基于分子动力学的单晶硅纳米切削过程中刀具磨损的研究

发布时间：2018-05-04 22:41

本文选题：金刚石刀具 + 单晶硅　；参考：《哈尔滨工业大学》2015年博士论文

【摘要】：单晶硅因其光学性能优异、机械强度高以及化学性质稳定等特点,被广泛地应用于光学、机械电子等高科技领域。然而,单晶硅的断裂强度和屈服强度比较接近,加工过程中容易发生脆性断裂,很难获得高质量的加工表面。目前,做为先进制造前沿技术之一的纳米切削技术,由于具有加工精度高、效率高、易于控制以及可加工复杂面形等特点,成为单晶硅加工领域的研究热点。在单晶硅的纳米切削过程中,金刚石刀具易在较短的时间内发生严重的磨损,导致加工表面质量迅速恶化。此外,当切削加工量进入纳观领域时,去除对象为具有离散性质的原子或分子,所涉及的理论已超出了建立在连续介质力学基础之上的常规切削理论,使得各国学者对金刚石刀具的磨损机理以及单晶硅的纳米加工机理的认识还存在着较大的争议。上述问题已经成为纳米切削技术进一步发展所亟需解决的问题。鉴于分子动力学方法能够从原子角度表征纳米切削的瞬态过程、分析研究其中的机理性问题。因此,本文围绕加工参数、材料各向异性和刀具几何形状等参数对单晶硅纳米切削行为以及刀具磨损行为的影响,采用分子动力学方法开展了如下几个方面的研究工作:首先,基于分子动力学基本原理,建立了金刚石刀具纳米切削单晶硅的分子动力学模型,并选择合适的势函数、积分方法和系综等参数。综合金刚石的晶格结构和热力学性质系统研究了金刚石石墨化的各向异性行为,得到了其随温度和晶体取向的变化规律。并且为了更好地分析金刚石的石墨化过程,本文提出了一种新方法—6元环法,可以准确地辩识出金刚石和石墨碳原子。此外,对传统的分子动力学刀具模型进行了修正,修正后的刀具能够更加真实地反映纳米切削过程中的刀具状态。通过对比分析传统和修正刀具的磨损程度,验证了后者比前者更适用于刀具磨损的研究。其次,基于大规模单晶硅工件(100×50×3nm3)的纳米切削仿真模型,模拟研究了单晶硅在纳米加工过程中的材料去除和表面形成机理。为了分析单晶硅各向异性对其纳米切削行为的影响,研究了金刚石刀具分别沿着单晶硅(100)、(110)和(111)面的典型晶向的切削过程,获得了切削方向变化对切屑和表面损伤层的影响规律,并对加工表面完整性进行量化比较,确定了每个晶面上更适合塑性域切削的晶向。同时,采用配位数法表征了加工表面中的损伤结构,并结合对工件中的静压和最大剪切应力的分析,揭示了表面非晶层和亚表面损伤层的形成机理。此外,系统研究了刀具几何形状和背吃刀量对单晶硅纳米切削行为的影响,通过分析切屑中的剪切面结构,详细阐述了单晶硅在纳米切削过程中的去除机理。再次,金刚石刀具表面石墨化磨损后会导致其表面软化,在硬质颗粒的刻划作用下会引起刀具发生剧烈磨损。因此,基于前面提出的修正刀具模型,系统研究了温度和剪切应力对金刚石刀具石墨化磨损的影响,并揭示了其形成机理。同时,分析了吸附在刀具表面的低配位数碳原子对刀具磨损的作用机制。此外,模拟研究了金刚石各向异性对刀具磨损行为的影响,获得了具有最强抗磨损能力的金刚石刀具前后刀面的晶向组合。最后,建立了具有不同几何形状的金刚石刀具,模拟研究刀具几何形状对刀具磨损的影响。对引起金刚石刀具磨损的主要因素进行了系统分析,深入剖析刀具前后角的变化对前后刀面磨损的影响。同时,研究了金刚石刀具在切削过程中的扩散磨损,通过分析磨损区中碳原子的杂化结构与热导率之间的关系,对其机理进行了解析。此外,在刀具后刀面上引入微沟槽,研究微沟槽深度和密度对刀具磨损的影响,并揭示了其作用机制,相关研究将为超精密加工金刚石刀具的设计及应用提供理论指导和技术支持。
[Abstract]:Because of its excellent optical properties, high mechanical strength and stable chemical properties, monocrystalline silicon is widely used in high tech fields such as optics, mechanical electronics and other fields. However, the fracture strength and yield strength of monocrystalline silicon are close, brittle fracture is easy to occur during processing, and it is difficult to obtain high quality processing surface. At present, it is advanced. Because of the characteristics of high machining precision, high efficiency, easy to control and machinable complex surface, one of the cutting edge technologies has become a hot topic in the field of monocrystalline silicon processing. In the process of nanometer cutting of monocrystalline silicon, the diamond tools are easily worn out in a short time, leading to the quality of the machined surface. In addition, the theory of removing the object as a discrete atom or molecule is beyond the conventional cutting theory based on the continuum mechanics, which makes the scholars of various countries understand the mechanism of the grinding loss of diamond tools and the mechanism of the nanocrystalline mechanism of monocrystalline silicon. There are still great disputes. The above problems have become an urgent problem to be solved in the further development of nano cutting technology. In view of the possibility that the molecular dynamics method can characterize the transient process of nano cutting from the atomic angle, the mechanism problems are analyzed and studied. Therefore, this article focuses on the addition parameters, the material anisotropy and the tool geometry. The influence of shape and other parameters on the behavior of nanoscale cutting and the wear behavior of single crystal silicon is studied by molecular dynamics method. First, based on the basic principle of molecular dynamics, the molecular dynamics model of diamond cutting tool nanocrystalline silicon is established, and the suitable potential function and integral method are selected. The lattice structure and the thermodynamic properties of the synthetic diamond are studied. The anisotropic behavior of the diamond graphitization is studied. The change law of the diamond with the temperature and crystal orientation is obtained. In order to better analyze the process of the graphitization of the diamond, a new method, 6 element ring method, can be accurately identified. Diamond and graphite carbon atoms. In addition, the traditional molecular dynamics tool model is modified. The modified tool can more truly reflect the tool state in the nano cutting process. By comparing and analyzing the wear degree of the traditional and correction tools, the latter is more suitable for tool wear research than the former. Secondly, based on the study. A simulation model of a large scale single crystal silicon workpiece (100 x 50 x 3nm3) is used to simulate the material removal and surface formation mechanism of monocrystalline silicon in the process of nanoscale processing. In order to analyze the effect of the anisotropy of monocrystalline silicon on its nano cutting behavior, the typical crystals of the diamond cutting tools along the single crystal silicon (100), (110) and (111) surfaces are studied. In the cutting process, the influence of cutting direction changes on the chip and surface damage layer is obtained, and the machined surface integrity is quantized and compared. It is determined that each crystal surface is more suitable for the crystal direction of the plastic field. At the same time, the coordination number method is used to characterize the damage structure in the machined surface, and the static pressure and maximum of the workpiece are combined. The analysis of shear stress reveals the formation mechanism of the surface amorphous and subsurface damage layers. In addition, the influence of the geometric shape of the cutter and the amount of the back knife on the nanocrystalline cutting behavior of monocrystalline silicon is systematically studied. By analyzing the shear surface structure in the chip, the removal mechanism of monocrystalline silicon in the process of nano cutting is elaborated. The surface softening of the tool surface will result in the softening of the surface of the tool and the sharp wear of the tool under the characterization of hard particles. Therefore, based on the revised tool model proposed earlier, the effect of temperature and shear stress on the graphitized wear of diamond tools is systematically studied and its formation mechanism is revealed. At the same time, the adsorption of the tool is analyzed. The effect mechanism of low coordination carbon atoms on tool wear on tool surface. In addition, the influence of diamond anisotropy on tool wear behavior is simulated and the crystal direction combination of the front and back surface of diamond tool with the strongest anti wear ability is obtained. Finally, the diamond cutting tools with different geometric shapes are established. The effect of tool geometry on tool wear is analyzed systematically. The influence of the change of the front and rear angle on the wear of the front and rear cutter faces is deeply analyzed. At the same time, the diffusion wear of the diamond cutting tool in the cutting process is studied, and the hybrid structure and thermal conductivity of the carbon atom in the wear zone are analyzed. In addition, the mechanism is analyzed. In addition, the effect of micro groove depth and density on tool wear is studied by introducing micro groove on the cutter surface, and its mechanism is revealed. The related research will provide theoretical guidance and technical support for the design and application of ultra precision machining diamond tools.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ127.2

【相似文献】