Laser-induced oxidation-assisted micromilling of deep narrow microgroove on Inconel 718

Abstract

The miniaturized components of Inconel 718 superalloy are widely used in aerospace industries due to its excellent properties at elevated temperatures. In this work, an innovative hybrid processing technology named laser-induced oxidation assisted micromilling (LOMM) was proposed. A deep narrow microgroove with a depth of 1500 μm and a width of 500 μm was fabricated successfully by LOMM. The effects of average laser power on morphology and microstructure of the oxide layer and sub-layer were studied. In addition, milling force, surface quality of the machined microgrooves, and tool wear were investigated. Under laser irradiation with average laser power of 4.5 W, a loose and soft oxide layer, as well as a sub-layer were formed, whose thicknesses were 24 μm and 16 μm, respectively. The milling force during removing of the oxide layer was only around 1.2 N, which was much lower than that (3~8 N) when removing of the substrate material. Owing to the low cutting force, no obvious tool wear was observed in removing of the oxide layer. However, tool wear in terms of coating peeling and microchipping was found in micromilling of the sub-layer and substrate material. For comparison, conventional micromilling (COMM) was used to machine a deep narrow microgroove under identical milling parameters. The tool diameter was reduced by 4.4% in LOMM, while that was reduced by 22% in COMM. The tool failure forms in COMM were catastrophic nose breakage and severe coating peeling. The bottom surface roughness Sa of the deep narrow microgroove machined with LOMM was 0.21 μm, while that machined with COMM reached 0.41 μm. This study validated that the proposed novel hybrid process can prolong tool life, and improve surface quality and material removal rate.