单晶硅超精密磨削过程的分子动力学仿真

对内部无缺陷的单晶硅超精密磨削过程进行了分子动力学仿真,从原子空间角度观察了微量磨削过程,解释了微观材料去除、表面形成和亚表面损伤机理,并分析了磨削过程中的磨削力和磨削能量消耗。研究表明:磨削过程中,在与磨粒接触的硅表面原子受到磨粒的挤压和剪切发生变形,堆积在磨粒的前方,当贮存在变形晶格中的应变能超过一定值时,硅的原子键断裂,即完成了材料的去除;随着磨粒的运动,磨粒前下方的硅晶格在磨粒的压应力作用下晶格被打破,形成了非晶层,非晶层不断向前向深处扩展,造成了单晶硅亚表面的损伤;同时部分非晶层原子在压应力的作用下与已加工表层断裂的原子键结合,重构形成已加工表面变质层。     

单晶硅纳米级磨削过程的理论研究

对内部无缺陷的单晶硅纳米级磨削过程进行了分子动力学仿真,从磨削过程中瞬间原子位置、磨削力、原子间势能、损伤层深度等角度研究了纳米级磨削加工过程,解释了微观材料去除、表面形成和亚表面损伤机理。研究表明：磨削过程中,单晶硅亚表面损伤的主要形式是非晶结构形式,无明显的位错产生,硅原子间势能的变化是导致单晶硅亚表面损伤的重要原因;另外,发现磨粒原子与硅原子之间有黏附现象发生,这是由于纳米尺度磨粒的表面效应而产生的。提出了原子量级条件下单晶硅亚表面损伤层的概念,并定义其深度为沿磨削深度方向原子发生不规则排列的原子层的最大厚度。     

氮化硅陶瓷磨削温度与表面变质层的仿真与实验

为了揭示氮化硅陶瓷磨削温度分布规律以及其对表面成形的影响,首先,建立氮化硅陶瓷纳米级切削的分子动力学模型;其次,研究切削过程中切削参数对切削温度的影响,以及加工过程中切削表面变质层的形成过程;最后,对 K 型热电偶测温和表面能谱分析的仿真与实验结果进行对比分析.结果表明:随着金刚石磨粒切削深度和切削速度的增加,原子晶格发生变形和非晶相变过程中时释放的能量增多,从而使切削温度升高;切削高温会引起氮化硅陶瓷发生非晶相变现象,非晶态原子重新与已加工表面断裂的原子键结合形成表面变质层;分子动力学仿真模型可以用来预测氮化硅陶瓷材料实际磨削加工中磨削温度变化情况,对生产加工具有参考价值.     

硅片低损伤磨削砂轮及其磨削性能

针对传统金刚石砂轮磨削硅片存在的表面/亚表面损伤问题,研制了一种用于硅片化学机械磨削加工的新型常温固化结合剂软磨料砂轮。根据化学机械磨削加工原理和单晶硅的材料特性,设计的软磨料砂轮以氧化铈为磨料,二氧化硅为添加剂,氯氧镁为结合剂。研究了软磨料砂轮的制备工艺,分析了软磨料砂轮的微观组织结构和成分。通过测量加工硅片的表面粗糙度、表面微观形貌和表面/亚表面损伤,进一步研究了软磨料砂轮的磨削性能。最后,与同粒度金刚石砂轮磨削和化学机械抛光(CMP)加工的硅片进行了对比分析。结果表明,采用软磨料砂轮磨削的硅片其表面粗糙度Ra1nm,亚表面损伤仅为深度30nm的非晶层,远好于金刚石砂轮磨削硅片,接近于CMP的加工水平,实现了硅片的低损伤磨削加工。     

光学镜片亚表面损伤形成数值模拟与分析

针对当前光学镜片亚表面损伤的研究重点主要集中在加工工艺参数及磨粒粒径、分布等方面的现状,基于脆性材料压痕断裂理论,深入分析了加工过程所导致光学镜片亚表面损伤,对不同锐度角的磨粒在相同载荷不同加工速度下与光学镜片表面间的抛光过程进行了微观动态仿真。获得了在不同加工参数作用下磨头与镜片表面间的摩擦接触、应力应变分布及亚表面损伤等情况,归纳出亚表面损伤裂纹深度、亚表面损伤空穴深度、体积去除率、表面破损率、磨粒锐度角及磨抛速度等相关参数之间的关系,并得出如下结论：当磨粒锐度角为54°~58°,加工速度为7～8m/s时,加工后的镜片在保证一定加工效率的同时,产生的亚表面损伤及表面破损率最小。     

Molecular dynamics modeling of a single diamond abrasive grain in grinding

In this paper the nano-metric simulation of grinding of copper with diamond abrasive grains, using the molecular dynamics (MD) method, is considered. An MD model of nano-scale grinding, where a single diamond abrasive grain performs cutting of a copper workpiece, is presented. The Morse potential function is used to simulate the interactions between the atoms involved in the procedure. In the proposed model, the abrasive grain follows a curved path with decreasing depth of cut within the workpiece to simulate the actual material removal process. Three different initial depths of cut, namely 4 ?, 8 ? and 12 ?, are tested, and the influence of the depth of cut on chip formation, cutting forces and workpiece temperatures are thoroughly investigated. The simulation results indicate that with the increase of the initial depth of cut, average cutting forces also increase and therefore the temperatures on the machined surface and within the workpiece increase as well. Furthermore, the effects of the different values of the simulation variables on the chip formation mechanism are studied and discussed. With the appropriate modifications, the proposed model can be used for the simulation of various nano-machining processes and operations, in which continuum mechanics cannot be applied or experimental techniques are subjected to limitations.     

湿式机械化学磨削单晶硅的软磨料砂轮及其磨削性能

针对干式机械化学磨削(Mechanical chemical grinding, MCG)单晶硅过程中易产生磨削烧伤、粉尘多、加工环境差等问题,研制一种可用于湿式MCG单晶硅的新型软磨料砂轮,并对砂轮的磨削性能及其磨削单晶硅的材料去除机理进行研究。根据湿式机械化学磨削单晶硅的加工原理和要求,制备出以二氧化硅为磨料、改性耐水树脂为结合剂的新型软磨料砂轮。采用研制的软磨料砂轮对单晶硅进行磨削试验,通过检测加工硅片的表面/亚表面质量对湿式MCG软磨料砂轮的磨削性能进行分析,并与传统金刚石砂轮、干式MCG软磨料砂轮的磨削性能进行对比。采用X射线光电子能谱仪对磨削前后硅片的表面成分进行检测,分析湿式MCG加工硅片过程中发生的化学反应。结果表明,采用湿式MCG软磨料砂轮加工硅片的表面粗糙度Ra值为0.98 nm,亚表面损伤层深度为15 nm,湿式MCG软磨料砂轮磨削硅片的表面/亚表面质量远优于传统金刚石砂轮,达到干式MCG软磨料砂轮的加工效果,可实现湿磨工况下硅片的低损伤磨削加工。在湿式MCG过程中,单晶硅、二氧化硅磨粒与水发生了化学反应,在硅片表面生成易于去除的硅酸化合物,硅酸化合物进一步通过砂...     

Subsurface crystal lattice deformation machined by ultraprecision grinding of soft-brittle CdZnTe crystals

Cd_0.96Zn_0.04Te (111) single crystals were ultraprecisely ground by #1500, #3000, and #5000 diamond grinding wheels, and the corresponding surface roughness Ra is 49.132, 18.746, and 5.762 nm. High-resolution field emission scanning electron microscope and transmission electron microscope were employed to investigate the surface and subsurface damage. After ultraprecision grinding by three kinds of diamond wheels, the subsurface can achieve ultra-low damage layer with thickness of 1–2 nm made of amorphous state material and lattice distortion layer. For the #1500 precision grinding, the subsurface damage is mainly multi-nanocrystal with diameter in the range of 5–20 nm. While for the #3000 precision grinding, the subsurface damage is made of amorphous state material containing nanocrystals with diameter mainly in the range of 2–5 nm, and the bending deformation is mainly conducted through dislocation pleat formation. For #5000 ultraprecision grinding, the subsurface damage is mainly amorphous state material, and nanocrystals with diameter in the range of 2–5 nm enrich adjacent to the ground surface. Moreover, the size of nanocrystal ground by #5000 diamond grinding wheel is mainly 2 nm. Fracture mechanism ground by #5000 diamond grinding wheel firstly turns onto thin amorphous state film, then fracture.     

Atomic scale deformation in silicon monocrystals induced by two-body and three-body contact sliding

This paper discusses the deformation of silicon monocrystals subjected to two-body and three-body contact sliding with the aid of the molecular dynamics analysis. It was found that amorphous phase transformation is the main deformation in silicon and the onset of such inelastic deformation can be well predicted by a stress criterion. In a two-body contact sliding, the deformation of silicon falls into no-wear, adhering, ploughing and cutting regimes, while in a three-body contact sliding it follows the regimes of no-wear, condensing, adhering and ploughing. Under certain conditions in three-body sliding, wear without any subsurface damage can also occur when the bonding strength among surface silicon atoms is weakened and material removal takes place through the mechanism of adhesion. Based on the detailed deformation analysis, a new friction law and a new concept for wearability evaluation were proposed.     

A state-of-the-art review of ductile cutting of silicon wafers for semiconductor and microelectronics industries

Silicon is a typical functional material for semiconductor and optical industry. Many hi-tech products like lenses in thermal imaging, solar cells, and some key products of semiconductor industry are made of single crystal silicon. Silicon wafers are used as substrate to build vast majority of semiconductor and microelectronic devices. To meet high surge in demand for microelectronics based products in recent years, the development of rapid and cost efficient processes is inevitable to produce silicon wafers with high-quality surface finish. The current industry uses a sequence of processes such as slicing, edge grinding, finishing, lapping, polishing, back thinning, and dicing. Most of these processes use grinding grains or abrasives for material removal. The mechanism of material removal in these processes is fracture based which imparts subsurface damage when abrasive particles penetrate into the substrate surface. Most of these traditional processes are extremely slow and inefficient for machining wafers in bulk quantity. Moreover, the depth of subsurface damage caused by these processes can be up to few microns and it is too costly and time consuming to remove this damage by heavy chemical–mechanical polishing process. Therefore, semiconductor industry requires some alternative process that is rapid and cost effective for machining silicon wafers. Ductile cutting of silicon wafer has the potential to replace the tradition wafer machining processes efficiently. If implemented effectively in industry, ductile cutting of silicon wafers should reduce the time and cost of wafer machining and consequently improve the productivity of the process. This paper reviews and discusses machining characteristics associated with ductile cutting of silicon wafers. The limitations of traditional wafer fabrication, the driving factors for switching to ductile cutting technology, basic mechanism of ductile cutting, cutting mechanics, cutting forces, surface topography, thermal aspects, and important factors affecting these machining characteristics have been discussed to give a systematic insight into the technology.     

Fundamental investigation of subsurface damage in single crystalline silicon caused by diamond machining

Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.     

工件旋转法磨削硅片的磨粒切削深度模型

半导体器件制造中,工件旋转法磨削是大尺寸硅片正面平坦化加工和背面薄化加工最广泛应用的加工方法。磨粒切削深度是反映磨削条件综合作用的磨削参量,其大小直接影响磨削工件的表面/亚表面质量,研究工件旋转法磨削的磨粒切削深度模型对于实现硅片高效率高质量磨削加工具有重要的指导意义。通过分析工件旋转法磨削过程中砂轮、磨粒和硅片之间的相对运动,建立磨粒切削深度模型,得到磨粒切削深度与砂轮直径和齿宽、加工参数以及工件表面作用位置间的数学关系。根据推导的磨粒切削深度公式,进一步研究工件旋转法磨削硅片时产生的亚表面损伤沿工件半径方向的变化趋势以及加工条件对磨削硅片亚表面损伤的影响规律,并进行试验验证。结果表明,工件旋转法磨削硅片的亚表面损伤深度沿硅片半径方向从边缘到中心逐渐减小,随着砂轮磨粒粒径、砂轮进给速度、工件转速的增大和砂轮转速的减小,加工硅片的亚表面损伤也随之变大,试验结果与模型分析结果一致。     

麻花钻复杂螺旋槽面分段成形磨削的砂轮廓形计算

针对高性能新型麻花钻螺旋面端截形复杂和不可能实现一次性磨削螺旋槽的技术难题,根据圆柱螺旋面成形的基本原理,对工件螺旋面和成形砂轮回转面的接触线及螺旋面端截形进行详细分析,提出了对麻花钻螺旋面端截形进行分段对应优化求砂轮廓形并多次磨削螺旋槽的方法,通过仿真验证了该技术的正确性。     

Influence of anisotropy of nickel-based single crystal superalloy in atomic and close-to-atomic scale cutting

Nickel-based single crystal superalloy is widely used in the field of aerospace and nuclear reaction equipment due to its good properties. Ultra-precision machining technology is an important means to ensure the surface quality of parts. However, the anisotropy of materials has great influence on the evolution of surface and subsurface defects and the removal of materials in the process of machining. In this paper, The MD (molecular dynamics) modeling and simulation verification of cutting anisotropic nickel-based single crystal superalloy workpiece with silicon nitride tool is carried out by using the mixed potential function simulation. Through cutting simulation and visualization, the types, number, deformation area and dislocation evolution of the machined surface defects and inside of the workpiece defect of nickel-based single crystal superalloy with different crystal orientations are analyzed. The evolutionary mechanism of the machined surface defects and the law of material removal are discussed. The research content provides a theoretical basis for parameter optimization and improvement of machining quality in the atomic and close-to-atomic scale (ACS) cutting process, and technical support for efficient and precise machining process of the nickel-based superalloy.     

基于图像处理的单颗粒金刚石曲率半径测定方法研究

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采用优质天然金刚石对研、精磨和钎焊工艺制备单颗粒金刚石磨具,用于研究陶瓷等硬脆材料磨削去除、砂轮磨粒磨损及工件表面损伤形成机理。通过扫描电镜获取金刚石磨粒尖端图像,运用灰质化、直方图均衡化、中值滤波、二值化分割及Canny算子预处理并提取磨粒尖端轮廓边缘。在Photoshop软件中测量图像标尺占据的横向像素数目,绘制不同尺寸的圆形与磨粒尖端轮廓线条内切,多次操作后选择最大内切圆。统计该内切圆半径对应的像素个数,利用代数学基本原理即可求出最大内切圆半径。该方法不依赖专用的小曲率半径精密测量设备,具有较高测量精度与可操作性。
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螺旋槽砂轮磨削非光滑表面形貌特征仿真

非光滑表面在机械摩擦磨损的过程中具有减少摩擦和降低能耗的作用。为获得平面工件的非光滑表面,采用磨削加工方式。将砂轮表面修整成螺旋槽形状,并建立螺旋槽砂轮表面的数学模型,根据磨削运动学建立磨粒运动轨迹方程,通过MATLAB仿真研究不同加工参数下磨削表面的形貌特征。     

Nanogrinding

Nanogrinding is an ultraprecision machining process well suited for surface machining of advanced ceramics. The machining kinematic is based on a lapping process, where the workpieces, forced by friction effects, revolve on a rotating plate. Lapping uses loose grain; however, for nanogrinding, the abrasive grain is completely embedded in a soft metallic plate, thus becoming the grinding tool. Therefore, nanogrinding is a two-step process. The first step is to create the grinding plate. In the second step, the workpiece is machined. Nanogrinding requires a significant grinding plate roughness, which is achieved by conditioning the plate with pumice. During this process, pumice is embedded in the grinding plate and remains there throughout the process. Between pumice particles, the basic soft metallic plate material forms plateus. Diamond grain is embedded here by a conditioning ring, with their summits aligned co-planar to the plate surface. This arrangement allows the performance of ductile machining, resulting in plastic material removal, minimal subsurface damage, and excellent surface finish.     

分子动力学仿真过程中硅晶体位错模型的构建

基于位错形成机理,在单晶硅晶体结构基础上描述了硅晶体位错形成的过程。应用偶极子模型,构建了60°滑移位错芯和螺旋位错芯,进而得到硅晶体含有60°滑移位错的模型和含有螺旋位错的模型。对含有螺旋位错的硅晶体模型进行了分子动力学仿真计算,分析了含有螺旋位错的硅晶体超精密磨削的加工过程,研究了含有螺旋位错缺陷的硅晶体纳米级磨削机理。     

镍铝青铜合金仿生表面的砂带磨削及其降噪特性

针对镍铝青铜合金材料难以加工出仿生沟槽表面从而提高其降噪性能的问题,利用金字塔砂带和空心球砂带在镍铝青铜合金材料表面上磨削出仿生沟槽,并搭建配套试验平台来对镍铝青铜合金材料表面进行仿生沟槽结构的磨削加工。提取了磨削表面的特征,据此进行流体噪声计算,对比分析了金字塔砂带磨削出的仿生表面和空心球砂带磨削出的仿生沟槽表面的噪声性能,结果显示：金字塔砂带磨削出的规则仿生沟槽表面声学能量等级的平均值为18.07 dB,空心球砂带磨削出的不规则仿生沟槽表面声学能量等级的平均值为37.6 dB。试验中,两种砂带磨削加工后的镍铝青铜合金表面均具有仿生沟槽结构,且金字塔砂带磨削出的规则仿生沟槽表面具有更好的水下降噪性能。     

Theoretical model of brittle material removal fraction related to surface roughness and subsurface damage depth of optical glass during precision grinding

Brittle material removal fraction (BRF) is defined as the area fraction of brittle material removed on machined surface. In the present study, a novel theoretical model of BRF was proposed based on indentation profile caused by intersecting of lateral cracks. The proposed model is related to surface roughness and the subsurface damage (SSD) depth of optical glass during precision grinding. To investigate the indentation profile, indentation tests of K9 optical glass were conducted using single random-shape diamond grains. The experimental results indicate that the indentation profile is an exponent function. To verify the proposed BRF model, BRF, surface roughness and SSD depth of K9 optical glasses were investigated by a series of grinding experiments with different cutting depths. The experimental results show that BRF is dependent on surface roughness and SSD depth. The relationship between BRF, surface roughness and SSD depth is in good accordance with the proposed theoretical model. The proposed BRF model is a reasonable approach for estimating surface roughness and SSD depth during precision grinding of optical glass.