An Investigation of Force Components in Orthogonal Cutting of Medical Grade Cobalt Chromium Alloy (ASTM F1537)

An aging population, increased physical activity and obesity, are identified as life style changes contributing to growth in the use of in-vivo prosthetics for total hip and knee arthroplasty. Cobalt chromium alloys, due to mechanical properties and excellent biocompatibility, uniquely qualify as a class of materials that meet the stringent functional requirements for these devices. To cost effectively assure the required dimensional and geometric tolerances, manufacturers invariably rely on high precision machining. However, a comprehensive literature review has shown that there has been limited research into mechanical cutting of these materials. This paper delineates the physical and mechanical properties that determine the machinability of a material, and compares medical grade cobalt chromium alloy ASTM F1537 with titanium alloy, Ti-6Al-4V ASTM F136. The results of a full factorial orthogonal cutting experiment are reported where cutting and thrust force components were measured over a range of cutting speeds (Vc) and levels of undeformed chip thickness (hm). It was found that the forces generated in cutting of ASTM F1537 are significantly higher than for ASTM F136, depending primarily on undeformed chip thickness, but with some influence of the cutting speed. The effect of chip segmentation on component force variations is also reported.