A Hybrid-Electrochemical Magnetorheological (H-ECMR) Finishing Process for Surface Enhancement of Biomedical Implants

The proposed novel polishing method, Hybrid-Electrochemical Magnetorheological (H-ECMR) finishing, combines electrochemical reaction and mechanical abrasion on the workpiece surface to reduce finishing time. Moreover, H-ECMR finishing on the biomaterial surface produces a uniform, thick passive oxide layer to improve corrosion resistance. Herein, the electrolytic solution facilitates the chemical reaction and acts as a carrier medium for Carbonyl Iron Particles (CIPs) in Magnetorheological (MR) fluid. The effectiveness of the H-ECMR process is evaluated based on various surface roughness parameters (i.e., average surface roughness (Ra), skewness (Rsk), and kurtosis (Rku)) and compared with the conventional Magnetorheological Finishing (MRF) process. A 96.41% reduction in Ra value is achieved in the H-ECMR finishing process compared to 49.63% in MRF for identical polishing time. Furthermore, an analytical model is developed to evaluate the final Ra achieved from the developed H-ECMR finishing process and agrees well with the experimental results. Moreover, the electrochemical reaction forms a uniform and thick oxide layer on the Ti-6Al-4V surface as layer thickness increases to 78 nm from its initial value of 8 nm. The impact of different process parameters on surface roughness values is also analyzed to determine the optimized value of the input variables. A case study is performed on the femoral head of the hip implant, and the Ra value is reduced to 21.36 nm from its initial value of 326 nm through the contour-parallel radial toolpath strategy during H-ECMR finishing.