Morphological characterization of surfaces manufactured by High-speed machining: fractal approach of surface topography of tibial insert in UHMWPE

Abstract

The complex surface geometry in tibial insert of the knee prosthesis, developed by High-speed machining, demands strict surface topography quality requirements, mainly to prevent osteolysis [1]. The fractal analysis is an effective tool in monitoring the milling of these components, since it is a technique sensitive to the self-affinity characteristics of these surfaces [2]. The objective of this work was to propose a method based on the fractal approach for the inspection of surface topography of the tibial insert manufactured by High-speed machining. Test pieces of tibial insert were prepared by varying the machining strategy. The material used was a UHMWPE. The evolution of fractal values were correlated to cutting tool trajectories and compared to average roughness, Ra. Extended depth-of-field method allowed the ordering of stacks of images obtained from optical microscopy, to quantitative investigation of behavior of surfaces. A method to establish the threshold between different scales for multi-fractal behavior of the machining surfaces was proposed, allowing comparing mono-fractal behavior with mixed fractal. The fractal analysis machined surfaces of the tibial insert can be successfully conducted from elevation maps resulting by combining conventional optical microscopy and 3-D reconstruction by extended depth-of-field.