Investigation on roller-type ultrasonic assisted magnetorheological finishing for biomedical small and complex surface of titanium alloy

Biomedical small workpieces made of titanium alloys are widely used in orthopedic implants. However, the poor abrasive resistance and the complex shape of the parts with small size could seriously reduce its finishing quality and efficiency. In this study, a roller-type ultrasonic assisted magnetorheological finishing (R-UMRF) for biomedical small and complex surface of titanium alloy was proposed. The R-UMRF principle was illustrated in detail. Then, the magnetic circuits of R-UMRF with three-pole electromagnet excitation device was designed and mathematical expressions of magnetic flux density in the MR fluid polishing region was further established. Moreover, simulation analysis of the designed magnetic circuit was performed as well. An experimental prototype was fabricated and tested to the feasibility of the developed MR polishing fluid and R-UMRF device. The results showed that the surface roughness decreases with the increase in spindle speed and roller speed, however, it first decreases and then increases with the increase in ultrasonic amplitude and the applied current. In addition, the surface roughness change rate increases with the increase in spindle speed and roller speed, however, it first increases and then decreases with the increase in ultrasonic amplitude and the applied current. The optimized process parameters for the titanium alloy screws are the MR polishing fluid of MRPF-2, the spindle speed of 240 r/min, the roller speed of 110 r/min, ultrasonic amplitude of 10 mu m, and applied current of 4 A. The surface roughness Ra of 0.089 mu m can be obtained after 140 min finishing under the optimized parameters. RUMRF is an adaptable and efficient method for finishing small and complex surface of titanium alloy.