ROTARY TRUING OF VITREOUS BOND DIAMOND GRINDING WHEELS USING METAL BOND DIAMOND DISKS

Experiments on rotary truing of vitreous bond diamond grinding wheels were conducted to investigate the effects of truing speed ratio, type of diamond in the metal bond truing disks (synthetic versus natural), and diamond grit size in the grinding wheel on the wear of truing disk and on the cylindrical grinding of zirconia. Similar to G-ratio, a new parameter called D-ratio is defined to quantify the wear rate of the diamond truing disks. Experimental results show that, under the same truing condition, the truing disk with blocky, low friability synthetic diamond has a higher D-ratio than the truing disk with natural diamond. Diamond wheels trued by the disk with synthetic diamond also generate lower grinding force and rougher surface finish. High truing disk surface speed, 1.8 times higher than the surface speed of the grinding wheel, was tested and did not show any improvement in D-ratio. This study indicates that μm-scale precision form truing of the vitreous bond diamond wheel is difficult due to excess wear of the metal bond diamond truing disk.     

Wear of the blade diamond tools in truing vitreous bond grinding wheels: Part II. Truing and grinding forces and wear mechanism

Truing and grinding forces and the wear mechanism of particle and rod diamond blade tools used to generate precise and intricate forms on rotating vitreous bond silicon carbide grinding wheels are presented. A Hall effect sensor was used to measure the change of grinding spindle power during truing and grinding. A signal processing procedure was developed to identify individual truing passes and to extract the average, peak-to-valley, and standard deviation of the variation of truing force for each pass. The truing force data and SEM micrographs of worn surfaces on blade tools reveal micro- and macro-fracturing of the diamond. The attritious and erosion wear of the diamond rod and particle, erosion of the metal bond, and pulling-out of the diamond particle are also identified. Grinding force data shows that, for the same truing parameters, a wheel trued by the rod diamond blade tool has higher grinding forces than one trued by a particle diamond blade tool.     

Wear mechanism of metal bond diamond wheels trued by wire electrical discharge machining

The stereographic scanning electron microscopy (SEM) imaging was used to investigate the wear mechanism in wire electrical discharge machining (EDM) truing of metal bond diamond wheels for ceramic grinding. A piece of the grinding wheel was removed after truing and grinding to enable the examination of wheel surface and measurement of diamond protrusion heights using a SEM and stereographic imaging software. The stereographic SEM imaging method was calibrated by comparing with the profilometer measurement results. On the wheel surface after wire EDM truing and before grinding, some diamond grain protruding heights were measured in the 32 μm level. Comparing to the 54 μm average size of the diamond grain, this indicated that over half of the diamond was exposed. During the wire EDM process, electrical sparks occur between the metal bond and EDM wire, which leaves the diamond protruded in the gap between the wire electrode and wheel. These protruding diamond grains with weak bond to the wheel were fractured under a light grinding condition. After heavy grinding, the diamond protrusion heights were estimated in the 5–15 μm range above the wear flat. A cavity created by grinding debris erosion wear of the wheel bond could be identified around the diamond grain.     

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.     

Wear of the blade diamond tools in truing vitreous bond grinding wheels: Part I. Wear measurement and results

The wear of stationary blade diamond tools used to generate a precise and intricate form on the vitreous bond grinding wheel is presented. Two types of blade tools made of rod and particle diamond were used. A method to measure the wear of the blade diamond tool in the μm-scale range using the size difference of two parts ground before and after truing was introduced. Two sets of experiments with four truing feeds and four tool traverse speeds across the grinding wheel were conducted on the rod and particle blade diamond tools, respectively. Experimental results showed the wear rate of blade diamond tools was improved at higher truing feeds and traverse speeds due to the brittle fracture of the abrasive and vitreous bond.     

树脂基圆弧金刚石砂轮的在位精密成形修整技术

针对球面、非球面及自由曲面超精密磨削加工用树脂基圆弧形金刚石砂轮难以精密修整的问题,提出基于旋转绿碳化硅(GC)磨棒的在位精密成形修整技术。在分析GC磨棒和圆弧砂轮几何关系的基础上,确定修整过程中圆弧插补轨迹的补偿方法及GC磨棒运动轨迹的设计方案。采用KEYENCE激光测微仪采集砂轮圆弧特征点,表征圆弧砂轮的修整状况。研究不同粒度的GC磨棒、进给深度和圆弧插补速度对圆弧金刚石砂轮修整率和修整精度的影响规律。研究结果表明,该修整方法可根据加工曲率半径要求实现不同圆弧半径砂轮的精密在位修整,修整后可自动消除砂轮垂直方向的位置偏差;采用400#和800#的GC磨棒对D3和D7砂轮均有较高的修整率(0.7~6.7);与400#和1500#的GC磨棒相比,800#GC磨棒更适合粒度为D3和D7圆弧金刚石砂轮的精密修整;相比圆弧插补速度,进给深度对砂轮的圆弧半径尺寸误差和形状误差影响更大,进给深度越小,圆弧半径尺寸误差和形状误差越小;修整后两种砂轮的圆弧半径误差均可控制在5%以内,D3砂轮的形状误差可控制在3μm/4 mm以内,D7金刚石砂轮可控制在6μm/4 mm以内,修整后比修整前形状误差提高14倍左右。     

基于气中放电辅助修整金刚石砂轮的试验研究

提出了一种新型的基于气中放电辅助金刚石砂轮在线修整法,它把气中火花放电修整法和金刚石笔机械修整法有机结合在一起,能实现光学曲线磨床上金刚石砂轮的高效、高精度、低成本和不得使用任何冷却液的在线修整。采用自制的试验装置在MK9025数控光学曲线磨床上对1A1／T2 200×6×32×4 MBD6 120／140 M75型号的砂轮进行了在线修整试验,得出了一些影响金刚笔磨损率的主要因素:火花放电时热源的能量分布状况、金刚石笔修整时的修整深度、进给量以及电源电压。相同工况下机械修整法和气中放电辅助修整法中金刚石笔的磨损率对比试验结果表明:气中放电辅助修整和机械修整有着不同的材料去除机理,它比一般机械修整更有利于提高金刚石砂轮的修整效率和降低金刚石笔的磨损量。磨削YG8硬质合金工件的试验表明,采用气中放电辅助法修整的金刚石砂轮和新的金刚石砂轮有着相近的磨削能力。     

SYSTEMS APPROACH FOR THE CERAMIC THRU-FEED CENTERLESS GRINDING

An approach for simulation and production implementation of thru-feed centerless grinding of transformation toughened zirconia using vitreous bond diamond grinding wheels is presented. A set of grinding tests was designed and conducted to identify the effects of abrasive product (diamond grit size), work-material, and operational factors (stock removal, thru-feed rate, number of thru-feed passes and truing and dressing methods) on grinding performance. Evaluation parameters of surface finish, grinding forces and C-ratio were utilized to determine machine tool features. Very fine surface finishes, in the order of 0.05 to 0.1 u.m R_a range, could be achieved using vitreous bond micro-grit diamond wheels, without additional part processing. Such a level of surface finish on ground ceramics has traditionally been generated only by using resinoid bonded diamond wheels. These test results were used to design and manufacture a full-size composite or sandwiched diamond grinding wheel. This grinding wheel has been successfully applied in high-volume ceramic production, which in turn has verified the proposed approach. Lastly, the surface finish data is interpreted based on SEM and AFM observations and materials properties.     

金刚石砂轮金属结合剂的气中单脉冲电火花放电去除机理

针对金属结合剂金刚石砂轮修锐困难的问题,提出采用气中电火花接触放电修锐的方法。为有效地实现微细金刚石砂轮的修锐,建立单脉冲电火花放电去除加工的试验系统,研究金属结合剂的气中和液中电火花放电去除机理。在试验研究中,主要分析无负荷电压和放电极性对脉冲放电电流、脉冲放电间隙、脉冲放电去除量、电极磨耗比等的影响。结果表明,正极性不易发生短路现象,而且气中的脉冲放电间隙小于液中的 ,适应于微细金刚石砂轮的修锐。此外,在气中放电中存在由绝缘破坏引起的火花放电向附有电弧柱的电弧放电转变的临界无负荷电压,且电火花放电的去除量可以明显小于电弧放电的去除量,但是当无负荷电压小于某一定值时电极消耗比会快速增加。修锐的试验结果显示,利用气中单脉冲电火花放电去除加工条件可以实现金属结合剂微细金刚石砂轮的修锐,产生较好的砂轮出刃形貌,改善磨削表面质量。     

HIGH SPEED AND HIGH MATERIAL REMOVAL RATE GRINDING OF CERAMICS USING THE VITREOUS BOND CBN WHEEL

High-speed (up to 127 m/s) and high material removal rate grinding experiments were conducted using a vitreous bond cubic boron nitride (CBN) wheel to investigate the effects of material removal rate, wheel speed, dwell time and truing speed ratio on cylindrical grinding of silicon nitride and zirconia. Experimental results show that operating the grinding wheel at a high surface speed can reduce grinding forces, enable high material removal rates, and achieve a higher grinding ratio (G-ratio). The material removal rate was increased to 9.6 and 7.6 mm³/s/mm for zirconia and silicon nitride, respectively, to explore the advantage of using high wheel speeds for cost-effective, high-material-removal-rate grinding of ceramics. Models for specific grinding force vs. the specific material removal rate and G-ratio vs. grinding wheel surface speed were developed based on the experimental results. Overall, this study showed that high grinding wheel surface speed is beneficial to the grinding of ceramics.     

金属基结合剂超硬砂轮的电火花修整

采用自行研制的ELID磨削专用脉冲电源对金属基结合剂超硬砂轮进行电火花整形 ,分析了不同电火花整形方式的电路原理及整形效果 ,并对砂轮的电火花整形机理及整形效率进行了研究。研究结果表明 ,采用方波脉冲式电火花修整金属基结合剂超硬砂轮可获得良好的砂轮表面质量和高的整形效率。     

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.     

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.     

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.     

Effect of parameters on grinding forces and energy while grinding Al (A356)/SiC composites

Abstract

Grinding processes require a high energy input per unit volume of material removed, which is converted to heat at the grinding zone, resulting in increased force and wear. In the present study, the influence of grinding parameters like work speed and depth of cut on grinding forces and energy was studied. An attempt has been made to study the forces and energy involved while grinding aluminium alloy (A356)/silicon carbide (SiC) composite material with different grinding wheels. Experiments were carried out on a surface grinding machine. Three different types of wheels like SiC, cubic boron nitride (CBN) and diamond wheels were used. The grinding forces increased with increase in depth of cut and work speed. SiC exhibited high grinding force compared to the CBN wheel. In the case of the diamond wheel, it was even less. The specific grinding energy was highest for the diamond wheel followed by CBN and SiC wheels. The specific grinding energy decreased with increase in depth of cut and work speed.     

超硬磨料砂轮的激光修锐技术研究

激光修整超硬磨料砂轮的原理,利用Ｎｄ：ＹＡＧ固体脉冲激光器进行激光修锐青铜结合剂和树脂结合剂硬磨料砂轮的试验,用扫描电镜观察了激光修锐前后砂轮表面的微观表貌,对激光作用下砂轮表面不同结合剂材料的去除机理进行了分析,通过磨削陶瓷试验,研究激光修锐的金刚石砂轮的磨削性能,并与普通砂轮磨削肖修锐的金刚石砂轮进行对比。结果表明,采用试验所确定的激光参数可选择性地去除砂轮表面的结合剂材料,而不损伤超硬磨粒,     

圆弧形砂轮精密修整及其声发射在线监测技术

针对球面、非球面及自由曲面超精密磨削加工用圆弧形金刚石砂轮难以精密修整的问题,提出基于旋转绿碳化硅（GC）磨棒的端部在位精密修整方法及修整过程的声发射在线监测技术。基于圆弧形金刚石砂轮的结构特性,制订圆弧形金刚石砂轮的在位精密修整与修整过程的声发射在线监测技术方案。依据修整与在线监测方案,对D64圆弧形金刚石砂轮进行修整实验及其声发射信号采集,修整后跳动误差小于10μm,比修整前减小30μm左右,砂轮精度显著提高。利用声发射信号均方根值获取砂轮修整结束的特征预警阈值,实现了旋转GC磨棒端部在位精密修整过程的在线监测以及修整结束时间的准确判断,可以有效提高球面非球面磨削加工过程的效率。     

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%.     

声光调Q YAG脉冲激光修锐和整形青铜金刚石砂轮

采用声光调Q钇铝石榴石(Yttriumaluminumgarnet,YAG)脉冲激光径向辐照,修锐和整形青铜金刚石砂轮。通过建立传热学数学模型和数值计算以及激光单脉冲烧蚀试验,分析了修锐和整形机理,找到了合理的修锐和整形的激光参数与工艺参数。设计和研发了一套在线检测闭环控制激光烧蚀系统,利用该系统控制激光烧蚀过程,进行了青铜金刚石砂轮修整,得到了较高的整形精度和良好的地形地貌,并且实现了一道工序同时整形与修锐。通过磨削对比试验分析了修整效果。     

MODELING OF DRESSING FORCES DURING ROTARY DIAMOND CUP DRESSING OF VITRIFIED CBN GRINDING WHEELS

This paper presents a mathematical model of dressing of vitrified CBN grinding wheels by a diamond cup dresser. It predicts the dressing forces during rotary diamond cup dressing of vitrified CBN grinding wheels. This model is based on the fracture of abrasive grits, the fracture of the bond and the contact forces between dresser and grinding wheel. It considers the kinematical influences and in particular speed ratio and overlap factor during the dressing process. A Weibull distribution is used to predict the probability of bond fracture and also the collision number between the diamond grits of a rotating dresser and the CBN grits. This model is validated by experimental results. The theoretical modeling values agree reasonably well with the experimental results. On the basis of this model the effect of different cup dressing parameters on dressing forces is theoretically discussed with the aim of establishing appropriate dressing process configurations. Furthermore the presented model provides a basis for further prediction of wheel topography and the grinding process.