声发射监测技术在磨削加工中的应用

在磨削加工中,砂轮的工作状况是不断变化的,因此,对砂轮的修整及磨削过程进行监测是非常必要的。本文将声发射(AE)信号应用到对磨削过程的监测上,通过监测砂轮修整过程可以得到一致的砂轮表面质量。通过监测AE信号的幅值和频谱特征即可确定砂轮的寿命。用AE信号可以成功地检测出砂轮和工件的初始接触时间,为砂轮向工件进给时的准确对刀及高精度表面质量的获得提供了有效的方法。     

GCr15钢的ELID磨削性能实验研究

为了探讨GCr15钢的ELID（Electrolytic In-process Dressing）磨削性能，在基于大量实验的基础上，对GCr15钢采用ELID磨削时磨削力的变化规律进行了详细分析，并将磨削力、磨削表面粗糙度与普通磨削进行了比较。结果表明，采用铸铁结合剂CBN砂轮进行ELID磨削时磨削力几乎不随时间的变化而变化，而采用白刚玉砂轮进行磨削时的磨削力随时间的变化不断增大，在线电解修整使CBN砂轮在磨削过程中始终保持良好的磨削性能，有利于节省砂轮修整时间，提高加工效率。在ELID磨削中，采用微细砂轮进行磨削可以获得很低的表面粗糙度，实现对GCr15钢的超精密镜面磨削。     

陶瓷喷涂层精密镜面磨削技术的实验研究

在工件表面用喷涂方法形成陶瓷涂层,可以显著改善其性能。但是由于陶瓷喷涂层的硬脆特性,难以进行精密加工。本文引入金属基超硬磨料砂轮在线电解修整（ＥＬＩＤ）技术,对陶瓷喷涂层进行精密镜面磨削的实验研究。结果表明,该技术加工精度高、表面质量好,极具应用前景。     

在线电解修整(ELID)超精密磨削中的金刚石磨具特性研究

ELID(Electrolytic In-process Dressing)磨削技术是在电化学加工、电解磨削原理基础上发展起来的一项磨削新技术,主要用于硬脆材料超精密磨削过程中金属基结合剂超硬微细磨粒砂轮的在线修整.本文以金刚石微粉砂轮在线电解修整(ELID)磨削氮化硅陶瓷为例,着重研究了磨具特性对硬脆材料超精密磨削过程的影响.研究表明,磨具组织沿砂轮圆周的不均匀性将会导致砂轮表面钝化膜状态的不一致,这将直接影响砂轮局部参与切削的磨粒数量,影响单个磨料的实际磨削厚度.这首先将对工件表面的磨削质量,特别是对表面粗糙度产生直接影响,同时也非常不利于实现材料的高效去除.     

Numerical modelling of ground surface topography: effect of traverse and helical superabrasive grinding with touch dressing

Grinding processes are often used for final finishing of components because of their ability to satisfy stringent requirements of surface roughness and dimensional tolerance. Surface topography generated during grinding depends upon many parameters like wheel parameters, wheel velocity, downfeed, grit density etc. and it also depends upon the type of grinding procedures (viz. plunge grinding, traverse grinding, helical grinding, touch dressing etc.) employed. Therefore, a correct examination of the parameters and type of process employed to carry out grinding are necessary. This paper is an attempt to develop the relation between the different grinding parameters and the grinding procedures like plunge, traverse and helical superabrasive grinding with touch dressing and the average surface roughness. For this purpose, a numerical simulation technique has been implemented to generate the grinding wheel topography. The ground workpiece surface has also been generated by simulating removal of work material depending upon the trajectory of the abrasive grits on the grinding wheel without taking rubbing and ploughing into consideration.     

Experimental study of ELID grinding based on the active control of oxide layer

The oxide layer state directly relates to the grinding efficiency and machining quality in Electrolytic In-process Dressing (ELID) grinding. In order to monitor and control the state of the oxide layer, a new high-frequency pulse power source is proposed for ELID grinding. It uses the superposition of big and small pulses to achieve periodical electrolysis and to adjust oxide layer state. Based on an analysis of current change with duty cycle, a pulse-based fuzzy control program was designed to control the state of the oxide layer within a certain range and the oxide layer grinding efficiency in different oxide layer states was studied. The results show that the new power source could maintain a stable grinding process and that the dressing current should be controlled according to the grinding wheel grain size.     

In-process evaluation of grit protrusion feature for fine diamond grinding wheel by means of electro-contact discharge dressing

This paper introduces a new in-process evaluation method for grit protrusion feature on wheel surface by monitoring discharge current trace during electro-contact discharge (ECD) dressing of metal-bonded fine diamond grinding wheel. First an impulse discharge machining experiment was carried out to investigate the correlation between metal bond removal and discharge parameters, namely discharge current I_e and discharge pulse duration τ_e. Then ECD dressing experiment for #600 diamond grinding wheel was conduced to analyses the quantitative effect of the discharge parameters (I_e and τ_e), derived from discharge current trace between wheel and dresser (electrode), on grit protrusion feature of wheel surface. The result shows that the grit protrusion feature is sensitive to the discharge parameters (I_e and τ_e) with reference to mean diamond grit size d_gm. Further, the discharge parameters (I_e and τ_e) in ECD dressing should conform to the discharge variables’ requirement of , by which the grit protrusion feature may be evaluated and the dressing process variables may be determined. Finally, the in-process evaluation method was successfully applied to ECD dressing of #1500 diamond grinding wheel for valid grinding of hard-brittle materials.     

Surface finishing of Ni–Cr–B–Si composite coatings by precision grinding

A Ni–Cr–B–Si/10vol%WC coating material has been precision ground to an optical quality surface finish (<10 nm R_a) using a combination of a very stiff precision machine tool, Tetraform “C”, 76 μm CBN grinding wheels and electrolytic in-process dressing (ELID) assisted grinding. When grinding without ELID, surface finish has been shown to be limited by damage to primary and secondary carbides. This damage may be in the form of carbide pull-out or localised fracture and removal of the larger primary WC particulate. ELID assisted grinding helps maintain CBN grit protrusion and sharpness and thus promotes efficient cutting during grinding, minimising pull-out and localised damage to the harder phases within the coating microstructure. ELID therefore improves both the overall surface finish and surface integrity of the workpiece.     

A fundamental study on the mechanism of electrolytic in-process dressing (ELID) grinding

Demands for high quality surface finish, dimensional and form accuracy are required for optical surfaces and it is very difficult to achieve these using conventional grinding methods. Electrolytic in-process dressing (ELID) grinding is one new and efficient method that uses a metal-bonded diamond grinding wheel in order to achieve a mirror surface finish especially on hard and brittle materials. However, studies reported so for have not explained the fundamental mechanism of ELID grinding and so it has been studied here by conducting experiments to establish optimal grinding parameters to obtain better surface finish under various in-process dressing conditions. In this research the results show that the cutting forces are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of the grinding wheel; however, a smoother surface can be obtained using a high dressing current duty ratio at the cost of high tool wear. ELID grinding is efficient for feed rates of less than 400 mm/min, and surface cracks are observed when it exceeds this limit.     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

氧化铝陶瓷ELID高效磨削技术的研究

陶瓷材料具有优异的机械性能，其应用越来越广泛。然而由于陶瓷的高硬度及其易碎性使其难于加工。在线电解修整磨削技术已经被应用于硬脆材料的超精密加工，由于可以实现砂轮的在线修整，尤其被广泛应用于细粒度砂轮的磨削中。本文在平面磨床上应用铸铁结合剂金刚石砂轮与ELID磨削技术进行高效磨削研究。实验结果表明，在同样的磨削条件下，采用ELID磨削时的磨削力约为使用树脂结合剂砂轮磨削力的2／5～3／5。实验结果说明采用ELID磨削技术加工效率可以得到极大提高。而且，在线电解修整作用可以保持砂轮的锋锐性，有利于保持硬脆材料高效磨削的连续性。     

ELID grinding of silicon wafers: A literature review

Silicon wafers are the most widely used substrates for fabricating integrated circuits. There have been continuous demands for higher quality silicon wafers with lower prices, and it becomes more and more difficult to meet these demands using current manufacturing processes. In recent years, research has been done on electrolytic in-process dressing (ELID) grinding of silicon wafers to explore its potential to become a viable manufacturing process. This paper reviews the literature on ELID grinding, covering its set-ups, wheel dressing mechanism, and experimental results. It also discusses the technical barriers that have to be overcome before ELID grinding can be used in manufacturing.     

碟轮修整单层钎焊金刚石砂轮的试验研究

单层钎焊金刚石砂轮在制作完成之初由于砂轮基体加工存在误差以及磨粒粒径大小不一等原因造成磨粒等高性不一致,这使其难以在硬脆材料的精密磨削中得到广泛的应用。采用自制的钎焊碟轮对80/100#单层钎焊金刚石砂轮进行了修整试验研究。在修整试验前后跟踪了砂轮磨粒等高性的变化,进行了SiC陶瓷的磨削试验,并观测了工件表面质量的变化情况。试验结果表明:采用此方法能够实现单层钎焊金刚石砂轮的高效精密修整。修整试验结束后砂轮磨粒等高性较好,磨削SiC陶瓷的表面质量得到明显改善,表面粗糙度Ra值达到了0.1μm以下。     

Influence of different grinding wheel and dressing roller specifications on grinding wheel wear

A targeted adjustment of the dressing results and the methodological influence of the dressing process on the non-stationary wear of a grinding wheel after dressing increases the productivity and the reproducibility of grinding processes. Despite the great economic importance of grinding processes with vitrified corundum grinding wheels and the great relevance of the dressing process for the application behavior of these grinding wheels, quantitative models are missing for the purposeful design of the dressing process. In previous studies, a dressing model was successfully developed which predicts the dressing force in the dressing process as well as the workpiece roughness and the grinding wheel wear behavior in a grinding process for a specific grinding wheel and form roller specification. However, a transferability of this model to other grinding wheel and form roller specifications is not possible because the influence of the grain size and the hardness of the grinding wheel as well as the dressing tool topography on the grinding wheel wear and thus on parameters of the dressing model are not known. The objective of this work was to extend the model to additional grinding wheel and form roller specifications to ensure a broad applicability of the model.     

Internal mirror grinding with a metal/metal–resin bonded abrasive wheel

Precision internal cylindrical surfaces are increasingly utilized in industries where highly efficient methods to fabricate such surfaces are of great importance. Presently, several processes usually performed on different machines are used successively to achieve a mirror finish. In this paper, a novel method is presented to accomplish roughing and finishing processes on one machine, using super abrasive cast–iron–bond CBN (CIB–CBN) wheels and metal–resin–bond CBN (MRB–CBN) wheels. Two dressing methods, electrolytic interval dressing and electrolytic in-process dressing (ELID), are also developed for these wheels respectively. The CIB–CBN wheel is trued by an on-machine electrical discharge truer (EDT) and dressed at intervals with a pipe-shape electrode; the MRB–CBN wheel is dressed in process, in which no specific dressing electrode is utilized, instead the conductive workpiece acts as a dressing electrode. Precision grinding has been carried out on an ordinary grinder with an attachment for internal cylindrical grinding. Wheels of #325, #1200, #2000, and #4000 grit sizes have been applied in the process to obtain mirror surfaces.     

On the mechanics of the grinding process, Part III—thermal analysis of the abrasive cut-off operation

This is Part III of a 3 part series on the Mechanics of the Grinding Process. Part I deals with the stochastic nature of the grinding process, Part II deals with the thermal analysis of the fine grinding process and this paper (Part III) deals with the thermal analysis of the cut-off operation. Heat generated in the abrasive cut-off operation can affect the life of resin bonded grinding wheels and cause thermal damage to the workpiece. Thermal analysis of the abrasive cut-off operation can, therefore, provide guidelines for proper selection of the grinding conditions and optimization of the process parameters for improved wheel life and minimal thermal damage to the workpiece. In this investigation, a new thermal model of the abrasive cut-off operation is presented based on statistical distribution of the abrasive grains on the surface of the wheel. Both cutting and ploughing/rubbing that take place between the abrasive grains and the work material are considered, depending on the depth of indentation of the abrasives into the work material. In contrast to the previous models, where the apparent contact area between the wheel and the workpiece was taken as the heat source, this model considers the real area of contact, namely, the cumulative area of actual contacting grains present at the interface as the heat source. It may be noted that this is only a small fraction of the total contact area as only a small percentage of the abrasive grains present on the surface of the cut-off wheel are in actual contact with the workpiece at any given time and even a smaller fraction of them are actual cutting grains taking part in the cut-off operation. Since, the Peclet number, N_Pe in the case of cut-off grinding is rather high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source with the same heat liberation intensity as the circular disc heat source. However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the wheel-work interface, for a longer period of time ( milliseconds) whereas the workpiece contacts the heat source for shorter period of time ( a few microseconds). The temperature in the grinding zone is taken as the sum of the background temperature due to the distributed action of the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip-workpiece interfaces (local thermal analysis), similar to the work reported in the literature [Proc Roy Soc (London) A 453 (1997) 1083]. The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The model developed provides a better appreciation of the cut-off operation; a realistic estimation of the heat partition between the wheel, the workpiece, and the chip; thermal gradients in the workpiece due to abrasive cut-off operation, and an insight into the wear of the cut-off wheels.     

单颗钎焊金刚石磨粒磨损试验研究

采用单颗磨粒试验方法,以碳钢碟轮为修整工具,研究金刚石和CBN磨粒修整过程中的磨损特征。结果表明:砂轮和修整碟轮的相对速度对金刚石磨粒的磨损有重要影响;相对速度为51.9 m/s时,金刚石磨粒的磨损高度为50.1 μm;相对速度为17.3 m/s时,金刚石磨粒的磨损高度显著减小,为19.5 μm。通过相同条件下金刚石与CBN磨粒的磨损特征对比,表明金刚石磨粒在磨损过程中同碟轮之间发生化学作用,加速金刚石磨粒的磨损;对试验后金刚石磨粒进行拉曼光谱分析,并未检测到石墨物质。      

超声振动辅助ELID复合内圆磨削系统中大负载变幅器的设计及应用

为解决超声振动辅助ELID复合内圆(UAEI)磨削陶瓷等硬脆材料的声学系统设计难题，对驱动几何尺寸大、质量重的金属结合剂金刚石砂轮用的小端较长的变幅器进行理论设计及优化。基于弹性波在介质中的传播规律，利用MATLAB确定变幅器取值方案，再根据加工要求并结合ANSYS模态分析筛选出符合要求的方案，然后采用零阶算法进一步优化处理，得到满足几何尺寸、应力及振动频率要求的变幅器尺寸。对设计出的变幅器进行振动特性测试，其谐振频率理论误差为0.192%～1.824%，符合预期设计要求。采用研制出的UAEI磨削系统进行加工特性测试，与在线电解修整砂轮(ELID)内圆磨削比较，其工件的表面粗糙度降低了44.2%，且工件三维形貌更加平整，砂轮表面状况获得改善。      

纳米结构金属陶瓷(n-WC/Co)涂层材料精密磨削的试验研究

本文对纳米结构金属陶瓷（n-WC/Co）涂层材料在金刚石砂轮精密磨削过程中的磨削力进行了较详细的试验研究。对常规结构金属陶瓷(n-WC/Co）和n-WC/Co涂层材料的磨削力作了对比磨削试验,分析了磨削工艺参数如砂轮磨削深度,工件进给速度,金刚石砂轮结合剂类型和磨粒尺寸以及被磨试件材料特性等对磨削力的影响,结合被磨试件表面的扫描电镜（SEM）的观察,分析了n-WC/Co涂层材料磨削的材料去除机理,研究结果表明：在相同磨削条件下,纳米结构陶瓷涂层的磨削力始终高于常规结构陶瓷涂层的磨削力;在其它磨削条件相同的情况下,用金属结合剂砂轮磨削工件所需的磨削力要比树脂结合剂砂轮,陶瓷结合剂砂轮所需的磨削力大些,磨粒尺寸小的砂轮磨削工件所需的总磨削力要比磨粒尺寸在的砂轮所需的磨削力大些,磨削力随砂轮磨削深度,工件进给速度的增加而增大;一般情况下,n-WC/Co涂层材料精密磨削过程的材料去除机理中,占主导方式的是塑性成形的材料去除方式。     

ELID grinding and tribological characteristics of TiAlN film

This paper presents the results of electrolytic in-process dressing (ELID) grinding experiments performed on TiAlN film and characterization of the tribological characteristics of the produced films. In advanced films coated by physical vapor deposition, such as CrN and TiAlN, the low surface roughness required for attaining superior tribological characteristics is difficult to attain by use of only a coating process. ELID of grinding wheels improves wheel performance, enabling the attainment of specular finishes on brittle materials, with surface roughness on the nanometer scale (4 to 6 nm). In the present study, high-quality TiAlN film surfaces were fabricated by the ELID technique, typically achieving a surface roughness of around Ra 0.0024 μm by employment of a SD#30,000 wheel. Scanning electron microscopy reveals that ELID improved the finish, as indicated by the shape of grinding marks. Chemical element analysis by an energy-dispersed x-ray diffraction system suggests that ELID grinding formed an oxide layer in the machined surface of TiAlN film. Therefore, in addition to the highly smooth surface, an oxide layer formed by ELID grinding imparts superior tribological properties to ELID-ground TiAlN film.