Rotational Magnetorheological Abrasive Flow Finishing Research Articles

A study on in-vitro behaviour of stainless steel 316L subjected to rotational magnetorheological abrasive flow finishing process

In Rotational Magnetorheological Abrasive Flow Finishing (R-MRAFF) process, Magnetic Field Intensity (MFI) is the primary factor for the formation of ferrous chains which is responsible for finishing. Changing the pole distance between magnets to achieve a difference in MFI values will alter the strength of the ferrous chains. In this study, three different MFI values such as 0.34, 0.36, and 0.40 Tesla were chosen for finishing on Stainless Steel 316L (SS 316L). Surface wettability, bio-corrosion, and hemocompatibility studies were conducted to investigate the in-vitro behavior of SS 316L. The wettability of the implants changed from hydrophobic (100.92°) to hydrophilic (83.452°) surface as the MFI value increased. Bio-corrosion studies revealed improved corrosion resistance for R-MRAFF process finished samples, with the corrosion rate reduced from 3.693 to 0.967 μm year−1. Hemocompatibility of SS 316L was improved with reduced platelet adhesion when compared to the pristine sample.

Design and development of ultrasonic assisted-rotational magnetorheological abrasive flow finishing (UA-RMRAFF) process

The rotational-magnetorheological abrasive flow finishing (R-MRAFF) process, as one of the derivatives of the abrasive flow finishing (AFF) process, has a high potential for surface modification. However, the R-MRAFF process is a major challenge in terms of finishing time. The present study aims to propose ultrasonic vibration has been proposed as a technical solution to deal with the technological challenges of the R-MRAFF process. A new finishing method called the ultrasonic assisted-rotational magnetorheological abrasive flow finishing (UA-RMRAFF) process has been developed for the first time in which ultrasonic vibrations are applied to the workpiece perpendicular to the magnetorheological polishing (MRP) fluid flow direction. For this purpose, the workpiece was first kept in dynamic condition. Then, an ultrasonic horn was designed using the finite element method (FEM) to apply maximum amplitude to the workpiece. To evaluate the finishing efficiency of the UA-RMRAFF process, experiments were conducted on the internal finishing of Al2024 tubes at different finishing times for investigating and observing its effect on surface roughness (Ra) and material removal (MR). In addition, a comparative study was performed between the UA-RMRAFF and R-MRAFF processes in terms of % change in Ra (%ΔRa) and % improvement in MR. Experimental findings illustrate that the UA-RMRAFF process provides a uniform and fine surface finish without surface defects such as a mirror up to the range of 25.5 nm, in addition to increasing MR. Based on the results of the comparative study, the UA-RMRAFF process performs surface modification faster than that of the R-MRAFF process. While confirming these findings, the morphological and topographic analysis of the surface of the finished samples emphasizes that the main difference between the UA-RMRAFF and R-MRAFF processes is in the sinusoidal motion path of abrasive particles on the workpiece surface asperities, which clearly shows the effect of ultrasonic vibrations.

Experimental investigations into the nano-finishing of Al2024 tubes using the rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

Aluminum alloy 2024 (Al2024) tubes have extensive applications in the aerospace industry; however, finishing their interior surfaces is a big challenge. In this case, many traditional and advanced machining processes are inefficient due to the limitations of machining tools. To overcome these challenges and limitations, rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been proposed. In this process, magnetorheological polishing (MRP) fluid, experiences a rotational motion in addition to the reciprocating motion on the workpiece surface asperities. In the present work, the effect of the R-MRAFF processing time on the internal finishing of Al2024 tubes has been investigated experimentally in terms of two essential parameters; surface roughness and material removal. In this regard, an industrial prototype of the R-MRAFF process has been developed. Experimental results express the efficiency of the R-MRAFF process for nano-finishing of Al2024 tubes. The surface roughness and material removal values at a processing time of 15 min are 26.3 nm and 41 mg, respectively. In addition to the morphological observations, the surface topography results emphasize the removal of peaks by the R-MRAFF process, besides creating deep scratches with negative skewness on the surface texture of Al2024 tubes, which results in increased oil holding capacity.

Magnetorheological finishing of small gear teeth profiles using novel workpiece fixture

Miniature gears are essential components of transmitting power in tiny motors used in the aviation, automobile, and healthcare sectors etc. Because of the intricacy of its shape, nanofinishing of tiny gear is a tough job. The rotational magnetorheological abrasive flow finishing (R-MRAFF) technique is a new hybrid methodology for the generation of nano-meter range surface finishing. These surfaces reduce friction between integrating parts, extending their life span. In the current study, a model for simulating the impacts of the R-MRAFF technique was developed using finite element (FE) analysis software, namely COMSOL® Multiphysics. The impacts of various process factors on the fluid flow characteristics while finishing the gear component are investigated using magnetostatic fluid flow analysis of magnetorheological polishing fluid (MRPF) in 3D computational domain of new workpiece fixture. To evaluate the forces operating in R-MRAFF technique, a viscosity model for MRP fluid flow around a complicated component (small steel gear) in an outside magnetic field is recognized and simulated. The magnetic field has a major impact on processing effectiveness by controlling the MRPF viscosity. During the polishing of the gear component, the surface finish attained at various places on working surfaces is uniform, which is confirmed by surface characterization of teeth profiles of small gear.

Effect of process parameters on machinability, hemocompatibility and surface integrity of SS 316L using R-MRAFF

Surface finish at nanometric scale is imperative for biomedical implants made up of stainless steel 316L (SS 316L) and titanium alloy to ensure the biocompatibility. However, such fine finishing is quite difficult to process. A rotational magnetorheological abrasive flow finishing process is used for nano-finishing. Rotational magnetorheological abrasive flow finishing (R-MRAFF) is one of the processes to achieve nano-level finishing. In this present study, a rotating die has been developed to perform the R-MRAFF processes with four rectangular-shaped permanent magnets held at an angle of 90° to one another. A new method for producing a variable magnetic field was investigated in this study by increasing or decreasing the distance between permanent magnets in the rotating die and workpiece fixtures. The increase in the distance between permanent magnets in rotating die and workpiece fixture leads to a decline in the value of material removal rate (MRR) as well as a percentage reduction in surface roughness (%ΔRa). This validates the importance of magnetic field intensity in the R-MRAFF process. A central composite design (CCD) in the response surface methodology (RSM) is employed to study the effect of process parameters on the response variables. The effect of the process parameter was evidenced with the help of the ANOVA technique. Optimization was carried out with constraints of maximizing both output response variables, the optimum MRR and %ΔRa, which were found as 2.02 mg/s and 50.66%. To quantify the effect of surface roughness on hemocompatibility, a platelet adhesion study was investigated. The platelet adhered area starts to decrease with the reduction in the surface roughness from 319 to 167 nm.

An overview of magnetorheological polishing fluid applied in nano-finishing of components

Surface quality is the most crucial factor affecting the product lifespan and performance of any component. Most earlier technologies display accuracy in the micrometre or submicrometre range, surface roughness in the nanometre range, and almost no surface defects in the production of optical, mechanical and electronic parts. Such finishing methods incorporate a magnetic field to control the finishing forces using magnetorheological fluid as the polishing medium. Magnetorheological fluid (MR) consists of ferromagnetic and abrasive particles. It is a type of modern intelligent fluid. An optimum selection of magnetorheological fluid constituents and their volume concentration plays an essential role for the ultra-fine finishing of newly developed engineering products. Rheological characteristics of magnetorheological fluid can change rapidly and effortlessly with the support of an activated magnetic field. Traditional finishing methods are comparatively inferior in finishing complex freeform surfaces, due to the lack of controlling finishing forces and limitations of polishing tool movement over the complex freeform contour of the components. There are different types of processes based on the magnetorheological fluid including magnetorheological finishing, magnetorheological abrasive flow finishing, rotational magnetorheological abrasive flow finishing and ball end magnetorheological finishing. This article discusses the development of different types of magnetorheological-fluid-based finishing processes and their modes of operation. The MR fluid devices developed in the last decade are thoroughly reviewed for their working principles, characteristics and applications. This article also highlights the study of rheological characterization of magnetorheological fluid and its applications in different polishing methods appropriate for finishing various complex freeform components.

Optimization of process parameters in nano-finishing of Co-Cr-Mo alloy knee joint

ABSTRACT Process of obtaining a high surface finish value, say Ra value, with the lowest standard deviation on the freeform surfaces especially on knee joint using the conventional finishing processes is an exigent task. Achieving a throughout uniform surface finish using a process called Rotational Magneto-rheological Abrasive Flow Finishing (R-MRAFF) is found to be a suitable approach with a designed, developed, and fabricated tool as an inverse replica. An inverse replica of femoral as a tool used for finishing where the medium flow is almost constant (minimum possible variation in velocities). To optimize the parameters, an effort has been made for reducing the time and achieving the more consistent surface finish. Total finishing time is reduced from 64.7 h to 2.0 h with a very low standard deviation of the final Ra value range over the surface of femoral. The minimum roughness of 50 nm is obtained which was originally 190.5 nm.

Development of inverse replica fixture for nano-finishing of knee joint using R-MRAFF process

Rotational-Magnetorheological Abrasive Flow Finishing (R-MRAFF) process is a technique of nano-finishing in general and free-form/sculptured surfaces in particular. Knee joint is one such example of free-form surface which is used by orthopedic surgeons. Knee joints are usually made of cobalt chromium alloy which is bio-compatible material, and it is difficult to finish. The present work deals with the development of an inverse replica for a knee joint. This inverse replica is used as a fixture so that the fluid can flow with constant velocity within the confined gap between the workpiece and inner surface of the fixture in order to achieve uniform nano-level finish. Using this technique, variation in the surface roughness ( Ra) over the knee joint surface can be minimized and productivity can be enhanced. The finishing efficiency of the R-MRAFF process depends on the input parameters such as extrusion pressure, number of finishing cycles, rotational speed of the magnet, etc. These parameters should be controlled and optimized for precision finishing which is the main objective of the present research work. The minimum average Ra of 52 nm is achieved from the initial average Ra of 194 nm on the knee joint surface. The percentage change in Ra (73.20%) was achieved using the proposed method.

Differential finishing of freeform surfaces (knee joint) using R-MRAFF process and negative replica of workpiece as a fixture

ABSTRACTIt is difficult and challenging to achieve uniform nanoscale surface finish in the contact zone, particularly on freeform (or sculptured) surfaces having different curvatures at different locations. Femoral (or, Knee joint component) is one of such biomedical freeform component which has complex profile along its curvature. Surface conditions of a femoral decide the life of the implant and they play a crucial role in its functionality. The variation in surface roughness of the femoral should be minimum in the contact zone. For this purpose, a special tooling is being proposed for rotational magnetorheological abrasive flow finishing (R-MRAFF) process. A negative replica of the workpiece (knee joint) as a tool (or a fixture) is used so that the medium flow velocity in the fluid flow channel is almost constant (or minimum possible variations) along the medium flow direction. It is able to do differential finishing also along the curvature. In addition, pulsating magnetic field has been used to generate vibrations in the medium in the finishing zone so that the possibility of fresh abrasive particles interacting with the surface of femoral is high. The surface finish has been achieved ranging from 26 nm to 62 nm using the proposed finishing technique and negative replica of the workpiece (femoral) as a fixture.

Preliminary investigations into nano-finishing of freeform surface (femoral) using inverse replica fixture

It is difficult to achieve nano-level surface finish on freeform surfaces. Femoral (knee joint) is one of such components which has freeform surface. Finishing operations are very costly and time consuming. Surface finish of femoral plays a major role in its functionality, efficiency, and life expectancy. To have uniform (or minimum variation) surface roughness value along its curvature, an inverse replica of the femoral component as a fixture has been designed and fabricated so that the magnetorheological (MR) fluid velocity is approximately constant in different areas of the femoral. In this work, an attempt has been made for achieving comparatively more uniform finish on different surfaces and reducing the time required for finishing femoral. For this, a special tooling is used in rotational-magnetorheological abrasive flow finishing (R-MRAFF) process. Different extrusion pressures have been used to examine the effect on percentage change in Ra, finishing rate, and final surface finish of the femoral in both directions, X and Y. Minimum surface roughness of 78 and 89 nm has been achieved on femoral from the initial surface roughness of 172 and 178 nm in X- and Y-directions, respectively.

Experimental Investigations into Nano-finishing of Freeform Surfaces Using Negative Replica of the Knee Joint

To achieve high level of surface finish is a difficult task especially in complex shaped components, 3-D components and components with freeform (or sculptured) surfaces. Knee joint is one of such components which has freeform surfaces. Surface finish is very expensive and time consuming operation. Moreover, surface finish of a knee joint plays a crucial role in its functionality and life expectancy. The range of variation of surface roughness value on the different faces is required to be minimum. With these objectives in view, Rotational - magnetorheological abrasive flow finishing (R-MRAFF) process is being proposed with special tooling to achieve the above said objectives.To have uniform (or minimum variation) surface roughness values on all the four faces, a negative replica of the knee joint has been fabricated as a fixture so that the medium flow velocity is approximately constant throughout the length of the joint. Secondly, pulsating magnetic field is used to create vibrations in the abrasive particles so that the probability of new abrasive particles interacting with the knee joint surface, is high.

Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

Freeform complex surfaces have become an inevitable part of many devices to perform specific functions. Some of these components require nanolevel surface roughness value to meet the desired requirements in their applications. Finishing of freeform surfaces to nanometer surface roughness value is always difficult for any process. Rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been applied so far for finishing internal surfaces of relatively simple geometry. In this work, an attempt has been made to improve external topography of freeform surfaces using this process. Large hydrodynamic pressure coupled with magnetic fluid is the principal idea behind these experiments. A smooth mirror like finished surface is achieved with improved finishing rate (nanometer/min) by controlling two motions (axial and rotational) simultaneously on stainless steel workpiece similar to knee joint implant. Magnetorheological polishing fluid with different mesh sizes of abrasive particles and at different extrusion pressures is used to reduce final surface roughness value, to increase uniformity of surface finish on the freeform surface and to enhance finishing rate. Surface roughness ranging from 35 to 78nm is achieved at various locations as compared to larger variation in Ra value obtained in the earlier research work.

Nanofinishing of flat workpieces using rotational–magnetorheological abrasive flow finishing (R-MRAFF) process

A new finishing process named as “rotational–magnetorheological abrasive flow finishing (R-MRAFF)” has been proposed to enhance the finishing performance of MRAFF process. In this process, a rotation cum reciprocating motion is provided to the polishing medium by a rotating magnetic field and hydraulic unit. By intelligently controlling these two motions, a uniform smooth mirror-like finished surface with improved material removal rate and finishing rate (nanometer per cycle) is achieved for both stainless steel and brass workpieces. From the preliminary experiments, it is found that R-MRAFF process produces better results than MRAFF. Experiments have been planned using design of experiments technique. Analysis of variance is conducted to find out the contribution of each model term affecting percent improvement in surface finish. The optimum finishing conditions are identified from optimization study. The present study shows that the combinations of rotational speed of the magnet and its square term together have the highest contribution to the percentage improvement in surface roughness. Other significant parameters in the order of decreasing percent contribution to the change in surface roughness value are finishing cycles, extrusion pressure, and fluid composition. The best surface finish obtained on stainless steel and brass workpieces with R-MRAFF process are 110 and 50 nm, respectively. From the scanning electron micrographs and atomic force micrographs, it has been observed that the abrasive cutting marks generate cross-hatch pattern on the surface finished by R-MRAFF process.

The Out-of-Roundness of the Internal Surfaces of Stainless Steel Tubes Finished by the Rotational–Magnetorheological Abrasive Flow Finishing Process

This article reports the experimental findings about the improvement in out-of-roundness (OOR) of stainless steel tubes finished by Rotational–Magnetorheological Abrasive Flow Finishing (R-MRAFF) process. In this process, a rotating motion is provided to the magnetorheological polishing (MRP) medium by means of a rotating magnetic field, and simultaneously, a reciprocating motion is provided to the polishing medium by a hydraulic unit. By controlling these two motions, nano level uniform smooth mirror like finished surface has been achieved and simultaneously OOR of internal surface of tube is reduced. Experiments are planned according to the central composite rotatable design of response surface methodology based on the selected range of process parameters obtained from the preliminary experiments. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting OOR improvement is calculated. It has been found that R-MRAFF process potentially reduces roundness error of axisymmetric parts (maximum improvement in OOR=2.04 µm) improving their reliability and wear resistance. The present study shows that, OOR improves with an increase in the rotational speed of the magnet up to an optimum value beyond which the improvement in OOR reduces. From the scanning electron micrographs and atomic force micrographs it has been found that the abrasive cutting marks in R-MRAFF process generate cross-hatch pattern which helps in oil retention in cylindrical workpieces to reduce friction.