Objective Copper-steel laminated plates exhibit the advantages of both copper and steel. Such plates are extensively used in the aerospace, instrumental, and military fields. However, some problems, such as high reflectivity, serious oxidation of the oxygen-assisted cutting surface, and large seam widths after cutting, can be observed when cutting 1-mm-thick copper-steel laminated plates with a fiber laser. Although some solution methods have been proposed in the existing researches, the protection of the original properties of the material surface, the processing precision, and the product processing technologies are still limited. The effects of lasers and materials can be improved using the pretreatment method proposed in this study, in which the element compositions, morphologies, and physicochemical properties of processing areas are adjusted to ensure processing quality, expand the processing range of a 1064 nm fiber laser, and design the experiment for processing slit gratings. The feasibility of this method is verified.
Methods Based on the analysis of the material properties and the laser processing characteristics, a shallow melting surface could be obtained by controlling the energy input. The plate surface was scanned using a low-power fiber laser by considering oxygen as the auxiliary gas to obtain morphology changes and material properties conducive to laser processing. The processing quality of this method is compared with those of other methods. A three-dimensional (3D) microscope was used to observe and measure the surface morphology, heat-affected zone (HAZ), and slit width. In addition, the Plus software was used to estimate the oxide distribution in the shallow melting area formed by pretreatment. Thus, the proportion of oxide area in the shallow melting area could be calculated. The surface roughness was measured using a Keynes laser confocal microscope. Further, the surface morphological changes in the shallow melting area were analyzed to investigate the influence of pretreatment on laser absorption and subsequent processing. The advantages of this method with respect to quality and technology were deduced via experiments in which different pretreatment methods were used. After reasonable processing parameters were obtained, the slit grating was processed by planning the processing path, and the deformation and accuracy were controlled within the required range.
Results and Discussions In this study, the plate surface is guided to obtain shallow melting and black oxide via pretreatment. The width of shallow melting on the material surface is smaller than the spot diameter, and the oxide and molten substance overlap with each other. Therefore, the main energy absorption area with respect to the spot diameter is segmented and reduced, and black oxide can effectively improve the laser absorption rate. Thus, the problem of low laser absorptivity on the surface of the copper-steel laminated plates can be solved and the appropriate energy utilization can be achieved. Hence, most of them are used to remove the materials within the irradiation range and reduce heat accumulation at the edge of the slit. The slit width is smaller than the spot diameter, and the HAZ of the slit is reduced. Thus, the cut accuracy and quality of the laser-cut copper-steel laminated plates are improved when the proposed pretreatment method is applied. Through pretreatment, a pretreated surface containing 36.54%--77.84% of oxidation area can be obtained. The larger the proportion of the oxidation area, the lesser is the amount of oxide copper spots in the shallow melting zone, the greater is the density of the molten pool, and the more uniform is the edge line. Compared with that of the oxygen-assisted cutting method, the seam width of the pretreatment method decreases by approximately 45% and that of the carbon black coating method decreases by 36%.
Conclusions The material surface melts in the form of a shallow layer when the energy density is controlled and the oxidation reaction is guided. The width of shallow melting on the material surface is smaller than the spot diameter. Compared with other methods, the material around the slit is not affected by oxidation or pollution before and after processing. Compared with other methods, the laser pretreatment method achieves a better cutting quality and requires shorter time. By conducting the complete experiment with respect to two factors and three levels, a pretreated surface in agreement with the shallow melting state can be obtained. In this treatment range, the processing parameters are selected based on the proportion of oxidation area to perform the cutting experiment, and the grating sample is produced. The results show that a slit grating satisfying all the quality requirements can be obtained using the proposed method. Further, the HAZ is considerably smaller after cutting, and there is no slag on the back. The properties of copper cladding before and after cutting are protected to ensure that the quality of the copper-steel laminated plates cut by the fiber laser meets the application requirements.
