Achieving high accuracy of Co-Cr-Mo femoral head for improving tribological properties of hip joint prosthesis via a three-axial MFAF process

Rough surface and low precision roundness of femoral head can significantly affect tribological properties of hip joint prosthesis such as wear, von Mises stress, friction coefficient, and scratches, resulting in failure of hip joint prosthesis. In this work, firstly, an ultra-smooth surface with a high precision roundness was achieved for Co-Cr-Mo femoral heads via a three-axial Magnetic Field Assisted Finishing (MFAF) process. Secondly, the effects of a rough and smooth surface of Co-Cr-Mo femoral head on wear rate of acetabular cup were evaluated via a wear simulator test. Finally, the von Mises stresses of both femoral heads and acetabular cup were evaluated via ABAQUS finite element (FE) model. Using this process, surface roughness (Sa) and roundness (RONt) of femoral head were reduced from 0.330 to 0.032 μm and from 26.15 to 2.17 μm, respectively. A high accuracy of Co-Cr-Mo femoral head was achieved by reducing its surface roughness and roundness, which reduced the wear rate of the acetabular cup by more than 68 % compared to an unfinished femoral head. In addition, an ultra-smooth surface of femoral head dramatically reduced the von Mises stresses at the contact area of hip joint prosthesis. Results of this work demonstrate that a three-axial MFAF process is an effective method to successfully achieve high accuracy of Co-Cr-Mo femoral head with advantages of simultaneously improving tribological properties of hip joint prosthesis.