Sustainable Machining of Mg-9Al-1.4Zn Foam Used for Temporary Biomedical Implant Using Cryogenic Cooling.

In this study, the drilling performance of biodegradable grade Mg-9Al-1.4Zn alloy reinforced with hollow thin-walled AlO microspheres is inspected under different coolant environments such as dry, Almag mineral oil, and liquid nitrogen. Drilling experiments were carried out using titanium aluminum nitride PVD coated and uncoated K10 tools on varying volume fractions of magnesium syntactic foams (5%, 10%, and 15%) reinforced with hollow AlO microspheres. Test results showed a 30-60% higher thrust force generated with liquid nitrogen drilling in comparison to dry and oil-based drilling while cutting higher volume fraction foams. Higher microsphere volume fractions of syntactic foam recorded higher machining forces, which is roughly a 200% increase as the volume fraction raised to 15%. The performance of TiAlN PVD tool coating is reflected through a reduction in thrust forces by 20% during cryogenic drilling. Scanning electron microscope (SEM) investigation of cryogenic-machined bore surfaces showed minimal drilling-induced surface defects compared to dry and Almag mineral oil conditions. A three-dimensional, thermo-mechanical finite element-based model for drilling Mg-9Al-1.4Zn syntactic foam using AdvantEdge is developed for different sustainable lubrication conditions. Surface finish (Ra) showed a 45-55% improvement during cryogenic drilling of 15% syntactic foams with minimized subsurface damages compared to dry and wet cutting conditions. The higher the volume fraction, the higher the surface roughness (Ra) and thrust force under cryogenic machining.