| This thesis develops an innovative strategy for machining ceramic mirrors. By taking advantage of the relative ductility of ceramics compared to glasses, it is shown that fixed-abrasive, ultraprecision grinding is a viable fabrication process for aspheric mirrors. Also, it is shown that ductile grinding of ceramic substrates can produce optical quality surfaces without post-polishing. Laboratory-scale ductile-regime grinding of chemically vapor deposited silicon carbide (CVD SiC) is described, as is a scale-up of the technology to a commercially available ultraprecision machine tool that has been retrofitted for grinding aspheric ceramic components.; It is further shown that acoustic emission (AE), the elastic stress waves generated in the grinding process, can be used as an indicator of material-removal regime in microgrinding of brittle materials. For a given volume of material removed from a given brittle material, the acoustic emission energy for fracture-dominated machining is found to be considerably lower than the acoustic emission energy for plastic-flow-dominated machining. This discovery is at odds with conventional thinking about AE, but can be explained in terms of the mechanism of the ductile-brittle transition in micro-machining.; An in-process dressing technique to maintain the sharpness of the grinding wheel is described. It is found that electrolysis can be used to "dress" the metal bonded wheel, continually exposing sharp diamond grains. Using a simplified experimental set-up, a relationship between the wear rate of the wheel bond and the electrolysis parameters is established. |
