Nano finish grinding of brittle materials using electrolytic in-process dressing (ELID) technique

Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.     

ELID精密磨削钢结硬质合金及其AFM表面形貌分析

对钢结硬质合金（GT35）进行在线电解修整（ELID）精密磨削,对钢结硬质合金难磨机理以及ELID磨削钢结硬质合金的磨削机理进行了分析,并通过原子力显微镜（AFM）对镜面钢结硬质合金表面不同区域进行了微观表面形貌的分析,研究结果表明,采用ELID磨削技术实现对钢结构硬质合质合金零件的精密磨削加工,钢结硬质合金磨削表面粗糙度可达nm级,Ra≤20nm。     

Ductile Regime Mirror Finish Grinding of Ceramics with Electrolytic In-process Dressing (ELED) Grinding

Advanced structural ceramics, such as silicon nitride based materials, are of interest owing to their unique physical and mechanical properties. However the cost of grinding these ceramics, which is an integral part of their fabrication, is very high. Moreover, grinding can result in surface and sub-surface damage in the material and these defects can significantly reduce the strength and reliability of the finished components. Grinding damage is sensitive to grinding parameters. Two types of silicon nitride based ceramic materials were ground with Electrolytic In-Process Dressing (ELID) using different grit sized metal bonded diamond grinding wheels. With the application of ELID technology, mirror surface finish was realized with a #4000 mesh size wheel (average grain size = 4μm). Differences in ground surface topography caused by wheel grain size were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM studies reveal that material was predominantly removed in the ductile mode when ELID grinding was performed with a #4000 grit size wheel or finer.     

Highly Efficient Grinding of Ceramic Parts by Electrolytic In-Process Dressing (ELID) Grinding

In the manfacture of structural ceramic components, it has been well documented that the grinding costs can be as high as 90% of the total cost. Grinding costs of ceramics can be reduced by maximizing the material removal rates (MRR). A novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels, known as Electrolytic In-Process Dressing (ELID) has been developed (1) which can significantly increase the MRR. This technique uses a metal bonded grinding wheel that is electrolytically dressed, during the grinding process, for continuous protrudent abrasive from superabrasi ve wheels. The principle of ELID grinding technology will be discussed in this paper as will its application for rough grinding. The effects of various parameters such as wheel bond type and type of power supply on the ELID grinding mechanism will also be addressed in this paper.     

Finishing of Hardened Boreholes: Grinding or Hard Cutting?

The finishing processes of parts have been carried out mainly by abrasive grinding techniques. Grinding is a theoretically well-elaborated and widespread machining process. That is why its replacement by another metal removal technique, hard cutting, requires very careful examination. In this article, the possibilities are outlined for finishing internal cylindrical surfaces of hardened steels (i.e., boreholes, by employing hard cutting instead of grinding). The process characteristics, the surface quality, and some economic and ecological features of the process are compared theoretically and experimentally, and discussed.     

ELID磨削砂轮表面氧化膜力学性能

砂轮表面的氧化膜对保证在线电解修整（ELID）磨削的非线性电解以及对改善磨削表面质量都具有极其重要的作用.利用纳米压痕技术研究了氧化膜的硬度、弹性模量及刚度.研究结果表明,氧化膜的硬度约为210MPa,是基体硬度的1/4-1/3,使氧化膜有效地隔离了基体与工件,避免基体划伤磨削表面;氧化膜弹性模量约为30-50 GPa,是基体弹性模量的1/6-1/3,因此弹性变形更易发生,有利于磨粒的协同性与等高性;氧化膜刚度约为15μN/nm,由于氧化膜的动态更新,其值与磨削参数有关.在精密磨削时,由于氧化膜发生弹性变形,减小了磨粒的出刃高度和磨削深度,使磨削表面质量得到改善.     

纳米结构陶瓷涂层的外圆磨削力以及磨削表面精度的实验研究

使用功率计监测磨削加工的能量消耗，探讨了纳米结构陶瓷涂层的外圆磨削过程；对纳米陶瓷涂层和传统陶瓷涂层在磨削力和磨削表面精度方面进行了比较．磨削实验使用了外圆磨床和陶瓷结合剂金刚石砂轮．通过测量主轴功率获得切向磨削力，讨论了加工参数，如切深、进给率以及砂轮粒度对切向磨削力的影响．还对磨削后的涂层表面用粗糙度仪和扫描电镜进行了评估，揭示了表面粗糙度与加工参数的关系．     

Grinding of Toroidal and Cylindrical Surfaces on SiC Using Diamond Grinding Wheels

This paper presents the methods and experimental results for grinding toroidal and cylindrical surfaces made of silicon carbide using diamond grinding wheels and an inexpensive CNC machining center. The mirrors were successfully obtained by automatic grinding operations with good shape accuracy, mirror surface finish, and low roughness heights. The time consumed in the process is very short. Industrial manufacture of lenses usually involves three operations — grinding without dressing, lapping, and polishing. In the laboratory studies, however, mirrors and lenses have been manufactured only with grinding process, because of 100% ductile-mode material removal in grinding with dressing. These processes were individually evaluated for surface roughness and surface integrity using surface roughness testers and a scanning electron microscope.     

An experimental investigation as to the effect of cutting parameters on roundness error and surface roughness in cylindrical grinding

This paper presents the results of an experimental investigation as to the effects of grinding parameters on roundness error and surface roughness in cylindrical grinding. Many variables including the wheel materials, wheel loading and dressing, workpiece metallurgy, work drive mechanisms, work holding methods, coolant types, feeds and speeds, machine stiffness and age, surface conditions, centre conditions, floor vibrations all influence the quality of ground parts. However, the composite sum of these grinding parameters creates static and dynamic forces. It is obvious that the roundness error and surface roughness are created by many parameters, but in this study, only the effects of the depth of cut, work speed and feed rate which create the grinding forces in cylindrical grinding are investigated. The grinding experiments were planned according to the principles of orthogonal arrays (OAs), developed by Taguchi, and were performed so as to understand the effects of these parameters on roundness error and surface roughness. The experimental data was analysed by using statistical tools: the percent contribution from an analysis of variance (ANOVA) and the correlation between machining parameters with roundness error (R) and also surface roughness (Ra). Roundness was found to be the most related with the cutting speed, grinding force and depth of cut, while surface roughness is related to feed rate and work speed.     

Effect of diamond surface grinding conditions on the strength of hard alloys

It was shown that diamond grinding produces an increase in the strength of hard alloys (cobalt-bonded carbides) as a result of the removal of defective surface layers. Procedures of diamond surface grinding of a hard alloy VK6 with wheels with organic, metallic and ceramic binders were established which ensure the highest alloy strength.     

Grinding Characteristics of Hard and Brittle Materials by ELID-Lap Grinding Using Fine Grain Wheels

In this investigation, ceramics such as zirconia and silicon carbide were ground by lap grinding using the ELID (electrolytic in-process dressing) method and using various-sized metal bonded wheels (mesh sizes of #1200-#8000). Differences in the ground finish, according to the wheel grain size, and surface roughness were investigated through the use of a Scanning Electron Microscope (SEM). It was found that the ground surface roughness improved proportionally to the grain size. The SEM observations also showed that the ground surfaces using wheels over #4000 were very smooth with several minute ground grooves crossing each other without brittle fracture. Brittle-ductile transition was studied using these wheels and the removal mechanisms of silicon and tungsten carbides were also investigated. It was found that for silicon, brittle-ductile transition was obtained using wheels over #8000 and for tungsten carbides, transition was achieved using wheels over #4000. Therefore, the work materials affect the changes in the removal mechanism.     

基于双盘直槽研磨的圆柱滚子自转运动研究

为了解决双盘直槽研磨方法实施过程中的关键技术问题,针对圆柱滚子在研磨状态下的自转运动展开相关研究.首先,对圆柱滚子在研磨状态下的自转运动进行理论分析,得到了其稳定自转的条件.然后,基于ADAMS(automatic dynamic analysis of mechanical systems,机械系统动力学自动分析)软...     

A novel magnetorheological honing process for nano-finishing of variable cylindrical internal surfaces

A novel magnetorheological honing process is designed and developed for nano-finishing of cylindrical internal surfaces with the help of permanent magnets. The radial movement of magnetic tool surface is adjusted as per the internal diameter of different cylindrical components and make it fixed before start of finishing so that it can maintain constant working gap while perform finishing. The present developed magnetic tool surface always constitutes higher magnetic field than the inner surface of ferromagnetic or non-ferromagnetic cylindrical workpiece. This is an important requirement to finish the internal surface of ferromagnetic or non-ferromagnetic cylindrical components because it ensures MR polishing fluid cannot stick on the workpiece surface while performing the finishing. Hence, present developed process is useful for finishing of ferromagnetic cylindrical molds, dies, hydraulic actuators, etc. for its better functional applications after the conventional honing or grinding process. The internal surface roughness of cylindrical ferromagnetic workpiece is dropped to 90?nm from its initial value of 360?nm in 100 minutes of finishing. Further scanning electron microscopy has also been done to understand the surface characteristics of finished workpiece. The results revealed that the developed magnetorheological honing process is capable to perform nano-finishing of internal surface of the ferromagnetic cylindrical components.     

Relationship Between Performance and Sparks Generated in Selected Cylindrical Grinding Experiments

The sparks observed in metal grinding are actually glowing chips. Thus, for a specific workpiece — wheel combination, it is possible to modulate the characteristic of the sparks by changing the size of the chip through the process speeds and feeds. An investigation into the sparks generated during cylindrical grinding of medium carbon steel is conducted with the aim of establishing a reliable and easy method to measure performance index. The investigation shows that illuminance and irradiance of the spark are functionally related to many desirable measures of the process performance, namely, surface roughness, wheel wear, power consumption and material removal rate. The results provide the user with new grinding data suitable for process control, especially on-line control.     

Simulation of cylindrical plunge grinding based on the behaviour of cutting edge wear

In cylindrical plunge grinding, a series of workpieces are ground successively without intermediate dressing of the wheel. Through the grinding, the wheel characteristic is continuously changed by the wear, fracture and new exposure of abrasive grains, having a profound effect on the grains on wheel surfaces in the cylindrical grinding process are developed to make it possible to describe the time dependent results of grinding and to establish the grinding operation standards capable of estimating grinding wheel performance and selecting grinding conditions, in which many parameters in actual grinding operations are considered. This simulation system can display its results in graphical form including the time dependent results and the effects of various parameters as well as optimization capabilities. This simulation has the same effects as many grinding experiments, and capable of selecting the optimum grinding wheels and conditions.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil III: Schleifen von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part III: Grinding of Hard Alloys Straight surface plunge grinding tests were performed at a peripheral wheel velocity of v_c = 15 m/s on exemplary iron based alloys FeCr12C2.1, FeCr13Nb9MoTiC2.3 and FeCr14Mo5WVC4.2 both in soft annealed and hardened and slightly relieved microstructural condition. Vitrified bonded wheels of type SC 60 3/4 (SiC) and 2B252 M6 V240 (CBN) with a diameter of D_S = 300 mm were used as abrasive tools. When selecting the machining parameters due consideration was given to materials related aspects and an acceptable volumetric removal rate per unit width of Q_w′ = 4 mm³/mms was taken into account. Subsequent examinations focused on the analysis of the thermomechanical load imposed on the microstructure. The grinding of hard alloys by means of conventional abrasives is significantly influenced by the content and type of the hard phases present. Due to their excessive hardness primarily solidified M₇C₃ are highly resistant to the ingressing abrasive grains. Accordingly, maximum grinding normal forces are encountered with the FeCr14Mo5WVC4.2 alloy. However, the normal forces are also found to be higher in case of a hardened metal matrix, when SiC is used as abrasive or a wet grinding process is applied. As regards tangential forces they also show a tendency of being influenced by structure-specific hard phases. Process temperature and stress condition ahead of the grain cutting edges are of great significance for the behaviour of the hard phases during grinding. If the mechanical component is predominant, accumulations of near-surface eutectic carbides are destroyed. Individual stalk-like carbides often break in the phase center. However, in the event of thermal load an eutectic M₇C₃ may also be deformed plastically. Through the cleavage fracture of coarse primary M₇C₃ phases microcracks are initiated that in the end will grow into macrocracks. Carbide fragments broken off will impair the surface quality. In particular the metal matrix reacts strongly to the process heat generated. In case of dry grinding using SiC a rehardening zone has been detected near the surface. The alloy-specific austenizing temperature of approximated 1000 °C was exceeded. As the distance to the surface increased a tempered area with hardness figures below those of the basic structure was found. No rehardening will occur if CBN is used as abrasive. The residual surface stresses determined correlate with the extent of thermal and mechanical load imposed. Whereas an extensive crack network is evident after dry grinding when SiC has been used as abrasive, no surface cracks were detected when employing the CBN abrasive. Due to the excellent thermal conductivity characteristics of this grinding medium a thermal damage during dry grinding can be avoided. While the use of grinding fluid will improve the surface roughness, cracks may form due to the abrupt quenching effect, especially if hardened material is involved. Increasing the workpiece velocity will also contribute to reduce the risk of crack development, but, on the other hand, leads to a surface quality deterioration that cannot be accepted.     

Increasing workpiece peripheral speed as a means for improving ergonomics of cylindrical up grinding with cubic boron nitride tools

The author pioneered in experimentally finding out that an increase in the workpiece peripheral speed proper in a wide range invariantly leads to a definitely better surface roughness, i.e., smaller thickness of cut, suggesting an improvement in the process ergonomics, in cylindrical centered up grinding under elastic attrition and linear wear conditions, with cubic boron nitride tools of various specifications, on the grinders differing in static stiffness (8.3 and 12.0 N/μm), with a wheel speed ranging from 32 to 91 m/s. A comparative assessment of grinding processes with a fixed and controllable levels of forced vibrations at idling speed has demonstrated that the weakening of the positive influence of the speed factor on the surface roughness and thickness of cut with increasing workpiece speed proper and/or wheel speed is due to the vibration-induced suppression—an increasing amplitude of the wheel-workpiece vibration displacements at rotational speeds of the wheel, workpiece, and other elements of the grinder-workpiece-tool system. Some recommendations are offered of how to improve the ergonomics of cylindrical up grinding with cBN tools by increasing the workpiece speed proper.     

Magnetorheological finishing of ferromagnetic blind-hole type surfaces

Products having blind-hole type surfaces such as bottle caps are being manufactured in today’s industry and are of great use. Such products are made in permanent blind-hole type mold cavities. At present, these cavities are being finished by internal grinding operations. After grinding, surface defects such as deep-seated groove, cavity, axial scratch, and ploughed material are induced because of uncontrollable finishing forces applied by grinding pins onto the workpiece surface. To obtain a better quality on final-made products, the blind-hole type mold cavities should be made defect-free. In the present process, two different tools based on magnetorheological fluid are developed to finish the lateral and bottom surfaces of cylindrical blind-hole type mold cavities. The workpiece used for finishing is the hardened EN31 die steel. The finite element studies determined the variation in magnetic field within the working gaps. The change in surface roughness (R_a) values of both inner lateral and bottom surfaces reduced by 67.7% and 69.5%, respectively, and found significant improvement in surface characteristics as compared to the initial grind surfaces. The results revealed the usefulness of present process to finish the blind-hole type mold cavities in manufacturing industries for producing a better quality of final-made products.     

The state of the surface layers of quench-hardened steel after diamond grinding

This article describes the results of a study of the effect of grinding cylindrical specimens, with the end face of a diamond-impregnated wheel, on the state of the surface layer of a rolled steel. It was shown that finishing diamond grinding does not eliminate surface defects produced by previous machining operations.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 5, pp. 577–580, September–October, 1969.     

Quality evaluation of internal cylindrical grinding process with multiple quality characteristics for gear products

Gears are among the most crucial components in the transmission systems of machine tools. Gear manufacturing includes a number of processing procedures. The grinding process is an important procedure involving high precision and fairly small grinding surfaces. For this reason, this study aimed at developing a quality assessment model for the internal cylindrical grinding process of gears. The Six Sigma quality indices (SSQIs) were used to directly assess the quality of the internal cylindrical grinding process due to their ability to directly reflect quality level and process yield. Since the process may include nominal-the-best (NTB), larger-the-better (LTB) and smaller-the-better (STB) quality characteristics, so we used the variable transformation method to normalise the specifications of each quality characteristic for the convenient and effective management and analysis of process performance for multiple quality characteristics. We then constructed a multi-characteristic process quality analysis chart (MPQAC) to simultaneously assess the quality levels of various quality characteristics. Furthermore, the MPQAC can provide references for process improvement. This ensures the quality of internal cylindrical grinding and enhances the quality of gear and machine tool products. Finally, a real-world application and numerical experiments demonstrate the effectiveness and practical applicability of the proposed method.