Magnetic Field Assisted Finishing Process Research Articles

Achieving high accuracy of Co-Cr-Mo femoral head for improving tribological properties of hip joint prosthesis via a three-axial MFAF process

Rough surface and low precision roundness of femoral head can significantly affect tribological properties of hip joint prosthesis such as wear, von Mises stress, friction coefficient, and scratches, resulting in failure of hip joint prosthesis. In this work, firstly, an ultra-smooth surface with a high precision roundness was achieved for Co-Cr-Mo femoral heads via a three-axial Magnetic Field Assisted Finishing (MFAF) process. Secondly, the effects of a rough and smooth surface of Co-Cr-Mo femoral head on wear rate of acetabular cup were evaluated via a wear simulator test. Finally, the von Mises stresses of both femoral heads and acetabular cup were evaluated via ABAQUS finite element (FE) model. Using this process, surface roughness (Sa) and roundness (RONt) of femoral head were reduced from 0.330 to 0.032 μm and from 26.15 to 2.17 μm, respectively. A high accuracy of Co-Cr-Mo femoral head was achieved by reducing its surface roughness and roundness, which reduced the wear rate of the acetabular cup by more than 68 % compared to an unfinished femoral head. In addition, an ultra-smooth surface of femoral head dramatically reduced the von Mises stresses at the contact area of hip joint prosthesis. Results of this work demonstrate that a three-axial MFAF process is an effective method to successfully achieve high accuracy of Co-Cr-Mo femoral head with advantages of simultaneously improving tribological properties of hip joint prosthesis.

Novel Process Modeling of Magnetic-Field Assisted Finishing (MAF) with Rheological Properties

The performance of a magnetic-field-assisted finishing (MAF) process, an advanced surface finishing process, is severely affected by the rheological properties of an MAF brush. The yield stress and viscosity of the MAF brush, comprising iron particles and abrasives mixed in a liquid carrier medium, change depending on the brush’s constituents and the applied magnetic field, which in turn affect the material removal mechanism and the corresponding final surface roughness after the MAF. A series of experiments was conducted to delineate the effect of MAF processing conditions on the yield stress of the MAF brush. The experimental data were fitted into commonly used rheology models. The Herschel–Bulkley (HB) model was found to be the most suitable fit (lowest sum of square errors (SSE)) for the shear stress–shear rate data obtained from the rheology tests and used to calculate the yield stress of the MAF brush. Processing parameters, such as magnetic flux density, weight ratio of iron and abrasives, and abrasive (black ceramic in this study) size, with p-values of 0.031, 0.001 and 0.037, respectively, (each of them lower than the significance level of 0.05), were all found to be statistically significant parameters that affected the yield stress of the MAF brush. Yield stress increased with magnetic flux density and the weight ratio of iron to abrasives in MAF brush and decreased with abrasive size. A new process model, a rheology-integrated model (RM), was formulated using the yield stress data from HB model to determine the indentation depth of individual abrasives in the workpiece during the MAF process. The calculated indentation depth enabled us to predict the material removal rate (MRR) and the instantaneous surface roughness. The predicted MRR and surface roughness from the RM model were found to be a better fit with the experimental data than the pre-existing contact mechanics model (CMM) and wear model (WM) with a R2 of 0.91 for RM as compared to 0.76 and 0.78 for CMM and WM. Finally, the RM, under parametric variations, showed that MRR increases and roughness decreases as magnetic flux density, rotational speed, weight ratio of iron to abrasive particles in MAF brush, and initial roughness increase, and abrasive size decreases.

Application of magnetic field assisted finishing process for nanofinishing of freeform femoral knee joint and performance analysis of finished surface

Finishing of femoral knee joint implant is very cumbersome due to its freeform nature. In the present study, a magnetic field-assisted finishing process is employed to uniformly finish the femoral knee implant over its surface curvature at the nanometer level. Experiments are conducted to analyze the freeform surface finishing capability of magnetic field-assisted finishing tool, which proves the tool’s capability to achieve the required surface properties of a femoral knee implant. A comparative analysis between the performance of the magnetic field assisted finishing process and manually polished surface relative to tibial bearing material, that is, ultra-high molecular weight polyethylene with the help of pin-on-disc tribometer, is carried out. It will help to understand the in vivo performance of a finished femoral component of the knee joint by a magnetic field-assisted finishing process. The wear tests prove that the volume loss of the disc material while considering magnetic field-assisted finished pins (11.79 mm3) are better in all cases than the manually polished pins (27.97 mm3). The tribology test also demonstrates that femoral knee implant polished using magnetic field-assisted finishing process will face fewer problems related to wear debris. It will also reduce the problems that occur due to the mixing of debris in the bloodstream. The polishing tool provides almost uniform nanometer-level surface finishing with a standard deviation of 19.23 along the surface curvature. The minimum achieved surface roughness of the femoral knee joint is 20 nm.

Magnetic field assisted finishing (MFAF) process for internal finishing of alumina ceramic tube

Nowadays, fine surface finish is in great demand for many industrial applications. An MFAF process is discussed in this conference paper to achieve a highly finished internal surface of non-ferromagnetic Alumina ceramic tube. Conventional grinding and polishing techniques cannot be used to finish this material because they cannot achieve high surface precision and produce surface defects like micro cracks. Therefore, MFAF process is an alternative method as it minimizes the surface damage because of flexible finishing conditions. MFAF Process, has flexible abrasive brush which can easily finish complex geometry of the workpiece. The workpiece material is alumina ceramic which is in higher demand as a substrate in electronic device applications. The MFAF process was done on alumina ceramic tube and 3 parameters, each having 2 different levels was selected. The parameters considered in the study are chuck speed (rpm), quantity of Diamond abrasive and iron power, machining time. 4 experiments with different levels of parameters were conducted. After finishing experiment using MINITAB 19 software, optimum parameters were determined. From the results of experiment, it was concluded that quantity of diamond abrasive and iron powder did not have much influence on finishing time compare to the chuck speed (r.p.m).

Optimization of magnetic field assisted finishing process during nanofinishing of titanium alloy (grade-5) implant using soft computing approaches

ABSTRACT The present study explores the potential of magnetic field assisted finishing (MFAF) in precise finishing of femoral knee implant made of bio-titanium alloy at the nanometric level. The process parameters, viz. rotational speed of tool, feed rate and carbonyl iron particle (CIP) concentration of MFAF have significant influence on the final surface topography of implants and thus selection of optimal set of their values is a difficult but an important task. In the present work, central composite rotatable design of response surface methodology is considered for nanofinishing of titanium alloy based femoral knee implants. Based on the experimental results, a polynomial regression prediction model for surface roughness is established in terms of MFAF process parameters. The fuzzy logic model with the help of ANOVA analysis is employed to analyze the effect of individual and interaction of parameters on surface roughness of implants. Finally, for further optimizing the final surface roughness of knee implant and determining the best settings of MFAF parameters, an improved salp swarm algorithm (ISSA) is proposed by introducing two important enhancements in basic SSA. The results reveal that SSA and ISSA metaheuristics achieved an improvement in final surface finish of knee implant by 4.04% and 14.24%, respectively, in comparison to default experimental trials during finishing.

Enhanced magnetic abrasive finishing of Ti–6Al–4V using shear thickening fluids additives

The available magnetic field assisted finishing process is considered as the critical stage for improvement of workpiece surface quality. This paper aims to investigate the key quality performance of an enhanced magnetic abrasive finishing in achieving nanolevel finish on Ti–6Al–4V workpieces with initial micrometer surface roughness values. The finishing media, combining the intelligent shear thickening fluids (STFs), carbonyl iron particles and SiC particles, is developed. Finishing experiments for Ti–6Al–4V workpieces are conducted using an established platform, aiming to investigate the effects of varying STFs concentration, working gap, feed rate and spindle rotational speed. It is observed from the experimental results that the developed finishing media is effective for surface finishing comparing to the finishing media without STFs. The surface roughness of 54 nm was achieved from the initial value of 1.17 μm, which improved by over 95%, under the experimental conditions of 0.8 mm working gap, 15000 mm/min feed rate, 900 rpm spindle rotational speed and 15 wt% STFs. Surface observations showed that a smooth surface without obvious scratches was obtained.

Fused silica contamination layer removal using magnetic field‐assisted finishing

AbstractFused silica optics used in lasing systems requires a high laser‐induced damage resistance. Processes typically used to polish fused silica lenses induce subsurface and surface damage that collect ceria abrasive, creating a layer of contamination. The contamination can be a precursor to laser damage during use. A preliminary study showed the feasibility of magnetic field‐assisted finishing (MAF) for polishing fused silica and suggested possible beneficial effects of the MAF‐polished surface on the laser‐induced damage threshold (LIDT). This paper proposes a method to examine the fundamental polishing characteristics of MAF for fused silica. Using the proposed method, this paper explores the material removal characteristics of the MAF process and improves the understanding of the MAF polishing mechanism. The 45% improvement of LIDT shows the efficacy of MAF for removing the contamination layer of fused silica surfaces with minimal changes in the surface roughness.

Force analysis during spot finishing of titanium alloy using novel tool in magnetic field assisted finishing process

Magnetic field assisted finishing process is a nanofinishing process which uses magnetic field for precise control of finishing forces. Magnetorheological fluid mixed with diamond abrasive particles in base medium of glycerol, hydrofluoric acid, nitric acid, and deionised water is used as the polishing medium. The novel tool is a magnet fixture made of mu-metal which is used to hold the magnet during finishing. In the present experimental study, finishing at a spot on flat titanium alloy is carried out to analyse the forces involved in the finishing. Normal force is the main force responsible for the indentation by the abrasive particles on the workpiece surface. Tangential force helps in removing indented material. The measured normal force and tangential force during the spot finishing are 3.285 N and 0.43 N, respectively. The final surface roughness achieved after spot finishing is 10 nm from initial surface roughness of 200 nm. The percentage improvement in surface roughness is 95%.

Magnetic field assisted finishing process for super-finished Ti alloy implant and its 3D surface characterization

Titanium alloy is used in medical industries due to its biocompatibility. Requirement of implant’s surface roughness and surface topography depends mainly upon its application. In the present study, application of titanium alloy is considered as femoral knee joint implant. The capability of magnetic field assisted finishing (MFAF) process and the polishing tool to provide implant worthy surface is analyzed here. In MFAF process, magnetorheological fluid mixed with abrasive powder in acidic base medium is used as the finishing medium. Characterization of the finished surface is carried out by analyzing 3D surface roughness parameters. The selected 3D surface parameters ( Sa, Spk, Sk and Svk) are considered due to their importance concerning load-bearing articulating surface of knee joint implant. Statistical design of experiment is used for experimental study and subsequently process parameters are optimized. From experimental investigation, the values of Sa, Spk, Sk and Svk are obtained as 11.32 nm, 15.82 nm, 6.51 nm and 41.15 nm, respectively, at optimum process parameter condition. The optimum process parameter values are 901 rpm of the tool, 0.60-mm working gap and 4.30 hrs of finishing time. The obtained values of 3D surface roughness parameters are in the nanometer range and the surface topography will render better wear properties, performance and longer implant life. Further confirmation experiments support the optimized values. The effect of individual process parameter on output responses is also analyzed.

A novel media properties-based material removal rate model for magnetic field-assisted finishing

Magnetic field assisted finishing (MFAF) is a category of non-conventional finishing processes that use magnetic field to manipulate finishing media typically consisting of magnetic particles and non-magnetic abrasives suspended in a carrier fluid. In order to better control the process, an improved understanding of the actual removal process is needed. This paper introduces a new material removal rate model for magnetic field-assisted finishing (MFAF) that aims to do so. The model considers the complexity of finishing media used in MFAF processes, where two different types of particles are present and interact with each other. The proposed material removal rate expression is based on contact mechanics and is a function of number of active magnetic particles, number of active abrasives, force per magnetic particle, and force per abrasive. Expressions for particle numbers were developed by considering an ideal face-centred cubic configuration for the magnetic particle network, while expressions for forces were developed based on a proposed framework for the particle interactions. The model was verified experimentally for a double-magnet MFAF process by varying the abrasive size and abrasive concentration. When the abrasive size was increased from 0.6 μm to 15 μm, the material removal rate decreased, consistent with the theoretical trend given by the model. Then, when abrasive concentration, given by the abrasives-to-carbonyl-iron volumetric ratio, was increased from 0 to 0.768, the material removal rate initially increased and then reached a maximum when the volume ratio is 0.259 before decreasing with further increase of the volume ratio. This is also in agreement with the theoretical trend given by the model.

Simulation and experimental investigation of finishing forces in magnetic field assisted finishing process

ABSTRACTFinishing forces in magnetic field assisted finishing process are normal force responsible for indentation and tangential force responsible for removal of indented materials. Analysis of finishing forces helps to understand the process mechanism and to control the process precisely. Simulation of finishing forces in magnetic field assisted finishing process is conducted using two finite element method based software packages. The experimental study confirms the simulation results as the difference between the obtained results from both the study is very small. A model is simulated for material removal using magnetorheological fluid having diamond abrasive particles on Ti alloy workpiece surface to predict material dislodgement during finishing. The significance of each process parameters is found out with the help of statistical analysis. The significant process parameters for normal force are abrasive volume concentration, working gap and carbonyl iron particle (CIP) volume concentration and for tangential force are tool rpm, working gap, and CIP volume concentration. It is perceived that the normal force rises with a surge in CIP concentration and reduction in abrasive concentration in MR fluid, working gap and tool rpm. The magnitude of tangential force rises with increased tool rpm, CIP concentration, abrasive concentration and decreased working gap.

Investigation on Surface Integrity of Rapidly Solidified Aluminum RSA 905 by Magnetic Field-Assisted Finishing.

RSA 905, a rapidly solidified aluminum alloy, has been widely utilized in optical, automotive, and aerospace industries owing to its superior mechanical properties such as hardness and strength compared to conventional aluminum alloys. However, the surface finishing of RSA 905 to achieve submicron surface roughness is quite challenging and was rarely addressed. This paper presents an experimental and analytical study on magnetic field-assisted finishing (MFAF) of RSA 905 through a systematic investigation on surface integrity in relation to the MFAF process parameters. The effect of abrasive and polishing speed conditions on material removal and surface roughness was quantitatively investigated. The surface and subsurface quality were evaluated by optical microscope and scanning electron microscope (SEM) observations, residual stress measurement, surface microhardness and tribology test. The results show that relatively high material removal and low surface roughness were obtained under conditions using the SiC abrasive with a grit size of 12 µm at polishing speed of 400 rpm or using the Al2O3 abrasive with a grit size of 5 µm at polishing speed of 800 rpm. Heat melt layer caused by wire electrical discharge machining (EDM) during the sample preparation was removed by MFAF without inducing new subsurface damage. The MFAF process also helps release the surface residual stress and improve the tribological performance although the surface microhardness was slightly reduced.

Toolpath generation and finishing of bio-titanium alloy using novel polishing tool in MFAF process

Nanofinishing of biomaterials is a necessary process to lengthen the prosthetic life and performance. Here, Magnetic Field Assisted Finishing (MFAF) process is used to finish biomaterials in the nanometer level. MFAF process uses Magnetorheological (MR) fluid mixed with abrasive particles as the polishing medium. In this study, titanium is used as the workpiece material. A specially designed tool is used to carry out the nanofinishing process. Two types of path planning i.e. parallel and spiral tool path are adopted during finishing. The surface roughness and surface texture differ for each generated tool path. The surface roughness generated from each of the path planning processes is analyzed and it is found that parallel toolpath generates lowest surface roughness (~10 nm) with better surface texture than spiral toolpath. Hence, the parallel toolpath is considered as the optimum toolpath for finishing biomaterials in MFAF process. Experimental investigations using parallel tool path are carried out to explore the capability of the developed novel tool along with the determination of the optimum range of the process parameters to explore finishing capability. Preliminary experimental study shows that best surface finish and surface topography is achieved using 1200 rpm tool rotational speed, 1 mm working gap, and 6.30 h. finishing time.

Soft computing techniques to model and optimize magnetic field-assisted finishing process and characterization of the finished surface

In magnetic field-assisted finishing process, magnetorheological polishing fluid is used for precision polishing of freeform surfaces in the nanometer range. An efficient model is derived to accurately relate the input and output process parameters for better prediction of finishing performance. In this study, the relationship between the input and output process parameters of magnetic field-assisted finishing process is established using back-propagation neural network technique. Also, a close comparison between the regression analysis and neural network model has been carried out. The simulation results from neural network model better matches with the experimental data. Hence, this particular neural network model can be utilized to predict the response variables. A further optimization study using genetic algorithm and simulated annealing techniques is carried out to optimize the input process parameters for achieving maximum finishing performance. It is found that the results obtained from the genetic algorithm is more accurate and matches with the experimental results than the simulated annealing. Further, a characterization study of the finished workpiece surface is carried out which shows that MFAF process can achieve surface finish in the nanometer range having a minimum surface roughness value of 70 nm.

Design and fabrication of a novel polishing tool for finishing freeform surfaces in magnetic field assisted finishing (MFAF) process

Surface finish is a critical requirement for different applications in industries and research areas. Freeform surfaces are widely used in medical, aerospace, and automobile sectors. Magnetic field assisted finishing process can be used very efficiently to finish freeform surfaces. In this process, magnetorheological fluid is used as the polishing medium and permanent magnet is used to control its rheological properties to generate finishing force during polishing. To avail sufficient magnetic field in the finishing zone, it is necessary to design an optimum polishing tool. In the present study, a specially designed polishing tool is designed using a finite element based software package (Ansys Maxwell®) based on Maxwell equations. At first, dimension of the permanent magnet is determined for designing optimum tool geometry. After that, dimension and configuration of the magnet fixture are optimized. A special type of metal named mu-metal which is a nickel-iron based alloy is selected for magnet fixture due to its magnetic-field shielding property. Mu-metal directs the magnetic flux lines in such a way that in the finishing zone the magnetic flux can be concentrated on the workpiece surface required for finishing. Also, the Mu-metal magnet fixture shields the magnetic field from outside environment so that MR fluid as well as any surrounding magnetic materials do not stick to the polishing tool. Experiments are carried out to validate the Maxwell simulation results to compare the magnetic flux distribution on the workpiece surface which shows good agreement between them. Also, finishing of flat titanium workpieces are carried out and it is found that the novel polishing tool has the capability to finish the workpieces in the nanometer range.

Simulation of Magnetic Field Assisted Finishing (MFAF) Process Utilizing Smart MR Polishing Tool

Magnetic field assisted finishing process is an advanced finishing process. This process is capable of producing nanometer level surface finish. In this process magnetic field is applied to control the finishing forces using magnetorheological polishing medium. In the current study, permanent magnet is used to provide the required magnetic field in the finishing zone. The working gap between the workpiece and the magnet is filled with MR fluid which is used as the polishing brush to remove surface undulations from the top surface of the workpiece. In this paper, the distribution of magnetic flux density on the workpiece surface and behaviour of MR polishing medium during finishing are analyzed using commercial finite element packages (Ansys Maxwell® and Comsol®). The role of magnetic force in the indentation of abrasive particles on the workpiece surface is studied. A two-dimensional simulation study of the steady, laminar, and incompressible MR fluid flow behaviour during finishing process is carried out. The material removal and surface roughness modelling of the finishing process are also presented. The indentation force by a single active abrasive particle on the workpiece surface is modelled during simulation. The velocity profile of MR fluid with and without application of magnetic field is plotted. It shows non-Newtonian property without application of magnetic field. After that the total material displacement due to one abrasive particle is plotted. The simulated roughness profile is in a good agreement with the experimental results. The conducted study will help in understanding the fluid behavior and the mechanism of finishing during finishing process. Also, the modelling and simulation of the process will help in achieving better finishing performance.

A 2D CFD simulation of MR polishing medium in magnetic field-assisted finishing process using electromagnet

Magnetic field-assisted finishing (MFAF) is developed for superfinishing of hard materials for both internal/external geometries with a wide range of industrial applications. This process makes use of a flexible polishing tool comprising the magnetorheological polishing (MRP) medium under varying magnetic field of an electromagnet. The relative motion between the polishing medium and the workpiece surface provides the required finishing action. The finishing performance of MFAF process depends on the axial and radial stresses generated due to the flow of magnetically stiffened MRP medium. A 2D computational fluid dynamics (CFD) simulation of MRP medium inside workpiece fixture is performed to calculate the stresses developed during polishing. The microstructure of the mixture of magnetic and abrasive particles in MRP medium is proposed in order to calculate the forces acting on an active abrasive particle. Modeling of surface finish is performed after analyzing the surface roughness profile data obtained from the surface roughness measuring instrument. They are found to agree well with the experimental results.

Estimation of magnetic and rheological properties of MR polishing fluid and their effects on magnetic field assisted finishing process

The finishing efficiency in magnetic field assisted finishing (MFAF) process mainly depends on the rheological properties of magnetorheological (MR) polishing medium. A detailed rheological study of MR polishing fluid at different volume concentration of fluid constituents and magnetic field is conducted to predict their contribution on yield stress and viscosity. Magnetic field has the highest contribution followed by carbonyl iron particles (CIPs) concentration to the yield stress and viscosity. It is observed that Herschel–Bulkley model better fits the rheological data than other two models. Also, it has been found that when total solid contents of MR polishing fluid exceeds more than 35%, there is a decrease in the yield stress. From magnetic characterisation, it is observed that saturation magnetisation increases with CIP concentration and decreases with abrasive concentration. The surface finish of stainless steel workpiece improves with an increase in the yield stress and viscosity at higher magnetic field and CIP concentration.

Nanoscale Surface Modifications by Magnetic Field-Assisted Finishing

A magnetic field-assisted finishing (MAF) process has been developed to reduce the sidewall surface roughness of the 5–20 μm wide curvilinear pores of microelectromechanical systems micropore X-ray optics to <1 nm Rq. Although the feasibility of this process has been demonstrated on these optics, a clear understanding of the MAF process' material removal mechanisms has not been attained. In an attempt to discover these mechanisms, the MAF process is applied to a flat workpiece, allowing for direct observation and tracking of changes to distinctive surface features before and after MAF. Atomic force microscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy are used to analyze the surface morphology and composition with respect to finishing time. These observations suggest that the MAF process modified the surface, reducing surface roughness (from 0.8 nm to 0.6 nm Rz on silicon) by removing relatively low-wavelength surface features. Moreover, the MAF process appears to modify the surface mechanically.

Effect of fluid composition on nanofinishing of single-crystal silicon by magnetic field-assisted finishing process

Magnetic field-assisted finishing is a deterministic process particularly used for finishing optical materials. The main component of this process is magnetorheological fluid which consists of magnetic particles, abrasive particles, carrier fluid such as water or oil, and some additives to impart stability. Under the influence of magnetic field (generated by either permanent magnet or electromagnet), magnetic particles form chain-like structure and support many abrasive particles to perform finishing of workpiece surface. Selection of abrasive and carrier fluid in this process is one of the major concerns which play vital role on finishing mechanism and surface quality. In the present experimental investigation, aluminum oxide and cerium oxide are chosen as abrasives while deionized water and paraffin oil are selected as carrier fluids. A set of experiments are carried out to study chemical interactions of abrasive and carrier fluid on the silicon surface. A rheological study is carried out to study behavior of magnetorheological fluid fluids under magnetic field.