An experimental study of the effects of surface roughness and coating of Cr2O3 layer on the laser-forming process

Today, laser is widely used in various applications including cutting, welding, surface operations (heat-treatment, coating, and cleaning), rapid prototyping, and forming. In these processes, since energy is not transmitted merely through radiation, the ability of a material to absorb the laser beam energy and control the level of this energy is of great importance. The present paper was aimed to investigate the effects of two factors, i.e. surface roughness and Cr2O3 oxide layer created on the AISI 304-stainless steel sheet, on the absorptivity and formability of the samples in the laser-forming (LF) process with ytterbium fiber laser beam. Various levels of surface roughness were created by hand sandpapers and EDM (electric discharge machining). Furthermore, the Cr2O3 layer with different thicknesses was deposited on the samples using the sol-gel dip-coating process. Through the absorption spectroscopy and the bending angle created during the LF process, the mathematical models of absorption and bending angle were obtained. Increasing the surface roughness and thickness of the Cr2O3 layer led to a significant increase in the samples' absorptivity and bending angle in the LF process. By roughening the samples' surface from Ra = 0.04 μm to Ra = 1.9 μm without coating and via depositing up to 6 μm without roughening, the absorptivity at the laser wavelength of 1064 nm and the bending angle were increased, respectively, by 2.3 and 1.8 times and 2.1 and 1.5 times in the LF process. Eventually, multi-objective optimization was conducted to determine the optimal process parameters that could enhance the laser light absorption and maximize the bending angle in the LF process. The validation test confirmed that the predicted value was in good agreement with the actual value.