Utilizing Small External Vibrational Sources to Increase Polishing Material Removal Rates

Although precision polishing of optical grade components using pitch based tools is still common practice, the process has not received the same level of scientific attention as other precision material removal processes. Building on previous research results, this paper demonstrates the relationship between low amplitude, broad spectrum vibrational power input and fused silica material removal rates obtained with different tool-polishing machine combinations. A low cost, easy to implement method of increasing vibrational power is presented and verified through polishing tests. The method uses small, off the shelf, high speed (>10 krpm), DC motors with eccentric masses (0.5 g and 4 g). Attachment of the battery driven motors to the underside of the platen and the workpiece holder increased the vibrational input from 0.7 W to 0.22 W resulting in an increase in the material removal rate from 0.96 mg/hr to 1.10 mg/hr. A method to attenuate process generated vibrations, and thus material removal rates, is also outlined. To achieve this the tool construction is modified by the addition of a cork layer between the substrate and the pitch layer. While this approach is not as flexible as that for increasing the vibrational power input, it successfully attenuated process vibrations (0.2 W to 0.14 W) and reduced the associated material removal rate (9.67 mg/hr to 6.13 mg/hr). The results outlined this paper demonstrate that recording and controlling process vibrations provides practitioners with viable process monitoring and optimization options.