Study on a two-step polishing method using pulsed fiber laser for SKD11 tool steel components

In this study, the authors propose and experimentally investigate a two-step polishing technique using a medium power pulsed fiber laser for cold work die components made of SKD11 tool steel. The objective is to improve the surface finish after milling by applying a high-precision laser polishing process that enables efficient and scalable automation. The experiments employed a pulsed fiber laser source with a maximum power of 35 W and a wavelength of 1064 nm, combined with a galvo scanning head and a digital control system. The polishing was performed under argon shielding gas with various scanning parameters. The study focused on evaluating the effects of laser power and the number of scanning passes on surface morphology, roughness, and near-surface microstructure. Results showed that the two-step polishing strategy, starting with high power laser passes (35 W) to remove major surface peaks, followed by low power passes (21 W) to smooth finer irregularities, effectively reduced surface roughness Ra from ~ 4.5 µm to ~ 1.2 µm (~73% reduction). Microstructural observations revealed phase transformations in the surface layer, with the formation of austenitic structures induced by the high-energy laser pulses. This study highlights the effectiveness of two-step pulsed laser polishing for difficult-to-machine materials like SKD11 and opens promising prospects for its application in precision mold manufacturing and automated surface finishing processes.