机械毕业设计英文外文翻译268金刚石刀具机械研磨过程中材料的去除机理.doc

1 附录 外文翻译： Material Removing Mechanism for Mechanical Lapping of Diamond Cutting Tools LI Zeng-qiang， ZONG Wen-jun， SUN Tao， DONG Shen （ Center for Precision Engineering， Harbin Institute of Technology， Harbin 150001， China） Abstract ： The material removing mechanism for mechanical lapping of diamond cutting tools was illuminated at the atomistic scale. In lapping process， phase transformation of the lapping region was the main reason for the material removal. Thus a three-dimensional model of a specimen of the diamond monocrystal and rigid diamond grit was built with the aid ofthe molecular dynamics（ MD） simulation. The force between all of the atoms was calculated by the Tersoff potential. After that， lapping with a certain cutting depth of 1.5 lattice constants was simulated. By monitoring the positions of atoms within the model， the microstructure in the lapping region changes as diamond transformed from its diamond cubic structure to amorphous carbon were identified. The change of structure was accomplished by the flattening of the tetrahedron structure in diamond. This was verified by comparing the radial distribution functions of atoms in the lapping and un-lapping regions.Meanwhile， the debris produced in lapping experiment was analyzed by XRD（ X-ray diffraction） . The results 2 show that the phase transformation happens indeed. Keywords： diamond cutting tools； mechanical lapping； material removing mechanism； molecular dynamics simulation It is an important way to turn the optical surface with natural diamond cutting tools to obtain high accuracy. The processed work-pieces surface has lower surface roughness and residual stress， and smaller metamorphic region than those machined in usual ways. Diamond is the most important material to make cutting tools in the ultra-precision machining， for it is an ideal brittle solid with the greatest hardness and resistance to plastic deformation of any material and has very high dimensional homogeneity. The sharpening method of diamond cutting tools is the key technology to obtain sharp cutting radius， good surface quality and small geometric tolerance1. There are many sharpening methods such as lapping， ion beam sputtering， thermal chemistry polishing， plasma polishing， oxide etching and laser erosion， etc. The most common and effective method is lapping2. The mechanism of the material removal in lapping has a lot of statements such as the micro-cleavage theory3， the thermal abrasion theory4， electro-abrasion theory5 and theory of fracture taking place in the hard direction6， etc. However， these explanations are only satisfactory in the particular situation. The explanation accepted by most people is that the hybridized orbit of the carbon converts from sp3 to sp2 in lapping， as demonstrated by van Bouwelen7， Grillo8， Hird and Field9. As yet， few man 3 has verified it at the atomistic level. The extremely powerful technique of molecular dynamics（ MD） simulation involves solving the classical many-body problem in contexts relating to the study of matter at the atomistic level. Since there is no alternative approach capable of handling this broad range of problems at the required level of detail， molecular dynamics methods have been proved indispensable in both pure and applied research， as demonstrated by Rapaport10. Molecular dynamics analysis is an effective method in studying indentation， adhesion，wear and friction， surface defects and nano-cutting at the atomistic scale. Nowadays ， MD analysis has already been employed to investigate the AFM-based nanolithography process using an AFM tool11 and atomic surface modification in monocrystalline silicon12. Therefore， it is an efficient way to approach the mechanism of the material removal in lapping using molecular dynamics simulation. From all the above， this study will focus on the material removing mechanism in diamond mechanical lapping using three-dimensional MD simulation. And the microcosmic phenomena in mechanical lapping will be presented and discussed. 1 Methods 1.1 Simulation modeling At the beginning， the mechanical lapping process of diamond cutting tools 4 is introduced. The scaife used was made from a grey cast iron and was medium “ striped”（ radial grooves to hold diamond grit） .It was prepared for use by applying a film of olive oil to the surface， before a few carats of graded diamond grits were rubbed evenly into it. With the scaife running at a high speed， a diamond cutting tool was lapped by applying a load. In this process， the diamond grit was fixed in the scaife. So， the process belongs to the fixed abrasive polishing category13. Therefore， a model of a specimen of the diamond monocrystal and rigid diamond grit was built， as shown in Fig.1. Fig.1 Molecular dynamics simulation model of mechanical lapping of diamond cutting tools The crystal lattice of the specimen and the grit belonged to the diamond cubic system. The lattice constant of this system was 0.356 67 nm， which was represented as a. The control volume of the specimen must be large enough to eliminate boundary effects.Taking this into consideration， an optimum control volume was chosen based on an iterative process of increasing the control 5 volume size until further increases did not affect the displacements and velocities of the atoms due to lapping. An optimum size of 50a 15a 30a was obtained， consisting of 183,930 atoms. Moreover， the periodic boundary condition was used in the z-direction to reduce the effects of the simulation scale. The specimen included three kinds of atoms ， namely ： boundary atoms， thermostat atoms and Newtonian atoms.To restrict the rigid-body motion of the specimen， the boundary atoms in the left and bottom layers of the specimen that were fixed in space were used to contain the Newtonian atoms.Thermostat atoms were also used to ensure reasonable outward heat conduction away from the control volume.Thermostat atoms and the Newtonian atoms obey the Newtons second law.The top surface of the specimen was（ 100） surface， which was exposed to the grit.The spherical diamond grit had a radius of 8a， consisting of 17,116 atoms.And it slid on the specimen with the depth of h. Before carrying out the molecular dynamics simulation on the lapping of diamond， it is important to ensure that the chosen potential function gives a reliable result for the simulation. Tersoff potential was used in the present simulation to dictate the interaction among the diamond atoms in this simulation14. The parameters in Tersoff potential for carbon were as follows ： A=1,393.6 eV， B=347.6 eV， =34.879 nm.1， =22.119nm.1 ，=1.572,4 10.7 ， n=0.727,51 ， c=380,49 ， d=4.384， h=.0.570 58， R=0.18 nm，and S=0.21 nm. Positions and velocities of the atoms were determined by the 6 Verlet method as demonstrated by Maekawa and Itoh15.To simulate lapping under room-temperature conditions， the diamond atoms were arranged in a perfectdiamond cubic structure with the lattice parameters equal to their equilibrium values at an ambient temperature of 293 K. The ambient temperature was maintained by scaling the velocities of the thermostat atoms at every special time step.In this simulation， the 0.5 fs was selected as the time step to obtain a high accuracy. This simulation was calculated by the Lammps software16， and visualized by the VMD software17. The velocity of the lapping was 100a with 1.5a in cutting depth and 40a in lapping length. Before the simulation， the specimen had been relaxed for 10 000 time steps in order to maintain the thermal balance. 1.2 Experiment The test apparatus of lapping experiment is shown in Fig.2.The abrasive used was diamond grit with an average radius of 0.1 m.They were coated on the scaife in a ring with a radius of 120 mm.The diamond cutting tool was fixed on the arm by a special fixture.Then， the tool was lapped with the scaife running at 3 000r/min(ca.38 m/s)， under a load of 5 N which was obtained by adjusting the place of the weight. The debris was collected after 30 min lapping.Thereafter， the XRD studies were carried out by SHIMADZU XRD-6000. 7 Fig.2 Schematic diagram of the lapping apparatus 2 Results and discussions 2.1 Molecular dynamics analysis The 3D view and cross-section view of the simulation are shown in Fig.3. The crystal lattices near the diamond grit are distorted when the diamond grit cuts into the specimen.The region including these crystal lattices is half-ellipse in shape.The region is under the diamond grit and a bit left to the center o. And the major axis of the ellipse is in the same direction as the composition of forces. Furthermore， this region moves left as the diamond grit slides. As shown in Fig.4 ， A1+A2A3 ， where O1O2 represents the surface of the workpiece.It shows that the removal materials do not pole up on both sides of the groove completely.Some materials are removed and form chips. It is a cutting process. Whereas， the existing A1 and A2 show that ploughing also 8 occurs.So this state is the cutting state accompanied by ploughing. Fig.3 Microstructure of specimen after the grit sliding 9 Fig.4 Section of the grooves in the longitudinal direction There are three key points in lapping， as shown in Fig.5. Firstly， atoms near the diamond grit are forced to make some displacement from their initial position.The crystal lattices including these atoms distort a little.The boundary between the distorted lattices and the perfect lattices is along the diamond（ 111） surface（ the black lines） as shown in Fig.5（ a） .The displacements of the atoms become bigger and bigger along with the diamond grit sliding left.More and more atoms deviate from their initial position.The lattices including these atoms distort seriously.The phase transformation that the diamond cubic diamond transforms into amorphous graphite starts on a few atoms （ in the dark circles） at the end of this moment.That is to say that the hybridized orbit converts from sp3 to sp2. Secondly， the lattices below the diamond grit have the worst distortion and the boundary faceting along the（ 111） surface extend to the deeper layer， as shown in Fig.5（ b） . More atoms transform from diamond cubic diamond to amorphous graphite ， especially 10 those in the dark circle. Besides， some atoms are taken away by the diamond grit.Thirdly， some lattices revert a little with the force minimizing， as shown in Fig.5（ c） . However， the atoms which have the phase transformation cannot revert to their initial phase， especially those in the dark circle. Therefore， the groove is to the left on the surface of the diamond specimen. Fig.5 Scattergrams of atoms in longitudinal section A in different states 11 2.2 Bond formation From the simulation， it is found that the phase transformation is due to the flattening of the tetrahedron structure in diamond cubic diamond， as shown in Fig.6.The position transformation at progressive time steps is demonstrated in Fig.7. Fig.6 Crystal cell of the diamond crystal lattice taken out from the circular region in Fig.5（ a） As shown in Fig.7（ a）， the tetrahedron is deformed when the grit slides close. And the deformation is serious when the grit cuts into section A， as shown in Fig.7（ b） . The tetrahedron is flattened a little.Soon after， the tetrahedron deforms badly， as shown in Fig.7（ c） .Its four vertexes are almost on a plane and some bonds are broken. At the same time the phase transformation is accomplished. Fig.7 Change of the tetrahedron marked in Fig.6 when the grit slides 12 2.3 Pair correlation function The pair correlation functions of the specimen and the chip are shown in Fig.8 and Fig.9 respectively.The curve in Fig.8 is syllabified to a lot of clear peaks， which are the same as the diamonds radial distribution fuction(RDF). However， there are only two peaks in Fig.9, and the peaks are continued, which illuminates that amorphous exists in debris atoms. Therefore， it is sure that the phase transformation takes place in lapping. Fig.8 Pair correlation function of specimen atoms Fig.9 Pair correlation function of debris atoms 13 2.4 XRD Fig.10 shows the X-ray diffraction（ XRD） analysis of the debris produced in the lapping experiment. It demonstrates that the amorphous carbon， small diamond particles or chips and Fe-C compositions（ like Fe7C3 and Fe5C2）exist together in the debris. Consequently， the amorphous carbon is produced in lapping， which corresponds to the simulation result. Fig.10 XRD analysis of the debris produced in the experiment 3 Conclusions （ 1） A three-dimensional MD model about the atoms of diamond cutting tools and diamond grit is built by using the molecular dynamics. Lapping at a special cutting depth is simulated. （ 2） The boundary of the transformation zone is regular ， faceting along 14 （ 111 ） surface. The microcleavage only occurs inside this boundary. （ 3） Interaction between the diamond grit and diamond specimen leads to a phase transformation event.An amorphous transformation appears as the grit slides.And it is expounded from the comparison between the bond formatting and pair correlation function. Moreover， it has also been proved in the lapping experiment. References： 1 Yuan Z J， Yao Y X， Zhou M， et al. Lapping of single crystal diamond tools J CIRP Annals-Manufacturing Technology， 2003， 52（ 1）： 285-288. 2 Uegami K ， Tamamura K ， Jang K K. Lapping and frictional properties of diamond，and characteristics of diamond cutting tool J Journal of Mechanical Working Technology，1988， 17（ 8）： 147-155. 3 Tolkowsky M. Research on the Abrading， Grinding or Polishing of Diamond D London： City and Guilds College， University of London， 1920. 4 Bowden F P， Tabor D. Physical Properties of Diamond M Oxford： Clarendon Press， 1965. 5 Brezoczky B ， Seki H. Triboattaction ： Friction under negative load J Langmuir，1990， 6（ 6）： 1141-1145. 6 Couto M， van Enckevort W J P， Seal M， et al. Scanning tunneling microscopy of polished diamond surfaces J Applied Surface Science， 1992， 62（ 4）： 263-268. 7 van Bouwelen F M. Mechanically Induced Degradation of Diamond D Cambridge ： University of Cambridge， 1996. 8 Grillo S E， Field J E， van Bouwelen F M. Diamond polishing： The dependency of friction and wear on load and crystal orientation J Journal of Physics D： Applied Physics， 2000， 33： 985-990. 9 Hird J R， Field J E. A wear mechanism map for the diamond polishing process J Wear， 2005， 258： 18-25. 10 Rapaport D C. The Art of Molecular Dynamics Simulation M Cambridge： Cambridge University Press， 2004. 11 Yan Y D， Sun T， Dong S， et al. Molecular dynamics simulation of processing using AFM pin tool J Applied Surface Science， 2006， 252： 7523-7531. 12 Zarudi I， Cheong W C D， Zou J， et al. Atomistic structure of monocrystalline silicon in surface nano-modification 15 J Nanotechnology， 2004， 15： 104-107. 13 Li Z Q， Sun T， Shi L Q， et al. Study on lapping process of diamond cutting tool J Key Eng Mater， 2006， 304/305： 104-108. 14 Tersoff J. Empirical interatomic potential for carbon， with applications to amorphous carbon J Phys Rev， 1988， 61（ 25）： 2879-2882. 15 Maekawa K， Itoh A. Friction and tool wear in nano-scale machining： A molecular dynamics J Wear， 1995， 188： 115-122. 16 Plimpton S J. Fast parallel algorithms for short-range molecular dynamics J J Comp Phys， 1995， 117： 1-19. 17 Humphrey W， Dalke A， Schulten K. VMD： Visual molecular dynamics J J Molec Graphics， 1996， 14： 33-38. 金刚石刀具机械研磨过程中材料的去除机理 李增强，宗文俊，孙 涛，董 申 （哈尔滨工业大学精密工程研究所，哈尔滨 150001） 摘要： 该材料，移除为的钻石切割工具的机械研磨的机制被照亮在的原子论的的的的规模。在研磨过程中研磨区，相转变材料去除的主要原因。因此，金刚石单晶和刚性金刚石磨粒的标本的三维模型的建立与援助的分子动力学（ MD）模拟。所有的原子之间的力量计算 Tersoff潜力 。后认为，与一个 1.5晶格常数的的一定的的切削深度研磨进行了数值模拟。通过监测模型内的原子的位置，在金刚石研磨地区的钻石立方结构转变为无定形碳的微观结构进行了鉴定。完成在钻石的四面体结构的扁平化结构的变化。这验证了原子的径向分布函数的研磨和联合国研磨 regions.Meanwhile的，研磨试验产生的碎片，通过 XRD（ X射线衍射）分析比较。的结果表明，的相位转型会发生确实。 这是一个重要途径，把光学表面与天然金刚石刀具获得高的精度。处理工作件表面具有较低的表面粗糙度和残余应力，小于常规方法加工的 变质地区。 钻石是最重要的物质，在超精密加工的切削工具，它是一种理想的最大的硬度和耐磨性的任何材料的塑性变形的脆性固体，具有非常高的维同质。金刚石刀具刃磨方法 16 的关键技术，获得锋利的切削半径，良好的表面质量和几何公差小 1。有许多方法，如研磨，离子束溅射，热化学抛光，等离子抛光，氧化腐蚀和激光侵蚀等锐化最常见和最有效的方法是研磨 2。在研磨材料去除机制有一个报表很多，如微切割理论 3，热磨损理论 4，电磨损理论 5和断裂理论的努力方向 6，等等。然而，这些解释是只有在特殊情况令人满意。 大多数人所接受的解释是，从 SP3 杂化轨道的碳转换到 SP2 作为由面包车 Bouwelen 证明，在研磨 7，格里洛 8，本手册所有提及和现场 9。到目前为止，一些人已证实它在原子水平。 极其强大的技术分子动力学（ MD）模拟涉及解决有关的物质在原子水平的研究背景的经典多体问题。由于没有替代方法能够在所需水平的细节处理这个问题的广泛，分子动力学方法已被证明是不可或缺的纯粹与应用研究，由 Rapaport 表明 10。分子动力学分析是一个有效的方法，在学习压痕，附着力，耐磨损和摩擦，表面缺陷，并在原子尺度 的纳米切割。如今，医师分析已经被调查基于 AFM 的纳米光刻过程中使用的原子力显微镜工具 11和硅原子在单晶硅表面改性 12。因此，它是一种有效的方式来处理的材料去除机制，研磨使用分子动力学模拟。 所有上述，本研究将集中在材料，消除金刚石机械研磨使用三维的 MD 模拟的机制。和机械研磨的微观现象，将介绍和讨论。 1 研究方法 1.1 仿真建模 在开始时，介绍了金刚石刀具机械研磨过程。斯凯夫使用了从灰铸铁中的 “条纹 ”（径向槽举行金刚石磨粒）。 通过膜表面的橄榄油，之前几克拉分级金刚石颗粒均匀揉入准备使用。 斯凯夫在高速运行，钻石刀具研磨应用负载。在这个过程中，金刚石磨粒固定在斯凯夫。所以，这个过程属于固定研磨抛光类 13 。 因 此 ， 始 建 金 刚 石 单 晶 和 刚 性 金 刚 石 磨 粒 的 标 本 模 型 ， 如 图 1 所示。 17 图 7-1 关于金刚石切割工具机械研磨的分子动力学仿真模型 晶格的标本和砂砾属于钻石的立方系统。该系统的晶格常数为 0.356 67 纳米，这是作为一个代表。试样的控制量必须足够大，消除边界 effects.Taking 考虑到这一点的，被选为最佳控制量的基础上增加控制音量大小，直到进一步增加并不影响原子的位移和速度的迭代过程由于研 磨。一个最佳规模为 50A15A30A， 183930 原子组成的。此外，周期性的边界条件是在 z 方向，以减少仿真规模的影响。标本包括原子 3 种，即：边界原子，恒温原子和牛顿 atoms.To 的限制的刚体运动的标本，在标本固定在空间的左侧和底部层的边界原子包含牛顿 atoms.Thermostat 原子也被用来确保合理向外热传导远离控制 volume.Thermostat 原子和牛顿原子服从牛顿第二 law.The 排在前面的标本（ 100）表面，这是暴露球形金刚石磨粒 grit.The 了一个 8A 的半径，它与深度 h 的标本下滑 17,116 atoms.And 组成。 开展对金刚石研磨的分子动力学模拟之前，重要的是要确保所选择的潜在功能提供了一个可靠的模拟结果。在目前的模拟 tersoff 潜力，决定在这个模拟 14钻石的原子之间的相互作用。 Tersoff 碳势参数如下： = 1,393.6 EV， = 347.6 EV， = 34.879 nm.1， = 22.119nm.1， = 1.572,410.7， N = 0.727,51， C = 380,49， D = 4.384， H = .0.570 58， r = 0.18纳米，和 S = 0.21 纳米。位置和原子的速度 Verlet 方法，确定由前川和伊藤表明 15为了模拟在室温条件下研磨，钻石的原子排列在 perfectdiamond 立方结构的晶格参数等于其均衡值 0.5 FS，通过扩大在每一个特殊的时间 step.In这个模拟恒温 原子的速度保持在 293 K 时的环境温度环境温度，被选定为时间步长，获得了很高的精度。 这由 Lammps 软件 16，模拟计算和可视