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.     

An experimental investigation of dry-electrical discharge assisted truing and dressing of metal bonded diamond wheel

Metal-bonded diamond wheels have superior qualities such as high bond strength, long wheel life, wear-resistant ability and high grinding efficiency. But it is very difficult to true and dress diamond wheel because of its highest hardness. Traditional mechanical truing does not guarantee truing accuracy of diamond wheel because of single diamond dresser wears out very quickly. To reduce wear of diamond dresser and hence guarantee a desired wheel surface, a novel truing and dressing method, namely, dry electrical discharge (dry-ECD) assisted truing and dressing, is proposed and tested to achieve good dressing quality and efficiency. Because the diamond wheel is mounted on the MK9025 optical profile grinder, dielectric liquid is forbidden. The new dry-ECD dressing/truing method basically eliminates the use of dielectric liquid. Therefore, it is free from the serious problem of electrolytic corrosion caused by electrolytic current flowing through water encountered in conventional ECD. The FE analysis of temperature distribution in dry-ECD assisted truing and dressing diamond wheel using ANSYS is performed in this study. Temperature field simulation helps to select optimized parameters under certain conditions. Energy dispersive X-ray (EDAX) analysis was used to measure the composition of diamond wheel before and after dry-ECD assisted truing and dressing. Further, hard alloy grinding experimental results proves that a little variation in material composition of diamond wheel after dry-ECD assisted truing and dressing does not influence grinding result. A series of experiments of dry-ECD assisted truing and dressing of metal bonded diamond wheel are conducted to investigate truing efficiency, truing accuracy, dresser wear, dressed wheel profiles and three-dimensional truing/dressing forces in comparison with those of the conventional single diamond methods. Experimental results show that the new dry-ECD assisted truing and dressing technique offers a number of advantages over the conventional single-tip diamond dressing and truing method. Furthermore, mechanism of the dry-ECD assisted truing and dressing is investigated through the careful analysis of the properties of chips.     

金刚石砂轮的ECD修锐和整形研磨及其对硬脆材料的加工

为研究金属结合剂金刚石砂轮切削刃修锐整形对硬脆材料加工表面形态的影响,先通过接触放电法对SD600金属结合剂砂轮切削刃进行修锐,再用整形研磨方法对砂轮表面金刚石磨粒的不同切削刃高度进行整形研磨,最后用修整好的砂轮磨削加工用于光学设备的硼硅玻璃、石英玻璃、石英晶体和蓝宝石等几种硬脆材料。结果表明:硬脆材料粗糙度的改善程度取决于材料的种类,硼硅玻璃、石英玻璃、石英晶体、蓝宝石的最大粗糙度R_y比砂轮整形前的分别减少了44%、34%、30%、26%,且石英晶体材料几乎可以实现延性磨削。      

Ground surface integrity of granite by using dry electro-contact discharge dressing of #600 diamond grinding wheel

Dry electro-contact discharge (ECD) dressing of metal-bonded #600 diamond grinding wheel is proposed for grinding of various granites. As compared to mechanical GC dressing, Dry ECD dressing can not only protrude fine diamond grains from wheel metal-bond without any damage, but also eliminate bond-tail behind the protruded grain. The objective is to understand how the synthetic factors including granite structure, grinding parameters and dressing method influence the ground surface integrity of multi-crystal granite such as surface roughness and surface crack appearance in contrast to homogeneous optic glass. First a micron-scale indentation experiment was carried out to display the growth mechanism of micro-cracks on polished surface, then Dry ECD dressing and mechanical GC dressing were carried out in grinding experiment, respectively, finally surface roughness and micro-surface crack were investigated in connection with granite crystal size, work speed and dressing method. It is found that in almost all cases the multi-crystal granite has always worse ground surface than homogeneous optic glass even if grinding parameter is changed. Moreover, the improvement of ground surface for granite is more sensitive to grain protrusion feature than that for optic glass. Although it is very difficult to find out obvious relationship between surface roughness and grinding parameter such as work speed, it has a good correlation with granite structure such as granite crystal size: it decreases with the increase of the granite crystal size. It is concluded that Dry ECD dressing may more greatly improve the ground surface integrity of various granites than mechanical GC dressing.     

3D laser investigation on micron-scale grain protrusion topography of truncated diamond grinding wheel for precision grinding performance

A grain tip (GT) truncation is proposed to truncate grain protrusion tips of #270 diamond grinding wheel in plunge grinding of hard and brittle material. In this study, a 3D laser microscopy was employed to measure the wheel working surface and parameterize its 3D grain protrusion topography. The objective is to investigate how micron-scale grain protrusion parameters influence grinding performance such as grinding force and surface roughness. First, the GT truncation was performed after dressing of diamond grinding wheel in grinding experiment of quartz glass; then its 3D grain protrusion topography was constructed by smoothing 3D measured noise, matching measured point cloud, transferring protrusion frame and extracting 3D diamond grains; finally, the grain protrusion parameters such as grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle, grain clearance angle, etc. were investigated in connection with ground surface and grinding force. It is shown that GT truncation averagely decreases grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle and grain clearance angle by about 44%, 74%, 75%, 24% and 70% on whole wheel surface, respectively. However, it greatly increases active grain number by about 32 times and active grain volume by about 181 times in actual grinding with the depth of cut in 1 μm, thus leading to a decrease (about 80%) in surface roughness and an increase (about 40 times) in grinding force. It is also found that truncated diamond grain tips are mostly shaped with nanometer-scale tip wedges along grain cutting direction, leading to about 75% very large negative grain rake angles and about 75% large grain clearance angles, thus contributing to ductile-mode grinding. It is confirmed that the active grain number and active grain volume for the actual depth of cut may be regarded as main grain protrusion parameters to evaluate and predict the precision grinding performance of a coarser diamond grinding wheel.     

Study on axial-feed mirror finish grinding of hard and brittle materials in relation to micron-scale grain protrusion parameters

An axial-feed mirror finish grinding of hard and brittle materials is proposed by controlling grain protrusion parameters. In this grinding, the grinding wheel feed is along the wheel axial direction rather than in the traditional wheel cutting direction. The objective is to understand how micron-scale grain protrusion parameters influence ductile-mode grinding and ultimately to realize efficient mirror finish grinding using a coarse diamond grinding wheel. In this study, the grain tip truncation (GT-truncation) was performed after dressing to improve grain protrusion topography. First, a formation model of axial-feed ground surface was constructed to analyze the effect of grain protrusion parameters and grinding parameters on the critical cutting depth transferred from brittle-mode removal to ductile-mode removal; then GC dressing and GT-truncation of #180 diamond grinding wheel were experimentally performed to investigate surface roughness and ductile-mode grinding behavior with reference to grinding parameters and grain protrusion parameters; finally, a truncated coarser #60 diamond grinding wheel was employed for mirror finish grinding to observe active grain number and grain protrusion angle. Theoretical analysis shows that this ductile-mode grinding is dominated by active grain number, active grain protrusion angle, wheel rotating speed and axial-feed speed, but it does not depend on the depth of cut assumed to be less than the grain protrusion height. Experimental results indicate that the GT-truncation may increase active grain number and grain protrusion angle for ductile-mode grinding when the axial-feed speed decreases to some extent. Moreover, the micro tip radius of diamond grain also influences the ground surface. It is confirmed that by increasing active grain number and grain protrusion angle synchronously, a truncated #60 diamond grinding wheel can be applied for efficient mirror finish grinding of the SiC ceramic plate at the axial-feed speed of 50 mm/min and the tool path interval of 0.1 mm.     

D杯形砂轮修整碟形金刚石砂轮试验研究

本文采用了D杯形砂轮与碟形砂轮对磨法来修整大直径树脂结合剂碟形金刚石砂轮。在分析研究杯形砂轮修整碟形砂轮的修整原理及修整方式的基础上，用自行研制的专用修整装置，从主轴转速、修整深度、修整工具结合剂类型等方面进行了对比工艺试验研究，总结了杯形砂轮修整碟形砂轮的不同工艺参数与修整效率、修整质量之间的工艺规律。试验结果表明，在本试验条件下主轴转速500r／min，修整深度0．02mm的修整效率较好；细粒度、中等浓度的青铜结合剂杯形金刚石砂轮与粗粒度、高浓度的杯形砂轮修整碟形砂轮相比，后者具有较好的修形效果和修整效率；D杯形砂轮与GC杯形砂轮交替配合使用可以大大提高碟形金刚石砂轮的修形效率和修锐效果。     

金刚石磨轮的接触放电修整方法

本文论述了该种修整方法的机理,对其工艺和评价指标进行了分析和总结。     

Application potential of coarse-grained diamond grinding wheels for precision grinding of optical materials

Fine-grained resin bonded diamond tools are often used for ultra-precision machining of brittle materials to achieve optical surfaces. A well-known drawback is the high tool wear. Therefore, grinding processes need to be developed exhibiting less wear and higher profitability. Consequently, the presented work focuses on conditioning a mono-layered, coarse-grained diamond grinding wheel with a spherical profile and an average grain size of 301 µm by combining a thermo-chemical and a mechanical-abrasive dressing technique. This processing leads to a run-out error of the grinding wheel in a low-micrometer range. Additionally, the thermo-chemical dressing leads to flattened grains, which supports the generation of hydrostatic pressure in the cutting zone and enables ductile-mode grinding of hard and brittle materials. After dressing, the application characteristics of coarse-grained diamond grinding wheels were examined by grinding optical glasses, fused silica and glass–ceramics in two different kinematics, plunge-cut surface grinding and cross grinding. For plunge-cut surface grinding, a critical depth of cut and surface roughness were determined and for cross-grinding experiments the subsurface damage was analyzed additionally. Finally, the identified parameters for ductile-machining with coarse-grained diamond grinding wheels were used for grinding a surface of 2000 mm² in glass–ceramics.     

3D graphical evaluation of micron-scale protrusion topography of diamond grinding wheel

A new graphical evaluation of micron-scale wheel protrusion topography is proposed by using 3D coordinate data derived from contact measuring of 180 diamond grinding wheel. The objective is to quantify 3D distribution of grain protrusion height, gain rake angle and grain relief angle on wheel working surface in dressing. First adaptive measuring was conducted on the base of topographical curvature to identify grain cutting edge in 3D space, second grain protrusion mode was established by polar coordinate transfer so as to ascertain datum plane of grain protrusion, then linear approximation graphics was conducted to display wheel protrusion topography, finally distributions of gain rake angle and grain relief angle were investigated with reference to grain protrusion height. Analytical results show that higher outer grains have more and shaper cutting edges, but lower layer grains retain approximately original crystal forms. In wheel protrusion topography, grain protrusion heights, grain rake angles and grain relief angles are dispersedly distributed in the range 0–28 μm, −45.0° to −89.1° and 1.2–73.1°, respectively, which can be increased by dressing. It is concluded that 3D grain protrusion attitudes distributed on wheel working surface can be quantified by 3D graphical evaluation method.     

Mechanism of material removal in electrical discharge diamond grinding

The paper presents the mechanism of material removal in electrical discharge diamond grinding, which integrates electrical discharge machining and diamond grinding for machining electrically conducting hard materials. The role of current and wheel speed on the material removal rate, the grinding forces and power is studied to elucidate the issue. The spark discharges thermally soften the work material in the grinding zone, and consequently decrease the normal force and the grinding power. The improved grinding performance is due to continuous, in-process dressing and declogging of the wheel surface.     

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。     

A study on laser touch dressing of electroplated diamond wheels using pulsed picosecond laser sources

An investigation to explore the possibility of touch dressing of electroplated diamond wheels using a pulsed picosecond laser (ps-laser) beam (Yb:YAG) is presented. The laser beam is irradiated on the wheel to cut the diamond grains within a defined grain protrusion without any thermal damage on the nickel bond. The laser parameters were systematically varied to achieve a reliable touch dressing process. The microscopic investigations prove thermal damages neither on the diamond grain nor on the bond. Series of SiC wheel dressing experiments were carried out to compare mechanical touch dressing of the electroplated diamond wheel with laser dressed wheels.     

Dressing of filigree fine-grained metal bonded grinding wheels

Metal bonded grinding tools offer a remarkable potential for micro grinding because of their favorable wear behavior. However, metal bonded grinding tools, especially dicing blades, are hard to dress by conventional dressing methods. Electro contact discharge dressing, which is presented in this paper, is a numerically controlled dressing process offering the possibility to create the geometry and topography of the grinding wheel simultaneously at negligible dressing forces. The power of an electric circuit thermally removes the metal bond of the grinding wheel during the dressing process. The quality of the created profiles and the influence of the dressing parameters on the specific material removal rate of the grinding tool as well as the wear of the electrode are investigated at fine-grained grinding wheels.     

Electrochemical discharge dressing of metal bond micro-grinding tools

Micromachining using miniature metal bond grinding tools is widely used in microelectromechanical systems. However, dressing of these micro-tools is time-consuming and likely to damage the abrasives. In this paper, a novel dressing technique called electrochemical discharge dressing (ECDD) is presented. A dull micro-end grinding bit and an auxiliary electrode are connected to the cathode and anode of a power supply, respectively. The auxiliary electrode is immersed in an electrolyte, and the grinding face of the tool is in contact with the electrolyte surface. During dressing, metal bond on the tool-electrolyte interface is progressively removed subjected to electrochemical discharge effect, thus creating grain protrusion. Experiments were conducted to evaluate the dressing performance of ECDD in terms of surface morphology of the tool, grinding force and surface roughness of the workpiece. Experimental results show that abrasive grains on the tool protrude without observable damage. The normal grinding force and the surface roughness of the workpiece are reduced by half after dressing.     

超硬磨料砂轮不同介质中电火花修整试验研究

超硬磨料砂轮的电火花修整受到极间放电间隙的限制,采用传统的放电介质条件难以达到粗粒度砂轮的修整要求。为此,结合混粉放电加工机理,提出混粉介质中的电火花修整方法,进行压缩空气、去离子水雾和混粉去离子水雾3种介质及不同放电参数下的放电间隙对比试验研究,并开展金刚石砂轮修整和工件磨削试验。试验结果表明:混粉介质电火花修整的放电间隙最大,能提高粗粒度青铜结合剂金刚石砂轮的修整效率,同时优化砂轮修整后的表面形貌、磨粒突出状况和磨削性能。在开路电压为90 V、峰值电流为13.33 A及占空比为50%的最佳放电参数下,混粉介质的电火花修整效率与前2种介质相比可提高28.2%～50.0%;且加入的SiO₂粉末使砂轮表面的Si元素分布更均匀、含量更高,进而提高其耐磨性。      

金刚石微粉烧结棒和D、GC杯型砂轮修整碟型金刚石砂轮对比研究

通过对D，GC杯型砂轮和金刚石微粉烧结棒修整大直径树脂结合剂碟型金刚石砂轮的对比实验，以反映砂轮平面度的周向跳动变化率和径向跳动变化率作为修整效率的评价依据，以被修砂轮加工出硬质合金插齿刀的齿形误差作为修整质量的评价依据，从修整原理及修整模型上分析了影响修整效率和修整质量的主要因素，分析结果表明：被修砂轮金刚石颗粒微切削频率以及修整力方向对修整效率有很大的影响；修整质量与作用在被修砂轮上的修整运动有关，磨削，单用GC杯型砂轮法修整后的碟形金刚石砂轮适合于粗磨和半精磨；D，GC杯型砂轮组合修整法既具有高的修整效率也具有高的修整质量，是一种可广泛应用的修整方法。     

金属结合剂金刚石砂轮表面微槽的激光修整技术

针对金属结合剂金刚石砂轮表面微槽修整困难的问题,采用红外纳秒激光器开展修整试验,探究激光功率、脉冲重复频率、激光烧蚀时间等因素对其材料去除的影响规律,并对U型和V型2种砂轮微槽提出梯度步进激光修整工艺。结果表明:修整后的砂轮微槽实际轮廓与设计轮廓对比,其顶部和底部实际宽度相对误差的绝对值最大为4.4%,实际深度相对误差的绝对值最大为9.6%。用修整后的砂轮V型微槽对直径为4英寸(10.16 cm)的蓝宝石晶圆边缘进行倒角,晶圆锐利的边缘被修整成规则形状,边缘轮廓对称度良好,且与激光修整后砂轮表面的微槽轮廓一致,验证了金属结合剂金刚石砂轮表面微槽激光成型修整的可行性。      

金属结合剂金刚石砂轮的修整研究(Ⅲ)——修整后结合剂形态对磨粒把持情况及砂轮磨削性能的影响

用杯形砂轮修整器整形和修锐结合剂密实型金刚石砂轮时,笔者发现在磨粒后方存在一部分结合剂残留物,并把它称之为结合剂三角洲。本文首先描述结合剂三角洲形成机理及其特性,然后讨论它对砂轮摩削性能的影响。主要结论如下:(1)结合剂三角洲形成在杯形砂轮和金刚石砂轮速度矢量差之方向(修整方向),当修整方向同磨削方向不一致时,它在磨削过程中可能和工件发生接触。(2)用杯形砂轮的两边交替进行修整,不仅可以保证结合剂三角洲的方向同磨削方向一致,并且还可以通过调整金刚石砂轮同杯形砂轮的速度比来控制结合剂三角洲的后背角φ。(3)结合剂三角洲越大,对金刚石磨粒的把持力也越大,使得修整后磨粒突出高度增大。(4)结合剂三角洲纵截面积增大会降低砂轮最外表层上的切削刃密度并使磨削力增加率减小。     

空心球造孔制备的多孔金属结合剂金刚石砂轮的磨削性能研究

本实验采用青铜结合剂为胎体,通过添加氧化铝空心球并采用热压烧结法,制备出多孔金属结合剂金刚石砂轮,并采用所制备的砂轮对工程陶瓷和铸铁材料进行磨削加工试验.实验结果表明:随着孔隙率的增加,含空心球的多孔金属结合剂金刚石砂轮的磨削阻力减小,砂轮的锋利性、磨削比和被加工工件的表面质量均得到提高;当孔隙率超过30%时,随着孔隙...