Ultraprecision cutting of graphite with monocrystalline diamond tools

现代由石墨制成的空气轴承对形状精度和表面质量有很高的要求。空气轴承具有良好的滑动、试运转和紧急运行性能，可以达到高刚度，表现出高的疲劳强度和良好的形状阻力，这导致了工业应用的日益增长的需求。不幸的是，石墨的机械加工表现出很高的漏钢行为以及相当大的刀具磨损。为了加工要求很高的石墨制造的空气轴承，超精密加工代表了一种既定的制造工艺，能够制造个位数纳米范围的表面粗糙度和亚微米范围的形状精度。与单晶金刚石相比，传统的聚晶金刚石和化学气相沉积金刚石刀具材料具有更高的半径波度wr、圆角刃口半径rβ和裂纹扩展Cg。因此，使用了MCD制成的工具。使用MCD刀具的特定几何属性，例如圆角刃口半径rβ，会导致不同的加工条件，从而改变应力条件、力的影响以及漏钢行为。该研究项目的目的是确定在用MCD制成的刀具加工石墨时的分离机制和漏钢行为。为了减少ξB的漏损率和刀具磨损，需要实现穿晶切割工艺。为了实现这一研究项目，对使用过的石墨材料进行了表征，获得了基本的分离机理，并对MCD刀具进行了详细的磨损研究。为了分析ξB的漏损率和刀具磨损，对超精密车削进行了研究。在此基础上，建立了描述切割过程机理的解释模型。为了显示切割过程中的温度ϑ和压力载荷，进行了基于粒子的模拟。该仿真模型实现了摩擦化学刀具磨损时间的确定。该研究项目的结果提供了使用MCD的石墨材料的切割过程和漏钢行为的基本知识，同时降低了工具磨损。

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.