Investigation into magnetorheological abrasive honing (MRAH)

A scheme to finish external curved surfaces, by imparting rotation while the abrasive-mixed magnetorheological fluid (or abrasive-mixed MR fluid) is pushed up and down, is presented in this paper. Since the relative motions resemble those present in conventional honing, the proposed method is named as ‘Magnetorheological Abrasive Honing’ (MRAH). This paper outlines the design and development of magnetorheological abrasive honing setup. A DC electromagnet with cylindrical pole faces is used and measurement for magnetic flux density is done. Experiments are conducted with aluminum and austenitic stainless steel workpieces to understand the effect of magnetic field. Effect of initial roughness, workpiece rotation and process duration on finishing was investigated with ground austenitic stainless steel workpieces. It is observed that the improvement in finish is better for rougher surface and higher rotation speed of workpiece and a reduction in roughness is consistent with process duration.     

Design and development of nanofinishing process for 3D surfaces using ball end MR finishing tool

A new precision finishing process for nanofinishing of 3D surfaces using ball end MR finishing tool is developed. The newly developed finishing process is used to finish ferromagnetic as well as nonmagnetic materials of 3D shapes using specially prepared magnetorheological polishing (MRP) fluid. The existing MR finishing devices and methods are likely to incapable of finish 3D intricate surfaces such as grooves in workpiece or complex in-depth profiles in the mold due to restriction on relative movement of finishing medium and workpiece. In this newly developed finishing device, the ball end MR finishing tool is used for finishing different kinds of 3D surfaces, as there is no limitation on relative movement of finishing medium and workpiece. It can finish the work surfaces similarly as the machining of 3D surfaces by CNC ball end milling cutter and open a new era of its applications in future. The developed process may have its potential applications in aerospace, automotive and molds manufacturing industries. A computer controlled experimental setup is designed and manufactured to study the process characteristics and performance. The magnetostatic simulations were done on ferromagnetic as well as nonferromagnetic materials of 3D surfaces to observe the ball end shape of magnetic field at the tip of the MR finishing tool. The experiments were performed on flat EN31 and groove surface of copper workpieces in the developed MR finishing setup to study the effect of finishing time on final surface roughness.     

Analysis of forces on the freeform surface in magnetorheological fluid based finishing process

The magnetorheological (MR) fluid based finishing process is a deterministic process for finishing of flat, curved and freeform surfaces. In case of finishing, the knowledge of forces acting on the curved workpiece surface in different conditions improves the understanding of the process. An experimental investigation is carried out to measure the forces on the freeform surface in real time. The effects of the process parameters such as angle of curvature of the workpiece, rotational speed of the tool and feed rate on normal, tangential and axial forces, are studied. The normal force is found to be more dominant compared to other forces. A theoretical model of normal force and tangential force acting on the workpiece is also proposed to improve the understanding of the workpiece–abrasive particles interaction in the MR fluid based finishing process. A comparison of theoretical and experimental results is carried out to validate the proposed models, which show that the trends are in good agreement.     

Experimental investigations into forces during magnetorheological fluid based finishing process

Magnetorheological fluid based finishing process is a fine finishing process that has been applied to a large variety of brittle materials, ranging from optical glasses to hard crystals. Under the influence of a magnetic field, the carbonyl iron particles (CIPs) and non-magnetic polishing abrasive particles remove material from the surface being polished. Knowledge of forces acting is important to understand the mechanism of material removal. A dynamometer and virtual instrumentation are used to on-line record the normal force and tangential force acting on the workpiece through the magnetorheological (MR) fluid. A full factorial design of experiments is used to plan the experiments and ANOVA to correlate the forces and process parameters. The selected process parameters (volume concentration of CIPs and abrasives, working gap, and wheel rotation) are varied over a range to measure forces during experimentation. The maximum contribution is made by a working gap on the forces developed on the workpiece surface followed by CIP concentration while the least contribution is noticed by the wheel speed.     

Design and development of the magnetorheological abrasive flow finishing (MRAFF) process

A new precision finishing process for complex internal geometries using smart magnetorheological polishing fluid is developed. Magnetorheological abrasive flow finishing (MRAFF) process provides better control over rheological properties of abrasive laden magnetorheological finishing medium. Magnetorheological (MR) polishing fluid comprises of carbonyl iron powder and silicon carbide abrasives dispersed in the viscoplastic base of grease and mineral oil; it exhibits change in rheological behaviour in presence of external magnetic field. This smart behaviour of MR-polishing fluid is utilized to precisely control the finishing forces, hence final surface finish. A hydraulically powered experimental setup is designed to study the process characteristics and performance. The setup consists of two MR-polishing fluid cylinders, two hydraulic actuators, electromagnet, fixture and supporting frame. Experiments were conducted on stainless steel workpieces at different magnetic field strength to observe its effect on final surface finish. No measurable change in surface roughness is observed after finishing at zero magnetic field. However, for the same number of cycles the roughness reduces gradually with the increase of magnetic field. This validates the role of rheological behaviour of magnetorheological polishing fluid in performing finishing action.     

磁流变变间隙动压平坦化加工的工艺及机理

为提高光电晶片的磁流变抛光效率并实现其超光滑平坦化加工,提出其磁流变变间隙动压平坦化加工方法,研究不同变间隙条件下蓝宝石晶片的材料去除率和表面粗糙度随加工时间的变化,并分析磁流变变间隙动压平坦化加工机理。结果表明:通过蓝宝石晶片对磁流变抛光液施加轴向低频挤压振动,其抛光压力动态变化且磁流变液产生挤压强化效应,使抛光效率与抛光效果显著提升。在工件下压速度为1.0 mm/s,拉升速度为3.5 mm/s,挤压振动幅值为1 mm条件下磁流变变间隙动压平坦化抛光120 min后,蓝宝石晶片的表面粗糙度R_a由 6.22 nm下降为0.31 nm,材料去除率为5.52 nm/min,相较于恒定间隙磁流变抛光,其表面粗糙度降低66%,材料去除率提高55%。改变变间隙运动速度可以调控磁流变液的流场特性,且合适的工件下压速度和工件拉升速度有利于提高工件的抛光效率和表面质量。      

An integrated tool for five-axis electrorheological fluid-assisted polishing

A five-axis electrorheological fluid-assisted polishing equipment is presented for the finishing of curved surfaces in this paper. An integrated electrode tool is specially designed to make the abrasive particles in the electrorheological fluid concentrate around the tool end when the electric field is applied and it is suitable to polish not only the conductive material such as tungsten carbide but also the non-conductive material such as optical glass. The polishing experiments for curved surfaces of tungsten carbide and optical glass are conducted to confirm the validity and suitability of the developed five-axis equipment with the designed integrated electrode tool and to reveal the influence of the process parameters on the workpiece surface roughness in electrorheological fluid-assisted polishing.     

氧化锆陶瓷大抛光模磁流变抛光试验研究

目的研发一种高效、高质量氧化锆陶瓷超光滑表面加工技术。方法采用大抛光模磁流变抛光方式加工氧化锆陶瓷,利用自主研发的磁流变平面抛光装置,配制含有金刚石磨粒的磁流变抛光液,通过设计单因素实验,研究抛光时间、工作间隙、工件转速和抛光槽转速等主要工艺参数对氧化锆陶瓷平面磁流变加工性能的影响,并对材料去除率和表面粗糙度进行分析。结果在工作间隙为1.4 mm、工件转速为100 r/min、抛光槽转速为25 r/min的工艺条件下,表面粗糙度在达到饱和之前随时间的增加而降低。抛光30 min达到饱和,表面粗糙度Ra达到0.7 nm。继续延长抛光时间,表面粗糙度不再改善。氧化锆陶瓷的材料去除率随着工件转速和抛光槽转速的增加而增大,随着工作间隙的增大而减小。当工件转速为300 r/min时,材料去除率可以达到1.03 mg/min;抛光槽转速为25 r/min时,材料去除率可以达到0.80 mg/min;工作间隙为1.0 mm时,材料去除率最高可达0.77 mg/min。结论采用大抛光模磁流变抛光方法可以提高氧化锆陶瓷的材料去除率,同时获得纳米级表面粗糙度,实现氧化锆陶瓷的高效超光滑表面加工。     

脉冲电磁场辅助平面磁粒研磨加工试验

目的 在传统的平面磁粒研磨加工中添加脉冲辅助磁场,增大加工区域中磁感应强度和加工时磁感应强度动态变化,丰富磨料粒子在加工时的运动形式,使研磨轨迹复杂化,降低工件表面粗糙度,获得更好的工件表面形貌.方法 通过分析磨料粒子在有无辅助磁场时各自的受力情况,探究辅助磁场对磨料在加工时运动状态的影响,研究脉冲辅助磁场下磨料的运动...     

基于响应面法的钛合金Halbach阵列增强磁流变抛光工艺参数优化

目的 提高钛合金磁流变抛光的表面质量和抛光效率。方法 用Halbach磁场阵列强化磁场,通过载液盘与磁铁反向旋转来增强磁流变抛光效率,使抛光头拥有更强的恢复性与自锐性。通过仿真模拟和实际测量对比研究Halbach阵列与N-S阵列的磁场分布和磁场梯度。依照试验结果描述抛光剪切力、表面粗糙度与表面微观形貌随时间的变化规律。采用响应面法优化载液盘转速、磁铁转速和加工间距等3个工艺参数,建立剪切力和表面粗糙度的拟合方程数学预测模型,并对其中的不显著项进行优化。结果 在响应面交互作用分析中,工艺参数对剪切力的影响的大小顺序为加工间距、磁铁转速、载液盘转速;对表面粗糙度影响的大小顺序为载液盘转速、磁铁转速、加工间距。根据不同的需求,确定选定范围内的工艺参数组合,需要快速去除材料时,使剪切力趋于最大值的工艺参数组合为载液盘转速227 r/min,磁铁转速64 r/min,加工间距0.1 mm,通过20 min抛光后得到了表面粗糙度Sa为34.911 nm的光滑表面。抛光过程中,钛合金抛光所受剪切力τ为0.812 N。需要最优表面质量时,使表面粗糙度值趋于最小值的工艺参数组合为载液盘转速300 r/min,磁铁转速150 r/min,加工间距0.1 mm,通过20 min抛光后得到了表面粗糙度Sa为26.723 nm的光滑表面。抛光过程中,钛合金抛光所受剪切力τ为0.796 N。结论 Halbach阵列拥有较高的磁场强度和富有空间变化的磁感线,能够使磁流变液中的磁链呈现出更多的姿态变化。根据响应面法优化后的剪切力和表面粗糙度预测模型,预测结果与验证试验结果相差很小,预测模型的准确度与可信度较高。     

Contents

The attempts of researchers to obtain accurate and high-quality surfaces have led to the invention of new methods of finishing. Magnetic abrasive finishing (MAF) is a relatively new type in which magnetic field is used to control the abrasive tools. Surfaces of moulds, for instance, are among those which require very high-surface smoothness. Usually, this type of part has freeform surfaces. In this study, the effect of magnetic abrasive process parameters on finishing freeform surfaces of aluminium parts has been examined. This method was achieved through a combination of the magnetic abrasive process and computer numerical control. The use of a simple hemisphere to be joined on the flat area of the magnet as well as spark machining for forming a sphere at the end of a magnet were performed during experimentation. Gap, rotational speed of the machining head, amount of abrasive powder and feed rate were among the parameters that were tested in experiments. The design of experiments is based on the response surface methodology. Significant parameters and the regression equations governing the process were also determined. The impact of intensity of the magnetic field was obtained using MAXWELL finite element software. In the MAF process, magnetic abrasives play the role of cutting tools. However, the magnetic abrasives are not easily available as these are produced by special techniques such as sintering method, adhesive based, plasma based or gel based. This study presents the basic polishing characteristics of the magnetic abrasives produced by the mechanical alloying process. After the mechanical alloying process fine magnetic abrasives are obtained, in which the abrasive particles adhere to the base metal matrix without any bonding material. In this study, investigation was performed only on the convex area of workpiece. Optimum parameters are gap size of 0.5?mm, feed rate of 10?mm?min^?1 rotational speed of 2100?rev?min^?1 and powder amount of 1.75?g. To help understand the effectiveness of the MAF process, scanning electron microscopy and atomic force microscopy of the machined surfaces have been carried out.     

钛合金曲面超声辅助磁性磨料光整加工材料去除规律及去除函数

目的研究工件曲率半径、驻留时间以及加工角度对钛合金曲面超声辅助磁性磨料光整加工材料去除深度和材料去除曲线偏置程度的影响,建立不同走刀方式下的材料去除函数。方法在不同工件曲率半径、驻留时间和加工角度下,对钛合金曲面工件进行单点抛光试验,利用方差分析法,研究各因素水平对材料去除深度及材料去除曲线偏置程度的影响规律,采用最小二乘法拟合材料去除点坑在xoz平面和yoz平面内的材料去除曲线,基于二次多项式逐步回归方法,构建不同加工工艺参数下,材料去除曲线函数系数与加工工艺参数间的函数表达式,建立不同走刀方式下的材料去除函数,并对其进行准确性检验。结果由材料去除深度方差分析可得:驻留时间的F值为8.06,加工角度的F值为2.296,材料去除深度随驻留时间和工件曲率半径的增加而增加,随加工角度的增大,先增加后减小。由材料去除曲线偏置程度方差分析可得:工件曲率半径的F值为2.176,加工角度的F值为7.647,材料去除曲线偏置程度随工件曲率半径的增大而减小,随驻留时间和加工角度的增加而增加。此外,拟合的材料去除函数相关系数值R^2在0.97~0.99范围内。结论驻留时间对材料去除深度的影响最显著,加工角度次之,工件曲率半径影响最小。加工角度对材料去除曲线的偏置程度影响最显著,工件曲率半径次之,驻留时间影响最小。材料去除函数拟合结果较为准确,能满足实际的加工要求。     

磁流变抛光技术的工艺试验

本文研究了利用自行配制的水基磁流变抛光液和抛光样机,进行了以抛光去除效率和表面粗糙度为考核指标的工艺实验,试验中所用工件为直径12mm的BK7玻璃零件,其初始表面粗糙度的均方根值为RMS1．41nm,经抛光后得到理想的表面粗糙度的均方根值为RMS0．61nm的玻璃工件,结果表明：随着磁流变抛光磁场强度的增加,抛光去除效率逐渐提高,但表面粗糙度的值随之降低;抛光盘转速的提高能促进抛光效率的提高,降低表面粗糙度值;抛光盘与工件间的间隙的减小有利于提高抛光效率但同时使表面粗糙度变差。     

Magnetic-Assistance Finishing Processes in Freeform Surfaces

A new finishing process that uses magnetic force with high efficiency to assist discharging dregs from the electrode gap during electrochemical finishing on freeform surfaces is investigated in the current study. The factors affecting electrochemical finishing and the effects of magnetic assistance are primarily discussed. The main experimental parameters are magnetic strength, distance between the two magnets, diameter of the electrode, current density, the on/off period of pulsed current, and rotational speed of the wire electrode. Providing a large magnetic field intensity or using a smaller distance between the two magnets produces a larger magnetic force and discharge efficiency, and results in a better finish. A higher current density with magnetic assistance reduces the finishing time and avoids difficulties in dreg removal. A high rotational speed of the wire electrode produces a better finish. Pulsed direct current can slightly promote the effect of electrochemical finishing, but the current density needs to be higher. Magnetic assistance during the electrochemical finishing process makes a greater contribution in a shorter time making the surface of the workpiece smooth and bright.     

基于PSO-ELM的316L不锈钢细长管磁粒研磨内表面粗糙度预测模型

针对316L不锈钢细长管磁粒研磨加工过程中,最佳工艺参数难以选择,以及加工后对工件内表面粗糙度（Ra）的预测问题,将影响磁粒研磨316L不锈钢细长管内表面粗糙度的四个工艺参数作为输入值,内表面粗糙度作为输出值,构建粒子群（PSO）优化极限学习机（ELM）模型来预测316L不锈钢细长管内表面粗糙度,利用PSO对工艺参数进行全局寻优,获得最佳工艺参数组合,最后通过试验与预测结果进行对比。构建的PSO-ELM表面粗糙度预测模型拟合优度R2为0.984 8,绝对误差（MAE）为0.013 4,均方根误差（RMSE）为0.021 4。得到的最佳工艺参数组合为：主轴转速2 389.011r/min,进给速度3.167 mm/s,磨料粒径216.185μm,加工时间35.856 min,预测Ra为0.178μm。对工艺参数进行调整,试验得到的Ra为0.182μm,与预测值相比误差为2.24%。基于PSO-ELM方法构建316L不锈钢细长管内表面粗糙度预测模型,实现对工件内表面粗糙度的精确预测,应用粒子群方法得到最佳工艺参数组合,提高了磁粒研磨316L不锈钢细长管的加工效率。     

Magnetorheological finishing process for hard materials using sintered iron-CNT compound abrasives

The use of magnetorheological fluids for finishing is one of the most promising smart processes for the fabrication of ultra-fine surfaces, particularly three-dimensional millimeter or micrometer structures. This process is not readily applicable to hard-surface materials, like an Al₂O₃–TiC hard disk slider, if a conventional rotating tool is used. This is due to the rotational speed and the resulting actual impressed abrasion energy limits, and the consequent low efficiency of the material removal rate. In this study, the main mechanism responsible for the decrease of the material removal rate on hard materials for a wheel-type magnetorheological finishing process is examined, both theoretically and experimentally, and a solution to this problem is devised via two approaches. The first uses a rectilinear alternating motion to improve processing conditions, and the second focuses on the use of more effective abrasives, namely magnetizable abrasives made of iron powders sintered with carbon nanotubes, which are new abrasives that have not yet been introduced in the field of surface finishing. Furthermore, it is shown that these abrasives increase the lifetime of consumables (magnetorheological fluid and abrasives) and the material removal rate.     

Fluid flow analysis of magnetorheological abrasive flow finishing (MRAFF) process

A new precision finishing process called magnetorheological abrasive flow finishing (MRAFF), which is basically a combination of abrasive flow machining (AFM) and magnetorheological finishing (MRF), has been developed for nano-finishing of parts even with complicated geometry for a wide range of industrial applications. This paper deals with the theoretical investigations into the mechanism of MRAFF process to study the effects of various process parameters. In the present work, an attempt has been made to analyze the medium flow through the fixture by finite difference method by assuming the medium as Bingham plastic to evaluate the stresses developed during the process. A capillary viscometer has been designed and fabricated to study the effect of magnetic field on the rheological properties of the medium. Microstructure of the mixture of ferromagnetic and abrasive particles in magnetorheological polishing fluid (MRPF) has been proposed, and normal force on the abrasive particles is calculated from the applied magnetic field. A model for the prediction of material removal and surface roughness has also been presented. Theoretical results compare well with the experimental data available in the literature.     

Modeling and simulation of cylindrical electro-chemical magnetic abrasive machining of AISI-420 magnetic steel

The objective of the present research is to simulate cylindrical electro-chemical magnetic abrasive machining (C-EMAM) process for magnetic stainless steel (AISI-420). C-EMAM is a new hybrid machining process used for high efficiency finishing of cylindrical jobs made of advanced engineering materials. The material is removed from the workpiece surface due to simultaneous effect of abrasion and electrochemical dissolution. Finite element method is used to calculate the distribution of magnetic field between the magnetic poles in which cylindrical shaped workpiece is placed. The cutting forces responsible for abrasion are calculated from the magnetic forces due to gradient of magnetic field in the working gap. The effect of electrochemical dissolution and abrasion-assisted dissolution are incorporated into the C-EMAM process model using empirical relation for average anodic current. The empirical relation is correlated with the input parameters in the present system based on experimental results. Finally a surface roughness model is developed by considering total volume of material removed with the assumption of triangular surface profile. The simulation results for material removal and surface roughness are validated using experimental results. The simulated results agree with experimental observations.     

蓝宝石光学曲面柱形宽缎带磁流变抛光仿真分析及实验研究

目的 针对目前光滑无损伤光学曲面蓝宝石加工成本高、效率低的问题,对加工过程中磁流变抛光缎带进行流体仿真,进而优化抛光轮表面结构。方法 设计并提出3种表面结构柱形宽缎带磁流变抛光轮,介绍了磁流变抛光轮加工的基本原理,建立了磁流变抛光垫Bingham流体特性加工仿真模型,分析了3种抛光轮表面结构对工件表面磁通密度模、流场流速、流场压力分布的影响。同时对3种抛光轮的抛光效果进行了实验探究,探究了抛光轮表面结构对材料去除率和抛光后表面粗糙度的影响规律。结果 仿真结果表明,抛光轮表面槽型结构具有能增强磁通密度模、增大流体流速和流体压力的特性。实验结果表明,螺旋槽抛光轮的抛光效果最好,在螺旋抛光轮作用下,材料去除率为0.22 mg/h,抛光后蓝宝石表面粗糙度为1.08 nm。最终抛光轮近壁区总压力和速度的乘积结果与抛光轮实验去除率结果具有较好的一致性。结论 槽型结构可以提高抛光液在抛光轮表面的固着效果,影响工件表面流场运动状态,增强工件表面受到抛光垫的作用力。相较于光滑和横条槽抛光轮,螺旋槽抛光轮的抛光效率最高,表面粗糙度最低,可有效提高抛光效果。     

Curved surface finishing with flexible abrasive tool

A flexible abrasive tool has been developed for automatic finishing of curved surfaces on three-axes machining centers. The tool is made of thermosetting polyurethane elastomer with an overcoat of aluminum oxide abrasives. The tool is capable of conducting finishing operations and deforming itself in conformity to the shape of work surface. The tool performance such as finishing capability, conformability, and durability is examined during finishing experiments on ball-end milled surfaces of high-alloyed tool steel. It is demonstrated that the tool can finish curved surfaces successfully on three-axes machining centers. The tool/work contact pressure, which influences significantly the tool performance, is analytically estimated and utilized to determine the tool path producing a constant contact pressure. It is experimentally verified that the tool path improves the finished surface roughness.