5-Axis Manufacturing Strategies for Low Wear Ceramic Knee Implants

5-Axis Manufacturing Strategies for Low Wear Ceramic Knee Implants

Kategorien Konferenz (reviewed)
Jahr 2012
Autoren Denkena, B., Köhler, J., Turger, A., van der Meer, A.:
Veröffentlicht in Proceedings of the 1st International Conference on Design and Processes for Medical Devices (PROMED), May 2nd to 4th, 2012, Bresica, Italy, S. 225-228.

The complication rate of knee implants amounts to approx. 25 %. One reason for the failure is the agglomeration of wear debris of the polyethylene tibia. As a consequence a revision surgery is required. Applying bioceramics for endoprostheses promises to improve the implant durability significantly due to low and biocompatible wear. However, to meet the demands on contour accuracy and surface quality high precision grinding and polishing processes for free-formed ceramic surfaces are essential. To achieve high geometrical accuracy 5-axis machining processes were developed. The paper will present the process chain of simultaneous grinding and polishing of ceramic knee implants. In a first step a 5-axis simultaneous grinding process with toric grinding pins is applied. The pins can be adapted to the curving of the complex surface geometry of the knee implant to generate a constant material removal. To ensure a constant material removal rate along the tool path the contact conditions for grinding with toric pins have been calculated. The developed model can be used to predict geometrical intersection. Furthermore, the grinding layer topography and the grinding kinematics are considered to predict the resulting roughness, which is verified by grinding experiments. In a second step, the ground surfaces are polished to remove the roughness peaks. Therefore, resilient diamond polishing tools are developed to keep the form accuracy of the ceramic implant. The wear behaviour of the tools during grinding and polishing will be described. At last, the wear behaviour of the ceramic implants was evaluated using a wear-gliding-teststation by project partner Laboratory of Biomechanics and Biomaterials of Medical School of Hannover (MHH-LBB). The results show that the wear of simplified ceramic pairings machined in the developed way is reduced by a factor of 30 compared to conventional cobalt-chrome – polyethylene pairings.