Single crystal sapphire is of significant interest due to its combination of excellent physical, optical, electrical, chemical and mechanical properties. However, fine grinding of sapphire is quite challenging because of its high hardness and low fracture toughness, making it sensitive to cracking. Furthermore, wheel loading is another common problem in conventional grinding of hard and brittle materials.
A new technique, Electrolytic In-process Dressing (ELID) grinding, shows great promise in overcoming the problems of conventional grinding of hard and brittle materials. This technology provides continuous dressing of metal-bonded wheels during the grinding process, while maintaining sharp abrasives from the superabrasive wheels.
In this research, ELID technique was applied in the grinding of sapphire in order to obtain super surface finish and to minimize the problems in conventional grinding of sapphire. The research was focused on the pre-dressing oxide layer thickness, surface finish quality, and acoustic emission monitoring of the ELID grinding process. The effects of processing parameters on the oxide layer thickness, surface finish, and acoustic emission signals were evaluated. Correlations were found among the dressing current intensity, oxide layer thickness, surface finish and acoustic emission signals. A smoother surface was obtained using a higher dressing current at the cost of a higher wheel wear rate. The wheel wear mechanism in ELID grinding of sapphire is dominated by bond fracture because the bond strength is reduced by electrolysis. Results indicate that the acoustic emission technique has the potential to be used for monitoring the ELID grinding process, detecting the condition of the grinding wheel, and investigating the mechanisms of ELID grinding.