Toolpath and machining parameters optimisation of the cavities of a knee prosthesis tibial insert

Abstract

The main purpose of this paper is to demonstrate the applicability of conventional cutting tools in the machining of a custom tibial insert of a knee prosthesis. This study also aims to reduce the roughness and minimise the production time. In this work, the optimisation of cutting strategies and parameters was achieved through the design and construction of a test-part containing the most important complex surfaces of the femoral cavities, the focus of the study. The milling was carried out in accordance with the Design Of Experiment and the Taguchi method and was performed in two stages to reduce the number of analysed factors. The achieved parameters are applied to the machining of a modelled tibial insert made of UHMWPE, using a NC machine with three axes. The initial parameters studied were the cutting method, axial and radial depth of cut, the direction of the feed and the feed rate. Three strategies were studied: two Blend, resulting in radial and spiral toolpaths, and one Parallel. According to the spiral strategy, an arithmetical mean roughness of Ra = 1.1 µm was obtained, representing an improvement of 45% relatively to the initial phase value of 2.0 µm, with the Parallel toolpath. An overall improvement of 34% in time efficiency of the finishing operation was achieved after changing the machine settings. This study supports the conclusion that high-speed milling is an expeditious process to produce customised tibial inserts.