Effects of Scanning Speed on the Polished Surface Quality of Mold Steel by Dual-Beam Coupling Nanosecond Laser

In this paper, a novel dual-beam coupled nanosecond laser was used to polish S136D mold steel. The effects of scanning speed, total fluence, spot overlap ratio, and SPSN on surface quality were analyzed. The polished surface roughness Ra without ultrasonic cleaning is too large due to slag, splash, and dust produced by laser polishing. When scanning speed is 1250 mm/min, surface roughness Ra with ultrasonic cleaning is reduced from the original surface 1.92 μm to 0.72 μm, and the surface roughness Ra is reduced by 62.50%. When the Ftot is 35.38 J/cm2, the minimum value of surface roughness Ra is 0.72 μm. If the total fluence is higher or lower, it is not conducive to reducing the surface roughness, the total fluence is higher, and there is a polished surface with SOM phenomenon. The polished surface with spot overlap ratio of 98.55% has a smooth morphology, and a minimum value of surface roughness Ra of 0.41 μm. When the specimen is inclined at a certain angle, the high-magnification camera captures color on the polished surface. It is found that the microscopic texture of molten material flow trace and polishing scanning track is obvious. Polished surface is mainly distributed with Fe, Cr, C, and O elements. The surface material processing speed per unit time is low, and the polishing surface quality is improved less. The maximum surface roughness Ra is 1.98 μm. The minimum Ra of polished surface with smoother morphology is 0.41 μm, and surface profile height is basically the same. The research results show that the new dual-beam coupled nanosecond laser polishing technology can improve surface quality of materials. This research work provides process guidance for laser polishing effect analysis and mechanism innovation.