Sunil Jha

Magnetorheological Ball End Finishing Process

Finishing of three-dimensional (3D) surfaces such as grooves, projections, or complex in depth profiles on workpiece surfaces is a challenging task for the many existing advanced fine finishing processes. The advanced fine finishing processes have been developed to precisely control the abrading forces through external magnetic field. The applications of state-of-art finishing processes are limited to specific geometries only such as concave, convex, flat, and aspherical shapes due to restriction on relative movement of finishing medium and workpiece. Many of these processes are incapable of finishing of 3D intricate shaped surfaces. To overcome this problem, a new finishing process for flat as well as 3D surfaces using ball-end magnetorheological (MR) finishing tool is developed for ferromagnetic as well as non-ferromagnetic materials. The smart behavior of MRP fluid is utilized to precisely control the finishing forces and hence the final surface finish. A computer controlled experimental setup is designed and developed to study the process characteristics and performance. The magnetostatic simulations of flux density in MRP fluid between tool and workpiece has been done to visualize the finishing spot shape and size in contact with the workpiece surface. EN31 magnetic steel and nonmagnetic copper workpieces were finished using developed machine to validate the process concept.

Nanofinishing of Fused Silica Glass Using Ball-End Magnetorheological Finishing Tool

The surface finishing of fused silica in nanometer range and in obtaining defect-free surface is a challenge and in high demand because of its applications for transmitting high energy laser pulses. A novel nanofinishing process using ball-end Magnetorheological (MR) finishing tool was developed for finishing of flat as well as three-dimensional (3D) surfaces of ferromagnetic and non-ferromagnetic materials. In this process, a magnetically controlled ball end of smart MR polishing fluid is generated at the tip of the cylindrical tool, and it is guided to follow the surface to be finished through computer controlled three-axes motion. The process is automated and used for finishing precise components in manufacturing system. The smart behavior of MR-polishing fluid is utilized to precisely control the finishing forces which exhibit change in rheological behavior in the presence of external magnetic field. The finishing of fused silica glass was done using cerium oxide Cerox 1663 abrasive powder. The effect of finishing time on final surface roughness was studied, and the finished surfaces were observed under atomic force microscope. Significant improvement in surface roughness (Ra), root mean square (RMS), and Rmax value has been obtained after 90 min of finishing. Ra as low as 0.146 nm was achieved from initial value of 0.74 nm.

Performance Analysis of Ball End Magnetorheological Finishing Process with MR Polishing Fluid

A ball end magnetorheological finishing (BEMRF) process was developed for finishing a flat as well as 3D workpiece surfaces. The BEMRF process has a wide scope in todays advanced manufacturing systems for finishing 3D complex surfaces. Magnetorheological (MR) polishing fluid is used as finishing medium in BEMRF process. The constituent of MR polishing (MRP) fluid includes ferromagnetic carbonyl iron powder, abrasives, and base fluid medium. The workpiece surface is mainly finished by abrasives contained in MRP fluid. Therefore, the different mesh size from 400 to 1200 and volume percent concentration from 5% to 25% of abrasives in MRP fluid were chosen as factors to study their effects on the developed process performance in terms of percent change in roughness values. Silicon carbide abrasives were chosen in the present experimental investigation. Experiments were performed on the ferromagnetic ground surfaces whose initial roughness values (Ra) were measured in the range of 0.428 to 0.767 µm. The experimental results revealed that the MRP fluid with 15 vol % abrasives of mesh number 400 demonstrated better improvements in surface texture of finished surface as compared to other MRP fluid compositions. The finished surface characteristics and textures were studied at microscopic level using scanning electron microscopy and atomic force microscopy.

Ball End Magnetorheological Finishing Using Bidisperse Magnetorheological Polishing Fluid

A scheme to finish workpiece surface in nanometer range and obtain defect free surface using bidisperse magnetorheological polishing fluid (MRPF) by ball end magnetorheological finishing (BEMRF) tool is presented. Bidisperse MRPF consist of micron size CS and HS grade of carbonyl iron powder (CIP) with different volume fraction combinations within 20 vol.% magnetic solid contents, 25 vol.% SiC abrasives and 55 vol.% base fluid. Vibration sample magnetometer (VSM) has been used to study the magnetization of magnetic abrasives. Maximum magnetization has been found for CIP of 16 vol.% CS grade, 4 vol.% HS grade and 25 vol.% SiC abrasives. Magnetorheological behavior of bidisperse MRPF was evaluated using magnetorheometer. Performance of MRPF was evaluated by steady state rheograms in magnetic field strength. The yield strength of MRPF was found maximum at CIP of 16 vol.% CS grade, 4 vol.% HS grade, 25 vol.% abrasives and 55 vol.% base fluid. After characterization, experiments were performed with BEMRF tool on mild steel workpiece material for 30 min with given machining conditions. Percentage reduction in surface roughness (%ΔR a) was calculated and compared with %ΔR a obtained by finishing the workpiece with existing monodispersed MRPF and superior results as compared to existing one was found.

Rheological Characterization of MR Polishing Fluid Used for Silicon Polishing in BEMRF Process

The finishing mechanism of the ball-end magnetorheological finishing (BEMRF) process mainly depends on the stiffened hemispheroid, which is formed at the tool tip. Magnetorheological (MR) polishing fluid imparts strength to the polishing spot because of the effect of magnetic field strength. Behavior of this polishing fluid mainly depends on the size and shape of its constituents, volume concentration, particle size distribution, and applied magnetic field strength. A detailed study was undertaken on the role of carbonyl iron particle (CIP) size on the rheological behavior of the MR polishing fluid under various magnetic flux densities. Evaluation of the behavior of MR polishing fluid for silicon polishing was attempted through designing and fabrication of a parallel-plate magnetorheometer. Rheological characterization study was carried out using the Casson fluid model and the MR polishing fluid rheological properties, namely field-induced yield stress and shear viscosity were evaluated.

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 silicon nitride workpieces using magnetorheological abrasive flow finishing

Magnetorheological Abrasive Flow Finishing (MRAFF) process was developed for deterministic finishing of internal and external surfaces by extruding magnetically stiffened magnetorheological abrasive polishing fluid. Silicon nitride is a brittle and hard, difficult-to-machine ceramic. Obtaining final surface finish in nanometer range and defect free surface is a challenge for manufacturing scientists. The finishing of silicon nitride workpieces was done using boron carbide, silicon carbide and diamond. The effectiveness of different abrasives was investigated and surface topography was observed under atomic force microscope.

Nanofinishing of Copper Using Ball End Magnetorheological Finishing (BEMRF) Process

The ball end magnetorheological finishing (BEMRF) is an advanced nanofinishing process for flat, curved and freeform surfaces of ferromagnetic as well as diamagnetic materials. While finishing copper (diamagnetic material) by this process, a low finishing effect is obtained as its surface repels the externally applied magnetic field. In this work a magnetic simulation is carried out over both copper and ferromagnetic material. For the ferromagnetic material the simulation result shows a high flux density region below the tool tip. However in case of copper the magnetic flux density is too low for finishing. It is also observed through simulations that when copper workpiece is placed on a mild steel base the flux density improves marginally. This led to the idea of using a permanent magnet (in place of mild steel) as a base for finishing of copper using the BEMRF process. Using this technique copper was finished and the experimental results indicate that this method can realize ultra-precision finishing of copper.Copyright

Experimental investigations into ultrasonic-assisted jet electrodeposition process

In this study, a new process namely, ultrasonic-assisted jet electrodeposition, has been conceived. The ultrasonic-assisted jet electrodeposition process integrates the use of ultrasonic vibrations and high-speed selective jet electrodeposition process to fabricate micro shapes with comparatively high accuracy and with no edge effect. The present study focuses on the development of ultrasonic-assisted jet electrodeposition setup. The impacts of voltage, pulse on time of ultrasonic vibration, concentration of CuSO4·5H2O and interelectrode gap for the fabrication of square-shaped micro part have been studied. Deposition rate and dimensional accuracy of fabricated micro features were considered as responses. The experimental results showed that the ultrasonic-assisted jet electrodeposition process has the capability to fabricate micro parts, which yield better dimensional accuracy and no edge effect but waviness of the order of 10–50 µm, as compared to uneven depositional width and edge effect (gap of 200–250 µm) obtained by jet electrodeposition process.

Synthesis of polishing fluid and novel approach for nanofinishing of copper using ball-end magnetorheological finishing process

ABSTRACT Ball-end magnetorheological (MR) finishing process utilizes the magnetically controlled stiffened ball of an MR fluid for finishing purposes. Copper is a mechanically soft and chemically reactive material, so it is difficult to finish up to the nanometer-order level by traditional and most of the advanced finishing processes. In this research work, the problems associated with ball-end MR finishing of copper have been explored and a fluid composition suitable for the finishing of copper has been developed. A novel approach using two opposite magnetic poles has been used to enhance the magnetic flux density distribution between the tool tip and the copper workpiece surface. The same has been magnetically simulated and verified experimentally. The effect of fluid composition parameters has been analyzed by the statistical model developed by response surface. After 30 minutes of finishing time, a nano-finished surface with very few shallow scratches was achieved.