Using inverse replica fixture technique for improving nano-finishing of hip joint implant in abrasive flow finishing process

The total hip arthroplasty (THA) is considered as one of the most successful orthopedic surgeries, through which the damaged hip joint is replaced with hip joint prosthesis. Besides, automatic nano-finishing of femoral head is of great importance in improving tribological, biological, and metallurgical properties of hip joint implants and increases the productivity of manufacturing process. In the present effort, to satisfy these requirements, a new inverse replica fixture of femoral head has been proposed in the abrasive flow finishing (AFF) process. In addition, the effect of AFF parameters including extrusion pressure, number of finishing cycles, and abrasive mesh size has been investigated on the surface roughness of the femoral head which is made of ASTM F 138 (SS 316 L). For conducting the experimental tests, a setup of AFF process is designed and fabricated. The experiments are performed according to the design of experiments and the full factorial method. Statistical analysis of the experimental data shows that the most significant parameter is the abrasive mesh size. Moreover, the surface topographic parameters of Ra, Rq, Rp, Rv, and Rt of femoral head under experimental conditions; extrusion pressure of 9 MPa, number of finishing cycles of 100, and abrasive mesh size of 1000 have improved by 91.71%, 91.21%, 81.84%, 88.46%, and 85.44%, respectively. Furthermore, SEM and AFM images of the surface texture of the femoral head before and after the AFF process demonstrate the elimination of CNC lathe traces along with achieving mirror-like surface up to the range of 20.3 nm. In addition, regarding the XRF results, no considerable variation in the chemical composition of femoral head before and after the AFF process is observed.