Development of magnetorheological fluid-based process for finishing of ferromagnetic cylindrical workpiece

A magnetorheological fluid-based process is developed for the internal surface finishing of ferromagnetic cylindrical workpiece. The existing finishing processes based on magnetorheological fluid are not equipped to finish the internal ferromagnetic cylindrical surface significantly as it obtained higher magnetic flux density than the MR polishing fluid. At present, magnetorheological fluid-based finishing tools are designed to ensure the maximum magnetic flux density always present on the outer finishing tool core surface as compared to internal surface of ferromagnetic cylindrical workpiece surface. To validate this present principal idea, the magnetostatic finite element analysis has been performed on the newly designed finishing tools. The preliminary experiments have also been conducted to evaluate the finishing performance with the two newly designed finishing tools. The percentage reduction in surface roughness (R_a) values with I-shaped tool core is found as 65–78% after 150 min of finishing, whereas, with rectangular shaped tool core is found as 78–81% after 90 min of finishing. The results clearly revealed that the present finishing tool with rectangular shaped core is more suitable for uniform significant finishing of ferromagnetic cylindrical internal workpiece than the I-shaped core. The developed process can be useful in finishing of cylindrical mold and dies, hydraulic cylinder, barrel for injection molding, etc.     

NANO-FINISHING OF STAINLESS-STEEL TUBES USING ROTATIONAL MAGNETORHEOLOGICAL ABRASIVE FLOW FINISHING PROCESS

A new polishing method called Rotational (R)-Magnetorheological Abrasive Flow Finishing (MRAFF) process has been proposed by rotating a magnetic field applied to the Magnetorheological polishing (MRP) medium in addition to the reciprocating motion provided by the hydraulic unit to finish internal surface of cylindrical stainless steel (non-magnetic) workpiece. By intelligently controlling these two motions uniform smooth mirror-like finished surface in the range of nm has been achieved. For parametric analysis of the process, the experiments have been planned using design of experiments technique and response surface regression analysis is performed to analyze the effects of process parameters on finishing performance. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting percent improvement in surface finish is calculated. The experimental results are discussed and optimum finishing conditions are identified from optimization study. The present study shows that rotational speed of the magnet has most significant effect on output response (percentage improvement in surface roughness, %ΔR _a ). The best surface finish obtained on stainless steel workpiece with R-MRAFF process is 16 nm.     

Modeling and simulation of magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is one of the advanced finishing processes, which produces a high level of surface quality and is primarily controlled by a magnetic field. In MAF, the workpiece is kept between the two poles of a magnet. The working gap between the workpiece and the magnet is filled with magnetic abrasive particles. A magnetic abrasive flexible brush (MAFB) is formed, acting as a multipoint cutting tool, due to the effect of the magnetic field in the working gap. This paper deals with the theoretical investigations of the MAF process. A finite element model of the process is developed to evaluate the distribution of magnetic forces on the workpiece surface. The MAF process removes a very small amount of material by indentation and rotation of magnetic abrasive particles in the circular tracks. A theoretical model for material removal and surface roughness is also proposed accounting for microcutting by considering a uniform surface profile without statistical distribution. Numerical experiments are carried out by providing different routes of intermittent motion to the tool. The simulation results are verified by comparing them with the experimental results available in the literature.     

Modeling and simulation of magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is one of the advanced finishing processes, which produces a high level of surface quality and is primarily controlled by a magnetic field. In MAF, the workpiece is kept between the two poles of a magnet. The working gap between the workpiece and the magnet is filled with magnetic abrasive particles. A magnetic abrasive flexible brush (MAFB) is formed, acting as a multipoint cutting tool, due to the effect of the magnetic field in the working gap. This paper deals with the theoretical investigations of the MAF process. A finite element model of the process is developed to evaluate the distribution of magnetic forces on the workpiece surface. The MAF process removes a very small amount of material by indentation and rotation of magnetic abrasive particles in the circular tracks. A theoretical model for material removal and surface roughness is also proposed accounting for microcutting by considering a uniform surface profile without statistical distribution. Numerical experiments are carried out by providing different routes of intermittent motion to the tool. The simulation results are verified by comparing them with the experimental results available in the literature.     

Simulation and experimental investigations into abrasive flow nanofinishing of surgical stainless steel tubes

Surface roughness is one of the critical properties that affect the performance of biomedical devices and human implant's functions. Higher surface roughness leads to the comparatively higher probability of body fluid retention in the surface valleys. Surface roughness peaks can easily obstruct the flow of body fluid and drug. Abrasive flow finishing (AFF) is an advanced finishing process, which can produce nano-level surface finish in complex components. In this paper, experimental investigations, including parametric study on nanofinishing of surgical stainless steel 316L tubes using AFF process has been reported. Indigenous multiple polymers blended base medium was developed to perform the nanofinishing experiments. Based on the experimental results, statistical model has been presented. To understand the AFF process in depth, finite element approach has been implemented to determine the finishing forces generated during the AFF experiments. Initial surface roughness on the internal surface of the workpiece varies in the range of (0.67–0.50) µm. The best surface finish of 48 nm with a percent improvement (% ΔR_a) of 92.20% has been achieved after processing the workpiece with AFF process. Simulated results are validated with the experimental results and the deviations are in the acceptable range.     

内圆表面磁性研磨加工的研究

通过对薄壁套筒内表面磁性研磨加工的原理分析和影响加工特性的各种加工因素的实验研究，探讨内表面的最佳磁磨工艺方法，同时表明磁性研磨加工有着十分广阔的应用前景和较主的经济效益。     

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.     

Effect of temperature on the magnetic abrasive finishing process of Mg alloy bars

Experiments were conducted to evaluate the effect of temperature during magnetic abrasive finishing of Mg alloy bars. A magnetic abrasive finishing process is an unconventional finishing technique that has been used to achieve high-quality surfaces with dimensional accuracy. In this study, a Mg alloy bar, which is widely used in automobiles, aircraft, IT, and the defense industry, was chosen as a cylindrical workpiece. The workpiece was then finished with a magnetic abrasive finishing process at three different temperatures, i.e., a cryogenic temperature, room temperature, and high temperature. In the cryogenic temperature condition, liquid nitrogen and argon gas were used as the cryogenic cooling gases in the finishing process; the results from this treatment were compared with those obtained at room temperature and high temperature conditions. At the room temperature condition, the finishing process of the cylindrical workpiece was performed at 24 °C. To carry out the high temperature condition, a hot air dryer was used to maintain a finishing temperature of 112 °C. The experimental results show that the room and cryogenic temperatures could yield excellent performance in terms of the surface roughness. However, in terms of the removal weight and change in diameter, the high temperature condition was found to be superior. In the present research, the improvements of the surface roughness (Ra) at room temperature (24 °C) and cryogenic temperature (-120 °C) conditions were 84.21 % and 55 %, respectively.

     

Experimental investigations and modeling of drill bit-guided abrasive flow finishing (DBG-AFF) process

Abrasive flow finishing (AFF) is one of the widely used advanced finishing processes in which a small quantity of work material is removed by flowing semisolid abrasive-laden putty over the workpiece surface to be finished. AFF is popular for finishing and deburring of difficult-to-access areas. This process is also used for radiusing, producing compressive residual stresses, and removal of recast layer. In order to enhance productivity of the process, several modifications in AFF process are being tried. In this paper, a concept of rotating the medium along its axis has been introduced to achieve higher rate of finishing and material removal. This process is termed as drill bit-guided abrasive flow finishing (DBG-AFF) process. In order to provide random motion to the abrasives in the medium and to cause frequent reshuffling of the medium, the medium is pushed through a helical fluted drill, which is placed in the finishing zone. The experiments are carried out to compare AFF and DBG-AFF processes with AISI 1040 and AISI 4340 as workpiece materials. The performance of DBG-AFF as compared to AFF is encouraging, specifically with reference to percentage change in average surface roughness (% ΔR _a) and amount of material removed. Modeling using non-linear multi-variable regression analysis and artificial neural networks are carried out to conduct parametric analysis and to understand, in depth, the DBG-AFF process. The simulation data of neural network show a good agreement with experimental results.     

A 3D model for magnetorheological fluid that considers neighboring particle interactions in 2D skewed magnetic fields

Magnetorheological (MR) fluid is used as the working medium in MR finishing. The viscosity of the MR fluid, which determines the shear acting on the workpiece surface stress, can be controlled by the intensity of the applied external magnetic field, and is thus an important design parameter in the finishing process. Most previous studies have used a shear stress value obtained experimentally under a limited set of conditions. Although a recent theoretical model that predicts the shear stress in an external vertical magnetic field has been developed, it treats the energy variation with respect to the strain and the intensity of the magnetic field only among the adjoining particles in a chain. Because that model assumes no multiparticle interactions, it is not well suited to a case in which the magnetic field is more than one dimension such as in MR finishing. In this study, a new three-dimensional model is proposed by expanding the one-dimensional model and considering multiparticle interactions. The proposed model assumes that each particle is surrounded by the 26 neighboring particles, and the total internal energy is estimated by calculating the magnetic dipole interactions among the particles. Therefore, the proposed model considers not only the particle-to-particle energy variations, but also the chain-to-chain energy variations. The behavior of MR fluid is evaluated using the proposed model in a two-dimensional skewed magnetic field.     

Experimental investigations into forces acting during a magnetic abrasive finishing process

A magnetic abrasive finishing (MAF) process is the one in which material is removed in such a way that surface finishing and deburring are performed simultaneously with the applied magnetic field in the finishing zone. Knowledge of forces acting during MAF is important to understand the mechanism of material removal. Forces have direct influence on the generation of a finished surface and accuracy of the workpiece. This paper reports the experimental findings about the forces acting during MAF and provides correlation between the surface finish and the forces. The resistance type force transducer (ring dynamometer) has been designed and fabricated. It is used to measure the normal magnetic force component responsible for microindentation into the workpiece and tangential cutting force component producing microchips. The force data have been recorded on-line by making use of virtual instruments (using Lab-View software). It is concluded that forces and change in surface roughness (ΔRa) increase with increase in current to the electromagnet (or magnetic flux density) and decrease in the working gap.On deputation from M.M.M.Engg. College, Gorakhpur (UP) India     

Enhancing AFM process productivity through improved fixturing

Abrasive flow machining (AFM) is a non-conventional finishing process that deburrs and polishes by forcing an abrasive laden media across the workpiece surface. The process embraces a wide range of applications from critical aerospace and medical components to high-production volumes of parts. One serious limitation of this process is its low productivity in terms of rate of improvement in surface roughness. Limited efforts have hitherto been directed towards enhancing the productivity of this process with regard to better quality of workpiece surface. This paper discusses improved fixturing as a technique for productivity enhancement in terms of surface roughness (R _a). A rotating centrifugal-force-generating (CFG) rod is used inside the cylindrical workpiece which provides the centrifugal force to the abrasive particles normal to the axis of workpiece. The effect of the key parameters on the performance of process has been studied. The results shows that for a given improvement in R _a value, the processing time can be reduced by as much as 70–80%. It is seen that the significant process parameters are revolutions per minute of CFG rod, extrusion pressure and abrasive mesh size.     

Prediction of surface roughness during abrasive flow machining

An analytical model is proposed to simulate and predict the surface roughness for different machining conditions in abrasive flow machining (AFM). The kinematic analysis is used to model the interaction between grain and workpiece. Fundamental AFM parameters, such as the grain size, grain concentration, active grain density, grain spacing, forces on the grain, initial topography, and initial surface finish (R _a value) of the workpiece are used to describe the grain-workpiece interaction. The AFM process is studied under a systematic variation of grain size, grain concentration and extrusion pressure with initial surface finish of the workpiece. Simulation results show that the proposed model gives results that are consistent with experimental results.     

Self-tuning fuzzy control with a grey prediction for wire rupture prevention in WEDM

Wire rupture in the wire electrical discharge machining (WEDM) process is one of the most troublesome problems in practical applications. In this paper, the abnormal ratio R_ab, defined as the proportion of abnormal sparks in a sampling period, is taken to represent the gap state in machining. The grey predictor is adopted to compensate the time-delayed R_ab caused by the low pass filter data processing. A gain self-tuning fuzzy control system has been developed to cope with the conditions that often occur with wire rupture in the WEDM process, such as an improper setting of machining parameters, machining the workpiece with varying thickness, etc. Experimental results of several cases show that the proposed controller results in a satisfactory performance. Not only can it immediately suppress transient situation once there is a sudden change of workpiece thickness, but a stable performance can also be achieved during machining a workpiece of constant thickness. As a result, wire rupture problems in most WEDM processes can be successively solved by the proposed control strategy.     

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.     

Fundamental investigation on nano-precision surface finishing of electroless Ni–P-plated STAVAX steel using magnetic compound fluid slurry

Electroless nickel–phosphorus (Ni–P) plating used in a range of hot embossing metal molds/dies and injection metal molds/dies must be manufactured to nano-precision roughness for proper operation of the molds/dies. We therefore developed a novel polishing technique for mirror surface finishing of this kind of magnetic material using a magnetic compound fluid (MCF) slurry. The effects of the magnetic and gravitational forces acting on the carbonyl iron particles (CIPs) and abrasive particles (APs) within the MCF slurry were studied first, and the behaviors of the CIPs and APs in the presence of an external magnetic field were predicted. Then, experiments were performed to confirm the predictions by investigating the distribution of the CIPs and APs on the working surface of the MCF slurry. Finally, four MCF slurries containing CIPs and APs with different diameters were employed to finish the Ni–P-plated STAVAX steel specimen at different working gaps. The results revealed that for the magnetic workpiece, the resultant vertical force attracted CIPs towards the work surface, whereas APs were pushed away from the work surface. However, the CIPs and APs showed opposite behaviors with the non-magnetic workpiece. The percentage of APs distributed on the working surface increased and the distribution became more even as either the diameter of the CIPs or the working gap increased, whereas that of CIPs had the opposite tendency. The MCF slurry containing bigger CIPs and smaller APs should be employed and the working gap should be set at a smaller value in order to perform mirror surface finishing of a magnetic Ni–P-plated surface. Under the experimental conditions in this work, the Ni–P-plated surface quality improved significantly, and a mirror surface roughness (Ra) of 4 nm was successfully achieved without leaving scratches or particle adhesion when using an MCF slurry containing CIPs 7 μm in diameter and APs 1 μm in diameter, showing that MCF slurries containing commercial CIPs are applicable to the nano-precision finishing of magnetic materials.     

Investigations on precision finishing of space curve meshing wheel by electrochemical brushing process

In this study, a novel finishing process named electrochemical brushing (ECB) is proposed, which integrates the merits of electrochemical polishing (ECP) and mechanical finishing (MF). It executes finishing for the space curve meshing wheel (SCMW), which was manufactured by the selective laser melting (SLM) rapid prototyping process. First, finishing experiments of ECP and ECB were carried out with optimal parameters, including an applied voltage of 10 V, a cathode and workpiece gap of 1 mm, and an ingredient electrolyte of NaNO₃ (10 %)?+?Al₂O₃ (0.1 %)?+?H₂O. Advantages of the ECB process were shown by analyzing the machining mechanism and comparing the experimental results. Furthermore, the cathode tools and finishing experimental rigs were designed to process SCMW samples. Finally, kinematics experiments were carried out, and the relation between the transmission ratio and the surface roughness of meshing tines is discussed. After ECB, as the surface roughness of meshing tines was reduced from 34 to 0.5 μm, the average transmission ratio of SCMW samples was improved from 3.922 to 3.993 and approached the theoretical value of 4, and its standard deviation was improved from 0.0317 to 0.0077. Therefore, the ECB process could be a feasible process to finish the SCMW to be able to perform precision meshing transmission.     

超声磁力复合研磨钛合金锥孔的试验研究

为了提高钛合金锥孔的研磨质量和研磨效率,提出了采用超声波振动辅助磁力研磨的复合加工方案。加工时,磨粒在磁场束缚下切削锥孔表面,并对其进行不断撞击,且因为磁场力、超声振动力和离心力等综合影响的原因,磨粒的切削轨迹呈现明显的多向性。针对钛合金锥孔,与传统磁力研磨法进行试验对比,并分析研磨后试件的材料去除量、表面粗糙度和表面形貌等来验证超声磁力复合研磨的效果。结果表明：超声磁力复合研磨加工效率得到提高;锥孔的材料去除量增加至1.6倍;研磨后锥孔平均表面粗糙度由原始的R_a1.23 μm降至R_a0.25 μm,下降率是传统工艺的1.3倍;试件表面的微波峰、凹坑和加工纹理均被去除,锥孔表面质量得到显著提高,且试件形状精度得到改善。     

Modelling and analysis of hybrid electrochemical turning-magnetic abrasive finishing of 6061 Al/Al2O3 composite

This paper integrates the electrochemical turning (ECT) process and magnetic abrasive finishing (MAF) to produce a combined process that improves the material removal rate (MRR) and reduces surface roughness (SR). The present study emphasizes the features of the development of comprehensive mathematical models based on response surface methodology (RSM) for correlating the interactive and higher-order influences of major machining parameters, i.e. magnetic flux density, applied voltage, tool feed rate and workpiece rotational speed on MRR and SR of 6061 Al/Al₂O₃ (10% wt) composite. The paper also highlights the various test results that also confirm the validity and correctness of the established mathematical models for in-depth analysis of the effects of hybrid ECT- MAF process parameters on metal removal rate and surface roughness. Further, optimal combination of these parameters has been evaluated and it can be used in order to maximize MRR and minimize SR. The results demonstrate that assisting ECT with MAF leads to an increase machining efficiency and resultant surface quality significantly, as compared to that achieved with the traditional ECT of some 147.6% and 33%, respectively.     

Internal finishing process for alumina ceramic components by a magnetic field assisted finishing process

This study presents the application of a new technique, magnetic field assisted finishing, for finishing of the inner surfaces of alumina ceramic components. The experiments performed on alumina ceramic tubes examine the effects of volume of lubricant, ferrous particle size, and abrasive grain size on the finishing characteristics. The finished surface is highly dependent on the volume of lubricant, which affects the abrasive contact against the surface; on the ferrous particle size, which changes the finishing force acting on the abrasive; and on the abrasive grain size, which controls the depth of cut. By altering these conditions, this process achieves surface finishes as fine as 0.02 μm in surface roughness (R_a) and imparts minimal additional residual stress to the surface. This study also reveals the mechanism to smooth the inner surface of alumina ceramic tube and to improve the form accuracy, i.e. the roundness of inside the alumina ceramic tube.