Prediction of contact conditions and theoretical roughness in manufacturing of complex implants by toric grinding tools.

Throughout the world, more and more artificial knee prostheses are implanted due to the rise in cases of arthrosis. Inspired by all-ceramic hip joint implants, recent research in the field aims at enhancing the durability of the complex knee implants by using wear-resistant ceramics in a hard/hard joint pairing. Due to its kinematics and its complex geometry, the ceramic knee implant makes high demands on the manufacturing process if a high-quality level has to be assured. Firstly, the grinding process has to provide high surface qualities in order to reduce efforts in the polishing process; secondly, high contouring accuracy is required to avoid stress peaks in the ceramic joint pairings. Constant material removal in 5-axis grinding is assured by using toric grinding pins and accounting for the constantly changing contact conditions. In this paper, the contact conditions for a frontal grinding process with toric grinding pins are determined. Firstly, the contact length is calculated to detect the engagement zone in frontal grinding with toric tools. An angle range for constant material removal was found out. Furthermore, a model for the prediction of the resulting roughness of grinding processes with toric, ceramic bonded diamond grinding pins is developed and verified by means of grinding tests.