Insights into the fabrication of microchannels on biomedical NiTinol

The nickel-titanium alloy (NiTinol) exhibits shape memory and superelasticity behavior, stemming from its remarkable ability to alter the atomic bonding types and mechanical properties significantly. NiTtinol is utilized in biomedical as well as aerospace applications. However, as reported by the recent literature, achieving the desired machinability characteristics on NiTinol at macro as well as micro levels is considerably challenging. In this context, this study aims to investigate the machinability of Biomedical grade NiTinol during its micromilling with minimum quantity lubrication (MQL), primarily focusing on the tool wear evolution, wear mechanisms, surface roughness, and burr formation. In addition, the frequency spectrum of the surface roughness profile was analyzed. For this purpose, experiments were conducted comprising the fabrication of microchannels measuring 27.0 mm in length using TiAlN coated 400 µm diameter micro end mills. A cutting speed of 12.57 m/min, feed rate of 1 µm/tooth, and axial depth of cut of 40 µm were employed. The results revealed that the formation of built-up edge (BUE) served as a protective barrier for the cutting-edge of the microtools, with adhesion or attrition identified as the predominant wear mechanisms. The measured surface roughness value Ra ranged from 0.0411 ± 0.0040 µm to 0.0461 ± 0.0070 µm. The frequency spectrum of the roughness profile analysis detected that feed rate was not the primary factor. Finally, the burr height and area on the down-milling side were consistently found to be larger than those observed on the up-milling side.