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.     

Simulation for the prediction of surface roughness in magnetic abrasive flow finishing (MAFF)

The final machining (or finishing) of precision parts with high level of surface finish and close tolerance is making the application of magnetic abrasive finishing technology increasingly important. Magnetic abrasive flow finishing (MAFF) is a new abrasive finishing process combining the features of abrasive flow finishing (AFF) and magnetic abrasive finishing (MAF). MAFF provides a high level of surface finish and close tolerances for wide range of industrial application. This paper focuses on the modeling and simulation for the prediction of surface roughness on the workpiece surface finished by MAFF process. A finite element model is developed to find the magnetic potential distribution in the magnetic abrasive brush formed during finishing action and then it is used to evaluate machining pressure, surface finish and material removal. The simulation results are compared with the experimental results available in the literature. The simulated workpiece surface roughness shows features similar in nature to the experimental results.     

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.     

On ultrasonic assisted abrasive flow finishing of bevel gears

Finishing of bevel gears is an important requirement in many machining shop floors. Variants of abrasive flow machining (AFM) could be plausible solutions for finishing such parts with intricate geometries. In the present work, a relatively new variant of AFM called ultrasonically assisted abrasive flow machining (UAAFM) technique was employed to finish bevel gears made of EN8 steel. An analysis of the process has been presented with suitable illustrations. A finite element simulation of the behavior of the medium during finishing of bevel gears using the UAAFM process has been presented. A 3D model was constructed to simulate the flow of medium through the outer wall of the gear tooth surface using computational fluid dynamics (CFD) approach. The velocity, pressure and temperature values along the length of the workpiece were computed for both UAAFM and the conventional AFM processes. Further, the effectiveness of the process was investigated through experimental trials by conducting a comparison study between classical AFM and UAAFM. Ultrasonic frequency, extrusion pressure, processing time and the media flow rate were considered as the input variables while improvements in surface finish and material removal were considered as the monitored outputs. Results confirm that improvements in surface roughness and material removal are significantly higher than those obtained with conventional abrasive flow machining. The study further reveals that, the applied high frequency (ultrasonic) vibration to the workpiece has the maximum influence on the process responses among the variables considered.     

小孔内表面磁力研磨加工技术研究进展

磁力研磨加工是提高小孔内表面质量的一种重要光整技术,利用该技术能高效提升小孔类零部件在极端环境下的使役性能。针对小孔内表面的磁力研磨光整加工,按其发展历程对磁力研磨加工技术进行总结,归纳了磁性磨粒研磨、磁针磁力研磨、液体磁性磨具研磨、超声辅助磁力研磨和电解磁力复合研磨等加工方法的技术特点,并分析评述了其局限性。对磁力研磨加工过程中材料去除机理进行了研究,材料主要以微量切削与挤压、塑性变形磨损、腐蚀磨损、电化学磨损等方式去除,材料种类不同,去除机理也不同。其中,硬脆性材料主要以脆性断裂、塑性变形和粉末化的形式去除;塑性材料在经历滑擦阶段、耕犁阶段和材料去除阶段后主要以切屑的形式去除。此外,还对磁力研磨加工过程中的材料去除模型进行了研究,对单颗磁性磨粒材料去除模型和“磁力刷”材料去除模型进行了分析讨论。最后,对磁力研磨加工技术今后的研究发展给出了建议并进行了展望。     

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...     

Deburring microparts using a magnetorheological fluid

It is difficult to deburr a micro-machined surface because the micro-features are easily damaged during the deburring processes. This paper proposes a new deburring process utilizing a magnetorheological fluid and applies it to the production of micromolds. A magnetorheological fluid is a functional fluid with a variable yield stress that is controlled by an external magnetic field. The proposed process utilizes two material removal mechanisms induced by the magnetorheological fluid flow. Extensive yielding of material is effective for deburring sheet-shaped burrs, and abrasive wear is effective for deburring protrusion-shaped burrs. A process model was developed to describe the effectiveness of each mechanism for specific burr geometries. The performance of the proposed method was verified experimentally. Metal burrs with a height of 200 μm and thickness of 1 μm were removed successfully with extensive yielding and abrasive wear. Burrs shorter than a few micrometers could be removed only by abrasive wear. The material removal behaviors of sheet-shaped and protrusion shaped burrs matched the proposed process model well.     

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.     

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.     

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.     

Development of magneto abrasive flow machining process

Abrasive flow machining (AFM) is a relatively new process among non-conventional machining processes. Low material removal rate happens to be one serious limitation of almost all such processes. Limited efforts have hitherto been directed towards improving the efficiency of these processes so as to achieve higher material removal rates by applying different techniques. This paper discusses the possible improvement in surface roughness and material removal rate by applying a magnetic field around the workpiece in AFM. A set-up has been developed for a composite process termed magneto abrasive flow machining (MAFM), and the effect of key parameters on the performance of the process has been studied. Relationships are developed between the material removal rate and the percentage improvement in surface roughness of brass components when finish-machined by this process. Analysis of variance has been applied to identify significant parameters and to test the adequacy of the models. Experimental results indicate significantly improved performance of MAFM over AFM.     

Rotational abrasive flow finishing (R-AFF) process and its effects on finished surface topography

The present study focus on abrasive flow finishing (AFF), a process that finishes complex internal and external geometries with the help of viscoelastic abrasive medium, while keeping in mind its low finish and material removal rates (MRR). Researchers have often strived to improve finishing rate and MRR. As an attempt to overcome the said limitations, this paper discusses rotational abrasive flow finishing (R-AFF) process wherein complete tooling is externally rotated and the medium reciprocates with the help of hydraulic actuators. In this study, preliminary experiments are conducted on Al alloy and Al alloy/SiC metal matrix composites (MMCs) at different extrusion pressures, and medium compositions are employed for finding optimum conditions of the same for higher change in roughness (ΔR_a). The same optimum conditions are used to study the effect of workpiece rotational speed on (ΔR_a), material removal (MR), change in workpiece hardness and surface topology. It is noted that as the workpiece rotational speed increases from 2 to 10 RPM, the experimental helix angle decreases from 22° to 9° and the helical path length increases from 67 to 160 mm. Based on these findings the mechanism of material removal of matrix and reinforcement in MMC using R-AFF have been proposed. Here the matrix material is removed by micro-cutting and three methods of material removal mechanisms for reinforcement are also explained. The scientific logic behind finishing mechanism of matrix and reinforcement, cross hatch patterns, helical path directions, micro-scratch (μ-scratch) width and depth variation with size, orientation and support that active abrasive grain obtains from neighboring abrasives is derived from scanning electron microscopy micrographs. Finally this study establishes that R-AFF can produce 44% better ΔR_a and 81.8% more MR compared to the AFF process. Accordingly, R-AFF generates micro cross hatch pattern on the finished surface that can improve lubricant holding capabilities.     

Study the characteristics of magnetic finishing with gel abrasive

Given the flexible polishing effect in magnetic abrasive finishing (MAF), the precise and mirrorlike surface can be obtained during this process. However, the abrasives are easily flown away from the working area regardless of what abrasives are used in MAF; this situation will reduce the polished efficiency and induce the pollution problem in the environment. Besides, the abrasives cannot recycle after the finishing process. Therefore, a novel abrasive medium, using the silicone gel to mix the ferromagnetic particles and abrasive, was developed to enhance the disadvantages in MAF. Magnetic finishing with gel abrasive (MFGA) was utilized in this study to polish the cylindrical rod of mold steel; furthermore, this cylindrical rod was fixed in a horizontal chuck that could rotate and vibrate in the axial direction. This study focused on the finishing efficiencies and the surface roughness of the workpieces after MFGA. Moreover, recycling times of gel abrasive were also the main effects that need to be approved. The results demonstrated that surface roughness of the cylinder part was reduced to 0.1 μm Ra from an initial value of 0.677 μm Ra within 10 min, and surface roughness could decrease to 0.038 μm Ra after 30 min in MFGA. Surface roughness reduction in MFGA was 3 times of surface roughness reduction in MAF using the unbonded magnetic abrasive as medium. Roughness improvement rate still remained at a high level of 90% when the same abrasive medium (35 g) was used 15 times to finish 15 workpieces; therefore, this result proved that the gel abrasive had excellent ability for recycling.     

Study on cylindrical magnetic abrasive finishing using unbonded magnetic abrasives

The process principle and the finishing characteristics of unbonded magnetic abrasive within cylindrical magnetic abrasive finishing are described in this study. The unbonded magnetic abrasive is a mechanical mixture of SiC abrasive and ferromagnetic particles with a SAE30 lubricant. Iron grit and steel grit, for which three various particle sizes were prepared for both, were used as ferromagnetic particles, each of them being mixed with 1.2 and 5.5 μm SiC abrasive, respectively. Also, the finishing characteristics on surface roughness and material removal as well as their mechanisms were investigated. Experimental results indicate that steel grit is more suitable for magnetic abrasive finishing because of its superior hardness and the polyhedron shape. The variations of material characteristics on the work surface both before and after finishing were also investigated. Si content was increased obviously, however its corrosion resistibility decreased on a surface that was finished via steel grit mixed with SiC abrasive.     

Study of magnetic field assisted mechanochemical polishing process for inner surface of Si3N4 ceramic components: Finishing characteristics under wet finishing using distilled water

This study discusses the finishing characteristics of a magnetic field assisted mechanochemical polishing process using Cr₂O₃ abrasive mixed with magnetic particles in the case of wet finishing using distilled water, which was proposed for internal finishing of Si₃N₄ fine ceramic tubes. It was clarified that a highly accurate finishing can be achieved more efficiently in the case of wet finishing using distilled water compared with dry finishing. Moreover, those conditions necessary to achieve high efficiency finishing are discussed.     

动态磁场集群磁流变抛光加工机理及试验研究

基于动态磁场集群磁流变平面抛光的加工机理以及动态磁场作用机理,对单晶硅基片进行动态磁场集群磁流变抛光试验研究。结果表明:动态磁场能使畸变的抛光垫实时自修复,磨料具有频繁的动态行为,克服了静态磁场作用下抛光垫变形难恢复且磨料堆聚的缺点,使材料去除过程稳定,抛光效果较好;在动态磁场作用下,不同抛光方式的加工效果也不同;在多工件同步抛光中,大尺寸的工具头高速自转使工件表面有更高的线速度,磨料对单晶硅表面缺陷去除作用更强。经过5 h抛光,硅片表面粗糙度R_a由0.48 μm下降到3.3 nm,获得超光滑表面。      

有限元法在旋转磁场磁粒研磨加工技术中的应用

磁场分布是影响磁粒研磨加工的重要因素之一，研究磁场分布的主要方法是数值计算法，本文介绍了旋转磁场磁粒研磨加工的基本原理，并用有限元法对旋转电磁场进行了计算，得到了一些重要结论。     

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.     

磁流变抛光中流量扰动问题分析与控制方法研究

流量稳定性控制是磁流变抛光工艺获取稳定去除函数、实现确定性抛光的重要条件。针对抛光头倒置式、离心泵传送构型的磁流变抛光系统中扬程变化对流量扰动的问题,研究了磁流阀控制流量扰动误差的方法,但该方法存在因流量计的测量积分时间导致控制响应滞后问题;分析了双Z轴随动结构未能抑制摆动轴运动而导致扬程变化对流量扰动的问题的原因,提出跟随多轴复合运动Z向同步驱动的双通道运行控制方法,从本质上解决了磁流变抛光工艺过程中离心泵扬程变化对流量扰动的问题,实现流量实时和高稳定性控制,将流量波动控制在1%以内。     

电解磁力复合加工对磁性磨粒性能的影响

利用单纯的磁力研磨工艺加工镍基高温合金等材料时,磁性磨粒失效严重,严重影响了磁力研磨工艺的研磨效果。为了解决这一技术难题,将电化学与单纯的磁力研磨加工工艺结合,通过电解加工在工件表面形成质地较软的钝化膜,再利用磁力研磨对其表面进行加工。对复合加工后的磁性磨粒进行电镜成分分析,得知铝的相对质量分数仅从27.60%降至23.48%,有效地降低了磁性磨粒中研磨相成分的损失,延缓了磁性磨粒的失效时间,提高了磁性磨粒的利用率和使用寿命,从而保证了工件的加工质量。