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 show that the phase transformation happens indeed.

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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 tolerance[1]. 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 lapping[2]. The mechanism of the material removal in lapping has a lot of statements such as the micro-cleavage theory[3]，the thermal abrasion theory[4]， electro-abrasion theory[5] and theory of fracture taking place in the hard direction[6]，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 Bouwelen[7]，Grillo[8]，Hird and Field[9]. As yet，few man has verified it at the atomistic level.

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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 Rapaport[10]. 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 tool[11] and atomic surface modification in monocrystalline silicon[12]. 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 is introduced. The scaife used was made from a grey cast iron and was

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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 category[13]. 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 volume size until further increases did not affect the displacements and

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