Effect of process parameters on machinability, hemocompatibility and surface integrity of SS 316L using R-MRAFF

Abstract

Surface finish at nanometric scale is imperative for biomedical implants made up of stainless steel 316L (SS 316L) and titanium alloy to ensure the biocompatibility. However, such fine finishing is quite difficult to process. A rotational magnetorheological abrasive flow finishing process is used for nano-finishing. Rotational magnetorheological abrasive flow finishing (R-MRAFF) is one of the processes to achieve nano-level finishing. In this present study, a rotating die has been developed to perform the R-MRAFF processes with four rectangular-shaped permanent magnets held at an angle of 90° to one another. A new method for producing a variable magnetic field was investigated in this study by increasing or decreasing the distance between permanent magnets in the rotating die and workpiece fixtures. The increase in the distance between permanent magnets in rotating die and workpiece fixture leads to a decline in the value of material removal rate (MRR) as well as a percentage reduction in surface roughness (%ΔRa). This validates the importance of magnetic field intensity in the R-MRAFF process. A central composite design (CCD) in the response surface methodology (RSM) is employed to study the effect of process parameters on the response variables. The effect of the process parameter was evidenced with the help of the ANOVA technique. Optimization was carried out with constraints of maximizing both output response variables, the optimum MRR and %ΔRa, which were found as 2.02 mg/s and 50.66%. To quantify the effect of surface roughness on hemocompatibility, a platelet adhesion study was investigated. The platelet adhered area starts to decrease with the reduction in the surface roughness from 319 to 167 nm.