/cooling rates and thermal gradients. Optimization of different laser processes requires control over heating/cooling rate and thermal gradient. Different processes have different requirements of heating/cooling rate and thermal gradient. Knowing these parameters and relevant metallurgical information, one can predict the microstructure and hence control the material properties. To date, majority of laser processing is carried out by using either circular or rectangular beam. At present, the variation in temperature distribution to control the heating/cooling rates and thermal gradients is caused by the variation either in laser power or in scanning speed. Variations in these parameters are often limited by other processing conditions. Although different beam intensity distributions with circular or rectangular laser beams have been studied to improve the process, no other beam geometries have been investigated. The effect of laser beam geometry on laser processing of materials has received very little attention. This article presents an investigation of the effects of different beam geometries including circular, rectangular, and triangular shapes on heating of metallic materials. Finite-element modelling technique has been used to simulate the transient effects of a moving beam for laser surface heating of metals. The temperature distributions, cooling rates, and thermal gradients have been calculated. Some of the results have been compared with the experimental data. © IMechE 2006.