The effect of laser beam defocusing on processing quality during laser surface alloying

The effect on final processing quality resulting from a deviation from optimum beam focus during laser surface alloying has been investigated in this research. An elliptical laser beam was used to experimentally process samples, which were then analyzed to determine processing characteristics such as melt depth. A linear relationship was found between the melt and heat affected zone depths and defocus distance, which was -13.3 µm/mm for the melt depth and -22.3 µm/mm for heat affected zone. The dynamics of an automated focus correction were investigated, and a required vertical velocity of 4000 mm/min was needed to correct a defocus distance of -4 mm. The maximum surface variation radius was found to require a horizontal resolution 3.5 times the radius. Finally, a simple moving source analytical heat flow model, which can approximate an elliptical laser beam, was examined and shown to be unsuitable for feedback control applications under the conditions of this study.