Ultraprecision cutting of graphite with monocrystalline diamond tools

现代空气轴承由石墨制成，对形状精度和表面质量的要求很高。空气轴承具有良好的滑动、尝试和紧急运行性能，可以达到高刚度，具有高疲劳强度和良好的抗形状性，因此在工业应用中的需求越来越大。不幸的是，石墨的加工表现出高断裂行为以及相当大的刀具磨损。为了加工高要求的石墨空气轴承，超精密加工代表了一种成熟的制造工艺，可以制造个位数纳米范围内的表面粗糙度值和亚微米范围内的形状精度。常规使用的聚晶金刚石（PCD）和化学气相沉积（CVD）金刚石制成的切削材料比单晶金刚石（MCD）具有更高的半径波纹度WR、圆角切削刃半径rβ和裂纹扩展Cg。因此，采用了由MCD制成的工具。利用MCD刀具的特定几何特性，例如圆形切削刃半径rβ，导致不同的工艺条件，这改变了应力条件，力的影响以及破裂行为。研究项目的目的是在用MCD制成的工具加工石墨时确定分离机制和破裂行为。为了降低漏料率和刀具磨损，要实现跨晶切削工艺。为了实现该研究项目，将对所使用的石墨材料进行表征，并获得基本的分离机制，并对mcd工具进行详细的磨损研究。对超精密车削刀具进行了研究，分析了刀具的断料率和刀具磨损情况。在此基础上，将开发一个解释性模型，描述切削过程中的机制。为了显示切削过程中的温度和压力载荷，进行了基于粒子的模拟。该仿真模型能够确定摩擦化学工具磨损的时间。研究项目的结果为使用MCD减少刀具磨损的切削过程和石墨材料的破裂行为提供了基础知识。

Modern air bearings made of graphite depend on highest requirements concerning shape accuracies as and surface qualities. Air bearings are characterised by good sliding, try and emergency running properties, can reach high stiffness and show a high fatigue strength as well as a good shape resistance, which results in an increasing demand for industrial applications. Unfortunately, the machining of graphite shows a high breakout behaviour as well as a considerable tool wear. In order to machine the air bearings made of graphite concerning the high requirements, the ultra-precision machining represents an established manufacturing process and enables the fabrication of surface roughness values in the single-digit nanometer range and shape accuracies as in the submicrometer range. The cutting materials made of polycrystalline diamond (PCD) and chemical-vapour-deposition(CVD)-diamond, which were conventionally used show a considerable higher radius waviness WR, rounded cutting edge radius rβ and crack growth Cg compared to monocrystalline diamonds (MCD). Therefore, tools made of MCD are applied. Using the specific geometric properties of the MCD tools e.g. the rounded cutting edge radius rβ leads to different process conditions, which changes the stress conditions, the effect of the forces as well as the breakout behaviour. The aim of the research project is the identification of the separation mechanisms and the breakout behaviour during the machining of graphite with tools made of MCD. In order to reduce the breakout rate ξB and the tool wear, a transcrystalline cutting process is to be achieved.To realise the research project, the used graphite materials are characterised as well as the basic separation mechanisms will be obtained and detailed wear investigations of the MCD-tools are carried out. In order to analyse the breakout rate ξB and the tool wear, investigations concerning of ultra-precision turning are applied. Based on this, an explanatory model will be developed, which describes the mechanisms during the cutting process. In order to show the temperatures ϑ and the pressure loads during the cutting process, a particle-based simulation is carried out. This simulation model enables the time determination of the tribo-chemical tool wear. The results of the research project provide a fundamental knowledge of the cutting process and the breakout behaviour of graphite materials using MCD with a reduced tool wear.