Improved surface quality components enabled by dual-laser additive/subtractive hybrid manufacturing process: Thermal behavior and ablation mechanisms

•A method of enhancing surface quality of ASHM-processed part was proposed.•Fine surface quality of dual-laser additive / subtractive hybrid process was obtained.•Effect of laser subtractive times and feed rate on surface quality was found.•Thermal behaviors and material melting-ablation mechanisms were discovered. A high roughness of the laser powder bed fusion (LPBF) process has been one of the most concerned issues in the integrated fabrication of complicated metal parts. In this research, a dual (continuous and ultrafast) laser additive-subtractive hybrid manufacturing (LASHM) process is introduced to improve the surface quality of the LPBF-processed components. Effects of the laser subtractive times and the feed rates on the side surface morphology of the LASHM-processed AISI 316L components were studied. Meanwhile, the VOF transient physical model of LPBF and double temperature physical model of LASHM were established to investigate the individual thermal behaviors and the material melting-ablation mechanisms. For the LPBF process, the operating temperature of the molten pool bottom was firstly stable in 300 K (< 25 ms), then increased to 630 K (25 ms-35 ms) and finally exponentially increased to 3000 K (>35 ms), implying the delayed thermal effect. Meanwhile, the operating temperature of the top region was linearly increased to 2050 K. While for the ultrafast laser subtractive process, the operating temperature of the top region was remained at ∼ 300 K with the temperature rapid increase to 2900 K below 104 ps in the bottom region, leading to the direct material ablation and maintaining the LPBF-processed microstructure. At the laser subtractive times equal to four with the sequence feed rates of 10 μm, 10 μm, 8 μm and 6 μm, the surface roughness Sa and the maximum surface height difference Sz were considerably reduced from 10.774 μm and 73.387 μm to 1.933 μm and 18.151 μm.