Fabrication of high aspect ratio microgroove on Ti6Al4V by laser-induced oxidation assisted micro milling

Abstract

High aspect ratio microstructures based on titanium alloys have a become driving demand for various fields such as aerospace, biomedicine, and turbine blades due to their high strength, low density, biocompatibility, and corrosion resistance. However, high aspect ratios in micro-machining domains come up with low material removal rate, poor machined microstructure quality, premature tool failures, and slow machining efficiency. In this paper, a novel hybrid processing method of laser-induced oxidation assisted micro milling (LOMM) is proposed to solve the aforementioned problems. The oxidation behavior of Ti6Al4V under nanosecond laser irradiation, cutting force, machined surface quality, burr formation and tool wear mechanisms were investigated. A microgroove on Ti6Al4V alloy with a width of 0.5 mm and an aspect ratio of 5.4 was fabricated successfully by LOMM. For comparison, the conventional micro milling (CONV) was also carried out to fabricate a high aspect ratio microgroove under the same cutting parameters. Under laser irradiation, a loose oxide layer and relatively dense sub-layer were formed. The thicknesses of the oxide layer and sub-layer were 18.2 μm and 2.3 μm, respectively. The cutting force and tool wear rate in LOMM were tremendously low in removing the oxide layer compared to those in CONV. The surface quality machined by LOMM was superior to that produced by CONV. The tool wear mechanisms observed in LOMM was coating spalling, while in CONV tool nose breakage, coating spalling and adhesive wear were observed. Compared to CONV, the tool service life in LOMM was prolonged significantly.