Recognition of diamond grains on surface of fine diamond grinding wheel

The accurate evaluation of grinding wheel surface topography, which is necessary for the investigation of the grinding principle, optimism, modeling, and simulation of a grinding process, significantly depends on the accurate recognition of abrasive grains from the measured wheel surface. A detailed analysis of the grain size distribution characteristics and grain profile wavelength of the fine diamond grinding wheel used for ultra-precision grinding is presented. The requirements of the spatial sampling interval and sampling area for instruments to measure the surface topography of a diamond grinding wheel are discussed. To recognize diamond grains, digital filtering is used to eliminate the high frequency disturbance from the measured 3D digital surface of the grinding wheel, the geometric features of diamond grains are then extracted from the filtered 3D digital surface, and a method based on the grain profile frequency characteristics, diamond grain curvature, and distance between two adjacent diamond grains is proposed. A 3D surface profiler based on scanning white light interferometry is used to measure the 3D surface topography of a #3000 mesh resin bonded diamond grinding wheel, and the diamond grains are then recognized from the 3D digital surface. The experimental result shows that the proposed method is reasonable and effective.     

细粒度金刚石砂轮形貌测量与评价

采用基于扫描白光干涉原理的三维表面轮廓仪对粒度为3 000的金刚石砂轮表面形貌进行测量,其图像拼接功能可以确保较高的横向分辨率、较高的垂直分辨率和较大的取样面积。利用频谱分析方法对砂轮表面的频率构成进行分析,通过理想的低通数字滤波消除测量仪器引起的系统噪声和砂轮表面的高频分量,然后重建砂轮表面的三维形貌,在此基础上得出砂轮的磨粒出刃高度、静态有效磨粒密度、磨粒平均间距。研究表明,采用细粒度金刚石砂轮进行超精密磨削时,磨粒出刃高度大体上服从正态分布,静态有效磨粒密度远低于理论磨粒密度,真正起切削作用的磨粒数量极少。     

Ultra-precision ductile grinding of BK7 using super abrasive diamond wheel

In this paper, a novel conditioning technique using copper bonded diamond grinding wheels of 91 μm grain size and electrolytic in-process dressing (ELID) is first developed to precisely and effectively condition a nickel-electroplated monolayer coarse-grained diamond grinding wheel of 151 μm grain size. Under optimised conditioning parameters, the super abrasive diamond wheel was well conditioned in terms of a minimized run-out error and flattened diamond grain surfaces of constant peripheral envelope. The conditioning force was monitored by a force transducer, while the modified wheel surface status was in-situ monitored by a coaxial optical distance measurement system. Finally, the grinding experiment on BK7 was conducted using the well-conditioned wheel with the corresponding surface morphology and subsurface damage measured by atomic force microscope (AFM) and scanning electric microscope (SEM), respectively. The experimental result shows that the newly developed conditioning technique is applicable and feasible to ductile grinding optical glass featuring nano scale surface roughness, indicating the potential of super abrasive diamond wheels in ductile machining brittle materials. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(10): 95–101 [译自: 机械工程学报]     

单层钎焊金刚石砂轮的修整实验研究

为满足单层钎焊金刚石砂轮高效精密加工的性能要求,对磨粒有序排布单层钎焊金刚石砂轮的修整进行了实验研究。采用磨粒有序排布的钎焊金刚石修整工具对钎焊砂轮进行了修整,该修整方法通过修整工具粒度的变化以及修整速比的调整来控制砂轮形貌,从而使氧化锆的磨削表面粗糙度达到了精密加工的水平。对砂轮形貌进行了观测统计,数据表明,砂轮磨粒的等高性得到明显改善且避免了磨粒端部的严重钝化。     

圆弧金刚石砂轮三维几何形貌的在位检测和误差评价

针对非球面光学元件加工对圆弧金刚石砂轮形状误差测量的需求,提出了砂轮三维几何形貌在位检测与误差评价方法。建立了砂轮外圆面螺旋扫描轨迹测量数学模型,利用位移传感器获取了砂轮表面轮廓数据;对得到的数据匀滑滤波后沿圆周展开并进行插值处理,得到砂轮三维几何形貌。然后,根据非球面平行磨削加工特点,提出评价圆弧砂轮形状精度的指标。通过提取三维几何形貌轴截面轮廓,进行最小二乘圆弧拟合得到不同相位处的圆弧半径与圆心坐标,并由误差分离获得砂轮表面圆弧的圆度误差、圆周跳动误差及轮廓圆心轴向偏差。最后,对非球面加工圆弧金刚石砂轮进行检测,获得了砂轮的三维几何形貌以及多个关键尺寸及其误差数据:即圆弧金刚石砂轮的平均圆弧半径为55.442 3mm,半径波动极差为0.16mm,中央±8mm环带内圆弧的圆度误差约为5μm,圆周跳动误差约为2μm,截面轮廓圆心轴向位置相对偏差为0.008mm。根据检测结果,进行了大口径复杂非球面磨削实验,得到的元件面形P-V值为4.62μm,RMS值优于0.7μm,满足工程的实际需求。     

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。     

单层钎焊金刚石砂轮的精密修整及效果评价

单层钎焊金刚石砂轮作为一种新型的磨削工具,具有磨粒固结强度高、磨粒出露大、容屑空间大等优点,比较适合高效率大切深的强力磨削,然而这种工具对高性能的脆性材料的精密磨削却比较困难。本文通过两种精密的修整工艺,使得加工表面质量大大提高。通过观察砂轮磨粒形态的变化可知,磨粒在修整过程中存在有磨损钝化、破碎、表面粘附等现象;通过对砂轮轮廓的激光测量可知,砂轮的磨粒等高性在修整过程中是明显改善的。通过修整磨粒粒径300μm的钎焊砂轮磨削氧化锆的表面粗糙度达到了Ra0.2μm。     

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151 μm (D151), 91 μm (D91) and 46 μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.     

全陶瓷球轴承套圈沟道精密磨削用砂轮修整试验

为提高金刚石圆弧砂轮外缘轮廓精度,减少全陶瓷球轴承套圈沟形误差,采用金刚石碟片对树脂基金刚石圆弧砂轮进行修整;对比修整前后砂轮的表面形貌及套圈沟形误差,验证砂轮的修整效果.修整后砂轮表面出现光泽,露出表面的金刚石磨粒明显增多,部分金刚石磨粒破碎,形成新切削刃或脱落,增大容屑空间;修整前沟形误差的平均值为5.823μm,...     

基于修整力的树脂结合剂金刚石砂轮机械修整

研究了树脂结合剂金刚石砂轮修整过程中修整力与修整效果的关系,基于修整力的变化表征了砂轮的表面形貌及磨削性能。首先,对碳化硼、碳化硅、白刚玉3种砂轮修整工具进行实验,并采集了修整过程中修整力的变化;然后,利用白光干涉仪观测修整后砂轮的表面形貌;最后,对修整后砂轮进行磨削验证实验,得到不同修整工具修整后砂轮的磨削性能。基于上述实验,分析并验证了修整力的变化与砂轮表面形貌和砂轮磨削性能的关系。结果表明,法向力Fn能够表征砂轮的磨粒切削刃密度以及磨粒突出高度;修整比率β反映了砂轮的锋锐程度,当β稳定时,砂轮达到充分修整。因此修整力反映了砂轮表面形貌和磨削性能,根据修整力的变化可以把握砂轮的修整进程。     

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,     

Experimental study on fabrication and evaluation of micro pyramid-structured silicon surface using a V-tip of diamond grinding wheel

A mechanical fabrication of micro pyramid-structured silicon surface is proposed using crossed grooving with a 60° V-tip of diamond grinding wheel. It can obtain high form-accuracy, good surface quality and efficient productivity in contrast to laser machining and etching, and also assure a high aspect ratio in contrast to other mechanical processes. In order to describe its micro-structured topography, a white-light interferometer was employed, and its measured point cloud was matched using an Iterative Closest Point (ICP) algorithm. In micro grinding, a novel CNC mutual-wear truing was first developed to sharpen the wheel V-tip; then, the effects of microscopic wheel topography, silicon crystal-orientation and grinding parameter were investigated on ground micro-topography, truing ratio and material removal ratio; finally, its form-accuracy, pyramid top radius, groove tip radius, surface roughness and aspect ratio were evaluated. It is shown that better microscopic grain protrusion topography on wheel V-tip produces much larger material removal ratio and much better micro-structured topography in micro grinding, but it leads to much less truing ratio in finer GC truing. In micro grinding, silicon crystal-orientation has little effect on micro-structured topography due to diamond crystal-orientations that are randomly distributed on wheel V-tip. Although the micro pyramid-structured form error is only about 3.4 μm, its V-groove bottom and pyramidal top have very large form errors (23.1-47.9 μm) due to the sharpness of wheel V-tip and the frangibility of micro pyramid top. On increasing feed speed, its pyramid top radius decreases and its groove tip radius slightly increases, ultimately leading to an increase in aspect ratio, whereas its surface quality descends. It is concluded that the micro-pyramid arrays may be precisely patterned on silicon surface using a SD600 wheel with crossed tool paths, on-machine V-tip truing and the depth of cut in 1 μm.     

椭圆振动修整超声磨削ＺrＯ２温度试验研究

采用椭圆超声振动辅助金刚石笔修整方法修整金属结合剂金刚石砂轮,考察声学系统参数及磨削参数对超声振动辅助磨削纳米氧化锆陶瓷过程中磨削温度的影响.试验结果表明,椭圆超声振动辅助修整的金刚石砂轮超声振动磨削中,磨削温度相对较低.相比其他修整参数,修整深度对磨削温度的影响较小.磨削参数中,磨削深度对磨削温度影响因子较大,砂轮速度影响较弱.此外,磨粒在切削过程中做超声振动,改变了切削条件及散热条件,弱化了砂轮表面地貌对磨削温度的影响,因此,不同修整方式的金刚石砂轮的磨削温度差别不大,两种修整方式下磨削温度下降的梯度大致相当.     

Simulation and assessment of diamond mill grinding wheel topography

The topography of grinding wheel has a remarkable effect on grinding process. In this paper, the topographies of two mill grinding wheels with different grain sizes were measured by using an Olympus confocal scanning laser microscope. Kolmogorov–Smirnov normality tests were carried out to obtain distribution characteristics of abrasive grains. The test results indicate that the surface of grind wheel is of non-Gaussian nature. Consequently, a non-Gaussian statistical model was proposed to simulate the mill grinding wheel topography. Simultaneously, some parameters of “Birmingham 14” were introduced to assess the grinding wheel surface quantitatively. Simulated profile of the grinding wheel is found to correspond well in appearance with that of the actual grinding wheel.     

F-Theta自由曲面透镜的精密与镜面磨削

针对光学玻璃的F-Theta自由曲面透镜加工困难等问题,提出将金刚石砂轮的椭圆环面代替圆环面,进行F-Theta自由曲面磨削加工,研究形状误差的补偿磨削方法和光学玻璃的镜面磨削工艺。根据F-Theta透镜的自由曲面建立砂轮与工件相切的刀具轨迹法向算法。采用#46粗金刚石砂轮修整成椭圆环面,提出自由曲面磨削的法向误差补偿加工模式。最后,采用#3000超细金刚石砂轮的椭圆环面进行轴向磨削试验。试验结果表明:传统的垂直误差补偿磨削可减小面形误差45.9%及其PV值11.6%;而新提出的法向误差补偿磨削可减小面形误差47.9%及其PV值41.5%。此外,超细砂轮磨削可使得自由曲面的粗糙度达到28 nm,其镜面磨削工艺有别于较粗砂轮磨削工艺。因此,椭圆环面砂轮的法向补偿磨削是提高自由曲面加工精度的有效方法,而且,无需研磨抛光就可以实现光学玻璃的自由曲面镜面磨削。     

光学自由曲面反射镜模芯的镜面成型磨削

采用精密修锐修整的圆弧形粗金刚石砂轮在CNC精密磨床上进行了数控成型磨削加工,实现了高效镜面磨削。分析金刚石砂轮圆弧形轮廓的成型修整原理,建立了圆弧形修整的数控模式。通过建立曲面数控成型磨削的行走轨迹算法,实现了自由曲面的圆弧包络成型磨削加工。分析了磨削工艺参数和砂轮出刃形貌参数与超光滑表面形成的作用机制,进行了镜面磨削试验并检测表面微观形貌和粗糙度,分析实现镜面磨削的脆/塑性磨削转换机理。理论分析表明,降低砂轮行走速度,提高砂轮转速以及改善出刃形貌可以获得纳米级粗糙度的超光滑磨削表面。试验结果显示,先将砂轮修锐修整再控制砂轮行走速度小至15 mm/min时,表面粗糙度小于10 nm以下,且微观加工表面没有发生脆性破坏,形成镜面。加工高速钢自由曲面时,面形误差(PV值)可以达到10 μm以下,表面粗糙度R_a可以达到约16 nm。实验结果表明:利用数控技术和粗金刚石砂轮可以实现自由曲面模芯的高效镜面磨削加工,保证了高精度的光学自由曲面反射镜注塑模芯。     

平面磨削中金刚石砂轮有效磨粒数的研究

采用4个不同排布方式的钎焊金刚石砂轮和1个电镀金刚石砂轮磨削天然黑色花岗石，用薄片热电偶检测磨削弧区温度信号，同时测量了磨床主轴的功率。通过分析温度信号中高频热脉冲的个数，确定金刚石砂轮实际参与磨削的磨粒数量和有效磨粒比，并计算出磨削过程中单颗金刚石磨粒的实际最大切削厚度及其消耗的切削功率。     

金刚石砂轮中磨粒出刃的分形分析

针对金刚石砂轮微观出刃形貌复杂的问题,提出分形维数和等价出刃尺寸的评价指标。目的是利用分形维数和等价出刃尺寸分别评价砂轮磨粒的破碎程度和砂轮磨粒出刃的均匀程度。试验和分析结果表明,进给深度越大,砂轮出刃的分形维数就越大,表明砂轮磨粒的破碎程度越大,会给加工表面造成较大的粗糙度或划伤表面。进给深度对磨粒出刃的等价出刃尺寸的影响不大。     

OPTIMIZATION OF DRESSING CONDITIONS FOR A RESIN-BONDED DIAMOND WHEEL BY TOPOGRAPHY ANALYSIS

The macro-geometry (run-out, shape, profile, etc.) and the micro-geometry (density, distribution, and shape of the grains) of a grinding wheel are measured after both truing and dressing. The effectiveness of the truing is studied by analysing the topography of the wheel to characterize the tool and its effect on workpiece surface quality during the grinding process. Using wheel replicas, the surfaces are analyzed with a non-contact interference microscope and the measurements are processed with MountainsMap Software. For different truing and dressing conditions, the dressing efficiency, the grain density, and its effects on the roughness and wear of the wheel in the grinding process are investigated.     

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.