MARKING METHOD BY LASER BEAM

PURPOSE:To provide the uniform shape of the letter line with less dross deposition at a low cost by setting the diameter of the laser beam to be the same as the width of the letter line on the surface to be machined, and executing the scanning so as to draw the letters and figure pattern through the overlapping irradiation of the laser beam pulse. CONSTITUTION:The laser beam 4 is scanned by the Miller transmission method to realize the marking on the shaft end surface 2 of a roll 1. The laser beam 4 to be emitted from a pulse excitation laser 3 is transmitted to a machining head 8 by deflecting mirrors 6, 7 mounted on an XZ moving device 5. A converging lens 9 to converge the laser beam 4 to the letter line width, an assist gas nozzle 10 to irradiate the assist gas, and a distance measuring sensor 11 to measure the distance between the shaft end surface 2 of the roll 1 and the machining head 8 are mounted on the machining head. The letter line shape whose line bottom part is uniform can be obtained due to the overlapped irradiation of the laser beam 4 which is expanded in the defocus manner with the machining diameter being the same as the width of the letter line.