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.     

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.     

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.     

Ultrasonic assisted magnetic abrasive finishing of hardened AISI 52100 steel using unbonded SiC abrasives

Ultrasonic assisted magnetic abrasive finishing (UAMAF) integrates the use of ultrasonic vibrations and magnetic abrasive finishing (MAF) process to finish surfaces to nanometer order in a relatively short time. The present study emphasizes on the fabrication of UAMAF setup. Using this experimental setup, experimental studies have been carried out with respect to five important process parameters namely supply voltage, abrasive mesh number, rotation of magnet, abrasive weight percentage, and pulse on time (T_on) of ultrasonic vibrations selected based on literature available in the area of MAF process and ultrasonic generator controls. Percentage change in surface roughness (?Ra) for AISI 52100 steel workpiece has been considered as response and unbonded SiC abrasives are used in the work. The experimental results showed that the UAMAF process has better finishing potential as compared to those obtainable by using MAF process for similar processing conditions. The surface roughness value obtained by UAMAF was as low as 22 nm within 80 s on hardened AISI 52100 steel workpiece using unbonded SiC abrasives. Scanning electron microscopy and atomic force microscopy studies were carried out to feel the surface texture produced and to identify finishing mechanism.     

磁流变即效微细砂轮精细加工研究

在对磁流变液特性分析的基础上,提出了基于磁流变效应即效微细砂轮研抛的新工艺方法。磁流变液与金刚石微粉磨料均匀混合形成的抛光液,在外加磁场作用下形成粘弹性的准固体磨粒球团构成的微细砂轮,以普通玻璃为工件材料,基础试验证明本加工方法在加工玻璃材料时可行和有效。试验结果表明,磁流变即效微细砂轮在加工玻璃过程中加工表面呈现塑性去除特征,加工工具无进给时加工痕迹表面有中间突边缘圆环凹陷的形状,工具尖端与加工表面越接近其材料去除率越高。     

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.     

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.     

转向球销球面加工组合机床设计

根据球面形成原理，将工件回转轴线和刀具回转轴线形成交角，利用两个圆运动，合成转向球球销的不完整球面。通过铣剧和滚压，在一台机床上完成球面精加工。     

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.     

Study of the Diffusion of Carbon, Its Sources, and Effect on Finishing Micro-EDM Performance of Cemented Carbide

Apart from the necessity of surface modification based on different applications, in most of the cases, diffusion of carbon or foreign particles on the workpiece surface during micro-electrodischarge machining (micro-EDM) is avoidable, especially in finishing micro-EDM. This study aims to investigate different sources of materials that migrate to the machined surface during fine-finishing of micro-EDM of cemented tungsten carbide (WC-Co). The machined surfaces have been examined under scanning electron microscope and energy dispersive x-ray to investigate the changes in chemical composition. It has been observed that during finishing of micro-EDM, the major source of materials' transfer to both the workpiece and electrode is the diffusion of carbon that comes from the decomposition of the hydrocarbon dielectric. In addition, materials from both workpiece and electrode transfer to each other based on machining conditions and discharge energy. The migration occurs more frequently at lower gap voltages during die-sinking with micro-EDM because of low spark gap and stationary tool electrode. Milling micro-EDM results in lower amount of carbon migration and fewer surface defects that improve the overall surface finish significantly.     

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.     

微小非球面碳化钨光学模具的磁流变抛光特性研究

超精密加工是光学模具获得高形状精度、表面精度和表面完整性的必要手段。通过实验比较抛光前后工件面形精度的PV值及RMS值来研究微小非球面碳化钨光学模具的磁流变抛光特性。结果表明:磁流变抛光技术对提高微小非球面碳化钨光学模具形状精度、表面精度等有较显著的作用。     

Comparison between multi-point and other 5-axis tool positioning strategies

A method of generating sculptured surfaces at multiple points of contact between the tool and the workpiece was developed and proven viable by the current authors in previous work. They denoted this finish machining method, “Multi Point Machining”, or simply MPM. This paper compares MPM with two other 5-axis tool positioning strategies; namely: the inclined tool, and the principal axis method. It is also compared with 3-axis ball nose machining. Comparisons are conducted using computer simulations and experimental cutting tests. Results obtained show that MPM produced scallop heights that are much smaller than those produced by the other tool positioning strategies.     

Chemo-mechanical magneto-rheological finishing (CMMRF) of silicon for microelectronics applications

A new finishing process, namely, chemo-mechanical magneto-rheological finishing (CMMRF) was developed for polishing silicon blanks that combines the beneficial features of chemical mechanical polishing (CMP) and magneto-rheological finishing (MRF) without the detrimental effects of either process involved. Chemical reactions associated with CMP are used to enhance the finish quality while the magneto-rheological polishing fluid is used to control the magnitude of the forces acting on the workpiece that controls the material removal rates (MRR) and minimizes the surface integrity problems. An apparatus for CMMRF was designed and built for nanometric finishing of silicon substrates. This process is able to finish silicon blanks with nanometric finish, minimal surface defects, and higher removal rates.     

Cutting process of glass with inclined ball end mill

Cutting processes with ball end mills are discussed for machining microgrooves on glasses. A surface is finished in undeformed chip thickness less than 1 μm at the beginning and at the end of the cut during the cutter rotation. The milling process is applied to glass machining. A crack-free surface can be finished in a large axial depth of cut more than 10 μm. Because glass undergoes almost no elastic deformation, roughness on a cutting edge in glass machining has a larger influence on surface finish than that of metal machining. The rotational axis of the tool is inclined to improve the surface finish. The cutting processes are modeled to show the effect of the tool inclination on the machined surface with considering the edge roughness. The tool inclination compensates for deterioration of the surface finish induced by the edge roughness in the presented model. The improvement of the surface finish is verified in the cutting experiments with the tool inclination. The orthogonal grooves 15–20 μm deep and 150–175 μm wide, then, are machined with the crack-free surfaces to prove efficiency and surface quality in the milling process.     

新型双刃可转位球头立铣刀设计及其加工仿真研究

球头立铣刀是数控机床上加工复杂曲面的高性能结构化刀具,为了提高球头立铣刀的性能,设计了一款新型双刃可转位球头立铣刀,并在CAD/CAM软件Pro/E中建立其三维实体模型;导入金属切削工艺有限元软件AdvantEdge中进行铣削加工模拟仿真,得到加工过程中切削性能参数随时间的变化关系,并与某标准整体式球头立铣刀的铣削加工进行对比分析。结果表明:该铣刀的性能均较优,验证了文中设计的可行性,分析结果为球头立铣刀的设计优化与加工应用提供了参考。     

Statistical analysis of the effects of machining parameters and workpiece hardness on the surface finish of machined medium carbon steel

The objective of this study is to ascertain the effect of machining parameters and workpiece hardness on surface roughness of machined components and to develop a better understanding of the effect of process parameters on the machined surface. Such an understanding can provide insight into the problems of controlling the finish of machined surfaces when the process parameters are adjusted to obtain a certain surface finish. The collected data were analyzed using parametric analyses of variance (ANOVA) with surface finish as the dependent variable and hardness of the workpiece material, cutting tool position from the surface of the clamping device (chuck), depth of cut, cutting velocity, and cutting feed as independent variables. The results showed that surface roughness is significantly affected by the workpiece hardness, cutting feed, cutting speed, depth of cut, cutting tool position from the chuck, and their interactions with each other. The results suggest that feed rate and cutting speed can be adjusted to produce a certain surface finish when the position of the cutting tool from the surface of a clamping device or the hardness of the workpiece is changed.     

Workpiece surface integrity of Ti-6-4 heat-resistant alloy when employing different polishing methods

The use of heat-resistant titanium alloys for the manufacture of gas turbine engines components for aerospace/energy applications has become a routine exercise. However, components with complex designs specifications might pose manufacturing challenges especially when finishing processes are needed to enable their compliance with tight industrial standards for workpiece surface integrity. Information on polishing processes for such sensitive industrial applications is scarce. The paper reports on the influence of polishing methods/strategies on the quality and integrity of workpiece surfaces obtained after different polishing methods on Ti-6-4 heat-resistant alloy. The research focuses on identifying an “optimised” polishing strategy that will enable finishing a family of targeted safety critical aero-engine (TSCA-E) components, on which the simultaneous fulfillment of the following technological/quality criteria is required: (i) tool life to enable polishing of minimum of workpiece surface areas that are related with specific features of TSCA-E components; (ii) removal of pre-machining (i.e. milling) marks while obtaining required surface finish; (iii) generation of damage-free polished surfaces, i.e. high workpiece surface integrity. Two (belt; bob) polishing methods with various media/grades (Al₂O₃, SiC, polycrystalline diamond) of the abrasive materials in conjunction with three cutting media (dry; chilled air; minimum quantity of lubricant) have been tested to address the overall finishing of TSCA-E components. Although significant differences in tool life performance exist between belt and bob polishing methods, both are capable to meet the requirements of minimum workpiece surface coverage if “optimised” operating parameters are employed. When considering surface roughness criteria, Al₂O₃ belts and SiC bob tools were found appropriate. Furthermore, surfaces obtained with these tools when employing cooling media (chilled air for belt polishing and minimum quantity of lubricant (MQL) for bob polishing) showed compliance with the tight requirements of industrial standards for workpiece surface integrity (metallurgical damage and residual stresses). This proved that belt and bob polishing methods can be employed in conjunction as “hybrid” technique to enable automated overall finishing of complex geometrical components.     

球头铣刀铣削斜面的三维有限元仿真研究

在能源动力、汽车、航空航天、模具制造等关键零部件的加工过程中,球头铣刀因其特有的刀具几何结构,常作为零件加工的最终成型刀具。考虑到在球头铣刀立铣加工中不同的刀具与工件相对姿态会对切削过程产生不同的影响,本文研究切屑形成和不同走刀方式下切削过程中各物理量(切削力、切削温度等)的变化情况,结合有限元仿真技术在切削加工中的应用,建立硬质合金球头铣刀铣削斜面的有限元模型,模拟相同切削参数下,八种不同走刀方式的球头铣削过程,分析刀具切入切出工件时切屑的形成过程,探究切削力和切削温度的变化规律。仿真结果表明:不同的走刀方式,平均切削合力各不相同,同时切屑和工件的最大切削温度也出现较大差异,而斜坡上坡逆铣的走刀方式所对应的平均切削合力和最大切削温度均最优。     

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.