Control of Lay on Cobalt Chromium Alloy Finished Surfaces Using Magnetic Abrasive Finishing and Its Effect on Wettability

Abstract

Freeform surfaces, including the femoral components of knee prosthetics, present a significant challenge in manufacturing. The finishing process is often performed manually, which leads to surface finish variations. In the case of knee prosthetics, this can be a factor leading to accelerated wear of the polyethylene tibial component. The wear resistance of polyethylene components might be influenced by not only the roughness but also the lay of femoral component surfaces. This study applies magnetic abrasive finishing (MAF) for nanometer-scale finishing of cobalt chromium alloys, which are commonly used in knee prosthetics and other freeform components. Using flat disks as workpieces, this paper shows the dominant parameters for controlling the lay in MAF and demonstrates the feasibility of MAF to alter the lay while controlling the surface roughness. The manually finished disk surfaces (with roughness around 3 nm Sa), consisting of random cutting marks, were compared to MAF-produced surfaces (also with roughness around 3 nm Sa) with different lays. Tests using deionized water droplets show that the lay influences the wetting properties even if the surface roughness changes by no more than a nanometer. Surfaces with unidirectional cutting marks exhibit the least wettability, and increasing the cross-hatch angle in the MAF-produced surfaces increases the wettability. Surfaces consisting of short, intermittent cutting marks were the most wettable by deionized water.