Ball End Magnetorheological Finishing Research Articles

Mechanism of material removal in ball end magnetorheological finishing process

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.

Parametric analysis of an improved ball end magnetorheological finishing process

A novel surface finishing method using an improved ball end magnetorheological finishing tool was developed for nanofinishing of flat, as well as three-dimensional workpiece surfaces. An improved magnetorheological finishing tool is the main part of the present finishing process, which has been made up of the central rotating core and stationary electromagnet coil integrated with a copper cooling coil. A magnetically generated ball end finishing spot of magnetorheological polishing fluid was used as a finishing segment at the tip surface of the rotating core. In this research, detailed study through statistical design of the experiments was conducted for nanofinishing of ferromagnetic workpieces by the proposed ball end magnetorheological finishing process. Response surface methodology has been used to plan and analyze the effect of rotational speed of the tool core, magnetizing current and working gap on percentage change in surface roughness. The experimental results were discussed and the best finishing conditions were identified within the experimental range of variables. Analysis of experimental data showed that the percentage change in surface roughness was highly influenced by the working gap, followed by magnetizing current and rotational speed of the tool core. The best surface finish obtained on the ferromagnetic workpieces was as low as 27.6 nm from the initial value of 142.9 nm in 30 min of finishing time. In order to study the finished surface morphology, scanning electron microscopy and atomic force microscopy were also conducted.

Nanofinishing of a typical 3D ferromagnetic workpiece using ball end magnetorheological finishing process

A nanofinishing process using ball end magnetorheological (MR) finishing tool was developed for finishing 3D workpiece surfaces. In this process a ball end shape of MR polishing fluid is generated at the tip surface of the rotating tool which is used as a finishing spot. This paper is focused on surface finishing and performance evaluation of a typical three-dimensional ferromagnetic workpiece using a ball end magnetorheological finishing process. A typical 3D workpiece surfaces were made by milling process at different angles of projection such as flat, 30°, 45° and curve surfaces. The experiments were performed on these typical workpiece surfaces by ball end MR finishing setup to study the effect of number of finishing passes on final surface roughness. The experiments were also performed on a flat ground surface to study the process performance as compared with the milled workpiece surfaces. The finite element analysis has been done to study the distribution of magnetic flux density at tip surface of the tool with an inserted typical 3D workpiece surfaces. When these typical workpiece surfaces were finished by proposed MR finishing process, the surface roughness were reduced as low as 16.6nm, 30.4nm, 71nm and 123.7nm respectively on flat, 30°, 45° and curve surfaces for 60 passes of finishing. The roughness of flat ground surface was reduced as low as 19.7nm for 120min of finishing. The experimental results demonstrated that the newly developed ball end magnetorheological finishing process was effective in finishing typical 3D ferromagnetic workpiece surfaces.