Influence of undeformed chip parameters on material load and resulting subsurface damage when ultra-precision grinding of hard and brittle materials with coarse-grained diamond grinding wheels

采用粗晶金刚石砂轮（dG > 301µm）对脆性材料进行延性磨削时接触区法向应力和剪应力的测定是本课题研究的重点。确定的应力将与磨削后的面层相关联，用物理量来描述材料的分离机制。表层是通过测量亚表面损伤来研究的，亚表面损伤可以通过裂纹的深度、数量和形态来确定。通常，决定材料分离机制是延性还是脆性的切屑厚度的计算是基于现象学的概念，但这些概念受到分离机制预测的限制。这是由于包含了磨削工具的形貌，它在最大未切削切屑厚度的公式中具有统计性质。当使用粗粒金刚石砂轮时，活动颗粒的数量及其形状不是统计的，而更像是只有几个活动切削刃，可与铣削过程相媲美。因此，必须描述研磨工具的整个地形，这是在本研究项目中通过结构光投影测量来完成的。通过对磨削方向的线性散射对测量形貌进行基于软件的分析，可以确定磨削过程中与工件接触的法向和切向区域。结合原位测量的过程力，可以计算接触区的法向应力和剪应力。通过测量亚表面损伤来研究它们对表层的影响。将确定的载荷应力和亚表面损伤转化为一个综合的过程模型，重新定义最大未切割切屑厚度的计算基础。在此过程模型中，物理量（在此情况下为法向应力和剪应力）应取代过程或系统变量。在拟研究项目中，采用包络曲线精度小于2微米的反镀单层不可修整金刚石砂轮进行磨削，因为这种类型的砂轮经过修整后无法达到所需的高精度。

The determination of normal and shear stresses in the contact zone while ductile grinding of brittle materials with coarse-grained diamond grinding wheels (dG > 301 µm) is the main focus of this research project. The determined stresses will be correlated with the surface layer after grinding for describing the material separation mechanism by physical quantities. The surface layer is meant to be investigated by measuring the subsurface damages, which can be determined by the depth, the amount and the morphology of cracks.Conventionally, the calculation of chip thickness, which determines if the material separation mechanism is ductile or brittle, is based on phenomenological concepts, but these are limited according to the prediction of the separation mechanism. This is due to the inclusion of the grinding tool topography, which has a statistical nature within the formulas for maximum uncut chip thickness. When applying coarse-grained diamond grinding wheels, the number of active grains and their shape is not statistical, but more like only a few active cutting edges, comparable to a milling process. Consequently, the whole topography of the grinding tool has to be described, which is performed by structured light projection measurements in this research project. A software-based analysis of the measured topographies by linear scattering into grinding direction enables the determination of normal and tangential areas which are in contact with the workpiece during the grinding process. In combination with in-situ measured process forces, normal and shear stresses in the contact zone can be calculated. Their influence on the surface layer are investigated by measuring subsurface damages. The determined load stresses and subsurface damages are meant to be transferred into a generally comprehensive process model, re-defining the calculation basis for the maximum uncut chip thickness. In this process model, physical quantities (in this case normal and shear stresses) should replace the process or system variables.In the proposed research project, reverse plated, single-layered non-dressable diamond grinding wheels with envelope curves with a precision of less than two micrometers are used for grinding, as the dressing of this type of grinding wheels would not lead to a comparable required high precision.