Characterization of Chip Morphology in Orthogonal Cutting of Medical Grade Cobalt Chromium Alloy (ASTM F1537)

Cobalt Chromium alloys (CoCr) are used in the manufacture of class 3 medical devices, notably knee and hip implants, due to singular mechanical properties such as wear resistance and biocompatibility. Notwithstanding the importance of the material, there has been limited research reported on the fundamental mechanism in machining of this alloy. This paper initially propounds on the properties that define a material as “difficult to cut” (DTC) in order to compare machining related properties of ASTM F1537 CoCr with other known DTC alloys. This is followed by a brief summary of literature specifically on the chip morphology produced in turning of ASTM F136 Ti-6Al-4V and Inconel 718. Orthogonal cutting tests are then undertaken to examine the chip morphology in cutting ASTM F1537 over a range of cutting speeds (Vc) and levels of undeformed chip thickness (hm). The findings of this research were compared with those found in literature. It is concluded that ASTM F1537 CoCr produced segmented chips under all tested conditions and chip segmentation frequency increases with the cutting speed but is independent of the undeformed chip thickness. Moreover, the ratio of the segment height to the maximum chip thickness was found to decrease with cutting speed.