Ajay Sidpara

Rheological Characterization of Magnetorheological Finishing Fluid

Magnetorheological finishing (MRF) is a precision material removal process that has been applied to a large variety of brittle materials, from optical glasses to hard crystals, such as sapphire. MRF is based on a magnetorheological (MR) fluid that consists of carbonyl iron powder (CIP), polishing abrasives, water, and stabilizers. To understand and model this process correctly, it is important to study the rheological properties (yield stress and viscosity) of the fluid under the influence of the magnetic field. A detailed study through statistical design of experiments (DOE) is conducted to characterize rheological properties of MR fluid. Three constitutive models viz. Bingham Plastic, Herschel–Bulkley, and Casson fluid are used to characterize the rheological behavior of MR fluid. Response surface methodology (RSM) is applied to predict the effect of volume concentration of each component in MR fluid. Analysis of Variance (ANOVA) is conducted, and contribution of each model term affecting improvement in yield stress and viscosity is calculated. To estimate the saturation magnetization of MR fluid, M-H curve is plotted using vibrating sample magnetometer (VSM), and effect of temperature on yield stress and viscosity is discussed. The experimental results are discussed, and optimum fluid composition is identified from the selected range.

Nanofinishing of freeform surfaces of prosthetic knee joint implant

The freeform complex surfaces have become an inevitable part of many components to perform specific functions. Many of these components require nanometer surface roughness to meet specific requirements in their application domain. Therefore, finishing operation as a final operation is necessary for such components. A magnetorheological fluid-based finishing tool is developed for finishing knee joint implant, which has complex freeform surfaces. Different types of magnetorheological fluids and various finishing steps are proposed to reduce finishing time. Surface characteristics of the knee joint implant are studied using a surface roughness measuring instrument and atomic force microscopy before and after finishing. A significant reduction in surface roughness (the best final surface roughness value obtained = 28 nm) is observed on the component after finishing. The surface roughness obtained on different surfaces is well within the values recommended in the ASTM standard for total knee joint prosthesis.

Rheological Properties and Their Correlation with Surface Finish Quality in MR Fluid-Based Finishing Process

The magnetorheological (MR) fluid-based finishing process is a well-known deterministic process for nanofinishing of soft, as well as brittle, materials. The quality of the finished surface mainly depends on the constituents of magnetorheological fluid and applied magnetic field. Rheological properties (yield stress and viscosity) of MR fluid significantly affect the quality of the final finished surface. An experimental investigation was carried out to study yield stress and viscosity of MR fluid based on the Bingham Plastic model by varying concentration of MR fluid constituents and magnetic flux density. The rheological properties are correlated with final surface roughness and material removal rate of single crystal silicon by MR fluid based finishing process. Viscosity and yield stress increased with an increase in percentage content of magnetic particles and magnetic flux density. Higher values of yield stress and viscosity increased the material removal rate and surface finish. Yield stress and viscosity decrease with increasing abrasive particles concentration. It was also observed that an optimum level of yield stress and viscosity is necessary to get low surface roughness values.

Magnetorheological finishing: a perfect solution to nanofinishing requirements

Abstract. Finishing of optics for different applications is the most important as well as difficult step to meet the specification of optics. Conventional grinding or other polishing processes are not able to reduce surface roughness beyond a certain limit due to high forces acting on the workpiece, embedded abrasive particles, limited control over process, etc. Magnetorheological finishing (MRF) process provides a new, efficient, and innovative way to finish optical materials as well many metals to their desired level of accuracy. This paper provides an overview of MRF process for different applications, important process parameters, requirement of magnetorheological fluid with respect to workpiece material, and some areas that need to be explored for extending the application of MRF process.

Parametric analysis of MR polishing fluid using statistical technique

Magnetorheological abrasive flow finishing (MRAFF) process has been developed for nanofinishing of parts especially for complicated geometry for a wide range of industrial applications. The finishing efficiency and finishing quality of MRAFF process relies mainly on the rheological properties (i.e., yield stress and viscosity) of magnetorheological polishing (MRP) fluid which must be characterised before it is used in any specific application. These properties are responsible for bonding strength of abrasive particles surrounding carbonyl iron particle (CIP) chains. Design of MRP fluid composition and volume ratio has an impact on rheological properties and stability directly. Response surface methodology (RSM) is applied to predict the effect of volume concentration of each component on yield stress and viscosity of MRP fluid.

Some Investigations Into Magnetorheological Finishing (MRF) of Hard Materials

Magnetorheological finishing (MRF) process is one of the fine abrasive finishing processes used to get better surface finish on a semi finished part. The present work is aimed at investigating the effectiveness and validity of magnetorheological finishing process and finding out the process parameters (such as finishing time, rotational speed of carrier wheel, abrasive concentration, and working gap) and their effectiveness on surface finish characteristics. MRF process is applied on brass and nonmagnetic stainless steel workpieces which were initially finished by the grinding process. The results of experiments were statistically analyzed by response surface methodology (RSM) to form an empirical model for the responses generated during the process. Also, an attempt has been made to model and simulate the finishing operation in MRF process. Apart from this, the micro structure of the mixture of magnetic and abrasive particles in magnetorheological polishing fluid (MR Fluid) has been proposed. Thereafter the normal force on the abrasive particles is calculated from the applied magnetic field and a model for the prediction of surface roughness has also been presented. Finally, theoretical results calculated using the proposed model, have been compared with the experimental results to validate the model developed.Copyright

Some Aspects of Micro-Fabrication Using Electro Discharge Deposition Process

The growing demand for micro-parts has led to the development of many processes for their production. One of the emerging processes in this category is the electric discharge deposition process in which a micro tool in the form of a wire is used. The tool wear is increased intentionally so that the worn out material gets deposited on the substrate. Experiments are designed using response surface methodology to identify the key operating parameters (voltage, current, duty cycle and pulse on-time) and then to study their effects on the structure’s height, and width. As a concluding part, micro parts (star and letters IITK) are fabricated on the substrate material and a method is proposed and demonstrated to detach micro parts from the metallic substrate material.Copyright

Fabrication of Optical Components by Ultraprecision Finishing Processes

The demand of ultraprecision optical components is increasing extensively with the rapid development of the modern optics. The optical components used in X-ray microscopy and extreme ultraviolet lithography (EUVL) demand surface roughness of about 0.1 nm rms, a figure accuracy about 1 nm peak-to-valley (p–v) and no induced subsurface crystallographic damage. Furthermore, an aspherical surface is gaining more interest over the past few years for its favourable properties, and many new optical materials are also being developed. Fabrication of ultraprecision optical components became a great challenge to the optical fabrication industry. Aspheric optical components are generally fabricated by shaping methods followed by precision finishing processes. Near net shape of the component can be accomplished by the shaping methods (e.g. single-point diamond turning, deterministic micro-grinding, etc.). The application of optical components fabricated by this method is limited to the infrared (IR) optics owing to the presence of high-spatial-frequency surface irregularities which lead to the possibility of scattering for shorter wavelength applications. Desired surface finish, figure accuracy and surface integrity can be attained by precision finishing techniques to make it suitable for shorter wavelength applications. In the recent years, ion beam figuring, elastic emission machining, nanoparticle colloid jet machining and magnetorheological finishing are extensively used for fabrication of ultraprecision optics. In this chapter, principle mechanism of material removal and applicability of aforementioned ultraprecision finishing processes to different materials are discussed.

Fabrication of Micro-cutting Tools for Mechanical Micro-machining

Micro-cutting processes are very effective manufacturing methods for complex micro-parts used in MEMS, micro-dies, micro-structured surfaces on nonconductive materials, etc. Main challenge in employing conventional machining methods for fabrication of micro-parts and features is the unavailability of the smaller tools. Popular method like grinding is failed in miniaturizing the cutting tools because of rigidity problems. This became a driving force to research the alternative processes. Different processes like electro-discharge machining, wire electro-discharge machining, laser beam machining, focused ion beam machining, etc., are evolved to accomplish the need of new fabrication methods for micro-cutting tools. Each process has showed its capabilities and limitations through various machining experiments. In this chapter, an overview of the micro-tool fabrication processes along with their characteristics is presented. New micro-end mill tool geometry and a tool fabrication method are also presented.

Analysis of forces and surface roughness in magnetic abrasive finishing with a ball-end tool

Magnetic Abrasive Finishing (MAF) is an efficient finishing technique because of the self-adaptability of the magnetic abrasive brush in accordance with the shape of the product. To make this MAF process more capable, a new ball-ended tool has been developed to finish a non-magnetic material (brass) of semi-cylindrical shapes. Knowledge of forces acting during the finishing operation is important, as it gives an insight to the mechanism of material removal and the surface generation during finishing. A dynamometer and virtual instrumentation have been used to study and analyse the forces acting on the workpiece during the finishing operation. These forces can well explain the mechanism of surface generation, and variation in surface roughness with the parameters selected for the present research work.