Mechanism of material removal in ball end magnetorheological finishing process

Abstract

Ball end magnetorheological finishing (BEMRF) process was developed for finishing flat and 3D workpiece surfaces. A finishing tool is used to flow pressurized magnetorheological polishing fluid through the center of the rotating tool core and gets stiffened in the form of a magnetically controlled ball end shape at the tip surface of the tool. This forms a polishing spot of controlled size and shape which is used as a finishing medium by guiding it to follow the surface to be finished through computer controlled 3-axes motion. In the present study, an attempt has been made to understand the material removal and surface finishing mechanism in BEMRF process on a ferromagnetic workpiece. Based on experimental observations and force measurements, a mathematical model has been developed for modelling of magnetic field-induced normal force during finishing by BEMRF process. It is very difficult to understand the complex structure of rotating MR-polishing fluid during finishing operation, so a model of magnetic normal force is developed based on certain assumptions. Finished surfaces were also analyzed using scanning electron microscope (SEM) and atomic force microscope (AFM) to understand mechanism of material removal. In order to understand the material removal process and wear behavior during finishing, different modes of abrasive-workpiece interaction have been analyzed with respect to measured magnetic normal forces. The developed mathematical model has been used to predict magnetic normal finishing force and compared with the experimentally obtained results. Both were found in close agreement. The effect of variation in magnetic normal force was also observed experimentally in terms of percentage change in surface roughness during finishing.