IN SITU TRUING/DRESSING OF DIAMOND WHEEL FOR PRECISION GRINDING

An application for achieving on-machine truing/dressing and monitoring of diamond wheel is dealt with in dry grinding. A dry electrical discharge （ED） assisted truing and dressing method is adopted in preparation of diamond grinding wheels. Effective and precise truing/dressing of a diamond wheel is carried out on a CNC curve grinding machine by utilizing an ED assisted diamond dresser. The dressed wheel is monitored online by a CCD vision system. It detects the topography changes of a wheel surface. The wear condition is evaluated by analyzing the edge deviation of a wheel image. The benefits of the proposed methods are confirmed by the grinding experiments. The designed truing/dressing device has high material removal rate, low dresser wear, and hence guarantees a desired wheel surface. Real-time monitoring of the wheel profile facilitates determining the optimum dressing amount, dressing interval, and the compensation error.     

CBN砂轮在轴承套圈内圆磨削中的应用

CBN砂轮以其优异的性能在高效、高精度磨削中具有广阔的应用前景。文中以树脂结合剂CBN砂轮轴承圈内圆磨削为研究对象,采用金刚石滚轮修整器,研究选择合适的修整及磨削参数,使CBN砂轮的性能在轴承磨削中得到充分发挥。通过对修整前后砂轮表面形貌分析,揭示了修整参数对修锐效果的影响,并结合磨削后试件表面的精度获得了合适磨削参数,试验结果对CBN砂轮在轴承圈的大批量磨削中的广泛应用具有重要的指导意义。     

垂直式超硬砂轮圆弧修整器设计与砂轮修整

针对圆弧形超硬砂轮修整难度大、修整精度低的问题,对树脂结合剂圆弧形金刚石砂轮进行了精密修整研究。设计制造了一种垂直式超硬砂轮圆弧修整器,通过修整试验研究了不同粒度的圆弧形砂轮在修整前后表面粗糙度、弧形精度、圆度、表面形貌的变化情况。砂轮修整前后对氮化硅陶瓷轴承套圈沟道进行了磨削,并测量了磨削后的轴承套圈沟形精度。研究结果表明：相比修整前,修整后砂轮表面粗糙度平均值由1.731 8 μm减小至0.772 4 μm,减小了55.4%;弧形精度平均值由33.604 7 μm减小至8.527 6 μm,减小了74.6%,修整后4个砂轮的弧形精度更加稳定,且随着砂轮粒度的减小,弧形精度略有减小趋势;砂轮圆度平均值由43.721 μm减小至18.002 μm,减小了58.8%,修整使大量新的磨粒露出。所设计的垂直式超硬砂轮圆弧形修整器可对圆弧砂轮进行精密修整,可改善圆弧形砂轮的弧形精度及圆度,修整后砂轮磨削的轴承套圈沟形精度得到了大幅提高。     

激光与电火花复合修整粗粒度弧形金刚石砂轮试验研究

因受到激光高斯光束特性的影响,辐照在砂轮表面上的光斑大小和激光能量都跟随修整路径变化,难以实现高精度的弧形金刚石砂轮的修整,为此,提出采用激光粗修整和电火花精修整的复合修整方法。先用激光修整高效去除多余磨料层来得到弧形轮廓,再用一高精度弧形电极匹配该轮廓进行电火花修整,得到较高精度的弧形砂轮。在粒度为120的金刚石砂轮上试验修整半径为13 mm的弧形轮廓,最终修整出的弧形轮廓半径为13.006 mm,轮廓误差PV值为10.90 μm。最后,通过磨削氧化铝陶瓷验证了砂轮修整效果。检测磨削工件的弧形轮廓拟合半径为13.012 mm,轮廓误差PV值为11.33 μm。     

碟型金刚石砂轮修整系统稳定性分析及修整装置的改进

对杯型砂轮修整碟型金刚石砂轮的修整系统进行了稳定性分析,分析结果表明:杯形砂轮磨损刚度、碟型金刚石砂轮磨损刚度以及两砂轮间的接触刚度对修整系统稳定性的影响明显,其中两砂轮间接触刚度的影响因具有双倍效应,故最为显著;在系统稳定的前提下提高两砂轮间的接触刚度可提高修整质量和修整效率。在此理论基础上对原有专用修整装置进行了改进,从而大大提高了修整效率和修整质量。     

Investigation of internal ultrasonically assisted grinding of small holes: effect of ultrasonic vibration in truing and dressing of small CBN grinding wheel

In internal grinding of small holes, it is hard to realize high accuracy truing and dressing for the grinding wheel when a conventional truing/dressing method using single diamond dresser or rotary cup wheel is employed. Because of the cantilever support condition of the spindle shaft the stiffness of shaft is reduced. Thus the truing force leads the shaft to a significant deformation during truing/dressing. In this study, for improving the truing and dressing accuracy, a new truing/dressing method was proposed, in which the grinding wheel is ultrasonically vibrated along its axis during truing/dressing with a GC rotary cup wheel. A series of experiments were carried out to investigate the effects of the wheel ultrasonication on the truing force reduction, the truing accuracy improvement and the wheel surface condition. In addition, the grinding force and work surface roughness experimentally obtained by using the wheels trued with or without ultrasonication were compared. The experimental results indicated that applying ultrasonic vibration to the wheel decreases the normal and tangential grinding forces by more than 20% and 24%, respectively, and the surface roughness by as much as 18%.     

超硬磨料砂轮修整及点轮修整技术

与普通磨料砂轮相比,采用金刚石车削法修整超硬磨料砂轮,修整力大、工具磨损快、修整时间长、效率低、精度低及质量差,致使超硬磨料砂轮的优异性能得不到充分发挥,砂轮修整已经成为制约超硬磨料砂轮工程应用的主要瓶颈.在超硬磨料砂轮修整研究方面,科研成果众多,技术各有特点,然而工程应用有限.点轮修整是集金刚石车削修整、金刚石滚轮磨...     

A novel technique for dressing metal-bonded diamond grinding wheel with abrasive waterjet and touch truing

The dressing of metal-bonded diamond grinding wheels is difficult despite their availabilities on hard and brittle materials. In this paper, a novel compound technology that combines abrasive waterjet (AWJ) and touch truing is proposed for dressing metal-bonded diamond grinding wheel precisely and efficiently. The dressing experiments of a coarse-grained and a fine-grained bronze-bonded diamond grinding wheel were carried out on a surface grinder with a developed AWJ system. The feasibility of this method was verified by analyzing the wheel runout, the truing forces, and the wheel surface topography. The variations of 3D surface roughness of wheel surface topography during the compound dressing process were quantitatively analyzed. The mechanism of AWJ and touch compound dressing is also discussed. Further, a reaction-bonded silicon carbide block was ground to validate the dressing quality. The experiment results indicate that the grinding wheels that were well dressed by the proposed technique leads to a smaller grinding force and a smaller surface roughness than that of undressed wheels.     

Experimental study of wheel wear in electrolytic in-process dressing and grinding

Profile accuracy of components ground with ultra-precision machine tools is primarily dependent on wheel wear. Quantitative analysis of wheel wear is therefore an important aspect for precision grinding with electrolytic in-process dressing (ELID). In this paper, wheel wear is measured from ELID grinding experiments with different dressing and machining parameters. The grinding forces and dressing current characteristics of the experiments are also compared. Based on the results, a benchmark function is defined for wheel wear rate. A relation for identifying insufficient dressing from sufficient dressing for particular machining conditions is also identified. It is found that insufficient dressing produces pitting and/or arcing on the wheel surface, and wheel wear can be linearly correlated to ELID grinding conditions when the wheels are sufficiently dressed.     

金刚石型面约束的自由磨粒挤磨修整超硬磨料砂轮方法

针对超硬磨料砂轮存在修整困难的问题,基于金刚石和普通材料在强度上存在巨大差异的特点,提出了一种在金刚石型面约束下将磨粒挤压和修磨相结合的修整方法,其基本原理是：表面有精密形状的金刚石工具通过高速旋转生成具有约束能力的高强度型面,型面通过约束自由磨粒对被修砂轮产生挤压划擦作用破坏砂轮结合剂完成砂轮高效修形,同时通过修整工具高强度金刚石磨料的微研削作用对被修砂轮型面进行进一步精密修磨。对约束型面的形成及自由磨粒在型面约束下挤压和研削作用机制进行了分析,并介绍了挤磨修整系统的构成和特性,对修整力、修磨速度和自由磨粒等参数影响规律进行了初步试验探索,结果表明,自由磨粒型面约束下的挤压能够实现超硬磨料砂轮的快速成形精密修整。     

砂轮表面形貌定量评价及修整效果研究

基于砂轮表面磨粒出刃面积,提出砂轮表面磨粒出刃面积率Sr的概念,在此基础上提出磨粒出刃度βd和磨粒出刃面积分散度δs两个指标来评价砂轮表面形貌特征。用滚轮修整器对树脂结合剂金刚石砂轮进行修整实验,分析了不同修整方式、修整深度和修整速比对βd和δs的影响。采用修整后的砂轮进行磨削实验,分析了不同特征参数的砂轮对磨削力和工件表面粗糙度的影响。研究结果表明,采用较小的修整深度、较小的修整速比,多次进给修整砂轮时,磨粒出刃度高、磨粒出刃面积分散度小,修整效果好。当βd为69.35%、δs为1 000 μm2时,磨削力、表面粗糙度最小,表明砂轮磨削性能最好,证明修整质量最高。因此所提出的βd、δs两个指标能对修整后的砂轮表面形貌进行有效评价,且磨粒出刃面积的检测方法简单,检测效率较高。     

A study on wear mechanism and wear reduction strategies in grinding wheels used for ELID grinding

Metal-bonded superabrasive diamond grinding wheels have superior qualities such as high bond strength, high stability and high grindability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the grinding wheel. Electrolytic in-process dressing (ELID) is an effective method to dress the grinding wheel during grinding. The wear mechanism of metal-bonded grinding wheels dressed using ELID is different form the conventional grinding methods because the bond strength of the wheel-working surface is reduced by electrolysis. The reduction of bond strength reduces the grit-depth-of-cut and hence the surface finish is improved. The oxide layer formed on the surface of the grinding wheel experiences macrofracture at the end of wheel life while machining hard and brittle workpieces. When the wheel wear is dominated by macrofracture, the wheel-working surface is free from loaded chips and worn diamond grits. When the oxide layer is removed from the wheel surface, the electrical conductivity of the grinding wheel increases, and that stimulates electrolytic dressing. The conditions applied to the pulse current influence the amount of layer oxidizing from the grinding wheel surface. Longer pulse ‘on’ time increases the wheel wear. Shorter pulse ‘on’ time can be selected for a courser grit size wheel since that type of wheel needs high grinding efficiency. Equal pulse ‘on’ and ‘off’ time is desired for finer grit size wheels to obtain stable and ultraprecision surface finish.     

修整成形砂轮的CAD／CHM系统

砂轮修整是成形磨削中的关键技术。本文介绍一种具有较好通用性和实用性的成形砂轮修整ＣＡＤ／ＣＡＭ系统。该系统具有方便灵活的输入方式和良好的人机界面，能够解决各种类型的蜗杆和齿轮的砂轮修整廓形自动生成、自动编程、加工仿真、误差补偿及修整自动控制等问题，同时能满足任意形状的成形砂轮修整要求。     

The Effect of Optimum In-Process Electrolytic Dressing in the Ultraprecision Grinding of Die Steel by a Superabrasive Wheel

In recent years, grinding techniques for precision machining of brittle materials used in dies, moulds and optical parts have been improved by using superabrasive wheels and precision grinding machines. Optimum dressing using a superabrasive wheel makes possible the effective ultraprecision grinding of die steel (STD-11). In this study, a new system and the grinding mechanism for optimum in-process electrolytic dressing are proposed. This method can carry out optimum in-process electrolytic dressing of a superabrasive wheel. Optimum in-process electrolytic dressing is a good method for obtaining efficiency and ultraprecision grinding of STD-11.     

Investigation and development of a molding process for the production of micro-hairs

Cubic boron nitride (cBN) is a unique synthetic material on account of its high hardness, high wear resistance, excellent cutting edge stability and relative chemical inertness compared to diamond. The introduction of monolayer electroplated cBN wheels replaced the complex pre-grinding wheel preparation work (truing and dressing) of composite cBN wheels and thereby extensively facilitating the application in high-efficiency deep grinding, creep feed grinding, etc. The present work has aimed at developing a precisely controlled brazing technique suitable for bonding the cBN grits to a steel substrate in monolayer form with higher bond strength, larger grit protrusion and more uniform grit distribution compared to that in the currently used galvanically bonded wheels. Experimental investigation have clearly demonstrated the potential of the newly developed brazed wheels under varying grinding conditions for processing materials like bearing steel. Improved capability of these wheels over galvanically bonded wheels could be better recognised during dry grinding at high material removal rate and for large stock removal when galvanically bonded wheels were found to suffer from severe wheel loading in grinding bearing steel and from unusual increase in grinding forces due to grit pullout. Creation of wider inter-grit spaces with strong bonding and uniform grit spacing happened to be the essence of the present brazed cBN wheel.     

On the grindability of low-carbon steel under dry, cryogenic and neat oil environments with monolayer brazed cBN and alumina wheels

Grinding of low-carbon steel often exhibits severe wheel loading due to the formation of long chips and high adhering tendency of the work material with the grits. Conventional composite-type alumina wheels are commercially utilised for grinding low-carbon steel. However, the actual nature of grit wear cannot be truly understood in a composite wheel. The truing and dressing conditions also have some influences on the wear mechanism. Therefore, in order to explore the wear pattern on a single layer of grits, monolayer brazed cBN, white and grey Al₂O₃ wheels were used in the present study. The grindability of AISI 1020 steel was evaluated under dry, liquid nitrogen and neat oil environments. The surface profile of the workpiece after being ground in each environmental condition was traced with a surface profilometer to reveal the mechanism of grit wear. The post-grinding conditions of the wheels were observed using scanning electron microscopy. The cBN wheel was found to outperform the alumina wheels in terms of grinding forces and grit wear. The wear of the cBN wheel was remarkably arrested with the application of neat oil. On the other hand, large-scale adhesion and breakage of grits in white alumina wheel were observed under cryogenic environment. In fact, the beneficial role of liquid nitrogen could not be realised in reducing grinding forces and grit wear with all the three types of wheel. A lubricating agent like neat oil appeared to be more suitable than cryogenic cooling when grinding low-carbon steel.     

砂轮修整技术研究现状与展望

砂轮修整在高速高效磨削、精密超精密磨削、成形磨削过程中具有至关重要的作用。磨削过程中主要是砂轮与工件表面相互作用，砂轮随着磨削的进行逐渐磨钝难以有效磨削。为了保证磨削质量和精度，需对砂轮定期修整。砂轮修整自提出以来，国内外学者对其不断改进和创新，取得大量开创性和突破性研究成果，但日益提高的高精度、高效率、高性能生产要求对砂轮修整技术提出挑战。为了推动砂轮修整技术的不断进步，总结分析了目前修整方法的发展现状、基本原理、主要特点以及发展瓶颈，概述了砂轮修整亟需解决的问题，并对砂轮修整探究方向进行了展望。     

弧形金属基超硬磨料砂轮在位精密修形的研究

采用电火花在位修形技术,对弧形金属基超硬磨料砂轮进行了精密成形修形实验,结果表明:与传统"对磨法"相比,修形精度和效率上都有大幅度提高:当放电间隙为55 μm,放电电流为15 A,占空比为20％,砂轮转速为1 200 r/min时,获得轮廓偏差PV值为4.58 μm的高精度砂轮.修形精度提高12.09％,修形效率提高3...     

Mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating

Diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses that problem in that it proposes an effective dressing technique—mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating. A conductive phase is coated on the wheel surface to increase the conductivity of the nonmetal bond. Electrical discharge model was built to analyze feasibility and select optimized parameters of MEDD. Experiments were conducted to evaluate the dressing performance of MEDD in terms of surface morphology of the wheel surface, grinding force, and surface roughness of the workpiece. Experimental results show that abrasive grains on the wheel protrude are satisfied. The discharge parameters have an important influence on the dressing result. The grinding force and the surface roughness of the workpiece significantly reduced after dressing.