单晶硅纳米级磨削过程中磨粒磨损的分子动力学仿真

建立了考虑磨粒磨损的三维分子动力学仿真模型,将固体物理学中的爱因斯坦模型引入到金刚石磨粒原子的温度转换过程中, 设计了分子动力学仿真程序.研究结果表明:在磨削的初期,磨粒有明显的磨损,但当磨损到一定阶段后,磨粒不再磨损, 磨削开始进入稳定的切削状态.金刚石磨粒的磨损主要发生在磨粒的最底部,这与表面效应有密切关系.由于表面效应,磨粒底部表面原子配位不足,导致磨粒底部结构表面存在许多缺陷,使磨粒底部表面具有很高的活性,极不稳定,根据最小能量原理,它将自发地向最低能量状态变化,也就是通过塑性变形、非晶相变等变化释放能量,使磨粒的表面能减少,从而发生磨损.     

原子量级条件下单晶硅磨削过程中的亚表面损伤

应用分子动力学仿真研究了原子量级条件下磨粒钝圆半径、磨削深度和磨削速度对单晶硅磨削后亚表面损伤层深度的影响.分子动力学仿真结果表明:在磨削深度和磨削速度相同情况下,随着磨粒钝圆半径的减小,损伤层深度和硅原子间势能亦减小.随着磨削深度的增大,损伤层深度和硅原子间势能增大.在磨削深度和磨粒钝圆半径相同的情况下,在20～200 m/s范围内,磨削速度对单晶硅亚表面损伤影响很小,说明分子动力学仿真对磨削速度的变化不敏感,因此可以适当提高仿真速度,从而缩短仿真时间和扩大仿真规模.单晶硅亚表面损伤主要是基于硅原子间势能的变化,并通过超精密磨削实验进行了实验验证.     

原子量级条件下单晶硅磨削过程中的亚表面损伤

应用分子动力学仿真研究了原子量级条件下磨粒钝圆半径、磨削深度和磨削速度对单晶硅磨削后亚表面损伤层深度的影响.分子动力学仿真结果表明:在磨削深度和磨削速度相同情况下,随着磨粒钝圆半径的减小,损伤层深度和硅原子间势能亦减小.随着磨削深度的增大,损伤层深度和硅原子间势能增大.在磨削深度和磨粒钝圆半径相同的情况下,在20～200 m/s范围内,磨削速度对单晶硅亚表面损伤影响很小,说明分子动力学仿真对磨削速度的变化不敏感,因此可以适当提高仿真速度,从而缩短仿真时间和扩大仿真规模.单晶硅亚表面损伤主要是基于硅原子间势能的变化,并通过超精密磨削实验进行了实验验证.     

青铜金刚石砂轮的激光整形与修锐

考虑蒸发效应、等离子体屏蔽效应与脉冲间能量累积效应基础上,建立脉冲激光烧蚀青铜金刚石砂轮传热物理模型,应用模型对脉冲光纤激光修锐青铜和整形金刚石分别进行传热数值计算,依据数值仿真结果,开展脉冲光纤激光烧蚀青铜轮和青铜金刚石砂轮的实验。理论研究和实验研究表明:相关条件下,当激光功率密度小于2.10108 W/cm2时,只能对青铜金刚石砂轮修锐;当激光功率密度大于2.10108 W/cm2小于2.52108 W/cm2时,能对青铜金刚石砂轮实现整形和修锐的合二为一;当激光功率密度大于2.52108 W/cm2时,能对青铜金刚石砂轮实现大深度修锐,但影响磨粒突出结合剂的高度和磨削性能,以上研究为脉冲激光烧蚀青铜金刚石砂轮研究提供理论指导与工艺优化,同时实验结果与数值模拟结果一致,也验证了传热模型的正确性。     

超声磨削表面三维形貌建模与试验研究

为了研究超声磨削的工件三维形貌,建立了砂轮表面三维形貌,通过对超声磨削磨粒运动轨迹分析,建立了磨粒在工件表面的切削过程模型。提出了大量随机分布磨粒切削工件路径的离散算法和最小高度值包络曲面提取算法,实现了超声磨削表面三维形貌的建立。进行超声磨削试验,结果表明：该模型能有效预测超声磨削的表面形貌,为超声磨削的工艺优化提供了理论依据。     

石墨转化纳米金刚石相变分子动力学模拟研究

为了探讨1维微尺度热传导模型不同激光能量对石墨转化纳米金刚石相变机理的影响，采用基于密度泛函理论的分子动力学方法模拟优化后的石墨结构，用有限差分法计算了激光辐照石墨表面的温度分布；基于sp³杂化键可以明显地区分金刚石和石墨结构，根据能量耦合得到不同激光能量条件下辐照石墨的态密度带隙，研究了碳原子键合条件。结果表明，只有当激光能量达到5 J时，才能形成少量sp³杂化碳原子；随着激光能量的增加，液相下受辐照的石墨表面的温度随之增加，碳原子中的自由电子更容易移动到成键分子轨道，电子的电负性增强，从而增强sp³键的极性，并有助于将sp²键转变为sp³键。该研究结果对在液相激光辐照下提升纳米金刚石制备效率、探究纳米金刚石制备机理有重要的现实意义。     

磨粒在线监测静电传感器设计

针对机器磨损状态监测要求,设计了一种油液磨粒在线监测静电传感器,并给出了静电传感器的结构模型.采用有限元法对传感器静电场进行数值求解,得到了传感器的灵敏度空间分布,并对影响传感器灵敏度的主要因素进行了仿真研究,对静电传感器的频率响应特性进行了分析.在此基础上,提出了油液磨粒在线监测静电传感器结构尺寸优化设计方法.最后,构建了油液磨粒静电监测实验系统,进行磨损监测实验研究.实验结果表明,静电传感器可有效监测到荷电颗粒物和油液磨粒,本系统适用于油液磨粒在线监测.     

激光辅助机械修整金刚石砂轮的温度场分析

激光辅助机械修整金刚石砂轮是一种金刚石砂轮修整新方法，它利用激光束加热砂轮表面使得金刚石修整笔的修整材料模式从脆性断裂变为塑性流动，从而提高砂轮表面修整质量，降低金刚石笔的磨损。运用ANSYS软件建立了激光辅助机械修整过程中金刚石砂轮温度场的有限元模型，并用热成像仪NEC TH7IOOWX／WV测量了实际工况下的温度场。结果表明，在相同工况下运用仿真模型所得分析结果与实测值拟合得很好。利用所建立的金刚石砂轮温度场的计算机仿真系统可对砂轮修整过程进行前期预测、工艺参数调整及优化等，避免加热温度过高使砂轮表面金刚石颗粒石墨化，或加热温度不足使砂轮表面硬度下降不够等情况的发生，从而减少了直接进行修整实验带来的盲目性。     

碳化硅晶片表面质量差异影响因素研究

分析了金刚石线锯多线切割150 mm SiC晶片的表面形貌及质量,通过测试SiC片Si面和C面的表面粗糙度(Ra),发现C面Ra值约为Si面的2倍。在切割过程中晶片向Si面弯曲,使锯丝侧向磨粒对Si面磨削修整作用更强,从而使晶片Si面更加光滑。此外,通过显微截面法测试了SiC晶片两面的损伤层深度。结果表明,Si面损伤层深度约为7.89 μm,明显低于C面的13.8 μm,显微镜下观察到截面边缘更加平整。该方法进一步证明了多线切割时晶片向Si面弯曲,使锯丝侧向磨粒对Si面的磨削效果更强,从而造成SiC晶片两面表面形貌和质量存在差异。     

金属加工的新方法—高能密度加工法综述

5.电解磨削电解磨削(ECG,Electrochemical Grainbing)是在1952年由美国的克莱列克(G.F.Keeleric)首先申请专利的。它和电解加工一起作为一种无形变的加工方法,有减少金刚石砂轮损耗的作用。电解磨削的基本构思是,在电极与工件之间放置兼作磨粒的绝缘体,使加工过程存在着电解作用     

Research on Fractal Feature of Wear Surface Topography Based on Gray Images of Rubber Surfaces

Abrasion performance is an important index for evaluating the performance of rubber products. The surface morphologies of rubber composites under different temperatures and loads were characterized based on fractal theory. The abrasion performance and characteristics of the surface morphology of rubber were investigated. Images of surface morphology of rubber samples were collected by a 3D measuring laser microscope and converted to black-and-white binary images. Based on the multifractal model, the relationship between the experimental conditions and the characteristic parameters of the abrasion surfaces, such as the width of multifractal spectrum Δα, the change in the multifractal spectrum Δf(α), wave length, wave height and the root mean square deviation of the outline were quantitatively analyzed. The results show that abrasion volume increased as the temperature increased. Similarly, abrasion volume increased as load increased. As the temperature or the load increases, the abrasion of the rubber surface increases in intensity and volume, the abrasion surface becomes more uneven, and the abrasive grain becomes more complex. The characteristic parameters, such as the wave length and wave height of the abrasive grain, the arithmetic mean deviation of the outline, the root mean square deviation of the outline and the 3D arithmetic mean deviation, increase in certain regularity.     

A study on the grinding of glass using electrolytic in-process dressing

Grinding of brittle materials such as glass is gaining importance due to the rapid developments in the areas of machining of storage devices, microlenses, and optical communication devices. Grinding of such glasses is difficult because grinding wheels wear out easily due to the hard and brittle nature of the materials being machined. Grinding wheels with fine abrasive size are required in order to achieve ductile mode grinding. Problems such as wheel loading and glazing can be encountered while grinding with fine abrasive wheels. Electrolytic in-process dressing (ELID) is an efficient method to dress the grinding wheel while performing grinding. In this paper, a fundamental study on the mechanism of the ELID grinding technique is discussed in detail. Several sets of experiments have been performed to determine the optimal grinding conditions. From the experiments, it has been established that surface roughness could be further improved if the current duty ratio to dress the grinding wheel were increased. The force patterns and the changes in the profile of the grinding wheel during machining are also presented and discussed in detail.     

Effects of abrasive particle size and tool surface irregularities on wear rates of work and tool in polishing processes

This study proposes a wear model to investigate the effects of abrasive particle size and tool surface irregularities on the wear rates of both work and tool in polishing processes. This model is derived on the basis of force equilibrium, principle of minimum potential energy, Johnson-Kendall-Roberts (JKR) contact theory, and probability statistics. The simulation results indicate that variations in both particle size and tool surface irregularities change the contact length between the tool and particle and between the particle and work, and consequently influence the wear rates of tool and work. In this study, a given adhesion at the particle interfaces, for example, it reveals that a large particle size leads to reductions in the wear rate ratio between tool and work. On the other hand, an increase in tool surface irregularities decreases the wear rate ratio between tool and work. The experimental results show that the qualitative trends of wear rate ratio versus particle size and tool surface irregularities can be well predicted by analytical analysis.     

平面光学元件研磨抛光磨粒运动轨迹研究

为提高平面光学元件的加工质量和效率,理解元件与抛光盘之间的相对运动轨迹变化规律是获得良好表面质量的重要前提.根据“运动学原理”和“坐标变换”建立了磨粒运动轨迹模型,推导了磨粒轨迹长度公式.利用Matlab软件模拟计算了各参数下的磨粒轨迹长度和磨粒轨迹变化形态.研究表明:不同转速比对材料去除速率和表面质量影响显著;随着磨粒径向距离和偏心距的增大,磨粒轨迹长度增加,考虑到偏心距对工件表面质量的影响,偏心距不宜太大或太小;同一转速比下,不同的磨粒初始角度对磨粒轨迹形状没有影响,只会使其转过相应角度.     

Material removal mechanism in chemical mechanical polishing: theoryand modeling

The abrasion mechanism in solid-solid contact mode of the chemical mechanical polishing (CMP) process is investigated in detail. Based on assumptions of plastic contact over wafer-abrasive and pad-abrasive interfaces, the normal distribution of abrasive size and an assumed periodic roughness of pad surface, a novel model is developed for material removal in CMP. The basic model is MRR=ρ_wNVol _removed, where ρ_w is the density of wafer N the number of active abrasives, and Vol_removed the volume of material removed by a single abrasive. The model proposed integrates process parameters including pressure and velocity and other important input parameters including the wafer hardness, pad hardness, pad roughness, abrasive size, and abrasive geometry into the same formulation to predict the material removal rate (MRR). An interface between the chemical effect and mechanical effect has been constructed through a fitting parameter H_w a “dynamical” hardness value of the wafer surface, in the model. It reflects the influences of chemicals on the mechanical material removal. The fluid effect in the current model is attributed to the number of active abrasives. It is found that the nonlinear down pressure dependence of material removal rate is related to a probability density function of the abrasive size and the elastic deformation of the pad. Compared with experimental results, the model accurately predicts MRR. With further verification of the model, a better understanding of the fundamental mechanism involved in material removal in the CMP process, particularly different roles played by the consumables and their interactions, can be obtained     

磨料层动态平衡对蓝宝石衬底粗磨过程影响研究

在对蓝宝石衬底进行粗磨时,需采用大颗粒高硬度磨料以缩短用时。考虑到大颗粒磨料流动性和悬浮性弱的特征,通过监测去除量的指针的摆动情况研究粗磨过程中磨料颗粒的分布和运动规律,表明磨料层的动态平衡性对衬底的厚度均匀性和表面质量具有决定性影响,而该平衡的建立依赖于致密、均匀的初始磨料层,粗磨过程中补充的磨料仅能维持已有的平衡,不能在已失衡的情况下进行补救。该工作有助于提高粗磨工艺控制水平,并对深入研究研磨过程中磨料颗粒的运动情况具有一定的指导意义。     

轴端沟槽底部激光强化工艺参数优化研究

分析了选用不同激光能量密度对HT300进行表面强化处理时，材料表面呈现的四种状况；未相变硬化、相变硬化、表面微熔与表面熔凝的金相组织。根据工艺要求，选取相变硬化方法对轴端沟槽底表面进行处理。分析了工件激光处理方法并通过试验研究，寻找轴端沟槽底部激光强化工艺参数；激光功率（P）、光斑直径（D）及扫描速度（V）的优化组合。硬度测试及耐磨性能试验表明：激光相变处理和激光熔凝处理后轴端沟槽底部表面较表面感应淬火硬度分别提高7%和34%，绝对磨损体积分别下降了13%和25%。实践证实，对轴端沟槽底部激光相变硬化处理方法较其他表面处理方法工艺简单，加工工件符合技术要求，试验结果对零件表面处理提供了可靠依据。     

Surface integrity and removal mechanism of silicon wafers in chemo-mechanical grinding using a newly developed soft abrasive grinding wheel

A new soft abrasive grinding wheel (SAGW) used in chemo-mechanical grinding (CMG) was developed for machining silicon wafers. The wheel consisted of magnesia (MgO) soft abrasives, calcium carbonate (CaCO₃) additives and magnesium oxychloride bond. Surface topography, roughness and subsurface damage of the silicon wafers ground using the new SAGW were comprehensively investigated. The results showed that the grinding with the new SAGW produced a surface roughness of about 0.5 nm in R_a and a subsurface damage layer of about 10 nm in thickness, which is comparable to that produced by chemo-mechanical polishing. This study also revealed that the chemical reactions between MgO abrasive, CaCO₃ additives and silicon material did occur during grinding, thereby generating a soft reactant layer on the ground surface. The reactant layer was easily removed during the grinding process.     

Ti-6Al-4V合金SiC粉激光表面合金化组织与耐磨性

利用预涂ＳｉＣ粉的方法对Ｔｉ－６Ａｌ－４Ｖ合金进行激光表面合金化实验,制得了以ＴｉＣ和金属间化合物Ｔｉ_５Ｓｉ_３为增强相的耐磨复合材料表面改性层,合金层硬度及在二体磨料磨损与滑动磨损条件下的耐磨性均大幅度提高。表明利用ＳｉＣ粉激光表面合金化是提高钛合金耐磨性的一种有效方法。