An experimental study on the correlation of polishing force and material removal for bonnet polishing of cobalt chrome alloy

Cobalt chrome alloys are the most extensively used biomaterials formanufacturing artificial prostheses,which need nanometer scale surface roughness and micrometer scale form tolerance to extend their lifespan in the tough environment of the human body. In order to machine bearing surfaces to sufficiently high accuracy, the way in which material is removed by the final finishing, such as bonnet polishing, must be completely understood. This study has experimentally investigated the influence of process parameters (precess angle, head speed, tool offset, and tool pressure) on the polishing forces as well as the material removal in bonnet polishing of a medical grade cobalt chrome alloy. Experimental results indicate that normal force increases with the increase in the precess angle, head speed and tool offset, but varies only slightly with the variation of the tool pressure. Tangential force increases with the increase in the precess angle and tool offset while it shows little variation with the change of the head speed and tool pressure. It is concluded that both normal force and tangential force can contribute to the material removal rate, but tangential force is found to be more correlated with the width of the influence function while normal force has a stronger correlation with the maximal height of the influence function.