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 Al₂O₃ 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 Al₂O₃ 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^TM 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.