Surface Roughness Generation Mechanism of Ultraprecision Grinding with Cup-Typed Resinoid-Bonded Diamond Wheels

The ultraprecision surface grinder1) having a glass-ceramic spindle of extremely-low thermal expansion has been developed, and very smooth surfaces better than conventional optically-polished surfaces can be obtained2) on various optical materials by cup-typed resinoid-bonded diamond wheels and the ultraprecision surface grinder. There are 3 grinding modes in grinding of optical glasses, such as the fracture mode, ductile & fracture mode and ductile mode3). The ductile mode grinding of NbF1 optical glass can be obtained by using a resinoid-bonded wheel having diamond grains less than 20 μm in grain size. There is no micro-crack observed under the surface ground in the ductile mode. The ground surface roughness less than 0.2nm rms or 2nm Rmax has been obtained on BSC7(BK7) glass sample with a SD3000-75-B wheel. So, there is big possibility of actualization that optical glasses will be finished into optical components by the ultraprecision grinding without polishing.