Evaluation of fluences and surface characteristics in laser polishing SKD 11 tool steel

The work applied a continuous-wave laser beam from a multimode fiber laser to study the polishing effect. Three kinds of surface morphologies were acquired by fast-speed (FS) & lower-speed (LS) wire electrical discharge machining (EDM), and milling processing methods on SKD11 tool steel. Then influence of laser fluence on the polished surface characteristics was analyzed. The results showed that surface roughness parameters (R-a, R-z, R-t, and S-a) were significantly affected by this effect. With the increasing laser fluence, the polished surface underwent a comprehensive topographical evolution from superficial surface melting to surface over-melting. The improvements by FS-EDM, LS-EDM, and milling in roughness were 86.83, 90.70 and 86.07%, respectively. The corresponding laser fluences were 14.26, 12.73 and 13.55 J/mm(2), indicating that LS-EDM tool steel surface has the optimal polishing effect. The comparative statistical results of the bearing area curve, bidirectional reflectance distribution function, and power spectral density from the LS-EDM surfaces showed the optimal polishing results. In addition, all the pre-prepared surfaces could be polished to R-a < 0.5 mu m using high polishing velocities. These findings signified that laser beam with top-hat distribution has a great potential for high efficiency polishing of tool steel surfaces.