This paper presents advanced tools for ultra precision grinding which offer a high wear resistance and can be used to generate high-quality parts with an ultraprecise surface finish. The first approach features defined dressed, coarse-grained, single layered, metal bonded diamond grinding wheels. These grinding wheels are called Engineered Grinding Wheels and have been dressed by an adapted conditioning process which leads to uniform abrasive grain protrusion heights and flattened grains. This paper shows the results from grinding optical glasses with such Engineered Grinding Wheels regarding the specific forces and the surface roughness. The results show that the cutting mechanism turns into ductile removal and optical surfaces are achievable. On the other hand, the specific normal force F´n increases due to increased contact area of the flattened diamond grains. It is shown that the topography of the Engineered Grinding Wheels has a strong beneficial influence on surface roughness. The second new tool for ultra precision grinding is made of a CVD (Chemical Vapour Deposition) poly-crystalline diamond layer with sharp edges of micrometre-sized diamond crystallites as a special type of abrasive. The sharp edges of the crystallites act as cutting edges which can be used for grinding. It is shown that by using CVD-diamond-coated grinding wheels a high material removal rate and a high surface finish with surface roughness in the nanometre range can be achieved. The CVD-diamond layers exhibit higher wear resistance compared to conventional metal and resin bonded diamond wheels. In conclusion, this paper shows that not only conventional fine grained, multi-layered resinoid diamond grinding wheels but also coarse-grained and binderless CVD-coated diamond grinding wheels can be applied to machine brittle and hard materials by ultra precision grinding.
Diamond abrasive layers produced by chemical vapour deposition (CVD) have proven their high potential for their application as grinding wheel abrasive layer. Besides the achievable superb workpiece surface qualities, the low wear rates of the tools show a further important advantage. The wear rates of CVD diamond layers were up to 80 times lower compared to wear rates of standard fine grained diamond grinding wheels. Additionally, it has been shown that worn CVD diamond layers can be resharpened by a short CVD coating processes. The topography of CVD diamond layers after recoating was nearly identical to the initial topography, thus the grinding performance was comparable. This paper introduces the CVD process, the manufacture and the topography of the CVD diamond grinding wheels and discusses the latest results of grinding tests on optical glass (N-BAK2) an PCBN, as well as the recoating procedure of the grinding tools
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