AISI 304 stainless steel marking by a Q-switched diode pumped Nd:YAG laser

Laser marking tests were carried out on AISI 304 steel, using a Q-switched diode pumped Nd:YAG laser. The aim was to determine the correlation occurring between working parameters (i.e. pulse frequency, beam scanning speed, and current intensity) and resulting mark visibility. The latter was evaluated as the contrast index measured from digital images of the marks. To characterize mark features, its width and roughness were estimated, and analyses employing optical and scanning electron microscopy coupled with energy dispersive X-ray technique were carried out. From the experimental results, both surface roughness and oxidation increased as a function of frequency, resulting in an improvement in contrast, up to a characteristic value, decreasing afterwards. Besides, the maximum visibility value was beneficially affected by lower scanning speeds and lower current intensities. An empirical model was built, and from it the best processing conditions for optimum mark visibility, taking into account the operating constraints of the laser system used, were drawn.