Finite Element Modeling of Drilling AZ91 Magnesium Foam Reinforced with Hollow Alumina Microspheres

Abstract

Novel AZ91 magnesium syntactic foams are a potential choice for temporary biomedical implants. In many cases, holes of various sizes need to be machined on the biomedical implants using the drilling process to facilitate placement of implants inside the human body. In this study, the drilling performance of AZ91-magnesium foam is investigated under different lubrication methods such as dry, wet (Almag® mineral Oil), and cryogenic cooling. Drilling experiments were carried out using titanium aluminium nitride (TiAlN) physical vapor deposition (PVD) coated and uncoated twist drills on varying volume fractions of AZ91 magnesium syntactic foams (5%, 10%, and 15%) reinforced with hollow alumina microspheres. Test results showed a 30%-60% higher thrust forces generated with cryogenic machining compared to dry and wet machining while cutting AZ91-15% hollow alumina foam. This phenomenon shows the influence of alumina hollow microspheres on controlling the plastic deformation of the AZ91 magnesium matrix through effective work hardening and characteristic load transfer. Scanning electron microscope (SEM) investigation of cryogenic machined bore surfaces showed minimal drilling-induced surface defects. Based on the analysis carried out, cryogenic machining is recommended as a sustainable drilling process for AZ91-magnesium syntactic foams. A three-dimensional, thermo-mechanical finite element-based model for drilling magnesium syntactic foam using AdvantEdgeTM is presented for different lubrication conditions. Metal cutting tests are performed and comparison with predicted data is provided. The predicted machining induced stress from the finite element model showed a compressive stress in case of cryogenic cooling compared to dry machining which will give a better surface integrity and quality to the machined surface and will reduce the danger of crack propagation and crack growth. Based on the analysis carried out, cryogenic machining is recommended as a sustainable drilling process for AZ91-magnesium syntactic foams.