Ti-6Al-4V miniature screws are widely used in medical implants, where surface quality strongly affects biocompatibility and service life. However, their threaded geometry, small radius of curvature, and poor machinability make high-quality finishing difficult. To address this challenge, a roller-type ultrasonic-assisted magnetorheological finishing (R-UMRF) process was proposed for Ti-6Al-4V miniature screws (M2.5 × 4 mm). A three-pole magnetic field generator was designed and optimized by finite element analysis to establish a stable finishing zone and a weak-field renewal zone for flexible-brush regeneration. Guided by the process mechanism, single-factor experiments were first performed to evaluate the effects of finishing time, spindle speed, roller speed, ultrasonic amplitude, and applied current on surface roughness (Ra). A four-factor, three-level orthogonal experiment was then conducted to optimize Ra and the change rate of surface roughness (ΔRa). The applied current showed the strongest effect on finishing performance, followed by roller speed; however, excessive current or ultrasonic amplitude deteriorated the surface because of over-aggressive abrasive action. The optimal parameters were a spindle speed of 260 r/min, a roller speed of 140 r/min, an ultrasonic amplitude of 10 μm, and an applied current of 4 A. Under these conditions, Ra decreased from 1.208 μm to 0.081 μm after 120 min, corresponding to a reduction of 93.29%. These results demonstrate that R-UMRF is an effective low-damage finishing method for Ti-6Al-4V miniature screws with complex threaded surfaces.
Bi et al. (Thu,) studied this question.