Influence of relative tool sharpness (RTS) on different ultra-precision machining regimes of Mg alloy

Abstract

Opportunities for new applications of lightweight Mg alloys are emerging in bio-medical fields, especially in medical devices and implants. The biodegradable Mg-based alloys wield advantages over their counterparts of SS 316 L, Co-Cr, and Ti-based alloys due to good biocompatibility observed during in-vivo and in-vitro assessments. However, in such aqueous environments, biodegradable magnesium alloys experience the limitation of higher corrosion rates, which causes loosening of the fixation implant. More importantly, it causes an undesirable chemical imbalance in the human body. This undesirable side effect of the promising Mg alloys can be subdued by improving the quality of the implant’s surface which interacts with the human biology. One way to do it is by imparting compressive stress via mechanical processing such as tool-based machining process. Mechanical micro-machining, especially the ultra-precision turning, could be a viable method to fabricate Mg alloy implants and components with the high surface finish necessary for superior corrosion resistance. However, the cutting mechanics of Mg alloy is poorly understood due to the scarcity of processing data and cutting parameters at ultra-precision level. In this paper, with ultra-precise cutting of Mg alloy (AZ91D), a novel “burnishing-like” surface finishing phenomena has been established. Additionally, some of the critical machining results are identified that are crucial for the comprehension of the cutting mechanics. These entities are cutting edge radius effect on the chip formation, material flow angle, machining-induced stress, surface burn marks, chip-tool contact surface, and the fallacy of “no chip formation” phenomenon. Therefore, knowledge derived from this study will enhance the understanding of cutting mechanics at ultra-precision level, and consequently improve the machining results of Mg alloy for bio-medical, electro-mechanical, and space-telecommunication applications.